Solid electrolyte, preparation method and solid-state battery

Abstract

The invention provides a solid electrolyte, the solid electrolyte comprises a halide solid electrolyte and a coating layer covering at least part of the surface of the halide solid electrolyte, the chemical formula of the halide solid electrolyte is Li3MC16-xFx, x is greater than 0 and less than or equal to 1, and M comprises at least one of group III metals. According to the solid electrolyte provided by the invention, the bulk phase property of the halide solid electrolyte can be effectively improved, and the antioxidant stability of the halide solid electrolyte is improved; a positive electrode electrolyte interface can be formed on the surface of the halide solid electrolyte through the coating layer, direct contact between an electrode and the electrolyte can be effectively isolated, oxidation of the halide solid electrolyte is prevented, and the coating layer can promote uniform deposition of lithium ions and inhibit growth of dendrites; and furthermore, the ionic conductivity and the electrochemical stability of the solid electrolyte can be further improved through the synergistic cooperation of the halide solid electrolyte and the surface coating layer.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, specifically to a solid electrolyte, its preparation method, and a solid battery. Background Technology

[0002] All-solid-state batteries have become a core candidate for next-generation electrochemical energy storage systems due to their higher energy density, superior safety performance, and longer cycle life. To develop all-solid-state lithium metal batteries, solid-state electrolytes are an indispensable component, replacing traditional organic separators and flammable organic liquid electrolytes. Based on the type of solid-state electrolyte used, all-solid-state batteries can be classified into four categories: polymer-based, oxide-based, sulfide-based, and halide-based. Among them, halide-based solid electrolytes have attracted attention due to their unique ion transport mechanism and compatibility with various electrode materials.

[0003] Halide solid electrolytes possess high ionic conductivity, high voltage cathode compatibility, and good mechanical properties from direct cold sintering. However, the high reduction potential of halide solid electrolytes inevitably leads to side reactions with low-potential anodes, such as Li metal, Li-Si alloys, and Li-In alloys. Therefore, optimizing the properties of halide solid electrolytes from the material structure perspective is a problem that needs to be solved. Summary of the Invention

[0004] To address the aforementioned problems of the prior art, this application provides a solid electrolyte. The specific technical solution is as follows: On one hand, this application provides a solid electrolyte comprising a halide solid electrolyte and a coating layer covering at least a portion of the surface of the halide solid electrolyte, wherein the chemical formula of the halide solid electrolyte is Li3MCl. 6-x F x , where 0 < x ≤ 1, and M includes at least one of group III metals.

[0005] In a possible implementation, the coating layer includes at least one of LiF and LiCl.

[0006] In a possible implementation, the thickness of the coating layer is 50-500 nm.

[0007] On the other hand, this application also provides a method for preparing a solid electrolyte, the method comprising: Provides lithium source, M source, ammonium salt and fluorinating agent, wherein M includes one or more group III metals; The lithium source, the M source, the ammonium salt, and the fluorinating agent are mixed in a solvent in a certain proportion to obtain a mixed solution; The mixed solution was freeze-dried to obtain a halide precursor powder; The halide precursor powder is heat-treated to obtain a solid electrolyte; the solid electrolyte comprises a halide solid electrolyte and a coating layer covering at least a portion of the surface of the halide solid electrolyte, and the chemical formula of the halide electrolyte is Li3MCl. 6-x F x , where 0 < x ≤ 1, and M includes at least one of group III metals.

[0008] In a possible implementation, the heat treatment of the halide precursor powder to obtain a solid electrolyte includes: During the heat treatment of the halide precursor powder, fluorine substitution occurs within the crystal lattice of the halide precursor powder to obtain the halide solid electrolyte; the coating layer is formed on the surface of the halide solid electrolyte to obtain the solid electrolyte.

[0009] In a possible implementation, the molar ratio of the lithium source, the M source, and the ammonium salt in the mixed solution is 3:1:2-3.

[0010] In a possible implementation, the molar ratio of the M source and the fluorinating agent in the mixed solution is 1-100:1.

[0011] In a possible implementation, the fluorinating agent includes at least one of HF and XeF2.

[0012] In a possible implementation, the freeze-drying process is carried out at a temperature of -70°C to -80°C.

[0013] In a possible implementation, the freeze-drying process takes 24 to 48 hours.

[0014] In a possible implementation, the heat treatment temperature is 100-400°C.

[0015] In a possible implementation, the heat treatment time is 1-4 hours.

[0016] On the other hand, this application also provides a solid-state battery, including the solid electrolyte as described above.

[0017] Based on the above technical solution, this application has the following beneficial effects: This application provides a solid electrolyte comprising a halide solid electrolyte and a coating layer covering at least a portion of the surface of the halide solid electrolyte, wherein the chemical formula of the halide solid electrolyte is Li3MCl. 6-x F xWhere 0 < x ≤ 1, and M includes at least one of group III metals, in fluorine-doped halide solid electrolytes, fluorine can effectively attract metal electrons, thereby reducing the orbital energy level of the metal center, effectively improving the bulk properties of the halide solid electrolyte, and enhancing its oxidation resistance. Furthermore, the coating layer can form a positive electrode electrolyte interface on the surface of the halide solid electrolyte, effectively isolating the electrode from direct contact with the electrolyte, preventing the oxidation of the halide solid electrolyte, and promoting uniform lithium ion deposition while inhibiting dendrite growth. In addition, through the synergistic effect of the halide solid electrolyte and its surface coating layer, the ionic conductivity and electrochemical stability of the solid electrolyte can be further improved. Attached Figure Description

[0018] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This application provides a flowchart of a method for preparing a solid electrolyte; Figure 2 This application provides an SEM image of a solid electrolyte. Figure 3 The present application provides a comparative example of a halide solid electrolyte SEM image. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] It should be noted that, in the description of this application, the following definitions shall apply unless a different definition is given elsewhere in the claims or this specification. All numerical values, whether or not explicitly indicated, are defined herein as being modified by the term "about". The term "about" generally refers to a range of numerical values ​​that a person skilled in the art would consider equivalent to the stated values ​​to produce substantially the same properties, functions, results, etc. A range of numerical values ​​indicated by a low value and a high value is defined as including all numerical values ​​within that range and all subranges included within that range.

[0022] It should be noted that in the description of this application, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0023] On one hand, this application provides a solid electrolyte, which includes a halide solid electrolyte and a coating layer covering at least a portion of the surface of the halide solid electrolyte, wherein the chemical formula of the halide solid electrolyte is Li3MCl. 6-x F x Where 0 < x ≤ 1, and M includes at least one group III metal. In fluorine-doped halide solid electrolytes, fluorine effectively attracts metal electrons, lowering the orbital energy levels of the metal center, effectively improving the bulk properties of the halide solid electrolyte and enhancing its oxidation stability. Furthermore, the coating layer can form a positive electrode electrolyte interface on the surface of the halide solid electrolyte, effectively isolating the electrode from direct contact with the electrolyte, preventing oxidation of the halide solid electrolyte, and promoting uniform lithium ion deposition while inhibiting dendrite growth. Thus, through the synergistic effect of the halide solid electrolyte and its surface coating layer, the ionic conductivity and electrochemical stability of the solid electrolyte can be further improved.

[0024] In a possible implementation, the coating layer includes at least one of LiF and LiCl. LiF has a wide electrochemical window, which can block electron passage, and when LiF comes into contact with lithium metal, it can form a stable interface to prevent lithium deposition in the electrolyte. LiCl has little hindrance to lithium-ion transport, which helps to reduce interfacial impedance, giving the coating layer good ion conductivity, which is beneficial to lithium-ion transport. It can also migrate during battery cycling, forming a smooth and uniform interfacial layer on the surface of the halide solid electrolyte. Furthermore, when the solid electrolyte comes into contact with the high-voltage positive electrode, the coating layer can effectively inhibit the oxidative decomposition of the electrolyte, forming a kinetically stable positive electrode electrolyte interfacial phase.

[0025] Preferably, the coating layer includes LiF and LiCl. The coating layer is a dense layer structure formed by LiF and LiCl, which can form a physical barrier on the surface of the halide solid electrolyte, isolating the highly active halide electrolyte from the highly reactive electrode material. Through the synergistic effect of LiF and LiCl, the coating layer can effectively inhibit the surface oxidation of the halide solid electrolyte, repair defects on the surface of the solid electrolyte, thereby inhibiting the side reaction between the solid electrolyte and lithium metal and the growth of lithium dendrites, effectively reducing the risk of lithium dendrites piercing the solid electrolyte and causing a short circuit in the battery.

[0026] In a possible implementation, the coating layer on the surface of the halide electrolyte has a nanometer-scale thickness; specifically, the thickness of the coating layer is 50-500 nm; understandably, the thickness of the coating layer can be any value within the 50-500 nm range; for example, the thickness of the coating layer can be 50 nm, 100 nm, 200 nm, 40 nm, 500 nm, etc. If the coating layer thickness is greater than the above range, the lithium ion transport path is prolonged, affecting the migration of lithium ions in the solid electrolyte; if the coating layer thickness is less than the above range, the mechanical stability of the coating layer is reduced, making it impossible to suppress the growth of lithium dendrites, thereby reducing the ionic conductivity of the solid electrolyte. Thus, by controlling the thickness of the coating layer within the above range, it is possible to effectively improve interface stability while ensuring ionic conductivity, thereby improving the electrochemical stability of the solid electrolyte and increasing the cycle life of the battery.

[0027] In a possible implementation, the coating layer covers the surface of the halide solid electrolyte, completely covering the surface of the halide solid electrolyte, forming a stable and dense coating layer on the surface of the halide solid electrolyte, effectively inhibiting the oxidation of the halide solid electrolyte, while inhibiting the growth of lithium dendrites, and improving the interface stability of the solid electrolyte.

[0028] The following describes a method for preparing a solid electrolyte according to embodiments of this application. This specification provides the method steps as described in the embodiments, but based on conventional or non-inventive methods, more or fewer steps may be included. The order of steps listed in the embodiments is merely one possible order among many and does not represent the only possible order. In actual implementation, the preparation method can be performed in the order shown in the embodiments or accompanying drawings, or in parallel. The following references... Figure 1 This application provides a method for preparing a solid electrolyte, which may include the following steps.

[0029] S1: Provides a lithium source, an M source, an ammonium salt, and a fluorinating agent, wherein M includes one or more group III metals.

[0030] In a possible implementation, the fluorinating agent includes at least one of HF and XeF2. This fluorinating agent can react with the halide solid electrolyte to introduce fluorine into the chlorine-dominated crystal lattice, resulting in fluorine substitution within the halide solid electrolyte lattice and the formation of metal fluorides and lithium fluoride on the surface of the halide solid electrolyte. Lithium fluoride has low electronic conductivity and high interfacial energy, which can suppress electron shuttle and lithium dendrite growth when in contact with the lithium metal anode, effectively blocking direct contact between the internal electrolyte and external moisture, improving the environmental stability of the material, and thus significantly enhancing battery safety. Furthermore, the fluorinating agent can react with the hydroxyl groups on the surface of the halide electrolyte, converting them into stable fluorides, thereby reducing the surface reactivity of the material and minimizing the adverse effects of impurities on ionic conductivity.

[0031] In possible implementations, the M source includes at least one of YCl3, InCl3, ScCl3, and ErCl3. In halide solid electrolytes, the choice of the M source can affect the crystal structure, ionic conductivity, electrochemical stability window, and interfacial compatibility with the electrode. Using the above materials as the M source to prepare halide solid electrolytes can yield solid electrolyte materials with high ionic conductivity and high-voltage stability.

[0032] In a possible implementation, the lithium source includes LiCl, which provides lithium ions. Lithium chloride has high reactivity and can directly participate in the reaction to form the target product. Specifically, the ammonium salt includes NH4Cl, which can act as a chlorine source and reaction promoter, converting stable metal oxides into more active chloride or chloride oxide intermediates. This helps to reduce the energy and temperature required for subsequent ion exchange reactions with lithium salts, allowing the reaction to proceed smoothly at medium and low temperatures, and contributing to the formation of a target product with good crystallinity and uniform composition.

[0033] S2: Mix the lithium source, M source, ammonium salt and fluorinating agent in a solvent in a certain proportion to obtain a mixed solution.

[0034] Specifically, the solvent can be water, which can fully disperse the reactants in ionic form, which is beneficial for the contact between ions and the reaction. At the same time, water can also participate in the reaction to form hydrated complexes.

[0035] In a possible implementation, the M source and the ammonium salt can undergo a complex formation reaction at room temperature, with the metal ion M... 3+ It has empty valence orbitals, and ammonium salts can provide halide ions as ligands, allowing the lone pair electrons of the halide ion to enter the metal ion M. 3+Empty orbitals are used to form coordinate bonds. Furthermore, the complex formed by the M source and the ammonium salt can undergo metathesis reaction with the lithium source. This is essentially due to the difference in the binding ability of different cations to the complex ion, as well as the recombination of ions in the solution, which causes the reaction to proceed in the direction of forming a more stable product.

[0036] In some embodiments, the lithium source is LiCl, the M source is MCl3, and the ammonium salt is NH4Cl. MCl3 and NH4Cl can undergo the following reaction in water at room temperature: MCl3 + 3NH4Cl → (NH4)3[MCl6]. In this reaction, Cl... - The lone pair of electrons enters the metal ion M 3+ The empty orbitals of the complex (NH4)3[MCl6] are thus formed. Furthermore, LiCl reacts with the complex (NH4)3[MCl6] in water at room temperature as follows: (NH4)3[MCl6] + 3LiCl + H2O → Li3MCl6·H2O + 3NH4Cl, where Li3MCl6·H2O is the halide precursor. In the reaction, the ammonium ions NH4+ in (NH4)3[MCl6] are... + Lithium ions in LiCl + An exchange occurred, releasing NH4Cl and generating Li3MCl6·H2O, which has higher stability.

[0037] In a possible implementation, the molar ratio of lithium source, M source, and ammonium salt in the mixed solution is 3:1:2-3; understandably, the molar ratio of lithium source, M source, and ammonium salt in the mixed solution can be any value within the range of 3:1:2-3; exemplaryly, the molar ratio of lithium source, M source, and ammonium salt in the mixed solution can be 3:1:2, 3:1:2.2, 3:1:2.5, 3:1:2.7, 3:1:3, etc. Thus, controlling the molar ratio of lithium source, M source, and ammonium salt within the above range ensures that the reaction proceeds fully, which is beneficial for preparing electrolyte materials with high purity and high performance; preferably, the molar ratio of lithium source, M source, and ammonium salt is 3:1:3.

[0038] In a possible implementation, the molar ratio of source M to fluorinator in the mixed solution is 1-100:1; understandably, the molar ratio of source M to fluorinator in the mixed solution can be any value between 1 and 100:1; exemplary, the molar ratio of source M to fluorinator in the mixed solution can be 1:1, 1:5, 1:10, 1:50, 1:100, etc. Thus, controlling the molar ratio of raw materials and fluorinator within the above range can effectively control the fluorination process, allowing the fluorinator to undergo lattice substitution within the halide solid electrolyte while simultaneously forming a coating layer on the surface of the halide electrolyte. This avoids excessively high fluorinator content, which would lead to a violent fluorination reaction, complete destruction of the crystal structure of the halide solid electrolyte, excessively high lithium fluoride content in the product, and a sharp decrease in the ionic conductivity of the solid electrolyte. Simultaneously, it avoids excessively low fluorinator content, which would cause the fluorinator to react only with a portion of the surface of the halide solid electrolyte, failing to form a coating layer or undergo fluorine substitution within the halide solid electrolyte lattice.

[0039] S3: Freeze-dry the mixed solution to obtain halide precursor powder.

[0040] Specifically, the halide precursor powder includes a halide precursor and a fluorinating agent. During freeze-drying, the mixed solution is rapidly frozen, causing water molecules to form ice crystals, which fix the various ions dissolved in the solution in situ. Compared with conventional heating and drying methods, freeze-drying can effectively prevent ion migration and phase separation caused by water evaporation and capillary action during conventional drying, avoid segregation and agglomeration of components in the mixed solution, and obtain a uniformly mixed halide precursor powder. Furthermore, freeze-drying can retain the stoichiometric ratio of each component in the mixed solution, which is beneficial for preparing a target product with high purity and consistent performance.

[0041] Specifically, halide precursors have a high specific surface area, which can increase the contact area between reactants during subsequent heat treatment, thereby reducing the reaction energy barrier and generating solid electrolyte materials with fine grains and excellent performance. In a possible implementation, the freeze-drying process is carried out under vacuum conditions, which can avoid the decomposition or reaction of heat-sensitive raw materials and help ensure the chemical consistency of the halide precursor powder. Specifically, the vacuum degree of the freeze-drying process is 1-20 Pa; understandably, the vacuum degree of the freeze-drying process can be any value within 1-20 Pa; exemplary examples include vacuum degrees of 1 Pa, 5 Pa, 10 Pa, 15 Pa, 20 Pa, etc. Thus, controlling the vacuum degree of the freeze-drying process within the above range is beneficial to achieving rapid and complete sublimation of ice crystals, while avoiding problems such as melting, recrystallization, or component segregation, thereby preserving the initial homogeneous mixing state.

[0042] In a possible implementation, the freeze-drying temperature is -70°C to -80°C; understandably, the freeze-drying temperature can be any value within the range of -70°C to -80°C; exemplary examples include freeze-drying temperatures of -70°C, -72°C, -75°C, -79°C, and -80°C. By controlling the freeze-drying temperature within this range, rapid deep freezing can be achieved, forming tiny ice crystals and preventing water molecules from arranging into large, orderly ice crystals that would otherwise repel solutes in the mixed solution, causing solute aggregation and component segregation.

[0043] In a possible implementation, the freeze-drying time is 24-48 hours; understandably, the freeze-drying time can be any value within 24-48 hours; for example, the freeze-drying time can be 24 hours, 27 hours, 30 hours, 40 hours, 48 ​​hours, etc. By controlling the freeze-drying time within the above range, it is possible to ensure that the mixed solution is thoroughly dried, ensuring the acquisition of anhydrous, porous, and chemically homogeneous highly active precursor materials. This avoids the possibility that excessively short freeze-drying times would lead to residual moisture disrupting the homogeneity of the halide precursor, while also preventing excessively long freeze-drying times from affecting experimental efficiency. S4: Heat-treat the halide precursor powder to obtain a solid electrolyte.

[0044] Specifically, the solid electrolyte includes a halide solid electrolyte and a coating layer covering at least a portion of the surface of the halide solid electrolyte, wherein the chemical formula of the halide electrolyte is Li3MCl. 6-x F x Where 0 < x ≤ 1, M includes at least one of group III metals, and the value of x depends on the amount of fluorinating agent in the reaction process.

[0045] In a possible implementation, the halide precursor powder is heat-treated to obtain a solid electrolyte, including: during the heat treatment of the halide precursor powder, fluorine substitution occurs within the crystal lattice of the halide precursor powder to obtain a halide solid electrolyte; a coating layer is formed on the surface of the halide solid electrolyte to obtain the solid electrolyte. The resulting solid electrolyte exhibits good stability, the coating layer effectively isolates the electrode from direct contact with the electrolyte, preventing oxidation of the halide solid electrolyte, and the coating layer promotes uniform lithium ion deposition and inhibits dendrite growth; furthermore, through the synergistic effect of the halide solid electrolyte and its surface coating layer, the ionic conductivity and electrochemical stability of the solid electrolyte can be further improved.

[0046] Specifically, during the heat treatment process, the fluorinating agent undergoes a fluorination reaction with the halide precursor. The reaction mechanism is as follows: First, oxidation byproducts are generated on the surface of the halide precursor powder. These byproducts can be LiF and LiCl particles. Then, fluorine substitution occurs within the crystal lattice of the halide precursor powder, generating a halide solid electrolyte. In essence, the fluorination reaction first forms byproducts on a localized surface of the material, followed by further fluorine substitution. As the amount of surface byproducts increases, these byproducts can form a coating layer on the surface of the fluorine-doped halide solid electrolyte, yielding the target product, the solid electrolyte. The more fluorine is substituted within the crystal lattice of the halide solid electrolyte, the higher the Gibbs free energy of the solid electrolyte material and the lower the lattice parameters, thus improving the electrochemical performance of the material. Thus, a solid electrolyte with a nanoscale coating is obtained. The coating can serve as a stable interface and maintain high lithium-ion conductivity. However, if the degree of fluorination is too high, the excessive generation of byproducts will lead to high interface impedance, which will hinder lithium-ion transport. Furthermore, excessive fluorination will also cause significant lattice shrinkage, which will reduce the diffusion of lithium ions.

[0047] In some embodiments, the lithium source is LiCl, the M source is MCl3, and the ammonium salt is NH4Cl. The freeze-dried halide precursor powder includes Li3MCl6·H2O and NH4Cl. During heat treatment, NH4Cl can decompose into ammonia and hydrogen chloride gas upon heating, which are released from the reaction system. When the fluorinating agent is HF, during heat treatment, Li3MCl6·H2O in the halide precursor powder can react with HF as follows: Li3MCl6·H2O + HF → MCl3 + LiCl + LiF + H2O. Under heating conditions and the action of HF, the coordination bonds in Li3MCl6·H2O are broken, resulting in thermal decomposition and the formation of coated particles on the material surface. Furthermore, fluorine substitution occurs within the lattice of the halide precursor powder, and Li3MCl6·H2O further reacts with HF as follows: Li3MCl6·H2O + HF → Li3MCl6·H2O. 6-x F x The reaction HCl + H₂O occurs because fluoride ions have a strong coordination ability with metal ions, and chloride ions are replaced by fluoride ions, resulting in a fluorine-containing halide solid electrolyte.

[0048] In other embodiments, the lithium source is LiCl, the M source is MCl3, the ammonium salt is NH4Cl, and the fluorinating agent is XeF. During heat treatment, Li3MCl6·H2O in the halide precursor powder can react with XeF as follows: Li3MCl6·H2O + XeF → MCl3 + LiCl + LiF + H2O + Xe. Under heating conditions and the action of XeF, the coordination bonds in Li3MCl6·H2O are broken, resulting in thermal decomposition and the formation of coated particles on the material surface. Furthermore, fluorine substitution occurs within the lattice of the halide precursor powder, as follows: Li3MCl6·H2O + XeF → Li3MCl6·H2O + XeF → LiCl3 + LiCl + LiF + H2O + XeF. 6-x F x The reaction is: +HCl + H₂O + Xe. Due to the strong coordination ability of fluoride ions with metal ions, chloride ions are replaced by fluoride ions, resulting in a fluorine-containing halide solid electrolyte.

[0049] In a possible implementation, the heat treatment temperature is 100-400°C; understandably, the heat treatment temperature can be any value within the range of 100-400°C; for example, the heat treatment temperature can be 100°C, 200°C, 300°C, 350°C, 400°C, etc. Thus, controlling the heat treatment temperature within the above range allows impurities in the reaction process to decompose thermally, completely removing water from the halide precursor powder, and promoting grain growth of the target product, increasing crystallinity, and facilitating the acquisition of a solid electrolyte with high ionic conductivity; it avoids incomplete reaction due to excessively low temperatures, while also avoiding decomposition of the target product and excessive grain growth due to excessively high temperatures, which would affect ionic conductivity.

[0050] In a possible implementation, the heat treatment time is 1-4 hours; understandably, the heat treatment time can be any value within the range of 1-4 hours; for example, the heat treatment time is 1 hour, 2 hours, 3 hours, 3.5 hours, 4 hours, etc. By controlling the heat treatment time within the above range, it is ensured that the gases generated by the decomposition of ammonium salt are completely discharged from the material system, and that the reaction proceeds fully, which is beneficial for the formation of an ordered crystal structure. This avoids incomplete reaction and insufficient cleanliness due to excessively low temperatures, resulting in low ionic conductivity, while also preventing excessive grain growth due to excessively high temperatures, which could lead to structural defects and performance degradation.

[0051] In the above preparation method, a mixed solution of halogenated precursors was obtained through a liquid-phase reaction. The mixed solution was then freeze-dried to obtain halide precursor powder. The halide precursor powder contains uniformly distributed halide precursors and fluorinating agents, which is beneficial for controlling the fluorination reaction process during subsequent heat treatment and avoiding local aggregation of fluorinating agents and halide precursors that affects the reaction rate. During heat treatment, the fluorinating agent and halide precursors can undergo a fluorination reaction, first forming byproducts on the local surface of the material, and then further substituting fluorine into the material. As the surface byproducts increase, they can form a coating layer on the surface of the fluorine-doped halide solid electrolyte, obtaining the target product solid electrolyte. Thus, the prepared solid electrolyte has good performance and effectively improves the controllability of the reaction.

[0052] On the other hand, this application also provides a solid-state battery, including a solid electrolyte as described in any of the above embodiments or including a solid electrolyte obtained by the preparation method described in any of the above embodiments. Specifically, the solid-state battery includes a positive electrode, a negative electrode, and an electrolyte layer. The coating layer of the solid electrolyte can form a stable interface between the solid electrolyte and the electrode material, improving the electrochemical stability of the solid electrolyte and thus improving the electrochemical performance of the solid-state battery. It is understood that the beneficial effects of the solid electrolyte provided in any of the above embodiments or the solid electrolyte prepared by the preparation method provided in any of the above embodiments are applicable to the solid-state battery.

[0053] The following describes specific embodiments of this application in conjunction with the aforementioned solid electrolyte, preparation method, and solid battery. The following embodiments describe the technical solutions of this application in more detail. These embodiments are for illustrative purposes only, as various modifications and variations within the scope of the disclosure of this application will be apparent to those skilled in the art. The reagents used in the embodiments are commercially available or synthesized using conventional methods and can be used directly without further processing. Similarly, the instruments and apparatus used in the embodiments are commercially available.

[0054] Example 1 This embodiment provides a solid electrolyte and its preparation method, specifically including the following steps: 1. Provide LiCl, YCl3, NH4Cl and HF; 2. In a nitrogen glove box, weigh out powders of LiCl, YCl3 and NH4Cl in a molar ratio of 3:1:3 to obtain a mixed powder; 3. In a fume hood, add the above mixed powder and HF to deionized water, with a molar ratio of YCl3 to HF of 100:1. Stir until completely dissolved to obtain a mixed solution. 4. The mixed solution was freeze-dried using a vacuum freeze dryer for 24 hours at a temperature of -70°C to obtain halide precursor powder. 5. The halide precursor powder was heat-treated in a vacuum atmosphere furnace in a nitrogen glove box at a temperature of 200℃ for 2 hours. During the heat treatment, the vacuum was continuously evacuated to -0.1 MPa to obtain a solid electrolyte material.

[0055] Specifically, the solid electrolyte includes a halide solid electrolyte and a coating layer that at least partially covers the surface of the halide solid electrolyte, see reference. Figure 2 , Figure 2 The SEM image of the solid electrolyte in this embodiment is shown. The solid electrolyte has a small particle size and a coating layer on its surface.

[0056] Example 2 This embodiment provides a solid electrolyte and its preparation method. The similarities with Example 1 will not be repeated. The difference from Example 1 is that LiCl, InCl3 and NH4Cl are provided.

[0057] Example 3 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The difference from Embodiment 1 is that LiCl, ScCl3 and NH4Cl are provided.

[0058] Example 4 This embodiment provides a solid electrolyte and its preparation method. The similarities with Example 1 will not be repeated. The difference from Example 1 is that LiCl, ErCl3 and NH4Cl are provided.

[0059] Example 5 This embodiment provides a solid electrolyte and its preparation method. The similarities with Example 1 will not be repeated. The difference from Example 1 is that the fluorinating agent is XeF2.

[0060] Example 6 This embodiment provides a solid electrolyte and its preparation method. The similarities with Example 1 will not be repeated. The difference from Example 1 is that the molar ratio of YCl3 to HF is 10:1.

[0061] Example 7 This embodiment provides a solid electrolyte and its preparation method. The similarities to Example 1 will not be repeated. The difference from Example 1 is that the molar ratio of YCl3 to HF is 1:1. Example 8 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The difference from Embodiment 1 is that the heat treatment temperature is 100°C.

[0062] Example 9 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The difference from Embodiment 1 is that the heat treatment temperature is 400℃.

[0063] Example 10 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The difference from Embodiment 1 is that the heat treatment time is 1 hour.

[0064] Example 11 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The difference from Embodiment 1 is that the heat treatment time is 3 hours.

[0065] Example 12 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The difference from Embodiment 1 is that the heat treatment time is 4 hours.

[0066] Comparative Example 1 1. Provide LiCl and YCl3 powders; 2. In a nitrogen glove box, weigh LiCl and YCl3 powders at a molar ratio of 3:1 to obtain a mixed powder; 3. Add the mixed powder to a 250ml zirconia ball mill jar, and add 10mm diameter zirconia balls to the zirconia ball mill jar at a ball-to-powder ratio of 10:1; seal the ball mill jar and ball mill at a speed of 250rpm for 20h to obtain white precursor powder; 4. The white precursor powder was heat-treated in a vacuum atmosphere furnace at 200℃ for 2 hours, with continuous evacuation to -0.1 MPa during the heat treatment process, to obtain Li3YCl6 halide solid electrolyte material. (Refer to...) Figure 3 , Figure 3 The SEM image of the halide solid electrolyte in this comparative example is shown, which has a non-uniform particle size.

[0067] Comparative Example 2 1. Provide LiCl, YCl3 and NH4Cl powders; 2. In a nitrogen glove box, weigh LiCl, YCl3 and NH4Cl powders in a molar ratio of 3:1:3 to obtain a mixed powder; 3. Add deionized water to the mixed powder and stir until completely dissolved to obtain a mixed solution; 4. The mixed solution was freeze-dried using a vacuum freeze dryer for 24 hours at a temperature of -70°C to obtain halide precursor powder. 5. The halide precursor powder was heat-treated in a vacuum atmosphere furnace in a nitrogen glove box at a temperature of 200℃ for 2 hours. The vacuum was continuously evacuated to -0.1 MPa during the heat treatment process to obtain Li3YCl6 halide solid electrolyte material.

[0068] Electrodes were prepared using the solid electrolyte materials obtained in Examples 1-12 and Comparative Examples 1-2, and their electrical performance was tested, including the following steps: Ionic conductivity testing: A Metrohm PGSTAT302 electrochemical workstation was used, with the test frequency range set to 10MHz-1Hz and the bias voltage set to 10mV. The ionic conductivity of the solid electrolyte was calculated using the conductivity calculation formula σ=L / (R*S), where L is the sample thickness, R is the total impedance, and S is the effective contact area between the sample and the electrode.

[0069] Positive electrode preparation: Weigh 5.6g of positive electrode material and 1.372g of solid electrolyte material powder prepared in the above examples and comparative examples and place them in a 100ml ball mill jar. Add 50g of zirconia balls with a diameter of 2mm to the ball mill jar and ball mill at a speed of 300rpm for 30min to obtain a mixture of positive electrode material and solid electrolyte. Add 0.014g of conductive carbon to the mixture and ball mill at a speed of 300rpm for 30min. Add 0.014g of PTFE to the ball-milled composite material and grind it with an agate grinding rod for 60min to obtain a composite positive electrode material. Place the composite positive electrode material in a roller press for repeated rolling. Set the upper roller temperature to 90℃ and the lower roller temperature to 100℃ to obtain a composite electrode sheet with a thickness of 85μm. Roll press the composite electrode sheet with carbon-coated aluminum foil to obtain the positive electrode sheet.

[0070] Electrochemical performance testing: The prepared positive electrode sheet was cut into 10mm diameter discs using a punching machine. The positive electrode sheet, solid electrolyte and lithium indium negative electrode were assembled into an all-solid-state battery and placed in the Blue Battery Testing System for electrochemical performance testing at 0.1C rate.

[0071] Table 1 shows the ionic conductivity of the solid electrolytes prepared in Examples 1-12 and Comparative Examples 1-2, as well as the first-cycle discharge specific capacity and capacity retention of the solid batteries.

[0072] Table 1

[0073] Referring to Table 1 and Examples 1-12, the ionic conductivity of the solid electrolytes prepared in Examples 1-12 is 1.59-2.12 mS / cm. The solid electrolytes prepared by the method provided in this application have good ionic conductivity. The specific capacity of the solid battery including this solid electrolyte in the first discharge cycle is 196.5-203.4 mAh / g. The specific capacity of the first discharge cycle is used to characterize the actual number of lithium ions available in the active material of the solid battery in the first cycle. During the first charge, some lithium ions are permanently consumed and cannot return during discharge. The high specific capacity of the solid battery in the first discharge cycle proves that the solid battery provided in this application has good interfacial performance between the positive electrode and the electrolyte. The solid battery has a capacity retention rate of 95.8%-98.2% after 100 cycles and a capacity retention rate of 87.5%-92.3% after 100 cycles. The solid battery has a high capacity retention rate and good structural stability.

[0074] In Comparative Example 1, a halide solid electrolyte was prepared using a dry method, while in Comparative Example 2, a halide solid electrolyte was prepared using a liquid-phase method. Compared to Examples 1-12, the halide solid electrolytes in Comparative Examples 1-2 were not fluorinated and lacked a surface coating. Referring to Table 1, the conductivity of the solid electrolytes provided in Comparative Examples 1-2 was 1.32 mS / cm and 1.49 mS / cm, respectively, and their ionic conductivity was lower than that of the solid electrolytes in Examples 1-12 (1.59-2.12 mS / cm). This demonstrates that the ionic conductivity of the halide solid electrolytes in the examples was improved after fluorination. The solid electrolytes prepared from the halide solid electrolytes in Comparative Examples 1-2... The specific capacities of the first discharge cycle were 186.7 mAh / g and 183.1 mAh / g, respectively. After 100 cycles, the capacity retention rates of the solid-state batteries were 90.6% and 90.7%, respectively, and 73.4% and 74.5%, respectively. It can be seen that the specific capacity and capacity retention rate of the first discharge cycle of the solid-state batteries in Comparative Examples 1-2 were significantly lower than those in Examples 1-12. The fluorine-free and coating-free halide solid electrolytes experienced irreversible capacity loss during the first charge, resulting in a low specific capacity of the first discharge cycle. The poor interfacial performance between the halide solid electrolyte and the cathode material led to faster capacity decay and reduced battery life.

[0075] refer to Figure 2 and Figure 3It can be seen that the solid electrolyte in Example 1 has a regular cluster structure, while the halide solid electrolyte in Comparative Example 1 contains large and small particles with uneven particle size, proving that the solid electrolyte provided in this application has a uniform structure and the preparation method provided in this application has good controllability.

[0076] In summary, within the preferred parameter range, the solid electrolytes prepared in Examples 1-12 exhibit good ionic conductivity and good interfacial stability between the solid electrolyte and the positive electrode, which is beneficial for improving the electrochemical performance of solid-state batteries and extending battery life.

[0077] The foregoing description has fully disclosed the specific embodiments of this application. It should be noted that any modifications made by those skilled in the art to the specific embodiments of this application do not depart from the scope of the claims. Accordingly, the scope of the claims of this application is not limited to the foregoing specific embodiments.

Claims

1. A solid electrolyte, characterized in that, The solid electrolyte comprises a halide solid electrolyte and a coating layer covering at least a portion of the surface of the halide solid electrolyte, wherein the chemical formula of the halide solid electrolyte is Li3MCl. 6-x F x , where 0 < x ≤ 1, and M includes at least one of group III metals.

2. The solid electrolyte according to claim 1, characterized in that, The coating layer includes at least one of LiF and LiCl.

3. The solid electrolyte according to claim 1, characterized in that, The thickness of the coating layer is 50-500 nm.

4. A method for preparing a solid electrolyte, characterized in that, The method includes: Provides lithium source, M source, ammonium salt and fluorinating agent, wherein M includes one or more group III metals; The lithium source, the M source, the ammonium salt, and the fluorinating agent are mixed in a solvent in a certain proportion to obtain a mixed solution; The mixed solution was freeze-dried to obtain a halide precursor powder; The halide precursor powder is heat-treated to obtain a solid electrolyte; the solid electrolyte comprises a halide solid electrolyte and a coating layer covering at least a portion of the surface of the halide solid electrolyte, and the chemical formula of the halide electrolyte is Li3MCl. 6-x F x , where 0 < x ≤ 1, and M includes at least one of group III metals.

5. The preparation method according to claim 4, characterized in that, The process of heat-treating the halide precursor powder to obtain a solid electrolyte includes: During the heat treatment of the halide precursor powder, fluorine substitution occurs within the crystal lattice of the halide precursor powder to obtain the halide solid electrolyte; the coating layer is formed on the surface of the halide solid electrolyte to obtain the solid electrolyte.

6. The preparation method according to claim 4, characterized in that, The mixed solution satisfies at least one of the following characteristics: The molar ratio of the lithium source, the M source, and the ammonium salt in the mixed solution is 3:1:2-3; The molar ratio of the M source and the fluorinating agent in the mixed solution is 1-100:

1.

7. The preparation method according to claim 4, characterized in that, The fluorinating agent includes at least one of HF and XeF2.

8. The preparation method according to claim 4, characterized in that, The freeze-drying process satisfies at least one of the following characteristics: The freeze-drying process is performed at a temperature of -70℃ to -80℃. The freeze-drying process takes 24 to 48 hours.

9. The preparation method according to claim 4, characterized in that, The heat treatment satisfies at least one of the following characteristics: The heat treatment temperature is 100-400℃; The heat treatment time is 1-4 hours.

10. A solid-state battery, characterized in that, Includes the solid electrolyte as described in any one of claims 1-3.

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