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 coating layer; the negative electrode sheet comprises a negative electrode active material layer, and the active material layer contains active material without lithium; the interface coating layer contains Li3P and elemental metal phase; wherein the interface coating layer is loaded on the surface of the negative electrode active material layer; wherein during the battery cycle process, the interface coating layer is obtained by in-situ conversion of a coating layer containing metal phosphide. The composite negative electrode sheet provided by the present application can effectively inhibit lithium dendrite growth and reduce interface impedance, which is helpful to the performance of rate capability; at the same time, the full solid-state battery containing the composite negative electrode sheet has high rate capability and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a composite negative electrode sheet, its preparation method and application, and an all-solid-state battery containing the composite negative electrode sheet. Background Technology

[0002] Lithium-ion batteries boast advantages such as high energy density, long lifespan, light weight, compact design, and environmental friendliness. Over the past decade, they have been widely used as energy storage devices in numerous fields, from consumer electronics (such as mobile phones and laptops) to the automotive industry and energy storage systems. Currently, commercially available lithium-ion batteries generally use liquid electrolytes. Because liquid batteries employ organic electrolytes, they are prone to leakage, flammability, and explosion, posing certain safety concerns. Solid-state batteries use solid positive and negative electrodes and solid electrolytes, containing no liquid; all materials are composed of solid materials. The inorganic solid electrolyte materials used in solid-state batteries are non-flammable, non-volatile, and do not have leakage problems. Therefore, all-solid-state batteries with solid electrolytes, such as those based on sulfide electrolytes, have high safety characteristics. Current solid-state battery assembly methods include cold isostatic pressing or hot pressing. Due to the relatively high contact resistance at the solid-solid interface, and the side reactions at the interface between the negative electrode and the sulfide electrolyte leading to the formation of interfacial product layers with low ionic conductivity, high interfacial impedance is generated, resulting in lower specific capacity at high rates.

[0003] CN100380712C discloses an ion-conducting composite for protecting an active metal anode. Specifically, a material capable of direct physical contact and alloying with the lithium metal is deposited on the surface of the active metal electrode, including metal nitrides, metal phosphides, and red phosphorus. This forms a protective layer through physical contact. This protective layer aims to protect the lithium metal from damage by air and electrolyte, and can react with the lithium metal to form Li3P. This ion-conducting composite uses an active lithium metal anode and does not address issues such as suppressing lithium dendrite growth, reducing interfacial impedance, or solving the problem of low specific capacity at high rates for non-lithium anode materials. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of lithium dendrite growth, high interfacial impedance, and low capacity volatilization at high rates in existing non-lithium anode materials and electrolyte interfaces. This invention provides a composite anode sheet, its preparation method and application, and an all-solid-state battery containing the composite anode sheet. The composite anode sheet effectively suppresses lithium dendrites and reduces interfacial impedance; simultaneously, the all-solid-state battery containing the composite anode sheet exhibits high rate performance and cycle performance.

[0005] The inventors of this invention discovered that by introducing a layer of metal phosphide onto the surface of the negative electrode active material layer, a layer of high ionic conductivity Li3P and a single-element metal phase are generated in situ during battery cycling (negative electrode lithiation process); wherein the ionic conductivity of Li3P can reach 10. -4 The high ionic conductivity interface coating (S / cm) enables the establishment of excellent lithium-ion transport channels, accelerating lithium-ion transport and improving the rate performance of all-solid-state batteries. Simultaneously, the elemental metallic phase generated at the interface exhibits high electronic conductivity, allowing for the modulation of Li... + Uniform deposition reduces interface resistance and helps improve battery rate performance and cycle performance.

[0006] Compared with CN100380712C, the present invention has the following advantages:

[0007] (1) CN100380712C discloses the use of metal phosphides on the surface of lithium metal, while this invention requests protection for the use of metal phosphides on the surface of non-lithium anode materials such as silicon, phosphorus, and silicon suboxide; wherein, the characteristics of lithium-free active materials are significantly different from those of lithium metal, lithium metal has high electronic conductivity, while lithium-free active materials have poor electronic conductivity; forming a Li3P phase with high ionic conductivity and a metallic phase with high electronic conductivity on the surface of lithium-free active materials can further improve their rate performance and suppress lithium dendrites;

[0008] (2) CN100380712C discloses using metal phosphides as a protective layer for lithium metal, protecting it from damage by air and electrolytes, and that it can react with lithium metal to form Li3P; while the specific interface coating claimed in this invention, during battery cycling, allows the Li3P at the positive electrode to be protected. + The Li3P and metallic phases involved in the reaction are different; that is, their mechanisms of action are different.

[0009] (3) The study of metal phosphides as negative electrode materials for lithium-ion batteries in CN100380712C is to use metal phosphides as negative electrode materials, which have the function of storing lithium and are related to cycle stability and specific capacity. However, this invention uses active materials that do not contain lithium (e.g., active materials that do not contain lithium ions or lithium metal, such as silicon and phosphorus) as negative electrode materials. The metal phosphides are only a coating on the surface of the negative electrode active material layer and are not used as active materials to store lithium metal. That is, the two have different functions.

[0010] (4) The "Room-Temperature Anode-less All-Solid-State Batteries via the Conversion Reaction of Metal Fluorides" directly uses metal fluorides as the anode material in an all-solid-state battery system, mainly addressing the problem of slow lithium-ion transport without an anode. It utilizes the conversion reaction of metal fluorides, where the metal nanodomains formed induce an alloying reaction with lithium ions, achieving uniform and sustainable deposition and delithiation. This invention coats metal phosphides onto the surface of intercalated anode materials such as graphite and silicon-based anode materials, forming a high-ionic-conductivity Li3P and a high-electronic-conductivity metal phase on the surface to solve the problem of poor rate performance in graphite and silicon-based anodes. Therefore, this invention differs from other inventions in structure, materials, and technical effects.

[0011] To achieve the above objectives, the first aspect of the present invention provides a composite negative electrode sheet, the composite negative electrode sheet comprising: a negative electrode sheet and an interface coating; the negative electrode sheet comprising: a negative electrode active material layer, wherein the active material layer contains a lithium-free active material; the interface coating comprises Li3P and a single metal phase; wherein the interface coating is loaded on the surface of the negative electrode active material layer;

[0012] During battery cycling, the interface coating is obtained by in-situ conversion of a coating containing metal phosphides.

[0013] Preferably, the metal in the metal phosphide does not form an alloy with lithium, and the metal is preferably selected from at least one of Fe, Ni, Cu and Mn.

[0014] Preferably, the metal phosphide is selected from at least one of FeP, Fe2P, FeP2, FeP4, NiP2, NiP3, Ni3P, Ni2P, Cu3P, and MnP4.

[0015] Preferably, the lithium-free active material is selected from non-metals and / or non-metallic alloys, and more preferably from at least one of graphite, hard carbon, silicon, SiO and Si / C.

[0016] A second aspect of this invention provides a method for preparing a composite negative electrode, the method comprising the following steps:

[0017] (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.

[0018] (2) Apply metal phosphide to the surface of the negative electrode, dry and compact it to form a coating on the surface of the negative electrode active material layer, and obtain a composite negative electrode precursor.

[0019] (3) During battery cycling, the composite negative electrode precursor is transformed in situ, so that the coating is transformed into an interface coating containing Li3P and a single metal phase, thus obtaining a composite negative electrode.

[0020] The third aspect of this invention provides a composite negative electrode sheet provided in the first aspect, or a composite negative electrode sheet prepared by the method provided in the second aspect, for use in all-solid-state batteries.

[0021] A fourth aspect of the present invention provides an all-solid-state battery, the all-solid-state battery comprising: a composite negative electrode sheet provided in the first aspect, or a composite negative electrode sheet prepared by the method provided in the second aspect, as well as a solid electrolyte and a positive electrode sheet.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) The composite negative electrode sheet provided by the present invention is obtained by in-situ conversion of a coating containing metal phosphides during battery cycling. It has an interface coating containing Li3P with high ionic conductivity and a single metal phase with high electronic conductivity. Combined with the composition of the negative electrode active material layer in the negative electrode sheet, the composite negative electrode sheet containing a specific interface coating can effectively suppress lithium dendrite growth and reduce interface impedance, which helps to improve rate performance. In particular, by adjusting the relevant parameters of the interface coating, it is more conducive to improving the performance parameters of the composite negative electrode sheet.

[0024] (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;

[0025] (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

[0026] Figure 1a This is the XPS spectrum of Cu in the interface coating of the composite negative electrode S1 prepared in Example 1;

[0027] Figure 1b This is the XPS spectrum of Li3P in the interfacial coating of the composite negative electrode S1 prepared in Example 1;

[0028] 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;

[0029] Figure 3The Rct2 interface impedance diagram is shown for the all-solid-state battery Q1 assembled from the composite negative electrode S1 provided in Example 1.

[0030] Figure 4 The Rct2 interface impedance diagram is shown for the all-solid-state battery DQ1 assembled from the composite negative electrode DS1 provided in Comparative Example 1. Detailed Implementation

[0031] 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.

[0032] The first aspect of the present invention provides a composite negative electrode sheet, the composite negative electrode sheet comprising: a negative electrode sheet and an interface coating; the negative electrode sheet comprising: a negative electrode active material layer, wherein the active material layer contains a lithium-free active material; the interface coating comprises Li3P and a single metal phase; wherein the interface coating is loaded on the surface of the negative electrode active material layer;

[0033] During battery cycling, the interface coating is obtained by in-situ conversion of a coating containing metal phosphides.

[0034] In this invention, unless otherwise specified, the negative electrode further includes a current collector, which includes, but is not limited to, copper foil. That is, the negative electrode includes a current collector and a layer of negative electrode active material loaded on the current collector.

[0035] In this invention, the composite negative electrode sheet provided by this invention includes: a negative electrode sheet and an interface coating. 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 a lithium-free active material. The interface coating contains Li3P and a single metal phase. The interface coating is loaded on the surface of the negative electrode active material layer. During battery cycling, the interface coating is obtained by in-situ conversion of a coating containing metal phosphides.

[0036] In this invention, unless otherwise specified, the battery cycling process refers to the lithiation process of the battery negative electrode, that is, during the lithiation process of the battery negative electrode, the metal phosphide in the coating and the Li-24 atoms transferred from the positive electrode... + The reaction forms Li3P, and metal ions are generated in situ into a single metal phase.

[0037] In this invention, a metal phosphide is transformed in situ to obtain a single-element metal phase. Preferably, the metal in the metal phosphide does not form an alloy with lithium; more preferably, the metal in the metal phosphide is selected from at least one of Fe, Ni, Cu, and Mn.

[0038] In some embodiments of the present invention, preferably, the metal phosphide is selected from at least one of FeP, Fe2P, FeP2, FeP4, NiP2, NiP3, Ni3P, Ni2P, Cu3P and MnP4, more preferably from at least one of FeP, NiP2, Cu3P and MnP4, and more preferably from Cu3P.

[0039] In some embodiments of the present invention, preferably, the average particle size D50 of the metal phosphide is 1-200 nm, and if the average particle size is too large, the electrode sheet with the required coating thickness cannot be coated.

[0040] In some embodiments of the present invention, preferably, the thickness of the interface coating is 0.5-10 μm, for example, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 8 μm, 10 μm, or any value within the range of any two values, preferably 0.5-5 μm, more preferably 0.5-2 μm, and most preferably 1 μm. When the thickness of the interface coating is too thick (i.e., the thickness is greater than 10 μm), conductive lithium-ion transport is hindered; when the thickness of the interface coating is too thin (i.e., the thickness is less than 0.5 μm), the interface coating cannot effectively improve rate performance and suppress lithium dendrite growth.

[0041] In some embodiments of the present invention, preferably, the thickness ratio of the coating to the negative electrode 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, 1:160, 1:200, 1:300, and any value within any range of any two values, preferably 1:10-200, more preferably 1:10-100, and most preferably 1:80. When the thickness ratio is too large, it indicates that the negative electrode active material layer is too thick and the coating is too thin, which cannot achieve good lithium-ion and electron transport effects; when the thickness ratio is too small, it indicates that the negative electrode active material layer is too thin and the coating is too thick, which is not suitable for use in high-energy-density negative electrode sheets.

[0042] In some embodiments of the present invention, preferably, the lithium-free active material is selected from non-metals and / or non-metallic alloys; more preferably, the lithium-free active material is selected from at least one of graphite, hard carbon, silicon, SiO and Si / C, and most preferably graphite.

[0043] In some embodiments of the present invention, preferably, the negative electrode active material layer further includes: optional electrolyte, optional conductive agent and binder; more preferably, the negative electrode active material layer is composed of lithium-free active material, electrolyte, conductive agent and binder.

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

[0045] In some embodiments of the present invention, preferably, the electrolyte is selected from sulfide electrolytes, and more preferably from xLi₂S·(100-x)P₂S₅(0≤x≤100), Li₃PS₄, and Li₇P₃S. 11 Li6PS5X (X = Cl, Br, I) and its derivatives, Li 10 MP2S 12 (M = 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 At least one of them.

[0046] In this invention, the derivatives of Li6PS5X (X = Cl, Br, I) include, but are not limited to, Li. 6-a PS 5-a Cl 1+a (0<a≤0.5), Li 6-b PS 5-b Br 1+b (0<b≤0.5), Li6PS 5-c Se c Br (0 < c ≤ 1), Li 6+d P 1-d M d S5I (M=Si, Ge, Sn) (0<d≤0.5).

[0047] In some embodiments of the present invention, preferably, the conductive agent is selected from at least one of acetylene black, Ketjen black, Super-P, KS-6, carbon fiber (VGCF), carbon nanotubes (CNTs) graphene, petroleum coke, needle coke, mesophase carbon microspheres, carbon fiber and vapor-grown carbon fiber (VGCF).

[0048] In some embodiments of the present invention, preferably, the adhesive is selected from at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), and carboxymethyl cellulose and their salts.

[0049] In some embodiments of the present invention, preferably, the ionic conductivity of the composite negative electrode is ≥5×10⁻⁶. -5 S / cm, for example, 5×10 -5 S / cm, 5.36×10 -5 S / cm, 6.16×10 -5 S / cm, 6.26×10 -5 S / cm, 6.75×10 -5 S / cm, 6.98×10 -5 S / cm, 7.17×10 -5 S / cm, 7.54×10 -5 S / cm, 7.61×10 -5 S / cm, 7.64×10 -5 S / cm, 7.83×10 -5 S / cm, 7.98×10 -5 S / cm, 8.03×10 -5 S / cm, 8.34×10 -5 S / cm, 8.43×10 -5 S / cm, 8.54×10 - 5 S / cm, and any value within the range of any two values, preferably (5-9)×10 -5 S / cm.

[0050] In this invention, unless otherwise specified, the ionic conductivity parameter is measured using the AC impedance method. The specific test includes: sandwiching the composite electrode between two stainless steel disc electrodes (SS), measuring the ionic conductivity (σ) using electrochemical impedance spectroscopy (EIS) within a frequency range of 1Hz-7MHz with an AC amplitude of 10mV, and calculating it according to formula (1): Among them, R b The volume resistivity (R) of the sample to be tested b (Determined by impedance spectroscopy), where L and S are the thickness and area of ​​the sample to be tested.

[0051] A second aspect of this invention provides a method for preparing a composite negative electrode, the method comprising the following steps:

[0052] (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.

[0053] (2) Apply metal phosphide to the surface of the negative electrode, dry and compact it to form a coating on the surface of the negative electrode active material layer, and obtain a composite negative electrode precursor.

[0054] (3) During battery cycling, the composite negative electrode precursor is transformed in situ, so that the coating is transformed into an interface coating containing Li3P and a single metal phase, thus obtaining a composite negative electrode.

[0055] In this invention, unless otherwise specified, the types of lithium-free active materials and metal phosphides are all as defined above, and will not be elaborated upon here.

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

[0057] In some embodiments of the present invention, preferably, the negative electrode active slurry further includes: an optional electrolyte, an optional conductive agent, a binder, and a solvent. The types of the electrolyte, conductive agent, and binder are all as defined above, and will not be elaborated further in this invention; the solvent includes, but is not limited to, N-methylpyrrolidone, toluene, xylene, acetone, hexane, and heptane.

[0058] In some embodiments of the present invention, more preferably, the mass ratio of the lithium-free active material, optional electrolyte, optional conductive agent and binder in the negative electrode 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 this invention, the negative electrode active slurry coating aims to evenly coat the negative electrode active slurry onto the surface of the current collector. Preferably, in step (1), the thickness of the negative electrode active material layer is 20-150 μm, for example, 20 μm, 50 μm, 80 μm, 100 μm, 150 μm, and any value within the range of any two values, preferably 50-100 μm, and most preferably 80 μm.

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

[0061] In this invention, the metal phosphide coating is intended to uniformly coat the surface of the negative electrode active material layer with metal phosphide to form a coating. This invention does not limit the thickness of the coating, as long as the coating is transformed in situ to obtain an interface coating of a specific thickness.

[0062] In some embodiments of the present invention, preferably, in step (2), the compaction conditions include: a pressure of 200-500 MPa, preferably 300-400 MPa, and most preferably 400 MPa; and a time of 1-10 min, preferably 1-5 min, and most preferably 2 min.

[0063] In this invention, the in-situ conversion aims to transform metal phosphides into Li3P and elemental metal phases. The conditions for in-situ conversion are not limited in this invention, and it can be achieved during any battery cycle.

[0064] The third aspect of this invention provides a composite negative electrode sheet provided in the first aspect, or a composite negative electrode sheet prepared by the method provided in the second aspect, for use in all-solid-state batteries.

[0065] The fourth aspect of the present invention provides an all-solid-state battery, the all-solid-state battery comprising: a composite negative electrode sheet provided in the first aspect, or a composite negative electrode sheet prepared by the method provided in the second aspect. Theoretically, after the coating is successively dried and compacted, an interface coating is obtained, so the thickness of the coating should be greater than the thickness of the interface coating.

[0066] In this invention, unless otherwise specified, the solid electrolyte is disposed between the interface coating and the positive electrode in the composite negative electrode.

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

[0068] In this invention, the source of the solid electrolyte has a wide range of choices; it can be obtained commercially or prepared.

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

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

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

[0072] In this invention, a wide range of types of positive electrode active materials can be selected. Preferably, the positive electrode active material is selected from LiFePO4, LiCoO2, and LiMn. x O 2x (x is selected from 1 or 2), LiNi 1-y Mn y O2 (0 < y < 1), LiNi 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<1, 0<v≤1, and z+v≤1) and gLi2MnO3·(1-g)LiMnO2 (0<g<1).

[0073] According to a particularly preferred embodiment of the present invention, a composite negative electrode sheet is provided, the composite negative electrode sheet comprising: a negative electrode sheet and an interface coating; the negative electrode sheet comprising: a negative electrode active material layer, wherein the negative electrode active material layer contains a lithium-free active material; the interface coating comprises Li3P and a single metal phase; wherein the interface coating is loaded on the surface of the negative electrode active material layer;

[0074] During battery cycling, the interface coating is obtained by in-situ conversion of a coating containing metal phosphides.

[0075] The metal phosphide is selected from at least one of FeP, NiP2, Cu3P and MnP4;

[0076] The thickness of the interface coating is 0.5-5 μm; the thickness ratio of the interface coating to 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, silicon, SiO, and Si / C.

[0078] The present invention will be described in detail below through embodiments.

[0079] The ionic conductivity parameter was measured using the AC impedance method. The specific test included: sandwiching the composite electrode between two stainless steel disc electrodes (SS), measuring the ionic conductivity (σ) by electrochemical impedance spectroscopy (EIS) within a frequency range of 1Hz-7MHz with an AC amplitude of 10mV, and calculating it according to formula (1). Among them, R b The volume resistivity (R) of the sample to be tested b (Determined by impedance spectroscopy), where L and S are the thickness and area of ​​the sample to be tested.

[0080] Example 1

[0081] (1) A negative electrode active slurry with a solid content of 50wt% is coated on the surface of the current collector (copper foil) and dried (at a temperature of 80°C for 24 hours) to form a negative electrode active material layer with a thickness of 80μm on the surface of the current collector, thereby obtaining a negative electrode sheet.

[0082] The negative electrode active slurry includes: lithium-free active material (graphite), electrolyte (Li6PS5Cl), conductive agent (Super-P), binder (PVDF) and solvent (heptane), with a mass ratio of lithium-free active material, electrolyte, conductive agent and binder of 60:35:2:3.

[0083] (2) A metal phosphide (Cu3P, average particle size D50 is 1nm) is coated on the surface of the above negative electrode sheet, dried (temperature is 80℃, time is 24h) and then compacted (pressure is 400MPa, time is 2min) to form a coating on the surface of the above negative electrode active material layer, and a composite negative electrode precursor is obtained.

[0084] (3) During battery cycling, the above-mentioned composite negative electrode precursor is subjected to in-situ transformation, so that the above coating is transformed into an interface coating containing Li3P and a single metal phase (Cu), to obtain composite negative electrode S1; wherein, the ionic conductivity of composite negative electrode S1 is 8.54 × 10⁻⁶. -5 S / cm.

[0085] Among them, the XPS spectra of Cu and Li3P in the interfacial coating of the composite negative electrode S1 are as follows: Figure 1a and Figure 1b As shown, by Figure 1a and Figure 1b It can be seen that the interface coating in the composite negative electrode S1 contains Li3P and elemental Cu.

[0086] Examples 2-4

[0087] Following the method of Example 1 and Table 1, except that the types of electrolytes and metal phosphides were replaced according to the data in Table 1, while the other conditions remained the same, composite negative electrode sheets S2-S4 were obtained.

[0088] Among them, the ionic conductivity of the composite negative electrode S2 is 7.64 × 10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S3 is 8.03×10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S4 is 7.17 × 10⁻⁶. -5 S / cm.

[0089] Examples 5-8

[0090] Following the method of Example 1 and Table 1, except that the thickness of the interface coating was replaced according to the data in Table 1, while the other conditions remained the same, composite negative electrode sheets S5-S8 were obtained.

[0091] Among them, the ionic conductivity of the composite negative electrode S5 is 6.98×10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S6 is 7.83×10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S7 is 6.26 × 10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S8 is 5.36 × 10⁻⁶. -5 S / cm.

[0092] Examples 9-11

[0093] Following the method of Example 1 and Table 1, except that the thickness of the negative electrode active material layer and the thickness of the interface coating were replaced according to the data in Table 1, while the other conditions remained the same, composite negative electrode sheets S9-S11 were obtained.

[0094] Among them, the ionic conductivity of the composite negative electrode S9 is 6.75×10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S10 is 7.61 × 10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S11 is 6.16 × 10⁻⁶. -5 S / cm.

[0095] Examples 12-14

[0096] Following the method of Example 1 and Table 1, except that the types of lithium-free active materials were replaced according to the data in Table 1, while the other conditions remained the same, composite negative electrode sheets S12-S14 were obtained.

[0097] Examples 15-16

[0098] Following the method of Example 1 and Table 1, except that the compaction pressure was replaced according to the data in Table 1, while the other conditions remained the same, composite negative electrode sheets S15-S16 were obtained.

[0099] Among them, the ionic conductivity of the composite negative electrode S15 is 8.43×10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S16 is 7.98 × 10⁻⁶. -5 S / cm.

[0100] Examples 17-19

[0101] Following the method of Example 1 and Table 1, except that the compaction time was replaced with the data in Table 1, while the other conditions remained the same, composite negative electrode sheets S17-S19 were obtained.

[0102] Among them, the ionic conductivity of the composite negative electrode S17 is 8.34 × 10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S18 is 8.03×10⁻⁶. -5 S / cm; The ionic conductivity of the composite negative electrode S19 is 7.54 × 10⁻⁶. -5 S / cm.

[0103] Comparative Example 1

[0104] The method of Example 1 and Table 1 are the same, except that steps (2)-(3) are omitted, and the negative electrode obtained in step (1) is directly used as the composite negative electrode DS1.

[0105] Among them, the ionic conductivity of the composite negative electrode DS1 is 1.01×10⁻⁶. -5 S / cm.

[0106] Comparative Example 2

[0107] Following the method of Example 1 and Table 1, except that the lithium-free active material was replaced according to the data in Table 1, while the other conditions remained the same, the composite negative electrode DS2 was obtained.

[0108] Comparative Example 3

[0109] The method of Example 1 and Table 1 are the same, except that there is no compaction step in step (2), and the other conditions are the same, to obtain the composite negative electrode DS3.

[0110] Among them, the ionic conductivity of the composite negative electrode DS3 is 4.06×10⁻⁶. -5 S / cm.

[0111] Comparative Example 4

[0112] The method of Example 1 and Table 1 are followed, except that in step (2), the metal phosphide is replaced with Cu3N, and the other conditions are the same, to obtain the composite negative electrode DS4.

[0113] Among them, the ionic conductivity of the composite negative electrode DS4 is 3.68 × 10⁻⁶. -5 S / cm.

[0114] Comparative Example 5

[0115] The method of Example 1 and Table 1 are followed, except that in step (2), the metal phosphide is replaced with Li3P, while the other conditions are the same, to obtain the composite negative electrode DS5.

[0116] Among them, the ionic conductivity of the composite negative electrode DS5 is 4.86×10⁻⁶. -5 S / cm.

[0117] Comparative Example 6

[0118] The method of Example 1 and Table 1 are followed, except that in step (2), the metal phosphide is replaced with AgF, while the other conditions are the same, to obtain the composite negative electrode DS6.

[0119] Among them, the ionic conductivity of the composite negative electrode DS6 is 4.21 × 10⁻⁶. -5 S / cm.

[0120] Table 1

[0121]

[0122]

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

[0124] Compared to the comparative example, the composite negative electrode obtained by the method provided in this invention has an ionic conductivity ≥ 5 × 10⁻⁶. -5 The composite negative electrode S1 prepared in Example 1 has a high ion transport capacity (S / cm). In particular, compared with Comparative Example 1, the ion conductivity of the composite negative electrode S1 prepared in Example 1 is increased by 7 times.

[0125] Test Example 1

[0126] Assemble all-solid-state batteries:

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

[0128] (2) After compacting 50 mg of solid electrolyte (Li6PS5Cl) at a pressure of 300 MPa, the composite negative electrode S1 prepared in Example 1 and the above-mentioned positive electrode were added to both sides respectively, and after compacting at a pressure of 370 MPa, an all-solid-state battery Q1 (LiNi) was obtained. 0.8 Co 0.1 Mn 0.1 O2 / / Li6PS5Cl / / Cu3P / graphite);

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

[0130] Among them, the above-mentioned all-solid-state batteries (Q1-Q19 and DQ1-DQ6) were subjected to rate performance tests (using Xinwei CT-4008 tester), and the test results are listed in Table 2. The test conditions included: voltage window: 2.7-4.2V, constant current charge and discharge, and test rate performance of 0.1C / 0.1C, 0.2C / 0.2C, 0.5C / 0.5C, 1C / 1C, and 2C / 2C.

[0131] Among them, the all-solid-state battery Q1 (LiNi) 0.8 Co 0.1 Mn 0.1 A schematic diagram of the structure of O2 / / Li6PS5Cl / / Cu3P / graphite is shown below. Figure 2 As shown, by Figure 2 It can be seen that the all-solid-state battery Q1 includes: a positive electrode, a solid electrolyte and a composite negative electrode S1, wherein the composite electrode S1 includes: a negative electrode and an interface coating loaded on the surface of the negative electrode.

[0132] Table 2

[0133]

[0134]

[0135] As can be seen from the results in Table 2, compared with Comparative Examples 1-6, the all-solid-state battery assembled using the composite negative electrode sheet with an interface coating provided by the present invention has better rate performance. Specifically, compared with Example 1, Comparative Example 1 shows that the all-solid-state battery assembled with a composite negative electrode sheet without an interface coating has a poorer rate performance; compared with Example 1, the all-solid-state battery assembled with a composite negative electrode sheet made of Li-containing negative electrode active slurry in Comparative Example 2 has a poorer rate performance; compared with Example 1, the surface of the interface coating in Comparative Example 3 was not compacted, i.e., no pressure was added, resulting in poorer rate performance; compared with Examples 1-19, the all-solid-state batteries assembled with negative electrode sheets made of non-limited metal phosphides in Comparative Examples 4-6 have poorer rate performance.

[0136] Meanwhile, compared to Examples 2-4, the all-solid-state battery assembled using the electrolyte (Li6PS5Cl) and metal phosphide (Cu3P) scheme specified in Example 1 exhibits the best rate performance. Compared to Examples 5-8, the all-solid-state battery assembled using the scheme specified in Example 1 with an interface coating thickness of 1 μm exhibits the best rate performance. Compared to Examples 9-11, the all-solid-state battery assembled using the scheme specified in Example 1 with an interface coating to negative electrode active material thickness ratio of 1:80 exhibits the best rate performance. Compared to Examples 12-14, the all-solid-state battery assembled using the scheme specified in Example 1 with graphite as the negative electrode active material exhibits the best rate performance. Compared to Examples 15-16, the all-solid-state battery assembled using the scheme specified in Example 1 with a compaction pressure of 400 MPa exhibits the best rate performance. Compared to Examples 17-19, the all-solid-state battery assembled using the scheme specified in Example 1 with a compaction time of 2 min exhibits the best rate performance.

[0137] Test Example 2

[0138] The above-mentioned all-solid-state batteries (Q1-Q19 and DQ1-DQ6) were subjected to cycle performance tests (using Xinwei CT-4008 tester). The test results are listed in Table 3. The test conditions included: voltage window: 2.7-4.2V, and cycle performance was tested under a rate of 0.1C.

[0139] Table 3

[0140] Example 1 Q1 339 Example 2 Q2 307 Example 3 Q3 327 Example 4 Q4 291 Example 5 Q5 304 Example 6 Q6 272 Example 7 Q7 261 Example 8 Q8 124 Example 9 Q9 302 Example 10 Q10 297 Example 11 Q11 128 Example 12 Q12 228 Example 13 Q13 106 Example 14 Q14 201 Example 15 Q15 321 Example 16 Q16 263 Example 17 Q17 228 Example 18 Q18 224 Example 19 Q19 158 Comparative Example 1 DQ1 102 Comparative Example 2 DQ2 100 Comparative Example 3 DQ3 128 Comparative Example 4 DQ4 134 Comparative Example 5 DQ5 127 Comparative Example 6 DQ6 188

[0141] As can be seen from the results in Table 3, compared with Comparative Examples 1-6, the all-solid-state battery assembled using the composite negative electrode sheet with interface coating provided by the present invention has better cycle performance.

[0142] Compared to Examples 2-4, the all-solid-state battery assembled using the electrolyte (Li6PS5Cl) and metal phosphide (Cu3P) scheme specified in Example 1 exhibits the best cycle performance. Compared to Examples 5-8, the all-solid-state battery assembled using the interface coating thickness of 1 μm specified in Example 1 exhibits the best cycle performance. Compared to Examples 9-11, the all-solid-state battery assembled using the interface coating to negative electrode active material layer thickness ratio of 1:80 specified in Example 1 exhibits the best cycle performance. Compared to Examples 12-14, the all-solid-state battery assembled using graphite as the negative electrode active material specified in Example 1 exhibits the best cycle performance. Compared to Examples 15-16, the all-solid-state battery assembled using a compaction pressure of 400 MPa specified in Example 1 exhibits the best cycle performance. Compared to Examples 17-19, the all-solid-state battery assembled using a compaction time of 2 min specified in Example 1 exhibits the best cycle performance.

[0143] Test Example 3

[0144] The above-mentioned all-solid-state batteries (Q1 and DQ1) were subjected to cycle stability tests, and the test results are listed in Table 4. The test conditions included: the interface impedance value was tested at a temperature of 25℃ and a rate of 0.1C. Among them, RSE represents the impedance of the solid electrolyte, Rct1 represents the interface impedance between the positive electrode and the solid electrolyte, and Rct2 represents the interface impedance between the negative electrode and the solid electrolyte.

[0145] The Rct2 interface impedance diagrams of the all-solid-state batteries (Q1 and DQ1) are as follows: Figure 3 and Figure 4 As shown, by Figure 3-4 It can be seen that, compared with the all-solid-state battery DQ1, the all-solid-state battery Q1 has a lower increase in Rct2 interface impedance as the number of cycles increases.

[0146] Table 4

[0147]

[0148] As can be seen from the results in Table 4, compared with Comparative Example 1, the all-solid-state battery Q1 assembled from the composite negative electrode sheet with interface coating prepared in Example 1 shows a lower increase in Rct2 interface impedance as the number of cycles increases.

[0149] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite negative electrode, characterized in that, The composite negative electrode sheet includes: a negative electrode sheet and an interface coating; 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 coating contains Li3P and a single metal phase; wherein, the interface coating is loaded on the surface of the negative electrode active material layer; During battery cycling, the interface coating is obtained by in-situ conversion of a coating containing metal phosphides. The metal phosphide does not form an alloy with lithium; The metal phosphide is selected from at least one of Fe, Ni, Cu and Mn.

2. The composite negative electrode according to claim 1, wherein the metal phosphide is selected from at least one of FeP, Fe2P, FeP2, FeP4, NiP2, NiP3, Ni3P, Ni2P, Cu3P and MnP4.

3. The composite negative electrode according to claim 2, wherein the metal phosphide is selected from at least one of FeP, NiP2, Cu3P and MnP4.

4. The composite negative electrode sheet according to claim 1, wherein, The thickness of the interface coating is 0.5-10µm.

5. The composite negative electrode sheet according to claim 4, wherein, The thickness of the interface coating is 0.5-5µm.

6. The composite negative electrode sheet according to claim 1, wherein, The thickness ratio of the interface coating to the negative electrode active material layer is 1:2-300.

7. The composite negative electrode sheet according to claim 6, wherein, The thickness ratio of the interface coating to the negative electrode active material layer is 1:10-200.

8. The composite negative electrode sheet according to claim 1, wherein, The lithium-free active material is selected from non-metals and / or non-metallic alloys.

9. The composite negative electrode sheet according to claim 8, wherein, The lithium-free active material is selected from at least one of graphite, hard carbon, silicon, SiO, and Si / C.

10. The composite negative electrode according to claim 1, wherein, The negative electrode active material layer also includes: optional electrolyte, optional conductive agent and binder.

11. The composite negative electrode according to claim 10, wherein, The mass ratio of the lithium-free active material, optional electrolyte, optional conductive agent, and binder is 50-95:0-40:0-5:0.5-5.

12. The composite negative electrode according to claim 11, wherein, The mass ratio of the lithium-free active material, optional electrolyte, optional conductive agent, and binder is 60-85:5-35:2-5:1-3.

13. The composite negative electrode according to claim 10, wherein, The electrolyte is selected from sulfide electrolytes.

14. The composite negative electrode according to claim 13, wherein, The electrolyte is selected from xLi₂S·(100-x)P₂S₅, Li₃PS₄, and Li₇P₃S. 11 Li6PS5X and its derivatives, 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 them; Where 0 ≤ x ≤ 100; X = Cl, Br, I; M = Ge, Sn, Si.

15. The composite negative electrode according to claim 10, wherein, The conductive agent is selected from at least one of acetylene black, Ketjen black, Super-P, KS-6, carbon fiber, and carbon nanotubes.

16. The composite negative electrode according to claim 10, wherein, The adhesive is selected from at least one of polyvinylidene fluoride, styrene-butadiene rubber, polytetrafluoroethylene, and carboxymethyl cellulose and their salts.

17. A method for preparing a composite negative electrode sheet according to any one of claims 1-16, 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, dry it and then compact it to form a coating on the surface of the negative electrode active material layer, so as to obtain 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 coating containing Li3P and a single metal phase, thus obtaining a composite negative electrode.

18. The method according to claim 17, wherein, In step (1), the negative electrode active slurry further includes: optional electrolyte, optional conductive agent, binder and solvent.

19. The method according to claim 18, wherein, In the negative electrode active slurry, the mass ratio of the lithium-free active material, optional electrolyte, optional conductive agent and binder is 50-95:0-40:0-5:0.5-5.

20. The method according to claim 19, wherein, In the negative electrode active slurry, the mass ratio of the lithium-free active material, optional electrolyte, optional conductive agent and binder is 60-85:5-35:2-5:1-3.

21. The method according to claim 18, wherein, The thickness of the negative electrode active material layer is 20-150µm.

22. The method according to claim 21, wherein, The thickness of the negative electrode active material layer is 50-100µm.

23. The method according to claim 17, wherein, In step (2), the compaction conditions include: pressure of 200-500 MPa and time of 1-10 min.

24. The method according to claim 23, wherein, In step (2), the compaction conditions include: pressure of 300-400 MPa and time of 1-5 min.

25. The method according to claim 17, wherein, In step (3), the thickness of the interface coating is 0.5-10µm.

26. The method of claim 25, wherein, In step (3), the thickness of the interface coating is 0.5-5µm.

27. The composite negative electrode sheet according to any one of claims 1-16, or the composite negative electrode sheet prepared by the method according to any one of claims 17-26, in an all-solid-state battery.

28. An all-solid-state battery, characterized in that, The all-solid-state battery includes: a composite negative electrode sheet as described in any one of claims 1-16, or a composite negative electrode sheet prepared by the method described in any one of claims 17-26; the all-solid-state battery further includes a solid electrolyte and a positive electrode sheet.

Images