Biaxial strain engineering of atomically thin MoS₂ for highly reversible Li–CO₂ batteries

Biaxial strain engineering of atomically thin MoS₂ for highly reversible Li–CO₂ batteries | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Biaxial strain engineering of atomically thin MoS₂ for highly reversible Li–CO₂ batteries Jun Xu, min Wang, hucheng Song, junnan Han, zehui Zhang, shijie Yang, and 11 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8285433/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Lithium-carbon dioxide (Li-CO 2 ) batteries have attracted considerable interest due to their high energy density and significant potential for achieving net-zero carbon emissions. However, the sluggish kinetics of the CO₂ evolution reaction leads to a substantial overpotential and severe energy loss in Li–CO₂ batteries, thereby drastically limiting their reversible cycling capability. Herein, we report the design of a cost-effective, catalytically active, and mechanically stable cathode catalyst for Li-CO 2 battery by introducing biaxial strain engineering into atomically thin MoS₂. The structurally stable 3D framework can accommodate high-levels of stress and strain at the catalytic sites, as evidenced by the intact structure and the low overpotential maintained after long and stable cycling. Theoretical calculations demonstrate that the synergistically adjusted d-band centers in biaxially strained atomically thin MoS₂ with functional in-plane S-vacancies facilitate orbital hybridization with both CO₂ and Li species. This unique electronic structure promotes reactant adsorption during discharging and enhances Li₂CO₃ decomposition during charging, ultimately leading to a minimized energy barrier for the rate-determining step. The resulting Li-CO₂ battery based on monolayer biaxially strained MoS₂ exhibits a ~ 0.6 V overpotential, ~ 85% energy-efficiency, and nearly 4000 cycles cycle-lifespan at 10 A g⁻¹ for a fixed 2000 mAh g − 1 capacity per cycle, surpassing those of previous catalysts under similar conditions. This work provides a strategic pathway for the rational design of advanced catalysts for practical Li–CO₂ batteries. Physical sciences/Materials science/Materials for energy and catalysis/Batteries Physical sciences/Materials science/Nanoscale materials/Two-dimensional materials Li-CO2 battery biaxial strain engineering MoS2 catalyst single atomic layer Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction To address global warming and climate change, the development of carbon-neutral technologies is essential, including high-value conversion and utilization of carbon dioxide (CO₂), clean energy systems, and high-specific-energy storage technologies [ 1 ] . Among them, lithium-carbon dioxide (Li-CO₂) batteries based on the reversible conversion reaction (4Li⁺ + 3CO₂ + 4e⁻ ↔ 2Li₂CO₃ + C) represent a promising frontier electrochemical energy storage technology, offering a high theoretical energy density of 1876 Wh kg⁻¹ and a theoretical equilibrium potential of 2.80 V (vs Li⁺/Li), while potentially enabling capture and convert CO₂ to realize net-zero carbon emissions [ 2 – 4 ] . However, the intrinsically sluggish kinetics of the CO 2 reduction reaction (CO₂RR) and CO 2 evolution reaction (CO₂ER) leads to a substantial charge-discharge overpotential and significant energy loss in Li-CO 2 batteries, thereby greatly restricting their reversible cycling capability [ 5 ] . Currently, extensive research has been dedicated to lowering the reaction energy barrier of the CO₂ER through the design of high-temperature battery systems and high-catalytic-activity cathode catalysts. These catalysts primarily include noble metals [ 6 – 10 ] , transition metal oxides/carbides/chalcogenides [ 11 – 14 ] , and transition metal single-atom catalysts [ 15 – 20 ] . Among them, two-dimensional transition metal dichalcogenides (TMDs), especially molybdenum disulfide (MoS₂), are an intriguing family of layered materials [ 21 ] . Owing to their unique crystal structure, high chemical stability, and facile preparation, MoS₂-based materials have been extensively explored as promising electrocatalysts in various electrochemical energy storage fields, including Li-CO₂ batteries [ 22 , 23 ] . For example, Ahmadiparidari et al. reported a highly reversible organic Li-CO₂ battery using MoS₂ nanoflakes as the cathode that achieved an excellent long-cycle lifespan of up to 500 cycles. However, the charge potential remained above 4.0 V, resulting in a large charge-discharge overpotential exceeding 1.5 V, which limited the cycle life [ 24 ] . This issue comes from the intrinsically low catalytic activity of the basal planes compared to edge sites in most TMDs, such as MoS₂ nanoflakes, due to their imited adsorption capacity for CO₂ and carbon-oxygen (C–O) intermediates [ 25 ] . Given that the basal plane dominates the major structure of MoS₂, its rational engineering is critical for achieving superior bifunctional activity toward both CO₂RR and CO₂ER, which determins the performance of Li–CO₂ batteries in practical applications. To address this challenge, surface engineering strategies such as defect creation, elemental doping, and single-atom decoration have been employed to enhance electrical conductivity and activate surface activity of MoS₂ [ 26 – 30 ] . However, the precise synthesis of dual active centers in the basal plane through these approaches remains challenging for achieving efficient bidirectional catalysis in Li–CO₂ batteries [ 31 ] . Alternatively, strain engineering provides a promising strategy by modulating nanomaterial lattice parameters to synergistically combine geometric and electronic effects, which optimizes reaction pathways through regulated adsorption/desorption energetics while overcoming scaling relation constraints, thereby enabling concurrent enhancement of catalytic activity and stability [ 21 , 25 ] . Notably, introducing strain to MoS₂ not only enables precise electronic structure modulation of active sites but also facilitates sulfur vacancy (Sv) generation, collectively establishing a favorable microenvironment for target reactions [ 32 ] . Moreover, traditional carbon-based cathodes suffer from severe corrosion, which leads to structural deformation or even collapse under severe local strain and stress at the catalytic sites, particularly under high mass-transport conditions with large current densities and high capacities, as well as during the repeated formation of low-efficiency lithium carbonate products [ 33 ] . On the contrary, strain-engineered 2D TMDs, especially MoS₂, can withstand high levels of strain and stress without destroying their local structure or catalytic sites, while maintaining high catalytic activity over long-term cycling. However, most strain-related investigations have concentrated on in-plane tension, compression, or bending-induced stretching (i.e., uniaxial strain), which offers limited dimensional control over 2D TMDs, thereby resulting in limited control on the local environment surrounding active sites [ 21 , 35 ] . Herein, by strategically replacing conventional graphite conductive agents with highly conductive spherical Al NPs and leveraging their naturally formed ultrathin Al₂O₃ surface layer as a growth interface, we have successfully constructed an atomically thin MoS₂ shell with biaxial strain (Fig. 1 a- 1 d). This design enables systematic study of how strain and defects collectively modulate the local electronic configuration to optimize both CO₂RR and CO₂ER in Li–CO₂ batteries. The biaxial strain and controllable atomic-layer number make this MoS 2 cathode catalysts highly efficient and stable (Fig. 1 a- 1 d). Theoretical calculations reveal that the adjusted d-band centers of atomically thin MoS 2 with the introduction of biaxial strain and in-plane S-vacancies are hybridized between CO 2 and Li species, respectively, which is conducive to the adsorption of reactants and the decomposition of Li 2 CO 3 during discharge and charge, resulting in a small energy barrier for the rate-determining step. Furthermore, the spherical Al NP core with an ultrathin oxide layer (~ 4 nm Al₂O₃) significantly enhances the electrical conductivity of the MoS 2 shell through electron tunneling while providing excellent structural stability (Fig. 1 d). The SEM images revealed that the MoS 2 structure maintained stable after cycling under high current densities and high specific capacities. Meanwhile, the low overpotential remained after prolonged cycling further confirms its structural integrity and stable catalytic activity. As a result, the Li–CO₂ battery using the biaxially strained MoS₂ with single atomic layer exhibits an ultra-long cycle life nearly 4000 cycles and ultra-low charge potentials of around 3.0 V at 10 A g − 1 with a limited capacity of 2000 mAh g⁻¹, far outperforming the best reported cycling stability for Li–CO₂ batteries to date. This work develops an innovative strategy for fabricating biaxially strained TMDs with precisely controlled layer numbers to enhance CO₂RR/CO₂ER kinetics, enabling high-performance battery devices. Results and discussion Figure 1 illustrates the strain definition and structural design of MoS₂. The two-dimensional (2D) planar MoS₂ without strain is defined as zero-strain state, while the nanospherical MoS₂ strained along two axes is termed biaxial strain. Typically, when 2D planar MoS 2 is fabricated into nanospherical structures, biaxial bending strain is naturally generated and the magnitude of this strain can be precisely tuned by adjusting the size of the nanospheres (Fig. 1 a, 1 d and Fig. S1 ) [ 21 ] . In comparison with zero-strain planar 2D materials, biaxial bending strain can not only optimize the electronic structure of d-orbitals in metal atoms but also induce uniform anionic vacancies on the 2D basal plane, thereby effectively enhancing the catalytic activity of the inherently inert basal plane (Fig. 1 b and Fig. 1 d) [ 35 ] . Density functional theory (DFT) calculations further reveal that the d-band structure of MoS₂ exhibits distinct variations under compressive and tensile strains where the d-band center of MoS₂ is located at -1.31 eV under a -5% compressive strain and shifts to -0.86 eV under a 5% tensile strain (Fig. 1 b). This strain-induced modulation of the d-band center confirms that strain can tailor the electronic structure of MoS₂ catalysts and regulate the bonding interactions between their surface and adsorbed species, thereby enabling the modulation of the catalysts' intrinsic activity. [ 25 ] It also indicates that the biaxial strain engineering of MoS₂ catalysts at the atomic scale can optimize key reaction processes (e.g., reactant adsorption, intermediate conversion) in Li–CO₂ batteries. Figure 1 c schematically illustrates the synthetic protocol for biaxially strained MoS₂ shell grown on spherical Al NP core, which are named Al@MoS₂ core-shell catalyst. Briefly, referring to the previous report by Hamid Reza Ghorbani, kilogram-scale Al NPs are first prepared as cores via the electrical explosion of wire (EEW) [ 36 ] . Owing to the ~ 5% lattice mismatch between Al₂O₃ and MoS₂ (within the ≤ 10% epitaxial tolerance of 2D TMDs) that facilitates high-quality MoS₂ growth by balancing strain and crystallographic alignment [ 21 ] , the native ultra-thin Al₂O₃ layer (~ 4 nm) on Al NPs serves as an ideal interface for the subsequent growth of biaxially strained MoS₂. Thus, by immersing Al NPs with a native Al₂O₃ layer in liquid-phase sulfur and molybdenum precursors, a biaxially strained MoS₂ shell layer is successfully grown on the spherical Al NP core with Al₂O₃ via a facile hydrothermal synthesis process maintained at 195°C for 10 hours (Fig. 1 c and S2). Notably, for the designed carbon-free cathode, the kilogram-scale Al NP cores with broad size distribution [ 36 ] directly yield biaxially strained MoS₂ shells with continuous curvature (Fig. 1 d). Such multi-scale strain system enhances CO₂RR/CO₂ER performance via a synergistic mechanism where the continuous curvature distribution modulates the electronic structure of MoS₂ by lowering its d-band center and optimizing intermediate adsorption, while simultaneously establishing a gradient defect distribution through curvature-dependent S v generation in high-curvature regions and lattice preservation in low-curvature regions (Fig. 1 d) [ 34 ] . As showed in Fig. 1 d, the strain-engineered MoS₂ cathode catalyst effectively accommodates the stress and strain induced by high-rate mass transport under high-capacity and high-current-density cycling. Its integrated pore network enhances reactant accessibility, while the synergistic coupling between strain fields and S v simultaneously strengthens CO₂ adsorption and lowers activation barriers, thereby collectively improving both reaction kinetics and structural durability [ 21 , 25 , 37 ] . In summary, this multi-scale synergistic strategy establishes a systematic design framework for advanced 2D TMD cathodes. It integrates d-band modulation for electronic regulation, curvature-induced S v for activated catalytic sites, and hierarchical pore/strain-vacancy synergy for optimized transport-adsorption coupling, ultimately enhancing the kinetics of CO₂RR/CO₂ER. The particle size distribution, characterized by transmission electron microscopy (TEM), reveals that the as-prepared Al@MoS₂ core-shell sample exhibits a broad diameter range of 20 nm to 2000 nm with a normal distribution centered at ~ 150 nm (Fig. 2 a- 2 c and S3). High-angle annular dark-field scanning TEM imaging and corresponding energy-dispersive X-ray spectroscopy (EDS) elemental mapping collectively demonstrate a distinct core-shell architecture in the pre-synthesized Al@MoS₂ material with Al and O localized in the core region and S and Mo uniformly distributed in the surrounding shell (Fig. 2 d). Furthermore, high-resolution transmission electron microscopy (HR-TEM) and aberration-corrected TEM (AC-TEM) were employed to characterize the core-shell structures with three distinct diameters/curvatures of approximately 25 nm, 130 nm, and 255 nm (Fig. 2 e- 2 h). All three Al@MoS₂ structures with distinct diameters/curvatures exhibit a typical core-shell architecture consisting of a spherical Al nanocore, Al₂O₃ interlayer, and MoS₂ nano-shell. Specifically, all the Al₂O₃ interlayer maintains a uniform thickness of ~ 4 nm, while the MoS₂ shell comprises approximately three atomic layers with a thickness of ~ 2.0 nm (Fig. 2 f- 2 h and Fig. S3). Furthermore, we observe a significant increase in defect density within the MoS₂ outer shell as the Al nanocore diameter decreases from ~ 255 nm to 25 nm, primarily due to enhanced biaxial tensile strain (Fig. 2 f- 2 h and Fig.S4- 6 ). Statistical analysis further reveals a progressive expansion in the interplanar spacing of the MoS₂ shell with increasing curvature where the dominant interplanar spacing measures approximately 0.64 nm in the 255 nm-diameter structure, 0.68 nm at 130 nm diameter, and multiple spacings (0.68, 0.76, and 0.83 nm) emerge in the 25 nm-diameter structure (Fig. 2 i- 2 k and Fig.S4- 6 ), all exceeding the 0.62 nm reference value of strain-free planar MoS₂ [ 21 ] . The tensile strain (ε) in MoS₂ shells, calculated using ε = d/2r where d represents the thickness of MoS₂ shell (0.62 nm) and r denotes the average curvature radius, exhibits a distribution dependent on curvature radius. Statistical analysis of curvature radii indicates that reducing the curvature radius from 255 nm to 25 nm increases the biaxial tensile strain from approximately 0.57% to 9.64%. This strain gradient aligns well with experimental observations, including the expansion of interplanar spacing (0.64 nm → 0.83 nm) and the variation in defect density, confirming the critical role of curvature-induced strain in regulating the electronic structure and catalytic performance of the material. Consequently, the broad size distribution of Al NP cores in the cathode generates significant curvature gradients in the MoS₂ shells, inducing gradient-distributed biaxial strain within the shell layers (Fig. 1 d and Fig. 2 a- 2 k). This curvature-induced biaxial strain induces lattice expansion (manifested as increased interplanar spacing, Fig. 2 i- 2 k), elevated defect/vacancy density (Fig. 2 f- 2 h), and an upward shift of Mo’s d-band center (Fig. 1 b). For Li-CO 2 batteries, the expanded lattice and increased defects provide abundant active sites and facilitate Li⁺/CO₂ transport, while the upward-shifted d-band center strengthens the adsorption of the intermediates and lowers the reaction’s activation energy barriers. [ 37 ] Furthermore, by precisely controlling the concentrations of molybdenum and sulfur precursors while maintaining constant reaction temperature (see Experimental Section), we achieved accurate regulation of MoS₂ shell thickness (i.e., atomic layer number) in the Al@MoS₂ core-shell structures. HRTEM characterization confirmed the successful synthesis of MoS₂ shells with tunable atomic layers on Al₂O₃-coated Al nanoparticle cores through precursor concentration modulation. Statistical analysis demonstrated that the four precursor concentrations (5%, 10%, 20%, and 50%) produced core-shell structures with MoS₂ shells predominantly consisting of 1 layer, 2 layers, 3 layers, and 4 layers, respectively (Fig. 3 a- 3 d and Fig. S7-S8), unequivocally validating the precise atomic-scale controllability of our synthetic strategy. Based on the strain formula ε = d/2r and statistical analysis of MoS₂ shell layer numbers, the calculated biaxial tensile strain values for monolayer to tetralayer MoS₂ are 0.85%, 2.64%, 4.01% and 4.8%, respectively (Fig. 3 e- 3 h and Fig. S7). The electron paramagnetic resonance (EPR) is employed to investigate the S-vacancies concentration in biaxially strained MoS₂ shells with different atomic layer numbers where the EPR signal loaded at 2.002 (g-factor = 2.002) directly corresponds to unsaturated sites with unpaired electrons, and its intensity positively correlates with S V concentration (Fig. 3 i). The results show that the EPR signal intensity of biaxially strained MoS₂ decreases significantly with increasing layer number. Specifically, the monolayer MoS 2 sample (ML, 5% sulfur and molybdenum precursor concentration) exhibits markedly higher peak intensity than the bilayer (BL, 10%), trilayer (TL, 20%), and tetralayer layer MoS 2 (TTL, 50%) samples, with all strained samples showing substantially stronger signals than unstrained planar MoS₂ (100%, see Fig. 3 i). This confirms that the biaxial strain of the monolayer MoS₂ exhibits the most pronounced charge-compensating effect [ 35 ] and the highest S v concentration, consistent with previous HRTEM observations (Fig. 3 a- 2 d). The identified relationship between strain magnitude and S v density further confirms suggest that the strong biaxial strain of the MoS 2 can effectively promote the formation of S-vacancies at adjacent sites [ 35 , 37 ] . Furthermore, depth-profiling X-ray photoelectron spectroscopy (XPS) analysis based on sequential etching was performed on the monolayer biaxially strained MoS₂ coated on Al NP to further elucidate the evolution of its electronic structure (Fig. 3 j). Under the condition of zero etching time, the high-resolution spectrum of the Mo exhibits typical doublet peaks located at 228.8 eV and 232.2 eV, corresponding to Mo⁴⁺ 3d₅/₂ and 3d₃/₂ states, respectively. As the etching time increases to 40 seconds, the binding energy of Mo 3d₅/₂ shifts significantly to 229.7 eV, indicating a more delocalized local electric structure (Fig. 3 j). [ 38 ] Additionally, the presence of a peak at 235.9 eV confirms the formation of surface Mo⁶⁺ species due to oxidation. [ 38 ] Furthermore, the S 2p₃/₂ peaks of the monolayer biaxially strained MoS₂ shift to higher binding energy of 162.3 eV when compared to those of the reported pure-MoS₂ (161.9eV) [ 38 ] . This means the biaxial strain engineering of the monolayer MoS₂ endows S v sites with abundant electrons, which enhances CO₂ adsorption and facilitates Li₂CO₃ desorption for Li–CO₂ batteries. [ 35 ] To further understand the local structures of the biaxially strained MoS₂ cathode catalyst, we performed X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses targeting Mo (Fig. 3 k- 3 q). Compared to planar MoS₂, the absorption edge of the biaxially strained MoS₂ grown on Al 2 O 3 -coated Al NP cores shifts slightly toward lower energy, indicating interfacial charge transfer between MoS 2 shell and the core support (Fig. 3 k) [ 35 ] . The characteristic peak observed at 20035 eV in the Mo K-edge XANES spectrum originates from the 1s→4pz electronic transition, which serves as a spectroscopic fingerprint for identifying the Mo-S coordination configuration [ 39 ] . In the biaxially strained MoS₂ system, a reduction in the intensity of the 1s → 4pz transition is observed, which is likely attributed to a decrease in symmetry from D₄h to C₄v. [ 40 ] The peaks near 20055–20065 eV originate from the 1s → 4pₓ, γ transition, where the exact peak position is dependent on the oxidation state of Mo (Fig. 3 k). [ 41 ] Fourier-transform EXAFS analysis demonstrates that the Mo–S bond elongates to 2.41 Å in monolayer biaxially strained MoS₂, exceeding that in tetralayer (2.39 Å) and planar MoS₂ (2.38 Å, Fig. 3 i). Accompanying shifts in Mo–S/Mo–Mo peaks confirm lattice distortion and the elongation of Mo–S bonds directly weaken their bonding strength and substantially reduces the CO₂ adsorption energy barrier (Fig. 3 i ~ 3q and Fig.S9) [ 39 , 43 ] . In addition, the EXAFS) (Fig. 3 i) and the corresponding wavelet transform (Fig. 3 o- 3 q) both show gradual decrease in intensity. Notably, the Mo coordination number decreases to ~ 5.1 in monolayer biaxially strained MoS 2 (vs. ~5.7 in tetralayer MoS 2 and ~ 6.0 in bulk MoS 2 ) [ 40 ] . Such a trend is mainly due to the increased strain dimension of MoS 2 , resulting in the breaking of Mo-S bonds and thus creating more S-vacancies. This synergistic mechanism achieves dual modulation by both optimizing the free energy of CO₂ adsorption and lowering the energy barrier of the rate-determining step, thereby effectively enhancing the kinetic performance of the CO₂RR/CO₂ER [ 42 ] . Befitting the design of biaxial strain engineering of atomically thin MoS 2 , the Li–CO₂ battery employing a ternary molten nitrate electrolyte, Li-metal anode, and MoS₂ cathode catalyst demonstrates a larger discharge capacity over 14 mAh than that of noble Ru NPs catalyst (~ 9.6 mAh) operating at 150 o C, with a current density of 2 Ag − 1 (Fig. 4 a). Notably, previously reported Li–CO₂ batteries utilizing noble Ru-based catalysts demonstrate optimal CO₂ER performance at an elevated temperature of 150°C [ 43 ] . The evaluation of the cost-effectiveness value shows that the biaxially strained MoS₂ catalyst achieves a value more than 250 times that of Ru NPs catalyst for the Li-CO 2 battery system (Fig. S10). Electrochemical evaluations reveal that the biaxially strained MoS 2 catalyst shows a lower overpotential (OP, ~ 0.43V with a 2.62 /2.97 V discharge/charge potential) and higher energy efficiency (EF, ~ 88.22%) compared with Ru NPs (~ 0.52 V OP with a 2.43/2.95 V discharge/charge potential, and ~ 82.4% EF) and pure planar MoS 2 (~ 0.96 V OP and ~ 69.9% EF). Notably, the battery using monolayer MoS 2 with biaxial strain exhibits the smallest OP (0.43 V) and highest EF (88.2%, see Fig. 4 b- 4 c and Fig. S11). As the MoS₂ shell thickness increases from monolayer to tetralayer, the discharge potentials of these batteries decrease from 2.62 to 2.23 V while the charge potentials increase from 2.97 to 3.18 V, which consistently surpass those of strain-free planar MoS₂ (Fig. 4 c). This electrochemical performance enhancement originates from the biaxially strained structure of atomically thin MoS₂, which not only promotes the kinetics of CO₂ RR/CO 2 ER by maximizing the exposure of active edge sites (i.e., Mo-edge and S-edge), but also optimizes the adsorption capability for key intermediates (e.g., CO₂⁻ and Li⁺) through modulation of the Mo d-band center [ 25 ] , thus leading to improved electrochemical performance in Li–CO₂ batteries. Although increasing the layer number induces interlayer van der Waals aggregation and strain shielding effects, resulting in reduced catalytic activity [ 21 ] , the residual strain present in multilayer MoS₂ still confers higher catalytic activity than strain-free planar MoS₂. Furthermore, the battery using the monolayer MoS 2 with biaxial strain was cycled at high current densities from 1.0 A g⁻¹ to 10.0 A g⁻¹ and back to 1.0 A g⁻¹ that shows a high charge-potential retention of ~ 99.34% from 2.99 V at the 1st cycle to 3.01 V at the 35th cycle (Fig. 4 d and Fig. S12). The battery demonstrates exceptional cycling stability at 1.0 A g⁻¹, 2.0 A g⁻¹, 5.0 A g⁻¹ and 10.0 A g⁻¹, achieving an excellent overpotential a cycle life at least ten times longer than that of the Li-CO 2 battery using Ru NPs catalyst (Fig. 4 e). Also, the battery using the monolayer MoS 2 with biaxial strain achieves an ultra-long cycle life approaching 4,000 cycles at 10.0 A g⁻¹ while maintaining approximately ~ 86.23%/95.96% charge/discharge potential retention from 2.47/3.08 V at the 1st cycle to 2.13/3.22 V at the last cycle (Fig. 4 f). This system demonstrates breakthrough cycling durability due to its low charging potential and high energy efficiency, outperforming all reported Li-CO₂ battery systems by an order of magnitude (Fig. 4 g and Table 1 in SI), including organic Li-CO 2 batteries (>4.0 V charge potential, 4.5 V, 4.2V, 3.0 V, < 980 cycles) [ 44 ] . To elucidate the discharge mechanism, the discharge products in the Li-CO 2 battery using the monolayer MoS₂ with biaxial strain, after being discharged to a capacity of 14 mAh at 2 A g⁻¹, were further characterized. The SEM image further confirms the flake-like morphology of the discharge products (Fig. 5 a). The refined X-ray diffraction pattern of the discharge products shows characteristic peaks at 31.8°, 21.3°, and 30.6°, which correspond to the (002), (110), and (-202) crystal planes of Li₂CO₃ (JCPDS 87–0728), respectively (Fig. 5 b) [ 44 ] . High-resolution XPS spectra showed characteristic peaks at 55.5 eV (Li 1s), 289.8 eV (C 1s), and 531.5 eV (O 1s) belong to Li₂CO₃, which further confirms that the flower-like discharge product is Li₂CO₃ (Fig. 5 c). Additionally, a C 1s signal corresponding to the C-C bond was detected at 284.8 eV. TEM characterization clearly reveals a core-shell architecture in the discharge products, consisting of an Al@ MoS₂ NP core and a discharged Li₂CO₃-based product shell with uniform thickness distribution in the 600–1000 nm range (Fig. 5 d). HR-TEM characterization was conducted at three distinct regions (A, B, and C) of the core-shell structured discharge products (Fig. 5 d). The discharge product at position A (the red-bordered region) exhibits a distinct hexagonal morphology, and its electron diffraction pattern and interplanar spacing (0.28 nm) are consistent with the Li₂CO₃ phase. HRTEM images and interplanar spacing analysis results of positions B (the bule-bordered region) and C (the green-bordered region) also confirm that the crystalline products at these two positions are Li₂CO₃ where the 0.28 nm interplanar spacing and 0.16 nm interplanar spacing responding to (002) crystal plane of Li 2 CO 3 and (022) crystal plane of Li₂O, respectively. The formation of Li₂O originates from the nitrate-mediated discharge pathway in the Li-CO₂ battery system [ 47 ] . Notably, distinct amorphous phases distributed between the crystalline Li₂CO₃ grains were observed in the HR-TEM images of positions A, B, and C (Fig. 5 d). Combined with XPS results, we infer that the amorphous phase is amorphous carbon formed during the discharge process (Fig. 5 c and 5 d). This result further confirms that the discharge products of the battery comprise both crystalline Li₂CO₃ and amorphous carbon, as clearly demonstrated by experimental evidence. In-situ electrochemical mass spectrometry (ECMS) analysis reveals a 4/3-electron transfer reaction mechanism for the battery during discharge and charge process which aligns closely with the well-established typical Li-CO₂ battery reaction of 3CO 2 + 4e − + 4Li + → 2Li 2 CO 3 + C [ 6 ] , consistent with previous ex-situ characterization results of the discharge products (Fig. 5 e). Based on these ex-situ and in-situ characterization results, combined with the distinct morphological and particle size differences between region A and other areas, we propose that the formation of discharge products follows a two-stage growth mechanism (Fig. 5 f and S13). During the initial discharge stage, Li⁺, e⁻, and CO₂ react on the surface of biaxially strained MoS₂ catalyst to form fine composite nuclei consisting of crystalline Li₂CO₃ and amorphous carbon (the green-bordered region in Fig. 5 d). Subsequently, continued nucleation and growth occur on the catalyst surface, leading to large-sized hexagonal nanosheets composed of crystalline Li₂CO₃ crystals and amorphous carbon, as shown at position A, B and C (Fig. 5 a and 5 d). DFT calculations further reveal a noticeable modulation of the d‑band structure in MoS₂ under applied bending strain. Specifically, bending induces a significant upward shift of the d‑band center in pristine MoS₂ from ‑0.93 eV (0% strain) to ‑0.55 eV (5.5% strain). Moreover, the introduction of S v further modifies this bending‑driven d‑band shift, moving the center from ‑0.64 eV (0% strain) to ‑0.49 eV (5.5% strain), as illustrated in Fig. 6 a. To further probe the synergistic effect of bending strain and S-vacancies on the adsorption behavior of the MoS₂, we computed the adsorption energies (Eₐdₛ) of key intermediates on four representative MoS₂ structures including pristine planar MoS₂ (Pr-MoS₂), MoS₂ with Sv (Vₛ-MoS₂), bent MoS₂ (Bent-MoS₂, under 11% tensile strain), and the bent MoS₂ with a single Sv (Bent-Vₛ-MoS₂). The synergistic effect of tensile strain and S-vacancies significantly enhances the adsorption strength of MoS₂ toward Li, LiCO₃, and CO₂, while maintaining moderate adsorption equilibrium for CO₃ intermediates (Fig. 6 b). Among the four MoS₂ structures (Pr-MoS₂, Vₛ-MoS₂, Bent-MoS₂ and Bent-Vₛ-MoS₂), the optimal reaction pathways are I, IV, I, and V, respectively, where the pathway V shows the lowest energy barrier (Fig. 6 c- 6 d and Fig.S13). The Bent-Vₛ-MoS₂ structure demonstrates the smallest free energy changes (ΔGf(r)) for the rate-determining steps in both reaction stages, with values of 2.15 eV in the first stage and 2.87 eV in the second stage. The reduced energy barriers originate from strain-vacancy synergy where the strain enhances catalytic activity by exposing more Mo active sites, elevating the Mo d-band center position, and reducing vacancy formation energy, while S-vacancies create localized electron-rich regions that promote interfacial charge transfer (Fig. 3 i and Fig. 6 a). This synergistic mechanism optimizes the adsorption properties of the MoS 2 , exhibiting strong adsorption toward CO₂/Li while maintaining moderate adsorption balance for intermediates/products, thus leading to the optimal reaction pathway V and significantly improving the kinetics of both CO₂RR and CO 2 ER (Fig. 6 b-Fig. 6d). Schematic diagrams of intermediate adsorption configurations reveal that the Bent-Vₛ-MoS₂ possesses more stable adsorption geometries and shorter Mo-adsorbate bond lengths, with these results corroborating the adsorption energy calculations and collectively validating the theoretical rationale of the strain-vacancy synergistic catalytic mechanism (Fig. S13 and Table S2 -S7). Conclusion In summary, we reported a high energy effciency and long cycle lifespan Li–CO₂ battery by biaxial strain engineering of atomically thin MoS 2 cathode catalyst. In-situ/ex-situ characterizations confirmed the biaxial strain engineering of atomically thin MoS 2 can effcient catalyze C–O bond cleavage and the formation of Li₂CO₃ and amorphous carbon during discharge, and accelerate CO₂ evolution during charge. The robust cathode structure remained stable under the intensive stress-strain conditions induced by high mass transport at elevated current densities and specifc capacities, as well as during repeated Li₂CO₃ formation and decomposition over prolonged cycling. Electrochemically, the Li-CO 2 batteries using monolayer biaxially strained MoS₂ maintained low charge potentional less than ~ 3.1 V and high energy effciency over 80% at 2.0 A g⁻¹, 5.0 A g⁻¹ and 10 A g⁻¹. Notably, it shows a record-breaking long cycle life of nearly 4000 cycles, accompanied by low charge potentials and high energy efficiency, thereby validating the role of C–O bond transformations in energy storage. Complementary DFT calculations elucidated the bending strain and S v synergy enhance Li/LiCO₃ adsorption, optimize the reaction pathway (Pathway V for bent-Vₛ-MoS₂), and reduced rate-determining step barriers to 2.15 eV (first stage) and 5.25 eV (second stage), thus boosting CO 2 RR and CO 2 ER kinetics. Strain elevated Mo’s d-band center and lowered S v formation energy, while S-vacancies created electron-rich regions to amplify adsorption. These findings clarify MoS₂ structure–activity relationships and provide a strain/defect engineering strategy for high-performance cathodes. This work guides the design of catalysts for sluggish CO₂ER and paves the way for integrating CO₂ into advanced energy-storage systems. Methods Synthetic of Al@MoS 2 core-shell NPs structure The Al nanoparticles were synthesized via electrical explosion of wire (EEW) in a 0.1 MPa argon atmosphere by applying a 25 kV high-voltage pulsed discharge to a 0.2 mm diameter Al wire, inducing instantaneous vaporization and explosion, followed by condensation and collection through circulating gas flow. Subsequently, the resulting Al nanoparticles with native oxide layers were introduced into liquid-phase precursors of sulfur and molybdenum, yielding Al@MoS₂ core-shell nanoparticles with an ultra-thin MoS₂ nanoshell after a 10 h reaction at 195°C. The morphology, elemental distribution, and structural characteristics of both as-prepared and post-cycled samples were characterized by X-ray diffraction (XRD, Bruker D8), X-ray photoelectron spectroscopy (XPS, ULVAC-PHI), scanning electron microscopy (SEM, Zeiss), transmission electron microscopy (TEM, Talos G2 F20), electron paramagnetic resonance (EPR, Bruker EMXplus), and synchrotron radiation X-ray absorption spectroscopy (XAS) at the Shanghai Synchrotron Radiation Facility (SSRF), beamline BL14W1. Electrolyte preparation A homogenized powder mixture composed of lithium nitrate (99.99%, Aladdin), potassium nitrite (ACS, Aladdin), and cesium nitrate (99.99%, Aladdin) with a molar ratio of 37:39:24 was heated to 120°C to form the eutectic molten salt electrolyte. Cathode preparation and characterization Two distinct cathode materials were fabricated. For the Al@MoS₂ catalyst cathode, the as-synthesized Al@MoS₂ core–shell nanoparticles were dispersed in a mixed solution of ethanol and Nafion ionomer (D520-1000EW, 5 wt%) at a volume ratio of 9.5:0.5. The dispersion was ultrasonicated for 30 min to form a homogeneous catalyst ink, which was then uniformly spray-coated onto carbon nanofibers (WOS1009) using a benchtop spray coater. The resulting cathode was subsequently dried for 12 h. For the Ru catalyst cathode, ruthenium nanoparticles were deposited directly onto carbon nanofibers (WOS1009) via direct current (DC) reactive magnetron sputtering employing a 99.999% pure ruthenium target. The deposition was conducted at a pressure of 0.2 Pa, a constant power of 100 W, and a current of 0.3 A for a duration of approximately 5 min. Cell assembly and electrochemical measurements All cells were assembled inside an argon-filled glovebox (MIKROUNA, UNIVERSAL 1800/750/900). As illustrated in Fig. S18, the cell configuration consisted of a metallic lithium anode, the eutectic molten salt electrolyte, and an MoS₂-based/Ru cathode. The assembled cells were sealed within custom-designed fixtures. After purging the chamber with pure CO₂ for 1 h, the cells were tested at 150°C under a continuous CO₂ flow of 20 cm³ min⁻¹. The discharge–charge cycling performance was evaluated using an electrochemical testing system (Hokuto Denko, HJ1001SD8), with specific capacity calculated based on the mass of loaded catalyst. In the calculation of the battery's specific capacity, the mass of the MoS₂ catalyst serves as the basis for evaluation. The MoS₂ mass is determined by deriving its actual amount in the cathode material from the mass ratio of the sulfur and molybdenum sources relative to the aluminum source in the hydrothermally synthesized Al@MoS₂ precursor. This derived MoS₂ mass loading (~ 5 ug/cm 2 to 100 ug/cm 2 ) is then used to calculate the discharge specific capacity of the battery. Declarations Acknowledgement This research was partially supported by the National Natural Science Foundation of China (Grant Nos. 61921005, 62474160, 61735008, 62104099 and 62004078), National Key Research & Development Program of China (2018YFB2200101), Natural Science Foundation of Jiangsu province (BK20190313 and BK 20201073) Author contributions Hucheng Song: Writing – review & editing, Writing – original draft, Visualization, Formal analysis. Min Wang: Data curation, Formal analysis, Methodology, Validation, Writing - Original draft. Junnan Han: Writing – review & editing, Software, Methodology, Investigation, Zehui Zhang : Writing – review & editing, Formal analysis. Shijie Yang: Writing – review & editing, Visualization. Zhihuan Li : Investigation. Gungbin Zhang : Formal analysis, Conceptualization. Changshun Wang: Project administration. Jing Wu: Formal analysis. Linlong Zhang: Investigation. Pei Zhang : Investigation. Zhongwei Yu: Conceptualization. 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J Phys Chem Lett 14:3222–3229 Guda AA et al (2021) Understanding X-ray absorption spectra via machine learning. npj Comput Mater 7:203 Wang S et al (2022) High-energy long-cycling solid-state lithium-metal battery at high temperatures. Adv Energy Mater 12:2201866 Sun X et al (2023) Binuclear Cu complex catalysis enabling Li-CO 2 battery above 3.0 V. Nat Commun 14:536 Li X et al (2019) Bamboo-like N-doped CNT forests for flexible Li-CO 2 batteries. Adv Mater 31:1903852 Zhu YG et al (2022) Nitrate-mediated four-electron oxygen reduction on metal oxides for lithium-oxygen batteries. Joule 6,8 Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation20251204.docx Supplementary Information Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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15:28:06","extension":"png","order_by":15,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":145847,"visible":true,"origin":"","legend":"","description":"","filename":"Onlinefloatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/a8aa5c0a9946a21d50bc27a9.png"},{"id":98887766,"identity":"413912be-5f9d-466b-92d6-10f49734d13d","added_by":"auto","created_at":"2025-12-23 15:28:06","extension":"xml","order_by":16,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":113769,"visible":true,"origin":"","legend":"","description":"","filename":"NCOMMS25985740structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/55826aa29c9adcd3e2a3c399.xml"},{"id":98887762,"identity":"706dc3ea-3f1b-456a-8ee5-d8f53e75af13","added_by":"auto","created_at":"2025-12-23 15:28:06","extension":"html","order_by":17,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":124964,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/a1589ac3cca46ecaa09953b7.html"},{"id":98887747,"identity":"8c95a3b8-0d68-45e1-9a99-b74a1697d033","added_by":"auto","created_at":"2025-12-23 15:28:06","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1602923,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDefinition, design and preparation of the biaxially strained MoS₂. \u003c/strong\u003e(a) Atomic structures of the MoS\u003csub\u003e2\u003c/sub\u003e from zero strain to biaxial strain, and corresponding transitions in microstructural features and intrinsic catalytic activity. (b) Changes in the d-band center of the MoS₂ under compressive and tensile strains\u003cbr\u003e\n. (c) Schematic illustration of the synthesis process where atomically thin MoS₂ is grown on spherical Al NP current collectors, ultimately forming a core-shell structured catalyst with biaxially strained MoS₂ shells supported on Al NP cores. (d) Schematic of the carbon conductive agent-free cathode consisting of a GDL and atomically thin MoS₂ shell catalysts supported on highly conductive Al NP cores with different diameters where the curvature-dependent lattice strain induces microstructural features and catalytic activity transitions from strain-free planar MoS₂ to biaxially strained spherical MoS₂.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/897d4a8a965731081ef24c34.png"},{"id":98887741,"identity":"e7deb1fe-567f-4b2c-b72d-1386bd79dd0d","added_by":"auto","created_at":"2025-12-23 15:28:05","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1372655,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterization of biaxially strained MoS₂ grown on Al₂O₃-coated Al NPs.\u003c/strong\u003e (a) TEM image, (b) HRTEM lattice image, (c) size distribution histogram, and (d) EDS elemental mapping of Al@MoS₂ core-shell nanoparticles. (f-h) Schematic diagrams with corresponding TEM/HRTEM images, and (i-k) interplanar spacing analysis of layered MoS₂ grown on Al₂O₃-coated Al cores with distinct diameters (~25 nm, ~130 nm, and ~255 nm).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/579d329902f361698b72638e.png"},{"id":99309542,"identity":"c96870bc-99d7-4962-9f19-8787e61156d3","added_by":"auto","created_at":"2025-12-31 16:10:43","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1459889,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterization of biaxially strained MoS₂ shell with controlled atomic-layer numbers grown on Al₂O₃-coated Al NP cores.\u003c/strong\u003e (a-d) TEM images of Al@MoS₂ core-shell structures with corresponding (e-h) MoS₂ shell thickness distributions. (i) EPR spectra and (j) high-resolution XPS spectra of Al 2p, Mo 3d, and S 2p core levels. (k) Mo K-edge XANES spectra, (l) Fourier-transform EXAFS spectra, (m, n) atomic models with R-space EXAFS fitting results, and (o-q) EXAFS wavelet transforms plots depicting Mo-S bond strength variation through color-scale intensity (blue to red indicates weak to strong).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/85490486b68f87560235f7c0.png"},{"id":98887743,"identity":"cc09055d-5156-4503-b5ed-4d24b438c8d8","added_by":"auto","created_at":"2025-12-23 15:28:05","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":523133,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical performance of the Li-CO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e batteries using biaxially strained MoS\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e \u003cstrong\u003ecathode catalysts with a limited capacity of 2000 mAh g\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e-1\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e.\u003c/strong\u003e (a) Comparative analysis of the capacity between biaxially strained MoS₂ and noble Ru NPs cathode catalyst after a full discharge process. (b) The first discharge and charge curves of the batteries using Ru, biaxially strained MoS₂ and pure MoS\u003csub\u003e2\u003c/sub\u003e cathode catalysts. (c) Comparison of the first charge/discharge protentional and corresponding energy efficiency of the batteries using biaxially strained MoS₂ with tunable atomic layer numbers and Ru NPs cathode catalysts. (d) Electrochemical cycle performance of the Li-CO\u003csub\u003e2\u003c/sub\u003e battery using monolayer biaxially strained MoS₂ operating at various current density from 1.0 A g\u003csup\u003e-1\u003c/sup\u003eto 10.0 A g\u003csup\u003e-1\u003c/sup\u003e and back to 1.0 A g\u003csup\u003e-1\u003c/sup\u003e. (e) Voltage-time curves of the batteries using the monolayer biaxial strained MoS\u003csub\u003e2\u003c/sub\u003e operating at 1.0 A g\u003csup\u003e-1\u003c/sup\u003e, 2.0 A g\u003csup\u003e-1\u003c/sup\u003e, 5.0 A g\u003csup\u003e-1\u003c/sup\u003e and 5.0 A g\u003csup\u003e-1\u003c/sup\u003e. (f) A long-term cycle performance of the battery using the monolayer biaxial strained MoS\u003csub\u003e2\u003c/sub\u003e operating at 10.0 A g\u003csup\u003e-1\u003c/sup\u003e. (g) Comparison of performance metrics for Li-CO₂ batteries including charging potential, energy efficiency, and cycle life where the red five-pointed stars represent the performance metrics achieved in our work.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/3f3b68f0a357bb207b023e79.png"},{"id":98887748,"identity":"869e4ee3-c1b0-4aa5-bfce-7fc554b31cc3","added_by":"auto","created_at":"2025-12-23 15:28:06","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1733156,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterization of discharge products of Li-CO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e batteries using biaxially strained MoS₂ catalysts. \u003c/strong\u003e(a) SEM image, (b) XRD spectrum, (c) XPS spectrum and (d) TEM images, EDS mapping and statistical results of the discharge products. (e) DEMS profile with discharge-charge curves at a current of 1 mA. (f) Schematic diagram of the battery during discharging and charging processes.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/98c6ce1919b691c5e91e9b87.png"},{"id":99309349,"identity":"98913ea9-87da-42f3-81cd-91037f4ac29b","added_by":"auto","created_at":"2025-12-31 16:10:13","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":638434,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTheoretical calculations of Li–CO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e battery charge and discharge mechanisms. \u003c/strong\u003e(a) Changes in the d-band center of the planar MoS₂ and MoS\u003csub\u003e2\u003c/sub\u003e with S\u003csub\u003ev\u003c/sub\u003e under compressive and tensile strains. (b) CO\u003csub\u003e2\u003c/sub\u003e, Li, and Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e adsorption energies for planar MoS\u003csub\u003e2\u003c/sub\u003e, planar MoS\u003csub\u003e2\u003c/sub\u003e with S\u003csub\u003ev\u003c/sub\u003e, bent MoS\u003csub\u003e2\u003c/sub\u003e and bent MoS\u003csub\u003e2\u003c/sub\u003e with S\u003csub\u003ev\u003c/sub\u003e. (c, d) Calculated best possible energy profiles for the nucleation of Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3 \u003c/sub\u003eand C on the basal plane of three samples (planar MoS\u003csub\u003e2\u003c/sub\u003e, bent MoS\u003csub\u003e2\u003c/sub\u003e, planar with Sv and bent MoS\u003csub\u003e2\u003c/sub\u003e with S\u003csub\u003ev\u003c/sub\u003e) at a theoretical equilibrium potential. The insets show the top views of adsorption systems on the planar MoS\u003csub\u003e2\u003c/sub\u003e and bent MoS\u003csub\u003e2\u003c/sub\u003e with S\u003csub\u003ev\u003c/sub\u003e respectively.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/ae9ae1c734ddb120a1a8369b.png"},{"id":100805913,"identity":"ffbd1e76-d232-4068-8825-07c2b888587e","added_by":"auto","created_at":"2026-01-21 14:51:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8269889,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/16a24806-cfa3-49a7-9108-2cf54ad17ca8.pdf"},{"id":98887760,"identity":"10a0d5fd-2c81-4747-a376-c5af7ef23ce3","added_by":"auto","created_at":"2025-12-23 15:28:06","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":17217265,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupplementaryInformation20251204.docx","url":"https://assets-eu.researchsquare.com/files/rs-8285433/v1/41a1cb294931dd4f3cc434f9.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Biaxial strain engineering of atomically thin MoS₂ for highly reversible Li–CO₂ batteries","fulltext":[{"header":"Introduction","content":"\u003cp\u003eTo address global warming and climate change, the development of carbon-neutral technologies is essential, including high-value conversion and utilization of carbon dioxide (CO₂), clean energy systems, and high-specific-energy storage technologies \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. Among them, lithium-carbon dioxide (Li-CO₂) batteries based on the reversible conversion reaction (4Li⁺ + 3CO₂ + 4e⁻ \u0026harr; 2Li₂CO₃ + C) represent a promising frontier electrochemical energy storage technology, offering a high theoretical energy density of 1876 Wh kg⁻\u0026sup1; and a theoretical equilibrium potential of 2.80 V (vs Li⁺/Li), while potentially enabling capture and convert CO₂ to realize net-zero carbon emissions \u003csup\u003e[\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. However, the intrinsically sluggish kinetics of the CO\u003csub\u003e2\u003c/sub\u003e reduction reaction (CO₂RR) and CO\u003csub\u003e2\u003c/sub\u003e evolution reaction (CO₂ER) leads to a substantial charge-discharge overpotential and significant energy loss in Li-CO\u003csub\u003e2\u003c/sub\u003e batteries, thereby greatly restricting their reversible cycling capability \u003csup\u003e[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. Currently, extensive research has been dedicated to lowering the reaction energy barrier of the CO₂ER through the design of high-temperature battery systems and high-catalytic-activity cathode catalysts. These catalysts primarily include noble metals \u003csup\u003e[\u003cspan additionalcitationids=\"CR7 CR8 CR9\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e, transition metal oxides/carbides/chalcogenides \u003csup\u003e[\u003cspan additionalcitationids=\"CR12 CR13\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e, and transition metal single-atom catalysts \u003csup\u003e[\u003cspan additionalcitationids=\"CR16 CR17 CR18 CR19\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e. Among them, two-dimensional transition metal dichalcogenides (TMDs), especially molybdenum disulfide (MoS₂), are an intriguing family of layered materials \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e. Owing to their unique crystal structure, high chemical stability, and facile preparation, MoS₂-based materials have been extensively explored as promising electrocatalysts in various electrochemical energy storage fields, including Li-CO₂ batteries \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. For example, Ahmadiparidari et al. reported a highly reversible organic Li-CO₂ battery using MoS₂ nanoflakes as the cathode that achieved an excellent long-cycle lifespan of up to 500 cycles. However, the charge potential remained above 4.0 V, resulting in a large charge-discharge overpotential exceeding 1.5 V, which limited the cycle life \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. This issue comes from the intrinsically low catalytic activity of the basal planes compared to edge sites in most TMDs, such as MoS₂ nanoflakes, due to their imited adsorption capacity for CO₂ and carbon-oxygen (C\u0026ndash;O) intermediates \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e. Given that the basal plane dominates the major structure of MoS₂, its rational engineering is critical for achieving superior bifunctional activity toward both CO₂RR and CO₂ER, which determins the performance of Li\u0026ndash;CO₂ batteries in practical applications.\u003c/p\u003e \u003cp\u003eTo address this challenge, surface engineering strategies such as defect creation, elemental doping, and single-atom decoration have been employed to enhance electrical conductivity and activate surface activity of MoS₂ \u003csup\u003e[\u003cspan additionalcitationids=\"CR27 CR28 CR29\" citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e. However, the precise synthesis of dual active centers in the basal plane through these approaches remains challenging for achieving efficient bidirectional catalysis in Li\u0026ndash;CO₂ batteries \u003csup\u003e[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/sup\u003e. Alternatively, strain engineering provides a promising strategy by modulating nanomaterial lattice parameters to synergistically combine geometric and electronic effects, which optimizes reaction pathways through regulated adsorption/desorption energetics while overcoming scaling relation constraints, thereby enabling concurrent enhancement of catalytic activity and stability \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e. Notably, introducing strain to MoS₂ not only enables precise electronic structure modulation of active sites but also facilitates sulfur vacancy (Sv) generation, collectively establishing a favorable microenvironment for target reactions \u003csup\u003e[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e. Moreover, traditional carbon-based cathodes suffer from severe corrosion, which leads to structural deformation or even collapse under severe local strain and stress at the catalytic sites, particularly under high mass-transport conditions with large current densities and high capacities, as well as during the repeated formation of low-efficiency lithium carbonate products \u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/sup\u003e. On the contrary, strain-engineered 2D TMDs, especially MoS₂, can withstand high levels of strain and stress without destroying their local structure or catalytic sites, while maintaining high catalytic activity over long-term cycling. However, most strain-related investigations have concentrated on in-plane tension, compression, or bending-induced stretching (i.e., uniaxial strain), which offers limited dimensional control over 2D TMDs, thereby resulting in limited control on the local environment surrounding active sites \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHerein, by strategically replacing conventional graphite conductive agents with highly conductive spherical Al NPs and leveraging their naturally formed ultrathin Al₂O₃ surface layer as a growth interface, we have successfully constructed an atomically thin MoS₂ shell with biaxial strain (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea-\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). This design enables systematic study of how strain and defects collectively modulate the local electronic configuration to optimize both CO₂RR and CO₂ER in Li\u0026ndash;CO₂ batteries. The biaxial strain and controllable atomic-layer number make this MoS\u003csub\u003e2\u003c/sub\u003e cathode catalysts highly efficient and stable (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea-\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). Theoretical calculations reveal that the adjusted d-band centers of atomically thin MoS\u003csub\u003e2\u003c/sub\u003e with the introduction of biaxial strain and in-plane S-vacancies are hybridized between CO\u003csub\u003e2\u003c/sub\u003e and Li species, respectively, which is conducive to the adsorption of reactants and the decomposition of Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e during discharge and charge, resulting in a small energy barrier for the rate-determining step. Furthermore, the spherical Al NP core with an ultrathin oxide layer (~\u0026thinsp;4 nm Al₂O₃) significantly enhances the electrical conductivity of the MoS\u003csub\u003e2\u003c/sub\u003e shell through electron tunneling while providing excellent structural stability (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). The SEM images revealed that the MoS\u003csub\u003e2\u003c/sub\u003e structure maintained stable after cycling under high current densities and high specific capacities. Meanwhile, the low overpotential remained after prolonged cycling further confirms its structural integrity and stable catalytic activity. As a result, the Li\u0026ndash;CO₂ battery using the biaxially strained MoS₂ with single atomic layer exhibits an ultra-long cycle life nearly 4000 cycles and ultra-low charge potentials of around 3.0 V at 10 A g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a limited capacity of 2000 mAh g⁻\u0026sup1;, far outperforming the best reported cycling stability for Li\u0026ndash;CO₂ batteries to date. This work develops an innovative strategy for fabricating biaxially strained TMDs with precisely controlled layer numbers to enhance CO₂RR/CO₂ER kinetics, enabling high-performance battery devices.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates the strain definition and structural design of MoS₂. The two-dimensional (2D) planar MoS₂ without strain is defined as zero-strain state, while the nanospherical MoS₂ strained along two axes is termed biaxial strain. Typically, when 2D planar MoS\u003csub\u003e2\u003c/sub\u003e is fabricated into nanospherical structures, biaxial bending strain is naturally generated and the magnitude of this strain can be precisely tuned by adjusting the size of the nanospheres (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea,\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed and Fig.\u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e. In comparison with zero-strain planar 2D materials, biaxial bending strain can not only optimize the electronic structure of d-orbitals in metal atoms but also induce uniform anionic vacancies on the 2D basal plane, thereby effectively enhancing the catalytic activity of the inherently inert basal plane (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb and Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) \u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e. Density functional theory (DFT) calculations further reveal that the d-band structure of MoS₂ exhibits distinct variations under compressive and tensile strains where the d-band center of MoS₂ is located at -1.31 eV under a -5% compressive strain and shifts to -0.86 eV under a 5% tensile strain (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). This strain-induced modulation of the d-band center confirms that strain can tailor the electronic structure of MoS₂ catalysts and regulate the bonding interactions between their surface and adsorbed species, thereby enabling the modulation of the catalysts' intrinsic activity.\u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e It also indicates that the biaxial strain engineering of MoS₂ catalysts at the atomic scale can optimize key reaction processes (e.g., reactant adsorption, intermediate conversion) in Li\u0026ndash;CO₂ batteries. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec schematically illustrates the synthetic protocol for biaxially strained MoS₂ shell grown on spherical Al NP core, which are named Al@MoS₂ core-shell catalyst. Briefly, referring to the previous report by Hamid Reza Ghorbani, kilogram-scale Al NPs are first prepared as cores via the electrical explosion of wire (EEW) \u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e. Owing to the ~\u0026thinsp;5% lattice mismatch between Al₂O₃ and MoS₂ (within the \u0026le;\u0026thinsp;10% epitaxial tolerance of 2D TMDs) that facilitates high-quality MoS₂ growth by balancing strain and crystallographic alignment \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e, the native ultra-thin Al₂O₃ layer (~\u0026thinsp;4 nm) on Al NPs serves as an ideal interface for the subsequent growth of biaxially strained MoS₂. Thus, by immersing Al NPs with a native Al₂O₃ layer in liquid-phase sulfur and molybdenum precursors, a biaxially strained MoS₂ shell layer is successfully grown on the spherical Al NP core with Al₂O₃ via a facile hydrothermal synthesis process maintained at 195\u0026deg;C for 10 hours (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec and S2). Notably, for the designed carbon-free cathode, the kilogram-scale Al NP cores with broad size distribution \u003csup\u003e[\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e directly yield biaxially strained MoS₂ shells with continuous curvature (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). Such multi-scale strain system enhances CO₂RR/CO₂ER performance via a synergistic mechanism where the continuous curvature distribution modulates the electronic structure of MoS₂ by lowering its d-band center and optimizing intermediate adsorption, while simultaneously establishing a gradient defect distribution through curvature-dependent S\u003csub\u003ev\u003c/sub\u003e generation in high-curvature regions and lattice preservation in low-curvature regions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) \u003csup\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e. As showed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, the strain-engineered MoS₂ cathode catalyst effectively accommodates the stress and strain induced by high-rate mass transport under high-capacity and high-current-density cycling. Its integrated pore network enhances reactant accessibility, while the synergistic coupling between strain fields and S\u003csub\u003ev\u003c/sub\u003e simultaneously strengthens CO₂ adsorption and lowers activation barriers, thereby collectively improving both reaction kinetics and structural durability \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e. In summary, this multi-scale synergistic strategy establishes a systematic design framework for advanced 2D TMD cathodes. It integrates d-band modulation for electronic regulation, curvature-induced S\u003csub\u003ev\u003c/sub\u003e for activated catalytic sites, and hierarchical pore/strain-vacancy synergy for optimized transport-adsorption coupling, ultimately enhancing the kinetics of CO₂RR/CO₂ER.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe particle size distribution, characterized by transmission electron microscopy (TEM), reveals that the as-prepared Al@MoS₂ core-shell sample exhibits a broad diameter range of 20 nm to 2000 nm with a normal distribution centered at ~\u0026thinsp;150 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec and S3). High-angle annular dark-field scanning TEM imaging and corresponding energy-dispersive X-ray spectroscopy (EDS) elemental mapping collectively demonstrate a distinct core-shell architecture in the pre-synthesized Al@MoS₂ material with Al and O localized in the core region and S and Mo uniformly distributed in the surrounding shell (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). Furthermore, high-resolution transmission electron microscopy (HR-TEM) and aberration-corrected TEM (AC-TEM) were employed to characterize the core-shell structures with three distinct diameters/curvatures of approximately 25 nm, 130 nm, and 255 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee-\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh). All three Al@MoS₂ structures with distinct diameters/curvatures exhibit a typical core-shell architecture consisting of a spherical Al nanocore, Al₂O₃ interlayer, and MoS₂ nano-shell. Specifically, all the Al₂O₃ interlayer maintains a uniform thickness of ~\u0026thinsp;4 nm, while the MoS₂ shell comprises approximately three atomic layers with a thickness of ~\u0026thinsp;2.0 nm (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef-\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh and Fig. S3). Furthermore, we observe a significant increase in defect density within the MoS₂ outer shell as the Al nanocore diameter decreases from ~\u0026thinsp;255 nm to 25 nm, primarily due to enhanced biaxial tensile strain (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef-\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh and Fig.S4-\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Statistical analysis further reveals a progressive expansion in the interplanar spacing of the MoS₂ shell with increasing curvature where the dominant interplanar spacing measures approximately 0.64 nm in the 255 nm-diameter structure, 0.68 nm at 130 nm diameter, and multiple spacings (0.68, 0.76, and 0.83 nm) emerge in the 25 nm-diameter structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei-\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ek and Fig.S4-\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), all exceeding the 0.62 nm reference value of strain-free planar MoS₂ \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e. The tensile strain (ε) in MoS₂ shells, calculated using ε\u0026thinsp;=\u0026thinsp;d/2r where d represents the thickness of MoS₂ shell (0.62 nm) and r denotes the average curvature radius, exhibits a distribution dependent on curvature radius. Statistical analysis of curvature radii indicates that reducing the curvature radius from 255 nm to 25 nm increases the biaxial tensile strain from approximately 0.57% to 9.64%. This strain gradient aligns well with experimental observations, including the expansion of interplanar spacing (0.64 nm \u0026rarr; 0.83 nm) and the variation in defect density, confirming the critical role of curvature-induced strain in regulating the electronic structure and catalytic performance of the material. Consequently, the broad size distribution of Al NP cores in the cathode generates significant curvature gradients in the MoS₂ shells, inducing gradient-distributed biaxial strain within the shell layers (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea-\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ek). This curvature-induced biaxial strain induces lattice expansion (manifested as increased interplanar spacing, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei-\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ek), elevated defect/vacancy density (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef-\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh), and an upward shift of Mo\u0026rsquo;s d-band center (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). For Li-CO\u003csub\u003e2\u003c/sub\u003e batteries, the expanded lattice and increased defects provide abundant active sites and facilitate Li⁺/CO₂ transport, while the upward-shifted d-band center strengthens the adsorption of the intermediates and lowers the reaction\u0026rsquo;s activation energy barriers. \u003csup\u003e[\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eFurthermore, by precisely controlling the concentrations of molybdenum and sulfur precursors while maintaining constant reaction temperature (see Experimental Section), we achieved accurate regulation of MoS₂ shell thickness (i.e., atomic layer number) in the Al@MoS₂ core-shell structures. HRTEM characterization confirmed the successful synthesis of MoS₂ shells with tunable atomic layers on Al₂O₃-coated Al nanoparticle cores through precursor concentration modulation. Statistical analysis demonstrated that the four precursor concentrations (5%, 10%, 20%, and 50%) produced core-shell structures with MoS₂ shells predominantly consisting of 1 layer, 2 layers, 3 layers, and 4 layers, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed and Fig. S7-S8), unequivocally validating the precise atomic-scale controllability of our synthetic strategy. Based on the strain formula ε\u0026thinsp;=\u0026thinsp;d/2r and statistical analysis of MoS₂ shell layer numbers, the calculated biaxial tensile strain values for monolayer to tetralayer MoS₂ are 0.85%, 2.64%, 4.01% and 4.8%, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee-\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh and Fig. S7).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe electron paramagnetic resonance (EPR) is employed to investigate the S-vacancies concentration in biaxially strained MoS₂ shells with different atomic layer numbers where the EPR signal loaded at 2.002 (g-factor\u0026thinsp;=\u0026thinsp;2.002) directly corresponds to unsaturated sites with unpaired electrons, and its intensity positively correlates with S\u003csub\u003eV\u003c/sub\u003e concentration (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei). The results show that the EPR signal intensity of biaxially strained MoS₂ decreases significantly with increasing layer number. Specifically, the monolayer MoS\u003csub\u003e2\u003c/sub\u003e sample (ML, 5% sulfur and molybdenum precursor concentration) exhibits markedly higher peak intensity than the bilayer (BL, 10%), trilayer (TL, 20%), and tetralayer layer MoS\u003csub\u003e2\u003c/sub\u003e (TTL, 50%) samples, with all strained samples showing substantially stronger signals than unstrained planar MoS₂ (100%, see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei). This confirms that the biaxial strain of the monolayer MoS₂ exhibits the most pronounced charge-compensating effect \u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e and the highest S\u003csub\u003ev\u003c/sub\u003e concentration, consistent with previous HRTEM observations (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea-\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). The identified relationship between strain magnitude and S\u003csub\u003ev\u003c/sub\u003e density further confirms suggest that the strong biaxial strain of the MoS\u003csub\u003e2\u003c/sub\u003e can effectively promote the formation of S-vacancies at adjacent sites \u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e. Furthermore, depth-profiling X-ray photoelectron spectroscopy (XPS) analysis based on sequential etching was performed on the monolayer biaxially strained MoS₂ coated on Al NP to further elucidate the evolution of its electronic structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej). Under the condition of zero etching time, the high-resolution spectrum of the Mo exhibits typical doublet peaks located at 228.8 eV and 232.2 eV, corresponding to Mo⁴⁺ 3d₅/₂ and 3d₃/₂ states, respectively. As the etching time increases to 40 seconds, the binding energy of Mo 3d₅/₂ shifts significantly to 229.7 eV, indicating a more delocalized local electric structure (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ej).\u003csup\u003e[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e Additionally, the presence of a peak at 235.9 eV confirms the formation of surface Mo⁶⁺ species due to oxidation. \u003csup\u003e[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e Furthermore, the S 2p₃/₂ peaks of the monolayer biaxially strained MoS₂ shift to higher binding energy of 162.3 eV when compared to those of the reported pure-MoS₂ (161.9eV) \u003csup\u003e[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e. This means the biaxial strain engineering of the monolayer MoS₂ endows S\u003csub\u003ev\u003c/sub\u003e sites with abundant electrons, which enhances CO₂ adsorption and facilitates Li₂CO₃ desorption for Li\u0026ndash;CO₂ batteries. \u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e To further understand the local structures of the biaxially strained MoS₂ cathode catalyst, we performed X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses targeting Mo (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ek-\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eq). Compared to planar MoS₂, the absorption edge of the biaxially strained MoS₂ grown on Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-coated Al NP cores shifts slightly toward lower energy, indicating interfacial charge transfer between MoS\u003csub\u003e2\u003c/sub\u003e shell and the core support (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ek) \u003csup\u003e[\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e. The characteristic peak observed at 20035 eV in the Mo K-edge XANES spectrum originates from the 1s\u0026rarr;4pz electronic transition, which serves as a spectroscopic fingerprint for identifying the Mo-S coordination configuration \u003csup\u003e[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]\u003c/sup\u003e. In the biaxially strained MoS₂ system, a reduction in the intensity of the 1s \u0026rarr; 4pz transition is observed, which is likely attributed to a decrease in symmetry from D₄h to C₄v. \u003csup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e The peaks near 20055\u0026ndash;20065 eV originate from the 1s \u0026rarr; 4pₓ,\u003csub\u003eγ\u003c/sub\u003e transition, where the exact peak position is dependent on the oxidation state of Mo (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ek).\u003csup\u003e[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/sup\u003e Fourier-transform EXAFS analysis demonstrates that the Mo\u0026ndash;S bond elongates to 2.41 \u0026Aring; in monolayer biaxially strained MoS₂, exceeding that in tetralayer (2.39 \u0026Aring;) and planar MoS₂ (2.38 \u0026Aring;, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei). Accompanying shifts in Mo\u0026ndash;S/Mo\u0026ndash;Mo peaks confirm lattice distortion and the elongation of Mo\u0026ndash;S bonds directly weaken their bonding strength and substantially reduces the CO₂ adsorption energy barrier (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei\u0026thinsp;~\u0026thinsp;3q and Fig.S9) \u003csup\u003e[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/sup\u003e. In addition, the EXAFS) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei) and the corresponding wavelet transform (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eo-\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eq) both show gradual decrease in intensity. Notably, the Mo coordination number decreases to ~\u0026thinsp;5.1 in monolayer biaxially strained MoS\u003csub\u003e2\u003c/sub\u003e (vs. ~5.7 in tetralayer MoS\u003csub\u003e2\u003c/sub\u003e and ~\u0026thinsp;6.0 in bulk MoS\u003csub\u003e2\u003c/sub\u003e) \u003csup\u003e[\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e. Such a trend is mainly due to the increased strain dimension of MoS\u003csub\u003e2\u003c/sub\u003e, resulting in the breaking of Mo-S bonds and thus creating more S-vacancies. This synergistic mechanism achieves dual modulation by both optimizing the free energy of CO₂ adsorption and lowering the energy barrier of the rate-determining step, thereby effectively enhancing the kinetic performance of the CO₂RR/CO₂ER \u003csup\u003e[\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBefitting the design of biaxial strain engineering of atomically thin MoS\u003csub\u003e2\u003c/sub\u003e, the Li\u0026ndash;CO₂ battery employing a ternary molten nitrate electrolyte, Li-metal anode, and MoS₂ cathode catalyst demonstrates a larger discharge capacity over 14 mAh than that of noble Ru NPs catalyst (~\u0026thinsp;9.6 mAh) operating at 150 \u003csup\u003eo\u003c/sup\u003eC, with a current density of 2 Ag\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea). Notably, previously reported Li\u0026ndash;CO₂ batteries utilizing noble Ru-based catalysts demonstrate optimal CO₂ER performance at an elevated temperature of 150\u0026deg;C \u003csup\u003e[\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]\u003c/sup\u003e. The evaluation of the cost-effectiveness value shows that the biaxially strained MoS₂ catalyst achieves a value more than 250 times that of Ru NPs catalyst for the Li-CO\u003csub\u003e2\u003c/sub\u003e battery system (Fig. S10). Electrochemical evaluations reveal that the biaxially strained MoS\u003csub\u003e2\u003c/sub\u003e catalyst shows a lower overpotential (OP, ~\u0026thinsp;0.43V with a 2.62 /2.97 V discharge/charge potential) and higher energy efficiency (EF, ~ 88.22%) compared with Ru NPs (~\u0026thinsp;0.52 V OP with a 2.43/2.95 V discharge/charge potential, and ~\u0026thinsp;82.4% EF) and pure planar MoS\u003csub\u003e2\u003c/sub\u003e (~\u0026thinsp;0.96 V OP and ~\u0026thinsp;69.9% EF). Notably, the battery using monolayer MoS\u003csub\u003e2\u003c/sub\u003e with biaxial strain exhibits the smallest OP (0.43 V) and highest EF (88.2%, see Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb-\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec and Fig. S11). As the MoS₂ shell thickness increases from monolayer to tetralayer, the discharge potentials of these batteries decrease from 2.62 to 2.23 V while the charge potentials increase from 2.97 to 3.18 V, which consistently surpass those of strain-free planar MoS₂ (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec). This electrochemical performance enhancement originates from the biaxially strained structure of atomically thin MoS₂, which not only promotes the kinetics of CO₂ RR/CO\u003csub\u003e2\u003c/sub\u003eER by maximizing the exposure of active edge sites (i.e., Mo-edge and S-edge), but also optimizes the adsorption capability for key intermediates (e.g., CO₂⁻ and Li⁺) through modulation of the Mo d-band center \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e, thus leading to improved electrochemical performance in Li\u0026ndash;CO₂ batteries. Although increasing the layer number induces interlayer van der Waals aggregation and strain shielding effects, resulting in reduced catalytic activity \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e, the residual strain present in multilayer MoS₂ still confers higher catalytic activity than strain-free planar MoS₂. Furthermore, the battery using the monolayer MoS\u003csub\u003e2\u003c/sub\u003e with biaxial strain was cycled at high current densities from 1.0 A g⁻\u0026sup1; to 10.0 A g⁻\u0026sup1; and back to 1.0 A g⁻\u0026sup1; that shows a high charge-potential retention of ~\u0026thinsp;99.34% from 2.99 V at the 1st cycle to 3.01 V at the 35th cycle (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed and Fig. S12). The battery demonstrates exceptional cycling stability at 1.0 A g⁻\u0026sup1;, 2.0 A g⁻\u0026sup1;, 5.0 A g⁻\u0026sup1; and 10.0 A g⁻\u0026sup1;, achieving an excellent overpotential a cycle life at least ten times longer than that of the Li-CO\u003csub\u003e2\u003c/sub\u003e battery using Ru NPs catalyst (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). Also, the battery using the monolayer MoS\u003csub\u003e2\u003c/sub\u003e with biaxial strain achieves an ultra-long cycle life approaching 4,000 cycles at 10.0 A g⁻\u0026sup1; while maintaining approximately\u0026thinsp;~\u0026thinsp;86.23%/95.96% charge/discharge potential retention from 2.47/3.08 V at the 1st cycle to 2.13/3.22 V at the last cycle (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef). This system demonstrates breakthrough cycling durability due to its low charging potential and high energy efficiency, outperforming all reported Li-CO₂ battery systems by an order of magnitude (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg and Table\u0026nbsp;1 in SI), including organic Li-CO\u003csub\u003e2\u003c/sub\u003e batteries (\u0026gt;4.0 V charge potential, \u0026lt;\u0026thinsp;400 cycles)\u003csup\u003e[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]\u003c/sup\u003e, solid-state Li-CO\u003csub\u003e2\u003c/sub\u003e batteries (\u0026gt;4.5 V, \u0026lt;\u0026thinsp;538 cycles)\u003csup\u003e[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]\u003c/sup\u003e, solar-driven Li-CO\u003csub\u003e2\u003c/sub\u003e batteries (\u0026gt;4.2V, \u0026lt;\u0026thinsp;50 cycles)\u003csup\u003e[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e and high-temperature molten salt Li-CO\u003csub\u003e2\u003c/sub\u003e batteries (\u0026gt;3.0 V, \u0026lt;\u0026thinsp;980 cycles)\u003csup\u003e[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo elucidate the discharge mechanism, the discharge products in the Li-CO\u003csub\u003e2\u003c/sub\u003e battery using the monolayer MoS₂ with biaxial strain, after being discharged to a capacity of 14 mAh at 2 A g⁻\u0026sup1;, were further characterized. The SEM image further confirms the flake-like morphology of the discharge products (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). The refined X-ray diffraction pattern of the discharge products shows characteristic peaks at 31.8\u0026deg;, 21.3\u0026deg;, and 30.6\u0026deg;, which correspond to the (002), (110), and (-202) crystal planes of Li₂CO₃ (JCPDS 87\u0026ndash;0728), respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb) \u003csup\u003e[\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]\u003c/sup\u003e. High-resolution XPS spectra showed characteristic peaks at 55.5 eV (Li 1s), 289.8 eV (C 1s), and 531.5 eV (O 1s) belong to Li₂CO₃, which further confirms that the flower-like discharge product is Li₂CO₃ (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). Additionally, a C 1s signal corresponding to the C-C bond was detected at 284.8 eV. TEM characterization clearly reveals a core-shell architecture in the discharge products, consisting of an Al@ MoS₂ NP core and a discharged Li₂CO₃-based product shell with uniform thickness distribution in the 600\u0026ndash;1000 nm range (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). HR-TEM characterization was conducted at three distinct regions (A, B, and C) of the core-shell structured discharge products (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). The discharge product at position A (the red-bordered region) exhibits a distinct hexagonal morphology, and its electron diffraction pattern and interplanar spacing (0.28 nm) are consistent with the Li₂CO₃ phase. HRTEM images and interplanar spacing analysis results of positions B (the bule-bordered region) and C (the green-bordered region) also confirm that the crystalline products at these two positions are Li₂CO₃ where the 0.28 nm interplanar spacing and 0.16 nm interplanar spacing responding to (002) crystal plane of Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e and (022) crystal plane of Li₂O, respectively. The formation of Li₂O originates from the nitrate-mediated discharge pathway in the Li-CO₂ battery system \u003csup\u003e[\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]\u003c/sup\u003e. Notably, distinct amorphous phases distributed between the crystalline Li₂CO₃ grains were observed in the HR-TEM images of positions A, B, and C (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). Combined with XPS results, we infer that the amorphous phase is amorphous carbon formed during the discharge process (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). This result further confirms that the discharge products of the battery comprise both crystalline Li₂CO₃ and amorphous carbon, as clearly demonstrated by experimental evidence. In-situ electrochemical mass spectrometry (ECMS) analysis reveals a 4/3-electron transfer reaction mechanism for the battery during discharge and charge process which aligns closely with the well-established typical Li-CO₂ battery reaction of 3CO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;4e\u003csup\u003e\u0026minus;\u003c/sup\u003e + 4Li\u003csup\u003e+\u003c/sup\u003e \u0026rarr; 2Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;C \u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]\u003c/sup\u003e, consistent with previous ex-situ characterization results of the discharge products (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee). Based on these ex-situ and in-situ characterization results, combined with the distinct morphological and particle size differences between region A and other areas, we propose that the formation of discharge products follows a two-stage growth mechanism (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef and S13). During the initial discharge stage, Li⁺, e⁻, and CO₂ react on the surface of biaxially strained MoS₂ catalyst to form fine composite nuclei consisting of crystalline Li₂CO₃ and amorphous carbon (the green-bordered region in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). Subsequently, continued nucleation and growth occur on the catalyst surface, leading to large-sized hexagonal nanosheets composed of crystalline Li₂CO₃ crystals and amorphous carbon, as shown at position A, B and C (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDFT calculations further reveal a noticeable modulation of the d‑band structure in MoS₂ under applied bending strain. Specifically, bending induces a significant upward shift of the d‑band center in pristine MoS₂ from ‑0.93 eV (0% strain) to ‑0.55 eV (5.5% strain). Moreover, the introduction of S\u003csub\u003ev\u003c/sub\u003e further modifies this bending‑driven d‑band shift, moving the center from ‑0.64 eV (0% strain) to ‑0.49 eV (5.5% strain), as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea. To further probe the synergistic effect of bending strain and S-vacancies on the adsorption behavior of the MoS₂, we computed the adsorption energies (Eₐdₛ) of key intermediates on four representative MoS₂ structures including pristine planar MoS₂ (Pr-MoS₂), MoS₂ with Sv (Vₛ-MoS₂), bent MoS₂ (Bent-MoS₂, under 11% tensile strain), and the bent MoS₂ with a single Sv (Bent-Vₛ-MoS₂). The synergistic effect of tensile strain and S-vacancies significantly enhances the adsorption strength of MoS₂ toward Li, LiCO₃, and CO₂, while maintaining moderate adsorption equilibrium for CO₃ intermediates (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). Among the four MoS₂ structures (Pr-MoS₂, Vₛ-MoS₂, Bent-MoS₂ and Bent-Vₛ-MoS₂), the optimal reaction pathways are I, IV, I, and V, respectively, where the pathway V shows the lowest energy barrier (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec-\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed and Fig.S13). The Bent-Vₛ-MoS₂ structure demonstrates the smallest free energy changes (ΔGf(r)) for the rate-determining steps in both reaction stages, with values of 2.15 eV in the first stage and 2.87 eV in the second stage. The reduced energy barriers originate from strain-vacancy synergy where the strain enhances catalytic activity by exposing more Mo active sites, elevating the Mo d-band center position, and reducing vacancy formation energy, while S-vacancies create localized electron-rich regions that promote interfacial charge transfer (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ei and Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea). This synergistic mechanism optimizes the adsorption properties of the MoS\u003csub\u003e2\u003c/sub\u003e, exhibiting strong adsorption toward CO₂/Li while maintaining moderate adsorption balance for intermediates/products, thus leading to the optimal reaction pathway V and significantly improving the kinetics of both CO₂RR and CO\u003csub\u003e2\u003c/sub\u003eER (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb-Fig.\u0026nbsp;6d). Schematic diagrams of intermediate adsorption configurations reveal that the Bent-Vₛ-MoS₂ possesses more stable adsorption geometries and shorter Mo-adsorbate bond lengths, with these results corroborating the adsorption energy calculations and collectively validating the theoretical rationale of the strain-vacancy synergistic catalytic mechanism (Fig. S13 and Table S2 -S7).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we reported a high energy effciency and long cycle lifespan Li\u0026ndash;CO₂ battery by biaxial strain engineering of atomically thin MoS\u003csub\u003e2\u003c/sub\u003e cathode catalyst. In-situ/ex-situ characterizations confirmed the biaxial strain engineering of atomically thin MoS\u003csub\u003e2\u003c/sub\u003e can effcient catalyze C\u0026ndash;O bond cleavage and the formation of Li₂CO₃ and amorphous carbon during discharge, and accelerate CO₂ evolution during charge. The robust cathode structure remained stable under the intensive stress-strain conditions induced by high mass transport at elevated current densities and specifc capacities, as well as during repeated Li₂CO₃ formation and decomposition over prolonged cycling. Electrochemically, the Li-CO\u003csub\u003e2\u003c/sub\u003e batteries using monolayer biaxially strained MoS₂ maintained low charge potentional less than ~\u0026thinsp;3.1 V and high energy effciency over 80% at 2.0 A g⁻\u0026sup1;, 5.0 A g⁻\u0026sup1; and 10 A g⁻\u0026sup1;. Notably, it shows a record-breaking long cycle life of nearly 4000 cycles, accompanied by low charge potentials and high energy efficiency, thereby validating the role of C\u0026ndash;O bond transformations in energy storage. Complementary DFT calculations elucidated the bending strain and S\u003csub\u003ev\u003c/sub\u003e synergy enhance Li/LiCO₃ adsorption, optimize the reaction pathway (Pathway V for bent-Vₛ-MoS₂), and reduced rate-determining step barriers to 2.15 eV (first stage) and 5.25 eV (second stage), thus boosting CO\u003csub\u003e2\u003c/sub\u003eRR and CO\u003csub\u003e2\u003c/sub\u003eER kinetics. Strain elevated Mo\u0026rsquo;s d-band center and lowered S\u003csub\u003ev\u003c/sub\u003e formation energy, while S-vacancies created electron-rich regions to amplify adsorption. These findings clarify MoS₂ structure\u0026ndash;activity relationships and provide a strain/defect engineering strategy for high-performance cathodes. This work guides the design of catalysts for sluggish CO₂ER and paves the way for integrating CO₂ into advanced energy-storage systems.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eSynthetic of Al@MoS\u003csub\u003e2\u003c/sub\u003e core-shell NPs structure\u003c/h2\u003e \u003cp\u003eThe Al nanoparticles were synthesized via electrical explosion of wire (EEW) in a 0.1 MPa argon atmosphere by applying a 25 kV high-voltage pulsed discharge to a 0.2 mm diameter Al wire, inducing instantaneous vaporization and explosion, followed by condensation and collection through circulating gas flow. Subsequently, the resulting Al nanoparticles with native oxide layers were introduced into liquid-phase precursors of sulfur and molybdenum, yielding Al@MoS₂ core-shell nanoparticles with an ultra-thin MoS₂ nanoshell after a 10 h reaction at 195\u0026deg;C. The morphology, elemental distribution, and structural characteristics of both as-prepared and post-cycled samples were characterized by X-ray diffraction (XRD, Bruker D8), X-ray photoelectron spectroscopy (XPS, ULVAC-PHI), scanning electron microscopy (SEM, Zeiss), transmission electron microscopy (TEM, Talos G2 F20), electron paramagnetic resonance (EPR, Bruker EMXplus), and synchrotron radiation X-ray absorption spectroscopy (XAS) at the Shanghai Synchrotron Radiation Facility (SSRF), beamline BL14W1.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eElectrolyte preparation\u003c/h3\u003e\n\u003cp\u003eA homogenized powder mixture composed of lithium nitrate (99.99%, Aladdin), potassium nitrite (ACS, Aladdin), and cesium nitrate (99.99%, Aladdin) with a molar ratio of 37:39:24 was heated to 120\u0026deg;C to form the eutectic molten salt electrolyte.\u003c/p\u003e\n\u003ch3\u003eCathode preparation and characterization\u003c/h3\u003e\n\u003cp\u003eTwo distinct cathode materials were fabricated. For the Al@MoS₂ catalyst cathode, the as-synthesized Al@MoS₂ core\u0026ndash;shell nanoparticles were dispersed in a mixed solution of ethanol and Nafion ionomer (D520-1000EW, 5 wt%) at a volume ratio of 9.5:0.5. The dispersion was ultrasonicated for 30 min to form a homogeneous catalyst ink, which was then uniformly spray-coated onto carbon nanofibers (WOS1009) using a benchtop spray coater. The resulting cathode was subsequently dried for 12 h. For the Ru catalyst cathode, ruthenium nanoparticles were deposited directly onto carbon nanofibers (WOS1009) via direct current (DC) reactive magnetron sputtering employing a 99.999% pure ruthenium target. The deposition was conducted at a pressure of 0.2 Pa, a constant power of 100 W, and a current of 0.3 A for a duration of approximately 5 min.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eCell assembly and electrochemical measurements\u003c/h2\u003e \u003cp\u003eAll cells were assembled inside an argon-filled glovebox (MIKROUNA, UNIVERSAL 1800/750/900). As illustrated in Fig. S18, the cell configuration consisted of a metallic lithium anode, the eutectic molten salt electrolyte, and an MoS₂-based/Ru cathode. The assembled cells were sealed within custom-designed fixtures. After purging the chamber with pure CO₂ for 1 h, the cells were tested at 150\u0026deg;C under a continuous CO₂ flow of 20 cm\u0026sup3; min⁻\u0026sup1;. The discharge\u0026ndash;charge cycling performance was evaluated using an electrochemical testing system (Hokuto Denko, HJ1001SD8), with specific capacity calculated based on the mass of loaded catalyst. In the calculation of the battery's specific capacity, the mass of the MoS₂ catalyst serves as the basis for evaluation. The MoS₂ mass is determined by deriving its actual amount in the cathode material from the mass ratio of the sulfur and molybdenum sources relative to the aluminum source in the hydrothermally synthesized Al@MoS₂ precursor. This derived MoS₂ mass loading (~\u0026thinsp;5 ug/cm\u003csup\u003e2\u003c/sup\u003e to 100 ug/cm\u003csup\u003e2\u003c/sup\u003e) is then used to calculate the discharge specific capacity of the battery.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was partially supported by the National Natural Science Foundation of China (Grant Nos. 61921005, 62474160, 61735008, 62104099 and 62004078), National Key Research \u0026amp; Development Program of China (2018YFB2200101), Natural Science Foundation of Jiangsu province (BK20190313 and BK 20201073)\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHucheng Song:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; review \u0026amp; editing, Writing \u0026ndash; original draft, Visualization, Formal analysis. \u003cstrong\u003eMin Wang:\u0026nbsp;\u003c/strong\u003eData curation, Formal analysis, Methodology, Validation, Writing - Original draft. \u003cstrong\u003eJunnan Han:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; review \u0026amp; editing, Software, Methodology, Investigation, \u003cstrong\u003eZehui Zhang\u003c/strong\u003e: Writing \u0026ndash; review \u0026amp; editing, Formal analysis.\u003cstrong\u003e\u0026nbsp;Shijie Yang:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; review \u0026amp; editing, Visualization.\u0026nbsp;\u003cstrong\u003eZhihuan Li\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003eInvestigation.\u0026nbsp;\u003cstrong\u003eGungbin Zhang\u003c/strong\u003e\u003cstrong\u003e:\u0026nbsp;\u003c/strong\u003eFormal analysis, Conceptualization. \u003cstrong\u003eChangshun Wang:\u0026nbsp;\u003c/strong\u003eProject administration. \u003cstrong\u003eJing Wu:\u0026nbsp;\u003c/strong\u003eFormal analysis. \u003cstrong\u003eLinlong Zhang:\u0026nbsp;\u003c/strong\u003eInvestigation.\u0026nbsp;\u003cstrong\u003ePei Zhang\u003c/strong\u003e: Investigation.\u003cstrong\u003e\u0026nbsp;Zhongwei Yu:\u0026nbsp;\u003c/strong\u003eConceptualization.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eDongke Li:\u0026nbsp;\u003c/strong\u003eSupervision, Resources,\u0026nbsp;\u003cstrong\u003eYijie Liu:\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; review\u0026nbsp;\u0026amp;\u0026nbsp;editing, Conceptualization.\u003cstrong\u003e\u0026nbsp;Sixie Yang:\u0026nbsp;\u003c/strong\u003eWriting \u0026ndash; review\u0026nbsp;\u0026amp;\u0026nbsp;editing, Formal analysis. \u003cstrong\u003eLinwei Yu:\u003c/strong\u003e Resources, Conceptualization,\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eProject administration.\u003cstrong\u003e\u0026nbsp;Jun Xu:\u003c/strong\u003e Supervision, Resources, Project administration, Funding acquisition, Conceptualization.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAger JW et al (2018) Energy storage chemical storage of renewable energy. 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Joule 6,8\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Li-CO2 battery, biaxial strain engineering, MoS2 catalyst, single atomic layer","lastPublishedDoi":"10.21203/rs.3.rs-8285433/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8285433/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eLithium-carbon dioxide (Li-CO\u003csub\u003e2\u003c/sub\u003e) batteries have attracted considerable interest due to their high energy density and significant potential for achieving net-zero carbon emissions. However, the sluggish kinetics of the CO₂ evolution reaction leads to a substantial overpotential and severe energy loss in Li\u0026ndash;CO₂ batteries, thereby drastically limiting their reversible cycling capability. Herein, we report the design of a cost-effective, catalytically active, and mechanically stable cathode catalyst for Li-CO\u003csub\u003e2\u003c/sub\u003e battery by introducing biaxial strain engineering into atomically thin MoS₂. The structurally stable 3D framework can accommodate high-levels of stress and strain at the catalytic sites, as evidenced by the intact structure and the low overpotential maintained after long and stable cycling. Theoretical calculations demonstrate that the synergistically adjusted d-band centers in biaxially strained atomically thin MoS₂ with functional in-plane S-vacancies facilitate orbital hybridization with both CO₂ and Li species. This unique electronic structure promotes reactant adsorption during discharging and enhances Li₂CO₃ decomposition during charging, ultimately leading to a minimized energy barrier for the rate-determining step. The resulting Li-CO₂ battery based on monolayer biaxially strained MoS₂ exhibits a\u0026thinsp;~\u0026thinsp;0.6 V overpotential, ~\u0026thinsp;85% energy-efficiency, and nearly 4000 cycles cycle-lifespan at 10 A g⁻\u0026sup1; for a fixed 2000 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e capacity per cycle, surpassing those of previous catalysts under similar conditions. This work provides a strategic pathway for the rational design of advanced catalysts for practical Li\u0026ndash;CO₂ batteries.\u003c/p\u003e","manuscriptTitle":"Biaxial strain engineering of atomically thin MoS₂ for highly reversible Li–CO₂ batteries","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-23 15:27:58","doi":"10.21203/rs.3.rs-8285433/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a16acb55-7b7f-44b6-bcfa-9fffdb49ab69","owner":[],"postedDate":"December 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":59333508,"name":"Physical sciences/Materials science/Materials for energy and catalysis/Batteries"},{"id":59333509,"name":"Physical sciences/Materials science/Nanoscale materials/Two-dimensional materials"}],"tags":[],"updatedAt":"2026-01-21T14:48:25+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-23 15:27:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8285433","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8285433","identity":"rs-8285433","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}