Composite negative electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a composite negative electrode material as well as a preparation method and application thereof. The composite negative electrode material comprises a base material layer, a first coating layer and a second coating layer, the first coating layer is located on the surface of the base material layer, and the second coating layer is located on the surface, away from the base material layer, of the first coating layer; the base material layer comprises a skeleton carbon material and nano silicon located in the skeleton carbon material; the first coating layer comprises a first sulfide electrolyte, a conductive carbon material and a polymer material; the second coating layer comprises a second sulfide electrolyte, and the ionic conductivity of the second sulfide electrolyte under the room temperature condition is larger than 10 mS / cm. According to the composite negative electrode material, through cooperation of all the layers, the structural stability is good, the rate capability and the cycle life of the high-energy-density all-solid-state battery can be greatly improved, and the safety performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a composite negative electrode material and a preparation method and application thereof. Background Art

[0002] All-solid-state batteries have garnered widespread attention from both academia and industry in recent years, as they significantly enhance the intrinsic safety of lithium-ion batteries by replacing flammable organic electrolytes with solid-state electrolytes. Solid-state electrolytes, as the core component of all-solid-state batteries, are crucial to their development. Solid-state electrolytes primarily fall into four categories: polymers, oxides, sulfides, and halides. Sulfide electrolytes are the optimal choice for all-solid-state battery electrolytes due to their high ionic conductivity and low Young's modulus. Silicon anode materials, with their high specific capacity, are the preferred anode material for high-energy-density all-solid-state batteries. However, high-capacity silicon anode materials exhibit large volume expansion, and their use with sulfide electrolytes can lead to poor interfacial contact, resulting in a rapid increase in cell impedance and a rapid deterioration in all-solid-state battery performance.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] One object of the present invention is to provide a composite negative electrode material having high ionic and electronic conductivity, good structural stability, and the characteristics of long cycle and high rate.

[0005] Another object of the present invention is to provide a method for preparing a composite negative electrode material, which is simple, easy to implement, and environmentally friendly, and can improve the electrochemical performance of the composite negative electrode material through the coordination of various steps.

[0006] Another object of the present invention is to provide a negative electrode sheet.

[0007] Another object of the present invention is to provide a battery.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted: A composite negative electrode material comprises a base material layer, a first coating layer and a second coating layer, wherein the first coating layer is located on the surface of the base material layer, and the second coating layer is located on the surface of the first coating layer away from the base material layer; the base material layer comprises a skeleton carbon material and nano-silicon located inside the skeleton carbon material; the first coating layer comprises a first sulfide electrolyte, a conductive carbon material and a polymer material; the second coating layer comprises a second sulfide electrolyte, and the ionic conductivity of the second sulfide electrolyte at room temperature is greater than 10mS / cm.

[0009] In some embodiments, the particle size of the skeleton carbon material is 3-5 μm.

[0010] In some embodiments, the skeleton carbon material has nanopores, and the volume of a single nanopore is 20-100 nm. 3 .

[0011] In some embodiments, the particle size of the nano-silicon is 2-4 nm.

[0012] In some embodiments, the nano-silicon accounts for 60% to 80% by mass of the base material layer.

[0013] In some embodiments, the mass percentage of the first coating layer to the base material layer is 2% to 5%.

[0014] In some embodiments, the mass percentage of the first sulfide electrolyte in the first coating layer is 60% to 80%, and the mass percentage of the conductive carbon material in the first coating layer is 3% to 10%.

[0015] In some embodiments, the first sulfide electrolyte comprises Li (6-x) PS (5-x) M (1+x) and at least one of yLi2S·(1-y)P2S5, wherein M is at least one of Cl, Br and I, 0≤x≤0.2; 0.6≤y≤0.8.

[0016] In some embodiments, the particle size of the first sulfide electrolyte is 0.5-1 μm.

[0017] In some embodiments, the conductive carbon material includes at least one of carbon nanotubes, carbon black, carbon nanofibers, Ketjen black, and graphene.

[0018] In some embodiments, the polymer material includes polyethylene oxide and / or polysiloxane, and the molecular weight of the polymer material is 800,000 to 1.5 million.

[0019] In some embodiments, the polymer material further comprises a lithium salt, and the mass percentage of the lithium salt in the polymer material is greater than 0% and less than or equal to 20%.

[0020] In some embodiments, the polymer material further comprises a lithium salt, and the total mass of the polymer material and the lithium salt accounts for 15% to 35% of the mass of the first coating layer.

[0021] In some embodiments, the polymer material further comprises a lithium salt, and the lithium salt comprises lithium bis(fluorosulfonyl)imide salt and / or lithium bis(trifluoromethanesulfonyl)imide.

[0022] In some embodiments, the mass percentage of the second coating layer to the base material layer is 0.7% to 2%.

[0023] In some embodiments, the second sulfide electrolyte includes Li 10 GeP2S 12 He Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 At least one of .

[0024] In some embodiments, the particle size of the second sulfide electrolyte is 30-50 nm.

[0025] In some embodiments, the specific capacity of a battery corresponding to the composite negative electrode material under 0.1C charge and discharge conditions is greater than 210 mAh / g.

[0026] In some embodiments, the first efficiency of a battery corresponding to the composite negative electrode material under 0.1C charge and discharge conditions is greater than 90%.

[0027] In some embodiments, the 1C rate capacity retention rate of the battery corresponding to the composite negative electrode material is greater than 91%.

[0028] In some embodiments, the battery corresponding to the composite negative electrode material has a capacity decay to 80% cycle number greater than 850 under 1C charge and discharge conditions.

[0029] The method for preparing the composite negative electrode material as described above comprises the following steps: The porous carbon material and the silicon source gas are subjected to a first heat treatment to obtain a base material.

[0030] The base material is first coated with a mixture of a first sulfide electrolyte and a conductive carbon material to obtain a first material, and the mixed system of the first material and a polymer material solution is dried to form a second material having a first coating layer.

[0031] The second material is subjected to a second coating using a second sulfide electrolyte, and then subjected to a second heat treatment to form a second coating layer, thereby obtaining a composite negative electrode material.

[0032] In some embodiments, the temperature of the first heat treatment is 400-500°C.

[0033] In some embodiments, the first coating and the second coating are each independently formed by fusion coating.

[0034] In some embodiments, the polymer material solution includes a polymer material and an organic solvent.

[0035] In some embodiments, the drying comprises spray drying.

[0036] In some embodiments, the temperature of the second heat treatment is 100-200° C., and the time of the second heat treatment is 1-3 hours.

[0037] A negative electrode sheet comprises the composite negative electrode material or the composite negative electrode material obtained by the method for preparing the composite negative electrode material.

[0038] A battery comprises the negative electrode sheet.

[0039] Compared with the prior art, the present invention has the following beneficial effects: (1) The composite negative electrode material of the present invention adopts a first sulfide electrolyte with high stability, a conductive carbon material and a polymer material as the first coating layer of the silicon-carbon matrix material, which is conducive to stabilizing the interface, realizing the dual conduction of ions and electrons, and maintaining a complete electron and ion transmission path; a second sulfide electrolyte with high ionic conductivity is adopted as the second coating layer to ensure that a complete ion transmission channel is formed with the first sulfide electrolyte of the first coating layer, reducing side reactions, thereby greatly improving the rate performance and cycle life of the high energy density all-solid-state battery and improving safety performance.

[0040] (2) The preparation method of the composite negative electrode material of the present invention forms a uniform first coating layer and a uniform second coating layer on the surface of the base material in sequence through the coordination of various steps. This method is beneficial to improving the cycle performance and rate performance of the composite negative electrode material.

[0041] (3) The battery of the present invention has the characteristics of long cycle performance, high rate performance and high safety performance. DETAILED DESCRIPTION

[0042] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0043] According to one aspect of the present invention, the present invention relates to a composite negative electrode material, comprising a base material layer, a first coating layer and a second coating layer, wherein the first coating layer is located on the surface of the base material layer, and the second coating layer is located on the surface of the first coating layer away from the base material layer; the base material layer comprises a skeleton carbon material and nano-silicon located inside the skeleton carbon material; the first coating layer comprises a first sulfide electrolyte, a conductive carbon material and a polymer material; the second coating layer comprises a second sulfide electrolyte, and the ionic conductivity of the second sulfide electrolyte at room temperature is greater than 10mS / cm.

[0044] The composite negative electrode material of the present invention adopts a high-stability first sulfide electrolyte, a conductive carbon material and a polymer material as the first coating layer of the silicon-carbon matrix material, which is conducive to stabilizing the interface, realizing dual conduction of ions and electrons, and maintaining a complete electron and ion transmission path; a second sulfide electrolyte with high ionic conductivity is adopted as the second coating layer to ensure that a complete ion transmission channel is formed with the first sulfide electrolyte of the first coating layer, reducing side reactions, thereby greatly improving the rate performance and cycle life of the high-energy density all-solid-state battery and improving safety performance.

[0045] In some embodiments, the particle size of the skeleton carbon material is 3-5µm, such as 3µm, 3.5µm, 4.5µm, 5µm, etc. In some embodiments, the skeleton carbon material has nanopores, and the volume of a single nanopore is 20-100nm. 3 , for example 20nm 3 , 30nm 3 , 50nm 3 , 80nm 3 or 100 nm 3 The skeleton carbon material of the present invention has both high specific surface area and structural stability, and its suitable pores are conducive to alleviating the volume expansion of silicon.

[0046] In some embodiments, the particle size of the nano-silicon is 2-4 nm, such as 2 nm, 2.5 nm, 3 nm or 4 nm. A suitable nano-silicon particle size is beneficial to alleviating stress and strain caused by volume expansion.

[0047] In some embodiments, the mass percentage of the nano-silicon in the matrix material layer is 60% to 80%, for example, 60%, 65%, 70%, 75%, 80%, etc. An appropriate nano-silicon content can ensure specific capacity while maintaining the structural integrity of the carbon skeleton material.

[0048] In some embodiments, the first coating layer accounts for 2% to 5% of the base material layer by mass, for example, 2%, 2.5%, 3%, 4%, 5%, etc. The first coating layer of the present invention accounts for an appropriate mass percentage of the base material layer, thereby ensuring the formation of a coating layer of appropriate thickness, thereby improving the performance of the composite negative electrode material and balancing the protective effect and ion conduction effect. If the mass percentage of the first coating layer to the base material layer is too low, the coating layer is too thin, and the effect of the first protective layer is not significant; if the mass percentage of the first coating layer to the base material layer is too high, the coating layer is too thick, which increases the interfacial impedance.

[0049] In some embodiments, the mass percentage of the first sulfide electrolyte in the first coating layer is 60% to 80%, for example, 60%, 65%, 70%, 75%, 80%, etc. The mass percentage of the conductive carbon material in the first coating layer is 3% to 10%, for example, 3%, 5%, 7%, 9%, or 10%, etc. The present invention defines the ratios of the first sulfide electrolyte, the conductive carbon material, and the polymer material, so that the three work in a coordinated manner to ensure the ion and electron transport performance of the first coating layer.

[0050] In some embodiments, the first sulfide electrolyte comprises Li (6-x) PS (5-x) M (1+x) and at least one of yLi2S·(1-y)P2S5, wherein M is at least one of Cl, Br, and I, and 0≤x≤0.2; 0.6≤y≤0.8. The first sulfide electrolyte of the present invention has high stability, and halogen doping can improve conductivity.

[0051] In some embodiments, the first sulfide electrolyte has a particle size of 0.5 to 1 µm, such as 0.5 µm, 0.6 µm, 0.7 µm, 0.9 µm, or 1 µm. The present invention uses a first sulfide electrolyte with an appropriate particle size to improve coating uniformity and ensure the performance of the first coating layer.

[0052] In some embodiments, the conductive carbon material includes at least one of carbon nanotubes, carbon black, carbon nanofibers, Ketjen black, and graphene, such as a combination of carbon nanotubes and carbon black, or a combination of carbon nanofibers and Ketjen black. Suitable conductive carbon materials facilitate the construction of a three-dimensional conductive network and improve electrical conductivity.

[0053] In some embodiments, the polymer material includes polyethylene oxide and / or polysiloxane, and the molecular weight of the polymer material is 800,000 to 1.5 million, for example, 800,000, 900,000, 1,000,000, 1,100,000, 1,200,000, 1,300,000, or 1,500,000. The polymer material of the present invention has an appropriate molecular weight and can form a flexible coating with high mechanical strength, thereby suppressing dendrites.

[0054] In some embodiments, the polymer material further comprises a lithium salt, and the lithium salt accounts for a mass percentage of greater than 0% and less than or equal to 20% of the polymer material, such as 1%, 2%, 5%, 8%, 10%, 15%, 18%, 20%, etc. The addition of a suitable proportion of lithium salt in the present invention is beneficial to improving the ionic conductivity of the polymer material. In some embodiments, the total mass of the polymer material and the lithium salt accounts for a mass percentage of 15% to 35% of the first coating layer, such as 15%, 20%, 25%, 30% or 35%, etc. The total mass of the polymer material and the lithium salt accounts for a suitable mass percentage of the first coating layer to ensure the formation of a continuous ion channel. In some embodiments, the lithium salt comprises lithium bis(fluorosulfonyl)imide (LiFSI) and / or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0055] In some embodiments, the mass percentage of the second coating layer to the base material layer is 0.7% to 2%, for example, 0.7%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc. The second coating layer of the present invention has an appropriate mass percentage to the base material layer, which helps ensure that the second coating layer has an appropriate thickness and uniformity. If the mass percentage of the second coating layer to the base material layer is too high or too low, it is not conducive to the performance of the second coating layer and reduces the electrochemical performance of the negative electrode material.

[0056] In some embodiments, the second sulfide electrolyte includes Li 10 GeP2S 12 He Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 The second sulfide electrolyte of the present invention has the characteristics of high ion conductivity and can improve good ion channels.

[0057] In some embodiments, the particle size of the second sulfide electrolyte is 30-50 nm, such as 30 nm, 35 nm, 40 nm, or 50 nm.

[0058] In some embodiments, the battery corresponding to the composite negative electrode material has a specific capacity greater than 210 mAh / g under 0.1C charge and discharge conditions, such as 211 mAh / g, 215 mAh / g, 220 mAh / g, 230 mAh / g, etc. The battery corresponding to the composite negative electrode material of the present invention has a high capacity characteristic.

[0059] In some embodiments, the first efficiency of the battery corresponding to the composite negative electrode material under 0.1C charge and discharge conditions is greater than 90%, for example, 91%, 92%, 93%, 95%, etc. The battery corresponding to the composite negative electrode material of the present invention has the characteristic of high first efficiency.

[0060] In some embodiments, the 1C rate capacity retention rate of the battery corresponding to the composite negative electrode material is greater than 91%, such as 92%, 93%, 95%, etc. The battery corresponding to the composite negative electrode material of the present invention has excellent capacity retention rate.

[0061] In some embodiments, the battery corresponding to the composite negative electrode material has a capacity decay to 80% cycle number under 1C charge and discharge conditions greater than 850 times, for example, 855 times, 860 times, 870 times, 880 times or 900 times.

[0062] According to another aspect of the present invention, the present invention also relates to a method for preparing the composite negative electrode material as described above, comprising the following steps: A porous carbon material and a silicon source gas are subjected to a first heat treatment to obtain a base material. The base material is then coated with a mixture of a first sulfide electrolyte and a conductive carbon material to obtain a first material. The mixture of the first material and a polymer solution is dried to form a second material having a first coating layer. The second material is then coated with a second sulfide electrolyte and subjected to a second heat treatment to form a second coating layer, thereby obtaining a composite negative electrode material.

[0063] The preparation method of the composite negative electrode material of the present invention forms a uniform first coating layer and a second coating layer on the surface of the base material in sequence through the coordination of various steps. The obtained composite negative electrode material has excellent cycle performance, rate performance and safety performance.

[0064] In some embodiments, the temperature of the first heat treatment is 400-500°C, such as 400°C, 430°C, 450°C, 480°C or 500°C. A suitable first heat treatment is beneficial to ensure the structure and performance of the base material.

[0065] In some embodiments, the first coating and the second coating are each independently performed by fusion coating; specifically, the fusion coating is performed by a mechanical fusion machine.

[0066] In some embodiments, the polymer material solution includes a polymer material and an organic solvent, and the organic solvent is selected from at least one of acetonitrile, tetrahydrofuran, anisole, chloroform, dichloroethane, and dimethylformamide.

[0067] In some embodiments, the drying comprises spray drying to form a uniform first coating layer.

[0068] In some embodiments, the temperature of the second heat treatment is 100-200°C, for example, 100°C, 120°C, 150°C, 180°C, or 200°C. The duration of the second heat treatment is 1-3 hours, for example, 1 hour, 1.5 hours, 2 hours, or 3 hours. An appropriate second heat treatment can ensure the performance of the coating layer and improve the coating effect.

[0069] According to another aspect of the present invention, the present invention also relates to a negative electrode sheet, comprising the composite negative electrode material, or the composite negative electrode material obtained by the method for preparing the composite negative electrode material.

[0070] The negative electrode sheet of the present invention has the characteristics of high energy density, long cycle time and high rate.

[0071] According to another aspect of the present invention, the present invention also relates to a battery comprising the above-mentioned negative electrode sheet.

[0072] The battery of the present invention has excellent cycle performance, rate performance and safety performance.

[0073] The battery includes an all-solid-state battery. The positive electrode material of the battery is selected from at least one of a ternary material, a lithium-rich material, and a lithium nickel manganese oxide material.

[0074] The following is further explained with reference to specific embodiments and comparative examples.

[0075] Example 1 A method for preparing a composite negative electrode material comprises the following steps: (1) The porous hard carbon and silane gas are subjected to a first heat treatment at 420°C in a fluidized bed furnace to form a matrix material. The matrix material includes a skeleton carbon material and nano-silicon. The particle size of the porous hard carbon is 4µm, and the volume of a single nanopore is 30nm. 3 The particle size of nano-silicon is 2nm, and the mass percentage of silicon in the matrix material is 70%.

[0076] (2) After uniformly mixing 0.6µm first sulfide electrolyte Li6PS5Cl and conductive carbon additive carbon nanotubes, the mixture was coated onto the surface of the above-mentioned base material using a mechanical fusion machine to obtain a first material. A polymer material polyethylene oxide with a molecular weight of 1 million was mixed with a solvent acetonitrile to form a uniform polymer material liquid. The polymer material solution and the first material were uniformly mixed and spray-dried to form a second material having a first coating layer; the mass ratio of the first sulfide electrolyte, carbon nanotubes, and polymer material was 70:5:25, and the mass percentage of the first coating layer to the base material was 3%.

[0077] (3) 40nm second sulfide electrolyte Li 9.54 Si 1.74 P 1.44 S11.7 Cl 0.3 The surface of the second material is coated with a mechanical fusion machine to form a second coating layer, in which the second sulfide electrolyte accounts for 1% by mass of the matrix material. A second heat treatment is then performed at 150°C for 2 hours to obtain a composite negative electrode material.

[0078] Example 2 A method for preparing a composite negative electrode material comprises the following steps: (1) The porous hard carbon and silane gas are subjected to a first heat treatment at 450°C in a fluidized bed furnace to form a matrix material. The matrix material includes a skeleton carbon material and nano-silicon. The particle size of the porous hard carbon is 4.5µm and the volume of the nanopores is 100nm. 3 The particle size of nano-silicon is 4nm, and the mass percentage of silicon in the matrix material is 75%.

[0079] (2) After uniformly mixing a 0.7µm first sulfide electrolyte Li6PS5Cl and a conductive carbon additive carbon nanofiber, the mixture was coated onto the surface of the above-mentioned base material using a mechanical fusion machine to obtain a first material. A polymer material polysiloxane with a molecular weight of 1 million was mixed with a solvent acetonitrile to form a uniform polymer material liquid. The polymer material solution and the first material were uniformly mixed and spray-dried to form a second material having a first coating layer; the mass ratio of the first sulfide electrolyte, carbon nanofiber, and polymer material was 75:8:17, and the mass percentage of the first coating layer to the base material was 3.5%.

[0080] (3) The 45nm second sulfide electrolyte Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 The surface of the second material is coated with a mechanical fusion machine to form a second coating layer, in which the second sulfide electrolyte accounts for 1.5% by mass of the matrix material. A second heat treatment is then performed at 170°C for 1.5 hours to obtain a composite negative electrode material.

[0081] Example 3 A method for preparing a composite negative electrode material, which differs from Example 1 in that: The mass percentage of the first coating layer to the base material layer is 2%.

[0082] The mass percentage of the second sulfide electrolyte in the matrix material is 0.7%.

[0083] Example 4 A method for preparing a composite negative electrode material, which differs from Example 1 in that: The mass percentage of the first coating layer to the base material layer is 5%.

[0084] The mass percentage of the second sulfide electrolyte in the matrix material is 2%.

[0085] Example 5 A method for preparing a composite negative electrode material, which differs from Example 1 in that: The mass ratio of the first sulfide electrolyte, carbon nanofibers, and polymer material is 60:10:30; The particle size of the first sulfide electrolyte is 0.5 μm.

[0086] The molecular weight of the polymer material is 800,000.

[0087] Example 6 A method for preparing a composite negative electrode material, which differs from Example 1 in that: The mass ratio of the first sulfide electrolyte, carbon nanofibers, and polymer material is 80:5:30; The particle size of the first sulfide electrolyte is 1µm.

[0088] The molecular weight of the polymer material is 1.5 million.

[0089] Example 7 A method for preparing a composite negative electrode material, which differs from Example 1 in that: The polymer material further contains lithium salt (lithium bis(fluorosulfonyl)imide salt and lithium bis(trifluoromethanesulfonyl)imide, with a mass ratio of 2:1), and the mass percentage of the lithium salt in the polymer material is 10%.

[0090] Comparative Example 1 A method for preparing a composite negative electrode material, comprising obtaining a base material using the method of Example 1.

[0091] Comparative Example 2 A method for preparing a composite negative electrode material comprises: obtaining a second material by the method of Example 1; and then subjecting the second material to a second heat treatment at 170° C. for 1.5 h.

[0092] Experimental example The composite negative electrode materials of each embodiment and comparative example were respectively prepared into battery cells, including: 3µm particle size Li6PS5Cl was placed in a mold battery, and a 1mm electrolyte original sheet was prepared under a pressure of 30MPa. Nickel cobalt manganese 811 and 1µm particle size Li6PS5Cl materials were evenly mixed in a ratio of 9:1 and placed on one side of the electrolyte sheet, and the above composite negative electrode material and Li were placed on the other side. 9.54 Si1.74P 1.44 S 11.7 Cl 0.3 mixture (mass ratio 9:1).

[0093] Perform performance tests on the above cells, including: First effect: Charge and discharge at a rate of 0.1C. The 0.1C discharge specific capacity is the material specific capacity, and the ratio of the first discharge capacity to the first charge capacity is the first effect.

[0094] Rate retention rate: Charge at 0.1C, discharge at 0.1C and 1C respectively. The ratio of 1C discharge capacity to 0.1C discharge capacity is the rate retention rate.

[0095] Cycle life: The number of cycles of charging and discharging at 1C until the capacity decays to 80%.

[0096] The performance test of the battery cell is shown in Table 1.

[0097] Table 1 Performance test results

[0098] As can be seen from the above, the preparation method of the composite negative electrode material of the present invention, in which a first coating layer and a second coating layer are sequentially coated on the surface of the base material layer, can significantly improve the rate performance and cycle life of high-energy-density all-solid-state batteries, and enhance safety performance. The batteries of various embodiments of the present invention have a specific capacity greater than 210 mAh / g, an initial efficiency greater than 90%, a 1C rate capacity retention rate greater than 91%, and the number of cycles to 80% capacity decay under 1C charge and discharge conditions is greater than 850.

[0099] The batteries obtained from the composite negative electrode materials of Comparative Examples 1 and 2 have relatively low rate capacity retention rates and low cycle times.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite negative electrode material, characterized in that The invention comprises a base material layer, a first cladding layer and a second cladding layer, wherein the first cladding layer is located on the surface of the base material layer, and the second cladding layer is located on the surface of the first cladding layer away from the base material layer; The matrix material layer comprises a skeleton carbon material and nano-silicon located inside the skeleton carbon material; The first coating layer comprises a first sulfide electrolyte, a conductive carbon material and a polymer material; The second coating layer comprises a second sulfide electrolyte, and the ionic conductivity of the second sulfide electrolyte at room temperature is greater than 10 mS / cm.

2. The composite negative electrode material according to claim 1, characterized in that Contains at least one of the following features (1) to (4): (1) The particle size of the skeleton carbon material is 3-5 μm; (2) The skeleton carbon material has nanopores, and the volume of a single nanopore is 20~100nm 3 ; (3) The particle size of the nano-silicon is 2-4 nm; (4) The mass percentage of the nano-silicon in the base material layer is 60% to 80%.

3. The composite negative electrode material according to claim 1, characterized in that Contains at least one of the following features (1) to (6): (1) The mass percentage of the first coating layer to the base material layer is 2% to 5%; (2) The mass percentage of the first sulfide electrolyte in the first coating layer is 60% to 80%, and the mass percentage of the conductive carbon material in the first coating layer is 3% to 10%; (3) The first sulfide electrolyte includes Li (6-x) PS (5-x) M (1+x) and at least one of yLi2S·(1-y)P2S5, wherein M is at least one of Cl, Br and I, 0≤x≤0.2; 0.6≤y≤0.8; (4) The particle size of the first sulfide electrolyte is 0.5-1 μm; (5) The conductive carbon material includes at least one of carbon nanotubes, carbon black, carbon nanofibers, Ketjen black and graphene; (6) The polymer material includes polyethylene oxide and / or polysiloxane, and the molecular weight of the polymer material is 800,000 to 1.5 million.

4. The composite negative electrode material according to claim 3, characterized in that Contains at least one of the following features (1) to (3): (1) The polymer material further comprises a lithium salt, and the mass percentage of the lithium salt in the polymer material is greater than 0% and less than or equal to 20%; (2) The polymer material further comprises a lithium salt, and the total mass of the polymer material and the lithium salt accounts for 15% to 35% of the mass of the first coating layer; (3) The polymer material further comprises a lithium salt, wherein the lithium salt comprises lithium bis(fluorosulfonyl)imide salt and / or lithium bis(trifluoromethanesulfonyl)imide.

5. The composite negative electrode material according to claim 3, characterized in that Contains at least one of the following features (1) to (3): (1) The mass percentage of the second coating layer to the base material layer is 0.7% to 2%; (2) The second sulfide electrolyte includes Li 10 GeP2S 12 He Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 At least one of; (3) The particle size of the second sulfide electrolyte is 30-50 nm.

6. The composite negative electrode material according to claim 3, characterized in that Contains at least one of the following features (1) to (4): (1) The specific capacity of the battery corresponding to the composite negative electrode material under 0.1C charge and discharge conditions is greater than 210 mAh / g; (2) The first efficiency of the battery corresponding to the composite negative electrode material under 0.1C charge and discharge conditions is greater than 90%; (3) The 1C rate capacity retention rate of the battery corresponding to the composite negative electrode material is greater than 91%; (4) The number of cycles for the battery corresponding to the composite negative electrode material to decay to 80% of its capacity under 1C charge and discharge conditions is greater than 850 times.

7. The method for preparing a composite negative electrode material according to any one of claims 1 to 6, wherein: The following steps are involved: subjecting the porous carbon material and the silicon source gas to a first heat treatment to obtain a base material; Performing a first coating on the base material with a mixture of a first sulfide electrolyte and a conductive carbon material to obtain a first material, and drying the mixture of the first material and a polymer material solution to form a second material having a first coating layer; The second material is subjected to a second coating using a second sulfide electrolyte, and then subjected to a second heat treatment to form a second coating layer, thereby obtaining a composite negative electrode material.

8. The method for preparing a composite negative electrode material according to claim 7, characterized in that: Contains at least one of the following features (1) to (5): (1) The temperature of the first heat treatment is 400-500°C; (2) The first coating and the second coating are independently fused; (3) The polymer material solution includes a polymer material and an organic solvent; (4) The drying comprises spray drying; (5) The temperature of the second heat treatment is 100-200°C, and the time of the second heat treatment is 1-3 hours.

9. A negative electrode sheet, characterized in that: The invention comprises the composite negative electrode material according to any one of claims 1 to 6, or the composite negative electrode material obtained by the preparation method of the composite negative electrode material according to any one of claims 7 to 8.

10. A battery, characterized in that: Including the negative electrode sheet according to claim 9.

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