Solid electrolyte, preparation method and solid-state battery

Abstract

The invention provides a solid electrolyte which is characterized in that the solid electrolyte comprises a fluorinated sulfide solid electrolyte and a fluorinated layer at least partially covering the surface of the fluorinated sulfide solid electrolyte, the chemical formula of the fluorinated sulfide solid electrolyte is Li7-xPS6-xClxFy, x is greater than or equal to 1 and less than or equal to 1.6, y is greater than 0 and less than 1, and y is used for representing the doping amount of fluorine. The solid-state electrolyte provided by the invention has the fluorine-doped fluorinated sulfide solid-state electrolyte, so that the bulk phase property of the sulfide solid-state electrolyte can be effectively improved, and the ionic conductivity of the fluorinated sulfide solid-state electrolyte is improved; through synergistic cooperation of the fluorinated sulfide solid-state electrolyte and the surface fluorinated layer, a positive electrode electrolyte interface can be formed on the surface of the fluorinated sulfide solid-state electrolyte, direct contact between an electrode and the electrolyte can be effectively isolated, oxidation of the fluorinated sulfide solid-state electrolyte is prevented, and the fluorinated layer can promote uniform deposition of lithium ions, so that the service life of the lithium ion battery is prolonged. The dendritic crystal growth is inhibited.

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] Lithium-ion batteries dominate the electronic device market due to their high operating voltage, large specific energy, long cycle life, and low environmental impact. Innovation in electrolyte materials is key to improving lithium-ion battery performance. Early lithium-ion batteries relied on liquid organic electrolytes containing carbonate solvents; subsequent advancements, through the introduction of functional additives, have resulted in increased energy density, reduced internal resistance, and extended cycle life. However, the flammability, leakage problems, and poor temperature stability of liquid electrolytes remain unresolved safety concerns. For example, the volatilization and leakage of liquid electrolytes require complex packaging measures, and they are prone to thermal runaway at high temperatures.

[0003] 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. All-solid-state batteries use solid electrolytes instead of liquid electrolytes, effectively addressing the risks of electrolyte leakage and thermal runaway, while simultaneously suppressing lithium dendrite formation by enhancing interfacial stability. Based on the type of solid electrolyte used, all-solid-state batteries can be classified into four categories: polymer-based, oxide-based, sulfide-based, and halide-based. Among them, sulfide-based all-solid-state batteries have enormous commercial potential due to their excellent ionic conductivity, good mechanical properties, thermal stability, and moderate production cost. Sulfide solid electrolytes possess unique characteristics, including extremely high ionic conductivity and extremely low interfacial resistance with the lithium metal anode, giving them a significant advantage in driving the development of all-solid-state battery technology. However, sulfide solid electrolyte interfacial failures, such as space charge layer formation, interfacial side reactions, and mechanical stress, can disrupt lithium-ion transport. Therefore, improving the interfacial stability between the sulfide solid electrolyte and the cathode material is currently a major bottleneck for the commercial application of solid-state batteries. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this application provides a solid electrolyte, a preparation method, and a solid-state battery. The specific technical solution is as follows: On one hand, this application provides a solid electrolyte comprising a fluorinated sulfide solid electrolyte and a fluorinated layer at least partially covering the surface of the fluorinated sulfide solid electrolyte, wherein the chemical formula of the fluorinated sulfide solid electrolyte is Li. 7-x PS 6-x Cl x F y , where 1≤x≤1.6, 0<y≤1, and y is used to characterize the amount of fluorine doping.

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

[0006] In a possible implementation, the thickness of the fluorinated layer is 20-200 nm.

[0007] On the other hand, this application also provides a method for preparing a solid electrolyte, the method comprising: Provides sulfide solid electrolytes and fluorinating agents; The sulfide solid electrolyte and the fluorinating agent are placed separately in the same reactor according to a certain ratio, and the reactor is subjected to low-temperature heat treatment to obtain the solid electrolyte; the solid electrolyte includes a fluorinated sulfide solid electrolyte and a fluorinated layer that at least partially covers the surface of the fluorinated sulfide solid electrolyte, and the chemical formula of the fluorinated sulfide solid electrolyte is Li. 7-x PS 6-x Cl x F y , where 1≤x≤1.6, 0<y≤1, and y is used to characterize the amount of fluorine doping.

[0008] In a possible implementation, the fluorinating agent includes at least one of XeF2, XeF4, and XeF6.

[0009] In a possible implementation, the molar ratio of the sulfide solid electrolyte to the fluorinating agent is 1-100:1.

[0010] In a possible implementation, the temperature of the low-temperature heat treatment is 50-200°C.

[0011] In a possible implementation, the low-temperature heat treatment lasts for 1-4 hours.

[0012] In a possible implementation, the preparation method further includes: Lithium sulfide, phosphorus pentasulfide and lithium chloride are available; The lithium sulfide, phosphorus pentasulfide, and lithium chloride are mixed in a certain proportion and ground to obtain a mixed powder. The mixed powder is heat-treated to obtain the sulfide solid electrolyte; the chemical formula of the sulfide solid electrolyte is Li. 7-x PS 6-x Cl x .

[0013] In a possible implementation, the molar ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride in the mixed powder is 3.8-5:1:2-3.2.

[0014] In a possible implementation, the grinding speed is 200-300 rpm.

[0015] In a possible implementation, the grinding time is 10-80 hours.

[0016] In a possible implementation, the heat treatment temperature is 400-600°C.

[0017] In a possible implementation, the heat treatment time is 8-16 hours.

[0018] On the other hand, this application also provides a solid-state battery, including the solid electrolyte as described above.

[0019] Based on the above technical solution, this application has the following beneficial effects: This application provides a solid electrolyte, including a fluorinated sulfide solid electrolyte and a fluorinated layer at least partially covering the surface of the fluorinated sulfide solid electrolyte. The fluorinated sulfide solid electrolyte with fluorine doping can effectively improve the bulk properties of the sulfide solid electrolyte and increase its ionic conductivity. Furthermore, the fluorinated layer can form a positive electrode electrolyte interface on the surface of the fluorinated sulfide solid electrolyte, which can effectively isolate the electrode from direct contact with the electrolyte, prevent the oxidation of the fluorinated sulfide solid electrolyte, and promote uniform lithium ion deposition and inhibit dendrite growth. In addition, through the synergistic effect of the fluorinated sulfide solid electrolyte and its surface fluorinated layer, the ionic conductivity and electrochemical stability of the solid electrolyte can be further improved. Attached Figure Description

[0020] 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.

[0021] Figure 1 This application provides a schematic flowchart of a method for preparing a solid electrolyte. Figure 2 This application provides an SEM image of a solid electrolyte. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] On one hand, this application provides a solid electrolyte, which includes a fluorinated sulfide solid electrolyte and a fluorinated layer at least partially covering the surface of the fluorinated sulfide solid electrolyte. The chemical formula of the fluorinated sulfide solid electrolyte is Li. 7-x PS 6-x Cl x F y Where 1≤x≤1.6, 0<y≤1, and y is used to characterize the amount of fluorine doping. Thus, fluorine-doped sulfide fluoride solid electrolytes can effectively improve the bulk properties of sulfide solid electrolytes and increase their ionic conductivity. Furthermore, the fluorination layer can form a positive electrode electrolyte interface on the surface of the sulfide fluoride solid electrolyte, effectively isolating the electrode from direct contact with the electrolyte, preventing oxidation of the sulfide fluoride solid electrolyte, and promoting uniform lithium ion deposition while inhibiting dendrite growth. Therefore, through the synergistic effect of the sulfide fluoride solid electrolyte and its surface fluorination layer, the ionic conductivity and electrochemical stability of the solid electrolyte can be further improved.

[0026] In a possible implementation, the fluorinated layer includes at least one of LiF and LiCl. LiF has a wide electrochemical window, which can resist the decomposition of sulfide solid electrolytes and block electron passage, preventing lithium deposition within the electrolyte. LiCl has good ion conductivity, which is beneficial for lithium ion transport and can migrate during battery cycling, forming a smooth and uniform interface layer on the surface of the fluorinated sulfide solid electrolyte. Preferably, the fluorinated layer includes LiF and LiCl. Through the synergistic effect of LiF and LiCl, the fluorinated layer can effectively inhibit the surface oxidation of the fluorinated sulfide solid electrolyte, repair defects on the surface of the solid electrolyte, and improve surface compactness, thereby inhibiting the side reactions between the solid electrolyte and metallic lithium 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.

[0027] In a possible implementation, the thickness of the fluorinated layer is 20-200 nm; understandably, the thickness of the fluorinated layer can be any value within the range of 20-200 nm; for example, the thickness of the fluorinated layer can be 20 nm, 50 nm, 100 nm, 150 nm, 200 nm, etc. If the thickness of the fluorinated layer 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 thickness of the fluorinated layer is less than the above range, the mechanical stability of the fluorinated 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 fluorinated 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.

[0028] In a possible implementation, a fluorinated layer is coated on the surface of the fluorinated sulfide solid electrolyte, which can completely cover the surface of the fluorinated sulfide solid electrolyte, forming a stable and dense fluorinated layer on the surface of the fluorinated sulfide solid electrolyte, effectively inhibiting the oxidation of the sulfide solid electrolyte, while inhibiting the growth of lithium dendrites and improving the interface stability of the solid electrolyte.

[0029] The following describes a method for preparing a solid electrolyte according to embodiments of this application. This specification provides the method operation steps as shown in the embodiments, but based on conventional or non-inventive methods, more or fewer operation steps may be included. The order of steps listed in the embodiments is merely one possible execution order among many steps and does not represent the only possible execution order. In actual preparation, the method can be executed 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.

[0030] S1: Provides sulfide solid electrolyte and fluorinating agent.

[0031] In a possible implementation, the sulfide solid electrolyte may include a sulfide solid electrolyte of the sulfide type, which has high ionic conductivity and good deformability, which is beneficial for reducing battery internal resistance, improving rate performance, and achieving high energy density.

[0032] In a possible implementation, the fluorinating agent includes at least one of XeF2, XeF4, and XeF6. By using the above-mentioned fluorinating agent and fluorinating the sulfide solid electrolyte through a low-temperature and controllable dry preparation process, the interfacial stability of the solid electrolyte can be effectively improved under a mild preparation process, while ensuring the ionic conductivity of the solid electrolyte.

[0033] S2: The sulfide solid electrolyte and fluorinating agent are placed separately in the same reactor according to the ratio, and the reactor is subjected to low-temperature heat treatment to obtain the solid electrolyte.

[0034] Specifically, the prepared solid electrolyte includes a fluorinated sulfide solid electrolyte and a fluorinated layer that at least partially covers the surface of the fluorinated sulfide solid electrolyte. The chemical formula of the fluorinated sulfide solid electrolyte is Li. 7-x PS 6-x Cl x F y Where 1≤x≤1.6, 0<y≤1, and y is used to characterize the amount of fluorine doping. The magnitude of y depends on the content of fluorinating agent during the reaction.

[0035] Specifically, the fluorinating agent decomposes during low-temperature heat treatment to produce fluorine gas, which then reacts with the sulfide solid electrolyte in the reactor. This effectively controls the fluorine content in the reactor, thereby controlling the fluorination reaction process. Simultaneously, fluorine substitution occurs within the sulfide solid electrolyte lattice, and a fluorinated layer forms on the surface of the sulfide solid electrolyte. Compared to directly introducing fluorine gas into the reactor for fluorination, the fluorinating agent used in this embodiment is solid at room temperature. During heating, the fluorinating agent decomposes into fluorine gas, which reacts with the sulfide solid electrolyte. Therefore, the fluorine doping content can be controlled by controlling the mass of the solid fluorinating agent during preparation. Furthermore, it avoids the introduction of large amounts of fluorine gas into the reactor, which could lead to a violent fluorination reaction, preventing the simultaneous formation of fluorine doping and the fluorinated layer. Thus, the preparation method provided in this application effectively improves the controllability of the reaction. During the fluorination reaction using xenon fluoride, the byproduct is inert xenon gas, which escapes from the reaction system, preventing impurities from being generated in the reaction products.

[0036] In some embodiments, the fluorinating agent is XeF2. During low-temperature heat treatment, solid XeF2 sublimates into XeF2 gas and undergoes the following reaction: XeF2(g) → Xe(g) + F2(g). The fluorine gas produced in the reaction can react with the sulfide solid electrolyte as follows: Li 7-x PS 6-x Cl x (s)+F2(g)→P2S7(s)+LiCl(s)+LiF(s)+S(s); Li 7-x PS 6-x Cl x (s)+F2(g)→Li 7-x PS 6-x Cl x F y (s)+Cl2(g); The reaction of sulfide solid electrolytes with fluorine gas can result in fluorine substitution within the crystal lattice of the sulfide solid electrolyte, forming a fluorinated sulfide solid electrolyte, Li. 7-x PS 6-x Cl x F y Meanwhile, the reaction between sulfide solid electrolyte and fluorine gas can generate lithium fluoride, lithium chloride and nano-sized particles on the surface of sulfide solid electrolyte. As the reaction continues, lithium fluoride and lithium chloride can form a dense and stable fluoride layer.

[0037] In a possible implementation, the above-mentioned method of separately placing the sulfide solid electrolyte and the fluorinating agent in the same reactor according to a certain ratio, and performing low-temperature heat treatment on the reactor to obtain the solid electrolyte includes: placing the sulfide solid electrolyte in a first container, placing the fluorinating agent in a second container, placing the first container and the second container in the same reactor, and performing low-temperature heat treatment on the reactor to obtain the solid electrolyte. Specifically, the first container and the second container can be polytetrafluoroethylene (PTFE) pans, which can effectively isolate the sulfide solid electrolyte and the fluorinating agent.

[0038] Specifically, step S2 is carried out in a protective gas atmosphere to prevent oxidation of the raw materials during the preparation process; preferably, the protective gas may include an inert gas, including at least one of argon, nitrogen, and helium. Understandably, the type of protective gas can be selected according to actual needs and is not limited herein.

[0039] In a possible implementation, the molar ratio of the sulfide solid electrolyte to the fluorinating agent is 1-100:1; it is understood that the molar ratio of the sulfide solid electrolyte to the fluorinating agent can be any value from 1 to 100:1; for example, the molar ratio of the sulfide solid electrolyte to the fluorinating agent can be 1:1, 10:1, 20:1, 50:1, 90:1, 100:1, etc. Thus, by controlling the molar ratio of sulfide solid electrolyte and fluorinating agent within the aforementioned range, the fluorination process can be effectively controlled. This allows the fluorinating agent to undergo lattice substitution within the sulfide solid electrolyte while simultaneously forming a fluorinated layer on the surface of the fluorinated sulfide electrolyte. This avoids excessively high fluorinating agent content, which would lead to a violent fluorination reaction, complete destruction of the crystal structure of the sulfide solid electrolyte, excessively high lithium fluoride content in the product, and a sharp decrease in the ionic conductivity of the solid electrolyte. At the same time, it avoids excessively low fluorinating agent content, which would cause the fluorinating agent to react only with a portion of the sulfide solid electrolyte surface without forming a fluorinated layer or undergoing fluorine substitution within the sulfide solid electrolyte lattice.

[0040] Specifically, the fluorinated sulfide solid electrolyte Li 7-x PS 6-x Cl x F y In this context, the fluorine doping amount y depends on the molar ratio of the sulfide solid electrolyte to the fluorinating agent. Understandably, the molar ratio of the sulfide solid electrolyte to the fluorinating agent can be selected according to the fluorine doping amount required for the actual application and the thickness of the fluorinated layer. The higher the fluorinating agent content, the higher the fluorine doping amount in the fluorinated sulfide solid electrolyte and the greater the thickness of the fluorinated layer.

[0041] In a possible implementation, the temperature for low-temperature heat treatment is 50-200°C; understandably, the temperature for low-temperature heat treatment can be any value within the range of 50-200°C; for example, the temperature for low-temperature heat treatment can be 50°C, 60°C, 100°C, 150°C, 200°C, etc. Thus, controlling the temperature of the low-temperature heat treatment within the above range can promote the occurrence of the fluorination reaction and control the reaction rate, while avoiding excessively high temperatures that could lead to an overly vigorous fluorination reaction, damaging the crystal structure and ionic conductivity of the sulfide solid electrolyte.

[0042] In a possible implementation, the low-temperature heat treatment time is 1-4 hours; understandably, the low-temperature heat treatment time can be any value within the range of 1-4 hours; for example, the low-temperature heat treatment time can be 1 hour, 1.5 hours, 2 hours, 3.5 hours, 4 hours, etc. Thus, controlling the low-temperature heat treatment time within the above range ensures that the fluorination reaction proceeds fully and uniformly at a mild temperature. Understandably, the temperature and time of the low-temperature heat treatment are coordinated and can be controlled through the actual preparation process.

[0043] In a possible implementation, the preparation method further includes: providing lithium sulfide, phosphorus pentasulfide, and lithium chloride; mixing lithium sulfide, phosphorus pentasulfide, and lithium chloride in a certain proportion, grinding them to obtain a mixed powder; and heat-treating the mixed powder to obtain a sulfide solid electrolyte; specifically, the sulfide solid electrolyte can be a sulfide-germanium sulfide type solid electrolyte, and the chemical formula of the sulfide solid electrolyte is Li. 7-x PS 6-x Cl x Where 1≤x≤1.6; thus, a sulfide solid electrolyte with good ionic conductivity can be prepared, which enables the subsequently prepared solid electrolyte to have high ionic conductivity.

[0044] In a possible implementation, the molar ratio of lithium sulfide, phosphorus pentasulfide, and lithium chloride in the mixed powder is 3.8-5:1:2-3.2; it is understood that the molar ratio of lithium sulfide, phosphorus pentasulfide, and lithium chloride in the mixed powder can be any value within the range of 3.8-5:1:2-3.2; for example, the molar ratio of lithium sulfide, phosphorus pentasulfide, and lithium chloride in the mixed powder can be 3.8:1:2, 5:1:2, 3.8:1:3.2, 4:1:3, 5:1:3.2, etc. By controlling the molar ratio of lithium sulfide, phosphorus pentasulfide, and lithium chloride within the aforementioned range, a sulfide solid electrolyte with good crystal structure and ionic conductivity can be prepared. The molar ratio of lithium sulfide, phosphorus pentasulfide, and lithium chloride in the mixed powder can be selected according to the sulfide solid electrolyte and fluorinated sulfide solid electrolyte materials required for the actual application. That is, the molar ratio of lithium sulfide, phosphorus pentasulfide, and lithium chloride can be determined according to the atomic ratio of the corresponding elements in the chemical formula of the sulfide solid electrolyte to be formed. In one embodiment, the required sulfide solid electrolyte is Li6PS5Cl, and the molar ratio of lithium sulfide, phosphorus pentasulfide, and lithium chloride in the mixed powder during the preparation of the sulfide solid electrolyte is 5:1:2; in another embodiment, the required sulfide solid electrolyte is Li 5.4 PS 4.4 Cl 1.6 In the preparation of sulfide solid electrolyte, the molar ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride in the mixed powder is 3.8:1.3:3.2.

[0045] In a possible implementation, the grinding speed is 200-300 rpm; understandably, the grinding speed can be any value within 200-300 rpm; for example, the grinding speed can be 200 rpm, 220 rpm, 250 rpm, 270 rpm, 300 rpm, etc. Thus, controlling the grinding speed within the above range enables uniform mixing of the raw materials, avoiding localized aggregation of raw material particles that could lead to the formation of impurity phases; and through the grinding process at the above speed, the raw material particles are mixed while avoiding excessive particle refinement that could damage the raw materials.

[0046] In a possible implementation, the grinding time is 10-80 hours; understandably, the grinding time can be any value within the range of 10-80 hours; for example, the grinding time can be 10 hours, 20 hours, 30 hours, 50 hours, 80 hours, etc. By controlling the grinding time within the above range, the raw materials can be thoroughly ground, and the particles can be reduced to submicron to nanometer scale through continuous grinding, resulting in a suitable size for the ground mixed powder. Furthermore, mechanical energy breaks the weak chemical bonds on the surface of the raw materials, which is beneficial for subsequent reactions. This avoids excessively large and unevenly distributed particles due to too short a grinding time, while also preventing particle oxidation due to too long a grinding time.

[0047] In a possible implementation, the grinding method can be ball milling. Specifically, the above-mentioned mixing and grinding of lithium sulfide, phosphorus pentasulfide, and lithium chloride in a certain proportion to obtain a mixed powder can include: mixing lithium sulfide, phosphorus pentasulfide, and lithium chloride in a certain proportion in an argon atmosphere to obtain a mixed raw material; placing the mixed raw material into a ball mill jar, adding zirconia balls to the ball mill jar, and grinding to obtain a mixed powder. Thus, ball milling the raw material can form a mixed powder with a suitable particle size, which can fully mix and refine the raw material, optimize the particle and grain boundary structure, facilitate subsequent heat treatment to form a high-quality sulfide solid electrolyte, and help ensure the high ionic conductivity of the prepared sulfide solid electrolyte.

[0048] Specifically, the zirconia balls have a particle size of 5 mm, and the mass ratio of zirconia balls to the mixed raw materials is 10:1. This allows for thorough grinding of the mixed raw materials, and the stable properties of zirconia prevent contamination of the materials during ball milling.

[0049] In a possible implementation, the heat treatment temperature is 400-600°C; understandably, the heat treatment temperature can be any value within the range of 400-600°C; exemplaryly, the heat treatment temperature can be 400°C, 450°C, 500°C, 550°C, 600°C, etc. Thus, controlling the heat treatment temperature within the above range enables the amorphous mixed powder to undergo a crystallization transformation, promoting grain growth and structural ordering, forming a sulfide-germanium ore-type structure, thereby reducing the resistance to lithium-ion migration and achieving high ionic conductivity.

[0050] In a possible implementation, the heat treatment time is 8-16 hours; understandably, the heat treatment time can be any value within the range of 8-16 hours; for example, the heat treatment time can be 8 hours, 9 hours, 10 hours, 14 hours, 16 hours, etc. Thus, controlling the heat treatment time within the above range ensures that the reaction proceeds fully, which is beneficial for forming a well-crystallized, homogeneous silver-germanium sulfide-type structure. It avoids incomplete reaction and insufficient purity due to excessively low temperatures, resulting in low ionic conductivity, while also avoiding excessive grain growth due to excessively high temperatures, which could lead to structural defects and performance degradation.

[0051] Based on the above preparation method, the sulfide solid electrolyte and the fluorinating agent are placed separately in a reactor for low-temperature heat treatment, which can effectively control the fluorination reaction process. This allows fluorine substitution to occur within the sulfide solid electrolyte lattice while a fluorinated layer is formed on the surface of the sulfide solid electrolyte. During heating, the fluorinating agent can decompose into fluorine gas and react with the sulfide solid electrolyte. Thus, the fluorine doping content can be controlled by controlling the mass of the fluorinating agent during the preparation process. Furthermore, the introduction of a large amount of fluorine gas into the reactor can prevent the fluorination reaction from becoming too vigorous, thus preventing the simultaneous formation of fluorine doping and the fluorinated layer. In addition, the xenon gas generated during the reaction is an inert gas, which can prevent the generation of impurities in the reaction products. Therefore, the preparation method provided in this application can ensure that the prepared solid electrolyte has good performance and effectively improve 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 fluorinated 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. Supply lithium sulfide, phosphorus pentasulfide and lithium chloride; 2. Weigh lithium sulfide, phosphorus pentasulfide, and lithium chloride in an argon glove box, and mix them in a molar ratio of 3.8:1:3.2 to obtain a mixed raw material; 3. Place the mixed raw materials in a ball mill jar, add zirconia balls with a diameter of 5 mm into the ball mill jar, and the mass ratio of zirconia balls to mixed raw materials is 10:1. Perform ball milling at a speed of 300 rpm for 50 hours to obtain mixed powder. 4. The mixed powder was placed in a muffle furnace for heat treatment at a temperature of 450°C for 16 hours to obtain a sulfide solid electrolyte. 5. Provide fluorinating agent XeF2; 6. Place the sulfide solid electrolyte in a polytetrafluoroethylene (PTFE) cassette and the fluorinating agent in another PTFE cassette. Place the two cassettes in the same reactor and subject the reactor to low-temperature heat treatment in a muffle furnace at a temperature of 60°C for 2 hours to obtain the solid electrolyte.

[0055] Specifically, the solid electrolyte includes a fluorinated sulfide solid electrolyte and a fluorinated layer that at least partially covers the surface of the fluorinated sulfide 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 fluorinated layer on its surface.

[0056] Example 2 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The differences from Embodiment 1 are as follows: the molar ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride is 4:1:3; during ball milling, the ball milling speed is 300 rpm and the ball milling time is 45 h; during heat treatment, the heat treatment temperature is 475 °C and the heat treatment time is 16 h.

[0057] Example 3 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The differences from Embodiment 1 are as follows: the molar ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride is 4.2:1:2.8; during the ball milling process, the ball milling speed is 300 rpm and the ball milling time is 40 h; during the heat treatment process, the heat treatment temperature is 500℃ and the heat treatment time is 12 h.

[0058] Example 4 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The differences from Embodiment 1 are as follows: the molar ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride is 4.4:1:2.6; during ball milling, the ball milling speed is 250 rpm and the ball milling time is 30 h; during heat treatment, the heat treatment temperature is 525℃ and the heat treatment time is 10 h.

[0059] Example 5 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The differences from Embodiment 1 are as follows: the molar ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride is 4.6:1:2.4; during the ball milling process, the ball milling speed is 250 rpm and the ball milling time is 25 h; during the heat treatment process, the heat treatment temperature is 550℃ and the heat treatment time is 8 h.

[0060] Example 6 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The differences from Embodiment 1 are as follows: the molar ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride is 4.8:1:2.2; during the ball milling process, the ball milling speed is 250 rpm and the ball milling time is 20 h; during the heat treatment process, the heat treatment temperature is 550℃ and the heat treatment time is 6 h.

[0061] Example 7 This embodiment provides a solid electrolyte and its preparation method. The similarities with Embodiment 1 will not be repeated. The differences from Embodiment 1 are as follows: the molar ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride is 5:1:2; during the ball milling process, the ball milling speed is 250 rpm and the ball milling time is 10 h; during the heat treatment process, the heat treatment temperature is 550℃ and the heat treatment time is 3 h.

[0062] Example 8 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 XeF4 is used.

[0063] Example 9 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 XeF6 is used.

[0064] 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 molar ratio of the sulfide solid electrolyte to the fluorinating agent is 10:1.

[0065] 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 molar ratio of the sulfide solid electrolyte to the fluorinating agent is 1:1.

[0066] 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 temperature of the low-temperature heat treatment is 100°C.

[0067] Example 13 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 low-temperature heat treatment temperature is 200℃.

[0068] Example 14 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 low-temperature heat treatment time is 1 hour.

[0069] Example 15 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 low-temperature heat treatment time is 4 hours.

[0070] Comparative Example 1 This comparative example provides a solid electrolyte and its preparation method, specifically including the following steps: 1. In an argon glove box, lithium sulfide, phosphorus pentasulfide and lithium chloride are mixed in a molar ratio of 3.8:1:1.6 to obtain a mixed raw material; 2. Place the mixed raw materials in a ball mill jar, add zirconia balls with a diameter of 5 mm into the ball mill jar, and the mass ratio of zirconia balls to mixed raw materials is 10:1. Perform ball milling at a speed of 300 rpm for 50 hours to obtain a mixed powder. 3. The mixed powder was placed in a muffle furnace for heat treatment at a temperature of 450°C for 16 hours to obtain a sulfide solid electrolyte.

[0071] Comparative Example 2 1. In an argon glove box, lithium sulfide, phosphorus pentasulfide and lithium chloride are mixed in a molar ratio of 3.8:1:1.6 to obtain a mixed raw material; 2. Place the mixed raw materials in a grinder and grind them to obtain mixed powder; 3. The mixed powder was placed in a muffle furnace for heat treatment at a temperature of 450°C for 16 hours to obtain a sulfide solid electrolyte.

[0072] Comparative 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 the low-temperature heat treatment temperature is 30°C.

[0073] Comparative Example 4 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 low-temperature heat treatment temperature is 400℃.

[0074] Comparative Example 5 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 low-temperature heat treatment time is 30 min.

[0075] Comparative Example 6 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 low-temperature heat treatment time is 8 hours.

[0076] Electrodes were prepared using the solid electrolyte materials obtained in Examples 1-15 and Comparative Examples 1-6, 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.

[0077] 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.

[0078] 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.

[0079] Table 1 shows the ionic conductivity of the solid electrolytes prepared in Examples 1-15 and Comparative Examples 1-6, as well as the first-cycle discharge specific capacity and capacity retention of the solid batteries.

[0080] Table 1

[0081] Referring to Table 1 and Examples 1-15, the conductivity of the solid electrolytes prepared in Examples 1-15 is 7.02-8.89 mS / cm. The solid electrolytes obtained by the preparation 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 196.5-205.5 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 capacity retention rate of the solid battery after 100 cycles is 96.5%-98.5%, and the capacity retention rate after 100 cycles is 86.0%-92.3%. The solid battery has a high capacity retention rate and good structural stability.

[0082] In Comparative Examples 1-2, sulfide solid electrolytes were prepared using a dry method. Compared to Examples 1-15, the sulfide solid electrolytes in Comparative Examples 1-2 were not fluorinated and did not have a fluorinated layer on their surface. Referring to Table 1, the conductivity of the solid electrolytes provided in Comparative Examples 1-2 was 8.63 mS / cm and 7.92 mS / cm, respectively, exhibiting good ionic conductivity. This proves that the ionic conductivity of the sulfide solid electrolytes in Examples 1-15 did not change significantly after fluorination. However, the specific capacity of the solid batteries prepared from the sulfide solid electrolytes in Comparative Examples 1-2 during the first discharge cycle was 190.8 mAh. With a capacity of 186.5 mAh / g and 186.5 mAh / g, the solid-state batteries retained 90.1% and 90.6% of their capacity after 100 cycles, respectively. The capacity retention rates of the solid-state batteries after 100 cycles were 72.5% and 74.6%, respectively. It can be seen that the first-cycle discharge specific capacity and capacity retention rate of the solid-state batteries in Comparative Examples 1-2 are significantly lower than those in Examples 1-15. The unfluorinated sulfide solid electrolyte undergoes irreversible capacity loss during the first charge, resulting in a low first-cycle discharge specific capacity. The poor interfacial performance between the sulfide solid electrolyte and the cathode material leads to faster capacity decay and reduced battery life.

[0083] In Comparative Example 3, the fluorination process of the sulfide solid electrolyte involved a low-temperature heat treatment of 30°C, lower than the 60-200°C used in Examples 1-15. Comparative Example 4 used a low-temperature heat treatment of 400°C, higher than the 60-200°C used in Examples 1-15. Comparative Example 5 used a low-temperature heat treatment time of 30 min, lower than the 2-4 h used in Examples 1-15. Comparative Example 6 used a low-temperature heat treatment time of 8 h, higher than the 2-4 h used in Examples 1-15. Furthermore, the conductivity of the solid electrolytes in Comparative Examples 3-6 was 3.36-5.32 mS / cm, and the solid batteries prepared with the solid electrolytes underwent a successful first discharge. The specific capacities of the solid-state batteries were 189.2-193.8 mAh / g, and their capacity retention rates after 100 cycles were 89.5%-91.2% and 71.9%-75.5%, respectively. It can be seen that the performance of the solid-state electrolytes in Comparative Examples 3-6 is significantly lower than that of the solid-state electrolytes in Examples 1-15. This proves that the temperature and time of low-temperature heat treatment during fluorination can significantly affect the performance of the fluorinated solid-state electrolyte. If the temperature and time of low-temperature heat treatment are too low, the fluorination reaction will be incomplete, and fluorine doping and a dense fluorinated layer cannot be generated. If the time and temperature of low-temperature heat treatment are too high, the grains will grow excessively, causing structural defects and performance degradation.

[0084] In summary, within the preferred parameter range, the solid electrolytes prepared in Examples 1-15 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.

[0085] 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 fluorinated sulfide solid electrolyte and a fluorinated layer at least partially covering the surface of the fluorinated sulfide solid electrolyte, wherein the chemical formula of the fluorinated sulfide solid electrolyte is Li. 7-x PS 6-x Cl x F y , where 1≤x≤1.6, 0<y<1, and y is used to characterize the amount of fluorine doping.

2. The solid electrolyte according to claim 1, characterized in that, The fluorinated layer satisfies at least one of the following characteristics: The fluorinated layer includes at least one of LiF and LiCl; The thickness of the fluorinated layer is 20-200 nm.

3. A method for preparing a solid electrolyte, characterized in that, The method includes: Provides sulfide solid electrolytes and fluorinating agents; The sulfide solid electrolyte and the fluorinating agent are placed separately in the same reactor according to a certain ratio, and the reactor is subjected to low-temperature heat treatment to obtain the solid electrolyte; the solid electrolyte includes a fluorinated sulfide solid electrolyte and a fluorinated layer that at least partially covers the surface of the fluorinated sulfide solid electrolyte, and the chemical formula of the fluorinated sulfide solid electrolyte is Li. 7-x PS 6-x Cl x F y , where 1≤x≤1.6, 0<y≤1, and y is used to characterize the amount of fluorine doping.

4. The preparation method according to claim 3, characterized in that, The preparation method satisfies at least one of the following characteristics: The fluorinating agent includes at least one of XeF2, XeF4 and XeF6; The molar ratio of the sulfide solid electrolyte to the fluorinating agent is 1-100:

1.

5. The preparation method according to claim 3, characterized in that, The low-temperature heat treatment satisfies at least one of the following characteristics: The temperature of the low-temperature heat treatment is 50-200℃; The low-temperature heat treatment lasts for 1-4 hours.

6. The preparation method according to claim 3, characterized in that, The preparation method further includes: Lithium sulfide, phosphorus pentasulfide and lithium chloride are available; The lithium sulfide, phosphorus pentasulfide, and lithium chloride are mixed in a certain proportion and ground to obtain a mixed powder. The mixed powder is heat-treated to obtain the sulfide solid electrolyte; the chemical formula of the sulfide solid electrolyte is Li. 7-x PS 6-x Cl x .

7. The preparation method according to claim 6, characterized in that, The molar ratio of lithium sulfide, phosphorus pentasulfide and lithium chloride in the mixed powder is 3.8-5:1:2-3.

2.

8. The preparation method according to claim 6, characterized in that, The grinding process satisfies at least one of the following characteristics: The grinding speed is 200-300 rpm; The grinding time is 10-80 hours.

9. The preparation method according to claim 6, characterized in that, The heat treatment satisfies at least one of the following characteristics: The heat treatment temperature is 400-600℃; The heat treatment time is 8-16 hours.

10. A solid-state battery, characterized in that, Includes the solid electrolyte as described in any one of claims 1 or 2.

Images