Negative electrode material and preparation method thereof and all-solid-state lithium battery

Abstract

The present application provides a negative electrode material, the negative electrode material comprising a core and a first coating layer and a second coating layer sequentially coating the core, the core comprising a material of Li 2 O, LiF, Li 2 CO 3 and LiCl, the material of the first coating layer is amorphous Li x Si, 0<x≤4.4, the material of the second coating layer includes Li 2 O, LiF, Li 2 CO 3 and at least one of LiCl. The negative electrode material has a small volume expansion effect, good cycle performance, and excellent electrochemical performance. The application also provides a preparation method of the negative electrode material and an all-solid-state lithium battery.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to negative electrode materials and preparation methods thereof and all-solid-state lithium batteries. Background Art

[0002] In recent years, all-solid-state lithium batteries using solid electrolytes have received widespread attention due to their high safety. Among them, silicon anodes with high theoretical specific capacity and high safety are considered to be an effective way to break through the energy density of all-solid-state lithium batteries. However, existing silicon anode materials are prone to huge volume changes during the process of lithium extraction / insertion, which leads to rapid capacity decay and poor cycle performance of all-solid-state lithium batteries, limiting the application of all-solid-state lithium batteries. Summary of the invention

[0003] In view of this, the present application provides a negative electrode material and a preparation method thereof, and an all-solid-state lithium battery. The negative electrode material has a small volume expansion effect, good cycle performance, and excellent electrochemical performance.

[0004] In a first aspect, the present application provides a negative electrode material, the negative electrode material comprising a core and a first coating layer and a second coating layer sequentially coating the core, the material of the core comprising at least one of Li2O, LiF, Li2CO3 and LiCl, the material of the first coating layer being amorphous Li x Si, 0<x≤4.4, the material of the second coating layer includes at least one of Li2O, LiF, Li2CO3 and LiCl.

[0005] Optionally, a thickness ratio between the first coating layer and the second coating layer is (2-50):1.

[0006] Optionally, the ratio of the particle size of the negative electrode material to the thickness of the first coating layer is (2.3-4):1.

[0007] Optionally, the core and the second cladding layer are made of the same material.

[0008] Optionally, the particle size of the inner core is 5nm-50nm.

[0009] Optionally, the thickness of the first coating layer is 20nm-500nm.

[0010] Optionally, the second coating layer has a thickness of 2nm-50nm.

[0011] In the negative electrode material provided in the first aspect of the present application, the amorphous Li x The first coating layer formed by Si has good cycle stability. At the same time, the core and the second coating layer can form a skeleton in the negative electrode material, which has a positive effect on the amorphous Li xSi plays a binding role, inhibiting its volume change during lithium insertion and extraction, protecting the electronic and ion conduction network, and further significantly improving the cycle performance of the negative electrode material, thereby obtaining a negative electrode material with excellent electrochemical performance.

[0012] In a second aspect, the present application also provides a method for preparing a negative electrode material, comprising:

[0013] A wrapping layer is formed on the surface of the core to obtain a first coating, wherein the material of the core includes at least one of Li2O, LiF, Li2CO3 and LiCl, and the material of the wrapping layer is amorphous Li x Si, 0<x≤4.4;

[0014] A second coating layer is formed on the surface of the first coating to obtain a negative electrode material, wherein the material of the second coating layer includes at least one of Li2O, LiF, Li2CO3 and LiCl.

[0015] Optionally, forming a second coating layer on the surface of the first coating includes:

[0016] The first coating is placed in at least one atmosphere of O2, F2, CO2 and Cl2, and heated to form a second coating layer.

[0017] Optionally, the heating includes treating at 100°C-250°C for 10 min-2 h.

[0018] The preparation method of the negative electrode material provided in the second aspect of the present application is simple, easy to operate, suitable for industrial production, and is conducive to the application of the negative electrode material.

[0019] In a third aspect, the present application also provides an all-solid-state lithium battery, comprising a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode, wherein the negative electrode comprises the negative electrode material described in the first aspect or the negative electrode material prepared by the preparation method described in the second aspect.

[0020] Optionally, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, and the negative electrode material layer includes the negative electrode material.

[0021] Furthermore, the negative electrode material layer does not contain solid electrolyte material and conductive agent.

[0022] The all-solid-state lithium battery provided in the third aspect of the present application has good cycle performance and excellent electrochemical performance, which is conducive to its application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the implementation modes of the present application, the drawings required for use in the implementation modes of the present application will be described below.

[0024] Figure 1 A schematic diagram of the structure of a negative electrode material provided in one embodiment of the present application.

[0025] Figure 2 A schematic diagram of a process for preparing a negative electrode material provided in one embodiment of the present application.

[0026] Figure 3 A schematic diagram of the structure of an all-solid-state lithium battery provided in one embodiment of the present application.

[0027] Description of labels:

[0028] Core-11, first coating layer-12, second coating layer-13, negative electrode material-10, negative electrode material layer-101, negative electrode current collector-102, negative electrode-100, positive electrode material layer-201, positive electrode current collector-202, positive electrode-200, solid electrolyte layer-300. DETAILED DESCRIPTION

[0029] The following are preferred implementations of the present application. It should be noted that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application, and these improvements and modifications are also considered to be within the scope of protection of the present application.

[0030] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the various specific processes and material examples provided by the present application, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0031] See also Figure 1 , is a schematic diagram of the structure of a negative electrode material provided in one embodiment of the present application, wherein the negative electrode material 10 comprises a core 11 and a first coating layer 12 and a second coating layer 13 sequentially coating the core 11, wherein the material of the core 11 comprises at least one of Li2O, LiF, Li2CO3 and LiCl, and the material of the first coating layer 12 is amorphous Li x Si, 0<x≤4.4, the material of the second coating layer 13 includes at least one of Li2O, LiF, Li2CO3 and LiCl.

[0032] In this application, amorphous Li x Si as silicon-based negative electrode material 10, amorphous Li x The degree of change in the internal structure of Si during long-term use is much smaller than that of crystalline Li x Si, hence amorphous Lix The cycling performance of Si is significantly better than that of crystalline Li x Si, and amorphous Li x Si has a small volume expansion effect during the process of inserting and extracting lithium ions, which is beneficial to improving the performance stability of the negative electrode material 10; the core 11 and the second coating layer 13 fix the first coating layer 12, further suppressing the volume expansion effect of the first coating layer 12, and at the same time, the core 11 and the second coating layer 13 can support the entire negative electrode material 10 to ensure the structural stability of the entire negative electrode material 10; the core 11, the first coating layer 12 and the second coating layer 13 interact and influence each other, thereby improving the cycle performance of the negative electrode material 10, so that the negative electrode material 10 has excellent electrochemical properties.

[0033] In the present application, the material of the first coating layer 12 is amorphous Li x Si, 0<x≤4.4. Further, 0<x<4.4. Specifically, x can be, but is not limited to, 1.71, 2.33, 3.25, 3.75 or 4.4, etc. In an embodiment of the present application, the mass fraction of the first coating layer 12 in the negative electrode material 10 is 50%-95%. Further, the mass fraction of the first coating layer 12 in the negative electrode material 10 is 60%-90%. Further, the mass fraction of the first coating layer 12 in the negative electrode material 10 is 70%-85%. Specifically, the mass fraction of the first coating layer 12 in the negative electrode material 10 can be, but is not limited to, 55%, 57%, 60%, 65%, 72%, 75%, 77%, 80%, 83%, 86% or 90%, etc. By setting the first coating layer 12 with the above content, it is more conducive to improving the specific capacity of the negative electrode material 10, which is conducive to its application in all-solid-state lithium batteries.

[0034] In an embodiment of the present application, the ratio of the particle size of the negative electrode material 10 to the thickness of the first coating layer 12 is (2.03-4): 1. Further, the ratio of the particle size of the negative electrode material 10 to the thickness of the first coating layer 12 is (2.1-3.8): 1. Further, the ratio of the particle size of the negative electrode material 10 to the thickness of the first coating layer 12 is (2.3-3.5): 1. Specifically, the ratio of the particle size of the negative electrode material 10 to the thickness of the first coating layer 12 may be, but is not limited to, 2.03, 2.2, 2.3, 2.5, 2.8, 3, 3.3, 3.5, 3.7 or 4, etc. The larger the proportion of the first coating layer 12, the more conducive to improving the specific capacity of the negative electrode material 10.

[0035] In the embodiment of the present application, the thickness of the first coating layer 12 is 20nm-500nm. Further, the thickness of the first coating layer 12 is 50nm-460nm. Further, the thickness of the first coating layer 12 is 100nm-400nm. Specifically, the thickness of the first coating layer 12 can be but not limited to 80nm, 150nm, 200nm, 250nm, 300nm, 380nm or 420nm, etc. By providing the first coating layer 12 of the above thickness, the specific capacity of the negative electrode material 10 can be better improved, and the electrochemical performance of the negative electrode material 10 can be enhanced.

[0036] In the present application, the shape of the kernel 11 is not limited, and specifically can be but not limited to spherical, quasi-spherical, etc. In the embodiment of the present application, the particle size of the kernel 11 is 5nm-50nm. It can be understood that when the material is quasi-spherical, the particle size is an equivalent particle size. Further, the particle size of the kernel 11 is 10nm-45nm. Further, the particle size of the kernel 11 is 15nm-40nm. Specifically, the particle size of the kernel 11 can be but not limited to 5nm, 8nm, 13nm, 15nm, 20nm, 25nm, 30nm, 32nm, 35nm, 40nm, 43nm or 47nm, etc. The kernel 11 with the above-mentioned particle size can better cooperate with the second coating layer 13, suppress the volume expansion of the first coating layer 12 material, and ensure the structural stability and cycle performance of the negative electrode material 10.

[0037] In the embodiment of the present application, the core 11 and the second coating layer 13 are made of the same material. The core 11 and the second coating layer 13 have the same performance, and the core 11 and the second coating layer 13 have better matching, which is more conducive to improving the structural stability of the negative electrode material 10. Specifically, the material of the core 11 and the second coating layer 13 can be, but is not limited to, Li2O, LiF, Li2CO3, LiCl, a mixture of Li2O and LiF, a mixture of Li2O and Li2CO3, a mixture of Li2O and LiCl, a mixture of LiF and Li2CO3, a mixture of LiF and LiCl, a mixture of Li2CO3 and LiCl, a mixture of Li2O, LiF and Li2CO3, a mixture of LiF, Li2CO3 and LiCl, a mixture of Li2O, LiF and Li2CO3, a mixture of LiF, Li2CO3 and LiCl, or a mixture of Li2O, LiF and LiCl.

[0038] In the embodiment of the present application, the thickness of the second coating layer 13 is 2nm-50nm. Further, the thickness of the second coating layer 13 is 5nm-45nm. Further, the thickness of the second coating layer 13 is 10nm-35nm. Specifically, the thickness of the second coating layer 13 can be but not limited to 8nm, 10nm, 12nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm or 43nm, etc. The thickness of the above-mentioned second coating layer 13 is relatively thin, which can not only inhibit the volume expansion of the first coating layer 12, but also serve as the skeleton of the entire negative electrode material 10 to ensure the structural stability of the entire negative electrode material 10, while not being too thick to avoid affecting the specific capacity of the negative electrode material 10.

[0039] In an embodiment of the present application, the thickness ratio of the first coating layer 12 to the second coating layer 13 is (2-50):1. Further, the thickness ratio of the first coating layer 12 to the second coating layer 13 is (8-45):1. Furthermore, the thickness ratio of the first coating layer 12 to the second coating layer 13 is (15-40):1. Specifically, the thickness ratio of the first coating layer 12 to the second coating layer 13 may be, but is not limited to, 5, 10, 12, 15, 20, 25, 30, 35, 40, 45 or 50. Through the above arrangement, the second coating layer 13 can not only inhibit the first coating layer 12, but also improve the specific capacity of the negative electrode material 10 and improve the electrochemical performance of the negative electrode material 10.

[0040] See also Figure 2 , is a schematic flow chart of a method for preparing a negative electrode material provided in one embodiment of the present application, comprising:

[0041] S101: forming a coating layer on the surface of the core to obtain a first coating, wherein the material of the core includes at least one of Li2O, LiF, Li2CO3 and LiCl, and the material of the coating layer is amorphous Li x Si, 0<x≤4.4.

[0042] S102: forming a second coating layer on the surface of the first coating to obtain a negative electrode material, wherein the material of the second coating layer includes at least one of Li2O, LiF, Li2CO3 and LiCl.

[0043] In an embodiment of the present application, a coating layer is formed on the surface of the inner core 11 to obtain a first coating, which includes: obtaining the first coating by mixing the inner core 11 material and the coating layer material through ball milling. At this time, the rotation speed of the mixed ball milling can be but is not limited to 50rpm-150rpm, and the time is 10min-30min. In one embodiment of the present application, the ball milling method can be wet ball milling or dry ball milling. Specifically, the solvent in the wet ball milling can be but is not limited to at least one selected from toluene, xylene, anisole, heptane, decane, ethyl acetate, ethyl propionate, butyl butyrate, N-methylpyrrolidone and acetone. In the present application, the inner core 11 material includes at least one of Li2O, LiF, Li2CO3 and LiCl, and the coating layer material is amorphous Li x Si, 0<x≤4.4. Further, the core 11 material and the wrapping layer material can also be obtained by reaction. Specifically, it can be but not limited to the reaction of silicon dioxide and lithium to generate Li2O and Li x Si, Li2SiF6 and lithium react to generate LiF and Li x Si, etc. Furthermore, the core 11 material obtained by the reaction is crystalline, and needs to be ball-milled to obtain an amorphous material. Specifically, the speed of the ball milling can be, but is not limited to, 200 rpm-300 rpm, and the time is 30 min-60 min.

[0044] In one embodiment of the present application, forming a second coating layer 13 on the surface of the first coating includes: placing the first coating in at least one atmosphere of O2, F2, CO2 and Cl2, and heating to form the second coating layer 13. Through the heating process, at least one of O2, F2, CO2 and Cl2 reacts with the lithium-silicon alloy of the coating layer, wherein the lithium is released by heat and reacts with the gas to form the second coating layer 13 material, and the second coating layer 13 covers the first coating. It can be understood that after the reaction, the coating layer becomes the first coating layer 12, and the material of the first coating layer 12 is amorphous Li xSi, 0<x<4.4, the materials of the encapsulation layer and the first encapsulation layer 12 are different, and the lithium content of the encapsulation layer is less than the lithium content of the first encapsulation layer 12. In one embodiment of the present application, the heating includes a treatment at 100℃-250℃ for 10min-30min. Under the above heating conditions, the lithium in the lithium-silicon alloy is easily released to react with the gas, while also ensuring that the lithium in the lithium-silicon alloy will not be completely released, thereby ensuring the material of the first encapsulation layer 12. Furthermore, the heating includes a treatment at 150℃-250℃ for 12min-25min. Furthermore, the heating includes a treatment at 180℃-250℃ for 15min-20min. It can be understood that when reacting in an O2 atmosphere, the material of the second coating layer 13 includes Li2O; when reacting in an F2 atmosphere, the material of the second coating layer 13 includes LiF; when reacting in a CO2 atmosphere, the material of the second coating layer 13 includes Li2CO3; when reacting in a Cl2 atmosphere, the material of the second coating layer 13 includes LiCl. The second coating layer 13 is obtained by introducing the corresponding gas for reaction, and the thickness of the obtained second coating layer 13 is controllable, and a second coating layer 13 with a relatively thin thickness can be obtained, which is beneficial to the improvement of the electrochemical performance of the negative electrode material 10.

[0045] In another embodiment of the present application, forming the second coating layer 13 on the surface of the first coating includes: mixing and ball milling the first coating and the second coating layer 13 materials to obtain the negative electrode material 10. The second coating layer 13 is directly formed on the surface of the first coating by mixed ball milling. After mixed ball milling, the coating layer is the first coating layer 12, and the materials of the two are the same. At this time, the speed of the mixed ball milling can be but is not limited to 50rpm-150rpm, and the time is 10min-30min.

[0046] In the embodiment of the present application, the negative electrode material 10 is further subjected to heat treatment. Thereby improving the interface compatibility between the layers in the negative electrode material 10 and improving the contact performance. In one embodiment of the present application, the treatment includes heating to 353K-393K at a rate exceeding 1K / min-10K / min, and keeping the temperature for 10min-60min. Specifically, it can be, but is not limited to, heating to 373K at a rate exceeding 2K / min, and keeping the temperature for 20min.

[0047] In the embodiment of the present application, the preparation of the negative electrode material 10 is carried out under a protective gas. Specifically, the protective gas includes at least one of nitrogen, helium, hydrogen, etc.

[0048] The relevant parameters and functions of the negative electrode material 10 prepared by the preparation method of the present application are as described above and will not be repeated here.

[0049] The preparation method of the negative electrode material 10 provided in the present application is simple, easy to operate, suitable for industrial production, and is conducive to the application of the negative electrode material 10.

[0050] See also Figure 3 , is a schematic structural diagram of an all-solid-state lithium battery provided in one embodiment of the present application, the all-solid-state lithium battery includes a positive electrode 200, a negative electrode 100 and a solid electrolyte layer 300 located between the positive electrode 200 and the negative electrode 100, and the negative electrode 100 includes the negative electrode material 10 in any of the above embodiments.

[0051] In the embodiment of the present application, the negative electrode 100 includes a negative electrode current collector 102 and a negative electrode material layer 101 disposed on the negative electrode current collector 102, and the negative electrode material layer 101 includes a negative electrode material 10. Specifically, the thickness of the negative electrode material layer 101 may be, but is not limited to, 5 μm-50 μm.

[0052] In the embodiment of the present application, the negative electrode material layer 101 does not contain solid electrolyte material and conductive agent. In this way, the negative electrode material layer 101 can include a large amount of negative electrode material 10 with electrochemical activity, thereby making the capacity of the negative electrode 100 larger and the energy density of the all-solid-state lithium battery higher.

[0053] In an embodiment of the present application, the negative electrode material layer 101 also includes at least one of the binders. Among them, the binder helps to firmly fix the negative electrode material layer 101 on the negative electrode current collector 102 and make the negative electrode material layer 101 have a certain elasticity. In an embodiment of the present application, the binder may include but is not limited to polythiophene, polypyrrole, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polystyrene, polyacrylamide, ethylene-propylene-diene copolymer resin, styrene butadiene rubber, polybutadiene, fluororubber, polyvinyl pyrrolidone, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, carboxypropyl cellulose, ethyl cellulose, polyethylene oxide, sodium carboxymethyl cellulose and styrene-butadiene rubber. In another embodiment of the present application, the mass percentage of the binder in the negative electrode material layer 101 is 0.5%-5%. Specifically, the mass percentage of the binder in the negative electrode material layer 101 may be, but is not limited to, 1%-5%, 1.5%-4.5%, 2%-4% or 2.5%-3.8%.

[0054] In the embodiment of the present application, the positive electrode 200 may include a positive electrode current collector 202 and a positive electrode material layer 201 disposed on the positive electrode current collector 202. The positive electrode material layer 201 may include a positive electrode active material, a conductive agent, a positive electrode solid electrolyte material, and a positive electrode binder.

[0055] In the embodiment of the present application, the positive electrode active material includes one or more of oxide type, sulfide type, polyanion type and composites of the above materials. In one embodiment of the present application, the oxide type positive electrode active material may include but is not limited to TiO2, Cr3O8, V2O5, MnO2, NiO, WO3, LiMn2O4, Li2CuO2, LiCo m Ni 1-m O2(0≤m≤1), LiCo a Ni 1-a-b Al b O2(0≤a≤1,0≤b≤1), LiFe c Mn d G e O4 (G is selected from at least one of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn and Mo, 0≤c≤1, 0≤d≤1, 0≤e≤1, c+d+e=1), Li 1+f L 1－g－h H g R h O2 (L, H and R are independently selected from at least one of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S and B, and L, H and R are different elements, and -0.1≤f≤0.2, 0≤g≤1, 0≤h≤1, 0≤g+h≤1) etc. Specifically, the oxide-type positive electrode active material may be, but is not limited to, one or more of LiCoO2, LiNiO2, LiMn2O4. In another embodiment of the present application, the sulfide-type positive electrode active material may include TiS2, V2S3, FeS, FeS2, WS2, LiJS i (J is selected from at least one of Ti, Fe, Ni, Cu and Mo, 1≤i≤2.5), etc. In another embodiment of the present application, the polyanionic positive electrode active material may specifically include at least one of LiFePO4, Li3V2(PO4)3, Li3V3(PO4)3 and LiVPO4F.

[0056] In the embodiment of the present application, the particle size of the positive electrode active material is 100 nm-500 μm. Specifically, the particle size of the positive electrode active material may be, but is not limited to, 100 nm-100 μm, 100 nm-50 μm or 500 nm-50 μm.

[0057] In the embodiment of the present application, the surface of the positive electrode active material may also have a coating layer to optimize the interface between the positive electrode material layer 201 and the solid electrolyte, reduce the interface impedance, and improve the cycle stability. Specifically, the coating layer on the surface of the positive electrode active material may be LiNbO3, LiTaO3, Li3PO4, Li4Ti5O 12 In a specific embodiment, 1000 g of LiCoO2, 51 mL of niobium ethoxide, 12 g of lithium ethoxide, 1000 mL of deionized water and 1000 mL of ethanol are fully mixed, and under continuous stirring, ammonia water is added dropwise to adjust the pH to 10, the solution is evaporated to dryness, and the obtained powder is heated at 400° C. for 8 h to obtain a LiCoO2 positive electrode active material coated with LiNbO3 on the surface.

[0058] In the present application, there is no particular restriction on the positive electrode binder in the positive electrode material layer 201, for example, it can be at least one of fluorine-containing resin, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyolefin, styrene-butadiene rubber, etc. There is no particular restriction on the conductive agent in the positive electrode material layer 201, and conventional materials available in the art can be used, such as at least one of conductive carbon black (such as acetylene black, Ketjen black), carbon nanotubes, carbon fibers and graphite. In one embodiment of the present application, the mass percentage content of the positive electrode binder in the positive electrode material layer 201 is 0.01%-10%. Specifically, the mass percentage content of the positive electrode binder in the positive electrode material layer 201 can be, but not limited to, 0.015%-8%, 0.02%-7%, 0.02%-5% or 0.05%-4.5%, etc. In another embodiment of the present application, the conductive agent can be, but not limited to, at least one of acetylene black, carbon nanowires, graphite and graphene. In another embodiment of the present application, the mass percentage of the conductive agent in the positive electrode material layer 201 is 0.1%-20%. Specifically, the mass percentage of the conductive agent in the positive electrode material layer 201 can be, but is not limited to, 0.5%-18%, 1%-15%, 1%-10% or 3%-8.5%, etc.

[0059] In the embodiment of the present application, the negative electrode current collector 102 and the positive electrode current collector 202 are independently selected from metal foil or alloy foil. Among them, the metal foil includes copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold or silver foil, and the alloy foil includes stainless steel, or an alloy containing at least one element of copper, titanium, aluminum, platinum, iridium, ruthenium, nickel, tungsten, tantalum, gold and silver. For example, the negative electrode current collector 102 can be specifically aluminum foil, and the positive electrode current collector 202 can be specifically copper foil. The thickness and surface roughness of the negative electrode current collector 102 and the positive electrode current collector 202 in the present application can be adjusted according to actual needs.

[0060] In an embodiment of the present application, the solid electrolyte layer 300 can be formed by coating and drying a slurry containing a solid electrolyte material and a solvent, and the components of the solid electrolyte layer 300 include a solid electrolyte material. In another embodiment of the present application, the solid electrolyte layer 300 may also contain a binder, and its material may be selected from the binder in the above-mentioned negative electrode material layer 101, which will not be repeated here. In one embodiment of the present application, the solid electrolyte layer 300 can be combined with the negative electrode material layer 101 by coating, and then the solid electrolyte layer 300 can be combined with the positive electrode 200 with the positive electrode material layer 201 by pressing.

[0061] In an embodiment of the present application, the solid electrolyte material for the positive electrode and the solid electrolyte material in the solid electrolyte layer 300 are independently selected from at least one of a garnet-type solid electrolyte and a sulfur-based solid electrolyte. The material of the solid electrolyte layer 300 is the same as or different from the solid electrolyte material for the positive electrode. For example, the composition of the solid electrolyte layer selects a reduction-resistant solid electrolyte material to protect the negative electrode material 10 of the negative electrode and further improve the cycle stability of the negative electrode material 10. Furthermore, when preparing the solid electrolyte layer 300 and the positive electrode material layer 201, the particle size of the solid electrolyte material used can be 100nm-5μm. In one embodiment of the present application, the chemical formula of the garnet-type solid electrolyte is Li 7+p-q-3u Al u La 3-p X p Zr 2- q Y q O 12 , wherein 0<p≤1, 0<q≤1, 0<u≤1, X is selected from at least one of La, Ca, Sr, Ba and K, and Y is selected from at least one of Ta, Nb, W and Hf. In another embodiment of the present application, the sulfur-based solid electrolyte includes crystalline Li r Q s P t1 S z , glassy Li2S-P2S5 and glass-ceramic Li2S-P2S5 and their dopants, wherein the crystalline Li r Q s P t1 S z In which Q is selected from one or more of Si, Ge and Sn, r+4s+5t1=2z, 0≤s≤1.5. Glassy Li2S-P2S5 includes different products composed of Li2S and P2S5, such as Li7P3S 11 Or 70Li2S-30P2S5, etc.

[0062] In an embodiment of the present application, a method for preparing an all-solid-state lithium battery is also provided, comprising:

[0063] S201: preparing the negative electrode 100: the negative electrode material 10 is mixed with the first solvent, and at least one of the binders is added to obtain a negative electrode mixed slurry; the negative electrode mixed slurry is coated on the negative electrode current collector 102, and after drying and pressing treatment, the negative electrode 100 is obtained.

[0064] S202: preparing a solid electrolyte layer 300: in the presence of a protective gas, the solid electrolyte material and the second solvent are evenly mixed to obtain a solid electrolyte mixed slurry, the solid electrolyte mixed slurry is continuously coated on the negative electrode, and after drying, a solid electrolyte layer 300 is formed on the negative electrode 100.

[0065] S203: preparing positive electrode 200: mixing positive electrode active material, positive electrode solid electrolyte, conductive agent, positive electrode binder and third solvent evenly to obtain positive electrode mixed slurry; coating the positive electrode mixed slurry on positive electrode collector 202, drying and pressing to obtain positive electrode 200.

[0066] S204: In the presence of a protective gas, align the negative electrode 100 with the solid electrolyte layer 300 with the prepared positive electrode 200, fit the tabs, and obtain an all-solid-state lithium battery after hot pressing, vacuum sealing and isostatic pressing.

[0067] In the embodiment of the present application, the first solvent, the second solvent and the third solvent are independently selected from at least one of water, ethanol, toluene, xylene, anisole, acetonitrile, heptane, decane, ethyl acetate, ethyl propionate, butyl butyrate, N-methylpyrrolidone, acetone, etc. The amount of each solvent can generally be 50wt%-400wt% of the mass of dry materials in the corresponding mixed slurry.

[0068] In the embodiment of the present application, the tabletting may be, but is not limited to, roller pressed at 0-5 MPa.

[0069] In the embodiment of the present application, the temperature of the hot pressing treatment may be but is not limited to about 100°C, and the hot pressing treatment time may be but is not limited to 0.5h-3h; the isostatic pressing pressure may be but is not limited to above 100MPa, for example, the pressure is 100MPa-300MPa; the isostatic pressing treatment time may be but is not limited to 3min-10min.

[0070] The all-solid-state lithium battery provided in the present application, because it contains the above-mentioned negative electrode material 10, has high battery capacity and good cycle performance, which is conducive to its application.

[0071] The present application is further described below with reference to a number of embodiments.

[0072] Example 1

[0073] A method for preparing an all-solid-state lithium battery comprises:

[0074] (1) Preparation of negative electrode

[0075] In an argon atmosphere, 1000 g of silicon dioxide material, 1018 g of lithium powder, and 1000 mL of toluene solution were placed in a ball mill, and an appropriate amount of ZrO2 ball milling beads were added. The ball milling was performed at a rate of 250 rpm for 30 min to generate Li 4.4 Si and Li2O; during the continuous ball milling process, Li 4.4 Si changes from crystalline to amorphous state and is coated on the surface of Li2O with high Young's modulus, forming an amorphous Li 4.4 The first coating of the Li2O core is coated with a Si layer. 1000g of the first coating is placed in a reaction chamber, and after a vacuum operation, O2 gas is slowly filled in until the pressure reaches 100KPa (about one atmosphere), and then the temperature is raised to 373K at a rate of 2K / min using an electric heating furnace surrounding the reaction chamber. The reaction is carried out for 20 minutes, and the product is taken out after it reaches room temperature. A Li2O layer can be formed on the surface of the first coating to obtain a negative electrode material. The scanning electron microscopy (SEM) results of the sample cut by focused ion beam (FIB) show that the particle size of the Li2O core in the negative electrode material is about 20nm, and the amorphous Li 4.4 The thickness of the Si layer is about 100 nm, and the thickness of the Li2O layer is about 5 nm.

[0076] 1000g of negative electrode material, 30g of binder SBR rubber, and 1500mL of toluene solution were placed in a disperser for 30 minutes to form a stable and uniform negative electrode slurry. The negative electrode slurry was evenly and intermittently coated on a copper foil (width 160mm, thickness 16μm), then dried at 373K, and pressed by a roller press to obtain a negative electrode.

[0077] (2) Fabrication of solid electrolyte layer

[0078] Under an argon atmosphere, 600 g of 70Li2S·30P2S5 glassy solid electrolyte material was placed in 1200 g of toluene solution containing 30 g of butadiene rubber binder, and heated and stirred until a stable and uniform slurry was obtained; the slurry was continuously coated on the negative electrode obtained in step (1), and then dried at 373K to form a solid electrolyte layer with a thickness of 50 μm on the negative electrode.

[0079] (3) Preparation of positive electrode

[0080] 1000g TiS2 positive electrode material, 150g Li 10 GeP2S 12Solid electrolyte material, 30g of binder butadiene rubber, 20g of acetylene black, and 20g of carbon fiber are added to 1500g of toluene solvent, and then stirred in a vacuum mixer to form a stable and uniform positive electrode mixed slurry; the positive electrode mixed slurry is uniformly and intermittently coated on an aluminum foil (width 160mm, thickness 16μm), and then dried at 393K. After being pressed by a roller press, a positive electrode material layer with a thickness of 100μm is formed on the aluminum foil to obtain a positive electrode.

[0081] (4) Fabrication of all-solid-state lithium batteries

[0082] Under a protective atmosphere, the positive electrode and the negative electrode with a solid electrolyte layer were aligned and placed in a tablet press, the tabs were fitted, hot pressed at 100°C for 1 hour, vacuum sealed with an aluminum-plastic film, and finally pressed at 200 MPa for 300 seconds in an isostatic press to obtain an all-solid-state lithium battery.

[0083] Example 2

[0084] A preparation method of an all-solid-state lithium battery is substantially the same as that of Example 1, except that 1000 g of silicon oxide material and 1018 g of lithium powder are replaced by 508 g of Li2SiF6 material, 90 g of lithium powder and 1243 g of Li 4.4 Si material, filled with O2 gas into F2 gas, pressure of 100KPa into 45KPa, reaction time of 20min into 10min. The results of scanning electron microscopy (SEM) of the sample cut by focused ion beam (FIB) show that the particle size of LiF core in the negative electrode material is about 15nm, and the amorphous Li 4.4 The thickness of the Si layer is about 100 nm, and the thickness of the LiF layer is about 5 nm.

[0085] Example 3

[0086] A preparation of an all-solid-state lithium battery is substantially the same as Example 1, except that the ball milling at a rate of 250 rpm for 30 min is changed to the ball milling at a rate of 50 rpm for 30 min; the electric heating furnace is heated to 373 K at a rate of 2 K / min, and the reaction is changed to the electric heating furnace is heated to 423 K at a rate of 2 K / min, and the reaction is 30 min. The scanning electron microscopy (SEM) results of the sample cut by focused ion beam (FIB) show that the particle size of the Li2O core in the negative electrode material is about 100 nm, and the amorphous Li 4.4 The thickness of the Si layer is about 1000 nm, and the thickness of the Li2O layer is about 100 nm.

[0087] In order to highlight the beneficial effects of the embodiments of the present application, the following comparative examples are provided:

[0088] Comparative Example 1

[0089] A preparation of an all-solid-state lithium battery, which is different from Example 1 in that a carbon-coated silicon negative electrode material is used to replace the negative electrode material, wherein the preparation method of the carbon-coated silicon negative electrode material comprises: placing 1000g of Si and 240g of sucrose in 1000mL of deionized water and stirring evenly, then heating to 100°C during stirring, taking out the solid after the water evaporates, and heating to 300°C in an inert atmosphere to obtain a carbon-coated silicon negative electrode material. The carbon-coated silicon negative electrode material is directly used as the negative electrode, and the other steps remain unchanged.

[0090] Comparative Example 2

[0091] A preparation of an all-solid-state lithium battery, which differs from Example 1 in that the specific operation of step (1) is as follows: 1000 g of Si and 240 g of sucrose are placed in 1000 mL of deionized water and stirred evenly, then heated to 100° C. during stirring, and after the water evaporates, the solid is taken out and heated to 300° C. under an inert atmosphere to obtain a carbon-coated silicon negative electrode material; 1000 g of the carbon-coated silicon negative electrode material is mixed with 150 g of 70Li2S·30P2S5 glassy electrolyte material, 100 g of acetylene black, 30 g of binder SBR, and 1000 mL of toluene to prepare a mixed slurry, which is coated on a copper foil, dried, and pressed into a sheet to obtain a negative electrode.

[0092] Comparative Example 3

[0093] A preparation of an all-solid-state lithium battery is different from Example 1 in that 1000 g of the first coating is directly mixed with 30 g of a binder SBR rubber and 1500 mL of toluene to prepare a negative electrode slurry, and the other steps remain unchanged.

[0094] Comparative Example 4

[0095] A method for preparing an all-solid-state lithium battery, which is different from Example 1 in that the amorphous Li 4.4 The Li2O layer was prepared on the Si surface, but the Li2O core was not prepared, and the other steps remained unchanged.

[0096] Performance Testing

[0097] The all-solid-state lithium batteries obtained in the above embodiments and comparative examples were tested for battery cycle life, and the testing method was as follows: 20 all-solid-state lithium battery samples prepared in each embodiment and comparative example were taken, and each battery was subjected to a charge and discharge cycle test at a rate of 0.1C at 298±1K on a LAND CT 2001C secondary battery performance testing device.

[0098] The test steps are as follows: leave for 10 minutes; charge at constant voltage to 4.25V / 0.05C and then stop; leave for 10 minutes; discharge at constant current to 3V, which is one cycle, and record the first cycle discharge capacity. Repeat the above cycle steps, when the battery capacity is lower than 80% of the first discharge capacity during the cycle, the cycle is terminated, and the number of cycles at the end of the cycle is the cycle life of the battery. The average value of each group is taken, and the results are shown in Table 1.

[0099] Table 1 Cycle life test data of each group of samples

[0100]

[0101] It can be seen from Table 1 that the discharge capacity and cycle life of Comparative Example 1 are very poor, and the discharge capacity and cycle life of Comparative Examples 2-4 are significantly lower than those of the embodiments; the battery performance of Comparative Example 1 using the carbon-coated silicon negative electrode material commonly used in lithium batteries with electrolyte is extremely poor, indicating that the negative electrode material is not very suitable for all-solid-state lithium batteries; but the carbon-coated silicon negative electrode material is mixed with a solid electrolyte (Comparative Example 2), the obtained battery performance is improved compared with Comparative Example 1, but it is still far inferior to the all-solid-state lithium battery made of the negative electrode material of the embodiment of the present application; the cycle performance of the all-solid-state lithium battery (Comparative Example 3 and Comparative Example 4) made of the negative electrode material using a single-layer coating method is improved, but it is still inferior to the all-solid-state lithium battery made of the negative electrode material of the embodiment of the present application; the all-solid-state lithium battery made of the negative electrode material of the present application has a higher negative electrode discharge specific capacity and a better battery cycle life, which is conducive to its widespread use.

[0102] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A negative electrode material, characterized in that: The negative electrode material comprises a core and a first coating layer and a second coating layer sequentially coating the core, wherein the material of the core comprises at least one of Li2O, LiF, Li2CO3 and LiCl, and the material of the first coating layer is amorphous Li x Si, 0<x≤4.4, the material of the second coating layer includes at least one of Li2O, LiF, Li2CO3 and LiCl, and the thickness ratio of the first coating layer to the second coating layer is (2-50):

1.

2. The negative electrode material according to claim 1, characterized in that The ratio of the particle size of the negative electrode material to the thickness of the first coating layer is (2.03-4):

1.

3. The negative electrode material according to claim 1, characterized in that The core and the second cladding layer are made of the same material.

4. The negative electrode material according to claim 1, characterized in that The particle size of the core is 5nm-50nm; the thickness of the first coating layer is 20nm-500nm; and the thickness of the second coating layer is 2nm-50nm.

5. A method for preparing a negative electrode material, characterized in that: include: A wrapping layer is formed on the surface of the core to obtain a first coating, wherein the material of the core includes at least one of Li2O, LiF, Li2CO3 and LiCl, and the material of the wrapping layer is amorphous Li x Si, 0<x≤4.4; A second coating layer is formed on the surface of the first coating to obtain a negative electrode material, wherein the negative electrode material includes the core and a first coating layer and a second coating layer that sequentially coat the core, the material of the second coating layer includes at least one of Li2O, LiF, Li2CO3 and LiCl, and the thickness ratio of the first coating layer to the second coating layer is (2-50):

1.

6. The preparation method according to claim 5, characterized in that: Forming a second coating layer on the surface of the first coating includes: The first coating is placed in an atmosphere of at least one of O2, F2, CO2 and Cl2, and heated to form a second coating layer.

7. The preparation method according to claim 6, characterized in that: The heating includes treating at 100° C.-250° C. for 10 min-2 h.

8. An all-solid-state lithium battery, characterized in that: It comprises a positive electrode, a negative electrode and a solid electrolyte layer located between the positive electrode and the negative electrode, wherein the negative electrode comprises the negative electrode material according to any one of claims 1 to 4 or the negative electrode material prepared by the preparation method according to any one of claims 5 to 7.

9. The all-solid-state lithium battery according to claim 8, characterized in that: The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector, wherein the negative electrode material layer includes the negative electrode material and does not contain a solid electrolyte material and a conductive agent.

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