Enhancement the discharge capacity of NiCl 2-x Br x thermal battery by inhibition overflow of electrloyte

Enhancement the discharge capacity of NiCl 2-x Br x thermal battery by inhibition overflow of electrloyte | 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 Research Article Enhancement the discharge capacity of NiCl 2-x Br x thermal battery by inhibition overflow of electrloyte Jun Tang, Yuhong Nong, Ling Ran, Licheng Tang, Zhiqiang Zhan, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6333156/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract Nickel chloride is a promising cathode material for high-power thermal batteries due to its high theoretical capacity, high discharge current density, and high electrode potential. Nevertheless, its substandard electrical conductivity, elevated-temperature melting properties, and electrolyte interface instability considerably constrain its practical applications. In this paper, NiCl 1.6 Br 0.4 with high electrical conductivity and high specific capacity was prepared through comparative experiments, and the merits of BN over MgO for LiB/NiCl 1.6 Br 0.4 thermal battery system were demonstrated by analysing the difference between electrochemical performance and melting leaching phenomenon. The LiB/BN-E/NiCl 2-x Br x thermal battery system demonstrates optimal discharge performance at 500 °C, achieving a specific capacity of 319 mAh g -1 , a specific energy of 744 Wh kg -1 , and a specific power of 7.0 kW kg -1 under a discharge condition of 0.2 A cm -2 . The LiB/BN-E/NiCl 2-x Br x thermal battery system has application prospects in high-energy thermal batteries. NiCl2 Thermal battery Cathode material BN separator Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction With the advancement of weapons and aeropace equipment, improving the performance of thermal batteries, a critical component in these systems, is of great significance. In order to obtain miniature thermal batteries with long discharge time, high specific power and high specific energy, the research modification of cathodematerials for thermal batteries has been widely concerned and explored by researchers. According to the research, NiCl 2 is considered to be a promising cathode material for thermal batteries due to its advantages of low cost, high electrode potential, high theoretical capacity, and the ability to prepare batteries with high specific power as a cathode material for thermal batteries. [1–5] The drawbacks of NiCl 2 as a material for batteries are the low conductivity and prone to be melt-immersed with the electrolyte, which leads to the difficulty of applying it in practical production. [6] However, NiCl 2 exhibits suboptimal conductivity and a forbidden bandwidth of 2.52 eV, which hinders efficient charge transfer as a cathode material. [7] Lin [8] et al. improved the electrical conductivity of NiCl 2 nanosheets by treating them with hydrogen etching and embedding trace amounts of Ni monomers with high conductivity at the edges of their surface area; Gui [8] et al. improved the electrical conductivity by using Cu + doping to introduce lattice defects into the NiCl 2 cathode material; Yao [9] et al.'s research showed that the introduction of anions such as O in NiCl 2 can form heterojunctions such as Ni-O-Cl, reducing the forbidden band width and internal resistance. Huang [10] et al. utilised Br − doping in NiCl 2 not only to lower the voltage decay, but also improved the conductivity of NiCl 2 . Elemental doping has been shown to enhance the discharge performance of the material; however, the interaction (e.g. melt leaching) phenomenon between NiCl 2 and the commonly used LiF-LiCl-LiBr electrolyte system during the discharge process due to its intrinsic properties still restricts its properties, such as effective utilisation and discharge time. The recent studies have shown that BN binder effectively inhibits the melting and leaching of NiCl 2 , enhancing its stability during discharge, compared with MgO, BN exhibited a better match with NiCl 2 In this paper, the cathode material NiCl 2 − x Br x was prepared by introducing halogen anion Br-doped NiCl 2 to explore the electrochemical performance and leaching behaviour of the LiB/BN-E/NiCl 2 − x Br x system, and the effect of the application of BN-E on the polarization internal resistance and interface infiltration of single cell was analyzed. 2. Experiments 2.1 BN separator (BN-E) preparation The BN-E was prepared via a solution impregnation-sintering process. First, a specific mass of LiF-LiCl-LiBr electrolyte was weighed and dissolved in water to make an electrolyte solution. Then, a BN fiber sheet was impregnated with the solution, taken out, and dried in a 450°C vacuum oven for 2 h to obtain the BN separator (BN-E). 2.2 NiCl 2 − x Brₓ Synthesis A simple liquid-phase sintering method was designed to synthesize bromine-ion-doped NiCl 2 (NiCl 2 − x Brₓ) cathode materials. Specifically, nickel chloride hexahydrate (NiCl 2 ·6H 2 O) and nickel bromide hydrate (NiBr 2 ·xH 2 O) were weighed according to certain atomic ratios, placed in a beaker, and mixed with a certain amount of anhydrous ethanol. The mixture was magnetically stirred for 4 h until fully dissolved, pre-dried at 120°C in a blast-drying oven, and then dehydrated in a vacuum tube furnace under an Ar atmosphere (held at 200°C for 2 h and 600°C for 3 h). After cooling to room temperature, the powder was collected, ground in a glove box, and sealed for storage. 2.3 Single Cell Testing The single cell experiments used NiCl 2 /halogen-anion-doped NiCl 2 (NiCl 2 − x Brₓ) as the cathode material, along with a LiF-LiCl-LiBr/BN separator sheet and a 17.5mm LiB alloy. A commercial magnesium oxide separator (MgO-E, 50 wt.% LiF-LiCl-LiBr − 50 wt.% MgO) was also used for comparison. 2.4 Material characterisation Material characterization was performed using a Rigaku MiniFlex 600 X-ray diffractometer (Cu-Kα radiation, λ = 0.15406 nm) operated at 40 kV and 15 mA. The XRD patterns were collected from 5° to 90° with a scanning speed of 10° min − 1 and 0.01° step size. Microstructural analysis was conducted using scanning electron microscopy (SEM) with a 5.0 kV accelerating voltage and 9.8 µA current at a 10.8 mm working distance. Boron nitride samples were gold-sputtered prior to SEM observation to enhance conductivity. Thermogravimetric analysis (TGA) was carried out under an Ar atmosphere from room temperature to 1000°C at a heating rate of 10°C min − 1 to evaluate thermal stability. BET surface area analysis was performed using nitrogen adsorption at 298 K after pre-drying samples at 120°C for 12 h. Transmission electron microscopy (TEM) was employed for high-resolution imaging of surface and interfacial properties. 3. Results and discussion 3.1 Preparation of NiCl 2-x Br x cathode materials and their physical phase analysis Bromine ion doped NiCl 2 (NiCl 2 − x Br x ) cathode material is prepared from nickel chloride hexahydrate (NiCl 2 •6H 2 O) and nickel bromide hydrate (NiBr 2 •xH 2 O) according to a certain atomic ratio, and the atom ratios and nomenclature to obtain the bromine ion doped NiCl 2 (NiCl 2 − x Br x ) are shown in Table 1 . Table 1 Atomic ratios of bromine ion doped NiCl 2 (NiCl 2-x Br x ) cathode materials NiCl 2 − x Br x NiCl 2 (at. %) NiBr 2 (at. %) NiCl 0.67 Br 1.33 1 2 NiCl 1 Br 1 1 1 NiCl 1.33 Br 0.67 2 1 NiCl 1.6 Br 0.4 4 1 Figure 1 shows the physical images of four powder samples, namely, NiCl 1.6 Br 0.4 , NiCl 1.33 Br 0.67 , NiCl 1 Br 1 and NiCl 0.67 Br 1.33 . As the content of NiBr 2 increased, the colour of the four samples gradually changed from orange to brown, which proved the gradual increase of bromine content in the above mentioned composites. In order to analyse the physical structure of the NiCl 2 − x Br x cathode material, the samples with different Br − doping were characterized by XRD, and their XRD patterns are shown in Fig. 3 (a). The XRD patterns of NiCl 1.6 Br 0.4 , NiCl 1.33 Br 0.67 , NiCl 1 Br 1 and NiCl 0.67 Br 1.33 closely resemble those of pure NiCl2. The diffraction peaks at 2θ = 15.26° correspond to the (003) crystallographic plane in the standard JCPDS card (no. 71-2032) for NiCl2. These peaks exhibit the highest intensity, indicating a preferential orientation of the (003) plane. (003) crystal plane has a selective orientation. In order to investigate whether Br − doping has an effect on the crystal structure of NiCl 2 , the local magnified XRD patterns of NiCl 2 − x Br x at 14–20° were intercepted (shown in Fig. 3 (b)). It can be observed from the local magnified image that Br − doping shifted the XRD diffraction peaks to a lower angle, and the angle of the diffraction peaks shifted more and more as the amount of Br − doping increased. The main reason is that the ionic radius of Br − is larger than that of Cl − , and Br − doping makes the crystal spacing increase. According to the Bragg diffraction Eq. (1), Br − doping causes the XRD diffraction peaks to be shifted to a lower angle due to the increase in the crystal plane spacing. This indicates that Br − successfully doped into the lattice of NiCl 2 . 2dsinθ = nλ (1) In order to determine the actual elemental distribution of Br − doped NiCl 2 , NiCl 1.6 Br 0.4 was selected for SEM and Mapping tests. The analytical characterisation of Br − doped NiCl 2 sample is shown in Fig. 3 . The Mapping diagram reveals a homogeneous distribution of Ni, Cl, and Br, indicating that Br- doping via the liquid-phase sintering method results in uniform dispersion within the sample. Table 2 shows the elemental content of NiCl 1.6 Br 0.4 in the surface scan, from which it can be seen that the atomic ratios of Cl and Br elements are 50.01% and 12.28%, respectively, which is close to a 4:1 ratio, which proves that the preparation ratios of NiCl 1.6 Br 0.4 are in accordance with the experimental expectations. Table 2 Elemental content of Br - doped NiCl 2 surface swept elements in SEM Element Signal Atomic % Ni 37.71 Cl 50.01 Br 12.28 3.2 Study on the effect of BN-E on the discharge performance of NiCl 2-x Br x thermal battery Figure 4 shows the discharge curves of NiCl 2 − x Br x /BN-E/LiB single cell at 500°C and current densities of 0.1 A cm − 2 , 0.2 A cm − 2 and 0.5 A cm − 2 , respectively (with a cut-off voltage of 2 V). From the figure, it can be found that the discharge voltage plateaus of the four cathode materials are not significantly different with the increase of Br − doping content, and the discharge curves are relatively smooth. Combined with Fig. 5 , it can be seen that the integrated discharge performance of the monolithic battery decreases with more content of Br − doping. In the LiB/NiCl 2 − x Br x thermal battery system, there are two reaction equations: NiCl 2 + 2Li→2LiCl + Ni; NiBr 2 + 2Li→2LiBr + Ni. With the increase of the doping content of Br − , the more the content of LiCl and LiBr in the reaction products, the easier it is to disrupt the physical phase ratio of the electrolyte, exacerbate the overflow of the molten electrolyte, and affect the discharge performance of the single cell. It is worth noting that the comparison of discharge performance in Fig. 4 (a) shows that the discharge voltage platform of NiCl 2 − x Br x cathode material increases, which is mainly due to the fact that Br − doped NiCl 2 reduces the forbidden bandwidth of the material, decreases the internal resistance, and improves the electrical conductivity of NiCl 2 [11–13] . Figure 5 shows that NiCl 1.6 Br 0.4 exhibited the best electrical properties with a specific capacity of 319 mAh g − 1 and a specific energy of 744 Wh kg − 1 at 500°C and a discharge of 0.2 A cm − 2 discharge. It can be seen from the figures that the NiCl 1.6 Br 0.4 /LiB system has the advantage of high-current discharge. Combined with Fig. 5 , the NiCl 1.6 Br 0.4 /BN-E system achieved a high power of 16.1 kW kg − 1 at 500°C and 0.5 A cm − 2 current density discharge, reflecting the high power characteristics of the NiCl 1.6 Br 0.4 cathode material. By increasing the discharge temperature to 550°C, the discharge curves of NiCl 2 − x Br x /BN-E/LiB single cell at different current densities (Fig. 6 ) were not as smooth as those of single cell with the corresponding cathode materials at 500°C, and the discharge platform fluctuated greatly, whereas the discharge voltage increased slightly with the increase in discharge temperature, and the specific capacity of the discharges decreased substantially (Fig. 6 ). The main reason for the specific capacity decay is that the high temperature increases the migration rate of Li + In order to maintain the charge equilibrium state inside the battery, the anions in the cathode accelerate to dissolve into the electrolyte, increasing the concentration polarisation inside the battery and leading to the early end of the discharge. In addition, when discharged at 550°C, NiCl 1.6 Br 0.4 still showed the optimal electrochemical performance, with a specific capacity of 270 mAh g − 1 at a current density of 0.5 A cm − 2 , a specific energy of discharge of 597 Wh kg − 1 , and a specific power of 16.5 kW kg − 1 , which has the advantage of high power discharge. In order to further determine the change of internal resistance of NiCl 2 − x Br x /BN-E single cell during the discharge process, it was subjected to pulse discharge test at 500°C under the conditions of constant current 0.1 A cm − 2 , pulse current 0.5 A cm − 2 , pulse duration of 1 s, and pulse interval of 15 s. The change curve of the resistance of the single cell were calculated from the pulse test by intercepting the discharge voltage at 2 V during the discharge at constant current, and the resistance change curve was calculated by the pulse test. As shown in Fig. 9 , the trend of the internal resistance of the four cathode materials is basically the same, and the internal resistance of the single cell is higher at the beginning of discharge, which is mainly due to the high resistivity of NiCl 2 itself. With the increase of discharge depth, the internal resistance of the battery gradually decreases, which is because the discharge product is Ni monomer with high conductivity; while in the middle and late stages of discharge, there is a large lithium ion concentration polarisation in the electrolyte, which leads to a slow increase in the internal resistance of the battery. As can be seen from the figure, with the decrease of Br − doping in the NiCl 2 − x Br x cathode, the average internal resistance of its corresponding single cell slightly decreases, and the corresponding pulse discharge platform is improved. Among them, the cathode material of NiCl 1.6 Br 0.4 has the best pulse discharge performance, with an average internal resistance of 0.23 Ω, which can be as high as 2.50 V vs. Li potential, which tends to the theoretical voltage value of NiCl 2 material (2.64 V vs. Li). 3.3 BN-E flow suppression characterisation of NiCl 2-x Br x thermal cell In order to compare the flow inhibition effects of BN and MgO on the NiCl 1.6 Br 0.4 /LiB thermo-cell system, a discharge comparison of 0.1 A/cm 2 and 0.2 A/cm 2 currents was carried out using the two bonding agents applied to the NiCl 1.6 Br 0.4 system at 500°C. As demonstrated in Fig. 8 (d) and Fig. 9 , the NiCl 1.6 Br 0.4 /BN-E/LiB system exhibits a higher discharge capacity, despite the NiCl 1.6 Br 0.4 /MgO-E/LiB system demonstrating a marginally higher discharge voltage plateau. This phenomenon may be attributed to the severe melting and leaching of MgO-E with the cathode material during the discharge process, leading to the depletion of the cathode active material as well as the overflow of the electrolyte, which resulted in the decrease of the specific capacity. This finding suggests that the NiCl 1.6 Br 0.4 /LiB system exhibits a high current discharge capacity, which is a significant advantage in battery technology. Figure 9 shows the comparison of electrode sheet morphology between NiCl 1.6 Br 0.4 /BN-E and NiCl 1.6 Br 0.4 /MgO-E after discharging at different discharge temperatures and different current densities, and it can be seen from Fig. 9 (a-c) that, at the same discharge temperature, there is no obvious overflow phenomenon in the electrostack of the BN-E single cell, on the contrary, the electrostack of the MgO-E single cell undergoes an obvious electrolyte overflow phenomenon (Fig. 9 ( d)), and the cathode layer also suffered serious breakage. This is mainly caused by the melting and leaching of the cathode and products with the electrolyte during the discharge process, and the structural collapse of the positive electrode during the discharge process. This phenomenon will reduce the active material in the cathode, shorten the discharge time, and end the discharge prematurely, and the overflow will lead to the short circuit in the battery in case of severe overflow, or even cause a fire, jeopardising the safety of the battery discharge. From Fig. 9 (e-h), it can be observed that with the increase of discharge temperature, the degree of overflow of the stack deepens. The main reason is that the increase in discharge temperature accelerates the reaction of the cathode material and its dissolution in the electrolyte, exacerbating the overflow of the electrostack. Among them, the overflow area of BN-E is obviously smaller than that of MgO-E, which can indicate, from the side, that BN-E has the advantage of inhibiting the flow of molten electrolyte. In order to visually compare the ability of MgO and BN to inhibit the extent of melt leaching in the NiCl₁.₆Br₀.₄/BN-E system, the electrostacks of NiCl 1.6 Br 0.4 /BN-E single cell and NiCl 1.6 Br 0.4 /MgO-E single cell after discharge were selected as the study object, and the discharged electrostacks were broken in the middle to observe the cross-section under the scanning electron microscope, and the SEM-Mapping is shown in Figs. 10 and 11 . From Fig. 10 (a), it can be seen that there is a clear demarcation line between the cathode layer and the separator layer of the electrostack after discharge of the BN-E thermal battery system. From the elemental distribution in Fig. 10 (b-f), it can be observed that the B, N, Br and Cl elements in the separator layer are uniformly distributed, which indicates that the structure of the separator layer is not seriously damaged after discharge, and there is no obvious flow phenomenon of the molten electrolyte. In the Ni element distribution diagram, the Ni elements are mainly concentrated in the cloth in the cathode layer, and a small amount exists in the separator layer, which laterally indicates that BN-E can well inhibit the melt flow of electrolyte and reduce the degree of electrolyte melt overflow in high temperature discharge. From Fig. 11 (a), it can be seen that there is no obvious demarcation line in the post-discharge stack of the MgO-E thermal battery system, and from Fig. 11 (d), it is observed that the Ni element has a wider range of distribution, and a large amount of Ni element also exists in the separator layer, which is mainly due to the intermixing of the cathode and the electrolyte in the high-temperature discharging process, and the Ni monomers are caused to flow with the molten electrolyte to the separator layer. The results show that the fixation effect of MgO-E on the molten electrolyte has limitations, and it barely inhibit the flow of molten electrolyte, which depletes the active material of the cathode, affects the discharge performance, shortens the discharge time, and leads to the early end of the discharge of the single cell. Bromine ion doping of NiCl 2 cathode material effectively improved the discharge voltage plateau of the corresponding single cell, however, the introduction of Br − exacerbated the leaching degree of NiCl 2 cathode with the molten salt electrolyte. BN-E was also applied to the NiCl 2 − x Br x system with a harsher degree of melt immersion, and it was found that the interface between the cathode and the separator layer was clear after discharge, and the Ni element was mainly concentrated in the cathode layer, which indicated that the molten electrolyte did not undergo obvious flow behavior during the high temperature discharge process, which reflected that BN-E had a stronger ability to inhibit the flow of the molten electrolyte. Meanwhile, BN-E has a lower internal resistance of discharge (0.23 Ω), indicating that the polarization internal resistance of the battery is smaller during the discharge process. 4. Conclusion In this paper, the cathode material NiCl 2 − x Br x was prepared by introducing halogen anion Br doping to NiCl 2 , and the optimal proportion of Br doping was discussed in combination with the discharge curve and pulse internal resistance, so as to solve the problem of inferior conductivity of NICl 2 -based materials. Subsequently, the research system was established as NiCl 1.6 Br 0.4 . A comparison of the electrochemical performance and leaching behavior of BN and MgO as electrolyte adhesive was conducted, which demonstrated that BN can effectively inhibit the interaction between NiCl 1.6 Br 0.4 and electrolyte, and improve the discharge performance of the battery. The cathode material for thermal batteries with high specific energy and low internal resistance was obtained by Br-doping NiCl 1.6 Br 0.4 , while BN-E was used as a diaphragm binder to inhibit the melt leaching between cathode and diaphragm layers. The experimental findings demonstrated that the Br doping of NiCl 2 resulted in a reduction of the forbidden band of the material and an enhancement of the conductivity and specific energy of discharge of NiCl 2 . The optimal discharge performance was observed at 500°C or 550°C for NiCl 1.6 Br 0.4 . Notably, it exhibited a specific capacity of 319 mAh g − 1 , a specific energy of 744 Wh kg − 1 , and a specific power of 7.0 kW kg − 1 during discharge at 500°C and 0.2 A cm − 2 . The investigation further examined the use of BN as the electrolyte binder in the NiCl 1.6 Br 0.4 thermal battery system in comparison with MgO. The post-discharge interface was analyzed, and the ability of BN-E to inhibit electrolyte flow during high-temperature discharge was confirmed by SEM and Mapping of the post-discharge collector overflow area and electrostack interface. The overflow area was found to be smaller in the BN-E sample than in the MgO-E sample. This finding suggests that BN-E has a stronger inhibition of molten electrolyte flow than MgO-E. Therefore, it can be concluded that BN-E is more suitable than MgO-E for use as cathode material in the NiCl 1.6 Br 0.4 system. Furthermore, BN-E exhibits a safer application in the LiB/BN-E/ NiCl 1.6 Br 0.4 thermal battery system. Declarations Author Contribution J.T. (Conceptualization, Methodology, Investigation, Writing - Original Draft), Y.N. (Formal Analysis, Data Curation, Visualization), L.R. (Methodology, Validation, Resources), L.T. (Investigation, Software), Z.Z. (Data Curation, Formal Analysis), Y.D. (Writing - Review & Editing), L.F. (Supervision, Project Administration, Funding Acquisition). All authors reviewed and approved the final manuscript Acknowledgments The research was carried out with financial support from the Young teacher development program of Hunan University (No. 2015031) References 1. Luo Z, Lin X, Tang L, et al. Novel NiCl 2 nanosheets synthesized via chemical vapor deposition with high specific energy for thermal battery[J]. ACS Applied Materials & Interfaces, 2020, 12(31): 34755–34762. 2. Chen F, Jiang C, Cao S, et al. Synergetic effect of functional additions on Li/NiCl 2 thermal battery with enhanced discharge performance[J]. Materials Letters, 2022,320: 132371. 3. Liu W, Liu H, Bi S, et al. Variable-temperature preparation and performance of NiCl 2 as a cathode material for thermal batteries[J]. Science China Materials, 2017, 60(3): 251–257. 4. Zhu Y, Xing J, Yang B, et al. Preparation of NiCl 2 nanorods with enhanced electrochemical properties in thermal batteries[J]. ECS Transactions, 2015, 69(18): 13–20. 5. Li R, Guo W, Qian Y. Recent developments of cathode materials for thermal batteries[J]. Frontiers in chemistry, 2022, 10: 832972. 6. Jin C, Fu L, Ge B, et al. The NiCl 2 /NiS 2 @C double active composite cathodes with surface synergistic effects for high-power thermal battery[J]. Journal of Alloys and Compounds, 2019, 800: 518–524. 7. Tan X, Ding L, Du G F, et al.Spin caloritronics in two-dimensional CrI 3 /NiCl 2 van derWaals heterostructures[J].Physical review, B, 2021(11):103.[8] Lin X, Fu L, Zhu J, et al. NiCl 2 cathode with the high load capacity for high specific power thermal battery[J]. IOP Conference Series: Materials Science and Engineering, 2019, 677(3): 032046. 9. Gui Y, Lin X, Fu L, et al. Shortening activation time of thermal battery by hydrogen etching of NiCl 2 cathode[J]. Materials Letters, 2020, 275: 128136. 10. Huang M, Li J, Li S, et al. Controlling the changes in electrolyte composition in the cathode to reduce the voltage decay of NiCl 2 thermal batteries[J]. ACS Applied Energy Materials, 2023, 6(3): 1511–1518. 11. Yao B, Fu L, Gui Y, et al. Instantaneous activation of NiCl 2 cathode towards thermal battery by constructing NiCl 2 -NiO heterojunction[J]. ACS Sustainable Chemistry & Engineering, 2023, 11(1): 199–207. 12. Tang J, Wei Z, Wang Q, et al. In situ oxygen doping of monolayer MoS 2 for novel electronics[J]. Small, 2020, 16: 2004276. 13. Zhang F, Lu Y, Schulman D, et al. Carbon doping of WS 2 monolayers: bandgap reduction and p-type doping transport[J]. Science advances, 2019,5(5):eeaav5003. Additional Declarations No competing interests reported. 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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-6333156","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":446914647,"identity":"42319c6a-5d36-42a1-a396-280bcc1ebdb7","order_by":0,"name":"Jun Tang","email":"","orcid":"","institution":"Hunan University","correspondingAuthor":false,"prefix":"","firstName":"Jun","middleName":"","lastName":"Tang","suffix":""},{"id":446914648,"identity":"b379fc07-1552-4b2d-8c6f-37ff40de6404","order_by":1,"name":"Yuhong Nong","email":"","orcid":"","institution":"Hunan 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University","correspondingAuthor":true,"prefix":"","firstName":"Licai","middleName":"","lastName":"Fu","suffix":""}],"badges":[],"createdAt":"2025-03-29 09:23:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6333156/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6333156/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":81318073,"identity":"6e27b3c7-e688-49c6-b58d-d3aee45dd915","added_by":"auto","created_at":"2025-04-24 16:43:35","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":42146,"visible":true,"origin":"","legend":"\u003cp\u003ePhysical view of Br\u003csup\u003e-\u003c/sup\u003e doped NiCl\u003csub\u003e2\u003c/sub\u003e sample\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/18e5c9f03548a6af4e434887.jpg"},{"id":81317276,"identity":"72b4c4e4-e823-405a-8e04-53db1c8e94d3","added_by":"auto","created_at":"2025-04-24 16:35:35","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":63447,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XRD image and (b) locally enlarged XRD image at 14-20° of NiCl\u003csub\u003e2-x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/54b587dd4d677d0c63a048ed.jpg"},{"id":81317280,"identity":"daa63f0b-d0bd-46d0-91fe-fae9667095a1","added_by":"auto","created_at":"2025-04-24 16:35:35","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":157821,"visible":true,"origin":"","legend":"\u003cp\u003e(a) SEM and (b-d) Mapping of NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/474e1412ae28d8348f2c1b21.jpg"},{"id":81317278,"identity":"00936a33-e78c-4201-95a4-535cc4414c52","added_by":"auto","created_at":"2025-04-24 16:35:35","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":135463,"visible":true,"origin":"","legend":"\u003cp\u003eDischarge curves of NiCl\u003csub\u003e2-x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e/BN-E at different current densities ((a) 0.1 A cm\u003csup\u003e-2\u003c/sup\u003e, (b) 0.2 A cm\u003csup\u003e-2\u003c/sup\u003e, (c) 0.5 A cm\u003csup\u003e-2\u003c/sup\u003e) and (d) discharge curves of different electrolyte separators at 500°C in the system NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/LiB\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/87459871d71f1c7f44a7e606.jpg"},{"id":81318375,"identity":"1f1f6644-7e38-4cf2-b33b-b6f82a935193","added_by":"auto","created_at":"2025-04-24 16:51:35","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":75564,"visible":true,"origin":"","legend":"\u003cp\u003eDischarge performance parameters of NiCl\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e2-x\u003c/sub\u003e /BN-E at 500℃ and different current densities.\u003c/p\u003e\n\u003cp\u003e(a) Specific energy, (b) Specific Power, (c) Specific capacity\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/f01fe2f82ca3a152358bcdbd.jpg"},{"id":81319160,"identity":"5b95b327-fb26-4e30-ad73-9c80992c6729","added_by":"auto","created_at":"2025-04-24 16:59:35","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":104436,"visible":true,"origin":"","legend":"\u003cp\u003eDischarge curves of NiCl\u003csub\u003e2-x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e/BN-E at 550 °C with different current densities\u003c/p\u003e\n\u003cp\u003e(a) 0.1 A cm\u003csup\u003e-2\u003c/sup\u003e, (b) 0.2 A cm\u003csup\u003e-2\u003c/sup\u003e, (c) 0.5 A cm\u003csup\u003e-2\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/a06abfec0d0d619ad6d3753f.jpg"},{"id":81317288,"identity":"9f93287b-c74e-49de-ac29-aa370bd3b240","added_by":"auto","created_at":"2025-04-24 16:35:35","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":62704,"visible":true,"origin":"","legend":"\u003cp\u003eDischarge performance parameters of NiCl\u003csub\u003ex\u003c/sub\u003eBr\u003csub\u003e2-x\u003c/sub\u003e /BN-E at 550°C and different current densities.\u003c/p\u003e\n\u003cp\u003e(a) Specific energy, (b) Specific Power, (c) Specific capacity\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/2e9afe9565647d94e345c662.jpg"},{"id":81318074,"identity":"3eb6e5ec-edea-4b75-8706-537bd2ae719e","added_by":"auto","created_at":"2025-04-24 16:43:35","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":127394,"visible":true,"origin":"","legend":"\u003cp\u003ePulsed discharge profile of NiCl\u003csub\u003e2-x\u003c/sub\u003e Br\u003csub\u003ex\u003c/sub\u003e /BN-E at 500 °C\u003c/p\u003e\n\u003cp\u003e(a) NiCl\u003csub\u003e0.67\u003c/sub\u003eBr\u003csub\u003e1.33\u003c/sub\u003e, (b) NiCl\u003csub\u003e1\u003c/sub\u003eBr\u003csub\u003e1\u003c/sub\u003e, (c) NiCl\u003csub\u003e1.33\u003c/sub\u003eBr\u003csub\u003e0.67\u003c/sub\u003e, (d) NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/363edeba98bb417938a75020.jpg"},{"id":81317287,"identity":"42d39748-49c8-496f-9359-60abc977fb9a","added_by":"auto","created_at":"2025-04-24 16:35:35","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":122438,"visible":true,"origin":"","legend":"\u003cp\u003ePositive (left) and negative (right) terminals of the collector after discharging BN-E/MgO-E single cells at different temperatures and current densities (the green dotted circle represents the position of the electrostack, and the overflow area is between the red dotted circle and the green dotted circle)\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/3e65a9398b646876d25111b1.jpg"},{"id":81317293,"identity":"a5da13db-3cf4-405e-9641-07eaab6a2e2a","added_by":"auto","created_at":"2025-04-24 16:35:35","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":225938,"visible":true,"origin":"","legend":"\u003cp\u003eNiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e /BN-E post-discharge electrostack interfaces (a) SEM and (b-f) Mapping\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/eb4c40b0aee6e9f5ff594ec0.jpg"},{"id":81319161,"identity":"63cdc134-f7c1-4044-9aed-8765cbe4896a","added_by":"auto","created_at":"2025-04-24 16:59:35","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":270208,"visible":true,"origin":"","legend":"\u003cp\u003eNiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e /MgO-E post-discharge electrostack interface (a) SEM and (b-f) Mapping diagrams\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/f03a1d84b9591864199d2317.jpg"},{"id":81319640,"identity":"f1693829-93ab-48ab-b378-5044d77426cc","added_by":"auto","created_at":"2025-04-24 17:07:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2096689,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6333156/v1/63e65b0b-bda9-46fa-a22a-37e173b146c0.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Enhancement the discharge capacity of NiCl 2-x Br x thermal battery by inhibition overflow of electrloyte","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWith the advancement of weapons and aeropace equipment, improving the performance of thermal batteries, a critical component in these systems, is of great significance. In order to obtain miniature thermal batteries with long discharge time, high specific power and high specific energy, the research modification of cathodematerials for thermal batteries has been widely concerned and explored by researchers. According to the research, NiCl\u003csub\u003e2\u003c/sub\u003e is considered to be a promising cathode material for thermal batteries due to its advantages of low cost, high electrode potential, high theoretical capacity, and the ability to prepare batteries with high specific power as a cathode material for thermal batteries.\u003csup\u003e[1\u0026ndash;5]\u003c/sup\u003e The drawbacks of NiCl\u003csub\u003e2\u003c/sub\u003e as a material for batteries are the low conductivity and prone to be melt-immersed with the electrolyte, which leads to the difficulty of applying it in practical production. \u003csup\u003e[6]\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eHowever, NiCl\u003csub\u003e2\u003c/sub\u003e exhibits suboptimal conductivity and a forbidden bandwidth of 2.52 eV, which hinders efficient charge transfer as a cathode material. \u003csup\u003e[7]\u003c/sup\u003e Lin\u003csup\u003e[8]\u003c/sup\u003e et al. improved the electrical conductivity of NiCl\u003csub\u003e2\u003c/sub\u003e nanosheets by treating them with hydrogen etching and embedding trace amounts of Ni monomers with high conductivity at the edges of their surface area; Gui\u003csup\u003e[8]\u003c/sup\u003e et al. improved the electrical conductivity by using Cu\u003csup\u003e+\u003c/sup\u003e doping to introduce lattice defects into the NiCl\u003csub\u003e2\u003c/sub\u003e cathode material; Yao\u003csup\u003e[9]\u003c/sup\u003e et al.'s research showed that the introduction of anions such as O in NiCl\u003csub\u003e2\u003c/sub\u003e can form heterojunctions such as Ni-O-Cl, reducing the forbidden band width and internal resistance. Huang\u003csup\u003e[10]\u003c/sup\u003e et al. utilised Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping in NiCl\u003csub\u003e2\u003c/sub\u003e not only to lower the voltage decay, but also improved the conductivity of NiCl\u003csub\u003e2\u003c/sub\u003e. Elemental doping has been shown to enhance the discharge performance of the material; however, the interaction (e.g. melt leaching) phenomenon between NiCl\u003csub\u003e2\u003c/sub\u003e and the commonly used LiF-LiCl-LiBr electrolyte system during the discharge process due to its intrinsic properties still restricts its properties, such as effective utilisation and discharge time. The recent studies have shown that BN binder effectively inhibits the melting and leaching of NiCl\u003csub\u003e2\u003c/sub\u003e, enhancing its stability during discharge, compared with MgO, BN exhibited a better match with NiCl\u003csub\u003e2\u003c/sub\u003e In this paper, the cathode material NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e was prepared by introducing halogen anion Br-doped NiCl\u003csub\u003e2\u003c/sub\u003e to explore the electrochemical performance and leaching behaviour of the LiB/BN-E/NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e system, and the effect of the application of BN-E on the polarization internal resistance and interface infiltration of single cell was analyzed.\u003c/p\u003e"},{"header":"2. Experiments","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 BN separator (BN-E) preparation\u003c/h2\u003e \u003cp\u003eThe BN-E was prepared via a solution impregnation-sintering process. First, a specific mass of LiF-LiCl-LiBr electrolyte was weighed and dissolved in water to make an electrolyte solution. Then, a BN fiber sheet was impregnated with the solution, taken out, and dried in a 450\u0026deg;C vacuum oven for 2 h to obtain the BN separator (BN-E).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBrₓ Synthesis\u003c/h2\u003e \u003cp\u003eA simple liquid-phase sintering method was designed to synthesize bromine-ion-doped NiCl\u003csub\u003e2\u003c/sub\u003e (NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBrₓ) cathode materials. Specifically, nickel chloride hexahydrate (NiCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO) and nickel bromide hydrate (NiBr\u003csub\u003e2\u003c/sub\u003e\u0026middot;xH\u003csub\u003e2\u003c/sub\u003eO) were weighed according to certain atomic ratios, placed in a beaker, and mixed with a certain amount of anhydrous ethanol. The mixture was magnetically stirred for 4 h until fully dissolved, pre-dried at 120\u0026deg;C in a blast-drying oven, and then dehydrated in a vacuum tube furnace under an Ar atmosphere (held at 200\u0026deg;C for 2 h and 600\u0026deg;C for 3 h). After cooling to room temperature, the powder was collected, ground in a glove box, and sealed for storage.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Single Cell Testing\u003c/h2\u003e \u003cp\u003eThe single cell experiments used NiCl\u003csub\u003e2\u003c/sub\u003e/halogen-anion-doped NiCl\u003csub\u003e2\u003c/sub\u003e (NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBrₓ) as the cathode material, along with a LiF-LiCl-LiBr/BN separator sheet and a 17.5mm LiB alloy. A commercial magnesium oxide separator (MgO-E, 50 wt.% LiF-LiCl-LiBr \u0026minus;\u0026thinsp;50 wt.% MgO) was also used for comparison.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Material characterisation\u003c/h2\u003e \u003cp\u003eMaterial characterization was performed using a Rigaku MiniFlex 600 X-ray diffractometer (Cu-Kα radiation, λ\u0026thinsp;=\u0026thinsp;0.15406 nm) operated at 40 kV and 15 mA. The XRD patterns were collected from 5\u0026deg; to 90\u0026deg; with a scanning speed of 10\u0026deg; min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 0.01\u0026deg; step size. Microstructural analysis was conducted using scanning electron microscopy (SEM) with a 5.0 kV accelerating voltage and 9.8 \u0026micro;A current at a 10.8 mm working distance. Boron nitride samples were gold-sputtered prior to SEM observation to enhance conductivity.\u003c/p\u003e \u003cp\u003eThermogravimetric analysis (TGA) was carried out under an Ar atmosphere from room temperature to 1000\u0026deg;C at a heating rate of 10\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e to evaluate thermal stability. BET surface area analysis was performed using nitrogen adsorption at 298 K after pre-drying samples at 120\u0026deg;C for 12 h. Transmission electron microscopy (TEM) was employed for high-resolution imaging of surface and interfacial properties.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Preparation of NiCl\u003csub\u003e2-x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e cathode materials and their physical phase analysis\u003c/h2\u003e\n \u003cp\u003eBromine ion doped NiCl\u003csub\u003e2\u003c/sub\u003e (NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e) cathode material is prepared from nickel chloride hexahydrate (NiCl\u003csub\u003e2\u003c/sub\u003e\u0026bull;6H\u003csub\u003e2\u003c/sub\u003eO) and nickel bromide hydrate (NiBr\u003csub\u003e2\u003c/sub\u003e\u0026bull;xH\u003csub\u003e2\u003c/sub\u003eO) according to a certain atomic ratio, and the atom ratios and nomenclature to obtain the bromine ion doped NiCl\u003csub\u003e2\u003c/sub\u003e (NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e) are shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u0026nbsp;\u003c/p\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAtomic ratios of bromine ion doped NiCl\u003csub\u003e2\u003c/sub\u003e (NiCl\u003csub\u003e2-x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e) cathode materials\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNiCl\u003csub\u003e2\u003c/sub\u003e (at. %)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNiBr\u003csub\u003e2\u003c/sub\u003e (at. %)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNiCl\u003csub\u003e0.67\u003c/sub\u003eBr\u003csub\u003e1.33\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNiCl\u003csub\u003e1\u003c/sub\u003eBr\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNiCl\u003csub\u003e1.33\u003c/sub\u003eBr\u003csub\u003e0.67\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows the physical images of four powder samples, namely, NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e, NiCl\u003csub\u003e1.33\u003c/sub\u003eBr\u003csub\u003e0.67\u003c/sub\u003e, NiCl\u003csub\u003e1\u003c/sub\u003eBr\u003csub\u003e1\u003c/sub\u003e and NiCl\u003csub\u003e0.67\u003c/sub\u003eBr\u003csub\u003e1.33\u003c/sub\u003e. As the content of NiBr\u003csub\u003e2\u003c/sub\u003e increased, the colour of the four samples gradually changed from orange to brown, which proved the gradual increase of bromine content in the above mentioned composites.\u003c/p\u003e\n \u003cp\u003eIn order to analyse the physical structure of the NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e cathode material, the samples with different Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping were characterized by XRD, and their XRD patterns are shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(a). The XRD patterns of NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e, NiCl\u003csub\u003e1.33\u003c/sub\u003eBr\u003csub\u003e0.67\u003c/sub\u003e, NiCl\u003csub\u003e1\u003c/sub\u003eBr\u003csub\u003e1\u003c/sub\u003e and NiCl\u003csub\u003e0.67\u003c/sub\u003eBr\u003csub\u003e1.33\u003c/sub\u003e closely resemble those of pure NiCl2. The diffraction peaks at 2\u0026theta;\u0026thinsp;=\u0026thinsp;15.26\u0026deg; correspond to the (003) crystallographic plane in the standard JCPDS card (no. 71-2032) for NiCl2. These peaks exhibit the highest intensity, indicating a preferential orientation of the (003) plane. (003) crystal plane has a selective orientation. In order to investigate whether Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping has an effect on the crystal structure of NiCl\u003csub\u003e2\u003c/sub\u003e, the local magnified XRD patterns of NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e at 14\u0026ndash;20\u0026deg; were intercepted (shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e(b)). It can be observed from the local magnified image that Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping shifted the XRD diffraction peaks to a lower angle, and the angle of the diffraction peaks shifted more and more as the amount of Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping increased. The main reason is that the ionic radius of Br\u003csup\u003e\u0026minus;\u003c/sup\u003e is larger than that of Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, and Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping makes the crystal spacing increase. According to the Bragg diffraction Eq. (1), Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping causes the XRD diffraction peaks to be shifted to a lower angle due to the increase in the crystal plane spacing. This indicates that Br\u003csup\u003e\u0026minus;\u003c/sup\u003e successfully doped into the lattice of NiCl\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Taba\" border=\"1\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2dsin\u0026theta;\u0026thinsp;=\u0026thinsp;n\u0026lambda;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e(1)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eIn order to determine the actual elemental distribution of Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doped NiCl\u003csub\u003e2\u003c/sub\u003e, NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e was selected for SEM and Mapping tests. The analytical characterisation of Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doped NiCl\u003csub\u003e2\u003c/sub\u003e sample is shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. The Mapping diagram reveals a homogeneous distribution of Ni, Cl, and Br, indicating that Br- doping via the liquid-phase sintering method results in uniform dispersion within the sample. Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e shows the elemental content of NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e in the surface scan, from which it can be seen that the atomic ratios of Cl and Br elements are 50.01% and 12.28%, respectively, which is close to a 4:1 ratio, which proves that the preparation ratios of NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e are in accordance with the experimental expectations.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u0026nbsp;\u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eElemental content of Br\u003csup\u003e-\u003c/sup\u003e doped NiCl\u003csub\u003e2\u003c/sub\u003e surface swept elements in SEM\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElement\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSignal Atomic %\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eNi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e37.71\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e50.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBr\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.28\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Study on the effect of BN-E on the discharge performance of NiCl\u003csub\u003e2-x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e thermal battery\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e shows the discharge curves of NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e/BN-E/LiB single cell at 500\u0026deg;C and current densities of 0.1 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, 0.2 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 0.5 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively (with a cut-off voltage of 2 V). From the figure, it can be found that the discharge voltage plateaus of the four cathode materials are not significantly different with the increase of Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping content, and the discharge curves are relatively smooth. Combined with Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, it can be seen that the integrated discharge performance of the monolithic battery decreases with more content of Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping. In the LiB/NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e thermal battery system, there are two reaction equations: NiCl\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;2Li\u0026rarr;2LiCl\u0026thinsp;+\u0026thinsp;Ni; NiBr\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;2Li\u0026rarr;2LiBr\u0026thinsp;+\u0026thinsp;Ni. With the increase of the doping content of Br\u003csup\u003e\u0026minus;\u003c/sup\u003e, the more the content of LiCl and LiBr in the reaction products, the easier it is to disrupt the physical phase ratio of the electrolyte, exacerbate the overflow of the molten electrolyte, and affect the discharge performance of the single cell. It is worth noting that the comparison of discharge performance in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e(a) shows that the discharge voltage platform of NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e cathode material increases, which is mainly due to the fact that Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doped NiCl\u003csub\u003e2\u003c/sub\u003e reduces the forbidden bandwidth of the material, decreases the internal resistance, and improves the electrical conductivity of NiCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e[11\u0026ndash;13]\u003c/sup\u003e. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e shows that NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e exhibited the best electrical properties with a specific capacity of 319 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a specific energy of 744 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 500\u0026deg;C and a discharge of 0.2 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e discharge. It can be seen from the figures that the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/LiB system has the advantage of high-current discharge. Combined with Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e, the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/BN-E system achieved a high power of 16.1 kW kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 500\u0026deg;C and 0.5 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e current density discharge, reflecting the high power characteristics of the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e cathode material.\u003c/p\u003e\n \u003cp\u003eBy increasing the discharge temperature to 550\u0026deg;C, the discharge curves of NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e/BN-E/LiB single cell at different current densities (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e) were not as smooth as those of single cell with the corresponding cathode materials at 500\u0026deg;C, and the discharge platform fluctuated greatly, whereas the discharge voltage increased slightly with the increase in discharge temperature, and the specific capacity of the discharges decreased substantially (Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). The main reason for the specific capacity decay is that the high temperature increases the migration rate of Li\u003csup\u003e+\u003c/sup\u003e In order to maintain the charge equilibrium state inside the battery, the anions in the cathode accelerate to dissolve into the electrolyte, increasing the concentration polarisation inside the battery and leading to the early end of the discharge. In addition, when discharged at 550\u0026deg;C, NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e still showed the optimal electrochemical performance, with a specific capacity of 270 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at a current density of 0.5 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, a specific energy of discharge of 597 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and a specific power of 16.5 kW kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which has the advantage of high power discharge.\u003c/p\u003e\n \u003cp\u003eIn order to further determine the change of internal resistance of NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e/BN-E single cell during the discharge process, it was subjected to pulse discharge test at 500\u0026deg;C under the conditions of constant current 0.1 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, pulse current 0.5 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, pulse duration of 1 s, and pulse interval of 15 s. The change curve of the resistance of the single cell were calculated from the pulse test by intercepting the discharge voltage at 2 V during the discharge at constant current, and the resistance change curve was calculated by the pulse test. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e, the trend of the internal resistance of the four cathode materials is basically the same, and the internal resistance of the single cell is higher at the beginning of discharge, which is mainly due to the high resistivity of NiCl\u003csub\u003e2\u003c/sub\u003e itself. With the increase of discharge depth, the internal resistance of the battery gradually decreases, which is because the discharge product is Ni monomer with high conductivity; while in the middle and late stages of discharge, there is a large lithium ion concentration polarisation in the electrolyte, which leads to a slow increase in the internal resistance of the battery. As can be seen from the figure, with the decrease of Br\u003csup\u003e\u0026minus;\u003c/sup\u003e doping in the NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e cathode, the average internal resistance of its corresponding single cell slightly decreases, and the corresponding pulse discharge platform is improved. Among them, the cathode material of NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e has the best pulse discharge performance, with an average internal resistance of 0.23 Ω, which can be as high as 2.50 V vs. Li potential, which tends to the theoretical voltage value of NiCl\u003csub\u003e2\u003c/sub\u003e material (2.64 V vs. Li).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 BN-E flow suppression characterisation of NiCl\u003csub\u003e2-x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e thermal cell\u003c/h2\u003e\n \u003cp\u003eIn order to compare the flow inhibition effects of BN and MgO on the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/LiB thermo-cell system, a discharge comparison of 0.1 A/cm\u003csup\u003e2\u003c/sup\u003e and 0.2 A/cm\u003csup\u003e2\u003c/sup\u003e currents was carried out using the two bonding agents applied to the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e system at 500\u0026deg;C. As demonstrated in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e(d) and Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e, the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/BN-E/LiB system exhibits a higher discharge capacity, despite the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/MgO-E/LiB system demonstrating a marginally higher discharge voltage plateau. This phenomenon may be attributed to the severe melting and leaching of MgO-E with the cathode material during the discharge process, leading to the depletion of the cathode active material as well as the overflow of the electrolyte, which resulted in the decrease of the specific capacity. This finding suggests that the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/LiB system exhibits a high current discharge capacity, which is a significant advantage in battery technology.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e shows the comparison of electrode sheet morphology between NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/BN-E and NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/MgO-E after discharging at different discharge temperatures and different current densities, and it can be seen from Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e(a-c) that, at the same discharge temperature, there is no obvious overflow phenomenon in the electrostack of the BN-E single cell, on the contrary, the electrostack of the MgO-E single cell undergoes an obvious electrolyte overflow phenomenon (Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e( d)), and the cathode layer also suffered serious breakage. This is mainly caused by the melting and leaching of the cathode and products with the electrolyte during the discharge process, and the structural collapse of the positive electrode during the discharge process. This phenomenon will reduce the active material in the cathode, shorten the discharge time, and end the discharge prematurely, and the overflow will lead to the short circuit in the battery in case of severe overflow, or even cause a fire, jeopardising the safety of the battery discharge. From Fig. \u003cspan class=\"InternalRef\"\u003e9\u003c/span\u003e (e-h), it can be observed that with the increase of discharge temperature, the degree of overflow of the stack deepens. The main reason is that the increase in discharge temperature accelerates the reaction of the cathode material and its dissolution in the electrolyte, exacerbating the overflow of the electrostack. Among them, the overflow area of BN-E is obviously smaller than that of MgO-E, which can indicate, from the side, that BN-E has the advantage of inhibiting the flow of molten electrolyte.\u003c/p\u003e\n \u003cp\u003eIn order to visually compare the ability of MgO and BN to inhibit the extent of melt leaching in the NiCl₁.₆Br₀.₄/BN-E system, the electrostacks of NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e/BN-E single cell and NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e /MgO-E single cell after discharge were selected as the study object, and the discharged electrostacks were broken in the middle to observe the cross-section under the scanning electron microscope, and the SEM-Mapping is shown in Figs. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e. From Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e(a), it can be seen that there is a clear demarcation line between the cathode layer and the separator layer of the electrostack after discharge of the BN-E thermal battery system. From the elemental distribution in Fig. \u003cspan class=\"InternalRef\"\u003e10\u003c/span\u003e(b-f), it can be observed that the B, N, Br and Cl elements in the separator layer are uniformly distributed, which indicates that the structure of the separator layer is not seriously damaged after discharge, and there is no obvious flow phenomenon of the molten electrolyte.\u003c/p\u003e\n \u003cp\u003eIn the Ni element distribution diagram, the Ni elements are mainly concentrated in the cloth in the cathode layer, and a small amount exists in the separator layer, which laterally indicates that BN-E can well inhibit the melt flow of electrolyte and reduce the degree of electrolyte melt overflow in high temperature discharge. From Fig. \u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e(a), it can be seen that there is no obvious demarcation line in the post-discharge stack of the MgO-E thermal battery system, and from Fig. \u003cspan class=\"InternalRef\"\u003e11\u003c/span\u003e(d), it is observed that the Ni element has a wider range of distribution, and a large amount of Ni element also exists in the separator layer, which is mainly due to the intermixing of the cathode and the electrolyte in the high-temperature discharging process, and the Ni monomers are caused to flow with the molten electrolyte to the separator layer. The results show that the fixation effect of MgO-E on the molten electrolyte has limitations, and it barely inhibit the flow of molten electrolyte, which depletes the active material of the cathode, affects the discharge performance, shortens the discharge time, and leads to the early end of the discharge of the single cell.\u003c/p\u003e\n \u003cp\u003eBromine ion doping of NiCl\u003csub\u003e2\u003c/sub\u003e cathode material effectively improved the discharge voltage plateau of the corresponding single cell, however, the introduction of Br\u003csup\u003e\u0026minus;\u003c/sup\u003e exacerbated the leaching degree of NiCl\u003csub\u003e2\u003c/sub\u003e cathode with the molten salt electrolyte. BN-E was also applied to the NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e system with a harsher degree of melt immersion, and it was found that the interface between the cathode and the separator layer was clear after discharge, and the Ni element was mainly concentrated in the cathode layer, which indicated that the molten electrolyte did not undergo obvious flow behavior during the high temperature discharge process, which reflected that BN-E had a stronger ability to inhibit the flow of the molten electrolyte. Meanwhile, BN-E has a lower internal resistance of discharge (0.23 Ω), indicating that the polarization internal resistance of the battery is smaller during the discharge process.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this paper, the cathode material NiCl\u003csub\u003e2\u0026thinsp;\u0026minus;\u0026thinsp;x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e was prepared by introducing halogen anion Br doping to NiCl\u003csub\u003e2\u003c/sub\u003e, and the optimal proportion of Br doping was discussed in combination with the discharge curve and pulse internal resistance, so as to solve the problem of inferior conductivity of NICl\u003csub\u003e2\u003c/sub\u003e-based materials. Subsequently, the research system was established as NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e. A comparison of the electrochemical performance and leaching behavior of BN and MgO as electrolyte adhesive was conducted, which demonstrated that BN can effectively inhibit the interaction between NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e and electrolyte, and improve the discharge performance of the battery. The cathode material for thermal batteries with high specific energy and low internal resistance was obtained by Br-doping NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e, while BN-E was used as a diaphragm binder to inhibit the melt leaching between cathode and diaphragm layers. The experimental findings demonstrated that the Br doping of NiCl\u003csub\u003e2\u003c/sub\u003e resulted in a reduction of the forbidden band of the material and an enhancement of the conductivity and specific energy of discharge of NiCl\u003csub\u003e2\u003c/sub\u003e. The optimal discharge performance was observed at 500\u0026deg;C or 550\u0026deg;C for NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e. Notably, it exhibited a specific capacity of 319 mAh g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, a specific energy of 744 Wh kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and a specific power of 7.0 kW kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e during discharge at 500\u0026deg;C and 0.2 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. The investigation further examined the use of BN as the electrolyte binder in the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e thermal battery system in comparison with MgO. The post-discharge interface was analyzed, and the ability of BN-E to inhibit electrolyte flow during high-temperature discharge was confirmed by SEM and Mapping of the post-discharge collector overflow area and electrostack interface. The overflow area was found to be smaller in the BN-E sample than in the MgO-E sample. This finding suggests that BN-E has a stronger inhibition of molten electrolyte flow than MgO-E. Therefore, it can be concluded that BN-E is more suitable than MgO-E for use as cathode material in the NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e system. Furthermore, BN-E exhibits a safer application in the LiB/BN-E/ NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e thermal battery system.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eJ.T. (Conceptualization, Methodology, Investigation, Writing - Original Draft), Y.N. (Formal Analysis, Data Curation, Visualization), L.R. (Methodology, Validation, Resources), L.T. (Investigation, Software), Z.Z. (Data Curation, Formal Analysis), Y.D. (Writing - Review \u0026amp; Editing), L.F. (Supervision, Project Administration, Funding Acquisition). All authors reviewed and approved the final manuscript\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe research was carried out with financial support from the Young teacher development program of Hunan University (No. 2015031)\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003e1. Luo Z, Lin X, Tang L, et al. Novel NiCl\u003csub\u003e2\u003c/sub\u003e nanosheets synthesized via chemical vapor deposition with high specific energy for thermal battery[J]. ACS Applied Materials \u0026amp; Interfaces, 2020, 12(31): 34755\u0026ndash;34762.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e2. Chen F, Jiang C, Cao S, et al. Synergetic effect of functional additions on Li/NiCl\u003csub\u003e2\u003c/sub\u003e thermal battery with enhanced discharge performance[J]. Materials Letters, 2022,320: 132371.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e3. Liu W, Liu H, Bi S, et al. Variable-temperature preparation and performance of NiCl\u003csub\u003e2\u003c/sub\u003e as a cathode material for thermal batteries[J]. Science China Materials, 2017, 60(3): 251\u0026ndash;257.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e4. Zhu Y, Xing J, Yang B, et al. Preparation of NiCl\u003csub\u003e2\u003c/sub\u003e nanorods with enhanced electrochemical properties in thermal batteries[J]. ECS Transactions, 2015, 69(18): 13\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e5. Li R, Guo W, Qian Y. Recent developments of cathode materials for thermal batteries[J]. Frontiers in chemistry, 2022, 10: 832972.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e6. Jin C, Fu L, Ge B, et al. The NiCl\u003csub\u003e2\u003c/sub\u003e/NiS\u003csub\u003e2\u003c/sub\u003e@C double active composite cathodes with surface synergistic effects for high-power thermal battery[J]. Journal of Alloys and Compounds, 2019, 800: 518\u0026ndash;524.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e7. Tan X, Ding L, Du G F, et al.Spin caloritronics in two-dimensional CrI\u003csub\u003e3\u003c/sub\u003e/NiCl\u003csub\u003e2\u003c/sub\u003e van derWaals heterostructures[J].Physical review, B, 2021(11):103.[8] Lin X, Fu L, Zhu J, et al. NiCl\u003csub\u003e2\u003c/sub\u003e cathode with the high load capacity for high specific power thermal battery[J]. IOP Conference Series: Materials Science and Engineering, 2019, 677(3): 032046.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e9. Gui Y, Lin X, Fu L, et al. Shortening activation time of thermal battery by hydrogen etching of NiCl\u003csub\u003e2\u003c/sub\u003e cathode[J]. Materials Letters, 2020, 275: 128136.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e10. Huang M, Li J, Li S, et al. Controlling the changes in electrolyte composition in the cathode to reduce the voltage decay of NiCl\u003csub\u003e2\u003c/sub\u003e thermal batteries[J]. ACS Applied Energy Materials, 2023, 6(3): 1511\u0026ndash;1518.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e11. Yao B, Fu L, Gui Y, et al. Instantaneous activation of NiCl\u003csub\u003e2\u003c/sub\u003e cathode towards thermal battery by constructing NiCl\u003csub\u003e2\u003c/sub\u003e-NiO heterojunction[J]. ACS Sustainable Chemistry \u0026amp; Engineering, 2023, 11(1): 199\u0026ndash;207.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e12. Tang J, Wei Z, Wang Q, et al. In situ oxygen doping of monolayer MoS\u003csub\u003e2\u003c/sub\u003e for novel electronics[J]. Small, 2020, 16: 2004276.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e13. Zhang F, Lu Y, Schulman D, et al. Carbon doping of WS\u003csub\u003e2\u003c/sub\u003e monolayers: bandgap reduction and p-type doping transport[J]. Science advances, 2019,5(5):eeaav5003.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"NiCl2 Thermal battery, Cathode material, BN separator","lastPublishedDoi":"10.21203/rs.3.rs-6333156/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6333156/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eNickel chloride is a promising cathode material for high-power thermal batteries due to its high theoretical capacity, high discharge current density, and high electrode potential. Nevertheless, its substandard electrical conductivity, elevated-temperature melting properties, and electrolyte interface instability considerably constrain its practical applications. In this paper, NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e with high electrical conductivity and high specific capacity was prepared through comparative experiments, and the merits of BN over MgO for LiB/NiCl\u003csub\u003e1.6\u003c/sub\u003eBr\u003csub\u003e0.4\u003c/sub\u003e thermal battery system were demonstrated by analysing the difference between electrochemical performance and melting leaching phenomenon. The LiB/BN-E/NiCl\u003csub\u003e2-x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e thermal battery system demonstrates optimal discharge performance at 500 °C, achieving a specific capacity of 319 mAh g\u003csup\u003e-1\u003c/sup\u003e, a specific energy of 744 Wh kg\u003csup\u003e-1\u003c/sup\u003e, and a specific power of 7.0 kW kg\u003csup\u003e-1 \u003c/sup\u003eunder a discharge condition of 0.2 A cm\u003csup\u003e-2\u003c/sup\u003e. The LiB/BN-E/NiCl\u003csub\u003e2-x\u003c/sub\u003eBr\u003csub\u003ex\u003c/sub\u003e thermal battery system has application prospects in high-energy thermal batteries.\u003c/p\u003e","manuscriptTitle":"Enhancement the discharge capacity of NiCl 2-x Br x thermal battery by inhibition overflow of electrloyte","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-24 16:35:30","doi":"10.21203/rs.3.rs-6333156/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-26T10:05:50+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-23T12:20:03+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-16T19:12:58+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-15T07:58:55+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"11947344576399128132404247756755420323","date":"2025-04-06T06:06:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"115142359855685071595386778643257634369","date":"2025-04-06T03:12:23+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"126352262368982761085945606872186906731","date":"2025-04-04T13:06:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"207167552262929941923943557713811727179","date":"2025-04-03T21:29:57+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-03T20:55:05+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-03T07:08:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-03T07:03:45+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2025-03-29T09:16:33+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8e6387ef-33f2-4fe7-aaaa-b0e27e6c004f","owner":[],"postedDate":"April 24th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-05-17T19:53:18+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-24 16:35:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6333156","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6333156","identity":"rs-6333156","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}