Negative electrode sheet, battery cell, battery, and electric device

Abstract

The application provides a negative electrode sheet, a battery monomer, a battery and an electric device, and relates to the field of batteries. The negative electrode sheet comprises a current collector and a negative electrode film layer. The negative electrode film layer comprises a composite active layer arranged on at least one side surface of the current collector. The composite active layer comprises at least one first conductive binder layer and at least two negative electrode active material layers along the thickness direction. The first conductive binder layer is arranged between two adjacent negative electrode active material layers. From the side of the negative electrode film layer close to the current collector to the side of the negative electrode film layer away from the current collector, the gram capacity of the negative electrode active material contained in the negative electrode active material layer increases with the increase of the layer number. Under the premise of making the battery have better energy density, the technical problem that the fast charging performance and the cycle stability of the battery are poor can be improved.

Description

TECHNICAL FIELD

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

[0002] As a new type of high-voltage and high-energy-density rechargeable battery, the secondary battery has the outstanding characteristics of light weight, high energy density, no pollution, no memory effect, long service life, etc., and is widely used in electric devices.

[0003] Among them, the consumer electronics market and the power battery market have an increasing demand for shortening the charging time, and the fast charging technology has become an important trend in the development of lithium ion battery technology in recent years. Fast charging mainly ensures that lithium ions are quickly extracted from the positive electrode and quickly embedded in the negative electrode, and cannot cause deposition of lithium ions (to ensure safety performance). Currently, the energy density of the battery is usually sacrificed to improve the fast charging capability of the battery, and the cycle stability is poor during the fast charging process of the existing battery. SUMMARY

[0004] In view of the above problems, the present application provides a negative electrode sheet, a battery monomer, a battery and an electric device, which can improve the technical problems of poor battery fast charging performance and cycle stability under the premise of having better energy density of the battery.

[0005] In a first aspect, the embodiments of the present application provide a negative electrode sheet, which comprises a current collector and a negative electrode film layer, the negative electrode film layer comprises a composite active layer arranged on at least one side surface of the current collector, the composite active layer comprises at least one layer of first conductive adhesive layer and at least two layers of negative electrode active material layer along the thickness direction, and the first conductive adhesive layer is located between the adjacent two layers of negative electrode active material layer; wherein from the side of the negative electrode film layer close to the current collector to the side away from the current collector, the gram capacity of the negative electrode active material contained in the negative electrode active material layer increases with the increase of the layer number.

[0006] In the technical scheme of the embodiments of the present application, the different gram capacities of the negative electrode active materials are used to cooperate with each other to adjust the total gram capacity of the negative electrode film layer, improve the energy density of the battery, and increase the gram capacity of the negative electrode active material contained in the negative electrode active material layer from the side of the negative electrode film layer close to the current collector to the side away from the current collector. That is, the gram capacity of the outer layer negative electrode active material is greater than that of the inner layer negative electrode active material, so that the battery can improve the fast charging performance under the premise of maintaining better energy density, and the use of the first conductive adhesive layer can alleviate the problem of poor cycle stability of the battery caused by interlayer peeling during the charging process.

[0007] In some embodiments, the composite active layer comprises a first conductive binder layer and two negative active material layers. The composite active layer has a simple structure, low processing difficulty, and can improve the fast charging performance and cycle performance of the battery while having a better energy density.

[0008] In some embodiments, the two negative active material layers are respectively a first negative active material layer and a second negative active material layer; the first negative active material layer contains negative active material with a gram capacity of 350-400 mAh / g, and the second negative active material layer contains negative active material with a gram capacity of 1000-3000 mAh / g. The use of high gram capacity negative active material in the second negative active material layer can improve the energy density of the battery when cooperating with the first negative active material layer.

[0009] Optionally, the first negative active material layer contains negative active material with a gram capacity of 350-380 mAh / g.

[0010] In some embodiments, the first negative active material layer contains graphite, and the second negative active material layer contains silicon-based material. The cooperation of silicon-based active material and graphite can effectively improve the energy density of the battery and improve the fast charging performance of the battery.

[0011] In some embodiments, the first negative active material layer and the second negative active material layer both contain a binder; the addition amount of the binder in the first negative active material layer is less than the addition amount of the binder in the second negative active material layer. Since the volume change of silicon-based material is large during charging compared with graphite, increasing the addition amount of the binder in the second negative active material layer can limit the expansion of silicon-based material, reduce the rebound of the negative electrode sheet, and improve the cycle performance of the battery.

[0012] In some embodiments, the first negative active material layer and the second negative active material layer both contain a conductive agent; the addition amount of the conductive agent in the first negative active material layer is equal to the addition amount of the conductive agent in the second negative active material layer, and the electrical conductivity of the conductive agent in the first negative active material layer is less than the electrical conductivity of the conductive agent in the second negative active material layer. Since the electrical conductivity of silicon-based active material is small and the electrical conductivity of graphite is large, the above-mentioned method is beneficial to improve the electrical conductivity of the second negative active material layer, alleviate the poor interlayer conductivity, and improve the cycle performance and fast charging performance of the battery.

[0013] In some embodiments, the thickness of the first negative active material layer is 140-210 μm, and optionally 140-199 μm. Within the above thickness range, the battery has better cycle performance and fast charging performance.

[0014] In some embodiments, the thickness of the second negative active material layer is 1-65 μm, and optionally 5-65 μm. Within the above thickness range, the battery has better cycle performance and fast charging performance.

[0015] In some embodiments, the thickness of the first conductive binder layer accounts for 0.98%-5.75% of the thickness of the negative electrode film layer, and the thickness of the first conductive binder layer is not less than 1 μm. Within the above thickness range of the first conductive binder layer, the cycle performance and fast charging performance of the battery are improved, the thickness is too large, which affects the lithium ion transmission rate, and the thickness is too small, which cannot stably bond the two negative active material layers.

[0016] Optionally, the thickness of the first conductive binder layer is 1-10 μm.

[0017] In some embodiments, the negative electrode film layer further comprises a second conductive binder layer, and the second conductive binder layer is formed on the side of the composite active layer away from the current collector. The second conductive binder layer is arranged to protect the negative active material layer on the side of the composite active layer away from the current collector, and when the negative active material layer on the side of the composite active layer away from the current collector contains a silicon-based active material, the second conductive binder layer is arranged to improve the electrical conductivity and improve the fast charging performance of the battery due to the poor electrical conductivity of the silicon-based active material.

[0018] In some embodiments, the electrical conductivity of the second conductive binder layer is 10 3 -10 7 S / cm. When the negative active material layer on the side of the composite active layer away from the current collector contains a silicon-based active material, the second conductive binder layer within the above electrical conductivity range is used to effectively improve the fast charging performance of the battery.

[0019] In some embodiments, the electrical conductivity of the second conductive binder layer is greater than that of the first conductive binder layer. Due to the different positions of the second conductive binder layer and the first conductive binder layer, the above arrangement is used to improve the cycle performance and fast charging performance of the battery.

[0020] In some embodiments, the second conductive binder layer and the first conductive binder layer both comprise a conductive agent, the amount of the conductive agent in the second conductive binder layer is the same as that in the first conductive binder layer, and the electrical conductivity of the conductive agent in the second conductive binder layer is greater than that in the first conductive binder layer. The above arrangement is used to quickly adjust and achieve the electrical conductivity of the second conductive binder layer being greater than that of the first conductive binder layer, thereby improving the cycle performance and fast charging performance of the battery.

[0021] In some embodiments, the conductive agent in the second conductive binder layer comprises at least one of a one-dimensional conductive agent and a two-dimensional conductive agent. Since the second conductive binder layer is located on the side of the composite active layer away from the current collector, the introduction of the one-dimensional conductive agent and the two-dimensional conductive agent is conducive to inhibiting the expansion of the composite active layer and improving the electrical conductivity of the second conductive binder layer, thereby improving the cycle performance and fast charging performance of the battery.

[0022] Optionally, the one-dimensional conductive agent comprises at least one of carbon nanotubes and carbon fibers.

[0023] Optionally, the two-dimensional conductive agent comprises graphene

[0024] In some embodiments, the thickness of the second conductive binder layer is 0.98%-5.75% of the total thickness of the negative electrode film layer, and the thickness of the second conductive binder layer is not less than 1 μm; the thickness of the second conductive binder layer is within a reasonable range, which is conducive to improving the cycle performance and fast charging performance of the battery.

[0025] Optionally, the thickness of the second conductive binder layer is 1-10 μm.

[0026] In a second aspect, the present application provides a battery cell comprising the negative electrode sheet in the above embodiments.

[0027] In a second aspect, the present application provides a battery comprising the battery cell in the above embodiments.

[0028] In a third aspect, the present application provides a use-electric device comprising the battery cell and / or the battery in the above embodiments, and the battery cell and / or the battery are used to provide electric energy for the use-electric device.

[0029] The above description is only a summary of the technical solutions of the present application. In order to enable the technical means of the present application to be more clearly understood, and to be implemented according to the content 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 easy to understand, the following specific embodiments of the present application are described in detail. BRIEF DESCRIPTION OF DRAWINGS

[0030] 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. The accompanying drawings are included to provide a description of the preferred embodiments and are not meant to limit the present application. Moreover, the same reference numerals in all the drawings represent the same or similar elements. In the drawings:

[0031] Figure 1 Structure schematic diagram of a vehicle of some embodiments of the present application;

[0032] Figure 2 Exploded structure schematic diagram of a battery of some embodiments of the present application;

[0033] Figure 3 A schematic diagram of a battery cell according to some embodiments of the application;

[0034] Figure 4 A schematic diagram of a negative electrode sheet according to some embodiments of the application.

[0035] Reference signs in the detailed description of the embodiments are as follows:

[0036] 1000 - vehicle;

[0037] 100 - battery; 200 - controller; 300 - motor;

[0038] 10 - case; 11 - first part; 12 - second part;

[0039] 20 - battery cell; 21 - end cap; 21a - electrode terminal; 22 - case; 23 - electrode assembly; 23a - tab;

[0040] 30 - negative electrode sheet; 31 - current collector; 32 - negative electrode film layer; 33 - composite active layer; 331 - first negative electrode active material layer; 332 - first conductive binder layer; 333 - second negative electrode active material layer; 34 - second conductive binder layer. DETAILED DESCRIPTION

[0041] The embodiments of the technical solutions of the application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the application, and therefore only serve as examples, and cannot limit the protection scope of the application.

[0042] 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 application belongs; the terms used herein are only for the purpose of describing specific embodiments of the application, and are not intended to limit the application; the terms "include" and "have" and any variations thereof in the specification and claims of the application and the above description of drawings are intended to cover non-exclusive inclusion.

[0043] In the description of the embodiments of the 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 application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0044] Reference to“an embodiment” herein 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 appearances of the phrase“in an embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. It is expressly understood that any of the embodiments described herein can be incorporated into any other embodiment.

[0045] In the description of the embodiments of the application, the term“and / or” only means an association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can mean that A exists alone, A and B exist together, and B exists alone. In addition, the character“ / ” herein generally means that the front and rear associated objects have an“or” relationship.

[0046] In the description of the embodiments of the 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).

[0047] In the description of the embodiments of the 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 shown in the drawings, which is only for the convenience of describing the embodiments of the application and simplifying the description, and does not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the application.

[0048] In the description of the embodiments of the application, unless otherwise explicitly specified and limited, the technical terms“mounting”,“connection”,“connection”,“fixing” and the like 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 mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the embodiments of the application can be understood according to the specific circumstances.

[0049] At present, from the development of market situation, the application of power battery is more and more extensive. The power battery is not only applied to the energy storage power supply system of water power, fire power, wind power and solar power station, but also widely applied to electric bicycles, electric motorcycles, electric vehicles 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.

[0050] But the existing lithium ion battery, the negative electrode can not withstand large current charging, in fast charging, the negative electrode will have metal precipitation, while the negative electrode surface will also produce a large amount of by-products, affecting the cycle life and safety of the battery.

[0051] The application adopts the technical solution that the gram capacity of the negative active material contained in the negative active material layer increases from the side of the negative electrode film layer close to the current collector to the side away from the current collector, uses the negative active materials with different gram capacities to cooperate with each other, adjusts the total gram capacity of the negative electrode film layer, improves the energy density of the battery, makes the battery maintain a better energy density, uses the setting mode that the gram capacity of the outer layer is greater than that of the inner layer, improves the fast charging performance of the battery under the premise of maintaining a better energy density, and uses the setting mode that the two adjacent negative active material layers are connected by the first conductive adhesive layer, which can alleviate the problem of poor cycle stability caused by interlayer peeling during charging. The battery monomer disclosed in the application examples can be used in, but is not limited to, electric equipment such as vehicles, ships or aircraft. The power supply system of the electric equipment can be composed of the battery monomer and the battery disclosed in the application, so that the problem of poor cycle performance of the battery during the lithium intercalation / deintercalation process when the negative electrode sheet is coated with a film layer composed of multiple negative active material layers can be alleviated.

[0052] The application examples provide a kind of electric equipment using battery as power supply, and the electric equipment can be, but is not limited to, mobile phone, tablet computer, notebook computer, electric toy, electric tool, electric car, electric car, ship, spacecraft and the like. Among them, electric toy can include fixed or mobile electric toy, for example, game machine, electric car toy, electric ship toy and electric aircraft toy and the like, spacecraft can include aircraft, rocket, space shuttle and spacecraft and the like.

[0053] The following examples are described for convenience with a vehicle 1000 as an example of an electric device of an embodiment of the application.

[0054] Please refer 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 automobile, a gas automobile, or a new energy automobile, 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 being used to control the battery 100 to supply power to the motor 300, for example, for the working power demand of the vehicle 1000 during starting, navigation and driving.

[0055] 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, instead of or partially instead of fuel or natural gas to provide driving power for the vehicle 1000.

[0056] Please refer 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 body 10 and a battery cell 20, and the battery cell 20 is contained in the box body 10. Among them, the box body 10 is used to provide a containing space for the battery cell 20, and the box body 10 can adopt various structures. In some embodiments, the box body 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 for containing the battery cell 20. The second part 12 can be a hollow structure with one end open, and the first part 11 can be a plate-shaped structure, the first part 11 covers the open side of the second part 12, so that the first part 11 and the second part 12 jointly define the containing space; 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. Of course, the box body 10 formed by the first part 11 and the second part 12 can be various shapes, such as a cylinder, a cuboid, etc.

[0057] In the battery 100, the battery cells 20 can be multiple, and the multiple battery cells 20 can be connected in series, in parallel, or in a mixed manner. The mixed manner means that the multiple battery cells 20 are connected in series and in parallel. The multiple battery cells 20 can be directly connected in series, in parallel, or in a mixed manner, and the whole of the multiple battery cells 20 is accommodated in the case 10. Of course, the battery 100 can also be in a form that the multiple battery cells 20 are connected in series, in parallel, or in a mixed manner to form a battery module, and the multiple battery modules are connected in series, in parallel, or in a mixed manner to form a whole, and the whole is accommodated in the case 10. The battery 100 can also include other structures. For example, the battery 100 can also include a current collecting component for electrically connecting the multiple battery cells 20.

[0058] Each of the battery cells 20 can be a secondary battery or a primary battery, and can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited thereto. The battery cell 20 can be in a shape of a cylinder, a flat body, a cuboid, or other shapes.

[0059] Please refer to Figure 3 , Figure 3 The battery cell 20 is the smallest unit of the battery 100, and a schematic diagram of a disassembled structure of the battery cell 20 is provided for some embodiments of the present application. Figure 3 The battery cell 20 includes an end cover 21, a shell 22, an electrode assembly 23, and other functional components.

[0060] The end cover 21 is a component that covers the opening of the shell 22 to isolate the internal environment of the battery cell 20 from the external environment. The shape of the end cover 21 can be adapted to the shape of the shell 22 to fit the shell 22, but is not limited thereto. Optionally, the end cover 21 can be made of a material with certain hardness and strength, such as an aluminum alloy, so that the end cover 21 is not easily deformed when subjected to extrusion and collision, and the battery cell 20 can have higher structural strength and safety performance. The end cover 21 can be provided with functional components such as an electrode terminal 21a. The electrode terminal 21a can be used to electrically connect with the electrode assembly 23 to output or input the electric energy of the battery cell 20. In some embodiments, the end cover 21 can also be provided with a pressure relief mechanism for relieving the internal pressure of the battery cell 20 when the internal pressure or temperature reaches a threshold value. The material of the end cover 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not make special limitations thereon. In some embodiments, an insulating piece can also be provided on the inner side of the end cover 21, and the insulating piece can be used to isolate the electrical connection components in the shell 22 from the end cover 21 to reduce the risk of short circuit. The insulating piece can be plastic, rubber, etc.

[0061] The shell 22 is a component for cooperating with the end cover 21 to form an internal environment of the battery cell 20, and the formed internal environment can be used to accommodate the electrode assembly 23, electrolyte and other components. The shell 22 and the end cover 21 can be independent components, and an opening can be provided on the shell 22, and the end cover 21 is used to cover the opening to form the internal environment of the battery cell 20. Without limitation, the end cover 21 and the shell 22 can also be integrated, specifically, the end cover 21 and the shell 22 can form a common connecting surface before other components enter the shell, and when it is necessary to seal the internal environment of the shell 22, the end cover 21 is used to cover the shell 22. The shell 22 can be various shapes and sizes, such as a cuboid, a cylinder, a hexagonal prism, etc. Specifically, the shape of the shell 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the shell 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiments of the present application do not make special limitations.

[0062] The electrode assembly 23 is a component where electrochemical reactions occur in the battery cell 20. One or more electrode assemblies 23 can be contained in the shell 22. The electrode assembly 23 is mainly formed by winding or stacking a positive electrode sheet and a negative electrode sheet, and a separator is usually arranged between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet and the negative electrode sheet have a portion with active material constituting a main body of the electrode assembly 23, and a portion without active material constituting a tab 23a of each of the positive electrode sheet and the negative electrode sheet. The positive electrode tab and the negative electrode tab can be located at one end of the main body or at two ends of the main body respectively. In the charging and discharging process of the battery 100, the positive active material and the negative active material react with the electrolyte, and the tab 23a is connected to the electrode terminal 21a to form a current loop.

[0063] According to some embodiments of the present application, referring to Figure 4 , the present application provides a negative electrode sheet 30, which comprises a current collector 31 and a negative electrode film layer 32, the negative electrode film layer 32 comprises a composite active layer 33 arranged on at least one side surface of the current collector 31, the composite active layer 33 comprises at least one first conductive adhesive layer 332 and at least two negative active material layers along the thickness direction, and the first conductive adhesive layer 332 is located between the adjacent two negative active material layers; wherein from the side of the negative electrode film layer 32 close to the current collector 31 to the side away from the current collector 31, the gram capacity of the negative active material contained in the negative active material layer increases with the increase of the layer number.

[0064] The thickness direction refers to the direction in which the functional layers are stacked.

[0065] The current collector has two opposite surfaces along the thickness direction, and the negative electrode film layer 32 is arranged on at least one side surface of the current collector 31, which means that the negative electrode film layer 32 can be arranged on only one surface, or Figure 4The negative electrode film layer 32 is arranged on the two opposite surfaces of the current collector 31 along the thickness direction.

[0066] The conductive adhesive layer is a film layer formed by curing of a glue solution composed of a conductive agent, an adhesive, and optionally an additive such as a thickening agent or calcium hydroxide for promoting adhesion.

[0067] The negative electrode active material layer refers to a film layer containing a negative electrode active material for reacting with an electrolyte during charging and discharging of the battery. In addition to the negative electrode active material, the negative electrode active material layer can also contain an adhesive, a conductive agent, and a thickening agent.

[0068] It can be understood that, since the composite active layer 33 includes at least one first conductive adhesive layer 332 and at least two negative electrode active material layers along the thickness direction, and the first conductive adhesive layer 332 is located between the two adjacent negative electrode active material layers, the number of negative electrode active material layers in the composite active layer 33 is n, and the number of first conductive adhesive layers 332 is n-1, where n≥2 and is a natural number.

[0069] In the technical solution of the embodiments of the present application, the different gram capacities of the negative electrode active materials are used to cooperate with each other to adjust the total gram capacity of the negative electrode film layer 32, to improve the energy density of the battery. The gram capacity of the negative electrode active material contained in the negative electrode active material layer increases with the increase of the number of layers from the side of the negative electrode film layer 32 close to the current collector 31 to the side of the negative electrode film layer 32 away from the current collector 31, that is, the gram capacity of the outer layer negative electrode active material is greater than that of the inner layer negative electrode active material, so that the battery improves the fast charging performance under the premise of maintaining a better energy density, and the use of the first conductive adhesive layer 332 can alleviate the problem of poor cycle stability of the battery caused by interlayer peeling during charging.

[0070] The current collector 31 is a metal foil or a composite current collector. For example, as a metal foil, a copper foil or an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0071] According to some embodiments of the present application, referring to Figure 4 , the composite active layer 33 includes one first conductive adhesive layer 332 and two negative electrode active material layers.

[0072] The composite active layer has simple structure, low processing difficulty, and can improve the fast charging performance and cycle performance of the battery under the premise of having better energy density.

[0073] According to some embodiments of the present application, referring to Figure 4 The first negative electrode active material layer 331 contains negative electrode active material with a gram capacity of 350-400 mAh / g, and the second negative electrode active material layer 333 contains negative electrode active material with a gram capacity of 1000-3000 mAh / g.

[0074] The second negative electrode active material layer 333 contains negative electrode active material with high gram capacity, which can improve the energy density of the battery when cooperating with the first negative electrode active material layer 331.

[0075] For example, the first negative electrode active material layer 331 contains negative electrode active material with a gram capacity of 350, 360, 370, 380, 390, 400 mAh / g or any value between any two values. The second negative electrode active material layer 333 contains negative electrode active material with a gram capacity of 1000, 1200, 1500, 1700, 2000, 2200, 2500, 2700, 3000 mAh / g or any value between any two values.

[0076] Optionally, the first negative electrode active material layer contains negative electrode active material with a gram capacity of 350-380 mAh / g.

[0077] In some embodiments, the first negative electrode active material layer contains graphite, and the second negative electrode active material layer contains silicon-based material.

[0078] The cooperation of silicon-based active material and graphite can effectively improve the energy density of the battery and the fast charging performance of the battery.

[0079] The graphite includes at least one of natural graphite and artificial graphite.

[0080] The silicon-based active material refers to at least one of silicon element and silicon-containing composite material, wherein the mass percentage of silicon in the silicon-containing composite material is not less than 50%, and the silicon-containing composite material includes at least one of silicon oxide and silicon alloy.

[0081] In some embodiments, the first negative active material layer and the second negative active material layer each comprises a binder; wherein the first negative active material layer has a smaller amount of the binder than the second negative active material layer.

[0082] Since the silicon-based material has a larger volume change during charging than graphite, increasing the amount of the binder in the second negative active material layer can limit the expansion of the second negative active material layer, reduce the rebound of the negative electrode sheet, and improve the cycle performance of the battery.

[0083] The binder includes, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyacrylic acid, polyacrylate, polyacrylonitrile, sodium carboxymethyl cellulose, styrene butadiene rubber, polyurethane, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0084] According to some embodiments of the present application, the first negative active material layer and the second negative active material layer each comprises a conductive agent; wherein the first negative active material layer has the same amount of the conductive agent as the second negative active material layer, and the first negative active material layer has a smaller electrical conductivity of the conductive agent than the second negative active material layer.

[0085] Since the electrical conductivity of the silicon-based active material is small, and the electrical conductivity of graphite is large, the above-mentioned method is beneficial to improve the electrical conductivity of the second negative active material layer, alleviate the poor interlayer conduction, and improve the cycle performance of the battery.

[0086] The conductive agent includes, but is not limited to, at least one of super-conductive carbon, acetylene black, carbon black (Super P), Ketjen black, carbon dots, carbon nanotubes (CNT), carbon nanofibers (VGCF), and graphene.

[0087] Since the electrical conductivity of the conductive agent in the first negative active material layer is smaller than that in the second negative active material layer, the conductive agent in the second negative active material layer is at least one of a one-dimensional conductive agent and a two-dimensional conductive agent, the one-dimensional conductive agent has a one-dimensional fibrous structure, the two-dimensional conductive agent has a two-dimensional planar structure, the one-dimensional conductive agent includes at least one of carbon fibers and carbon nanotubes, and the two-dimensional conductive agent includes graphene, when the conductive agent in the first negative active material layer is a zero-dimensional conductive agent (such as super-conductive carbon, acetylene black, carbon black, Ketjen black, and carbon dots).

[0088] According to some embodiments of the present application, the thickness of the first negative active material layer is 140-210 μm.

[0089] In the above-mentioned thickness range, the battery has better cycle performance and fast charging performance.

[0090] Exemplarily, the thickness of the first negative active material layer is any one of 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 199 μm, 200 μm, 210 μm or between any two values.

[0091] Optionally, the thickness of the first negative active material layer is 140-199 μm.

[0092] According to some embodiments of the present application, the thickness of the second negative active material layer is 1-60 μm.

[0093] Within the above thickness range, the battery has better cycle performance and fast charging performance.

[0094] Exemplarily, the thickness of the second negative active material layer is any one of 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm or between any two values.

[0095] According to some embodiments of the present application, the thickness of the first conductive binder layer accounts for 0.98%-5.75% of the thickness of the negative electrode film layer, and the thickness of the first conductive binder layer is not less than 1 μm.

[0096] With the thickness of the first conductive binder layer within a reasonable range, the cycle performance and fast charging performance of the battery are improved. If the thickness is too large, the lithium ion transmission rate is affected. If the thickness is too small, the two negative active material layers cannot be stably bonded.

[0097] Exemplarily, the thickness of the first conductive binder layer accounts for any one of 0.98%, 1.00%, 2.00%, 3.00%, 4.00%, 5.00%, 5.78% of the thickness of the negative electrode film layer or between any two values, and the thickness of the first conductive binder layer is not less than 1 μm.

[0098] Optionally, the thickness of the first conductive binder layer is 1-10 μm.

[0099] According to some embodiments of the present application, please refer to Figure 4 The negative electrode film layer 32 further comprises a second conductive binder layer 34, which is formed on the side of the composite active layer 33 away from the current collector 31.

[0100] With the arrangement of the second conductive binder layer 34, the negative active material layer on the side of the composite active layer 33 away from the current collector 31 can be protected. When the negative active material layer on the side of the composite active layer 33 away from the current collector 31 contains a silicon-based active material, the electrical conductivity can be improved by the arrangement of the second conductive binder layer 34 due to the poor electrical conductivity of the silicon-based active material, thereby improving the fast charging performance of the battery.

[0101] In some embodiments, the second conductive binder layer has an electrical conductivity of 10 3 -10 7 S / cm.

[0102] When the negative active material layer on the side of the composite active layer facing away from the current collector contains a silicon-based active material, the use of the second conductive binder layer with the above electrical conductivity range can effectively improve the fast charging performance of the battery.

[0103] Illustratively, the second conductive binder layer has an electrical conductivity of 10 3 S / cm, 10 4 S / cm, 10 5 S / cm, 10 6 S / cm, 10 7 S / cm.

[0104] According to some embodiments of the present application, the electrical conductivity of the second conductive binder is greater than the electrical conductivity of the first conductive binder layer.

[0105] Due to the different positions of the second conductive binder layer and the first conductive binder layer, the use of the above arrangement is beneficial to improve the cycle performance and fast charging performance of the battery.

[0106] According to some embodiments of the present application, the second conductive binder layer and the first conductive binder layer both include a conductive agent, the amount of the conductive agent in the second conductive binder layer is the same as the amount of the conductive agent in the first conductive binder layer, and the electrical conductivity of the conductive agent in the second conductive binder layer is greater than the electrical conductivity of the conductive agent in the first conductive binder layer.

[0107] The use of the above arrangement can quickly adjust and achieve the electrical conductivity of the second conductive binder layer being greater than the electrical conductivity of the first conductive binder layer, thereby improving the cycle performance and fast charging performance of the battery.

[0108] Optionally, the second conductive binder layer and the first conductive binder layer both include a conductive agent, a binder, and an auxiliary agent in a mass ratio of 78-90:10-12:0-10, respectively, and the auxiliary agent is, for example, a thickening agent or calcium hydroxide for increasing viscosity.

[0109] According to some embodiments of the present application, the conductive agent in the second conductive binder layer includes at least one of a one-dimensional conductive agent and a two-dimensional conductive agent.

[0110] Since the second conductive binder layer is located on the side of the composite active layer facing away from the current collector, the use of the one-dimensional conductive agent and the two-dimensional conductive agent is beneficial to inhibit the swelling of the composite active layer and to improve the electrical conductivity of the second conductive binder layer, thereby improving the cycle performance and fast charging performance of the battery.

[0111] The one-dimensional conductive agent has a one-dimensional fibrous structure, and the two-dimensional conductive agent has a two-dimensional planar structure.

[0112] Optionally, the one-dimensional conductive agent includes at least one of carbon fibers and carbon nanotubes; and optionally, the two-dimensional conductive agent includes graphene.

[0113] According to some embodiments of the present application, the thickness of the second conductive binder is 0.98%-5.75% of the thickness of the negative electrode film layer, and the thickness of the second conductive binder layer is not less than 1 μm.

[0114] With the thickness of the second conductive binder layer being within a reasonable range, it is beneficial to avoid peeling of the composite active layer from the current collector and improve the cycle performance of the battery.

[0115] For example, the thickness of the second conductive binder layer is any one of 0.98%, 1.00%, 2.00%, 3.00%, 4.00%, 5.00%, 5.78% of the thickness of the negative electrode film layer or between any two values, and the thickness of the second conductive binder layer is not less than 1 μm.

[0116] Optionally, the thickness of the second conductive binder layer is 1-10 μm.

[0117] According to some embodiments of the present application, please refer to Figure 4 , the negative electrode sheet 30 includes a current collector 31 and a negative electrode film layer 32, the negative electrode film layer 32 includes a composite active layer 33 disposed on at least one side surface 31 of the current collector and a second conductive binder layer 34, from the side close to the current collector 31 to the side away from the current collector 31, the composite active layer 33 includes a first negative electrode active material layer 331 disposed on the surface of the current collector 31, a first conductive binder layer 332 stacked on the surface of the first negative electrode active material layer 331, and a second negative electrode active material layer 333 stacked on the surface of the first conductive binder layer 332, wherein the second conductive binder layer 34 is disposed on the surface of the second negative electrode active material layer 333. The negative electrode active material in the first negative electrode active material layer 331 is graphite, the negative electrode active material in the second negative electrode active material layer 333 is a silicon-based active material, and the electrical conductivity of the second conductive binder layer 34 is greater than that of the first conductive binder layer 332.

[0118] According to some embodiments of the present application, the present application also provides a battery including the battery monomer of any one of the above schemes.

[0119] According to some embodiments of the present application, the present application also provides a power consuming device including the battery monomer and / or the battery of any one of the above schemes, and the battery monomer and / or the battery are used to provide electrical energy to the power consuming device.

[0120] The power consuming device can be a device or system of any one of the above applications.

[0121] Some specific embodiments are listed below to better illustrate the present application.

[0122] Example 1

[0123] Preparation of the negative electrode sheet

[0124] Current collector: aluminum foil

[0125] Artificial graphite, carbon black, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were stirred and dispersed in deionized water in a mass ratio of 95:1:2:2 to form a first slurry.

[0126] Styrene-butadiene rubber (SBR), carbon black, and calcium hydroxide were stirred and dispersed in N-methyl pyrrolidone in a mass ratio of 10:80:10 to form a second slurry.

[0127] Silicon-carbon composite material (gravimetric capacity of 2000 mAh / g), carbon nanotubes, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were stirred and dispersed in deionized water in a mass ratio of 94:1:2:3 to form a third slurry.

[0128] Styrene-butadiene rubber (SBR), conductive agent, and calcium hydroxide were stirred and dispersed in N-methyl pyrrolidone in a mass ratio of 10:80:10 to form a fourth slurry.

[0129] The first slurry was coated on the current collector to form a first coating layer, then the second slurry was coated on the first coating layer to form a second coating layer, then the third slurry was coated on the second coating layer to form a third coating layer, and then the fourth slurry was coated on the third coating layer to form a fourth coating layer, followed by drying at 80°C, and then cold pressing to obtain a negative electrode sheet 30 as shown in Figure 4 The negative electrode sheet 30 includes a current collector 31 and a negative electrode film layer 32, and the negative electrode film layer 32 includes, from the side close to the current collector 31 to the side away from the current collector 31, a first negative electrode active material layer 331, a first conductive binder layer 332, a second negative electrode active material layer 333, and a second conductive binder layer 34 arranged in sequence.

[0130] Preparation of the positive electrode sheet

[0131] The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2, conductive agent Super-P, and binder polyvinylidene fluoride were stirred and dispersed in N-methyl pyrrolidone in a mass ratio of 96:2:2 to form a positive electrode slurry, which was coated on a positive electrode current collector aluminum foil, and then cold pressed to obtain a positive electrode sheet.

[0132] Preparation of the electrolyte

[0133] In a mixed solvent of ethylene carbonate (EC) and methyl ethyl carbonate (EMC) with a mass ratio of 35:65, lithium salt LiPF6 was added and uniformly mixed to obtain an electrolyte, wherein the molar concentration of LiPF6 in the electrolyte was 1 mol / L.

[0134]

Separator

[0135] A 12 μm thick polyethylene porous film was selected.

[0136]

Preparation of lithium ion battery

[0137] The above negative electrode sheet, the separator and the positive electrode sheet were stacked in order, with the separator between the positive and negative electrode sheets to play a separating role, and were wound to obtain a bare battery cell, which was then inserted into a battery shell, and subjected to processes of baking, liquid injection, standing, packaging, formation and capacity distribution to obtain a lithium ion battery.

[0138] Examples 2-16 and Comparative Example 1-2

[0139] The difference from Example 1 is only that the negative electrode sheet parameters shown in Table 1 are different.

[0140] In Example 15, no second conductive adhesive layer was provided.

[0141] In Example 16, artificial graphite, carbon black, sodium carboxymethyl cellulose and butadiene-styrene rubber were stirred and dispersed in deionized water in a mass ratio of 94:1:2:3 to serve as a first slurry.

[0142] The difference between Comparative Example 1 and Example 1 is only that the positions of the first negative electrode active material layer and the second negative electrode active material layer are exchanged.

[0143] In Comparative Example 2, no first conductive adhesive layer was provided.

[0144]

Performance determination of lithium ion batteries prepared from each example and comparative example

[0145] (1) Cycle performance test of battery

[0146] The lithium ion batteries prepared from each example and comparative example were respectively charged at 1C rate and discharged at 1C rate at 25℃ to perform full charge and full discharge cycle test until the capacity of the battery was attenuated to 80% of the initial capacity, and the cycle number was recorded, in cycles.

[0147] (2) Capacity test of battery

[0148] The lithium ion battery prepared in each example and comparative example was discharged at 1C rate to the lower limit of voltage at 25℃, and then charged to the upper limit of voltage at 1 / 3C and 1C rate in turn (without CV charging), and the 1 / 3C capacity and 1C capacity were recorded.

[0149] (3) Test method of direct current resistance (DCR)

[0150] The lithium ion battery was charged at 1.5C constant current to 4.45V at 25℃, and then charged at 4.45V constant voltage to 0.05C, and then rested for 30 minutes. Then, it was discharged at 0.1C for 10 seconds, and the voltage value U1 was recorded; then it was discharged at 1C for 360 seconds, and the voltage value U2 was recorded. "1C" is the current value that completely discharges the battery capacity within 1 hour. The direct current resistance R of the lithium ion battery was calculated according to the following formula: R = (U2-U1) / (1C-0.1C). Unless otherwise specified, the DCR of the lithium ion battery in this application is tested at 10% state of charge (SOC), and the unit is Ω.

[0151] (4) Weight energy density

[0152] The lithium ion battery was charged and discharged at 1C / 1C rate and voltage range of 2.5-4.25V on a new wei tester at 25℃, and the weight energy density of the battery was calculated by dividing the energy released during the first cycle of charge and discharge by the weight of the battery, and the unit was Wh / kg.

[0153] (5) Fast charging performance:

[0154] The preparation of three-electrode battery and lithium plating was the same as the preparation method of the lithium ion battery, and the copper wire was connected to the battery as a reference electrode during the preparation of the lithium ion battery. The negative electrode was plated with lithium at a current of 20μA for 6h, and then charged at the same rate at 25℃, and the anode potential was recorded.

[0155] Under the same rate, the higher the anode potential, the better the fast charging performance.

[0156] Table 1 negative electrode sheet

[0157]

[0158]

[0159] Table 2 performance test results

[0160]

[0161] According to Table 1 and Table 2, the negative electrode sheet provided by the application can improve the fast charging performance and cycle stability of the battery under the premise of making the battery have better weight energy density.

[0162] According to embodiments 1-3, it can be seen that the selection of the conductive agent in the second conductive binder layer affects the conductivity of the negative electrode film layer, thereby affecting the direct current resistance, cycle number and fast charging performance of the battery. When the conductive agent in the second conductive binder layer is carbon nanotubes and graphene, the battery has better cycle performance and fast charging performance.

[0163] The difference between embodiments 1, 4 and 5 is only that the gram capacity of the artificial graphite added in the first negative electrode active material layer is different. It can be seen that when the gram capacity of the negative electrode active material in the first negative electrode active material layer is 350-380 mAh / g, the battery has better cycle performance and fast charging performance.

[0164] The difference between embodiments 1, 6-8 is that the thickness of the first conductive binder layer and the thickness of the second conductive binder layer are changed. It can be seen that when the thickness of the first conductive binder layer / thickness of the second conductive binder layer is 0.98%-5.75% of the total thickness of the negative electrode film layer, the battery has better cycle performance and fast charging performance.

[0165] The difference between embodiments 1, 9-11 is that the thickness of the second negative electrode active material layer is different. When the thickness of the second negative electrode active material layer is 1-65 μm, optionally 5-65 μm, the battery has better cycle performance and fast charging performance.

[0166] The difference between embodiments 1, 12-14 is that the thickness of the first negative electrode active material layer is different. When the thickness of the first negative electrode active material layer is 140-210 μm, optionally 140-199 μm, the battery has better cycle performance and fast charging performance.

[0167] The difference between embodiment 15 and embodiment 1 is that embodiment 15 does not set the second conductive binder layer. It can be seen that the setting of the second conductive binder layer can effectively improve the fast charging performance of the battery.

[0168] In embodiment 16, although the raw material ratio of the first negative electrode active material layer is changed, the battery still has better fast charging performance and cycle stability.

[0169] Comparative example 1 and embodiment 1 are compared, and the positions of the first negative electrode active material layer and the second negative electrode active material layer are exchanged. In comparative example 1, the negative electrode film layer includes, from the side close to the current collector to the side away from the current collector, the second negative electrode active material layer, the first conductive binder layer, the first negative electrode active material layer and the second conductive binder layer arranged in turn. It can be seen from the comparison between comparative example 1 and embodiment 1 that the exchange of the order causes the cycle number and the fast charging performance of the battery to decrease.

[0170] Comparative Example 2, which lacks the first electrically conductive adhesive layer, shows a significant decrease in cycle count as compared to Example 1.

[0171] Finally, it should be noted that the above examples are merely intended to illustrate the technical solutions of the present application, and are not intended to limit the same. Even though the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that modifications can still be made to the technical solutions described in the foregoing examples, or some or all of the technical features thereof can be replaced equivalently, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the examples of the present application, and they should all be encompassed within the scope of the claims and the specification of the present application. In particular, the technical features mentioned in each of the examples can be combined in any manner as long as there is no structural conflict. The present application is not limited to the specific examples disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A negative electrode sheet, characterized in that, The device includes a current collector and a negative electrode film layer. The negative electrode film layer includes a composite active layer and a second conductive binder layer disposed on at least one surface of the current collector. The second conductive binder layer is formed on the side of the composite active layer facing away from the current collector. The composite active layer includes a first conductive binder layer and two negative electrode active material layers along its thickness direction. The first conductive binder layer is located between two adjacent negative electrode active material layers. Wherein, from the side of the negative electrode film layer closest to the current collector to the side away from the current collector, the specific capacity of the negative electrode active material contained in the negative electrode active material layer increases with the increase of the number of layers; The two negative electrode active material layers are respectively used as the first negative electrode active material layer and the second negative electrode active material layer. The negative electrode active material contained in the first negative electrode active material layer includes graphite; the negative electrode active material contained in the second negative electrode active material layer includes silicon-based material. Both the first negative electrode active material layer and the second negative electrode active material layer include a binder, and the amount of binder added in the first negative electrode active material layer is less than the amount of binder added in the second negative electrode active material layer. The thickness of the first negative electrode active material layer is 140-210 μm, and the thickness of the second negative electrode active material layer is 5-65 μm.

2. The negative electrode sheet according to claim 1, characterized in that, The first negative electrode active material layer contains a specific capacity of 350mAh / g-400mAh / g, and the second negative electrode active material layer contains a specific capacity of 1000mAh / g-3000mAh / g.

3. The negative electrode sheet according to claim 2, characterized in that, The specific capacity of the negative electrode active material contained in the first negative electrode active material layer is 350mAh / g-380mAh / g.

4. The negative electrode sheet according to claim 1, characterized in that, Both the first negative electrode active material layer and the second negative electrode active material layer include a conductive agent; Wherein, the amount of conductive agent added in the first negative electrode active material layer is equal to the amount of conductive agent added in the second negative electrode active material layer, and the conductivity of the conductive agent in the first negative electrode active material layer is less than the conductivity of the conductive agent in the second negative electrode active material layer.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The thickness of the first negative electrode active material layer is 140-199 μm.

6. The negative electrode sheet according to any one of claims 1-4, characterized in that, The thickness of the first conductive adhesive layer is 0.98%-5.75% of the total thickness of the negative electrode film layer, and the thickness of the first conductive adhesive layer is not less than 1 μm.

7. The negative electrode sheet according to claim 6, characterized in that, The thickness of the first conductive adhesive layer is 1-10 μm.

8. The negative electrode sheet according to any one of claims 1-4, characterized in that, The conductivity of the second conductive adhesive layer is 10. 3 -10 7 S / cm.

9. The negative electrode sheet according to any one of claims 1-4, characterized in that, The conductivity of the second conductive adhesive layer is greater than that of the first conductive adhesive layer.

10. The negative electrode sheet according to any one of claims 1-4, characterized in that, Both the second conductive adhesive layer and the first conductive adhesive layer include a conductive agent. The amount of conductive agent added in the second conductive adhesive layer is the same as that in the first conductive adhesive layer. The conductivity of the conductive agent in the second conductive adhesive layer is greater than that of the conductive agent in the first conductive adhesive layer.

11. The negative electrode sheet according to claim 10, characterized in that, The conductive agent in the second conductive adhesive layer is at least one of a one-dimensional conductive agent and a two-dimensional conductive agent.

12. The negative electrode sheet according to claim 11, characterized in that, The one-dimensional conductive agent includes at least one of carbon nanotubes and carbon fibers; and / or, The two-dimensional conductive agent includes graphene.

13. The negative electrode sheet according to any one of claims 1-4, characterized in that, The thickness of the second conductive adhesive layer is 0.98%-5.75% of the total thickness of the negative electrode film layer, and the thickness of the second conductive adhesive layer is not less than 1 μm.

14. The negative electrode sheet according to claim 13, characterized in that, The thickness of the second conductive adhesive layer is 1-10 μm.

15. A single battery cell, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-14.

16. A battery, characterized in that, Includes the battery cell as described in claim 15.

17. An electrical appliance, characterized in that, Includes the battery cell as described in claim 15 and / or the battery as described in claim 16, wherein the battery cell and / or the battery is used to provide electrical energy to the electrical device.

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