阅读说明：本技术 锂离子电池及包含其的用电设备 (Lithium ion battery and electric equipment comprising same ) 是由 邹海林 张明 韩昌隆 张翠平 于 2019-07-10 设计创作，主要内容包括：本发明提供了一种锂离子电池及包含其的用电设备,涉及电池领域。锂离子电池包括：电极组件；以及用于浸润所述电极组件的电解液；其中,所述电极组件,包括电极主体、正极极耳和负极极耳,所述电极主体包括围绕轴线卷绕在一起的正极极片、负极极片以及设置在所述正极极片和所述负极极片之间的隔离膜；所述正极极耳连接于所述正极极片,所述负极极耳连接于所述负极极片；沿轴线方向(X),所述电极主体具有相对设置的两侧部,所述正极极耳和所述负极极耳分别从所述电极主体的两侧部延伸出；所述正极极片包括正极集流体和设置于所述正极集流体至少一个表面的正极材料层,所述电解液含有添加剂A,所述电解液在所述电极主体中的扩散速率v为0.01μg/s～5μg/s。该锂离子电池具有高能量密度、高循环性能和高安全性的优点。(The invention provides a lithium ion battery and electric equipment comprising the same, and relates to the field of batteries. The lithium ion battery includes: an electrode assembly; and an electrolyte for wetting the electrode assembly; the electrode assembly comprises an electrode main body, a positive electrode lug and a negative electrode lug, wherein the electrode main body comprises a positive electrode piece, a negative electrode piece and a separation film, the positive electrode piece and the negative electrode piece are wound together around an axis, and the separation film is arranged between the positive electrode piece and the negative electrode piece; the positive electrode tab is connected to the positive electrode piece, and the negative electrode tab is connected to the negative electrode piece; the electrode main body is provided with two opposite side parts along an axial direction (X), and the positive electrode lug and the negative electrode lug respectively extend out of the two side parts of the electrode main body; the positive pole piece comprises a positive current collector and a positive material layer arranged on at least one surface of the positive current collector, the electrolyte contains an additive A, and the diffusion rate v of the electrolyte in the electrode main body is 0.01-5 mug/s. The lithium ion battery has the advantages of high energy density, high cycle performance and high safety.)

1. A lithium ion battery, comprising:

an electrode assembly; and an electrolyte for wetting the electrode assembly; wherein the content of the first and second substances,

the electrode assembly includes an electrode main body, a positive electrode tab and a negative electrode tab,

the electrode main body comprises a positive pole piece, a negative pole piece and an isolating film arranged between the positive pole piece and the negative pole piece, wherein the positive pole piece and the negative pole piece are wound together around an axis;

the electrode main body is provided with two opposite side parts along the axis direction (X), and the positive electrode lug and the negative electrode lug respectively extend out of the two side parts of the electrode main body;

the electrolyte contains an additive A, wherein the additive A comprises a phosphate compound containing unsaturated bonds and-SO₂-at least one of a cyclic compound of a bond and a cyclic siloxane compound containing an unsaturated bond, the diffusion rate v of the electrolytic solution in the electrode body being 0.01 μ g/s to 5 μ g/s;

the diffusion rate v is γ × H/L (μ g/s),

wherein γ is a liquid suction rate (μ g/s) of the positive electrode tab to the electrolyte, H is a maximum length (mm) of the side portion in a width direction (Z) of the electrode main body, and L is a length (mm) of the electrode main body in the axis direction (X).

2. The lithium ion battery of claim 1, wherein the diffusion rate v of the electrolyte in the electrode body is 0.2 μ g/s to 2 μ g/s.

3. The lithium ion battery of claim 1, wherein H and L satisfy: 0.05H/L0.8, preferably 0.1H/L0.6, more preferably 0.15H/L0.5.

4. The lithium ion battery of claim 1, wherein the imbibition rate γ satisfies: gamma is more than or equal to 0.42 and less than or equal to 6.51.

5. The lithium ion battery according to any one of claims 1 to 4, wherein the axial direction (X) of the electrode main body is a horizontal direction.

6. The lithium ion battery according to any one of claims 1 to 5, wherein the mass ratio w (%) of the additive A in the electrolyte and the diffusion rate v (μ g/s) satisfy: 0.1. ltoreq. wxv. ltoreq.10, preferably 0.4. ltoreq. wxv. ltoreq.5.

7. The lithium ion battery according to any one of claims 1 to 6, wherein the unsaturated bond-containing phosphate ester compound is at least one compound of formula 1,

wherein R is₁、R₂And R₃Independently selected from alkyl, alkenyl, alkynyl, halogenated alkyl, halogenated alkenyl and halogenated alkynyl with 1-6 carbon atoms, aryl or halogenated aryl with 6-10 carbon atomsAnd R is₁、R₂And R₃Contains a double or triple bond;

preferably, in said compound of formula 1, R₁、R₂And R₃At least one of them is terminated with a carbon-carbon unsaturated bond;

more preferably, in said compound of formula 1, R₁、R₂And R₃Wherein all the terminals are carbon-carbon unsaturated bonds.

8. The lithium ion battery according to claim 7, wherein the compound of formula 1 is selected from one or more of the following compounds:

9. the lithium ion battery according to any one of claims 1 to 8, wherein the-SO-containing material is selected from the group consisting of₂The cyclic compound of bond includes at least one of the compounds of formula 2 to formula 4,

wherein R is₄Is an alkylene group having 1 to 4 carbon atoms, a fluoroalkylene group having 1 to 4 carbon atoms, an alkenylene group having 2 to 4 carbon atoms, a fluoroalkenyl group having 2 to 4 carbon atoms, an arylene group having 6 to 14 carbon atoms, or a fluoroarylene group having 6 to 10 carbon atoms;

R₅、R₆、R₇and R₈Each independently is H, alkyl with 1-6 carbon atoms, alkenyl, alkynyl, halogenated alkyl, halogenated alkenyl or halogenated alkynyl, aryl with 6-10 carbon atoms or halogenated aryl, and n is 1,2 or 3.

10. The lithium ion battery according to claim 9, wherein the compound of formula 2 is selected from one or more of the following compounds:

11. the lithium ion battery according to any one of claims 1 to 10, wherein the unsaturated bond-containing cyclic siloxane compound comprises at least one of compounds of formula 5,

in the formula 5, R₉、R₁₀、R₁₁、R₁₂、R₁₃、R₁₄、R₁₅、R₁₆Each independently selected from substituted or unsubstituted alkyl with 1-4 carbon atoms, and R₉、R₁₀、R₁₁、R₁₂、R₁₃、R₁₄、R₁₅、R₁₆Contains a double bond or a triple bond, and the substituent group is a halogen element.

12. The lithium ion battery according to claim 11, wherein the compound of formula 5 is selected from one or more of the following compounds:

13. the lithium ion battery according to any one of claims 1 to 12, wherein the additive a is at least one selected from 1, 3-propane sultone, propylene sultone, methylene methanedisulfonate, triallyl phosphate, tetramethyltetravinylcyclotetrasiloxane;

preferably, the additive a is selected from at least one of methylene methanedisulfonate, triallyl phosphate, and tetramethyltetravinylcyclotetrasiloxane.

14. The lithium ion battery according to any one of claims 1 to 13, wherein the viscosity of the electrolyte at 25 ± 3 ℃ is 0.5 mPa-s to 5.0 mPa-s.

15. The lithium ion battery according to claim 14, wherein the viscosity of the electrolyte at 0 ℃ is 1 to 6.0 mPa-s.

16. The lithium ion battery according to any one of claims 1 to 15, wherein the electrolyte comprises a low viscosity solvent having a viscosity of not higher than 0.65 mPa-s at 25 ± 3 ℃,

preferably, the low viscosity solvent is selected from at least one of dimethyl carbonate DMC, methyl formate MF, ethyl formate EF, methyl acetate MA, ethyl acetate EA, ethyl propionate EP, ethyl butyrate EB, tetrahydrofuran THF, 2 methyl tetrahydrofuran, dioxolane DOL, 1, 2-dimethoxyethane DME, acetonitrile AN, methyl nonafluorobutyl ether MFE, or ethyl nonafluorobutyl ether EFE;

more preferably, the mass fraction of the low-viscosity solvent in the electrolyte is 10% to 80%.

17. The lithium ion battery according to claim 16, wherein the mass fraction of the low-viscosity solvent in the electrolyte is 20% to 60%.

18. The lithium ion battery of any one of claims 1 to 17, wherein the electrolyte comprises a wetting agent, and the wetting agent includes but is not limited to at least one of 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether, 1H, 5H-octafluoropentyl-1, 1,2, 2-tetrafluoroethyl ether, or 1,1,2, 2-tetrafluoroethyl-2, 2, 2-trifluoroethyl ether; the weight percentage of the impregnating compound in the electrolyte is 0.1-10%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 3%, 5%, 7%, 9% or 10%.

19. The lithium ion battery according to any one of claims 1 to 18, wherein the porosity of the positive electrode material layer is 10% to 50%, preferably 20% to 40%.

20. The lithium ion battery according to any one of claims 1 to 19, wherein the specific surface area of the positive electrode material layer is 0.5m²/g～1.5m²/g。

21. The lithium ion battery according to any one of claims 1 to 20, wherein the positive electrode material layer has a grain orientation OI value of 5 to 120, preferably the OI value is 30 to 70.

22. The lithium ion battery according to any one of claims 1 to 21, wherein the positive electrode material layer contains a positive electrode active material containing at least one of compounds represented by formulae (1) to (3):

Li_1+xNi_aCo_bM_1-a-bO_2-yA_yformula (1)

Li_1+x’Ni_a’M’_2-a’O_4-y’A’_y’Formula (2)

c[Li₂MnO₃]·(1-c)[LiM”₂O_2-y”A_y”]Formula (3)

In the formula (1), x is more than or equal to 0.1 and less than or equal to 0.2, a is more than or equal to 0.5 and less than or equal to 1, b is more than or equal to 0.02 and less than 0.3, a + b is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 0.2, M comprises one or more of Mn, Fe, Cr, Ti, Zn, V, Al, Zr and Ce, A comprises one or more of S, N, F, Cl, Br and I,

in the formula (2), x ' is more than or equal to 0.1 and less than or equal to 0.2, a ' is more than or equal to 0.4 and less than or equal to 0.6, y ' is more than or equal to 0 and less than or equal to 0.2, M ' comprises Mn or Mn and one or more of Fe, Cr, Ti, Zn, V, Al, Zr, Mg and Ce, A ' comprises one or more of S, N, F, Cl, Br and I,

in the formula (3), 0< c <1, 0< y ≦ 0.2, and M' is Ni, Co and Mn, or one or more of Ni, Co and Mn, Fe, Cr, Ti, Zn, V, Al, Zr and Ce.

23. The lithium ion battery according to any one of claims 1 to 22, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector.

24. An electric device comprising the lithium ion battery according to any one of claims 1 to 23.

Technical Field

The invention relates to the field of batteries, in particular to a lithium ion battery and electric equipment comprising the same.

Background

Lithium ion batteries are the most popular energy storage systems due to their characteristics of high working potential, long service life and environmental friendliness, and have been widely used in the fields of pure electric vehicles, hybrid electric vehicles, smart grids and the like. But are currently based on LiFePO₄The lithium ion battery made of the anode material is difficult to meet the higher requirement of people on the cruising ability, and the development of a lithium ion battery system with higher energy density is urgently needed to solve the problem of mileage anxiety of people on electric automobiles.

The energy density of the battery can be improved by adopting a positive electrode material with high energy density, such as high-voltage LiNi_0.5Mn_1.5O₄High-capacity high-nickel ternary NCM811 and lithium-rich ternary materials. However, compared with other positive active materials, the materials have high content of surface impurity lithium and strong side reaction activity between the particle surface and the electrolyte, so that the high-temperature gas production rate of the lithium ion battery using the positive material is high, and safety risk is brought. Meanwhile, for a wound battery, the current industrialized method for improving the energy density is to improve the energy density by improving the space utilization rate of a packaging material, for example, the length direction of a battery core is lengthened, and the space occupied by a lug for leading out the current of a positive plate and a negative plate is reduced. However, according to research and development experience, the electrolyte is more difficult to enter the winding type battery cell by increasing the space utilization rate, especially in the circulation process, because the formation and consumption of the SEI film on the surface of the positive pole piece are a dynamic process, the free electrolyte can be extruded out to the two ends of the winding type battery cell by the volume expansion-contraction inside the battery cell, and if the electrolyte cannot flow back to the middle part of the battery cell in time, lithium precipitation of the winding type battery cell can be caused due to insufficient dynamics in the circulation process; meanwhile, since the SEI on the surface of the positive electrode plate is consumed and a new SEI film cannot be formed in time, the gas production performance of the battery cell is deteriorated and even a serious safety risk may occur.

Disclosure of Invention

The first objective of the present invention is to provide a lithium ion battery to solve the problem that the high energy density and the high cycle performance of the conventional winding type cell cannot be achieved at the same time.

The second purpose of the invention is to provide an electric device comprising the lithium ion battery of the invention.

In order to achieve the purpose, the invention adopts the following technical scheme:

a lithium ion battery comprising:

an electrode assembly; and an electrolyte for wetting the electrode assembly; wherein the content of the first and second substances,

the electrode assembly comprises an electrode main body, a positive electrode lug and a negative electrode lug, wherein the electrode main body comprises a positive electrode piece, a negative electrode piece and an isolating film arranged between the positive electrode piece and the negative electrode piece, the positive electrode piece and the negative electrode piece are wound together around an axis, the positive electrode piece comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, the positive electrode lug is connected to the positive electrode piece, and the negative electrode lug is connected to the negative electrode piece;

the electrode main body is provided with two opposite side parts along the axis direction (X), and the positive electrode lug and the negative electrode lug respectively extend out of the two side parts of the electrode main body;

the electrolyte contains an additive A, wherein the additive A comprises a phosphate compound containing unsaturated bonds and-SO₂-at least one of a cyclic compound of a bond and a cyclic siloxane compound containing an unsaturated bond, and a diffusion rate v of the electrolytic solution in the electrode main body is 0.01 to 5 μ g/s, preferably 0.2 to 2 μ g/s.

An electric device comprising a lithium ion battery of the invention.

The technical scheme provided by the invention can achieve the following beneficial effects:

the lithium ion battery is a winding type lithium ion battery, the positive electrode lug and the negative electrode lug are respectively arranged on the two side parts of the electrode main body along the axial direction, the utilization rate of the internal space of the single battery can be effectively improved, and the volume energy density of the battery is improved. The additive A capable of forming a compact SEI film on the surface of the positive pole piece is added into the electrolyte, meanwhile, the wettability of the electrolyte is matched with the microstructure of the pole piece and the structure of the electrode main body, the diffusion rate of the electrolyte containing the additive A in the electrode main body is controlled within the range of 0.01-5 mug/s, the electrolyte can be ensured to rapidly enter the winding type battery cell in the circulation process, a new SEI film is formed on the surface of the positive pole piece in time, the circulation performance and the safety of the lithium ion battery are improved, and the gas production problem of the high-capacity lithium ion battery is solved. Therefore, the lithium ion battery provided by the invention has the characteristics of high energy density, high cycle stability and high safety.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a schematic view of an electrode assembly provided in an embodiment of the present application.

Fig. 2 is an exploded schematic view of a hard-shell lithium ion battery provided in an embodiment of the present application.

Fig. 3 is a schematic structural diagram of a soft package lithium ion battery provided in an embodiment of the present application.

Reference numerals:

1-an electrode assembly;

11-an electrode body;

12-positive pole tab;

13-a negative electrode tab;

14-side part.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

It should be noted that: in the present invention, all the embodiments and preferred methods mentioned herein can be combined with each other to form a new technical solution, if not specifically stated. In the present invention, all the technical features mentioned herein and preferred features may be combined with each other to form a new technical solution, if not specifically stated. In the present invention, the percentage (%) or parts means the weight percentage or parts by weight with respect to the composition, if not otherwise specified. In the present invention, the components referred to or the preferred components thereof may be combined with each other to form a novel embodiment, if not specifically stated. In the present invention, unless otherwise stated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "6 to 22" means that all real numbers between "6 to 22" have been listed herein, and "6 to 22" is simply a shorthand representation of the combination of these values. The "ranges" disclosed herein may have one or more lower limits and one or more upper limits, respectively, in the form of lower limits and upper limits. In the present invention, unless otherwise specified, the individual reactions or operation steps may be performed sequentially or may be performed in sequence. Preferably, the reaction processes herein are carried out sequentially.

Unless otherwise defined, technical and scientific terms used herein have the same meaning as is familiar to those skilled in the art. In addition, any methods or materials similar or equivalent to those described herein can also be used in the present invention.

In one aspect, the present invention provides a lithium ion battery, comprising:

the electrode assembly comprises an electrode assembly 1 (shown in figure 1) and electrolyte for infiltrating the electrode assembly 1, wherein the electrode assembly 1 comprises an electrode main body 11, a positive electrode tab 12 and a negative electrode tab 13, the electrode main body 11 comprises a positive electrode piece, a negative electrode piece and a separation film arranged between the positive electrode piece and the negative electrode piece, the positive electrode piece is wound together around an axis and comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector; the positive electrode tab 12 is connected to the positive electrode plate, and the negative electrode tab 13 is connected to the negative electrode plate; in the lithium ion battery, the electrode main body has two side portions 14 arranged to face each other in the axial direction (X), and the two side portions 14 of the electrode main body 11 extend to form a positive electrode tab 12 and a negative electrode tab 13, respectively. Wherein, the X direction is the axial direction of winding of the positive electrode plate and the negative electrode plate of the electrode main body 11 and the isolating film arranged between the positive electrode plate and the negative electrode plate, and is also the main diffusion direction of the electrolyte in the electrode main body; the Y direction is the thickness direction of the electrode main body 11; the Z direction is the width direction of the electrode main body 11.

In the invention, the positive electrode tab 12 and the negative electrode tab 13 are respectively arranged at the two side parts 14 of the electrode main body 11, and particularly, after the positive electrode tab and the negative electrode tab are further bent towards the thickness direction of the electrode main body, the volume occupancy rate of the electrode main body in the battery shell is increased, which is beneficial to improving the content of active substances in the internal space of the battery, thereby effectively improving the volume energy density of the lithium ion battery. However, for the battery core with the winding structure, the electrolyte can only diffuse and enter from the two side parts of the electrode main body to the middle part of the electrode main body, and particularly after the tab is further bent in the thickness direction (Y) of the electrode main body, the diffusion path of part of the electrolyte is easily blocked, so that the difficulty in infiltrating the electrolyte to the electrode main body is increased; meanwhile, in the charging process of the battery, the positive and negative pole piece active material layers can expand in volume, the space between the pole pieces is shortened, partial electrolyte in the middle of the battery core is extruded out, in the discharging process of the battery, the positive and negative pole piece active material layers can contract in volume, the space between the pole pieces is increased, and free electrolyte needs to be replenished into the positive and negative pole pieces again. If the electrolyte is not supplemented in time, in the following circulation process, free lithium ions between the positive and negative plates can cause the problem of lithium precipitation because the electrolyte is insufficient and cannot be inserted in time; meanwhile, since the SEI on the surface of the positive electrode plate is consumed and a new SEI film cannot be formed in time, the gas production performance of the battery cell deteriorates, and further the cycle performance of the battery becomes poor, and even a safety risk exists.

In the present invention, in order to improve the high temperature applicability and safety of the lithium ion battery of the present invention, the electrolyte contains an additive a. The additive A comprises unsaturated bond-containing phosphate ester compound and-SO-containing₂At least one of a cyclic compound having a bond and a cyclic siloxane compound having an unsaturated bond, and the diffusion rate v of the electrolytic solution in the electrode main body is 0.01 to 5 μ g/s, preferably 0.2 to 2 μ g/s. The additive A is introduced to preferentially form a film on the surface of the anode, so that a passivation layer with a compact structure and good stability is formed, the direct contact between the anode and a solvent is blocked, and the oxidation gas generation of the solvent is effectively inhibited. In the invention, the film-forming additive is especially suitable for gas generationHeavy high capacity battery systems. Meanwhile, the diffusion rate v of the electrolyte in the electrode main body is adjusted to be 0.01-5 mug/s, preferably 0.2-2 mug/s, the electrolyte has good wettability in the electrode main body, can quickly enter the electrode main body, and forms a new SEI film on the surface of the positive pole piece in time, so that the cycle performance and the safety of the lithium ion battery are improved, and the problem of gas generation in the cycle process is solved.

In the present invention, the diffusion rate v of the electrolyte in the electrode main body is γ × H/L, where γ is the rate of absorption of the electrolyte by the positive electrode sheet (μ g/s), H is the maximum length (mm) of the side portion in the width direction (Z) of the electrode main body, and L is the length (mm) of the electrode main body in the axial direction (X). In the invention, the diffusion rate v is measured by taking the imbibition rate of the positive pole piece in the electrode main body to the electrolyte as a main influence factor, and is mainly based on the following reasons: the additive A in the electrolyte mainly acts on the surface of active substance particles of the positive pole piece to form a passivation film with a compact structure, so that the gas production performance of the lithium ion battery is improved; meanwhile, the compaction density of the positive pole piece is higher than that of the negative pole piece, the internal structure of the pole piece is tighter, and the diffusivity of the electrolyte on the positive pole piece has more obvious influence on the cycle performance of the battery.

In the invention, the imbibition rate gamma of the positive pole piece to the electrolyte can be determined by the following method: filling electrolyte into a dropper with a certain inner diameter and standard scales, wherein the diameter of a lower opening of the dropper is 0.2 mm; fully drying the positive pole piece (for example, drying at 70-90 ℃ for 10-15 h), and then cutting a square positive pole piece of 5cm multiplied by 5 cm; in a drying room with the humidity lower than 2%, the lower opening of the dropper is in contact with the square positive pole piece, the dropper is ensured to be perpendicular to the surface of the square positive pole piece, the electrolyte in the dropper is gradually infiltrated into the square positive pole piece, and the quality of the electrolyte infiltrated into the square positive pole piece every second is recorded, namely the imbibition rate of the positive pole piece to the electrolyte.

Meanwhile, the diffusion rate v of the electrolyte in the electrode body is also affected by the structure of the electrode body. In the present invention, H is the maximum length (mm) of the side portion in the width direction (Z) of the electrode main body, and L is the length (mm) of the electrode main body in the axis direction (X). When the H is smaller, the passage of the electrolyte entering the electrode main body from the outside is narrower; as L is longer, the path along which the electrolyte diffuses to the central region of the electrode body is longer. In the invention, when the length L of the electrode main body is smaller than the width H, the volume energy density of the electrode main body is higher, but the electrolyte is not favorable for entering the battery core rapidly, and the diffusion rate v of the electrolyte has stronger dependence on the size H, L of the electrode main body.

In summary, in the present invention, the diffusion rate v of the electrolyte in the electrode body is defined as: v ═ γ × H/L (μ g/s), where γ is in μ g/s and H and L are in mm.

In some embodiments of the present invention, the maximum length h (mm) of the side portion in the width direction (Z) of the electrode main body and the length l (mm) of the electrode main body in the axis direction (X) satisfy: H/L is more than or equal to 0.05 and less than or equal to 0.8. In some preferred embodiments of the present invention, H/L is 0.1 to 0.6. In a further preferred embodiment of the present invention, H/L is 0.15 to 0.5. Specifically, the value of H/L may be 0.8, 0.75, 0.7, 0.65, 0.6, 0.55, 0.5, 0.45, 0.4, 0.35, 0.3, 0.25, 0.2, 0.1, 0.05, or the like. Compared with batteries with relatively close length and width, the electrode main body structure with the small H/L ratio reduces the occupation ratio of the positive pole lug and the negative pole lug in the positive pole piece and the negative pole piece to the maximum extent, relatively improves the space utilization rate of the lithium ion battery, and further improves the energy density of the lithium ion battery. Meanwhile, the lugs are respectively arranged at the two ends of the electrode main body, so that the circuit design during module assembly can be simplified, the assembly efficiency is improved, and the cost can be reduced.

In some embodiments of the invention, the axial direction (X) of the electrode body is a horizontal direction. At the moment, the winding shaft direction of the electrode main body is basically parallel to the horizontal direction, and the electrolyte can infiltrate and diffuse into the electrode main body from the two ends of the electrode main body, so that the rapid infiltration of the electrolyte is facilitated.

As one embodiment of the present invention, as shown in fig. 2, the winding axis direction of the electrode assembly is horizontal, the electrode assembly is placed in a battery case and sealed with a top cap, and a lithium ion secondary battery is assembled. According to different application scenarios, the lithium ion secondary battery can be placed vertically (i.e. the Z direction is parallel to the gravity direction) or horizontally (i.e. the Y direction is parallel to the gravity direction).

As one embodiment of the present invention, as shown in fig. 3, the winding axis direction of the electrode assembly is horizontal, the electrode assembly is packaged by an aluminum plastic film, and the edges of the package bag are sealed by hot pressing, colloid fixation, and the like, thereby assembling a lithium ion secondary battery. According to different application scenarios, the lithium ion secondary battery can be placed vertically (i.e. the Z direction is parallel to the gravity direction) or horizontally (i.e. the Y direction is parallel to the gravity direction).

In some embodiments of the present invention, the mass ratio w (%) of the additive a in the electrolyte and the diffusion rate v (μ g/s) satisfy: w x v is more than or equal to 0.1 and less than or equal to 10.

In some preferred embodiments of the present invention, the mass ratio w (%) of the additive a in the electrolyte and the diffusion rate v (μ g/s) satisfy: w x v is more than or equal to 0.4 and less than or equal to 5.

In the circulation process of the battery, the electrolyte is easily extruded to two ends of the battery core, the content of the additive A in the battery core is much lower than that of the positive active material, the SEI formed on the surface of the positive active material in the battery core is continuously consumed, and the content of the additive A is relatively low, so that the surface of the positive active material in the battery core cannot continuously form a stable protective film, a large amount of side reactions are easily caused when the electrolyte and the positive active material are contacted again, and the problem of gas generation is caused. Meanwhile, the resistance of the SEI film formed by additive a is generally high. The inventor of the invention discovers, through research, that the correlation between the mass percent w of the additive A in the electrolyte and the diffusion rate v of the electrolyte in the electrode main body has great influence on the film forming quality and the interface impedance of the positive electrode plate, so that the gas production rate and the cycle performance of the battery are influenced. When the mass ratio w of the additive A in the electrolyte and the diffusion rate v meet the relational expression, the electrolyte can be ensured to have higher infiltration rate, enough additive A can be ensured to form a stable protective film to inhibit gas generation, and meanwhile, the dosage of the additive A is moderate, and the cycle performance of the lithium ion battery is ensured to be good.

In the present invention, the unsaturated bond-containing phosphate ester compound is at least one of the compounds of formula 1,

wherein R is₁、R₂And R₃Each independently selected from one of alkyl, alkenyl, alkynyl, halogenated alkyl, halogenated alkenyl and halogenated alkynyl with 1-6 carbon atoms, aryl or halogenated aryl with 6-10 carbon atoms, and R₁、R₂And R₃Contains a double or triple bond;

preferably, in the compound of formula 1, R₁、R₂And R₃At least one of them is terminated with a carbon-carbon unsaturated bond;

more preferably, in the compound of formula 1, R₁、R₂And R₃Wherein all the terminals are carbon-carbon unsaturated bonds.

In some preferred embodiments of the present invention, the unsaturated branched phosphate ester compound represented by formula 1 may be selected from one or more of the following compounds:

in the present invention, it contains-SO₂The cyclic compound of bond includes at least one of the compounds of formula 2 to formula 4,

wherein R is₄Is C1-4 alkylene, C1-4 fluoroalkylene, C2-4 alkenylene, C2-4 fluorineAn alkenylene group, an arylene group having 6 to 14 carbon atoms, or a fluoroarylene group having 6 to 10 carbon atoms;

R₅、R₆、R₇and R₈Each independently is H, alkyl with 1-6 carbon atoms, alkenyl, alkynyl, halogenated alkyl, halogenated alkenyl or halogenated alkynyl, aryl with 6-10 carbon atoms or halogenated aryl, and n is 1,2 or 3.

In some preferred embodiments of the present invention, in the compound of formula 2, the alkylene group having 1 to 4 carbon atoms is a linear or branched alkylene group. Examples of alkyl groups include: methylene, ethylene, propylene, isopropylene, butylene, isobutylene, sec-butylene, 1-methylpropylene, 2-methylpropylene, and the like.

In the above formula 2, the number of fluorine atoms substituted and the substitution position thereof in the fluoroalkylene group having 1 to 4 carbon atoms are not particularly limited, and fluorine atoms may be selected according to actual needs to substitute a part of or all of the hydrogen atoms in the alkylene group. For example, the number of fluorine atoms may be 1,2,3,4 or more.

Specific examples of fluoroalkylene groups include: 1-fluoromethylene, 1-fluoroethylene, 1,1,2, 2-tetrafluoroethylene, 1-fluoropropylene, 2-fluoropropylene, 1,1, 1-trifluoropropylene, 1-fluoroisopropylene, 1-fluorobutylene, 1-fluoroisobutylene, 1-fluorosec-butylene, etc.

In the above formula, the alkenylene group having 2 to 4 carbon atoms is a linear or branched alkenylene group, preferably a linear alkenylene group, and the number of double bonds in the alkenyl group may be 1 or 2. Examples of alkenylene groups include: vinylidene, allylidene, isopropenylidene, butenylidene, butadienylidene, 1-methylvinylidene, 1-methylpropenylidene, 2-methylpropenylidene, and the like.

In the above formula 2, the number of fluorine atoms substituted and the substitution position thereof in the fluoroalkenylene group having 2 to 4 carbon atoms are not particularly limited, and a part or all of the hydrogen atoms in the alkenylene group may be substituted with fluorine atoms according to actual needs. For example, the number of fluorine atoms may be 1,2 or more.

Examples of fluoroalkenylene groups include: 1-fluorovinylidene group, 1, 2-difluorovinylidene group, 1-fluoroallylidene group, 1-fluoroisopropenylene group, 1-fluorobutenylene group, 1-fluorobutadienylene group, 1,2,3, 4-tetrafluorobutadienylene group and the like.

In the above formula 2, the specific type of the aryl group in the arylene group having 6 to 10 carbon atoms is not particularly limited and may be selected according to actual requirements, for example, phenylene, naphthylene, phenylalkylene, and other substituent groups such as alkyl may be bonded to the phenyl group.

Specific examples of the arylene group include: phenylene, benzylene, 1-naphthylene, 2-naphthylene, o-methylphenylene, m-methylphenylene, p-ethylphenylene, m-ethylphenylene, o-ethylphenylene, 1-tetrahydronaphthylene, 2-tetrahydronaphthylene, 4-vinylphenylene, 3-isopropylphenylene, 4-butylphenyl, 4-isobutylphenylene, 4-tert-butylphenyl, 2, 3-dimethylphenylene, 2, 4-dimethylphenylene, 2, 5-dimethylphenylene, 2, 6-dimethylphenylene, 3, 4-dimethylphenylene, 3, 5-dimethylphenylene, 2,4, 5-trimethylphenylene, 2,4, 6-trimethylphenylene and the like.

In the fluoroarylene group having 6 to 10 carbon atoms in formula 2, the number of fluorine atoms and their substitution positions are not particularly limited, and the number of halogen atoms may be 1,2,3,4, 5 or more.

Specific examples of the fluorinated arylene group include: 2-fluorophenylene, 3-fluorophenylene, 4-fluorophenylene, 2-fluoro-4-methylphenylene, 3-fluoro-4-methylphenylene, 4-fluoro-2-methylphenylene, 2, 4-difluorophenylene, 3, 4-difluorophenylene, 2, 6-difluoro-4-methylphenylene, 2, 6-difluoro-3-methylphenylene, 2-fluoro-naphthylene, 4-fluoro-naphthylene, 2,4, 6-trifluorophenylene, 2,3,4, 6-tetrafluorophenylene, 4-trifluoromethylphenylene, 2,3,4, 5-tetrafluorophenylene, pentafluorophenylene, 3, 5-bis (trifluoromethyl) phenylene, and the like.

As some preferred embodiments of the present invention, the compound of formula 2 is selected from one or more of the following compounds:

in the present invention, the unsaturated bond-containing cyclic siloxane compound includes at least one of the compounds of formula 5:

in the formula 5, R₉、R₁₀、R₁₁、R₁₂、R₁₃、R₁₄、R₁₅、R₁₆Each independently selected from substituted or unsubstituted alkyl with 1-4 carbon atoms, and R₉、R₁₀、R₁₁、R₁₂、R₁₃、R₁₄、R₁₅、R₁₆At least one of which contains a double or triple bond, and the substituent is a halogen element.

As some preferred embodiments of the present invention, the compound of formula 5 is selected from one or more of the following compounds:

in some preferred embodiments of the present invention, additive A includes, but is not limited to, at least one of 1, 3-propane sultone, propylene sultone, methylene methanedisulfonate, triallyl phosphate, tetramethyltetravinylcyclotetrasiloxane.

In a further preferred embodiment, additive a is at least one of methylene methanedisulfonate, triallyl phosphate, or tetramethyltetravinylcyclotetrasiloxane.

In some embodiments of the invention, the viscosity of the electrolyte is 0.5 to 5.0 mPas at 25. + -. 3 ℃. In the invention, when the viscosity of the electrolyte is in the range, the flow rate of the electrolyte is higher, and the infiltration rate of the electrolyte in the positive pole piece and the diffusion rate of the electrolyte in the electrode main body can be effectively improved. In some preferred embodiments of the present invention, the viscosity of the electrolyte solution at 0 ℃ is 1 to 6.0 mPas. Therefore, the electrolyte can be ensured to have good fluidity at normal temperature and low temperature, and the battery can be ensured to have good dynamic performance at high and low temperatures.

In some embodiments of the present invention, the electrolyte includes a low viscosity solvent, and optionally a certain amount of wetting agent may be added; wherein the viscosity of the low-viscosity solvent is less than or equal to 0.65mPa & s at 25 +/-3 ℃. The low-viscosity solvent is used, or the wetting agent is selectively added into the electrolyte, so that the electrolyte obtains a specific flow rate, and the wetting rate of the electrolyte on the positive pole piece is improved.

In some embodiments of the invention, the low viscosity solvent includes, but is not limited to, at least one of dimethyl carbonate DMC, methyl formate MF, ethyl formate EF, methyl acetate MA, ethyl acetate EA, ethyl propionate EP, ethyl butyrate EB, tetrahydrofuran THF, 2 methyl tetrahydrofuran, dioxolane DOL, 1, 2-dimethoxyethane DME, acetonitrile AN, methyl nonafluorobutyl ether MFE, or ethyl nonafluorobutyl ether EFE.

In some embodiments of the present invention, in order to obtain an electrolyte with good wettability, the mass fraction of the low-viscosity solvent in the electrolyte may be 10% to 80%, preferably 20% to 60%. This mass fraction may be, for example, typically but not by way of limitation, 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%.

In some embodiments of the present invention, the electrolyte solution contains a wetting agent, which includes but is not limited to at least one of 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether, 1H, 5H-octafluoropentyl-1, 1,2, 2-tetrafluoroethyl ether, or 1,1,2, 2-tetrafluoroethyl-2, 2, 2-trifluoroethyl ether.

Wherein the weight percentage of the impregnating compound in the electrolyte is, for example, 0.1-10%. Specifically, for example, it may be 0.1%, 0.5%, 1%, 1.5%, 2%, 3%, 5%, 7%, 9%, or 10%.

The positive electrode active material in the positive electrode material layer of the lithium ion battery of the present invention is typically, but not limited to, selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, or olivine-structured lithium-containing phosphate, etc., but the present application is not limited to these materials, and other conventionally known materials that can be used as a positive electrode active material of a lithium ion battery may also be used. These positive electrode active materials may be used alone or in combination of two or more.

In some embodiments of the present invention, the positive electrode active material includes at least one of the compounds represented by formulae (1) to (3):

Li_1+xNi_aCo_bM_1-a-bO_2-yA_yformula (1)

Li_1+x’Ni_a’M’_2-a’O_4-y’A’_y’Formula (2)

c[Li₂MnO₃]·(1-c)[LiM”₂O_2-y”A_y”]Formula (3)

Wherein, in the formula (1), x is more than or equal to 0.1 and less than or equal to 0.2, a is more than or equal to 0.5 and less than 1, b is more than 0.02 and less than 0.3, a + b is more than 0.55 and less than 1, y is more than or equal to 0 and less than 0.2, M comprises one or more of Mn, Fe, Cr, Ti, Zn, V, Al, Zr and Ce, and A comprises one or more of S, N, F, Cl, Br and I; in the formula (2), x ' is more than or equal to 0.1 and less than or equal to 0.2, a ' is more than or equal to 0.4 and less than or equal to 0.6, y ' is more than or equal to 0 and less than or equal to 0.2, M ' comprises Mn or Mn and one or more of Fe, Cr, Ti, Zn, V, Al, Zr, Mg and Ce, and A ' comprises one or more of S, N, F, Cl, Br and I; in the formula (3), 0< c <1, 0< y ≦ 0.2, and M' is Ni, Co and Mn, or one or more of Ni, Co and Mn, Fe, Cr, Ti, Zn, V, Al, Zr and Ce.

When the positive electrode active material is selected from the compounds represented by the formulas (1) to (3), the positive electrode active material has a high Ni content or a high operating voltage during charge and discharge cycles, so that the probability of side reactions between the surface of the positive electrode active material particles and the electrolyte is increased, and the problem of gas generation is more likely to occur. When the diffusion rate of the electrolyte in the electrode main body is 0.01-5 mug/s, an SEI film with good film forming quality can be formed on the surface of the anode material in time, and the gas production problem of a lithium ion battery using the anode material is effectively improved.

In some preferred embodiments of the present invention, the positive active material may be selected from LiNi_0.5Co_0.2Mn_0.3O₂(NCM523)、LiNi_0.55Co_0.05Mn_0.4O₂、LiNi_0.55Co_0.1Mn_0.35O₂、LiNi_0.55Co_0.12Mn_0.33O₂、LiNi_0.55Co_0.15Mn_0.3O₂、LiNi_0.6Co_0.15Mn_0.25O₂、LiNi_0.6Co_0.18Mn_0.22O₂、LiNi_0.6Co_0.2Mn_0.2O₂(NCM622)、LiNi_0.65Co_0.05Mn_0.3O₂、LiNi_0.65Co_0.09Mn_0.26O₂、LiNi_0.65Co_0.12Mn_0.23O₂、LiNi_0.65Co_0.15Mn_0.2O₂、LiNi_0.8Co_0.1Mn_0.1O₂(NCM811)、LiNi_0.85Co_0.15Al_0.05O₂、LiNi_0.5Mn_1.5O₄、0.2[Li₂MnO₃]·0.8[LiNi_0.5Co_0.2Mn_0.3O₂]、LiNi_0.88Co_0.05Mn_0.07O₂Or 0.3[ Li ]₂MnO₃]·0.7[LiNi_0.8Co_0.1Mn_0.1O₂]At least one of (1).

In some embodiments of the present invention, the positive electrode material layer further includes a conductive agent and a binder, and the kind of the conductive agent and the binder is not particularly limited and may be selected according to actual needs.

The inventors of the present invention found through research that the porosity, specific surface area, and OI value of the positive electrode material layer also have a large influence on the diffusion rate of the electrolyte.

In some embodiments of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer coated on the surface of the positive electrode current collector, and the porosity of the positive electrode material layer is 10% to 50%, preferably 20% to 40%. The larger the porosity of the positive electrode material layer is, the more and more the path of the electrolyte entering the inside of the positive electrode piece is, so that the electrolyte can more quickly infiltrate the positive electrode piece. The porosity of the positive electrode material layer is limited to 10% -50%, so that the electrolyte can more quickly and better infiltrate the positive electrode piece, the filling amount of the electrolyte can be kept in a reasonable range, and meanwhile, the electrode main body has higher volume energy density and mass energy density.

In some embodiments of the invention, the positive electrode material layer has a specific surface area of 0.5m²/g～1.5m²(ii) in terms of/g. The larger the specific surface area of the positive electrode material layer is, the easier the electrolyte is to be absorbed, and the infiltration of the electrolyte on the positive electrode piece can be accelerated. By setting the specific surface area of the positive electrode material layer to 0.5m²/g～1.5m²And the electrolyte can quickly infiltrate the positive pole piece, the contact area between the positive material layer and the electrolyte can be controlled within a reasonable range, and the side reaction of the electrolyte and the positive pole piece is effectively prevented.

In the invention, the grain orientation OI value of the positive electrode material layer is 5-120. Preferably, the positive electrode material layer has an OI value of 30 to 70. In the invention, the OI value of the positive electrode membrane is the ratio of the peak areas of the (003) diffraction peak and the (110) diffraction peak in the X-ray diffraction spectrum of the positive electrode sheet. The OI value of the positive electrode material layer can reflect the stacking orientation degree of lithium-containing compound particles with a layered structure in the positive electrode membrane, and the surface energy of each crystal face of the positive electrode particles in the positive electrode piece is different, so that the positive electrode piece has different affinities for electrolyte. The OI value of the positive electrode material layer is adjusted to be within the range, so that the wettability of the electrolyte and the positive electrode piece can be improved to a certain degree, and the diffusion rate of the electrolyte in the electrode main body is improved.

In the lithium ion battery according to the present invention, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector and containing a negative electrode active material. The kind of the negative electrode active material is not particularly limited and may be selected according to actual needs. Specifically, the negative electrode active material is a material capable of reversibly releasing and inserting lithium, and includes one or more of graphite, silicon, tin, metal oxide, silicon oxide, tin oxide, silicon alloy, tin alloy, silicon-carbon composite, tin-carbon composite, lithium titanate, and the like. Preferably, the negative active material is selected from natural graphite, artificial graphite, or a mixture of both. The negative electrode material layer further comprises a conductive agent and a binder, and the types of the conductive agent and the binder are not particularly limited and can be selected according to actual requirements. In addition, the negative pole piece can also be directly selected from a metal lithium piece.

In the lithium ion battery according to the invention, the material of the isolation film is not limited, and can be selected according to actual requirements.

In a second aspect, the present invention provides an electrical device comprising the lithium ion battery of the present invention.

Under the condition that the lithium ion battery has high energy density, high cycle performance and high safety, the electric equipment comprising the lithium ion battery also has the advantages, and the description is omitted.

The electric equipment of the present invention may be, for example, a new energy vehicle, an electronic device, an electric tool, an electric power storage facility, and the like.

The lithium ion battery of the present invention will be described in further detail with reference to examples and comparative examples.

Example 1

The embodiment is a lithium ion battery, which comprises an electrode main body formed by sequentially winding a positive pole piece, an isolating film and a negative pole piece, a positive pole lug and a negative pole lug which are respectively arranged at two ends of the electrode main body, a specific structure of the lithium ion battery refers to fig. 1, and electrolyte for infiltrating the electrode main body. Specifically, the preparation process of the lithium ion battery of the embodiment is as follows:

(1) preparation of positive pole piece

LiNi serving as a positive electrode active material_0.8Co_0.1Mn_0.1O₂(NCM811), a conductive agent Super P and a binder polyvinylidene fluoride (PVDF) are mixed according to the mass ratio of 94:3:3, added into a solvent N-methyl pyrrolidone (NMP), and stirred under the action of a vacuum stirrer until the system is uniform, so as to obtain positive electrode slurry, wherein the solid content in the positive electrode slurry is 77 wt%; uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil with the thickness of 14 mu m, drying at 85 ℃, then carrying out cold pressing, edge cutting, slitting and drying for 4h under the vacuum condition of 85 ℃ to obtain a positive electrode piece;

(2) preparation of negative pole piece

Mixing a negative electrode active material graphite, a conductive agent Super P, a thickening agent carboxymethylcellulose sodium CMC and a binder styrene butadiene rubber emulsion SBR according to a mass ratio of 94:2:2:2, adding the mixture into solvent deionized water, and obtaining negative electrode slurry under the action of a vacuum stirrer, wherein the solid content in the negative electrode slurry is 54 wt%; uniformly coating the negative electrode slurry on a negative electrode current collector copper foil with the thickness of 8 mu m, drying at 85 ℃, then carrying out cold pressing, trimming, cutting, slitting and drying for 12h at 120 ℃ under a vacuum condition to obtain a negative electrode plate;

(3) preparation of the electrolyte

At water content<In a 10ppm argon atmosphere glove box, EC, EMC and EA were mixed at a ratio of 30:60:10 as an organic solvent, followed by a fully dried lithium salt LiPF₆Dissolving in the mixed organic solvent, adding 2 wt% of additive A triallyl phosphate, and uniformly mixing to obtain electrolyte;

in the electrolyte, LiPF₆The concentration of (A) is 1 mol/L;

(4) preparation of the separator

Coating a coating layer containing ceramic particles on at least one surface of a PE porous membrane by taking a polyethylene membrane PE with the thickness of 16 mu m as a base membrane to form a separation membrane;

(5) preparation of lithium ion battery

The method comprises the steps of sequentially stacking a positive pole piece, an isolating film and a negative pole piece, enabling the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, then winding the positive pole piece, the isolating film and the negative pole piece into a square electrode main body, welding lugs at two ends of the electrode main body in the length direction, placing the electrode main body into a packaging aluminum plastic film or a steel shell, then baking the electrode main body at 80 ℃ to remove water, injecting corresponding electrolyte into the electrode main body and sealing the electrode main body, and then carrying out standing, hot and cold pressing, formation, air exhaust, reshaping, capacity testing and other procedures to obtain the finished product lithium ion battery.

Examples 2 to 18 and comparative examples 1 to 3

Examples 2 to 18 and comparative examples 1 to 3 are lithium ion batteries, respectively, and the differences from example 1 are shown in table 1. In table 1, the addition amounts of each solvent and additive a are mass percentages calculated based on the total mass of the electrolyte. The rest is the same as in example 1.

Performance testing

Next, the performance of the lithium ion batteries of the respective examples and comparative examples was tested.

1) Method for testing liquid absorption rate gamma of positive pole piece to electrolyte

The positive electrode plates described in examples and comparative examples were sufficiently dried, then cut into a square of 5cm × 5cm, and fixed on a sample stage. Then, a capillary having a diameter d of 0.2mm was selected to suck the electrolyte described in examples and comparative examples to a certain height h. And vertically contacting the capillary tube absorbed with the electrolyte with the anode pole piece, and timing by using a stopwatch while the liquid level of the capillary tube descends. And reading the liquid suction time t after the liquid level is completely lowered. Finally, according to the formula gamma, pi x (d/2)²Calculating the multiplied by rho/t to obtain a liquid absorption rate value, wherein rho is the density of the electrolyte.

The test results of each example and comparative example are shown in table 1.

2) Lithium ion battery 25 ℃ cycle performance test

Fresh lithium ion secondary batteries prepared in examples and comparative examples were left to stand at 25 ℃ for 5 minutes, and were subjected to constant current charging at a rate of 1C to 4.2V, constant voltage charging until the current became 0.05C or less, and then left to stand for 5 minutes, and were subjected to constant current discharging at a rate of 1C to 2.8V, which is a charge-discharge cycle, and the discharge capacity of this time was recorded as the discharge capacity of the 1 st cycle of the lithium ion secondary battery. And (3) performing 800 times of cyclic charge and discharge tests on the lithium ion battery according to the method, and recording the discharge capacity of each cycle. The test results of each example and comparative example are shown in table 2.

The capacity retention (%) of the lithium ion battery after 400 cycles of 1C/1C at 25 ℃ was equal to the discharge capacity at 800 cycles/discharge capacity at 1 cycle × 100%.

3) High temperature storage volume expansion test for lithium ion batteries

Charging at 25 deg.C with 1C constant current to 4.2V, then charging at 4.2V constant voltage to 0.05C, and testing the volume of the lithium ion battery and recording as V₂(ii) a Then the fully charged lithium ion battery is put into a thermostat with the temperature of 80 ℃, stored for 10 days, and the volume is tested by adopting a drainage method and is recorded as V₃。

Volume expansion rate (%) after storage of lithium ion battery at 80 ℃ for 10 days₃-V₂)/V₂X 100%. The test results of each example and comparative example are shown in table 2.

TABLE 1

TABLE 1 continuation

TABLE 2

In embodiments 1 to 18, by using an electrolyte containing an additive a and limiting the diffusion rate of the electrolyte in an electrode main body to be in a range of 0.01 μ g/s to 5 μ g/s, since the film formation quality of the cathode passivation film is high, a side reaction of the electrolyte on the surface of a cathode active material can be effectively inhibited, and the electrolyte has a good wettability, the obstruction of the high energy density design on the electrolyte diffusion can be effectively alleviated, the additive a can be timely replenished into the electrode main body in the circulation process, and the SEI film consumed on the surface of the cathode active material can be quickly repaired, so that the cell can achieve high energy density, high capacity retention rate and low volume expansion rate. In examples 1 to 5, when the diffusion rate of the electrolyte in the electrode main body was 0.2 μ g/s to 2 μ g/s, the energy density, cycle performance, and gassing problems of the lithium ion battery could be further optimized.

In comparative example 1, the diffusion rate v of the electrolyte in the electrode main body is significantly smaller than the diffusion rate defined in the present invention. It can be seen from the experimental data that when the diffusion rate v of the electrolyte in the battery cell is small, the effective wetting rate cannot be achieved, and therefore, the cycle performance of the lithium ion battery is affected.

In comparative example 2, the diffusion rate v of the electrolyte in the electrode main body was significantly larger than that defined in the present invention. It can be seen from the experimental data that when the diffusion rate v of the electrolyte in the battery cell is large, the cycle performance of the lithium ion battery is reduced. This is because the solvent (e.g., ethylene carbonate EC) and the lithium salt in the electrolyte deteriorate the wetting rate of the electrolyte on the positive electrode sheet, and a certain amount of ethylene carbonate EC is required in the electrolyte for dissociating the lithium salt, increasing the conductivity, and a certain amount of lithium salt is required for supplying lithium ions. Too high a diffusion rate of the electrolyte may affect the dissociation and conductivity of the electrolyte to the lithium salt.

Furthermore, as can be seen from the data of examples 1 to 18, the correlation between the mass percentage content of the positive electrode film-forming additive in the electrolyte and the diffusion rate v of the electrolyte in the electrode main body has a large influence on the film-forming quality and the interface impedance of the positive electrode sheet. When the product of the mass ratio w (%) of the additive A in the electrolyte and the diffusion rate v (mug/s) is 0.01-10, especially in the range of 0.4-5, the electrolyte can be ensured to have a high infiltration rate, sufficient additive A can be ensured to form a stable protective film to inhibit gas generation, and meanwhile, the dosage of the additive A is moderate, and the cycle performance of the lithium ion battery is ensured to be good.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.