Electrolyte

Abstract

The present invention provides an electrolyte additive, an electrolyte containing the same, a lithium ion secondary battery, and uses thereof. [Solution] The electrolyte additive comprises a substance represented by the following formula (1), in which R1 is a substituted or unsubstituted C1-6 alkyl group, and R2 is selected from the group consisting of a substituted or unsubstituted C1-6 aliphatic hydrocarbylene group, a 6-10 membered substituted or unsubstituted carbocyclic or heterocyclic aromatic group, wherein the heterocyclic aromatic group contains 1 to 3 heteroatoms selected from N, S, O, or any combination thereof.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion secondary batteries, and specifically to an electrolyte additive, an electrolyte containing the same, a lithium-ion secondary battery, and its use.

Background Art

[0002] With the rapid development of the economic society, there is an urgent demand for lithium-ion batteries with high energy density and long cycle life. High-nickel / silicon-carbon type lithium-ion batteries are considered to be a feasible solution to solve the current problems. However, the high-nickel type positive electrode and the silicon-carbon type negative electrode have insufficient structural stability in the charge and discharge cycle, which may lead to a severe decline in battery performance under high-temperature and high-rate conditions.

[0003] During the charge and discharge process of a lithium-ion battery, the solvent may decompose, and the decomposed products form a cathode electrolyte interface film (CEI film) on the surface of the battery cathode and a solid electrolyte interface film (SEI film) on the surface of the anode. The CEI film and the SEI film can effectively suppress the further reaction of the solvent with the electrode. However, during the charge and discharge cycle, the structure of the high-nickel cathode is unstable, the CEI film is easily destroyed, and transition metal ions elute. In addition, the silicon anode material is prone to volume expansion during the charge and discharge process, the SEI film ruptures, the electrode structure collapses, and the battery performance significantly deteriorates.

[0004] Currently, a commonly used method to improve battery performance is to add multiple types of film-forming additives to the electrolyte so that stable protective interfaces (CEI film and SEI film) can be formed on the surfaces of the positive electrode and the negative electrode respectively. In the prior art, such film-forming additives include phosphate ester-based, nitrile-based, and sulfonic acid ester-based compounds. During the first charge-discharge cycle, the film-forming additives undergo decomposition reactions preferentially over the solvent, and their decomposition products form a stable and dense CEI film on the surface of the positive electrode. Also, to protect the negative electrode, it is necessary to add film-forming additives such as borate salts, nitrogen-containing lithium salts, and carbonates to form a stable negative electrode SEI film on the surface of the negative electrode during the first charge-discharge cycle. However, to protect both the positive electrode and the negative electrode simultaneously, it is necessary to use multiple types of additives in combination, which brings in more impurities, induces side reactions, and increases the uncontrollability of the reaction process. Controlling the types and amounts of additives as much as possible is crucial for improving the performance of the battery. Therefore, to solve the problems mentioned above, it is necessary to develop electrolyte additives that can effectively form SEI films and CEI films and ensure the electrical performance of lithium-ion secondary batteries.

Summary of the Invention

Problems to be Solved by the Invention

[0005] The main object of the present invention is to provide an electrolyte additive, an electrolyte containing the same, a lithium-ion secondary battery, and its use, in order to solve the problems in the prior art that using multiple types of electrolyte additives in combination brings in more impurities, induces side reactions, and increases the uncontrollability of the reaction process.

Means for Solving the Problems

[0006] To achieve the above object, according to one aspect of the present invention, there is provided an electrolyte additive containing a substance represented by the following formula (1).

Chemical Formula

[0007] Furthermore, in the above electrolyte additive, R1 is a halogen-substituted C 1-3 alkyl group or a C 1-3 alkyl group.

[0008] Furthermore, in the above electrolyte additive, R2 is a C 1-6 alkylene group, a halogen, or a C 1-3 alkyl group-substituted C 1-6 alkylene group, a phenylene group, a halogen, or a C 1-3 alkyl group-substituted phenylene group, a benzothiazolylene group, and a halogen or a C 1-3 alkyl group-substituted benzothiazolylene group, and is selected from the group consisting thereof.

[0009] Furthermore, in the above electrolyte additive, the substance represented by formula (1) is any one of the following.

Chemical formula

[0010] According to another aspect of the present invention, there is provided an electrolyte containing an organic solvent, a lithium salt, and the electrolyte additive described above.

[0011] Furthermore, in the above electrolyte, based on the total weight of 100 parts by weight of the organic solvent and the lithium salt, the amount of the electrolyte additive is in the range of 0.1 part by weight to 1 part by weight.

[0012] Furthermore, in the above electrolyte, based on the total weight of 100 parts by weight of the organic solvent and the lithium salt, the amount of the electrolyte additive is in the range of 0.1 part by weight to 0.5 part by weight.

[0013] Furthermore, in the above electrolytic solution, the lithium salt is selected from the group consisting of LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiN(SO2F)2, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, or any combination thereof.

[0014] Furthermore, in the above electrolytic solution, the organic solvent is selected from the group consisting of propylene carbonate, butylene carbonate, fluoroethylene carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, or any combination thereof. According to a further aspect of the present invention, there is provided a lithium ion secondary battery including a positive electrode sheet, a negative electrode sheet, a separator, and the electrolytic solution described above. According to a further aspect of the present invention, there is provided the use of the above-described electrolytic solution additive in the preparation of an electrolytic solution for a lithium ion secondary battery and / or a lithium ion secondary battery.

Advantages of the Invention

[0015] By means of the electrolytic solution additive of the present invention, the electrolytic solution containing the same, the lithium ion secondary battery, and its use, technical effects such as improvement of the stability of the electrode, reduction of the battery impedance, improvement of the high temperature cycle performance and rate performance of the battery are realized.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0017] In the case of no conflict, the examples and features in the present application can be combined with each other. Hereinafter, the present invention will be described in detail by combining examples. The following examples are merely illustrative and do not constitute a limitation on the protection scope of the present invention.

[0018] As described in the background art, in a lithium-ion secondary battery in the prior art, a plurality of types of electrolyte additives are generally used in combination to form a CEI film and an SEI film on the positive electrode and the negative electrode, respectively. However, this method brings in more impurities, induces side reactions, and increases the uncontrollability of the reaction process. In response to the problems of the prior art, a typical embodiment of the present invention provides an electrolyte additive containing a substance represented by the following formula (1).

[0019]

Chemical formula

[0020] As a result of a large number of experiments, the inventors of the present invention surprisingly found that when the compound of formula (1) is used as an electrolyte additive, it is preferentially decomposed in the electrolyte during the first cycle process of the lithium-ion secondary battery, and a solid electrolyte film can be simultaneously formed on both the positive electrode and the negative electrode, that is, a CEI film can be efficiently formed on the positive electrode and an SEI film can be formed on the negative electrode.

[0021] The present invention selects the compound of formula (1) as an inner salt series compound. Different groups within its molecule are partially positively and negatively charged, but overall it shows electrical neutrality. The positively charged morpholine group part shows a strong electron adsorption effect, and when decomposed into morpholine radical ions, it can form a stable SEI film on the negative electrode surface. On the other hand, the negatively charged sulfonic acid group shows a strong electron donation effect, and when decomposed into sulfonic acid group ions, it is oxidized on the positive electrode surface and can form a stable CEI film. The inner salt compound of formula (1) in this application can simultaneously form an interfacial protective film on the surfaces of the positive and negative electrodes, thus effectively avoiding the reaction between the solvent and the electrodes, suppressing the elution of metal ions, effectively improving the stability of the electrodes, reducing the battery impedance, and improving the cycle maintenance rate and rate performance of the battery. Also, when the compound of formula (1) in this application is adopted, since it is not necessary to simultaneously add multiple kinds of additives to form a solid electrolyte film on the positive and negative electrodes at the same time, only one kind of electrolyte can be added, so the possibility of side reactions between the electrolyte additives is eliminated. Therefore, the formation of impurities on the electrolyte and the electrode surface can be effectively suppressed, thereby reducing the battery impedance.

[0022] Specifically, in the initial cycle process of the battery, due to the generation of the hydrolysis product HF, the compound of formula (1) is decomposed into positively charged morpholine radical ions and negatively charged sulfate ions under the action of HF. The positively charged morpholine radical binds to the transition metal ion M n+ on the positive electrode surface of the battery, and through cycling, a stable CEI film is formed on the positive electrode surface to suppress the elution of the transition metal. Since the morpholine radical has a cyclic structure, it can more effectively cover the positive electrode, protect the positive electrode material from reacting with the electrolyte, avoid the reaction between the solvent and the electrode, and suppress the elution of metal ions. The negatively charged sulfate ions obtain electrons at the negative electrode and then continuously react to form a network-like SEI film, thereby improving the battery cycle performance and rate performance.

[0023] In some embodiments, R1 in formula (1) can be selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, neobutyl, n-pentyl, isopentyl, neopentyl, n-hexyl, isohexyl or neohexyl. In some other embodiments, R2 in formula (1) is C 1-6 a straight-chain aliphatic hydrocarbylene group, a monocyclic or bicyclic arylene group, and a heterocyclic aromatic group containing a bicyclic ring, and can be selected from the group consisting of. In a preferred embodiment, R2 is C 1-6 an alkylene group, C 1-6 an alkenylene group, C 1-6 an alkynylene group, a phenylene group, a naphthalene group, a benzothiazolylene group, a benzofuranylene group, a benzothiophene group, a benzopyrazole group, and can be selected from the group consisting of. In other embodiments, R2 is C 3-6 an alicyclic hydrocarbylene group, and can be selected from.

[0024] In some embodiments of the present invention, the electrolyte additive of formula (1) is N-methyl-N-(3-methylsulfonyl)morpholine, N-ethyl-N-(3-methylsulfonyl)morpholine, N-n-propyl-N-(3-methylsulfonyl)morpholine, N-isopropyl-N-(3-methylsulfonyl)morpholine, N-n-butyl-N-(3-methylsulfonyl)morpholine, N-isobutyl-N-(3-methylsulfonyl)morpholine, N-tert-butyl-N-(3-methylsulfonyl)morpholine, N-n-pentyl-N-(3-methylsulfonyl)morpholine, N-isopentyl-N-(3-methylsulfonyl)morpholine, N-neopentyl-N-(3-methylsulfonyl)morpholine, N-n-hexyl-N-(3-methylsulfonyl)morpholine, N-isohexyl-N-(3-methylsulfonyl)morpholine, N-neohexyl-N-(3-methylsulfonyl)morpholine, N-methyl-N-(3-ethylsulfonyl)morpholine, N-ethyl-N-(3-ethylsulfonyl)morpholine, N-n-propyl-N-(3-ethylsulfonyl)morpholine, N-isopropyl-N-(3-ethylsulfonyl)morpholine, N-n-butyl-N-(3-ethylsulfonyl)morpholine, N-isobutyl-N-(3-ethylsulfonyl)morpholine, N-tert-butyl-N-(3-ethylsulfonyl)morpholine, N-n-pentyl-N-(3-ethylsulfonyl)morpholine, N-isopentyl-N-(3-ethylsulfonyl)morpholine, N-neopentyl-N-(3-ethylsulfonyl)morpholine, N-n-hexyl-N-(3-ethylsulfonyl)morpholine, N-isohexyl-N-(3-ethylsulfonyl)morpholine, N-neohexyl-N-(3-ethylsulfonyl)morpholine, N-methyl-N-(3-propylsulfonyl)morpholine, N-ethyl-N-(3-propylsulfonyl)morpholine, N-n-propyl-N-(3-propylsulfonyl)morpholine, N-isopropyl-N-(3-propylsulfonyl)morpholine, N-n-butyl-N-(3-propylsulfonyl)morpholine, N-isobutyl-N-(3-propylsulfonyl)morpholine, N-tert-butyl-N-(3-propylsulfonyl)morpholine,One or any combination thereof can be included in a substituted or unsubstituted substance from N-n-pentyl-N-(3-propylsulfonyl)morpholine, N-isopentyl-N-(3-propylsulfonyl)morpholine, N-neopentyl-N-(3-propylsulfonyl)morpholine, N-n-hexyl-N-(3-propylsulfonyl)morpholine, N-isohexyl-N-(3-propylsulfonyl)morpholine, N-neohexyl-N-(3-propylsulfonyl)morpholine, N-methyl-N-(3-butylsulfonyl)morpholine, N-ethyl-N-(3-butylsulfonyl)morpholine, N-n-propyl-N-(3-butylsulfonyl)morpholine, N-isopropyl-N-(3-butylsulfonyl)morpholine, N-n-butyl-N-(3-butylsulfonyl)morpholine, N-isobutyl-N-(3-butylsulfonyl)morpholine, N-tert-butyl-N-(3-butylsulfonyl)morpholine, N-n-pentyl-N-(3-butylsulfonyl)morpholine, N-isopentyl-N-(3-butylsulfonyl)morpholine, N-neopentyl-N-(3-butylsulfonyl)morpholine, N-n-hexyl-N-(3-butylsulfonyl)morpholine, N-isohexyl-N-(3-butylsulfonyl)morpholine, N-neohexyl-N-(3-butylsulfonyl)morpholine, N-methyl-N-(3-pentylsulfonyl)morpholine, N-methyl-N-(3-hexylsulfonyl)morpholine, N-ethyl-N-(3-pentylsulfonyl)morpholine or N-ethyl-N-(3-hexylsulfonyl)morpholine.,

[0025] In some other embodiments, the electrolyte additive of formula (1) is N-methyl-N-parasulfobenzothiazole morpholine, N-ethyl-N-parasulfobenzothiazole morpholine, N-n-propyl-N-parasulfobenzothiazole morpholine, N-isopropyl-N-parasulfobenzothiazole morpholine, N-n-butyl-N-parasulfobenzothiazole morpholine, N-isobutyl-N-parasulfobenzothiazole morpholine, N-tert-butyl-N-parasulfobenzothiazole morpholine, N-n-pentyl-N-parasulfobenzothiazole morpholine, N-isopentyl-N-parasulfobenzothiazole morpholine, N-neopentyl-N-parasulfobenzothiazole morpholine, N-n-hexyl-N-parasulfobenzothiazole morpholine, N-isohexyl-N-parasulfobenzothiazole morpholine, N-neohexyl-N-parasulfobenzothiazole morpholine, N-methyl-N-(2'-methyl-5'-sulfonyl-benzothiazole-1') morpholine, N-methyl-N-(8'-methyl-5'-sulfonyl-benzothiazole-1') morpholine, N-methyl-N-(9'-methyl-5'-sulfonyl-benzothiazole-1') morpholine, N-methyl-N-(2'-ethyl-5'-sulfonyl-benzothiazole-1') morpholine, N-methyl-N-(8'-ethyl-5'-sulfonyl-benzothiazole-1') morpholine, N-methyl-N-(9'-ethyl-5'-sulfonyl-benzothiazole-1') morpholine, N-methyl-N-(2',8'-dimethyl-5'-sulfonyl-benzothiazole-1') morpholine, N-methyl-N-(8',9'-dimethyl-5'-sulfonyl-benzothiazole-1') morpholine, N-methyl-N-(2',9'-dimethyl-5'-sulfonyl-benzothiazole-1') morpholine, N-methyl-N-(2',8',9'-trimethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(2'-methyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(8'-methyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(9'-methyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(2'-ethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(8'-ethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(9'-ethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(2',8'-dimethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(8',9'-dimethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(2',9'-dimethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-ethyl-N-(2',8',9'-trimethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-n-propyl-N-(2'-methyl-5'-sulfonyl-benzothiazole-1')morpholine, N-n-propyl-N-(8'-methyl-5'-sulfonyl-benzothiazole-1')morpholine, N-n-propyl-N-(9'-methyl-5'-sulfonyl-benzothiazole-1')morpholine, N-n-propyl-N-(2'-ethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-n-propyl-N-(8'-ethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-n-propyl-N-(9'-ethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-n-propyl-N-(2',8'-dimethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-n-propyl-N-(8',9'-dimethyl-5'-sulfonyl-benzothiazole-1')morpholine, N-n-propyl-N-(2',9'-dimethyl-5'-sulfonyl-benzothiazole-1')morpholine or N-n-propyl-N-(2',8',It may contain one or any combination of them of substituted or unsubstituted substances from 9'-trimethyl-5'-sulfonyl-benzothiazole-1')morpholine.,

[0026] In a further embodiment of the present invention, the electrolyte additive may be a compound of the following formula (1).

Chemical formula

[0027] In a further embodiment of the present invention, the electrolyte additive may be a compound of the following formula (1).

Chemical formula

[0028] In some specific embodiments of the present invention, the electrolyte additive of the present invention is N-methyl-N-(3-chloromethylsulfonyl)morpholine, N-methyl-N-(3-fluoromethylsulfonyl)morpholine, N-methyl-N-(3-fluoroethylsulfonyl)morpholine, N-methyl-N-(3-fluoropropylsulfonyl)morpholine, N-methyl-N-(2'-chloro-4'-sulfonyl-phenyl-1')-morpholine, N-methyl-N-(2'-fluoro-4'-sulfonyl-phenyl-1')-morpholine, N-methyl-N-(2'-methyl-3-fluoro-4'-sulfonyl-phenyl-1')-morpholine, N-methyl-N-(2'-fluoro-3-fluoro-4'-sulfonyl-phenyl-1')-morpholine, N-methyl-N-(2'-methyl-5'-sulfonyl-benzothiazol-1')morpholine, N-methyl-N-(2'-fluoro-5'-sulfonyl-benzothiazol-1')morpholine, N-methyl-N-(2',8'-difluoro-5'-sulfonyl-benzothiazol-1')morpholine or N-methyl-N-(2'-fluoro-8'-methyl-5'-sulfonyl-benzothiazol-1')morpholine, and can include one kind or any combination thereof in the substances.

[0029] In a preferred embodiment of the present invention, the electrolyte additive of the present invention can include one kind or any combination thereof in the following substances.

Chemical formula

[0030]

Chemical formula

[0031] In one embodiment of the present application, the electrolyte additive is N-methyl-N-(3-propylsulfonyl)morpholine. In the process of initially cycling a lithium-ion secondary battery containing N-methyl-N-(3-propylsulfonyl)morpholine, the electrolyte additive undergoes the following reaction: N-methyl-N-(3-propylsulfonyl)morpholine decomposes, under the catalytic action of hydrogen fluoride, into a positively charged N-methyl-N-propane moiety and a negatively charged sulfone group moiety. The positively charged N-methyl-N-propane moiety gathers at the positive electrode of the lithium-ion secondary battery under the action of the current and deposits on the surface of the positive electrode to form a CEI film. The negatively charged sulfone group moiety gathers at the negative electrode portion of the lithium-ion secondary battery under the action of the current and reacts under the action of lithium ions to form a network-structured SEI film. After the formation of the CEI film and the SEI film, both the positive electrode and the negative electrode of the lithium-ion secondary battery are protected, so the elution of transition metal ions is suppressed.

[0032] In another embodiment of the present application, the electrolyte additive is N-methyl-N-para-sulfophenylmorpholine. In the process of initially cycling a lithium-ion secondary battery containing N-methyl-N-para-sulfophenylmorpholine, the electrolyte additive undergoes the following reaction: N-methyl-N-para-sulfophenylmorpholine decomposes, under the catalytic action of hydrogen fluoride, into a positively charged N-methyl-N-benzene moiety and a negatively charged sulfone group moiety. The positively charged N-methyl-N-benzene moiety gathers at the positive electrode of the lithium-ion secondary battery under the action of the current and deposits on the surface of the positive electrode to form a CEI film. The negatively charged sulfone group moiety gathers at the negative electrode portion of the lithium-ion secondary battery under the action of the current and reacts under the action of lithium ions to form a network-structured SEI film. After the formation of the CEI film and the SEI film, both the positive electrode and the negative electrode of the lithium-ion secondary battery are protected, so the elution of transition metal ions is suppressed.

[0033] In one embodiment of the present application, the electrolyte additive is N-methyl-N-para-sulfobenzo-thiazole morpholine. In the process of initially cycling a lithium-ion secondary battery containing N-methyl-N-para-sulfobenzo-thiazole morpholine, the electrolyte additive undergoes the following reactions: N-methyl-N-para-sulfobenzo-thiazole morpholine decomposes, under the catalytic action of hydrogen fluoride, into a positively charged N-methyl-N-benzothiazole moiety and a negatively charged sulfone group moiety. The positively charged N-methyl-N-benzothiazole moiety gathers on the positive electrode of the lithium-ion secondary battery under the action of the current and deposits on the surface of the positive electrode to form a CEI film. The negatively charged sulfone group moiety gathers on the negative electrode portion of the lithium-ion secondary battery under the action of the current and reacts under the action of lithium ions to form a network-structured SEI film. After the CEI film and the SEI film are formed, both the positive and negative electrodes of the lithium-ion secondary battery are protected, so the elution of transition metal ions is suppressed.

[0034] In another typical embodiment of the present invention, an electrolyte is provided that includes an organic solvent, a lithium salt, and the electrolyte additive described above. Since it contains the electrolyte additive of the present invention, the electrolyte of the present invention can effectively form a CEI film on the surface of the positive electrode and an SEI film on the surface of the negative electrode during the initial cycle of the battery. Therefore, it can avoid the reaction between the solvent and the electrode, suppress the elution of metal ions, improve the electrode stability, reduce the battery impedance, and improve the battery cycle retention rate and rate performance. In addition, since the electrolyte of the present application employs the electrolyte additive described above, there is no need to add multiple types of additives simultaneously, and only one type of electrolyte additive is required, thus eliminating the possibility of side reactions between the electrolyte additive solutions, effectively suppressing the formation of impurities on the electrolyte and the electrode surface, and reducing the battery impedance.

[0035] In some embodiments of the present invention, in the electrolytic solution of the present invention, the amount of the electrolytic solution additive is in the range of 0.1 part by weight to 1 part by weight based on the total weight of 100 parts by weight of the organic solvent and the lithium salt. Since the electrolytic solution additive of the present application forms the CEI film and the SEI film simultaneously during the first cycle process, there is no need to add other additives for film formation. Further, by adding the electrolytic solution additive of the present invention within the above range, an electrolyte film can be efficiently formed. If the amount of the electrolytic solution additive is less than 0.1 part by weight, a dense and good electrolyte film cannot be formed on both the positive electrode and the negative electrode. If the amount of the electrolytic solution additive exceeds 1 part by weight, the formed electrolyte film becomes too thick, which will adversely affect the cycle efficiency of the lithium ion secondary battery and increase the battery impedance unfavorably.

[0036] In different embodiments of the present invention, according to different combinations of the lithium salt and the organic solvent, the minimum value of the amount of the electrolytic solution additive should exceed 0.1 part by weight, 0.11 part by weight, 0.12 part by weight, 0.13 part by weight, 0.15 part by weight, 0.16 part by weight, 0.17 part by weight, 0.18 part by weight or 0.19 part by weight based on the total weight of 100 parts by weight of the organic solvent and the lithium salt. And according to different combinations of the organic solvent and the lithium salt, the maximum value of the amount of the electrolytic solution additive in the electrolytic solution should not satisfy 1 part by weight, 0.9 part by weight, 0.8 part by weight, 0.7 part by weight, 0.6 part by weight, 0.5 part by weight, 0.49 part by weight, 0.48 part by weight, 0.47 part by weight, 0.46 part by weight, 0.45 part by weight, 0.44 part by weight, 0.43 part by weight, 0.42 part by weight, 0.41 part by weight, 0.4 part by weight, 0.35 part by weight, 0.3 part by weight, 0.25 part by weight or 0.2 part by weight based on the total weight of 100 parts by weight of the organic solvent and the lithium salt.

[0037] Specifically, the amount of the electrolyte additive in the electrolyte may be in the range of 0.1 part by weight to 1 part by weight, 0.2 part by weight to 0.9 part by weight, 0.3 part by weight to 0.8 part by weight, 0.4 part by weight to 0.7 part by weight, 0.5 part by weight to 0.6 part by weight, 0.1 part by weight to 0.5 part by weight, 0.1 part by weight to 0.4 part by weight, 0.1 part by weight to 0.3 part by weight, 0.1 part by weight to 0.2 part by weight, 0.1 part by weight to 0.41 part by weight, 0.11 part by weight to 0.4 part by weight, 0.12 part by weight to 0.35 part by weight, 0.13 part by weight to 0.3 part by weight, 0.14 part by weight to 0.25 part by weight, 0.15 part by weight to 0.2 part by weight, 0.15 part by weight to 0.5 part by weight, 0.13 part by weight to 0.5 part by weight, or 0.12 part by weight to 0.25 part by weight based on the total weight of 100 parts by weight of the organic solvent and the lithium salt in the electrolyte.

[0038] The lithium salt component contained in the electrolyte of the present invention is not particularly limited, and those known to be usable in lithium battery electrolytes in the prior art can be adopted. Examples of the lithium salt include, but are not limited to, LiPF6, LiBF4, LiAsF6, LiCF3SO3, LiN(SO2F)2, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, or a group consisting of any combination of the above.

[0039] In the present invention, the organic solvent of the non-aqueous electrolyte may be any non-aqueous solvent that has been used in non-aqueous electrolyte solutions. Examples include linear or cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, and fluoroethylene carbonate; ethers such as 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, and diethyl ether; sulfones such as cyclobutane sulfone and methyl cyclobutane sulfone; nitriles such as acetonitrile, propionitrile, and acrylonitrile; esters such as acetic acid esters, propionic acid esters, and butyric acid esters, etc., but are not limited thereto. These non-aqueous solvents may be used alone or in combination of multiple solvents. In some embodiments of the present invention, preferred electrolytes include ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene carbonate and / or dimethyl carbonate, and any combination thereof. In one preferred embodiment, at least one carbonate is used as the organic solvent of the electrolyte of the present invention. In some other preferred embodiments, the above non-aqueous solvents can be arbitrarily combined and used to form an electrolyte solution that meets specific requirements.

[0040] In a further typical embodiment of the present invention, a lithium-ion secondary battery is provided that includes a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte described above. Since the lithium-ion secondary battery of the present invention uses the electrolyte described above, it has excellent electrode stability, cycle retention rate, and rate performance.

[0041] The positive electrode sheet of the present invention includes a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material. The positive electrode active material layer is formed on both sides of the positive electrode current collector. As the positive electrode current collector, metal foils such as aluminum foil, nickel foil, and stainless steel foil can be used.

[0042] The positive electrode active material layer contains one or more of positive electrode materials that are positive electrode active materials and can occlude and release lithium ions. Optionally, it may also contain other materials such as a positive electrode binder and / or a positive electrode conductive agent.

[0043] Preferably, the positive electrode material is a lithium-containing compound. Examples of this lithium-containing compound include lithium-transition metal composite oxides, lithium-transition metal phosphate compounds, etc. The lithium-transition metal composite oxide is an oxide containing Li and one or more transition metal elements as constituent elements, and the lithium-transition metal phosphate compound is a phosphate compound containing Li and one or more transition metal elements as constituent elements. Among them, the transition metal element is preferably any one or more of Co, Ni, Mn, Fe, etc.

[0044] Examples of the lithium-transition metal composite oxide include, for example, LiCoO2, LiNiO2, etc. Examples of the lithium-transition metal phosphate compound include, for example, LiFePO4, LiFe 1-u Mn u PO4 (0 < u < 1), etc.

[0045] In some embodiments of the present application, the positive electrode material may be a ternary positive electrode material, such as lithium nickel cobalt aluminate (NCA) or lithium nickel cobalt manganese oxide (NCM). Specific examples are NCA, that is, Li x Ni y Co z Al 1-y-z O2 (1 ≤ x ≤ 1.2, 0.5 ≤ y ≤ 1, and 0 ≤ z ≤ 0.5); NCM, that is, LiNi x Co y Mn zIt may be O2(x + y + z = 1, 0 < x < 1, 0 < y < 1, 0 < z < 1). Specific examples of the positive electrode material include LiNiO2, LiCoO2, LiCo 0.98 Al 0.01 Mg 0.01 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.2 Mn 0.52 Co 0.175 Ni 0.1 O2 and Li 1.15 (Mn 0.65 Ni 0.22 Co 0.13 )O2, LiFePO4, LiMnPO4, LiFe 0.5 Mn 0.5 PO4 and LiFe 0.3 Mn 0.7 PO4 may be included, but are not limited to these materials.

[0046] In addition, the positive electrode material may be, for example, any one or two or more of oxides, disulfides, chalcogenides, conductive polymers, lithium cobaltate, lithium manganate, nickel cobalt manganese ternary materials, etc. Examples of oxides include, for example, titanium oxide, vanadium oxide, manganese dioxide, etc. Examples of disulfides include, for example, titanium disulfide, molybdenum sulfide, etc. Examples of chalcogenides include, for example, niobium selenide, etc. Examples of conductive polymers include, for example, sulfur, polyaniline, polythiophene, etc. However, the positive electrode material may be a material different from the above.

[0047] Examples of the positive electrode conductive agent include carbon materials such as graphite, carbon black, acetylene black, Ketjen black, etc. These can be used alone or in combination of two or more. In addition, the positive electrode conductive agent may be a metal material, a conductive polymer or the like as long as it has conductivity.

[0048] Examples of the positive electrode binder include, for example, synthetic rubber and polymer materials. The synthetic rubber may be, for example, styrene-butadiene rubber, fluororubber, ethylene-propylene-diene, etc., and the polymer materials may be, for example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, lithium polyacrylate, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, and polyimide, etc. These can be used alone or in combination of two or more.

[0049] The negative electrode sheet of the present invention includes a negative electrode current collector and a negative electrode active material layer containing a negative electrode active material. The negative electrode active material layer is formed on both sides of the negative electrode current collector. As the negative electrode current collector, metal foils such as copper (Cu) foil, nickel foil, and stainless steel foil can be used.

[0050] The negative electrode active material layer contains a material capable of occluding and releasing lithium ions, which is a negative electrode active material, and may optionally contain other materials such as a negative electrode binder and / or a negative electrode conductive agent. Details of the negative electrode binder and the negative electrode conductive agent are, for example, the same as those of the positive electrode binder and the positive electrode conductive agent. The active material of the negative electrode is selected from any one or a combination of lithium metal, lithium alloy, carbon material, silicon or tin and their oxides.

[0051] Since carbon materials have a low potential when absorbing lithium ions, high energy density can be obtained and the battery capacity can be increased. In addition, carbon materials function as conductive agents. Such carbon materials are, for example, natural graphite, artificial graphite, materials obtained by coating them with amorphous carbon, or the like. Note that the carbon materials are in fibrous, spherical, granular, flaky or similar shapes. The silicon-based materials include nanosilicon, silicon alloys, and silicon-carbon composite materials in which SiOw and graphite are combined. Preferably, SiOw is silica suboxide, silicon oxide or other silicon-based materials.

[0052] In addition, the negative electrode material may be, for example, one or more of graphitizable carbon, non-graphitizable carbon, metal oxides, polymer compounds, etc. Examples of metal oxides include, for example, iron oxide, ruthenium oxide, molybdenum oxide, etc. Examples of polymer compounds include, for example, polyacetylene, polyaniline, polypyrrole, etc. However, the negative electrode material may be other materials different from the materials described above.

[0053] The separator of the present invention separates the positive electrode sheet and the negative electrode sheet in the battery and prevents current short circuit due to contact between the two electrode sheets while allowing ions to pass through. The separator is, for example, a porous membrane formed from synthetic resin, ceramics or similar substances, and may also be a laminated membrane in which two or more porous membranes are laminated. Examples of synthetic resins include, for example, polytetrafluoroethylene, polypropylene, polyethylene, cellulose, etc.

[0054] In the embodiment of the present invention, when charging, for example, lithium ions are released from the positive electrode and absorbed by the negative electrode by the non-aqueous electrolyte impregnated in the separator. When discharging, for example, lithium ions are released from the negative electrode and absorbed by the positive electrode by the non-aqueous electrolyte impregnated in the separator.

[0055] In another typical embodiment of the present invention, there is provided the use of the electrolyte additive described in the foregoing of the present invention in the preparation of an electrolyte for a lithium-ion secondary battery and / or a lithium-ion secondary battery. After adding the electrolyte additive of the present application to a lithium-ion secondary battery, during the first charging cycle, the electrolyte additive of the present application preferentially decomposes in the electrolyte to generate morpholine-based radical ions and sulfonic acid group-based ions. Therefore, a CEI film and an SEI film are respectively formed on the surfaces of the positive electrode and the negative electrode of the lithium-ion secondary battery, thereby effectively avoiding the reaction between the solvent and the electrode, suppressing the elution of metal ions, effectively improving the stability of the electrode, reducing the battery impedance, and improving the battery cycle retention rate and rate performance.

[0056] Hereinafter, the present application will be described in more detail with reference to specific examples, but these examples should not be understood as limiting the scope of protection required by the present application.

[0057] Example 1 Preparation of negative electrode Under vacuum and completely dry conditions, at a temperature of 20°C, 94.0 g of silica oxide (SiO x , 1 < x < 2) and graphite powder (where the amount of silica oxide is 9.4 g), 1.9 g of Super-P conductive agent, 3.15 g of CMC binder (sodium carboxymethyl cellulose), and styrene-butadiene rubber SBR (where the weight ratio of CMC to SBR is 1:1) were weighed and added to water, and uniformly stirred to obtain a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper foil to obtain a negative electrode current collector, and the negative electrode current collector was dried and a negative electrode sheet was formed by a pressing process.

[0058] Preparation of positive electrode Under vacuum and completely dry conditions, at a temperature of 20 °C, 93.0 g of lithium nickel cobalt aluminate as the positive electrode active material, 4.0 g of conductive carbon black, and 3.0 g of polyvinylidene fluoride were mixed to obtain a positive electrode mixture. The obtained positive electrode mixture was dispersed in N-methylpyrrolidone to obtain a positive electrode mixture slurry. Then, the positive electrode mixture slurry was applied to an aluminum foil to obtain a positive electrode current collector, and the positive electrode current collector was dried, and a positive electrode sheet was formed by a pressing process.

[0059] Preparation of Electrolyte 20.0 g of ethylene carbonate, 62.0 g of dimethyl carbonate, and 18.0 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.1 g of N-methyl-N-(3-propylsulfonyl)morpholine (MSPM) was added to the basic electrolyte to obtain the electrolyte for the battery. Here, MSPM is shown by the following chemical formula. [Chemical Formula]

[0060] Assembly of Battery CR2016 button batteries were assembled in a dry laboratory. The positive electrode sheet prepared by the above procedure was used as the positive electrode, and the negative electrode sheet was used as the negative electrode. The positive electrode, negative electrode, separator, and the battery case of the button battery were assembled and the electrolyte was injected. The positive electrode, negative electrode, separator, and the battery case of the button battery were assembled. After the battery was assembled, it was left standing for about 24 h for aging to obtain a lithium nickel cobalt manganate button battery.

[0061] Example 2 A lithium nickel cobalt manganate button battery was prepared in the same manner as in Example 1, except that 0.5 g of MSPM was added to the basic electrolyte to obtain the electrolyte for the battery.

[0062] Example 3 A lithium nickel cobalt manganate button battery was prepared in the same manner as in Example 1, except that 1.0 g of MSPM was added to the basic electrolyte to obtain the electrolyte for the battery.

[0063] Example 4 A lithium nickel cobalt manganese oxide button cell was prepared in the same manner as in Example 1, except that 0.1 g of MSIM was added to the basic electrolyte to obtain the electrolyte of the cell. Here, MSIM is represented by the following chemical formula. [Chemical Formula]

[0064] Example 5 A lithium nickel cobalt manganese oxide button cell was prepared in the same manner as in Example 1, except that 0.5 g of MSIM was added to the basic electrolyte to obtain the electrolyte of the cell.

[0065] Example 6 A lithium nickel cobalt manganese oxide button cell was prepared in the same manner as in Example 1, except that 1.0 g of MSIM was added to the basic electrolyte to obtain the electrolyte of the cell.

[0066] Comparative Example 1 A lithium nickel cobalt manganese oxide button cell was prepared in the same manner as in Example 1, except that the electrolyte of the cell was obtained without adding any electrolyte additive.

[0067] Comparative Example 2 A lithium nickel cobalt manganese oxide button cell was prepared in the same manner as in Example 1, except that 0.05 g of MSPM was added to the basic electrolyte to obtain the electrolyte of the cell.

[0068] Comparative Example 3 A lithium nickel cobalt manganese oxide button cell was prepared in the same manner as in Example 1, except that 3.0 g of MSPM was added to the basic electrolyte to obtain the electrolyte of the cell.

[0069] Comparative Example 4 A lithium nickel cobalt manganese oxide button cell was prepared in the same manner as in Example 1, except that 0.05 g of MSIM was added to the basic electrolyte to obtain the electrolyte of the cell.

[0070] Comparative Example 5 A lithium nickel cobalt manganese oxide button battery was prepared in the same manner as in Example 1, except that 3.0 g of MSIM was added to the basic electrolyte to obtain the electrolyte of the battery.

[0071] Battery performance test Cycle retention rate and impedance after cycling At room temperature, charge-discharge tests and impedance tests were performed on the lithium nickel cobalt manganese oxide button batteries of Examples 1 to 6 and Comparative Examples 1 to 5 at a voltage of 3.0 V to 4.2 V. The batteries in the above Examples and Comparative Examples were first subjected to a 0.1C cycle test at 25°C once, and then a 1C charge and discharge cycle test was performed 100 times under the condition of 60°C to determine the cycle retention rate and impedance of the battery. The experimental results are shown in Table 1 below.

[0072]

Table 1

[0073] As can be seen from the comparison between Examples 1 to 6 and Comparative Example 1, the lithium ion secondary battery using the electrolyte additive of the present invention exhibited a significantly improved cycle retention rate and a significantly reduced impedance after cycling. As can be seen from the comparison between Example 3 and Comparative Example 2 and the comparison between Example 5 and Comparative Example 4, when the addition amount of the electrolyte additive was less than the range limited in the present application, the decrease in the cycle retention rate was not large, but the impedance after cycling increased significantly. That is because the amount of the electrolyte additive was not sufficient to form a complete and dense solid electrolyte film on the surfaces of the positive electrode and the negative electrode, and the transition elements in the electrode eluted. As can be seen from the comparison between Example 3 and Comparative Example 3 and the comparison between Example 6 and Comparative Example 5, when the addition amount of the electrolyte additive exceeded the range limited in the present application, the cycle retention rate of the secondary battery decreased significantly, and the impedance after cycling increased significantly. That is because a too thick solid electrolyte film was formed on the surfaces of the positive electrode and the negative electrode, resulting in a decrease in the efficiency of lithium intercalation and deintercalation.

[0074] Rate discharge test The lithium nickel cobalt manganese oxide button batteries prepared in Example 2, Example 5 and Comparative Example 1 were subjected to a rate discharge test at 25 °C from 0.5C to 10C, and the test results are shown in Fig. 1.

[0075] As can be seen from Fig. 1, both Example 2 and Example 5 using the electrolyte additive of the present application show excellent rate discharge performance. Among them, even when Example 2 is subjected to a rate discharge test at 5C, it can maintain a discharge capacity of 90%.

[0076] Float charge test The lithium nickel cobalt manganese oxide button batteries prepared in Example 2, Example 5 and Comparative Example 1 were subjected to a float charge test at 25 °C, and the test results are shown in Fig. 2.

[0077] As can be seen from Fig. 2, since no electrolyte additive is added to Comparative Example 1, its positive and negative electrodes are not protected by a solid electrolyte membrane. When performing a float charge test, since the electrodes are in direct contact with the electrolyte, the transition metals in the electrodes react with the electrolyte and elute into the electrolyte, increasing the float charge current. Both Example 2 and Example 5 show a much lower float charge current (almost zero) than Comparative Example 1, indicating that the batteries containing 0.5% MSPM or 0.5% MSIM form more stable CEI and SEI films.

[0078] The above are only preferred embodiments of the present invention and do not limit the present invention. For those skilled in the art, various modifications and changes are possible to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should all be included within the protection scope of the present invention.

Claims

1. An electrolyte for a lithium-ion secondary battery, comprising an organic solvent, a lithium salt, and an electrolyte additive containing a substance represented by the following formula (1). 【Chemical 1】 In the formula, R １ is a substituted or unsubstituted C １－６ alkyl group, R ２ is selected from the group consisting of a substituted or unsubstituted C １－６ aliphatic hydrocarbylene group, a 6- to 10-membered substituted or unsubstituted carbocyclic or heterocyclic aromatic group, provided that the heterocyclic aromatic group contains 1 to 3 heteroatoms, and the heteroatoms are selected from N, S, O, or any combination thereof.

2. R １ is a halogen-substituted C １－３ alkyl group or a C １－３ alkyl group, and the electrolytic solution according to claim 1, characterized in that.

3. R ２ is a C １－６ alkylene group, halogen or C １－３ alkyl group-substituted C １－６ alkylene group, phenylene group, halogen or C １－３ alkyl group-substituted phenylene group, benzothiazolylene group, and halogen or C １－３ The electrolytic solution according to claim 1, characterized in that it is selected from the group consisting of an alkyl group-substituted benzothiazolylene group.

4. The electrolyte according to Claim 1, wherein the substance represented by formula (1) is any one of the following. 【Chemical Formula 2】

5. The amount of the electrolyte additive is in the range of 0.1 part by weight to 1 part by weight based on the total weight of 100 parts by weight of the organic solvent and the lithium salt, according to any one of Claims 1 to 4.

6. The amount of the electrolyte additive is in the range of 0.1 part by weight to 0.5 part by weight based on the total weight of 100 parts by weight of the organic solvent and the lithium salt, according to Claim 5.

7. The lithium salt is LiPF ６ 、LiBF ４ 、LiAsF ６ 、LiCF ３ SO ３ 、LiN(SO ２ F) ２ 、LiN(SO ２ CF ３ ) ２ 、LiC(SO ２ CF ３ ) ３ 、Li ２ SiF ６ 、or selected from the group consisting of any combination of the above, characterized in that the electrolyte according to any one of claims 1 to 4

8. The organic solvent is selected from the group consisting of propylene carbonate, butylene carbonate, fluoroethylene carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, or any combination thereof, according to any one of Claims 1 to 4.

9. Positive electrode sheet, Negative electrode sheet, Separator, and The electrolyte according to any one of Claims 1 to 4 A lithium-ion secondary battery, characterized by comprising the same.

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