Electrolyte and secondary battery

Abstract

The invention discloses an electrolyte and a secondary battery, wherein the electrolyte comprises an organic solvent, a lithium salt and an additive; wherein the additive comprises an additive A, wherein the additive A comprises a mixed additive generated by the reaction of an anhydrous acidic additive and an organic base; the anhydrous acidic additive comprises at least one of sulfur dioxide, carbon dioxide and sulfur trioxide; the organic base comprises at least one of (4-(dimethylamino)phenylvinyl)pyridine, N,N-diethylpropargylamine, dimethylthioformamide, N,N-dimethylbenzylamine and N,N-dimethylbenzamide, and the pH value of the additive A is neutral. Compared with the prior art, the additive in the electrolyte of the invention can promote the formation of a good SEI film, improve the cycle performance and safety performance of the battery at different ambient temperatures, and reduce the cost of purchasing additives for the electrolyte.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to an electrolyte and a secondary battery. Background Art

[0002] With the rapid development of society, electronic products have fully penetrated into people's daily lives and are widely used in various scenarios, such as mobile phones, tablets, laptops, wireless headphones, electric bicycles, and electric new energy vehicles. As one of the core components of these electronic products, the performance of the battery directly affects the product's user experience and market competitiveness. Consumers' demand for batteries is also increasing. Not only do they require lightweight batteries to adapt to the design of portable products, but they also put forward higher requirements for their safety, durability, and long life. In this context, lithium-ion batteries are widely used in various electronic products and electric vehicles due to their high operating voltage, high energy density, long cycle life, good sealing, and environmental friendliness. It has become the mainstream energy storage battery technology solution in the current market.

[0003] However, lithium-ion batteries also face many technical bottlenecks in actual use. For example, in low-temperature environments, lithium-ion batteries will experience significant capacity attenuation, increased internal resistance, and decreased discharge efficiency, which makes them unable to meet normal use requirements in cold climates. In high-temperature environments, batteries are prone to safety hazards such as electrolyte decomposition, gas expansion, and even fire and explosion, which seriously threaten the safety of product use. Therefore, how to make lithium-ion batteries work stably in both high and low temperature environments has become one of the technical problems that the industry is concerned about.

[0004] As one of the core materials of lithium-ion batteries, the performance of electrolyte directly determines the discharge efficiency, cycle life and safety of the battery. The electrolyte is mainly composed of solvents, electrolyte salts and a variety of functional additives. Its function is to provide a channel for the migration of lithium ions between the positive and negative electrodes and maintain electrochemical stability. The existing electrolyte formula is stable at room temperature, but it is often difficult to take into account ionic conductivity, interface stability and chemical stability at the same time under high and low temperature environments. For example, under low temperature conditions, the viscosity of the electrolyte increases, and the resistance to lithium ion migration becomes larger, resulting in a significant decrease in the capacity and power output of the battery; under high temperature conditions, the electrolyte is prone to oxidative decomposition or side reactions with the positive and negative electrode materials, resulting in gas generation and causing safety hazards. Therefore, the existing electrolyte formula has obvious deficiencies in dealing with extreme temperature changes. Summary of the invention

[0005] The purpose of the present invention is to provide an electrolyte to improve the problem of performance degradation of current lithium-ion batteries at high and low temperatures.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] An electrolyte comprising: an organic solvent, a lithium salt and an additive;

[0008] The additive includes additive A, and the additive A includes a mixed additive generated by the reaction of an anhydrous acidic additive and an organic base;

[0009] The anhydrous acidic additive includes at least one of sulfur dioxide, carbon dioxide, and sulfur trioxide;

[0010] The organic base includes at least one of (4-(dimethylamino)phenylvinyl)pyridine, N,N-diethylpropargylamine, dimethylthioformamide, NN-dimethylbenzylamine, and N,N-dimethylbenzamide,

[0011] The pH value of the additive A is neutral. Preferably, the mass of the additive A accounts for 0.1% to 10% of the total mass of the electrolyte.

[0012] Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bistrifluoromethanesulfonyl imide and lithium bisfluorosulfonyl imide, and the concentration of the lithium salt in the electrolyte is 0.8 to 1.5 mol / L.

[0013] Preferably, the organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, dipropyl carbonate, diphenyl carbonate, dibutyl carbonate, butylene carbonate, methylpropyl carbonate, methyl acetate, ethyl acetate, isobutyl acetate, propyl acetate, butyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate, methenyl carbonate, ethyl 3-ethoxypropionate, and fluorobenzene.

[0014] Preferably, the additive further includes a carbonate additive, and the carbonate additive includes at least one of vinylene carbonate, vinyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate and derivatives thereof.

[0015] Preferably, the mass of the carbonate additive accounts for 0.02% to 5% of the total mass of the electrolyte.

[0016] Preferably, the additive further includes additive B, and the additive B includes at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, vinyl sulfate, vinyl sulfite, 4-methyl-vinyl sulfate, 4-fluorovinyl sulfate, 4-n-propyl vinyl sulfate, 4,4'-bisulfate, 4-vinyl-vinyl sulfate, 4-ethyl vinyl sulfate, 4,5-difluorovinyl sulfate, 1,3,6,8-tetraoxy-2,7-disulfide-spiro[4.4]nonane-2,2,7,7-tetraoxide, glyoxal disulfate, 4,5-dimethyl vinyl sulfate, 1,2-cyclopentadiene sulfate, vinyl cyanide sulfate, di(sulfoglyceryl) sulfate, glyceryl sulfate, and glyceryl sulfate methyl ether.

[0017] Preferably, the mass of the additive B added accounts for 0.02% to 5% of the mass of the electrolyte.

[0018] Preferably, the additive further includes additive C, which is a nitrile compound, and the nitrile compound includes at least one of succinonitrile, adiponitrile, glutaronitrile, suberonitrile, sebaconitrile, 1,3,6-hexanetricarboxylic acid nitrile, 1,3,5-pentanetricarboxylic acid nitrile, p-fluorobenzonitrile / p-methylbenzonitrile, 2-fluoroadiponitrile, 2,2-difluorosuccinonitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,2-bis(cyanoethoxy)ethane, and 1,2,3-tris(cyanoethoxy)propane, and the mass of the additive C added accounts for 0.02% to 5% of the mass of the electrolyte.

[0019] A second object of the present invention is to provide a secondary battery, comprising the electrolyte described in any one of the above items, a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet.

[0020] The beneficial effects of the present invention are as follows: the present invention adds additive A to the electrolyte, and additive A includes a mixed additive generated by the reaction of sulfur dioxide and an organic base; it is beneficial to the elasticity and stability of the SEI film structure formed during the first charge and discharge of the battery, and cooperates with other components in the electrolyte to make the SEI film more diverse, improve the electrical cycle performance and safety performance of the battery at different ambient temperatures, and reduce the cost of purchasing additives for the electrolyte. DETAILED DESCRIPTION

[0021] In order to make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] According to a first aspect of the present invention, the present invention provides an electrolyte solution, comprising: an organic solvent, a lithium salt and an additive;

[0023] The additive includes additive A, and the additive A includes a mixed additive generated by the reaction of an anhydrous acidic additive and an organic base;

[0024] The anhydrous acidic additive includes at least one of sulfur dioxide, carbon dioxide, and sulfur trioxide;

[0025] The organic base includes at least one of (4-(dimethylamino)phenylvinyl)pyridine, N,N-diethylpropargylamine, dimethylthioformamide, NN-dimethylbenzylamine, and N,N-dimethylbenzamide,

[0026] The pH value of the additive A is neutral. The anhydrous acidic additive in the present invention can form an excellent SEI film on the surface of the carbon negative electrode, which has chemical stability, solvent insolubility, and good Li + Conductivity, reduce the side reactions caused by direct contact between the electrolyte and the negative electrode active material, thereby inhibiting the solvent from embedding reduction performance on the negative electrode, preventing electrode peeling, reducing the interface impedance between the positive and negative electrodes, and increasing the battery capacity, thereby improving the high and low temperature performance of the battery.

[0027] However, the anhydrous acidic additive is directly dissolved in the electrolyte, which inevitably leads to an increase in the acidity of the electrolyte. The electrolyte with too high acidity has a significant negative impact on the performance and safety of the battery, causing the battery to self-discharge faster, and the acidic substances in the electrolyte react with the active substances inside the battery, resulting in battery power loss; in addition, the electrolyte with too high acidity may corrode the electrode materials inside the battery and damage the internal structure of the battery; and the electrolyte with too high acidity may accelerate the decomposition of the electrolyte and the additive, resulting in the thickening of the SEI film on the negative electrode surface, the increase of the internal resistance of the battery, and the impact on the cycle life of the battery. Therefore, the addition of anhydrous acidic additives to the electrolyte needs to be controlled. The present invention neutralizes the excessive acidity of the anhydrous acidic additive by adding an organic base to control the acidity of the electrolyte. The anhydrous acidic additive in the present invention is preferably sulfur dioxide.

[0028] The additives and additive combinations used in the present invention, combined with lithium salts, solvents, and other additives in the electrolyte, achieve the storage performance, cycle performance, and rate performance of lithium-ion batteries in a wide range of high and low temperatures and at high voltages, while improving the safety performance and service life of lithium-ion batteries.

[0029] In an embodiment of the present invention, the mass of additive A accounts for 0.1% to 10% of the total mass of the electrolyte, and can specifically be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and may include but are not limited to the values ​​listed above.

[0030] In an embodiment of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bistrifluoromethanesulfonyl imide and lithium bisfluorosulfonyl imide, and the concentration of the lithium salt in the electrolyte is 0.8 to 1.5 mol / L.

[0031] In an embodiment of the present invention, the organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, dipropyl carbonate, diphenyl carbonate, dibutyl carbonate, butylene carbonate, methyl propyl carbonate, methyl acetate, ethyl acetate, isobutyl acetate, propyl acetate, butyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate, methenyl carbonate, ethyl 3-ethoxypropionate, and fluorobenzene. The organic solvent in the present invention is a non-aqueous organic solvent.

[0032] In an embodiment of the present invention, the additive further includes a carbonate additive, and the carbonate additive includes at least one of vinylene carbonate, vinyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate and derivatives thereof.

[0033] In the embodiment of the present invention, the mass of the carbonate additive accounts for 0.02% to 5% of the total mass of the electrolyte.

[0034] In an embodiment of the present invention, the additive further includes additive B, and additive B includes at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, vinyl sulfate, vinyl sulfite, 4-methyl-vinyl sulfate, 4-fluorovinyl sulfate, 4-n-propyl vinyl sulfate, 4,4'-bisulfate, 4-vinyl-vinyl sulfate, 4-ethyl vinyl sulfate, 4,5-difluorovinyl sulfate, 1,3,6,8-tetraoxy-2,7-disulfide-spiro[4.4]nonane-2,2,7,7-tetraoxide, glyoxal disulfate, 4,5-dimethyl vinyl sulfate, 1,2-cyclopentadiene sulfate, vinyl cyanide sulfate, di(sulfoglyceryl) sulfate, glyceryl sulfate, and glyceryl sulfate methyl ether.

[0035] The main functions of ester additives in electrolytes are to improve SEI film performance, enhance low temperature and high voltage performance of electrolytes, reduce interfacial impedance, enhance the activity of electrode materials, and reduce harmful substances, thereby improving the overall performance and life of the battery.

[0036] In the embodiment of the present invention, the mass of additive B added accounts for 0.02% to 5% of the mass of the electrolyte.

[0037] In an embodiment of the present invention, the additive further includes additive C, which is a nitrile compound, and the nitrile compound includes at least one of succinonitrile, adiponitrile, glutaronitrile, suberonitrile, sebaconitrile, 1,3,6-hexanetricarboxylic acid nitrile, 1,3,5-pentanetricarboxylic acid nitrile, p-fluorobenzonitrile / p-methylbenzonitrile, 2-fluoroadiponitrile, 2,2-difluorosuccinonitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,2-bis(cyanoethoxy)ethane, and 1,2,3-tris(cyanoethoxy)propane.

[0038] In the electrolyte, nitrile compounds are not easily oxidized due to the high bond energy of the C≡N bond in the cyano group, and have good stability on the positive electrode and strong oxidation resistance. At the same time, the cyano group has a strong coordination ability and can combine with the active sites on the electrode surface to mask these active ions on the positive electrode surface and reduce the decomposition effect of the electrode on the electrolyte; in addition, the cyano group in the nitrile compound has the ability to inhibit the generation of acid, can react with HF in the electrolyte, and slowly react with water, which can improve the voltage resistance and the ability to complex with metal ions.

[0039] The compound having 2 to 4 cyano groups in the structural formula in the non-aqueous electrolyte has two or more cyano groups, which brings about complexation, adsorption and other strong interactions with the transition metal contained in the positive electrode active material, thereby stabilizing the positive electrode in the charged state. As a result, the reaction between the positive electrode and the non-aqueous electrolyte during high-temperature storage after charging is suppressed, and the generation of gas and the deterioration of battery characteristics can be suppressed.

[0040] According to the second aspect of the present invention, the present invention further provides a secondary battery, comprising an electrolyte, a positive electrode sheet, a negative electrode sheet and a separator between the positive electrode sheet and the negative electrode sheet, wherein the electrolyte is the above-mentioned electrolyte.

[0041] The present invention also provides a method for preparing the above-mentioned lithium-ion battery, the steps of which include: stacking the negative electrode sheet, the separator, and the positive electrode sheet in order, or winding them to obtain a battery core, placing the battery core in a packaging shell, adding an electrolyte and packaging it, and obtaining a lithium-ion battery after processes such as formation, hot and cold pressing, and capacity separation.

[0042] Among them, the positive electrode sheet can be made by the following method: the positive electrode active material, the conductive agent, the binder and N-methylpyrrolidone are mixed evenly to obtain a positive electrode slurry. Then the positive electrode slurry is coated on the positive electrode collector, and the positive electrode sheet is obtained after drying and rolling. The positive electrode active material is at least one of a transition metal oxide and a polyanionic compound; preferably lithium cobalt oxide; the conductive agent is at least one of carbon nanotubes, acetylene black, Ketjen black, carbon black, graphene and carbon nanofibers, preferably carbon black; the binder is at least one of polyvinylidene fluoride, polyacrylic acid, polyimide, sodium polyacrylate, styrene-butadiene rubber, sodium alginate and nitrile rubber, preferably polyvinylidene fluoride; the positive electrode collector can be a carbon-coated foil, a metal foil or a composite foil, preferably aluminum foil.

[0043] Among them, the negative electrode sheet can be made by the following method: firstly, the negative electrode active material hard carbon and silicon carbon are mixed in a weight ratio of 3:1, and then the active material, conductive agent, thickener and binder are mixed in a weight ratio of 97:1.1:0.6:1.3 in an appropriate amount of deionized water to obtain a negative electrode slurry; then the negative electrode slurry is coated on the negative electrode collector, and the negative electrode sheet is obtained after drying and rolling. The binder is at least one of polyaniline, polyurethane, polyvinyl alcohol, polyacrylic acid, sodium polyacrylate, sodium alginate, and styrene-butadiene rubber, preferably a mixture of polyaniline and polyurethane; the conductive agent is at least one of acetylene black, carbon black, Ketjen black, graphene, carbon nanotubes and carbon nanofibers, preferably carbon nanotubes; the thickener is at least one of sodium carboxymethyl cellulose, alginic acid, and starch, preferably sodium carboxymethyl cellulose; the negative electrode collector can be a carbon-coated foil, a metal foil or a composite foil, preferably a copper foil.

[0044] The diaphragm may be a single-layer or multi-layer diaphragm of at least one of glass fiber, polypropylene, polyethylene, non-woven fabric and polyvinylidene fluoride.

[0045] The present invention will be further described below by means of specific examples.

[0046] Comparative Example 1:

[0047] 1. The lithium salt LiPF6 was dissolved in a mixed solvent of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate (mass ratio 3 / 3 / 5), 5% of propylene carbonate, 1.5% of the total mass of vinylene carbonate, 3% of fluoroethylene carbonate, 2% of 1,3-propane sultone, and 0.5% of the total mass of lithium difluorophosphate, wherein the LiPF6 concentration was 1.25 mol / L, to obtain a comparative electrolyte.

[0048] 2. Select batteries with a nominal capacity of 1500mAh and no electrolyte injection. Select batteries from the same batch that have no electrolyte injection. Bake them at 80±5℃ in a vacuum oven. Replace the atmosphere with nitrogen every 2 hours. Bake for 24 hours. Then cool them to room temperature in a vacuum and inject the electrolyte.

[0049] 3. After the electrolyte is injected, the battery is left to stand at room temperature for 24 hours under the protection of anhydrous nitrogen seal.

[0050] 4. Perform pre-charge formation operation and battery cycle operation test.

[0051] Comparative Example 2

[0052] The difference from Comparative Example 1 is that SO2 is introduced in step 1 to saturation.

[0053] Example 1-42

[0054] The difference from Comparative Example 2 is that, based on the mass of the electrolyte, the additives of the present invention and their combinations are added in different proportions, as shown in Table 1 for details.

[0055] Additives and their combination additives are prepared according to the formula and purified, and the moisture content is not more than 100ppm. Additives and their combinations in different proportions are first dissolved and added to ethyl methyl carbonate for compounding, and then SO2 gas is introduced for acid-base reaction to form a uniform compound. The above-mentioned additive solvent mixture is heated and vacuumed to extract excess SO2 gas, and the components and pH value of the test components and mixed solvents are neutral to obtain mixed additives. The sulfur dioxide gas content is counted as "dissolved" in Table 1 below.

[0056] Table 1

[0057]

[0058]

[0059] The following performance tests were performed on the batteries prepared in the examples and comparative examples:

[0060] Cycle performance test: Shenzhen Xinwei battery tester is used to test the cycle performance of the battery.

[0061] Comparative Example 1 and Examples 1-43 were charged at 1C rate, with a cut-off voltage of 4.2V and a cut-off current of 0.05C, and then discharged at 1C current rate to 2.8V, and cycled sequentially, and the discharge capacity retention rate was counted for 500 times. The data at -10°C and 45°C were compared, and the statistics are shown in Table 2 below.

[0062] Table 2

[0063]

[0064]

[0065] The charge and discharge cycle performance test data of the batteries of the embodiments and comparative examples in the table show that after the electrolyte prepared by the present invention is injected into a lithium ion battery, the cycle life of charge and discharge at a rate of 1C at 2.8-4.2V is significantly better than that of the battery prepared by the comparative example non-aqueous electrolyte.

[0066] In the examples of the present invention, sulfur dioxide and an organic base are added. Compared with the comparative example, the secondary battery can exhibit a good capacity retention rate at both low and high temperatures.

[0067] In summary, the electrolyte system of the present invention adds additive A to the electrolyte, and additive A includes a mixed additive generated by the reaction of an anhydrous acidic additive and an organic base; it is beneficial to the elasticity and stability of the SEI film structure formed by the first charge and discharge of the battery, and cooperates with other components in the electrolyte to make the SEI film more diverse, thereby improving the electrical cycle performance and safety performance of the battery at different ambient temperatures.

[0068] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can also change and modify the above embodiment. Therefore, the present invention is not limited to the above specific embodiment, and any obvious improvement, replacement or modification made by those skilled in the art on the basis of the present invention belongs to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. An electrolyte, characterized in that: include: Organic solvents, lithium salts and additives; The additive includes additive A, and the additive A includes a mixed additive generated by the reaction of an anhydrous acidic additive and an organic base; The anhydrous acidic additive includes at least one of sulfur dioxide, carbon dioxide, and sulfur trioxide; The organic base includes at least one of (4-(dimethylamino)phenylvinyl)pyridine, N,N-diethylpropargylamine, dimethylthioformamide, N,N-dimethylbenzylamine, and N,N-dimethylbenzamide, The pH value of the additive A is neutral.

2. The electrolyte according to claim 1, characterized in that: The mass of the additive A accounts for 0.1% to 10% of the total mass of the electrolyte.

3. The electrolyte according to claim 1, characterized in that The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bistrifluoromethanesulfonyl imide and lithium bisfluorosulfonyl imide, and the concentration of the lithium salt in the electrolyte is 0.8 to 1.5 mol / L.

4. The electrolyte according to claim 1, characterized in that The organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, dipropyl carbonate, diphenyl carbonate, dibutyl carbonate, butylene carbonate, methylpropyl carbonate, methyl acetate, ethyl acetate, isobutyl acetate, propyl acetate, butyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, propyl propionate, methenyl carbonate, ethyl 3-ethoxypropionate, and fluorobenzene.

5. The electrolyte according to claim 1, characterized in that The additives further include carbonate additives, and the carbonate additives include at least one of vinylene carbonate, vinyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate and derivatives thereof.

6. The electrolyte according to claim 5, characterized in that The mass of the carbonate additive accounts for 0.02% to 5% of the total mass of the electrolyte.

7. The electrolyte according to claim 1, characterized in that The additive also includes additive B, which includes at least one of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, vinyl sulfate, vinyl sulfite, 4-methyl-vinyl sulfate, 4-fluorovinyl sulfate, 4-n-propyl vinyl sulfate, 4,4'-bisulfate, 4-vinyl-vinyl sulfate, 4-ethyl vinyl sulfate, 4,5-difluorovinyl sulfate, 1,3,6,8-tetraoxy-2,7-disulfide-spiro[4.4]nonane-2,2,7,7-tetraoxide, glyoxal disulfate, 4,5-dimethyl vinyl sulfate, 1,2-cyclopentadiene sulfate, vinyl cyanide sulfate, di(sulfoglyceryl) sulfate, glyceryl sulfate, and glyceryl sulfate methyl ether.

8. The electrolyte according to claim 7, characterized in that The mass of the additive B added accounts for 0.02% to 5% of the mass of the electrolyte.

9. The electrolyte according to claim 1, characterized in that The additives also include additive C, which is a nitrile compound. The nitrile compound includes at least one of succinonitrile, adiponitrile, glutaronitrile, suberonitrile, sebaconitrile, 1,3,6-hexanetricarboxylic acid nitrile, 1,3,5-pentanetricarboxylic acid nitrile, p-fluorobenzonitrile / p-methylbenzonitrile, 2-fluoroadiponitrile, 2,2-difluorosuccinonitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,2-bis(cyanoethoxy)ethane, and 1,2,3-tris(cyanoethoxy)propane. The mass of the additive C added accounts for 0.02% to 5% of the mass of the electrolyte.

10. A secondary battery, characterized in that: The electrolyte comprises the electrolyte described in any one of claims 1 to 9.

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