Negative electrode material and preparation method therefor, negative electrode sheet, and all-solid-state battery

Abstract

A negative electrode material and a preparation method therefor, a negative electrode sheet, and an all-solid-state battery. The negative electrode material has a core-shell structure, and comprises a lithium-free active material and a coating layer thereof, wherein the coating layer is selected from metal phosphorus sulfides having a general formula of MxPySz, M is selected from non-lithium metal elements, and x, y and z are all selected from natural numbers. The negative electrode material is subjected to in-situ conversion during battery cycle to obtain a modified active substance, improving an interface between a non-lithium negative electrode material and an electrolyte, and effectively improving the ionic conductivity and the electronic conductivity of the negative electrode sheet. Moreover, the all-solid-state battery assembled by the negative electrode sheet has high cycle performance and energy density.

Description

Negative electrode material and preparation method thereof, negative electrode sheet, and all-solid-state battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of Chinese patent application 202311869916.6 filed on December 29, 2023, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to the technical field of lithium-ion batteries, and in particular to a negative electrode material and a preparation method thereof, a negative electrode plate and an all-solid-state battery. Background Art

[0004] The existing SEI technology introduced in all-solid-state mainly uses "electrolyte + lithium salt" to modify the interface polarity between the electrolyte and the negative electrode. This method will cause side reactions of the sulfide electrolyte material at the interface, affecting battery performance, resulting in increased interface impedance and decreased battery performance.

[0005] CN110061285A discloses a solid-state lithium battery based on a borohydride / sulfide double-layer fast ion conductor, comprising a positive electrode, a negative electrode, and a double-layer electrolyte consisting of a borohydride fast ion conductor layer and a sulfide fast ion conductor layer. However, borohydride has poor electrochemical stability and is very easy to decompose into BH4 - Catalyzes the decomposition of sulfide electrolytes and degrades the battery.

[0006] CN115621417A discloses a composite lithium negative electrode, which is made from metallic lithium, carbon material and a lithiophilic metal as raw materials, fully reacted at high temperature, and cooled to room temperature. LiC6 formed after the carbon material is lithiated serves as the skeleton inside the composite lithium negative electrode. The lithiophilic metal and lithium are alloyed to form a lithiophilic alloy phase. Neither LiC6 nor the alloy phase participates in the electrochemical cycle. Only the metallic lithium inside the composite lithium negative electrode is the electrochemically active component. The use of this negative electrode in an all-solid-state battery system will result in poor lithium ion conductivity, which will result in poor performance of the specific capacity of the all-solid-state battery. Summary of the Invention

[0007] In order to overcome the interface problems between existing lithium-free active material and electrolyte, such as corrosion of battery, electrochemical instability, high impedance, etc., which in turn affect the low volatility of battery specific capacity at high rate, etc., the present invention provides a negative electrode material and a preparation method thereof, a negative electrode plate and an all-solid-state battery.

[0008] In order to achieve the above object, the first aspect of the present invention provides a negative electrode material having a core-shell structure, comprising an active material without lithium and a coating layer thereof, wherein the coating layer is selected from the general formula M x Py S z wherein M is selected from non-lithium metal elements, and x, y and z are all selected from natural numbers.

[0009] Preferably, M is selected from metal elements that do not form an alloy with lithium and / or metal elements that form an alloy with lithium.

[0010] Further preferably, the M is selected from at least one of Sn, Fe, Ni, Cu, Mn, Na, Ge, Al, Mg, In, Zn and Co, and preferably selected from at least one of Fe, Ni, Cu, Co and Mn.

[0011] Preferably, the metal phosphosulfide is selected from at least one of Cu3PS4, Cu4P2S7, Cu2P2S6, FePS4, Ni3PS4, Mn2P2S7, MnP2S6, NaP3S4, AlPS4, SnP2S7, InPS4, MgP2S6, GeP2S7 and Co2P2S7.

[0012] The second aspect of the present invention provides a method for preparing a negative electrode material, the preparation method comprising the following steps: in the presence of an inert gas, mixing a metal sulfide, P2S5 and an organic solvent to obtain a metal sulfide containing M x P y S z The solution containing M x P y S z The solution and the lithium-free active material are mixed for the second time, and the obtained mixture is subjected to low-pressure static treatment and sintering in sequence to coat the surface of the lithium-free active material with the general formula M x P y S z metal phosphosulfide to obtain the negative electrode material;

[0013] Wherein, M is selected from non-lithium metal elements; x, y and z are all selected from natural numbers.

[0014] The third aspect of the present invention provides a negative electrode plate, which includes: an active material layer and a current collector, the active material layer contains a modified active material, and the modified active material is obtained by in-situ conversion of the negative electrode material provided by the first aspect, or the negative electrode material prepared by the preparation method provided by the second aspect during the battery cycle.

[0015] A fourth aspect of the present invention provides a negative electrode plate, comprising: an active material layer and a current collector, wherein the active material layer comprises a modified active material, wherein the modified active material comprises an active material that does not contain lithium, and an interface layer coated on the surface of the active material that does not contain lithium; wherein the interface layer comprises Li2S, Li3P, and a metal single phase and / or an alloy phase;

[0016] The metal in the metal single phase and / or alloy phase is selected from metal elements that do not form an alloy with lithium and / or metal elements that form an alloy with lithium.

[0017] The fifth aspect of the present invention provides an all-solid-state battery, comprising: a negative electrode sheet, a solid electrolyte and a positive electrode sheet, wherein the negative electrode sheet is selected from the negative electrode sheet provided in the third aspect and / or the fourth aspect.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The negative electrode material provided by the present invention is limited to coating M on the surface of the active material without lithium x P y S z , so that the negative electrode material is converted in situ during the battery cycle to obtain a modified active material, the modified active material including an active material that does not contain lithium and a specific interface layer, that is, containing Li2S, Li3P, and a metal single phase and / or alloy phase;

[0020] Specifically, Li3P has high ionic conductivity; the metal single phase / alloy phase has high electronic conductivity, which improves the cycle performance of the battery; the negative electrode sheet containing a specific interface layer avoids the degradation of battery performance caused by electrolyte decomposition and improves cycle stability;

[0021] (2) The present invention provides a method for preparing a negative electrode material, which uses a liquid phase method to obtain a negative electrode material having a core-shell structure. Compared with conventional physical mixing, the interface layer of the modified active substance obtained by in-situ conversion of the specific negative electrode material has higher density and stability. At the same time, the preparation method simplifies the process flow and is convenient for industrial production.

[0022] (3) The negative electrode provided by the present invention is used in an all-solid-state battery. By regulating the electrochemical stability and interfacial impedance of the negative electrode and the electrolyte, the battery capacity at a high rate is effectively improved, so that the all-solid-state battery containing the negative electrode has higher cycle stability, cycle performance and energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a SEM image of the negative electrode material S1 prepared in Example 1;

[0024] FIG2 is a SEM image of the negative electrode material DS2 prepared in Comparative Example 2.

[0025] FIG3 is an XRD pattern of the negative electrode material S1 obtained in Example 1 after cycling;

[0026] FIG4 is an XPS graph of the negative electrode material S1 prepared in Example 1 before lithiation. DETAILED DESCRIPTION

[0027] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0028] In the present invention, unless otherwise specified, the terms "first" and "second" do not indicate a sequential order or limit the materials or steps involved. They are used only to distinguish or indicate that they are not the same materials or steps. For example, in "first sintering" and "second sintering," the terms "first" and "second" are used only to indicate that they are not the same sintering.

[0029] The first aspect of the present invention provides a negative electrode material having a core-shell structure, comprising an active material containing no lithium and a coating layer thereof, wherein the coating layer is selected from a general formula M x P y S z wherein, M is selected from non-lithium metal elements, and x, y and z are all selected from natural numbers.

[0030] The inventors of the present invention have discovered that the interface between the all-solid-state negative electrode and the sulfide electrolyte can cause battery failure due to electrochemical instability. To improve the interface problem between the negative electrode and the electrolyte, the present invention coats the surface of a lithium-free active material with a specific metal phosphosulfide. The metal phosphosulfide is used to undergo in-situ conversion during the battery cycle to form in-situ metal single phases and / or alloy phases, Li2S and Li3P, on the negative electrode surface. These products have high electrical conductivity, which can satisfy the requirement for free conduction inside the negative electrode in the absence of an electrolyte or conductive agent, resulting in a composite negative electrode with high electronic conductivity, thereby improving the battery energy density.

[0031] Compared with the non-in situ introduction of Li2S and Li3P, the interface layer formed in situ in the present invention is more uniform; compared with Li2S generated solely in situ, the present invention also simultaneously introduces Li3P with high ionic conductivity, a metal single phase and / or alloy phase with high electronic conductivity, which can improve the critical current density of the all-solid-state battery and make the battery less prone to short circuit at high current density; compared with simply introducing Li3P with high electronic conductivity and a metal single phase and / or alloy phase with high electronic conductivity, the present invention simultaneously introduces a certain amount of Li2S and Li3P with high ionic conductivity and high electronic conductivity, making the interface more stable.

[0032] In the present invention, unless otherwise specified, the negative electrode material having a core-shell structure means that the core layer is an active material that does not contain lithium, and the shell layer is selected from the general formula M x P y S z of metal phosphosulfides.

[0033] In the present invention, unless otherwise specified, the metal phosphosulfide is a non-lithium metal phosphosulfide, that is, M is a non-lithium metal element; at the same time, the metal M in the metal phosphosulfide can be selected from metal elements that do not form an alloy with lithium, or metal elements that form an alloy with lithium, or even metal elements that do not form an alloy with lithium and other metal elements that form an alloy with lithium can be selected at the same time.

[0034] In the present invention, M is a non-lithium metal element.

[0035] In some embodiments of the present invention, preferably, M is selected from metal elements that do not form an alloy with lithium, and / or metal elements that form an alloy with lithium, preferably selected from metal elements that do not form an alloy with lithium.

[0036] In some embodiments of the present invention, further preferably, the M is selected from at least one of Sn, Fe, Ni, Cu, Mn, Na, Ge, Al, Mg, In, Zn and Co, and is preferably selected from at least one of Fe, Ni, Cu, Co and Mn.

[0037] In a specific embodiment of the present invention, the M is selected from metal elements that do not form an alloy with lithium, for example, M is selected from at least one of Fe, Ni, Cu, Co and Mn.

[0038] In another specific embodiment of the present invention, the M is selected from metal elements that form alloys with lithium, for example, M is selected from at least one of Sn, Na, Ge, Al, Mg, In and Zn.

[0039] In the present invention, M is preferably selected from metal elements that do not form an alloy with lithium, rather than metal elements that form an alloy with lithium, so that it is less likely to react with the sulfide electrolyte in the electrolyte layer and deteriorate the sulfide electrolyte.

[0040] In the present invention, x, y and z are all selected from natural numbers. Preferably, x is selected from an integer of 1-4, y is selected from an integer of 1-3, and z is selected from an integer of 4-7.

[0041] In some specific embodiments of the present invention, preferably, the metal phosphosulfide is selected from at least one of Cu3PS4, Cu4P2S7, Cu2P2S6, FePS4, Ni3PS4, Mn2P2S7, MnP2S6, NaP3S4, AlPS4, SnP2S7, InPS4, MgP2S6, GeP2S7 and Co2P2S7.

[0042] In some embodiments of the present invention, preferably, based on the total weight of the negative electrode material, the content of the lithium-free active material is 80-99.9wt%, for example, 80wt%, 82wt%, 85wt%, 88wt%, 90wt%, 92wt%, 95wt%, 98wt%, 99wt%, 99.9wt%, and any value in the range of any two numerical values, preferably 85-99.9wt%, more preferably 90-99wt%; the content of the coating layer is 0.1-20wt%, for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, and any value in the range of any two numerical values, preferably 0.1-15wt%, more preferably 1-10wt%. Meeting the above range is more conducive to improving the electrochemical stability of the negative electrode material containing the modified active material obtained by in-situ conversion of the negative electrode material, thereby improving the rate performance and cycle performance of the battery.

[0043] In some embodiments of the present invention, preferably, the D of the metal phosphosulfide 50 is selected from 1-200 nm, for example, 1 nm, 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, and any value in the range of any two values, preferably 5-50 nm. 50 If the electrolyte particles are too large for liquid phase synthesis, the coating density will be affected and uniform coating cannot be achieved. 50If it is too large, the coating area of ​​the negative electrode active material is large, resulting in the coating layer material not being able to evenly cover the active material, which will also affect the coating uniformity and further lead to a decrease in density.

[0044] In the present invention, unless otherwise specified, D 50 The parameters were measured using a laser particle size analyzer.

[0045] In some embodiments of the present invention, preferably, the lithium-free active material is selected from non-metallic materials; further preferably, the lithium-free active material is selected from at least one of graphite, hard carbon, soft carbon, silicon, SiO and Si / C; more preferably, the lithium-free active material is selected from graphite, silicon and Si / C.

[0046] In some embodiments of the present invention, it is further preferred that the D of the lithium-free active material 50 It is 0.1-100 μm, for example, 0.1 μm, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 20 μm, 50 μm, 80 μm, 100 μm, and any value in a range consisting of any two values, and is preferably 1-10 μm.

[0047] In some embodiments of the present invention, preferably, the thickness of the coating layer is 1-300 nm, for example, 1 nm, 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, 30 nm, 50 nm, 80 nm, 100 nm, 150 nm, 200 nm, and any value in the range consisting of any two values, preferably 50-300 nm.

[0048] In the present invention, unless otherwise specified, the thickness parameters are measured using SEM.

[0049] The second aspect of the present invention provides a method for preparing a negative electrode material, the preparation method comprising the following steps: in the presence of an inert gas, mixing a metal sulfide, P2S5 and an organic solvent to obtain a metal sulfide containing M x P y S z The solution containing M x P y S z The solution and the lithium-free active material are mixed for the second time, and the obtained mixture is subjected to low-pressure static treatment and sintering in sequence to coat the surface of the lithium-free active material with the general formula M x P y S z metal phosphosulfide to obtain the negative electrode material;

[0050] Wherein, M is selected from non-lithium metal elements; x, y and z are all selected from natural numbers.

[0051] The inventors of the present invention have found that by using the liquid phase method, M x P y S z Compatibility with organic solvents makes M x P y S z Dissolved in an organic solvent; mixed with an active material that does not contain lithium, so that M x P y S z The modified active substance is uniformly coated on the surface of the active material to obtain a negative electrode material with a core-shell structure. Compared with conventional physical mixing, the interface layer containing the modified active substance obtained by in-situ conversion of this specific negative electrode material has higher density and stability.

[0052] In the present invention, the inert gas includes but is not limited to nitrogen, helium, argon, neon, etc., preferably argon.

[0053] In some embodiments of the present invention, preferably, M is selected from metal elements that do not form an alloy with lithium and / or metal elements that form an alloy with lithium; preferably, M is selected from metal elements that do not form an alloy with lithium.

[0054] In some embodiments of the present invention, further preferably, the M is selected from at least one of Sn, Fe, Ni, Cu, Mn, Na, Ge, Al, Mg, In, Zn and Co, and is preferably selected from at least one of Fe, Ni, Cu, Co and Mn.

[0055] In the present invention, unless otherwise specified, the metal sulfide is a non-lithium metal sulfide.

[0056] In some embodiments of the present invention, preferably, the metal sulfide is selected from at least one of FeS, CuS, NiS, MnS, Na2S, ZnS, Al2S3, GeS2, SnS, In2S3, CoS and MgS.

[0057] In the present invention, the amount of the metal sulfide and P2S5 has a wide range of selection, as long as the metal sulfide + P2S5 → M x P y S z In the present invention, the limitations on metal phosphosulfides are in accordance with the above limitations, and the present invention will not elaborate on them here.

[0058] In the present invention, the first mixing is intended to obtain a uniform M-containing x P y S zPreferably, the first mixing conditions include: temperature of 15-40°C, rotation speed of 300-1500 rpm, and time of 1-72 hours.

[0059] In the present invention, the second mixing is to mix M x P y S z The second mixing step is performed at a temperature of 15-40° C. and a time of 1-72 hours.

[0060] In some embodiments of the present invention, preferably, the M in g x P y S z The ratio of the amount of the organic solvent in mL is 1-10:5-200. x P y S z , the amount of the organic solvent is 5-200mL.

[0061] In some embodiments of the present invention, preferably, the M-containing x P y S z M in the solution x P y S z The mass ratio of the metal phosphosulfide to the lithium-free active material is (0.1-20): (80-99.9), for example, 0.1:99.9, 1:99, 2:98, 5:95, 8:92, 10:90, 12:88, 15:85, 18:82, 20:80, and any value in a range consisting of any two values, preferably (0.1-15): (85-99.9), more preferably (1-10): (90-99). In the present invention, when the mass ratio is less than 0.1:99.9, the amount of metal phosphosulfide added is too small and cannot be completely and evenly distributed within the negative electrode, a uniform interface layer cannot be achieved, and thus the effect of the present invention cannot be achieved. When the mass ratio is greater than 20:80, the amount of metal phosphosulfide added is too large, resulting in a decrease in battery energy density.

[0062] In some embodiments of the present invention, preferably, the lithium-free active material is selected from non-metallic materials; further preferably, the lithium-free active material is selected from at least one of graphite, hard carbon, soft carbon, silicon, SiO and Si / C; more preferably, the lithium-free active material is selected from graphite and / or silicon.

[0063] In some embodiments of the present invention, preferably, the organic solvent is selected from at least one of tetrahydrofuran, ethanol, tetrahydrofuran, ethanol, acetonitrile, methanol, propylene glycol, glycerol, chloroform, butyl ether, petroleum ether, ethyl acetate and acetone.

[0064] In the present invention, the purpose of the low pressure static treatment is to control M x P y S z The precipitation rate controls the size of the precipitated crystal particles, i.e., controls the D 50 Preferably, the conditions for the low-pressure static treatment include: a pressure of -200 to 0 kPa, for example, -200 kPa, -180 kPa, -150 kPa, -120 kPa, -100 kPa, -80 kPa, -60 kPa, -50 kPa, -30 kPa, -20 kPa, -10 kPa, 0 kPa, and any value in a range consisting of any two numerical values; a temperature of 15-40°C, for example, 15°C, 20°C, 25°C, 30°C, 40°C, and any value in a range consisting of any two numerical values; and a time of 10-24 h, for example, 10 h, 12 h, 14 h, 15 h, 18 h, 20 h, 24 h, and any value in a range consisting of any two numerical values.

[0065] In the present invention, the sintering is to remove the solvent remaining on the surface of the active material without lithium for carbonization, and after sintering, a glass ceramic state and / or ceramic state M is formed. x P y S z Preferably, the sintering conditions include: a temperature of 100-350°C, for example, 100°C, 200°C, 250°C, 300°C, 350°C, and any value in a range consisting of any two values; a time of 1-10h, for example, 1h, 2h, 3h, 4h, 5h, 8h, 10h, and any value in a range consisting of any two values.

[0066] The third aspect of the present invention provides a negative electrode plate, which includes: an active material layer and a current collector, the active material layer contains a modified active material, and the modified active material is obtained by in-situ conversion of the negative electrode material provided by the first aspect, or the negative electrode material prepared by the preparation method provided by the second aspect during the battery cycle.

[0067] A fourth aspect of the present invention provides a negative electrode plate, comprising: an active material layer and a current collector, wherein the active material layer comprises a modified active material, wherein the modified active material comprises an active material that does not contain lithium, and an interface layer coated on the surface of the active material that does not contain lithium; wherein the interface layer comprises Li2S, Li3P, and a metal single phase and / or an alloy phase;

[0068] The metal in the metal single phase and / or alloy phase is selected from metal elements that do not form an alloy with lithium and / or metal elements that form an alloy with lithium.

[0069] In the present invention, unless otherwise specified, the negative electrode sheet comprises: a current collector and an active material layer supported on the current collector, wherein the active material layer contains a modified active material. The current collector of the negative electrode sheet includes but is not limited to copper foil.

[0070] In the present invention, unless otherwise specified, the battery cycle process refers to the lithiation process of the battery negative electrode, that is, during the lithiation process of the battery negative electrode, the coating layer of the negative electrode material has the general formula M x P y S z metal phosphosulfide and Li transported from the positive electrode + The Li2S, Li3P formed by the reaction, and the metal ions in situ generate a single metal phase M phase, and / or the metal ions react with Li + In situ generation of an alloy phase, M-Li. Specifically, when the metal phosphosulfide contains a metal element that does not form an alloy with lithium, the coating layer in the negative electrode material is in situ converted into Li2S, Li3P, and a single metal phase. When the metal phosphosulfide contains a metal element that forms an alloy with lithium, the coating layer in the negative electrode material is in situ converted into Li2S, Li3P, and an alloy phase.

[0071] In the present invention, unless otherwise specified, the metal single phase refers to the M phase, and the alloy phase refers to the lithium alloy phase, that is, the M-Li phase.

[0072] In a specific embodiment of the present invention, when M in the metal phosphosulfide is selected from a metal element that does not form an alloy with lithium, for example, M is selected from at least one of Fe, Ni, Cu, Co and Mn, an interface layer containing Li2S, Li3P and a metal single phase is formed.

[0073] In another specific embodiment of the present invention, when M in the metal phosphosulfide is selected from a metal element that forms an alloy with lithium, for example, M is selected from at least one of Sn, Na, Ge, Al, Mg, In and Zn, an interfacial layer containing Li2S, Li3P and an alloy phase is formed.

[0074] In some embodiments of the present invention, the active material layer further includes an optional conductive agent and a binder; in some embodiments of the present invention, the active material layer may be composed of a modified active material, a conductive agent, and a binder.

[0075] In some embodiments of the present invention, in the active material layer, the mass ratio of the modified active material, the conductive agent, and the binder is 90-95:0-5:0.5-5, preferably 92-95:2-5:1-3.

[0076] In some embodiments of the present invention, 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, mesocarbon microbeads, carbon fiber and vapor grown carbon fiber (VGCF).

[0077] In some embodiments of the present invention, the binder is selected from at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), carboxymethyl fiber and salts thereof.

[0078] In some embodiments of the present invention, the density of the negative electrode sheet is preferably ≥80%, for example, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 96%, 97%, 98%, 99%, 100%, and any value in a range consisting of any two values, preferably 80-100%, more preferably 95-100%. Meeting the above density range allows for uniform distribution of the coating layer, as well as uniform distribution of ionic conductivity and electronic conductivity, thereby improving electrochemical performance.

[0079] Because all-solid-state batteries use powdered electrolyte materials instead of the electrolyte with a wetting effect, the ionic and electronic conduction between electrode material particles is significantly affected by the physical contact between the particles. Therefore, the internal conduction efficiency of the electrode is affected by the density of the electrode sheet. The active material and its surface coating material of the present invention use a complementary method of large and small particles to improve the density of the negative electrode sheet, which is beneficial for ionic and electronic conduction.

[0080] In some embodiments of the present invention, preferably, the ionic conductivity of the negative electrode sheet at 25°C is ≥1×10 -5 S / cm, preferably ≥5×10 -5 S / cm.

[0081] In some embodiments of the present invention, preferably, the electronic conductivity of the negative electrode sheet at 25°C is ≥ 1×10 -5 S / cm, preferably ≥5×10 -5 S / cm.

[0082] A fifth aspect of the present invention provides an all-solid-state battery, comprising: a negative electrode sheet, a solid electrolyte and a positive electrode sheet, wherein the negative electrode sheet is selected from the negative electrode sheet provided above.

[0083] In the present invention, unless otherwise specified, the solid electrolyte is disposed between the interface layer in the negative electrode sheet and the positive electrode sheet.

[0084] In the present invention, there is a wide range of choices for the source of the solid electrolyte, which can be obtained commercially or prepared.

[0085] In a specific embodiment of the present invention, the solid electrolyte is prepared by the following method: in a glove box under an argon atmosphere, Li2S, LiCl, and P2S5 are mixed in a weight ratio of 43.08:41.64:15.28 to obtain a raw material composition; and ball milling and sintering are performed to obtain the solid electrolyte Li6PS5Cl.

[0086] Compared with existing all-solid-state composite negative electrode materials, the composite negative electrode provided by the present invention does not require the addition of sulfide electrolyte materials, and the usage amount is relatively small, which can effectively improve the energy density of the battery using the negative electrode.

[0087] The present invention will be described in detail below through examples.

[0088] The ionic conductivity parameters at 25°C were measured using the AC impedance method, which included sandwiching the negative electrode to be tested between two stainless steel disc electrodes (SS), measuring the ionic conductivity (σ) by electrochemical impedance spectroscopy (EIS), and calculating it according to formula (1): Among them, R b is the volume resistance of the negative electrode to be tested (R b Determined by impedance spectrum), L and S are the thickness and area of ​​the negative electrode to be tested.

[0089] The electronic conductivity parameters at 25°C were measured using the AC impedance method. The specific test included: sandwiching the negative electrode to be tested between two electrolyte layers, measuring the electronic conductivity (σ') by electrochemical impedance spectroscopy (EIS), and calculating it according to formula (2): Among them, R' b is the volume resistance of the negative electrode to be tested (R' b Determined by impedance spectrum), L and S are the thickness and area of ​​the negative electrode to be tested.

[0090] The density parameter is tested by the solvent infiltration method, and the test solvent is a low-polarity solvent. The specific test includes: placing the negative electrode plate to be tested in a container filled with heptane, and after the negative electrode plate to be tested is fully infiltrated, the negative electrode plate is taken out and the mass M1 is weighed; the above-mentioned negative electrode plate is dried and the dried negative electrode plate is weighed, and the mass of the plate is weighed M2; the density of the heptane solvent ρ, the apparent volume of the negative electrode plate V (area S×thickness L), the density = [1-(M1-M2) / ρ / V]%; repeat the test 3 times, calculate the average value, and obtain the density of the negative electrode plate to be tested.

[0091] Energy density test method: Test the battery mass M, use a charge and discharge instrument to test the energy W released after the battery is discharged at a cut-off voltage of 2.7-4.2V. Battery energy density = W / M.

[0092] Example 1

[0093] (1) In an argon atmosphere, 10 g of Cu2S and P2S5 were mixed and then mixed with 100 mL of ethanol (temperature 25°C, rotation speed 1500 rpm, time 4 h) to obtain an ethanol solution containing Cu3PS4; wherein the molar ratio of Cu2S to P2S5 was 75:25;

[0094] (2) Add silicon into the above ethanol solution containing Cu3PS4, wherein Cu3PS4 and silicon (D 50 The obtained mixture was subjected to low-pressure standing treatment (temperature of 25°C, pressure of -25kPa, time of 24h), sintering temperature of 250°C, time of 2h, and obtained negative electrode material S1.

[0095] The SEM image of the negative electrode material S1 is shown in FIG1 . The negative electrode material S1 has a core-shell structure, wherein the core layer is silicon and the shell layer is Cu 3 PS 4 .

[0096] Among them, the XPS graph of the above-mentioned negative electrode material S1 before lithiation is shown in Figure 4. From the XPS spectrum P 2p, it can be observed that the characteristic peaks of 132.6 / 133.0eV and 133.7 / 134.4eV represent PS4 3- group, indicating that Cu3PS4 was successfully synthesized, that is, the above-mentioned negative electrode material S1 contains Cu3PS4.

[0097] Example 2

[0098] According to the method of Example 1, the difference is that

[0099] In step (2), the mass ratio of Cu3PS4 to silicon in the above-mentioned ethanol solution containing Cu3PS4 is replaced with 15:85,

[0100] The other conditions are the same to obtain the negative electrode material S2.

[0101] Example 3

[0102] According to the method of Example 1, the difference is that

[0103] In step (2), the mass ratio of Cu3PS4 to silicon in the above-mentioned ethanol solution containing Cu3PS4 is replaced with 20:80,

[0104] The other conditions were the same to obtain the negative electrode material S3.

[0105] Example 4

[0106] According to the method of Example 1, the difference is that

[0107] In step (2), the mass ratio of Cu3PS4 to silicon in the above-mentioned ethanol solution containing Cu3PS4 is replaced with 45:55,

[0108] The other conditions were the same to obtain the negative electrode material S4.

[0109] Example 5

[0110] According to the method of Example 1, the difference is that

[0111] In step (2), the silicon D 50 Replaced with 20μm,

[0112] The other conditions were the same to obtain the negative electrode material S5.

[0113] Example 6

[0114] The method of Example 1 is as follows, except that

[0115] In step (2), the silicon D 50 Replaced with 0.5μm,

[0116] The other conditions were the same to obtain the negative electrode material S6.

[0117] Example 7

[0118] According to the method of Example 1, the difference is that

[0119] In step (1), 10 g of Cu2S and P2S5 were replaced with 10 g of Na2S and P2S5, and the molar ratio of Na2S to P2S5 was 75:25;

[0120] The other conditions were the same to obtain the negative electrode material S7.

[0121] Example 8

[0122] According to the method of Example 1, the difference is that

[0123] In step (2), the sintering temperature is changed to 400°C.

[0124] The other conditions were the same to obtain the negative electrode material S8.

[0125] Comparative Example 1

[0126] According to the method of Example 1, the difference is that

[0127] In step (1), 10 g of Cu2S and P2S5 were replaced with 10 g of Li2S and P2S5, and the molar ratio of Li2S to P2S5 was 75:25;

[0128] The other conditions were the same to obtain the negative electrode material DS1.

[0129] Comparative Example 2

[0130] The method of Example 1 is as follows, except that

[0131] In step (1), 10 g of Cu2S and P2S5 were directly mixed without adding ethanol to obtain Cu3PS4;

[0132] The other conditions were the same to obtain the negative electrode material DS2.

[0133] The SEM image of the negative electrode material DS2 is shown in FIG2 , and Cu 3 PS 4 is not evenly coated on the silicon surface.

[0134] Table 1

[0135] Test Case

[0136] Batteries were assembled with the negative electrode materials prepared in Examples 1-8 and Comparative Examples 1-2, and electrochemical performance tests were performed. The nominal specific capacity of silicon was 3200 mAh / g.

[0137] Assembling the battery:

[0138] A 20μm Li6PS5Cl electrolyte membrane prepared using a dry electrode process was pressed into a sheet using a polytetrafluoroethylene mold at a pressing pressure of 200MPa; 50μm metallic lithium was attached to the electrolyte sheet and covered with copper foil; 3mg of the above negative electrode material was spread flat on the other side of the electrolyte and covered with aluminum foil; and the battery was assembled using a stainless steel mold and pressed at 100MPa to obtain an all-solid-state battery.

[0139] Li6PS5Cl electrolyte membrane: prepared by dry process, using PTFE as binder with a binder content of 2%, and prepared by roller pressing.

[0140] Electrochemical performance test:

[0141] The LAND charge-discharge instrument was used for charging and discharging. The voltage was set to 0.1-1.5V and the current was set to 0.1C / 0.1C. After 3 cycles, the charge and discharge were cycled at a rate of 1C / 1C for 100 cycles. The test results are listed in Table 2.

[0142] Figure 3 is the XRD pattern of the negative electrode material S1 prepared in Example 1 after cycling. It can be seen that after cycling, the powder XRD of Cu3PS4 is tested after lithiation conversion. After analysis, it is confirmed that 26.89°, 42.5° and 46.8° represent the characteristic peaks of Li2S, while 24.09°, 26.91°, 33.79°, 42.19° and 47.70° represent the characteristic peaks of Li3P, and 43.29° and 50.433° represent the characteristic peaks of Cu, 39.98° and 46.38° represent the characteristic peaks of Si, and 30.09°, 34.88° and 50.16° represent the characteristic peaks of LiCl, indicating that Cu3PS4 is fully converted into Li3P, Li2S, Cu, and LiCl after lithiation, and no characteristic peaks of other materials are observed, indicating that the characteristic peaks of Cu3PS4 have disappeared due to the conversion reaction after cycling. The background peaks of silicon still exist, that is, 39.98° and 46.38° are the characteristic peaks of silicon.

[0143] Table 2

[0144] Table 2

[0145] It can be seen from the data in Table 1-2 that compared with Comparative Examples 1-2, Example 1-8 adopts the general formula M x P y S z The metal phosphosulfide is coated with a lithium-free active material, and the obtained negative electrode material is converted in situ to obtain a negative electrode sheet with high density, high ionic conductivity and high electronic conductivity; at the same time, the obtained battery also has a high specific capacity, capacity retention rate and energy density.

[0146] In Comparative Example 1, Li3PS4 is introduced into the negative electrode material. Since Li3PS4 will decompose into Li2S and Li3P after the reaction, the lack of metal material causes the overall electronic resistance of the composite negative electrode to be relatively large, affecting the battery performance, resulting in poor electronic conductivity, so the negative electrode performance is low.

[0147] In Comparative Example 2, since Cu3PS4 was introduced by the solid phase method (grinding and mixing), the coating was uneven, resulting in poor electrochemical performance of the negative electrode sheet, which in turn led to low battery performance.

[0148] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A negative electrode material, characterized in that, The negative electrode material has a core-shell structure, including a lithium-free active material and its coating layer, and the coating layer is selected from metal phosphosulfides with the general formula M x P y S z ; Among them, M is a non-lithium metal element; x, y, and z are all selected from natural numbers.

2. The negative electrode material according to claim 1, wherein, M is selected from metal elements that do not form alloys with lithium, and / or metal elements that form alloys with lithium, preferably selected from metal elements that do not form alloys with lithium; Preferably, M is selected from at least one of Sn, Fe, Ni, Cu, Mn, Na, Ge, Al, Mg, In, Zn, and Co, preferably selected from at least one of Fe, Ni, Cu, Co, and Mn; Preferably, the metal phosphosulfide is selected from at least one of Cu3PS4, Cu4P2S7, Cu2P2S6, FePS4, Ni3PS4, Mn2P2S7, MnP2S6, NaP3S4, AlPS4, SnP2S7, InPS4, MgP2S6, GeP2S7, and Co2P2S7; and / or, the lithium-free active material is selected from non-metallic materials, preferably selected from at least one of graphite, hard carbon, soft carbon, silicon, SiO, and Si / C.

3. The negative electrode material according to claim 1 or 2, wherein Based on the total weight of the negative electrode material, the content of the lithium-free active material is 80-99.9 wt%, preferably 85-99.9 wt%, more preferably 90-99 wt%; the content of the coating layer is 0.1-20 wt%, preferably 0.1-15 wt%, more preferably 1-10 wt%; and / or, D of the metal phosphosulfide 50 selected from 1 - 200 nm, preferably 5 - 50 nm; and / or, D of the lithium-free active material 50 is 0.1 - 100 μm, preferably 1 - 10 μm.

4. The negative electrode material according to any one of claims 1-3, wherein, The thickness of the coating layer is 1-300 nm, preferably 50-300 nm.

5. A method for preparing a negative electrode material, characterized in that, The preparation method includes: in the presence of an inert gas, first mixing a metal sulfide, P2S5 and an organic solvent to obtain a solution containing M x P y S z ; second mixing the solution containing M x P y S z and an active material without lithium, and subjecting the obtained mixture to low-pressure standing treatment and sintering in sequence to coat the surface of the active material without lithium with a metal phosphosulfide having the general formula M x P y S z to obtain a negative electrode material; Among them, M is selected from non-lithium metal elements; x, y, and z are all selected from natural numbers.

6. The preparation method according to claim 5, wherein, M is selected from metal elements that do not form alloys with lithium, and / or metal elements that form alloys with lithium; preferably selected from metal elements that do not form alloys with lithium; Preferably, M is selected from at least one of Sn, Fe, Ni, Cu, Mn, Na, Ge, Al, Mg, In, Zn, and Co, preferably selected from at least one of Fe, Ni, Cu, Co, and Mn; and / or, the solution containing M x P y S z and the mass ratio of M x P y S z and the lithium-free active material is (0.1 - 20):(80 - 99.9), preferably (0.1 - 15):(85 - 99.9), more preferably (1 - 10):(90 - 99); and / or, the lithium-free active material is selected from non-metallic materials, preferably selected from at least one of graphite, hard carbon, soft carbon, silicon, SiO, and Si / C; and / or, the organic solvent is selected from at least one of tetrahydrofuran, ethanol, acetonitrile, methanol, propylene glycol, glycerol, chloroform, dibutyl ether, petroleum ether, ethyl acetate, and acetone.

7. A negative electrode sheet, characterized in that, The negative electrode plate includes: an active material layer and a current collector, the active material layer contains a modified active material, and the modified active material is obtained by in-situ conversion of the negative electrode material described in any one of claims 1-4, or the negative electrode material prepared by the preparation method described in claim 5 or 6 during the battery cycle.

8. A negative electrode plate, characterized in that, The negative electrode plate includes: an active material layer and a current collector, the active material layer contains a modified active material, and the modified active material contains a lithium-free active material and an interface layer coated on the surface of the lithium-free active material; the interface layer contains Li2S, Li3P, and a metal single-phase and / or alloy phase; Among them, the metal in the metal single-phase and / or alloy phase is selected from metal elements that do not form alloys with lithium, and / or metal elements that form alloys with lithium.

9. The negative electrode sheet according to claim 8, wherein The active material layer further includes an optional conductive agent and a binder; and / or, the density of the negative electrode sheet is ≥80%, preferably 80-100%, more preferably 95-100%; and / or, the ionic conductivity of the negative electrode sheet at 25 °C ≥ 1×10 -5 S / cm, preferably ≥ 5×10 -5 S / cm; and / or, the electronic conductivity of the negative electrode sheet at 25 °C ≥ 1×10 -5 S / cm, preferably ≥ 5×10 -5 S / cm.

10. A all-solid-state battery, characterized in that, The all-solid-state battery includes: a negative electrode sheet, a solid electrolyte, and a positive electrode sheet, wherein the negative electrode sheet is selected from the negative electrode sheets described in any one of claims 7-9.

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