Lithium secondary battery and power consumption device

Abstract

The present application provides a lithium secondary battery and a power consuming device, the lithium secondary battery comprising: a negative electrode plate including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the porosity of the negative electrode active material layer being P; and an electrolyte solution 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 electrolyte solution being W1, W1 and P satisfying 0.65≦W1 / P≦4.4, and optionally 1.1≦W1 / P≦3.5: JPEG2025517654000028.jpg26170, where R 1 and R 2 each independently contains at least one of an alkyl group having 1 to 3 carbon atoms and a halogenated alkyl group having 1 to 3 carbon atoms. This lithium secondary battery can improve the transmission rate of lithium ions in the negative electrode active material layer when the porosity of the negative electrode plate is relatively low, and can improve the energy density of the lithium secondary battery while simultaneously improving the cycle performance and safety performance of the lithium secondary battery.

Description

[Technical field]

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

[0002] In recent years, lithium secondary batteries have been widely used in various electronic products and electric vehicles due to their relatively high power density and volumetric capacity. However, with the tremendous development and wide range of applications of lithium secondary batteries, higher requirements are being placed on their energy density, cycle life, etc.

[0003] Improving the powder compression density of the negative electrode plate is a commonly used method to increase the energy density of lithium secondary batteries. However, with the increase in powder compression density, the porosity of the negative electrode active material layer decreases, which affects the transmission of lithium ions in the negative electrode active material layer, leading to problems such as lithium precipitation and gas generation in the negative electrode, which seriously affects the cycle performance and safety of lithium secondary batteries. Therefore, how to improve the energy density of lithium secondary batteries and at the same time improve the cycle performance and safety of lithium secondary batteries is a technical problem that needs to be solved as soon as possible. Summary of the Invention [Problem to be solved by the invention]

[0004] The present application has been made in view of the above technical problems, and aims to provide a lithium secondary battery and a power consuming device that can improve the energy density of the lithium secondary battery and at the same time improve the cycle performance and safety performance of the lithium secondary battery by improving the transmission rate of lithium ions in the negative electrode active material layer when the porosity of the negative electrode plate is relatively low. [Means for solving the problem]

[0005] According to a first aspect, the present application provides a lithium secondary battery, the lithium secondary battery comprising: a negative electrode plate including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the negative electrode active material layer having a porosity of P; and an electrolyte solution 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, the mass fraction W1 of the compound of formula (I) and the porosity P of the negative electrode active material layer satisfying 0.65≦W1 / P≦4.4, and optionally 1.1≦W1 / P≦3.5: Here, R 1 and R 2 each independently contains at least one of an alkyl group having 1 to 3 carbon atoms and a halogenated alkyl group having 1 to 3 carbon atoms.

[0006] [ka]

[0007] In the embodiment of the present application, the compound represented by formula (I), as a solvent or part of the solvent, can reduce the viscosity of the electrolyte and improve the conductivity of the electrolyte. By controlling the mass fraction W1 of the compound represented by formula (I) in the electrolyte within a suitable range according to the porosity P of the negative electrode active material layer, the infiltration ability of the electrolyte can be effectively improved, and the negative electrode active material layer with a relatively large compression density and a relatively low porosity can also be quickly infiltrated by the electrolyte, thereby improving the transmission efficiency of lithium ions in the negative electrode active material layer, improving the energy density of the lithium secondary battery, and at the same time improving the cycle performance and safety performance of the lithium secondary battery.

[0008] In some embodiments, R 1 and R 2 each independently contains at least one of a methyl group, an ethyl group, a propyl group, a fluoromethyl group, a fluoroethyl group, and a fluoropropyl group.

[0009] In some embodiments, the porosity P of the negative electrode active material layer satisfies 18%≦P≦30.5%, and optionally 20%≦P≦27%.

[0010] In the examples of the present application, by controlling the porosity of the negative electrode active material layer within an appropriate range, the powder compressed density of the negative electrode plate corresponding to this porosity becomes relatively large, and the negative electrode plate per unit area or volume can support more negative electrode active material, thereby achieving a high energy density of the lithium secondary battery.

[0011] In some embodiments, the mass fraction W1 of the compound of formula (I) satisfies 20%≦W1≦80%, and optionally 30%≦W1≦70%.

[0012] In some embodiments, the compound of formula (I) comprises at least one of the following compounds: 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).

[0013] [ka]

[0014] In some embodiments, the electrolyte comprises a first additive, the first additive comprising at least one of a compound of formula (II) and a compound of formula (III): Here, R 3 , R 4 each independently includes a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a halogenated alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms; R 5 , R 6 , R 7 , R 8each independently includes a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a halogenated alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms; and R 5 , R 6 , R 7 , R 8 is different, it is a hydrogen atom.

[0015] [ka]

[0016] In the embodiment of the present application, a first additive is introduced into the electrolyte to contribute to the formation of a protective organic-inorganic composite SEI (Solid Electrolyte Interface, SEI) film on the surface of the negative electrode active material layer of a lithium secondary battery, thereby blocking direct contact between the electrolyte and the negative electrode active material, improving the stability of the solid-liquid interface between the negative electrode active material layer and the electrolyte, and improving the problem of the electrolyte generating gas on the surface of the negative electrode active material layer in the lithium secondary battery, thereby further improving the cycle performance and safety performance of the lithium secondary battery. In addition, the compounds represented by formula (II) and formula (III) have good film formation effect on the surface of the negative electrode active material layer, and can uniformly and quickly form an SEI film during the chemical formation process of the lithium secondary battery to protect the negative electrode active material layer and prevent direct contact between the negative electrode active material layer and the electrolyte.

[0017] In some embodiments, R 3 , R 4 each independently includes a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms; R 5 , R 6 , R 7 , R 8each independently comprises a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms; and R 5 , R 6 , R 7 , R 8 is different, it is a hydrogen atom.

[0018] In some embodiments, the mass fraction of the first additive in the electrolyte is W2, and W2, W1, and P satisfy 0.00006≦W2×W1 / P≦0.88, optionally 0.0006≦W2×W1 / P≦0.44, and optionally 0.0013≦W2×W1 / P≦0.22.

[0019] In some embodiments, 0.01%≦W2≦20%, optionally 0.1%≦W2≦10%, and optionally 0.2%≦W2≦5%.

[0020] In some embodiments, the first additive comprises at least one of the following compounds:

[0021] [ka]

[0022] In some embodiments, the second additive comprises at least one of compounds of Formula 1, Formula 2, Formula 3, and Formula (IV).

[0023] [ka]

[0024] [ka]

[0025] Here, 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 each represent a natural number; 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 and a phosphorus atom; R 9 includes a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted halogenated alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, and a substituted or unsubstituted halogenated arylene group having 6 to 20 carbon atoms, q represents an integer of 0 to 1, and m represents an integer of 1 to 3.

[0026] In the embodiment of the present application, the second additive is introduced into the electrolyte to form an SEI film with a relatively small impedance on the surface of the negative electrode active material layer, further improving the stability of the solid-liquid interface between the negative electrode active material layer and the electrolyte, and improving the problem of the electrolyte generating gas on the surface of the negative electrode active material layer, thereby further improving the cycle performance and safety performance of the lithium secondary battery. In addition, the second additive has a relatively small effect on the impedance of the lithium secondary battery after forming the SEI film on the surface of the negative electrode active material layer, and prevents the lithium secondary battery from generating excessive heat during charging and discharging due to an excessively large impedance, thereby helping to improve the charging and discharging performance and safety performance of the lithium secondary battery.

[0027] In some embodiments, the mass fraction of the second additive in the electrolyte is W3, and W3, W1, and P satisfy 0.00006≦W3×W1 / P≦0.88, optionally 0.0006≦W3×W1 / P≦0.44, and optionally 0.0013≦W3×W1 / P≦0.22.

[0028] In some embodiments, 0.01% ≦ W3 ≦ 20%, optionally 0.1% ≦ W3 ≦ 10%, and optionally 0.2% ≦ W3 ≦ 5%.

[0029] In some embodiments, in Chemical Formula 4, M a+ is + Li + Na + K + Rb + Cs 2+ Mg 2+ Ca 2+ Ba 3+ Al 2+ Fe 2+ Cu 3+ Fe 2+ Ni 3+ includes at least one of

[0030]

Chemical Formula

[0031] In some embodiments, the negative electrode active material layer contains a negative electrode active material, and the average particle diameter Dv50 0 of the negative electrode active material satisfies 6μm ≦ Dv50 0 and optionally 15μm ≦ Dv50 0 ≦ 20μm

[0032] In some embodiments, the specific surface area of the negative electrode active material satisfies 0.5m 2 / g ≦ BET ≦ 2.0m 2 / g, and optionally 0.8m 2 / g ≦ BET ≦ 1.5m 2 / g

[0033] In some embodiments, the lithium secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, and the average particle diameter Dv50 1 of the first positive electrode active material satisfies 8μm ≦ Dv50 1≦50 μm, and the average particle size Dv50 of the second positive electrode active material is 2 0.02μm≦Dv50 2 Meets ≦8μm.

[0034] 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%.

[0035] According to a second aspect, there is provided a power consuming device, the power consuming device comprising a lithium secondary battery according to any one of the embodiments of the first aspect.

[0036] As a result, the lithium secondary battery of the present application achieves high energy density while also exhibiting good cycle performance and safety performance.

[0037] In order to more clearly describe the technical solutions of the embodiments of the present application, the following briefly introduces the drawings that need to be used in the embodiments of the present application, it is obvious that 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 making creative efforts. In the drawings, the drawings are not drawn to actual scale. [Brief description of the drawings]

[0038] [Figure 1] FIG. 1 is a schematic diagram of one lithium secondary battery of the present application. [Diagram 2] FIG. 1 is a schematic structural diagram of a lithium secondary battery according to the present application. [Diagram 3] FIG. 2 is a schematic structural diagram of one battery module of the present application. [Figure 4] FIG. 2 is a schematic diagram of one battery pack of the present application. [Diagram 5] FIG. 2 is a schematic structural diagram of one battery pack of the present application. [Figure 6] 1 is a schematic diagram of one power consuming device of the present application; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Hereinafter, with appropriate reference to the drawings, an embodiment specifically disclosing the lithium secondary battery and power consumption device of the present application will be described in detail. However, unnecessary detailed description may be omitted. For example, detailed description of well-known matters and duplicated description of structures that are actually the same may be omitted. This is to avoid the following description becoming unnecessarily long and to allow those skilled in the art to easily understand. Note that the drawings and the following description are provided to allow those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0040] The "ranges" disclosed in this application are defined in the form of lower and upper limits, and 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 particular range. Such defined ranges may be inclusive or exclusive of the extreme values, and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also envisaged. However, if 1 and 2 are listed as minimum range values, and 3, 4, and 5 are listed as maximum range values, the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all envisaged. In this application, unless otherwise specified, the numerical range "ab" represents a shorthand representation of any combination of real numbers from a to b, where a and b are both real numbers. For example, the numerical range "0-5" represents a list of all real numbers between "0-5" already listed in this specification, and "0-5" is just a shorthand representation of combinations of these numbers. Also, expressing 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.

[0041] In the description of this application, it should be explained that unless otherwise specified, the meaning of "plurality" is two or more, and the orientation or positional relationship indicated by the terms "up", "down", "left", "right", "inside", "outside", etc. is merely for convenience and simplification of the description of this application, and does not indicate or imply that the device or element referred to has a particular orientation and must be configured and operated in a particular orientation, and should not be understood as a limitation on this application. In addition, the terms "first", "second", "third", etc. are used for descriptive purposes only, and should not be understood as indicating or implying relative importance. "Perpendicular" is not strictly perpendicular, but has a margin of error. "Parallel" is not strictly parallel, but has a margin of error.

[0042] Unless otherwise specified, the terms "comprise" and "comprises" referred to in this application may be open ended or closed ended. For example, the terms "comprise" and "comprises" may further include or include other ingredients not listed, or may include or include only the ingredients listed.

[0043] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied in the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) but B is true (or exists); and A and B are both true (or exist).

[0044] Unless otherwise specified, all steps of this application may be performed in order or randomly, and preferably, they are performed in order. For example, the fact that the method includes steps (a) and (b) means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, the fact that the method mentioned above may further include step (c) means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0045] Unless otherwise specified, all embodiments and alternative embodiments of this application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all technical features and alternative technical features of this application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, the following terms have the following meanings. Any term that is not defined has its technically recognized meaning.

[0048] The term "alkyl group" has its general meaning and is a hydrocarbon group formed by the reduction of one hydrogen atom in an alkane molecule. Optionally, the number of carbon atoms is 1-3. For example, the alkyl group includes linear hydrocarbon groups and branched hydrocarbon groups, such as methyl group, ethyl group, n-propyl group, isopropyl group, etc.

[0049] The term "halogenated alkyl group" has its general meaning and is an alkyl group in which one or more hydrogen atoms on one or more carbon atoms in a linear, branched or cyclic skeleton are substituted by halogen atoms. For example, monochloromethyl group, monofluoromethyl group, trifluoromethyl group, monofluoroethyl group, monofluoropropyl group, etc.

[0050] The term "alkoxy group" has its general meaning and is an alkyl group bonded to oxygen. Optionally, the number of carbon atoms is 2-6. For example, it is an ethoxy group or the like.

[0051] The term "alkenyl group" has its general meaning and is a hydrocarbon group having one or more carbon atoms and at least one double-bond unsaturated site. Optionally, the number of carbon atoms is 2-6. By way of example, alkenyl groups include linear alkenyl groups and branched alkenyl groups. For example, they are an ethylene group, a propenyl group, an n-butenyl group, etc. In some other examples, alkenyl groups may further include cyclic alkenyl groups, bicyclic alkenyl groups, etc. For example, it is a cyclohexyl group.

[0052] The term "alkynyl group" has its general meaning and is a hydrocarbon group having one or more carbon-carbon triple bonds. Optionally, the number of carbon atoms is 2-6. For example, it is an ethynyl group.

[0053] The term "halogen atom" has its general meaning and is a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, or an astatine atom.

[0054] The term "alkylene group" has its general meaning and is a divalent hydrocarbon group having one or more carbon atoms. Optionally, the number of carbon atoms is 1-10. By way of example, alkylene groups include divalent linear hydrocarbon groups and divalent branched-chain hydrocarbon groups, such as an ethylene group, a methylethylene group, an n-propylene group, etc.

[0055] The term "substituted alkylene group" has its general meaning and is an alkylene group in which one or more hydrogen atoms on one or more carbon atoms of a linear, branched-chain or cyclic skeleton are substituted by the same or different heteroatoms or groups. The heteroatoms or groups include, but are not limited to, halogen atoms, phenyl groups, etc.

[0056] The term "alkylenyl halide group" has its common meaning and is an alkylene group in which one or more hydrogen atoms on one or more carbon atoms of a linear, branched or cyclic skeleton are substituted with the same or different halogen atoms.

[0057] The term "substituted alkylenyl halide group" has its common meaning and is an alkylenyl halide group in which one or more hydrogen atoms on one or more carbon atoms of a linear, branched or cyclic skeleton are substituted with the same or different heteroatoms or groups.

[0058] The term "arylene group" has its common meaning and is 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.

[0059] The term "substituted arylene group" has its common meaning and is an arylene group in which one or more hydrogen atoms on one or more carbon atoms of a linear, branched or cyclic skeleton are substituted with the same or different heteroatoms or groups.

[0060] The term "arylenyl halide group" has its common meaning and is an arylene group in which one or more hydrogen atoms on one or more carbon atoms of a linear, branched or cyclic skeleton are substituted with the same or different halogen atoms.

[0061] The term "substituted arylenyl halide group" is an arylenyl halide group in which one or more hydrogen atoms on one or more carbon atoms of a linear, branched or cyclic skeleton are substituted with the same or different heteroatoms or groups.

[0062] Next, the examples of this application will be introduced.

[0063] In recent years, secondary batteries have been widely applied in multiple fields such as power tools, electronic products, electric vehicles, and aerospace due to their relatively high energy density and long service life, and have thus achieved remarkable development. Generally, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. During the charge and discharge of the battery, active ions are reciprocally intercalated and deintercalated between the positive electrode plate and the negative electrode plate. Here, the electrolyte serves to conduct active ions between the positive electrode plate and the negative electrode plate. The separator is installed between the positive electrode plate and the negative electrode plate, preventing short-circuiting between the positive and negative electrodes while allowing active ions to pass through, enabling the electrochemical reaction of the secondary battery to proceed normally.

[0064] Taking the lithium secondary ion battery as an example, the lithium secondary battery is a typical secondary battery. Since it performs charge and discharge through a chemical reaction in which lithium ions are intercalated and deintercalated between the positive and negative electrodes, the lithium secondary battery is also called a rocking chair type battery. During the charging of the lithium secondary battery, lithium ions are detached from the positive electrode active material, move to the negative electrode through the conduction of the electrolyte, and are intercalated into the negative electrode active material. On the other hand, during discharge, lithium ions are detached from the negative electrode active material, move to the positive electrode through the conduction of the electrolyte, and are incorporated into the positive electrode active material.

[0065] It should be understood that the "lithium intercalation" and "intercalation" processes described in this application are processes in which lithium ions are intercalated into the positive electrode active material or the negative electrode active material through an electrochemical reaction, and the "deintercalation", "lithium release", and "intercalation and deintercalation" processes described in this application are processes in which lithium ions are deintercalated from the positive electrode active material or the negative electrode active material through an electrochemical reaction.

[0066] As lithium secondary batteries are increasingly widely applied, higher requirements are imposed on the energy density of lithium secondary batteries. By improving the powder compression density of the positive and negative electrode plates, the negative electrode plate per unit area or volume can carry more positive and negative electrode active materials, thereby effectively increasing the energy density of the lithium secondary battery. Taking the negative electrode plate as an example, with the improvement of the powder compression density of the negative electrode plate, the porosity of the negative electrode active material layer decreases. As can be seen from the above, during the charging of a lithium secondary battery, lithium ions detach from the positive electrode active material, move to the negative electrode through electrolyte conduction, and are occluded in the negative electrode active material. If the powder compression density is too high, the electrolyte cannot infiltrate the negative electrode active material layer, making it difficult for lithium ions to transmit inside the negative electrode active material layer, leading to lithium precipitation on the negative electrode plate and problems such as the electrolyte undergoing side reactions to generate gas, threatening the cycle performance and safety performance of the lithium secondary battery.

[0067] In view of this, the embodiments of the present application provide a lithium secondary battery. In this lithium secondary battery, the solvent of the electrolyte contains a linear carboxylic acid ester compound represented by formula (I). The viscosity of the compound represented by formula (I) is relatively low, which can improve the fluidity and infiltration ability of the electrolyte. And in this lithium secondary battery, the mass fraction of the compound represented by formula (I) is adjusted and controlled within an appropriate range according to the porosity of the negative electrode active material layer, so that the negative electrode active material layer with a relatively low porosity can be infiltrated by the electrolyte, and the lithium ion transmission situation inside the negative electrode active material layer with a low porosity is improved. Thereby, a lithium secondary battery with a high energy density is realized, and at the same time, the cycle performance and safety performance of the lithium secondary battery are improved.

[0068] In one embodiment of the present application, a lithium secondary battery is provided. Generally, a lithium secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator. Next, the lithium secondary battery according to the present application and each part in the lithium secondary battery will be introduced.

[0069] In one embodiment of the present application, a lithium secondary battery is provided, and the lithium secondary battery includes a negative electrode plate and an electrolyte.

[0070] Here, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, and the porosity of the negative electrode active material layer is P.

[0071] The electrolyte includes a solvent, the solvent includes at least one of the following compounds of formula (I), and the mass fraction of the compound of formula (I) in the solvent is W1. The mass fraction W1 of the compound shown in formula (I) and the porosity P of the negative electrode active material layer satisfy 0.65 ≦ W1 / P ≦ 4.4, and optionally, 1.1 ≦ W1 / P ≦ 3.5, Here, R 1 and R 2 each independently include at least one of an alkyl group having 1 to 3 carbon atoms and a halogenated alkyl group having 1 to 3 carbon atoms.

[0072]

Chemical formula

[0073] Specifically, W1 / P may be 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.5, 3.6, 3.8, 4.0, 4.2, 4.4, or the numerical value may be within the range obtained by combining any two of the above numerical values.

[0074] In this embodiment, the lithium secondary battery has a negative electrode active material layer with a porosity of P and an electrolytic solution combined with this negative electrode active material layer. The solvent of this electrolytic solution contains the compound shown in formula (I), making the viscosity of the electrolytic solution relatively low and giving it good fluidity. According to the porosity P of the negative electrode active material layer, the mass fraction W1 of this compound in the solvent is adjusted and controlled so that W1 / P is within an appropriate range, enabling the negative electrode active material layer with a porosity of P to be effectively infiltrated by the electrolytic solution. Thereby, the transmission efficiency of lithium ions inside the negative electrode active material layer is improved, the rate performance of the lithium secondary battery is improved, and the lithium secondary battery realizes a relatively high energy density while having excellent cycle performance and safety performance.

[0075] In one embodiment of this application, the solvent may contain only the compound of formula (I). When the solvent contains only the compound of formula (I), due to the relatively high conductivity and relatively low viscosity of the compound of formula (I), the electrolytic solution has relatively good conductivity and fluidity, can improve the infiltration ability of the electrolytic solution, and can improve the transmission efficiency of lithium ions inside the negative electrode active material layer when the porosity of the negative electrode active material layer is relatively low, thereby realizing a lithium secondary battery with a high energy density and at the same time assisting in improving the cycle performance and safety performance of the lithium secondary battery.

[0076] Optionally, R 1 and R 2 each independently contain at least one of a methyl group, an ethyl group, a propyl group, a fluoromethyl group, a fluoroethyl group, and a fluoropropyl group.

[0077] Optionally, the compound of formula (I) contains at least one of the following compounds, Optionally, the compound of formula (I) contains at least one of the compound of formula (I-I), the compound of formula (I-II), the compound of formula (I-IV), and the compound of formula (I-VIII).

[0078]

Chemical formula

[0079] Hereinafter, the positive electrode plate, electrolyte, negative electrode plate, and separator in this lithium secondary battery will be introduced in detail.

[0080] [Electrolyte] The electrolyte serves to conduct lithium ions between the positive electrode plate and the negative electrode plate. The electrolyte includes a solute and a solvent, and the solute is dissolved in the solvent to form a homogeneous electrolyte in the bulk phase.

[0081] In the lithium secondary battery according to the present application, the solvent of the electrolyte includes the compound represented by formula (I).

[0082] Optionally, the mass fraction W1 of the compound represented by formula (I) in the electrolyte and the porosity P of the negative electrode active material layer have a negative correlation.

[0083] Specifically, as the porosity P of the negative electrode active material decreases, it is necessary to reduce the viscosity of the electrolyte with a high proportion of the compound of formula (I) and improve the fluidity of the electrolyte to ensure effective infiltration into the negative electrode active material layer.

[0084] Optionally, the mass fraction W1 of the compound of formula (I) satisfies 20% ≤ W1 ≤ 80%, and optionally, 30% ≤ W1 ≤ 70%.

[0085] Specifically, W1 may be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or the numerical value may be within the range obtained by combining any two of the above numerical values.

[0086] Optionally, in some other embodiments, the solvent may further comprise at least one 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, ethyl methyl sulfone and diethyl sulfone.

[0087] Optionally, the solute of the electrolyte comprises 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 difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate and lithium tetrafluoro(oxalato)phosphate.

[0088] Optionally, the electrolyte comprises a first additive, and the first additive comprises at least one of a compound of formula (II) and a compound of formula (III), wherein R 3 and R 4 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1-6 carbon atoms, a halogenated alkyl group having 1-6 carbon atoms, an alkoxy group having 1-6 carbon atoms, an alkenyl group having 2-6 carbon atoms, or an alkynyl group having 2-6 carbon atoms, and R 5 and R 6 and R 7 and R 8 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1-6 carbon atoms, a halogenated alkyl group having 1-6 carbon atoms, an alkoxy group having 1-6 carbon atoms, an alkenyl group having 2-6 carbon atoms, or an alkynyl group having 2-6 carbon atoms, and R 5, R 6 , R 7 , R 8 When they are different, it is a hydrogen atom.

[0089]

Chemical formula

[0090] Specifically, the electrolytic solution may further contain an additive, for example, this first additive. The first additive belongs to the negative electrode film-forming additive and can form a stable organic-inorganic composite solid electrolyte interface (SEI) film on the surface of the negative electrode active material layer to reduce the direct contact between the negative electrode active material layer and the electrolytic solution. In the electrolytic solution, introducing the compound represented by formula (I) as a solvent or as part of the solvent contributes to reducing the viscosity of the electrolytic solution and improving the infiltration ability of the electrolytic solution. On the other hand, the compound represented by formula (I) may undergo side reactions on the surface of the negative electrode active material during charge and discharge of the lithium secondary battery to generate gas, which consumes the electrolytic solution in the lithium secondary battery and causes destruction of the negative electrode active material and the negative electrode active material layer structure, affecting the cycle performance and safety performance of the lithium secondary battery.

[0091] Thereby, in this embodiment, by introducing the first additive into the electrolytic solution, the negative electrode active material layer is effectively protected from direct contact with the electrolytic solution, reducing the possibility that the electrolytic solution generates gas on the surface of the negative electrode active material layer, thereby improving the cycle performance and safety performance of the lithium secondary battery. In addition, the compounds represented by formula (II) and formula (III) form an organic-inorganic composite SEI film on the surface of the negative electrode active material layer, with good film-forming effect, contributing to forming an SEI film uniformly and rapidly on the surface of the negative electrode active material layer during the formation process of the lithium secondary battery.

[0092] Optionally, R 3 , R 4Each independently contains a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms, and R 5 、R 6 、R 7 、R 8 Each independently contains a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms, and when R 5 、R 6 、R 7 、R 8 are different, it is a hydrogen atom.

[0093] Optionally, the mass fraction of the first additive in the electrolyte is W2, and the mass fraction W2 of the first additive in the electrolyte, the mass fraction W1 of the compound of formula (I) in the electrolyte, and the porosity P of the negative electrode active material layer satisfy 0.00006 ≦ W2 × W1 / P ≦ 0.88, optionally 0.0006 ≦ W2 × W1 / P ≦ 0.44, and optionally 0.0013 ≦ W2 × W1 / P ≦ 0.22.

[0094] Specifically, W2 × W1 / P may be 0.00006, 0.00009, 0.00012, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.0010, 0.0011, 0.0012, 0.0013, 0.0014, 0.0015, 0.0016, 0.0017, 0.0018, 0.002, 0.004, 0.006, 0.008, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30, 0.35, 0.40, 0.42, 0.44, 0.46, 0.48, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.82, 0.84, 0.86, 0.88, or the numerical value may be within the range obtained by combining any two of the above numerical values.

[0095] Optionally, the mass fraction W2 of the first additive in the electrolyte solution and the mass fraction W1 of the compound of formula (I) in the electrolyte solution have a positive correlation.

[0096] Specifically, as the content of the compound shown in formula (I) in the electrolyte solution increases, the possibility that the compound shown in formula (I) generates gas on the surface of the negative electrode active material layer increases. Therefore, in order to avoid more compounds shown in formula (I) from undergoing a reduction reaction on the surface of the negative electrode active material layer to generate gas, more of the first additive needs to form a film on the surface of the negative electrode active material layer.

[0097] Optionally, 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%, 0.4%, 0.6%, 0.8%, 1%, 5%, 10%, 20%, or the numerical value may also be within the range obtained by combining any two of the above numerical values.

[0099] Optionally, the first additive contains at least one of the following compounds.

[0100]

Chemical formula

[0101] Optionally, the electrolyte solution contains a second additive, and the second additive contains at least one of chemical formula 1, chemical formula 2, chemical formula 3, and the compound of formula (IV). Here, M a+contains at least one of lithium ion, sodium ion, potassium ion, rubidium ion, cesium ion, magnesium ion, calcium ion, barium ion, aluminum ion, iron ion, copper ion, nickel ion, and organic cation, a, b, and c all represent natural numbers, t represents an integer from 0 to 3, w represents an integer from 1 to 6, X contains at least one of halogen atoms, n represents an integer from 0 to 4, Y contains at least one of boron atom and phosphorus atom, and R 9 contains a substituted or unsubstituted alkylene group with 1 to 10 carbon atoms, a substituted or unsubstituted halogenated alkylene group with 1 to 10 carbon atoms, a substituted or unsubstituted arylene group with 6 to 20 carbon atoms, and a substituted or unsubstituted halogenated arylene group with 6 to 20 carbon atoms, q represents an integer from 0 to 1, and m represents an integer from 1 to 3.

[0102]

Chemical formula

[0103]

Chemical formula

[0104] Specifically, the electrolytic solution may further contain another negative electrode film-forming additive, i.e., this second additive. The second additive can also form a stable SEI film on the surface of the negative electrode active material layer, thereby blocking the direct contact between the electrolytic solution and the negative electrode active material layer, protecting the negative electrode active material, avoiding the generation of gas on the surface of the negative electrode active material layer by the electrolytic solution, and further improving the cycle performance of the lithium secondary battery. In addition, the influence of the second additive on the impedance of the lithium secondary battery after film formation is relatively small, avoiding the situation where the impedance is too large and lithium precipitation occurs during the charge and discharge of the lithium secondary battery, which affects the charge and discharge performance and safety performance of the battery.

[0105] It should be understood that the electrolytic solution may contain only the first additive, only the second additive, or both the first additive and the second additive at the same time. When the electrolytic solution contains both the first additive and the second additive, the first additive and the second additive exhibit a synergistic effect and jointly form a SEI film on the surface of the negative electrode active material layer, resulting in a good film-forming effect and relatively little impact on the impedance of the lithium secondary battery.

[0106] Optionally, the mass fraction of the second additive in the electrolytic solution is W3, and the mass fraction W3 of the second additive in the electrolytic solution, the mass fraction W1 of the compound of formula (I) in the electrolytic solution, and the porosity P of the negative electrode active material satisfy 0.00006 ≦ W3 × W1 / P ≦ 0.88. Optionally, 0.0006 ≦ W3 × W1 / P ≦ 0.44. Optionally, 0.0013 ≦ W3 × W1 / P ≦ 0.22.

[0107] Specifically, W3 × W1 / P may be 0.00006, 0.00009, 0.00012, 0.0002, 0.0003, 0.0004, 0.0005, 0.0006, 0.0007, 0.0008, 0.0009, 0.0010, 0.0011, 0.0012, 0.0013, 0.0014, 0.0015, 0.0016, 0.0017, 0.0018, 0.002, 0.004, 0.006, 0.008, 0.01, 0.02, 0.04, 0.06, 0.08, 0.10, 0.15, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30, 0.35, 0.40, 0.42, 0.44, 0.46, 0.48, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.82, 0.84, 0.86, 0.88, or the numerical value may be within the range obtained by combining any two of the above numerical values.

[0108] Optionally, the mass fraction W3 of the second additive in the electrolytic solution and the mass fraction W1 of the compound of formula (I) in the electrolytic solution have a positive correlation.

[0109] Similar to the first additive, as the content of the compound represented by formula (I) in the electrolyte increases, the possibility of the compound represented by formula (I) generating gas on the surface of the negative electrode active material layer increases. Therefore, in order to avoid more of the compound represented by formula (I) undergoing a reduction reaction on the surface of the negative electrode active material layer to generate gas, more negative electrode film-forming additives are required to form a film on the surface of the negative electrode active material layer.

[0110] Optionally, 0.01% ≤ W3 ≤ 20%, optionally, 0.1% ≤ W3 ≤ 10%, optionally, 0.2% ≤ W3 ≤ 5%.

[0111] 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%, 0.4%, 0.6%, 0.8%, 1%, 5%, 10%, 20%, or the numerical value may also be within the range obtained by combining any two of the above numerical values.

[0112] Optionally, in Chemical Formula 4, M a+ is + Li + Na + K + Rb + Cs 2+ Mg 2+ Ca 2+ Ba 3+ Al 2+ Fe 2+ Fe 3+ Ni 2+ Ni 3+ and includes at least one of them.

[0113]

Chemical Formula

[0114] Optionally, the electrolyte may further contain additives that can improve some battery performances, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0115] [Negative electrode plate] The negative electrode plate generally includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer contains a negative electrode active material.

[0116] As an example, the negative electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode active material layer is disposed on either one or both of the two opposing surfaces of the negative electrode current collector.

[0117] Optionally, the negative electrode current collector may employ a metal foil sheet or a composite current collector. For example, a copper foil may be employed as the metal foil sheet. The composite current collector may include a polymer material-based layer and a metal layer formed on at least one surface of the polymer 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, and silver alloy) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] Optionally, the porosity P of the negative electrode active material layer satisfies 18% ≤ P ≤ 30.5%, and optionally, 20% ≤ P ≤ 27%.

[0119] Specifically, P may be 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 30.5%, 31%, 31.5%, 32%, or the numerical value may be in the range obtained by combining any two of the above numerical values.

[0120] In this embodiment, by controlling the porosity of the negative electrode active material layer within an appropriate range, the powder compression density of the negative electrode plate corresponding to this porosity is relatively large, and the negative electrode plate per unit area or volume can carry more negative electrode active material, thereby realizing the high energy density of the lithium secondary battery.

[0121] Optionally, the average (volume) particle diameter Dv50 of the negative electrode active material 0 satisfies 6 μm ≤ Dv50 0 and, optionally, 15 μm ≤ Dv50 0 ≤ 20 μm.

[0122] Specifically, Dv50 0 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 the numerical value may be within the range obtained by combining any two of the above numerical values.

[0123] In this example, by setting the average (volume) particle diameter of the negative electrode active material within an appropriate range, it contributes to improving the powder compression density of the negative electrode active material layer. And 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 diameter of the negative electrode active material on the surface of the negative electrode active material layer increases, the specific surface area decreases, which contributes to further reducing the contact between the negative electrode active material and the electrolytic solution, thereby reducing the probability of the electrolytic solution generating gas on the surface of the negative electrode active material layer and assisting in improving the cycle performance of the lithium secondary battery.

[0124] Optionally, the specific surface area of the negative electrode active material satisfies 0.5 m 2 / g ≤ BET ≤ 2.0 m 2 / g, and, optionally, 0.8 m 2 / g ≤ BET ≤ 1.5 m 2 / g.

[0125] Specifically, BET may be 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.1 m 2 / g, 1.2 m 2 / g, 1.3 m 2 / g, 1.5 m 2 / g, 1.6 m2 / g, 1.7 m 2 / g, 1.8 m 2 / g, 1.9 m 2 / g, 2.0 m 2 It may be / g, or the numerical value may be within the range obtained by combining any two of the above numerical values.

[0126] 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 further decreases, assisting in reducing the probability that the electrolytic solution generates gas on the surface of the negative electrode active material layer, thereby further improving the cycle performance of the lithium secondary battery.

[0127] Optionally, the negative electrode active layer material layer further includes an adhesive. The adhesive may 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).

[0128] Optionally, in one embodiment, the negative electrode active material layer further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0129] Optionally, the negative electrode active material layer further includes other auxiliaries, such as a thickening agent (such as sodium carboxymethyl cellulose (CMC-Na)), etc.

[0130] In some embodiments, the negative electrode plate can be manufactured in the following manner. The components for manufacturing the negative electrode plate are each formed as a negative electrode slurry. For example, a negative electrode active material, a conductive agent, an adhesive, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a negative electrode slurry. Then, the negative electrode slurry is coated on a negative electrode current collector, and after processes such as drying and cold pressing, a negative electrode plate is obtained.

[0131] [Positive electrode plate] 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.

[0132] As an example, the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode active material layer is provided on either one or both of the two opposing surfaces of the positive electrode current collector.

[0133] Optionally, the positive electrode current collector may employ a metal foil sheet or a composite current collector. For example, as the metal foil sheet, an aluminum foil may be employed. The composite current collector may include a polymer material-based layer and a metal layer formed on at least one surface of the polymer material-based layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0134] Optionally, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material.

[0135] Optionally, the first positive electrode active material may employ a positive electrode active material used in batteries known in the art. By way of example, the first positive electrode active material may include at least one of materials of lithium-containing phosphates having an olivine structure, lithium transition metal oxides, and modified compounds thereof. However, this application is not limited to these materials, and conventional materials that can be used as other battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Here, examples of lithium transition metal oxides are lithium cobalt oxide (e.g., LiCoO 2 ), lithium nickel oxide (e.g., LiNiO 2 ), lithium manganese oxide (e.g., LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which may be abbreviated as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which may be abbreviated as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which may be abbreviated as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which may be abbreviated as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which may be abbreviated as NCM811), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O 2) and may include, but are not limited to, at least one of them and its modified compounds. Examples of olivine-structured lithium-containing phosphates include lithium iron phosphate (e.g., LiFePO 4 (which may be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and may include, but are not limited to, at least one of a composite material of lithium manganese iron phosphate and carbon.

[0136] Optionally, the average (volume) particle size Dv50 of the first positive electrode active material 1 satisfies 8 μm ≦ Dv50 1 ≦ 50 μm.

[0137] Specifically, Dv50 1 may be 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or the numerical value may also be within the range obtained by combining any two of the above numerical values.

[0138] Optionally, the second positive electrode active material may adopt a positive electrode active material used in batteries known in the art, as long as the average (volume) particle diameter of the second positive electrode active material is smaller than the average (volume) particle diameter of the first positive electrode active material whose average (volume) particle diameter is selected. As an example, the second positive electrode active material may include at least one of materials such as lithium-containing phosphates having an olivine structure, lithium transition metal oxides, and modified compounds thereof. Here, examples of the lithium transition metal oxide may 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 the lithium-containing phosphate having an olivine structure may include, but are not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon. These positive electrode active materials may be used alone or in combination of two or more.

[0139] Optionally, the average (volume) particle diameter Dv50 of the second positive electrode active material 2 satisfies 0.02 μm ≦ Dv50 2 ≦ 8 μm.

[0140] Specifically, Dv50 2 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 the numerical value may be within the range obtained by combining any two of the above numerical values.

[0141] 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%.

[0142] Specifically, W4 may be 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 25%, 30%, 40%, 50%, or 60%, or the numerical range may be within the range obtained by combining any two of the above numerical values.

[0143] It should be understood that the first positive electrode active material and the second positive electrode active material may be of the same type of active material. For example, the first positive electrode active material is lithium iron phosphate with an average volume particle size on the micron order, and the second positive electrode active material is lithium iron phosphate with an average volume particle size on the nanometer order. The first positive electrode active material and the second positive electrode active material may also be of different types of active materials. For example, the first positive electrode active material is lithium iron phosphate with an average particle size on the micron order, and the second positive electrode active material is lithium iron manganese phosphate with an average volume particle size on the nanometer order.

[0144] In this embodiment, by combining the first active material with a relatively large average (volume) particle size and the second active material with a relatively small average (volume) particle size, it contributes to improving the powder compression density of the positive electrode active material layer, thereby improving the energy density of the lithium secondary battery.

[0145] Optionally, the positive electrode active material layer further contains an adhesive. As an example, the adhesive may contain at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0146] Optionally, the positive electrode active material layer further contains a conductive agent. As an example, the conductive agent may contain at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0147] In some embodiments, the positive electrode plate can be manufactured in the following manner. The components for manufacturing the positive electrode plate are each formed as a positive electrode slurry. For example, the first positive electrode active material and / or the second positive electrode active material, a conductive agent, an adhesive, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. Then, the positive electrode slurry is coated on a positive electrode current collector, and after undergoing processes such as drying and cold pressing, a positive electrode plate is obtained.

[0148] [Separator] Optionally, in one embodiment, the lithium secondary battery further includes a separator. The present application is not particularly limited with respect to the type of separator, and for example, any known porous structure separator having good chemical stability and mechanical stability may be selected.

[0149] Optionally, in one embodiment, the material of the separator may be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, and there is no particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and there is no particular limitation.

[0150] Optionally, 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 lamination process.

[0151] Optionally, in one embodiment, the lithium secondary battery includes an outer package. This outer package may be used for packaging the above electrode assembly and electrolyte.

[0152] Optionally, in one embodiment, the exterior of the lithium secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the lithium secondary battery may be a pouch, such as a bag-shaped pouch. The material of the pouch may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0153] This application is not particularly limited to the shape of the lithium secondary battery, and it may be cylindrical, square, or any other arbitrary shape. For example, FIG. 1 shows a lithium secondary battery 10 having a square structure as an example.

[0154] In some embodiments, referring to FIG. 2, the exterior may include a case 22 and a cover plate 21. Here, the case 22 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodation cavity. The case 22 has an opening communicating with the accommodation cavity, and the cover plate 21 can cover the opening so as to seal the accommodation cavity. The positive electrode plate, the negative electrode plate, and the separator can form an electrode assembly 23 by a winding process or a lamination process. The electrode assembly 23 is packaged in the above accommodation cavity. The electrode assembly 23 is infiltrated with an electrolytic solution. The number of electrode assemblies 23 included in the lithium secondary battery 10 may be one or more, and those skilled in the art can specifically select according to actual needs.

[0155] In some embodiments, the lithium secondary battery 10 may be assembled into a battery module, and the number of lithium secondary batteries 10 included in the battery module may be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0156] FIG. 3 shows a battery module 300 as an example. Referring to FIG. 3, in the battery module 300, a plurality of lithium secondary batteries 10 may be arranged in sequence along the longitudinal direction of the battery module 300. Of course, they may be arranged in any other manner. Furthermore, these plurality of lithium secondary batteries 10 can be fixed by fasteners.

[0157] Optionally, in one embodiment, the battery module 300 may further include a housing having an accommodation space, and the plurality of lithium secondary batteries 10 are accommodated in this accommodation space.

[0158] Optionally, in one embodiment, the battery module 300 may further be assembled into a battery pack. The number of battery modules 300 included in the battery pack may 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.

[0159] FIGS. 4 and 5 show a battery pack 400 as an example. Referring to FIGS. 4 and 5, the battery pack 400 may include a battery box and a plurality of battery modules 300 installed in the battery box. The battery box includes an upper housing 401 and a lower housing 402. The upper housing 401 covers the lower housing 402 and can form a sealed space for accommodating the battery module 300. The plurality of battery modules 300 may be arranged in the battery box in any manner.

[0160] The lithium secondary battery 10 described in this application may also be referred to as a lithium battery cell. Optionally, in one embodiment, first, a plurality of lithium battery cells are integrated as a battery module, and then the battery module is attached to the housing of the battery to form a battery pack. In some other production and processing technologies, a plurality of lithium battery cells may be directly attached to the housing to form a battery pack, and by removing the intermediate state of the battery module, the mass of the battery pack can be reduced and the energy density of the battery pack can be improved.

[0161] FIG. 6 is a schematic diagram of a power consumption device 600 provided by itself.

[0162] It should be understood that the power consumption device 600 includes at least one of the lithium secondary battery 10, battery module 300, or battery pack 400 according to this application. The lithium secondary battery 10, battery module 300, or battery pack 400 may be used as a power source for the power consumption device 600, or may be used as an energy storage unit of the power consumption device 600. The power consumption device 600 may include, but is not limited to, mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0163] As the power consumption device 600, the lithium secondary battery 10, battery module 300, or battery pack 400 can be selected according to its usage requirements.

[0164] An example of the power consumption device 600 is as shown in FIG. 6. This power consumption device 600 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of high output and high energy density for the lithium secondary battery 10 of this power consumption device 600, the battery pack 400 or battery module 300 may be adopted.

[0165] Another example of the power consumption device 600 may be a mobile phone, a tablet computer, a notebook computer, etc. This device generally requires thinning, and the lithium secondary battery 10 may be adopted as a power source.

[0166] The following describes the embodiments of the present application. The embodiments described below are exemplary ones used only for interpreting the present application and should not be construed as limitations to the present application. When specific technologies or conditions are not specified in the embodiments, they are carried out according to the technologies or conditions described in the literature in the relevant field or according to the product manuals. When the reagent or instrument to be used is not specified by the manufacturer, they are all ordinary commercially available products.

[0167] Embodiment Embodiment 1 (1) Manufacture of the positive electrode plate D V Lithium iron phosphate with a particle size of 50 being 10 μm was selected as the positive electrode active material. The positive electrode active material, acetylene black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder were dissolved in the solvent N-methylpyrrolidone (NMP) at a mass ratio of 90:5:5, and after sufficient stirring and uniform mixing, a slurry was obtained. This slurry was uniformly coated on the positive electrode current collector aluminum foil, and then further dried, cold pressed, and slit to obtain the positive electrode plate. The powder compression density of the positive electrode plate is 2.5 g / cm 3 It is.

[0168] (2) Manufacture of the negative electrode plate Artificial graphite was selected as the negative electrode active material. The negative electrode active material, acetylene black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethyl cellulose (CMC) as the thickener were dissolved in the solvent deionized water at a mass ratio of 90:4:4:2, and after uniform mixing, a negative electrode slurry was obtained. This slurry was uniformly coated on the negative electrode current collector copper foil, and then further dried, cold pressed, and slit to obtain the negative electrode plate. The specific surface area of the negative electrode active material in the negative electrode plate is 0.8 m 2 / g, and the porosity of the negative electrode active material layer in the negative electrode plate is 25%.

[0169] (3) Manufacture of the electrolyte A glove box in an argon gas atmosphere (H 2 O <0.1 ppm, O 2At (less than 0.1 ppm), ethylene carbonate (EC), which is an organic solvent, and ethyl methyl carbonate (EMC) were uniformly mixed at a volume ratio of 3:7. Further, a compound represented by formula (I-II), namely methyl acetate, was added to produce a solvent. The addition amount of methyl acetate was adjusted so that its mass fraction W1 in the solvent was 60%, and they were uniformly mixed. Thereafter, lithium hexafluorophosphate (LiPF 6 ) was added and dissolved in the solvent, and the mass fraction of the solute in the electrolyte solution was made 12.5%, and it was uniformly stirred to obtain an electrolyte solution.

[0170] (4) Assembly of lithium secondary battery The separator was positioned between the positive electrode plate and the negative electrode plate so that the positive electrode plate and the negative electrode plate could be isolated. The positive electrode plate, the separator, and the negative electrode plate were laminated in order, and the laminated members were wound to obtain an electrode assembly. The electrode assembly was installed in a case, the electrolyte solution was injected after drying, and after undergoing processes such as formation and standing, the lithium secondary battery of Example 1 was obtained.

[0171] Example 2 Compared with the lithium secondary battery of Example 1, in Example 2, the porosity P of the negative electrode active material layer in the negative electrode plate was 22%, and the mass fraction W1 of the compound represented by formula (I-II) in the solute was 70%.

[0172] Example 3 Compared with the lithium secondary battery of Example 1, the porosity P of the negative electrode active material layer in the negative electrode plate of Example 3 was 22%.

[0173] Example 4 Compared with Example 1, the solvent in Example 4 contained the compound represented by formula (I-V), and the mass fraction W1 of the compound represented by formula (I-V) in the solvent was 60%.

[0174] Example 5 Compared with Example 1, the solvent in 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%.

[0175] Example 6 Compared with Example 1, the electrolyte in Example 6 contains a first additive, and this first additive is a compound represented by formula (II-XI). The mass fraction W2 of the compound represented by formula (II-XI) in the electrolyte is 0.8%.

[0176] Example 7 Compared with Example 1, the electrolyte in Example 7 contains a first additive. This first additive is the compound represented by formula (II-I). The mass fraction W2 of the compound represented by formula (II-I) in the electrolyte is 0.05%, and the mass fraction W1 of the compound represented by formula (I-II) in the solvent is 70%.

[0177] Example 8 Compared with Example 7, the electrolyte in Example 8 contains a first additive. This first additive is the compound represented by formula (II-I). The mass fraction W2 of the compound represented by formula (II-I) in the electrolyte is 1.0%, and the mass fraction W1 of the compound represented by formula (I-II) in the solvent is 70%.

[0178] Example 9 Compared with Example 1, the electrolyte in Example 9 contains a second additive. This second additive is lithium difluoro(oxalato)borate (LiDFOB). The mass fraction W3 of LiDFOB in the electrolyte is 0.05%, and the mass fraction W1 of the compound represented by formula (I-II) in the solvent is 70%.

[0179] Example 10 Compared with Example 1, the electrolyte in Example 10 contains a second additive. This second additive is lithium difluorobis(oxalato)phosphate (LiBODFP). The mass fraction W3 of LiBODFP in the electrolyte is 0.8%.

[0180] Example 11 Compared with Example 2, the electrolyte in Example 11 contains a second additive, which is LiDFOB. The mass fraction W3 of LiDFOB in the electrolyte is 1.0%, and the mass fraction W1 of the compound shown in formula (I-II) in the solvent is 70%.

[0181] Example 12 Compared with Example 1, the electrolyte in Example 12 contains the first additive and the second additive at the same time. The first additive is the compound shown in formula (II-I), and the second additive is LiDFOB. The mass fraction W2 of the compound shown in formula (II-I) in the electrolyte is 0.5%, and the mass fraction W3 of LiDFOB in the electrolyte is 0.5%.

[0182] Example 13 Compared with Example 1, Example 13 is D V Select lithium iron phosphate with Dv50 of 10 μm as the first positive electrode active material and lithium iron phosphate with Dv50 of 2 μm as the second positive electrode active material. The first positive electrode active material, the second positive electrode active material, acetylene black as the conductive agent, and polyvinylidene fluoride (PVDF) as the adhesive are dissolved in the solvent N-methylpyrrolidone (NMP) at a mass ratio of 63:27:5:5, stirred well and mixed uniformly to obtain a slurry. This slurry is uniformly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and slit to obtain a positive electrode plate. Here, the mass fraction W4 of the second positive electrode active material in the positive electrode active material layer is 30%, and the powder compression density of the positive electrode plate is 2.65 g / cm 3 It is.

[0183] Example 14 Compared with Example 13, in Example 14, the mass fraction W4 of the second positive electrode active material in the positive electrode active material layer is 10%, and the powder compression density of the positive electrode plate is 2.55 g / cm 3 It is.

[0184] Example 15 Compared with Example 1, Example 15 selects artificial graphite with a BET of 1.5 m 2 / g as the negative electrode active material.

[0185] Example 16 Compared with Example 1, the solvent in Example 16 contains the compound shown in formula (I-I) and the compound shown in formula (I-II), that is, the solvent contains methyl acetate and ethyl acetate. Here, the mass ratio of methyl acetate to ethyl acetate is 30:30.

[0186] Comparative Example 1 Compared with Example 1, in Comparative Example 1, dimethyl carbonate (DMC) was selected as the solvent.

[0187] Comparative Example 2 Compared with Example 1, lithium iron phosphate was selected as the positive electrode active material, the porosity P of the negative electrode active material was 16%, and the mass fraction W1 of the compound shown in formula (I-II) in the solvent was 80%.

[0188] Details of the product parameters of the examples and comparative examples are as shown in Table 1.

[0189]

Table 1

[0190] In Table 1, P is the porosity P of the negative electrode active material layer of the negative electrode plate, BET is the specific surface area of the negative electrode active material, Dv501 is the average volume particle size of the first positive electrode active material, Dv502 is the average volume particle size of the second positive electrode active material, W4 is the mass fraction of the second positive electrode active material in the positive electrode active material layer, the compound is the compound contained in the solvent, W1 is the mass fraction of this compound in the solvent, W2 is the mass fraction of the first additive in the electrolyte, W3 is the mass fraction of the second additive in the electrolyte, additive 1 is the first additive, and additive 2 is the second additive.

[0191] Details of the battery performance test results of the above Examples 1-16 and Comparative Examples 1-2 are as shown in Table 2.

[0192]

Table 2

[0193] As can be seen from the comparison between Example 1, Example 4, Example 5, Example 16 and Comparative Example 1, by introducing the compounds shown in Formula (I-II), Formula (I-V), Formula (I-VIII) and Formula (I-I) into the solvent, the infiltration ability of the electrolyte can be effectively enhanced, and the discharge capacity, rapid charging ability and cycle life of the lithium secondary batteries in Example 1, Example 4, Example 5 and Example 16 can all be made superior to those of Comparative Example 1 in which the compound shown in Formula (I) is not contained in the solvent. At the same time, the volume expansion rate of the lithium secondary batteries in Example 1, Example 4, Example 5 and Example 16 is also lower than that of the lithium secondary battery in Comparative Example 1, and the safety performance is also improved synchronously. When the porosity P of the negative electrode active material layer is relatively low, the electrolyte in which the compound shown in Formula (I) is introduced into the solvent can rapidly infiltrate the negative electrode active material layer and assist in improving the transmission efficiency of lithium ions in the negative electrode active material layer. Thereby, while improving the energy density of the lithium secondary battery, the cycle performance and safety performance of the lithium secondary battery are also enhanced.

[0194] As can be seen from the comparison between Example 1 and Comparative Example 2, when the compound shown in Formula (I-II) is introduced into the solvent, the ratio W1 / P of the mass fraction W1 of this compound in the solvent to the porosity P of the negative electrode active material layer in Example 1 is 2.4, within the range of 0.65 - 4.4, and further within the range of 1.1 - 3.5. On the other hand, W1×Ds in Comparative Example 2 is 5, exceeding the above range. The discharge capacity, rapid charging ability and cycle life of Comparative Example 2 are all worse than those of Example 1, and the volume expansion rate of Comparative Example 2 is much larger than that of Example 1. Thereby, it is shown that by controlling W1 / P within an appropriate range, when the porosity of the negative electrode active material layer is relatively low, the infiltration ability of the electrolyte can be enhanced, thereby improving the energy density of the lithium secondary battery and at the same time improving the cycle performance and safety performance of the lithium secondary battery.

[0195] As can be seen from the comparison between Example 3 and Example 2, when P decreased, Example 2 increased W1 simultaneously, while Example 3 did not increase W1. Each performance of the lithium secondary battery in Example 3 was slightly inferior to that in Example 2. Thereby, by controlling P and W1 to have a positive correlation, it contributed to improving the discharge capacity, rapid charging ability, cycle life and safety performance of the lithium secondary battery.

[0196] As can be seen from the comparison between Examples 6 and 7 and Example 1, in Examples 6 and 7, the compounds shown in Formula (II-XI) and Formula (II-I) were introduced as the first additive into the electrolyte respectively. The cycle performance of the lithium secondary batteries in Examples 6 and 7 was significantly better than that of the lithium secondary battery in Example 1, and the volume expansion rate of the lithium secondary batteries in Examples 6 and 7 was also significantly smaller than that of the lithium secondary battery in Example 1. Thereby, it was shown that introducing the first additive into the electrolyte could improve the infiltration ability of the electrolyte and at the same time effectively reduce the side reactions on the surface of the negative electrode active material layer of the electrolyte, thereby improving the cycle performance and safety performance of the lithium secondary battery.

[0197] As can be seen from the comparison between Example 8, Example 7 and Example 6, when W1 increased, Example 8 increased W2 synchronously, while Example 7 decreased W2. Each performance of the lithium secondary battery in Example 8 was superior to that of the lithium secondary battery in Example 7. Thereby, by controlling W2 and W1 to have a positive correlation, it contributed to further enhancing each performance of the lithium secondary battery, especially improving the cycle performance and reducing the volume expansion rate.

[0198] As can be seen from the comparison between Example 9, Example 10 and Example 1, in Example 9 and Example 1, LiDFOB and LiBODFP are respectively introduced into the electrolyte as the second additive. The cycle performance of the lithium secondary battery in Example 9 and Example 10 is significantly better than that of the lithium secondary battery in Example 1, and the volume expansion rate of the lithium secondary battery in Example 9 and Example 10 is also significantly smaller than that of the lithium secondary battery in Example 1. Thereby, it is shown that introducing the first additive into the electrolyte can improve the infiltration ability of the electrolyte, and at the same time, effectively reduce the side reaction on the surface of the negative electrode active material layer of the electrolyte, thereby improving the cycle performance and safety performance of the lithium secondary battery.

[0199] As can be seen from the comparison between Example 9, Example 11 and Example 10, when W1 increased, in Example 11, W3 was increased synchronously, while in Example 9, W3 was decreased. The cycle performance and volume expansion rate of the lithium secondary battery in Example 11 are both better than those of the lithium secondary battery in Example 9. Thereby, controlling W3 and W1 to have a positive correlation contributed to further enhancing the cycle performance and safety performance of the lithium secondary battery.

[0200] As can be seen from the comparison between Example 12 and Example 6, Example 10, in Example 12, the first additive and the second additive are simultaneously introduced into the electrolyte. The cycle performance of the lithium secondary battery in Example 12 is significantly improved, and the volume expansion rate is significantly decreased. Thereby, it is found that the first additive and the second additive have a synergistic effect on the electrolyte, and can further improve the cycle performance and safety performance of the lithium secondary battery.

[0201] As can be seen from the comparison between Example 13 and Example 1, Dv50 in the positive electrode active material layer of Example 13 2A second positive electrode active material with a relatively small particle size was introduced to increase the powder compression density of the positive electrode plate. In Example 13, the discharge capacity of the lithium secondary battery was improved compared to Example 1. Thus, it was shown that combining positive electrode active materials with different particle sizes contributed to improving the powder compression density of the positive electrode active material layer, thereby assisting in improving the discharge capacity of the lithium secondary battery.

[0202] As can be seen from the comparison between Example 14 and Example 13, in Example 14, Dv50 2 The mass fraction W4 in the positive electrode active material layer of the second positive electrode active material with a relatively small particle size decreased, the powder compression density of the positive electrode plate decreased, and the discharge capacity of the lithium secondary battery also decreased. Thus, it was shown that by controlling the mass fraction W4 in the positive electrode active material layer of the second positive electrode active material with a relatively small average volume particle size, the powder compression density of the positive electrode plate could be affected, thereby affecting the energy density of the lithium secondary battery and further affecting the discharge capacity of the lithium secondary battery.

[0203] It should be understood that the average volume particle size of a material and its specific surface area are physical quantities that are interrelated. The larger the average volume particle size of a material, the smaller its BET generally becomes, while the smaller the average volume particle size of a material, the larger its BET generally becomes.

[0204] As can be seen from the comparison between Example 15 and Example 1, in Example 15, the BET of the negative electrode active material was larger, and the discharge capacity, rapid charging performance, and cycle performance of the lithium secondary battery in Example 1 were 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 was smaller. Thus, it was found that the average volume particle size or specific surface area of the negative electrode active material affected the performance of the lithium secondary battery, and a negative electrode active material with a relatively large average volume particle size and a relatively small BET had a smaller contact area with the electrolyte, which could reduce the probability of side reactions of the electrolyte on the surface of the negative electrode active material layer, thereby assisting in improving each performance of the lithium secondary battery.

[0205] Briefly introduce the test methods for the physical parameters and performance parameters mentioned in the embodiments of this application.

[0206] 1. Calculation method for the porosity of the negative electrode active material layer The porosity of the negative electrode active material layer can be calculated by the following formula.

[0207]

Equation

[0208] Here, ρ 1 is the powder density of the negative electrode active material under normal pressure, and ρ 2 is the powder compression density of the negative electrode active material under a pressure of 30 KN.

[0209] 2. Test method for powder compression density The powder compression density of the negative electrode active material has a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, referring to the standard GB / T 24533-2009, it can be measured by an electronic pressure tester (such as UTM7305 type). An exemplary test method is as follows. Weigh 1 g of the negative electrode active material, add it to a mold with a bottom area of 1.327 cm 2 , apply a pressure of 3000 kg (corresponding to 30 KN), hold the pressure for 30 s, then release the pressure and hold it for 10 s, and record and calculate the powder compression density of the negative electrode active material under a pressure of 30 KN.

[0210] 3. Test method for average (volume) particle size Dv50 represents the particle size corresponding when the cumulative volume distribution percentage of the negative electrode active material reaches 50%. In this application, Dv50 has a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, referring to the GB / T 19077-2016 laser diffraction method for particle size distribution, it can be measured using a laser particle size analyzer (such as Master Size 300).

[0211] 4. BET test method The test method referred to the standard GB / T19587-2004 "Measurement of Specific Surface Area of Solid Substances by Gas Adsorption BET Method".

[0212] 8 g - 15 g of the sample to be measured was taken and put into the sample tube, and the initial mass of the sample to be measured was recorded. The weighed sample to be measured was put into the instrument NOVA2000e. Then degassing was started, and after heating the sample to be measured to 200 °C, it was held for 2 h. After that, the mass of the sample to be measured after degassing was recorded. Then the sample to be measured after degassing was put into the instrument again, and liquid nitrogen was injected to conduct the BET test. The nitrogen gas pressure was set to 0.08 MPa - 0.12 MPa, and the heating temperature was set to 40 °C - 350 °C. After the test, the specific surface area was read from the test results.

[0213] 5. Battery Core Capacity Test At 25 °C, the lithium secondary battery was charged at a constant current of 0.5 C until 3.65 V, and then charged at a constant voltage of 3.65 V until the current became less than 0.05 C. Then the lithium secondary battery was discharged at a constant current of 0.5 C until 2.5 V, and the discharge capacity at 0.5 C was obtained.

[0214] 6. Fast Charging Time At 25 °C, the battery was charged at 0.33 C to 10% state of charge (SOC), charged for s minutes based on the given rapid determination procedure until 80% SOC, left standing for 30 minutes, then discharged at 1 C, then left standing for 30 minutes. After 20 cycles, after full charge, the battery core was disassembled to observe whether lithium was deposited on the negative electrode. If no lithium was deposited, it indicated that this battery core had the fast charging ability for s minutes.

[0215] 7. Cycle Performance Test Method At 60 °C, the lithium secondary battery was charged at a constant current of 0.5 C until 3.65 V, and then charged at a constant voltage of 3.65 V until the current became less than 0.05 C, and then the lithium secondary battery was discharged at a constant current of 0.5 C until 2.5 V. This was taken as one charge-discharge process. By repeating charging and discharging in this way, the number of cycles after the capacity of the lithium secondary battery decayed to 80% was calculated.

[0216] 8. Volume Expansion Rate Test At 25°C, first charge the lithium secondary battery manufactured at a constant current of 0.33C to 3.65V respectively, then charge it to a current of 0.05C at a constant voltage of 3.65V, and then discharge the lithium secondary battery to 2.5V at a constant current of 0.33C. The discharge capacity this time is the discharge capacity of the lithium secondary battery before high-temperature storage. Then charge the lithium secondary battery to 3.65V at a constant current of 0.33C and charge it to a current of 0.05C at a constant voltage of 3.65V to fully charge the lithium secondary battery. The volume of the battery was tested using the drainage method. Then store the lithium secondary battery at 60°C for 60 days. After the storage is completed, place the lithium secondary battery in an environment of 25°C and test the volume of the battery using the drainage method. The volume expansion rate of the battery = (volume after storage / volume before storage - 1)%.

[0217] It should be noted that this application is not limited to the above embodiments. The above embodiments are illustrative. Embodiments that have substantially the same configuration as the technical idea within the scope of the technical solution of this application and exhibit the same effects are all included within the technical scope of this application. In addition, within the scope not departing from the spirit of this application, various modifications that those skilled in the art can conceive of for the embodiments, and other forms constituted by combining some components in the embodiments are also included within the scope of this application.

Claims

1. A lithium secondary battery comprising: a negative electrode plate including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the porosity of the negative electrode active material layer is P; an electrolytic solution containing a solvent, the solvent including at least one of the compounds of the following formula (I), and the mass fraction of the compound of formula (I) in the solvent being W1, and the mass fraction W1 of the compound of formula (I) and the porosity P of the negative electrode active material layer satisfying 0.65 ≤ W1 / P ≤ 4.4, and optionally 1.1 ≤ W1 / P ≤ 3.5; 【Chemical 1】 Here, R １ and R ２ each independently contains at least one of an alkyl group having 1 to 3 carbon atoms and a halogenated alkyl group having 1 to 3 carbon atoms, and is a lithium secondary battery.

2. Said R １ and said R ２ 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, the lithium secondary battery according to claim 1.

3. The lithium secondary battery according to claim 1 or 2, wherein the porosity P of the negative electrode active material layer satisfies 18% ≤ P ≤ 30.5%, and optionally 20% ≤ P ≤ 27%.

4. The lithium secondary battery according to any one of claims 1 to 3, wherein the mass fraction W1 of the compound of formula (I) satisfies 20% ≤ W1 ≤ 80%, and optionally 30% ≤ W1 ≤ 70%.

5. The compound of formula (I) includes at least one of the following compounds [Chemical 2] and optionally, the compound of formula (I) includes at least one of the compound of formula (II), the compound of formula (III), the compound of formula (IV), and the compound of formula (VIII). The lithium secondary battery according to any one of claims 1 to 4.

6. The electrolytic solution includes a first additive, and the first additive includes at least one of the compound of formula (II) and the compound of formula (III).

7. 【Chemical Formula 3】 Here, R ３ , R ４ each independently includes a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a halogenated alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms, R ５ 、 R ６ 、 R ７ 、 R ８ each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a halogenated alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 2 to 6 carbon atoms, and when R ５ 、 R ６ 、 R ７ 、 R ８ are different, it is a hydrogen atom. The lithium secondary battery according to any one of claims 1 to 5.

8. Said R ３ , R ４ each independently contains a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms, Said R ５ , R ６ , R ７ , R ８ each independently contains a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, an alkynyl group having 2 to 4 carbon atoms, and when said R ５ , R ６ , R ７ , R ８ are different, is a hydrogen atom, The lithium secondary battery according to claim 6. The mass fraction of the first additive in the electrolytic solution is W2, and W2, W1, and P satisfy 0.00006 ≤ W2 × W1 / P ≤ 0.88, and optionally 0.0006 ≤ W2 × W1 / P ≤ 0.44, and optionally 0.0013 ≤ W2 × W1 / P ≤ 0.

22. The lithium secondary battery according to claim 6 or 7.

9. 0.01% ≤ W2 ≤ 20%, and optionally 0.1% ≤ W2 ≤ 10%, and optionally 0.2% ≤ W2 ≤ 5%. The lithium secondary battery according to claim 8.

10. The first additive includes at least one of the following compounds The lithium secondary battery according to any one of claims 6 to 9. 【Chemical Formula 4】

11. The electrolytic solution includes a second additive, and the second additive is and 【Chemical 5】 and 【Chemical Formula 6】 ​ 【Chemical Formula 7】 and includes at least one of the compound of formula (IV), [Chemical 8] Here, M ａ＋ contains at least one of lithium ion, sodium ion, potassium ion, rubidium ion, cesium ion, magnesium ion, calcium ion, barium ion, aluminum ion, iron ion, copper ion, nickel ion, and organic cation, and a, b, and c all represent natural numbers, t represents an integer from 0 to 3, and w represents an integer from 1 to 6, X includes at least one of halogen atoms, and n represents an integer from 0 to 4, Y includes at least one of a boron atom and a phosphorus atom, R ９ includes a substituted or unsubstituted alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted halogenated alkylene group having 1 to 10 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, and a substituted or unsubstituted halogenated arylene group having 6 to 20 carbon atoms; q represents an integer of 0 to 1; m represents an integer of 1 to 3. The lithium secondary battery according to any one of claims 1 to 10.

12. The mass fraction of the second additive in the electrolyte is W3, and W3, W1 and P satisfy 0.00006 ≤ W3 × W1 / P ≤ 0.88, optionally 0.0006 ≤ W3 × W1 / P ≤ 0.44, and optionally 0.0013 ≤ W3 × W1 / P ≤ 0.

22. The lithium secondary battery according to claim 11.

13. 0.01% ≤ W3 ≤ 20%, optionally 0.1% ≤ W3 ≤ 10%, and optionally 0.2% ≤ W3 ≤ 5%. The lithium secondary battery according to claim 12.

14. 【Chemical Formula 9】 In this case, M ａ＋ is 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 11 to 13, comprising at least one of the above.

15. The negative electrode active material layer contains a negative electrode active material, and the average particle diameter Dv50 of the negative electrode active material ０ satisfies 6 μm ≤ Dv50 ０ and preferably satisfies 15 μm ≤ Dv50 ０ ≤ 20 μm. The lithium secondary battery according to any one of claims 1 to 14

16. The specific surface area of the negative electrode active material satisfies 0.5 m ２ / g ≤ BET ≤ 2.0 m ２ / g, and optionally, 0.8 m ２ / g ≤ BET ≤ 1.5 m ２ / g, and the lithium secondary battery according to claim 15.

17. The lithium secondary battery includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and 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 satisfies 8 μm ≤ Dv50 １ ≤ 50 μm, The average particle diameter Dv50 of the second positive electrode active material ２ satisfies 0.02 μm ≤ Dv50 ２ ≤ 8 μm, and the lithium secondary battery according to any one of claims 1 to 16

18. The mass fraction W4 of the second positive electrode active material in the positive electrode active material layer satisfies 0% ≤ W4 ≤ 60%, optionally 20% ≤ W4 ≤ 40%. The lithium secondary battery according to claim 17.

19. A power consumption device including the lithium secondary battery according to any one of claims 1 to 18.

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