Composite positive electrode material, preparation method thereof, battery positive electrode sheet and all-solid-state battery

Abstract

The application provides a composite positive electrode material and a preparation method thereof, a battery positive electrode sheet, and a full-solid-state battery. The composite positive electrode material is used in the full-solid-state battery, and the composite positive electrode material comprises a core part of a ternary positive electrode material and a coating layer on the core surface. The coating layer comprises a first coating layer and a second coating layer, and the first coating layer is located between the core surface of the ternary positive electrode material and the second coating layer. The first coating layer is nanoscale LLZCO, and the second coating layer is a polymer-based solid-state electrolyte. The first coating layer can improve the strength of the positive electrode particles, protect the structural integrity in the cycle process, and also improve the lithium ion diffusion coefficient and reduce the charge transfer resistance. The second coating layer can inhibit the high-pressure decomposition reaction of the sulfide electrolyte, and the lower Young's modulus can well buffer the volume deformation between the positive electrode particles during ion insertion and extraction, thereby preventing the contact failure of the positive electrode-electrolyte interface.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of all-solid-state lithium ion battery material preparation, in particular to a composite cathode material, a preparation method thereof, a battery cathode sheet and an all-solid-state battery. BACKGROUND

[0002] Lithium batteries are one of the fastest growing batteries at present. However, as the market demand for lithium batteries increases, the safety of lithium batteries is increasingly highlighted. Many mobile phone and car fire accidents are caused by short circuit in the battery, which produces a large amount of heat, causing decomposition of the internal electrolyte.

[0003] From the perspective of the cathode, the traditional lithium iron phosphate cathode cannot meet the daily demand, and the nickel content of the ternary cathode material is also increasing. However, as the nickel content of the ternary material increases, the cycle stability and high-temperature stability of the material decrease. The phase change of the cathode material during the cycle process causes the unit cell to shrink sharply, which brings about the problems of particle fragmentation and material pulverization, affecting the capacity and cycle stability of the material, and also causing a large amount of gas production. In addition, the layered structure of the cathode material collapses under low lithium intercalation state, releasing oxygen, which brings about more serious safety problems. Therefore, coating the electrode material is a necessary and effective means. However, the current commercial coating methods are relatively single, and the inorganic coating commonly used has poor lithium ion conductivity, so it cannot meet the needs of the next generation of lithium ion batteries.

[0004] Therefore, there is an urgent need for a composite cathode material that can overcome the problems of particle fragmentation and material pulverization of the cathode material during the cycle process and also improve the lithium ion diffusion coefficient. SUMMARY

[0005] To solve the above-mentioned background technology problems of cathode material particle fragmentation and material pulverization during the cycle process of all-solid-state batteries, the present application provides the following technical solutions:

[0006] The first aspect of the present application provides a composite cathode material for an all-solid-state battery, which comprises:

[0007] a core of a ternary cathode material and a coating layer located on the surface of the core;

[0008] the coating layer comprises a first coating layer and a second coating layer, and the first coating layer is located between the surface of the core of the ternary cathode material and the second coating layer;

[0009] the first coating layer is nanoscale LLZCO, and the second coating layer is a polymer-based solid-state electrolyte.

[0010] Preferably, the nanoscale LLZCO ranges from 1 nm to 100 nm.

[0011] Preferably, the ternary positive electrode material is one of lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA).

[0012] Preferably, the preparation method of the nanoscale LLZCO is one of sol-gel method, hydrothermal synthesis method, high-energy ball milling method and co-precipitation method.

[0013] Preferably, the nanoscale LLZCO is prepared by mixing La2O3, ZrO2, Co2O3 and Li2CO3, and then high-temperature calcining the mixture into a powder, and then ball milling the powder into the nanoscale LLZCO.

[0014] Preferably, the polymer-based solid electrolyte is one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polypropylene oxide (PPO) and polyvinylidene chloride (PVDC).

[0015] Preferably, the mass ratio of the core part to the first coating layer is greater than 20.

[0016] Preferably, the mass ratio of the second coating layer to the first coating layer is (1:1) to (10:1).

[0017] Preferably, the thickness of the first coating layer is 1 nm to 5 nm.

[0018] Preferably, the thickness of the second coating layer is 1 nm to 5 nm.

[0019] Preferably, the second coating layer is coated on the surface of the first coating layer by a wet chemical method.

[0020] The second aspect of the present application provides a preparation method of the composite positive electrode material of the first aspect, comprising the following steps:

[0021] S1: the core part and the nanoscale LLZCO are ball-mixed according to a mass ratio;

[0022] S2: the material after ball-milling in step S1 is calcined in an oxygen atmosphere to obtain a LLZCO primary coating material;

[0023] S3: the polymer-based solid electrolyte is dissolved in a solvent to obtain a polymer-based solid electrolyte dispersion;

[0024] S4: the primary coating material prepared in step S2 is added to the dispersion in step S3 and stirred;

[0025] S5: centrifugal drying, finally obtaining the core-shell structured composite cathode material.

[0026] The third aspect of the present application provides a battery cathode using the composite cathode material of the first aspect, the first solid-state electrolyte, the conductive agent and the binder.

[0027] The fourth aspect of the present application provides a full solid-state battery using the cathode sheet of the third aspect, the anode sheet and the second solid-state electrolyte.

[0028] The beneficial effects of the present application are:

[0029] (1) The first coating layer can improve the strength of the composite cathode material particles, protect the structural integrity during the cycle process, and also improve the lithium ion diffusion coefficient and reduce the charge transfer resistance. The second coating layer can inhibit the high-pressure decomposition reaction of the sulfide electrolyte, and the lower Young's modulus can well buffer the volume deformation between the anode particles during ion insertion and extraction, prevent the contact failure of the anode-electrolyte interface, and improve the structural stability of the composite cathode material in the full solid-state battery.

[0030] (2) The second coating layer can fill the area of the composite cathode material that is not wrapped by the first coating layer of LLZCO, making the surface coating layer of the composite cathode material more uniform, avoiding direct contact between the core and the electrolyte, and effectively inhibiting the oxidation of the electrolyte by the high-voltage anode. Secondly, the polymer is relatively soft and can fill the gap between the core and the electrolyte, which is conducive to the conduction of Li + , and reduces the impedance. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, which together with the embodiments of the present application, serve to explain the present application, and do not constitute a limitation on the present application. In the drawings:

[0032] Figure 1 SEM image of the battery cathode surface of the full solid-state battery after cycle in Example 1 of the present application. DETAILED DESCRIPTION

[0033] The technical solutions of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the summary is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the use of the terms "including," "comprising," or "having" and variations thereof herein is intended to be broad and encompass the terms "consisting of" and "consisting essentially of" and variations thereof, unless otherwise noted. The description of the application and embodiments and the examples provided herein serve only to elucidate the application. It is to be understood that no limitation of the scope of the application is intended by the description or examples.

[0035] In the description of the embodiments of the application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the technical features indicated. In the description of the embodiments of the application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0036] In the present application, the phrase "embodiments" means that the specific features, structures or properties described in conjunction with the embodiments can be included in at least one embodiment of the application. The appearance of this phrase at various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the application can be combined with other embodiments.

[0037] Throughout this application, numerical expressions of ranges of values are approximate measures and limits of the range to encompass minor deviations and embodiments having about the value recited as well as embodiments having the exact value. Except in the operating examples provided at the end of the detailed description, all numerical values of parameters (e.g., amounts or conditions) in the specification, including the appended claims are to be understood as approximations based on the value of the term "about" being used in the description and are not to be construed as being open-ended ranges unless otherwise indicated in the specific example. "About" indicates that a stated numerical value is not a precise value, but rather is close to the precise value within some acceptable limit of error. If the inexactness of an "about" is not otherwise understood in the art using this ordinary meaning, then "about" will indicate that there are variations that can exist in the value that can be accepted as a reasonable result under the circumstances. For example, "about" can include a variation less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.

[0038] In addition, the disclosure of ranges includes all values and further divisions of ranges within the entire range, including the endpoints and subranges given for the ranges.

[0039] With the increase of nickel content in ternary material, the cycle stability and high temperature stability of the material are decreasing. The phase transition of the positive electrode material during the cycle process leads to the sharp contraction of the unit cell, which in turn causes the particle fragmentation and material pulverization, affecting the capacity and cycle stability of the material, and also causing a large amount of gas production. In addition, the layered structure of the positive electrode material is easy to collapse in the low lithium intercalation state, and oxygen is released at the same time, which in turn causes more serious safety problems. Therefore, coating the electrode material is a necessary and effective means. However, the current commercial coating method is relatively single, and the commonly used inorganic coating has poor lithium ion conductivity, so it cannot meet the needs of the next generation of lithium ion batteries.

[0040] To solve the above technical problems, a composite positive electrode material, a battery positive electrode and a full solid-state battery are disclosed in the present application. The composite positive electrode material is coated with a first coating layer of nanoscale LLZCO and a second coating layer of a polymer-based solid electrolyte on the surface of the ternary positive electrode material. The composite positive electrode material used in the full solid-state battery can effectively improve the cycle performance of the battery.

[0041] The technical scheme of the present application is implemented as follows:

[0042] The first aspect of the present application provides a composite positive electrode material for a full solid-state battery, which comprises:

[0043] A core part of a ternary positive electrode material and a coating layer on the surface of the core;

[0044] The coating layer comprises a first coating layer and a second coating layer, and the first coating layer is located between the surface of the core of the ternary positive electrode material and the second coating layer.

[0045] The first coating layer is nanoscale LLZCO, and the second coating layer is a polymer-based solid electrolyte.

[0046] Specifically, the second coating layer can fill the area of the composite positive electrode material that is not coated by the LLZCO first coating layer, so that the surface coating layer of the composite positive electrode material is more uniform.

[0047] The first coating layer can improve the strength of the positive electrode particles, protect the structural integrity during the cycle process, and also improve the lithium ion diffusion coefficient and reduce the charge transfer resistance. The second coating layer can inhibit the high-pressure decomposition reaction of the sulfide electrolyte, and the low Young's modulus can well buffer the volume change between the positive electrode particles during ion intercalation and deintercalation, prevent the contact failure of the positive electrode-electrolyte interface, and improve the structural stability of the positive electrode composite material in the full solid-state battery.

[0048] In an embodiment, the ternary positive electrode material is one of lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA); and / or.

[0049] In one embodiment, the method for preparing the nanoscale LLZCO is one of sol-gel method, hydrothermal synthesis method, high-energy ball milling method and co-precipitation method.

[0050] In one embodiment, the nanoscale LLZCO is prepared by mixing La2O3, ZrO2, Co2O3 and Li2CO3, and then high-temperature calcining the mixture to form a powder, and then ball-milling the powder to form the nanoscale LLZCO.

[0051] In one embodiment, the polymer-based solid electrolyte is one of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polypropylene oxide (PPO) and polyvinylidene chloride (PVDC).

[0052] In one embodiment, the mass ratio of the core part to the first coating layer is greater than 20.

[0053] In one embodiment, the mass ratio of the core part to the first coating layer can be selected as 25, 33, 50, 83, 100, 120, 200, 250, etc. The above listed numerical ratios are only examples, and the present application does not make any limitation in this regard.

[0054] In one embodiment, the mass ratio of the second coating layer to the first coating layer is (1:1) to (10:1).

[0055] In one embodiment, the mass ratio of the second coating layer to the first coating layer can be selected as 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc. The above listed numerical ratios are only examples, and the present application does not make any limitation in this regard.

[0056] In one embodiment, the thickness of the first coating layer is 1 nm to 5 nm.

[0057] In one embodiment, the thickness of the first coating layer can be selected as 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, etc. The above listed numerical ratios are only examples, and the present application does not make any limitation in this regard.

[0058] In one embodiment, the thickness of the second coating layer is 1 nm to 5 nm.

[0059] In one embodiment, the thickness of the second coating layer can be selected as 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, etc. The above listed numerical ratios are only examples, and the present application does not make any limitation in this regard.

[0060] In one embodiment, the second coating layer is coated on the surface of the pre-prepared material by a wet chemical method.

[0061] The second aspect of the present application provides a preparation method of the composite positive electrode material of the first aspect, comprising the following steps:

[0062] S1: the core part and the nanoscale LLZCO are ball-milled and mixed according to the mass ratio;

[0063] S2: the material after ball-milling in step S1 is calcined under an oxygen atmosphere to obtain LLZCO primary coating material;

[0064] S3: the polymer-based solid electrolyte is dissolved in a solvent to obtain a polymer-based solid electrolyte dispersion;

[0065] S4: the primary coating material prepared in step S2 is added to the dispersion in step S3 and stirred;

[0066] S5: centrifugal drying is performed, and finally the composite positive electrode material with a core-shell structure is obtained.

[0067] In an embodiment, the preparation method of the composite positive electrode material, in step S1, the nanometer LLZCO particles are wrapped on the surface of the positive electrode material by using a ball-milling method, 0.02-0.2 g of LLZCO nanoparticles and 5 g of LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) positive electrode material are weighed and ball-milled, the ball-to-material ratio is (3-10):1, the ball-milling speed is 150 rpm-300 rpm, and the ball-milling time is 1 h-6 h; in step S2, the material after ball-milling is calcined under an oxygen atmosphere at 500℃-650℃ for 4 h-10 h to obtain the LLZCO primary coating material.

[0068] In an embodiment, the preparation method of the composite positive electrode material, the mass of the LLZCO nanoparticles can be selected as 0.02 g, 0.06 g, 0.1 g, 0.15 g, 0.2 g, etc., the ball-to-material ratio during ball-milling can be selected as 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc., the ball-milling speed can be selected as 150 rpm, 200 rpm, 250 rpm, 300 rpm, etc., the ball-milling time can be selected as 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, etc., the calcination temperature can be selected as 500℃, 550℃, 600℃, 650℃, etc., and the calcination time can be selected as 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, etc. The above listed numerical ratios are only examples, and the present application does not make any limitation in this regard.

[0069] In an embodiment, the preparation method of the composite positive electrode material, in step S3, the polymer-based solid electrolyte is wrapped on the surface of the LLZCO primary coating material by using a wet chemical method. 0.01 g-0.25 g of polymer-based solid electrolyte with an average molecular weight of 50,000 g mol -1~ 200000 g mol -1 The polymer-based solid electrolyte is dissolved in 5 g to 20 g of solvent, and each is ultrasonically stirred for 10 min to 30 min to obtain a polymer-based solid electrolyte dispersion liquid; step S4 adds the primary coating material prepared in step S2 into the dispersion liquid of step S3, and each is ultrasonically stirred for 10 min to 30 min; step S5 is centrifuged at a speed of 2000 rpm to 8000 rpm for 5 min to 10 min, and the solid sample is dried at 60 °C to 100 °C for 6 h to 18 h to obtain a double-coated positive electrode material.

[0070] In an embodiment, the solvent is one of dimethylformamide (DMF), N-methyl pyrrolidone (NMP), N,N-dimethylpropionamide (DMF), N-methyl-2-pyrrolidone (NMPyr), and N-ethyl pyrrolidone (NEP).

[0071] In an embodiment, the preparation method of the composite positive electrode material, the mass of the polymer-based solid electrolyte in step S3 can be selected from 0.01 g, 0.03 g, 0.05 g, 0.07 g, 0.1 g, 0.12 g, 0.14 g, 0.16 g, 0.18 g, 0.2 g, 0.22 g, 0.25 g, etc., and the average molecular weight can be selected from 50000 g·mol -1 , 60000 g·mol -1 , 70000 g·mol -1 , 80000 g·mol -1 , 90000 g·mol -1 , 100000 g·mol -1 , 110000 g·mol -1 , 120000 g·mol -1 , 130000 g·mol -1 , 140000 g·mol -1 , 150000 g·mol -1 , 160000 g·mol -1 , 170000 g·mol -1 , 180000 g·mol -1 , 190000 g·mol -1 , 200000 g·mol -1The solvent quality can be selected as 5g, 10g, 15g, 20g, etc., the ultrasonic stirring time can be selected as 10min, 15min, 20min, 25min, 30min, etc., the centrifugal speed can be selected as 2000rpm, 3000rpm, 4000rpm, 5000rpm, 6000rpm, 7000rpm, 8000rpm, etc., the centrifugal time can be selected as 5min, 6min, 7min, 8min, 9min, 10min, etc., the drying temperature can be selected as 60 DEG C, 70 DEG C, 80 DEG C, 90 DEG C, 100 DEG C, etc., and the drying time can be selected as 6h, 8h, 10h, 12h, 14h, 16h, 18h, etc. The above listed values are only examples, and the application does not make any limitation in this regard.

[0072] The third aspect of the application provides a battery positive electrode, which uses the composite positive electrode material of the first aspect, the first solid-state electrolyte, the conductive agent and the binder.

[0073] In an embodiment, the first solid-state electrolyte material refers to one or more of sulfide solid-state electrolytes: Li6PS5X (LPSX, X = Cl, Br, I), Li 10 GeP2S 12 (LGPS); and / or.

[0074] In an embodiment, the conductive agent material refers to one or more of conductive carbon black, conductive graphite, carbon nanotubes, carbon nanofibers, graphene.

[0075] In an embodiment, the binder material refers to one or more of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), nitrile rubber (NBR), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA).

[0076] The fourth aspect of the application provides a full solid-state battery, which uses the positive electrode sheet of the third aspect and the second solid-state electrolyte.

[0077] For example, the full solid-state battery is manufactured by the following preparation method:

[0078] Battery positive electrode preparation: the composite positive electrode material obtained in the first aspect is mixed with Li6PS5Cl solid-state electrolyte, conductive agent carbon nanofiber and binder PTFE according to the mass ratio of 70:26:3:1, and then uniform slurry coating is performed, and the coating is coated on the positive electrode current collector (aluminum foil), and after drying, rolling, cutting, the battery positive electrode is obtained.

[0079] Battery negative electrode preparation: 95% negative electrode active material, 2% solid electrolyte, 2% conductive agent and 1% binder are mixed to prepare negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector (copper foil). After drying, rolling, and cutting, a negative electrode sheet is obtained. Among the negative electrode active material, graphite: silicon oxide = 80%:20%.

[0080] Solid-state electrolyte layer preparation method: The solid-state electrolyte layer is composed of a second solid-state electrolyte and a binder (PTFE); the mass ratio of the two is 99:1.

[0081] In one embodiment, the second solid-state electrolyte material refers to one or more of sulfide solid-state electrolytes: Li6PS5X (LPSX, X = Cl, Br, I), Li 10 GeP2S 12 (LGPS); and / or.

[0082] All-solid-state battery preparation: The battery anode, solid-state electrolyte layer and negative electrode sheet are stacked in turn and packaged in an aluminum plastic film. After applying vacuum to the aluminum plastic film, it is sealed and the battery is isostatically pressed at 460 MPa, and an all-solid-state lithium ion battery is obtained.

[0083] The embodiments of the present application will be described more specifically by examples and comparative examples. Among them, all examples and comparative examples are a group of all-solid-state battery samples prepared by the same process.

[0084] In order to intuitively and comprehensively reflect the advantages of the present application, all examples and comparative examples are recorded or tested as follows: 0.1C initial discharge specific capacity, 0.1C initial coulombic efficiency, capacity retention rate after 0.5C cycling for 100 times, capacity retention rate after 1C cycling for 100 times and ionic conductivity.

[0085] It should be noted that the embodiments of the present application are not limited to only these examples.

[0086] Example 1

[0087] I. Li 7.5 La3Zr 1.5 Co 0.5 O 12 Preparation method of material:

[0088] 1) According to the proportion of each element in LLZCO, weigh the corresponding mass of La2O3, ZrO2, Co2O3 and Li2CO3.

[0089] 2) Mix the raw materials through a ball mill, the ball mill speed is 300 r·min -1 , and the ball milling time is 12 h.

[0090] 3) The mixture is sintered at 880°C for 8h, and finally the calcined powder material is dried at 500r·min -1 ball-milled for 40h to obtain the LLZCO nanomaterial.

[0091] II. Preparation of composite cathode material

[0092] 1) 0.1g Li 7.5 La3Zr 1.5 Co 0.5 O 12 nanoparticles are ball-milled with 5g LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) cathode material, the ball-to-material ratio is 3:1, the rotation speed is 200rpm, and the ball-milling time is 2h.

[0093] 2) The ball-milled material is calcined at 550°C for 6h in an oxygen atmosphere to obtain Li 7.5 La3Zr 1.5 Co 0.5 O 12 primary coated material, and the first coating layer has a thickness of 2nm.

[0094] 3) 0.2g PEO with an average molecular weight of 100000g mol -1 is dissolved in 10g dimethylformamide (DMF) solution, and each is ultrasonically stirred for 30min to obtain a PEO dispersion; and the primary coated material prepared above is added to the dispersion, and each is ultrasonically stirred for 20min, and then centrifuged and dried, and the second coating layer has a thickness of 2nm; and finally a double-coated cathode material with a core-shell structure, i.e., PEO@LLZCO-NCM811 composite cathode material, is obtained.

[0095] II. Preparation of battery cathode

[0096] The composite cathode material obtained in the first step is mixed with Li6PS5Cl solid-state electrolyte, conductive agent carbon nanofiber and binder PTFE respectively according to a mass ratio of 70:26:3:1, and then uniformly grinded and coated, and coated on a cathode current collector (aluminum foil), and after drying, roll-pressed, and cut to obtain a battery cathode.

[0097] III. Preparation of battery anode

[0098] 95% anode active material, 2% solid-state electrolyte Li6PS5Cl, 2% conductive agent conductive carbon black and 1% binder PAA are mixed to prepare an anode slurry, and the anode slurry is coated on an anode current collector (copper foil), and after drying, roll-pressed, and cut to obtain an anode sheet. Among the anode active material, graphite: silicon oxide = 80%:20%.

[0099] Four, solid electrolyte layer preparation method

[0100] The solid electrolyte layer is composed of the second solid electrolyte Li6PS5Cl and the binder PTFE; the mass ratio of the two is 99:1.

[0101] Five, all-solid-state battery preparation

[0102] The battery anode, the solid electrolyte layer and the negative electrode sheet are stacked in turn and packaged in an aluminum plastic film. After vacuum is applied to the aluminum plastic film, it is sealed, and the battery is isostatically pressed at 460 MPa, thereby obtaining an all-solid-state lithium ion battery.

[0103] Example 2

[0104] Example 1 provides a composite anode material, a battery anode and an all-solid-state battery, which have the same coating material and preparation method as in Example 1. The only difference from Example 1 is that the mass of LLZCO is 0.02 g.

[0105] Example 3

[0106] Example 1 provides a composite anode material, a battery anode and an all-solid-state battery, which have the same coating material and preparation method as in Example 1. The only difference from Example 1 is that the mass of LLZCO is 0.06 g.

[0107] Example 4

[0108] Example 1 provides a composite anode material, a battery anode and an all-solid-state battery, which have the same coating material and preparation method as in Example 1. The only difference from Example 1 is that the mass of LLZCO is 0.15 g.

[0109] Example 5

[0110] Example 1 provides a composite anode material, a battery anode and an all-solid-state battery, which have the same coating material and preparation method as in Example 1. The only difference from Example 1 is that the mass of LLZCO is 0.2 g.

[0111] Comparative Example 1

[0112] The coating material and preparation method used in Example 1 are the same as in Example 1. The difference from Example 1 is that no LLZCO material is coated, nor is PEO material coated.

[0113] Comparative Example 2

[0114] The coating material and preparation method used in Example 1 are the same as in Example 1. The difference from Example 1 is that only LLZCO is coated, and the mass of the material is 0.2 g.

[0115] Comparative Example 3

[0116] The coating material and the preparation method used in Example 1 are the same as those used in Example 1, except that only PEO material is coated, and the mass of the PEO material is 0.2 g.

[0117] Comparative Example 4

[0118] The coating material and the preparation method used in Example 1 are the same as those used in Example 1, except that the mass of the coated LLZCO material is 0.3 g, and the mass of the coated PEO material is 0.3 g.

[0119] The positive electrode materials obtained in Examples 1-5 and Comparative Examples 1-4 are prepared into battery positive electrodes, and the battery positive electrodes are used in full solid-state batteries, and the performance of the full solid-state batteries is tested.

[0120] The composite positive electrode materials prepared in the above Examples 1-5 and Comparative Examples 1-3 are used to prepare full solid-state batteries, and the performance of the full solid-state batteries is tested, and the test results are shown in Table 1 below:

[0121] First discharge capacity test:

[0122] At room temperature (25°C), the fully charged battery is discharged at a constant current of 0.1C to a cutoff voltage of 2.5V, and the first discharge capacity is obtained.

[0123] First coulombic efficiency:

[0124] The first discharge specific capacity / first charge specific capacity when the current is 0.1C times.

[0125] The first coulombic efficiency refers to the coulombic efficiency in the first charging and discharging process of the battery. The coulombic efficiency is the use efficiency of the charge in the battery during charging and discharging, and is expressed as: coulombic efficiency = (discharge capacity / charge capacity) x 100%.

[0126] Cycle battery capacity retention rate:

[0127] At a temperature of 45°C, charge to a charge cutoff voltage of 4.2V at a current of 0.5C and 1C, respectively, and then to a cutoff current of 0.05C at a constant voltage, stand for 0.5h, and then discharge to a cutoff voltage of 2.5V at a current of 0.5C and 1C, respectively, stand for 0.5h, and enter the next charging and discharging cycle, and so on, a total of 100 charging and discharging cycles.

[0128] Ionic conductivity:

[0129] The AC impedance of the sample is measured, and then the ionic conductivity of the sample is calculated by the formula σ = L / (R x S), where L is the thickness, R is the impedance, and S is the cross-sectional area.

[0130] The performance test results are shown in Table 1.

[0131] Table 1: Comparison of material performance test in examples 1-5 and comparative examples 1-4

[0132]

[0133] According to the above table: comparative examples 1-5 and comparative examples 1-4, the present application provides a kind of composite positive material, Li 7.5 La3Zr 1.5 Co 0.5 O 12 (first coating layer, close to the positive electrode) and polymer layer (second coating layer), the first coating layer can improve the strength of composite positive material particles, protect the structural integrity during the cycle process;Second coating layer can inhibit the high pressure decomposition reaction of sulfide electrolyte, and the lower Young's modulus can well buffer the volume deformation between positive particles when ion insertion and extraction, prevent the contact failure of positive electrode-electrolyte interface, improve the structural stability of composite positive material in all-solid-state battery.Second coating layer can fill the area of composite positive material that first coating layer of LLZCO fails to wrap, make the surface coating layer of composite positive material more uniform, avoid the direct contact of core part and electrolyte, effectively inhibit the oxidation of electrolyte by high voltage positive electrode.Secondly, polymer is relatively soft, can fill the gap between core part and electrolyte, conducive to the conduction of Li + .

[0134] Examples 1-5, keep the second coating layer PEO coating amount as 0.2g, with the increase of LLZCO coating amount, 0.1C initial discharge specific capacity, 0.1C initial coulombic efficiency, 0.5C cycle 100 times after capacity retention, 1C cycle 100 times after capacity retention and ionic conductivity are all in the trend of first rising and then falling, when LLZCO coating amount is 0.1g, i.e. PEO and LLZCO mass ratio is 2:1, the performance of battery reaches the peak value. Therefore, double-coated material can improve the initial efficiency, cycle performance and ion conduction capacity of the battery.

[0135] Comparative example 1 and comparative examples 1-4, when not coating LLZCO material, also not coating PEO material, the initial efficiency, cycle performance and ion conduction capacity reach the lowest, as shown in comparative example 2, when only coating LLZCO and only coating PEO, the comprehensive performance of battery is slightly improved, and when the coating amount of two coating materials is excessive, the comprehensive performance of battery will decrease.

[0136] Figure 1 The SEM diagram of battery positive electrode of all-solid-state battery after cycle in example 1 can be seen that the positive electrode particles after cycle are relatively complete, which indicates good contact with electrolyte.

[0137] It should be pointed out that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A composite cathode material, characterized in that, The composite cathode material includes: The core of the ternary cathode material and the coating layer on the surface of the core; The coating layer includes a first coating layer and a second coating layer, wherein the first coating layer is located between the core surface of the ternary cathode material and the second coating layer; The first coating layer is nano-sized LLZCO, and the second coating layer is a polymer-based solid electrolyte; The mass ratio of the core to the first coating layer is greater than 20; The molecular formula of the LLZCO is Li 7.5 La3Zr 1.5 Co 0.5 O 12 .

2. The composite cathode material as described in claim 1, characterized in that, The polymer-based solid electrolyte is one of polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, polypropylene oxide, and polyvinylidene chloride.

3. The composite cathode material as described in claim 1, characterized in that, The mass ratio of the second coating layer to the first coating layer is (1:1) to (10:1).

4. The composite cathode material as described in claim 1, characterized in that, The thickness of the first coating layer is 1 nm to 5 nm.

5. The composite cathode material as described in claim 1, characterized in that, The thickness of the second coating layer is 1 nm to 5 nm.

6. The composite cathode material as described in claim 1, characterized in that, The second coating layer is applied to the surface of the first coating layer by a wet chemical method.

7. A method for preparing a composite cathode material, used to prepare the composite cathode material as described in any one of claims 1 to 6, characterized in that, Includes the following steps: S1: The core and the nano-sized LLZCO are ball-milled and mixed at a mass ratio; S2: The material ball-milled in step S1 is calcined in an oxygen atmosphere to obtain LLZCO primary coated material; S3: Dissolve the polymer-based solid electrolyte in a solvent to obtain a polymer-based solid electrolyte dispersion; S4: Add the primary coating material prepared in step S2 to the dispersion in step S3 and stir. S5: Centrifuge drying to finally obtain a core-shell structured composite cathode material.

8. A positive electrode sheet for a battery, characterized in that, It includes the composite cathode material, the first solid electrolyte, the conductive agent, and the binder as described in any one of claims 1 to 6.

9. An all-solid-state battery, characterized in that, It includes the positive electrode, negative electrode, and second solid electrolyte as described in claim 8.

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