Lithium-ion secondary battery

Abstract

The present application relates to the technical field of lithium batteries, and in particular to a lithium-ion secondary battery. The battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte; the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises a silicon-carbon composite material; the silicon-carbon composite material has a first diffraction peak of a (002) crystal plane at 2θ=28.4±1°, and has a second diffraction peak of a (100) crystal plane at 2θ=43.4±1°; the full width at half maximum (FWHM) of the first diffraction peak is denoted as W1°, and the FWHM of the second diffraction peak is denoted as W2°; W1 satisfies: 0.3≤W1≤10; W2 satisfies: 2≤W2≤30; and the electrolyte comprises a compound A represented by formula I, wherein R1 and R2 are independently selected from a hydrocarbon group and a hydrocarbyloxy group with 1 to 6 carbon atoms, which are substituted or unsubstituted by H, N, F, and Cl, and at least one of R1 and R2 contains F. The nail penetration performance of the battery is effectively improved and the cycle life of the battery is prolonged.

Description

A lithium ion secondary battery

[0001] The present application claims priority to the Chinese patent application No. 202411362199.2, filed on September 27, 2024, and entitled "A lithium ion secondary battery", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of lithium batteries, in particular to a lithium ion secondary battery. BACKGROUND

[0003] Lithium ion battery technology is developing rapidly and has become the core force of energy storage, but it also faces multiple challenges. With the popularity and increasing functionality of mobile devices such as smartphones and tablets, the power consumption of these devices has also increased. Traditional slow charging methods have been unable to meet users' demand for fast charging. Fast-charging lithium ion batteries are currently facing a series of severe challenges. On the technical level, the first problem is how to shorten the charging time while ensuring that the energy density, cycle life, and safety of the battery are not affected. High-power fast charging causes the internal temperature of the battery to rise sharply when a needle is inserted, which puts higher requirements on the needle safety performance of the battery, and effective improvement of needle safety is needed to prevent thermal runaway and accelerated battery aging.

[0004] Therefore, the development of fast-charging lithium ion batteries with high safety performance not only needs to meet the rapid migration of lithium ions, but also needs to ensure that the battery can dissipate heat in time when a needle is inserted to prevent the temperature from rising too high and causing thermal runaway. SUMMARY

[0005] The present application aims to overcome the above-mentioned problems existing in the prior art, and provides a lithium ion secondary battery, which adds a silicon-carbon composite material with a specific structure in the negative electrode sheet, the silicon-carbon composite material has a first diffraction peak and a second diffraction peak; and adds a compound A in the electrolyte. When the first diffraction peak half-width FWHM and the second diffraction peak half-width FWHM of the silicon-carbon composite material and the mass ratio of the compound A in the electrolyte satisfy a specific relationship, the needle performance of the battery can be effectively improved, and the cycle life of the battery can be improved.

[0006] In order to achieve the above-mentioned purpose, the present application provides a lithium ion secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte.

[0007] The negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises a silicon-carbon composite material; the silicon-carbon composite material has a first diffraction peak of a (002) crystal face at 2θ = 28.4±1° and a second diffraction peak of a (100) crystal face at 2θ = 43.4±1°; the half-peak width FWHM of the first diffraction peak is denoted as W1°, and the half-peak width FWHM of the second diffraction peak is denoted as W2°; W1 satisfies 0.3≤W1≤10; and W2 satisfies 2≤W2≤30.

[0008] The electrolyte comprises a compound A shown in Formula I; Formula I: wherein R1 and R2 are independently selected from H, N, F, Cl, or a substituted or unsubstituted hydrocarbon group or hydrocarbonoxy group with 1-6 carbon atoms, and at least one of R1 and R2 contains F.

[0009] The technical solution has the following beneficial effects:

[0010] The lithium ion secondary battery provided in the application adds a silicon-carbon material with a specific structure in the negative electrode sheet, the silicon-carbon composite material has a first diffraction peak of a (002) crystal face at 2θ = 28.4±1° and a second diffraction peak of a (100) crystal face at 2θ = 43.4±1°; and the electrolyte comprises a compound A shown in Formula I, which can effectively improve the needle penetration performance of the battery and improve the cycle life of the battery.

[0011] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and the values are approximate values and should be understood to include values approximately near these ranges and values within these ranges. For ranges with endpoints, the endpoints are included in the ranges. For ranges without endpoints, the ranges are intended to include approximate values near the recited values. BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. 1 shows an X-ray diffraction (XRD) spectrum of the silicon-carbon composite material of the application. DETAILED DESCRIPTION

[0013] The specific embodiments of the application are described in detail below. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the application, and are not intended to limit the application.

[0014] Unless otherwise defined, all scientific and technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0015] Glossary

[0016] In the present application, the terms "battery", "lithium battery", "lithium ion battery", "lithium ion secondary battery" all have the same meaning, and all refer to a lithium ion secondary battery, which generally includes an electrode assembly (e.g., a positive electrode sheet, a negative electrode sheet, and a separator), a container (a case) that houses the electrode assembly, and an electrolyte.

[0017] In the present application, the term "hydrocarbon group" refers to a group formed by replacing a hydrogen atom in a hydrocarbon with another group (e.g., an alkyl group, a halogen atom, a hydroxyl group, a nitro group, etc.).

[0018] In the present application, the term "hydrocarbon oxy group", also referred to as "alkoxy group", refers to a group formed by connecting a hydrocarbon group with an oxygen atom.

[0019] The present application provides a lithium ion secondary battery, the battery including a positive electrode sheet, a negative electrode sheet, and an electrolyte;

[0020] The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon composite material; the silicon-carbon composite material has a first diffraction peak of a (002) crystal face at 2θ = 28.4 ± 1° and a second diffraction peak of a (100) crystal face at 2θ = 43.4 ± 1°; the half-peak width FWHM of the first diffraction peak is denoted as W1°, and the half-peak width FWHM of the second diffraction peak is denoted as W2°.

[0021] W1 satisfies: 0.3 ≤ W1 ≤ 10; and W2 satisfies: 2 ≤ W2 ≤ 30.

[0022] The electrolyte includes a compound A represented by Formula I; Formula I: wherein R1, R2 are independently selected from H, N, F, Cl, a substituted or unsubstituted hydrocarbon group having 1-6 carbon atoms, a hydrocarbon oxy group, and at least one of R1, R2 contains F.

[0023] For example, the half-peak width FWHM (W1°) of the first diffraction peak can be, for example, 0.3°, 0.6°, 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, or any value within a range defined by any two of the above values; and the half-peak width FWHM (W2°) of the second diffraction peak can be, for example, 2°, 4°, 6°, 8°, 10°, 12°, 14°, 16°, 18°, 20°, 22°, 24°, 26°, 28°, 30°, or any value within a range defined by any two of the above values.

[0024] Exemplarily, the measurement method of the half-peak width of the diffraction peak in the X-ray diffraction (XRD) spectrum can include the following steps: first, connecting the left and right lowest points of the characteristic peak to form a baseline L1; then drawing a straight line L2 perpendicular to the horizontal coordinate axis at the maximum diffraction intensity of the characteristic peak (the maximum diffraction intensity is denoted as I1), and the diffraction intensity of the intersection point of L1 is denoted as I2; draw a straight line L3 parallel to the horizontal coordinate axis with the diffraction intensity of (I1+I2) / 2, and the 2θ values of the left and right two points of the intersection point of L3 and the characteristic peak are denoted as θ1 and θ2 respectively, then the half-peak width W of the diffraction peak is θ2-θ1.

[0025] The silicon-carbon composite material with the specific structure is added in the negative plate in the application, and the X-ray diffraction (XRD) spectrum of the silicon-carbon composite material is shown in FIG. 1. Compared with the traditional silicon-carbon composite material, the silicon and carbon in the silicon-carbon composite material of the application have a suitable degree of amorphousness, which can optimize the crystal structure, the grain size is smaller, the peak width is larger, and the crystal lattice defects are fewer. Due to fewer crystal lattice defects, the silicon-carbon composite material can guide the uniform deposition of lithium ions and inhibit the growth of lithium dendrites, thereby improving the structural stability of the battery. When subjected to external impact such as needle puncture, a large amount of heat is generated due to the positive and negative short circuit of the battery. Since the silicon-carbon composite material improves the stability of the negative material, it can reduce the short circuit current and is not easy to react at high temperature, thereby reducing the heat generation and reducing the risk of thermal runaway. The crystal structure with fewer crystal lattice defects can reduce the resistance of electron transmission and more effectively control the release and diffusion of heat, so the application can improve the needle puncture performance of the battery. At the same time, since the grain size of the silicon-carbon composite material is small, it can also increase the contact area with the electrolyte, improve the rate of lithium ion extraction and embedding, and further improve the fast charging cycle performance of the battery.

[0026] The present application further studies and finds that, due to the small grain size of the silicon-carbon composite material, the grains are arranged compactly, and when swelling occurs during the cycle process, the space available for swelling is also smaller, and the stress on other particles is greater, thereby generating greater mechanical stress, leading to the problem of structural damage and capacity attenuation of the negative electrode material. To further solve the above problems caused by the small grain size of the silicon-carbon composite material, the present application further adds the compound A represented by Formula I to the electrolyte. The compound A represented by Formula I is a para-substituted fluorobenzene derivative. Due to para-substitution, the interaction between the two substituents is weak, and the influence on the electron cloud density of the benzene ring is small, which is conducive to maintaining the stability of the benzene ring. In the electrolyte, the benzene ring is not easy to decompose and open, so that the compound A can form a more stable protective film (SEI film) on the surface of the negative electrode material, thereby reducing the mechanical stress of the battery, inhibiting the swelling of the battery, and at the same time, reducing the growth rate of the alternating current internal resistance ACIR and the direct current internal resistance DCIR of the battery, more effectively protecting the integrity of the negative electrode material structure. At the same time, the compound A forms a more stable SEI film to inhibit the side reaction of direct contact between the electrolyte and the electrode material, thereby improving the cycle stability of the battery.

[0027] In summary, by adding the silicon-carbon composite material with the special structure to the negative electrode material and adding the compound A to the electrolyte, the present application can effectively improve the needle penetration performance of the battery, and improve the cycle life and fast charging performance of the battery.

[0028] In some embodiments, W1, W2 satisfy: 3≤W1+W2≤35, W2>W1, and the value of W1+W2 may, for example, be 3, 6, 10, 15, 20, 25, 30, 35, or any point value in the range formed by any two of the above-mentioned point values. Adjusting W1 and W2 to further satisfy the above relationship can further optimize the crystal structure of the silicon-carbon composite material, further reduce lattice defects, more evenly deposit lithium ions, and inhibit the growth of lithium dendrites, thereby further improving the structural stability of the battery, reducing the risk of thermal runaway, and further improving the needle penetration performance of the battery. Avoiding too large W1 and / or W2 can cause greater damage to the structural stability of the battery during the cycle process, thereby significantly reducing the cycle life of the battery.

[0029] In some embodiments, in the compound A represented by Formula I, R1, R2 are independently selected from H, N, F, Cl-substituted or unsubstituted hydrocarbon groups having 1-6 carbon atoms (for example, alkyl groups having 1-6 carbon atoms, alkenyl groups having 1-6 carbon atoms, alkynyl groups having 1-6 carbon atoms), alkoxy groups having 1-6 carbon atoms, and at least one of R1 and R2 contains F.

[0030] In some embodiments, in the compound A shown in formula I, R1, R2 are independently selected from H, N, F-substituted or unsubstituted alkyl, alkenyl, alkynyl, alkoxy with 1-4 carbon atoms, and both R1 and R2 contain F. Compound A further satisfies the above conditions, and the para-substituted fluorobenzene derivative of compound A can make the protective film formed on the electrode surface more uniform and stable, further reduce the ACIR and DCIR growth rate of the battery, reduce the swelling rate of the battery, and further improve the cycle stability of the battery.

[0031] In some embodiments, the mass fraction of compound A is x%, based on the total mass of the electrolyte; x satisfies: 0.1≤x≤5, and the mass fraction x(%) of compound A may, for example, be 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range defined by any two of the above values. Adjusting the mass fraction of compound A to further satisfy the above range can better solve the problems of structural damage and capacity decay of the negative electrode material caused by the small grain size of the silicon-carbon composite material, and stabilize the battery structure; when the content of compound A is too high, the film formed is too thick, which increases the interfacial impedance and further leads to the degradation of the cycle performance of the battery.

[0032] In some embodiments, the compound A shown in formula I includes at least one of the following compounds:

[0033] The silicon-containing substance in the negative electrode material is mainly a silicon-carbon composite material. The greater the content of silicon elements in the negative electrode material and the greater the content of the silicon-carbon composite material, the higher the theoretical capacity of the negative electrode material will be. However, the volume change of the silicon-containing negative electrode material during the charging and discharging process will be more significant, which will lead to the crushing of negative electrode material particles, the separation of active substances and current collectors, and the formation of an unstable solid electrolyte interphase (SEI) film. The rupture of the SEI film will lead to the continuous consumption of the electrolyte, thereby greatly affecting the cycle stability and performance of the battery.

[0034] In some embodiments, W1, W2, and x satisfy: 0<2x / (W1+W2)≤3; preferably 0<2x / (W1+W2)≤1, and for example, the value of 2x / (W1+W2) may, for example, be 0.01, 0.5, 1, 1.5, 2, 2.5, 3, or any value within the range defined by any two of the above values, and preferably 0<2x / (W1+W2)≤1. The present application uses a specific structure of silicon-carbon composite material in combination with compound A, and adjusts W1, W2, and x to satisfy the above conditions, which can further improve the needle penetration performance of the battery, and improve the cycle stability and fast charging performance of the battery.

[0035] The application further provides: the electrolyte comprises a lithium salt; the mass percentage of the lithium salt in the total mass of the electrolyte is denoted as y%; the content percentage of silicon in the negative electrode active material is denoted as z%; y and z satisfy: 0 < z / y ≤ 2. Exemplarily, the value of z / y may be, for example, 0.01, 0.1, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, or any point value in the range consisting of any two of the above point values.

[0036] Compared with the conventional amount of lithium salt added in the electrolyte in the prior art, the content of the lithium salt in the electrolyte of the application is higher. When W1, W2 and x satisfy: 0 < 2x / (W1+W2) ≤ 3, and the mass percentage y% of the lithium salt and the content percentage z% of silicon further satisfy the above range, the number of free lithium ions in the electrolyte is larger, which can improve the ionic conductivity of the electrolyte, improve the charge and discharge efficiency of the battery, and improve the fast-charging performance of the battery; increasing the content of the lithium salt in the electrolyte can increase the concentration of the electrolyte, thereby helping to form a more stable SEI film, improving the structural stability of the negative electrode material, and reducing the decomposition of the electrolyte and the consumption of active lithium; the high-concentration electrolyte can also slow down the damage of the volume expansion of the silicon-containing negative electrode material to the SEI film during the charging and discharging process, and improve the cycle stability of the battery.

[0037] In some embodiments, the mass percentage y(%) of the lithium salt in the electrolyte satisfies: 20 ≤ y ≤ 30, and the mass percentage y(%) of the lithium salt may be, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or any point value in the range consisting of any two of the above point values. Increasing the mass percentage of the lithium salt will increase the number of movable lithium ions in the battery, and the heat generation will also increase, which will reduce the safety performance of the battery, but can increase the cycle life of the battery; reducing the mass percentage of the lithium salt will reduce the fast-charging performance of the battery, degrade the cycle life of the battery, and the strength of the formed SEI film will also decrease, causing the degradation of the safety performance.

[0038] In some embodiments, the content percentage z(%) of silicon in the negative electrode active material satisfies: 0 < z ≤ 50, and the content percentage z(%) of silicon may be, for example, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any point value in the range consisting of any two of the above point values. The greater the content percentage of silicon, the stronger the stress effect on the SEI film, which will degrade the cycle and safety performance; and reducing the content of silicon will reduce the capacity of the battery, and the number of lithium ions that can be embedded and extracted during the charging and discharging process will be significantly reduced, and under the condition of the high-lithium salt electrolyte of the application, lithium precipitation is more likely to occur, which will significantly reduce the cycle life of the battery.

[0039] When W1, W2, x satisfy: 0 < 2x / (W1+W2)≤3, y and z satisfy: 0 < z / y≤2, and y and / or z are adjusted to further satisfy the above range, the ionic conductivity of the electrolyte can be further improved, the charge and discharge efficiency of the battery can be improved, the fast-charging performance of the battery can be improved, a more stable SEI layer can be formed, the decomposition of the electrolyte and the consumption of active lithium can be reduced; the structural stability of the negative electrode material can be further improved while providing higher energy density, and the cycle stability of the battery can be improved.

[0040] Exemplarily, the content of the silicon element in the negative active material can be tested by a thermogravimetric analysis method, for example, using a Shimadzu DTG-60 thermal gravimetric analyzer for testing, and the test conditions include: a sample amount of 5 mg, air as the atmosphere, a temperature rising rate of 10 ℃ / min from room temperature to 900 ℃ and constant temperature for 40 min. The relationship between the mass percentage of the silicon-carbon material (denoted as x) and the final weight residue percentage of the entire test (denoted as y) is: x = 7y / 15.

[0041] In some embodiments, the lithium ion electrolyte further comprises a lithium salt, which can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium hexafluoroantimonate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium bis-trifluoromethylsulfonylimide (LiTFSI), lithium trifluoromethylsulfonate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide, or lithium bis(trifluoromethylsulfonyl)imide, lithium difluoro oxalato borate (LiDFOB), lithium difluorobisoxalate phosphate, lithium tetrafluoroborate (LiBF4), lithium bis(difluorophosphoryl)oxy difluoroborate, lithium tetrakis(difluorophosphoryl)oxy borate.

[0042] Preferably, the lithium salt is a combination of LiFSI and LiPF6; further, the mass ratio of LiFSI and LiPF6 is 1:(1.5-4), and the mass ratio of LiFSI and LiPF6 can be, for example, 1:1.5, 1:2, 1:2.5, 1:3, 1:4, or any point value in the range consisting of any two of the above point values.

[0043] The inventors of the present application have further found that, due to the higher content of lithium salt in the electrolyte of the present application than in the conventional electrolyte, the optimization of the battery performance is significantly improved, but it also brings the problem of significantly increasing the viscosity of the electrolyte, enhancing the interaction between ions, increasing the resistance of ion migration, and increasing the heat generation of the battery. To further solve this problem, the present application further provides that the electrolyte further comprises a compound B represented by formula II and / or a compound C represented by formula III.

[0044] Formula II: wherein, R3, R4 are independently selected from H, O, halogen, or unsubstituted or substituted hydrocarbon group with carbon number 1-6;

[0045] Formula III: wherein, R5, R6, R7 are independently selected from H, O, halogen, or unsubstituted or substituted hydrocarbon group with carbon number 1-10.

[0046] In some embodiments, the electrolyte can further add one of compound B including Formula II, one of compound C including Formula III, or both compound B including Formula II and compound C including Formula III, preferably add compound B including Formula II and compound C including Formula III.

[0047] The present application further adds compound B including Formula II in the electrolyte, which has small viscosity and good solubility to lithium salt, and compound B has a compact and orderly chemical structure, the distance between atoms in the molecule is moderate, and has stable chemical bonds. Under the premise that W1, W2, x satisfy: 0 < 2x / (W1+W2)≤3, y and z satisfy: 0 < z / y≤2, the further addition of compound B can make the electrolyte maintain small viscosity when the lithium salt concentration in the electrolyte is high by its small viscosity characteristics and good solubility to lithium salt; the distance between atoms in the molecule of compound B is moderate, the chemical structure is compact and orderly, and the stable chemical bonds formed can effectively promote molecular collision and vibration heat transfer during heat transfer, reduce battery heat accumulation, prolong battery service life, and improve battery safety.

[0048] The present application further adds compound C including Formula III in the electrolyte, and the phosphate group at the core of compound C is a hydrophilic group, and the outside is a hydrophobic group, so that it has both hydrophilic and hydrophobic groups, and can better infiltrate various media. The compound C forms a protective layer with lyophilicity on the surface of the positive and negative electrodes of the battery, which can guide the electrolyte to better spread and infiltrate on the electrode surface, improve the lithium precipitation problem of the electrode interface, and improve the battery cycle life. Moreover, the protective layer formed by compound C has good thermal stability and is difficult to break even at high temperature, which prevents the side reaction between the electrode and the electrolyte, protects the structural stability of the electrode material, and also improves the thermal box safety performance of the battery.

[0049] In summary, when y and z satisfy 0 < z / y < 2, further adding compound B represented by formula II and compound C represented by formula III in the electrolyte can avoid the problem of increased electrolyte viscosity and increased resistance caused by high concentration of lithium salt in the electrolyte, further maintain the structural stability of the negative electrode material, improve the cycle life of the battery, and improve the thermal box safety performance of the battery.

[0050] In some embodiments, the mass percentage of compound B is denoted as m%, and the mass percentage of compound C is denoted as n%; m and n satisfy 0 < n / m < 1. For example, the value of n / m can be 0.01, 0.03, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any value within the range formed by any two of the above values. When y and z satisfy 0 < z / y < 2, and the mass percentages of compound B and compound C added in the electrolyte satisfy the above relationship, the viscosity of the electrolyte can be further reduced, the structural stability of the negative electrode material can be improved, the thermal accumulation of the battery can be reduced, the cycle life of the battery can be more effectively improved, and the thermal box safety performance of the battery can be improved.

[0051] In some embodiments, the mass percentage m (%) of compound B in the electrolyte satisfies 5 < m < 70. For example, the mass percentage m (%) of compound B can be 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any value within the range formed by any two of the above values. When m and n satisfy 0 < n / m < 1, the mass percentage m of compound B in the electrolyte further satisfies the above range, which can avoid the problem that when m < 5, the reduction in electrolyte viscosity is not obvious, ion migration overcomes increased resistance, and the battery generates more heat. When m > 70, the electrolyte has poor wettability at the electrode interface, which can lead to interface lithium precipitation and reduced cycle life.

[0052] In some embodiments, the mass percentage n (%) of compound C in the electrolyte satisfies 0 < n < 5. For example, the mass percentage n (%) of compound C can be 0.01%, 0.03%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%. When m and n satisfy 0 < n / m < 1, the mass percentage n of compound C in the electrolyte further satisfies the above range, which can more effectively solve the problem of poor wettability of the electrolyte at the electrode interface when compound B is added in the electrolyte, which can easily lead to interface lithium precipitation, and further improve the thermal box safety performance of the battery.

[0053] In some embodiments, the compound B shown in formula II includes at least one of the following compounds:

[0054] In some embodiments, the compound C shown in formula III includes at least one of the following compounds:

[0055] When m, n satisfy: 0 < n / m < 1, further selection of the above-mentioned compound B and / or compound C can further improve the structural stability of the negative electrode material, the cycle life of the battery, and the thermal box safety performance of the battery.

[0056] In some embodiments, the silicon-carbon composite material is doped with N elements and / or P elements. Further doping of N elements and P elements in the silicon-carbon composite material can make the surface of the negative electrode material have polarity, interact with the solvent molecules in the electrolyte, and promote the film formation reaction rate of compound A on the electrode surface. Under the action of N elements and P elements in the negative electrode material, a more stable and low-interfacial-resistance SEI film is formed, thereby improving the charge-discharge performance of the battery.

[0057] In some embodiments, the content of N elements in the silicon-carbon composite material is ≤6%, and the content of N elements may, for example, be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 5.9%, 6%, or any point value in the range formed by any two of the above point values, and is preferably 2%-5%. In some embodiments, the content of P elements in the silicon-carbon composite material is 0.05%-6%, and the content of P elements may, for example, be 0.05%, 0.08%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or any point value in the range formed by any two of the above point values, and is preferably 1%-5%. Further satisfying the above range of the content of N elements and P elements can further promote the film formation reaction rate of compound A on the electrode surface and improve the charge-discharge performance of the battery. Avoiding too large content of N and P elements can make the polarity of the electrode material increase and the force on the solvent molecules increase, which can make the film on the electrode surface thicker and increase the consumption of the solvent, thereby causing the cycle life of the battery to decay.

[0058] In some embodiments, the silicon-carbon composite material can be doped with only N elements, only P elements, or both N elements and P elements, and preferably doped with both N elements and P elements.

[0059] The test method of the mass content of the doping element is as follows: taking a lithium ion battery, removing the negative electrode sheet, dissolving with a mixed solvent (1:1 volume ratio of aqua regia and deionized water), obtaining a mixed solution, using deionized water to dilute the mixed solution to 100 mL, and then using an ICP analyzer to test the mass content of N and P elements in the solution.

[0060] To further reduce the volume change of the silicon-containing negative electrode material and reduce the generation of large mechanical stress inside the battery, the application further provides that the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector; the positive electrode active material layer is provided with a recessed area; the depth of the recessed area is denoted as b μm, and b satisfies: 5≤b≤25. Exemplarily, the depth b (μm) of the recessed area may be, for example, 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm or any point value in the range formed by any two of the above point values.

[0061] The recessed area arranged on the positive electrode active material layer may be formed by embossing the positive electrode sheet to form an embossed pattern, i.e., to form the recessed area. When the mechanical stress is transmitted to the positive electrode through the internal structure of the battery, the arrangement of the recessed area on the positive electrode active material layer can effectively prevent the positive electrode material from being extruded or stretched, thereby causing cracks or pulverization, weakening the bonding force between the active material and the current collector in the positive electrode material, and causing delamination or peeling. In addition, the arrangement of the recessed area can further prevent the capacity of the positive electrode material from being reduced and the cycle performance from being degraded. When the depth b (μm) of the recessed area further satisfies the above range, the effect of improving the cycle performance can be improved when the embossing depth is too small (b<5); and the positive electrode material internal passage can be prevented from being too narrow or broken due to excessive extrusion when the embossing depth is too large (b>25), the internal structure of the positive electrode material is damaged, the internal resistance of the positive electrode sheet is increased, the energy loss of the battery during charging and discharging is increased, and the cycle life and safety performance of the battery are reduced. Therefore, by arranging the recessed area b (μm) on the positive electrode active material layer and satisfying: 5≤b≤25, the structural stability of the positive electrode material can be further enhanced, and the cycle stability and cycle life of the battery can be improved.

[0062] In some embodiments, the recessed area arranged on the positive electrode active material layer is an embossed pattern, and the embossed pattern is a regular or irregular pattern, preferably a regular pattern, and more preferably a honeycomb pattern. The recessed area is arranged in a honeycomb embossed pattern, forming a microstructure similar to a honeycomb. When the negative electrode expands and generates mechanical stress, the concave-convex texture can act as a stress dispersion point to disperse the stress to a larger area, thereby reducing the direct impact on the positive electrode material, maintaining the structural integrity and performance stability of the positive electrode material, further alleviating the damage caused by mechanical stress to the positive electrode material, and improving the cycle stability and cycle life of the battery.

[0063] In some embodiments, the recessed area can be provided at all or part of the positive active material layer; for a wound battery, the recessed area is preferably provided at at least one of the bending portion of the positive electrode sheet, the top and bottom edges of the positive electrode sheet; for a stacked battery, the recessed area is preferably provided at the four peripheral edges of the positive active material layer.

[0064] To further protect the positive and negative electrodes of the battery and improve the cycle performance of the battery, the application further provides that the electrolyte further comprises a combination of one or more of a nitrile compound, fluoroethylene carbonate and a sulfonic acid compound. In the present application, the nitrile compound is used as a positive electrode protection additive, which can complex with positive electrode ions and prevent the dissolution of positive electrode metal ions during the cycle process, thereby causing instability of the positive electrode structure and deterioration of the electrochemical performance. Since the nitrile additive is not compatible with the negative electrode, to further improve the performance of the battery, the application further adds fluoroethylene carbonate and a sulfonic acid negative electrode protection additive to the electrolyte to form a protective film on the negative electrode and reduce the deterioration of the negative electrode caused by the nitrile additive. Therefore, the application further adds a combination of one or more of a nitrile compound, fluoroethylene carbonate and a sulfonic acid compound to the electrolyte, which can effectively protect the positive and negative electrodes of the battery and improve the cycle performance of the battery.

[0065] In some embodiments, the mass fraction of the nitrile compound in the total mass of the electrolyte is 1% to 5%, for example, the mass fraction of the nitrile compound can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any point value in the range formed by any two of the above point values. The mass fraction of the nitrile compound further satisfies the above range, which can further prevent the dissolution of positive electrode metal ions during the cycle process, stabilize the positive electrode structure and improve the electrochemical performance of the battery.

[0066] Illustratively, the nitrile compound includes but is not limited to one or more of a mono-nitrile additive, a di-nitrile additive and a tri-nitrile additive.

[0067] Illustratively, the mono-nitrile additive includes but is not limited to one or more of benzonitrile, p-tolunitrile and 3,5-difluorobenzonitrile.

[0068] Illustratively, the di-nitrile additive includes but is not limited to one or more of adiponitrile (AND), succinonitrile (SN) and ethylene glycol bis(propionitrile) ether.

[0069] Illustratively, the tri-nitrile additive includes but is not limited to one or more of 1,3,6-hexanetricarbonitrile (HTCN), 1,2,6-hexanetricarbonitrile and 1,2,3-tris(2-cyanethoxy)propane.

[0070] In some embodiments, the mass fraction of fluoroethylene carbonate is 5%-20% based on the total mass of the electrolyte, for example, the mass fraction of fluoroethylene carbonate can be 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20% or any point value in the range consisting of any two of the above point values. The mass fraction of the sulfonic compound is 0.1%-5% based on the total mass of the electrolyte, for example, the mass fraction of the sulfonic compound can be 0.1%, 0.4%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or any point value in the range consisting of any two of the above point values. When the fluoroethylene carbonate and the sulfonic compound as the negative electrode protection additive further meet the above range, the risk of increased battery gas production caused by excessive mass fraction of the negative electrode protection additive can be avoided.

[0071] For example, the sulfonic compound includes but is not limited to one or more of 1,3-propane sultone, 1-propene-1,3-sultone, 5-methylthiolane 2,2-dioxide, 1,3-propene sultone, 2,4-butane sultone, 1,4-butane sultone, 1,3-butane sultone, fluoro-1,3-propane sultone.

[0072] It should be noted that in this application, the amount of negative electrode protection additive (such as fluoroethylene carbonate, sulfonic compound) should be greater than that of positive electrode protection additive (nitrile compound) to form effective protection.

[0073] In some embodiments, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes lithium cobaltate (LiCoO2). Further selecting LiCoO2 as the positive electrode active material, lithium ions can quickly migrate in the positive electrode material, and the lithium cobaltate positive electrode material has stable structure, which can reduce the performance decay caused by material structure change during charging and discharging. Therefore, the combination of the positive and negative electrode materials described in this application can not only improve the fast charging performance of the battery, but also improve the overall energy density of the battery, meeting the use demand of higher energy density.

[0074] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0075] The materials, reagents and the like used in the following examples can be obtained from commercial channels unless otherwise specified.

[0076] The present application will be described in detail below in combination with specific embodiments, which are used for understanding rather than limiting the present application.

[0077] Example 1-1

[0078] 1) Preparation of positive electrode sheet

[0079] The positive electrode active material lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), conductive carbon black SP (super P) and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) was added, and stirring was carried out under the action of a vacuum stirrer until the mixed system became a positive electrode active paste with uniform fluidity; the positive electrode active paste was uniformly coated on both surfaces of an aluminum foil; the coated aluminum foil was dried, then rolled, and cut to obtain the desired positive electrode sheet.

[0080] 2) Preparation of negative electrode sheet

[0081] The negative electrode active material artificial graphite, silicon-carbon composite material, sodium carboxymethyl cellulose (CMC-Na), butadiene rubber, SP and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 74.5:40:2.5:1.5:1:0.5, deionized water was added, and a negative electrode active paste was obtained under the action of a vacuum stirrer; the negative electrode active paste was uniformly coated on both surfaces of a copper foil; the coated copper foil was air-dried at room temperature, then transferred to a 80°C oven for drying for 10h, and then cold-pressed and cut to obtain the negative electrode sheet.

[0082] 3) Preparation of electrolyte

[0083] In an argon-filled glove box (H2O <0.1 ppm, O2 <0.1 ppm), EC, PC, DEC, PP were mixed in a mass ratio of 10:20:20:50. Then, y% of fully dried LiPF6 (15%) and LiFSI (7%) based on the total mass of the electrolyte were quickly added, 1% of compound A of formula I-1 based on the total mass of the electrolyte was added after dissolution, finally 1% of ADN, 1.5% of SN, 2.5% of HTCN based on the total mass of the electrolyte were added, 12% of fluoroethylene carbonate based on the total mass of the electrolyte was added, and 3% of PS based on the total mass of the electrolyte was added, after stirring uniformly, the obtained electrolyte passed the moisture and free acid detection, and the desired electrolyte was obtained.

[0084] 4) Preparation of battery

[0085] The positive electrode sheet of step 1), the negative electrode sheet of step 2) and the separator were stacked in the order of positive electrode sheet, separator and negative electrode sheet, and then wound to obtain a battery cell; the battery cell was placed in an outer packaging aluminum foil, the electrolyte of step 3) was injected into the outer packaging, and then vacuum packaging, standing, formation, shaping, sorting and other processes were carried out to obtain a lithium ion battery. The battery of the present application has a charge-discharge range of 3-4.53V.

[0086] 5) Test battery

[0087] (i) 25℃ 4C cycle test

[0088] The battery obtained from the examples and comparative examples was charged at 25℃ with a constant current of 4C to a voltage of 4.53V, then charged at a constant voltage of 4.53V to a current of 0.05C, rested for 5min, and then discharged at a constant current of 1C to a voltage of 3.0V, which was one charge-discharge cycle. The discharge capacity of the first week was counted as x mAh, and the discharge capacity of the Nth week was counted as y mAh; the capacity of the Nth week divided by the capacity of the first week, the cycle capacity retention rate R of the Nth week = y / x, and the cycle number of the battery when the capacity retention rate of the battery was 80% was recorded.

[0089] (ii) Needle test

[0090] The battery obtained from the examples and comparative examples was discharged at 25℃ with a current of 0.5C to a voltage of 3.0V, then charged at a constant current of 0.5C to a voltage of 4.53V, and then charged at a constant voltage of 4.53V to a current of 0.05C, rested for 5min, and then a steel needle with a length of 100mm, a diameter of 3mm, and a taper of 15° was inserted into the middle of the battery at a speed of 25mm / s, the steel needle was retained in the battery for 5min after the test, and the battery was observed for fire or smoke, if there was fire or smoke, it was unqualified, and the needle test pass rate was recorded.

[0091] (iii) Hot box test

[0092] The battery obtained from the examples and comparative examples was charged at room temperature with a constant current of 1C to 4.53V, rested for 60min, and the appearance was checked and photographed. Then the temperature was increased to 132℃±2℃ at a rate of 3℃ / min±2℃ / min and maintained for 60min. The sample was observed, and if there was no leakage, no smoke, no fire, and no explosion, it was recorded as passing the test. Ten samples were tested for each example or comparative example, and the hot box test pass rate was recorded.

[0093] Examples 1-2 groups and Comparative Examples 1-2 were carried out according to Example 1-1, and the main differences are shown in Table 1. Among them, in the Example 1 group, the mass fraction of compound A in the electrolyte was changed. In the Example 2 group, different silicon-carbon materials were used, and the half-peak width of the first and second diffraction peaks was changed. In Comparative Example 1, a common silicon-carbon material (purchased from Shanghai Sunsheng Technology Co., Ltd., model SG50) was used. In Comparative Example 2, compound A was not added.

[0094] Table 1 Note: " / " indicates that the corresponding parameter is not tested.

[0095] As can be seen from Table 1, by adding the silicon-carbon composite material in the negative plate, the application can improve the fast-charging cycle performance of the battery, improve the anti-piercing performance and reduce the risk of thermal runaway; by adding compound A in the electrolyte and adjusting the addition amount of compound A, the application can improve the cycle stability of the battery; when the silicon-carbon composite material with a specific structure is used in cooperation with compound A and W1, W2 and x are adjusted to meet the above conditions, the battery piercing performance can be further improved, and the cycle stability and fast-charging performance of the battery can be improved.

[0096] Example 3 group is prepared by referring to Example 1-1, and the main difference is shown in Table 2. Among them, Example 3 group changes the type of compound A

[0097] Table 2

[0098] As can be seen from Table 2, by changing the type of compound A in the electrolyte, the application can achieve similar technical effects, which can improve the cycle stability of the battery and better solve the problems of structure damage and capacity attenuation of the negative material caused by the small grain size of the silicon-carbon composite material.

[0099] Example 4 group-6 group, refer to Example 1-1, the main difference is shown in Table 3. Among them, the content of silicon element in the negative material is changed in Example 4 group. The mass ratio of lithium salt (combination of LiFSI and LiPF6) in the electrolyte is changed in Example 5 group. The type of lithium salt in the electrolyte is changed in Example 6 group. Among them, only LiPF6 is added in Example 6-1, and the mass ratio of lithium salt is unchanged, which is the same as Example 1-1. Only LiFSI is added in Example 6-2, and the mass ratio of lithium salt is unchanged, which is the same as Example 1-1.

[0100] Table 3

[0101] As can be seen from Table 3, by adjusting the mass ratio y% of lithium salt in the electrolyte and the content ratio z% of silicon element to further meet 0<z / y≤2, the application can further improve the fast-charging performance of the battery and improve the cycle stability of the battery.

[0102] Example 7 group-8 group, refer to Example 1-1, further add compound B and compound C in the electrolyte, the main difference is shown in Table 4. Among them, the mass ratio of compound B in the electrolyte is changed in Example 7 group; the addition amount of lithium salt is changed to LiPF6(5%) and LiFSI(2.5%) in Example 7-3 group. The mass ratio of compound C in the electrolyte is changed in Example 8 group.

[0103] Table 4 Note: " / " means that the corresponding parameter is not tested.

[0104] As can be seen from Table 4, by further adding compound B and compound C in the electrolyte, adjusting the mass ratio (m) of compound B and the mass ratio (n) of compound C in the electrolyte to satisfy 0 < n / m < 1, the viscosity of the electrolyte can be further reduced, the structural stability of the negative electrode material can be improved, the heat accumulation of the battery can be reduced, the cycle life of the battery can be more effectively improved, and the safety performance of the battery in the hot box can be improved.

[0105] The group of Example 9 is prepared with reference to Example 7-1, and the main difference is shown in Table 5. Among them, the type of compound B and compound C in the electrolyte is changed in the group of Example 9.

[0106] Table 5

[0107] As can be seen from Table 5, by changing the type of compound B added in the electrolyte, the similar technical effects can be achieved, the service life of the battery can be prolonged, and the safety of the battery can be improved.

[0108] The group of Example 10 is prepared with reference to Example 7-1, and further embossing treatment is performed on the positive electrode active material layer, and the embossing pattern is a honeycomb pattern. The recessed area is arranged at all positions on the positive electrode active material layer, and the main difference is shown in Table 6. Among them, the depth of the recessed area is changed in the group of Example 10.

[0109] Table 6

[0110] As can be seen from Table 6, by arranging the recessed area on the positive electrode active material layer and adjusting the depth of the recessed area, the structural stability of the positive electrode material can be further enhanced, and the cycle stability and cycle life of the battery can be improved.

[0111] The group of Example 11 is prepared with reference to Example 10-1, and P element and N element are further doped in the negative electrode silicon-carbon composite material, and the main difference is shown in Table 7. Among them, the content of the doped N element or P element is changed in the group of Example 11.

[0112] Table 7 Note: " / " indicates that the corresponding parameter is not tested.

[0113] As can be seen from Table 7, by further doping P element and N element in the silicon-carbon composite material and adjusting the content of N element and P element, the cycle life and safety performance of the battery can be further improved by promoting film formation.

[0114] It should be noted that, as used in this document, the terms "comprises" or "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element. Furthermore, it should be noted that the methods and apparatus of the present embodiments are not limited to the order of execution of the steps recited as the order of execution can vary depending on the implementation. For example, the described methods can be executed in an order different than that described, and / or various steps can be added, omitted, or combined, and / or various steps can be executed at substantially the same time, etc. Also, features described with respect to certain examples can be combined in other examples.

[0115] The foregoing is merely illustrative of the principles of this application and various modifications can be made by those skilled in the art without departing from the scope and spirit of the application.

Claims

1. A lithium-ion secondary battery, wherein, The battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; The negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises a silicon-carbon composite material; the silicon-carbon composite material has a first diffraction peak of a (002) crystal face at 2θ = 28.4±1° and a second diffraction peak of a (100) crystal face at 2θ = 43.4±1°; a half-peak width FWHM of the first diffraction peak is denoted as W1°, and a half-peak width FWHM of the second diffraction peak is denoted as W2°; W1 satisfies: 0.3≤W1≤10; and W2 satisfies: 2≤W2≤30; The electrolyte comprises a compound A shown in Formula I; Formula I: wherein R1 and R2 are independently selected from H, N, F, a Cl-substituted or unsubstituted hydrocarbon group with 1-6 carbon atoms, and a hydrocarbon-oxy group, and at least one of R1 and R2 contains F.

2. The lithium-ion secondary battery according to claim 1, wherein W1 and W2 satisfy: 3≤W1+W2≤35, and W2>W1.

3. The lithium-ion secondary battery according to claim 1, wherein In Formula I, R1 and R2 are independently selected from H, N, F-substituted or unsubstituted alkyl, alkenyl, alkynyl and alkoxy with 1-4 carbon atoms, and both R1 and R2 contain F; Preferably, a mass percentage of the compound A in the total mass of the electrolyte is denoted as x%; x satisfies: 0.1≤x≤5; Preferably, the compound A of formula I comprises at least one of the following compounds:

4. The lithium-ion secondary battery according to claim 1, wherein W1, W2 and x satisfy: 0<2x / (W1+W2)≤3; preferably, 0<2x / (W1+W2)≤1.

5. The lithium-ion secondary battery according to claim 1, wherein The electrolyte comprises a lithium salt; a mass percentage of the lithium salt in the total mass of the electrolyte is denoted as y%; In the negative electrode active material, a content percentage of silicon element is denoted as z%; y and z satisfy: 0<z / y≤2; Preferably, y satisfies: 20≤y≤30; and / or, z satisfies: 0<z≤50; The lithium salt is a combination of LiFSI and LiPF6, and more preferably, a mass ratio of LiFSI to LiPF6 is 1:(1.5-4).

6. The lithium-ion secondary battery according to claim 1, wherein The electrolyte further comprises a compound B shown in Formula II and / or a compound C shown in Formula III; Formula II: wherein R3 and R4 are independently selected from H, O, a halogen-substituted or unsubstituted hydrocarbon group with 1-6 carbon atoms; Formula III: wherein R5, R6 and R7 are independently selected from H, O, a halogen-substituted or unsubstituted hydrocarbon group with 1-10 carbon atoms; Preferably, a mass percentage of the compound B in the total mass of the electrolyte is denoted as m%, and a mass percentage of the compound C in the total mass of the electrolyte is denoted as n%; m and n satisfy: 0<n / m≤1; Preferably, m satisfies: 5≤m≤70; and / or, n satisfies: 0<n≤5.

7. The lithium-ion secondary battery according to claim 6, wherein Compounds B represented by Formula II include at least one of the compounds represented by: and / or, the compound C represented by Formula III includes at least one of the compounds represented by the following formulae:

8. The lithium-ion secondary battery according to any one of claims 1 to 7, wherein The silicon-carbon composite material is doped with N element and / or P element; Preferably, in the silicon-carbon composite material, a content of N element is ≤6%; Preferably, in the silicon-carbon composite material, a content of P element is 0.05%-6%.

9. The lithium-ion secondary battery according to claim 8, wherein In the silicon-carbon composite material, a content of N element is 2%-5%; and in the silicon-carbon composite material, a content of P element is 1%-5%.

10. The lithium-ion secondary battery according to any one of claims 1 to 9, wherein The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one side surface of the positive electrode current collector; and the positive electrode active material layer is provided with a recessed area; Preferably, a depth of the recessed area is b μm, and b satisfies: 5≤b≤25.

11. The lithium-ion secondary battery according to claim 10, wherein The lithium ion secondary battery is a winding type battery, and the recessed area is preferably arranged at at least one of a bending portion of the positive electrode sheet, a top portion of the positive electrode sheet, and a bottom edge of the positive electrode sheet. Alternatively, the lithium ion secondary battery is a stacking type battery, and the recessed area is preferably arranged at a periphery edge of the positive active material layer.

12. The lithium-ion secondary battery according to any one of claims 1 to 7, wherein The electrolyte further comprises a combination of one or more of a nitrile compound, a fluorinated ethylene carbonate, and a sulfonic acid compound; Preferably, the mass fraction of the nitrile compound is 1%-5% based on the total mass of the electrolyte. Preferably, the mass fraction of the fluorinated ethylene carbonate is 5%-20% based on the total mass of the electrolyte. Preferably, the mass fraction of the sulfonic acid compound is 0.1%-5% based on the total mass of the electrolyte.

13. The lithium-ion secondary battery according to claim 12, wherein The nitrile compound includes but is not limited to one or more of a mono-nitrile compound, a di-nitrile compound, and a tri-nitrile compound.

14. The lithium-ion secondary battery according to claim 13, wherein The mono-nitrile compound includes but is not limited to one or more of benzonitrile, p-tolunitrile, and 3,5-difluorobenzonitrile; and / or, the di-nitrile compound includes but is not limited to one or more of adipodinitrile, butanedinitrile, and ethylene glycol bis(propionitrile) ether; and / or, the tri-nitrile compound includes but is not limited to one or more of 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, and 1,2,3-tris(2-cyanethoxy)propane.

15. The lithium-ion secondary battery according to claim 12, wherein The sulfonic acid compound includes but is not limited to one or more of 1,3-propane sultone, 1-propene-1,3-sulfonic acid lactone, 5-methylthiolane 2,2-dioxide, 1,3-propene sulfonic acid lactone, 2,4-butane sultone, 1,4-butane sulfonic acid lactone, 1,3-butane sulfonic acid lactone, and fluorinated 1,3-propane sultone.

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