Negative electrode material, negative electrode sheet, electrode assembly, battery, and electric device

Abstract

The application discloses a negative electrode material, a negative electrode sheet, an electrode assembly, a battery and an electric device. The negative electrode material comprises a silicon-based material, the silicon-based material comprises a porous silicon-based material and a fine silicon-based material used for filling between the porous silicon-based material, and the median particle size of the porous silicon-based material is larger than that of the fine silicon-based material. The technical scheme of the application fills the fine silicon-based material with small particles between the porous silicon-based material with large particles, utilizes the channel structure on the porous silicon-based material and the gap between the porous silicon-based material and the fine silicon-based material to relieve the stress generated when the two silicon-based materials embed and extract lithium, thereby limiting the expansion of the two silicon-based materials inside the two silicon-based materials and reducing the expansion rate of the negative electrode material.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries are widely used due to their high energy density and long cycle life. With the development of new energy vehicles and other fields, traditional graphite as a negative electrode material of lithium ion batteries cannot meet people's demand for higher energy density batteries. Silicon-based materials, including but not limited to silicon, silicon oxide, etc., are concerned due to their high theoretical specific capacity, abundant reserves and other advantages. However, silicon-based materials are prone to large volume expansion and contraction during charging and discharging, which causes the negative electrode material layer and the current collector to separate and fall off, resulting in rapid capacity decline. SUMMARY

[0003] In view of the above problems, the present application provides a negative electrode material, a negative electrode sheet, an electrode assembly, a battery and an electric device, aiming to alleviate the problem of expansion of silicon-based negative electrode materials.

[0004] In a first aspect, the embodiments of the present application provide a negative electrode material, comprising a silicon-based material, wherein the silicon-based material comprises a porous silicon-based material and a micro-powder silicon-based material for filling between the porous silicon-based material, and the median particle size of the porous silicon-based material is greater than the median particle size of the micro-powder silicon-based material.

[0005] By setting the negative electrode material to include silicon-based materials with high theoretical specific capacity, and at the same time the silicon-based material includes large-particle porous silicon-based material and small-particle micro-powder silicon-based material, the small-particle micro-powder silicon-based material is filled between the large-particle porous silicon-based material, and the stress generated by the two kinds of silicon-based materials during lithium intercalation and deintercalation is relieved by using the channel structure on the porous silicon-based material and the gap between the porous silicon-based material and the micro-powder silicon-based material, so as to limit the expansion of the two kinds of silicon-based materials within the two kinds of silicon-based materials, and the negative electrode material expansion rate is reduced. When the negative electrode material is applied to the negative electrode material layer, it can prevent the negative electrode material layer from expanding outward, thereby inhibiting the peeling of the negative electrode material layer and the current collector. At the same time, the addition of micro-powder silicon-based material can also improve the theoretical specific capacity of the negative electrode material, and further improve the energy density of the battery using the negative electrode material. In addition, the micro-powder silicon-based material with smaller particles has a larger specific surface and more active sites, ensuring fast lithium ion diffusion and charge exchange, so that the battery using the negative electrode material has better kinetic performance.

[0006] In some embodiments, the chemical formula of the silicon-based material is SiO x , wherein 0≤x<2.

[0007] By setting the silicon-based material as elemental silicon and / or silicon monoxide with a higher theoretical specific capacity, the theoretical specific capacity of the negative electrode material is improved, and the energy density of the battery is improved.

[0008] In some embodiments, 0.9≤x≤1.1.

[0009] By setting x to be 0.9-1.1, i.e., the silicon-based material is silicon monoxide, and the content of oxygen in the silicon monoxide is close to the content of silicon, the silicon monoxide in this ratio range not only has a much higher specific capacity than graphite, but also does not undergo severe volume expansion during charging like elemental silicon, while also ensuring the generation of sufficient elemental silicon during lithiation, ensuring the conductivity and effective capacity.

[0010] In some embodiments, the internal pore size of the porous silicon-based material is 1-100 nm.

[0011] Generally, a too large internal pore size of the porous silicon-based material causes capacity loss and polarization increase of the negative electrode material, but a too small internal pore size causes increased expansion of the negative electrode material. By setting the internal pore size of the porous silicon-based material to be 1-100 nm, the negative electrode material in this range has good capacity and good expansion resistance.

[0012] In some embodiments, the median particle size of the micro-powder silicon-based material is 0.1-0.8 μm.

[0013] If the median particle size of the micro-powder silicon-based material is too small, the gap between the filled micro-silicon powder material and the porous silicon-based material and the gap between the micro-silicon powder materials is too small, and the internal stress during expansion of the micro-silicon powder material cannot be well released; if the median particle size of the micro-powder silicon-based material is too large, the filling amount of the micro-silicon powder material is reduced. By setting the median particle size of the micro-powder silicon-based material to be 0.1-0.8 μm, the expansion resistance and specific capacity of the negative electrode material obtained in this range are both better.

[0014] In some embodiments, the median particle size of the porous silicon-based material is 3-9 μm.

[0015] If the median particle size of the porous silicon-based material is too small or too large, it is not conducive to forming pores on the porous silicon-based material, so that the porous silicon-based material cannot well release internal stress. By setting the median particle size of the porous silicon-based material to be 3-9 μm, the expansion resistance of the negative electrode material obtained in this range is better. At the same time, in this range, it is conducive to shortening the diffusion path of lithium ions in the porous silicon-based material and improving the rate performance of the negative electrode material.

[0016] In some embodiments, the proportion of the micro-powder silicon-based material based on the total weight of the negative electrode material is 5-15 wt%.

[0017] The specific capacity of the negative electrode material can be improved by filling the micropowder silicon-based material between the porous silicon-based materials, but if the filling amount of the micropowder silicon-based material is too high, the percentage content of the porous silicon-based material will be reduced, thereby reducing the anti-expansion property of the overall negative electrode material. In addition, the micropowder silicon-based material is filled in the pores between the porous silicon-based materials, and the micropowder silicon-based material will also expand in volume when lithium is inserted. If the amount of the micropowder silicon-based material filled in the solid particles is larger, the volume of the micropowder silicon-based material expanded when lithium is inserted will be larger. If the volume of the micropowder silicon-based material expanded exceeds a limit, the electrode may expand and even the negative electrode material may fall off. By setting the mass ratio of the micropowder silicon-based material in the negative electrode material to 5wt%-15wt%, the volume of the porous silicon-based material and the micropowder silicon-based material expanded when lithium is inserted can be just absorbed by the gap between the porous silicon-based materials in this range, and the expansion of the micropowder silicon-based material when lithium is inserted can be offset by the expansion of the porous silicon-based material when lithium is inserted, thereby preventing the negative electrode material from expanding excessively outward.

[0018] In some embodiments, the negative electrode material further comprises a carbon material.

[0019] Since the carbon material has a small volume expansion during the charging and discharging process, by adding the carbon material to the micropowder silicon-based material and the porous silicon-based material, the expansion rate of the negative electrode material can be reduced by using the carbon material to buffer the expansion of the silicon-based material. At the same time, since the main components of the porous silicon-based material and the micropowder silicon-based material are elemental silicon and / or silicon oxide, the conductivity is poor. By adding the carbon material to the negative electrode material, a conductive network can be constructed in the negative electrode material by using the good conductivity of the carbon material, thereby ensuring better contact between the silicon-based material and the current collector and between the silicon-based materials.

[0020] In some embodiments, the carbon material comprises graphite.

[0021] By adding graphite to the micropowder silicon-based material and the porous silicon-based material, the expansion rate of the negative electrode material can be reduced while the conductivity of the negative electrode material is improved.

[0022] In some embodiments, the median particle size of the graphite is 12μm-20μm.

[0023] Generally, a too large median particle size of the graphite is not conducive to the uniform dispersion of the graphite in the silicon-based material, and a too small median particle size of the graphite cannot well buffer the expansion stress of the silicon-based material. By setting the median particle size of the graphite to 12μm-20μm, the anti-expansion property and the conductivity of the negative electrode material prepared in this range are relatively good.

[0024] In some embodiments, the mass specific capacity of the negative electrode material is 750mAh / g-1700mAh / g.

[0025] 1700mAh / g.

[0026] Generally, the theoretical mass specific capacity of the negative electrode material can be changed by changing the components in the negative electrode material, and the theoretical mass specific capacity of the negative electrode material can also be changed by changing the proportion of each component in the negative electrode material. The theoretical mass specific capacity of the negative electrode material is 750 mAh / g-1700 mAh / g. It can be known that the negative electrode material cannot be entirely elemental silicon, because the theoretical mass specific capacity of elemental silicon is much higher than 1700 mAh / g, and the volume expansion rate of elemental silicon is also higher during the charging and discharging process. Therefore, the negative electrode material must contain substances whose theoretical mass specific capacity is less than that of elemental silicon, including but not limited to silicon monoxide or carbon materials, etc. The volume expansion rate of these substances during the charging and discharging process is often also less than that of elemental silicon.

[0027] In some embodiments, the specific surface area of the negative electrode material is 5 m 2 / g-10 m 2 / g.

[0028] Due to the existence of the pores on the porous silicon-based material and the relatively small median particle size of the silicon-based material powder, the specific surface area of the negative electrode material is increased. Although the increase of the specific surface area of the negative electrode material can improve the kinetic performance to a certain extent, the increase of the specific surface area of the negative electrode material will also correspondingly increase the area of the SEI film, thereby increasing the consumption of lithium ions and reducing the charging and discharging efficiency of the negative electrode material. By setting the specific surface area of the negative electrode material to 5 m 2 / g-10 m 2 / g, the electrochemical performance of the negative electrode material is relatively good in this range.

[0029] In some embodiments, the porous silicon-based material has a core-shell structure, the core structure of the core-shell structure is a porous silicon particle, and the shell structure is a carbon coating layer.

[0030] By setting the porous silicon-based material as a core-shell structure, on the one hand, the carbon coating layer is used to wrap the porous silicon particle with pores inside, so that the silicon-based material powder is not easy to enter the pores and cause the filling of the pores, effectively buffering the volume expansion effect of the silicon-based material. At the same time, the carbon coating layer can also effectively improve the electronic conductivity of the porous silicon-based material.

[0031] In a second aspect, the embodiments of the present application provide a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer arranged on at least one side of the negative electrode current collector, and the negative electrode material layer comprises the negative electrode material provided in the first aspect of the embodiments of the present application.

[0032] By setting the small-particle micro-powder silicon-based material to fill between the large-particle porous silicon-based material in the negative electrode material layer, the stress generated by the two silicon-based materials during lithium intercalation and deintercalation is relieved by using the channel structure on the porous silicon-based material and the gap between the porous silicon-based material and the micro-powder silicon-based material, so as to limit the expansion of the two silicon-based materials within the two silicon-based materials, prevent the negative electrode material layer from expanding outward, and thus inhibit the peeling of the negative electrode material layer from the current collector.

[0033] In some embodiments, the porosity of the negative electrode material layer is 10% to 25%.

[0034] By retaining some pores in the negative electrode material layer, the expansion of the silicon-based material in the negative electrode material layer is buffered, and the fragmentation and pulverization of the negative electrode material layer are inhibited. However, too high porosity in the negative electrode material layer will reduce the specific capacity of the negative electrode material layer. Therefore, by reasonably setting the porosity of the negative electrode material layer to be 10% to 25%, the anti-expansion property of the negative electrode material layer is optimized while ensuring good electrochemical performance of the negative electrode material layer.

[0035] In a third aspect, the embodiments of the present application provide an electrode assembly, which comprises the negative electrode sheet provided in the second aspect of the embodiments of the present application; and a separator film covering at least one side of the negative electrode sheet.

[0036] By using the negative electrode sheet with low expansion rate, the cycle stability of the electrode assembly is improved.

[0037] In a fourth aspect, the embodiments of the present application provide a battery, which comprises the electrode assembly provided in the third aspect of the embodiments of the present application.

[0038] By using the negative electrode sheet with low expansion rate, the cycle stability of the battery is improved.

[0039] In a fifth aspect, the embodiments of the present application provide a power utilization device, which comprises the battery provided in the fourth aspect of the embodiments of the present application.

[0040] By using the battery with better cycle stability, the working stability of the power utilization device is improved.

[0041] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, the specific embodiments of the present application can be implemented in accordance with the content of the description, and in order to make the above and other purposes, characteristics and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0042] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments with reference made to the accompanying drawings. The drawings are for purposes of illustration only and are not intended to limit the scope of the present application. The same reference numbers in different drawings identify the same components throughout the text. In the drawings:

[0043] Figure 1 Structure diagram of a vehicle for some embodiments of the present application;

[0044] Figure 2 Structure diagram of an explosion of a battery for some embodiments of the present application;

[0045] Figure 3 Structure diagram of an explosion of a battery cell for some embodiments of the present application;

[0046] Figure 4 Structure diagram of an electrode assembly for some embodiments of the present application;

[0047] Figure 5 Structure diagram of a cross section of a pole piece for some embodiments of the present application.

[0048] Reference signs in the detailed description of the embodiments are as follows:

[0049] 10 - pole piece; 1 - current collector; 2 - active material layer;

[0050] 20 - electrode assembly; 101 - negative pole piece; 102 - positive pole piece; 201 - negative pole tab; 202 - positive pole tab; 203 - separator;

[0051] 30 - battery cell; 301 - shell; 302 - end cover; 303 - negative pole adapter; 304 - positive pole adapter; 305 - insulating member;

[0052] 40 - battery; 401 - box body; 4011 - box body; 4012 - box cover;

[0053] 50 - electric device; 501 - controller; 502 - motor. DETAILED DESCRIPTION

[0054] The embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0055] 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 this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application; the use of the terms "including," "comprising," or "having" and variations thereof herein is intended to be broad and encompass the terms "consisting of" and "consisting essentially of" and variations thereof. Unless otherwise noted, the terms "including" and "comprising" are open-ended and do not exclude the presence of unrecited elements or limitations.

[0056] In the description of the embodiments of the present application, the technical terms "first", "second", etc. 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. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0057] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily independent or alternative embodiments to each other. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0058] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents that the front and rear associated objects are a "or" relationship.

[0059] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0060] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional 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 limiting the embodiments of the present application. The orientation or position of the device or element indicated, and therefore cannot be understood as limiting the embodiments of the present application.

[0061] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "connecting", "fixing" and the like should be understood in a broad sense, for example, can be fixed connection, or detachable connection, or integral; can be mechanical connection, or electrical connection; can be direct connection, or indirect connection through an intermediate medium, or internal communication of two elements or interaction relationship between two elements. For those skilled in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0062] Lithium ion batteries are widely used due to their high energy density and long cycle life. With the development of new energy vehicles and other fields, traditional graphite as the negative electrode material of lithium ion batteries cannot meet the demand for higher energy density batteries. Silicon-based materials, including but not limited to silicon, silicon monoxide, etc., have attracted attention due to their high theoretical specific capacity, abundant reserves, and other advantages. However, silicon-based materials are prone to large volume expansion and contraction during charging and discharging, which causes the active material to break and pulverize, and the active material and the current collector to separate and fall off, resulting in rapid capacity decline. In addition, the large volume expansion also makes the electrode unable to form a stable solid electrolyte interface (SEI) film, irreversibly consumes lithium ions, and reduces the charging and discharging efficiency of the electrode.

[0063] Therefore, the inventors propose a negative electrode material, which includes at least two kinds of silicon-based materials, i.e., a porous silicon-based material with larger particles and a micro-powder silicon-based material with smaller particles. The micro-powder silicon-based material with smaller particles is used to fill the gaps between the porous silicon-based material with larger particles. The stress generated during the intercalation and deintercalation of lithium ions is relieved by the channel structure on the porous silicon-based material and the gap between the porous silicon-based material and the micro-powder silicon-based material, so as to limit the expansion of the two kinds of silicon-based materials within the two kinds of silicon-based materials, thereby reducing the expansion rate of the negative electrode material. When the negative electrode material is applied to a negative electrode material layer, the negative electrode material layer can be prevented from expanding outward. At the same time, the addition of the micro-powder silicon-based material can also improve the theoretical specific capacity of the negative electrode material, thereby improving the energy density of the battery using the negative electrode material. In addition, the micro-powder silicon-based material with smaller particles has a larger specific surface area and more active sites, ensuring fast lithium ion diffusion and charge exchange, so that the battery using the negative electrode material has better kinetic performance.

[0064] Some embodiments of the present application disclose a battery that can be used in an electric device such as a vehicle, a ship, or an aircraft, but is not limited thereto. A power supply system of the electric device can be composed of the battery disclosed in the present application.

[0065] Some embodiments of the present application provide a power consuming device using a battery as a power source. The power consuming device can be, but is not limited to, a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle can be, but is not limited to, a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be, but is not limited to, a pure electric vehicle, a hybrid electric vehicle, or a range extended electric vehicle. The spacecraft includes an airplane, a rocket, a space shuttle, a spacecraft, and the like. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric vehicle toy, an electric ship toy, an electric airplane toy, and the like. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembling electric tool, and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact electric drill, a concrete vibrator, an electric planer, and the like.

[0066] The following embodiments are described by taking a vehicle 50 as an example for convenience of description.

[0067] Please refer to Figure 1 , Figure 1 A structural schematic diagram of the vehicle 50 is provided for some embodiments of the present application. The vehicle 50 is internally provided with a battery 40. The battery 40 can be arranged at the bottom, the head, or the tail of the vehicle 50. The battery 40 can be used for power supply of the vehicle 50, for example, the battery 40 can be used as an operating power source of the vehicle 50. The vehicle 50 can further include a controller 501 and a motor 502. The controller 501 is used to control the battery 40 to supply power to the motor 502, for example, to meet the power demand of the vehicle 50 during starting, navigation, and driving.

[0068] In some embodiments of the present application, the battery 40 can not only be used as an operating power source of the vehicle 50, but also be used as a driving power source of the vehicle 50, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 50.

[0069] In some embodiments of the present application, the battery 40 is a secondary battery. The secondary battery has various forms, including but not limited to a battery monomer, a battery module, a battery pack, and the like. Here, the secondary battery refers to a battery that can be activated by charging after discharging.

[0070] Please refer to Figure 2 , Figure 2 An exploded view of the battery 40 is provided for some embodiments of the present application. The battery 40 includes a box body 401 and a battery monomer 30. The battery monomer 30 is accommodated in the box body 401. The box body 401 is used to provide an accommodation space for the battery monomer 30. The box body 401 can have various structures.

[0071] In some embodiments, the box 401 can include a box body 4011 and a box cover 4012, which are coupled to each other and together define a containing space for containing the battery cell 30. Optionally, the box body 4011 can be a hollow structure with one end open, and the box cover 4012 can be a plate-shaped structure, which is coupled to the open end of the box body 4011.

[0072] In the battery 40, the battery cell 30 can be multiple, and the multiple battery cells 30 can be connected in series, in parallel, or in a mixed connection. The mixed connection means that the multiple battery cells 30 are connected in series and in parallel. The multiple battery cells 30 can be directly connected in series, in parallel, or in a mixed connection, and then the multiple battery cells 30 are contained in the box 401; of course, the battery 40 can also be that the multiple battery cells 30 are first connected in series, in parallel, or in a mixed connection to form a battery module, and then the multiple battery modules are connected in series, in parallel, or in a mixed connection to form a whole, and are contained in the box 401. The battery 40 can also include other structures, such as a busbar component (not shown in the figure), for realizing the electrical connection between the multiple battery cells 30.

[0073] Among them, the battery cell 30 can be a secondary battery or a primary battery; it can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 30 can be in the shape of a cylinder, a flat body, a cuboid, or other shapes.

[0074] Please refer to Figure 3 , Figure 3 is an exploded view of the battery cell 30 in some embodiments of the present application. The battery cell 30 refers to the smallest unit that constitutes a battery. As Figure 3 , the battery cell 30 includes a shell 301, an end cover 302, an electrode assembly 20, and other functional components.

[0075] The shell 301 is a hollow structure with one end open, and the shell 301 is used to cooperate with the end cover 302 to form an internal environment for containing the electrode assembly 20, the electrolyte, and other functional components. The shell 301 can be in various shapes and sizes, such as a cuboid, a cylinder, a hexagonal prism, etc. Specifically, the shape of the shell 301 can be determined according to the specific shape and size of the electrode assembly 20. The material of the shell 301 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not limited herein.

[0076] The end cover 302 refers to a component that covers the opening of the housing 301 to isolate the internal environment of the battery cell 30 from the external environment. Optionally, the shape of the end cover 302 can be adapted to the shape of the housing 301 to fit the housing 301. Optionally, the end cover 302 can be made of a material with certain hardness and strength, such as aluminum alloy, so that the end cover 302 is less likely to deform when subjected to extrusion collision, allowing the battery cell 30 to have higher structural strength and improved safety performance. The material of the end cover 302 can be, but is not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not limited herein.

[0077] The housing 301 can contain one or more electrode assemblies 20.

[0078] In some embodiments, the battery cell 30 further includes functional components such as a negative tab 303 and a positive tab 304, where the negative tab 303 is used to electrically connect with the negative tab on the electrode assembly 20, and the positive tab 304 is used to electrically connect with the positive tab on the electrode assembly 20 for outputting or inputting the electrical energy of the battery cell 30. It can be understood that the negative tab 303 is made of conductive material, and the material of the negative tab 303 can be, but is not limited to, copper, iron, aluminum, etc. The positive tab 304 is made of conductive material, and the material of the positive tab 304 can be, but is not limited to, copper, iron, aluminum, etc.

[0079] In some embodiments, the battery cell 30 further includes an insulating member 305 located on the inner side of the housing 301 to isolate the housing 301 from the electrode assembly 20 and reduce the risk of short circuit. For example, the insulating member 305 can be plastic, rubber, etc.

[0080] Please refer to Figure 4 , Figure 4 FIG. 1 is a structural schematic diagram of an electrode assembly 20 in some embodiments of the present application. The electrode assembly 20 is a component in which electrochemical reactions occur in the battery cell 30. The electrode assembly 20 is mainly formed by winding or stacking the electrode sheet structure in which the negative electrode sheet 101 and the positive electrode sheet 102 are integrated, and a separator 203 is usually arranged between adjacent negative electrode sheets 101 and positive electrode sheets 102.

[0081] The negative electrode sheet 101 includes a negative current collector and a negative material layer coated on the surface of the negative current collector. Taking a lithium ion battery as an example, the material of the negative current collector can be copper, and the negative material layer includes a negative material, which can be a silicon-based material, etc.

[0082] The positive electrode tab 102 includes a positive current collector and a positive material layer, which is coated on the surface of the positive current collector. Taking a lithium ion battery as an example, the material of the positive current collector can be aluminum, and the positive material layer includes a positive material, which can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganate, etc.

[0083] The separator 203 is a porous plastic film that allows lithium ions in the electrolyte to pass freely, but separates the negative electrode tab 101 and the positive electrode tab 102, so that the electrons inside the battery cannot pass freely. The material of the separator 203 can be PP (polypropylene) or PE (polyethylene), etc.

[0084] The negative current collector and the positive current collector also have parts that are not coated with the active material layer, and these parts without the active material layer are provided with the connecting tabs. Specifically, the negative current collector is connected with the negative tab 201, and the positive current collector is connected with the positive tab 202. During the charging and discharging process of the battery, the positive material layer and the negative material layer react with the electrolyte, the tab 201 is connected with the negative adapter tab 303 and the positive tab 202 is connected with the positive adapter tab 304 to form a current loop. Of course, in some embodiments, the parts of the negative current collector and the positive current collector that are not coated with the active material layer each constitute a tab.

[0085] Please refer to Figure 5 , Figure 5 is a schematic view of the structure of the electrode tab 10 in some embodiments of the present application. The electrode tab 10 includes a current collector 1 and an active material layer 2, and the active material layer 2 is arranged on at least one side of the current collector 1.

[0086] The current collector 1 refers to a component for converging current. The current collector 1 can be a negative current collector or a positive current collector according to different applications. When the current collector 1 is a negative current collector, the active material layer 2 coated on the negative current collector is a negative material layer, and the resulting electrode tab 10 is a negative electrode tab; when the current collector 1 is a positive current collector, the active material layer 2 coated on the positive current collector is a positive material layer, and the resulting electrode tab 10 is a positive electrode tab. Taking a lithium ion battery as an example, the negative current collector can be a copper foil, and the positive current collector can be an aluminum foil. In addition, the current collector 1 can have various shapes, such as a strip shape or a square shape, which are not limited here.

[0087] The active material layer 2 includes an active material, a conductive agent, and a binder. The active material refers to a material that participates in an electrochemical oxidation / reduction reaction. Optionally, the active material is a powder. When the active material layer 2 is a negative electrode material layer, the active material is a negative electrode material. When the active material layer 2 is a positive electrode material layer, the active material is a positive electrode material. Taking a lithium ion battery as an example, the negative electrode material can be silicon and / or a silicon oxide; the positive electrode material can be, but is not limited to, lithium cobaltate, lithium manganate, lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobaltate, lithium nickel manganate, lithium nickel cobalt manganate, lithium-rich manganese-based material, etc. The conductive agent refers to a material that collects micro-currents between the active materials, between the active material and the current collector 1. The conductive agent can be, but is not limited to, conductive graphite, carbon nanotubes, acetylene black, etc. The binder is a material that binds the active material together to enhance the electronic contact between the active material and the conductive agent and between the active material and the current collector 1. The binder can be, but is not limited to, styrene-butadiene rubber (SBR), acrylonitrile, acrylate, polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), etc.

[0088] The current collector 1 has a first surface and a second surface opposite along the thickness direction of the current collector 1. At least one side of the current collector 1 includes the first surface and / or the second surface of the current collector 1. Understandably, the active material layer 2 can be disposed on the first surface, on the second surface, or on both the first surface and the second surface.

[0089] Some embodiments of the present application provide a negative electrode material, which includes a silicon-based material, the silicon-based material including a porous silicon-based material and a fine powder silicon-based material for filling between the porous silicon-based material, the median particle size of the porous silicon-based material being greater than the median particle size of the fine powder silicon-based material.

[0090] Here, the silicon-based material refers to a negative electrode material containing silicon elements. The silicon-based material includes, but is not limited to, elemental silicon or silicon monoxide. The porous silicon-based material refers to a silicon-based material having a pore structure inside. Here, the pore structure can include at least one of micropores, mesopores, and macropores. The porous silicon-based material can be, but is not limited to, flaky, spherical, etc. The fine powder silicon-based material refers to a silicon-based material with a fine powder structure, specifically a silicon-based material with a median particle size D50 less than 1 μm.

[0091] Here, the porous silicon-based material and the fine powder silicon-based material refer to two silicon-based materials with different morphologies, the porous silicon-based material being a porous structure and the fine powder silicon-based material being a fine powder particle, and do not necessarily refer to two silicon-based materials with different compositions. In some embodiments, the porous silicon-based material and the fine powder silicon-based material can have the same composition, for example, both being elemental silicon, and in other embodiments, the porous silicon-based material and the fine powder silicon-based material can have different compositions, for example, the porous silicon-based material being elemental silicon and the fine powder silicon-based material being silicon monoxide.

[0092] The micro-powder silicon-based material is used to fill the space between the porous silicon-based materials, which means that the micro-powder silicon-based material is located outside the porous silicon-based material, rather than in the pore structure of the porous silicon-based material, specifically, the micro-powder silicon-based material is used to fill the space between the porous silicon-based materials.

[0093] The median particle size of the porous silicon-based material is greater than the median particle size of the micro-powder silicon-based material, which can be 2 times, 4 times, 6 times, 8 times, or 10 times the median particle size of the micro-powder silicon-based material. Understandably, the smaller the median particle size of the micro-powder silicon-based material, the more the micro-powder silicon-based material can fill the space between the porous silicon-based materials, and the higher the content of the silicon-based material on the anode material.

[0094] By setting the anode material to include a silicon-based material with a higher theoretical specific capacity, while the silicon-based material includes a porous silicon-based material with large particles and a micro-powder silicon-based material with small particles, by filling the micro-powder silicon-based material with small particles between the porous silicon-based material with large particles, and by using the pore structure of the porous silicon-based material and the gap between the porous silicon-based material and the micro-powder silicon-based material to relieve the stress generated by the two silicon-based materials during lithium intercalation and deintercalation, the expansion of the two silicon-based materials is limited within the two silicon-based materials, and the expansion rate of the anode material is reduced; when the anode material is applied to the anode material layer, the anode material layer can be prevented from expanding outward, thereby inhibiting the separation of the anode material layer and the current collector; in addition, the micro-powder silicon-based material with smaller particles has a larger specific surface area and more active sites, ensuring fast lithium ion diffusion and charge exchange, and making the battery using the anode material have better kinetic performance.

[0095] According to some embodiments of the present application, the chemical formula of the silicon-based material is SiO x , and 0≤x<2.

[0096] The chemical formula of the silicon-based material is SiO x , and 0≤x<2. Understandably, the silicon-based material here can be elemental silicon or silicon monoxide, i.e., an incomplete oxide of silicon. Here, x represents the oxygen content in the silicon-based material, and x can be 0 or any value between 0 and 2, such as 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 1.99, etc. When x=0, the silicon-based material contains elemental silicon. When 0

[0097] By setting the silicon-based material as elemental silicon and / or silicon monoxide with a higher theoretical specific capacity, the theoretical specific capacity of the negative electrode material is improved, and the energy density of the battery is improved.

[0098] According to some embodiments of the present application, 0.9≤x≤1.1.

[0099] The main reason for the large volume effect of the silicon-based material is that the silicon-based material forms Li x Si during the lithiation process. Generally, SiO x During the first lithiation process, elemental silicon, lithium oxide, and lithium silicate (Li x SiO y ) are generated. The elemental silicon generated by the reaction is the true lithium storage function. Therefore, the volume effect of SiO x is closely related to the oxygen content, i.e., the value of x. As the value of x decreases, the content of elemental silicon increases, the effective capacity increases, but the volume effect also increases, and the cycle stability of the negative electrode material decreases. As the value of x increases, the content of elemental silicon decreases, the effective capacity decreases, and the conductivity decreases, but the volume effect is slowed down, and the cycle stability of the negative electrode material is improved.

[0100] Alternatively, x is 0.9, 0.95, 1.0, 1.05, or 1.1.

[0101] By setting x to be 0.9-1.1, i.e., the silicon-based material is silicon monoxide, and the content of oxygen in the silicon monoxide is close to the content of silicon, the silicon monoxide in this ratio range not only has a much higher specific capacity than graphite, but also does not undergo severe volume expansion during the charging process like elemental silicon, while also ensuring the generation of sufficient elemental silicon during the lithiation process, ensuring the conductivity and effective capacity.

[0102] According to some embodiments of the present application, the internal pore size of the porous silicon-based material is 1-100 nm.

[0103] Alternatively, the internal pore size of the porous silicon-based material is 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm.

[0104] Generally, a too large internal pore size of the porous silicon-based material causes capacity loss and polarization increase of the negative electrode material, but a too small internal pore size causes the expansion of the negative electrode material to increase. By setting the internal pore size of the porous silicon-based material to be 1-100 nm, within this range, the negative electrode material not only has good capacity but also has good anti-expansion properties.

[0105] According to some embodiments of the present application, the median particle size of the micro-powder silicon-based material is 0.1-0.8 μm.

[0106] Optionally, the median particle size of the micro-powder silicon-based material is 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, or 0.8 μm.

[0107] If the median particle size of the micro-powder silicon-based material is too small, the gap between the filled micro-silicon powder material and the porous silicon-based material and the gap between the micro-silicon powder materials are too small, and the internal stress of the micro-silicon powder material when swelling cannot be well released; if the median particle size of the micro-powder silicon-based material is too large, the filling amount of the micro-silicon powder material will be reduced. By setting the median particle size of the micro-powder silicon-based material to 0.1 μm to 0.8 μm, the anti-swelling property and specific capacity of the negative electrode material obtained in this range are both relatively good.

[0108] According to some embodiments of the present application, the median particle size of the porous silicon-based material is 3 μm to 9 μm.

[0109] Optionally, the median particle size of the porous silicon-based material is 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, or 9 μm.

[0110] If the median particle size of the porous silicon-based material is too small or too large, it is not conducive to forming pores on the porous silicon-based material, so that the porous silicon-based material cannot well release internal stress. By setting the median particle size of the porous silicon-based material to 3 μm to 9 μm, the anti-swelling property of the negative electrode material obtained in this range is relatively good. At the same time, in this range, it is beneficial to shorten the diffusion path of lithium ions in the porous silicon-based material and improve the rate performance of the negative electrode material.

[0111] According to some embodiments of the present application, the proportion of the micro-powder silicon-based material is 5 wt% to 15 wt% based on the total weight of the negative electrode material.

[0112] Optionally, the proportion of the micro-powder silicon-based material is 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%.

[0113] The specific capacity of the negative electrode material can be improved by filling the micropowder silicon-based material between the porous silicon-based materials. However, if the filling amount of the micropowder silicon-based material is too high, the percentage of the porous silicon-based material will be reduced, thereby reducing the anti-expansion performance of the negative electrode material as a whole. In addition, the micropowder silicon-based material is filled in the pores between the porous silicon-based materials. Since the micropowder silicon-based material also expands in volume when lithium is inserted, the greater the amount of the micropowder silicon-based material filled in the solid particles, the greater the expansion volume of the micropowder silicon-based material when lithium is inserted. If the expansion volume of the micropowder silicon-based material exceeds a limit, the electrode may expand or even fall off the negative electrode material. By setting the mass percentage of the micropowder silicon-based material in the negative electrode material to 5wt%-15wt%, the expansion volume of the porous silicon-based material and the micropowder silicon-based material when lithium is inserted can be just absorbed by the gap between the porous silicon-based materials, thereby preventing the negative electrode material from expanding excessively outward.

[0114] According to some embodiments of the present application, the negative electrode material further comprises a carbon material.

[0115] The carbon material refers to a carbon-based material that can participate in the insertion and extraction of lithium ions. The carbon material includes but is not limited to graphite, carbon nanotubes, graphene, and conductive carbon black.

[0116] Optionally, the median particle size of the carbon material is greater than the median particle size of the porous silicon-based material. It can be understood that, since the median particle size of the porous silicon-based material is greater than the median particle size of the micropowder silicon-based material, the median particle size of the micropowder silicon-based material is also smaller than the median particle size of the carbon material. By filling the micropowder silicon-based material between the carbon material and the porous silicon-based material, since the expansion of the carbon material is small, the carbon material can be used to buffer the expansion stress of the silicon-based material, thereby preventing the negative electrode material layer from being cracked due to excessive local stress when the negative electrode material forms a negative electrode material layer. At the same time, by filling the micropowder silicon-based material with small particles between the carbon material with large particles and the porous silicon-based material, the contact between the large and small particles is improved, and the conductivity is improved. Otherwise, a large amount of conductive agent needs to be added to link the porous silicon-based materials, thereby reducing the specific capacity of the negative electrode material.

[0117] Since the carbon material has a small volume expansion during charging and discharging, by adding the carbon material to the micropowder silicon-based material and the porous silicon-based material, the carbon material can be used to buffer the expansion of the silicon-based material, thereby reducing the expansion rate of the negative electrode material. At the same time, since the main components of the porous silicon-based material and the micropowder silicon-based material are elemental silicon and / or silicon oxide, the conductivity is poor. By adding the carbon material to the negative electrode material, the carbon material can be used to build a conductive network in the negative electrode material, thereby ensuring better contact between the silicon-based material and the current collector and between the silicon-based materials.

[0118] According to some embodiments of the present application, the carbon material comprises graphite.

[0119] Graphite is a material that is resistant to high temperature and corrosion and has good electrical conductivity, thermal conductivity and stable chemical properties. Here, the graphite can be, but is not limited to, natural graphite, artificial graphite and composite graphite. The graphite can be, but is not limited to, flaky, blocky and the like.

[0120] By adding graphite to the micro-powder silicon-based material and the porous silicon-based material, the expansion rate of the negative electrode material is reduced while the electrical conductivity of the negative electrode material is improved.

[0121] According to some embodiments of the present application, the median particle size of the graphite is 12 μm to 20 μm.

[0122] Optionally, the median particle size of the graphite is 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm or 20 μm.

[0123] Generally, the median particle size of the graphite is too large, which is not conducive to the uniform dispersion of the graphite in the silicon-based material, and the median particle size of the graphite is too small, which cannot well buffer the expansion stress of the silicon-based material. By setting the median particle size of the graphite to be 12 μm to 20 μm, the anti-expansion property and the electrical conductivity of the negative electrode material prepared in this range are relatively optimal.

[0124] According to some embodiments of the present application, the theoretical mass specific capacity of the negative electrode material is 750 mAh / g to 1700 mAh / g.

[0125] The theoretical mass specific capacity of the negative electrode material refers to the weighted average of the theoretical mass specific capacities of the components in the negative electrode material. Optionally, the negative electrode material comprises a porous silicon-based material, a micro-powder silicon-based material and a carbon material. For example, the negative electrode material contains 0.4 g of the porous silicon-based material, 0.1 g of the micro-powder silicon-based material and 0.5 g of the carbon material, wherein the porous silicon-based material is silicon monoxide, the micro-powder silicon-based material is elemental silicon and the carbon material is graphite, the theoretical mass specific capacity of the silicon monoxide is 2100 mAh / g, the theoretical mass specific capacity of the elemental silicon is 4200 mAh / g and the theoretical mass specific capacity of the graphite is 372 mAh / g, and then the theoretical mass specific capacity of the negative electrode material is:

[0126] (0.4 g*2100 mAh / g+0.1 g*4200 mAh / g+0.5 g*372 mAh / g) /

[0127] (0.6 g*2100 mAh / g+0.15 g*2100 mAh / g

[0128] + 0.25g * 372mAh / g) / (0.6g + 0.15g + 0.25g) = 1668mAh / g.

[0129] Generally, the theoretical mass specific capacity of the negative electrode material can be changed by changing the components in the negative electrode material, and the theoretical mass specific capacity of the negative electrode material can also be changed by changing the proportion of each component in the negative electrode material. The theoretical mass specific capacity of the negative electrode material is 750mAh / g-1700mAh / g, and it can be known that the negative electrode material cannot be all elemental silicon, because the theoretical mass specific capacity of elemental silicon is much higher than 1700mAh / g, and the volume expansion rate of elemental silicon is also higher during the charging and discharging process. Therefore, the negative electrode material must contain substances with a theoretical mass specific capacity less than that of elemental silicon, including but not limited to silicon monoxide or carbon materials, etc., and the volume expansion rate of these substances during the charging and discharging process is often also less than that of elemental silicon.

[0130] Optionally, the theoretical mass specific capacity of the negative electrode material is 750mAh / g, 800mAh / g, 900mAh / g, 1000mAh / g, 1100mAh / g, 1200mAh / g, 1300mAh / g, 1400mAh / g, 1500mAh / g, 1600mAh / g or 1700mAh / g.

[0131] By setting the theoretical mass specific capacity of the negative electrode material to 750mAh / g-1700mAh / g, compared with the traditional graphite negative electrode material, the theoretical mass specific capacity of the negative electrode material is improved, and compared with the elemental negative electrode material, the volume expansion rate of the negative electrode material is also well inhibited. On the one hand, materials with a lower expansion rate than elemental silicon are used, and on the other hand, small-particle micro-powder silicon-based materials are filled between large-particle porous silicon-based materials, and the two are combined to limit the expansion of the two silicon-based materials to the inside of the two silicon-based materials. When the negative electrode material is formed into a negative electrode material layer, the negative electrode material layer is inhibited from expanding outward.

[0132] According to some embodiments of the present application, the specific surface area of the negative electrode material is 5m 2 / g-10m 2 / g.

[0133] Optionally, the specific surface area of the negative electrode material is 5m 2 / g, 5.5m 2 / g, 6m 2 / g, 6.5m 2 / g, 7m 2 / g, 7.5m 2 / g, 8m 2 / g, 8.5m 2 / g, 9m 2 / g, 9.5m2 / g or 10 m 2 / g.

[0134] Due to the existence of the pores on the porous silicon-based material and the small median particle size of the fine powder silicon-based material, the specific surface area of the negative electrode material is increased. The increase of the specific surface area of the negative electrode material will improve the kinetic performance to a certain extent, but the increase of the specific surface area will also increase the area of the SEI film, thereby increasing the consumption of lithium ions and reducing the charge and discharge efficiency of the negative electrode material. By setting the specific surface area of the negative electrode material to 5 m 2 / g~10 m 2 / g, within the range, the electrochemical performance of the negative electrode material is relatively optimal.

[0135] According to some embodiments of the present application, the porous silicon-based material has a core-shell structure, the core structure of the core-shell structure is a porous silicon particle, and the shell structure is a carbon coating layer.

[0136] The core-shell structure is an ordered assembly structure formed by one material coating another material through chemical bonds or other forces. The core structure of the core-shell structure is a porous silicon particle, which refers to a silicon-based material in the form of particles and having a pore structure inside. The shell structure is a carbon coating layer, which means that the carbon coating layer is wrapped around the outer surface of the core structure.

[0137] By setting the porous silicon-based material as a core-shell structure, on the one hand, the carbon coating layer wraps the porous silicon particle with pores inside, so that the fine powder silicon-based material is not easy to enter the pores and cause filling of the pores, effectively buffering the volume expansion effect of the silicon-based material, and on the other hand, the carbon coating layer can also effectively improve the electronic conductivity of the porous silicon-based material.

[0138] Some embodiments of the present application also provide a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer arranged on at least one side of the negative electrode current collector, and the negative electrode material layer comprises the above-mentioned negative electrode material.

[0139] Optionally, the negative electrode material layer is arranged on one side of the negative electrode current collector. Optionally, the negative electrode material layer is arranged on the opposite surfaces of the negative electrode current collector along the thickness direction

[0140] By setting the fine powder silicon-based material with small particles to fill between the porous silicon-based material with large particles in the negative electrode material layer, the pore structure on the porous silicon-based material and the gap between the porous silicon-based material and the fine powder silicon-based material are utilized to relieve the stress generated when the two kinds of silicon-based materials are embedded and de-embedded lithium, so as to limit the expansion of the two kinds of silicon-based materials inside the two kinds of silicon-based materials, prevent the negative electrode material layer from expanding outward, and thereby inhibit the peeling of the negative electrode material layer from the current collector.

[0141] According to some embodiments of the present application, the porosity of the negative electrode material layer is 10%~25%.

[0142] Optionally, the porosity of the negative electrode material layer is 10%, 15%, 20%, or 25%.

[0143] By retaining some pores in the negative electrode material layer, the pores are used to provide a buffer space for the expansion of the silicon-based material in the negative electrode material layer, and the fragmentation and pulverization of the negative electrode material layer are inhibited. However, too high porosity in the negative electrode material layer will reduce the specific capacity of the negative electrode material layer. Therefore, by reasonably setting the porosity range of the negative electrode material layer to 10% to 25%, the anti-expansion property of the negative electrode material layer is optimized while ensuring that the negative electrode material layer has good electrochemical performance.

[0144] Some embodiments of the present application also provide a preparation method of the porous silicon-based material. The preparation method uses a silicon-based material (SiO x , 0≤x<2) as a raw material, mixes the silicon-based material with an etching solution, the etching solution including a fluorine source, a metal salt, and a weak acid, and then stirs and processes the mixture at a first temperature for a first duration.

[0145] Optionally, the fluorine source includes but is not limited to hydrofluoric acid, lithium fluoride.

[0146] Optionally, the metal salt includes but is not limited to at least one of lithium carbonate, lithium nitrate, zinc nitrate, magnesium nitrate, and magnesium silicate.

[0147] Optionally, the weak acid includes but is not limited to at least one of boric acid, oxalic acid, and carbonic acid.

[0148] Optionally, the etching solution further includes an organic substance. The organic substance includes an alcohol, such as glycerol. Optionally, the organic substance includes a phenol, such as phenol.

[0149] Optionally, the etching solution further includes an oxidizing agent. Optionally, the oxidizing agent includes at least one of potassium permanganate, permanganic acid, and hydrogen peroxide.

[0150] Optionally, the first temperature is 50°C to 80°C. Optionally, the first temperature is 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C.

[0151] Optionally, the first duration is 2h to 24h. Optionally, the first duration is 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24h.

[0152] Optionally, the stirring speed of the stirring and processing is 100 rdm / min to 500 rdm / min. Optionally, the stirring speed is 100 rdm / min, 200 rdm / min, 300 rdm / min, 400 rdm / min, or 500 rdm / min.

[0153] Optionally, the preparation method further comprises a crushing treatment and a classification treatment on the product obtained by the stirring treatment. The particle size of the porous silicon-based material prepared finally can be controlled by adjusting the degree of the crushing treatment.

[0154] Optionally, the preparation method further comprises a carbon-coating treatment on the composite material by a chemical vapor deposition (CVD) method, and the carbon source is at least one of methane, ethylene and acetylene. The following will be described in combination with specific examples.

[0155] Example 1

[0156] S1: Preparation of a porous silicon-based material

[0157] (1) The silicon-based material (specifically, silicon monoxide) is mixed with a fluorine source LIF, metal salts lithium carbonate, lithium nitrate and zinc nitrate, a weak acid oxalic acid, an oxidizing agent potassium permanganate and hydrogen peroxide, and is stirred and etched at 70°C for 12h at a stirring speed of 300 rdm / min.

[0158] (2) The product after the mixing and etching is crushed and classified to obtain the porous silicon-based material.

[0159] (3) The porous silicon-based material is subjected to a CVD deposition carbon-coating, and the carbon source is methane and acetylene.

[0160] S2: Preparation of a negative electrode material: The porous silicon-based material prepared in S1, graphite and a micro-powder silicon-based material (specifically, elemental silicon) are mixed and matched to obtain a negative electrode material. The D50 of the negative electrode material contains three peaks, respectively at 6μm, 15μm and 0.2μm. The proportion of the micro-powder silicon-based material in the negative electrode material is 8wt%, and the theoretical specific capacity of the negative electrode material is 1250mAh / g.

[0161] S3: Preparation of a battery

[0162] (1) The positive electrode slurry is coated on a 10μm-thick aluminum foil, and the sheet is pressed to obtain a positive electrode sheet with a thickness of 400μm. The positive electrode slurry is NCM98:SP:SWCNT:PVDF=96:2:0.6:0.2:1.2; the viscosity of the positive electrode slurry is 7500mpa·s, and the solid content is 68wt%. The above NCM98 is a positive electrode material, SP is conductive carbon black, SWCNT is a carbon nanotube, and PVDF is a binder.

[0163] (2) The negative electrode slurry was coated on a 4.5 μm thick copper foil with a coating thickness of 125 μm, and the sheet was pressed to obtain a negative electrode sheet with a thickness of 110 μm. The negative electrode slurry was SiO:SP:SWCNT:PAALi = 96.8:1.04:0.06:2.1, where SiO refers to the negative electrode material prepared in step S2 above, SP is conductive carbon black, SWCNT is carbon nanotube, and PAALi is the binder.

[0164] (3) The composite lithium foil negative electrode sheet, the positive electrode sheet, the separator, and the electrolyte were assembled into a soft pack battery, which was placed at 45°C for 24 h.

[0165] (4) After high-temperature standing, formation and capacity distribution were performed to record the initial efficiency and the middle voltage. The specific steps of formation and capacity distribution included: the battery after high-temperature standing was placed for 12 h, then charged at a current of 0.02 C to 3.5 V, then discharged at a current of 0.1 C to 4.6 V, then charged at a voltage of 4.6 V to a current of 0.02 C, and placed for 3 min, then discharged at a current of 0.1 C to 2.5 V, then sealed by pressure reduction and air extraction, and the formation and capacity distribution were completed.

[0166] (5) After formation and capacity distribution, 0.5 C cycling was performed.

[0167] Example 2

[0168] The difference from Example 1 is that the micro-powder silicon-based material accounts for 15 wt% in the negative electrode material, and the theoretical specific capacity of the negative electrode material is 1419 mAh / g.

[0169] Example 3

[0170] The difference from Example 1 is that the micro-powder silicon-based material accounts for 5 wt% in the negative electrode material, and the theoretical specific capacity of the negative electrode material is 1190 mAh / g.

[0171] Example 4

[0172] The difference from Example 1 is that the median particle size of the porous silicon-based material in the negative electrode material is 9 μm.

[0173] Example 5

[0174] The difference from Example 1 is that the median particle size of the porous silicon-based material in the negative electrode material is 3 μm.

[0175] Example 6

[0176] The difference from Example 1 is that the median particle size of the micro-powder silicon-based material in the negative electrode material is 0.5 μm.

[0177] Example 7

[0178] The difference from Example 1 is that the median particle size of the micro-powder silicon-based material in the negative electrode material is 0.8 μm.

[0179] Comparative Example 1

[0180] The difference from Example 1 is that no micro-powder silicon is added, and the theoretical specific capacity of the negative electrode material is 970 mAh / g.

[0181] Comparative Example 2

[0182] The difference from Example 1 is that no porous silicon-based material is added, and the theoretical specific capacity of the negative electrode material is 3000 mAh / g.

[0183] In order to verify the progressiveness of the embodiments of the present application, the samples of the examples and comparative examples were respectively tested as follows:

[0184] 1. The energy density of the batteries prepared from Example 1 to Example 7 and Comparative Example 1 to Comparative Example 2 was tested, and the test results are shown in Table 1. From the results in Table 1, it can be seen that in Examples 1 to 3, with the increase of the proportion of the micro-powder silicon-based material in the negative electrode material, the theoretical gram capacity of the negative electrode material also increases, thereby increasing the energy density of the finally prepared battery. Compared with Comparative Example 1, the energy density of the battery is increased.

[0185] 2. The expansion rate of the electrode sheets prepared in Examples 1 to 7 and Comparative Examples 1 to 2 was tested, wherein the thickness of the electrode sheet after cold pressing at the beginning of the test was L0, the full charge thickness at the beginning of the test was L1, and P1 = (L1-L0) / L0*100% was calculated; the full charge thickness at the end of the test was L2, and P2 = (L2-L0) / L0*100% was calculated, and the test results are shown in Table 1. As can be seen from the results in Table 1, in Examples 1 to 3 and Comparative Example 1, as the proportion of the micro-powder silicon-based material in the negative electrode material increases, the expansion rate of the electrode sheet first decreases and then increases, because the volume of the micro-powder silicon-based material and the porous silicon-based material will expand when lithium is inserted, and because the micro-powder silicon-based material is used to fill the gaps between the porous silicon-based materials, the expanded micro-powder silicon-based material and the expanded porous silicon-based material are pressed against each other, inhibiting the outward expansion of the negative electrode material layer on the electrode sheet, thereby reducing the expansion rate of the electrode sheet; but as the content of the micro-powder silicon-based material continues to increase, it is difficult to buffer the expansion effect of all the micro-powder silicon-based material in the gap between the porous silicon-based materials, thereby increasing the expansion rate of the electrode sheet. In Examples 1, 4 and 5, as the median particle size of the porous silicon-based material increases, the expansion rate of the electrode sheet decreases, because the larger the median particle size of the porous silicon-based material, the larger the gap between the porous silicon-based materials, which is more conducive to buffering the volume expansion of the micro-powder silicon-based material, thereby reducing the expansion rate of the electrode sheet. In Examples 1, 6 and 7, as the median particle size of the micro-powder silicon-based material increases, the expansion rate of the electrode sheet increases, because the smaller the particle size of the micro-powder silicon-based material, the more conducive it is to filling the gap between the porous silicon-based materials, and by using the gap to buffer the volume expansion of the micro-powder silicon-based material, the expansion rate of the electrode sheet is reduced.

[0186] Compared with Comparative Example 1, in the negative electrode material, by adding the micro-powder silicon-based material to the porous silicon-based material, not only the energy density of the battery is increased, but also the expansion of the electrode sheet is alleviated.

[0187] Compared with Comparative Example 2, although the use of the micro-powder silicon-based material can increase the energy density of the battery, the expansion rate of the electrode sheet is high, and by using the micro-powder silicon-based material in combination with the porous silicon-based material, the expansion of the electrode sheet can be effectively controlled.

[0188] Table 1

[0189]

[0190] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than limit them. Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features can be replaced equivalently. Such modifications or replacements do not change the essence of the corresponding technical solutions, which should be covered in the scope of the claims and the specification of the present application. In particular, the technical features mentioned in each embodiment can be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A negative electrode material, characterized by, The silicon-based material comprises a porous silicon-based material and a fine silicon-based material for filling between the porous silicon-based material, the median particle size of the porous silicon-based material being greater than that of the fine silicon-based material; the median particle size of the fine silicon-based material is 0.1-0.8 μm, and the median particle size of the porous silicon-based material is 3-9 μm. The proportion of the fine silicon-based material is 5-15 wt% based on the total weight of the negative electrode material.

2. The negative electrode material according to claim 1, characterized in that, The chemical formula of the silicon-based material is SiO x wherein 0≤x<2.

3. The negative electrode material according to claim 2, characterized in that, 0.9≤x≤1.1。 4. The negative electrode material of claim 1, wherein, The internal pore size of the porous silicon-based material is 1-100 nm.

5. The negative electrode material according to any one of claims 1 to 4, characterized in that, The negative electrode material further comprises a carbon material.

6. The negative electrode material according to claim 5, characterized in that, The carbon material comprises graphite.

7. The negative electrode material according to claim 6, characterized in that, The median particle size of the graphite is 12-20 μm.

8. The negative electrode material according to any one of claims 1 to 4, characterized by, The mass specific capacity of the negative electrode material is 750-1700 mAh / g.

9. The negative electrode material according to any one of claims 1 to 4, characterized by, The specific surface area of the negative electrode material is 5 m 2 / g~10 m 2 / g.

10. The negative electrode material according to any one of claims 1 to 4, characterized by, The porous silicon-based material has a core-shell structure, the core structure of the core-shell structure being a porous silicon particle, and the shell structure being a carbon coating layer.

11. A negative electrode sheet characterized by comprising: The negative electrode material layer comprises the negative electrode material according to any one of claims 1-10.

12. The negative electrode sheet according to claim 11, wherein The porosity of the negative electrode material layer is 10-25%.

13. An electrode assembly, characterized by, The electrode assembly comprises: The negative electrode sheet according to any one of claims 11-12; The separator film covers at least one side of the negative electrode sheet.

14. A battery, characterized by The electrode assembly according to claim 13.

15. An electrical device, comprising: The battery according to claim 14.

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