阅读说明：本技术 电解液添加剂组合物、电解液、二次电池 (Electrolyte additive composition, electrolyte, and secondary battery ) 是由 李家玉 于 2021-07-20 设计创作，主要内容包括：本发明属于电池技术领域,尤其涉及一种电解液添加剂组合物,以及一种电解液,一种二次电池。其中,电解液添加剂组合物包括含有如下结构式I的第一添加剂、腈类化合物和1,3二氧六环；其中,R-(1)～R-(5)分别独立的选自氢原子、氟原子、取代或未取代的烷基中的任意一种,且R-(1)～R-(5)中至少有一个为氟原子或被氟原子取代；A选自烷基、烷氧基、烯烃基、酰基、卤素原子中的任意一种。本发明电解液添加剂组合物,通过含氟苯基的磺酸酯类化合物第一添加剂与腈类化合物和1,3二氧六环的协同作用,能够兼顾电池的常温和高温表现,提高电池的常温和高温循环性能,尤其是对高镍三元锂离子电池体系的性能起到较好的优化效果。(The invention belongs to the technical field of batteries, and particularly relates to an electrolyte additive composition, an electrolyte and a secondary battery. Wherein the electrolyte additive composition comprises a first additive containing the following structural formula I, a nitrile compound and 1,3 dioxane; wherein R is 1 ～R 5 Each independently selected from any one of a hydrogen atom, a fluorine atom and a substituted or unsubstituted alkyl group, and R 1 ～R 5 At least one of which is a fluorine atom or is substituted by a fluorine atom; a is selected from any one of alkyl, alkoxy, alkylene, acyl and halogen atom. The electrolyte additive composition of the invention is prepared by using sulfonate containing fluorine phenylThe synergistic effect of the first additive of the compound, the nitrile compound and the 1, 3-dioxane can give consideration to the normal-temperature and high-temperature performances of the battery, improve the normal-temperature and high-temperature cycle performance of the battery, and especially play a good optimization effect on the performance of a high-nickel ternary lithium ion battery system.)

1. An electrolyte additive composition, characterized in that the electrolyte additive composition comprises a first additive comprising the following structural formula I, a nitrile compound and 1,3 dioxane;

wherein R is₁～R₅Each independently selected from any one of a hydrogen atom, a fluorine atom and a substituted or unsubstituted alkyl group, and R₁～R₅At least one of which is a fluorine atom or is substituted by a fluorine atom; a is selected from any one of alkyl, alkoxy, alkylene, acyl and halogen atom.

2. The electrolyte additive composition as recited in claim 1 wherein when a is selected from the group consisting of alkyl, alkoxy, alkenyl, and acyl, at least one hydrogen atom in a is substituted with a halogen atom;

and/or the nitrile compound is selected from at least one of trinitrile compounds, tetranitrile compounds and dinitrile compounds.

3. The electrolyte additive composition of claim 2 wherein the first additive is selected from the group consisting of At least one of;

and/or the nitrile compound is selected from at least one of 1,3, 5-pentanitrile, 1,2, 3-propanetricitrile, 1,3, 6-hexanetrinitrile, ethylene-1, 1, 2-trimethylnitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile and suberonitrile.

4. The electrolyte additive composition as recited in any one of claims 1 to 3, wherein the nitrile compound and the 1, 3-dioxane are present in a mass ratio of (1 to 2): (1-3);

the ratio of the mass of the first additive to the total mass of the nitrile compound and the 1, 3-dioxane is (2-5): (2-5).

5. An electrolyte comprising an electrolyte salt, an organic solvent, and an electrolyte additive composition, wherein the electrolyte additive composition comprises a first additive comprising the following structural formula I, a nitrile compound, and 1,3 dioxane;

wherein R is₁～R₅Each independently selected from any one of a hydrogen atom, a fluorine atom and a substituted or unsubstituted alkyl group, and R₁～R₅At least one of which is a fluorine atom or is substituted by a fluorine atom; a is selected from any one of alkyl, alkoxy, alkylene, acyl and halogen atom.

6. The electrolyte of claim 5, wherein the electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis-fluorosulfonimide, lithium bis-trifluoromethylsulfonyl imide, lithium bis-pentafluoroethanesulfonyl imide;

and/or the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, gamma-butyrolactone, vinylene carbonate, ethylene carbonate and fluoroethylene carbonate;

and/or the electrolyte also comprises at least one auxiliary additive of a lithium salt compound, a sultone compound and a cyclic phosphazene compound.

7. The electrolyte of claim 6, wherein the lithium salt-based compound is selected from at least one of lithium difluorooxalato borate, lithium bis-oxalato borate, lithium difluorophosphate, lithium methylsulfate, and lithium ethylsulfate;

and/or the sultone compound is selected from at least one of 1, 3-propane sultone, 1, 3-propylene sultone, 1, 4-butane sultone, 1, 4-butene sultone and 1-methyl-1, 3-propylene sultone;

and/or the cyclic phosphazene compound is selected from at least one of methoxy pentafluorocyclotriphosphazene, ethoxy pentafluorocyclotriphosphazene and phenoxy pentafluorocyclotriphosphazene;

and/or in the electrolyte, the mass percentage of the lithium salt compound is 0.01-2.5%;

and/or in the electrolyte, the mass percentage of the sultone compound is 0.05-3%;

and/or the mass percentage of the cyclic phosphazene compound in the electrolyte is 0.05-5%.

8. The electrolyte according to any one of claims 5 to 7, wherein the concentration of the electrolyte salt in the electrolyte is 0.5 to 1.5 mol/L;

and/or in the electrolyte, the mass percentage of the electrolyte additive composition is 0.25-10%;

and/or the mass ratio of the nitrile compound to the 1, 3-dioxane is (1-2): (1-3); the ratio of the mass of the first additive to the total mass of the nitrile compound and the 1, 3-dioxane is (2-5): (2-5).

9. A secondary battery comprising the electrolyte additive composition of any one of claims 1 to 4 or the electrolyte of any one of claims 5 to 8.

10. The secondary battery of claim 9, wherein the positive electrode of the secondary battery comprises a high nickel positive electrode material.

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to an electrolyte additive composition, an electrolyte and a secondary battery.

Background

The power lithium ion battery for the electric automobile has wide market prospect, and compared with the lithium iron phosphate anode material, the ternary anode material with higher specific capacity is increasingly accepted by batteries and related manufacturers, and the demand is continuously increased. At present, in order to improve the energy density of the battery and ensure the endurance capacity of the electric automobile, the ternary material is continuously developing towards higher nickel content. Common high nickel positive electrode materials include NCM622, NCM811, NCA, and the like. However, the increase of the content of nickel element also leads to the oxidative enhancement of the anode material, and the electrolyte is easier to react on the surface of the electrode, so that the problems of electrode plate transition metal dissolution, battery gas expansion and the like are caused, and finally the cycle performance of the battery is reduced and even the battery fails. On the other hand, power-type applications also place higher demands on battery performance, such as: the device can adapt to the large fluctuation of the environmental temperature, can meet the high-power charge and discharge requirements and the like. The battery is in a high temperature state for a short or longer period of time due to internal or external factors, which may reduce the service life of the battery. And for the high nickel material with poor structural stability and high temperature performance, the method faces greater test.

At present, the solution aiming at the heat-resistant characteristic of the electrolyte cannot completely meet the expectation of the market on the power battery, and the research suitable for the high-nickel ternary lithium ion system is very limited. In this regard, it is necessary to provide more new electrolyte solutions to fully exert the capacity advantages of the high nickel material and effectively expand the application range thereof.

Disclosure of Invention

The invention aims to provide an electrolyte additive composition, an electrolyte and a secondary battery, and aims to solve the problems of high reaction activity, poor heat resistance and poor stability of the conventional electrolyte and high-capacity electrode materials such as high nickel and the like to a certain extent.

In order to achieve the purpose of the application, the technical scheme adopted by the invention is as follows:

in a first aspect, the present invention provides an electrolyte additive composition comprising a first additive having the following structural formula I, a nitrile compound, and 1,3 dioxane;

wherein R is₁～R₅Each independently selected from a hydrogen atom,Fluorine atom, substituted or unsubstituted alkyl group, and R₁～R₅At least one of which is a fluorine atom or is substituted by a fluorine atom; a is selected from any one of alkyl, alkoxy, alkylene, acyl and halogen atom.

According to the electrolyte additive composition provided by the first aspect of the invention, through the synergistic effect of the first additive of the sulfonate compound containing the fluorophenyl, the nitrile compound and the 1, 3-dioxane, the normal-temperature and high-temperature performance of the battery can be considered, the normal-temperature and high-temperature cycle performance of the battery is improved, and particularly, the electrolyte additive composition has a good optimization effect on the performance of a high-nickel ternary lithium ion battery system.

Further, when a is selected from alkyl, alkoxy, alkenyl or acyl, at least one hydrogen atom in a is substituted by a halogen atom, more preferably by fluorine; the halogen can further improve the film forming and flame retardant effects of the additive on the surface of the negative electrode.

Further, the first additive is selected from At least one of; the first additives can participate in the formation of an SEI film on the surface of the battery pole piece, so that the toughness of the protective film is improved, the interface impedance of the film layer is reduced, and the normal-temperature and high-temperature cycling stability of the battery is improved.

Further, the nitrile compound is at least one selected from the group consisting of a trinitrile compound, a tetranitrile compound, and a dinitrile compound. Further, the nitrile compound is at least one selected from the group consisting of 1,3, 5-pentanitrile, 1,2, 3-propanetricitrile, 1,3, 6-hexanetrinitrile, ethylene-1, 1, 2-trimethylnitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile and suberonitrile. The nitrile compounds all have cyano groups with strong electronegativity, and can generate strong complexation with the surface of the positive electrode of the transition metal oxide to inhibit the dissolution of ions of the transition metal oxide; meanwhile, the nitrile substances can also absorb a small amount of water and HF gas to form amide substances, so that the corrosion effect of the amide substances on electrodes is reduced, and the gas generation of the battery is reduced.

Further, in the electrolyte additive composition, the mass ratio of the nitrile compound 1,3 dioxane is (1-2): (1-3); the ratio of the mass of the first additive to the total mass of the nitrile compound and 1, 3-dioxane is (2-5): (2-5). The proportioning fully ensures the cooperative coordination effect among the components, so that the three components have the optimal film forming effect on the surface of the pole piece, have the optimal effect of reducing the impedance of the film layer and improve the migration transmission efficiency of ions on the interface layer.

In a second aspect, the present invention is an electrolyte comprising an electrolyte salt, an organic solvent, and an electrolyte additive composition, wherein the electrolyte additive composition comprises a first additive comprising the following structural formula I, a nitrile compound, and 1,3 dioxane;

wherein R is₁～R₅Each independently selected from any one of a hydrogen atom, a fluorine atom and a substituted or unsubstituted alkyl group, and R₁～R₅At least one of which is a fluorine atom or is substituted by a fluorine atom; a is selected from any one of alkyl, alkoxy, alkylene, acyl and halogen atom.

In the electrolyte provided by the second aspect of the invention, the electrolyte additive composition comprises three components, namely a first additive containing a structural formula I, a nitrile compound and 1, 3-dioxane; the additive can optimize the formation of an SEI protective film on the surfaces of the positive electrode and the negative electrode, not only improves the elasticity of the protective film, but also has better relieving and inhibiting effects on the volume expansion effect of an active material in a pole piece in the cyclic charge-discharge process; the impedance of the protective film can be reduced, migration and transmission of ions are facilitated, the de-intercalation efficiency of the ions in the charging and discharging process is ensured, and the rate capability of the battery is ensured.

Further, the electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethylsulfonyl imide and lithium bis-pentafluoroethanesulfonyl imide; the electrolyte salts are easy to dissociate lithium ions, play a role in transferring in the lithium ion interaction process, and realize the cyclic charge and discharge of the battery through the insertion and extraction of the lithium ions in the positive and negative electrodes.

Further, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, gamma-butyrolactone, vinylene carbonate, ethylene carbonate and fluoroethylene carbonate; the organic solvents have good compatibility with electrolyte additive compositions and electrolyte salts, and are beneficial to the migration and transmission of lithium ions in the charge and discharge processes of the battery.

Furthermore, the electrolyte also comprises at least one auxiliary additive of lithium salt compounds, sultone compounds and cyclic phosphazene compounds. The film forming effect of the electrolyte on the surface of the electrode can be further improved by the auxiliary additives.

Further, the lithium salt compound is at least one selected from lithium difluoro oxalate borate, lithium bis oxalate borate, lithium difluoro phosphate, lithium methyl sulfate and lithium ethyl sulfate. Further, the sultone compound is at least one selected from 1, 3-propane sultone, 1, 3-propene sultone, 1, 4-butane sultone, 1, 4-butene sultone and 1-methyl-1, 3-propene sultone. Further, the cyclic phosphazene compound is at least one selected from the group consisting of methoxy pentafluorocyclotriphosphazene, ethoxy pentafluorocyclotriphosphazene, and phenoxy pentafluorocyclotriphosphazene. The auxiliary additives can further improve the high-temperature stability of the electrolyte, improve the film forming effect of the electrolyte on the surface of an electrode, and form an electrolyte interface (SEI) with excellent elasticity on the surface of the electrode, so that the interface reaction on the surface of the electrode is prevented, and the stability and the safety performance of a battery are improved.

Further, in the electrolyte, the mass percentage of the lithium salt compound is 0.01-2.5%; furthermore, in the electrolyte, the mass percentage of the sultone compound is 0.05-3%; furthermore, in the electrolyte, the mass percentage of the cyclic phosphazene compound is 0.05-5%. The content of auxiliary additives such as lithium salt compounds, sultone compounds, cyclic phosphazene compounds and the like in the electrolyte is not suitable to be too high, and if the addition amount is too high, the transition film formation on the surface of an electrode can be caused, the impedance of an SEI protective film is increased, and the ion migration transmission is not facilitated.

Further, the concentration of the electrolyte salt in the electrolyte is 0.5-1.5 mol/L; the electrolyte salt with the concentration provides sufficient lithium ions for the electrolyte, and the migration and transmission efficiency of the ions in the electrolyte is ensured.

Furthermore, in the electrolyte, the mass percentage of the electrolyte additive composition is 0.25-10%; the electrolyte additive composition with the content is beneficial to better considering both the normal-temperature and high-temperature cycle performance and the rate performance of the battery.

Further, in the electrolyte additive composition, the mass ratio of the nitrile compound 1,3 dioxane is (1-2): (1-3); the ratio of the mass of the first additive to the total mass of the nitrile compound and 1, 3-dioxane is (2-5): (2-5). The proportioning fully ensures the cooperative coordination effect among the components, so that the three components have the optimal film forming effect on the surface of the pole piece, have the optimal effect of reducing the impedance of the film layer and improve the migration transmission efficiency of ions on the interface layer.

In a third aspect, the present invention provides a secondary battery comprising the above electrolyte additive composition, or comprising the above electrolyte.

According to the secondary battery provided by the third aspect of the invention, because the electrolyte additive composition or the electrolyte is contained, the film forming effect of SEI films on the surfaces of positive and negative pole pieces in the battery can be optimized, the volume expansion effect of the pole pieces in the cyclic charge-discharge process can be better adapted and even inhibited, and the normal-temperature and high-temperature cycle life of the battery is prolonged; but also can generate flame retardant effect and improve the safety performance of the battery.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In the present invention, the term "and/or" describes the association relationship of the associated objects, and means that there may be three relationships, for example, a and/or B, which may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the present invention, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (one) of a, b, or c," or "at least one (one) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, and c may be single or plural, respectively.

It should be understood that, in various embodiments of the present invention, the sequence numbers of the above-mentioned processes do not mean the execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present invention.

The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the examples of the invention and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weight of the related components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present invention as long as it is in accordance with the description of the embodiments of the present invention. Specifically, the mass in the description of the embodiments of the present invention may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.

The terms "first" and "second" are used for descriptive purposes only and are used for distinguishing purposes such as substances from one another, and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the invention. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

In a first aspect, embodiments of the present invention provide an electrolyte additive composition, which includes a first additive having a structural formula I, a nitrile compound, and 1,3 dioxane;

wherein R is₁～R₅Each independently selected from any one of a hydrogen atom, a fluorine atom and a substituted or unsubstituted alkyl group, and R₁～R₅At least one of which is a fluorine atom or is substituted by a fluorine atom; a is selected from any one of alkyl, alkoxy, alkylene, acyl and halogen atom.

According to a first aspect of embodiments of the present invention, there is provided an electrolyte additive composition comprising a first additive comprising structural formula I, a nitrile compound, and 1,3 dioxane; the nitrile compound not only has strong electronegative cyano group and can generate strong complexation with transition metal ions on the surface of the positive electrode to inhibit metal ions from dissolving out and improve the stability of the electrode, but also can absorb a small amount of water and HF gas to form amide substances by mixing the nitrile compound, so that the corrosion effect of the substances on the electrode is reduced, the gas generated by the battery is reduced, and the cycle safety performance of the battery is improved. However, the nitrile additives increase the internal resistance of the battery to a certain extent, and the effect of improving the normal temperature performance of the battery is not good. Meanwhile, the 1, 3-dioxane participates in the formation of a surface protective film of the positive electrode through ring-opening polymerization, so that the reaction activity of a positive electrode material and an electrolyte is reduced, the thermal stability of the positive electrode protective film is further improved in cooperation with a nitrile material, the contact between the electrolyte and the positive electrode material is reduced, the gas generation of the battery is reduced, and the safety performance of the battery is improved. However, 1,3 dioxane generates oxidation products when participating in film formation of a positive electrode, the oxidation products move to a negative electrode, a reduction reaction without a film formation effect occurs at the negative electrode, film formation properties of the surface of the negative electrode are inhibited, active lithium is consumed, initial capacity of a battery is reduced, and 1,3 dioxane increases impedance of the battery, and low-temperature and normal-temperature cycle properties of the battery are affected. In addition, the reduction potential of the first additive in the electrolyte system is 1-1.5V, the first additive can be reduced in preference to the solvent and the 1,3 dioxane side reaction product, and participates in the formation of an SEI film on the surface of the negative electrode in preference to the solvent and the 1,3 dioxane side reaction product, so that the reduction decomposition of the organic solvent is inhibited, the interface impedance of the SEI film is reduced, and the high-temperature and normal-temperature cycle performance of the battery is improved; on the other hand, due to the existence of the benzene ring and the sulfonic acid group in the first additive, the structure and the components of the negative electrode film can be optimized, the transmission and diffusion efficiency of lithium ions at an electrode-electrolyte interface is improved, the electrode interface impedance is reduced, the influence of the nitrile compound and the 1,3 dioxane additive on the battery impedance is compensated, and the rate capability of the power battery under the conditions of low temperature and room temperature is improved. In addition, the first additive can be oxidized in preference to the solvent, and further participate in the formation of the positive electrode surface protective film. According to the electrolyte additive composition provided by the embodiment of the invention, through the synergistic effect of the first additive of the sulfonate compound containing the fluorophenyl, the nitrile compound and the 1, 3-dioxane, the low-temperature, normal-temperature and high-temperature performances of the battery can be considered, the cycle performance of the battery is improved, and particularly, the electrolyte additive composition has a good optimization effect on the performance of a high-nickel ternary lithium ion battery system.

The 1, 3-dioxane in the electrolyte additive composition can improve the film forming effect of an electrode, has low gas production at high temperature, and is suitable for a 2.5-4.3V battery system, especially for a high-nickel ternary lithium ion battery system. And the 1, 4-dioxane, 1, 3-dioxolane and the like have low decomposition potential, generate gas seriously at high temperature and have poor stability, so the lithium-sulfur battery is more suitable for a 1.8-2.6V lithium-sulfur battery system.

In some embodiments, the first additive of formula I is a fluorinated phenyl sulfonateWhen A is selected from alkyl, alkoxy, alkenyl or acyl, at least one hydrogen atom in A is substituted by halogen atom, and is preferably substituted by fluorine. In the first additive of formula I of the examples of the invention, R₁～R₅At least one of which is a fluorine atom or is substituted by a fluorine atom (i.e. when R is₁～R₅And when the alkyl is the alkyl, at least one alkyl is the alkyl substituted by fluorine atoms), the reduction potential of the first additive in the electrolyte system is 1-1.5V, the first additive can be reduced in preference to the solvent and the 1, 3-dioxane side reaction product, and participates in the formation of an SEI film on the surface of the negative electrode in preference to the solvent and the side reaction product, so that the interfacial resistance of the SEI film is reduced, and the low-temperature cycle performance of the battery is improved. The existence of benzene ring and sulfonic acid group in the first additive can optimize the structure and components of the negative electrode film, improve the transmission and diffusion efficiency of lithium ions at the electrode-electrolyte interface, reduce the electrode interface impedance, compensate the increase of nitrile compound to the battery impedance, and improve the multiplying power performance of the power battery under the room temperature condition. In addition, the A position or R₁～R₅The halogen in the position, especially fluorine element, can further improve the film forming and flame retardant effect of the additive on the surface of the negative electrode.

In some embodiments, the first additive is selected from At least one of; the first additives can participate in the formation of an SEI film on the surface of the battery pole piece, so that the toughness of the protective film is improved, the interface impedance of the film layer is reduced, and the normal-temperature and high-temperature cycling stability of the battery is improved. Compared with other fluoride or sulfonic acid compounds, the first additive containing the fluorine phenyl sulfonate has better high-temperature stability, does not generate gas under high-temperature conditions, has better reduction potential and higher reduction efficiency, and can be reduced before side reaction of a solvent and 1,3 dioxane.

In some embodiments, the nitrile compound is at least one selected from the group consisting of trinitrile compounds, tetracyronitrile compounds, dinitrile compounds, and nitrile compounds, wherein the nitrile compounds have cyano groups with strong electronegativity, and can generate strong complexation with the surface of the positive electrode of the transition metal oxide to inhibit the ion elution of the transition metal oxide; meanwhile, the nitrile substances can also absorb a small amount of water and HF gas to form amide substances, so that the corrosion effect of the amide substances on electrodes is reduced, and the gas generation of the battery is reduced. In some embodiments, the nitrile compound is selected from at least one of 1,3, 5-penta-nitrile, 1,2, 3-propanetriformitrile, 1,3, 6-hexanetrinitrile, ethylene-1, 1, 2-trimethylnitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile.

In some preferred embodiments, the nitrile compound is selected from the group consisting of trinitriles, which have higher activity and more significant effect on improving the high temperature performance of the battery.

In some embodiments, in the electrolyte additive composition, the mass ratio of the nitrile compound 1,3 dioxane is (1-2): (1-3); the ratio of the mass of the first additive to the total mass of the nitrile compound and 1, 3-dioxane is (2-5): (2-5). The proportion of the first additive, the nitrile compound and the 1, 3-dioxane in the electrolyte fully ensures the synergistic cooperation effect among the components, so that the three components have the optimal film forming effect on the surface of a pole piece, have the optimal effect of reducing the impedance of a film layer and improve the migration and transmission efficiency of ions in an interface layer. If the proportion of the first additive, the nitrile compound or the 1,3 dioxane is too high, the film formed on the surface of the pole piece is too thick, the internal resistance of the film is increased, the ion migration transmission is not facilitated, and the electrochemical performance of the battery is reduced. Further, since the nitrile compound and 1,3 dioxane have large self-impedance, when the mixing ratio is too high, it is difficult for the first additive to compensate the impedance effect of the nitrile compound. Therefore, the proportioning relationship of the three components in the additive not only influences the film forming effect of the electrode surface, but also influences the synergistic cooperation effect of the three components, thereby influencing the electrochemical performance.

In a second aspect, embodiments of the present invention provide an electrolyte comprising an electrolyte salt, an organic solvent, and an electrolyte additive composition, wherein the electrolyte additive composition comprises a first additive comprising a nitrile compound, a 1, 3-dioxane, and a first additive represented by structural formula I;

wherein R is₁～R₅Each independently selected from any one of a hydrogen atom, a fluorine atom and a substituted or unsubstituted alkyl group, and R₁～R₅At least one of which is a fluorine atom or is substituted by a fluorine atom; a is selected from any one of alkyl, alkoxy, alkylene, acyl and halogen atom.

The electrolyte provided by the second aspect of the embodiment of the invention comprises electrolyte salt, an organic solvent and an electrolyte additive composition, wherein the electrolyte additive composition comprises a first additive containing a structural formula I, a nitrile compound and 1, 3-dioxane; the formation of the SEI protective film on the surfaces of the positive electrode and the negative electrode can be optimized through the synergistic cooperation of the three components in the electrolyte additive composition, so that the elasticity of the protective film is improved, and the volume expansion effect of an active material in a pole piece in the cyclic charge-discharge process is better relieved and inhibited; the impedance of the protective film can be reduced, migration and transmission of ions are facilitated, the de-intercalation efficiency of the ions in the charging and discharging process is ensured, and the rate capability of the battery is ensured. According to the electrolyte disclosed by the embodiment of the invention, normal-temperature and high-temperature performances of the battery can be considered at the same time through the synergistic effect of different additive components, the normal-temperature and high-temperature cycle performance of the battery is improved, and the further optimization effect on the performance of the full battery is achieved.

In some embodiments, the electrolyte additive composition is 0.25-10% by weight of the electrolyte; the electrolyte additive composition with the content is beneficial to better considering both the normal-temperature and high-temperature cycle performance and the rate performance of the battery. If the content of the electrolyte additive composition is too high, a film layer formed on the surface of an electrode by polymerization is too thick, the impedance is too large, ion migration and transmission are not facilitated, and the electrochemical performance is reduced; if the content of the additive is too low, the performance of the electrolyte and the SEI protective film layer on the surface of the electrode is not remarkably improved, and the improvement effects on the normal temperature/high temperature cycle stability, safety performance, rate performance and the like of the battery are not good. In some embodiments, the electrolyte additive composition may be 0.25-1%, 1-3%, 3-5%, 5-8%, 8-10%, etc. by weight.

In some embodiments, in the electrolyte additive composition, the mass ratio of the nitrile compound 1,3 dioxane is (1-2): (1-3); the ratio of the mass of the first additive to the total mass of the nitrile compound and 1, 3-dioxane is (2-5): (2-5), the proportion fully ensures the cooperative coordination effect among all the components, so that the three components have the optimal film forming effect on the surface of the pole piece, and meanwhile, the optimal film resistance reducing effect is achieved, and the migration transmission efficiency of ions in an interface layer is improved. If the proportion of the first additive, the nitrile compound or the 1,3 dioxane is too high, the film formed on the surface of the pole piece is too thick, the internal resistance of the film is increased, the ion migration transmission is not facilitated, and the electrochemical performance of the battery is reduced. Further, since the nitrile compound itself has a large impedance, when the compounding ratio is too high, it is difficult for both the first additive and the 1,3 dioxane to compensate for the impedance effect of the nitrile compound. Therefore, the proportioning relationship of the three components in the additive not only influences the film forming effect of the electrode surface, but also influences the synergistic cooperation effect of the three components, thereby influencing the electrochemical performance.

In some embodiments, the first additive is selected from At least one of; the first additives can participate in the formation of an SEI film on the surface of the battery pole piece, so that the toughness of the protective film is improved, the interface impedance of the film layer is reduced, and the normal-temperature and high-temperature cycling stability of the battery is improved.

In some embodiments, the nitrile compound is at least one selected from the group consisting of 1,3, 5-pentanitrile, 1,2, 3-propanetricitrile, 1,3, 6-hexanetrinitrile, ethylene-1, 1, 2-trimethylnitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile and suberonitrile, and the nitrile compound has cyano groups with strong electronegativity, and can perform strong complexation with the positive electrode surface of the transition metal oxide to inhibit ion elution; meanwhile, the nitrile substances can also absorb a small amount of water and HF gas to form amide substances, so that the corrosion effect of the amide substances on electrodes is reduced, and the gas generation of the battery is reduced.

In some embodiments, the electrolyte salt is selected from lithium hexafluorophosphate LiPF₆Lithium tetrafluoroborate (LiBF)₄Lithium hexafluoroarsenate LiAsF₆At least one of bis (fluorosulfonyl) imide lithium LiFSI, bis (trifluoromethylsulfonyl) imide lithium LiTFSI and bis (pentafluoroethanesulfonyl) imide lithium LiBETI; the electrolyte salts are easy to dissociate lithium ions, play a role in transferring in the lithium ion interaction process, and realize the cyclic charge and discharge of the battery through the insertion and extraction of the lithium ions in the positive and negative electrodes.

In some embodiments, the concentration of the electrolyte salt in the electrolyte is 0.5-1.5 mol/L, and the electrolyte salt at the concentration provides sufficient lithium ions for the electrolyte, so that the migration and transmission efficiency of the ions in the electrolyte is ensured. If the concentration of the electrolyte lithium salt is too low, the conductivity of the electrolyte is low, and the multiplying power and the cycle performance of the whole battery system can be influenced; if the concentration of the electrolyte lithium salt is too high, the viscosity of the electrolyte is too high, and the rate characteristics of the whole battery system are also affected. In some embodiments, the concentration of the electrolyte salt in the electrolyte solution can be 0.5-0.8 mol/L, 0.8-1 mol/L, 1-1.2 mol/L, 1.2-1.5 mol/L, etc.

In some embodiments, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, gamma-butyrolactone, vinylene carbonate, ethylene carbonate, fluoroethylene carbonate; the organic solvents have good compatibility with electrolyte additive compositions and electrolyte salts, and are beneficial to the migration and transmission of lithium ions in the charge and discharge processes of the battery.

In some embodiments, the organic solvent in the electrolyte may be formulated by using various solvents, such as a mixed organic solvent of Ethylene Carbonate (EC), methyl ethyl carbonate (EMC) and dimethyl carbonate (DMC), wherein EC is cyclic carbonate, the dielectric constant is high but the viscosity is high, EMC and DMC are linear esters, the viscosity is low but the dielectric constant is also low, and the balance between the viscosity and the dielectric constant of the solvent can be achieved by compounding, so that the ionic conductivity of the electrolyte is moderate and the viscosity is high. In some embodiments, the ratio by volume is 3:3:4 preparing Ethylene Carbonate (EC), methyl ethyl carbonate (EMC) and dimethyl carbonate (DMC) into a mixed organic solvent.

In some embodiments, the electrolyte further includes at least one auxiliary additive selected from a lithium salt compound, a sultone compound, and a cyclic phosphazene compound, and the auxiliary additive can further improve the film forming effect of the electrolyte on the surface of the electrode.

In some embodiments, the lithium salt-based compound is selected from at least one of lithium difluorooxalato borate, lithium bis-oxalato borate, lithium difluorophosphate, lithium methylsulfate, and lithium ethylsulfate. In some embodiments, the sultone-based compound is selected from at least one of 1, 3-propane sultone, 1, 3-propene sultone, 1, 4-butane sultone, 1, 4-butene sultone, 1-methyl-1, 3-propene sultone. In some embodiments, the cyclic phosphazene compound is selected from at least one of methoxy pentafluorocyclotriphosphazene, ethoxy pentafluorocyclotriphosphazene, phenoxy pentafluorocyclotriphosphazene. The auxiliary additives in the embodiments of the present invention can further improve the high temperature stability of the electrolyte, improve the film forming effect of the electrolyte on the surface of the electrode, and form an electrolyte interface (SEI) with excellent elasticity on the surface of the electrode, thereby preventing the interface reaction on the surface of the electrode and improving the stability and safety performance of the battery.

In some embodiments, the mass percentage of the lithium salt compound in the electrolyte is 0.01-2.5%, preferably 0.01-2%. In some embodiments, the mass percentage of the sultone compound in the electrolyte is 0.05-3%; preferably 0.1 to 2%. In some embodiments, the content of the cyclic phosphazene compound in the electrolyte is 0.05 to 5% by mass, preferably 0.1 to 3% by mass. The content of auxiliary additives such as lithium salt compounds, sultone compounds and cyclic phosphazene compounds in the electrolyte is not suitable to be too high, and if the addition amount is too high, the transition film formation on the surface of an electrode can be caused, the impedance of an SEI protective film is increased, and the ion migration transmission is not facilitated.

A third aspect of embodiments of the invention provides a secondary battery comprising the above electrolyte additive composition, or comprising the above electrolyte.

According to the secondary battery provided by the third aspect of the embodiment of the invention, because the electrolyte additive composition or the electrolyte is contained, the film forming effect of SEI films on the surfaces of positive and negative pole pieces in the battery can be optimized, the volume expansion effect of the pole pieces in the cyclic charge-discharge process can be better adapted and even inhibited, and the normal-temperature and high-temperature cycle life of the battery is prolonged; but also can generate flame retardant effect and improve the safety performance of the battery.

The anode, the cathode, the diaphragm and the like in the secondary battery can be made of any materials meeting the requirements of practical application, and the secondary battery has no strict limitation and wide adaptability.

In some embodiments, the positive electrode material comprises a lithium composite metal oxide comprising lithium and at least one metal, such as cobalt, manganese, nickel, or aluminum, and the like, such as common lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, and the like.

In some embodiments, the positive electrode of the secondary battery comprises a high nickel positive electrode material. In some embodiments, the positive electrode material is preferably a ternary positive electrode material, i.e., lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate, more preferably a ternary positive electrode material with a high nickel content, in which the nickel element accounts for not less than 50% of the total transition metal elements in the positive electrode material, i.e., LiNi_xCo_yM_(1-x-y)O₂(M is Mn or Al), x is more than or equal to 0.5, and the preferred nickel element accounts for not less than 80% of the total transition metal elements of the positive electrode material, namely LiNi_xCo_yM_(1-x-y)O₂(M is Mn or Al), and x is more than or equal to 0.8. In some embodiments, the high nickel positive electrode material is selected from LiNi_0.8Co_0.1Mn_0.1O₂、LiNi_0.83Co_0.1Mn_0.07O₂、LiNi_0.8Co_0.2O₂、LiNi_0.8Co_0.15Al_0.05O₂One kind of (1). The electrolyte additive composition and the electrolyte provided by the embodiment of the invention have a more obvious effect on improving the cycle stability of a battery adopting a high-nickel anode material and having a strong oxidizing environment.

In some embodiments, the negative electrode material may be a silicon-based negative electrode material, a graphite negative electrode material, a tin-based negative electrode material, a lithium titanate material, or the like. In some embodiments, the negative electrode material may be carbon-coated silicon or silica, or a silicon-carbon negative electrode material in which carbon and silicon or silica are both mixed directly.

In some embodiments, the diaphragm may be a ceramic diaphragm, a rubberized diaphragm, or the like.

In order to make the above implementation details and operations of the present invention clearly understood by those skilled in the art and to make the advanced performance of the electrolyte additive composition, the electrolyte and the secondary battery thereof according to the embodiments of the present invention remarkably manifest, the above technical solutions are exemplified by a plurality of examples below.

Letters appearing in examples and comparative examples are abbreviated as follows:

x1 has a structural formulaX2 has a structural formula

LiPF₆Is lithium hexafluorophosphate; LiFSI is lithium bis (fluorosulfonyl) imide;

EC is ethylene carbonate; EMC is methyl ethyl carbonate; DMC is dimethyl carbonate;

DXA is 1, 3-dioxane; PTCN is 1,3, 5-pentanetrimethylnitrile; HTCN is 1,3, 6-hexanetricarbonitrile.

Example 1

Electrolyte solutionThe preparation method comprises the following steps: mixing EC, EMC and DMC in a volume ratio of 3:3:4 in a glove box with water content less than 1ppm and oxygen content less than 2ppm to form a mixed organic solvent; then, the user can use the device to perform the operation,adding a proper amount of fully dried LiPF₆The concentration of lithium salt in the electrolyte was set to 1.2mol/L to obtain a base electrolyte. Then, 1% of X1, 1% of PTCN and 1% of DXA additive are added into the basic electrolyte to obtain an electrolyte E1.

Lithium ion batteryThe manufacturing method comprises the following steps:

firstly, the positive active material adopts nickel cobalt lithium manganate LiNi_0.82Co_0.12Mn_0.06O₂B, carrying out the following steps of; preparing a nickel cobalt lithium manganate active material: carbon black: PVDF (polyvinylidene fluoride) according to a mass ratio of 97.1: 1.6: 1.3, coating the mixture on an aluminum foil after uniformly mixing, and then drying the aluminum foil at 85 ℃ to obtain the positive plate.

The negative active material adopts a composite product of silicon oxide and artificial graphite, wherein the silicon oxide accounts for 5 percent of the total mass of the negative active material; mixing the negative electrode active material: carbon black: CMC: SBR (styrene butadiene rubber) is mixed according to the mass ratio of 96.5: 0.5: 1.2: 1.8, coating the mixture on a copper foil after uniformly mixing, and then drying the copper foil at 90 ℃ to obtain the negative plate.

③ the electrolyte was the electrolyte of example 1.

And fourthly, assembling the positive plate, the negative plate and the ceramic diaphragm into a soft package battery with the capacity of 1.1Ah in a lamination mode, injecting electrolyte, and obtaining the lithium ion battery C1 through a formation aging and capacity grading process.

Example 2

Electrolyte solutionIt differs from example 1 in that: 2% of X1, 1% of PTCN and 1% of DXA additive are added into the electrolyte to obtain an electrolyte E2.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E2 is adopted, and the obtained lithium ion battery is C2.

Example 3

Electrolyte solutionIt differs from example 1 in that: 2% of X2, 1% of PTCN and 1% of DXA additive are added into the electrolyte to obtain an electrolyte E3.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E3 is adopted, and the obtained lithium ion battery is C3.

Example 4

Electrolyte solutionIt differs from example 1 in that: and adding 1% of X1, 1% of HTCN and 1% of DXA additive into the electrolyte to obtain an electrolyte E4.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E4 is adopted, and the obtained lithium ion battery is C4.

Example 5

Electrolyte solutionIt differs from example 1 in that: 2% of X1, 0.5% of HTCN and 0.5% of DXA additive are added into the electrolyte to obtain an electrolyte E5.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E5 is adopted, and the obtained lithium ion battery is C5.

Example 6

Electrolyte solutionIt differs from example 1 in that: 2% of X1, 0.5% of HTCN and 1% of DXA additive are added into the electrolyte to obtain an electrolyte E6.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E6 is adopted, and the obtained lithium ion battery is C6.

Example 7

Electrolyte solutionIt differs from example 1 in that: 1M LiPF6 and 0.2M LiFSI, 2% X1, 0.5% HTCN and 1% DXA additive were added to the electrolyte to obtain an electrolyte E7.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E7 is adopted, and the obtained lithium ion battery is C7.

Example 8

Electrolyte solutionIt differs from example 1 in that: electrolyte E8 was obtained by adding 1% X1, 1% HTCN and 3.5% DXA additive to the electrolyte.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E8 is adopted, and the obtained lithium ion battery is C8.

Example 9

Electrolyte solutionIt differs from example 1 in that: electrolyte E9 was obtained by adding 1% X1, 2.5% HTCN and 1% DXA additive to the electrolyte.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E9 is adopted, and the obtained lithium ion battery is C9.

Example 10

Electrolyte solutionIt differs from example 1 in that: electrolyte E10 was obtained by adding 1% X1, 1.5% HTCN and 1.5% DXA additive to the electrolyte.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E10 is adopted, and the obtained lithium ion battery is C10.

Example 11

Electrolyte solutionIt differs from example 1 in that: 3.5% of X1, 3% of HTCN and 3.5% of DXA additive are added into the electrolyte to obtain an electrolyte E11.

Lithium ion batteryIt differs from example 1 in that: the electrolyte E11 is adopted, and the obtained lithium ion battery is C11.

Comparative example 1

Electrolyte solutionIt differs from example 1 in that: without addition of additives to the electrolyte, an electrolyte DE1 was obtained.

Lithium ion batteryIt differs from example 1 in that: the electrolyte DE1 was used to obtain a lithium ion battery DC 1.

Comparative example 2

Electrolyte solutionIt differs from example 1 in that: 1% of X1 additive was added to the electrolyte to obtain an electrolyte DE 2.

Lithium ion batteryIt differs from example 1 in that: the electrolyte DE2 was used to obtain a lithium ion battery DC 2.

Comparative example 3

Electrolyte solutionIt differs from example 1 in that: 1% of PTCN additive was added to the electrolyte to obtain an electrolyte DE 3.

Lithium ion batteryIt differs from example 1 in that: the electrolyte DE3 was used to obtain a lithium ion battery DC 3.

Comparative example 4

Electrolyte solutionIt differs from example 1 in that: 1% DXA additive is added into the electrolyte to obtain an electrolyte DE 4.

Lithium ion batteryIt differs from example 1 in that: the electrolyte DE4 was used to obtain a lithium ion battery DC 4.

Comparative example 5

Electrolyte solutionIt differs from example 1 in that: to the electrolyte was added 1% X1 and 1% HTCN additive to give electrolyte DE 5.

Lithium ion batteryIt differs from example 1 in that: the electrolyte DE5 was used to obtain a lithium ion battery DC 5.

Comparative example 6

Electrolyte solutionIt differs from example 1 in that: to the electrolyte was added 1% X1 and 1% HTCN additive to give electrolyte DE 6.

Lithium ion batteryIt differs from example 1 in that: the electrolyte DE6 was used to obtain a lithium ion battery DC 6.

Comparative example 7

Electrolyte solutionIt differs from example 1 in that: 1% of HTCN and 1% of DXA additive were added to the electrolyte to obtain an electrolyte DE 7.

Lithium ion batteryIt differs from example 1 in that: the electrolyte DE7 was used to obtain a lithium ion battery DC 7.

In the electrolyte of each example and each comparative example, the components and the proportions are shown in table 1 below:

TABLE 1

Further, in order to verify the advancement of the examples of the present invention, the following performance tests were performed for examples 1 to 7 and comparative examples 1 to 7:

1. pre-circulation: charging at 25 deg.C with constant current and constant voltage, charging to 4.25V with 0.2C constant current, maintaining constant voltage until current is reduced to below 0.05C, and discharging to 3V with 0.2C constant current; (so-called formation step, so-called charge and discharge, through a full cycle, and then two cycles, for the sake of safe small-scale experimental operation)

2. And (3) normal-temperature circulation: after the pre-circulation is finished, cutting off an air bag part in a glove box of inert gas, carrying out final sealing on the battery, carrying out charge-discharge circulation test in a constant temperature box at 25 ℃ after the battery is finally sealed, wherein the constant voltage is kept after the battery is charged to 4.25V at a constant current of 1C until the current is reduced to be below 0.05C, the interval is 10 minutes, then the battery is discharged to 3V at a constant current of 1C, and the steps are repeated.

The retention ratio of the discharge capacity at 25 ℃ and 300 cycles was 100% of the discharge capacity at 300 cycles/the discharge capacity at 1 cycle at 25 ℃.

3. High-temperature circulation: after the pre-circulation is finished, cutting off an air bag part in a glove box of inert gas, carrying out final sealing on the battery, carrying out charge-discharge circulation test in a constant temperature box at 60 ℃ after the battery is finally sealed, wherein the constant voltage is kept after the battery is charged to 4.25V at a constant current of 1C until the current is reduced to be below 0.05C, the interval is 10 minutes, then the battery is discharged to 3V at a constant current of 1C, and the steps are repeated.

The discharge capacity maintenance rate at 60 ℃, 100 cycles was 100% of the discharge capacity at 100 th cycle of 60 ℃/100% of the discharge capacity at 1 st cycle of 60 ℃.

The results of the above tests are shown in table 2 below:

TABLE 2

From the test results in table 2, it can be seen that by comparing examples 1 to 7 with comparative example 1, the retention rate of the normal temperature (25 ℃) cycle capacity and the retention rate of the high temperature (60 ℃) cycle capacity are both improved and the improvement effect on the high temperature cycle is more significant when the three additive compositions of the present invention are used under the same conditions of other components.

It can be found by comparing example 1 with comparative examples 2 to 4 that, under the same conditions of other components, the three additive compositions of example 1 of the invention have better improvement effect on normal temperature and high temperature circulation through the synergistic effect of the additives, and the improvement effect is better than that of one additive in the same mass fraction. As can be seen from comparative example 2, the use of only the first additive has an effect of improving the normal temperature and high temperature cycles, but the effect is not significant. Comparative examples 3 and 4, the nitrile compound or the 1,3 dioxane additive is used alone, and the improvement effect on high-temperature circulation is obvious, but the improvement effect on normal-temperature circulation is not good, and even the deterioration effect is good.

In addition, by comparing example 4 with comparative examples 5 to 7, it can be found that the battery performance is better than the improvement effect of only using two additives in the same mass fraction by using the three additive compositions of example 4 of the invention, and the improvement effect of the high-temperature cycle performance is particularly obvious.

Comparing example 4 with examples 5 and 6, it can be found that the improvement effect of the battery on the retention of the normal-temperature and high-temperature cycle capacity can be further optimized by adjusting the mass ratio of the three additives.

Further, as in examples 8 to 10, the proportion of the additive is not within a suitable compounding ratio range; and example 11, the total content of additives is higher. Compared with a comparative example, the high-temperature cycle still has a certain improvement effect, but the normal-temperature cycle has a general improvement effect.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.