Negative electrode composite, method for preparing the same, negative electrode sheet, electrode assembly, battery cell, battery, and electric device

Abstract

The application discloses a negative electrode composite material and a preparation method thereof, a negative electrode sheet, an electrode assembly, a battery monomer, a battery and an electric device, and belongs to the technical field of batteries. The negative electrode composite material comprises a silicon-based inner core, a first coating layer and a second coating layer. The first coating layer comprises lithium fluoride, and the second coating layer comprises fluorine-containing organic matter. The negative electrode composite material can effectively inhibit the corrosion of electrolyte byproducts on the silicon-based inner core and relieve the expansion of the silicon-based inner core through multi-layer composite coating of the silicon-based negative electrode. The prepared battery monomer has high initial coulomb efficiency and excellent cycle performance (for example, high capacity retention rate after 500 cycles).

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a negative electrode composite material and a preparation method thereof, a negative electrode sheet, an electrode assembly, a battery monomer, a battery and an electric device. BACKGROUND

[0002] In recent years, with the increasing demand for clean energy and the rapid development of new energy field, batteries are widely used in energy storage power supply systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Due to the great development of batteries, higher requirements for their electrochemical performance are put forward.

[0003] In order to further meet the needs of users and improve user experience, how to improve the first coulomb efficiency and cycle performance of the battery has become a technical problem to be solved. SUMMARY

[0004] In view of the above problems, the present application provides a negative electrode composite material and a preparation method thereof, a negative electrode sheet, an electrode assembly, a battery monomer, a battery and an electric device, which can significantly improve the first coulomb efficiency and cycle performance (such as higher capacity retention rate after 500 cycles) of the battery.

[0005] The embodiments of the present application are implemented as follows:

[0006] In a first aspect, the embodiments of the present application provide a negative electrode composite material, which comprises a silicon-based inner core, a first coating layer arranged on at least part of the surface of the silicon-based inner core, the first coating layer comprising lithium fluoride, and a second coating layer arranged on at least part of the surface of the first coating layer, the second coating layer comprising fluorine-containing organic matter.

[0007] In the technical solution of the embodiments of the present application, the silicon-based inner core can be a material mainly providing the capacity of the negative electrode sheet. Lithium fluoride as the main substance of the first coating layer (i.e. the coating layer on the surface of the silicon-based inner core) can inhibit the corrosion of HF and other by-products in the electrolyte on the silicon-based inner core, and can effectively improve the storage performance and cycle performance of the battery. The fluorine-containing organic matter as the main substance of the second coating layer has a certain flexibility, which can alleviate the volume expansion of the silicon-based negative electrode during the cycle process of the battery. Therefore, in the embodiments of the present application, the negative electrode composite material can effectively inhibit HF corrosion and alleviate silicon-based expansion by multi-layer composite coating of the silicon-based negative electrode, thereby effectively improving the first coulomb efficiency and cycle performance of the battery.

[0008] In some embodiments, the mass ratio of the fluorine-containing organic compound to the silicon-based inner core is (0.2%-2%):1. In this embodiment, the mass ratio of the fluorine-containing organic compound to the silicon-based inner core meets a certain lower limit requirement, avoiding too little fluorine-containing organic compound in the negative electrode composite material, because further reducing the mass ratio of the fluorine-containing organic compound, the role of the fluorine-containing organic compound in relieving the volume expansion of the silicon-based inner core will become limited, thereby affecting the initial coulombic efficiency and cycle performance of the battery. The mass ratio of the fluorine-containing organic compound to the silicon-based inner core meets a certain upper limit requirement, avoiding too much fluorine-containing organic compound in the negative electrode composite material, because further increasing the mass ratio of the fluorine-containing organic compound, the mass ratio of the silicon-based inner core decreases accordingly, thereby reducing the capacity of the battery.

[0009] In some embodiments, the thickness of the second coating layer is 5-20 nm. In this embodiment, the thickness of the second coating layer meets a certain lower limit requirement, avoiding the second coating layer being too thin, which can effectively relieve the expansion of the silicon-based inner core. The thickness of the second coating layer meets a certain upper limit requirement, avoiding the second coating layer being too thick, so as to maintain a suitable proportion in the negative electrode composite material, balancing the capacity, initial coulombic efficiency and cycle performance of the battery.

[0010] In some embodiments, the second coating layer is amorphous. In this embodiment, the amorphous second coating layer can have good ion conductivity.

[0011] In some embodiments, the fluorine-containing organic compound includes at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyperfluoroalkoxy (PFA), polyperfluoroethylene propylene (PEP9), and CYTOP. In this embodiment, the fluorine-containing organic compound within the above range can relieve the volume expansion of the silicon-based inner core during the battery cycle, thereby improving the initial coulombic efficiency and cycle performance of the battery.

[0012] In some embodiments, the silicon-based inner core includes at least one of silicon, silicon oxide, lithiated silicon, and lithiated silicate, wherein the silicon oxide includes SiOx (0 11 In this embodiment, the silicon-based inner core includes the above range of lithiated silicon-based materials, which can improve the initial coulombic efficiency and cycle performance of the battery.

[0013] In some embodiments, the second coating layer further comprises a fluorine-containing carbon material. In this embodiment, the fluorine-containing carbon material can increase the electrical conductivity of the negative electrode composite, thus being beneficial to better improve the first coulombic efficiency and cycle performance of the battery.

[0014] In a second aspect, the embodiments of the present application provide a preparation method of a negative electrode composite, comprising mixing a silicon-based material and a first lithium source under a first non-active atmosphere, ball milling at 25-400℃ to obtain a silicon-based core; mixing the silicon-based core, an organic fluorine source and a second lithium source, ball milling, drying, and performing heat treatment under a second non-active atmosphere, the heat treatment comprising: increasing from room temperature to a first temperature interval, and maintaining for a time t1; and increasing from the first temperature interval to a second temperature interval, and maintaining for a time t2, wherein the first temperature interval is 25-200℃, and the second temperature interval is 400-800℃.

[0015] In the technical solution of the embodiments of the present application, the first temperature interval can be lower than the melting temperature of the organic fluorine source added during preparation, and the second temperature interval can be higher than the decomposition temperature of the organic fluorine source added during preparation. The setting of the above two temperature intervals can make the organic fluorine source generate fluorine radicals, react with the silicon-based core lithiated by the first lithium source and the second lithium source, and generate lithium fluoride and a fluorine-containing carbon material.

[0016] In some embodiments, t1 is 0.5-2h. In this embodiment, t1 meeting the above range is beneficial to improve the uniformity of LiF in the prepared negative electrode composite and improve the cycle performance of the battery cell.

[0017] In some embodiments, t2 is 1-12h. In this embodiment, t2 meeting the above range is beneficial to improve the electronic conductivity and ionic conductivity of the prepared negative electrode composite.

[0018] In some embodiments, the heating rate C1 of increasing from room temperature to the first temperature interval is 5-10℃ / min; and / or, the heating rate C2 of increasing from the first temperature interval to the second temperature interval is 10-20℃ / min. In this embodiment, when the heating rates C1 and / or C2 respectively meet the above ranges, it is beneficial to the preparation of the negative electrode composite and the performance of the prepared negative electrode composite.

[0019] In some embodiments, the mass ratio of the organic fluorine source to the silicon-based material is (0.5%-5%):1. In this embodiment, the organic fluorine source and the silicon-based material meeting the mass ratio in the above range are beneficial to the generation of the first coating layer and the second coating layer and the substances included therein in the negative electrode composite.

[0020] In some embodiments, the organic fluorine source includes at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyperfluoroalkoxy (PFA), polyperfluoroethylene propylene (PEP9), and CYTOP. In this embodiment, the negative electrode composite prepared from the organic fluorine source within the above range is beneficial to alleviate the volume expansion of the silicon-based inner core, and improve the initial coulombic efficiency and cycle performance of the battery.

[0021] In some embodiments, the silicon-based material includes at least one of amorphous silicon, silicon nanoparticles, silicon nanowires, porous silicon, and silicon oxide; and / or the volume average particle size D50 of the silicon-based material is 4-7 μm; and / or the volume particle size distribution SPAN of the silicon-based material is (D90-D10) / D50, and the value is 0.5-2.5. In this embodiment, when one or more of the type of the silicon-based material, the volume average particle size D50, and the volume particle size distribution SPAN meet the above ranges, the initial coulombic efficiency of the battery cell is improved.

[0022] In some embodiments, the alkalinity of the second lithium source is weaker than or equal to the alkalinity of the first lithium source, and optionally, the first lithium source includes at least one of lithium hydroxide, lithium aluminum hydride, lithium borohydride, lithium hydride, lithium ethoxide, lithium isopropoxide, lithium acetate, lithium oxalate, and lithium carbonate; and the second lithium source includes at least one of lithium bicarbonate, lithium sulfate, lithium chloride, lithium hydroxide, lithium aluminum hydride, lithium borohydride, lithium hydride, lithium ethoxide, lithium isopropoxide, lithium acetate, lithium oxalate, and lithium carbonate. In this embodiment, the first lithium source has strong alkalinity, strong lithiation reactivity, and low required reaction conditions, and can generate the silicon-based inner core with the silicon-based material at a first temperature range with a low temperature; and the second lithium source has weak alkalinity, weak lithiation reactivity, and can react with the organic fluorine source to generate the lithium fluoride of the first coating layer at a second temperature range with a high temperature.

[0023] In a third aspect, the embodiments of the present application provide a negative electrode tab, which includes the negative electrode composite provided in the first aspect or prepared by the preparation method of the negative electrode composite provided in the second aspect.

[0024] In a fourth aspect, the embodiments of the present application provide an electrode assembly, which includes the negative electrode tab provided in the third aspect.

[0025] In a fifth aspect, the embodiments of the present application provide a battery cell, which includes the electrode assembly provided in the fourth aspect.

[0026] In a sixth aspect, the embodiments of the present application provide a battery, which includes the battery cell provided in the fifth aspect.

[0027] In a seventh aspect, the embodiments of the present application provide a power utilization device, comprising the battery monomer provided in the fifth aspect or the battery provided in the sixth aspect.

[0028] The above description is only a summary of the technical solutions of the present application. In order to enable one of ordinary skill in the art to better understand the technical means of the present application and implement the same according to the contents of the description, and in order to enable the above and other purposes, characteristics and advantages of the present application to be more apparent and understandable, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those of ordinary skill in the art, other related drawings can also be obtained without creative labor.

[0030] Figure 1 A structural schematic diagram of a vehicle provided for some embodiments of the present application;

[0031] Figure 2 An exploded view of a battery provided for some embodiments of the present application;

[0032] Figure 3 An exploded view of a battery monomer provided for some embodiments of the present application;

[0033] Figure 4 A structural schematic diagram of an electrode assembly provided for some embodiments of the present application;

[0034] Figure 5 A structural schematic diagram of a first negative electrode sheet provided for some embodiments of the present application;

[0035] Figure 6 A structural schematic diagram of a second negative electrode sheet provided for some embodiments of the present application.

[0036] Icon:

[0037] 1000-vehicle;

[0038] 100-battery; 200-controller; 300-motor;

[0039] 10-box; 11-first part; 12-second part; 13-containing space;

[0040] 20-battery monomer; 21-housing; 22-electrode assembly; 23-electrode terminal; 24-pressure relief structure;

[0041] 211-housing; 212-cover; 213-sealed space;

[0042] 221 - negative electrode sheet; 222 - positive electrode sheet; 223 - separator;

[0043] 2211 - negative electrode current collector; 2212 - negative electrode active material layer. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Unless the specific conditions are specified in the embodiments, the conventional conditions or the conditions suggested by the manufacturers are adopted. The reagents or instruments used are not specified by the manufacturers, and are all conventional products that can be purchased in the market.

[0045] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to make the technical solutions of the present application clearer, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments of the present application, and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0047] In the description of the embodiments of the present application, the technical terms "first", "second" and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0048] In the description of the embodiments of the present application, the technical terms "inner", "outer" and the like indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the indicated device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0049] In the description of the embodiments of the present application, the technical term "and / or", such as "feature 1 and / or feature 2", means that it can be "feature 1" alone, "feature 2" alone, or "feature 1" plus "feature 2", and the three cases.

[0050] In the description of the embodiments of the present application, unless otherwise specified, the meaning of "multiple" in "one or more" is two or more.

[0051] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mount", "connect", "connect", "fix" and other terms should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0052] Reference herein to "embodiments" means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily all refer to the same embodiments, nor does it necessarily exclude alternative or additional embodiments from being claimed. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0053] In the embodiments of the present application, the same reference signs represent the same parts, and for the sake of brevity, detailed description of the same parts is omitted in different embodiments. It should be understood that the height, length, width, etc. of various components in the embodiments of the present application shown in the drawings, and the overall height, length, width, etc. of the integrated device are only exemplary and should not constitute any limitation on the present application.

[0054] At present, in the field of power batteries, the application of silicon-based negative electrode materials has the following problems: taking lithium-ion batteries as an example, the by-product HF generated by the reaction of LiPF6 in the electrolyte can cause corrosion to the silicon-based negative electrode material; the silicon-based negative electrode material itself has a large volume expansion rate during the battery cycle process. The above problems will cause the first coulomb efficiency and cycle performance of the battery to deteriorate.

[0055] In order to improve the above problems, in some technical solutions, a multi-layer composite coated silicon-based negative electrode material is proposed, which forms a carbon layer on the surface of the silicon-based material, and then forms a fluorinated layer on the surface of the carbon layer. However, in this technical solution, on the one hand, the carbon layer is arranged below the inner surface of the fluorinated layer, which cannot play the role of the conductivity of the carbon layer; on the other hand, the preparation process uses fluorine gas, which will produce harmful tail gas during production, causing great damage to the environment, and additional tail gas treatment operations are required.

[0056] In some technical solutions, a silicon-based negative electrode composite material is proposed, which has a silicon monoxide core, a lithium-silicon composite material intermediate layer, a fluoride outer layer, and a carbon outermost layer. However, in this technical solution, on the one hand, the structure and composition of the composite material are complex, and the preparation process involves multiple steps, which reduces production efficiency and also increases production cost; on the other hand, the preparation process uses active metal lithium as the lithium source, which has certain danger in specific operation, which is contrary to the safety and green environmental protection requirements in the industry.

[0057] In summary, the above technical solutions are not conducive to large-scale promotion and application.

[0058] The applicant has noticed that, in some cases, the first coulombic efficiency and cycle performance of a battery cell comprising the negative electrode material can be significantly improved by pre-lithiation and surface fluorination of a silicon-based material.

[0059] On this basis, the applicant has found through in-depth research that a silicon-based negative electrode composite material with a multi-layer composite coating layer can be simply and effectively prepared in situ by adopting a synergistic strategy of low-temperature lithiation, high-temperature lithiation, fluorination and carbonization, which can effectively inhibit HF corrosion and relieve silicon-based expansion, simplify the preparation process and meet green environmental protection requirements, so that a battery cell comprising the above-mentioned silicon-based negative electrode material has high first coulombic efficiency and excellent cycle performance with fewer process operations.

[0060] Based on this, the embodiment of the present application provides a negative electrode composite material, which comprises a silicon-based core; a first coating layer arranged on at least part of the surface of the silicon-based core, the first coating layer comprising lithium fluoride; and a second coating layer arranged on at least part of the surface of the first coating layer, the second coating layer comprising fluorine-containing organic matter. The first coating layer comprising lithium fluoride of the negative electrode composite material can effectively inhibit the corrosion of the silicon-based core by HF and other electrolyte by-products, and the second coating layer comprising fluorine-containing organic matter can effectively relieve the volume expansion of the silicon-based core, thereby effectively improving the first coulombic efficiency and cycle performance of the battery.

[0061] From the development of market situation, the application of power battery is more and more extensive. Power battery is not only applied to energy storage power supply system of hydroelectric, thermal, wind and solar power station, but also widely applied to electric bicycle, electric motorcycle, electric vehicle and other electric vehicles, military equipment, aerospace and other fields. With the continuous expansion of the application field of power battery, the demand of its market is also increasing.

[0062] The following embodiments are described with a vehicle as an example for convenience of illustration.

[0063] Referring to Figure 1 , Figure 1A structural schematic diagram of a vehicle 1000 is provided for some embodiments of the present application. The vehicle 1000 can be a fuel vehicle, a gas vehicle, or a new energy vehicle, which can be a pure electric vehicle, a hybrid vehicle, or a range extended vehicle, etc. The vehicle 1000 is internally provided with a battery 100, which can be arranged at the bottom, head, or tail of the vehicle 1000. The battery 100 can be used for power supply of the vehicle 1000, for example, the battery 100 can be used as an operating power source of the vehicle 1000. The vehicle 1000 can further include a controller 200 and a motor 300, the controller 200 is used to control the battery 100 to supply power to the motor 300, for example, to meet the power demand of the vehicle 1000 during starting, navigation, and driving.

[0064] In some embodiments of the present application, the battery 100 can not only be used as an operating power source of the vehicle 1000, but also be used as a driving power source of the vehicle 1000, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 1000.

[0065] In the present application, the battery 100 refers to a single physical module including a plurality of battery monomers 20 to provide higher voltage and capacity, which can be in the form of a battery pack, a battery module, etc. The battery 100 can include a box 10 for packaging a plurality of battery monomers 20, and the box 10 can avoid the influence of liquid or other foreign matters on the charging or discharging of the battery monomers 20.

[0066] Referring to Figure 2 , Figure 2 An exploded view of the battery 100 is provided for some embodiments of the present application. The battery 100 includes a box 10 and a plurality of battery monomers 20, and the plurality of battery monomers 20 are contained in the box 10. Among them, the box 10 is used to contain the battery monomers 20, and the box 10 can be of various structures. In some embodiments, the box 10 can include a first part 11 and a second part 12, the first part 11 and the second part 12 are mutually covered, and the first part 11 and the second part 12 jointly define a containing space 13 for containing the battery monomers 20. The second part 12 can be a hollow structure with one end open, and the first part 11 is a plate-shaped structure, which covers the open side of the second part 12 to form the box 10 with the containing space 13; the first part 11 and the second part 12 can also be hollow structures with one side open, and the open side of the first part 11 covers the open side of the second part 12 to form the box 10 with the containing space 13. Of course, the first part 11 and the second part 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0067] In the battery 100, a plurality of battery cells 20 can be connected in series or in parallel or in a mixed manner, where the mixed manner refers to a manner in which a plurality of battery cells 20 are connected in series and in parallel. The plurality of battery cells 20 can be directly connected in series or in parallel or in a mixed manner, and the plurality of battery cells 20 can be accommodated in the case 10 as a whole. Alternatively, the plurality of battery cells 20 can be connected in series or in parallel or in a mixed manner to form a module, and a plurality of modules can be connected in series or in parallel or in a mixed manner to form a whole and can be accommodated in the case 10. The battery 100 can further include other structures, for example, a plurality of battery cells 20 can be electrically connected by a busbar to be connected in parallel or in series or in a mixed manner.

[0068] The battery cell 20 refers to the smallest unit constituting a battery pack. The battery cell 20 can be a secondary battery 100 or a primary battery 100, and can be a lithium-sulfur battery 100, a sodium-ion battery 100, or a magnesium-ion battery 100, but is not limited thereto.

[0069] Referring to Figure 3 The battery cell 20 can include a case 21, an electrode assembly 22, and an electrolyte, and the electrode assembly 22 and the electrolyte can be accommodated in the case 21.

[0070] The case 21 can include a case body 211 and a cover 212. The case body 211 is a component for fitting the cover 212 to form an internal sealed space 213 of the battery cell 20, and the formed sealed space 213 can be used to accommodate the electrode assembly 22, the electrolyte, and other components. The cover 212 is a component that is fitted to an opening of the case body 211 to isolate the internal environment of the battery cell 20 from the external environment, and the shape of the cover 212 can be adapted to the shape of the case body 211 to fit the case body 211. The cover 212 can further include functional components such as an electrode terminal 23, a pressure relief structure 24, etc. A sealing ring can be disposed between the opening of the case body 211 and the cover 212 to seal the case body 211 and the cover 212.

[0071] The case body 211 and the cover 212 can have various shapes and sizes, such as a rectangular parallelepiped shape, a cylindrical shape, a hexagonal prism shape, etc. Specifically, the shape of the case body 211 and the cover 212 can be determined according to the specific shape and size of the electrode assembly 22. The case body 211 and the cover 212 can be made of various materials, such as, but not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, etc. The sealing ring can be made of various materials, such as, but not limited to, PP (polypropylene), PC (polycarbonate), PET (polyethylene terephthalate), etc. The outer surface of the case body 211 can be plated with a plating layer, and the plating layer can be made of various materials, such as, but not limited to, Ni, Cr, etc.

[0072] Referring to Figure 4The electrode assembly 22 can be composed of a negative electrode tab 221, a positive electrode tab 222, and a separator 223. The battery cell 20 mainly relies on the movement of metal ions between the negative electrode tab 221 and the positive electrode tab 222 to work. The negative electrode tab 221 includes a negative electrode current collector 2211 and a negative electrode active material layer 2212 disposed on the surface of the negative electrode current collector 2211, and the material of the negative electrode current collector 2211 can be copper. The positive electrode tab 222 includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector, and the material of the positive electrode current collector can be aluminum, and the positive electrode active material in the positive electrode active material layer can be lithium cobaltate, lithium iron phosphate, ternary lithium, lithium manganate, lithium-rich manganese-based material, lithium-sulfur, etc. In addition, the electrode assembly 22 can be a winding type structure or a laminated type structure, and the embodiments of the present application are not limited thereto.

[0073] In the embodiments of the present application, the negative electrode active material layer 2212 includes a negative electrode composite material.

[0074] Next, the negative electrode composite material proposed in the embodiments of the present application will be described in detail.

[0075] In a first aspect, the embodiments of the present application provide a negative electrode composite material, including a silicon-based inner core; a first coating layer disposed on at least part of the surface of the silicon-based inner core, the first coating layer including lithium fluoride; and a second coating layer disposed on at least part of the surface of the first coating layer, the second coating layer including fluorine-containing organic matter.

[0076] The negative electrode composite material can include two or more materials, and at least one of the materials is a negative electrode active material. The negative electrode active material can be a silicon-containing material.

[0077] The silicon-based inner core can be located inside the negative electrode composite material and can be a silicon-containing material.

[0078] The at least part of the surface can be a part of the surface coated by the coating layer, or the entire surface coated by the coating layer.

[0079] The number of coating layers can be two, and the coating layers can be divided into a first coating layer and a second coating layer according to the relative distance between the coating layer and the outer surface of the silicon-based inner core. The first coating layer can be the coating layer closest to the silicon-based inner core. The second coating layer can be disposed on the outer surface of the first coating layer and can be the second coating layer closest to the silicon-based inner core.

[0080] The chemical formula of lithium fluoride can be LiF.

[0081] The fluorine-containing organic matter can be an organic matter containing fluorine elements in the group.

[0082] In the technical solutions of the embodiments of the present application, the silicon-based inner core can be a material mainly providing the capacity of the negative electrode sheet 221. The silicon-based negative electrode is subjected to multi-layer composite coating, the first coating layer and the second coating layer are arranged on the outer surface of the silicon-based inner core, the first coating layer comprises lithium fluoride with certain corrosion resistance, and the second coating layer comprises fluorine-containing organic matter with certain flexibility. The combination of the first coating layer and the second coating layer can effectively inhibit HF corrosion and alleviate the expansion of the silicon-based inner core, thereby playing a protective effect on the silicon-based inner core during the cycle process of the battery 100, and effectively improving the first coulomb efficiency and cycle performance of the battery 100.

[0083] In some embodiments, the mass ratio of the fluorine-containing organic matter to the silicon-based inner core is (0.2%-2%):1.

[0084] For example, the mass ratio of the fluorine-containing organic matter to the silicon-based inner core can be, for example but not limited to, any one of the point values or the range values between any two of 0.2%:1, 0.3%:1, 0.4%:1, 0.5%:1, 0.6%:1, 0.7%:1, 0.8%:1, 0.9%:1, 1.0%:1, 1.1%:1, 1.2%:1, 1.3%:1, 1.4%:1, 1.5%:1, 1.6%:1, 1.7%:1, 1.8%:1, 1.9%:1 and 2.0%:1.

[0085] In this embodiment, the mass ratio of the fluorine-containing organic matter to the silicon-based inner core meets certain lower limit requirements, avoiding too little fluorine-containing organic matter, so that the second coating layer comprising the fluorine-containing organic matter can better alleviate the expansion of the silicon-based inner core; the mass ratio of the fluorine-containing organic matter to the silicon-based inner core meets certain upper limit requirements, avoiding too much fluorine-containing organic matter, because further increasing the mass ratio of the fluorine-containing organic matter will correspondingly reduce the mass ratio of the silicon-based inner core in the negative electrode composite material, thereby causing the capacity of the negative electrode sheet 221 to decrease.

[0086] In some embodiments, the thickness of the second coating layer is 5-20 nm.

[0087] The thickness of the second coating layer can be the distance between the inner surface and the outer surface of the second coating layer, and the unit is nm. For example, the thickness of the second coating layer can be, for example but not limited to, any one of the point values or the range values between any two of 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm and 20 nm.

[0088] In this embodiment, the thickness of the second cladding layer meets a certain lower limit requirement, avoiding that the thickness of the second cladding layer is too small, which is conducive to relieving the expansion of the silicon-based inner core; the thickness of the second cladding layer meets a certain upper limit requirement, avoiding that the thickness of the second cladding layer is too large, because the further increase of the thickness of the second cladding layer will lead to the decrease of the mass proportion of the silicon-based inner core in the negative electrode composite material, and further lead to the decrease of the capacity of the negative electrode plate 221.

[0089] In some embodiments, the second cladding layer is amorphous.

[0090] Amorphous can refer to a state in which the arrangement of atoms of a solid-state substance has short-range order and long-range disorder.

[0091] In this embodiment, the second cladding layer is amorphous, which has good ion conductivity.

[0092] In some embodiments, the fluorine-containing organic matter includes at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyperfluoroalkoxy (PFA), polyperfluoroethylene propylene (PEP9), and CYTOP.

[0093] The fluorine-containing organic matter can be an organic matter containing fluorine elements in a group. The fluorine-containing organic matter can be divided into a fluorine-containing homopolymer and a fluorine-containing copolymer according to the number of polymerized monomers. The polymerized monomer of the fluorine-containing homopolymer is one kind, which can include but is not limited to polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), polyperfluoroalkoxy (PFA), polyperfluoroethylene propylene (PEP9), and CYTOP. The polymerized monomer of the fluorine-containing copolymer is two or more kinds, which can be, for example, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP).

[0094] In this embodiment, in the negative electrode composite material, the fluorine-containing organic matter within the above range is conducive to relieving the volume expansion of the silicon negative electrode.

[0095] In some embodiments, the silicon-based inner core includes at least one of silicon, silicon oxide, lithiated silicon, and lithiated silicate, wherein the silicon oxide includes SiOx (0 < x ≤ 1.5); the lithiated silicon includes LiaSi (0 < a ≤ 4.4); and the lithiated silicate includes at least one of Li2SiO3, Li2Si2O5, Li2Si5O7, Li6Si2O7, Li8SiO6, and Li4SiO4. 11

[0096] The chemical formula of silicon can be Si.

[0097] ​The silicon oxide can be a material containing at least two elements of silicon and oxygen.

[0098] The lithiated silicon can be a material containing at least two elements of silicon and lithium.

[0099] The lithiated silicate can be a material containing at least three elements of silicon, oxygen and lithium.

[0100] In this embodiment, the silicon-based inner core includes the material in the above range, which can provide the main capacity of the negative electrode sheet 221 and is beneficial to the improvement of the first coulomb efficiency and the cycle performance.

[0101] In some embodiments, the second coating layer further includes a fluorine-containing carbon material.

[0102] The fluorine-containing carbon material can be a material containing fluorine and carbon elements.

[0103] In this embodiment, the fluorine-containing carbon material in the second coating layer can increase the electrical conductivity of the negative electrode composite material, and thus is beneficial to better improving the first coulomb efficiency and the cycle performance of the battery monomer 20.

[0104] In a second aspect, the embodiments of the present application provide a preparation method of a negative electrode composite material, including mixing a silicon-based material and a first lithium source under a first non-active atmosphere, ball milling at 25-400°C to obtain a silicon-based inner core; mixing the silicon-based inner core, an organic fluorine source and a second lithium source, ball milling, drying, and performing heat treatment under a second non-active atmosphere, the heat treatment including increasing from room temperature to a first temperature interval, and the holding time is t1; and increasing from the first temperature interval to a second temperature interval, and the holding time is t2, wherein the first temperature interval is 25-200°C, and the second temperature interval is 400-800°C.

[0105] The non-active atmosphere can be an atmosphere that will not chemically react under certain conditions, and can include an inert atmosphere. As an example, the non-active atmosphere may, for example, but not limited to, be at least one of nitrogen, helium, neon, argon, krypton, xenon, and radon.

[0106] The silicon-based material can be a silicon-containing material.

[0107] The lithium source can be a lithium-containing material. The first lithium source can be beneficial to the generation of the lithiated silicon-based inner core. The second lithium source can be beneficial to the generation of the first coating layer.

[0108] The organic fluorine source can be an organic substance containing fluorine elements in a group.

[0109] Ball milling can include crushing, pulverizing, mixing, and the like, and can be performed by a ball mill. The temperature of ball milling can be 25-400°C, and as an example, the temperature of ball milling can be, for example but not limited to, any one of 25°C, 50°C, 75°C, 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, and 400°C, or a range value between any two of them.

[0110] Drying can include removing water and the like from the material.

[0111] Room temperature can be, for example but not limited to, 25°C.

[0112] As an example, the first temperature range can be, for example but not limited to, any one of 25°C, 50°C, 75°C, 100°C, 125°C, 150°C, 175°C, and 200°C, or a range value between any two of them.

[0113] As an example, the second temperature range can be, for example but not limited to, any one of 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, and 800°C, or a range value between any two of them.

[0114] In the technical solution of the embodiments of the present application, the first temperature range can be lower than the melting temperature of the organic fluorine source added during preparation, and the second temperature range can be higher than the decomposition temperature of the organic fluorine source added during preparation. The setting of the above two temperature ranges can make the organic fluorine source generate fluorine radicals, react with the silicon-based core lithiated by the first lithium source and the second lithium source, and generate lithium fluoride and fluorine-containing carbon material.

[0115] In some embodiments, t1 is 0.5-2h.

[0116] t1 can refer to the length of time for which the temperature is maintained in the first temperature range, and as an example, t1 can be, for example but not limited to, any one of 0.5h, 1h, 1.5h, and 2h, or a range value between any two of them.

[0117] In this embodiment, t1 meeting the above range is beneficial to improve the uniformity of LiF in the prepared negative electrode composite material and improve the cycle performance of the battery monomer 20.

[0118] In some embodiments, t2 is 1-12h.

[0119] t2 can refer to the length of time for which the temperature is maintained in the second temperature range, and as an example, t2 can be, for example but not limited to, any one of 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, and 12h, or a range value between any two of them.

[0120] In this embodiment, t2 in the above range is advantageous to improve the electronic conductivity and ionic conductivity of the prepared negative electrode composite material.

[0121] In some embodiments, the heating rate C1 of the room temperature to the first temperature interval is 5-10℃ / min; and / or, the heating rate C2 of the first temperature interval to the second temperature interval is 10-20℃ / min.

[0122] The heating rate can be the rate of temperature increase, with the unit of ℃ / min.

[0123] C1 can refer to the rate of temperature increase from room temperature to the first temperature interval. As an example, C1 can be, for example but not limited to, any one of the point values of 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min and 10℃ / min or a range value between any two of them.

[0124] C2 can refer to the rate of temperature increase from the first temperature interval to the second temperature interval. As an example, C2 can be, for example but not limited to, any one of the point values of 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min and 20℃ / min or a range value between any two of them.

[0125] In this embodiment, the heating rates C1 and / or C2 respectively meet the above ranges, which is advantageous to the reaction of the preparation of the negative electrode composite material and to improve the performance of the prepared negative electrode composite material.

[0126] In some embodiments, the mass ratio of the organic fluorine source to the silicon-based material is (0.5%-5%):1.

[0127] The mass ratio of the organic fluorine source to the silicon-based material can be the mass ratio of the added organic fluorine source to the silicon-based material in the preparation of the negative electrode composite material. As an example, the mass ratio of the organic fluorine source to the silicon-based material can be, for example but not limited to, any one of the point values of 0.5%:1, 1%:1, 2%:1, 3%:1, 4%:1, 5%:1 or a range value between any two of them.

[0128] In this embodiment, the mass ratio of the organic fluorine source to the silicon-based material in the above range is advantageous to the formation of the first coating layer containing LiF and the second coating layer containing fluorine-containing organic matter.

[0129] In some embodiments, the organic fluorine source includes at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyperfluoroalkoxy (PFA), polyperfluoroethylene propylene (PEP9), and CYTOP.

[0130] In this embodiment, the negative electrode composite prepared from the organic fluorine source within the above range is beneficial to alleviate the volume expansion of the silicon-based inner core, and improve the initial coulombic efficiency and cycle performance of the battery 100.

[0131] In some embodiments, the silicon-based material includes at least one of amorphous silicon, silicon nanoparticles, silicon nanowires, porous silicon, and silicon oxide; and / or the volume average particle size D50 of the silicon-based material is 4-7 μm; and / or the volume particle size distribution SPAN of the silicon-based material is (D90-D10) / D50, which is 0.5-2.5.

[0132] The volume average particle size D50 of the silicon-based material can be the particle size corresponding to the cumulative particle size distribution percentage of 50% of the silicon-based material. The volume particle size distribution SPAN of the silicon-based material is (D90-D10) / D50, wherein D90 can be the particle size corresponding to the cumulative particle size distribution percentage of 90% of the silicon-based material, and D10 can be the particle size corresponding to the cumulative particle size distribution percentage of 10% of the silicon-based material.

[0133] The volume average particle size D50 and the volume particle size distribution SPAN of the silicon-based material can be measured by a method known in the art, for example, the method can be referred to the national standard GB / T19077-2016, and a Malvern laser particle size analyzer (model: Mastersizer-3000) can be used for characterization test.

[0134] In this embodiment, when one or more of the type, the volume average particle size D50, and the volume particle size distribution SPAN of the silicon-based material meet the above ranges, respectively, the initial coulombic efficiency of the battery cell 20 can be improved.

[0135] In some embodiments, the alkalinity of the second lithium source is weaker than or equal to the alkalinity of the first lithium source, and optionally, the first lithium source includes at least one of lithium hydroxide, lithium aluminum hydride, lithium borohydride, lithium hydride, lithium ethoxide, lithium isopropoxide, lithium acetate, lithium oxalate, and lithium carbonate; and the second lithium source includes at least one of lithium bicarbonate, lithium sulfate, lithium chloride, lithium hydroxide, lithium aluminum hydride, lithium borohydride, lithium hydride, lithium ethoxide, lithium isopropoxide, lithium acetate, lithium oxalate, and lithium carbonate.

[0136] The basicity of the first lithium source and the second lithium source can be inferred according to the proton acid-base theory and the Lewis acid-base theory, wherein the lithium source that does not react with water can be measured by a pH meter to measure the basicity of the solution of the same concentration.

[0137] The second lithium source has weaker basicity than or equal to the basicity of the first lithium source, including that the second lithium source has weaker basicity than the first lithium source, and the second lithium source has the same basicity as the first lithium source.

[0138] In this embodiment, the first lithium source has stronger basicity, and has strong lithiation reactivity, and the required reaction condition is low, so that the first lithium source can react with the silicon-based material to form a silicon-based inner core in a first temperature range with a lower temperature; the second lithium source has weaker basicity, and has weaker lithiation reactivity, so that the second lithium source can react with the organic fluorine source to form lithium fluoride of the first coating layer in a second temperature range with a higher temperature.

[0139] Referring to Figure 5 and Figure 6 , in a third aspect, the embodiments of the present application provide a negative electrode tab 221, which comprises a negative electrode current collector 2211, and a negative electrode active material layer 2212 arranged on the surface of the negative electrode current collector 2211, wherein the negative electrode active material layer 2212 comprises the negative electrode composite material according to the above embodiments or is prepared by the preparation method of the negative electrode composite material according to the above embodiments.

[0140] In the negative electrode tab 221, the negative electrode active material layer 2212 can be arranged on one side surface of the negative electrode current collector 2211, as shown in Figure 5 ; or the negative electrode active material layer 2212 can be arranged on both side surfaces of the negative electrode current collector 2211, as shown in Figure 6 .

[0141] In a fourth aspect, the embodiments of the present application provide an electrode assembly 22, which comprises the negative electrode tab 221 according to the above embodiments.

[0142] In a fifth aspect, the embodiments of the present application provide a battery monomer 20, which comprises the electrode assembly 22 according to the above embodiments.

[0143] In a sixth aspect, the embodiments of the present application provide a battery 100, which comprises the battery monomer 20 according to the above embodiments.

[0144] In a seventh aspect, the embodiments of the present application provide an electric device, which comprises the battery monomer 20 according to the above embodiments or the battery 100 according to the above embodiments.

[0145] Based on the negative electrode composite material provided by the embodiments of the present application, the mass ratio of the fluorine-containing organic matter to the silicon-based inner core can be reversely calculated by a thermogravimetric analyzer.

[0146] Some specific embodiments are listed below to better illustrate the present application.

[0147] I. Preparation of battery cell

[0148] Preparation of negative electrode composite

[0149] Under an inert atmosphere, lithium hydroxide (first lithium source) and silicon-based material are mixed according to a certain mass ratio, ball-milled to obtain a silicon-based core; the above-mentioned silicon-based core, organic fluorine source and lithium carbonate (second lithium source) are mixed according to a certain mass ratio, ball-milled, dried, and heat-treated under an inert atmosphere, which includes rising from room temperature to a first temperature interval, keeping for a certain time; and rising from the first temperature interval to a second temperature interval, keeping for a certain time, wherein the first temperature interval is 25-200℃, and the second temperature interval is 400-800℃. After heat treatment, a solid powder is obtained, which is added to water, stirred for 0.5h, suction filtered, washed with water and ethanol, and dried to obtain a negative electrode composite.

[0150] Preparation of negative electrode sheet

[0151] The active material negative electrode composite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickening agent sodium hydroxymethyl cellulose (CMC) are dissolved in deionized water according to a weight ratio of 96.2:0.8:0.8:1.2, and uniformly mixed to prepare a negative electrode slurry; the negative electrode slurry is coated on a copper foil one or more times and dried at 90℃, and then cold-pressed and cut to obtain a negative electrode sheet.

[0152] Preparation of positive electrode sheet

[0153] Lithium iron phosphate, conductive carbon, and polyvinylidene fluoride (PVDF) are dissolved in solvent N-methyl pyrrolidone (NMP) according to a mass ratio of 96:2:2, stirred for 4h, and the viscosity is adjusted to 10000mPa·s with NMP. The slurry is stirred uniformly, coated on an aluminum foil and dried at 90℃, and then cold-pressed and cut to obtain a positive electrode sheet.

[0154] Preparation of electrolyte

[0155] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), organic solvent ethylene carbonate (EC) / ethyl methyl carbonate (EMC) is mixed uniformly according to a volume ratio of 3 / 7, 12.5% LiPF6 lithium salt is dissolved in organic solvent, stirred uniformly, and an electrolyte is obtained.

[0156] Preparation of separator

[0157] A polyethylene film is used as a separator.

[0158] Preparation of lithium ion battery

[0159] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then are wound, welded with the tabs, put into the aluminum shell, and baked at 105°C to remove water, and then the electrolyte is injected and sealed to obtain a non-charged battery monomer. The non-charged battery monomer is sequentially subjected to the processes of standing, hot and cold pressing, formation, shaping, capacity test, and the like to obtain a lithium ion battery monomer.

[0160] II. Test method

[0161]

Thickness test of the coating layer

[0162] 0.1-0.5 mg of the above negative electrode composite material is dispersed in 1 mL of ethanol, ultrasonically treated for 5-10 min, left to stand for 5 min, and the supernatant is taken and dropped onto an ultrathin carbon film, and baked for 10-15 min with an infrared baking lamp. The thickness of the silicon-based core interface, the first coating layer, and the second coating layer of the negative electrode composite material is observed by transmission electron microscopy. In addition, the amorphous state of the second coating layer can also be determined by linear scanning.

[0163]

First round efficiency test and capacity retention test of the battery monomer

[0164] At 25°C, the above lithium ion battery is charged at 1 / 3C constant current to 3.65V, then charged at 3.65V constant voltage to a current of 0.05C, left to stand for 5 min, and then discharged at 1 / 3C rate to 2.5V. This is one charge and discharge cycle process. The discharge capacity of this time is the discharge capacity of the first cycle. The lithium ion battery is repeatedly subjected to the above steps for charge and discharge cycle test, and the discharge capacity of the 500th cycle is taken.

[0165] The first round efficiency of the lithium ion battery = (the first discharge capacity) / (the first charge capacity) x 100%.

[0166] The capacity retention rate of the lithium ion battery after 500 cycles = (the discharge capacity of the 500th cycle) / (the discharge capacity of the first cycle) x 100%.

[0167] III. Experimental conditions and test results

[0168] The parameters of the negative electrode composite material used in the negative electrode sheet 221 in each experimental group are shown in Table 1, and the electrochemical performance test results of the battery monomer are shown in Table 2, wherein the electrochemical performance of the battery monomer includes the first coulombic efficiency of the battery monomer and the capacity retention rate after 500 cycles.

[0169] Table 1

[0170]

[0171]

[0172] In the negative electrode active material in Comparative Example 1, the silicon-based inner core has no coating layer. In the negative electrode composite material in Comparative Example 2, the negative electrode composite material is prepared by physical mixing, and no chemical coating process involving heat treatment is involved.

[0173] Table 2

[0174]

[0175]

[0176] According to Table 1 and Table 2, it can be seen that:

[0177] The negative electrode composite materials in Examples 1-21 each include a composite coating layer (the first coating layer includes LiF, and the second coating layer includes a fluorine-containing organic substance) prepared by chemical coating (e.g., heat treatment), and the first coulombic efficiency and the cycle performance (e.g., the capacity retention rate after 500 cycles) of the battery cell are obviously improved compared with the silicon-based negative electrode material without a coating layer in Comparative Example 1 and the negative electrode composite material prepared by physical blending in Comparative Example 2.

[0178] In Examples 1-6, when the mass ratio of the fluorine-containing organic substance to the silicon-based inner core is within a certain range, as the mass ratio gradually increases, the thickness of the second coating layer gradually increases, and the first coulombic efficiency of the battery cell also gradually increases. When the mass ratio is not more than 1.0%:1, as the mass ratio gradually increases, the capacity retention rate of the battery cell gradually increases; when the mass ratio is more than 1.0%:1, as the mass ratio gradually increases, the capacity retention rate of the battery cell begins to decrease to a certain extent.

[0179] In Examples 3, 7-9, when the value of x in the silicon-based material SiOx is 0.5, 1 or 1.5 (Examples 7, 8 and 9), the first coulombic efficiency and the capacity retention rate of the battery cell are obviously improved.

[0180] In Examples 3, 10-19, when the heat treatment time t1 is within the range of 0.5-2h and t2 is within the range of 1-12h (Examples 3, 12-19), the prepared negative electrode composite material has a high coating degree, and the battery cell has good performance.

[0181] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art, without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. A negative electrode composite material, characterized by comprising: The composite material comprises a silicon-based core; a first coating layer disposed on at least part of the surface of the silicon-based core, the first coating layer comprising lithium fluoride; and a second coating layer disposed on at least part of the surface of the first coating layer, the second coating layer comprising fluorine-containing organic matter; The preparation method of the negative electrode composite material comprises at least the following steps: mixing the silicon-based core, an organic fluorine source and a second lithium source, ball milling, drying, and heat treatment in a second non-active atmosphere, the heat treatment comprising: increasing the temperature from room temperature to a first temperature range, and maintaining the temperature for a time period t1; and increasing the temperature from the first temperature range to a second temperature range, and maintaining the temperature for a time period t2, wherein the first temperature range is 25-200°C, and the second temperature range is 400-800°C.

2. The negative electrode composite material according to claim 1, wherein the mass ratio of the fluorine-containing organic matter to the silicon-based core is (0.2%-2%):

1.

3. The negative electrode composite material according to claim 1 or 2, wherein the thickness of the second coating layer is 5-20 nm.

4. The negative electrode composite material according to any one of claims 1-3, wherein the second coating layer is in an amorphous state.

5. The negative electrode composite material according to any one of claims 1-4, wherein the fluorine-containing organic matter comprises at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyperfluoroalkoxy (PFA), polyperfluoroethylene propylene (PEP9), and perfluoro cyclic polymer (CYTOP).

6. The anode composite of any one of claims 1-5, the silicon-based inner core comprising at least one of silicon, silicon oxide, lithiated silicon, lithiated silicate, wherein, The silicon oxide comprises SiOx(0 < x < 1.5); the lithiated silicon comprises LiaSi (0 < a < 4.4); the lithiated silicate comprises at least one of Li2SiO3, Li2Si2O5, Li2Si5O 11 7, Li8SiO6, Li4SiO4.

7. The negative electrode composite material according to any one of claims 1-6, wherein the second coating layer further comprises fluorine-containing carbon material.

8. A method for producing a negative electrode composite material, characterized by The preparation method comprises: mixing a silicon-based material and a first lithium source in a first non-active atmosphere, ball milling at 25-400°C to obtain a silicon-based core; mixing the silicon-based core, an organic fluorine source and a second lithium source, ball milling, drying, and heat treatment in a second non-active atmosphere, the heat treatment comprising: increasing the temperature from room temperature to a first temperature range, and maintaining the temperature for a time period t1; and increasing the temperature from the first temperature range to a second temperature range, and maintaining the temperature for a time period t2, wherein the first temperature range is 25-200°C, and the second temperature range is 400-800°C.

9. The method of claim 8, wherein the negative electrode composite is prepared by mixing the active material, the binder, and the conductive agent in a solvent. The t1 is 0.5-2 h.

10. The method for producing a negative electrode composite according to claim 8 or 9, characterized by, The t2 is 1-12 h.

11. The method of producing a negative electrode composite according to any one of claims 8 to 10, characterized by, The heating rate C1 of increasing the temperature from room temperature to the first temperature range is 5-10°C / min; and / or The heating rate C2 of increasing the temperature from the first temperature range to the second temperature range is 10-20°C / min.

12. The method of producing a negative electrode composite according to any one of claims 8 to 11, characterized by, The mass ratio of the organic fluorine source to the silicon-based material is (0.5%-5%):

1.

13. The method for producing a negative electrode composite material according to any one of claims 8 to 12, characterized by, The organic fluorine source comprises at least one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene (FEP), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyperfluoroalkoxy (PFA), polyperfluoroethylene propylene (PEP9), and perfluoro cyclic polymer (CYTOP).

14. The method for producing a negative electrode composite according to any one of claims 8 to 13, characterized by, The silicon-based material comprises at least one of amorphous silicon, silicon nanoparticles, silicon nanowires, porous silicon, silicon oxide; and / or The silicon-based material has a volume average particle size D50 of 4-7 μm; and / or The silicon-based material has a volume particle size distribution SPAN=(D90-D10) / D50 of 0.5-2.

5.

15. The method of producing a negative electrode composite according to any one of claims 8 to 14, wherein The second lithium source has a basicity weaker than or equal to that of the first lithium source, and the first lithium source comprises at least one of lithium hydroxide, lithium aluminum tetrahydride, lithium borohydride, lithium hydride, lithium ethoxide, lithium isopropoxide, lithium acetate, lithium oxalate, lithium carbonate; and the second lithium source comprises at least one of lithium bicarbonate, lithium sulfate, lithium chloride, lithium hydroxide, lithium aluminum tetrahydride, lithium borohydride, lithium hydride, lithium ethoxide, lithium isopropoxide, lithium acetate, lithium oxalate, lithium carbonate.

16. A negative electrode sheet comprising a negative electrode current collector, and a negative electrode active material layer provided on a surface of the negative electrode current collector, characterized by The negative electrode active material layer comprises the negative electrode composite material according to any one of claims 1-7 or prepared by the method according to any one of claims 8-15.

17. An electrode assembly, characterized by, The negative electrode sheet comprises the negative electrode composite material according to claim 16.

18. A battery cell, characterized by The electrode assembly comprises the electrode according to claim 17.

19. A battery, characterized by The battery cell comprises the battery cell according to claim 18.

20. An electrical device, comprising: The battery comprises the battery cell according to claim 18 or the battery according to claim 19.

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