Negative electrode sheet, lithium-ion battery monomer, lithium-ion battery and electrical equipment

Abstract

The present application provides a negative electrode plate, a lithium-ion battery cell, a lithium-ion battery and an electrical device, and relates to the field of batteries. The negative electrode plate includes: a current collector and a lithium-free negative electrode film layer, the lithium-free negative electrode film layer is coated on the surface of the current collector, the lithium-free negative electrode film layer contains a first negative electrode active material, the first negative electrode active material includes a hollow hollow carbon material and a lithium-philic substance, and the lithium-philic substance is not loaded with lithium metal, and the lithium-philic substance is loaded on the inner surface of the hollow carbon material. The above-mentioned negative electrode plate can be directly used as a negative electrode of a lithium-ion battery in which the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate is less than 1, so as to suppress the dendrites generated during the deposition / precipitation of lithium metal during the charging process, improve the cycle life and coulomb efficiency of the battery, and the lithium-free setting of the negative electrode plate can further significantly improve the energy density of the battery.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to a negative electrode plate, a lithium-ion battery cell, a lithium-ion battery, and electrical equipment. Background Art

[0002] When existing lithium-ion batteries are fully charged, lithium metal is easily deposited on the surface of the negative electrode plate, which is easy to form lithium dendrites. A large number of lithium dendrites cause damage to the SEI film, reducing the energy density and coulomb efficiency of the battery, and may pierce the diaphragm to cause an internal short circuit in the battery, bringing safety hazards and limiting its cycle life. The commonly used method is to pre-store excess lithium metal in the negative electrode to supplement the consumption of active lithium during the cycle. However, this method will reduce the energy density of the battery. Summary of the invention

[0003] In view of the above problems, the present application proposes a negative electrode plate, a lithium-ion battery cell, a lithium-ion battery and an electrical device, which can improve the technical problems of the lithium-ion battery's negative electrode being prone to lithium dendrites and the low battery energy density.

[0004] In the first aspect, an embodiment of the present application provides a negative electrode plate, which includes: a current collector and a lithium-free negative electrode film layer, the lithium-free negative electrode film layer is coated on the surface of the current collector, the lithium-free negative electrode film layer contains a first negative electrode active material, the first negative electrode active material includes a hollow carbon material and a lithium-philic substance, and the lithium-philic substance is not loaded with lithium metal, and the lithium-philic substance is loaded on the inner surface of the hollow carbon material.

[0005] In the technical solution of the embodiment of the present application, the negative electrode plate can be directly used as the negative electrode of a lithium-ion battery in which the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate is less than 1, so that during the charging process, the hollow carbon material is used as a supporting skeleton, which not only provides a storage space for lithium metal, but also buffers the volume change of the negative electrode plate during the deposition / dissolution of lithium metal, and limits the generation of lithium dendrites. On the other hand, it has conductivity and can induce the uniform deposition of lithium metal. The lithium deposition site is optimized by using a lithium-philic substance, and lithium ions are induced to enter the interior of the hollow carbon material and deposit evenly on the lithium-philic substance, effectively inhibiting the dendrites generated during the deposition / precipitation of lithium metal, greatly reducing the danger of the lithium metal negative electrode, and can improve the cycle life and coulomb efficiency of the battery, reduce voltage polarization, and the lithium-free setting of the negative electrode plate can further significantly improve the energy density of the battery.

[0006] In some embodiments, the number of wall layers of the hollow carbon material is ≥ 2. That is, the hollow carbon material is a multi-walled hollow carbon material, which facilitates lithium metal to enter the hollow carbon material.

[0007] In some embodiments, the lithium metal potential is 0 V, and the lithium plating overpotential of the first negative electrode active material is less than 0 V and not less than -0.03 V. Within the above range, the first negative electrode active material has a lithium affinity to lithium metal, so that lithium ions are selectively induced to enter the hollow carbon material and uniformly deposited in the hollow carbon material to connect with the lithium affinity material.

[0008] In some embodiments, the hollow carbon material has an inner surface forming a cavity, and at least one opening penetrating the inner surface and communicating with the cavity. The above arrangement, utilizing the at least one opening, facilitates loading the lithium-philic substance into the hollow carbon material, thereby reducing the difficulty of preparation.

[0009] Optionally, the hollow carbon material is in a tubular shape. The tubular hollow carbon material itself can become a conductive path, which is conducive to the uniform deposition of lithium metal in the hollow carbon material.

[0010] In some embodiments, the lithiophilic substance is at least one of a lithiophilic metal and a compound thereof. Those skilled in the art may select the lithiophilic substance according to actual needs to achieve the lithiophilicity of the first negative electrode active material.

[0011] In some embodiments, the lithium-philic metal includes at least one of Au, Ag, Zn, Fe, Co, Ni, Ga, Sn, In, Ge, Ti, Mu, Pt, Al, and Mg. The above lithium-philic metals all have obvious lithium affinity to lithium metal, which can reduce the nucleation overpotential of lithium metal on the negative electrode sheet, facilitate the nucleation of lithium ions in the hollow carbon material, realize the uniform deposition of lithium metal in the hollow carbon material, and effectively inhibit the formation of lithium dendrites.

[0012] In some embodiments, the mass content of the lithium-philic metal in the first negative electrode active material is 0.5%-20%, and can be 2%-10%. The lithium-philic metal content within the above range is reasonable, so that the first negative electrode active material has a good lithium-philic effect, which can improve the initial coulombic efficiency and cycle life.

[0013] In some embodiments, the lithium-philic metal compound includes one or more of oxides, sulfides, fluorides, nitrides, chlorides, and carbides. The above lithium-philic metal compounds all have obvious lithium affinity for lithium metal, which can reduce the nucleation overpotential of lithium metal on the negative electrode plate, facilitate the nucleation of lithium ions in the hollow carbon material, and can achieve uniform deposition of lithium metal in the hollow carbon material, effectively inhibiting the formation of lithium dendrites.

[0014] In some embodiments, the mass content of the lithium-philic metal compound in the first negative electrode active material is 0.5%-30%, optionally 3%-15%, calculated as metal element. The lithium-philic effect is good within the above range and the cycle life can be improved.

[0015] In some embodiments, the lithium-free negative electrode film layer contains a second negative electrode active material and a conductive agent, wherein the lithium metal potential is 0 V, and the lithium precipitation overpotential of the second negative electrode active material is less than 0 V and not less than -0.5 V. On the one hand, the second negative electrode activity is less than 0 V and not less than -0.5 V, so that its lithium precipitation overpotential matches the lithium metal potential, so that when the above-mentioned negative electrode plate is directly used as the negative electrode of a lithium ion battery with a total capacity ratio of the negative electrode plate to the total capacity of the positive electrode plate less than 1, it is conducive to forming a lithium metal composite negative electrode during the charging process. On the other hand, the gaps between the second negative electrode active materials can provide space for lithium deposition, and the conductive agent can effectively and evenly deposit lithium ions, thereby reducing the deposition of lithium metal on the surface of the negative electrode plate, and forming a more uniform composite lithium metal negative electrode.

[0016] Optionally, the second negative electrode active material is at least one of a carbon-based material, a silicon-based material and a metal oxide. The lithium plating overpotential of the negative electrode active material can easily meet the above requirements and is easy to obtain.

[0017] In some embodiments, the lithium-free negative electrode film layer includes: at least two film layers stacked in the thickness direction, each film layer contains the second negative electrode active material, and at least one film layer contains the first negative electrode active material. The above configuration is simple to prepare, and the lithium-free negative electrode film layer can also be provided with the first negative electrode active material only in part of the film layer, or in all the film layers, according to actual needs, thereby expanding the specific configuration of the lithium-free negative electrode film layer.

[0018] In some embodiments, the lithium-free negative electrode film layer includes: a first film layer and a second film layer, the first film layer and the second film layer are alternately stacked in the thickness direction, the first film layer contains the second negative electrode active material and the first negative electrode active material, the second film layer contains the second negative electrode active material and does not contain the first negative electrode active material; the side of the lithium-free negative electrode film layer connected to the current collector is the first film layer. Using the side of the lithium-free negative electrode film layer connected to the current collector as the first film layer is conducive to the deposition of lithium metal in the direction close to the current collector, reducing lithium dendrites on the surface of the negative electrode sheet.

[0019] In some embodiments, the amount of the first negative electrode active material added to the lithium-free negative electrode film layer is 0.125%-5% by mass. Within the above range, the formation of lithium dendrites can be effectively suppressed, and the battery cycle life is good. If the amount added is too little, the effect of reducing lithium dendrites on the surface of the negative electrode plate is limited. If the amount added is too much, the cycle life is poor.

[0020] In some embodiments, the lithium-free negative electrode film layer includes: a third film layer, the third film layer contains the first negative electrode active material and does not contain the second negative electrode active material. That is to say, in actual use, only the third film layer can be used as the lithium-free negative electrode film layer, or a multi-layer arrangement with part of the third film layer can be used, thereby expanding the specific arrangement method of the lithium-free negative electrode film layer.

[0021] In some embodiments, the lithium-free negative electrode film layer further includes: a fourth film layer, the third film layer and the fourth film layer are alternately stacked along the thickness direction of the lithium-free negative electrode film layer, the fourth film layer contains the second negative electrode active material and does not contain the first negative electrode active material, and the side of the lithium-free negative electrode film layer connected to the current collector is the third film layer. The introduction of the second negative electrode active material in the fourth film layer is beneficial to improving the battery cycle life, and the side of the lithium-free negative electrode film layer connected to the current collector is the third film layer, which is beneficial to the deposition of lithium metal in the direction close to the current collector, reducing lithium dendrites on the surface of the negative electrode sheet.

[0022] In some embodiments, the amount of the first negative electrode active material added to the third film layer is 10%-60% by mass. Within the above range, the formation of lithium dendrites can be effectively suppressed, and the battery cycle life is good. If the amount added is too little, the effect of reducing lithium dendrites on the surface of the negative electrode plate is limited. If the amount added is too much, the cycle life is poor.

[0023] In a second aspect, the present application provides a lithium-ion battery cell, which includes a positive electrode plate and a negative electrode plate provided in the above embodiment, and the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate is N / P, where N / P<1; optionally, 0.4≤N / P<1.

[0024] In the technical solution of the embodiment of the present application, since the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate is N / P<1, that is, lithium-rich material is used as the positive electrode active material, so that the amount of lithium ions in the positive electrode plate is much greater than the amount of lithium ions that the negative electrode plate can accommodate, after one cycle, the excess lithium in the positive electrode is stored in the negative electrode in the form of lithium metal, and the active lithium consumed by side reactions in the subsequent cycle process is supplemented to obtain high coulomb efficiency and cycle life. And during the assembly process of the battery and the initial state after the assembly is completed, the battery does not contain lithium metal, which greatly reduces the cost and safety hazards of the assembly and storage and transportation processes. And within the above-mentioned N / P value range, a better cycle life and a higher energy density can be taken into account. If the N / P value is too small, the lithium metal content is high and the battery cycle is poor; if the N / P value is too large, the lithium metal content is low and the energy density is low.

[0025] In some embodiments, after the lithium-ion battery cell is discharged, the lithium-philic substance of the negative electrode plate is not loaded with lithium metal. Under the above settings, since the negative electrode plate is a lithium-free negative electrode film layer, after the lithium-ion battery cell is discharged, the lithium-philic substance of the negative electrode plate is not loaded with lithium metal, and after the lithium-ion battery cell is charged, the lithium-philic substance of the negative electrode plate is loaded with lithium metal, thereby replenishing the active lithium consumed by side reactions in the subsequent cycle process, so as to obtain high coulombic efficiency and cycle life.

[0026] In a third aspect, the present application provides a lithium-ion battery, which includes a box and a plurality of lithium-ion battery cells provided by the above embodiments, wherein the plurality of lithium-ion battery cells are accommodated in the box.

[0027] In a fourth aspect, the present application provides an electrical device, which includes the lithium-ion battery in the above embodiment, and the lithium-ion battery is used to provide electrical energy.

[0028] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0030] Figure 1 A schematic diagram of the structure of a vehicle according to some embodiments of the present application;

[0031] Figure 2 A schematic diagram of the exploded structure of a lithium-ion battery according to some embodiments of the present application;

[0032] Figure 3 A schematic diagram of the exploded structure of a lithium-ion battery cell according to some embodiments of the present application;

[0033] Figure 4 A schematic diagram of the negative electrode structure of some embodiments of the present application;

[0034] Figure 5 A schematic diagram of the negative electrode structure of some embodiments of the present application;

[0035] Figure 6 Schematic diagram of the negative electrode structure of some embodiments of the present application.

[0036] The reference numerals in the specific implementation manner are as follows:

[0037] 1000-Vehicles;

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

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

[0040] 20-lithium-ion battery cell; 21-end cover; 21a-electrode terminal; 22-housing; 23-electrode assembly; 23a-electrode ear;

[0041] 24 - negative electrode plate; 241 - current collector; 243 - lithium-free negative electrode film layer; 244 - first film layer; 245 - second film layer; 246 - third film layer; 247 - fourth film layer. DETAILED DESCRIPTION

[0042] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0044] 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 "multiple" is more than two, unless otherwise clearly and specifically defined.

[0045] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0046] 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, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0047] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0048] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0049] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill 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.

[0050] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0051] The inventors have noticed that the following problems exist in the actual use of lithium-ion batteries: (1) Lithium dendrites are easily generated during the charge and discharge process of the battery. A large amount of lithium dendrites damage the SEI film, reduce the coulombic efficiency of the battery, and may pierce the diaphragm to cause an internal short circuit in the battery, posing a safety hazard; (2) Lithium metal will produce an infinite relative volume change during repeated deposition / dissolution, which will lead to serious rupture of the solid electrolyte membrane (SEI). Due to the extremely high reactivity of lithium metal, the exposed fresh lithium metal will immediately react with the electrolyte. The repeated rupture / repair of the SEI membrane will lead to the continuous consumption of active substances and electrolytes, resulting in lower cycle coulombic efficiency and short cycle life. In order to solve the above problems, the commonly used method is to pre-store excess lithium metal in the negative electrode to supplement the consumption of active lithium during the cycle. However, this method will reduce the energy density of the battery.

[0052] In order to alleviate the generation of lithium dendrites and the electrode volume effect, as well as to improve the energy density of the battery, the applicant has found that a non-lithiation setting of the negative electrode plate can be adopted and a hollow carbon material containing a lithium-philic substance can be introduced into the negative electrode plate, and the N / P value can be adjusted so that the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate is less than 1, that is, the amount of lithium ions in the positive electrode plate is much larger than the amount of lithium ions that the negative electrode plate can accommodate. Then, during the charging process, the excess lithium ions in the positive electrode plate can be combined with the lithium-philic substance in the hollow carbon material in the form of lithium metal, and finally a composite lithium metal material is formed, which effectively buffers the volume change of the negative electrode plate during the deposition / dissolution of lithium metal, and effectively inhibits the dendrites generated during the deposition / precipitation of lithium metal, thereby improving the safety performance, cycle life and energy density of the battery.

[0053] Based on the above considerations, in order to solve the problem of alleviating the generation of lithium dendrites and the electrode volume effect, as well as improving the energy density of the battery, the inventors have designed a negative electrode plate after in-depth research, which includes: a current collector and a lithium-free negative electrode film layer, the lithium-free negative electrode film layer is coated on the surface of the current collector, the lithium-free negative electrode film layer contains a first negative electrode active material, the first negative electrode active material includes a hollow carbon material and a lithium-philic substance, and the lithium-philic substance is not loaded with lithium metal, and the lithium-philic substance is loaded on the inner surface of the hollow carbon material.

[0054] When the above-mentioned negative electrode plate is directly used as the negative electrode of a lithium-ion battery in which the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate is less than 1, the hollow carbon material can be used as a supporting skeleton during the charging process, which not only provides a storage space for lithium metal, but also buffers the volume change of the negative electrode plate during the deposition / dissolution of lithium metal, thereby limiting the generation of lithium dendrites; the lithium-philic substance can be used to optimize the lithium deposition site, induce lithium ions to enter the interior of the hollow carbon material and evenly deposit on the lithium-philic substance, effectively inhibit the dendrites generated during the deposition / precipitation of lithium metal, greatly reduce the danger of the lithium metal negative electrode, improve the cycle life and coulomb efficiency of the battery, reduce voltage polarization, and the lithium-free setting of the negative electrode plate can further significantly improve the energy density of the battery.

[0055] The lithium-ion battery cell disclosed in the embodiment of the present application can be used in, but not limited to, electric devices such as vehicles, ships or aircraft. A power supply system comprising the lithium-ion battery cell and battery disclosed in the present application can be used to form the electric device, which is conducive to improving the lithium dendrites that are easy to be generated at the negative electrode of the lithium-ion battery and the low energy density of the battery, thereby improving the stability of the battery performance and the battery life.

[0056] The embodiment of the present application provides an electric device using a lithium-ion battery as a power source, and the electric device may be, but is not limited to, a mobile phone, a tablet, a laptop, an electric toy, an electric tool, a battery car, an electric car, a ship, a spacecraft, etc. Among them, the electric toy may include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, etc., and the spacecraft may include an airplane, a rocket, a space shuttle, and a spacecraft, etc.

[0057] For the convenience of description, the following embodiments are described by taking a vehicle 1000 as an example of an electrical device according to an embodiment of the present application.

[0058] Please refer to Figure 1 , Figure 1 A schematic diagram of the structure of a vehicle 1000 provided for some embodiments of the present application. The vehicle 1000 may be a fuel vehicle, a gas vehicle or a new energy vehicle, and the new energy vehicle may be a pure electric vehicle, a hybrid vehicle or an extended-range vehicle, etc. A lithium-ion battery 100 is provided inside the vehicle 1000, and the lithium-ion battery 100 may be provided at the bottom, head or tail of the vehicle 1000. The lithium-ion battery 100 may be used to power the vehicle 1000, for example, the lithium-ion battery 100 may be used as an operating power source for the vehicle 1000. The vehicle 1000 may also include a controller 200 and a motor 300, and the controller 200 is used to control the lithium-ion battery 100 to power the motor 300, for example, for the starting, navigation and working power requirements of the vehicle 1000 during driving.

[0059] In some embodiments of the present application, the lithium-ion battery 100 can not only serve as the operating power source of the vehicle 1000, but also serve as the driving power source of the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0060] Please refer to Figure 2 , Figure 2An exploded view of a lithium-ion battery 100 provided for some embodiments of the present application. The lithium-ion battery 100 includes a housing 10 and a lithium-ion battery cell 20, and the lithium-ion battery cell 20 is contained in the housing 10. Among them, the housing 10 is used to provide a storage space for the lithium-ion battery cell 20, and the housing 10 can adopt a variety of structures. In some embodiments, the housing 10 may include a first part 11 and a second part 12, and the first part 11 and the second part 12 cover each other, and the first part 11 and the second part 12 jointly define a storage space for accommodating the lithium-ion battery cell 20. The second part 12 may be a hollow structure with one end open, and the first part 11 may be a plate-like structure, and 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 a storage space; the first part 11 and the second part 12 may 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 in various shapes, such as a cylinder, a cuboid, etc.

[0061] In the lithium-ion battery 100, there may be multiple lithium-ion battery cells 20, and the multiple lithium-ion battery cells 20 may be connected in series, in parallel, or in a mixed connection. A mixed connection means that the multiple lithium-ion battery cells 20 are both connected in series and in parallel. The multiple lithium-ion battery cells 20 may be directly connected in series, in parallel, or in a mixed connection, and then the whole formed by the multiple lithium-ion battery cells 20 is accommodated in the box 10; of course, the lithium-ion battery 100 may also be a battery module formed by connecting multiple lithium-ion battery cells 20 in series, in parallel, or in a mixed connection, and then the multiple battery modules are connected in series, in parallel, or in a mixed connection to form a whole, and accommodated in the box 10. The lithium-ion battery 100 may also include other structures, for example, the lithium-ion battery 100 may also include a busbar component for realizing electrical connection between the multiple lithium-ion battery cells 20.

[0062] Each lithium-ion battery cell 20 may be a secondary battery or a primary battery, or a lithium-sulfur battery, a sodium-ion battery or a magnesium-ion battery, but is not limited thereto. The lithium-ion battery cell 20 may be cylindrical, flat, rectangular or in other shapes.

[0063] Please refer to Figure 3 , Figure 3 The schematic diagram of the exploded structure of a lithium-ion battery cell 20 provided in some embodiments of the present application. The lithium-ion battery cell 20 refers to the smallest unit that constitutes a battery. Figure 3 The lithium-ion battery cell 20 includes an end cover 21, a shell 22, an electrode assembly 23 and other functional components.

[0064] The end cap 21 refers to a component that covers the opening of the shell 22 to isolate the internal environment of the lithium-ion battery cell 20 from the external environment. Without limitation, the shape of the end cap 21 can be adapted to the shape of the shell 22 to match the shell 22. Optionally, the end cap 21 can be made of a material with a certain hardness and strength (such as aluminum alloy), so that the end cap 21 is not easily deformed when squeezed and collided, so that the lithium-ion battery cell 20 can have a higher structural strength and the safety performance can also be improved. Functional components such as electrode terminals 21a can be provided on the end cap 21. The electrode terminal 21a can be used to electrically connect with the electrode assembly 23 to output or input the electrical energy of the lithium-ion battery cell 20. In some embodiments, the end cap 21 can also be provided with a pressure relief mechanism for releasing the internal pressure when the internal pressure or temperature of the lithium-ion battery cell 20 reaches a threshold. The material of the end cap 21 can also be a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and the embodiment of the present application does not impose any special restrictions on this. In some embodiments, an insulating member may be provided inside the end cap 21, and the insulating member may be used to isolate the electrical connection components in the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating member may be plastic, rubber, or the like.

[0065] The shell 22 is a component used to cooperate with the end cap 21 to form the internal environment of the lithium-ion battery cell 20, wherein the formed internal environment can be used to accommodate the electrode assembly 23, the electrolyte and other components. The shell 22 and the end cap 21 can be independent components, and an opening can be set on the shell 22, and the internal environment of the lithium-ion battery cell 20 is formed by covering the opening with the end cap 21 at the opening. Without limitation, the end cap 21 and the shell 22 can also be integrated. Specifically, the end cap 21 and the shell 22 can form a common connection surface before other components are put into the shell, and when the interior of the shell 22 needs to be encapsulated, the end cap 21 covers the shell 22. The shell 22 can be of various shapes and sizes, such as a rectangular parallelepiped, a cylindrical shape, 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 embodiment of the present application does not impose any special restrictions on this.

[0066] The electrode assembly 23 is a component in the lithium-ion battery cell 20 where electrochemical reactions occur. One or more electrode assemblies 23 may be contained in the housing 22. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and a separator is usually provided between the positive and negative electrode sheets. The parts of the positive and negative electrode sheets with active materials constitute the main body of the electrode assembly 23, and the parts of the positive and negative electrode sheets without active materials each constitute a tab 23a. The positive tab and the negative tab may be located together at one end of the main body or at both ends of the main body respectively. During the charge and discharge process of the battery, the positive active material and the negative active material react with the electrolyte, and the tab 23a connects the electrode terminal 21a to form a current loop.

[0067] See also Figures 4 to 6 According to some embodiments of the present application, the negative electrode plate 24 includes: a current collector 241 and a lithium-free negative electrode film layer 243, the lithium-free negative electrode film layer 243 is coated on the surface of the current collector 241, the lithium-free negative electrode film layer 243 contains a first negative electrode active material, the first negative electrode active material includes a hollow carbon material and a lithium-philic substance, and the lithium-philic substance is not loaded with lithium metal, and the lithium-philic substance is loaded on the inner surface of the hollow carbon material.

[0068] The lithium-free negative electrode film layer 243 means that the film layer does not contain lithium element.

[0069] Lithophilic substances refer to substances that easily react chemically with lithium ions and reduce the nucleation overpotential of lithium ions on hollow carbon materials.

[0070] In the technical solution of the embodiment of the present application, the negative electrode plate 24 can be directly used as the negative electrode of the lithium-ion battery 100 in which the ratio of the total capacity of the negative electrode plate 24 to the total capacity of the positive electrode plate is less than 1, so that during the charging process, the hollow carbon material is used as a supporting skeleton, which not only provides a storage space for lithium metal, but also buffers the volume change of the negative electrode plate 24 during the deposition / dissolution of lithium metal, and limits the generation of lithium dendrites. On the other hand, it has conductivity and can induce the uniform deposition of lithium metal. The lithium deposition site is optimized by using lithium-philic substances, and lithium ions are induced to enter the interior of the hollow carbon material and evenly deposit on the lithium-philic substances, effectively inhibiting the dendrites generated during the deposition / precipitation of lithium metal, greatly reducing the danger of lithium metal negative electrode, and can improve the cycle life and coulomb efficiency of the battery, reduce voltage polarization, and the lithium-free setting of the negative electrode plate 24 can further significantly improve the energy density of the battery.

[0071] The material of the current collector 241 is, for example, a conductive metal such as copper or copper alloy.

[0072] The current collector 241 has two opposite surfaces, wherein the lithium-free negative electrode film layer 243 may be coated on only one surface of the current collector 241 . Optionally, the lithium-free negative electrode film layer 243 is coated on both surfaces of the current collector 241 .

[0073] The first negative electrode active material can be prepared by itself or purchased directly from the market, which is not limited here.

[0074] The wall layer number of the hollow carbon material can be a single layer or multiple layers.

[0075] According to some embodiments of the present application, optionally, the number of wall layers of the hollow carbon material is ≥2.

[0076] That is, the hollow carbon material is a multi-walled hollow carbon material, and the multi-walled hollow carbon material is conducive to the entry of lithium metal into the hollow carbon material.

[0077] In some embodiments, optionally, based on the lithium metal potential of 0 V, the lithium plating overpotential of the first negative electrode active material is less than 0 V and not less than -0.03 V.

[0078] Within the above range, the first negative electrode active material has a lithium affinity to lithium metal, so that lithium ions are selectively induced to enter the hollow carbon material and uniformly deposited in the hollow carbon material to connect with the lithium affinity material.

[0079] For example, taking the lithium metal potential as 0 V, the lithium plating overpotential of the first negative electrode active material is any value among -0.1 V, -0.2 V, and -0.03 V, or between any two values.

[0080] That is, in actual use, the lithium plating overpotential of the first negative electrode active material can be used as a basis for judging whether the first negative electrode active material has lithium affinity.

[0081] The method for determining the lithium plating overpotential of the first negative electrode active material includes: using the first negative electrode active material as a working electrode, Li 0.5 FePO4 was used as the reference electrode and lithium metal as the counter electrode. -2 ) deposits metallic lithium on the working electrode. + ) is the voltage as the ordinate and the capacity as the abscissa. When the capacity increases, the voltage first decreases and then remains flat. During this process, if the curve has no inflection point or the absolute value of the voltage corresponding to the inflection point is ≤0.03V, the material to be tested has lithium affinity. If there is an inflection point and the absolute value of the voltage corresponding to the inflection point is >0.03V, the material does not have lithium affinity.

[0082] Since lithium ions can diffuse into the hollow carbon material, the hollow carbon material can be in a hollow spherical shape.

[0083] According to some embodiments of the present application, optionally, the hollow carbon material has an inner surface forming a cavity, and at least one opening penetrating the inner surface and communicating with the cavity.

[0084] The above arrangement, utilizing at least one opening, facilitates loading the lithium-philic substance into the hollow carbon material, thereby reducing the difficulty of preparation.

[0085] According to some embodiments of the present application, optionally, the hollow carbon material is in a tubular shape.

[0086] The tubular hollow carbon material itself can become a conductive path, which is conducive to the uniform deposition of lithium metal in the hollow carbon material. At the same time, the first negative electrode active material composed of the tubular hollow carbon material is easy to purchase on the market.

[0087] According to some embodiments of the present application, optionally, the lithiophilic substance is at least one of a lithiophilic metal and a compound thereof.

[0088] Those skilled in the art may make a selection according to actual needs to achieve the lithium affinity of the first negative electrode active material.

[0089] According to some embodiments of the present application, optionally, the lithium-philic metal includes at least one of Au, Ag, Zn, Fe, Co, Ni, Ga, Sn, In, Ge, Ti, Mu, Pt, Al, and Mg.

[0090] The above-mentioned lithium-philic metals all have obvious lithium affinity for lithium metal, which can reduce the nucleation overpotential of lithium metal on the negative electrode plate 24, is conducive to the nucleation of lithium ions in the hollow carbon material, and can achieve uniform deposition of lithium metal in the hollow carbon material, effectively inhibiting the formation of lithium dendrites.

[0091] Exemplarily, the lithium-philic metal may be Au, Ag, Zn, Fe, Co, Ni, Ga, Sn, In, Ge, Ti, Mu, Pt, Al or Mg. The lithium-philic metal may also be a mixture or alloy of at least two of the above-mentioned metal elements, for example, the lithium-philic metal is a mixture or alloy of Au and Ag.

[0092] According to some embodiments of the present application, optionally, the mass content of the lithium-philic metal in the first negative electrode active material is 0.5%-20%.

[0093] The lithium-philic metal content within the above range is reasonable, so that the first negative electrode active material has a good lithium-philic effect, which can improve the initial coulombic efficiency and cycle life.

[0094] Exemplarily, the mass content of the lithium-philic metal in the first negative electrode active material is any value of 0.5%, 1%, 2%, 3%, 5%, 7%, 10%, 12%, 15%, 17%, 19%, 20%, or between any two values.

[0095] Optionally, the mass content of the lithium-philic metal in the first negative electrode active material is 2%-10%.

[0096] According to some embodiments of the present application, optionally, the lithium-philic metal compound includes one or more of oxides, sulfides, fluorides, nitrides, chlorides, and carbides.

[0097] The above-mentioned lithium-philic metal compounds all have obvious lithium affinity for lithium metal, which can reduce the nucleation overpotential of lithium metal on the negative electrode plate 24, is conducive to the nucleation of lithium ions in the hollow carbon material, and can achieve uniform deposition of lithium metal in the hollow carbon material, effectively inhibiting the formation of lithium dendrites.

[0098] Among them, the lithium-philic metal includes at least one of Au, Ag, Zn, Fe, Co, Ni, Ga, Sn, In, Ge, Ti, Mu, Pt, Al, and Mg, and the lithium-philic metal compound is one or more of the oxides, sulfides, fluorides, nitrides, chlorides, and carbides of the above-mentioned lithium-philic metals.

[0099] Exemplarily, the lithium-philic metal compound is at least one of Ag2O, ZnO, FeC, etc.

[0100] In some embodiments, optionally, the mass content of the lithium-philic metal compound in the first negative electrode active material is 0.5%-30% calculated as the metal element.

[0101] The above range has a good lithium affinity effect and can improve the cycle life.

[0102] Exemplarily, the mass content of the lithium-philic metal compound in the first negative electrode active material is any value of 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 20%, 25%, 30%, or between any two values, calculated as the metal element.

[0103] Optionally, the mass content of the lithium-philic metal compound in the first negative electrode active material is 3%-15% calculated as the metal element.

[0104] In some embodiments, optionally, the lithium-free negative electrode film layer 243 contains a second negative electrode active material and a conductive agent, wherein the lithium metal potential is 0V, and the lithium deposition overpotential of the second negative electrode active material is less than 0V and not less than -0.5V.

[0105] The above arrangement, on the one hand, utilizes the second negative electrode activity less than 0V and not less than -0.5V to match its lithium deposition overpotential with the lithium metal potential, so that when the above negative electrode plate 24 is directly used as the negative electrode of the lithium ion battery 100 in which the ratio of the total capacity of the negative electrode plate 24 to the total capacity of the positive electrode plate is less than 1, it is beneficial to form a lithium metal composite negative electrode during the charging process. On the other hand, the gaps between the second negative electrode active materials can provide space for lithium deposition, and the conductive agent can effectively and evenly deposit lithium ions, thereby reducing the deposition of lithium metal on the surface of the negative electrode plate 24 and forming a more uniform composite lithium metal negative electrode.

[0106] For example, taking the lithium metal potential as 0 V, the lithium plating overpotential of the second negative electrode active material is any value among -0.5 V, -0.4 V, -0.3 V, -0.2 V, and -0.1 V, or between any two values.

[0107] According to some embodiments of the present application, optionally, the second negative electrode active material is at least one of a carbon-based material, a silicon-based material and a metal oxide.

[0108] The lithium plating overpotential of the above-mentioned negative electrode active material can easily meet the above-mentioned requirements and is easy to obtain.

[0109] Among them, the carbon-based material can be at least one of graphite, mesophase carbon microbeads, hard carbon, soft carbon, etc., the silicon-based material can be at least one of silicon carbon and silicon oxide, and the metal oxide can be at least one of iron oxide and tin oxide.

[0110] See also Figures 4 to 6 In the actual setting process, there are many ways to set the lithium-free negative electrode film layer 243, and those skilled in the art can set it according to actual needs.

[0111] In some embodiments, optionally, the lithium-free negative electrode film layer 243 includes: at least two film layers stacked along the thickness direction, each film layer contains the second negative electrode active material, and at least one film layer contains the first negative electrode active material.

[0112] At least one film layer contains the first negative electrode active material, including a configuration in which only part of the film layers contain the first negative electrode active material, and also including a configuration in which all the film layers contain the first negative electrode active material.

[0113] The preparation method is simple under the above setting, and the lithium-free negative electrode film layer 243 can also be provided with the first negative electrode active material only in part of the film layer, or in all the film layers according to actual needs, thereby expanding the specific setting method of the lithium-free negative electrode film layer 243.

[0114] The number of the at least two film layers may be, for example, two layers, three layers, four layers, five layers, etc., and those skilled in the art may set it according to actual needs.

[0115] It should be noted that the content of the first negative electrode active material contained in each film layer can be the same or different. Similarly, the content of the second negative electrode active material contained in each film layer can be the same or different. Those skilled in the art can make a selection according to actual needs.

[0116] For ease of preparation, optionally, each film layer contains the same content of the first negative electrode active material, and each film layer containing the second negative electrode active material also contains the same content of the second negative electrode active material.

[0117] When all the film layers contain the first negative electrode active material and the second negative electrode active material, and the content of the first negative electrode active material contained in each film layer is the same, and the content of the second negative electrode active material contained in each film layer is the same, then during preparation, in addition to the layered coating to a preset thickness, the slurry containing the first negative electrode active material and the second negative electrode active material can also be directly coated on the current collector 241 to a preset thickness, and the structures of the lithium-free negative electrode film layer 243 finally obtained by the two coating methods are the same.

[0118] See also Figure 4 In some embodiments, optionally, the lithium-free negative electrode film layer 243 includes: a first film layer 244 and a second film layer 245, the first film layer 244 and the second film layer 245 are alternately stacked along the thickness direction, the first film layer 244 contains the second negative electrode active material and the first negative electrode active material, the second film layer 245 contains the second negative electrode active material and does not contain the first negative electrode active material; the side of the lithium-free negative electrode film layer 243 connected to the current collector 241 is the first film layer 244.

[0119] The side where the lithium-free negative electrode film layer 243 is connected to the current collector 241 is used as the first film layer 244 , which is conducive to the deposition of lithium metal in the direction close to the current collector 241 and reduces lithium dendrites on the surface of the negative electrode plate 24 .

[0120] Optionally, the first film layer 244 and the second film layer 245 are alternately stacked in sequence along the thickness direction.

[0121] Optionally, the number of the first film layer 244 is at least one layer, and the number of the second film layer 245 is at least one layer. For example, the number of the first film layer 244 is two layers, and the number of the second film layer 245 is two layers. In this case, the side of the lithium-free negative electrode film layer 243 connected to the current collector 241 is the first film layer 244, and the layer of the lithium-free negative electrode film layer 243 away from the current collector 241 is the second film layer 245.

[0122] like Figure 4As shown, the number of the first film layer 244 is one layer, and the number of the second film layer 245 is one layer. At this time, the side of the lithium-free negative electrode film layer 243 connected to the current collector 241 is the first film layer 244, and the layer of the lithium-free negative electrode film layer 243 away from the current collector 241 is the second film layer 245.

[0123] When the lithium-free negative electrode film layer 243 includes: at least two film layers stacked along the thickness direction, each film layer contains the second negative electrode active material, and at least one film layer contains the first negative electrode active material, in some embodiments, optionally, the amount of the first negative electrode active material added to the lithium-free negative electrode film layer 243 is 0.125%-5% by mass.

[0124] The formation of lithium dendrites can be effectively suppressed within the above range, and the battery cycle life is good. If the added amount is too little, the effect of reducing lithium dendrites on the surface of the negative electrode plate 24 is limited. If the added amount is too much, the cycle life is poor.

[0125] Exemplarily, the amount of the first negative electrode active material added to the lithium-free negative electrode film layer 243 is any one of 0.125%, 0.2%, 0.5%, 0.7%, 1%, 1.3%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or between any two values, as a percentage by mass.

[0126] See also Figure 5 as well as Figure 6 In some embodiments, optionally, the lithium-free negative electrode film layer 243 includes: a third film layer 246 , wherein the third film layer 246 contains the first negative electrode active material and does not contain the second negative electrode active material.

[0127] In other words, in actual use, only the third film layer 246 can be used as the lithium-free negative electrode film layer 243 , or a multi-layer arrangement with part of the third film layer 246 can be used, thereby expanding the specific arrangement of the lithium-free negative electrode film layer 243 .

[0128] like Figure 5 As shown, the lithium-free negative electrode film layer 243 is the third film layer 246 .

[0129] See also Figure 6 In some embodiments, optionally, the lithium-free negative electrode film layer 243 further includes: a fourth film layer 247, a third film layer 246 and a fourth film layer 247 are alternately stacked along the thickness direction of the lithium-free negative electrode film layer 243, the fourth film layer 247 contains the second negative electrode active material and does not contain the first negative electrode active material, and the side of the lithium-free negative electrode film layer 243 connected to the current collector 241 is the third film layer 246.

[0130] The above configuration utilizes the introduction of the second negative electrode active material in the fourth film layer 247 to improve the battery cycle life. The configuration of the third film layer 246 on one side of the lithium-free negative electrode film layer 243 connected to the current collector 241 is conducive to the deposition of lithium metal in the direction close to the current collector 241, reducing lithium dendrites on the surface of the negative electrode sheet 24.

[0131] In some embodiments, optionally, the amount of the first negative electrode active material added to the third film layer 246 is 10%-60% by mass.

[0132] The formation of lithium dendrites can be effectively suppressed within the above range, and the battery cycle life is good. If the added amount is too little, the effect of reducing lithium dendrites on the surface of the negative electrode plate 24 is limited. If the added amount is too much, the cycle life is poor.

[0133] Exemplarily, the amount of the first negative electrode active material added to the third film layer 246 is any one of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% by mass or between any two values.

[0134] According to some embodiments of the present application, the present application also provides a lithium-ion battery cell, which includes a positive electrode plate and a negative electrode plate provided in the above embodiments, and the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate is N / P, where N / P<1.

[0135] N / P definition: N: total capacity of negative electrode plate; P: total capacity of positive electrode plate, N = gram capacity of negative electrode material * surface density * negative electrode proportion * plate size, P = gram capacity of positive electrode material * surface density * positive electrode proportion * plate size, N / P < 1, that is, the capacity of negative electrode < the capacity of positive electrode.

[0136] N / P<1, that is, lithium-rich material is used as the positive electrode active material, so that the amount of lithium ions in the positive electrode plate is much greater than the amount of lithium ions that the negative electrode plate can accommodate.

[0137] With the above settings, since N / P<1, after one cycle, the excess lithium in the positive electrode is stored in the negative electrode in the form of lithium metal, which replenishes the active lithium consumed by side reactions in subsequent cycles to obtain high coulombic efficiency and cycle life. In addition, during the assembly process of the battery and the initial state after assembly, the battery does not contain lithium metal, which greatly reduces the cost and safety hazards of the assembly, storage and transportation processes. And within the above N / P value range, both a better cycle life and a higher energy density can be taken into account. If the N / P value is too small, the lithium metal content is high and the battery cycle is poor; if the N / P value is too large, the lithium metal content is low and the energy density is low.

[0138] Optionally, 0.4≤N / P<1.

[0139] Exemplarily, the value of N / P is any value among 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, etc., or between any two values.

[0140] In some embodiments, optionally, after the lithium-ion battery cell is discharged, the lithium-philic substance of the negative electrode plate is not loaded with lithium metal.

[0141] According to some embodiments of the present application, the present application further provides a lithium-ion battery, which includes a box and a plurality of lithium-ion battery cells according to any of the above schemes, wherein the plurality of lithium-ion battery cells are accommodated in the box.

[0142] According to some embodiments of the present application, the present application further provides an electrical device, comprising a lithium-ion battery according to any of the above schemes, and the lithium-ion battery is used to provide electrical energy to the electrical device.

[0143] Some specific embodiments are listed below to better illustrate the present application.

[0144] Examples and Comparative Examples

[0145] Preparation of positive electrode sheets: Add N-methylpyrrolidone to cobalt manganese (NCM) ternary material, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:2, mix and stir for 0.5-6h to obtain positive electrode slurry; then evenly coat it on the positive electrode collector, dry, cold press, and cut to obtain positive electrode sheets.

[0146] The preparation method of the negative electrode sheet of each embodiment and comparative example is as follows:

[0147] The raw material selection of the negative electrode plates of each embodiment and comparative example is shown in Table 1.

[0148] [Negative electrode sheets of Examples 1-6, 10-18, and Comparative Examples 5-9]: The second negative electrode active material, conductive agent carbon black, binder styrene-butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), and the first negative electrode active material are mixed, then added into deionized water, mixed and stirred for 0.5-6 hours, the obtained slurry is evenly coated on the negative electrode current collector, and the result is dried.

[0149] Among them, the weight ratios of the second negative electrode active material, conductive agent carbon black, styrene-butadiene rubber, sodium hydroxymethyl cellulose, and the first negative electrode active material contained in the first film layer in Examples 1 to 7 are 96.7:0.3:1.25:1.25:0.5 respectively. The content of the first negative electrode active material can be adjusted by adjusting the above ratios in the remaining examples and comparative examples.

[0150] [Negative electrode plate of Example 7]: The plate is double-coated. First, the second negative electrode active material, conductive agent carbon black, binder styrene butadiene rubber (SBR), thickener sodium hydroxymethyl cellulose (CMC), and the first negative electrode active material are mixed in a weight ratio of 96.7:0.3:1.25:1.25:0.5, added into deionized water, mixed and stirred for 0.5-6h, evenly coated on the negative electrode collector, dried to obtain a first film layer, and a layer of slurry obtained by mixing the second negative electrode active material, conductive agent carbon black, binder styrene butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) in a weight ratio of 96.7:0.8:1.25:1.25 is coated on the surface thereof, and dried to obtain a second film layer.

[0151] [Negative electrode sheet of Example 8 and Comparative Examples 10-13]: The first negative electrode active material, binder styrene butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) are mixed according to a weight ratio and deionized water is added, and the mixture is stirred for 0.5-6 hours to obtain a current collector surface coating slurry, which is evenly coated on the negative electrode current collector and dried to obtain a third film layer; the second negative electrode active material, conductive agent carbon black, binder styrene butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) are mixed according to a weight ratio of 96.7:0.8:1.25:1.25 and coated on the third film layer to obtain a fourth film layer. The content of the first negative electrode active material can be adjusted according to the ratio.

[0152] [Negative electrode sheet of Example 9]: Add deionized water to the first negative electrode active material, binder styrene-butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) in a weight ratio of 1:0.5:0.5, and mix and stir for 0.5-6 hours to obtain a current collector surface coating slurry, which is evenly coated on the negative electrode current collector and dried.

[0153] [Negative electrode sheet of Comparative Examples 1-3]: The only difference from Example 1 is that Comparative Examples 1-3 do not contain the first negative electrode active material. The second negative electrode active material, conductive agent carbon black, binder styrene butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) are mixed in a weight ratio of 96.7:0.8:1.25:1.25, and then uniformly coated on the negative electrode collector and dried.

[0154] [Negative electrode sheet of comparative example 4]: The current collector is directly used as the negative electrode sheet.

[0155] [Negative electrode sheet of comparative example 14]: The only difference from example 7 is that the coating sequence is opposite, the second film layer is coated first and then the first film layer is coated on the surface of the second film layer and then obtained.

[0156] Isolation film: Polypropylene film is used as the isolation film.

[0157] Electrolyte: Dissolve LiPF6 in a solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1 to prepare an electrolyte with a concentration of 1 mol / L.

[0158] Production of lithium-ion batteries: stack the above-mentioned positive electrode plates, isolation membranes, and negative electrode plates in order to obtain bare cells; place the bare cells in a packaging shell, inject electrolyte after drying, and obtain lithium-ion batteries through vacuum packaging, standing, forming, shaping and other processes.

[0159] The energy density and cycle life of the lithium-ion batteries obtained in each embodiment and comparative example were measured, and the results are shown in Table 2.

[0160] 1) Energy density test of lithium-ion batteries

[0161] At 25°C, the lithium ion batteries of the embodiment and the comparative example are charged to 4.3V at 1C constant current, then charged to 0.05C at constant voltage, and then discharged to 2.8V at 1C constant current, which is a charge and discharge cycle. The battery is charged and discharged 30 times in this way, and the energy density of the battery is obtained by dividing the discharge energy of the 30th cycle by the total weight of the battery.

[0162] 2) Lithium-ion battery cycle performance test method

[0163] At 25°C, the lithium ion batteries of the embodiment and the comparative example are charged to 4.3V at 1C constant current, then charged to 0.05C at constant voltage, and then discharged to 2.8V at 1C constant current, which is a charge and discharge cycle. The first discharge capacity is 100%, and the number of cycles when the discharge capacity drops to 80% is the cycle life.

[0164] Table 1 Test parameters of negative electrode sheets of various embodiments and comparative examples

[0165]

[0166] In Table 1, when the lithiophilic substance is a lithium-philic metal compound, the lithiophilic substance loading refers to the mass content of the lithium-philic metal compound in the first negative electrode active material in terms of metal element. When the lithiophilic substance is a lithium-philic metal, the lithiophilic substance loading refers to the mass content of the lithium-philic metal in the first negative electrode active material.

[0167] Table 2 Test parameters and test results of negative electrode sheets of various embodiments and comparative examples

[0168]

[0169] Compared with Examples 1-3, Comparative Examples 1-3 do not contain the corresponding first negative electrode active material, and directly mix the second negative electrode active material, conductive agent carbon black, binder styrene butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) in a weight ratio of 96.7:0.8:1.25:1.25 and evenly coat the mixture on the negative electrode current collector. It can be seen that in the absence of the first negative electrode active material, the cycle life of the lithium-ion battery prepared in Comparative Examples 1-3 is significantly reduced, indicating that lithium dendrites are generated on the surface of the negative electrode plate.

[0170] Comparative Example 4 directly uses the current collector as the negative electrode. It can be seen that the cycle life of the prepared lithium-ion battery is significantly reduced and cannot meet the use requirements of the lithium-ion battery.

[0171] The only difference between Comparative Example 5 and Example 1 is that its designed N / P value = 1. At this time, the energy density of the lithium-ion battery prepared in Comparative Example 5 is only 270Wh / kg, the electrical energy stored per unit volume is too little, and it has no industrial application value.

[0172] In Comparative Example 6, the loading amount of the lithium-philic substance in the first negative electrode active material is too small. Compared with Example 14, the amount of the first negative electrode active material added in the lithium-free negative electrode film layer is adjusted to make the amount of the lithium-philic substance added in the negative electrode plate similar. At this time, the energy density values ​​of Comparative Example 6 and Example 14 are similar, but the cycle life of Comparative Example 6 is significantly lower than that of Example 14, indicating that the loading amount of the lithium-philic substance in the first negative electrode active material in Comparative Example 6 is too small. At this time, even if the content of the first negative electrode active material in the negative electrode plate is increased, the precipitation of lithium dendrites on the surface of the negative electrode plate cannot be effectively improved.

[0173] In Comparative Example 7, the loading amount of the lithium-philic substance in the first negative electrode active material is too much. Compared with Example 15, the amount of the first negative electrode active material added in the lithium-free negative electrode film layer is adjusted to make the amount of the lithium-philic substance added in the negative electrode plate similar. Under the premise that the energy density values ​​of the lithium-ion batteries obtained in Comparative Example 7 and Example 15 are similar, the cycle life of Comparative Example 7 is significantly lower than that of Example 15, indicating that the loading amount of the lithium-philic substance in the first negative electrode active material in Comparative Example 7 is too much. At this time, even if the content of the first negative electrode active material in the negative electrode plate is reduced, the precipitation of lithium dendrites on the surface of the negative electrode plate cannot be effectively improved.

[0174] Compared with Example 1, the amount of the first negative electrode active material added to the lithium-free negative electrode film layer in Comparative Example 8 is too small, resulting in the lithium ion battery prepared by the two having an energy density difference of only 2Wh / kg. The cycle life of the lithium ion battery prepared in Comparative Example 8 is significantly lower than the cycle life of the lithium ion battery prepared in Example 1, indicating that the amount of the first negative electrode active material added to the lithium-free negative electrode film layer is too small to effectively improve the precipitation of lithium dendrites on the surface of the negative electrode plate.

[0175] Compared with Example 1, Comparative Example 9 has an excessive amount of the first negative electrode active material added to the lithium-free negative electrode film layer, resulting in the lithium ion battery prepared in Comparative Example 9 not only having a lower energy density than Example 1, but also a cycle life of the lithium ion battery significantly lower than Example 1, indicating that an excessive amount of the first negative electrode active material added to the lithium-free negative electrode film layer not only reduces the battery energy density, but also fails to effectively improve the precipitation of lithium dendrites on the surface of the negative electrode sheet.

[0176] Compared with Example 8, the loading amount of the lithium-philic substance in the first negative electrode active material of Comparative Example 10 is too small. The amount of the first negative electrode active material added in the lithium-free negative electrode film layer is adjusted to make the amount of the lithium-philic substance added in the negative electrode plates of the two similar. However, according to Table 2, it can be seen that the above settings will cause the energy density value of the lithium-ion battery prepared in Comparative Example 10 to be slightly smaller than that of Example 8, and the cycle life of Comparative Example 10 is significantly lower than that of Example 8, indicating that the loading amount of the lithium-philic substance in the first negative electrode active material is too small. Even if the content of the first negative electrode active material in the negative electrode plate is increased at this time, the precipitation of lithium dendrites on the surface of the negative electrode plate cannot be effectively improved.

[0177] Compared with Example 8, Comparative Example 11 has an excessive amount of lithium-philic substance loaded in the first negative electrode active material. The amount of the first negative electrode active material added in the lithium-free negative electrode film layer is adjusted to make the amount of lithium-philic substance added in the negative electrode sheets of the two similar. However, according to Table 2, the above setting will result in the lithium-ion batteries of Comparative Example 11 and Example 8 having the same energy density, while the cycle life of Comparative Example 11 is significantly lower than that of Example 8, indicating that the amount of lithium-philic substance loaded in the first negative electrode active material in Comparative Example 11 is too small. Even if the content of the first negative electrode active material in the negative electrode sheet is increased at this time, the precipitation of lithium dendrites on the surface of the negative electrode sheet cannot be effectively improved.

[0178] Compared with Example 8, in Comparative Example 12, the amount of the first negative electrode active material added in the lithium-free negative electrode film layer is the same, but the amount of the first negative electrode active material added in the third film layer is too small, so that compared with Example 8, the cycle life is significantly reduced on the basis of similar energy density. Compared with Example 8, in Comparative Example 13, the amount of the first negative electrode active material added in the lithium-free negative electrode film layer is the same, but the amount of the first negative electrode active material added in the third film layer is too much, so that compared with Example 8, not only the energy density is reduced, but also the cycle life is significantly reduced. In summary, Comparative Examples 12 and 13 show that under the condition that the amount of the first negative electrode active material added in the lithium-free negative electrode film layer is the same, the amount of the first negative electrode active material added in the third film layer will affect the precipitation of lithium dendrites on the surface of the negative electrode sheet.

[0179] The only difference between Comparative Example 14 and Example 7 is that the coating method is opposite. According to Table 2, the arrangement of the first film layer containing the first negative electrode active material on the side where the lithium-free negative electrode film layer is connected to the current collector is beneficial to the deposition of lithium metal toward the direction close to the current collector, which can not only reduce the lithium dendrites on the surface of the negative electrode sheet, effectively improve the cycle life of the lithium-ion battery, but also improve the energy density of the lithium-ion battery.

[0180] In summary, the negative electrode plate provided in the present application can be directly used as the negative electrode of a lithium-ion battery in which the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate is less than 1, so as to inhibit the dendrites generated during the lithium metal deposition / precipitation process during the charging process, thereby improving the cycle life and coulombic efficiency of the battery. In addition, the lithium-free setting of the negative electrode plate can further significantly improve the energy density of the battery.

[0181] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A negative electrode plate, characterized in that: include: current collector; as well as A lithium-free negative electrode film layer is coated on the surface of the current collector, wherein the lithium-free negative electrode film layer contains a first negative electrode active material, wherein the first negative electrode active material includes a hollow carbon material and a lithium-philic substance, and the lithium-philic substance does not carry lithium metal; Wherein, the lithium-philic substance is loaded on the inner surface of the hollow carbon material.

2. The negative electrode sheet according to claim 1, characterized in that: The number of wall layers of the hollow carbon material is ≥2.

3. The negative electrode sheet according to claim 1, characterized in that: Taking the lithium metal potential as 0 V, the lithium deposition overpotential of the first negative electrode active material is less than 0 V and not less than -0.03 V.

4. The negative electrode sheet according to claim 1, characterized in that: The hollow carbon material has the inner surface forming a cavity, and at least one opening penetrating the inner surface and communicating with the cavity.

5. The negative electrode sheet according to claim 4, characterized in that: The hollow carbon material is in a tubular shape.

6. The negative electrode sheet according to claim 1, characterized in that: The lithium-philic substance is at least one of a lithium-philic metal and a compound thereof.

7. The negative electrode sheet according to claim 6, characterized in that: The lithium-philic metal includes at least one of Au, Ag, Zn, Fe, Co, Ni, Ga, Sn, In, Ge, Ti, Mu, Pt, Al, and Mg.

8. The negative electrode sheet according to claim 6, characterized in that: The mass content of the lithium-philic metal in the first negative electrode active material is 0.5%-20%.

9. The negative electrode sheet according to claim 6, characterized in that: The mass content of the lithium-philic metal in the first negative electrode active material is 2%-10%.

10. The negative electrode sheet according to claim 6, characterized in that: The lithium-philic metal compound includes one or more of oxides, sulfides, fluorides, nitrides, chlorides, and carbides.

11. The negative electrode sheet according to claim 6, characterized in that: Calculated as metal element, the mass content of the lithium-philic metal compound in the first negative electrode active material is 0.5%-30%.

12. The negative electrode sheet according to claim 6, characterized in that: Calculated as metal element, the mass content of the lithium-philic metal compound in the first negative electrode active material is 3%-15%.

13. The negative electrode sheet according to any one of claims 1 to 12, characterized in that: The lithium-free negative electrode film layer contains a second negative electrode active material and a conductive agent, wherein the lithium metal potential is 0V, and the lithium deposition overpotential of the second negative electrode active material is less than 0V and not less than -0.5V.

14. The negative electrode sheet according to claim 13, characterized in that: The second negative electrode active material is at least one of a carbon-based material, a silicon-based material and a metal oxide.

15. The negative electrode sheet according to claim 13, characterized in that: The lithium-free negative electrode film layer comprises: at least two film layers stacked in a thickness direction, each of the film layers contains the second negative electrode active material, and at least one of the film layers contains the first negative electrode active material.

16. The negative electrode sheet according to claim 15, characterized in that: The lithium-free negative electrode film layer comprises: a first film layer and a second film layer, the first film layer and the second film layer are alternately stacked in a thickness direction, the first film layer contains the second negative electrode active material and the first negative electrode active material, and the second film layer contains the second negative electrode active material and does not contain the first negative electrode active material; The side of the lithium-free negative electrode film layer connected to the current collector is the first film layer.

17. The negative electrode sheet according to claim 16, characterized in that: Calculated by mass percentage, the amount of the first negative electrode active material added to the lithium-free negative electrode film layer is 0.125%-5%.

18. The negative electrode sheet according to claim 13, characterized in that: The lithium-free negative electrode film layer includes: a third film layer, wherein the third film layer contains the first negative electrode active material and does not contain the second negative electrode active material.

19. The negative electrode sheet according to claim 18, characterized in that: The lithium-free negative electrode film layer further includes: a fourth film layer, the third film layer and the fourth film layer are alternately stacked along the thickness direction of the lithium-free negative electrode film layer, and the fourth film layer contains the second negative electrode active material and does not contain the first negative electrode active material; The side of the lithium-free negative electrode film layer connected to the current collector is the third film layer.

20. The negative electrode sheet according to claim 18, characterized in that: Calculated by mass percentage, the amount of the first negative electrode active material added to the third film layer is 10%-60%.

21. A lithium-ion battery cell, characterized in that: It comprises a positive electrode sheet and a negative electrode sheet as described in any one of claims 1 to 20, wherein the ratio of the total capacity of the negative electrode sheet to the total capacity of the positive electrode sheet is N / P, wherein N / P<1.

22. The lithium-ion battery cell according to claim 21, characterized in that: 0.4≤N / P<1.

23. The lithium-ion battery cell according to claim 21, characterized in that: After the lithium-ion battery cell is discharged, the lithium-philic substance of the negative electrode plate does not load lithium metal.

24. A lithium ion battery, characterized in that: It comprises a box body and a plurality of lithium-ion battery cells as claimed in any one of claims 21 to 23, wherein the plurality of lithium-ion battery cells are accommodated in the box body.

25. An electrical device, characterized in that: The lithium-ion battery of claim 24 is used to provide electrical energy.

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