Negative electrode material, negative electrode pole piece, secondary battery and device

Abstract

The invention provides a negative electrode material, preparation thereof, a negative electrode plate and a secondary battery, the negative electrode material comprises a negative electrode material base material, a first coating layer located on the surface of the negative electrode material base material, and a second coating layer located on the surface of the first coating layer, the first coating layer comprises a carbon-based material; the second coating layer comprises a metal oxide, and the carbon-based material comprises graphene. According to the invention, the surface of the negative electrode material base material is subjected to multilayer coating, that is, the surface of the negative electrode material base material is preferentially coated with the carbon-based material (porous carbon material), so that the subsequent coating area of the metal oxide is increased, and meanwhile, the metal oxide is synthesized by adopting a sol-gel method, so that uniform coating on the surface of the negative electrode material is facilitated, and the sensitivity of the metal oxide to the temperature is improved.

Description

Technical Field

[0001] The present application relates to a negative electrode material, and particularly to a negative electrode material, a negative electrode plate, a secondary battery and a device, belonging to the field of batteries. Background Art

[0002] Lithium batteries are currently widely used in consumer products such as mobile phones and laptops, and large-scale energy storage systems such as electric vehicles and energy storage power stations. However, due to the limitation of its own energy density, during actual use, it is often criticized by consumers for insufficient battery life, which brings consumers' range anxiety about the products. To solve the problem of range anxiety, using ternary materials (i.e., high nickel) with higher specific capacity and silicon-carbon negative electrode materials has become the mainstream direction in the industry, but the safety problems brought by them cannot be ignored. Based on the law of conservation of energy, the main energy of a fully charged lithium battery is concentrated on the negative electrode side, and the heat accumulation contribution in the early stage of thermal runaway also mainly comes from the decomposition of the SEI on the negative electrode side and the reaction between the negative electrode and the electrolyte. Therefore, timely blocking the energy conduction on the negative electrode side can significantly improve the thermal safety performance of the lithium battery itself.

[0003] Regarding the improvement of thermal runaway, the current existing methods mainly focus on improving the structural stability of high nickel materials themselves and inhibiting structural collapse by complexing with high nickel materials on the surface through electrolyte additives; another method is to block the conduction between the positive and negative electrodes to achieve the purpose of hindering thermal runaway. Specifically, it mainly focuses on improving the low closing and high bursting of the separator, while there is less improvement on the negative electrode material itself.

[0004] Therefore, there is an urgent need to develop a novel negative electrode material to improve thermal runaway. Summary of the Invention

[0005] To solve the above technical problems, the present application provides a negative electrode material, a secondary battery and a device. By coating the surface of the negative electrode side with metal oxides, as heat accumulates, the metal oxides respond to high temperature in a timely manner, resulting in a significant increase in resistance, thereby blocking the occurrence of side reactions. The negative electrode material of the present application has significantly improved thermal abuse resistance.

[0006] In the first aspect of the present application, a negative electrode material is provided, which includes a negative electrode material matrix, a first coating layer on the surface of the negative electrode material matrix, and a second coating layer on the surface of the first coating layer. The second coating layer includes metal oxides, where the metal oxides include at least one of sodium bismuth titanate, potassium bismuth titanate and their derivatives.

[0007] In the second aspect of the present application, a negative electrode plate is provided, which includes a negative electrode current collector and a negative electrode material layer provided on the surface of the negative electrode current collector. The negative electrode material layer includes the negative electrode active material described in the first aspect.

[0008] In the third aspect of the present application, a secondary battery is provided, which includes the negative electrode sheet and the positive electrode sheet described in the second aspect. In the fourth aspect of the present application, a device is provided, which includes the secondary battery described in the third aspect.

[0009] The present application has the following beneficial effects:

[0010] 1. Compared with the defense in the late stage of thermal runaway, the present application mainly starts from the initial stage of thermal runaway and strangles the process of heat accumulation in the early stage of thermal runaway in the cradle. Since the heat accumulation in the initial stage of thermal runaway mainly comes from the negative electrode side, a metal oxide is coated on the surface of the negative electrode side. As the heat accumulates, the coated metal oxide responds to the high temperature in a timely manner, blocking the continuous decomposition of SEI and the side reaction between the negative electrode and the electrolyte by increasing the impedance of the negative electrode side;

[0011] 2. The surface of the negative electrode material matrix is preferentially coated with a porous carbon-based material to increase the specific surface area of the negative electrode material matrix, improve the surface coating amount of the subsequent metal oxide, and help to enhance the temperature sensitivity of the metal oxide;

[0012] 3. The metal oxide is coated on the surface of the negative electrode material by the sol-gel method, with better uniformity, which helps to enhance the temperature sensitivity of the metal oxide and performs better in the actual hot box. Detailed implementation manners

[0013] For the sake of simplicity, the present application only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recorded; and any lower limit can be combined with other lower limits to form a range not explicitly recorded. Similarly, any upper limit can be combined with any other upper limit to form a range not explicitly recorded. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recorded.

[0014] Unless otherwise specified, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in the present application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0015] A list of items joined by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single component or multiple components. Item B may include a single component or multiple components. Item C may include a single component or multiple components.

[0016] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and not to limit the scope of the present application.

[0017] I. Anode material

[0018] The anode material provided by the present application includes an anode material matrix, a first coating layer located on the surface of the anode material matrix, and a second coating layer located on the surface of the first coating layer. The second coating layer includes a metal oxide, wherein the metal oxide includes at least one of sodium bismuth titanate, potassium bismuth titanate, and its derivatives. The present application modifies the surface of the anode material by coating to inhibit the heat accumulation caused by side reactions on the anode side in the early stage of thermal runaway. Specifically, the present application performs multi-layer coating on the surface of the anode material matrix, that is, by preferentially coating a carbon-based material (porous carbon material) on the surface to increase the area of subsequent metal oxide coating, and at the same time using the sol-gel method to synthesize the metal oxide, which helps the uniform coating of the metal oxide on the surface of the anode material and improves the sensitivity of the metal oxide to temperature, so as to block conduction in time during the start of thermal runaway to inhibit the aggravation of thermal runaway.

[0019] In some embodiments, the derivative includes (1-x)Bi 0.5 Na 0.5 TiO3-xM1TiO3, (1-x)Bi 0.5 Na 0.5 TiO3-xM2NbO3, (1-x)Bi 0.5 Na 0.5 TiO3-xABO3, (1-x-y)Bi 0.5 Na 0.5 TiO3-xM3NbO3-y / 2(Bi2O3·Sc2O3), (1-x-y)Bi 0.5 Na 0.5 TiO3-xBaTiO3-yBiFeO3, (1-x-y)Bi 0.5 Na 0.5TiO3-xBaTiO3-yBi 0.5 K 0.5 TiO3, (1 - x)Bi 0.5 Na 0.5 TiO3 - xSrCaTiO3, (1 - x)Bi 0.5 Na 0.5 TiO3 - xBa[ZryTi(1 - y)]O3, (Bi 0.5 Na 0.5 )1 - xBaxTiO3 - ySb2O3 and Bi 0.5 (Na1 - x - yKxLiy) 0.5 At least one of TiO3, where M1 includes at least one of Ba, Sr, and Ca; M2 includes at least one of K, Li, and Na; A includes at least one of Bi and La; B includes at least one of Cr, Fe, and Mn; M3 includes at least one of K and Na; x ranges from 0 to 1; y ranges from 0 to 1.

[0020] In some embodiments, the anode material matrix includes one or more of graphite, nano - silicon, and silicon - carbon.

[0021] In some embodiments, the first coating layer includes a carbon - based material.

[0022] In some embodiments, the carbon - based material includes one or more of graphene, carbon nanotubes, and conductive graphite.

[0023] In some embodiments, the mass ratio of the second coating layer to the anode material matrix is 1:0.7 - 5.5; in some embodiments, the mass ratio of the second coating layer to the anode material matrix is 1:0.7, 1:1.2, 1:1.7, 1:2.5, 1:3.2, 1:3.7, 1:4.2, 1:4.7, 1:5.2, 1:5.5, or any range therebetween. If the mass ratio of the second coating layer to the anode material matrix is too small, the requirements for temperature sensitivity cannot be met; if the mass ratio of the second coating layer to the anode material matrix is too large, it will result in too high a mass fraction, which is not conducive to the effective utilization of the material. For example, too high a mass of the second - layer coating will result in the need to use a larger mass of anode material to achieve the same specific capacity performance.

[0024] In some embodiments, the mass ratio of the first coating layer to the negative electrode material matrix is 1:2.5 to 4.5; in some embodiments, the mass ratio of the first coating layer to the negative electrode material matrix is 1:2.5, 1:2.8, 1:3.1, 1:3.4, 1:3.7, 1:4.0, 1:4.2, 1:4.5 or any range therebetween. If the mass ratio of the first coating layer to the negative electrode material matrix is too small, the first coating cannot provide sufficient carrier to coat the second coating; if the mass ratio of the first coating layer to the negative electrode material matrix is too large, it will result in too high a mass ratio, which is not conducive to the effective utilization of the material. For example, too high a coating mass will result in the need to use more mass of the negative electrode material to achieve the same specific capacity performance.

[0025] According to an embodiment of the present application, the method for preparing the negative electrode material of the present application includes the following steps:

[0026] (1) Preparation of a carbon-based material-coated negative electrode material matrix

[0027] (a) Mix the carbon-based material and the negative electrode material matrix, and then add a reducing agent thereto to obtain a first mixture;

[0028] (b) Heat the first mixed solution prepared in step (a) at 90°C to 100°C for 6h to 10h to obtain a second mixture;

[0029] (c) Stir and dry the second mixture prepared in step (b) at -50°C for 36h - 48h to obtain a third mixture;

[0030] (d) Irradiate the third mixture prepared in step (c) for 10s to 120s to obtain a carbon-based material-coated negative electrode material matrix, wherein the power of the irradiation is 300W to 1000W;

[0031] (2) Preparation of a metal oxide@carbon-based material-coated negative electrode material

[0032] (e) Mix the carbon-based material-coated negative electrode material matrix prepared in step (1) with a first metal source to obtain a first mixed solution;

[0033] (f) Mix the second mixed solution including the second metal source with the first mixed solution, adjust the pH to 8 - 9, and store at 60°C - 90°C for 12h - 24h to form a fourth mixture;

[0034] (g) Dry the fourth mixture obtained in step (f) at 300°C - 400°C for 4h - 6h, and then calcine at 500°C - 700°C for 4h - 6h to obtain a metal oxide@carbon-based material-coated negative electrode material matrix.

[0035] II. Secondary battery

[0036] The secondary battery provided by the present application includes a negative electrode sheet, a positive electrode sheet, an electrolyte, and a separator. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on the negative electrode current collector, and the negative electrode material layer includes the above-mentioned negative electrode material.

[0037] In some embodiments, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of a nickel-cobalt-based ternary material and a phosphate-based material.

[0038] In some embodiments, the nickel-cobalt-based ternary material includes at least one of LiNi m Co n A (1-m-n) O2 materials, where A is selected from at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver, or niobium, 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, and m + n ≤ 1.

[0039] In some embodiments, m is 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a range composed of any two of these values. In some embodiments, n is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or a range composed of any two of these values.

[0040] In some embodiments, the nickel-cobalt-based ternary material includes at least one of NCA, NCM111, NCM523, NCM622, NCM811, Ni90, Ni92, or Ni95.

[0041] In some embodiments, the phosphate-based material includes at least one of LiMn k B (1-k) PO4, where 0 ≤ k ≤ 1, and the B element is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, or lead. In some embodiments, k is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a range composed of any two of these values. In some embodiments, the phosphate-based material includes lithium iron phosphate, LiMn 0.6 Fe 0.4 PO4, or at least one of LiMn 0.8 Fe 0.2 PO4.

[0042] In some embodiments, the positive electrode active material includes at least one of lithium nickel oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese cobalt magnesium oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate.

[0043] In some embodiments, the positive electrode active material layer further includes a binder, and optionally includes a conductive material. The binder improves the binding between the positive electrode active material particles and also improves the binding between the positive electrode active material and the current collector.

[0044] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0045] In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0046] In some embodiments, the positive electrode further includes a positive electrode current collector, and the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0047] In some embodiments, the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material.

[0048] In some embodiments, the silicon-based material includes at least one of silicon, silicon alloy, silicon oxide compound, and silicon carbide compound.

[0049] In some embodiments, based on the mass of the negative electrode active material, the mass content g% of the silicon-based material satisfies: 10 ≤ g ≤ 100. In some embodiments, g is 11, 13, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or any value between them.

[0050] In some embodiments, the negative electrode active material layer further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0051] In some embodiments, the conductive agent includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0052] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode current collector includes: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0053] In some embodiments, a separator is provided between the positive electrode and the negative electrode to prevent short circuit. There are no particular limitations on the materials and shapes of the separator that can be used in the embodiments of the present application, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer, an inorganic substance, etc. formed of a material stable to the electrolyte of the present application. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0054] In some embodiments, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer, an inorganic substance layer, or a layer formed by mixing a polymer and an inorganic substance.

[0055] In some embodiments, the inorganic layer comprises inorganic particles and a binder. The inorganic particles include at least one of alumina, silica, magnesia, titania, hafnium dioxide, tin dioxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0056] In some embodiments, the polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride - hexafluoropropylene).

[0057] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some examples, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0058] In some embodiments, the secondary battery may include an outer package, and the outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch - type soft package. The material of the soft package can be a plastic, such as one or several of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0059] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other arbitrary shape.

[0060] In some embodiments, the present application also provides a battery module. The battery module includes the above - mentioned secondary battery. Since the battery module of the present application adopts the above - mentioned secondary battery, it has at least the same advantages as the secondary battery. The number of secondary batteries included in the battery module of the present application can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0061] In some embodiments, the present application also provides a battery pack, which includes the above - mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0062] III. Device

[0063] The present application also provides a device, and the device includes at least one of the above - mentioned secondary battery, battery module, or battery pack.

[0064] In some embodiments, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, energy storage systems, etc. To meet the device's requirements for high power and high energy density of secondary batteries, battery packs or battery modules can be used.

[0065] In some other embodiments, the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires being thin and light, and secondary batteries can be used as the power source.

[0066] Examples and Comparative Examples

[0067] Example 1

[0068] Preparation of the positive electrode plate: The positive electrode active material NCM811, the conductive agent Super P / multi-walled carbon nanotubes, and the binder PVDF were dispersed in an appropriate amount of NMP according to a mass ratio of 97.5:0.9 / 0.5:1.1 to form a uniform positive electrode slurry; the positive electrode slurry was coated on aluminum foil, and after processes such as drying and rolling, the positive electrode plate was obtained.

[0069] Preparation of the negative electrode plate:

[0070] (1) Preparation of graphene-coated silicon-carbon negative electrode material

[0071] (a) 12.55 g of graphene oxide and 50.2 g of silicon-carbon material (commercially available) were dissolved in deionized water, and then 100.4 g of ethylenediamine (EDA) was added thereto to obtain a mixed solution;

[0072] (b) By means of hydrothermal heating, the mixed solution prepared in step (a) was heated at 100 °C for 10 h. Among them, the graphene oxide was reduced to obtain a hydrogel of graphene-coated silicon-carbon material;

[0073] (c) Using liquid nitrogen freezing, the hydrogel of graphene-coated silicon-carbon material prepared in step (b) was stirred and dried in a freeze-drying vacuum dryer at -50 °C for 48 h to obtain an aerogel of graphene-coated silicon-carbon material;

[0074] (d) The aerogel of graphene-coated silicon-carbon material prepared in step (c) was ground evenly, and then transferred to a microwave oven. The power of microwave irradiation was 500 W and the time was 50 s to obtain a porous graphene-coated silicon-carbon negative electrode material.

[0075] (2) Preparation of metal oxide@graphene-coated silicon-carbon negative electrode material

[0076] (e) Dissolve 11.28 g of bismuth nitrate Bi(NO3)3·5H2O in glacial acetic acid to obtain a mixed solution A; dissolve 3.16 g of sodium acetate Na(CH3COO)·3H2O in glacial acetic acid to obtain a mixed solution B; dissolve 0.89 g of barium acetate Ba(CH3COO)2 in glacial acetic acid to obtain a mixed solution C; dissolve 17 g of tetrabutyl titanate Ti[OCH(CH3)2]4 in a mixed solution of ethylene glycol methyl ether and acetylacetone to obtain a mixed solution D1, wherein the molar ratio of bismuth nitrate, sodium acetate, barium acetate and tetrabutyl titanate is 0.465:0.465:0.07:1;

[0077] (f) Dissolve 62.7 g of the porous graphene-coated silicon-carbon anode material prepared in step (1) in the above mixed solution D1 to obtain a mixed solution D2; fully mix and stir the above mixed solution A and mixed solution B to obtain a mixed solution E; add the above mixed solution C to the above mixed solution E to obtain a mixed solution F, then slowly add the above mixed solution F to the above mixed solution D2, add ammonia water to adjust the pH to 9, and keep it at 90 °C for 24 h to form a gel;

[0078] (g) Grind the gel obtained in step (f), dry it at 400 °C for 6 h, and then calcine it at 700 °C for 6 h to obtain a ceramic PTC@porous graphene-coated silicon-carbon anode material;

[0079] Among them, the mass ratio of the second coating layer (1-x)Bi 0.5 Na 0.5 TiO3-xBaTiO3 and the anode material matrix is 1:4.7, where x is 0.07.

[0080] (3) Preparation of the anode electrode

[0081] Homogenize the above anode material, conductive agent carbon black / carbon nanotubes, thickener CMC, binder SBR and PAA according to a mass ratio of 96:0.9 / 0.1:0.6:1.2:1.2 to obtain a uniformly dispersed slurry. Coating the above slurry on a 6 μm or 8 μm copper foil, drying at 100 °C, and then obtaining the anode electrode by roll pressing.

[0082] Preparation of the electrolyte: Dissolve LiPF6 in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate (volume ratio 1:1:1), and at the same time add 10 wt% of fluoroethylene carbonate as a film-forming additive to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0083] Separator: Polyethylene separator.

[0084] Outer packaging: Aluminum-plastic film.

[0085] Preparation of Lithium-Ion Battery: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator placed in the middle of the positive and negative electrode sheets, and then wound to obtain a bare battery core. The bare battery core is placed in an aluminum-plastic film outer package, and after sufficient drying, the prepared lithium-ion battery electrolyte is injected. After the battery is left standing at 45°C for 48 hours, subjected to high-temperature formation, and secondary sealing, it undergoes 0.33C CC (constant current) + CV (constant voltage to 0.05C) conventional capacitance measurement.

[0086] In this embodiment, the maximum passing hot box temperature of the lithium-ion battery is 190°C.

[0087] Examples 2 to 7 and Comparative Example 1

[0088] Examples 2 to 7 and Comparative Example 1 are achieved by adjusting the types, contents, etc. of the metal source precursors in the negative electrode material on the basis of Example 1. The specific adjustment measures and detailed data are shown in Table 1.

[0089] Test Methods

[0090] Thermal Abuse Test: The fully charged battery is placed in a temperature chamber, and the temperature chamber is heated from the ambient temperature to 130 ± 2°C at a rate of 5°C / min and maintained at this temperature for 60 minutes. Then, the temperature chamber continues to heat up by 10°C at a rate of 5°C / min to 140 ± 2°C and is maintained at this temperature for 60 minutes until the battery test gets out of control.

[0091] Test Results

[0092] Table 1

[0093]

[0094] As can be seen from Table 1, in this application, by performing multi-layer coating on the surface of the negative electrode material matrix, that is, by preferentially surface-coating a carbon-based material (porous carbon material) to increase the area of subsequent metal oxide coating, and at the same time using the sol-gel method to synthesize metal oxides, it helps to uniformly coat the metal oxides on the surface of the negative electrode material, improve the sensitivity of the metal oxides to temperature, and thus achieve timely blocking of conduction during the initial stage of thermal runaway to inhibit the aggravation of thermal runaway.

[0095] Although some exemplary embodiments of the present application have been described and illustrated, the present application is not limited to the disclosed embodiments. On the contrary, those of ordinary skill in the art will recognize that some modifications and changes can be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A negative electrode material, which comprises a negative electrode material matrix, a first coating layer located on the surface of the negative electrode material matrix, and a second coating layer located on the surface of the first coating layer, wherein the second coating layer comprises a metal oxide, and The metal oxide includes one or more of sodium bismuth titanate, potassium bismuth titanate and their derivatives.

2. The negative electrode material according to claim 1, wherein The negative electrode material matrix includes one or more of graphite, nano-silicon and silicon carbide.

3. The negative electrode material according to claim 1, wherein The first coating layer includes a carbon-based material.

4. The negative electrode material according to claim 3, wherein The carbon-based material includes one or more of graphene, carbon nanotubes and conductive graphite.

5. The negative electrode material according to claim 1, wherein The mass ratio of the second coating layer to the negative electrode material matrix is 1:0.7 to 5.

5.

6. The negative electrode material according to claim 1, wherein The mass ratio of the first coating layer to the negative electrode material matrix is 1:2.5 to 4.

5.

7. A negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer provided on the surface of the negative electrode current collector, and the negative electrode material layer comprises the negative electrode active material according to any one of claims 1-6.

8. A secondary battery, which comprises the negative electrode sheet according to claim 7 and a positive electrode sheet.

9. A device, which comprises the secondary battery according to claim 8.

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