Modified inorganic solid electrolyte and preparation method thereof, battery pole piece and all-solid-state lithium ion battery

Abstract

The invention provides a modified inorganic solid electrolyte and a preparation method thereof, a battery pole piece and an all-solid-state lithium ion battery, and belongs to the technical field of all-solid-state lithium ion battery manufacturing. The modified inorganic solid-state electrolyte is of a core-shell structure, the core is made of inorganic solid-state electrolyte, the shell is made of graphite, and the problems that the inorganic solid-state electrolyte is poor in air stability and prone to side reaction after being in direct contact with an active material can be effectively solved through the modified inorganic solid-state electrolyte; therefore, the corresponding all-solid-state lithium ion battery has relatively excellent cycle performance.

Description

Technical Field

[0001] The present application relates to the technical field of all-solid-state lithium-ion battery manufacturing, and specifically to a modified inorganic solid electrolyte and a preparation method thereof, a battery pole piece, and an all-solid-state lithium-ion battery. Background Art

[0002] In existing technologies, all-solid-state electrolytes have received widespread attention due to their advantages such as high safety, high energy density, long cycle life, and a wide temperature range of application. However, inorganic solid electrolytes in all-solid-state electrolytes still have some problems in their application. For example, sulfide solid electrolytes and halide solid electrolytes in inorganic solid electrolytes have poor air stability and are prone to side reactions after direct contact with active materials, which in turn leads to poor cycle performance of the corresponding batteries. Summary of the Invention

[0003] The purpose of this application is to provide a modified inorganic solid electrolyte and its preparation method, battery electrode and all-solid-state lithium-ion battery, which can effectively improve the problems of poor air stability of inorganic solid electrolytes and the easy occurrence of side reactions after direct contact with active materials, so that the corresponding all-solid-state lithium-ion battery has relatively excellent cycle performance.

[0004] The embodiment of the present application is implemented as follows: In a first aspect, an embodiment of the present application provides a modified inorganic solid electrolyte, which has a core-shell structure, wherein the inner core is made of an inorganic solid electrolyte and the outer shell is made of graphite.

[0005] In the above technical solution, the surface of the inorganic solid electrolyte core material has a graphite shell. Compared with inorganic solid electrolytes, graphite has more ideal air stability. In addition, graphite has a regular crystalline layered structure (compared with amorphous carbon, graphite has higher ionic conductivity). After the inorganic solid electrolyte is coated with graphite, on the one hand, the air stability of the inorganic solid electrolyte can be effectively improved while also ensuring that the coated solid electrolyte still has relatively ideal ionic conductivity. On the other hand, the coating and isolation of the inorganic solid electrolyte by the graphite shell can also improve the problem of side reactions that are prone to occur after the inorganic solid electrolyte directly contacts the active material (specifically, when a sulfide solid electrolyte directly contacts the active material, especially a high-voltage positive electrode and a lithium metal negative electrode, harmful interfacial side reactions are very likely to occur; when a halide solid electrolyte directly contacts lithium metal, the metal elements in its structure are easily reduced to form metal elements, resulting in its own structure being destroyed. When it is in direct contact with a high-voltage positive electrode, redox side reactions are easily generated during the charge and discharge process, resulting in the destruction of the structural integrity of the positive electrode), thereby enabling the corresponding all-solid-state lithium-ion battery to have relatively excellent cycle performance. In addition, graphite is often used as a negative electrode material and has a certain lithium storage function. Applying the inorganic solid electrolyte coated on it in the negative electrode can also make the corresponding battery have a more ideal energy density.

[0006] In some optional embodiments, the shell has a thickness of 10 to 1000 nm.

[0007] In the above technical solution, the thickness of the shell is limited to a relatively suitable range, which can better take into account the air stability and ionic conductivity of the modified inorganic solid electrolyte.

[0008] In some alternative embodiments, the shell has a thickness of 50-300 nm.

[0009] In the above technical solution, limiting the thickness of the shell to a more appropriate range can better balance the air stability and ionic conductivity of the modified inorganic solid electrolyte.

[0010] In some optional embodiments, the inorganic solid electrolyte is selected from at least one of a sulfide solid electrolyte and a halide solid electrolyte.

[0011] In the above technical solution, the coating layer provided in the embodiment of the present application can be well adapted to sulfide solid electrolytes and halide solid electrolytes.

[0012] In some optional embodiments, the inorganic solid electrolyte is a sulfide solid electrolyte, and the material of the sulfide solid electrolyte is Li6PS5Cl; or / and, the inorganic solid electrolyte is a halide solid electrolyte, and the material of the halide solid electrolyte is Li3InCl6.

[0013] In the above technical solution, the coating layer provided in the embodiment of the present application can be well adapted to Li6PS5Cl and Li3InCl6.

[0014] In a second aspect, the present application provides a method for preparing a modified inorganic solid electrolyte as provided in the first aspect, comprising the following steps: An inorganic solid electrolyte, a graphite precursor and an organic solvent are ball-milled to obtain a mixture; the mixture is dried to remove the organic solvent in the mixture to obtain a sintered precursor; and the sintered precursor is sintered to graphitize the graphite precursor coated on the surface of the inorganic solid electrolyte to obtain a modified inorganic solid electrolyte with a core-shell structure.

[0015] In the above technical solution, a graphite shell is formed on the surface of the inorganic solid electrolyte by wet ball milling combined with sintering, so that the prepared shell has the advantages of relatively uniform thickness, high density and high coverage rate of the core.

[0016] In some optional embodiments, in the mixture, the ratio of the sum of the mass of the inorganic solid electrolyte and the graphite precursor to the mass of the organic solvent is (2-10):1.

[0017] In the above technical solution, the mass ratio of the solid phase to the liquid phase in the mixture is limited to the above range so that the mixture contains a relatively appropriate amount of organic solvent. The appropriate amount of organic solvent helps to improve the fluidity of the mixture, reduce the friction resistance between the solid particles, and make the material easier to flow and disperse during the ball milling process, thereby allowing the graphite precursor to be more completely and evenly coated on the surface of the core.

[0018] In some optional embodiments, the mass ratio of the inorganic solid electrolyte to the graphite precursor is 100:(0.1~50); optionally, the mass ratio of the inorganic solid electrolyte to the graphite precursor is 100:(5~10).

[0019] In the above technical solution, the mass ratio of the inorganic solid electrolyte and the graphite precursor is limited to a more suitable range, so that the formed graphite shell has a more suitable thickness, thereby being able to better take into account the air stability and ionic conductivity of the modified inorganic solid electrolyte; further, the mass ratio of the inorganic solid electrolyte and the graphite precursor is limited to an even more suitable range, so that the formed graphite shell has a more suitable thickness, thereby being able to better take into account the air stability and ionic conductivity of the modified inorganic solid electrolyte.

[0020] In some optional embodiments, the ball milling mixing step includes: first premixing at a first speed, and then mixing at a second speed, wherein the first speed is less than the second speed; optionally, in the step of premixing at the first speed, the processing speed is 30~60 rpm, and the processing time is 3~8 min; optionally, in the step of mixing at the second speed, the processing speed is 500~800 rpm, and the processing time is 20~30 min.

[0021] In the above technical solution, during the ball milling mixing process, premixing is first carried out at a low speed and then mixing is carried out at a high speed, and the processing speed and time of the premixing stage and the mixing stage are respectively limited to the above ranges, which helps to improve the mixing uniformity of the inorganic solid electrolyte and the graphite precursor, thereby allowing the graphite precursor to be more completely and evenly coated on the surface of the core.

[0022] In some optional embodiments, the sintering treatment step includes: pre-sintering at a first temperature, and then sintering at a second temperature, wherein the first temperature is lower than the second temperature; optionally, in the step of pre-sintering at the first temperature, the treatment temperature is 500~1000℃, and the treatment time is 1~3 h; optionally, in the step of sintering at the second temperature, the treatment temperature is 1500~4000℃, and the treatment time is 2~10 h.

[0023] In the above technical solution, during the sintering process, pre-sintering is first carried out at a low temperature and then sintering is carried out at a high temperature, and the processing temperature and time of the pre-sintering and sintering stages are respectively limited to the above ranges; wherein, pre-sintering under the above temperature and time conditions, on the one hand, can preliminarily remove non-carbon elements (such as nitrogen, hydrogen, oxygen, etc.) in the graphite precursor, thereby reducing the interference of impurities in the graphitization process, and on the other hand, can also enable the graphite precursor to form a carbon-rich chaotic layer structure, thereby facilitating subsequent graphitization at a high temperature; sintering under the above temperature and time conditions can make the chaotic layer structure graphite more easily and thoroughly converted into a three-dimensional ordered graphite structure (i.e., a graphite shell with a three-dimensional layered structure); through the joint action of the two stages, the graphitization degree and efficiency of the graphite precursor can be improved, thereby making the prepared modified inorganic solid electrolyte have a more ideal air stability.

[0024] In some optional embodiments, the organic solvent is selected from at least one of xylene, petroleum ether, decane, heptane and dodecane; or / and the graphite precursor is selected from at least one of asphalt coke, biomass material, petroleum coke, needle coke and asphalt coal.

[0025] In the above technical solution, the above organic solvent is not easy to react with the inorganic solid electrolyte, so that the mixture system has higher chemical stability; at the same time, the boiling point of the above organic solvent is low, which is convenient for subsequent removal in the drying step; in addition, the embodiments of the present application are applicable to a wide variety of graphite precursors, and more feasible implementation plans can be provided, thereby facilitating the promotion and application of the technical solution provided in the embodiments of the present application.

[0026] In a third aspect, an embodiment of the present application provides a battery electrode, comprising the modified inorganic solid electrolyte provided in the embodiment of the first aspect.

[0027] In the above technical solution, the battery electrode includes the modified inorganic solid electrolyte provided by the first embodiment. Since the modified inorganic solid electrolyte has relatively ideal air stability and relatively suitable ionic conductivity, and it is not easy to cause side reactions after direct contact with the active material, the corresponding battery electrode has relatively excellent cycle performance.

[0028] In a fourth aspect, an embodiment of the present application provides an all-solid-state lithium-ion battery, comprising the battery electrode provided in the embodiment of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 This is a process flow chart of a method for preparing a modified inorganic solid electrolyte provided in an embodiment of the present application. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0032] It should be noted that “and / or” in this application, such as “Feature 1 and / or Feature 2”, refers to three situations: “Feature 1” alone, “Feature 2” alone, or “Feature 1” plus “Feature 2”.

[0033] In addition, in the description of this application, unless otherwise specified, the "multiple" in "one or more" means two or more; the range of "value a~value b" includes the two end values ​​"a" and "b", and the "unit of measurement" in "value a~value b+unit of measurement" represents the "unit of measurement" of both "value a" and "value b".

[0034] In the prior art, a common modification method for inorganic solid electrolytes is to provide a coating layer on their surface to address the problems of poor air stability and the susceptibility to side reactions after direct contact with active materials. For example, in patent CN111403806A, a carbon shell (i.e., an amorphous carbon coating) is provided outside the core of the solid electrolyte. Although this can solve the problems of poor air stability and the susceptibility to side reactions after direct contact with active materials of inorganic solid electrolytes to a certain extent, it also brings some new problems, specifically the following: (1) Amorphous carbon-coated inorganic solid electrolytes (such as sulfide solid electrolytes) are easily decomposed under the catalytic action of electricity, resulting in a sharp decrease in the cycle performance of the corresponding battery.

[0035] (2) The ionic conductivity of amorphous carbon is low, which leads to a significant decrease in the ionic conductivity of the electrolyte after coating, thereby affecting the performance of the corresponding battery.

[0036] Therefore, when using coating methods to solve the problems of poor air stability of inorganic solid electrolytes and the easy occurrence of side reactions after direct contact with active materials, the material selection of the coating layer is particularly important. In addition to solving the defects of inorganic solid electrolytes, the ideal coating layer material should not introduce new problems.

[0037] Based on this, the inventors discovered through research that the innovative use of graphite with a three-dimensional layered structure as a coating layer can not only solve the problems of poor air stability of inorganic solid electrolytes and the susceptibility to side reactions after direct contact with active materials, but also has the following advantages compared to using amorphous carbon as a coating layer: (1) Graphite with a three-dimensional layered structure does not have a catalytic effect and will not cause inorganic solid electrolytes (such as sulfide solid electrolytes) to be catalytically decomposed during use.

[0038] (2) Graphite has a regular crystalline layered structure. Compared with amorphous carbon, graphite has higher ionic conductivity. Using graphite as a coating layer for the electrolyte will not significantly reduce the ionic conductivity of the electrolyte.

[0039] (3) Graphite is often used as a negative electrode material and has a certain lithium storage function. When the inorganic solid electrolyte coated on graphite is used in the negative electrode, the corresponding battery can also have a more ideal energy density.

[0040] The following is a detailed description of a modified inorganic solid electrolyte, a preparation method thereof, a battery electrode, and an all-solid-state lithium-ion battery according to an embodiment of the present application.

[0041] In a first aspect, an embodiment of the present application provides a modified inorganic solid electrolyte, which has a core-shell structure, wherein the inner core is made of an inorganic solid electrolyte and the outer shell is made of graphite.

[0042] In the present application, the surface of the inorganic solid electrolyte core material has a shell of graphite material. Compared with inorganic solid electrolytes, graphite has more ideal air stability. In addition, graphite has a regular crystalline layered structure (compared with amorphous carbon, graphite has higher ionic conductivity). After using graphite to coat the inorganic solid electrolyte, on the one hand, the air stability of the inorganic solid electrolyte can be effectively improved and the coated solid electrolyte still has a relatively ideal ionic conductivity; on the other hand, the graphite shell coats and isolates the inorganic solid electrolyte, and can also improve the problem of side reactions that are prone to occur after direct contact between the inorganic solid electrolyte and the active material (specifically, after direct contact between the sulfide solid electrolyte and the active material, especially the high-voltage positive electrode and the lithium metal negative electrode, harmful interfacial side reactions are very likely to occur; after direct contact between the halide solid electrolyte and lithium metal, the metal elements in its structure are easily reduced to form metal elements, causing its own structure to be destroyed. After direct contact with the high-voltage positive electrode, redox side reactions are easily caused during the charge and discharge process, causing the integrity of the positive electrode structure to be destroyed), thereby making the corresponding all-solid-state lithium-ion battery have relatively excellent cycle performance. In addition, graphite is often used as a negative electrode material and has a certain lithium storage function. Applying the inorganic solid electrolyte coated on it in the negative electrode can also make the corresponding battery have a more ideal energy density.

[0043] It should be noted that the thickness of the shell is not limited and can be adaptively adjusted according to actual needs.

[0044] As an example, the thickness of the shell is 10-1000 nm, such as but not limited to any one of 10 nm, 50 nm, 100 nm, 200 nm, 400 nm, 600 nm, 800 nm and 1000 nm, or a range between any two of the thicknesses.

[0045] In this embodiment, the thickness of the outer shell is limited to a relatively suitable range, which can better take into account the air stability and ionic conductivity of the modified inorganic solid electrolyte.

[0046] As an example, the thickness of the shell is 50~300 nm, such as but not limited to the thickness of any one of 50 nm, 80 nm, 100 nm, 140 nm, 180 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm and 300 nm, or a range between any two of them.

[0047] In this embodiment, the thickness of the shell is limited to a more suitable range, which can better balance the air stability and ionic conductivity of the modified inorganic solid electrolyte.

[0048] As an example, the inorganic solid electrolyte is selected from at least one of a sulfide solid electrolyte and a halide solid electrolyte.

[0049] In this embodiment, the coating layer provided in the embodiment of the present application can be well adapted to the sulfide solid electrolyte and the halide solid electrolyte.

[0050] It should be noted that the specific types of inorganic solid electrolytes and halide solid electrolytes are not limited and can be set according to conventional selection in the field. For example, sulfide solid electrolytes are selected from Li3PS4, Li 10 GeP2S 12 , at least one of Li6PS5Br, Li6PS5I and Li6PS5Cl; for example, the halide solid electrolyte is selected from at least one of Li3InCl6, Li3ScCl6, Li2ZrCl6 and Li3YCl6.

[0051] As an example, the inorganic solid electrolyte is a sulfide solid electrolyte, and the material of the sulfide solid electrolyte is Li6PS5Cl; or / and, the inorganic solid electrolyte is a halide solid electrolyte, and the material of the halide solid electrolyte is Li3InCl6.

[0052] In this embodiment, the coating layer provided in the embodiment of the present application can be well adapted to Li6PS5Cl and Li3InCl6.

[0053] It should be noted that any structural or functional units not specifically described or limited in the modified inorganic solid electrolyte may be arranged according to conventional selections in the art.

[0054] In a second aspect, the present application provides a method for preparing a modified inorganic solid electrolyte as provided in the first aspect, comprising the following steps: An inorganic solid electrolyte, a graphite precursor and an organic solvent are ball-milled to obtain a mixture; the mixture is dried to remove the organic solvent in the mixture to obtain a sintered precursor; and the sintered precursor is sintered to graphitize the graphite precursor coated on the surface of the inorganic solid electrolyte to obtain a modified inorganic solid electrolyte with a core-shell structure.

[0055] It should be noted that during the ball milling mixing process, the organic solvent cannot react with the inorganic solid electrolyte.

[0056] In this application, a wet ball milling combined with sintering process is used to form a graphite shell on the surface of the inorganic solid electrolyte, so that the prepared shell has the advantages of relatively uniform thickness, high density and high coverage of the core.

[0057] As an example, in the mixture, the ratio of the sum of the masses of the inorganic solid electrolyte and the graphite precursor to the mass of the organic solvent is (2~10):1, for example, but not limited to, the mass ratio is any one of 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 and 10:1 or a range between any two of them.

[0058] In this embodiment, the mass ratio of the solid phase and the liquid phase in the mixture is limited to the above range so that the mixture contains a relatively appropriate amount of organic solvent. The appropriate amount of organic solvent helps to improve the fluidity of the mixture, reduce the friction resistance between the solid particles, and make the material easier to flow and disperse during the ball milling process, thereby allowing the graphite precursor to be more completely and evenly coated on the surface of the core.

[0059] As an example, the mass ratio of the inorganic solid electrolyte and the graphite precursor is 100:(0.1~50), for example, but not limited to, the mass ratio is any one of 100:0.1, 100:0.5, 100:1, 100:5, 100:10, 100:20, 100:30, 100:40 and 100:50 or a range value between any two of them.

[0060] In this embodiment, the mass ratio of the inorganic solid electrolyte to the graphite precursor is limited to a relatively suitable range so that the formed graphite shell has a relatively suitable thickness, thereby better balancing the air stability and ionic conductivity of the modified inorganic solid electrolyte.

[0061] As an example, the mass ratio of the inorganic solid electrolyte and the graphite precursor is 100:(5~10), for example, but not limited to, the mass ratio is any one of 100:5, 100:6, 100:7, 100:8, 100:9 and 100:10 or a range value between any two of them.

[0062] In this embodiment, the mass ratio of the inorganic solid electrolyte to the graphite precursor is limited to a more suitable range, so that the formed graphite shell has a more suitable thickness, thereby better balancing the air stability and ionic conductivity of the modified inorganic solid electrolyte.

[0063] As an example, the ball milling mixing step includes: premixing at a first rotational speed, and then mixing at a second rotational speed, wherein the first rotational speed is lower than the second rotational speed.

[0064] As an example, in the step of premixing at a first speed, the processing speed is 30-60 rpm, for example, but not limited to, any one of 30 rpm, 40 rpm, 50 rpm and 60 rpm, or a range between any two of them; the processing time is 3-8 min, for example, but not limited to, any one of 3 min, 4 min, 5 min, 6 min, 7 min and 8 min, or a range between any two of them.

[0065] As an example, in the step of mixing at the second speed, the processing speed is 500-800 rpm, for example, but not limited to, any one of 500 rpm, 600 rpm, 700 rpm and 800 rpm, or a range between any two of them; the processing time is 20-30 min, for example, but not limited to, any one of 20 min, 22 min, 24 min, 26 min, 28 min and 30 min, or a range between any two of them.

[0066] In this embodiment, during the ball milling mixing process, premixing is first performed at a low speed and then mixing is performed at a high speed, and the processing speed and time of the premixing stage and the mixing stage are respectively limited to the above ranges, which helps to improve the mixing uniformity of the inorganic solid electrolyte and the graphite precursor, thereby allowing the graphite precursor to be more completely and evenly coated on the surface of the core.

[0067] As an example, the sintering process includes: pre-sintering at a first temperature, and then sintering at a second temperature, wherein the first temperature is lower than the second temperature.

[0068] In the step of pre-sintering at the first temperature, the processing temperature is 500~1000℃, for example but not limited to the processing temperature of any one point value of 500℃, 600℃, 700℃, 800℃, 900℃ and 1000℃, or the range value between any two of them; the processing time is 1~3 h, for example but not limited to the processing time of any one point value of 1 h, 1.5 h, 2 h, 2.5 h and 3 h, or the range value between any two of them.

[0069] As an example, in the step of sintering at the second temperature, the processing temperature is 1500~4000℃, for example but not limited to the processing temperature of any one point value among 1500℃, 2000℃, 2500℃, 3000℃, 3500℃ and 4000℃, or the range value between any two of them; the processing time is 2~10 h, for example but not limited to the processing time of any one point value among 2 h, 4 h, 6 h, 8 h and 10 h, or the range value between any two of them.

[0070] In this embodiment, during the sintering process, pre-sintering is first performed at a low temperature and then sintering is performed at a high temperature, and the processing temperature and time of the pre-sintering and sintering stages are respectively limited to the above-mentioned ranges; wherein, pre-sintering is performed under the above-mentioned temperature and time conditions, on the one hand, non-carbon elements (such as nitrogen, hydrogen, oxygen, etc.) in the graphite precursor can be preliminarily removed to reduce the interference of impurities in the graphitization process, and on the other hand, the graphite precursor can be made to form a carbon-rich chaotic layer structure; sintering under the above-mentioned temperature and time conditions can make the chaotic layer structure graphite more easily and thoroughly converted into a three-dimensional ordered graphite structure (i.e., a graphite shell with a three-dimensional layered structure); through the joint action of the two stages, the graphitization degree and efficiency of the graphite precursor can be improved, thereby making the prepared modified inorganic solid electrolyte have a more ideal air stability.

[0071] As an example, the organic solvent is selected from at least one of xylene, petroleum ether, decane, heptane and dodecane.

[0072] In this embodiment, the organic solvent does not easily react with the inorganic solid electrolyte, so that the mixture system has high chemical stability; at the same time, the boiling point of the organic solvent is low, which facilitates its removal in the subsequent drying step.

[0073] As an example, the graphite precursor is selected from at least one of pitch coke, biomass material, petroleum coke, needle coke and bituminous coal.

[0074] In this embodiment, the embodiments of the present application are applicable to a wide variety of graphite precursors, and a wide variety of feasible implementation plans can be provided, thereby facilitating the promotion and application of the technical solutions provided in the embodiments of the present application.

[0075] It should be noted that the type of biomass material is not limited and can be selected according to conventional methods in the art, for example, it can be at least one of lignin and cellulose.

[0076] It should be noted that any process or step not specifically described or limited in the preparation process may be arranged according to conventional selection in the art.

[0077] As an example, after the sintering step is completed, the sintered product is further subjected to the steps of grinding, grading, demagnetizing and screening in sequence.

[0078] As an example, the steps of ball milling, drying and sintering are all performed under an inert atmosphere.

[0079] It should be noted that the type of inert atmosphere is not limited, and it can be nitrogen and / or argon, for example.

[0080] As an example, the process flow chart of the preparation method of the modified inorganic solid electrolyte is shown in FIG. Figure 1 .

[0081] In a third aspect, an embodiment of the present application provides a battery electrode, comprising the modified inorganic solid electrolyte provided in the embodiment of the first aspect.

[0082] In the present application, the battery electrode includes the modified inorganic solid electrolyte provided in the first embodiment. Since the modified inorganic solid electrolyte has relatively ideal air stability and relatively suitable ionic conductivity, and it is not easy to cause side reactions after direct contact with the active material, the corresponding battery electrode has relatively excellent cycle performance.

[0083] It should be noted that the type of electrode plate is not limited, for example, it can be a positive electrode plate or a negative electrode plate.

[0084] It should be noted that the specific composition of the positive electrode sheet and the negative electrode sheet is not limited and can be set according to conventional selection in the field.

[0085] As an example, the positive electrode sheet includes NCM622 (positive electrode active material), super-P (conductive agent), CNT (conductive agent), Li6PS5Cl (sulfide solid electrolyte) and PVDF (binder) in a mass ratio of 87:1.5:0.3:10:1.2; the negative electrode sheet includes graphite (negative electrode active material), conductive carbon black (conductive agent), Li6PS5Cl (sulfide solid electrolyte) carboxymethyl cellulose, sodium cellulose (binder) and styrene-butadiene rubber (binder) in a mass ratio of 85.6:2:10:1.2:2.2.

[0086] In other possible implementations, Li6PS5Cl (sulfide solid electrolyte) can be completely replaced with Li3InCl6 (halide solid electrolyte); similarly, the types and amounts of other functional components in the positive and negative electrodes can also be adaptively adjusted.

[0087] It should be noted that the solid electrolytes of the positive electrode sheet and the negative electrode sheet can be either one of them using the modified solid electrolyte provided in the embodiment of the present application, or both of them using the modified solid electrolyte provided in the embodiment of the present application, and specific adaptive adjustments can be made according to actual needs.

[0088] In a fourth aspect, an embodiment of the present application provides an all-solid-state lithium-ion battery, comprising the battery electrode provided in the embodiment of the third aspect.

[0089] It should be noted that each functional unit in the all-solid-state lithium-ion battery can be configured according to conventional selections in the art and is not specifically limited in the embodiments of the present application.

[0090] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0091] Example 1 The present invention provides a method for preparing an all-solid-state lithium-ion battery, comprising the following steps: (1) Preparation of modified inorganic solid electrolytes S1: 1 kg of Li6PS5Cl, 0.1 kg of pitch coke, and 0.5 kg of petroleum ether were added to a ball mill under a nitrogen atmosphere, premixed at 50 rpm for 5 min, and then mixed at 600 rpm for 25 min to obtain a mixture.

[0092] S2 The mixture was placed in an oven under a nitrogen atmosphere at 100 °C for 1 h to remove petroleum ether from the mixture.

[0093] S3 The dried mixture is transferred to a mullite sagger, and then the sagger containing the mixture is transferred to a sintering furnace filled with a nitrogen atmosphere. It is first pre-sintered at 800°C for 8 hours and then sintered at 3500°C for 4 hours to graphitize the graphite precursor coated on the surface of the inorganic solid electrolyte. The sintered product is then ground, graded, demagnetized and sieved in sequence to obtain a modified inorganic solid electrolyte with a core-shell structure, wherein the thickness of the graphite shell is 94 nm.

[0094] (2) Preparation of all-solid-state lithium-ion batteries Preparation of positive electrode sheet: NCM622 (positive electrode active material), super-P (conductive agent), CNT (conductive agent), the coated sulfide solid electrolyte prepared in step (1) and PVDF (binder) were stirred and mixed with N-methylpyrrolidone (NMP) in a vacuum mixer in a mass ratio of 87:1.5:0.3:10:1.2 to obtain positive electrode sheet slurry; the positive electrode sheet slurry was evenly coated on both sides of the aluminum foil (thickness 13 μm) current collector, and the positive electrode sheet was obtained after drying, cold pressing and die-cutting.

[0095] Negative electrode sheet preparation: Graphite (negative electrode active material), conductive carbon black (conductive agent), Li6PS5Cl (uncoated sulfide solid electrolyte), sodium carboxymethyl cellulose (binder), and styrene-butadiene rubber (binder) were mixed with deionized water in a vacuum mixer in a mass ratio of 85.6:2:10:1.2:2.2 to obtain a negative electrode sheet slurry. The negative electrode sheet slurry was evenly coated on both sides of a copper foil (8 μm thickness) current collector, and the negative electrode sheet was obtained after drying, cold pressing, and die-cutting.

[0096] A 20 μm-thick sulfide solid electrolyte membrane (composed of Li6PS5Cl and a binder in a mass ratio of 98:2) was placed between the positive and negative electrode sheets, and a bare cell was prepared by stacking the sheets. The bare cell was then placed in a packaging bag made of an aluminum-plastic film composite material and packaged to obtain a dry cell. The dry cell was baked to remove water to reduce the water content to less than 250 ppm. The dry cell then underwent isostatic pressing, sealing, standing, formation, degassing packaging, and capacity division to obtain a soft-pack all-solid-state lithium-ion battery.

[0097] Example 2 The embodiment of the present application provides a method for preparing an all-solid-state lithium-ion battery, which differs from Example 1 only in that all the asphalt coke is replaced by petroleum coke, and the thickness of the graphite shell is 106 nm.

[0098] Example 3 The embodiment of the present application provides a method for preparing an all-solid-state lithium-ion battery, which differs from Example 1 only in that all the pitch coke is replaced by needle coke, and the thickness of the graphite shell is 88 nm.

[0099] Comparative Example 1 The comparative example of the present application provides a method for preparing an all-solid-state lithium-ion battery, which differs from Example 1 only in that: in step (1), no graphite coating layer is formed on the surface of Li6PS5Cl, that is, there is no graphite shell on the surface of Li6PS5Cl in the positive electrode sheet.

[0100] Comparative Example 2 The comparative example of the present application provides a method for preparing an all-solid-state lithium-ion battery, which differs from Example 1 only in that: Step (I), S3: transferring the dried mixture to a mullite sagger, then transferring the sagger containing the mixture to a sintering furnace filled with a nitrogen atmosphere, sintering at 800°C for 12 h, and then grinding, grading, demagnetizing and sieving the sintered product in sequence to obtain a modified inorganic solid electrolyte with a core-shell structure, wherein the thickness of the shell layer is 116 nm.

[0101] Example 4 The present invention provides a method for preparing an all-solid-state lithium-ion battery, comprising the following steps: (1) Preparation of modified inorganic solid electrolytes S1 Li3InCl61 kg, pitch coke 0.1 kg, and petroleum ether 0.5 kg were added to a ball mill under nitrogen atmosphere, premixed at 50 rpm for 5 min, and then mixed at 600 rpm for 25 min to obtain a mixture.

[0102] S2 The mixture was placed in an oven under a nitrogen atmosphere at 100 °C for 1 h to remove petroleum ether from the mixture.

[0103] S3 The dried mixture is transferred to a mullite sagger, and then the sagger containing the mixture is transferred to a sintering furnace filled with a nitrogen atmosphere. It is first pre-sintered at 800°C for 8 hours and then sintered at 3500°C for 4 hours to graphitize the graphite precursor coated on the surface of the inorganic solid electrolyte. The sintered product is then ground, graded, demagnetized and sieved in sequence to obtain a modified inorganic solid electrolyte with a core-shell structure, wherein the thickness of the graphite shell is 96 nm.

[0104] (2) Preparation of all-solid-state lithium-ion batteries Preparation of positive electrode sheet: NCM622 (positive electrode active material), super-P (conductive agent), CNT (conductive agent), Li3InCl6 (uncoated halide solid electrolyte) and PVDF (binder) were stirred and mixed with N-methylpyrrolidone (NMP) in a vacuum mixer in a mass ratio of 87:1.5:0.3:10:1.2 to obtain positive electrode sheet slurry; the positive electrode sheet slurry was evenly coated on both sides of the aluminum foil (thickness 13 μm) current collector, and the positive electrode sheet was obtained after drying, cold pressing and die-cutting.

[0105] Preparation of negative electrode sheet: Graphite (negative electrode active material), conductive carbon black (conductive agent), the coated halide solid electrolyte prepared in step (1), sodium carboxymethyl cellulose (binder), and styrene-butadiene rubber (binder) are mixed uniformly with deionized water in a vacuum mixer in a mass ratio of 85.6:2:10:1.2:2.2 to obtain a negative electrode sheet slurry; the negative electrode sheet slurry is evenly coated on both sides of a copper foil (thickness 8 μm) current collector, and the negative electrode sheet is obtained after drying, cold pressing, and die-cutting.

[0106] A 20 μm thick sulfide solid electrolyte membrane (composed of Li3InCl6 and a binder in a mass ratio of 98:2) was placed between the positive and negative electrode sheets, and a bare cell was prepared by stacking the sheets. A packaging bag was made of an aluminum-plastic film composite material, and the bare cell was placed in the packaging bag and packaged to obtain a dry cell. The dry cell was baked to remove water to reduce the water content to less than 250 ppm. Then, the dry cell was subjected to isostatic pressing, sealing, standing, formation, degassing packaging, and capacity division to obtain a soft-pack all-solid-state lithium-ion battery.

[0107] Example 5 This embodiment of the present application provides a method for preparing an all-solid-state lithium-ion battery, which differs from Example 4 only in that all the asphalt coke is replaced by petroleum coke, and the thickness of the graphite shell is 102 nm.

[0108] Example 6 This embodiment of the present application provides a method for preparing an all-solid-state lithium-ion battery, which differs from Example 4 only in that all pitch coke is replaced by needle coke, and the thickness of the graphite shell is 90 nm.

[0109] Comparative Example 3 The comparative example of the present application provides a method for preparing an all-solid-state lithium-ion battery, which differs from Example 4 only in that: in step (1), no graphite coating layer is formed on the surface of Li3InCl6, that is, there is no graphite shell on the surface of Li3InCl6 in the negative electrode sheet.

[0110] Comparative Example 4 The comparative example of the present application provides a method for preparing an all-solid-state lithium-ion battery, which differs from Example 4 only in that: Step (I), S3: transferring the dried mixture to a mullite sagger, then transferring the sagger containing the mixture to a sintering furnace filled with a nitrogen atmosphere, sintering at 800°C for 12 h, and then grinding, grading, demagnetizing and sieving the sintered product in sequence to obtain a modified inorganic solid electrolyte with a core-shell structure, wherein the thickness of the shell layer is 120 nm. Test Example 1. Air stability test of solid electrolyte Examples 1-3 and Comparative Examples 1-2, as well as Examples 4-6 and Comparative Examples 3-4, were divided into two groups according to the solid electrolyte material. The air stability of the solid electrolyte samples prepared in step (1) was then tested respectively, and the test results were statistically summarized in Table 1.

[0111] The test steps for air stability are as follows: The lithium ion conductivity of the solid electrolyte powder was tested before and after being exposed to moisture with a relative humidity of 5% for 24 hours, and the retention rate of the lithium ion conductivity was calculated.

[0112] Table 1

[0113] It should be noted that in Table 1, the ionic conductivity retention rate of Comparative Example 1 and Comparative Example 3 is 0. This is because there is no coating layer on the internal surface of the solid electrolyte, and the reaction activity of the material is high, resulting in severe decomposition of the material after exposure to moisture with a relative humidity of 5% for 24 hours.

[0114] Referring to Table 1, the test results of Examples 1 to 3 and Comparative Example 1, and Examples 4 to 6 and Comparative Example 3 show that the provision of a graphite shell outside the inner core of the inorganic solid electrolyte is more stable in the air than that without a shell, i.e., it has better air stability. Moreover, the electrolyte after coating still has relatively excellent lithium ion conductivity.

[0115] Referring to Table 1, the test results of Examples 1-3 and Comparative Example 2, and Examples 4-6 and Comparative Example 4 show that providing a graphite shell layer outside the inner core of the inorganic solid electrolyte has better lithium ion conductivity than providing an amorphous carbon layer.

[0116] 2. Cycle performance test of all-solid-state lithium-ion batteries Examples 1-3 and Comparative Examples 1-2, as well as Examples 4-6 and Comparative Examples 3-4, were divided into two groups according to the solid electrolyte material, and the cycle performance of each battery sample in the two groups was tested respectively. The test results are then statistically summarized in Table 2.

[0117] Among them, the test parameters of the battery cycle performance are as follows: the obtained all-solid-state lithium-ion battery is subjected to a charge and discharge cycle test, with a charging current of 1.5 A, a cut-off voltage of 4.9 V, a discharge current of 1.5 A, a cut-off voltage of 2.5 V, and a test environment temperature of 25°C. The number of cycles when the battery capacity decays to 80% is counted.

[0118] Table 2

[0119] It should be noted that in Examples 3 and 6, the cycle performance of the graphite shell prepared from needle coke was poor, which may be due to the hard material of needle coke, resulting in poor uniformity of the coating layer formed therefrom.

[0120] It should be noted that compared with Comparative Example 1, the cycle performance of the corresponding battery in Comparative Example 2 is lower after the amorphous carbon layer is used for coating. This is because the sulfide solid electrolyte undergoes catalytic decomposition under the action of current and partially fails.

[0121] Referring to Table 2, the test results of Examples 1-3 and Comparative Examples 1-2, and Examples 4-6 and Comparative Examples 3-4 show that the provision of a graphite shell outside the inner core of the inorganic solid electrolyte has a better cycle performance than the provision of no shell or the provision of an amorphous carbon layer.

[0122] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A modified inorganic solid electrolyte, characterized in that: The modified inorganic solid electrolyte is a core-shell structure, wherein the core is made of inorganic solid electrolyte and the shell is made of graphite.

2. The modified inorganic solid electrolyte according to claim 1, wherein The thickness of the shell is 10-1000 nm.

3. The modified inorganic solid electrolyte according to claim 2, characterized in that The thickness of the shell is 50-300 nm.

4. The modified inorganic solid electrolyte according to any one of claims 1 to 3, characterized in that The inorganic solid electrolyte is selected from at least one of a sulfide solid electrolyte and a halide solid electrolyte.

5. The modified inorganic solid electrolyte according to claim 4, characterized in that The inorganic solid electrolyte is a sulfide solid electrolyte, and the material of the sulfide solid electrolyte is Li6PS5Cl; Or / and, the inorganic solid electrolyte is a halide solid electrolyte, and the material of the halide solid electrolyte is Li3InCl6.

6. A method for preparing a modified inorganic solid electrolyte according to any one of claims 1 to 5, characterized in that: The following steps are involved: ball-milling an inorganic solid electrolyte, a graphite precursor, and an organic solvent to obtain a mixture; Drying the mixture to remove the organic solvent in the mixture to obtain a sintering precursor; The sintered precursor is sintered to graphitize the graphite precursor coated on the surface of the inorganic solid electrolyte, thereby obtaining the modified inorganic solid electrolyte with a core-shell structure.

7. The preparation method according to claim 6, characterized in that In the mixture, the ratio of the sum of the mass of the inorganic solid electrolyte and the graphite precursor to the mass of the organic solvent is (2-10):

1.

8. The preparation method according to claim 6, characterized in that In the mixture, the mass ratio of the inorganic solid electrolyte to the graphite precursor is 100:(0.1-50); Optionally, the mass ratio of the inorganic solid electrolyte to the graphite precursor is 100:(5-10).

9. The preparation method according to claim 6, characterized in that The ball milling mixing step includes: premixing at a first rotational speed, and then mixing at a second rotational speed, wherein the first rotational speed is lower than the second rotational speed; Optionally, in the step of premixing at the first speed, the processing speed is 30-60 rpm and the processing time is 3-8 min; Optionally, in the step of mixing at the second rotation speed, the processing rotation speed is 500-800 rpm, and the processing time is 20-30 min.

10. The preparation method according to claim 6, characterized in that The sintering step includes: pre-sintering at a first temperature and then sintering at a second temperature, wherein the first temperature is lower than the second temperature; Optionally, in the step of pre-sintering at the first temperature, the treatment temperature is 500-1000° C., and the treatment time is 1-3 h; Optionally, in the step of sintering at the second temperature, the treatment temperature is 1500-4000° C., and the treatment time is 2-10 h.

11. The preparation method according to any one of claims 6 to 10, characterized in that The organic solvent is selected from at least one of xylene, petroleum ether, decane, heptane and dodecane; Or / and, the graphite precursor is selected from at least one of pitch coke, biomass material, petroleum coke, needle coke and bituminous coal.

12. A battery pole piece, characterized in that: The modified inorganic solid electrolyte comprises the modified inorganic solid electrolyte according to any one of claims 1 to 5.

13. An all-solid-state lithium-ion battery, characterized in that: Comprising the battery electrode as claimed in claim 12.

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