Composite negative electrode sheet, preparation method and application thereof, and all-solid-state battery

Abstract

The present application relates to the technical field of lithium ion batteries, in particular to a composite negative electrode sheet, a preparation method and application thereof, and a full solid-state battery containing the composite negative electrode sheet. The composite negative electrode sheet comprises: a negative electrode sheet and an interface layer loaded on the surface of the negative electrode sheet; the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer contains active material without lithium; the interface layer contains Li3P and an alloy phase; wherein, during the battery cycle process, the interface layer is obtained by in-situ conversion of a coating containing a metal phosphide; wherein, the metal in the metal phosphide forms the alloy phase with metallic lithium from a positive electrode sheet. The composite negative electrode sheet provided by the present application can effectively inhibit lithium dendrite growth and reduce interface impedance, and is helpful to the exertion of rate performance; at the same time, the full solid-state battery containing the composite negative electrode sheet has high rate performance and cycle performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a composite negative electrode sheet, a preparation method and application thereof, and a full solid-state battery containing the composite negative electrode sheet. BACKGROUND

[0002] In recent years, the development of liquid lithium ion batteries has been relatively slow compared to previous developments. People's pursuit of high energy density, long cycle performance and high safety is increasingly urgent, and the slow development of lithium ion liquid batteries has caused a contradiction. Since solid-state electrolyte can replace liquid electrolyte to solve the safety problems existing in current commercial lithium batteries, solid-state lithium batteries have become a research hotspot in recent years. Common solid-state electrolytes are divided into polymer solid-state electrolytes and inorganic solid-state electrolytes. Polymer solid-state electrolytes have good thermal stability, high stability to lithium, good cycle performance, and can be made into flexible thin film batteries; but the low ion conductivity and working power, and poor electrode wettability limit the development and application of polymer solid-state lithium batteries. Inorganic solid-state electrolytes have high ionic conductivity, wide electrochemical window, and good stability, and have been widely concerned. Inorganic solid-state electrolytes are divided into sulfide solid-state electrolytes and oxide solid-state electrolytes. Sulfide has an ionic conductivity as high as 10 -2 S / cm, which is comparable to liquid electrolyte. It also has high deformability, small grain boundary impedance, and can be applied to high-rate full solid-state battery systems, so it has attracted much attention. However, in the full solid-state battery system, each interface is a solid-solid contact, and there is a certain contact interface impedance.

[0003] Document one [“A mixed ion-electron conducting network derived from a porous CoP film for stable lithium metal anodes” (Materials Chemistry Frontiers, 2021)] discloses that CoP is deposited on a Cu foil by electrodeposition process, then lithium is continuously deposited on the surface of CoP to obtain a negative electrode sheet, and then a battery is assembled. The negative electrode mainly solves the problem of lithium dendrite growth, and a certain capacity of metal lithium is pre-deposited on the surface of CoP. The metal lithium directly contacts with the electrolyte, which cannot fundamentally solve the problem of lithium dendrite. The negative electrode uses active metal lithium, and does not involve how to suppress lithium dendrite growth, reduce interface impedance, solve the problem of low capacity of the battery under high rate, etc. for non-lithium negative electrode materials, and the coating is used on the surface of active materials without lithium.

[0004] CN100380712C discloses an ion conductive composite for protecting an active metal anode, specifically a layer of material capable of direct alloying with lithium metal in physical contact with the surface of the lithium metal electrode, including metal nitrides, metal phosphides, red phosphorus and other materials, a protective layer is formed by physical contact, wherein the protective layer aims to protect the lithium metal from damage by air and electrolyte, and can react with lithium metal to form Li3P. However, the negative electrode uses active lithium metal, and does not involve non-lithium negative electrode materials, how to inhibit lithium dendrite growth, reduce interface impedance, solve the problem of low battery capacity at high rate, etc.

[0005] Document two [“Room-Temperature Anode-less All-Solid-State Batteries via the Conversion Reaction of Metal Fluorides” (Advanced Materials, 2022)] discloses coating metal fluoride AgF on the surface of the current collector stainless steel, using the conversion reaction to form LiF and alloy metal phase, the metal nanodomain produced by the reaction reduces the nucleation overpotential of the subsequent alloying reaction with Li, and the LiF and Li-Ag alloy formed on the surface improves the cycle performance of the full battery. However, this document uses metal fluoride in lithium-free negative electrodes, and does not involve using the coating surface of the negative electrode, and the problems solved are different, and the present patent solves the problems of lithium dendrite growth, high interface impedance, and low battery capacity at high rate, etc. SUMMARY

[0006] The purpose of the present application is to overcome the problems of lithium dendrite growth, high interface impedance, and low battery capacity at high rate, etc. at the interface between the existing non-lithium negative electrode material and the electrolyte, to provide a composite negative electrode sheet and its preparation method and application, and a full solid-state battery containing the composite negative electrode sheet, which can effectively inhibit lithium dendrite growth and reduce interface impedance. At the same time, the full solid-state battery containing the composite negative electrode sheet has high rate capability and cycle performance.

[0007] To achieve the above purpose, the first aspect of the present application provides a composite negative electrode sheet, which comprises: a negative electrode sheet and an interface layer loaded on the surface of the negative electrode sheet; the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer contains lithium-free active material; the interface layer contains Li3P and an alloy phase;

[0008] Wherein, during the battery cycle process, the interface layer is obtained in situ by conversion of a coating containing metal phosphide; wherein the metal in the metal phosphide forms the alloy phase with lithium metal from the positive electrode sheet.

[0009] Preferably, the metal in the metal phosphide is selected from at least one of Sn, Ge, Al and Mg.

[0010] Preferably, the metal phosphide is selected from at least one of Sn4P3, GeP5, GeP, AlP and Mg3P2.

[0011] Preferably, the interface layer has a thickness of 0.5-10 μm, preferably 0.5-5 μm.

[0012] Preferably, the lithium-free active material is a non-metallic material, preferably selected from at least one of graphite, hard carbon, soft carbon, silicon, SiO, Si / C and P.

[0013] The second aspect of the present application provides a method for preparing a composite negative electrode sheet, comprising the following steps:

[0014] (1) coating a negative electrode active paste containing a lithium-free active material on the surface of a current collector and drying to form a negative electrode active material layer on the surface of the current collector, to obtain a negative electrode sheet;

[0015] (2) coating a metal phosphide on the surface of the negative electrode sheet and compacting to form a coating layer on the surface of the negative electrode active material layer, to obtain a composite negative electrode sheet precursor;

[0016] (3) in-situ converting the composite negative electrode sheet precursor during battery cycling, so that the coating layer is converted into an interface layer containing Li3P and an alloy phase, to obtain a composite negative electrode sheet;

[0017] wherein the metal in the metal phosphide forms the synthetic phase with metallic lithium from the positive electrode sheet.

[0018] The third aspect of the present application provides a composite negative electrode sheet according to the first aspect, or a composite negative electrode sheet prepared by the method according to the second aspect, for use in a full solid-state battery.

[0019] The fourth aspect of the present application provides a full solid-state battery, comprising a composite negative electrode sheet according to the first aspect, or a composite negative electrode sheet prepared by the method according to the second aspect.

[0020] Compared with the prior art, the present application has the following advantages:

[0021] (1) The composite negative electrode sheet provided by the present invention obtains Li3P and alloy phase by in-situ conversion of a coating containing metal phosphide in the interface layer during battery cycling. Specifically, Li3P has high ionic conductivity, which enables lithium ions to migrate quickly and improves the rate performance of the battery. At the same time, the alloy phase has both high ionic conductivity and electronic conductivity, which not only enables the uniform embedding of metallic lithium into the negative electrode structure, but also reduces the interface impedance and accelerates lithium ion transport, thereby improving the rate performance of the battery. That is, the composite negative electrode sheet containing a specific interface layer can effectively suppress lithium dendrite growth and reduce interface impedance, which helps to improve the rate performance. In particular, by controlling the relevant parameters of the interface layer, it is more conducive to improving the performance parameters of the composite negative electrode sheet.

[0022] (2) The method for preparing the composite negative electrode provided by the present invention simplifies the operating conditions and process flow, and facilitates industrial production;

[0023] (3) The composite negative electrode provided by the present invention is used in all-solid-state batteries. By controlling the lithium dendrite growth and interface impedance of the composite negative electrode and solid electrolyte, the specific capacity of the battery under high rate can be effectively improved, so that the all-solid-state battery containing the composite negative electrode has high rate performance and cycle performance. Attached Figure Description

[0024] Figure 1a This is the XPS spectrum of Li-Sn in the interface layer of the composite negative electrode S1 prepared in Example 1;

[0025] Figure 1b This is the XPS spectrum of Li3P in the interface layer of the composite negative electrode S1 prepared in Example 1;

[0026] Figure 2 This is a schematic diagram of the structure of the all-solid-state battery Q1 assembled from the composite negative electrode S1 provided in Example 1;

[0027] Figure 3 The graphs show the first charge-discharge curves of the all-solid-state battery Q1 assembled from the composite negative electrode S1 prepared in Example 1 and the all-solid-state battery DQ1 assembled from the composite negative electrode DS1 prepared in Comparative Example 1 under the conditions of 2.7-4.1V and 0.1C. Detailed Implementation

[0028] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0029] The first aspect of the present application provides a composite negative electrode sheet, comprising: a negative electrode sheet and an interface layer loaded on the surface of the negative electrode sheet; the negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer contains lithium-free active material; the interface layer contains Li3P and an alloy phase;

[0030] Wherein, during the battery cycle process, the interface layer is in-situ converted from a coating containing metal phosphide; wherein the metal in the metal phosphide forms the alloy phase with metal lithium from the positive electrode sheet.

[0031] The inventors of the present application have found that: due to the high impedance interface product Li2S generated by the negative electrode and the sulfide electrolyte during the cycle process, the lithium ion transmission at the interface layer is not conducive, thereby reducing the rate performance and cycle performance of the all-solid-state battery. Therefore, the present application introduces a layer of metal phosphide on the surface of the negative electrode active material layer, in-situ generates ion conductivity (up to 10 -4 S / cm) Li3P and an alloy phase, the high ion conductivity interface layer can establish a good lithium ion transmission channel, accelerate lithium ion transmission, and thus improve the rate performance of the all-solid-state battery; at the same time, the alloy phase has high ion conductivity and electronic conductivity, which can not only regulate the uniform deposition of metal lithium, but also further improve the interface transmission between the electrolyte layer and the negative electrode layer due to its fast lithium ion transmission capacity, thereby improving the rate and cycle performance of the overall battery.

[0032] Compared with CN100380712C, the present application has the following advantages: 1) CN100380712C uses metal phosphide on the surface of metal lithium, while the present application requests to use metal phosphide on the surface of lithium-free active materials such as silicon, phosphorus and silicon monoxide; wherein the characteristics of lithium-free active materials and metal lithium are significantly different, the electronic conductivity of metal lithium is very high, while the electronic conductivity of lithium-free active materials is very poor; forming high ion conductivity Li3P on the surface of lithium-free active materials, and the alloy phase with high ion conductivity and high electronic conductivity, can further improve the rate performance and cycle performance, and inhibit lithium dendrites; 2) CN100380712C uses metal phosphide as a protective layer for metal lithium to protect metal lithium from being damaged by air and electrolyte, and it can react with metal lithium to form Li3P; while the specific interface layer defined in the present application, during the battery cycle process, Li +Li3P and alloy phase formed by participating in the reaction; that is, the two mechanisms of action are different; 3) the research of metal phosphide as a negative electrode material for lithium ion batteries in CN100380712C is to use metal phosphide as a negative electrode material, which has the function of storing lithium, and is related to cycle stability and specific capacity; while the present application uses active material (such as silicon, phosphorus, etc.) without lithium as a negative electrode material, and the metal phosphide is only a coating on the surface of the negative electrode active material layer, not as an active material to store metal lithium; that is, the two functions are different.

[0033] In the present application, the negative electrode sheet also includes a current collector, which includes but is not limited to a copper foil. That is, the negative electrode sheet includes a current collector and a negative electrode active material layer loaded on the current collector.

[0034] In the present application, the composite negative electrode sheet provided by the present application includes a negative electrode sheet and an interface layer loaded on the surface of the negative electrode sheet, the negative electrode sheet includes a current collector and a negative electrode active material layer loaded on the current collector, and the negative electrode active material layer contains active material without lithium; the interface layer contains Li3P and alloy phase; wherein, during the battery cycle process, the interface layer is obtained in situ by conversion of the coating containing metal phosphide.

[0035] In the present application, the battery cycle process refers to the lithiation process of the battery, that is, during the lithiation process of the battery, the P 3- and the positive electrode Li + reacts to form Li3P, and the metal in the metal phosphide forms an alloy phase with lithium metal from the positive electrode sheet.

[0036] In the present application, only the metal in the metal phosphide can form an alloy with lithium. Preferably, the metal in the metal phosphide is selected from at least one of Sn, Ge, Al and Mg, In, Zn.

[0037] In some embodiments of the present application, preferably, the metal phosphide is selected from at least one of Sn4P3, GeP5, GeP, AlP, Mg3P2, InP and Zn3P2, and most preferably Sn4P3.

[0038] In the present application, the particle size of the supplementary metal phosphide affects the technical effect of the present application. Preferably, the average particle size D50 of the metal phosphide is 1-200 nm.

[0039] In some embodiments of the present application, preferably, the thickness of the negative active material layer is 20-150 μm, for example, 20 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, and any value in the range consisting of any two of the aforementioned values, preferably 20-100 μm, and most preferably 80 μm.

[0040] In some embodiments of the present application, preferably, the thickness of the interface layer is 0.5-10 μm, for example, 0.5 μm, 0.6 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, and any value in the range consisting of any two of the aforementioned values, preferably 0.5-5 μm, more preferably 1-3 μm, and most preferably 1 μm. When the thickness of the interface layer is too thick (i.e., the thickness is higher than 10 μm), the transport of lithium ions is hindered; when the thickness of the interface layer is too thin (i.e., the thickness is lower than 0.5 μm), the interface layer cannot effectively transport lithium ions, and thus cannot improve the rate capability and inhibit the growth of lithium dendrites.

[0041] In some embodiments of the present application, preferably, the thickness ratio of the interface layer to the negative active material layer is 1:2-300, for example, 1:2, 1:5, 1:8, 1:10, 1:16, 1:20, 1:50, 1:80, 1:100, 1:133.33, 1:160, 1:200, 1:300, and any value in the range consisting of any two of the aforementioned values, preferably 1:10-200, more preferably 1:20-100, and most preferably 1:80. When the thickness ratio is too large, it indicates that the negative active material layer is too thick and the interface layer is too thin, and thus cannot effectively transport lithium ions and electrons; when the thickness ratio is too small, it indicates that the negative active material layer is too thin and the interface layer is too thick, and thus is not suitable for use in high-energy-density negative electrode sheets.

[0042] In some embodiments of the present application, preferably, the lithium-free active material is a non-metallic material; further preferably, the lithium-free active material is selected from at least one of graphite, hard carbon, soft carbon, silicon, SiO, Si / C, and P, and most preferably graphite.

[0043] In some embodiments of the present application, preferably, the negative active material layer further comprises: an optional electrolyte, an optional conductive agent, and a binder; further preferably, the negative active material layer is composed of the lithium-free active material, the electrolyte, the conductive agent, and the binder.

[0044] In some embodiments of the present application, preferably, the weight ratio of the lithium-free active material, the optional electrolyte, the optional conductive agent, and the binder is 50-95:0-40:0-5:0.5-5, preferably 60-85:5-35:2-5:1-3, and most preferably 60:35:2:3.

[0045] In some embodiments of the application, preferably, the electrolyte is selected from a sulfide electrolyte, preferably from at least one of xLi2S-(100-x)P2S5(0≤x≤100), Li3PS4, Li7P3S 11 10 MP2S 12 (M=MGe, Sn, Si), Li 3.25 Ge 0.25 P 0.75 S4, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li4GeS4and Li 11 Sn2PS 12 .

[0046] In some embodiments of the application, preferably, the conductive agent is selected from at least one of acetylene black, ketjen black, Super-P, KS-6, carbon fibers (VGCF) carbon nanotubes (CNTs), graphene, petroleum coke, needle coke, mesocarbon microbeads, carbon fibers and vapor grown carbon fibers (VGCF).

[0047] In some embodiments of the application, preferably, the binder is selected from at least one of polyvinylidene chloride (PVDF), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE) and carboxymethyl cellulose and its salts.

[0048] According to the application, preferably, the ionic conductivity of the composite negative electrode sheet is ≥ 1 x 10 -4 S / cm, for example, 1 x 10 - 4 S / cm, 1.86 x 10 -4 S / cm, 3 x 10 -4 S / cm, 3.26 x 10 -4 S / cm, 3.64 x 10 -4 S / cm, 4.03 x 10 -4 S / cm, 4.13 x 10 -4 S / cm, 4.17 x 10 -4 S / cm, 4.18 x 10 -4 S / cm, 4.19 x 10 -4 S / cm, 4.67 x 10 -4 S / cm, 4.97 x 10 -4 S / cm, 5.25 x 10 -4 S / cm, 6 x 10​-4 S / cm, 7.61 x 10 -4 S / cm, 8 x 10 -4 S / cm, and any value in the range consisting of any two of the numerical values mentioned above, preferably (1-8) x 10 -4 S / cm, more preferably (3-6) x 10 -4 S / cm.

[0049] In the present application, without special circumstances, the ion conductivity parameter is tested by direct current polarization method, and the specific test method is as follows: a solid-state battery mold is used, first, 100 mg of electrolyte is placed on both sides of the composite negative electrode sheet, and is pressed tightly under a pressure of 300 MPa, and then Li-In alloy is pasted on both sides of the electrolyte, and is pressed tightly under a pressure of 200 MPa. Test conditions: constant voltage 0.5V, running time: 8000S, the steady-state current can be passed, the impedance value can be obtained by the formula R=U / I, and the impedance value can be obtained by the formula σ=L / (R x S), wherein L is the thickness of the composite negative electrode sheet, R is the impedance measured by direct current polarization, and S is the thickness of the composite negative electrode sheet.

[0050] The second aspect of the present application provides a preparation method of a composite negative electrode sheet, which comprises the following steps:

[0051] (1) coating a negative electrode active slurry containing a lithium-free active material on the surface of a current collector and drying to form a negative electrode active material layer on the surface of the current collector, to obtain a negative electrode sheet;

[0052] (2) coating a metal phosphide on the surface of the negative electrode sheet and compacting to form a coating layer on the surface of the negative electrode active material layer, to obtain a composite negative electrode sheet precursor;

[0053] (3) in-situ converting the composite negative electrode sheet precursor during battery cycling, so that the coating layer is converted into an interface layer containing Li3P and an alloy phase, to obtain a composite negative electrode sheet;

[0054] Wherein, the metal in the metal phosphide forms the synthetic phase with the metal lithium from the positive electrode sheet.

[0055] In the present application, without special circumstances, the types of the lithium-free active material and the metal phosphide are in accordance with the above definition, which is not repeated here.

[0056] In some embodiments of the present application, preferably, in step (1), the solid content of the negative electrode active slurry is 40-60wt%, for example, 40wt%, 50wt%, 55wt%, 60wt%, and any value in the range consisting of any two of the numerical values mentioned above, preferably 50-60wt%.

[0057] In some embodiments of the present application, preferably, the negative active slurry further comprises: an optional electrolyte, an optional conductive agent, a binder and a solvent. Among them, the solvent is selected from N-methyl pyrrolidone, toluene, xylene, acetone, hexane and heptane, etc.; the types of the electrolyte, the conductive agent and the binder are as defined above, and the present application does not make any further description.

[0058] In some embodiments of the present application, further preferably, the weight ratio of the lithium-free active material, the optional electrolyte, the optional conductive agent and the binder in the negative active slurry is 50-95:0-40:0-5:0.5-5, preferably 60-85:5-35:2-5:1-3, and most preferably 60:35:2:3.

[0059] In the present application, the coating of the negative active slurry aims to uniformly coat the negative active slurry on the surface of the current collector. Preferably, in step (1), the thickness of the negative active material layer is 20-150 μm, for example, 20 μm, 50 μm, 80 μm, 100 μm, 120 μm, 150 μm, and any value in the range between any two numerical values, preferably 20-100 μm, and most preferably 80 μm.

[0060] In the present application, in step (1), the drying aims to remove the solvent in the negative active slurry to obtain a negative active material layer. Preferably, the conditions of the drying include: the temperature is 60-100 ℃, preferably 80 ℃; and the time is 1-36 h, preferably 4-24 h.

[0061] In some embodiments of the present application, preferably, in step (2), the compaction conditions include: the pressure is 200-500 MPa, preferably 300-400 MPa, and more preferably 400 MPa; and the time is 1-10 min, preferably 1-5 min, and more preferably 2 min.

[0062] In the present application, the coating of the metal phosphide aims to uniformly coat the metal phosphide on the surface of the negative active material layer to form a coating layer, and the present application does not make any limitation on the thickness of the coating layer as long as the coating layer is in situ converted to obtain an interface layer with a specific thickness.

[0063] In some embodiments of the present application, preferably, the thickness of the interface layer is 0.5-10 μm, for example, 0.5 μm, 0.6 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, and any value in the range between any two numerical values, preferably 0.5-5 μm, more preferably 1-3 μm, and most preferably 1 μm.

[0064] The third aspect of the present application provides an application of the composite negative electrode sheet provided by the first aspect or the composite negative electrode sheet prepared by the method provided by the second aspect in a full solid-state battery.

[0065] The fourth aspect of the present application provides a full solid-state battery, which comprises the composite negative electrode sheet provided by the first aspect or the composite negative electrode sheet prepared by the method provided by the second aspect.

[0066] In the present application, the solid-state electrolyte is arranged between the interface layer of the composite negative electrode sheet and the positive electrode sheet without special circumstances.

[0067] In some embodiments of the present application, preferably, the solid-state electrolyte is selected from sulfide solid-state electrolytes, preferably selected from xLi2S·(100-x)P2S5 (0≤x≤100), Li3PS4, Li7P3S 11 , Li6PS5X (X is selected from Cl, Br, I), Li 10 MP2S 12 (M is selected from Ge, Sn, Si), Li 3.25 Ge 0.25 P 0.75 S4, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li4GeS4 and Li 11 Sn2PS 12 .

[0068] In the present application, the source of the solid-state electrolyte has a wide selection range, which can be obtained by commercial purchase or preparation.

[0069] In a specific embodiment of the present application, the solid-state electrolyte is prepared by the following method: in an argon atmosphere glove box, Li2S, LiCl / LiBr and P2S5 are mixed in a weight ratio of 43.08:41.64:15.28 to obtain a raw material composition; after mixing the raw material composition in an agate mortar for 10-60 min, the planetary ball mill is mechanically ground at a speed of 100-1000 rpm for 5-30 h to obtain the solid-state electrolyte Li6PS5Cl.

[0070] In a specific embodiment of the present application, the positive electrode sheet is prepared by the following method: the positive electrode active paste is coated on the surface of the current collector (aluminum foil) and dried (the temperature is 60-100°C, preferably 60-90°C; the time is 1-36 h, preferably 5-24 h) to form a positive electrode active material layer on the surface of the current collector, thereby obtaining the positive electrode sheet.

[0071] The positive electrode active paste comprises a positive electrode active material, an optional electrolyte, an optional conductive agent, a binder and a solvent, and the solid content of the positive electrode active paste is 40-70wt%; the weight ratio of the positive electrode active material, the electrolyte, the conductive agent and the binder is 60-95:0-30:2-5:2-5.

[0072] In the present application, the type of the positive electrode active material has a wide selection range. Preferably, the positive electrode active material is selected from LiFePO4, LiCoO2, LiMn x O 2x (x is selected from 1 or 2), LiNi 1-y Mn y O2(0 z Co v M’ 1-z-v O2(M’ is selected from at least one of Mn, Al, Mg, Sn, Y and Cr, 0≤z

[0073] According to a particularly preferred embodiment of the present application, a composite negative electrode sheet comprises: a negative electrode sheet and an interface layer loaded on the surface of the negative electrode sheet, the negative electrode sheet comprises: a negative electrode active material layer, and the negative electrode active material layer contains lithium-free active material; the interface layer contains Li3P and an alloy phase;

[0074] During the battery cycle, the interface layer is in-situ converted from a coating layer containing metal phosphide; the metal in the metal phosphide forms the alloy phase with metal lithium from the positive electrode sheet;

[0075] The metal phosphide is selected from at least one of Sn4P3, GeP5, GeP, AlP, Mg3P2, InP and Zn3P2;

[0076] The thickness of the interface layer is 0.5-5μm; the thickness ratio of the interface layer and the negative electrode active material layer is 1:10-200;

[0077] The lithium-free active material is selected from at least one of graphite, hard carbon, soft carbon, silicon, SiO, Si / C and P.

[0078] The present application will be described in detail below through examples.

[0079] The ion conductivity parameter is tested by a direct current polarization method. The specific testing method is as follows: a solid-state battery mold is used. First, 100 mg of electrolyte is placed on both sides of the composite negative electrode sheet, and then the electrolyte is compressed under a pressure of 300 MPa. Then, Li-In alloy is attached to both sides of the electrolyte, and the electrolyte is compressed under a pressure of 200 MPa. The test conditions are as follows: constant voltage 0.5 V, running time: 8000 s. The steady-state current is passed, and the impedance value is obtained by the formula R = U / I. The impedance value is obtained by the formula σ = L / (R x S), wherein L is the thickness of the composite negative electrode sheet, R is the impedance value measured by the direct current polarization, and S is the thickness of the composite negative electrode sheet.

[0080] Example 1

[0081] (1) The negative electrode active slurry is coated on the surface of the current collector (copper foil) and dried (at a temperature of 80°C for 24 h) to form a negative electrode active material layer with a thickness of 80 μm on the surface of the current collector, thereby obtaining a negative electrode sheet;

[0082] In the formula, the negative electrode active slurry comprises: a lithium-free active material (graphite), an electrolyte (Li6PS5Cl), a conductive agent (Super-P), a binder (PVDF), and a solvent (heptane). The solid content of the negative electrode active slurry is 50 wt%, and the weight ratio of the lithium-free active material, the optional electrolyte, the optional conductive agent, and the binder is 60:35:2:3.

[0083] (2) The metal phosphide (Sn4P3, average particle size D50 of 1 nm) is coated on the surface of the negative electrode sheet and compacted (under a pressure of 400 MPa for 2 min) to form a coating layer on the surface of the negative electrode active material layer, thereby obtaining a composite negative electrode sheet precursor;

[0084] (3) In the battery cycle process, the composite negative electrode sheet precursor is converted in situ, so that the coating layer is converted into an interface layer containing Li3P and an alloy phase (Li-Sn), thereby obtaining a composite negative electrode sheet S1. The ion conductivity of the composite negative electrode sheet S1 is 5.25 x 10 -4 S / cm.

[0085] In the formula, the XPS spectra of Li-Sn and Li3P in the interface layer in the composite negative electrode sheet S1 are shown in Figure 1a and Figure 1b It can be seen from Figure 1a and Figure 1b that the interface layer in the composite negative electrode sheet S1 contains Li-Sn and Li3P.

[0086] Examples 2-5

[0087] The method and Table 1 of Example 1 are followed, except that the type of electrolyte and the type of metal phosphide are replaced according to the data in Table 1, and the remaining conditions are the same, to obtain composite negative electrode sheet S2-S5.

[0088] The ionic conductivity of the composite negative electrode sheet S2 is 4.17 x 10 -4 S / cm; the ionic conductivity of the composite negative electrode sheet S3 is 4.03 x 10 -4 S / cm; the ionic conductivity of the composite negative electrode sheet S4 is 3.64 x 10 -4 S / cm; and the ionic conductivity of the composite negative electrode sheet S5 is 4.18 x 10 -4 S / cm.

[0089] Examples 6-9

[0090] The method and Table 1 of Example 1 are followed, except that the thickness of the interface layer is replaced according to the data in Table 1, and the remaining conditions are the same, to obtain composite negative electrode sheet S6-S9.

[0091] The ionic conductivity of the composite negative electrode sheet S6 is 4.19 x 10 -4 S / cm; the ionic conductivity of the composite negative electrode sheet S7 is 4.97 x 10 -4 S / cm; the ionic conductivity of the composite negative electrode sheet S8 is 1.86 x 10 -4 S / cm; and the ionic conductivity of the composite negative electrode sheet S9 is 7.61 x 10 -4 S / cm.

[0092] Examples 10-12

[0093] The method and Table 1 of Example 1 are followed, except that the thickness of the negative electrode active material layer and the thickness of the interface layer are replaced according to the data in Table 1, respectively, and the remaining conditions are the same, to obtain composite negative electrode sheet S10-S12.

[0094] The ionic conductivity of the composite negative electrode sheet S10 is 4.67 x 10 -4 S / cm; the ionic conductivity of the composite negative electrode sheet S11 is 4.13 x 10 -4 S / cm; the ionic conductivity of the composite negative electrode sheet S12 is 3.26 x 10 -4 S / cm.

[0095] Examples 13-14

[0096] The method and Table 1 of Example 1 are followed, except that the type of active material without lithium is replaced according to the data in Table 1, and the remaining conditions are the same, to obtain composite negative electrode sheet S13-S14.

[0097] Examples 15-16

[0098] The method and Table 1 of Example 1 were followed, except that the compaction pressure was replaced by the data in Table 1, and the other conditions were the same, to obtain composite negative electrode sheet S15-S16.

[0099] The ion conductivity of the composite negative electrode sheet S15 was 5.02 x 10 -4 S / cm; the ion conductivity of the composite negative electrode sheet S16 was 4.98 x 10 -4 S / cm.

[0100] Examples 17-19

[0101] The method and Table 1 of Example 1 were followed, except that the compaction time was replaced by the data in Table 1, and the other conditions were the same, to obtain composite negative electrode sheet S17-S19.

[0102] The ion conductivity of the composite negative electrode sheet S17 was 5.11 x 10 -4 S / cm; the ion conductivity of the composite negative electrode sheet S18 was 5.06 x 10 -4 S / cm; the ion conductivity of the composite negative electrode sheet S19 was 4.64 x 10 -4 S / cm.

[0103] Comparative Example 1

[0104] The method of Example 1 was followed, except that steps (2)-(3) were not performed, and the negative electrode sheet prepared in step (1) was directly used as the composite negative electrode sheet DS1.

[0105] The ion conductivity of the composite negative electrode sheet DS1 was 1.01 x 10 -5 S / cm.

[0106] Comparative Example 2

[0107] The method and Table 1 of Example 1 were followed, except that the active material not containing lithium was replaced by Li according to the data in Table 1, and the other conditions were the same, to obtain composite negative electrode sheet DS2.

[0108] Comparative Example 3

[0109] The method and Table 1 of Example 1 were followed, except that in step (2), the compaction step was not performed, and the other conditions were the same, to obtain composite negative electrode sheet DS3.

[0110] The ion conductivity of the composite negative electrode sheet DS3 was 2.65 x 10 -5 S / cm.

[0111] Comparative Example 4

[0112] The method of Example 1 and Table 1 was used, except that in step (2), the metal phosphide was replaced by Cu3N, and the other conditions were the same, to obtain a composite negative electrode sheet DS4.

[0113] The ionic conductivity of the composite negative electrode sheet DS4 was 3.06 x 10 -5 S / cm.

[0114] Comparative Example 5

[0115] The method of Example 1 and Table 1 was used, except that in step (2), the metal phosphide was replaced by Li3P, and the other conditions were the same, to obtain a composite negative electrode sheet DS5.

[0116] The ionic conductivity of the composite negative electrode sheet DS5 was 5.21 x 10 -5 S / cm.

[0117] Comparative Example 6

[0118] The method of Example 1 and Table 1 was used, except that in step (2), the metal phosphide was replaced by CuF, and the other conditions were the same, to obtain a composite negative electrode sheet DS6.

[0119] The ionic conductivity of the composite negative electrode sheet DS6 was 2.64 x 10 -5 S / cm.

[0120] Table 1

[0121]

[0122]

[0123] Note: The thickness ratio * refers to the thickness ratio of the interface layer and the negative electrode active material layer.

[0124] Compared with the comparative examples, the ionic conductivity of the composite negative electrode sheet obtained by the method provided by the application is ≥ 1 x 10 -4 S / cm, which has a higher ion transmission capacity.

[0125] Test Example 1

[0126] Assemble a full solid-state battery:

[0127] (1) The positive electrode active material paste (thickness 200 μm) was coated on the surface of the current collector (aluminum foil) and dried (temperature 80°C, time 24h) to form a positive electrode active material layer on the surface of the current collector, to obtain a positive electrode sheet; the positive electrode active material paste comprises: positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1O, theoretical capacity: 200 mAh / g), electrolyte (Li6PS5Cl), conductive agent (Super-P), binder (PVDF) and solvent (toluene); the solid content of the positive active slurry is 60 wt%, and the weight ratio of the positive active material, electrolyte, conductive agent and binder is 75:20:3:2;

[0128] (2) 50 mg of the solid-state electrolyte (Li6PS5Cl) was compacted at a pressure of 300 MPa, then the composite negative electrode sheet S1 prepared in Example 1 and the above positive electrode sheet were added to both sides respectively, and then compacted at a pressure of 370 MPa to obtain a full solid-state battery Q1 (LiNi 0.8 Co 0.1 Mn 0.1 O2 / / Li6PS5Cl / / Sn4P3 / graphite);

[0129] Similarly, according to the method of the full solid-state battery Q1, the composite negative electrode sheets (S2-S19, DS1-DS6) prepared in Examples 2-19 and Comparative Examples 1-6 were respectively used as the negative electrode to obtain full solid-state batteries (Q2-Q19 and DQ1-DQ6);

[0130] Among them, the above full solid-state batteries (Q1-Q19 and DQ1-DQ6) were respectively subjected to rate performance tests (using a new Wei tester CT-4008), and the test results are listed in Table 2, wherein the test conditions include: voltage window: 2.7-4.1 V, constant current charging and discharging, test rate performance 0.1C / 0.1C, 0.2C / 0.2C, 0.5C / 0.5C, 1C / 1C, 2C / 2C.

[0131] Among them, the above full solid-state batteries (Q1-Q19 and DQ1-DQ6) were respectively subjected to rate performance tests (using a new Wei tester CT-4008), and the test results are listed in Table 2, wherein the test conditions include: voltage window: 2.7-4.1 V, constant current charging and discharging, test rate performance 0.1C / 0.1C, 0.2C / 0.2C, 0.5C / 0.5C, 1C / 1C, 2C / 2C. 0.8 Co 0.1 Mn 0.1 O2 / / Li6PS5Cl / / Sn4P3 / graphite) is shown in Figure 2 As shown in Figure 2 It can be seen that the full solid-state battery Q1 comprises: a positive electrode sheet, a solid-state electrolyte and a composite negative electrode sheet S1, wherein the composite negative electrode sheet S1 comprises: a negative electrode sheet and an interface layer loaded on the surface of the negative electrode sheet.

[0132] Table 2

[0133]

[0134]

[0135] From the results of Table 2, it can be seen that, compared with Comparative Examples 1-6, the full solid-state battery assembled by using the composite negative electrode sheet containing the specific interface layer provided by the application has better rate performance. Specifically, compared with Example 1, Comparative Example 1 shows that the full solid-state battery assembled by using the composite negative electrode sheet without the interface layer has poor rate performance; compared with Example 1, Comparative Example 2 shows that the full solid-state battery assembled by using the composite negative electrode sheet prepared by using the negative electrode active paste containing Li has poor rate performance; compared with Example 1, Comparative Example 3 shows that the full solid-state battery assembled by using the composite negative electrode sheet without compaction of the surface of the interface layer, i.e., without adding pressure, has poor rate performance; compared with Examples 1-19, Comparative Examples 4-7 show that the full solid-state battery assembled by using the negative electrode sheet prepared by using the non-limited metal phosphide has poor rate performance.

[0136] Meanwhile, Examples 1-5, although using different metal phosphides and types of electrolytes, have comparable rate performance of the assembled full solid-state batteries. Compared with Examples 6-9, the full solid-state battery assembled by using the scheme of Example 1 in which the thickness of the interface layer is limited to 1 μm has the best rate performance. Compared with Examples 10-12, the full solid-state battery assembled by using the scheme of Example 1 in which the thickness ratio of the interface layer to the negative electrode active material layer is limited to 1:80 has the best rate performance. Compared with Examples 13-14, the full solid-state battery assembled by using the scheme of Example 1 in which the negative electrode active material is limited to graphite has the best rate performance. Compared with Examples 15-16, the full solid-state battery assembled by using the scheme of Example 1 in which the compaction pressure is limited to 400 MPa has the best rate performance. Compared with Examples 17-19, the full solid-state battery assembled by using the scheme of Example 1 in which the compaction time is limited to 2 min has the best rate performance.

[0137] Test Example 2

[0138] The above full solid-state batteries (Q1-Q19 and DQ1-DQ6) were subjected to cycle performance tests (using a new Wei tester CT-4008), and the test results are shown in Table 3, wherein the test conditions include: voltage window: 2.7-4.1 V, rate 0.1 C, and cycle performance was tested under the condition.

[0139] Among them, the first charge-discharge curves of the full solid-state batteries Q1 and DQ1 under the conditions of 2.7-4.1 V and 0.1 C are as shown in Figure 3 It can be seen from Figure 3 that, compared with the full solid-state battery DQ1 prepared from Comparative Example 1, the full solid-state battery Q1 prepared from Example 1 has a higher first discharge specific capacity.

[0140] Table 3

[0141]

[0142]

[0143] It can be seen from the results in Table 3 that, compared with Comparative Examples 1-6, the full solid-state battery assembled by using the composite negative electrode sheet containing the interface layer provided by the application has better cycle performance.

[0144] Meanwhile, compared with Example 2-5, the cycle performance of the full solid-state battery assembled by using Sn4P3 in Example 1 is optimal. Compared with Examples 6-9, the cycle performance of the full solid-state battery assembled by using the scheme in which the thickness of the interface layer is limited to 1 μm in Example 1 is optimal. Compared with Examples 10-12, the cycle performance of the full solid-state battery assembled by using the scheme in which the thickness ratio of the interface layer and the negative electrode active material layer is limited to 1:80 in Example 1 is optimal. Compared with Examples 13-14, the cycle performance of the full solid-state battery assembled by using the scheme in which the negative electrode active material is limited to graphite in Example 1 is optimal. Compared with Examples 15-16, the cycle performance of the full solid-state battery assembled by using the scheme in which the compaction pressure is limited to 400 MPa in Example 1 is optimal. Compared with Examples 17-19, the cycle performance of the full solid-state battery assembled by using the scheme in which the compaction time is limited to 2 min in Example 1 is optimal.

[0145] Test Example 3

[0146] The above full solid-state batteries (Q1 and DQ1) were subjected to cycle stability tests, and the test results are shown in Table 4. The test conditions included: the temperature was 25℃, and the interface impedance value was tested under the condition of a rate of 0.1C. Among them, RSE represents the impedance of the solid-state electrolyte, Rct1 represents the interface impedance of the positive electrode and the solid-state electrolyte, and Rct2 represents the interface impedance of the negative electrode and the solid-state electrolyte.

[0147] Table 4

[0148]

[0149] It can be seen from the results in Table 4 that, compared with Comparative Example 1, the full solid-state battery Q1 assembled by using the composite negative electrode sheet containing the interface layer prepared from Example 1 has a lower growth rate of Rct2 interface impedance with the increase of the cycle number. Specifically, compared with Comparative Example 1, Example 1 has smaller Rct2 interface impedance values under the conditions of a rate of 0.1C, 50 cycles and 100 cycles.

[0150] The above describes the preferred embodiments of the application, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the application and fall within the protection scope of the application.

Claims

1. A composite negative electrode for an all-solid-state battery, characterized in that, The composite negative electrode sheet includes: a negative electrode sheet and an interface layer loaded on the surface of the negative electrode sheet; the negative electrode sheet includes: a negative electrode active material layer, and the negative electrode active material layer contains a lithium-free active material; the interface layer contains Li3P and an alloy phase; During battery cycling, the interface layer is obtained by in-situ conversion of a metal phosphide coating; wherein the metal in the metal phosphide forms the alloy phase with lithium metal from the positive electrode. The metal in the metal phosphide is selected from at least one of Sn, Ge, Al, Mg, In, and Zn; the thickness of the interface layer is 0.5-10 μm; and the thickness ratio of the interface layer to the negative electrode active material layer is 1:2-300.

2. The composite negative electrode sheet according to claim 1, wherein, The metal phosphide is selected from at least one of Sn4P3, GeP5, GeP, AlP, Mg3P2, InP, and Zn3P2.

3. The composite negative electrode sheet according to claim 1, wherein, The thickness of the interface layer is 0.5-5 μm.

4. The composite negative electrode sheet according to claim 1, wherein, The thickness ratio of the interface layer to the negative electrode active material layer is 1:10-200.

5. The composite negative electrode sheet according to claim 1, wherein, The lithium-free active material is a non-metallic material.

6. The composite negative electrode sheet according to claim 5, wherein, The lithium-free active material is selected from at least one of graphite, hard carbon, soft carbon, silicon, SiO, Si / C, and P.

7. The composite negative electrode sheet according to any one of claims 1-6, wherein the negative electrode active material layer further comprises: Electrolytes, conductive agents, and binders; The weight ratio of the lithium-free active material, electrolyte, conductive agent and binder is 50-95:0-40:0-5:0.5-5.

8. The composite negative electrode sheet according to claim 7, wherein, The weight ratio of the lithium-free active material, electrolyte, conductive agent, and binder is 60-85:5-35:2-5:1-3.

9. A method for preparing a composite negative electrode sheet for an all-solid-state battery, characterized in that, The method includes the following steps: (1) A negative electrode active slurry containing lithium-free active material is coated on the surface of the current collector and dried to form a negative electrode active material layer on the surface of the current collector, thereby obtaining a negative electrode sheet; (2) Apply metal phosphide to the surface of the negative electrode sheet and compact it to form a coating on the surface of the negative electrode active material layer, thereby obtaining a composite negative electrode precursor; (3) During battery cycling, the composite negative electrode precursor is transformed in situ, so that the coating is transformed into an interface layer containing Li3P and alloy phase, and a composite negative electrode is obtained. The metal in the metal phosphide forms the alloy phase with lithium metal from the positive electrode; the metal in the metal phosphide is selected from at least one of Sn, Ge, Al, Mg, In, and Zn; the thickness of the interface layer is 0.5-10 μm; and the thickness ratio of the interface layer to the negative electrode active material layer is 1:2-300.

10. The method according to claim 9, wherein, The thickness of the interface layer is 0.5-5µm.

11. The preparation method according to claim 10, wherein, The compaction conditions include: a pressure of 200-500 MPa and a time of 1-10 min.

12. The preparation method according to claim 11, wherein, The compaction conditions include: a pressure of 300-400 MPa and a time of 1-5 min.

13. An all-solid-state battery, characterized in that, The all-solid-state battery includes: the composite negative electrode sheet according to any one of claims 1-8, or the composite negative electrode sheet prepared by the method according to any one of claims 9-12; The all-solid-state battery also includes a solid electrolyte and a positive electrode.

14. The all-solid-state battery according to claim 13, wherein, The solid electrolyte is selected from sulfide solid electrolytes. The sulfide solid electrolyte is selected from xLi₂S·(100-x)P₂S₅, Li₃PS₄, and Li₇P₃S. 11 Li6PS5X, Li 10 MP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Li4GeS4 and Li 11 Sn2PS 12 At least one of the following, wherein 0 ≤ x ≤ 100, X is selected from Cl, Br, I, and M is selected from Ge, Sn, Si.

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