Lithium ion secondary battery and electric equipment

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a lithium ion secondary battery and electric equipment. According to the invention, the compound A with a specific general formula is doped into the electrolyte, so that a LiF-rich SEI film is formed on the negative electrode and is interwoven with an organic SEI film component, the mechanical property of the SEI film is improved, the adaptability of the SEI film and the silicon negative electrode with huge volume change is improved, and the volume expansion of the silicon negative electrode in the cycle process is improved; however, the compound A can influence the positive electrode active material, so that the damage of side reaction products to the structural stability of the positive electrode active material due to poor oxidation resistance of the electrolyte is inhibited by doping the positive electrode active material and regulating and controlling the content relationship between the doped element and the compound A, and the cycle stability of the battery is comprehensively improved; in addition, the doped elements also broaden a lithium ion transmission channel, so that the transmission efficiency of lithium ions in the positive electrode active material can be improved, and the rate capability of the battery is improved.

Description

Technical Field

[0001] This application belongs to the technical field of secondary batteries, and particularly relates to a lithium-ion secondary battery and an electrical device. Background Art

[0002] With the application of new anode materials expanding from 3C consumer electronics to the power battery field, the market penetration rate of silicon anodes is gradually increasing. However, the development of silicon-doped anode batteries also faces some difficulties. In the pursuit of high energy density, the cyclic swelling problem of silicon anode batteries has always been a technical obstacle that is difficult to overcome. Silicon materials will undergo significant volume expansion during the lithium intercalation process, and the expansion rate can be as high as over 300%. This characteristic causes the silicon anode to experience drastic volume changes during charge and discharge cycles. This repeated expansion and contraction of volume will not only cause mechanical fragmentation of silicon particles but also lead to the connection failure between the active material and the current collector, thereby causing the battery capacity to rapidly decay and the cycle stability to be greatly reduced.

[0003] Therefore, although silicon anode batteries have attracted much attention due to their high energy density potential, how to effectively solve their cyclic swelling problem and achieve commercial applications with long life and high stability is still a key problem that needs to be overcome urgently in the current battery technology field. Summary of the Invention

[0004] Therefore, the technical problem to be solved by this application is to overcome the defect that the silicon anode in the prior art undergoes volume expansion during charge and discharge, which affects the cycle performance of the battery, so as to provide a lithium-ion secondary battery and an electrical device.

[0005] For this purpose, this application provides the following technical solutions:

[0006] According to one aspect of this application, there is provided a lithium-ion secondary battery, including a positive electrode sheet, a negative electrode sheet, and an electrolyte,

[0007] wherein, the negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-based material and a carbon-based material, and the silicon-based material includes silicon elements;

[0008] The electrolyte includes compound A, and the mass percentage content of compound A is a%, 0.1 ≤ a ≤ 10 based on the total mass of the electrolyte;

[0009] The general formula composition of compound A is as follows:

[0010]

[0011] Wherein L is O or a linking bond; R is selected from unsubstituted or Ra-substituted C2-C6 alkyl, unsubstituted or Ra-substituted C2-C6 alkenyl, unsubstituted or Ra-substituted C2-C6 alkynyl, unsubstituted or Ra-substituted C2-C6 nitrogen-containing heteroaryl, unsubstituted or Ra-substituted C6-C 12 one of aryls, and the substituents Ra of each group are each independently selected from fluorine or C1-C6 fluoroalkyl; R1 is selected from one of fluorine or C1-C6 fluoroalkyl;

[0012] The positive electrode sheet includes a positive electrode active material, and the positive electrode active material contains doping elements Mg and Al. Based on the mass of the positive electrode active material, the mass percentage content of Mg element is c%, and the mass percentage content of Al element is d%;

[0013] The relationship among a, c, and d satisfies: 0.05 < a / (c + d) ≤ 20.

[0014] In some alternative embodiments, c and d satisfy: 0.05 ≤ c ≤ 0.4, 0.3 ≤ d ≤ 1.

[0015] In some alternative embodiments, based on the total mass of the negative electrode active material, the mass percentage content of silicon element is b%, and a and b satisfy: 0.5 ≤ b ≤ 50, 0.1 ≤ b / a ≤ 10.

[0016] In some alternative embodiments, the compound A has any one of the following structures:

[0017]

[0018]

[0019] In some alternative embodiments, the electrolyte further includes a compound G, and the compound G has any one of the following general formulas:

[0020]

[0021] Wherein, R7 and R9 are each independently selected from C1-C10 hydrocarbyl, C1-C10 hydrocarbyloxy; R8 is selected from O, C1-C10 hydrocarbyloxy;

[0022] Preferably, the compound G has any one of the following structures:

[0023]

[0024] In some alternative embodiments, based on the total mass of the electrolyte, the mass percentage content of the compound G is g%, 5 ≤ g ≤ 60;

[0025] Preferably, a and g satisfy: 1 ≤ g / a ≤ 6.

[0026] In some alternative embodiments, the electrolyte further includes a fluorinated solvent and / or an ether-bond-containing nitrile additive;

[0027] Preferably, based on the total mass of the electrolyte, the mass percentage of the fluorinated solvent is j%, where 5 ≤ j ≤ 50; more preferably, a and j satisfy: 6 ≤ j + a ≤ 40;

[0028] Preferably, based on the total mass of the electrolyte, the mass percentage of the ether-bond-containing nitrile additive is k%, where 0.1 ≤ k ≤ 5;

[0029] Preferably, the electrolyte further includes an unsaturated nitrile compound, and based on the total mass of the electrolyte, the mass percentage of the unsaturated nitrile compound is m%, where 0.1 ≤ m ≤ 3.

[0030] In some alternative embodiments, the fluorinated solvent includes at least one of ethyl difluoroacetate, fluorinated ethylene carbonate, difluoroethylene carbonate, methyl trifluoroethyl carbonate, trifluoromethyl ethylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and methyl trifluoroacetate;

[0031] and / or the ether-bond-containing nitrile additive includes one of penta(2-cyanoethoxy)pentane, ethylene glycol bis(2-cyanoethyl) ether, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, ethylene glycol bis(4-cyanobutyl) ether, and ethylene glycol bis(propionitrile) ether;

[0032] and / or the unsaturated nitrile compound includes at least one of 1,4-dicyano-2-butene, 2-butenenitrile, fumarodinitrile, and acrylonitrile.

[0033] In some alternative embodiments, the positive electrode active material further contains a doped element Ti and / or Zr;

[0034] Preferably, based on the mass of the positive electrode active material, the mass percentage of the Ti element is e%, where 0.02 ≤ e ≤ 0.2;

[0035] Preferably, based on the mass of the positive electrode active material, the mass percentage of the Zr element is f%, where 0.01 ≤ f ≤ 0.15.

[0036] In some alternative embodiments, the Dv50 particle size of the positive electrode active material is h μm, and the specific surface area is i m 2 / g, where 5 ≤ h ≤ 25 and 0.05 ≤ i ≤ 0.5;

[0037] And / or, in the XRD pattern of the positive electrode active material, there is a characteristic diffraction peak 1 at a diffraction angle of 15-20°, with a peak intensity of H1, and a characteristic diffraction peak 2 at a diffraction angle of 44-47°, with a peak intensity of H2, and the peak intensities satisfy: 1.7 ≤ H1 / H2 ≤ 2.1.

[0038] It should be noted that H1 / H2 mainly reflects the degree of order of the positive electrode active material. The larger the ratio, the greater the degree of order. Those skilled in the art can understand that the addition of doping elements will change the crystal structure of the positive electrode active material, increase the disorder of the crystal structure, and the ratio will decrease; in addition, when the grain size becomes smaller, the diffraction intensity will decrease. Therefore, the grain size can also be controlled by controlling the synthesis conditions (such as reducing the synthesis reaction time to reduce the grain growth size), thereby affecting the diffraction intensity and the value of H1 / H2.

[0039] According to another aspect of the present application, an electrical device is provided, including the above-mentioned lithium-ion secondary battery.

[0040] The technical solution of the present application has the following advantages:

[0041] The lithium-ion secondary battery provided by the present application includes a positive electrode sheet, a negative electrode sheet and an electrolyte. Among them, the negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-based material and a carbon-based material, and the silicon-based material includes silicon element; the electrolyte includes compound A, and based on the total mass of the electrolyte, the mass percentage content of compound A is a%, 0.1 ≤ a ≤ 10; the general formula composition of compound A is as follows:

[0042]

[0043] Among them, L is O or a connecting bond; R is selected from an unsubstituted or Ra-substituted C2-C6 alkyl group, an unsubstituted or Ra-substituted C2-C6 alkenyl group, an unsubstituted or Ra-substituted C2-C6 alkynyl group, an unsubstituted or Ra-substituted C2-C6 nitrogen-containing heteroaryl group, an unsubstituted or Ra-substituted C6-C 12One of the aryl groups, and the substituents Ra of each group are each independently selected from fluorine or C1-C6 fluoroalkyl; R1 is selected from one of fluorine or C1-C6 fluoroalkyl; the positive electrode sheet includes a positive electrode active material, and the positive electrode active material contains doping elements Mg and Al. Based on the mass of the positive electrode active material, the mass percentage content of Mg element is c%, and the mass percentage content of Al element is d%; the relationship among a, c, and d satisfies: 0.05 < a / (c + d) ≤ 20. In this application, by incorporating compound A with a specific general formula composition into the electrolyte, a LiF-rich SEI film is formed on the negative electrode, which is intertwined with the organic components of the SEI film, improving the mechanical properties and elasticity of the SEI film, enhancing the compatibility with the silicon-doped negative electrode with large volume changes, and improving the volume expansion during the cycling of the silicon-doped negative electrode; in this application, by cooperating with doping the positive electrode active material and regulating the relationship between the doping elements and the content of compound A, the destruction of the structural stability of the positive electrode active material by side reaction products due to the poor oxidation resistance of compound A is inhibited, comprehensively improving the cycle stability of the battery; in addition, the doping elements also broaden the lithium ion transmission channels, can improve the transmission efficiency of lithium ions in the positive electrode active material, and improve the rate performance of the battery.

[0044] Additional aspects and advantages of the embodiments of the present application will be described and shown in part in the following description, or will be explained through the implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0046] Figure 1 It is the XRD pattern of the positive electrode active material in Example 10 of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] The following embodiments are provided to better further understand the present application. They are not limited to the best embodiments, and do not limit the content and protection scope of the present application. Any product that is the same as or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior art features falls within the protection scope of the present application.

[0048] For those steps or conditions not specified in the examples, the operations or conditions of the conventional experimental steps described in the literature in the art can be followed. For the reagents or instruments not specified for the manufacturers, they are all conventional reagent products that can be obtained through commercial purchase.

[0049] Those skilled in the art can understand that the silicon negative electrode will expand in volume during charge and discharge, which affects the cycle performance of the battery. In the prior art, introducing a film-forming additive into the electrolyte is one of the important means to improve the expansion problem of the silicon negative electrode. For example, ethylene carbonate is introduced into the electrolyte, but the SEI film formed by it is prone to cracking or peeling when the volume of the negative electrode changes, resulting in an unsatisfactory effect of suppressing the expansion of the silicon negative electrode; in addition, the additives introduced into the electrolyte are unstable at high voltages (≥4.5V) and will also affect the positive electrode material, deteriorating the cycle performance of the battery. Therefore, the present application provides the following technical solutions:

[0050] According to one aspect of the present application, a lithium-ion secondary battery is provided, including a positive electrode sheet, a negative electrode sheet and an electrolyte,

[0051] wherein, the negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a silicon-based material and a carbon-based material, and the silicon-based material includes silicon element;

[0052] The electrolyte includes compound A, and the mass percentage content of compound A is a%, 0.1≤a≤10 based on the total mass of the electrolyte;

[0053] The general formula composition of the compound A is as follows:

[0054]

[0055] wherein L is O or a connecting bond; R is selected from one of an unsubstituted or Ra-substituted C2-C6 alkyl group, an unsubstituted or Ra-substituted C2-C6 alkenyl group, an unsubstituted or Ra-substituted C2-C6 alkynyl group, an unsubstituted or Ra-substituted C2-C6 nitrogen-containing heteroaryl group, and an unsubstituted or Ra-substituted C6-C 12 aryl group, and the substituents Ra of each group are independently selected from fluorine or a C1-C6 fluoroalkyl group; R1 is selected from one of fluorine or a C1-C6 fluoroalkyl group;

[0056] The positive electrode sheet includes a positive electrode active material, and the positive electrode active material contains doping elements Mg and Al. Based on the mass of the positive electrode active material, the mass percentage content of Mg element is c%, and the mass percentage content of Al element is d%;

[0057] The relationship among a, c, and d satisfies: 0.05<a / (c + d)≤20.

[0058] As an example, the mass percentage a% of the compound A in the electrolyte can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or within the range composed of any of the above values; the value of the content relationship a / (c + d) between the doping elements Mg and Al in the positive electrode active material and the compound A in the electrolyte can be 0.05, 1, 3, 5, 7, 9, 10, 12, 14, 15, 16, 18, 20, or within the range composed of any of the above values.

[0059] In this application, by incorporating the compound A with a specific general formula composition into the electrolyte, a LiF-rich SEI film is formed on the negative electrode, which is intertwined with the organic components of the SEI film, improving the mechanical properties and elasticity of the SEI film, enhancing the compatibility with the silicon-doped negative electrode with large volume changes, and improving the cyclic swelling of the silicon-doped negative electrode; through the cooperation of doping the positive electrode active material and regulating the content relationship between the doping elements and the compound A in this application, the destruction of the structural stability of the positive electrode active material by side reaction products due to the poor oxidation resistance of the compound A is inhibited, comprehensively improving the cyclic stability of the battery; in addition, the doping elements also broaden the lithium ion transport channels, can improve the transport efficiency of lithium ions in the positive electrode active material, and improve the rate performance of the battery. Specifically, the compound A of this application has a lower LUMO energy level than carbonate solvents / additives, and the compound A has a fluorine-containing functional group, so it can form a LiF-rich SEI film on the surface of the negative electrode faster, and the lithium ions (Li +)It can form strong ion-dipole interactions with specific functional groups (such as carboxyl groups, ester groups, etc.) in the organic components of the SEI film, thereby enhancing the adhesion between LiF and the organic components, making the organic and inorganic components in the SEI film interweave with each other, constructing a strong, stable and elastic SEI film, which can better adapt to the expansion and contraction of the silicon anode and is not easily broken, improving the cyclic expansion of the anode material. However, compound A also has a relatively high HOMO energy level and is easily decomposed at a voltage of 4.5 V, thereby producing harmful substances such as HF, corroding the cathode active material, causing the dissolution of transition metals in the cathode, destroying the structural stability of the cathode active material, and rapidly decreasing the cycle life of the battery. In this application, by doping Mg and Al in the cathode active material, the unit cell volume of the cathode active material is enlarged, which helps to alleviate the volume change during charge and discharge, reduce stress, inhibit the irreversible phase change of the cathode active material, improve the structural stability of the cathode active material, reduce the active sites for the reaction between HF and the cathode active material, and improve the cyclic stability of the battery. When a, c, and d satisfy the relationship: 0.05 < a / (c + d) ≤ 20, the doping elements Mg and Al can improve the structural stability of the cathode material, reduce the reactive sites, and minimize the damage degree of the by-products decomposed from compound A at high voltage to the cathode material. When the ratio of a / (c + d) is too small, the film-forming effect of compound A on the anode weakens, the protective effect on the anode decreases, the anode expansion cannot be inhibited, and the battery cycle deteriorates; when the ratio of a / (c + d) is too large, the damage of compound A to the cathode will be greater than the protection of the doping elements to the cathode, and the cyclic stability of the battery will also deteriorate.

[0060] In some optional embodiments, c and d satisfy: 0.1 ≤ a ≤ 10, 0.05 ≤ c ≤ 0.4, 0.3 ≤ d ≤ 1. As an example, in the positive electrode active material, the mass percentage of Mg element can be 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, or within the range composed of any of the above values; the mass percentage of Al element can be 0.3%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or within the range composed of any of the above values. By specifically regulating the content of compound A and the doping elements in the positive electrode active material in this application, the cycle performance of the battery can be further improved. If the content of compound A is too low, the SEI film formed on the negative electrode surface is mainly organic components and cannot well adapt to the volume change of the negative electrode; if the content of compound A is too high, the film formed on the negative electrode surface will be too thick, increasing the interfacial impedance, and the decomposition of the excess compound A will produce more by-products, which will cause greater damage to the positive electrode. When the content of the doping elements Mg and Al is low, the structural stability and protective effect on the positive electrode material are weak, and the damage of the decomposition by-products of compound A to the positive electrode cannot be inhibited; when the content is too high, it will reduce the energy density of the battery material and cause serious lattice distortion, deteriorating the cycle performance of the battery.

[0061] In some optional embodiments, based on the total mass of the negative electrode active material, the mass percentage of silicon element is b%, and a and b satisfy: 0.5 ≤ b ≤ 50, 0.1 ≤ b / a ≤ 10. As an example, in the negative electrode active material, the mass percentage of silicon element can be 0.5%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or within the range composed of any of the above values; the ratio b / a of the silicon element in the negative electrode active material to the content of compound A in the electrolyte can be 0.1, 1, 3, 5, 7, 9, 10, or within the range composed of any of the above values. Those skilled in the art can understand that doping silicon in the battery negative electrode material can provide more lithium storage sites and effectively improve the fast charging performance of the battery. When the silicon content is low, the improvement effect on the fast charging performance is weak; but when the content is too high, due to the large volume expansion of the silicon negative electrode, the SEI film will rupture, and the electrolyte will continue to be consumed to form a new SEI film, deteriorating the cycle performance of the battery. When b / a satisfies the above relationship, the film formed by compound A can better adapt to the expansion of the silicon negative electrode, inhibit the continuous consumption of the electrolyte to form a film, and improve the cycle life of the silicon negative electrode battery.

[0062] In some optional embodiments, compound A has any of the following structures:

[0063]

[0064]

[0065] In some optional embodiments, the electrolyte further includes compound G, and compound G has a structure represented by any of the following general formulas:

[0066]

[0067] Wherein, R7 and R9 are each independently selected from C1-C10 hydrocarbon groups and C1-C10 hydrocarbon oxy groups; R8 is selected from O and C1-C10 hydrocarbon oxy groups;

[0068] Preferably, compound G has a structure represented by any of the following:

[0069]

[0070] Those skilled in the art can understand that compound A in the electrolyte is easily oxidized and decomposed at high voltages, generating acidic substances that corrode and damage other components of the battery. Although the performance of the positive electrode material has been improved through element doping of the positive electrode active material, the damage of the electrolyte to other components of the battery has not been solved. For example: (1) The acidic substances will react with the SEI film on the surface of the negative electrode, destroying its structural stability, exposing the negative electrode material directly to the electrolyte, and reacting with the electrolyte to cause performance degradation; (2) The acidic substances will damage the separator, causing the separator to degrade and age, reducing the mechanical strength and thermal stability of the separator, and increasing the risk of internal short circuit in the battery; (3) The acidic substances will corrode the battery current collector and the battery casing, resulting in problems such as a decrease in the conductivity and mechanical strength of the current collector and leakage of the battery casing. Therefore, compound G is further added to the electrolyte of the present application. Compound G has excellent electrochemical stability, can improve the overall oxidation resistance of the electrolyte, reduce the decomposition of other components in the electrolyte, especially compound A, at high voltages, and improve the internal short circuit and thermal runaway of the battery caused by the damage of the acidic substances generated by the decomposition of compound A at high voltages, further improving the cycle performance and safety performance of the electrolyte.

[0071] In some optional embodiments, based on the total mass of the electrolyte, the mass percentage content of compound G is g%, and 5 ≤ g ≤ 60; as an example, the mass percentage content of compound G in the electrolyte can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 50%, 60%, or within the range composed of any of the above values. By limiting the content of compound G in the present application, the balance between the rate performance and the cycle performance can be achieved. When the content of compound G is small, the improvement effect on the overall oxidation resistance of the electrolyte is small; when the content of compound G in the electrolyte is too large, since the viscosity of compound G is slightly larger than that of ordinary carbonates, it will increase the viscosity of the electrolyte and reduce the transport efficiency of lithium ions in the electrolyte, deteriorating the rate performance of the battery.

[0072] Preferably, a and g satisfy: 1 ≤ g / a ≤ 6. As an example, the ratio g / a of the content of compound G to compound A can be 1, 2, 3, 4, 5, 6, or within the range composed of any of the above values.

[0073] Those skilled in the art can understand that compound G mainly improves the oxidation resistance of the electrolyte, especially the high-voltage resistance of compound A. When the content of compound G is less than that of compound A, the effect of enhancing the oxidative decomposition of compound A is relatively small; since the viscosity of compound G is slightly higher than that of ordinary carbonates, when the content of compound G in the electrolyte is too high, it will significantly increase the viscosity of the electrolyte, reduce the transport efficiency of lithium ions in the electrolyte, and deteriorate the rate performance of the battery. Therefore, only when compound G and compound A satisfy the above relationship can the battery performance be optimized.

[0074] In some alternative embodiments, the electrolyte further includes a fluorinated solvent and / or an ether-bond-containing nitrile additive;

[0075] Preferably, based on the total mass of the electrolyte, the mass percentage content of the fluorinated solvent is j%, 5 ≤ j ≤ 50; more preferably, a and j satisfy: 6 ≤ j + a ≤ 40; as an example, the mass percentage content of the fluorinated solvent in the electrolyte can be 5%, 10%, 20%, 30%, 40%, 50%, or within the range composed of any of the above values; the sum j + a of the content of the fluorinated solvent and compound A can be 6%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or within the range composed of any of the above values.

[0076] Those skilled in the art can understand that the fluorinated solvent has high oxidation resistance and can form a film on the surface of the negative electrode to protect the negative electrode material. However, if the content of the fluorinated solvent in the electrolyte is too high, it is easy to decompose and generate gas at high temperatures, increasing the internal pressure of the battery and resulting in the attenuation of battery performance. In this application, the content of the fluorinated solvent is limited to the above range, which can achieve a balance between various performances. When j + a satisfies the above relationship, the overall electrolyte has high oxidation resistance and will not cause electrolyte decomposition and gas generation due to excessive fluorinated solvent, resulting in deterioration of battery safety and cycle performance. When the value is too small, it cannot provide sufficient protection for the negative electrode material, and when the value is too large, there is a risk of gas generation in the electrolyte.

[0077] Preferably, based on the total mass of the electrolyte, the mass percentage content of the ether-bond-containing nitrile additive is k%, 0.1 ≤ k ≤ 5; as an example, the mass percentage content of the ether-bond-containing nitrile additive in the electrolyte can be 0.1%, 1%, 2%, 3%, 4%, 5%, or within the range composed of any of the above values.

[0078] It should be noted that the introduction of ether bonds in nitrile additives can enhance the stability of molecules. Because the presence of oxygen atoms increases the electron cloud density between adjacent carbon atoms, making nitrile compounds with ether bonds relatively stable and not easily decomposed. At the same time, the oxygen atoms on the ether bonds carry partial negative charges and are more likely to react with transition metal elements with positive charges, preventing the dissolution of some transition metals and doped metal ions in the positive electrode active material from damaging the SEI film formed by the participation of negative electrode compound A, and further improving the cycle stability of the battery. If the content of nitrile additives containing ether bonds is too low, it cannot form good protection for the positive electrode structure. If the content is too high, it will increase the interfacial impedance of the positive electrode material, and too much nitrile additives containing ether bonds will also damage the negative electrode structure, resulting in unstable negative electrode structure due to co-insertion of solvents and deteriorating the cycle performance of the battery.

[0079] Preferably, the electrolyte further includes unsaturated nitrile compounds. Based on the total mass of the electrolyte, the mass percentage content of the unsaturated nitrile compounds is m%, where 0.1 ≤ m ≤ 3. As an example, the mass percentage content of the unsaturated nitrile compounds in the electrolyte can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or within the range composed of any of the above values.

[0080] It should be noted that the unsaturated functional groups in nitrile compounds can preferentially react with acidic by-products in the electrolyte, reducing the corrosion and damage of acidic by-products in the electrolyte to other components of the battery, and further improving the cycle stability of the battery. If the content of unsaturated nitrile compounds is too low, the effect of inhibiting further side reactions of by-products in the electrolyte on the battery is weak; if the content is too high, it will also cause an increase in the interfacial impedance of the battery positive electrode and deteriorate the cycle performance of the battery.

[0081] In some alternative embodiments, the fluorinated solvent includes at least one of ethyl difluoroacetate, fluorinated ethylene carbonate, difluoroethylene carbonate, methyltrifluoroethyl carbonate, trifluoromethyl ethylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0082] and / or, the nitrile additives containing ether bonds include 1,2,3,4,5-penta(2-cyanoethoxy)pentane (CAS: 55726-81-3), ethylene glycol bis(2-cyanoethyl) ether (CAS: 59086-77-0), diethylene glycol bis(2-cyanoethyl) ether triethylene glycol bis(2-cyanoethyl) ether tetraethylene glycol bis(2-cyanoethyl) ether ethylene glycol bis(4-cyanobutyl) ether and one of ethylene glycol bis(propionitrile) ether (CAS: 3386-87-6);

[0083] And / or, the unsaturated nitrile compound includes at least one of 1,4-dicyano-2-butene, 2-butenenitrile, fumarodinitrile, and acrylonitrile.

[0084] In some alternative embodiments, the positive electrode active material further contains a doping element Ti and / or Zr;

[0085] Preferably, based on the mass of the positive electrode active material, the mass percentage content of the Ti element is e%, and 0.02 ≤ e ≤ 0.2; as an example, the mass percentage content of the Ti element in the positive electrode active material can be 0.02%, 0.05%, 0.1%, 0.13%, 0.15%, 0.18%, 0.2%, or within the range composed of any of the above values;

[0086] Preferably, based on the mass of the positive electrode active material, the mass percentage content of the Zr element is f%, and 0.01 ≤ f ≤ 0.15. As an example, the mass percentage content of the Zr element in the positive electrode active material can be 0.01%, 0.02%, 0.05%, 0.1%, 0.13%, 0.15%, or within the range composed of any of the above values;

[0087] The positive electrode material of the present application further contains a doping element titanium and / or zirconium. Since its ionic radius is larger than that of the transition metal ions in the positive electrode active material, it will cause a change in the lattice structure of the positive electrode active material, refine the grain size, and can increase the values of the unit cell parameters a and c, expand the lattice, reduce the lithium ion transmission distance, and can provide a wider channel for lithium ion diffusion, improve the lithium ion diffusion coefficient, and improve the rate performance of the battery. If the content of Ti and Zr is too small, the impact on the battery structure is small, and the improvement effect on the battery rate performance is not obvious. However, when the content is too large, first, the energy density of the positive electrode material will be reduced, and second, it will cause a large structural distortion of the positive electrode material, affect the structural stability of the positive electrode material, and further deteriorate the cycle performance.

[0088] In some alternative embodiments, the Dv50 particle size of the positive electrode active material is h μm, and the specific surface area is i m 2 / g, where 5 ≤ h ≤ 25 and 0.05 ≤ i ≤ 0.5; as an example, the Dv50 particle size of the positive electrode active material can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, or within the range composed of any of the above values; the specific surface area of the positive electrode active material can be 0.05 m 2 / g, 0.1 m 2 / g, 0.15 m 2 / g, 0.2 m 2 / g, 0.3 m 2 / g, 0.4 m 2 / g, 0.5 m2 / g, or within the range composed of any of the above values.

[0089] It should be noted that due to element doping in the positive electrode active material of this application, the crystal grains are refined, so that the positive electrode active material has a smaller Dv50 particle size and a larger specific surface area. Therefore, the contact area between the positive electrode active material and the electrolyte is larger, which can provide more active sites, increase the utilization efficiency of the active material, and the smaller particle size is beneficial to the insertion and extraction of lithium ions, which can significantly improve the initial efficiency and rate performance of the battery. If the Dv50 particle size of the positive electrode active material is too small, the positive electrode active materials will be closely packed, and it is difficult for the electrolyte to penetrate the electrode material, which will cause the active material to be insufficiently utilized and deteriorate the battery performance; if the Dv50 is too large, the path for lithium ion insertion and extraction will become longer, the internal resistance will increase, and the rate performance of the battery will deteriorate. If the specific surface area of the positive electrode active material is too small, the rate of lithium ion insertion and extraction will also be small, affecting the rate performance of the battery; while if the specific surface area is too large, it means that the particle size of the positive electrode active material is too small, which will also deteriorate the battery performance.

[0090] And / or, in the XRD diffraction pattern of the positive electrode active material, there is a characteristic diffraction peak 1 at the diffraction angle of 15-20°, the peak intensity is H1, and there is a characteristic diffraction peak 2 at the diffraction angle of 44-47°, the peak intensity is H2, and the peak intensities satisfy: 1.7 ≤ H1 / H2 ≤ 2.1. As an example, the ratio H1 / H2 of the peak intensities of the characteristic diffraction peak 1 and the characteristic diffraction peak 2 can be 1.7, 1.8, 1.9, 2, 2.1, or within the range composed of any of the above values.

[0091] It should be noted that in this application, the characteristic diffraction peak 1 of the positive electrode active material represents the hexagonal structure of the positive electrode active material, while the characteristic diffraction peak 2 represents the sum of the hexagonal structure and the cubic structure of the positive electrode active material. The larger the value of H1 / H2, the higher the degree of order of the material unit cell, the more complete the crystal structure, the lower the degree of cation mixing, the better the structural stability of the positive electrode active material, and the better the battery cycle stability. If the ratio of the two is too small, it means that the degree of disorder in the positive electrode active material is too large, the lattice distortion is serious, the structural stability of the positive electrode active material is low, and the battery cycle stability is poor; when the ratio is too large, the degree of order of the unit cell is too high, which will cause the crystal structure to be too rigid, not conducive to the insertion and extraction of lithium ions, the strain capacity of the positive electrode active material during charge and discharge decreases, and the risk of material structure collapse increases, deteriorating the battery cycle performance.

[0092] In this application, the positive electrode active material includes but is not limited to lithium cobaltate positive electrode material.

[0093] Those skilled in the art can understand that during the charging and discharging process of the battery, lithium ions are intercalated and deintercalated back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly playing a role in preventing short circuit between the positive and negative electrodes, and at the same time allowing lithium ions to pass through.

[0094] As an example, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector. The materials, compositions, and manufacturing methods of the positive electrode plate used in the lithium ion secondary battery of the present application may include any techniques disclosed in the prior art.

[0095] As an example, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector. The materials, compositions, and manufacturing methods of the negative electrode plate used in the lithium ion secondary battery of the present application may include any techniques disclosed in the prior art.

[0096] There are no particular limitations on the materials and shapes of the separators used in the lithium ion secondary battery of the present application, and they may include any techniques disclosed in the prior art.

[0097] The electrolytes used in the lithium ion secondary battery of the present application may include any techniques disclosed in the prior art.

[0098] As an example, the organic solvents in the electrolyte of the present application are selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, ethyl butyrate, methyl propionate, ethyl acetate, methyl acetate, n-propyl acetate, n-butyl acetate, isopropyl propionate, isopropyl acetate, vinylene carbonate, vinyl ethylene carbonate, etc. The mass percentage content of the organic solvent in the electrolyte is below 60%.

[0099] The lithium salts may be selected from lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bisfluorosulfonimide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium difluorodioxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methyl, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethanesulfonate, lithium hexafluorozirconate (Li2ZrF6), etc. The mass percentage content of the lithium salt in the electrolyte may be 10 - 30%.

[0100] The electrolyte of the present application may further include at least one of phosphorus-containing additives, sulfur-containing additives, conventional nitrile additives, etc.

[0101] As an example, the sulfur-containing additive is selected from at least one of 1,3-propane sultone, propene sultone, ethylene sulfate, vinyl methyl sulfate, propylene sulfate, ethylene sulfite, butane sultone, methylene methanedisulfonate, bis(ethylene sulfate), etc., and its mass percentage content in the electrolyte may be 0.1-5%.

[0102] The phosphorus-containing additive is selected from at least one of tetraphenylphosphonium amide, ethoxypentafluorocyclotriphosphazene, triallyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, etc., and its mass percentage content in the electrolyte may be 0.1-5%.

[0103] The conventional nitrile additive is selected from at least one of succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, glutaronitrile, malononitrile, isobutyronitrile, butyronitrile, etc., and its mass percentage content in the electrolyte may be 0.1-6%.

[0104] In the present application, the preparation method of the lithium-ion secondary battery is conventional in the art. As an example, the preparation method may include:

[0105] Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, ensure that the separator is between the positive and negative electrode sheets to play an isolation role, and then obtain an un-injected bare battery cell by winding; place the bare battery cell in an outer packaging foil, inject the prepared electrolyte into the dried bare battery cell, and obtain the required lithium-ion secondary battery through processes such as vacuum packaging, standing, formation, shaping, sorting, etc.

[0106] According to another aspect of the present application, there is provided an electrical device including the above-mentioned lithium-ion secondary battery.

[0107] The lithium-ion secondary battery provided by the present application can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be but is not limited to mobile devices (such as mobile phones, laptop 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, satellites, energy storage systems, etc.

[0108] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0109] Example 1

[0110] This embodiment provides a lithium-ion secondary battery, and its specific composition and preparation method are as follows:

[0111] 1) Preparation of the positive electrode sheet

[0112] Mix lithium cobaltate positive electrode active material containing doping elements (where the doping amount of Al is 0.7%, the doping amount of Mg is 0.2%, the Dv50 particle size is 15 μm, the specific surface area is 0.2 m 2 / g, and H1 / H2 is 1.8), polyvinylidene fluoride (PVDF), SP (super P), and carbon nanotubes (CNT) according to a mass ratio of 96:2:1.5:0.5, add N-methylpyrrolidone (NMP), and stir under a vacuum mixer until the mixed system becomes a homogeneous and flowing positive electrode active paste; uniformly coat the positive electrode active paste on both surfaces of the aluminum foil; dry the coated aluminum foil, and then roll and slit it to obtain the required positive electrode sheet, and the areal density of the positive electrode sheet is 0.015 g / cm 2 , and the compaction is 4.2 g / cm 3 .

[0113] 2) Preparation of the negative electrode sheet

[0114] Mix negative electrode active materials artificial graphite, silicon-carbon composite material (silicon content is 50%), sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) according to a mass ratio of 54.5:40:2.5:1.5:1:0.5, add deionized water, and obtain a negative electrode active paste under a vacuum mixer; uniformly coat the negative electrode active paste on both surfaces of the copper foil; air-dry the coated copper foil at room temperature, then transfer it to an 80°C oven and dry for 10 h, and then obtain the negative electrode sheet after cold pressing and slitting. The areal density of the negative electrode sheet is 0.006 g / cm 2 , and the compaction is 1.72 g / cm 3 .

[0115] 3) Preparation of the electrolyte

[0116] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), mix ethylene carbonate (EC) / propylene carbonate (PC) / propyl propionate (PP) / ethyl propionate (EP) evenly according to a mass ratio of 10:10:60:20. Then add compound A (the compound shown in formula 1) based on 6% of the total mass of the electrolyte and mix evenly. Then quickly add fully dried LiPF6 based on 16% of the total mass of the electrolyte, dissolve it, add methyl trifluoroacetate, a fluorinated solvent, based on 25% of the total mass of the electrolyte, and then add succinonitrile based on 3% of the total mass of the electrolyte. After stirring evenly and passing the moisture and free acid detection, the required electrolyte is obtained.

[0117] 4) Preparation of Lithium-Ion Battery

[0118] After laminating the positive electrode sheet in step 1), the negative electrode sheet in step 2), and a polypropylene separator with a thickness of 8 μm in the order of positive electrode sheet, separator, and negative electrode sheet, winding is then carried out to obtain an electrode core; the electrode core is placed in an outer packaging aluminum foil with an aluminum foil PP layer thickness of 70 μm, and the electrolyte in step 3) is injected into the outer packaging. After processes such as vacuum packaging, standing, formation, shaping, and sorting, a lithium-ion battery with a capacity of 6 Ah is obtained. The charge and discharge range of the battery of the present invention is 3.0 - 4.55V.

[0119] Example 2

[0120] This example provides a lithium-ion secondary battery. Compared with Example 1, the only difference is that: 0.07% of Ti element is also doped in the positive electrode active material.

[0121] Example 3

[0122] This example provides a lithium-ion secondary battery. Compared with Example 1, the only difference is that: 0.05% of Zr element is also doped in the positive electrode active material.

[0123] Example 4

[0124] This example provides a lithium-ion secondary battery. Compared with Example 1, the only difference is that: 0.07% of Ti element and 0.05% of Zr element are also doped in the positive electrode active material.

[0125] Example 5

[0126] This example provides a lithium-ion secondary battery. Compared with Example 1, the only difference is that: the electrolyte also includes 20% by mass of Compound G (the compound shown in Formula a).

[0127] Example 6

[0128] This example provides a lithium-ion secondary battery. Compared with Example 1, the only difference is that: the electrolyte also includes 19% by mass of Compound G (the compound shown in Formula a).

[0129] Example 7

[0130] This example provides a lithium-ion secondary battery. Compared with Example 1, the only difference is that: 25% of the fluorinated solvent methyl trifluoroacetate is replaced by 15% of fluorinated ethylene carbonate and 10% of ethyl difluoroacetate.

[0131] Example 8

[0132] This embodiment provides a lithium-ion secondary battery. Compared with Embodiment 1, the only difference is that 1,2,3,4,5-penta(2-cyanoethoxy)pentane of equal mass is used to replace succinonitrile.

[0133] Example 9

[0134] This embodiment provides a lithium-ion secondary battery. Compared with Embodiment 1, the only difference is that 1,4-dicyano-2-butene of equal mass is used to replace succinonitrile.

[0135] Example 10

[0136] This embodiment provides a lithium-ion secondary battery. Compared with Embodiment 1, the difference lies in the different compositions of the lithium cobalt oxide cathode active material and the electrolyte. Among them, the doping amount of Al in the lithium cobalt oxide cathode active material is 0.7%, the doping amount of Mg is 0.2%, the doping amount of Ti is 0.07%, the doping amount of Zr is 0.05%, the Dv50 particle size is 15 μm, and the specific surface area is 0.2 m 2 / g. Its XRD pattern is as Figure 1 shown, and H1 / H2 is calculated according to the intensity of the characteristic diffraction peaks;

[0137] The specific composition and preparation method of the electrolyte are as follows:

[0138] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC) / propylene carbonate (PC) / propyl propionate (PP) / ethyl propionate (EP) are mixed evenly according to a mass ratio of 10:10:60:20. Then, 6% of Compound A (the compound shown in Formula 1) based on the total mass of the electrolyte and 20% of Compound G (the compound shown in Formula a) based on the total mass of the electrolyte are added thereto and mixed evenly. Then, 16% of fully dried LiPF6 based on the total mass of the electrolyte is quickly added. After dissolution, 25% of the fluorinated solvent ethyl difluoroacetate based on the total mass of the electrolyte is added. Subsequently, 2% of 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 1% of 1,4-dicyano-2-butene based on the total mass of the electrolyte are added. After stirring evenly and passing the water and free acid detection, the required electrolyte is obtained.

[0139] Examples 11 - 34

[0140] Compared with Example 10, Examples 11 - 34 are only different in the composition of the electrolyte and / or the anode active material. See the following table for details.

[0141] Table 1

[0142]

[0143] Examples 35 - 45

[0144] Examples 35 - 45 are different from Example 10 only in the composition of the positive electrode active material, as shown in the following table.

[0145] Table 2

[0146]

[0147] Comparative Example 1

[0148] Comparative Example 1 is different from Example 1 in that the electrolyte does not include Compound A.

[0149] Comparative Example 2

[0150] Comparative Example 2 is different from Example 1 in that the mass percentage of Compound A in the electrolyte is 0.05%, the doping amount of Mg in the positive electrode active material is 1%, the doping amount of Al is 1%, and a / (c + d) = 0.025.

[0151] Comparative Example 3

[0152] Comparative Example 3 is different from Example 1 in that the mass percentage of Compound A in the electrolyte is 10%, the doping amount of Mg in the positive electrode active material is 0.3%, the doping amount of Al is 0.05%, and a / (c + d) = 28.

[0153] Comparative Example 4

[0154] Comparative Example 4 is different from Example 1 only in that the positive electrode active material does not contain doping elements.

[0155] Comparative Example 5

[0156] Comparative Example 5 is different from Example 1 only in that the structure shown in the following formula is used to replace Compound A in Formula 1 of the electrolyte.

[0157]

[0158] Comparative Example 6

[0159] Comparative Example 6 is different from Example 1 only in that p - difluorobenzene is used to replace Compound A in Formula 1 of the electrolyte.

[0160] Comparative Example 7

[0161] Comparative Example 7 is different from Example 1 in that the mass percentage of Compound A in the electrolyte is 15%.

[0162] Test Example

[0163] Perform performance tests on the lithium - ion secondary batteries provided in each example and comparative example. The specific test methods are as follows:

[0164] (1) 2C cycle test

[0165] Discharge the batteries obtained in each example and comparative example at 25 °C with a current of 0.5C until the voltage reaches 3.0V. Then charge at a constant current of 3C until the voltage reaches 4.55V, then charge at a constant voltage of 4.55V until the current reaches 0.05C, let it stand for 5 minutes, and then discharge at a constant current of 3C until the voltage reaches 3.0V. This is one charge-discharge cycle (i.e., the first week). The discharge capacity of the first week is measured as x mAh, the full charge thickness is d1 mm, the discharge capacity of the Nth week is measured as y mAh, and the full charge thickness is d2 mm; divide the capacity of the Nth week by the capacity of the first week to obtain the cycle capacity retention rate R = y / x × 100% of the Nth week, and the thickness change rate is D = (d2 - d1) / d1 × 100%. Record the capacity retention rate of the battery and the thickness change rate of the battery when cycling for 500 weeks.

[0166] (2) 5C discharge performance test (rate performance test)

[0167] Discharge the batteries obtained in each example and comparative example at 25 °C with a current of 0.5C until the voltage reaches 3.0V. Then charge at a constant current of 5C until the voltage reaches 4.55V, then charge at a constant voltage of 4.55V until the current reaches 0.05C, let it stand for 5 minutes, and then discharge at a constant current of 5C until the voltage reaches 3.0V. This is one charge-discharge cycle. Record the discharge capacities at the 1st week and the 5th week of the cycle, and calculate the discharge capacity retention rate of the battery.

[0168] (3) Safety performance

[0169] At room temperature, charge the batteries obtained in each example and comparative example at a constant current of 1C until the voltage reaches 4.55V, let it stand for 60 minutes, check the appearance and take pictures. Then heat it at a rate of 3 °C / min ± 2 °C / min to 130 °C ± 2 °C and hold for 60 minutes. Observe the samples. If there is no leakage, no smoking, no fire, and no explosion, it is recorded as passing the test. Test 10 samples for each example or comparative example, and record the number of batteries n that pass the hot box performance test, which is recorded as n / 10.

[0170] The specific test results are shown in the following table.

[0171] Table 3

[0172]

[0173]

[0174] From the data in the above table, it can be seen that using compound A in the electrolyte can effectively inhibit the cyclic swelling of the battery and greatly improve the battery safety performance. Additionally, through the element doping of the cathode material and the regulation of the relationship between the doping element and the content of compound A, the destruction of the structural stability of the cathode active material caused by the poor oxidation resistance of the electrolyte and the side reaction products is inhibited, comprehensively improving the cycle stability and rate performance of the battery. Through the regulation of the composition and parameters of the cathode active material, the silicon doping of the anode material, and the synergistic effect of the additives and solvents in the electrolyte, the cycle, rate, and safety performance of the battery at high voltage are further optimized. From the comparison between Examples 10 - 13 and Examples 29 - 24, when L is O and R is an unsubstituted or Ra-substituted C6-C 12 aryl group in the structure of compound A, the cycle, rate, and safety performance of the battery at high voltage can be further optimized.

[0175] Obviously, the above examples are merely illustrations for clear explanation and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A lithium ion secondary battery, characterized in that: Including positive electrode, negative electrode and electrolyte, Wherein, the negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprises a silicon-based material and a carbon-based material, and the silicon-based material comprises silicon element; The electrolyte includes compound A, and the mass percentage of compound A is a%, 0.1≤a≤10, based on the total mass of the electrolyte; The general formula of the compound A is as follows: Wherein, L is O or a connecting bond; R is selected from C1-C6 alkyl which is unsubstituted or substituted by Ra, C2-C6 alkenyl which is unsubstituted or substituted by Ra, C2-C6 alkynyl which is unsubstituted or substituted by Ra, C2-C6 nitrogen-containing heteroaryl which is unsubstituted or substituted by Ra, C6-C 12 One of the aryl groups, the substituents Ra of each group are independently selected from fluorine or C1-C6 fluoroalkyl; R1 is selected from one of fluorine or C1-C6 fluoroalkyl; The positive electrode sheet comprises a positive electrode active material, wherein the positive electrode active material contains doping elements Mg and Al, and based on the mass of the positive electrode active material, the mass percentage of the Mg element is c%, and the mass percentage of the Al element is d%; The a, c, d satisfy the following: 0.05<a / (c+d)≤20.

2. The lithium ion secondary battery according to claim 1, characterized in that: The c and d satisfy: 0.05≤c≤0.4, 0.3≤d≤1; And / or, based on the total mass of the negative electrode active material, the mass percentage of silicon element is b%, and a and b satisfy: 0.5≤b≤50, 0.1≤b / a≤10.

3. The lithium ion secondary battery according to claim 1, characterized in that: The compound A has any of the following structures:

4. The lithium-ion secondary battery according to claim 1, characterized in that: The electrolyte also includes a compound G, and the compound G has a structure shown in any of the following general formulas: Wherein, R7 and R9 are independently selected from C1-C10 hydrocarbon groups and C1-C10 hydrocarbon oxy groups; R8 is selected from O and C1-C10 hydrocarbon oxy groups; Preferably, the compound G has any of the following structures:

5. The lithium ion secondary battery according to claim 4, characterized in that: Based on the total mass of the electrolyte, the mass percentage of the compound G is g%, 5≤g≤60; Preferably, a and g satisfy: 1≤g / a≤6.

6. The lithium ion secondary battery according to claim 1, characterized in that: The electrolyte also includes a fluorinated solvent and / or an ether bond-containing nitrile additive; Preferably, based on the total mass of the electrolyte, the mass percentage of the fluorinated solvent is j%, 5≤j≤50; further preferably, a, j satisfy: 6≤j+a≤40; Preferably, based on the total mass of the electrolyte, the mass percentage of the ether bond nitrile additive is k%, 0.1≤k≤5; Preferably, the electrolyte further comprises an unsaturated nitrile compound, and the mass percentage of the unsaturated nitrile compound is m%, based on the total mass of the electrolyte, and 0.1≤m≤3.

7. The lithium ion secondary battery according to claim 6, characterized in that: The fluorinated solvent includes at least one of ethyl difluoroacetate, fluoroethylene carbonate, difluoroethylene carbonate, methyl trifluoroethyl carbonate, trifluoromethylethylene carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and methyl trifluoroacetate; And / or, the ether bond-containing nitrile additive includes one of 1,2,3,4,5-penta(2-cyanoethoxy)pentane, ethylene glycol di(2-cyanoethyl) ether, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, ethylene glycol di(4-cyanobutyl) ether, and ethylene glycol bis(propionitrile) ether; And / or, the unsaturated nitrile compound includes at least one of 1,4-dicyano-2-butene, 2-butenenitrile, butylene dinitrile and acrylonitrile.

8. The lithium ion secondary battery according to any one of claims 1 to 7, characterized in that: The positive electrode active material also contains doping elements Ti and / or Zr; Preferably, based on the mass of the positive electrode active material, the mass percentage of the Ti element is e%, and 0.02≤e≤0.2; Preferably, based on the mass of the positive electrode active material, the mass percentage of the Zr element is f%, and 0.01≤f≤0.

15.

9. The lithium ion secondary battery according to claim 1, characterized in that: The Dv50 particle size of the positive electrode active material is h μm, and the specific surface area is im 2 / g, where 5≤h≤25, 0.05≤i≤0.5; And / or, in the XRD spectrum of the positive electrode active material, there is a characteristic diffraction peak 1 at a diffraction angle of 15-20°, with a peak intensity of H1, and there is a characteristic diffraction peak 2 at a diffraction angle of 44-47°, with a peak intensity of H2, and the peak intensity satisfies: 1.7≤H1 / H2≤2.

1.

10. An electrical device, characterized in that: A lithium ion secondary battery comprising any one of claims 1 to 9.

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