CN115832213A

CN115832213A - Negative pole piece, lithium ion battery monomer, lithium ion battery and consumer

Info

Publication number: CN115832213A
Application number: CN202210727115.5A
Authority: CN
Inventors: 李璇; 董苗苗; 陈兴布; 孙信; 吴李力; 李书银
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-06-24
Filing date: 2022-06-24
Publication date: 2023-03-21

Abstract

The application provides a negative pole piece, lithium ion battery monomer, lithium ion battery and consumer relates to the battery field. The negative pole piece includes: the lithium-free negative electrode film layer is coated on the surface of the current collector and contains a first negative electrode active material, the first negative electrode active material comprises a hollow carbon material and a lithium-philic substance, 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 negative pole piece can be directly used as the negative pole of the lithium ion battery with the ratio of the total capacity of the negative pole piece to the total capacity of the positive pole piece being less than 1, so that dendritic crystals generated in the deposition/precipitation process of lithium metal are inhibited in the charging process, the cycle life and the coulombic efficiency of the battery are improved, and the energy density of the battery can be further obviously improved due to the fact that the negative pole piece is not provided with lithium.

Description

Negative pole piece, lithium ion battery monomer, lithium ion battery and consumer

Technical Field

The application relates to the field of batteries, in particular to a negative pole piece, a lithium ion battery monomer, a lithium ion battery and electric equipment.

Background

The existing lithium ion battery is easy to deposit lithium metal on the surface of a negative pole piece when fully charged, lithium dendrite is easy to form, a large amount of lithium dendrite causes damage of an SEI (solid electrolyte interphase) film, energy density and coulombic efficiency of the battery are reduced, and a diaphragm is possibly pierced to cause internal short circuit of the battery, so that potential safety hazards are brought and the cycle life of the battery is restricted. A currently common approach is to pre-store excess lithium metal at the negative electrode to replenish the consumption of active lithium during cycling. But this approach can reduce the energy density of the battery.

Disclosure of Invention

In view of the above problems, the present application provides a negative electrode sheet, a lithium ion battery cell, a lithium ion battery, and an electric device, which can solve the technical problems that a negative electrode of a lithium ion battery is likely to generate lithium dendrite and the energy density of the battery is low.

In a first aspect, an embodiment of the present application provides a negative electrode sheet, which includes: the lithium-free negative electrode film layer is coated on the surface of the current collector and contains a first negative electrode active material, the first negative electrode active material comprises a hollow carbon material and a lithium-philic substance, 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.

Among the technical scheme of this application embodiment, can be less than 1 lithium ion battery's negative electrode with the direct total capacity as negative electrode pole piece of negative electrode pole piece and the total capacity's of positive electrode pole piece ratio, in order in charging process, utilize the setting of hollow carbon material, on the one hand as supporting framework, not only for lithium metal provides the accommodation space, but also can cushion the volume change that lithium metal negative electrode pole piece produced in deposit/dissolution process, the production of restriction lithium dendrite, on the other hand has electric conductivity, can induce the even deposit of lithium metal. The lithium deposition sites are optimized by the lithium-philic substances, lithium ions are induced to enter the hollow carbon material and are uniformly deposited on the lithium-philic substances, dendritic crystals generated in the lithium metal deposition/precipitation process are effectively inhibited, the danger of a lithium metal negative electrode is greatly reduced, the cycle life and the coulombic efficiency of the battery can be improved, the voltage polarization is reduced, and the energy density of the battery can be further remarkably improved due to the fact that no lithium is arranged on a negative electrode piece.

In some embodiments, the number of wall layers of the hollow carbon material is greater than or equal to 2. Namely, the hollow carbon material is a multi-wall hollow carbon material which is beneficial to lithium metal entering the hollow carbon material.

In some embodiments, the first anode active material has a lithium extraction overpotential of less than 0V and not less than-0.03V, in terms of a lithium metal potential of 0V. Within the above range, the first negative active material has lithium-philic properties to lithium metal, so that lithium ions are selectively induced into the hollow carbon material and uniformly deposited in the hollow carbon material to be connected to the lithium-philic material.

In some embodiments, the hollow carbon material has an inner surface forming a cavity, and at least one opening extending through the inner surface and communicating with the cavity. Above-mentioned setting utilizes at least one open-ended setting, is convenient for load lithium-philic substance in hollow carbon material, reduces the preparation degree of difficulty.

Optionally, the hollow carbon material is tubular in shape. The tubular hollow carbon material can become a conductive path, which is beneficial to the lithium metal to be uniformly deposited in the hollow carbon material.

In some embodiments, the lithium-philic substance is at least one of a lithium-philic metal and a compound thereof. Those skilled in the art can select the first negative active material according to actual needs to achieve lithium affinity of the first negative active material.

In some embodiments, the lithium-philic metal comprises at least one of Au, ag, zn, fe, co, ni, ga, sn, in, ge, ti, mu, pt, al, mg. The lithium-philic metal has obvious lithium-philic property on the lithium metal, can reduce the nucleation overpotential of the lithium metal on the negative pole piece, is beneficial to the nucleation of lithium ions in the hollow carbon material, can realize the uniform deposition of the lithium metal in the hollow carbon material, and effectively inhibits the formation of lithium dendrite.

In some embodiments, the lithium-philic metal is present in the first anode active material in an amount of 0.5% to 20%, optionally 2% to 10%, by mass. The content of the lithium-philic metal in the range is reasonable, so that the first negative active material has a good lithium-philic effect, and the initial coulombic efficiency and the cycle life can be improved.

In some embodiments, the lithium-philic metal compound comprises one or more of an oxide, a sulfide, a fluoride, a nitride, a chloride, a carbide. The lithium-philic metal compound has obvious lithium-philic property on lithium metal, can reduce the nucleation overpotential of the lithium metal on a negative pole piece, is beneficial to the nucleation of lithium ions in a hollow carbon material, can realize the uniform deposition of the lithium metal in the hollow carbon material, and effectively inhibits the formation of lithium dendrite.

In some embodiments, the lithium-philic metal compound is present in the first anode active material in an amount of 0.5% to 30%, optionally 3% to 15%, by mass of the metal element. The above range has excellent effect of attracting lithium and can improve cycle life.

In some embodiments, the lithium-free negative electrode film layer contains a second negative electrode active material and a conductive agent, wherein the second negative electrode active material has a lithium-extraction overpotential of less than 0V and not less than-0.5V, based on a lithium metal potential of 0V. On one hand, the second negative electrode is used for matching the lithium-precipitation overpotential with the lithium metal potential, so that when the negative electrode plate is directly used as a negative electrode of a lithium ion battery with the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate being less than 1, the lithium metal composite negative electrode is formed in the charging process, on the other hand, a gap between the second negative electrode active materials can provide a space for lithium deposition, and the conductive agent can enable lithium ions to be effectively and uniformly deposited, so that the deposition of lithium metal on the surface of the negative electrode plate can be reduced, and a uniform composite lithium metal negative electrode is formed.

Alternatively, the second negative active material is at least one of a carbon-based material, a silicon-based material, and a metal oxide. The lithium-precipitating overpotential of the negative electrode active material is easy to meet the requirement and is easy to obtain.

In some embodiments, the lithium-free negative electrode film layer comprises: at least two film layers are arranged in a stacked manner in the thickness direction, each film layer contains a second negative electrode active material, and at least one film layer contains a first negative electrode active material. The preparation method is simple under the arrangement, and the lithium-free negative electrode film layer can be only provided with the first negative electrode active material in part of the film layer or all the film layers according to actual requirements, so that the specific arrangement mode of the lithium-free negative electrode film layer is expanded.

In some embodiments, the lithium-free negative electrode film layer comprises: the negative electrode active material comprises a first film layer and a second film layer, wherein the first film layer and the second film layer are alternately stacked in the thickness direction, the first film layer contains a second negative electrode active material and a 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 with the current collector is a first film layer. One side of the lithium-free negative pole film layer connected with the current collector is used as a first film layer, so that the lithium metal is deposited towards the direction close to the current collector, and lithium dendrites on the surface of the negative pole piece are reduced.

In some embodiments, the first anode active material is added in an amount of 0.125% to 5% by mass in the lithium-free anode film layer. The lithium dendrite formation can be effectively inhibited in the range, the cycle life of the battery is good, if the addition amount is too small, the effect of reducing the lithium dendrite on the surface of the negative pole piece is limited, and if the addition amount is too large, the cycle life is poor.

In some embodiments, the lithium-free negative electrode film layer comprises: a third membrane layer containing the first negative active material and not containing the second negative active material. That is, in actual use, only the third film layer may be used as the lithium-free negative electrode film layer, or the third film layer may be provided in multiple layers and partially as the third film layer, so as to expand the specific arrangement manner of the lithium-free negative electrode film layer.

In some embodiments, the lithium-free anode film layer further comprises: the fourth film layer, the third film layer and the fourth film layer are alternately stacked and arranged along the thickness direction of the lithium-free negative electrode film layer, the fourth film layer contains a second negative electrode active material and does not contain a first negative electrode active material, and the third film layer is arranged on the side, connected with the current collector, of the lithium-free negative electrode film layer. The introduction of the second negative active material in the fourth film layer is utilized, the cycle life of the battery is favorably prolonged, the third film layer is favorable for the deposition of lithium metal towards the direction close to the current collector on one side where the lithium-free negative film layer is connected with the current collector, and lithium dendrites on the surface of the negative pole piece are reduced.

In some embodiments, the first negative active material is added to the third film layer in an amount of 10% to 60% by mass percentage. The lithium dendrite formation can be effectively inhibited in the range, the cycle life of the battery is good, if the addition amount is too small, the effect of reducing the lithium dendrite on the surface of the negative pole piece is limited, and if the addition amount is too large, the cycle life is poor.

In a second aspect, the present application provides a lithium ion battery cell, which includes a positive electrode plate and the negative electrode plate provided in the foregoing embodiment, wherein a ratio of a total capacity of the negative electrode plate to a total capacity of the positive electrode plate is N/P, where N/P is less than 1; alternatively, 0.4 ≦ N/P <1.

In the technical scheme of the embodiment of the application, as the ratio N/P of the total capacity of the negative pole piece to the total capacity of the positive pole piece is less than 1, namely, a lithium-rich material is used as a positive active material, the amount of lithium ions in the positive pole piece is far larger than the amount of lithium ions which can be accommodated by the negative pole piece, after one cycle, the excessive lithium in the positive pole is stored in the negative pole in a lithium metal form, and the active lithium consumed due to side reaction in the subsequent cycle process is supplemented, so that high coulombic efficiency and cycle life are obtained. In addition, the battery does not contain lithium metal in the assembling process of the battery and the initial state after the assembling is finished, so that the cost and potential safety hazards in the assembling, storing and transporting processes are greatly reduced. In addition, within the range of the N/P value, the better cycle life and higher energy density can be considered, if the N/P value is too small, the content of lithium metal is high, and the battery cycle is poor; an excessively large N/P value results in a low lithium metal content and a low energy density.

In some embodiments, the lithium-philic material of the negative electrode sheet is not loaded with lithium metal after the lithium-ion battery cell is discharged. Under the above arrangement, 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, so as to supplement active lithium consumed due to side reaction in the subsequent cycle process, thereby obtaining high coulombic efficiency and cycle life.

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 in the foregoing embodiments, where the plurality of lithium ion battery cells are accommodated in the box.

In a fourth aspect, the present application provides an electric device, which includes the lithium ion battery in the above embodiments, and the lithium ion battery is used for providing electric energy.

The foregoing description is only an overview of the technical solutions of the present application, and the present application can be implemented according to the content of the description in order to make the technical means of the present application more clearly understood, and the following detailed description of the present application is given in order to make the above and other objects, features, and advantages of the present application more clearly understandable.

Drawings

Various additional 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 drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Moreover, like reference numerals are used to refer to like elements throughout. In the drawings:

FIG. 1 is a schematic structural diagram of a vehicle according to some embodiments of the present application;

FIG. 2 is an exploded view of a lithium-ion battery according to some embodiments of the present disclosure;

fig. 3 is an exploded view of a lithium ion battery cell according to some embodiments of the present disclosure;

FIG. 4 is a schematic view of a negative pole piece structure according to some embodiments of the present disclosure;

FIG. 5 is a schematic view of a negative pole piece structure according to some embodiments of the present disclosure;

fig. 6 is a schematic view of a negative electrode tab structure according to some embodiments of the present disclosure.

The reference numbers in the detailed description are as follows:

1000-a vehicle;

100-a lithium ion battery; 200-a controller; 300-a motor;

10-a box body; 11-a first part; 12-a second part;

20-lithium ion battery monomer; 21-end cap; 21 a-electrode terminal; 22-a housing; 23-an electrode assembly; 23 a-a tab;

24-a negative pole piece; 241-a current collector; 243-lithium free negative electrode film layer; 244 — first film layer; 245-a second film layer; 246-third film layer; 247-fourth film layer.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following examples are merely used to more clearly illustrate the technical solutions of the present application, and therefore are only examples, and the protection scope of the present application is not limited thereby.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "including" and "having," and any variations thereof, in the description and claims of this application and the description of the above figures are intended to cover non-exclusive inclusions.

In the description of the embodiments of the present application, the technical terms "first", "second", and the like are used only for distinguishing different objects, and are not to be construed as indicating or implying relative importance or implicitly indicating the number, specific order, or primary-secondary relationship of the technical features indicated. In the description of the embodiments of the present application, "a plurality" means two or more unless specifically defined otherwise.

Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.

In the description of the embodiments of the present application, the term "and/or" is only one kind of association relationship describing an associated object, and means that three relationships may exist, for example, a and/or B, and may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.

In the description of the embodiments of the present application, the term "plurality" refers to two or more (including two), and similarly, "plural sets" refers to two or more (including two), and "plural pieces" refers to two or more (including two).

In the description of the embodiments of the present application, the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", and the like, indicate the directions or positional relationships indicated in the drawings, and are only for convenience of description of the embodiments of the present application and for simplicity of description, but do not indicate or imply that the referred device or element must have a specific direction, be constructed and operated in a specific direction, and thus, should not be construed as limiting the embodiments of the present application.

In the description of the embodiments of the present application, unless otherwise explicitly stated or limited, the terms "mounted," "connected," "fixed," and the like are used in a broad sense, and for example, may be fixedly connected, detachably connected, or integrated; mechanical connection or electrical connection is also possible; either directly or indirectly through intervening media, either internally or in any other relationship. Specific meanings of the above terms in the embodiments of the present application can be understood by those of ordinary skill in the art according to specific situations.

At present, the application of the power battery is more and more extensive from the development of market situation. The power battery is not only applied to energy storage power supply systems such as hydraulic power, firepower, wind power and solar power stations, but also widely applied to electric vehicles such as electric bicycles, electric motorcycles, electric automobiles and the like, and a plurality of fields such as military equipment and aerospace. With the continuous expansion of the application field of the power battery, the market demand is also continuously expanding.

The inventors have noted that lithium ion batteries exist during actual use: (1) Lithium dendrites are easily generated in the charging and discharging processes of the battery, a large number of lithium dendrites cause damage of an SEI film, the coulombic efficiency of the battery is reduced, and the separator is possibly punctured to cause short circuit inside the battery, so that potential safety hazards are brought; (2) Lithium metal undergoes infinite relative volume changes during repeated deposition/dissolution processes, which can lead to severe solid electrolyte membrane (SEI) cracking. Due to the ultrahigh reactivity of lithium metal, exposed fresh lithium metal can immediately react with the electrolyte, and repeated breakage/repair of the SEI film can lead to continuous consumption of active substances and electrolyte, thereby resulting in lower cyclic coulombic efficiency and short cycle life. In order to solve the above problem, a currently common method is to pre-store an excess amount of lithium metal in the negative electrode to supplement the consumption of active lithium during the cycle. But this approach can reduce the energy density of the battery.

In order to relieve the generation of lithium dendrites and the volume effect of an electrode and also consider the problem of improving the energy density of a battery, the applicant researches and discovers that the negative electrode plate can be set without lithiation, a hollow carbon material containing a lithium-philic substance is introduced into the negative electrode plate, and the N/P value is adjusted to ensure that the ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate is smaller than 1, namely the quantity of lithium ions in the positive electrode plate is far larger than that of the lithium ions which can be accommodated by the negative electrode plate, then in the charging process, the excessive lithium ions in the positive electrode plate can be compounded with the lithium-philic substance in the hollow carbon material in the lithium metal form to finally form a composite lithium metal material, so that the volume change of the negative electrode plate in the deposition/dissolution process of the lithium metal is effectively buffered, the dendrites generated in the deposition/precipitation process of the lithium metal are effectively inhibited, and the safety performance, the cycle life and the energy density of the battery are improved.

Based on the above considerations, in order to solve the problems of alleviating the generation of lithium dendrites and the electrode volume effect, and also improving the energy density of the battery, the inventors have conducted intensive research and design a negative electrode plate, which includes: the lithium-free negative electrode film layer is coated on the surface of the current collector and contains a first negative electrode active material, the first negative electrode active material comprises a hollow carbon material and a lithium-philic substance, 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.

When the negative pole piece is directly used as the negative pole electrode of the lithium ion battery with the ratio of the total capacity of the negative pole piece to the total capacity of the positive pole piece being less than 1, the hollow carbon material can be used as a supporting framework in the charging process, so that not only is a containing space provided for lithium metal, but also the volume change generated by the negative pole piece in the deposition/dissolution process of the lithium metal can be buffered, and the generation of lithium dendrite is limited; the lithium deposition sites can be optimized by utilizing the lithium-philic substance, lithium ions are induced to enter the hollow carbon material and are uniformly deposited on the lithium-philic substance, dendritic crystals generated in the deposition/precipitation process of lithium metal are effectively inhibited, the danger of a lithium metal negative electrode is greatly reduced, the cycle life and the coulombic efficiency of the battery can be improved, the voltage polarization is reduced, and the energy density of the battery can be further remarkably improved due to the arrangement of no lithium on a negative electrode piece.

The lithium ion battery cell disclosed in the embodiment of the application can be used in electric devices such as vehicles, ships or aircrafts, but not limited thereto. The power supply system with the power consumption device can be formed by the lithium ion battery monomer, the battery and the like disclosed by the application, so that the lithium ion battery cathode is favorable to easily generating lithium dendrite and the energy density of the battery is low, and the performance stability and the service life of the battery are improved.

The embodiment of the application provides an electric device using a lithium ion battery as a power supply, and the electric device can be but is not limited to a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, a battery car, an electric automobile, a ship, a spacecraft and the like. The electric toy may include a stationary or mobile electric toy, such as a game machine, an electric car toy, an electric ship toy, an electric airplane toy, and the like, and the spacecraft may include an airplane, a rocket, a space shuttle, a spacecraft, and the like.

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

Referring to fig. 1, fig. 1 is a schematic structural diagram of a vehicle 1000 according to some embodiments of the present disclosure. The vehicle 1000 may be a fuel automobile, a gas automobile, or a new energy automobile, and the new energy automobile may be a pure electric automobile, a hybrid electric automobile, or a range-extended automobile, etc. The lithium ion battery 100 is disposed inside the vehicle 1000, and the lithium ion battery 100 may be disposed at the bottom or the head or the tail of the vehicle 1000. The lithium ion battery 100 may be used for power supply of the vehicle 1000, for example, the lithium ion battery 100 may serve as an operation power source of the vehicle 1000. The vehicle 1000 may further include a controller 200 and a motor 300, the controller 200 being used to control the lithium ion battery 100 to supply power to the motor 300, for example, for start-up, navigation, and operational power demand while the vehicle 1000 is traveling.

In some embodiments of the present application, the lithium ion battery 100 may be used not only as an operating power source of the vehicle 1000, but also as a driving power source of the vehicle 1000, instead of or partially in place of fuel or natural gas, to provide driving power for the vehicle 1000.

Referring to fig. 2, fig. 2 is an exploded view of a lithium ion battery 100 according to some embodiments of the present disclosure. The lithium ion battery 100 includes a case 10 and a lithium ion battery cell 20, and the lithium ion battery cell 20 is accommodated in the case 10. The case 10 is used to provide a receiving space for the lithium ion battery cell 20, and the case 10 may have various structures. In some embodiments, the case 10 may include a first portion 11 and a second portion 12, the first portion 11 and the second portion 12 cover each other, and the first portion 11 and the second portion 12 together define a receiving space for receiving the lithium ion battery cell 20. The second part 12 may be a hollow structure with one open end, the first part 11 may be a plate-shaped 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 containing space; the first portion 11 and the second portion 12 may be both hollow structures with one side open, and the open side of the first portion 11 may cover the open side of the second portion 12. Of course, the box 10 formed by the first and second portions 11 and 12 may have various shapes, such as a cylinder, a rectangular parallelepiped, and the like.

In the lithium ion battery 100, the number of the lithium ion battery cells 20 may be multiple, and the multiple lithium ion battery cells 20 may be connected in series or in parallel or in series-parallel, where in series-parallel refers to that the multiple lithium ion battery cells 20 are connected in series or in parallel. The plurality of lithium ion battery cells 20 can be directly connected in series or in parallel or in series-parallel, and the whole formed by the plurality of lithium ion battery cells 20 is accommodated in the box body 10; of course, the lithium ion battery 100 may also be a battery module formed by connecting a plurality of lithium ion battery cells 20 in series, in parallel, or in series-parallel, and then connecting a plurality of battery modules in series, in parallel, or in series-parallel to form a whole, and accommodated in the box 10. The lithium ion battery 100 may further include other structures, for example, the lithium ion battery 100 may further include a bus bar component for realizing electrical connection between the plurality of lithium ion battery cells 20.

Each lithium ion battery cell 20 may be a secondary battery or a primary battery; but is not limited to, a lithium sulfur battery, a sodium ion battery, or a magnesium ion battery. The lithium ion battery cell 20 may be in a cylinder, a flat body, a rectangular parallelepiped, or other shapes.

Referring to fig. 3, fig. 3 is an exploded schematic view of a lithium ion battery cell 20 according to some embodiments of the present disclosure. The lithium ion battery cell 20 refers to the smallest unit constituting the battery. As shown in fig. 3, the lithium ion battery cell 20 includes an end cap 21, a case 22, an electrode assembly 23, and other functional components.

The end cap 21 is a member that covers an opening of the case 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 may be adapted to the shape of the housing 22 to fit the housing 22. Optionally, the end cap 21 may be made of a material (e.g., an aluminum alloy) having a certain hardness and strength, so that the end cap 21 is not easily deformed when being extruded and collided, and the lithium ion battery cell 20 can have a higher structural strength and an improved safety performance. The end cap 21 may be provided with functional components such as the electrode terminals 21 a. The electrode terminal 21a may be used to electrically connect with the electrode assembly 23 for outputting or inputting electric power of the lithium ion battery cell 20. In some embodiments, the end cap 21 may further be provided with a pressure relief mechanism for relieving the internal pressure when the internal pressure or temperature of the lithium ion battery cell 20 reaches a threshold value. The material of the end cap 21 may also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not limited in this embodiment. In some embodiments, insulation may also be provided on the inside of the end cap 21, which may be used to isolate the electrical connection components within the housing 22 from the end cap 21 to reduce the risk of short circuits. Illustratively, the insulator may be plastic, rubber, or the like.

The case 22 is an assembly for mating with the end cap 21 to form an internal environment of the lithium ion battery cell 20, wherein the formed internal environment may be used to house the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 may be separate components, and an opening may be provided in the housing 22, and the opening may be covered by the end cap 21 at the opening to form an internal environment of the lithium ion battery cell 20. Without limitation, the end cap 21 and the housing 22 may be integrated, and specifically, the end cap 21 and the housing 22 may form a common connecting surface before other components are inserted into the housing, and when it is necessary to enclose the inside of the housing 22, the end cap 21 covers the housing 22. The housing 22 may be a variety of shapes and sizes, such as rectangular parallelepiped, cylindrical, hexagonal prism, etc. Specifically, the shape of the case 22 may be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 may be various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., which is not limited in the embodiments of the present invention.

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 within the case 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 generally provided between the positive electrode sheet and the negative electrode sheet. The portions of the positive and negative electrode sheets having the active material constitute the main body of the electrode assembly 23, and the portions of the positive and negative electrode sheets having no active material constitute tabs 23a, respectively. The positive electrode tab and the negative electrode tab may be located at one end of the main body portion together or at both ends of the main body portion, respectively. During the charge and discharge of the battery, the positive electrode active material and the negative electrode active material react with the electrolyte, and the tab 23a is connected to the electrode terminal 21a to form a current loop.

Referring to fig. 4-6, according to some embodiments of the present application, the negative pole piece 24 includes: 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 comprises a hollow carbon material and a lithium-philic substance, 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 lithium-free negative electrode film layer 243 means that no lithium element is contained in the film layer.

The lithium-philic substance is a substance which is easy to chemically react with lithium ions and reduces the nucleation overpotential of the lithium ions on the hollow carbon material.

In the technical scheme of this application embodiment, can be less than 1 lithium ion battery 100's negative electrode with negative pole piece 24 direct total capacity as negative pole piece 24 and the total capacity's of positive pole piece ratio to in the charging process, utilize the setting of hollow carbon material, on the one hand as the support chassis, not only provide the accommodation space for lithium metal, but also can cushion the volume change that lithium metal negative pole piece 24 produced in deposit/dissolution process, restrict the production of lithium dendrite, on the other hand has electric conductivity, can induce lithium metal uniform deposition. The lithium deposition sites are optimized by the lithium-philic substances, lithium ions are induced to enter the hollow carbon material and are uniformly deposited on the lithium-philic substances, dendritic crystals generated in the lithium metal deposition/precipitation process are effectively inhibited, the danger of a lithium metal negative electrode is greatly reduced, the cycle life and the coulombic efficiency of the battery can be improved, the voltage polarization is reduced, and the energy density of the battery can be further remarkably improved due to the fact that the negative electrode piece 24 is free of lithium.

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

The current collector 241 has opposite two surfaces, wherein the lithium-free negative electrode film layer 243 may be coated only on either surface of the current collector 241, and optionally, the lithium-free negative electrode film layer 243 is coated on both surfaces of the current collector 241.

The first negative active material may be prepared by itself or may be purchased directly from the market, and is not limited thereto.

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

According to some embodiments of the present application, optionally, the number of wall layers of the hollow carbon material is greater than or equal to 2.

Namely, the hollow carbon material is a multi-wall hollow carbon material which is beneficial to lithium metal entering the hollow carbon material.

In some embodiments, optionally, the first anode active material has a lithium extraction overpotential of less than 0V and not less than-0.03V, based on a lithium metal potential of 0V.

Within the above range, the first negative active material has lithium-philic properties to lithium metal, so that lithium ions are selectively induced into the hollow carbon material and uniformly deposited in the hollow carbon material to be connected to the lithium-philic material.

Illustratively, the first negative electrode active material has a lithium extraction overpotential of any one value or between any two values of-0.1V, -0.2V, -0.03V, in terms of a lithium metal potential of 0V.

That is, in actual use, the lithium-deposition overpotential of the first negative electrode active material may be used as a criterion for judging whether the first negative electrode active material has lithium-philic property.

Wherein the first negative electrode active material is measured in a lithium-deposition overpotential manner including: using the first negative active material as a working electrode, li _0.5 FePO ₄ As a reference electrode, lithium metal was used as a counter electrode. At very low current densities (e.g., 10 μ A cm) ^-2 ) Depositing metallic lithium on the working electrode. With working electrode against Li metal (Li/Li) ⁺ ) Voltage of (2) is ordinate and capacity is abscissa. When the capacity is increased, the voltage tends to decrease first and then level, and in the process, when the curve has no inflection point or the absolute value of the voltage corresponding to the inflection point is less than or equal to 0.03V, the material to be detected has lithium affinity. With inflection point corresponding to the absolute value of voltage>At 0.03V, the material does not have lithium affinity.

Since lithium ions can diffuse into the hollow carbon material, the hollow carbon material can be a hollow sphere.

According to some embodiments of the application, optionally, the hollow carbon material has an inner surface forming a cavity, and at least one opening extending through the inner surface and communicating with the cavity.

Above-mentioned setting utilizes at least one open-ended setting, is convenient for load lithium-philic substance in hollow carbon material, reduces the preparation degree of difficulty.

According to some embodiments of the application, optionally, the hollow carbon material is tubular in shape.

The tubular hollow carbon material can become a conductive path, which is beneficial to the uniform deposition of lithium metal in the hollow carbon material, and the first cathode active material formed by the tubular hollow carbon material is convenient to purchase in the market.

According to some embodiments of the application, optionally, the lithium-philic substance is at least one of a lithium-philic metal and a compound thereof.

Those skilled in the art can select the first negative active material according to actual needs to achieve lithium affinity of the first negative active material.

According to some embodiments of the present application, optionally, the lithium-philic metal comprises at least one of Au, ag, zn, fe, co, ni, ga, sn, in, ge, ti, mu, pt, al, mg.

The lithium-philic metal has obvious lithium-philic property on the lithium metal, can reduce the nucleation overpotential of the lithium metal on the negative pole piece 24, is beneficial to the nucleation of lithium ions in the hollow carbon material, can realize the uniform deposition of the lithium metal in the hollow carbon material, and effectively inhibits the formation of lithium dendrite.

Illustratively, the lithium-philic metal can be Au, ag, zn, fe, co, ni, ga, sn, in, ge, ti, mu, pt, al, or Mg, and the lithium-philic metal can also be a mixture or alloy of at least two of the above simple metals, for example, the lithium-philic metal is a mixture or alloy of Au and Ag.

According to some embodiments of the present application, optionally, the lithium-philic metal is present in the first anode active material in an amount of 0.5% to 20% by mass.

The content of the lithium-philic metal in the range is reasonable, so that the first negative active material has a good lithium-philic effect, and the initial coulombic efficiency and the cycle life can be improved.

Illustratively, the mass content of the lithium-philic metal in the first anode active material is any one value or between any two values of 0.5%, 1%, 2%, 3%, 5%, 7%, 10%, 12%, 15%, 17%, 19%, 20%.

Optionally, the mass content of the lithium-philic metal in the first anode active material is 2% to 10%.

According to some embodiments of the present application, optionally, the lithium-philic metal compound comprises one or more of an oxide, a sulfide, a fluoride, a nitride, a chloride, a carbide.

The lithium-philic metal compound has obvious lithium-philic property on lithium metal, can reduce the nucleation overpotential of the lithium metal on the negative pole piece 24, is beneficial to the nucleation of lithium ions in the hollow carbon material, can realize the uniform deposition of the lithium metal in the hollow carbon material, and effectively inhibits the formation of lithium dendrite.

Wherein, the lithium-philic metal comprises at least one of Au, ag, zn, fe, co, ni, ga, sn, in, ge, ti, mu, pt, al and Mg, and the compound of the lithium-philic metal is one or more of oxides, sulfides, fluorides, nitrides, chlorides and carbides of the lithium-philic metal.

Illustratively, the lithium-philic metal compound is Ag ₂ At least one of O, znO, feC, etc.

In some embodiments, optionally, the mass content of the lithium-philic metal compound in the first anode active material is 0.5% to 30% by mass of the metal element.

The above range has excellent effect of attracting lithium and can improve cycle life.

Illustratively, the mass content of the lithium-philic metal compound in the first anode active material is any one value or between any two values, in terms of the metal element, of 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 20%, 25%, 30%.

Optionally, the mass content of the lithium-philic metal compound in the first anode active material is 3% to 15% in terms of the metal element.

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 extraction over potential of the second negative electrode active material is less than 0V and not less than-0.5V, in terms of a lithium metal potential of 0V.

According to the arrangement, on one hand, the second negative electrode is used with the activity of less than 0V and not less than-0.5V, so that the lithium-precipitation overpotential is matched with the lithium metal potential, so that when the negative electrode pole piece 24 is directly used as the negative electrode of the lithium ion battery 100 with the ratio of the total capacity of the negative electrode pole piece 24 to the total capacity of the positive electrode pole piece being less than 1, the lithium metal composite negative electrode is formed in the charging process, on the other hand, a gap between the second negative electrode active materials can provide a space for lithium deposition, and the conductive agent can effectively and uniformly deposit lithium ions, so that the deposition of lithium metal on the surface of the negative electrode pole piece 24 can be reduced, and a uniform composite lithium metal negative electrode is formed.

Illustratively, the lithium extraction overpotential of the second negative electrode active material is any one value or between any two values of-0.5V, -0.4V, -0.3V, -0.2V, -0.1V, in terms of the lithium metal potential being 0V.

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

The lithium-precipitating overpotential of the negative electrode active material is easy to meet the requirement and is easy to obtain.

Wherein, the carbon-based material can be at least one of graphite, mesocarbon microbeads, hard carbon, soft carbon and the like, 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.

Referring to fig. 4 to fig. 6, in the actual setting process, there are various setting manners of the lithium-free negative electrode film layer 243, and those skilled in the art can set the setting according to actual requirements.

In some embodiments, optionally, the lithium-free negative electrode film layer 243 includes: at least two film layers are arranged in a stacked manner in the thickness direction, each film layer contains a second negative electrode active material, and at least one film layer contains a first negative electrode active material.

The at least one layer containing the first negative electrode active material includes an arrangement in which only a part of the layer contains the first negative electrode active material, and also includes an arrangement in which all the layers contain the first negative electrode active material.

The preparation method is simple under the above arrangement, and the lithium-free negative electrode film layer 243 can be provided with the first negative electrode active material only in a part of the film layers or all the film layers according to actual requirements, so that the specific arrangement method of the lithium-free negative electrode film layer 243 is expanded.

The number of at least two film layers is, for example, two, three, four or five, etc., and those skilled in the art can set the number according to actual requirements.

It should be noted that the content of the first negative electrode active material contained in each film layer may be the same or different, and similarly, the content of the second negative electrode active material contained in each film layer may be the same or different, and those skilled in the art can select the first negative electrode active material according to actual needs.

For convenience of preparation, optionally, each film layer contains the same content of the first anode active material, and each film layer containing the second anode active material also contains the same content of the second anode active material.

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, at this time, in addition to the mode of coating the film layers to the preset thickness in a layered manner, the slurry containing the first negative electrode active material and the second negative electrode active material can be directly coated on the current collector 241 to the preset thickness, and the structures of the lithium-free negative electrode film layers 243 finally obtained by the two coating modes are the same.

Referring to fig. 4, in some embodiments, optionally, the lithium-free negative electrode film layer 243 includes: first and second film layers 244 and 245, the first and second film layers 244 and 245 being alternately stacked in a thickness direction, the first film layer 244 containing a second anode active material and a first anode active material, the second film layer 245 containing the second anode active material and not containing the first anode active material; the side of the non-lithium negative electrode film layer 243 connected to the current collector 241 is the first film layer 244.

The first film 244 is arranged on the side where the lithium-free negative electrode film 243 is connected with the current collector 241, so that lithium metal is deposited towards the direction close to the current collector 241, and lithium dendrite on the surface of the negative electrode piece 24 is reduced.

Alternatively, the first film layers 244 and the second film layers 245 are alternately stacked in sequence in the thickness direction.

Optionally, the number of first film layers 244 is at least one and the number of second film layers 245 is at least one. For example, the number of the first film layer 244 is two, the number of the second film layer 245 is two, at this time, the side of the lithium-free negative electrode film layer 243 connected with 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.

As shown in fig. 4, the number of the first film layers 244 is one, the number of the second film layers 245 is one, and 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.

When the lithium-free negative electrode film layer 243 includes: when at least two film layers are 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, in some embodiments, optionally, the amount of the first negative electrode active material added in the lithium-free negative electrode film layer 243 is 0.125% to 5% by mass percentage.

The formation of lithium dendrites can be effectively inhibited within the range, the cycle life of the battery is good, if the addition amount is too small, the effect of reducing the lithium dendrites on the surface of the negative electrode plate 24 is limited, and if the addition amount is too large, the cycle life is poor.

Illustratively, the amount of the first anode active material added in the lithium-free anode film layer 243 is any one of or between 0.125%, 0.2%, 0.5%, 0.7%, 1%, 1.3%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, by mass%.

Referring to fig. 5 and fig. 6, in some embodiments, optionally, the lithium-free negative electrode film layer 243 includes: a third membrane layer 246, the third membrane layer 246 containing the first negative active material and not containing the second negative active material.

In other words, in actual use, only the third film layer 246 may be used as the lithium-free negative electrode film layer 243, or the third film layer 246 may be provided in multiple layers and partially, thereby expanding the specific arrangement manner of the lithium-free negative electrode film layer 243.

As shown in fig. 5, the lithium-free negative electrode film layer 243 is the third film layer 246.

Referring to fig. 6, in some embodiments, optionally, the lithium-free negative electrode film layer 243 further includes: the fourth film layers 247, the third film layers 246, and the fourth film layers 247 are alternately stacked in the thickness direction of the lithium-free negative electrode film layer 243, the fourth film layers 247 contain the second negative electrode active material and do not contain the first negative electrode active material, and the third film layer 246 is provided on the side where the lithium-free negative electrode film layer 243 is connected to the current collector 241.

With the above arrangement, the introduction of the second negative active material in the fourth film layer 247 is beneficial to the improvement of the cycle life of the battery. The third film layer 246 is arranged on the side where the lithium-free negative electrode film layer 243 is connected with the current collector 241, so that lithium metal is deposited towards the direction close to the current collector 241, and lithium dendrites on the surface of the negative electrode piece 24 are reduced.

In some embodiments, optionally, the first negative active material is added in the third film layer 246 in an amount of 10% -60% by mass percentage.

The formation of lithium dendrites can be effectively inhibited within the range, the cycle life of the battery is good, if the addition amount is too small, the effect of reducing the lithium dendrites on the surface of the negative pole piece 24 is limited, and if the addition amount is too large, the cycle life is poor.

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

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

N/P defines: n: the total capacity of the negative pole piece; p total capacity of positive pole piece, N = negative material gram capacity x surface density negative electrode to pole piece size, P = positive material gram capacity x surface density positive electrode to pole piece size, N/P <1, that is, the capacity of negative electrode < the capacity of positive electrode.

N/P <1, namely, a lithium-rich material is used as a positive active material, so that the amount of lithium ions in the positive pole piece is far larger than that of the lithium ions which can be accommodated in the negative pole piece.

With the arrangement, since N/P is less than 1, after one cycle, the excessive lithium of the positive electrode is stored in the negative electrode in the form of lithium metal, and active lithium consumed due to side reaction in the subsequent cycle process is replenished, so that high coulombic efficiency and cycle life are obtained. In addition, the battery does not contain lithium metal in the assembling process of the battery and the initial state after the assembling is finished, so that the cost and potential safety hazards in the assembling, storing and transporting processes are greatly reduced. In addition, within the range of the N/P value, the better cycle life and higher energy density can be considered, if the N/P value is too small, the content of lithium metal is high, and the battery cycle is poor; an excessively large N/P value results in a low lithium metal content and a low energy density.

Alternatively, 0.4 ≦ N/P <1.

Illustratively, the value of N/P is any one or between any two of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, etc.

In some embodiments, optionally, the lithium-philic material of the negative electrode sheet is not loaded with lithium metal after discharge of the lithium ion battery cell.

According to some embodiments of the present application, the present application further provides a lithium ion battery, which includes a box body 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 body.

According to some embodiments of the present application, the present application further provides an electric device, including the lithium ion battery of any of the above aspects, and the lithium ion battery is used for providing electric energy for the electric device.

Some specific examples are listed below to better illustrate the present application.

Examples and comparative examples

Preparing a positive pole piece: the composite material is prepared from a cobalt manganese (NCM) ternary material, a conductive agent carbon black and a binder polyvinylidene fluoride (PVDF) according to the mass ratio of 97:1:2, adding N-methyl pyrrolidone, mixing and stirring for 0.5-6h to obtain anode slurry; and then uniformly coating the anode current collector on the anode current collector, and drying, cold pressing and slitting to obtain the anode piece.

The preparation method of the negative electrode plate of each example and comparative example is as follows:

the raw material selection of each example and comparative negative electrode sheet is shown in table 1.

[ negative electrode sheets of examples 1 to 6, 10 to 18, and comparative examples 5 to 9 ]: mixing the second negative electrode active material, the conductive agent carbon black, the binder Styrene Butadiene Rubber (SBR), the thickening agent sodium carboxymethyl cellulose (CMC) and the first negative electrode active material, then adding the mixture into deionized water, mixing and stirring for 0.5-6h, uniformly coating the obtained slurry on a negative electrode current collector, and drying to obtain the composite material.

In examples 1 to 7, the weight ratio of the second negative electrode active material, the conductive agent carbon black, the styrene-butadiene rubber, the sodium carboxymethyl cellulose, and the first negative electrode active material contained in the first film layer is 96.7:0.3:1.25:1.25:0.5, the remaining examples and comparative examples can adjust the content of the first anode active material according to the above-mentioned ratio.

[ negative electrode sheet of example 7 ]: the pole piece is coated with double layers, and a second negative active material, a conductive agent carbon black, a binder Styrene Butadiene Rubber (SBR), a thickening agent sodium carboxymethylcellulose (CMC) and a first negative active material are coated according to the weight ratio of 96.7:0.3:1.25:1.25:0.5, adding the mixture into deionized water, mixing and stirring for 0.5-6h, uniformly coating the mixture on a negative current collector, drying to obtain a first film layer, coating a layer of a second negative active material, a conductive agent carbon black, a binder Styrene Butadiene Rubber (SBR) and a thickening agent sodium carboxymethyl cellulose (CMC) on the surface of the first film layer, and mixing the materials according to a weight ratio of 96.7:0.8:1.25:1.25 mixing the obtained slurry, and drying to obtain a second film layer.

[ example 8, negative electrode sheet of comparative examples 10 to 13 ]: mixing a first negative electrode active material, styrene Butadiene Rubber (SBR) serving as a binder and sodium carboxymethyl cellulose (CMC) serving as a thickening agent according to a weight ratio, adding deionized water, mixing and stirring for 0.5-6h to obtain a current collector surface coating slurry, uniformly coating the current collector surface coating slurry on a negative electrode current collector, and drying to obtain a third film layer; mixing a second negative electrode active material, a conductive agent carbon black, a binder Styrene Butadiene Rubber (SBR), and a thickening agent sodium carboxymethylcellulose (CMC) according to a weight ratio of 96.7:0.8:1.25:1.25 and coating the mixture on the third film layer to obtain a fourth film layer. The content of the first anode active material may be adjusted according to the adjustment ratio.

[ negative electrode sheet of example 9 ]: mixing a first negative electrode active material, styrene Butadiene Rubber (SBR) serving as a binder and sodium carboxymethyl cellulose (CMC) serving as a thickening agent according to a weight ratio of 1:0.5:0.5, adding deionized water, mixing and stirring for 0.5-6h to obtain current collector surface coating slurry, uniformly coating the current collector surface coating slurry on a negative current collector, and drying to obtain the cathode current collector.

(negative electrode sheet of comparative examples 1 to 3): the only difference from example 1 is: comparative examples 1 to 3, which did not contain the first negative electrode active material, were prepared by mixing a second negative electrode active material, a conductive agent, carbon black, a binder Styrene Butadiene Rubber (SBR), and a thickener, sodium carboxymethylcellulose (CMC), in a weight ratio of 96.7:0.8:1.25:1.25, uniformly coating on a negative current collector after mixing, and drying to obtain the product.

(negative electrode sheet of comparative example 4): and directly taking a current collector as a negative pole piece.

[ 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 and obtained firstly, and the first film layer is coated and obtained on the surface of the second film layer.

And (3) isolation film: polypropylene film was used as the separator.

Electrolyte solution: mixing LiPF ₆ Dissolving ethylene carbonate, ethyl methyl carbonate and diethyl carbonate in a volume ratio of 1:1:1, an electrolyte solution having a concentration of 1mol/L is prepared.

Manufacturing the lithium ion battery: stacking the positive pole piece, the isolating membrane and the negative pole piece in sequence to obtain a naked electric core; placing the naked electric core in a packaging shell, injecting electrolyte after drying, and obtaining the lithium ion battery through vacuum packaging, standing, formation, shaping and other processes.

The energy density and cycle life of the lithium ion batteries obtained in each example and comparative example were measured, and the results are shown in table 2.

1) Energy density testing of lithium ion batteries

The lithium ion batteries of examples and comparative examples were charged at 25 ℃ to 4.3V at a constant current of 1C, then charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to 2.8V as one charge-discharge cycle. The battery is subjected to 30 charge-discharge cycles according to the method, and the discharge energy of the 30 th cycle is divided by the total weight of the battery to obtain the energy density of the battery.

2) Method for testing cycle performance of lithium ion battery

The lithium ion batteries of examples and comparative examples were charged at 25 ℃ to 4.3V at a constant current of 1C, then charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to 2.8V as one charge-discharge cycle. The cycle number when the discharge capacity is reduced to 80% is the cycle life, taking the first discharge capacity as 100%.

TABLE 1 examples and comparative negative pole piece test parameters

In table 1, when the lithium-philic substance is a lithium-philic metal compound, the lithium-philic substance loading refers to a mass content of the lithium-philic metal compound in the first anode active material in terms of a metal element. When the lithium-philic substance is a lithium-philic metal, the lithium-philic substance loading refers to the mass content of the lithium-philic metal in the first anode active material.

Table 2 test parameter holes and test results for each example and comparative negative electrode sheet

Comparative examples 1 to 3 did not contain the corresponding first negative active material as compared with examples 1 to 3, and the second negative active material, carbon black as a conductive agent, styrene Butadiene Rubber (SBR) as a binder, and sodium carboxymethylcellulose (CMC) as a thickener were directly mixed in a weight ratio of 96.7:0.8:1.25:1.25, and the mixture was uniformly coated on a negative current collector, and it can be seen that the cycle life of the lithium ion batteries prepared in comparative examples 1-3 was significantly reduced in the absence of the first negative active material, indicating that lithium dendrites were generated on the surface of the negative electrode sheet.

In comparative example 4, the current collector is directly used as the negative electrode, and it can be seen that the cycle life of the prepared lithium ion battery is remarkably reduced, and the use requirement of the lithium ion battery cannot be met.

Comparative example 5 is different from example 1 only in that the designed N/P value =1, and the energy density of the lithium ion battery prepared in comparative example 5 is only 270Wh/kg, and the stored electric energy per unit volume is too small, so that the lithium ion battery has no industrial application value.

The first negative active material in comparative example 6 has too little lithium-philic material loading, and compared to example 14, the addition amount of the first negative active material in the lithium-free negative electrode film layer is adjusted to make the addition amount of the lithium-philic material in the negative electrode sheet 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 shorter than that of example 14, which indicates that the first negative active material in comparative example 6 has too little lithium-philic material loading, and at this time, even if the content of the first negative active material in the negative electrode sheet is increased, the lithium dendrite precipitation on the surface of the negative electrode sheet cannot be effectively improved.

The first negative electrode active material in comparative example 7 has an excessive lithium-philic material loading, and compared to example 15, the addition amount of the first negative electrode active material in the lithium-free negative electrode film layer is adjusted so that the addition amount of the lithium-philic material in the negative electrode sheet is similar, so that on the premise that the energy density values of the lithium ion batteries prepared in comparative example 7 and example 15 are similar, the cycle life of comparative example 7 is significantly shorter than that of example 15, which indicates that the first negative electrode active material in comparative example 7 has an excessive lithium-philic material loading, and even if the content of the first negative electrode active material in the negative electrode sheet is reduced at this time, the precipitation of lithium dendrites on the surface of the negative electrode sheet cannot be effectively improved.

Compared with example 1, on the premise that the addition amount of the first negative electrode active material in the lithium-free negative electrode film layer is too small, and the energy density phase difference of the lithium ion batteries prepared by the first negative electrode active material and the lithium ion batteries prepared by the second negative electrode active material is only 2Wh/kg, the cycle life of the lithium ion battery prepared by the comparative example 8 is remarkably shorter than that of the lithium ion battery prepared by the example 1, which indicates that the addition amount of the first negative electrode active material in the lithium-free negative electrode film layer is too small, and the precipitation of lithium dendrites on the surface of the negative electrode sheet cannot be effectively improved.

Compared with example 1, the addition amount of the first negative electrode active material in the lithium-free negative electrode film layer is too much, so that the energy density of the lithium ion battery prepared in comparative example 9 is lower than that of example 1, and the cycle life of the lithium ion battery is remarkably lower than that of example 1, which shows that the addition amount of the first negative electrode active material in the lithium-free negative electrode film layer is too much, so that the energy density of the battery is reduced, and lithium dendrite precipitation on the surface of the negative electrode pole piece cannot be effectively improved.

Comparative example 10 compared with example 8, the loading amount of the lithium-philic substance in the first negative electrode active material was too small, and the addition amount of the lithium-philic substance in the negative electrode sheet was adjusted to be similar by adjusting the addition amount of the first negative electrode active material in the lithium-free negative electrode film layer, but according to table 2, the above arrangement resulted in the energy density value of the lithium ion battery prepared in comparative example 10 being slightly smaller than that of example 8, and the cycle life of comparative example 10 being significantly lower than that of example 8, which indicates that the loading amount of the lithium-philic substance in the first negative electrode active material was too small, and even if the content of the first negative electrode active material in the negative electrode sheet was increased at this time, the precipitation of lithium dendrites on the surface of the negative electrode sheet could not be effectively improved.

Comparative example 11 compared with example 8, the loading amount of the lithium-philic substance in the first negative electrode active material is too much, and the addition amount of the lithium-philic substance in the negative electrode plate is made to be similar by adjusting the addition amount of the first negative electrode active material in the lithium-free negative electrode film layer, but according to table 2, on the premise that the energy densities of the lithium ion batteries manufactured in comparative example 11 and example 8 are the same, the cycle life of comparative example 11 is significantly lower than that of example 8, which shows that the loading amount of the lithium-philic substance in the first negative electrode active material in comparative example 11 is too little, and 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.

Comparative example 12 is the same as example 8 in the amount of the first negative electrode active material added to the lithium-free negative electrode film layer, but the amount of the first negative electrode active material added to the third film layer is too small to significantly reduce the cycle life on the basis of a small difference in energy density compared to example 8, and comparative example 13 is the same as example 8 in the amount of the first negative electrode active material added to the lithium-free negative electrode film layer, but the amount of the first negative electrode active material added to the third film layer is too large to significantly reduce the cycle life compared to example 8, and it is demonstrated by comparison example 12 and comparative example 13 that the amount of the first negative electrode active material added to the third film layer affects the precipitation of lithium dendrites on the surface of the negative electrode sheet under the condition that the amount of the first negative electrode active material added to the lithium-free negative electrode film layer is the same.

The difference between the comparative example 14 and the example 7 is only that the coating mode is opposite, and it can be seen from table 2 that the arrangement that the first film layer containing the first negative active material is arranged on the side where the lithium-free negative electrode film layer is connected with the current collector is beneficial to the deposition of lithium metal in the direction close to the current collector, so that lithium dendrite on the surface of the negative electrode plate can be reduced, the cycle life of the lithium ion battery can be effectively prolonged, and the energy density of the lithium ion battery can be improved.

In summary, the negative electrode plate provided by the present application can be directly used as a negative electrode of a lithium ion battery having a ratio of the total capacity of the negative electrode plate to the total capacity of the positive electrode plate less than 1, so as to suppress dendrites generated during deposition/precipitation of lithium metal during charging, improve the cycle life and coulombic efficiency of the battery, and further significantly improve the energy density of the battery due to the absence of lithium in the negative electrode plate.

Finally, it should be noted that: the above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present disclosure, and the present disclosure should be construed as being covered by the claims and the specification. In particular, the technical features mentioned in the embodiments can be combined in any way as long as there is no structural conflict. The present application is not intended to be limited to the particular embodiments disclosed herein, but rather to cover all embodiments falling within the scope of the appended claims.

Claims

1. A negative electrode sheet, comprising:

a current collector; and

the lithium-free negative electrode film layer is coated on the surface of the current collector and contains a first negative electrode active material, the first negative electrode active material comprises a hollow carbon material and a lithium-philic substance, and the lithium-philic substance is not loaded with lithium metal;

wherein the lithium-philic substance is supported on an inner surface of the hollow carbon material.

2. The negative electrode plate as claimed in claim 1, wherein the number of the wall layers of the hollow carbon material is not less than 2.

3. The negative electrode tab of claim 1, wherein the first negative electrode active material has a lithium extraction overpotential of less than 0V and not less than-0.03V, as measured at a lithium metal potential of 0V.

4. The negative electrode tab of claim 1, wherein the hollow carbon material has the inner surface forming a cavity, and at least one opening extending through the inner surface and communicating with the cavity;

optionally, the hollow carbon material is tubular in shape.

5. The negative electrode tab of claim 1, wherein the lithium-philic material is at least one of a lithium-philic metal and a compound thereof.

6. The negative electrode tab of claim 5, wherein the lithium-philic metal comprises at least one of Au, ag, zn, fe, co, ni, ga, sn, in, ge, ti, mu, pt, al, mg.

7. The negative electrode sheet of claim 5, wherein the mass content of the lithium-philic metal in the first negative electrode active material is 0.5% to 20%, optionally 2% to 10%.

8. The negative electrode tab of claim 5, wherein the lithium-philic metal compound comprises one or more of an oxide, a sulfide, a fluoride, a nitride, a chloride, a carbide.

9. The negative electrode sheet of claim 5, wherein the mass content of the lithium-philic metal compound in the first negative electrode active material is 0.5 to 30%, optionally 3 to 15%, calculated on the basis of the metal element.

10. The negative electrode plate as claimed in any one of claims 1 to 8, wherein the lithium-free negative electrode film layer contains a second negative electrode active material and a conductive agent, wherein the second negative electrode active material has a lithium-out overpotential of less than 0V and not less than-0.5V, calculated by the lithium metal potential of 0V;

optionally, the second anode active material is at least one of a carbon-based material, a silicon-based material, and a metal oxide.

11. The negative electrode tab of claim 10, wherein the lithium-free negative electrode film layer comprises: at least two film layers arranged in a stacked manner in a thickness direction, each film layer containing the second negative electrode active material, and at least one film layer containing the first negative electrode active material.

12. The negative electrode tab of claim 11, wherein the lithium-free negative electrode film layer comprises: first and second film layers alternately stacked in a thickness direction, the first film layer containing the second negative electrode active material and the first negative electrode active material, the second film layer containing the second negative electrode active material and not containing the first negative electrode active material;

and one side of the lithium-free negative electrode film layer, which is connected with the current collector, is the first film layer.

13. The negative electrode sheet of claim 12, wherein the first negative electrode active material is added in the lithium-free negative electrode film layer in an amount of 0.125-5% by mass.

14. The negative electrode tab of claim 10, wherein the lithium-free negative electrode film layer comprises: a third membrane layer containing the first negative active material and not containing the second negative active material.

15. The negative electrode tab of claim 14, wherein the lithium-free negative electrode film layer further comprises: a fourth film layer, wherein the third film layer and the fourth film layer are alternately stacked in a 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;

and the third film layer is arranged on one side of the lithium-free negative electrode film layer connected with the current collector.

16. The negative electrode sheet of claim 14, wherein the first negative active material is added to the third film layer in an amount of 10% to 60% by mass.

17. A lithium ion battery cell, comprising a positive electrode sheet and the negative electrode sheet of any one of claims 1 to 16, 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;

alternatively, 0.4 ≦ N/P <1.

18. The lithium ion battery cell of claim 17, wherein the lithium-philic material of the negative electrode sheet is not loaded with lithium metal after discharge of the lithium ion battery cell.

19. A lithium ion battery comprising a case and a plurality of lithium ion battery cells of claims 17-18, the plurality of lithium ion battery cells being housed in the case.

20. An electrical consumer, comprising a lithium-ion battery according to claim 19, for providing electrical energy.