Preparation methods and applications of halide solid electrolytes

Abstract

This invention discloses a method for preparing a halide solid electrolyte. The method includes obtaining a mixed solution of raw materials LiCl and MCl3 in a stoichiometric ratio, freezing the mixed solution into a solid at a freezing temperature below -60°C, then sublimating and evaporating the water in a vacuum environment to obtain the intermediate product Li3MCl6·2H2O, and then sintering it at 180°C-220°C in a vacuum environment to remove the water of crystallization to obtain Li3MCl6. The resulting halide solid electrolyte exhibits high capacity and excellent cycle performance. This invention yields a halide solid electrolyte with small particle size and good particle dispersion, which is beneficial for forming a good kinetic transport network with the conductive agent and active material. This ensures that ions / electrons pass through at most one active material particle before reaching the conductive solid electrolyte / carbon, thereby improving the battery's capacity utilization and rate capability.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state battery electrolyte technology, specifically to the preparation method and application of halide solid electrolytes. Background Technology

[0002] Currently, oxide solid-state electrolytes and sulfide solid-state electrolytes are two widely used inorganic superionic conductors in all-solid-state batteries. Oxide solid-state electrolytes exhibit significant contact resistance with electrode materials, while sulfide solid-state electrolytes, although possessing high ionic conductivity, are unstable in air, readily react with water, and exhibit poor electrochemical performance when used with high-voltage cathode materials without a protective layer. Halide solid-state electrolytes have attracted widespread attention from researchers due to their excellent ionic conductivity; halide anions react with Li... + The weaker bond strength between them reduced the Li + The diffusion barrier is reduced, and the deformation resistance of halide solid electrolytes is improved. Furthermore, the excellent electrochemical stability of halide solid electrolytes allows them to be used with high-voltage cathodes, achieving high capacity and initial coulombic efficiency. Currently, the ceramic-based halide family Li3MCl6 (M = Sc, Y, In, Yb, Er, etc.) exhibits ionic conductivity up to 1 mS / cm at room temperature. The particles of these halides favor close packing, such as hexagonal close-packed (hcp), triangular and cubic close-packed (ccp), which facilitates the regulation of Li migration. + The concentration of cations in ceramic-based halides can increase ionic conductivity; at the same time, the particle size of cations in ceramic-based halides may also affect the formation efficiency and results of close packing, thereby affecting the dispersion performance of the final product and its electrochemical performance in batteries.

[0003] Methods for preparing ceramic-based halide solid electrolytes include high-temperature solid-state reactions, melt quenching, coprecipitation, and mechanochemical methods. These methods significantly influence crystal arrangement, thereby affecting ionic conductivity. While the high temperatures of high-temperature solid-state reactions and melt quenching promote close-packing of particles, they also increase particle size, potentially leading to increased particle-electron interaction, reduced particle dispersion, higher battery resistance, and decreased battery capacity utilization. Coprecipitation may produce agglomerates, resulting in insufficient and uneven particle dispersion, further increasing battery resistance and reducing capacity utilization. Mechanochemical methods tend to produce amorphous or nanocrystalline phase structures, typically metastable phases. Studying the local structural evolution of halide solid electrolytes using mechanochemical methods is a hot research topic.

[0004] In all-solid-state batteries, particle dispersion leading to kinetic transport limitations is one of the factors affecting the low current density and low areal load of all-solid-state batteries. Halide solid electrolytes prepared by traditional methods have large particle sizes, which prevents the formation of an active material particle / conductive solid electrolyte / carbon particle network in the electrode. This may result in the solid electrolyte particles and carbon particles not being uniformly dispersed on the surface of the active material particles, and the generation of voids between the solid electrolyte particles and the active material particles. This means that ions / electrons may pass through more than one active material particle before reaching the conductive solid electrolyte / carbon, thereby increasing the battery resistance and reducing the battery's capacity utilization and rate capability. Summary of the Invention

[0005] This invention addresses the problems in existing technologies by disclosing a method for preparing halide solid electrolytes. This method employs vacuum freeze-drying to prepare a mixed solution, ensuring thorough and uniform dispersion of particles. Rapid freezing at low temperatures overcomes the problem of particle size increase caused by high temperatures, facilitating the formation of a small-particle intermediate product, Li3MCl6·2H2O, containing a certain amount of water of crystallization. The appropriate amount of water of crystallization promotes close packing of particles during the two stepwise heating processes and slows down particle size growth, thereby improving the uniformity of particle dispersion. This results in a halide solid electrolyte with high capacity and excellent cycling performance.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a method for preparing a halide solid electrolyte. The method includes obtaining a mixed solution of raw materials LiCl and MCl3 (where M includes one of Sc, Y, In, Yb, and Er) in a stoichiometric ratio, freezing the mixed solution into a solid at a freezing temperature below -60°C, then sublimating and evaporating the water in a vacuum environment to obtain the intermediate product Li3MCl6·2H2O, and then sintering at 180°C-220°C in a vacuum environment to remove the water of crystallization to obtain Li3MCl6.

[0008] The above-described design of this invention, the vacuum freeze-drying method, involves rapidly freezing a solution into ice, and then sublimating the ice under vacuum to obtain an intermediate product with structural characteristics, Li3MCl6·2H2O. In the mixed solution state, a large-scale, low-density, uniform dispersion of particles is ensured first. Simultaneously, rapid freezing at low temperatures allows for fine nucleation under this dispersed state, overcoming the particle size increase caused by high temperatures, thus facilitating the acquisition of small-sized particles. The intermediate product with suitable water of crystallization promotes the acquisition of small-sized particles and uniform dispersion of the final product Li3MCl6, and facilitates close packing of particles during the two stepwise heating processes. This is beneficial for obtaining halide electrolyte particles that can form a good kinetic transport network with active material particles and carbon particles, ensuring that ions / electrons pass through at most one active material particle before reaching the conductive solid electrolyte / carbon, thereby improving the battery's capacity utilization and rate capability.

[0009] As a further option, M in MCl3 includes one of Sc, Y, In, Yb, and Er.

[0010] As a further refinement, M in MCl3 is In. The particle size of In is more suitable, which is conducive to the formation of the intermediate product Li3MCl6·2H2O. The intermediate product is beneficial to the final product halide, which has small particle size and good uniform dispersion among particles.

[0011] As a further option, the freezing temperature is -75°C to -85°C.

[0012] As a further embodiment, during the freezing process, the cooling rate from room temperature to the freezing temperature is greater than 2°C / min.

[0013] As a further embodiment, the sintering temperature is 200°C.

[0014] As a further embodiment, the X-ray powder diffraction pattern of the halide solid electrolyte Li3InCl6 obtained by the vacuum freeze-drying method, expressed in terms of diffraction angle 2θ, has characteristic diffraction peaks at 14.7°, 21.7°, 28.26°, 28.41°, 34.14°, 49.28°, 61.57°, and 73.2°.

[0015] As a further embodiment, in the halide solid electrolyte Li3InCl6 obtained by the vacuum freeze-drying method, the proportion of particles with a diameter less than 200 nm in the total number of particles is greater than 80%. The absolute dominance of particles with a diameter less than 200 nm in the halide solid electrolyte Li3InCl6 is beneficial for forming a good electron and ion transport network with the active material particles and conductive carbon particles.

[0016] The present invention also provides the application of the halide solid electrolyte obtained by the preparation method of the halide solid electrolyte in all-solid-state batteries.

[0017] The features and beneficial effects of this invention are as follows:

[0018] (1) A halide solid electrolyte with high capacity and good cycling performance is obtained. The preparation method of the present invention can obtain small-diameter particles, and the intermediate product Li3MCl6·2H2O obtained improves the dispersibility between particles.

[0019] (2) In the two-step drying process, not only can the dense packing of particles be promoted, but the rapid increase in particle size due to the increase in temperature can also be slowed down.

[0020] (3) The halide solid electrolyte obtained by the method of the present invention is beneficial for regulating the migration of Li + The concentration of ions increases the conductivity and improves the electrochemical performance of the battery.

[0021] (4) Obtaining a halide solid electrolyte with small particle size and good particle dispersion is beneficial to forming a good power transmission network with conductive agents and active materials, so that ions / electrons are most likely to pass through only one active material particle before reaching the conductive solid electrolyte / carbon, thereby improving the capacity utilization and rate capability of the battery. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 The discharge capacity variation of halide solid electrolytes prepared at different sintering temperatures under different discharge rates is shown in the embodiments of the present invention.

[0024] Figure 2 The halide solid electrolytes prepared at different sintering temperatures provided in the embodiments of the present invention are at 15°C (6.1 mA / cm²). 2 The specific capacity of the battery at a current density of ).

[0025] Figure 3 The discharge capacity variation of halide solid electrolytes synthesized by hydration and ball milling methods according to embodiments of the present invention at different discharge rates.

[0026] Figure 4The halide solid electrolyte synthesized by the hydration method and ball milling method provided in the embodiments of the present invention is at 10C (5mA / cm). 2 The specific capacity of the battery at a current density of ).

[0027] Figure 5 The halide solid electrolyte synthesized by the hydration method and ball milling method provided in the embodiments of the present invention has a capacity of 2.5 mAh / cm³. 2 The charge-discharge curves at the current density.

[0028] Figure 6 The halide solid electrolyte synthesized by the hydration method and ball milling method provided in the embodiments of the present invention has a capacity of 3 mAh / cm³. 2 The charge-discharge curves at the current density.

[0029] Figure 7 The halide solid electrolyte synthesized by the hydration method and ball milling method provided in the embodiments of the present invention has a capacity of 4.4 mAh / cm³. 2 The charge-discharge curves at the current density.

[0030] Figure 8 The electrochemical performance test results of a solid electrolyte battery obtained by freeze-drying method are provided in this embodiment of the invention. Figure 8 a represents the charge-discharge curves of the battery at different rates; Figure 8 b is a battery rate curve at different rates; Figure 8 c represents a comparison of electrolytes prepared by freeze-drying and hydration methods at 20°C (10 mA / cm²). 2 Battery cycle performance under ( ) conditions; Figure 8 d- Figure 8 f represents a comparison between this embodiment and halide solid electrolytes in other literature.

[0031] Figure 9 The test results for high-activity ratio (wherein the mass of the active material accounts for 95% of the total mass of the positive electrode slurry) and high-area-capacity battery provided in the embodiments of the present invention are as follows. Figure 9 a represents the charge-discharge curves at different rates under high activity ratios; Figure 9 b represents the cycle performance at different discharge rates; Figure 9 c is a comparison chart of the proportion of positive electrode active material in this embodiment and in existing articles; Figure 9 d represents the charge-discharge curve of the highly active material; Figure 9 e is at 5C (1.58mA / cm) 2 The cycle performance of the battery at a current density of ) is the specific capacity; Figure 9 f is the charge-discharge curve under high surface capacity (where the mass of the active material accounts for 60% of the total mass of the positive electrode slurry); Figure 9 g represents the positive electrode surface capacity of 5 mA / cm².2 The cycle performance of the battery (where the mass of the active material accounts for 60% of the total mass of the positive electrode slurry); Figure 9 h represents the charge-discharge curves of batteries with different areal capacities (where the mass of the active material accounts for 60% of the total mass of the positive electrode slurry); Figure 9 i represents the charge-discharge curves under different areal capacities (where the mass of the active material accounts for 60% of the total mass of the positive electrode slurry); Figure 9 j represents the maximum discharge capacity of the embodiment compared to other references.

[0032] Figure 10 XRD diffraction patterns of three different synthesis methods provided in the embodiments of the present invention.

[0033] Figure 11 Electron microscopy images of particles obtained using three different methods provided in embodiments of the present invention. Figure 11 a- Figure 11 c is an electron micrograph of the solid electrolyte synthesized by freeze-drying method; Figure 11 d- Figure 11 f is an electron micrograph of the solid electrolyte synthesized by hydration; Figure 11 g- Figure 11 i is an electron micrograph of the solid electrolyte synthesized by ball milling.

[0034] Figure 12 The electrolyte impedance spectra obtained by freeze-drying with different solution concentrations are provided for embodiments of the present invention.

[0035] Figure 13 The particle size distribution diagram provided for an embodiment of the present invention.

[0036] Figure 14 Particle size distribution diagram provided for the control group liquid phase method.

[0037] Figure 15 Particle size distribution diagram provided for the ball milling method (control group). Detailed Implementation

[0038] To facilitate understanding of the preparation method of the halide solid electrolyte of the present invention, the preparation method of the halide solid electrolyte of the present invention will be described more comprehensively below, and embodiments of the present invention will be given, but this does not limit the scope of the present invention.

[0039] This invention uses Li3InCl6 as an example to prepare Li3InCl6 solid electrolyte:

[0040] The raw materials LiCl and InCl3 were dissolved in deionized water according to the stoichiometric ratio. After the reaction was complete, the solution was rapidly frozen into a solid at -80°C. Then, the water was sublimated and evaporated in a vacuum to obtain Li3InCl6·2H2O. Finally, the water of crystallization was removed under a vacuum at 200°C to obtain Li3InCl6.

[0041] Water law [1] The raw materials LiCl and InCl3 were dissolved in deionized water according to the stoichiometric ratio. After the reaction was complete, the water in the solution was evaporated to dryness at 50°C to obtain Li3InCl6·2H2O. Then, the water of crystallization was removed under vacuum at 200°C to obtain Li3InCl6.

[0042] Ball milling method [2] The raw materials LiCl and InCl3 were fed into a ball mill at a stoichiometric ratio and milled at 300 rpm for 24 hours to obtain preliminary Li3InCl6. Then, the electrolyte was pressed into sheets under a pressure of 2 tons and then sintered at 260°C in a vacuum environment for 5 hours to obtain the final Li3InCl6.

[0043] Fabrication of all-solid-state batteries:

[0044] (1) Positive electrode: The positive electrode active material is mixed with LIC (LIC is a halide solid electrolyte Li3InCl6) (wherein, there are three different mass ratios of positive electrode active material and LIC to obtain the positive electrode, the mass ratio of positive electrode active material to LIC is 80:20 or 95:5 or 60:40 respectively) in a mortar, wherein the positive electrode active material includes Ni90 (nickel 90).

[0045] One of the types of LCO (lithium cobalt oxide).

[0046] (2) Electrolytes: LIC 40mg, pressed into powder cake in a pressure mold (pressure 1 ton); Li6PS5Cl 40mg, pressed into powder cake in a pressure mold (pressure 1 ton).

[0047] (3) Negative electrode: Graphite and PTFE (polytetrafluoroethylene) are mixed to form a film and then attached to a copper-lithium composite tape.

[0048] (4) Assembly: From top to bottom, positive electrode - LIC - LI6 - negative electrode, pressed into a battery under 7 tons of pressure. Among them, LI6 is a sulfide solid electrolyte Li6PS5Cl.

[0049] Impedance testing was performed on the obtained battery: 80mg of solid electrolyte was sprinkled into the battery mold, then pressed into a powder cake under 3 tons of pressure, and tested in an environment of 25℃ with a test frequency of 1MHz-1Hz.

[0050] Validation Result Analysis

[0051] We first compared the rate performance of batteries at different sintering temperatures, from... Figure 1 and Figure 2 The study found that halide solid electrolytes sintered at 200℃ exhibited the best rate and cycle performance. At 200℃, the battery could release a specific capacity of 207 mAh / g at 0.5C, while batteries assembled with halide electrolytes sintered at 300℃ and 400℃ only achieved specific capacities of 174 mAh / g and 154 mAh / g, respectively, at the same rate. We believe that as the sintering temperature increases, the particle size of the solid electrolyte increases. This larger particle size reduces the dispersion and coating ability of the solid electrolyte and carbon particles on the surface of the active material particles. The active material particles may lack good bridging connections between the solid electrolyte and carbon particles, resulting in larger gaps or agglomeration between them. This significantly hinders the kinetic transport of ions / electrons between the active material particles, affecting the utilization rate of the active material and ultimately leading to a decline in the battery's electrochemical performance. Our further investigation revealed the effect of concentration on the impedance of the obtained halide solid electrolyte after freeze-drying with mixed solutions of different concentrations, such as... Figure 12 As shown, changing the solution concentration did not affect the impedance of the halide solid electrolyte. Therefore, we used a series of electrochemical characterization methods to screen out the halide solid electrolyte sintered at 200℃, which had the best performance.

[0052] To further verify the superiority of freeze-drying technology, we conducted a series of electrochemical performance comparisons with halide solid electrolytes synthesized using hydration and ball milling methods in previous literature. First, we compared rate performance and long-cycle performance. Figure 3 As can be seen from this, the solid electrolyte obtained by freeze-drying at 200°C (in the method of this invention, the solid electrolyte is obtained by sintering at 200°C) corresponds to... Figure 3 Batteries assembled with solid-state electrolytes synthesized using Freeze-Drying-200 can still achieve a specific capacity of 201 mAh / g even at an initial rate of 0.5C. In comparison, batteries synthesized using the hydration method and ball milling method can only achieve specific capacities of 185 mAh / g and 163 mAh / g, respectively. Long-term cycling data also shows that the halide solid-state electrolyte synthesized using Freeze-Drying-200 exhibits better performance in terms of both cycle stability and capacity utilization compared to the hydration and ball milling methods. Figure 4 It was found that using freeze-dried halide solid electrolytes at -200°C, at 10°C (5 mA / cm²), 2At the current density, it still exhibits a specific capacity of 125 mAh / g, while batteries assembled using solid electrolytes prepared by the hydration method and the ball milling method only release specific capacities of 104 mAh / g and 100 mAh / g, respectively, at 10C. To compare the performance of solid electrolytes prepared by the three methods in practical battery applications, such as... Figure 5 , Figure 6 , Figure 7 As shown, we investigated the areal capacities (2.5 mAh / cm³) of three solid electrolytes. 2 3mAh / cm 2 4.4mAh / cm 2 Based on the capacity performance under different areal capacities and current densities, we can see that freeze-drying at -200°C is the best method, followed by hydration, and ball milling is the worst. We believe this may be because freeze-drying produces smaller particle sizes. Rapid freezing overcomes particle size variations, which is beneficial for obtaining the small-particle-size intermediate product Li3MCl6·2H2O. This intermediate product acts as a pivot for close-packed nucleation and slows down grain growth in a dispersed environment. An appropriate amount of water of crystallization in the intermediate product not only promotes close-packed nucleation but also slows down grain growth during the staged heating process, thus obtaining the small-particle-size, uniformly dispersed final product Li3MCl6. To further verify this hypothesis, we studied the particle size of halides obtained by different methods.

[0053] We further investigated the particle size and particle distribution of halide solid electrolytes obtained by different methods, such as... Figures 13-15 As shown, the freeze-drying-200 method yielded a high proportion of particles smaller than 200 nm in the halide solid electrolyte, reaching 80.77%, significantly higher than the proportion of particles smaller than 200 nm in halide solid electrolytes prepared by hydration and ball milling. This can be seen from the XRD diffraction pattern (e.g. Figure 10 As shown in the image, a wider diffraction peak was obtained through freeze-drying, indicating that freeze-drying achieves a smaller grain size. This is further confirmed by scanning electron microscopy at different magnifications, demonstrating that freeze-drying can indeed produce smaller particle sizes. Figure 11 As shown.

[0054] To further verify the superiority of the halide solid electrolyte obtained by the freeze-drying-200 method, we conducted a series of electrochemical characterizations on it. Because the particle size obtained by the freeze-drying-200 method is very small, it can form a very good ion pathway, thus exhibiting excellent rate and cycling performance. Figure 8 a, Figure 8 b shows the charge / discharge curves and rate graphs of the battery at different rates, from... Figure 8As can be seen from a, even with a high activity ratio of 80% for the positive electrode active material, at an ultra-high rate of 49C (12.48 m / cm²), its activity remains high. 2 It still has a normal charge / discharge curve and a specific capacity greater than 20mAh / g. Figure 8 c. A comparison was made between the freeze-drying-200 method and the hydration method for preparing halide solid electrolytes at 20°C (10 mA / cm²). 2 The battery cycle performance under various conditions was compared, showing that the battery using the freeze-drying-200 method showed almost no capacity decay even after 30,000 cycles, while the halide solid electrolyte battery prepared by the hydration method failed to reach its full capacity after about 16,000 cycles. This is attributed to the smaller particle size of the solid electrolyte in the freeze-drying-200 method, which effectively increases the battery's mechanical properties. We also compared the rate capability and cycle performance of halide batteries in current literature, finding that the electrochemical performance of the halide solid electrolyte battery prepared in this invention is significantly superior. Figure 8 d- Figure 8 f is shown [1 -16].

[0055] To further illustrate the potential of halide solid electrolytes in practical applications, we also conducted tests on batteries with higher activity ratios and higher surface capacity. Figure 9 a- Figure 9 e fully demonstrates the battery performance when the positive electrode active material accounts for 95% of the battery mass. It can be seen that the battery can release a high specific capacity of 185mAh / g at 0.2C, while also having good rate and cycle performance. Figure 9 f and Figure 9 g shows the battery capacity at 5mAh / cm². 2 Charge-discharge curves and cycle performance at high surface capacity, where the mass ratio of the positive electrode active material in the battery is 60%. Figure 9 h and Figure 9 i shows the charge-discharge curves of batteries under different ultra-high surface capacities, and finds that even at 15mAh / cm²... 2 Despite its compact design, the battery still delivers an ultra-high capacity of 13.69mAh / g. Finally, we compared the data with current halide batteries. [1-16] The halide solid electrolyte prepared by this invention also exhibits good capacity even at the highest areal capacity, such as... Figure 9 As shown in j.

[0056] In summary, using vacuum freeze-drying to obtain halide solid electrolytes, and rapidly freezing at low temperatures, not only overcomes the problem of particle size increase caused by high temperatures and yields small-particle-size intermediates like Li3MCl6·2H2O, but we also found that appropriate amounts of water of crystallization in the intermediates are beneficial for obtaining halide solid electrolytes with small particle sizes and uniform dispersion. In battery applications, halide solid electrolytes can form a good kinetic transport network with conductive carbon and active material particles, ensuring that ions / electrons pass through at most one active material particle before reaching the conductive solid electrolyte / carbon, thereby improving battery capacity utilization and rate capability. Even with high active content and high surface capacity, the battery can still exhibit good rate and cycle performance. Therefore, the small-particle-size halide solid electrolytes obtained by vacuum freeze-drying are beneficial for improving the electrochemical performance of solid-state batteries, including capacity and cycle performance.

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[0074] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a halide solid electrolyte, characterized in that, The method includes obtaining a mixed solution of raw materials LiCl and MCl3 according to a stoichiometric ratio, freezing the mixed solution into a solid in an environment with a freezing temperature below -60°C, then sublimating and evaporating the water in a vacuum environment to obtain the intermediate product Li3MCl6·2H2O, and then sintering at 180°C-220°C in a vacuum environment to remove the water of crystallization to obtain Li3MCl6. The M in MCl3 includes one of Sc, Y, In, Yb, and Er.

2. The method for preparing halide solid electrolyte according to claim 1, characterized in that, In the MCl3, M stands for In.

3. The method for preparing a halide solid electrolyte according to claim 1, characterized in that, The freezing temperature is -75°C to -85°C.

4. The method for preparing a halide solid electrolyte according to claim 1, characterized in that, During the freezing process, the cooling rate from room temperature to freezing temperature is greater than 2°C / min.

5. The method for preparing a halide solid electrolyte according to claim 1, characterized in that, The sintering temperature is 200°C.

6. The method for preparing a halide solid electrolyte according to claim 2, characterized in that, The obtained halide solid electrolyte Li3InCl6 exhibits characteristic diffraction peaks at 14.7°, 21.7°, 28.26°, 28.41°, 34.14°, 49.28°, 61.57°, and 73.2° in its X-ray powder diffraction pattern expressed as a diffraction angle of 2θ.

7. The method for preparing a halide solid electrolyte according to claim 1, characterized in that, In the obtained halide solid electrolyte Li3InCl6, the proportion of particles with a diameter of less than 200 nm in the total number of particles is greater than 80%.

8. The application of the halide solid electrolyte obtained by the preparation method of the halide solid electrolyte according to any one of claims 1-7 in all-solid-state batteries.

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