Lithium secondary batteries and electrical devices

Abstract

The present application provides a lithium secondary battery and an electric device, the lithium secondary battery including a positive electrode plate and an electrolyte, the positive electrode plate including a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector, the positive electrode active material layer having a lithium ion diffusion coefficient Ds, the electrolyte including a solvent, the solvent including at least one compound of the following formula (I), the mass fraction of the compound of formula (I) in the solvent being W1, and the relationship between the mass fraction W1 of the compound of formula (I) and the lithium ion diffusion coefficient Ds of the positive electrode active material layer being 2×10 -18 cm 2 / s ≤ W1 × Ds ≤ 8 × 10 -6 cm 2 / s, selectively 3 × 10 -14 cm 2 / s ≤ W1 × Ds ≤ 7 × 10 -10 cm 2 / s, and R1 and R2 each independently comprise at least one of an alkyl group having 1 to 3 carbon atoms and a haloalkyl group having 1 to 3 carbon atoms. In this lithium secondary battery, by adjusting the lithium ion diffusion coefficient Ds of the positive electrode material and the amount of the compound of formula (I) used, the transfer rate of lithium ions in the electrolyte can be effectively increased, thereby improving the energy density and high-speed charging performance of the lithium secondary battery. [C1] JPEG2025538199000030.jpg39170

Description

[Technical Field]

[0001] The present application relates to the field of battery technology, and in particular to lithium secondary batteries and electrical devices. [Background technology]

[0002] In recent years, secondary batteries have been widely applied to various electronic products and electric vehicles due to their high power density and volumetric capacity. With the rapid development and widespread application of secondary batteries, there are increasing demands for their energy density, fast charging performance, etc.

[0003] The fast charging of lithium secondary batteries is due to the rapid desorption of lithium ions from the positive electrode active material, their migration to the negative electrode through the electrolyte, and their rapid insertion into the negative electrode active material. Therefore, the fast charging performance of lithium secondary batteries is closely related to the lithium ion transfer rate in the electrode material and electrolyte. The lithium ion diffusion coefficient in the electrode material and electrolyte is one of the parameters that reflects the lithium ion transfer rate in the electrode material and electrolyte. However, the lithium ion diffusion coefficient in the electrode material and the lithium ion diffusion coefficient in the electrolyte are difficult to match, which has a serious impact on the charge / discharge performance of lithium ions. Therefore, how to improve the charge / discharge performance of lithium secondary batteries is a technical issue that must be resolved as soon as possible. Summary of the Invention

[0004] The present application has been made in view of the above technical problems, and its purpose is to provide a lithium secondary battery and an electrical device that can increase the transfer rate of lithium ions in the positive electrode active material layer and the electrolyte solution, thereby contributing to improving the high-speed charging performance of the lithium secondary battery.

[0005] In a first aspect, the present application provides a lithium secondary battery, the lithium secondary battery including a positive electrode plate and an electrolyte, the positive electrode plate including a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector, the positive electrode active material layer having a lithium ion diffusion coefficient Ds, the electrolyte including a solvent, the solvent including at least one compound of the following formula (I), the mass fraction of the compound of formula (I) in the solvent being W1, and the relationship between the mass fraction W1 of the compound of formula (I) and the lithium ion diffusion coefficient Ds of the positive electrode active material layer being 2×10 -18 cm 2 / s ≤ W1 × Ds ≤ 8 × 10 -6 cm 2 / s, selectively 3 × 10 -14 cm 2 / s ≤ W1 × Ds ≤ 7 × 10 -10 cm 2 / s fulfilled, [ka] R1 and R2 each independently include at least one of an alkyl group having 1 to 3 carbon atoms and a haloalkyl group having 1 to 3 carbon atoms.

[0006] In the embodiments of the present application, the compound represented by formula (I), as a solvent or part of the solvent, can impart high conductivity to the electrolyte. During charging of a lithium secondary battery, lithium ions are desorbed from the positive electrode active material, migrate to the surface of the negative electrode active material layer through the electrolyte, and then inserted into the negative electrode active material. By controlling the amount of the compound represented by formula (I) used based on the lithium ion diffusion coefficient Ds of the positive electrode material in the lithium secondary battery, the transfer rate of lithium ions in the electrolyte can be effectively increased, allowing the electrolyte to transfer a large amount of lithium ions desorbed from the positive electrode active material to the negative electrode in a timely manner, thereby improving the high-speed charging performance of the lithium secondary battery.

[0007] In some embodiments, R1 and R2 each independently comprise at least one of a methyl group, an ethyl group, a propyl group, a fluoromethyl group, a fluoroethyl group, and a fluoropropyl group.

[0008] In some embodiments, 10 -16 cm 2 / s≦Ds≦10 -5 cm 2 / s, optionally 10 -14 cm 2 / s≦Ds≦10 -9 cm 2 / s.

[0009] In some embodiments, 20%≦W1≦80%, optionally 30%≦W1≦70%.

[0010] In some embodiments, the compound of formula (I) is [ka] and Optionally, the compound of formula (I) includes at least one of a compound of formula (II), a compound of formula (I-II), a compound of formula (IV), and a compound of formula (I-VIII).

[0011] In some embodiments, the electrolyte includes a first additive, the first additive including at least one compound of formula (II): [ka] R3 includes at least one of an alkylene group substituted or unsubstituted with Ra and having 2 to 10 carbon atoms, a heteroalkylene group substituted or unsubstituted with Ra and having 2 to 10 carbon atoms, an arylene group substituted or unsubstituted with Ra and having 6 to 18 carbon atoms, a heteroarylene group substituted or unsubstituted with Ra and having 6 to 18 carbon atoms, a divalent alicyclic group substituted or unsubstituted with Ra and having 3 to 18 carbon atoms, and a heterodivalent alicyclic group substituted or unsubstituted with Ra, Ra includes at least one of a halogen atom, a cyano group, an isocyanate group, a hydroxy group, a carboxy group, a sulfonic acid group, an ester group, an alkyl group having 2 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and an oxaalkyl group having 2 to 10 carbon atoms.

[0012] In the present embodiment, the introduction of a first additive into the electrolyte helps form a protective SEI (Solid Electrolyte Interface) film on the surface of the negative electrode active material layer of a lithium secondary battery, effectively increasing the stability of the solid-liquid interface between the negative electrode and the electrolyte, and alleviating the problem of gas generation at the interface between the electrolyte and the negative electrode active material layer during high-speed charging of the lithium secondary battery, which contributes to improving the cycle performance of the lithium secondary battery.

[0013] In some embodiments, the mass fraction of the first additive in the electrolyte is W2, and W2, W1, and Ds are 2×10 -22 cm 2 / s≦W2×W1×Ds≦1.6×10 -6 cm 2 / s, selectively 2 × 10 -21 cm 2 / s≦W2×W1×Ds≦8×10 -7 cm 2 / s, selectively 4 × 10 -21 cm 2 / s≦W2×W1×Ds≦4×10 -7 cm 2 Satisfy / s.

[0014] In some embodiments, W2 satisfies 0.01%≦W2≦20%, optionally 0.1%≦W2≦10%, optionally 0.2%≦W2≦5%.

[0015] In some embodiments, the first additive is: [ka] [ka] The compound contains at least one of the following compounds:

[0016] In some embodiments, the electrolyte solution includes a second additive, the second additive comprising: [ka] and at least one compound of formula (III): [ka] M a+ contains at least one of a lithium ion, a sodium ion, a potassium ion, a rubidium ion, a cesium ion, a magnesium ion, a calcium ion, a barium ion, an aluminum ion, an iron ion, a copper ion, a nickel ion, and an organic cation; a, b, and c all represent natural numbers; t represents an integer of 0 to 3; w represents an integer of 1 to 6; X contains at least one halogen atom; n represents an integer of 0 to 4; Y contains at least one boron atom or a phosphorus atom; R4 contains a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted haloalkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, or a substituted or unsubstituted haloarylene group having 6 to 20 carbon atoms; q represents an integer of 0 to 1, and m represents an integer of 1 to 3.

[0017] In the examples of the present application, the introduction of a second additive into the electrolyte solution helps to form an SEI film on the surface of the negative electrode active material layer, further increasing the stability of the solid-liquid interface between the negative electrode and the electrolyte solution, and further improving the cycle performance of the lithium secondary battery.

[0018] In some embodiments, the mass fraction of the second additive in the electrolyte is W3, and W3, W1, and Ds are 2×10 -22 cm 2 / s≦W3×W1×Ds≦1.6×10-6 cm 2 / s, selectively 2 × 10 -21 cm 2 / s≦W3×W1×Ds≦8×10 -7 cm 2 / s, selectively 4 × 10 -21 cm 2 / s≦W3×W1×Ds≦4×10 -7 cm 2 Satisfy / s.

[0019] In some embodiments, 0.01%≦W3≦20%, alternatively 0.1%≦W3≦10%, alternatively 0.2%≦W3≦5%.

[0020] In some embodiments, [ka] In M a+ Li + , Na + , K. + , Rb + , Cs + , Mg 2+ , Ca 2+ , Ba 2+ , Al 3+ , Fe 2+ , Cu 2+ , Fe 3+ , Ni 2+ , Ni 3+ It includes at least one of the following:

[0021] In some embodiments, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, wherein an average particle size Dv501 of the first positive electrode active material satisfies 8 μm≦Dv501≦50 μm, and an average particle size Dv502 of the second positive electrode active material satisfies 0.02 μm≦Dv502≦8 μm.

[0022] In the examples of the present application, the combination of a first active material having a large average (volume) particle size and a second active material having a small average (volume) particle size helps to increase the powder compression density of the positive electrode plate, thereby contributing to increasing the energy density of the lithium secondary battery.

[0023] In some embodiments, the mass fraction W4 of the second positive electrode active material in the positive electrode active material layer satisfies 0%≦W4≦60%, and optionally 20%≦W4≦40%.

[0024] In some embodiments, the lithium secondary battery includes a negative electrode plate, the negative electrode plate including a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer including a negative electrode active material, and an average particle diameter Dv503 of the negative electrode active material satisfies 6 μm≦Dv503, optionally 15 μm≦Dv503≦20 μm.

[0025] In the examples of the present application, by setting the average (volume) particle size of the negative electrode active material within an appropriate range, after the first additive and / or the second additive form an SEI film of a certain thickness on the surface of the negative electrode active material layer, the average volume particle size of the surface negative electrode active material increases and the specific surface area decreases, contributing to reducing the contact area between the surface negative electrode active material and the electrolyte, reducing the probability of side reactions occurring on the surface of the electrolyte negative electrode active material layer, and improving the cycle performance of the lithium secondary battery.

[0026] In some embodiments, the specific surface area of ​​the negative electrode active material is 0.5 m 2 / g≦BET≦2.0m 2 / g, selectively 0.8m 2 / g≦BET≦1.5m 2 / g is met.

[0027] In the examples of the present application, by setting the specific surface area of ​​the negative electrode active material within an appropriate range, after the first additive and / or the second additive form an SEI film of a certain thickness on the surface of the negative electrode active material layer, the specific surface area of ​​the surface negative electrode active material is reduced, the contact area between the negative electrode active material and the electrolyte is reduced, the probability of the electrolyte causing a side reaction on the surface of the negative electrode active material layer is reduced, and the cycle performance of the lithium secondary battery is improved.

[0028] A second aspect provides an electrical device including the lithium secondary battery according to any one of the embodiments of the first aspect. As a result, the lithium secondary battery provided by the present application has good high-speed charging performance and cycle performance, and the electrical device provided by the present application can be efficiently charged at high speed and has a long service life.

[0029] In order to more clearly explain the technical solutions of the embodiments of the present application, the drawings that need to be used in the embodiments of the present application will be briefly described below. Obviously, the drawings described below are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on the drawings without any creative efforts. In the drawings, the drawings are not drawn to actual scale. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic diagram of a secondary battery according to the present invention; [Figure 2] 1 is a schematic structural diagram of a secondary battery according to the present invention; [Figure 3] 1 is a schematic structural diagram of a battery module according to the present invention; [Figure 4] 1 is a schematic diagram of a battery pack according to the present application. [Figure 5] 1 is a schematic structural diagram of a battery pack according to the present application; [Figure 6] 1 is a schematic diagram of an electrical device of the present application; DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the lithium secondary battery and electric device of the present application will be described in detail. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of substantially the same structures may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate easy understanding by those skilled in the art. Furthermore, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the scope of the claims.

[0032] The "ranges" disclosed herein are defined in the form of lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the given range. Such defined ranges may be inclusive or exclusive of the endpoints and may be arbitrarily combined; i.e., any lower limit may be combined with any upper limit to form a single range. For example, if ranges of 60 to 120 and 80 to 110 are recited for a given parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if 1 and 2 are recited as minimum range values ​​and 3, 4, and 5 are recited as maximum range values, then the ranges of 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all contemplated. Unless otherwise specified herein, a numerical range "a to b" represents a shorthand notation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 and 5" are listed herein, and "0 to 5" is simply shorthand for combinations of these numbers. Note that describing a parameter as an integer ≧2 is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] In this description, unless otherwise specified, "multiple" means two or more, and any orientation or positional relationship indicated by terms such as "up," "down," "left," "right," "inside," and "outside" is merely for ease of explanation and brevity, and does not indicate or suggest that the designated device or element necessarily has a particular orientation, is configured, or operates in a particular orientation, and should not be understood as limiting the present application. Furthermore, terms such as "first," "second," and "third" are merely for descriptive purposes and should not be understood as indicating or suggesting relative importance. "Perpendicular" does not mean perpendicular in the strict sense, but within a tolerance range. "Parallel" does not mean parallel in the strict sense, but within a tolerance range.

[0034] Unless otherwise specified, the terms "comprise" and "comprises" used herein may be open-ended or closed-ended. For example, the terms "comprise" and "comprises" may indicate that the compound may further include or include other components not listed, or may include or include only the listed components.

[0035] Unless otherwise stated, the term "or" in this application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any one of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or A and B are both true (or exist).

[0036] Unless otherwise specified, all steps herein may be performed in sequence or randomly, preferably in sequence. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in sequence, or may include steps (b) and (a) performed in sequence. For example, when it is stated that the method may further include step (c), it means that step (c) can be added to the method in any order; for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b).

[0037] Unless otherwise stated, all embodiments and alternative embodiments in the present application can be combined with each other to form new technical solutions.

[0038] Unless otherwise stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0039] Unless otherwise explained, the following terms have the following meanings: Any undefined terms have their art-recognized meanings.

[0040] The term "alkyl group" has its conventional meaning and refers to a monovalent saturated hydrocarbon group having one or more carbon atoms, optionally from 1 to 3 carbon atoms. For example, alkyl groups include straight-chain and branched-chain hydrocarbon groups, such as, for example, methyl, ethyl, n-propyl, isopropyl, and the like.

[0041] The term "haloalkyl group" has its usual meaning and refers to an alkyl group in which one or more hydrogen atoms on one or more carbon atoms in a straight, branched, or cyclic backbone are replaced by halogen atoms, such as monochloromethyl, monofluoromethyl, trifluoromethyl, monofluoroethyl, monofluoropropyl, and the like.

[0042] The term "alkylene group" has its conventional meaning and refers to a divalent hydrocarbon group having one or more carbon atoms, optionally from 1 to 10 carbon atoms. For example, alkylene groups include divalent linear hydrocarbon groups and divalent branched hydrocarbon groups, such as ethylene, methylethylene, n-propylene, and the like.

[0043] The term "alkylene group substituted by Ra" refers to an alkylene group in which one or more hydrogen atoms on one or more carbon atoms in its straight, branched, or cyclic backbone have been replaced by Ra.

[0044] The term "heteroalkylene group" has its conventional meaning and refers to an alkylene group in which one or more carbon atoms in its straight, branched, or cyclic backbone are each independently replaced with the same or different heteroatoms or groups, including, but not limited to, halogen atoms, oxygen atoms, sulfur atoms, peroxy groups, persulfide groups, oxysulfide groups, phenyl groups, and the like.

[0045] The term "heteroalkylene group substituted by Ra" refers to a heteroalkylene group in which one or more hydrogen atoms on one or more carbon atoms in its straight, branched, or cyclic backbone have been replaced by Ra.

[0046] The term "arylene group" has its conventional meaning and refers to a divalent aryl group derived by removing one hydrogen atom from each of two different carbon atoms of an aromatic compound or by removing two hydrogen atoms from one carbon atom of an aromatic compound.

[0047] The term "arylene group substituted by R a " refers to an arylene group in which one or more hydrogen atoms on one or more carbon atoms in its straight, branched, or cyclic backbone have been replaced by R a .

[0048] The term "heteroarylene group" has its conventional meaning and refers to an arylene group in which one or more carbon atoms are each independently replaced with the same or different heteroatoms or groups.

[0049] The term "heteroarylene group substituted by R a " refers to a heteroarylene group in which one or more hydrogen atoms on one or more carbon atoms in its straight-chain, branched-chain or cyclic backbone have been replaced by R a .

[0050] The term "divalent alicyclic radical" has its conventional meaning and refers to a divalent alicyclic radical derived by removing two hydrogen atoms from an alicyclic hydrocarbon molecule.

[0051] The term "divalent alicyclic radical substituted by Ra" refers to a divalent alicyclic radical in which one or more hydrogen atoms on one or more carbon atoms in its straight-chain, branched-chain, or cyclic backbone have been replaced by Ra.

[0052] "Heterobivalent alicyclic radical" has its usual meaning and refers to a heterobivalent alicyclic radical in which one or more carbon atoms in a straight, branched, or cyclic backbone are each independently replaced with the same or different heteroatoms or groups.

[0053] The term "divalent alicyclic radical substituted by Ra" refers to a heterodivalent alicyclic radical in which one or more hydrogen atoms on one or more carbon atoms in its straight-chain, branched-chain, or cyclic backbone are replaced by Ra.

[0054] The term "halogen atom" has its ordinary meaning and refers to fluorine, chlorine, bromine, iodine and astatine atoms.

[0055] The term "alkenyl group" has its usual meaning and refers to a hydrocarbon group having one or more carbon atoms and at least one double bond unsaturation site. Optionally, the number of carbon atoms is 2 to 10. For example, alkenyl groups include linear alkenyl groups and branched alkenyl groups. Examples include vinyl groups, propenyl groups, and n-butenyl groups. In other examples, alkenyl groups can further include cyclic alkenyl groups, bicyclic alkenyl groups, and the like. For example, a cyclohexyl group can be mentioned.

[0056] The term "alkynyl group" has its usual meaning and refers to a hydrocarbon group having one or more carbon-carbon triple bonds, optionally containing 2 to 10 carbon atoms, such as vinyl.

[0057] The term "oxaalkyl" has its conventional meaning and refers to an alkyl group in which one or more carbon atoms in its straight, branched or cyclic backbone has been replaced by an oxygen atom.

[0058] The term "substituted alkylene group" has its usual meaning and refers to an alkylene group in which one or more hydrogen atoms on one or more carbon atoms in its straight, branched, or cyclic backbone have been replaced by the same or different heteroatoms or groups.

[0059] The term "haloalkylene group" has its conventional meaning and refers to an alkylene group in which one or more hydrogen atoms on one or more carbon atoms in a straight, branched, or cyclic backbone have been replaced by the same or different halogen atoms.

[0060] The term "substituted haloalkylene group" has its conventional meaning and refers to a haloalkylene group in which one or more hydrogen atoms on one or more carbon atoms in its straight, branched, or cyclic backbone have been replaced by the same or different heteroatoms or groups.

[0061] The term "substituted arylene group" refers to an arylene group in which one or more hydrogen atoms on one or more carbon atoms in its straight, branched, or cyclic backbone have been replaced with the same or different heteroatoms or groups.

[0062] The term "haloarylene group" refers to an arylene group in which one or more hydrogen atoms on one or more carbon atoms in its straight, branched or cyclic backbone have been replaced by the same or different halogen atoms or groups.

[0063] The term "substituted haloarylene group" refers to a haloarylene group in which one or more hydrogen atoms on one or more carbon atoms in its straight, branched, or cyclic backbone have been replaced with the same or different heteroatoms or groups.

[0064] The term "lithium ion diffusion coefficient" refers to the average number of lithium ions passing through a unit area of ​​a medium in a unit time, and can represent the permeation rate of lithium ions through the medium. The diffusion process of lithium ions in the solid phase not only includes diffusion based on the rearrangement mechanism within ionic crystals, but also diffusion due to the influence of a concentration gradient and diffusion due to the influence of chemical potential. In the embodiments of the present application, the lithium ion diffusion coefficient may be expressed as the chemical diffusion coefficient of lithium ions, and the chemical diffusion coefficient encompasses the above-mentioned multiple diffusion processes.

[0065] In the examples herein, the particle size distribution reflects the average (volume) particle size of the material.

[0066] The term "Dv50" refers to the particle size corresponding to the point where the cumulative particle size distribution of a material reaches 50%. Its physical meaning is that particles larger than or smaller than the particle size in question account for 50% of the total number of particles in the material. The "1" in "Dv501" is a corner mark and is used to represent the Dv50 of a material and to distinguish it from the Dv50 of other materials, and has no other limiting meaning.

[0067] Next, an embodiment of the present invention will be described.

[0068] In recent years, secondary batteries have achieved remarkable development due to their high energy density and long service life, and are widely used in many fields, including power tools, electronic products, electric vehicles, and aerospace. A typical secondary battery contains a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the battery's charge and discharge process, active ions are repeatedly inserted and removed between the positive and negative electrodes. The electrolyte, located between the positive and negative electrodes, serves to conduct the active ions. The separator, located between the positive and negative electrodes, prevents short-circuiting between the positive and negative electrodes while allowing the active ions to pass through it, ensuring the normal electrochemical reaction of the secondary battery.

[0069] Taking a lithium secondary ion battery as an example, a lithium secondary battery is a typical secondary battery that is charged and discharged by a chemical reaction of lithium ions released between the positive and negative electrodes, and is also called a rocking chair battery. During the charging process of a lithium secondary battery, lithium ions are desorbed from the positive electrode active material and migrate to the negative electrode by the conduction of the electrolyte and are inserted into the negative electrode active material. During the discharging process, lithium ions are desorbed from the negative electrode active material and migrate to the positive electrode by the conduction of the electrolyte and are inserted into the positive electrode active material.

[0070] It should be understood that the "lithium insertion" and "insertion" processes described herein refer to a process in which lithium ions are inserted into a positive electrode active material or a negative electrode active material through an electrochemical reaction, and the "deintercalation," "lithium deintercalation," and "release" processes described herein refer to a process in which lithium ions are deintercalated from a positive electrode active material or a negative electrode active material through an electrochemical reaction.

[0071] As lithium secondary batteries are increasingly widely used, the performance requirements for lithium secondary batteries are also increasing in various fields. For example, in the field of electric vehicles, lithium secondary batteries are required to have high energy density and fast charging capability. As can be seen from the above, during the charging process of a lithium secondary battery, lithium ions are desorbed from the positive electrode active material, transported to the negative electrode via the electrolyte, and inserted into the negative electrode active material. To achieve high energy density, the positive and negative electrode plates must carry more positive and negative electrode active material, which results in thicker positive and negative electrode active material layers on the plates than in conventional lithium secondary batteries. For example, in the case of a positive electrode plate, the lithium ion diffusion coefficient of the positive electrode active material layer is usually large to ensure smooth desorption of lithium ions from the positive electrode active material away from the surface of the positive electrode active material layer. Meanwhile, the positive electrode active material layer and the electrolyte have different lithium ion conduction capabilities. Typically, the lithium ion diffusion coefficient of lithium ions in the positive electrode active material layer (solid phase) is larger than the lithium ion diffusion coefficient of lithium ions in the electrolyte (liquid phase). Due to the mismatch between the solid-phase diffusion coefficient and liquid-phase diffusion coefficient of lithium ions, during the fast charging process of a lithium secondary battery, a large number of lithium ions are released from the positive electrode active material and are limited by the lithium ion conductivity of the electrolyte, preventing them from being transported to the negative electrode in a timely manner, thereby limiting the fast charging performance of the lithium secondary battery.

[0072] In view of this, the present invention provides a lithium secondary battery, in which a solvent for an electrolyte solution contains a linear carboxylic acid ester compound represented by formula (I), which has a high dielectric constant, a low viscosity, and enhances the lithium ion conductivity of the electrolyte solution. Furthermore, by adjusting the mass fraction of the compound represented by formula (I) within an appropriate range depending on the lithium ion diffusion coefficient of the positive electrode active material layer, the lithium secondary battery has high energy density and good fast charging performance.

[0073] In one embodiment of the present application, a lithium secondary battery is provided. Typically, a lithium secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. The lithium secondary battery provided by the present application and each component of the lithium secondary battery will now be described.

[0074] In one embodiment of the present application, a lithium secondary battery is provided, which includes a positive electrode plate and an electrolyte.

[0075] The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector, and the positive electrode active material layer has a lithium ion diffusion coefficient Ds.

[0076] The electrolyte solution contains a solvent, and the solvent contains at least one compound represented by the following formula (I), and the mass fraction of the compound represented by formula (I) in the electrolyte solution is W1. The mass fraction W1 of the compound represented by formula (I) and the lithium ion diffusion coefficient Ds of the positive electrode active material layer are 2×10 -18 cm 2 / s ≤ W1 × Ds ≤ 8 × 10 -6 cm 2 / s, selectively 3 × 10 -14 cm 2 / s ≤ W1 × Ds ≤ 7 × 10 -10 cm 2 / s fulfilled, [ka] R1 and R2 each independently include at least one of an alkyl group having 1 to 3 carbon atoms and a haloalkyl group having 1 to 3 carbon atoms.

[0077] Specifically, W1 × Ds is 2 × 10 -18 cm 2 / s, 2 × 10 -17 cm 2 / s, 2 × 10 -16 cm 2 / s, 2 × 10 -15 cm 2 / s, 2 × 10 -14 cm 2 / s, 3 × 10 -14 cm2 / s, 2 × 10 -12 cm 2 / s, 2 × 10 -11 cm 2 / s, 7 × 10 -10 cm 2 / s, 2 × 10 -9 cm 2 / s, 2 × 10 -8 cm 2 / s, 2 × 10 -7 cm 2 / s, 8 × 10 -6 cm 2 / s, or the value is within the range obtained by combining any two of the above values.

[0078] In this embodiment, the lithium secondary battery has a positive electrode active material layer with a lithium ion diffusion coefficient Ds, and an electrolyte combined with the positive electrode active material layer. The solvent of the electrolyte contains the compound represented by formula (I), so that the electrolyte has high conductivity. By adjusting the mass fraction W1 of the compound in the electrolyte according to the lithium ion diffusion coefficient Ds of the positive electrode active material layer, the product of the two is kept within an appropriate range, thereby solving the problem of a mismatch between the lithium ion diffusion capacities of the positive electrode active material layer and the electrolyte in the lithium secondary battery, and achieving a high energy density of the lithium secondary battery while also improving the high-speed charging capability of the lithium secondary battery.

[0079] The lithium ion diffusion coefficient Ds of a positive electrode active material is related to factors such as the particle size of the positive electrode active material, its morphology, and the ion conduction capacity of the positive electrode active material itself. The lithium ion diffusion coefficient Ds of a positive electrode active material can be adjusted by adjusting the particle size of the positive electrode active material and changing its morphology.

[0080] As an example, the lithium ion diffusion coefficient (Ds) of the positive electrode active material can be adjusted using the following method. The raw materials Li2CO3, H3PO4, and FeCl2·4H2O are added to anhydrous ethanol in a molar ratio of 1:1:1, and the mixture is stirred uniformly. After the raw materials have reacted, the stirring is stopped and the sol immediately converts to a gray gel. After leaving the mixture at room temperature, the gray gel is transferred to an air-blast drying oven at 80°C and dried for 12 hours. The dried gel is then placed in an alumina porcelain boat and transferred to a tubular atmosphere furnace for heat treatment in an argon atmosphere. A two-stage calcination process, consisting of pre-calcination and final calcination, can be used. The pre-calcination heat treatment conditions are 350°C for 5 hours, and the final calcination heat treatment conditions are 500°C–800°C for 10–25 hours. To adjust the lithium ion diffusion coefficient (Ds), an appropriate amount of citric acid (e.g., 0 mol, 0.2 mol, 0.5 mol, 1 mol, or 2 mol) can be added to the sol after the raw materials have reacted, and the stirring time can be extended by 3 hours. Citric acid is added to the sol after the raw materials have reacted. During the subsequent calcination process, the citric acid is thermally decomposed to produce amorphous carbon, which can coat the particle surfaces. The presence of this carbon coating layer restricts further diffusion of the reactants, exerts a steric hindrance effect, slows the crystal growth rate, and contributes to grain refinement through the introduction of carbon. Therefore, by adjusting the amount of citric acid added, it is possible to obtain positive electrode materials with different particle sizes and, therefore, different lithium ion diffusion coefficients. The lithium ion diffusion coefficient (Ds) can be directly determined by constant current intermittent titration (GITT) method.

[0081] In one embodiment of the present application, the solvent may contain only the compound of formula (I). When the solvent contains only the compound of formula (I), the electrode solution has excellent conductivity and fluidity due to the high conductivity and low viscosity of the compound of formula (I), which can also alleviate the problem of a mismatch between the lithium ion diffusion capabilities of the positive electrode active material layer and the electrolyte in a lithium secondary battery, thereby realizing a lithium secondary battery with a high energy density and simultaneously improving the high-speed charging capability of the lithium secondary battery.

[0082] Optionally, R1 and R2 each independently comprise at least one of a methyl group, an ethyl group, a propyl group, a fluoromethyl group, a fluoroethyl group, and a fluoropropyl group.

[0083] Alternatively, the compound of formula (I) is [ka] and Optionally, the compound of formula (I) includes at least one of a compound of formula (II), a compound of formula (I-II), a compound of formula (IV), and a compound of formula (I-VIII).

[0084] The positive electrode plate and the electrolyte in the lithium secondary battery will be described in detail below.

[0085] [Electrolyte] The electrolyte serves to conduct lithium ions between the positive and negative electrodes, and includes a solute and a solvent, where the solute dissolves in the solvent to form a bulk phase of the electrolyte.

[0086] In the lithium secondary battery provided by the present application, the solvent of the electrolyte contains the compound represented by formula (I).

[0087] Alternatively, the mass fraction W1 of the compound represented by formula (I) in the electrolyte solution is positively correlated with the lithium ion diffusion coefficient Ds of the positive electrode active material layer.

[0088] Specifically, as the loading of the positive electrode active material increases, a positive electrode active material with a larger lithium ion diffusion coefficient Ds is selected, and a higher proportion of the compound represented by formula (I) is required to enhance the lithium ion conducting ability of the electrolyte to match the lithium ion conducting ability of the positive electrode active material layer.

[0089] Alternatively, the mass fraction W1 of the compound represented by formula (I) in the electrolyte satisfies 20%≦W1≦80%, more preferably 30%≦W1≦70%.

[0090] Specifically, W1 may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or any combination of any two of the above values ​​within the range.

[0091] Optionally, in other embodiments, the solvent can further comprise one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0092] Optionally, the solute of the electrolyte includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0093] Optionally, the electrolyte solution comprises a first additive, and the first additive comprises at least one compound of formula (II): [ka] R3 includes at least one of an alkylene group substituted or unsubstituted with Ra and having 2 to 10 carbon atoms, a heteroalkylene group substituted or unsubstituted with Ra and having 2 to 10 carbon atoms, an arylene group substituted or unsubstituted with Ra and having 6 to 18 carbon atoms, a heteroarylene group substituted or unsubstituted with Ra and having 6 to 18 carbon atoms, a divalent alicyclic group substituted or unsubstituted with Ra and having 3 to 18 carbon atoms, and a heterodivalent alicyclic group substituted or unsubstituted with Ra, Ra includes at least one of a halogen atom, a cyano group, an isocyanate group, a hydroxy group, a carboxy group, a sulfonic acid group, an ester group, an alkyl group having 2 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and an oxaalkyl group having 2 to 10 carbon atoms.

[0094] Specifically, the electrolyte solution can contain an additive such as the first additive. The first additive is a negative electrode film-forming additive that forms a stable SEI (Solid Electrolyte Interface, SEI) film on the surface of the negative electrode active material layer, thereby reducing direct contact between the negative electrode active material and the electrolyte solution. Introducing the compound represented by formula (I) into the electrolyte solution as a solvent or as part of the solvent helps improve the lithium ion conductivity of the electrolyte solution. However, the compound represented by formula (I) may undergo a side reaction on the surface of the negative electrode active material layer during the charge / discharge process of a lithium secondary battery, generating gas. This consumes the electrolyte solution in the lithium secondary battery and can cause structural damage to the negative electrode active material and the negative electrode active material layer, affecting the cycle performance and safety of the lithium secondary battery.

[0095] Therefore, in this embodiment, by introducing the first additive into the electrolyte, the negative electrode active material layer can be effectively protected from direct contact with the electrolyte, the stability of the solid-liquid interface between the negative electrode active material layer and the electrolyte can be increased, and the possibility that the compound represented by formula (I) will generate gas on the surface of the negative electrode active material layer can be reduced. This can achieve high energy density and high-speed charging performance of the lithium secondary battery, while also contributing to improving the cycle performance of the lithium secondary battery.

[0096] Optionally, the first additive is [ka] [ka] The compound contains at least one of the following compounds:

[0097] Optionally, the mass fraction W2 of the first additive in the electrolyte satisfies 0.01%≦W2≦20%, optionally 0.1%≦W2≦10%, optionally 0.2%≦W2≦5%.

[0098] Specifically, W2 may be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a value within a range obtained by combining any two of the above values.

[0099] Alternatively, the mass fraction W2 of the first additive in the electrolyte solution, the mass fraction W1 of the compound of formula (I) in the electrolyte solution, and the lithium ion diffusion coefficient Ds of the positive electrode active material layer are 2 × 10 -22 cm 2 / s≦W2×W1×Ds≦1.6×10 -6 cm 2 / s, selectively 2 × 10 -21 cm 2 / s≦W2×W1×Ds≦8×10 -7 cm 2 / s, selectively 4 × 10 -21 cm 2 / s≦W2×W1×Ds≦4×10 -7 cm 2 Satisfy / s.

[0100] Specifically, W2 × W1 × Ds is 2 × 10 -22 cm 2 / s, 2 × 10 -21 cm 2 / s, 4 × 10 -21 cm 2 / s, 2 × 10 -20 cm 2 / s, 2 × 10 -19 cm 2 / s, 2 × 10 -18 cm 2 / s, 2 × 10 -17 cm 2 / s, 2 × 10 -16 cm 2 / s, 2 × 10 -15 cm 2 / s, 2 × 10 -14 cm 2 / s, 2 × 10 -13 cm 2 / s, 2 × 10 -12 cm 2 / s, 2 × 10 -11 cm 2 / s, 2 × 10 -10 cm 2 / s, 2 × 10 -9 cm 2 / s, 2 × 10 -8 cm 2 / s, 4 × 10 -7 cm 2 / s, 8 × 10 -7 cm 2 / s, 1.6 × 10 -6 cm 2 / s, or the value is within the range obtained by combining any two of the above values.

[0101] Alternatively, the mass fraction W2 of the first additive in the electrolyte and the mass fraction W1 of the compound of formula (I) in the electrolyte are positively correlated.

[0102] Specifically, as the content of the compound represented by formula (I) in the electrolyte solution increases, the possibility that the compound represented by formula (I) will generate gas on the surface of the negative electrode active material layer increases. Therefore, a larger amount of the first additive needs to be formed as a film on the surface of the negative electrode active material layer so as to reduce the possibility that the compound represented by formula (I) will undergo a reduction reaction on the surface of the negative electrode active material layer to generate gas.

[0103] Optionally, the electrolyte solution includes a second additive, the second additive being [ka] and at least one compound of formula (III): [ka] M a+ contains at least one of a lithium ion, a sodium ion, a potassium ion, a rubidium ion, a cesium ion, a magnesium ion, a calcium ion, a barium ion, an aluminum ion, an iron ion, a copper ion, a nickel ion, and an organic cation; a, b, and c all represent natural numbers; t represents an integer of 0 to 3; w represents an integer of 1 to 6; X contains at least one halogen atom; n represents an integer of 0 to 4; Y contains at least one boron atom or a phosphorus atom; R4 contains a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted haloalkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, or a substituted or unsubstituted haloarylene group having 6 to 20 carbon atoms; q represents an integer of 0 to 1, and m represents an integer of 1 to 3.

[0104] Specifically, the electrolyte solution can further include another negative electrode film-forming additive as the second additive. The second additive also forms a stable SEI film on the surface of the negative electrode active material layer, isolating the electrolyte solution from the negative electrode active material layer, protecting the negative electrode active material, and reducing the possibility of the electrolyte solution generating gas on the surface of the negative electrode active material layer, thereby further improving the cycle performance of the lithium secondary battery. Furthermore, the second additive has little effect on the impedance of the lithium secondary battery after film formation, reducing the possibility of lithium deposition during the charge and discharge process of the lithium secondary battery due to excessively high impedance, thereby helping to improve the charge and discharge performance of the battery.

[0105] It should be understood that the electrolyte may contain only the first additive, only the second additive, or both the first and second additives. When the electrolyte contains both the first and second additives, the first and second additives exert a synergistic effect to form an SEI film on the surface of the negative electrode active material layer, which not only has an excellent film-forming effect but also has little effect on the impedance of the lithium secondary battery.

[0106] Optionally, the mass fraction W3 of the second additive in the electrolyte satisfies 0.01%≦W3≦20%, optionally 0.1%≦W3≦10%, optionally 0.2%≦W3≦5%.

[0107] Specifically, W3 may be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a value within a range obtained by combining any two of the above values.

[0108] Alternatively, the mass fraction W3 of the second additive in the electrolyte solution, the mass fraction W1 of the compound represented by formula (I) in the electrolyte solution, and the lithium ion diffusion coefficient Ds of the positive electrode active material layer are 2 × 10-22 cm 2 / s≦W3×W1×Ds≦1.6×10 -6 cm 2 / s, selectively 2 × 10 -21 cm 2 / s≦W3×W1×Ds≦8×10 -7 cm 2 / s, selectively 4 × 10 -21 cm 2 / s≦W3×W1×Ds≦4×10 -7 cm 2 Satisfy / s.

[0109] Specifically, W3 × W1 × Ds is 2 × 10 -22 cm 2 / s, 2 × 10 -21 cm 2 / s, 4 × 10 -21 cm 2 / s, 2 × 10 -20 cm 2 / s, 2 × 10 -19 cm 2 / s, 2 × 10 -18 cm 2 / s, 2 × 10 -17 cm 2 / s, 2 × 10 -16 cm 2 / s, 2 × 10 -15 cm 2 / s, 2 × 10 -14 cm 2 / s, 2 × 10 -13 cm 2 / s, 2 × 10 -12 cm 2 / s, 2 × 10 -11 cm 2 / s, 2 × 10 -10 cm 2 / s, 2 × 10 -9 cm 2 / s, 2 × 10 -8 cm 2 / s, 4 × 10 -7 cm 2 / s, 8 × 10 -7 cm 2 / s, 1.6 × 10 -6 cm 2 / s, or the value is within the range obtained by combining any two of the above values.

[0110] Alternatively, the mass fraction W3 of the second additive in the electrolyte and the mass fraction W1 of the compound of formula (I) in the electrolyte are positively correlated.

[0111] As with the first additive, as the content of the compound represented by formula (I) in the electrolyte solution increases, the possibility that the compound represented by formula (I) will generate gas on the surface of the negative electrode active material layer increases. Therefore, it is necessary to form a film of a larger amount of the negative electrode film-forming additive on the surface of the negative electrode active material layer so as to reduce the possibility that the compound represented by formula (I) will undergo a reduction reaction on the surface of the negative electrode active material layer to generate gas.

[0112] Selectively, [ka] In M a+ Li + , Na + , K. + , Rb + , Cs + , Mg 2+ , Ca 2+ , Ba 2+ , Al 3+ , Fe 2+ , Cu 2+ , Fe 3+ , Ni 2+ , Ni 3+ It includes at least one of the following:

[0113] Optionally, the electrolyte may further contain an additive capable of improving a specific performance of the battery, such as an additive that improves the overcharge performance of the battery, or an additive that improves the high-temperature or low-temperature performance of the battery.

[0114] [Positive electrode] The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector.

[0115] As an example, the positive electrode current collector has two surfaces facing each other in the thickness direction thereof, and the positive electrode active material layer is provided on either one or both of the two facing surfaces of the positive electrode current collector.

[0116] Alternatively, a metal foil or a composite current collector can be used as the positive electrode current collector. For example, an aluminum foil can be used as the metal foil. The composite current collector can include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0117] Optionally, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material.

[0118] Alternatively, the first positive electrode active material may be a positive electrode active material for batteries known in the art. For example, the first positive electrode active material may include at least one of materials such as lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO), lithium nickel oxide (e.g., LiNiO), lithium manganese oxide (e.g., LiMnO, LiMnO), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (may be abbreviated as NCM333), LiNi 0.5 Co 0.2Mn 0.3 O2 (may be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (may be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (may be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which may be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate having an olivine structure can include, but are not limited to, at least one of lithium iron phosphate (LiFePO4, which may be abbreviated as LFP), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0119] Optionally, the average (volume) particle size Dv501 of the first positive electrode active material satisfies 8 μm≦Dv501≦50 μm.

[0120] Specifically, Dv501 may be 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or any combination of any two of the above values.

[0121] Alternatively, the second positive electrode active material may be a positive electrode active material for batteries known in the art, provided that the average (volume) particle size of the second positive electrode active material is smaller than that of the selected first positive electrode active material. For example, the second positive electrode active material may include at least one of materials such as an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and modified compounds thereof. Examples of lithium transition metal oxides include, but are not limited to, at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Examples of lithium phosphates with an olivine structure include, but are not limited to, at least one of lithium iron phosphate, a lithium iron phosphate-carbon composite, lithium manganese phosphate, a lithium manganese phosphate-carbon composite, lithium manganese iron phosphate, and a lithium manganese iron phosphate-carbon composite. These positive electrode active materials may be used alone or in combination of two or more.

[0122] Optionally, the average (volume) particle size Dv502 of the second positive electrode active material satisfies 0.02 μm≦Dv502≦8 μm.

[0123] Specifically, Dv502 may be 0.02 μm, 0.04 μm, 0.06 μm, 0.08 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, or any combination of any two of the above values.

[0124] Optionally, the mass fraction W4 of the second positive electrode active material in the positive electrode active material layer satisfies 0%≦W4≦60%, and more optionally 20%≦W4≦40%.

[0125] Specifically, W4 may be 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 25%, 30%, 40%, 50%, 60%, or a range of values ​​within the range obtained by combining any two of the above values.

[0126] It should be understood that the first positive electrode active material and the second positive electrode active material may be the same type of active material. For example, the first positive electrode active material may be lithium iron phosphate having an average volume particle size on the micron scale, and the second positive electrode active material may be lithium iron phosphate having an average volume particle size on the nanoscale. The first positive electrode active material and the second positive electrode active material may be different types of active materials. For example, the first positive electrode active material may be lithium iron phosphate having an average volume particle size on the micron scale, and the second positive electrode active material may be lithium iron manganese phosphate having an average volume particle size on the nanoscale.

[0127] In this embodiment, by combining a first active material having a large average (volume) particle size with a second active material having a small average (volume) particle size, the powder compression density of the positive electrode active material layer is increased, which helps to increase the energy density of the lithium secondary battery.

[0128] Optionally, the positive electrode active material layer may further include a binder, for example, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0129] Optionally, the positive electrode active material layer may further include a conductive agent, for example, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments, a positive electrode plate can be manufactured by the following method. The components for manufacturing the positive electrode plate are each formed into a positive electrode slurry. For example, the first and / or second positive electrode active materials, the conductive agent, the binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then applied to at least one side of a positive electrode current collector, and after processes such as baking and cold pressing, a positive electrode plate can be obtained.

[0131] [Negative electrode] The negative electrode plate usually includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material.

[0132] As an example, the negative electrode current collector has two surfaces that face each other in the thickness direction of the negative electrode current collector, and the negative electrode active material layer is provided on either one or both of the two facing surfaces of the negative electrode current collector.

[0133] Alternatively, a metal foil or a composite current collector can be used as the negative electrode current collector. For example, a copper foil can be used as the metal foil. The composite current collector can include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0134] Alternatively, the average (volume) particle size Dv503 of the negative electrode active material satisfies 6 μm≦Dv503, and optionally 15 μm≦Dv503≦20 μm.

[0135] Specifically, Dv503 may be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any combination of any two of the above values.

[0136] In this embodiment, setting the average (volume) particle size of the negative electrode active material within an appropriate range helps to increase the powder compression density of the negative electrode active material layer. Furthermore, after the first additive and / or the second additive form an SEI film on the surface of the negative electrode active material layer, the average (volume) particle size of the negative electrode active material on the surface of the negative electrode active material layer increases, reducing the specific surface area, which helps to further reduce contact between the negative electrode active material and the electrolyte, reducing the probability of the electrolyte generating gas on the surface of the negative electrode active material layer, and contributing to improving the cycle performance of the lithium secondary battery.

[0137] Optionally, the specific surface area of ​​the negative electrode active material is 0.5 m 2 / g≦BET≦2.0m 2 / g, selectively 0.8m 2 / g≦BET≦1.5m 2 / g is met.

[0138] Specifically, BET is 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g, or the value is within the range obtained by combining any two of the above values.

[0139] In this embodiment, by setting the specific surface area of ​​the negative electrode active material within an appropriate range, after the first additive and / or the second additive form an SEI film on the surface of the negative electrode active material layer, the specific surface area of ​​the negative electrode active material on the surface of the negative electrode active material layer becomes even smaller, reducing the probability that the electrolyte will generate gas on the surface of the negative electrode active material layer and contributing to further improving the cycle performance of the lithium secondary battery.

[0140] Optionally, the negative electrode active material layer further includes a binder, which can be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0141] Optionally, in one embodiment, the negative electrode film layer further includes a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0142] Optionally, the negative electrode membrane layer further contains other auxiliary agents, such as a thickener (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0143] In some embodiments, a negative electrode plate can be manufactured by the following method. The components for manufacturing the above-mentioned negative electrode plate are each formed into a negative electrode slurry. For example, the negative electrode active material, conductive agent, binder, and optional other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a negative electrode slurry. The negative electrode slurry is then applied to a negative electrode current collector, and after processes such as baking and cold pressing, a negative electrode plate can be obtained.

[0144] [Separator] Optionally, in one embodiment, the lithium secondary battery further includes a separator. In this application, the type of separator is not particularly limited, and for example, any separator with a known porous structure having good chemical stability and mechanical stability can be selected.

[0145] Optionally, in one embodiment, the separator material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, and are not particularly limited.

[0146] Alternatively, in one embodiment, the positive electrode plate, the negative electrode plate, and the separator can be manufactured into an electrode assembly by a winding process or a stacking process.

[0147] Optionally, in one embodiment, the lithium secondary battery includes an exterior case, which can be used to package the electrode assembly and the electrolyte.

[0148] Alternatively, in one embodiment, the exterior of the lithium secondary battery may be a hard case, such as a hard plastic case, an aluminum case, or a steel case. Alternatively, the exterior of the lithium secondary battery may be a soft pack, such as a bag-type soft pack. The soft pack may be made of plastic, such as polypropylene, polybutylene terephthalate, or polybutylene succinate.

[0149] In the present application, the shape of the lithium secondary battery is not particularly limited, and may be cylindrical, rectangular, or any other shape. For example, Fig. 1 shows an example of a lithium secondary battery 10 having a rectangular structure.

[0150] In some embodiments, referring to FIG. 2 , the exterior body may include a case 22 and a cover plate 21. The case 22 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a storage chamber. The case 22 has an opening communicating with the storage chamber, and the cover plate 21 may cover the opening to seal the storage chamber. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 23 by a winding process or a stacking process. The electrode assembly 23 is packaged in the storage chamber. The electrode assembly 23 is immersed in an electrolyte. The number of electrode assemblies 23 included in the lithium secondary battery 10 may be one or more, and can be selected by those skilled in the art according to specific actual requirements.

[0151] In some embodiments, the lithium secondary batteries 10 can be assembled into a battery module, and the number of lithium secondary batteries 10 included in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0152] Fig. 3 shows an example of a battery module 300. Referring to Fig. 3, in the battery module 300, a plurality of lithium secondary batteries 10 may be arranged in order along the longitudinal direction of the battery module 300. Of course, they may be arranged in any other form. Furthermore, the plurality of lithium secondary batteries 10 may be fixed by a fastening member.

[0153] Optionally, in one embodiment, the battery module 300 may further include a housing having an accommodating space, and the plurality of lithium secondary batteries 10 are accommodated in the accommodating space.

[0154] Optionally, in one embodiment, the battery module 300 can be further assembled into a battery pack, and the number of battery modules 300 included in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0155] 4 and 5 show an example of a battery pack 400. Referring to FIGS. 4 and 5, the battery pack 400 may include a battery box and a plurality of battery modules 300 provided in the battery box. The battery box may include an upper box 401 and a lower box 402, and the upper box 401 may cover the lower box 402 to form an enclosed space for accommodating the battery modules 300. The plurality of battery modules 300 may be arranged in the battery box according to any method.

[0156] The lithium secondary battery 10 described herein may also be referred to as a lithium battery cell. Alternatively, in one embodiment, multiple lithium battery cells may be first integrated into a battery module, and then the battery module may be mounted in a battery box to form a battery pack. Another manufacturing and processing technique may involve directly mounting multiple lithium battery cells in a battery box to form a battery pack, eliminating the intermediate stage of a battery module and reducing the mass and increasing the energy density of the battery pack.

[0157] FIG. 6 is a schematic diagram of an electrical device 600 provided by the present application.

[0158] It should be understood that the electric device 600 includes at least one of the lithium secondary battery 10, the battery module 300, or the battery pack 400 provided by the present application. The lithium secondary battery 10, the battery module 300, or the battery pack 400 may be used as a power source for the electric device 600, or may be used as an energy storage unit for the electric device 600. The electric device 600 may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., rechargeable battery electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric cars, ships and satellites, energy storage systems, etc.

[0159] The electric device 600 can be selected from the lithium secondary battery 10, the battery module 300, or the battery pack 400 according to the needs of its use.

[0160] 6, an example of an electric device 600 may be a secondary battery electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the lithium secondary battery 10 of the electric device 600, a battery pack 400 or a battery module 300 may be employed.

[0161] As another example, the electrical device 600 may be a mobile phone, a tablet, a laptop, etc. Such devices usually require light weight and thinness, and may employ a lithium secondary battery 10 as a power source.

[0162] Examples of the present application are described below. The examples described below are illustrative and are intended merely to interpret the present application and should not be understood as limiting the present application. If specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in the field or according to the product specifications. If the manufacturers of the reagents or equipment used are not specified, they are all commercially available ordinary products. [Example]

[0163] Example 1 (1) Manufacturing of positive electrode plates Lithium iron phosphate with a Dv50 of 10 μm was selected as the positive electrode active material. The positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were dissolved in N-methylpyrrolidone (NMP) as a solvent in a mass ratio of 90:5:5. The mixture was thoroughly stirred to obtain a slurry. The slurry was then uniformly applied to an aluminum foil positive electrode current collector, followed by baking, cold pressing, and cutting to obtain a positive electrode plate. The lithium ion diffusion coefficient Ds of the positive electrode active material layer in the positive electrode plate was 3.4 × 10 -12 cm 2 / s, and the powder compression density of the positive electrode plate is 2.5 g / cm 3 It was.

[0164] (2) Manufacturing of negative electrodes Natural graphite was selected as the negative electrode active material. The negative electrode active material, acetylene black as a conductive agent, styrene butadiene rubber (SBR) as a binder, and sodium carboxymethyl cellulose (CMC) as a thickener were dissolved in deionized water in a mass ratio of 90:4:4:2 and mixed uniformly to obtain a negative electrode slurry. The slurry was then uniformly applied to a copper foil negative electrode current collector, followed by baking, cold pressing, and cutting to obtain negative electrode plate 1. The specific surface area of ​​the negative electrode active material in negative electrode plate 1 was 0.8 m. 2 / g.

[0165] (3) Electrolyte production In an argon atmosphere glove box (HO<0.1 ppm, O<0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 3:7, and the compound represented by formula (I-II) was added to prepare a solvent. The amount of the compound represented by formula (I-II) added was adjusted to a mass fraction W1 of 60%. The mixture was then uniformly mixed. The solute lithium hexafluorophosphate (LiPF6) was then dissolved in the solvent, and the mass fraction of the solute in the electrolyte was adjusted to 12.5%. The mixture was then stirred uniformly to obtain an electrolyte solution.

[0166] (4) Assembly of lithium secondary batteries A positive electrode plate, a separator, and a negative electrode plate were stacked in this order, and a separator was interposed between the positive electrode plate and the negative electrode plate so as to isolate the positive electrode plate and the negative electrode plate. The stacked members were then wound up to obtain an electrode assembly. The electrode assembly was placed in a case, dried, and then an electrolyte solution was injected. After undergoing processes such as chemical formation and standing, the lithium secondary battery of Example 1 was obtained.

[0167] Example 2 Compared with the lithium secondary battery of Example 1, in Example 2, lithium iron phosphate with a Dv50 of 10 μm was selected as the positive electrode active material, and the lithium ion diffusion coefficient Ds of the positive electrode active material layer in the positive electrode plate was 2.7 × 10-9 cm 2 / s, and the mass fraction W1 of the compound represented by formula (I-II) in the solvent was 70%.

[0168] Example 3 Compared with the lithium secondary battery of Example 1, in Example 3, lithium iron phosphate with a Dv50 of 10 μm was selected as the positive electrode active material, and the lithium ion diffusion coefficient Ds of the positive electrode active material layer in the positive electrode plate was 2.7 × 10 -9 cm 2 / s.

[0169] Example 4 Compared with Example 1, the solvent of Example 4 contained the compound represented by formula (IV), and the mass fraction W1 of the compound represented by formula (IV) in the solvent was 60%.

[0170] Example 5 Compared with Example 1, the solvent of Example 5 contained the compound represented by formula (I-VIII), and the mass fraction W1 of the compound represented by formula (I-VIII) in the solvent was 60%.

[0171] Example 6 Compared with Example 1, the electrolyte solution of Example 6 contained a first additive, which was a compound represented by formula (II-XXXII), and the mass fraction W2 of the compound represented by formula (II-XXXII) in the electrolyte solution was 1.0%.

[0172] Example 7 Compared with Example 1, the first additive in Example 7 was a compound represented by formula (II-XVII), and the mass fraction W2 of the compound represented by formula (II-XVII) in the electrolyte was 1.0%.

[0173] Example 8 Compared with Example 6, the first additive in Example 8 was a compound represented by formula (II-XXXII), and the mass fraction W2 of the compound represented by formula (II-XXXII) in the electrolyte was 1.5%.

[0174] Example 9 Compared with Example 1, the electrolyte of Example 9 contained a second additive, which was lithium difluorooxalatoborate LiDFOB, and the mass fraction W3 of LiDFOB in the electrolyte was 0.05%.

[0175] Example 10 Compared with Example 1, the second additive in Example 10 was lithium difluorodioxalatophosphate LiBODFP, and the mass fraction W3 of LiBODFP in the electrolyte was 1.0%.

[0176] Example 11 Compared with Example 2, the second additive in Example 11 was LiDFOB, the mass fraction W1 of the compound represented by formula (I-II) in the solvent was 70%, and the mass fraction W3 of LiDFOB in the electrolyte was 1.0%.

[0177] Example 12 Compared with Example 1, the first additive in Example 12 was the compound represented by formula (I-II), the second additive was LiDFOB, the mass fraction W2 of the compound represented by formula (I-II) in the electrolyte was 0.5%, and the mass fraction W3 of LiDFOB in the electrolyte was 0.5%.

[0178] Example 13 In Example 13, lithium iron phosphate with a Dv50 of 10 μm was used as the first positive electrode active material, and lithium iron phosphate with a Dv50 of 2 μm was used as the second positive electrode active material. The first positive electrode active material, the second positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were dissolved in N-methylpyrrolidone (NMP) as a solvent in a mass ratio of 63:27:5:5, thoroughly stirred to obtain a uniform mixture, and then a slurry was obtained. The slurry was uniformly applied to an aluminum foil positive electrode current collector, and further baked, cold-pressed, and cut to obtain a positive electrode plate. The mass fraction W4 of the second positive electrode active material in the positive electrode active material layer was 30%, and the powder compressed density of the positive electrode plate was 2.6 g / cm. 3 It was.

[0179] Example 14 Compared with Example 13, the mass fraction W4 of the second positive electrode active material in the positive electrode active material layer in Example 14 was 10%, and the powder compressed density of the positive electrode plate was 2.55 g / cm 3 It was.

[0180] Example 15 Compared with Example 1, Example 15 has a specific surface area of ​​1.5 m 2 / g of artificial graphite was selected as the negative electrode active material.

[0181] Example 16 Compared with Example 1, the solvent in Example 16 simultaneously contained the compound represented by formula (I-II) and the compound represented by formula (II). The mass ratio of the compound represented by formula (I-II) to the compound represented by formula (II) was 30:30.

[0182] Comparative Example 1 Compared with Example 1, in Comparative Example 1, dimethyl carbonate (DMC) was selected as the solvent.

[0183] Comparative Example 2 Compared with Example 1, lithium iron phosphate was selected as the positive electrode active material, and the lithium ion diffusion coefficient Ds of the positive electrode active material layer was 7.3 × 10 -20 cm 2 / s, and the mass fraction W1 of the compound represented by formula (I-II) in the solvent was 60%.

[0184] Details of the product parameters of the examples and comparative examples are shown in Table 1.

[0185] [Table 1]

[0186] In Table 1, positive electrode Ds is the lithium ion diffusion coefficient Ds of the positive electrode active material layer of the positive electrode plate, positive electrode powder compressed density is the powder compressed density of the positive electrode plate, negative electrode BET is the BET of the negative electrode active material, compound is a compound contained in the solvent, W1 is the mass fraction of the compound in the solvent, W2 is the mass fraction of the first additive in the electrolyte, and W3 is the mass fraction of the second additive in the electrolyte.

[0187] Since the difference in the lithium ion diffusion coefficient Ds is usually directly reflected in the order of magnitude, it should be understood that the lithium ion diffusion coefficient Ds of the positive electrode active material layer in the above table indicates the order of magnitude of the lithium ion diffusion coefficient. For example, Ds in Example 1 is specifically 3.4 × 10 -12 and Table 1 shows 10 -12 Only the following is shown.

[0188] The details of the results of the battery performance tests for Examples 1 to 16 and Comparative Examples 1 and 2 are shown in Table 2.

[0189] [Table 2]

[0190] As can be seen from a comparison of Examples 1, 4, 5, and 16 with Comparative Example 1, the introduction of the compounds represented by formula (I-II), formula (IV), formula (I-VIII), and formula (II) into the solvent solves the problem of a mismatch between the lithium ion diffusion capabilities of the positive electrode active material layer and the electrolyte in the lithium secondary battery. The discharge capacity, high-speed charging capability, and cycle life of the lithium secondary batteries in Examples 1, 4, 5, and 16 are all superior to those of Comparative Example 1, in which the solvent does not contain the compound represented by formula (I). Furthermore, the lithium secondary batteries in Examples 1, 4, 5, and 16 also have low volume expansion coefficients and significantly improved safety performance.

[0191] As can be seen from the comparison between Example 1 and Comparative Example 2, when the compound represented by formula (I) was introduced into the solvent, in Example 1, the product W1 × Ds of the mass fraction W1 of the compound in the solvent and the lithium ion diffusion coefficient Ds of the positive electrode active material layer was 6 × 10 -11 cm 2 / s, which is 2 × 10 -18 cm 2 / s~8×10 -6 cm 2 / s interval, and 3 × 10 -14 cm 2 / s~7×10 -10 cm 2 / s. In Comparative Example 2, W1 × Ds is 9 × 10 -19 cm 2 / s, which exceeds the above range, and the discharge capacity, high-speed charge capability, and cycle life of Comparative Example 2 are all inferior to those of Example 1. As shown by this, controlling Ds×W1 within an appropriate range can alleviate the problem of mismatch between the lithium ion diffusion capabilities of the positive electrode active material layer and the electrolyte in the lithium secondary battery, thereby contributing to improvements in the discharge capacity, high-speed charge capability, cycle life, and safety performance of the lithium secondary battery.

[0192] As can be seen from a comparison between Example 3 and Example 2, when Ds was increased, W1 was also increased in Example 2, but W1 was not increased in Example 3. The performance of the lithium secondary battery of Example 3 was slightly inferior to that of Example 2. Therefore, controlling Ds and W1 so that there is a positive correlation helps to improve the discharge capacity, high-speed charging capability, cycle life, and safety performance of the lithium secondary battery.

[0193] As can be seen from a comparison of Examples 6 and 7 with Example 1, in Examples 6 and 7, the compounds represented by formula (II-XXXII) and formula (II-XVII) were respectively introduced as first additives into the electrolyte solution, and the lithium secondary batteries in Examples 6 and 7 had significantly better cycle performance and lower volume expansion rates than the lithium secondary battery of Example 1. As shown by this, the introduction of the first additive into the electrolyte solution can increase the lithium ion conductivity of the electrolyte solution while effectively reducing side reactions on the surface of the negative electrode active material layer of the electrolyte solution, thereby improving the cycle performance and safety of the lithium secondary battery.

[0194] As can be seen from a comparison between Example 8 and Example 6, when W1 was increased, W2 was increased in Example 8. The volume expansion rate of the lithium secondary battery in Example 8 was lower than that of the lithium secondary battery in Example 6. This helps to further improve the safety performance of the lithium secondary battery by controlling W2 and W1 so that they have a positive correlation.

[0195] As can be seen from a comparison of Examples 9 and 10 with Example 1, in Examples 9 and 10, LiDFOB and LiBODFP were respectively introduced as second additives into the electrolyte, and the cycle performance of the lithium secondary batteries in Examples 9 and 10 was significantly better than that of the lithium secondary battery in Example 1, and the volume expansion rate was smaller than that of the lithium secondary battery in Example 1. As shown by this, the introduction of a second additive into the electrolyte not only increased the lithium ion conductivity of the electrolyte but also effectively reduced side reactions on the surface of the negative electrode active material layer of the electrolyte, thereby improving the cycle performance and safety of the lithium secondary battery.

[0196] As can be seen from a comparison between Example 11 and Example 9, when W1 was increased, W2 was increased in Example 11. The volume expansion rate of the lithium secondary battery in Example 11 was lower than that of the lithium secondary battery in Example 9. This helps to further improve the safety performance of the lithium secondary battery by controlling W3 and W1 so that they have a positive correlation.

[0197] A comparison of Example 12 with Examples 6 and 9 shows that in Example 12, the first additive and the second additive were simultaneously added to the electrolyte, and the lithium secondary battery in Example 12 exhibited significantly improved cycle performance and significantly reduced volume expansion rate. This shows that the first additive and the second additive have a synergistic effect in the electrolyte, which can further improve the cycle performance and safety of the lithium secondary battery.

[0198] As can be seen from a comparison between Example 13 and Example 1, a second positive electrode active material with a small Dv502 was introduced into the positive electrode active material layer in Example 13, increasing the powder compaction density of the positive electrode plate. In Example 13, the discharge capacity of the lithium secondary battery was improved to a certain extent compared to Example 1. As shown by this, combining positive electrode active materials with different particle sizes helps increase the powder compaction density of the positive electrode active material layer, contributing to improving the discharge capacity of the lithium secondary battery.

[0199] As can be seen from a comparison between Example 14 and Example 13, in Example 14, the mass fraction W4 of the second positive electrode active material having a small Dv502 in the positive electrode active material layer was small, the powder compressed density of the positive electrode plate was small, and the discharge capacity of the lithium secondary battery was also reduced to some extent. As shown by this, controlling the mass fraction W4 of the second positive electrode active material having a small average volume particle size in the positive electrode active material layer can affect the powder compressed density of the positive electrode plate, which in turn affects the energy density of the lithium secondary battery and further affects the discharge capacity of the lithium secondary battery.

[0200] It should be understood that the average volume particle size of a material and its specific surface area are interrelated physical quantities: the larger the average volume particle size of a material, the smaller its BET will typically be, while the smaller the average volume particle size of a material, the larger its BET will typically be.

[0201] As can be seen from a comparison between Example 15 and Example 1, Example 15 uses a negative electrode active material with a smaller Dv503 and a larger BET, and the discharge capacity, fast charge performance, and cycle performance of the lithium secondary battery in Example 1 are all superior to those of the lithium secondary battery in Example 15, and the volume expansion rate of the lithium secondary battery in Example 1 is smaller. As can be seen from this, the average volume particle size or specific surface area of ​​the negative electrode active material affects the performance of the lithium secondary battery, and a negative electrode active material with a larger Dv503 and a smaller BET has a smaller contact area with the electrolyte, reducing the probability of side reactions of the electrolyte on the surface of the negative electrode active material layer and contributing to improving the performance of the lithium secondary battery.

[0202] Next, a brief description will be given of the test methods for the physical and performance parameters mentioned in the examples of this application.

[0203] 1. Lithium ion diffusion coefficient test method The lithium ion diffusion coefficient can be obtained by testing using methods commonly used in the art, such as cyclic voltammetry (CV method), electrochemical impedance spectroscopy (EIS method), potentiostatic intermittent titration (PITT method), and galvanostatic intermittent titration (GITT method), and by calculation according to Fick's first law and Fick's second law.

[0204] Taking electrochemical impedance spectroscopy as an example, the steps for testing the lithium ion diffusion coefficient of the positive electrode active material layer are as follows: The positive electrode active material prepared in the examples and comparative examples of this application, the conductive agent acetylene black, and the binder polyvinylidene fluoride were uniformly mixed in a mass ratio of 85:10:5, and N-methylpyrrolidone was added to prepare a slurry. This slurry was then applied to an aluminum sheet and vacuum-dried at 60°C for 5 hours to prepare a positive electrode plate sample. Each sample was used as the positive electrode, a metallic lithium sheet as the negative electrode, and a Celgard 2400 polypropylene microporous membrane as the separator. A solution of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC) was mixed in a 1:1 volume ratio to form the electrolyte. This was then assembled into a CR2032 button cell sample in a high-purity argon atmosphere. The battery was subjected to AC impedance (EIS) testing using a Shanghai Chenhua CHI660b electrochemical workstation at an amplitude of 5mV and a frequency range of 10mHz to 100KHz to obtain the electrochemical impedance spectrum (Nyquist spectrum) of the battery sample. By performing curve fitting on the electrochemical impedance spectrum, the Warburg constant of the battery sample can be calculated according to Fick's second law and the Nernst equation, and the lithium ion diffusion coefficient of the positive electrode active material layer can be calculated using the following equation in conjunction with the Bulter-Volmer equation:

number

[0205] 2. Test method for average (volume) particle size In this application, the average volume particle size Dv50 of the active material has the meaning known in the art and can be measured by instruments and methods known in the art, for example, GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, using a laser particle size analyzer (e.g., Master Size 3000).

[0206] 3. BET Testing Method For the test method, refer to specification GB / T19587-2004 "Measurement of the specific surface area of ​​solid materials by the gas adsorption BET method."

[0207] A test sample weighing 8g to 15g was placed in a sample tube, and the initial mass of the test sample was recorded. The weighed test sample was then placed in the NOVA2000e apparatus. Degassing was then initiated, and the test sample was heated to 200°C and maintained at that temperature for 2 hours. The mass of the test sample after degassing was then recorded. The degassed test sample was then placed back into the apparatus, and liquid nitrogen was poured in to perform the BET test. The nitrogen gas pressure was set to 0.08MPa to 0.12MPa, and the heating temperature was set to 40°C to 350°C. After the test was completed, the specific surface area was read from the test results.

[0208] 4. Powder compression density test method Area is 1540.25mm 2 Taking a circular positive electrode plate as a basic unit, the total weight of the positive electrode plate with positive active material applied to both sides is A (g), the weight of the positive electrode current collector is B (g), the thickness of the positive electrode current collector is T (mm), and the thickness of the aluminum foil is U (mm), the powder compacted density (PD) of the positive electrode plate can be calculated by the following formula.

number

[0209] 5. Battery capacity test At 25°C, the lithium secondary battery was charged to 3.65V at a constant current of 0.5C, then charged at a constant voltage of 3.65V until the current became smaller than 0.05C, and then discharged to 2.5V at a constant current of 0.5C to obtain the discharge capacity at 0.5C.

[0210] 6. Fast charging time test At 25°C, charge at 0.33C to 10% state of charge (SOC), charge for s minutes according to the specified fast charging steps, charge to 80% SOC, let stand for 30 minutes, then discharge at 1C, let stand for another 30 minutes, and after 20 cycles, fully charge the lithium secondary battery. Disassemble the battery and observe whether lithium deposition occurs on the negative electrode. If no lithium deposition occurs, it indicates that the lithium secondary battery has fast charging capability of s minutes.

[0211] 7. Cycle performance test At 60°C, the lithium secondary battery was charged to 3.65V at a constant current of 0.5C, then charged to a constant voltage of 3.65V until the current became less than 0.05C, and then discharged to 2.5V at a constant current of 0.5C, which constituted one charge-discharge cycle. By repeating this charge-discharge cycle, the number of cycles until the lithium secondary battery was reduced to 80% was calculated.

[0212] 8.Volume expansion rate test At 25°C, each fabricated lithium secondary battery was first charged to 3.65V at a constant current of 0.33C, then further charged at a constant voltage of 3.65V until the current reached 0.05C. The lithium secondary battery was then discharged to 2.5V at a constant current of 0.33C. This discharge capacity is the discharge capacity before high-temperature storage. The lithium secondary battery was then charged to 3.65V at a constant current of 0.33C, and then charged at a constant voltage of 3.65V until the current reached 0.05C, resulting in a full charge. The battery volume was measured using the drainage method. The lithium secondary batteries were then stored at 60°C for 60 days. After storage, the lithium secondary batteries were placed in a 25°C environment and the battery volume was measured using the drainage method. The battery volume expansion rate = (volume after storage / volume before storage - 1) x 100%.

[0213] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and all embodiments that have substantially the same configuration as the technical idea and exhibit the same functions and effects within the scope of the technical solution of the present application are encompassed within the technical scope of the present application. Furthermore, various modifications that can be conceived by a person skilled in the art without departing from the spirit of the present application, and other forms configured by combining some of the components of the embodiments, are also encompassed within the scope of the present application.

Claims

1. A lithium secondary battery including a positive electrode plate and an electrolyte, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on at least one side of the positive electrode current collector, the positive electrode active material layer having a lithium ion diffusion coefficient Ds; The electrolyte solution includes a solvent, and the solvent includes at least one compound of the following formula (I): a mass fraction of the compound of formula (I) in the solvent is W1; and the mass fraction W1 of the compound of formula (I) and the lithium ion diffusion coefficient Ds of the positive electrode active material layer are 2×10 －１８ cm ２ / s≦W1×Ds≦8×10 －６ cm ２ / s, optionally 3 x 10 －１４ cm ２ / s≦W1×Ds≦7×10 －１０ cm ２ / s is satisfied, 【Chemistry 1】 R １ and R ２ and each independently contains at least one of an alkyl group having 1 to 3 carbon atoms and a haloalkyl group having 1 to 3 carbon atoms.

2. R １ and R ２ and each independently include at least one of a methyl group, an ethyl group, a propyl group, a fluoromethyl group, a fluoroethyl group, and a fluoropropyl group.

3. 10 －１６ cm ２ / s≦Ds≦10 －５ cm ２ / s, optionally 10 －１４ cm ２ / s≦Ds≦10 －９ cm ２ 3. The lithium secondary battery according to claim 1, wherein the ionic current is 0.1 V / s.

4. 4. The lithium secondary battery according to claim 1, wherein 20%≦W1≦80%, optionally 30%≦W1≦70%.

5. The compound of formula (I) is 【Chemistry 2】 and Optionally, the compound of formula (I) includes at least one of a compound of formula (II), a compound of formula (I-II), a compound of formula (IV), and a compound of formula (I-VIII). The lithium secondary battery according to any one of claims 1 to 4.

6. the electrolyte solution includes a first additive; The first additive comprises at least one compound of formula (II): 【Transformation 3】 R ３ includes at least one of an alkylene group substituted or unsubstituted by Ra and having 2 to 10 carbon atoms, a heteroalkylene group substituted or unsubstituted by Ra and having 2 to 10 carbon atoms, an arylene group substituted or unsubstituted by Ra and having 6 to 18 carbon atoms, a heteroarylene group substituted or unsubstituted by Ra and having 6 to 18 carbon atoms, a divalent alicyclic group substituted or unsubstituted by Ra and having 3 to 18 carbon atoms and having 3 to 18 carbon atoms, 6. The lithium secondary battery according to claim 1, wherein Ra includes at least one of a halogen atom, a cyano group, an isocyanate group, a hydroxy group, a carboxy group, a sulfonic acid group, an ester group, an alkyl group having 2 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, and an oxaalkyl group having 2 to 10 carbon atoms.

7. The mass fraction of the first additive in the electrolytic solution is W2; The W2, the W1, and the Ds are 2×10 －２２ cm ２ / s≦W2×W1×Ds≦1.6×10 －６ cm ２ / s, optionally 2 x 10 －２１ cm ２ / s≦W2×W1×Ds≦8×10 －７ cm ２ / s, optionally 4 x 10 －２１ cm ２ / s≦W2×W1×Ds≦4×10 －７ cm ２ The lithium secondary battery according to claim 6, wherein the above formula (1) satisfies the above formula (1).

8. The lithium secondary battery according to claim 7 , wherein W2 satisfies 0.01%≦W2≦20%, optionally 0.1%≦W2≦10%, optionally 0.2%≦W2≦5%.

9. The first additive is 【Chemistry 4】 【Transformation 5】 9. The lithium secondary battery according to claim 6, comprising at least one of the compounds:

10. The electrolyte solution includes a second additive, and the second additive is 【Transformation 6】 and at least one compound of formula (III): 【Transformation 7】 M ａ＋ contains at least one of lithium ions, sodium ions, potassium ions, rubidium ions, cesium ions, magnesium ions, calcium ions, barium ions, aluminum ions, iron ions, copper ions, nickel ions, and organic cations; a, b, and c are all natural numbers, t represents an integer of 0 to 3; w represents an integer of 1 to 6; X contains at least one halogen atom, and n represents an integer of 0 to 4; Y contains at least one of a boron atom and a phosphorus atom; R ４ includes a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted haloalkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, and a substituted or unsubstituted haloarylene group having 6 to 20 carbon atoms; q represents an integer of 0 to 1; 10. The lithium secondary battery according to claim 1, wherein m represents an integer of 1 to 3.

11. The mass fraction of the second additive in the electrolytic solution is W3; The W3, W1, and Ds are 2×10 －２２ cm ２ / s≦W3×W1×Ds≦1.6×10 －６ cm ２ / s, optionally 2 x 10 －２１ cm ２ / s≦W3×W1×Ds≦8×10 －７ cm ２ / s, optionally 4 x 10 －２１ cm ２ / s≦W3×W1×Ds≦4×10 －７ cm ２ The lithium secondary battery according to claim 10, wherein the above formula (I) satisfies the above formula (I).

12. 12. The lithium secondary battery according to claim 11, wherein 0.01%≦W3≦20%, optionally 0.1%≦W3≦10%, optionally 0.2%≦W3≦5%. 【Request Item 13】 【Chemistry 8】 In this case, M ａ＋ Li ＋ , Na ＋ , K. ＋ , Rb ＋ , Cs ＋ , Mg ２＋ , Ca ２＋ , Ba ２＋ , Al ３＋ , Fe ２＋ , Cu ２＋ , Fe ３＋ , Ni ２＋ , Ni ３＋ The lithium secondary battery according to any one of claims 10 to 12, comprising at least one of:

14. the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, The average particle size Dv50 of the first positive electrode active material １ 8 μm≦Dv50 １ ≦50 μm, Average particle size Dv50 of the second positive electrode active material ２ 0.02 μm≦Dv50 ２ The lithium secondary battery according to any one of claims 1 to 13, wherein the thickness satisfies ≦8 μm.

15. The lithium secondary battery according to claim 14 , wherein a mass fraction W4 of the second positive electrode active material in the positive electrode active material layer satisfies 0%≦W4≦60%, and optionally 20%≦W4≦40%.

16. The lithium secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer contains a negative electrode active material, Average particle size Dv50 of the negative electrode active material ３ 6 μm≦Dv50 ３ , optionally 15 μm≦Dv50 ３ The lithium secondary battery according to any one of claims 1 to 15, wherein the thickness satisfies ≦20 μm.

17. The specific surface area of ​​the negative electrode active material is 0.5 m ２ / g≦BET≦2.0m ２ / g, optionally 0.8m ２ / g≦BET≦1.5m ２ The lithium secondary battery according to claim 16, wherein the lithium secondary battery satisfies the above formula (1).

18. An electrical device comprising the lithium secondary battery according to any one of claims 1 to 17.

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