Hydrogen plasma reduction for direct upcycling of battery waste into high-performance alloys

Hydrogen plasma reduction for direct upcycling of battery waste into high-performance alloys | 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 Physical Sciences - Article Hydrogen plasma reduction for direct upcycling of battery waste into high-performance alloys Se-Ho Kim, Dierk Raabe, Baptiste Gault, Jae-Pyoung Ahn, Jinyeon Hwang, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7339880/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Achieving carbon neutrality makes sustainable recycling approaches for end-of-life batteries critical to accommodate the rapid growth of the electric vehicle market. Conventional hydrometallurgical and pyrometallurgical processes are energy-intensive, time-consuming, and generate hazardous by-products. Here, we showcase how hydrogen plasma reduction enables rapid recovery of valuable metals from spent battery cathodes, reducing energy consumption by over 25% compared to traditional extraction techniques. Beyond metal recovery, the method allows direct waste-to-alloy synthesis of high-performance materials, including super invar, high-entropy, and titanium-based systems, through a streamlined process using battery waste as starting material. This approach offers a simple, efficient, and environmentally friendly route for upcycling battery waste into advanced functional alloys. Physical sciences/Materials science/Structural materials/Metals and alloys Physical sciences/Chemistry/Green chemistry/Sustainability Battery waste upcycling Hydrogen plasma reduction Metal recovery Single-step alloy design Circular economy Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction The global imperative for carbon neutrality, coupled with the accelerating demand for secondary batteries, particularly in the electric vehicle (EV) sector, has intensified the search for transformative recycling strategies [1, 2]. In 2023, global EV sales reached ~14 million units, a six-fold increase since 2018, signalling a sharp rise in end-of-life batteries requiring recycling in the coming decades [3]. By 2030, an estimated 4.1 million EV batteries will need recycling, with projections exceeding 42 million by 2040. Simultaneously, rising costs and dwindling supplies of critical metals such as Ni, Co, and Li [4] are placing increasing pressure on global supply chains, underscoring the urgency of sustainable recycling methods [5] that not only recover valuable elements but also enable the direct synthesis of novel materials, including alloy precursors. Conventional recycling approaches, including wet chemical leaching and high-temperature pyrometallurgy, present significant challenges. Hydrometallurgical processes [6, 7] typically require extensive pre-treatment to convert battery waste into a 'black mass', followed by aggressive acid or base leaching to dissolve metal oxides into ionic forms. While several commercial processes exist for the selective extraction of target elements, they are often slow, generate large volumes of hazardous wastewater, and require costly multiple purification steps. Pyrometallurgical methods [8, 9] rely on high-temperature melting to separate metals from slag based on differential melting points and densities. As such, they are energy-intensive, emit substantial quantities of CO 2 , and demand significant capital investment for post-processing infrastructure. Mechanical and direct recovery methods [10], which seek to extract active materials without chemical transformation, have also been investigated; however, they do not consistently yield products that are immediately suitable for industrial applications. Hydrogen plasma reduction (HPR) offers a fundamentally different, sustainable, and electrified alternative by replacing fossil-based reductants with hydrogen, producing water instead of CO 2 as a by-product [11]. In HPR, a plasma arc is ignited directly on the surface of metal oxides in a hydrogen-rich atmosphere (10 vol.% H 2 ), simultaneously melting the oxides and dissociating hydrogen gas into highly reactive atoms, protons, and radicals at temperatures exceeding 2500 °C [12]. Direct interaction between the molten oxide and high-energy plasma species enables rapid reduction to the metallic state [13-15]. This process is inherently fast and energy-efficient, outperforming conventional hydrometallurgical and pyrometallurgical methods [16]. For instance, HPR reduces energy consumption by ~19% compared with the rotary kiln–electric furnace route used in nickel laterite ore processing, by consolidating drying, calcination, reduction, and refining into a single step, thus lowering both energy consumption and CO 2 emissions [12]. As an example, the reduction of one mole of LiCoO 2 requires two moles of H 2 , equivalent to ~0.07 kg of hydrogen per kilogram of recovered Co. This eliminates the need for fossil-based reductants and hazardous chemicals [17, 18]. The use of green hydrogen, derived from renewable energy, further decreases the carbon footprint, enabling sustainable conversion of battery waste into high-purity metallic precursors [19, 20]. These plasma-derived metals and alloys exhibit impurity levels comparable to commercial standards, obviating the extensive post-treatment typically required in carbon-based reduction processes [12, 21]. Moreover, plasma environments turn reductants into highly excited states, thus enhancing their reactivity, effectively replacing part of the (expensive, indirect) chemical driving force with an (inexpensive, direct) electrical one, ideally supplied by renewable energy sources. In parallel, the development of sustainable alloys is critical in an era of resource constraints and increasing environmental accountability. Current global metal production, at ~2 billion tonnes annually, accounts for ~40% of industrial greenhouse gas emissions [22]. HPR enables direct conversion of ores into high-purity metals and subsequently into advanced alloys [23]. Recent analyses suggest HPR holds considerable promise as an economically viable alternative to traditional steelmaking methods, particularly for processing medium-grade iron ore (approximately 59 wt.% Fe [24]), demonstrating promising scalability, process simplification, and reductions in carbon emissions. Moreover, previous studies indicate that HPR could offer cost savings of up to 20% compared to conventional blast furnace processes [25, 26]. Additionally, achieving plasma efficiency of at least 82% is considered necessary to ensure economic viability [24]. While plasma technologies from the 1990s typically reached efficiency of ~80% [27], current advancements suggest achievable efficiency up to 92% [28]. Given the technological maturity and widespread adoption of electric arc furnace (EAF) in the steel industry, the integration of hydrogen-rich gas mixtures and modified plasma torches into existing EAF infrastructures emerges as a practical and efficient pathway [29]. The global EAF market, expected to grow at a compound annual growth rate (CAGR) of 12% [30], further highlights the substantial potential for the rapid adoption of HPR technologies. Considering the prospect for battery waste worldwide, HPR has the potential to support a circular economy, reducing dependence on primary resource extraction and substantially lowering energy use and associated emissions, but also to be used as an integrated process for making high-performance alloys [31, 32]. Given that spent batteries contain valuable elements compatible with advanced alloy systems, Figure 1 illustrates examples of their direct integration into existing engineering alloys. Here, we present a novel approach underpinned by detailed experimental results showcasing the successful recovery and upcycling of diverse metals from battery wastes including, the most commonly used electrode materials as well as metallic contacts, and the synthesis of an array of alloys with potential for application as structural and functional materials. Our work highlights the versatility and effectiveness of this emerging recycling approach with broad implications for sustainable metallurgy. Figure 2 summarises the HPR results for spent cathodes of Li(Ni 0.8 Co 0.1 Mn 0.1 )O 2 (NCM811) as well as commercial pristine cathodes of LiCoO 2 (LCO) and LiFePO 4 (LFP). These three materials represent the leading cathode chemistries currently dominating the global market, which is projected to expand from ~4.2 TWh in 2024 to ~7.5 TWh by 2030. Due to laboratory safety constraints, a gas mixture comprising 10 vol.% H 2 and 90 vol.% Ar was used. Although pure (100 vol.%) H 2 would enhance the reduction kinetics, the chosen mixture still yielded substantial benefits in terms of reaction efficiency and energy savings. The cathode powders, Figure 2a, were pelletised and positioned beneath a tungsten electrode within the plasma reactor (Figure 2b), with the partial pressure of hydrogen (P H ) maintained at 4.13 × 10 3 Pa during the reduction process. Within just 1 min of plasma exposure, metallic beads were formed (Figure 2c), indicating rapid and effective reduction. To evaluate the influence of H 2 partial pressure on reduction efficiency, thermogravimetric analysis (TGA) was carried out, comparing samples processed in an H 2 -containing reactive atmosphere with those processed in an inert Ar atmosphere. As shown in Figure 2d, reduction initiated earlier in H 2 . The decomposition rate of NCM811 was ~2.5 times faster in H 2 -containing Ar than in pure Ar. Similar behaviour was observed for LCO and LFP, confirming enhanced reduction kinetics attributable to the higher reactivity of hydrogen (Figure S2). The reaction kinetics under the two atmospheres were further quantified using the Kissinger–Akahira–Sunose (KAS) method [33], focusing on NCM811 (Figures 2e and S3–S4). Distinct peaks corresponding to sequential reduction steps were identified by varying the heating rates (5, 10, 15, 20, and 25 °C/min). These peaks represent the phase transition from a layered into a spinel structure [34], the reduction from Ni 4+ to Ni 2+ [35], and the reduction of Ni 2+ to Ni 0 [35], respectively. The activation energies for these reactions in H 2 were 1.8, 1.8, and 6.2 times lower, respectively, than those in Ar, confirming significantly faster reaction kinetics in the presence of H 2 . Additional TGA results for LCO under varying heating rates are provided in Figure S5. Microstructural characterisation of LCO confirmed complete conversion to metallic Co. X-ray diffraction (XRD) combined with Rietveld refinement verified the formation of high-purity Co, demonstrating the efficacy of HPR (Figures 2f and S6) [36]. Scanning electron microscopy (SEM)-based techniques, including electron backscatter diffraction (EBSD) and energy-dispersive X-ray spectroscopy (EDS), together with atom probe tomography (APT), revealed a hexagonal close-packed structure with no detectable Li in the ingot. Figures 2g and 2h further confirmed high purity, with residual O [37] and C contents below 0.11 and 0.12 at.%, respectively (see Figures S7–S10). No Li was detected in the metallic ingots, indicating that it likely reacted with residual C and O to form Li 2 CO 3 , which was collected as oxide and dust in the reactor chamber (Figures S11–S13). Consistent with this observation, Hu et al. [38] reported that 10–15 wt.% of Li typically remains as Li 2 CO 3 dust in smelting processes for lithium-ion battery recycling. Characterisation of NCM811 similarly demonstrated efficient conversion to face-centred cubic (FCC) Ni phase from the XRD result in Figure S6 [39]. Mn, which is thermodynamically stable as an oxide even under hydrogen plasma conditions, remained as surface oxides (Figure S14) [23, 40, 41]. SEM confirmed a homogeneous metallic grain structure with minimal structural variation and high chemical purity, with residual elements below 0.7 at.%. In contrast, the reduction product of LFP consisted of 99.6% Fe 3 P and 0.4% α-Fe from XRD in Figure S6. SEM-EBSD and APT analyses revealed significant residual P (~26 at.%), which remained within the Fe matrix due to the reducing environment, which prevents formation of P 2 O 5 . Fe 3 P is known to function as an effective hydrogenation catalyst in both acidic [42] and alkaline [43] media. However, residual P can be detrimental, causing grain boundary embrittlement and temper embrittlement in Fe alloys intended for mechanical applications [44, 45]. These findings emphasise the need for additional strategies to remove P from HPR-Fe alloys derived from battery waste. The recovery yields are to be 54.8, 41.4, and 82.5% for LCO, NCM811, and LFP, respectively (see Table S1). Despite the inherent limitations of experiments carried out on a lab-scale, HPR’s ability to successfully recover significant proportions of valuable transition metals from spent cathodes even within short treatment times. Notably, LFP exhibited the highest yield (82.5%), indicating excellent efficiency for Fe-based cathodes. Further HPR’s flexibility allows for targeted optimization, through adjusting pre-treatment conditions, treatment duration, or hydrogen partial pressure to enhance yields for specific cathode materials on an industrial scale. To explore the direct conversion of battery waste into functional alloys, waste NCM811 was combined with LFP powders to produce a composition analogous to Invar, an alloy with near-zero thermal expansion [48]. By precisely controlling the mass ratio of these waste materials, the composition of the HPR-processed alloy closely matched that of super invar (Figure 3a). The alloy had a nominal composition of 35 at.% Ni, 5 at.% Co, balanced by Fe, exhibiting a thermal expansion at room temperature up to 60% lower than that of conventional invar alloys. However, residual P was initially detected in the recycled alloy. P is detrimental to Fe–Ni alloys as it degrades magnetic and mechanical properties through the formation of (Fe, Ni, Co) 3 P phases during cooling [49]. SEM-EBSD and EDS analyses revealed Fe 2 NiP phases along grain boundaries, with a phosphorus concentration of ~3.8 at.% in the examined region. To mitigate P contamination, Fe 3 P derived from LFP was further treated under hydrogen plasma for 2 min at a constant current of 100 A, partially converting it to pure Fe (Figure S15). While this treatment was effective for partial P removal, it is unlikely to be sufficient for commercial application. A more practical and energy-efficient approach was achieved by introducing CaCO 3 as a P absorbent. During HPR, CaCO 3 reacted to form a CaO·P 2 O 5 slag, effectively capturing phosphorus. This by-product can be repurposed as a valuable raw material for cement production and bioactive materials [50-52]. In this study, CaCO 3 was sourced from recycled oyster shells (Figure S16), addressing a major waste management challenge in the seafood industry, where nearly 400,000 tonnes of oyster shells are discarded annually in South Korea alone. Recycling 1 tonne of oyster shells can reduce greenhouse gas emissions by ~0.3 tonnes [53]. Incorporating CaCO 3 into the LFP reduction process, therefore, enabled sustainable P removal from the resulting metals. Experiments with different mixing ratios of NCM811, LFP, and CaCO 3 are presented in Figures S17–S29. Following pelletisation and HPR, a super invar alloy was successfully synthesised, with no detectable residual P and an average grain size of ~200 µm (Figures 3b and S30). The thermal expansion behaviour of the HPR-synthesised invar alloy was evaluated to confirm its near-zero thermal expansion. As shown in Figure 3c, the alloy exhibited a thermal expansion coefficient of 9.21 × 10 -7 /°C at room temperature, outperforming conventional invar and closely matching super invar. After five hours of heat treatment at 1200 °C, the room-temperature thermal expansion coefficient increased slightly to 2.03 × 10 -6 /°C, while the coefficient between 150 and 350 °C decreased by two-thirds (Figure S31). These properties can be further improved through additional mechanical processing and heat treatment [54]. Recovered metals integrated into a one-step alloy design strategy using green hydrogen represent a significant step towards achieving a circular economy [23, 55]. Importantly, this approach extends beyond the invar alloy family, as the diverse elemental composition of battery wastes provides access to a wide range of alloy systems. Cathode materials are rich sources of Ni, Fe and Co; anode materials can supply Ti from Li 4 Ti 5 O 12 (LTO), Ag and In from Ag–In alloys, or Si; while current collectors contribute Cu and Al. Using this approach, we demonstrate that green HPR enables the direct synthesis of a broad range of conventional and advanced alloys (Figures 4a and 4f). A high-entropy alloy (HEA) was synthesised from NCM811, LFP, LCO and a commercial Cu current collector, forming a homogeneous FCC structure with near equiatomic Fe, Ni, Co and Cu, as confirmed by SEM-EBSD-EDS and XRD analyses (Figures 4b and 4c) [56]. This FeNiCoCu HEA composition has previously been reported to exhibit distinctive magnetic behaviour [57-59]. The synthesised HEA demonstrated a high saturation magnetisation of 129.6 ± 0.2 emu/g, a low coercivity of 22.5 Oe at room temperature and a high Curie temperature of 928 K. These values substantially exceed those reported for FeCoNi or FeCoNiCu(Al) HEAs [60, 61], indicating that the material retains soft magnetic behaviour at elevated temperatures, surpassing the operational limits of many existing soft magnets (Figures 4d and 4e). Further heat treatment improved both the magnetic performance and the Curie temperature of the HEA shown in Figure 4a. The alloy retained its FCC structure and displayed a homogeneous elemental distribution without Cu segregation (Figure S39). TiAl alloys, key materials in one of the most advanced alloy families for aerospace turbine applications, were synthesised by combining LTO anode material with an Al current collector through HPR (Figure 4f and Figure S40). Characterisation confirmed the formation of a single-phase γ-TiAl alloy (Figures 4g and 4h). Controlled processing conditions additionally produced α 2 -Ti 3 Al phases (Figure S40). Both γ-TiAl and α 2 -Ti 3 Al/γ-TiAl alloys, valued for their exceptional specific strength and high-temperature creep resistance, are regarded as critical materials for aerospace applications [67-69]. Nanoindentation and Vickers hardness measurements revealed a hardness of 350 ± 4.8 HV and a Young’s modulus of 208.8 ± 4.8 GPa, closely matching the properties of conventional aerospace-grade TiAl alloys (Figures 4i, 4j and S41). These results demonstrate the direct synthesis of both soft magnetic and aerospace-alloys from battery wastes through a streamlined, single-step HPR process. The demonstrated capability of HPR to rapidly convert diverse battery waste streams into high-performance alloys underscores its transformative potential for sustainable metallurgy, aligning with global sustainability objectives and circular economy strategies. Gas chromatography of gases collected from the HPR reactor (Figure S42) confirmed CO formation, indicating that residual carbon from the battery black mass participates in the reaction. This utilization of carbon contributes to improved process efficiency and sustainability. Additionally, Li- and Mn-rich particulates generated during plasma reduction represent valuable secondary resources for recovery and recycling. Preliminary evaluations show that HPR exhibits a clear energy advantage over the current extraction methods. Integration of the proposed HPR process into existing EAF infrastructure is feasible by incorporating pre-heated hydrogen-rich gas mixtures lines along with a plasma torch, but economic viability, regulatory frameworks, and market acceptance for recovered metals and alloys will require detailed analysis [24]. Yet already, the energy consumption was evaluated for NCM811, yielding 2.7 g of pure Ni at ~511 MJ/kg. By comparison, conventional commercial Ni production consumes between 576 [70] and 697 MJ/kg [71] for smelting and refining from Ni laterite ores. Even at laboratory scale, the HPR method already demonstrates energy savings of 11.3% to 26.7% accompanied by a significantly lower carbon footprint and the elimination of hazardous chemicals. Nevertheless, transitioning HPR technology from the laboratory to industrial scales presents several challenges, including continuous reactor operation, efficient secondary slag management, and safe, economically viable reactor scaling [72, 73]. Future research should prioritize reactor optimization for enhanced plasma stability and detailed life-cycle analyses to fully evaluate environmental impacts and sustainability benefits. The ongoing pilot-scale project H2PlasmaRed, aimed at reaching technology readiness level (TRL) 7, will provide critical insights into the scalability and performance of HPR technology regarding battery wastes [74]. To summarize, these findings highlight HPR as a viable alternative to conventional extraction processes, with considerable potential for extracting critical metals, precursors and ready-to-use alloys from highly mixed and contaminated waste streams. By strategically designing alloys through precise combinations of different battery waste materials, this approach offers a sustainable and energy efficient pathway for industrial alloy production. The comprehensive utilisation of by-products further underscores the value of HPR as an integrated solution for sustainable materials management and circular economy practices. More compositionally complex alloys could be explored in the future. Elements commonly used as dopants or coating agents, such as W, Nb, Cr, Ta, Mo and Zn [75-79] could be recovered, while the shift towards all-solid-state batteries introduces opportunities to integrate La and Zr from Li 7 La 3 Zr 2 O 12 into high-strength, high-conductivity alloys, such as Cu- and Al-based systems, together with dopant elements such as B [80-82]. Additionally, Si recovered from spent Si-based anodes could potentially be recycled as an alloying element in electrical steels (<6.5 wt.% Si) or repurposed for photovoltaic cell production, further broadening the scope of HPR applicability. Solid-state electrolytes may also provide rare earth elements such as Gd, Er, and Y [83, 84]. Even Li, although largely consumed during reduction, can be used in fabricating Al 2000-series alloys [85]. Given the diverse elements available from emerging battery waste streams, systematic exploration, potentially assisted by machine learning, could help identify promising alloy compositions tailored to specific industrial applications [86-88]. This study presents a rapid and sustainable route for upcycling waste battery materials into high-purity metals and high-performance alloys via HPR. We show that critical metals can be efficiently recovered and directly transformed into functional alloys with properties comparable to those of conventional industrial alloys, enabling immediate application without additional post-processing. This single-step method eliminates the reliance on toxic chemicals and fossil-based reducing agents, substantially reduces environmental impact. Extensive characterisation confirmed that the alloys synthesized via HPR exhibited phase purity, minimal impurities (<0.7 at.%), and structural homogeneity comparable or superior to commercial-grade alloys. The approach sets a new benchmark for sustainable metallurgy, providing a pathway to high-performance materials manufacturing in alignment with global sustainability goals. It shows that even the most contaminated and mixed waste materials can have the same or even higher value for the synthesis of critical high-tech materials than today’s expensive and critical mineral feedstock, giving recycling a completely new, disruptive and strategic face. Materials and Methods Materials Commercial spent cathodes of Li(Ni 0.8 Co 0.1 Mn 0.1 )O 2 (NCM811) and pristine LiCoO 2 (LCO) and LiFePO 4 (LFP) powders (Figure S43) were used to recover transition metals and design alloys via arc plasma reduction under a hydrogen atmosphere. All cathodes were prepared using co-precipitation method. Discharged spent pouch cells, containing NCM811 materials on Al electrodes, were dismantled in an Ar-filled glove box to avoid air contamination and any possible ignition. The detailed configuration of the NCM811 pouch cell, along with its electrochemical performance prior to dismantling, is summarized in S44 and Table S2. The recovered cathode materials were used directly for the reduction experiments, while for LCO and LFP, a commercial powder was employed for HPR. During the production of the HEA and TiAl alloys, high-purity Cu and Al pellets (99.9%) were used to represent the Cu and Al current collectors present in battery systems, where also high-purity foils are used. For Ti source, a commercial Li 4 Ti 5 O 12 (LTO) was adopted. For residual P removal in Figure S16, oyster shell waste (Tongyeong, Korea) was used as CaCO 3 source. Arc plasma reduction under a hydrogen atmosphere To prevent powder scattering during arc melting, less than 2 g of NCM811, LFP, LCO, or mixed powders were pelletised in a Φ13 stainless steel mould at 6000 psi using a hydraulic press. Hydrogen plasma smelting reduction of the pellets was carried out in a laboratory-scale arc melting furnace (Compact Arc Melter MAM-1, Edmund Bühler GmbH). The pellets were placed on a water-cooled Cu hearth (anode), with the W electrode (cathode) positioned ~4 mm above. The chamber was purged three times and filled with an Ar–10 vol.% H 2 mixture at 4.13 × 10 4 Pa before plasma ignition at 100 A. Due to lab-scale instrument constraints, plasma treatment was conducted intermittently, with ~20 s of plasma application followed by ~20 min of cooling, repeated sequentially. During each plasma application, the chamber was re-purged with an Ar–H 2 mixture, maintaining a hydrogen partial pressure of 4.13 × 10 3 Pa. The development of a continuous processing cycle should be explored in future work. For the synthesis of super invar alloy, NCM811, LFP, LCO and CaCO 3 powders were mixed using a vortex mixer at 3000 rpm for 3 min in a ratio of NCM811:LFP:CaCO 3 = 1:5.5:5.5 (by weight). The pelletised mixture underwent direct HPR for ~20 s per cycle, with Ar–10% H 2 reintroduced before each cycle. The reduction process was repeated at least three times, and the resulting alloy and oxide slag were separated by mechanical crushing (Figure S1). For the HEA, a powder mixing ratio of NCM811:LFP:LCO:Cu = 6:24:5:6 (by weight) was used. Cu pellets, representing the anode current collectors of spent Li-ion batteries, were placed adjacent to the pelletised powder mixture. Both were subjected to HPR for ~20 s per cycle, repeated at least five times, after which the alloy and oxide slag were easily separated by mechanical crushing. For TiAl alloy synthesis, pure Al pellets, representing the cathode current collector, were placed adjacent to the LTO pellets. The weight ratio of LTO to Al was 1:3.4 for synthesising γ-TiAl and 1:3.2 for α 2 -Ti 3 Al/γ-TiAl alloys. Both LTO and Al pellets underwent HPR for ~20 s per cycle, repeated ten times to yield fully reduced metallic alloys without residual oxide slags. Characterisation The recovered metals and alloys were hot-mounted and ground using SiC sandpapers of 80, 800, 1200, 2000, and 4000 grit. Samples were subsequently polished with 3 and 1 μm diamond suspensions, followed by final polishing with a 0.25 μm colloidal silica suspension. Microstructural and chemical characterisation was conducted using scanning electron microscopy (SEM, Hitachi SU5000) equipped with an EDS (Oxford Instruments Ultim Max40) detector. EBSD (Hitachi, S-4300SE, Symmetry S3) was used to determine crystallographic orientations over an area of 190 × 130 μm 2 with a step size of 0.4 μm. XRD (Rigaku, SmartLab) was performed using Cu Kα radiation (λ = 0.154 nm) at 40 kV and 200 mA. Scans were acquired at a rate of 1°/min over a 2θ range of 40–90° for reduced Ni, Co, and Fe samples, and 30–110° for the HEA and TiAl alloys. Quantitative phase analysis was carried out using Rietveld refinement with Profex software (version 5.3.0) [89]. TGA (HITACHI, STA200RV) was conducted from 30 to 1000 °C at a heating rate of 5 °C/min. Approximately 10 mg of each NCM811, LFP, and LCO pellet was placed on a Pt holder and analysed under Ar and Ar–5 vol.% H 2 atmospheres, which corresponded to the maximum hydrogen concentration permitted by the thermogravimetric equipment. APT specimens were prepared by sharpening samples into needle-shaped tips using a focused ion beam (FIB, FEI Nova Nano Lab 600, FEI Helios G4). The region of interest was first milled into a wedge shape above and below using a 30 kV Ga ion beam at a stage tilt of 22°. The wedge was lifted out and mounted onto a commercial 22-array Si coupon using a Pt gas injection system. The mounted specimen was annularly milled with a 30 kV Ga ion beam, gradually reducing the current from 0.5 nA to 50 pA. To minimise Ga-induced damage, final milling was performed at 5 kV, yielding the required tip geometry (Figure S45). APT measurements were conducted using a LEAP 4000X HR instrument (CAMECA) under the following conditions: pulse rate, 125–200 kHz; specimen temperature, 50–60 K; laser energy, 60–80 pJ; and detection rate, 0.5–1% (Figure S46). Thermo-mechanical analysis (TMA, NETZSCH TMA 402 F1) was performed from 30 °C to 500 °C at a heating rate of 2 °C/min for both as-cast and annealed super invar alloys. Magnetic properties were measured using a magnetic property measurement system (MPMS3-Evercool, Quantum Design Inc.) at 300 K under a magnetic field of 1.5 T for both as-cast and annealed FeCoNiCu HEA alloys. Nano-indentation tests (Bruker TI-950) were conducted at a load of 10 mN, while Vickers hardness tests (Matsuzawa MMT X7-B) were carried out at 500 gf for TiAl alloys and 200 gf for the super invar and HEA alloys, with a dwell time of 15 s. Declarations Acknowledgement This work was supported by the National R&D Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (RS-2024-00450561 and RS-2025-00520824) and the Korea Institute of Energy Technology Evaluation and Planning (KETEP) (No. RS-2024-00401917). Conflict of interest The authors declare no conflict of interest. References “Carbon neutrality strategies for sustainable batteries: from structure, recycling, and properties to applications - Energy & Environmental Science (RSC Publishing).” Accessed: July 03, 2025. [Online]. Available: https://pubs.rsc.org/en/content/articlelanding/2008/4v/d2ee03257k/unauth A. 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Supplementary Files SupportingInformationbatteryhydrogenreduction.docx Supplementary Information: Hydrogen plasma reduction for direct upcycling of battery waste into high-performance alloys Cite Share Download PDF Status: Under Review 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7339880","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":626078456,"identity":"9398416c-497d-4629-9cd7-b4728691ae12","order_by":0,"name":"Se-Ho Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIiWNgGAWjYFACHjBpwMDeBhdiJkaLgQEDzzGStUikEalFvr334OOCij/G5jOfJT6uqLBj4G8/wGxcgUeLwZlzycYzzhiYydxOO2x45kwyg8SZBObEM/i0SOSYSfO2GdhISKe3STa2Ad10g4H5YAM+h81/A9TyD6hF8jhQy796BnlCWhhu8AC1NBiYSUiwHZNsbDjMYADUkohPi8GZHGNjnmPGxhI8acmGDceO8xieSWw2xOuw9jOGj3lq5AxnsB8zfNhQUy0nd/zwYUm8DkMHwGhiJEnDKBgFo2AUjAIsAAAajkNaQPZOkgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-1227-8897","institution":"Korea University","correspondingAuthor":true,"prefix":"","firstName":"Se-Ho","middleName":"","lastName":"Kim","suffix":""},{"id":626078457,"identity":"716da1b2-2008-4917-87fd-91cd733e483c","order_by":1,"name":"Dierk Raabe","email":"","orcid":"","institution":"Max Planck Institute for Sustainable Materials","correspondingAuthor":false,"prefix":"","firstName":"Dierk","middleName":"","lastName":"Raabe","suffix":""},{"id":626078458,"identity":"c98f8c50-bb9f-4e60-9ea4-24512f853aa6","order_by":2,"name":"Baptiste Gault","email":"","orcid":"","institution":"Max-Planck-Institut for Sustainable Materials","correspondingAuthor":false,"prefix":"","firstName":"Baptiste","middleName":"","lastName":"Gault","suffix":""},{"id":626078459,"identity":"9eacfe3b-278d-4698-bc55-1c235685016c","order_by":3,"name":"Jae-Pyoung Ahn","email":"","orcid":"https://orcid.org/0000-0003-2657-7425","institution":"Korea Institute of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Jae-Pyoung","middleName":"","lastName":"Ahn","suffix":""},{"id":626078460,"identity":"23f7d252-ff34-4375-a314-8fa23df94823","order_by":4,"name":"Jinyeon Hwang","email":"","orcid":"","institution":"Remplir Inc.","correspondingAuthor":false,"prefix":"","firstName":"Jinyeon","middleName":"","lastName":"Hwang","suffix":""},{"id":626078461,"identity":"86dfb1ed-5635-4660-a89c-de0b627aeaf8","order_by":5,"name":"Ubaid Manzoor","email":"","orcid":"","institution":"Max Planck Institute for Sustainable Materials","correspondingAuthor":false,"prefix":"","firstName":"Ubaid","middleName":"","lastName":"Manzoor","suffix":""},{"id":626078462,"identity":"f804eb47-ace4-48e8-b7a6-70f942d35ad2","order_by":6,"name":"Won-Hyoung Lee","email":"","orcid":"","institution":"Korea University","correspondingAuthor":false,"prefix":"","firstName":"Won-Hyoung","middleName":"","lastName":"Lee","suffix":""},{"id":626078463,"identity":"f0487bc0-da7d-475a-b610-b0425ba605ba","order_by":7,"name":"Chang-Gi Lee","email":"","orcid":"","institution":"Korea University","correspondingAuthor":false,"prefix":"","firstName":"Chang-Gi","middleName":"","lastName":"Lee","suffix":""},{"id":626078464,"identity":"a529bfc1-cba1-4fd6-b269-aa32711bc434","order_by":8,"name":"I-Jun Ro","email":"","orcid":"","institution":"Korea University","correspondingAuthor":false,"prefix":"","firstName":"I-Jun","middleName":"","lastName":"Ro","suffix":""}],"badges":[],"createdAt":"2025-08-10 16:00:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7339880/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7339880/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109236738,"identity":"9a938872-566b-4dbc-aa0b-a8bbb7bd9621","added_by":"auto","created_at":"2026-05-14 05:11:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2895345,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of alloy design from battery waste components. Super invar (Fe\u003csub\u003e63\u003c/sub\u003eNi\u003csub\u003e32\u003c/sub\u003eCo\u003csub\u003e5\u003c/sub\u003e), invar (Fe\u003csub\u003e64\u003c/sub\u003eNi\u003csub\u003e36\u003c/sub\u003e), kovar (Fe\u003csub\u003e53\u003c/sub\u003eNi\u003csub\u003e29\u003c/sub\u003eCo\u003csub\u003e17\u003c/sub\u003e), and platinite (Fe\u003csub\u003e55\u003c/sub\u003eNi\u003csub\u003e45\u003c/sub\u003e) alloys exhibit excellent thermal expansion control. Constantan (Cu\u003csub\u003e55\u003c/sub\u003eNi\u003csub\u003e45\u003c/sub\u003e) maintains stable electrical resistivity across a wide temperature range, while aluminium 1000 series alloys are known for high electrical conductivity and corrosion resistance. High-entropy alloys synthesised from various combinations of Al, Fe, Co, Ni, Cu, and Ti can exhibit diverse properties, including high strength, low weight, corrosion resistance, and either soft or hard magnetic characteristics. Supra (Fe\u003csub\u003e50\u003c/sub\u003eNi\u003csub\u003e50\u003c/sub\u003e), permendur (Fe\u003csub\u003e50\u003c/sub\u003eCo\u003csub\u003e50\u003c/sub\u003e), and permalloy (Ni\u003csub\u003e80\u003c/sub\u003eFe\u003csub\u003e20\u003c/sub\u003e) are soft magnetic alloys. Alnico (Al\u003csub\u003e10\u003c/sub\u003eNi\u003csub\u003e20\u003c/sub\u003eCo\u003csub\u003e6\u003c/sub\u003eTi\u003csub\u003e1\u003c/sub\u003e) is a permanent magnetic alloy, while cunife (Cu\u003csub\u003e60\u003c/sub\u003eNi\u003csub\u003e20\u003c/sub\u003eFe\u003csub\u003e20\u003c/sub\u003e) is a magnetic alloy with strong resistance to seawater corrosion. Ti64 (Ti\u003csub\u003e90\u003c/sub\u003eAl\u003csub\u003e6\u003c/sub\u003eV\u003csub\u003e4\u003c/sub\u003e), nickel aluminide (Ni\u003csub\u003e50\u003c/sub\u003eAl\u003csub\u003e50\u003c/sub\u003e), aluminium 2000 series, hiduminium (Al\u003csub\u003e96\u003c/sub\u003eCu\u003csub\u003e2\u003c/sub\u003eNi\u003csub\u003e1\u003c/sub\u003eFe\u003csub\u003e1\u003c/sub\u003e), aluminium bronze (Cu\u003csub\u003e86\u003c/sub\u003eAl\u003csub\u003e10\u003c/sub\u003eFe\u003csub\u003e4\u003c/sub\u003e), and monel (Ni\u003csub\u003e60\u003c/sub\u003eCu\u003csub\u003e40\u003c/sub\u003e) are widely used in aerospace craft. Nitinol (Ni\u003csub\u003e45\u003c/sub\u003eTi\u003csub\u003e55\u003c/sub\u003e) is a shape memory alloy, and ferro aluminium (Fe\u003csub\u003e60\u003c/sub\u003eAl\u003csub\u003e40\u003c/sub\u003e) is employed as a deoxidising agent in steel making. Cupronickel alloy (Cu\u003csub\u003e70\u003c/sub\u003eNi\u003csub\u003e30\u003c/sub\u003e) is used in marine and coinage applications.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-7339880/v1/9e5c0b4363f301705fc5dfd8.png"},{"id":109236645,"identity":"a7650f1a-ad93-408e-9e17-b02138463c68","added_by":"auto","created_at":"2026-05-14 05:11:20","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":17131636,"visible":true,"origin":"","legend":"\u003cp\u003eHPR process for direct metal recovery from spent Li-ion battery cathodes and microstructural characterisation. (a) Scanning electron micrographs of commercial LiCoO\u003csub\u003e2\u003c/sub\u003e (LCO), Li(Ni\u003csub\u003e0.8\u003c/sub\u003eCo\u003csub\u003e0.1\u003c/sub\u003eMn\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e2\u003c/sub\u003e (NCM811), and LiFePO\u003csub\u003e4\u003c/sub\u003e (LFP) powders. (b) Schematic diagram of the arc melting process conducted in an atmosphere containing 90 vol.% Ar and 10 vol.% H\u003csub\u003e2\u003c/sub\u003e. (c) Photographs and backscattered electron scanning electron microscopy (BSE-SEM) images of Co, Ni, and Fe metals recovered via hydrogen plasma reduction (HPR) from LCO, NCM811, and LFP, respectively (see Figure S1). (d) Thermogravimetric analysis (TGA) profiles showing percentage reduction versus time for LCO, NCM811, and LFP under both Ar and Ar–H\u003csub\u003e2\u003c/sub\u003e atmospheres. (e) Kissinger–Akahira–Sunose (KAS) plot for NCM811. (f) X-ray diffraction (XRD) patterns of metals obtained via HPR from LCO, NCM811, and LFP. (g) Electron backscatter diffraction (EBSD) and energy-dispersive X-ray spectroscopy (EDS) maps showing Co, Ni, and Fe\u003csub\u003e3\u003c/sub\u003eP distribution. (h) 3D reconstruction maps of Co, Ni, and Fe\u003csub\u003e3\u003c/sub\u003eP from atom probe tomography (APT). Scale bars: 10 μm (a); 2.5 mm (black bar in c); 500 μm (white bar in c); 50 μm (g); and 50 nm (h).\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-7339880/v1/69241e1c2f0c251bbe91440c.png"},{"id":109236646,"identity":"ebc408e3-9a83-439e-8737-1b52295bbec2","added_by":"auto","created_at":"2026-05-14 05:11:20","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":12507370,"visible":true,"origin":"","legend":"\u003cp\u003eOne-step synthesis and characterisation of super-invar alloy from battery waste mixtures via HPR. (a) Scanning electron microscopy electron backscatter diffraction (SEM-EBSD) and energy-dispersive X-ray spectroscopy (EDS) analyses of the hydrogen plasma-reduced alloy from a mixed pellet of spent Li(Ni\u003csub\u003e0.8\u003c/sub\u003eCo\u003csub\u003e0.1\u003c/sub\u003eMn\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e2\u003c/sub\u003e (NCM811) and LiFePO\u003csub\u003e4\u003c/sub\u003e. (b) SEM-EBSD and EDS analyses of the alloy synthesised from a mixed pellet of NCM811, LFP, and CaCO\u003csub\u003e3\u003c/sub\u003e. Scale bars: 50 μm. (c) Thermo-mechanical analysis (TMA) showing the measured coefficient of thermal expansion (α) between 30 and 500 °C, compared with reference values [46, 47].\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-7339880/v1/69469319391415567ddd5026.png"},{"id":109236676,"identity":"c6d5a620-b2ae-401a-94c8-0918e401b4e0","added_by":"auto","created_at":"2026-05-14 05:11:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":17966731,"visible":true,"origin":"","legend":"\u003cp\u003eDirect synthesis and characterisation of advanced alloys: microstructure, chemistry and property evaluation. (a) Scanning electron microscopy (SEM) images of a hydrogen plasma reduced alloy synthesised from a pellet composed of Li(Ni\u003csub\u003e0.8\u003c/sub\u003eCo\u003csub\u003e0.1\u003c/sub\u003eMn\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e2\u003c/sub\u003e (NCM811) + LiFePO\u003csub\u003e4\u003c/sub\u003e (LFP) + LiCoO\u003csub\u003e2\u003c/sub\u003e (LCO) mixed powder and a Cu current collector. (b) X-ray diffraction (XRD) pattern of the high-entropy alloy (HEA) shown in (a). (c) Scanning electron microscopy-electron backscatter diffraction (SEM-EBSD) and energy-dispersive X-ray spectroscopy (EDS) analysis of the alloy in (a). Detailed SEM-EDS results for alloys obtained from various NCM811:LFP:LCO:Cu ratios are provided in Figures S32–S37. (d) Measured Curie temperature of the alloy in (a) with reference values [60, 62]. (e) Magnetic properties of the as-cast FeCoNiCu alloy in (a) with reference data [60, 61]. (f) SEM images of a hydrogen plasma reduced γ-TiAl phase synthesised from Li\u003csub\u003e4\u003c/sub\u003eTi\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e (LTO) powder and an Al current collector. (g) XRD pattern of the γ-TiAl alloy in (f). (h) SEM-EBSD and EDS analyses of alloys in (f). (i) Nanoindentation results for the γ-TiAl alloy in (f). (j) Calculated Young’s modulus and Vickers hardness measured under a 500 g load, with reference values from the literature [63-66]. Figure S38 presents SEM-EDS results for varying LTO:Al ratios. Scale bars: 500 μm (a and f); 50 μm (c); and 200 μm (h).\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-7339880/v1/36c384ea1d980ad7bc9c4ab1.png"},{"id":109296527,"identity":"65fcfbbf-3aff-4802-af46-befbc8685fbf","added_by":"auto","created_at":"2026-05-15 08:47:57","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":51607625,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7339880/v1/b5048fdd-6015-4b2b-8204-542a76fa3de2.pdf"},{"id":109236735,"identity":"05c2499a-53e9-441b-87f9-963af1f1ad3c","added_by":"auto","created_at":"2026-05-14 05:11:23","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":34589489,"visible":true,"origin":"","legend":"Supplementary Information: Hydrogen plasma reduction for direct upcycling of battery waste into high-performance alloys","description":"","filename":"SupportingInformationbatteryhydrogenreduction.docx","url":"https://assets-eu.researchsquare.com/files/rs-7339880/v1/cf3bc1feb9b4999f5f0e8719.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Hydrogen plasma reduction for direct upcycling of battery waste into high-performance alloys","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe global imperative for carbon neutrality, coupled with the accelerating demand for secondary batteries, particularly in the electric vehicle (EV) sector, has intensified the search for transformative recycling strategies [1, 2]. In 2023, global EV sales reached ~14 million units, a six-fold increase since 2018, signalling a sharp rise in end-of-life batteries requiring recycling in the coming decades [3]. By 2030, an estimated 4.1 million EV batteries will need recycling, with projections exceeding 42 million by 2040. Simultaneously, rising costs and dwindling supplies of critical metals such as Ni, Co, and Li [4] are placing increasing pressure on global supply chains, underscoring the urgency of sustainable recycling methods [5] that not only recover valuable elements but also enable the direct synthesis of novel materials, including alloy precursors.\u003c/p\u003e\n\u003cp\u003eConventional recycling approaches, including wet chemical leaching and high-temperature pyrometallurgy, present significant challenges. Hydrometallurgical processes [6, 7] typically require extensive pre-treatment to convert battery waste into a \u0026apos;black mass\u0026apos;, followed by aggressive acid or base leaching to dissolve metal oxides into ionic forms. While several commercial processes exist for the selective extraction of target elements, they are often slow, generate large volumes of hazardous wastewater, and require costly multiple purification steps. Pyrometallurgical methods [8, 9] rely on high-temperature melting to separate metals from slag based on differential melting points and densities. As such, they are energy-intensive, emit substantial quantities of CO\u003csub\u003e2\u003c/sub\u003e, and demand significant capital investment for post-processing infrastructure. Mechanical and direct recovery methods [10], which seek to extract active materials without chemical transformation, have also been investigated; however, they do not consistently yield products that are immediately suitable for industrial applications.\u003c/p\u003e\n\u003cp\u003eHydrogen plasma reduction (HPR) offers a fundamentally different, sustainable, and electrified alternative by replacing fossil-based reductants with hydrogen, producing water instead of CO\u003csub\u003e2\u003c/sub\u003e as a by-product [11]. In HPR, a plasma arc is ignited directly on the surface of metal oxides in a hydrogen-rich atmosphere (10 vol.% H\u003csub\u003e2\u003c/sub\u003e), simultaneously melting the oxides and dissociating hydrogen gas into highly reactive atoms, protons, and radicals at temperatures exceeding 2500 \u0026deg;C [12]. Direct interaction between the molten oxide and high-energy plasma species enables rapid reduction to the metallic state [13-15]. This process is inherently fast and energy-efficient, outperforming conventional hydrometallurgical and pyrometallurgical methods [16]. For instance, HPR reduces energy consumption by ~19% compared with the rotary kiln\u0026ndash;electric furnace route used in nickel laterite ore processing, by consolidating drying, calcination, reduction, and refining into a single step, thus lowering both energy consumption and CO\u003csub\u003e2\u003c/sub\u003e emissions [12].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAs an example, the reduction of one mole of LiCoO\u003csub\u003e2\u003c/sub\u003e requires two moles of H\u003csub\u003e2\u003c/sub\u003e, equivalent to ~0.07 kg of hydrogen per kilogram of recovered Co. This eliminates the need for fossil-based reductants and hazardous chemicals [17, 18]. The use of green hydrogen, derived from renewable energy, further decreases the carbon footprint, enabling sustainable conversion of battery waste into high-purity metallic precursors [19, 20]. These plasma-derived metals and alloys exhibit impurity levels comparable to commercial standards, obviating the extensive post-treatment typically required in carbon-based reduction processes [12, 21]. Moreover, plasma environments turn reductants into highly excited states, thus enhancing their reactivity, effectively replacing part of the (expensive, indirect) chemical driving force with an (inexpensive, direct) electrical one, ideally supplied by renewable energy sources.\u003c/p\u003e\n\u003cp\u003eIn parallel, the development of sustainable alloys is critical in an era of resource constraints and increasing environmental accountability. Current global metal production, at ~2 billion tonnes annually, accounts for ~40% of industrial greenhouse gas emissions [22]. HPR enables direct conversion of ores into high-purity metals and subsequently into advanced alloys [23]. Recent analyses suggest HPR holds considerable promise as an economically viable alternative to traditional steelmaking methods, particularly for processing medium-grade iron ore (approximately 59 wt.% Fe [24]), demonstrating promising scalability, process simplification, and reductions in carbon emissions. Moreover, previous studies indicate that HPR could offer cost savings of up to 20% compared to conventional blast furnace processes [25, 26]. Additionally, achieving plasma efficiency of at least 82% is considered necessary to ensure economic viability [24]. While plasma technologies from the 1990s typically reached efficiency of ~80% [27], current advancements suggest achievable efficiency up to 92% [28].\u003c/p\u003e\n\u003cp\u003eGiven the technological maturity and widespread adoption of electric arc furnace (EAF) in the steel industry, the integration of hydrogen-rich gas mixtures and modified plasma torches into existing EAF infrastructures emerges as a practical and efficient pathway [29]. The global EAF market, expected to grow at a compound annual growth rate (CAGR) of 12% [30], further highlights the substantial potential for the rapid adoption of HPR technologies.\u003c/p\u003e\n\u003cp\u003eConsidering the prospect for battery waste worldwide, HPR has the potential to support a circular economy, reducing dependence on primary resource extraction and substantially lowering energy use and associated emissions, but also to be used as an integrated process for making high-performance alloys [31, 32]. Given that spent batteries contain valuable elements compatible with advanced alloy systems, Figure 1 illustrates examples of their direct integration into existing engineering alloys.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHere, we present a novel approach underpinned by detailed experimental results showcasing the successful recovery and upcycling of diverse metals from battery wastes including, the most commonly used electrode materials as well as metallic contacts, and the synthesis of an array of alloys with potential for application as structural and functional materials. Our work highlights the versatility and effectiveness of this emerging recycling approach with broad implications for sustainable metallurgy.\u003c/p\u003e\n\u003cp\u003eFigure 2 summarises the HPR results for spent cathodes of Li(Ni\u003csub\u003e0.8\u003c/sub\u003eCo\u003csub\u003e0.1\u003c/sub\u003eMn\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e2\u003c/sub\u003e (NCM811) as well as commercial pristine cathodes of LiCoO\u003csub\u003e2\u003c/sub\u003e (LCO) and LiFePO\u003csub\u003e4\u003c/sub\u003e (LFP). These three materials represent the leading cathode chemistries currently dominating the global market, which is projected to expand from ~4.2 TWh in 2024 to ~7.5 TWh by 2030. Due to laboratory safety constraints, a gas mixture comprising 10 vol.% H\u003csub\u003e2\u003c/sub\u003e and 90 vol.% Ar was used. Although pure (100 vol.%) H\u003csub\u003e2\u003c/sub\u003e would enhance the reduction kinetics, the chosen mixture still yielded substantial benefits in terms of reaction efficiency and energy savings. The cathode powders, Figure 2a, were pelletised and positioned beneath a tungsten electrode within the plasma reactor (Figure 2b), with the partial pressure of hydrogen (P\u003csub\u003eH\u003c/sub\u003e) maintained at 4.13 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e Pa during the reduction process. Within just 1 min of plasma exposure, metallic beads were formed (Figure 2c), indicating rapid and effective reduction.\u003c/p\u003e\n\u003cp\u003eTo evaluate the influence of H\u003csub\u003e2\u003c/sub\u003e partial pressure on reduction efficiency, thermogravimetric analysis (TGA) was carried out, comparing samples processed in an H\u003csub\u003e2\u003c/sub\u003e-containing reactive atmosphere with those processed in an inert Ar atmosphere. As shown in Figure 2d, reduction initiated earlier in H\u003csub\u003e2\u003c/sub\u003e. The decomposition rate of NCM811 was ~2.5 times faster in H\u003csub\u003e2\u003c/sub\u003e-containing Ar than in pure Ar. Similar behaviour was observed for LCO and LFP, confirming enhanced reduction kinetics attributable to the higher reactivity of hydrogen (Figure S2).\u003c/p\u003e\n\u003cp\u003eThe reaction kinetics under the two atmospheres were further quantified using the Kissinger\u0026ndash;Akahira\u0026ndash;Sunose (KAS) method [33], focusing on NCM811 (Figures 2e and S3\u0026ndash;S4). Distinct peaks corresponding to sequential reduction steps were identified by varying the heating rates (5, 10, 15, 20, and 25 \u0026deg;C/min). These peaks represent the phase transition from a layered into a spinel structure [34], the reduction from Ni\u003csup\u003e4+\u003c/sup\u003e to Ni\u003csup\u003e2+\u0026nbsp;\u003c/sup\u003e[35], and the reduction of Ni\u003csup\u003e2+\u003c/sup\u003e to Ni\u003csup\u003e0\u0026nbsp;\u003c/sup\u003e[35], respectively. The activation energies for these reactions in H\u003csub\u003e2\u0026nbsp;\u003c/sub\u003ewere 1.8, 1.8, and 6.2 times lower, respectively, than those in Ar, confirming significantly faster reaction kinetics in the presence of H\u003csub\u003e2\u003c/sub\u003e. Additional TGA results for LCO under varying heating rates are provided in Figure S5.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eMicrostructural characterisation of LCO confirmed complete conversion to metallic Co. X-ray diffraction (XRD) combined with Rietveld refinement verified the formation of high-purity Co, demonstrating the efficacy of HPR (Figures 2f and S6) [36]. Scanning electron microscopy (SEM)-based techniques, including electron backscatter diffraction (EBSD) and energy-dispersive X-ray spectroscopy (EDS), together with atom probe tomography (APT), revealed a hexagonal close-packed structure with no detectable Li in the ingot. Figures 2g and 2h further confirmed high purity, with residual O [37] and C contents below 0.11 and 0.12 at.%, respectively (see Figures S7\u0026ndash;S10). No Li was detected in the metallic ingots, indicating that it likely reacted with residual C and O to form Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e, which was collected as oxide and dust in the reactor chamber (Figures S11\u0026ndash;S13). Consistent with this observation, \u003cem\u003eHu et al.\u0026nbsp;\u003c/em\u003e[38] reported that 10\u0026ndash;15 wt.% of Li typically remains as Li\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e dust in smelting processes for lithium-ion battery recycling.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCharacterisation of NCM811 similarly demonstrated efficient conversion to face-centred cubic (FCC) Ni phase from the XRD result in Figure S6 [39]. Mn, which is thermodynamically stable as an oxide even under hydrogen plasma conditions, remained as surface oxides (Figure S14) [23, 40, 41]. SEM confirmed a homogeneous metallic grain structure with minimal structural variation and high chemical purity, with residual elements below 0.7 at.%.\u003c/p\u003e\n\u003cp\u003eIn contrast, the reduction product of LFP consisted of 99.6% Fe\u003csub\u003e3\u003c/sub\u003eP and 0.4% \u0026alpha;-Fe from XRD in Figure S6. SEM-EBSD and APT analyses revealed significant residual P (~26 at.%), which remained within the Fe matrix due to the reducing environment, which prevents formation of P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e. Fe\u003csub\u003e3\u003c/sub\u003eP is known to function as an effective hydrogenation catalyst in both acidic [42] and alkaline [43] media. However, residual P can be detrimental, causing grain boundary embrittlement and temper embrittlement in Fe alloys intended for mechanical applications [44, 45]. These findings emphasise the need for additional strategies to remove P from HPR-Fe alloys derived from battery waste.\u003c/p\u003e\n\u003cp\u003eThe recovery yields are to be 54.8, 41.4, and 82.5% for LCO, NCM811, and LFP, respectively (see Table S1). Despite the inherent limitations of experiments carried out on a lab-scale, HPR\u0026rsquo;s ability to successfully recover significant proportions of valuable transition metals from spent cathodes even within short treatment times. Notably, LFP exhibited the highest yield (82.5%), indicating excellent efficiency for Fe-based cathodes. Further HPR\u0026rsquo;s flexibility allows for targeted optimization, through adjusting pre-treatment conditions, treatment duration, or hydrogen partial pressure to enhance yields for specific cathode materials on an industrial scale.\u003c/p\u003e\n\u003cp\u003eTo explore the direct conversion of battery waste into functional alloys, waste NCM811 was combined with LFP powders to produce a composition analogous to Invar, an alloy with near-zero thermal expansion [48]. By precisely controlling the mass ratio of these waste materials, the composition of the HPR-processed alloy closely matched that of super invar (Figure 3a). The alloy had a nominal composition of 35 at.% Ni, 5 at.% Co, balanced by Fe, exhibiting a thermal expansion at room temperature up to 60% lower than that of conventional invar alloys. However, residual P was initially detected in the recycled alloy. P is detrimental to Fe\u0026ndash;Ni alloys as it degrades magnetic and mechanical properties through the formation of (Fe, Ni, Co)\u003csub\u003e3\u003c/sub\u003eP phases during cooling [49]. SEM-EBSD and EDS analyses revealed Fe\u003csub\u003e2\u003c/sub\u003eNiP phases along grain boundaries, with a phosphorus concentration of ~3.8 at.% in the examined region.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo mitigate P contamination, Fe\u003csub\u003e3\u003c/sub\u003eP derived from LFP was further treated under hydrogen plasma for 2 min at a constant current of 100 A, partially converting it to pure Fe (Figure S15). While this treatment was effective for partial P removal, it is unlikely to be sufficient for commercial application. A more practical and energy-efficient approach was achieved by introducing CaCO\u003csub\u003e3\u003c/sub\u003e as a P absorbent. During HPR, CaCO\u003csub\u003e3\u003c/sub\u003e reacted to form a CaO\u0026middot;P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e slag, effectively capturing phosphorus. This by-product can be repurposed as a valuable raw material for cement production and bioactive materials [50-52]. In this study, CaCO\u003csub\u003e3\u003c/sub\u003e was sourced from recycled oyster shells (Figure S16), addressing a major waste management challenge in the seafood industry, where nearly 400,000 tonnes of oyster shells are discarded annually in South Korea alone. Recycling 1 tonne of oyster shells can reduce greenhouse gas emissions by ~0.3 tonnes [53]. Incorporating CaCO\u003csub\u003e3\u003c/sub\u003e into the LFP reduction process, therefore, enabled sustainable P removal from the resulting metals.\u003c/p\u003e\n\u003cp\u003eExperiments with different mixing ratios of NCM811, LFP, and CaCO\u003csub\u003e3\u003c/sub\u003e are presented in Figures S17\u0026ndash;S29. Following pelletisation and HPR, a super invar alloy was successfully synthesised, with no detectable residual P and an average grain size of ~200 \u0026micro;m (Figures 3b and S30). The thermal expansion behaviour of the HPR-synthesised invar alloy was evaluated to confirm its near-zero thermal expansion. As shown in Figure 3c, the alloy exhibited a thermal expansion coefficient of 9.21 \u0026times; 10\u003csup\u003e-7\u003c/sup\u003e/\u0026deg;C at room temperature, outperforming conventional invar and closely matching super invar. After five hours of heat treatment at 1200 \u0026deg;C, the room-temperature thermal expansion coefficient increased slightly to 2.03 \u0026times; 10\u003csup\u003e-6\u003c/sup\u003e/\u0026deg;C, while the coefficient between 150 and 350 \u0026deg;C decreased by two-thirds (Figure S31). These properties can be further improved through additional mechanical processing and heat treatment [54].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eRecovered metals integrated into a one-step alloy design strategy using green hydrogen represent a significant step towards achieving a circular economy [23, 55]. Importantly, this approach extends beyond the invar alloy family, as the diverse elemental composition of battery wastes provides access to a wide range of alloy systems. Cathode materials are rich sources of Ni, Fe and Co; anode materials can supply Ti from Li\u003csub\u003e4\u003c/sub\u003eTi\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e (LTO), Ag and In from Ag\u0026ndash;In alloys, or Si; while current collectors contribute Cu and Al.\u003c/p\u003e\n\u003cp\u003eUsing this approach, we demonstrate that green HPR enables the direct synthesis of a broad range of conventional and advanced alloys (Figures 4a and 4f). A high-entropy alloy (HEA) was synthesised from NCM811, LFP, LCO and a commercial Cu current collector, forming a homogeneous FCC structure with near equiatomic Fe, Ni, Co and Cu, as confirmed by SEM-EBSD-EDS and XRD analyses (Figures 4b and 4c) [56]. This FeNiCoCu HEA composition has previously been reported to exhibit distinctive magnetic behaviour [57-59]. The synthesised HEA demonstrated a high saturation magnetisation of 129.6 \u0026plusmn; 0.2 emu/g, a low coercivity of 22.5 Oe at room temperature and a high Curie temperature of 928 K. These values substantially exceed those reported for FeCoNi or FeCoNiCu(Al) HEAs [60, 61], indicating that the material retains soft magnetic behaviour at elevated temperatures, surpassing the operational limits of many existing soft magnets (Figures 4d and 4e). Further heat treatment improved both the magnetic performance and the Curie temperature of the HEA shown in Figure 4a. The alloy retained its FCC structure and displayed a homogeneous elemental distribution without Cu segregation (Figure S39).\u003c/p\u003e\n\u003cp\u003eTiAl alloys, key materials in one of the most advanced alloy families for aerospace turbine applications, were synthesised by combining LTO anode material with an Al current collector through HPR (Figure 4f and Figure S40). Characterisation confirmed the formation of a single-phase \u0026gamma;-TiAl alloy (Figures 4g and 4h). Controlled processing conditions additionally produced \u0026alpha;\u003csub\u003e2\u003c/sub\u003e-Ti\u003csub\u003e3\u003c/sub\u003eAl phases (Figure S40). Both \u0026gamma;-TiAl and \u0026alpha;\u003csub\u003e2\u003c/sub\u003e-Ti\u003csub\u003e3\u003c/sub\u003eAl/\u0026gamma;-TiAl alloys, valued for their exceptional specific strength and high-temperature creep resistance, are regarded as critical materials for aerospace applications [67-69].\u0026nbsp;Nanoindentation\u0026nbsp;and Vickers hardness measurements revealed a hardness of 350 \u0026plusmn; 4.8 HV and a Young\u0026rsquo;s modulus of 208.8 \u0026plusmn; 4.8 GPa, closely matching the properties of conventional aerospace-grade TiAl alloys (Figures 4i, 4j and S41). These results demonstrate the direct synthesis of both soft magnetic and aerospace-alloys from battery wastes through a streamlined, single-step HPR process.\u003c/p\u003e\n\u003cp\u003eThe demonstrated capability of HPR to rapidly convert diverse battery waste streams into high-performance alloys underscores its transformative potential for sustainable metallurgy, aligning with global sustainability objectives and circular economy strategies. Gas chromatography of gases collected from the HPR reactor (Figure S42) confirmed CO formation, indicating that residual carbon from the battery black mass participates in the reaction. This utilization of carbon contributes to improved process efficiency and sustainability. Additionally, Li- and Mn-rich particulates generated during plasma reduction represent valuable secondary resources for recovery and recycling.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePreliminary evaluations show that HPR exhibits a clear energy advantage over the current extraction methods. Integration of the proposed HPR process into existing EAF infrastructure is feasible by incorporating pre-heated hydrogen-rich gas mixtures lines along with a plasma torch, but economic viability, regulatory frameworks, and market acceptance for recovered metals and alloys will require detailed analysis [24]. Yet already, the energy consumption was evaluated for NCM811, yielding 2.7 g of pure Ni at ~511 MJ/kg. By comparison, conventional commercial Ni production consumes between 576 [70] and 697 MJ/kg [71] for smelting and refining from Ni laterite ores. Even at laboratory scale, the HPR method already demonstrates energy savings of 11.3% to 26.7% accompanied by a significantly lower carbon footprint and the elimination of hazardous chemicals.\u003c/p\u003e\n\u003cp\u003eNevertheless, transitioning HPR technology from the laboratory to industrial scales presents several challenges, including continuous reactor operation, efficient secondary slag management, and safe, economically viable reactor scaling [72, 73]. Future research should prioritize reactor optimization for enhanced plasma stability and detailed life-cycle analyses to fully evaluate environmental impacts and sustainability benefits. The ongoing pilot-scale project H2PlasmaRed, aimed at reaching technology readiness level (TRL) 7, will provide critical insights into the scalability and performance of HPR technology regarding battery wastes [74].\u003c/p\u003e\n\u003cp\u003eTo summarize,\u0026nbsp;these findings highlight HPR as a viable alternative to conventional extraction processes, with considerable potential for extracting critical metals, precursors and ready-to-use alloys from highly mixed and contaminated waste streams. By strategically designing alloys through precise combinations of different battery waste materials, this approach offers a sustainable and energy efficient pathway for industrial alloy production. The comprehensive utilisation of by-products further underscores the value of HPR as an integrated solution for sustainable materials management and circular economy practices. More compositionally complex alloys could be explored in the future. Elements commonly used as dopants or coating agents, such as W, Nb, Cr, Ta, Mo and Zn [75-79]\u0026nbsp;could be recovered, while the shift towards all-solid-state batteries introduces opportunities to integrate La and Zr from Li\u003csub\u003e7\u003c/sub\u003eLa\u003csub\u003e3\u003c/sub\u003eZr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e into high-strength, high-conductivity alloys, such as Cu- and Al-based systems, together with dopant elements such as B [80-82]. Additionally, Si recovered from spent Si-based anodes could potentially be recycled as an alloying element in electrical steels (\u0026lt;6.5 wt.% Si) or repurposed for photovoltaic cell production, further broadening the scope of HPR applicability. Solid-state electrolytes may also provide rare earth elements such as Gd, Er, and Y [83, 84]. Even Li, although largely consumed during reduction, can be used in fabricating Al 2000-series alloys [85]. Given the diverse elements available from emerging battery waste streams, systematic exploration, potentially assisted by machine learning, could help identify promising alloy compositions tailored to specific industrial applications [86-88].\u003c/p\u003e\n\u003cp\u003eThis study presents a rapid and sustainable route for upcycling waste battery materials into high-purity metals and high-performance alloys via HPR. We show that critical metals can be efficiently recovered and directly transformed into functional alloys with properties comparable to those of conventional industrial alloys, enabling immediate application without additional post-processing. This single-step method eliminates the reliance on toxic chemicals and fossil-based reducing agents, substantially reduces environmental impact. Extensive characterisation confirmed that the alloys synthesized via HPR exhibited phase purity, minimal impurities (\u0026lt;0.7 at.%), and structural homogeneity comparable or superior to commercial-grade alloys. The approach sets a new benchmark for sustainable metallurgy, providing a pathway to high-performance materials manufacturing in alignment with global sustainability goals. It shows that even the most contaminated and mixed waste materials can have the same or even higher value for the synthesis of critical high-tech materials than today\u0026rsquo;s expensive and critical mineral feedstock, giving recycling a completely new, disruptive and strategic face.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cp\u003e\u003cem\u003eMaterials\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eCommercial spent cathodes of Li(Ni\u003csub\u003e0.8\u003c/sub\u003eCo\u003csub\u003e0.1\u003c/sub\u003eMn\u003csub\u003e0.1\u003c/sub\u003e)O\u003csub\u003e2\u003c/sub\u003e (NCM811) and pristine LiCoO\u003csub\u003e2\u003c/sub\u003e (LCO) and LiFePO\u003csub\u003e4\u003c/sub\u003e (LFP) powders (Figure S43) were used to recover transition metals and design alloys via arc plasma reduction under a hydrogen atmosphere. All cathodes were prepared using co-precipitation method. Discharged spent pouch cells, containing NCM811 materials on Al electrodes, were dismantled in an Ar-filled glove box to avoid air contamination and any possible ignition. The detailed configuration of the NCM811 pouch cell, along with its electrochemical performance prior to dismantling, is summarized in S44 and Table S2. The recovered cathode materials were used directly for the reduction experiments, while for LCO and LFP, a commercial powder was employed for HPR. During the production of the HEA and TiAl alloys, high-purity Cu and Al pellets (99.9%) were used to represent the Cu and Al current collectors present in battery systems, where also high-purity foils are used. For Ti source, a commercial Li\u003csub\u003e4\u003c/sub\u003eTi\u003csub\u003e5\u003c/sub\u003eO\u003csub\u003e12\u003c/sub\u003e (LTO) was adopted. For residual P removal in Figure S16, oyster shell waste (Tongyeong, Korea) was used as CaCO\u003csub\u003e3\u003c/sub\u003e source.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eArc plasma reduction under a hydrogen atmosphere\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eTo prevent powder scattering during arc melting, less than 2 g of NCM811, LFP, LCO, or mixed powders were pelletised in a Φ13 stainless steel mould at 6000 psi using a hydraulic press. Hydrogen plasma smelting reduction of the pellets was carried out in a laboratory-scale arc melting furnace (Compact Arc Melter MAM-1, Edmund Bühler GmbH). The pellets were placed on a water-cooled Cu hearth (anode), with the W electrode (cathode) positioned ~4 mm above. The chamber was purged three times and filled with an Ar–10 vol.% H\u003csub\u003e2\u003c/sub\u003e mixture at 4.13 × 10\u003csup\u003e4\u003c/sup\u003e Pa before plasma ignition at 100 A. Due to lab-scale instrument constraints, plasma treatment was conducted intermittently, with ~20 s of plasma application followed by ~20 min of cooling, repeated sequentially. During each plasma application, the chamber was re-purged with an Ar–H\u003csub\u003e2\u003c/sub\u003e mixture, maintaining a hydrogen partial pressure of 4.13 × 10\u003csup\u003e3\u003c/sup\u003e Pa. The development of a continuous processing cycle should be explored in future work.\u003c/p\u003e\n\u003cp\u003eFor the synthesis of super invar alloy, NCM811, LFP, LCO and CaCO\u003csub\u003e3\u003c/sub\u003e powders were mixed using a vortex mixer at 3000 rpm for 3 min in a ratio of NCM811:LFP:CaCO\u003csub\u003e3\u003c/sub\u003e = 1:5.5:5.5 (by weight). The pelletised mixture underwent direct HPR for ~20 s per cycle, with Ar–10% H\u003csub\u003e2\u003c/sub\u003e reintroduced before each cycle. The reduction process was repeated at least three times, and the resulting alloy and oxide slag were separated by mechanical crushing (Figure S1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFor the HEA, a powder mixing ratio of NCM811:LFP:LCO:Cu = 6:24:5:6 (by weight) was used. Cu pellets, representing the anode current collectors of spent Li-ion batteries, were placed adjacent to the pelletised powder mixture. Both were subjected to HPR for ~20 s per cycle, repeated at least five times, after which the alloy and oxide slag were easily separated by mechanical crushing.\u003c/p\u003e\n\u003cp\u003eFor TiAl alloy synthesis, pure Al pellets, representing the cathode current collector, were placed adjacent to the LTO pellets. The weight ratio of LTO to Al was 1:3.4 for synthesising γ-TiAl and 1:3.2 for α\u003csub\u003e2\u003c/sub\u003e-Ti\u003csub\u003e3\u003c/sub\u003eAl/γ-TiAl alloys. Both LTO and Al pellets underwent HPR for ~20 s per cycle, repeated ten times to yield fully reduced metallic alloys without residual oxide slags.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCharacterisation\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe recovered metals and alloys were hot-mounted and ground using SiC sandpapers of 80, 800, 1200, 2000, and 4000 grit. Samples were subsequently polished with 3 and 1 μm diamond suspensions, followed by final polishing with a 0.25 μm colloidal silica suspension. Microstructural and chemical characterisation was conducted using scanning electron microscopy (SEM, Hitachi SU5000) equipped with an EDS (Oxford Instruments Ultim Max40) detector. EBSD (Hitachi, S-4300SE, Symmetry S3) was used to determine crystallographic orientations over an area of 190 × 130 μm\u003csup\u003e2\u003c/sup\u003e with a step size of 0.4 μm.\u003c/p\u003e\n\u003cp\u003eXRD (Rigaku, SmartLab) was performed using Cu Kα radiation (λ = 0.154 nm) at 40 kV and 200 mA. Scans were acquired at a rate of 1°/min over a 2θ range of 40–90° for reduced Ni, Co, and Fe samples, and 30–110° for the HEA and TiAl alloys. Quantitative phase analysis was carried out using Rietveld refinement with Profex software (version 5.3.0)\u0026nbsp;[89].\u003c/p\u003e\n\u003cp\u003eTGA (HITACHI, STA200RV) was conducted from 30 to 1000 °C at a heating rate of 5 °C/min. Approximately 10 mg of each NCM811, LFP, and LCO pellet was placed on a Pt holder and analysed under Ar and Ar–5 vol.% H\u003csub\u003e2\u003c/sub\u003e atmospheres, which corresponded to the maximum hydrogen concentration permitted by the thermogravimetric equipment.\u003c/p\u003e\n\u003cp\u003eAPT specimens were prepared by sharpening samples into needle-shaped tips using a focused ion beam (FIB, FEI Nova Nano Lab 600, FEI Helios G4). The region of interest was first milled into a wedge shape above and below using a 30 kV Ga ion beam at a stage tilt of 22°. The wedge was lifted out and mounted onto a commercial 22-array Si coupon using a Pt gas injection system. The mounted specimen was annularly milled with a 30 kV Ga ion beam, gradually reducing the current from 0.5 nA to 50 pA. To minimise Ga-induced damage, final milling was performed at 5 kV, yielding the required tip geometry (Figure S45). APT measurements were conducted using a LEAP 4000X HR instrument (CAMECA) under the following conditions: pulse rate, 125–200 kHz; specimen temperature, 50–60 K; laser energy, 60–80 pJ; and detection rate, 0.5–1% (Figure S46).\u003c/p\u003e\n\u003cp\u003eThermo-mechanical analysis (TMA, NETZSCH TMA 402 F1) was performed from 30 °C to 500 °C at a heating rate of 2 °C/min for both as-cast and annealed super invar alloys. Magnetic properties were measured using a magnetic property measurement system (MPMS3-Evercool, Quantum Design Inc.) at 300 K under a magnetic field of 1.5 T for both as-cast and annealed FeCoNiCu HEA alloys. Nano-indentation tests (Bruker TI-950) were conducted at a load of 10 mN, while Vickers hardness tests (Matsuzawa MMT X7-B) were carried out at 500 gf for TiAl alloys and 200 gf for the super invar and HEA alloys, with a dwell time of 15 s.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the National R\u0026amp;D Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (RS-2024-00450561 and RS-2025-00520824) and the Korea Institute of Energy Technology Evaluation and Planning (KETEP) (No. RS-2024-00401917).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003e\u0026ldquo;Carbon neutrality strategies for sustainable batteries: from structure, recycling, and properties to applications - Energy \u0026amp; Environmental Science (RSC Publishing).\u0026rdquo; Accessed: July 03, 2025. 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Crystallogr.\u003c/em\u003e, vol. 48, no. 5, pp. 1573\u0026ndash;1580, Oct. 2015, doi: 10.1107/S1600576715014685.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"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":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Battery waste upcycling, Hydrogen plasma reduction, Metal recovery, Single-step alloy design, Circular economy","lastPublishedDoi":"10.21203/rs.3.rs-7339880/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7339880/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Achieving carbon neutrality makes sustainable recycling approaches for end-of-life batteries critical to accommodate the rapid growth of the electric vehicle market. Conventional hydrometallurgical and pyrometallurgical processes are energy-intensive, time-consuming, and generate hazardous by-products. Here, we showcase how hydrogen plasma reduction enables rapid recovery of valuable metals from spent battery cathodes, reducing energy consumption by over 25% compared to traditional extraction techniques. Beyond metal recovery, the method allows direct waste-to-alloy synthesis of high-performance materials, including super invar, high-entropy, and titanium-based systems, through a streamlined process using battery waste as starting material. This approach offers a simple, efficient, and environmentally friendly route for upcycling battery waste into advanced functional alloys.","manuscriptTitle":"Hydrogen plasma reduction for direct upcycling of battery waste into high-performance alloys","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-14 05:10:28","doi":"10.21203/rs.3.rs-7339880/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"ce1aa3bd-aaca-4f39-88ae-e901eaa7399d","owner":[],"postedDate":"May 14th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":66629511,"name":"Physical sciences/Materials science/Structural materials/Metals and alloys"},{"id":66629512,"name":"Physical sciences/Chemistry/Green chemistry/Sustainability"}],"tags":[],"updatedAt":"2026-05-14T05:10:28+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-14 05:10:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7339880","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7339880","identity":"rs-7339880","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}