Additive of lithium ion battery electrolyte, electrolyte and lithium ion secondary battery

Abstract

The invention provides an additive of a lithium ion battery electrolyte, the electrolyte and a lithium ion secondary battery. Specifically, the invention provides the additive for the lithium ion battery electrolyte, the additive comprises a compound with a structure shown as a formula (1), R1 and R2 are respectively alkyl with 1-10 carbon atoms, substituted or unsubstituted phenyl, or substituted or unsubstituted aryl containing heteroatoms, and Rf is fluorine or fluorine substituted alkyl with 1-10 carbon atoms. According to the additive of the lithium ion battery electrolyte, the electrolyte and the lithium ion secondary battery, the technical effects of reducing the use amount of the film-forming additive such as FEC and improving the capacity retention rate of the battery are achieved. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the field of lithium ion secondary batteries, and in particular to an additive for lithium ion battery electrolyte, an electrolyte containing the additive, and a lithium ion secondary battery. Background Art

[0002] In recent years, with the continuous updating of electronic technology, people's demand for battery devices used to support the energy supply of electronic devices has also been increasing. Nowadays, batteries that can store more electricity and output high power are needed. Traditional lead-acid batteries and nickel-metal hydride batteries can no longer meet the needs of new electronic products. Therefore, lithium batteries have attracted widespread attention. In the process of developing lithium batteries, their capacity and performance have been effectively improved.

[0003] Lithium batteries have the advantages of high voltage, high specific energy, environmental protection and no memory effect, and are widely used in digital, military, energy storage and power fields. As a key component of lithium batteries, non-aqueous electrolyte is a bridge connecting the positive and negative electrode materials of lithium-ion batteries. However, during the charging and discharging process, the electrolyte will react with the positive and negative electrodes, resulting in an increase in battery impedance and cycle attenuation.

[0004] Studies have found that the performance of traditional organic carbonate electrolytes can be significantly improved by introducing fluorine into the structure of electrolyte salts, solvents / co-solvents or functional additives. The high oxidation stability of fluorinated organic compounds makes them ideal for high-voltage lithium-ion battery electrolyte components. The introduction of fluorine into electrolyte salts, solvents / co-solvents and functional additive molecules is a key method to improve the overall performance and reliability of lithium-ion batteries. It can more effectively form solid electrolyte interphases (SEI) and positive electrolyte interphases (CEI), with better thermal and electrochemical stability, as well as low and high temperature characteristics. Another advantage of fluorine is that it makes normally flammable electrolytes less flammable. It has been widely verified that fluorination of electrolyte components helps improve the performance and safety of high-voltage batteries. The replacement of hydrogen by fluorine atoms leads to a decrease in activation energy and a decrease in HOMO and LUMO energy levels, resulting in an increase in reduction potential and oxidation potential. A high reduction potential can form an effective SEI film, which inhibits further electrolyte decomposition and significantly improves the cycle performance of the battery. For example, in the prior art, fluoroethylene carbonate (FEC) is a commonly used electrolyte additive for improving battery performance.

[0005] However, the FEC additives used in the prior art are mainly used to form films at the negative electrode, so it is necessary to add positive electrode film-forming additives to the electrolyte separately, and FEC often needs to be used at a higher content in lithium batteries, which not only increases the cost of use, but also the high-content FEC has poor stability and is easily decomposed during the cycle process, thereby affecting the high-temperature storage and cycle performance of the battery. Summary of the invention

[0006] The main purpose of the present invention is to provide an additive for lithium-ion battery electrolyte, an electrolyte containing the same and a lithium-ion secondary battery, so as to solve the problems in the prior art that the additive (such as FEC) for lithium-ion battery electrolyte is used in high dosage, has poor stability and leads to battery performance degradation.

[0007] In order to achieve the above object, according to one aspect of the present invention, the present invention provides an additive for lithium ion battery electrolyte, the additive comprising a compound having a structure of the following formula (1):

[0008]

[0009] Wherein R1 and R2 are respectively an alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted aryl group containing heteroatoms, and Rf is fluorine or a fluorine-substituted alkyl group having 1 to 10 carbon atoms.

[0010] Furthermore, in the above additive, in formula (1), R1 and R2 are substituted or unsubstituted phenyl groups, and Rf is fluorine or a fluorinated alkyl group.

[0011] Furthermore, in the above-mentioned additives, the compound of the structure of formula (1) is selected from any one of the following:

[0012]

[0013] Best

[0014] A-1:

[0015] A-2:

[0016] A-3:

[0017] According to another aspect of the present invention, an electrolyte for a lithium ion battery is provided. The electrolyte comprises the additives according to the above aspects of the present invention, an organic solvent and a lithium salt.

[0018] Further, in the above electrolyte, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the additive is in the range of 0.1 parts by weight to 2.0 parts by weight.

[0019] Furthermore, in the above-mentioned additives, the organic solvent includes cyclic carbonate, linear carbonate or a combination thereof.

[0020] Furthermore, in the above-mentioned additives, the organic solvent includes ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate or any combination thereof.

[0021] Furthermore, among the above-mentioned additives, the lithium salt is selected from the group consisting of LiCl, LiBr, LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiAlCl4, Li2SiF6 or a combination thereof.

[0022] Furthermore, in the above-mentioned additives, the electrolyte further comprises a fluorine-substituted cyclic carbonate compound.

[0023] According to another aspect of the present invention, a lithium-ion secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte according to the above aspects of the present invention.

[0024] According to another aspect of the present invention, there is provided a use of the compound of formula (1) defined in the above various aspects of the present invention for preparing an additive for lithium ion battery electrolyte.

[0025] Through the additive for lithium-ion battery electrolyte, the electrolyte containing the additive and the lithium-ion secondary battery of the present invention, a technical effect of providing an electrolyte system for lithium-ion batteries that can form films on positive and negative electrodes at the same time and significantly improve battery performance, and reducing the amount of additives (such as FEC) used in lithium-ion battery electrolytes in the prior art is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 dQ / dV graphs showing the first charge of the batteries prepared according to Example 5 of the present invention and Comparative Examples 1 and 5. DETAILED DESCRIPTION

[0028] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0029] As described in the background technology section, the lithium battery electrolyte additives (such as FEC) in the prior art have problems such as high usage, poor stability, and affecting battery performance.

[0030] In view of the above problems, the present invention provides an additive for lithium-ion battery electrolyte, an electrolyte containing the additive, and a lithium-ion secondary battery, wherein a new electrolyte additive of a fluorosulfoxide compound is used, which can form a film on the positive and negative electrodes at the same time, significantly improve the battery performance, and reduce the amount of additives (such as FEC) used in the lithium-ion battery electrolyte in the prior art.

[0031] According to a typical embodiment of the present invention, there is provided an additive for lithium ion battery electrolyte, the additive comprising a compound having a structure of the following formula (1):

[0032]

[0033] Wherein R1 and R2 are respectively an alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted aryl group containing heteroatoms, and Rf is fluorine or a fluorine-substituted alkyl group having 1 to 10 carbon atoms.

[0034] The inventors unexpectedly found that the compound according to the present invention can provide a fluorine source to form LiF after redox decomposition during the lithium battery cycle, ensuring good cycle activity, and on the other hand, the reaction product after defluorination is an excellent conductor of lithium ions, which is more conducive to conducting lithium ions, thereby improving the performance of the battery. In addition, the compound itself is an efficient fluorine reagent that can fluorinate components (such as carbonate compounds) in the electrolyte in an electrochemical reaction. After the introduction of fluoride, the wettability of the electrolyte can be effectively improved, while the oxidation resistance and high temperature performance of the battery are improved. In addition, the compound of the present invention has high reaction activity and low reaction potential during battery charge and discharge, and is more easily decomposed to form a stable SEI film, protecting the electrode material and preventing the electrolyte from directly contacting the electrode.

[0035] In a preferred embodiment, in formula (1), R1 and R2 are substituted or unsubstituted phenyl groups, and Rf is fluorine or a fluoroalkyl group. For example, Rf can be selected from fluorine, a monofluoroalkyl group, a perfluoroalkyl group, and the like.

[0036] The inventors have found that the sulfoxide structure in the compound of the present invention has good reactivity and can efficiently perform fluorination reaction with the Rf group connected thereto as a fluorine source. R1 and R2 as substituents can adjust the overall electronic configuration of the compound, further affecting the reactivity of the Rf group, and the above selection of R1, R2 and Rf in the present invention can obtain a compound with optimal performance.

[0037] In a preferred embodiment, the compound of the structure of formula (1) is selected from any one of the following:

[0038]

[0039] Best

[0040] A-1:

[0041] A-2:

[0042] A-3:

[0043] According to another typical embodiment of the present invention, an electrolyte for a lithium ion battery is provided. The electrolyte comprises the additive according to the above embodiments of the present invention, an organic solvent and a lithium salt.

[0044] In a preferred embodiment, the amount of the additive is in the range of 0.1 parts by weight to 2.0 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt.

[0045] In a preferred embodiment, the organic solvent comprises cyclic carbonate, linear carbonate or a combination thereof.

[0046] In a preferred embodiment, the organic solvent includes ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate or any combination thereof.

[0047] In a preferred embodiment, the lithium salt is selected from the group consisting of LiCl, LiBr, LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiAlCl4, Li2SiF6 or a combination thereof.

[0048] In a preferred embodiment, the electrolyte further includes a fluorine-substituted cyclic carbonate compound.

[0049] As described above, the compound of the present invention can act as a fluorinating agent in the electrolyte system as an additive, and has good reactivity, and can efficiently fluorinate the components in the electrolyte in the electrochemical reaction. For example, when ethylene carbonate is included in the electrolyte system as an organic solvent, the compound of the present invention can fluorinate ethylene carbonate to produce FEC, thereby reducing the amount of FEC in the electrolyte, and in some cases, even no additional FEC is needed. In addition, as described above, after the introduction of fluoride, the wettability of the electrolyte can be effectively improved, while the oxidation resistance and high temperature performance of the battery are improved. The inventors also unexpectedly found that when the compound of the present invention and FEC are used in combination, the SEI formed at the negative electrode is more stable, which is more conducive to improving the cycle performance of the negative electrode of the lithium battery, especially the silicon-containing negative electrode. Therefore, the compound of the present invention and other film-forming additives such as FEC are used in combination, and the generated SEI is stable, which can significantly reduce the amount of film-forming additive FEC used, while improving the capacity retention rate of the battery. In addition, the present inventors have found that the best performance can be obtained when the compound of the present invention is used in an amount of 0.1 to 2.0 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt in the electrolyte.

[0050] According to another typical embodiment of the present invention, a lithium-ion secondary battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte according to the above embodiments of the present invention.

[0051] According to another typical embodiment of the present invention, there is provided use of the compound of the structure of formula (1) defined in the above-mentioned embodiments of the present invention for preparing an additive for lithium-ion battery electrolyte.

[0052] The present invention will be described in detail below through examples. Each example only lists key technical indicators, but the present invention is not limited to these examples.

[0053] The electrolyte solutions used in Examples and Comparative Examples were prepared by the following steps.

[0054] Example 1: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.1 g of the compound of formula A-1 was added to the electrolyte as an electrolyte additive. The mixture was stirred evenly and then used for later use.

[0055] Example 2: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.3 g of the compound of formula A-1 was added to the electrolyte as an electrolyte additive. The mixture was stirred evenly and then used for later use.

[0056] Example 3: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.5 g of the compound of formula A-1 was added to the electrolyte as an electrolyte additive. The mixture was stirred evenly and then used for later use.

[0057] Example 4: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.7 g of the compound of formula A-1 was added to the electrolyte as an electrolyte additive. The mixture was stirred evenly and then used for later use.

[0058] Example 5: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 1.0 g of the compound of formula A-1 was added to the electrolyte as an electrolyte additive. The mixture was stirred evenly and then used for later use.

[0059] Example 6: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 2.0 g of the compound of formula A-1 was added to the electrolyte as an electrolyte additive. The mixture was stirred evenly and then used for later use.

[0060] Example 7: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate, 3.0 g of fluoroethylene carbonate FEC and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.5 g of the compound of formula A-1 was added to the electrolyte as an electrolyte additive. The mixture was stirred evenly and then used for later use.

[0061] Example 8: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.5 g of the compound of formula A-2 was added to the electrolyte as an electrolyte additive. The mixture was stirred evenly and then used for later use.

[0062] Example 9: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.5 g of the compound of formula A-3 was added to the electrolyte as an electrolyte additive. The mixture was stirred evenly and then used for later use.

[0063] Comparative Example 1: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte, which was stirred evenly and set aside.

[0064] Comparative Example 2: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 0.5 g of electrolyte additive FEC was added to the electrolyte. The mixture was stirred evenly and then used for later use.

[0065] Comparative Example 3: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 1.0 g of electrolyte additive FEC was added to the electrolyte. The mixture was stirred evenly and then used for later use.

[0066] Comparative Example 4: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 3.0 g of electrolyte additive FEC was added to the electrolyte. The mixture was stirred evenly and then used for later use.

[0067] Comparative Example 5: 20.75 g of ethylene carbonate, 56.76 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate and 18.6 g of lithium hexafluorophosphate were mixed to prepare a basic electrolyte. 3.75 g of electrolyte additive FEC was added to the electrolyte. The mixture was stirred evenly and set aside.

[0068] Using the electrolytes prepared in the above examples and comparative examples, a lithium ion battery was prepared by the following steps.

[0069] Preparation of positive electrode sheet: The positive electrode active material is lithium nickel cobalt aluminum oxide NCA (specifically LiNi 0.8 Co 0.15 Al 0.05 O2) (95.50g), conductive carbon black (2.50g), binder polyvinylidene fluoride (1.90g) and dispersant polyvinyl pyrrolidone (0.10g) are mixed to obtain a positive electrode mixture, and the positive electrode mixture is dispersed in N-methylpyrrolidone to obtain a positive electrode mixture slurry. The positive electrode mixture slurry is then coated on a positive electrode collector made of aluminum foil, which is dried and stamped to form a positive electrode sheet.

[0070] Preparation of negative electrode sheet: A mixture of negative electrode active material silicon oxide and graphite powder (wherein the weight ratio of silicon oxide to graphite is 9:1) (95.85g), conductive carbon black (1.00g), binder carboxymethyl cellulose and styrene butadiene latex (3.15g) and an appropriate amount of water were stirred to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was then uniformly coated on a negative electrode collector made of copper foil, dried and stamped to form a negative electrode sheet.

[0071] Battery assembly: CR2016 button cells were assembled in a dry laboratory. The positive electrode sheet prepared in the above steps was used as the positive electrode, the negative electrode sheet was used as the negative electrode, and the electrolyte prepared in the above embodiment and comparative example was used as the electrolyte, which was assembled with the separator and the battery shell of the button cell. After the battery was assembled, it was left to stand for 12 hours to age, and an NCA button cell was obtained.

[0072] The battery prepared above was subjected to the first charge and discharge and cycle test on the Xinwei charge and discharge instrument. The battery was first subjected to a 0.1C cycle test at 23°C for one time, and then a 0.5C charge and 5C discharge cycle test was performed at 60°C for 100 times. The capacity retention rate of the battery was calculated by the following formula: 100-week capacity retention rate of the battery = discharge capacity of the 100th week of 5C discharge / discharge capacity of the first week of 5C discharge * 100%. The types and contents of additives used in the electrolytes prepared in Examples 1-11 and Comparative Examples 1-5, as well as the capacity retention rates of the batteries prepared therefrom are shown in Table 1 below.

[0073] Table 1

[0074]

[0075] In the results of Table 1, by comparing Examples 1-6 with Comparative Example 1, it can be seen that when the electrolyte additive of the present invention (the compound of formula A-1) is added within the dosage range specified in the present invention, the cycle retention rate of the battery increases. In addition, Examples 8 and 9 prove that other compounds of the present invention (A-2 and A-3) also achieve the same effect.

[0076] It can be seen from the results of Example 7 that the combined use of the electrolyte additive of the present invention and the film-forming additive FEC can further improve the battery performance. And by comparing Example 7 with Comparative Example 5, it can be seen that under the same total amount of additives, the combined use of the electrolyte additive of the present invention and the film-forming additive FEC achieves a significantly higher cycle retention rate than using only FEC.

[0077] By comparing Example 3 with Comparative Example 2, and Example 5 with Comparative Example 3, it can be seen that the cycle performance of the battery using the additive of the present invention is better than that of the battery adding FEC at the same dosage. In other words, the additive of the present invention requires a smaller amount of addition to achieve the same cycle performance than FEC. By comparing Example 5 with Comparative Examples 4 and 5, it can be seen that when a similar cycle retention rate is achieved, the amount of additive used in Comparative Examples 4 and 5 is much greater than that in Example 5. Therefore, when the electrolyte additive of the present invention is used, the use of film-forming additives such as FEC can be greatly reduced. When the additive of the present invention is used instead of FEC, or the additive of the present invention is used in combination with FEC, costs can be saved and the instability problem caused by the use of a large amount of FEC additive can be improved.

[0078] In addition, the dQ / dV curves of the batteries prepared using the electrolytes of Example 5, Comparative Example 1 and Comparative Example 5 were also measured. Figure 1 As shown. Figure 1 It can be seen that the reduction peaks of the substances in the electrolytes of Example 5, Comparative Example 1 and Comparative Example 5 undergo electrochemical reactions during the battery cycle. It can be seen that for the battery using the electrolyte of Comparative Example 1 (without additives), only the reduction peak of ethylene carbonate (EC) is shown, the battery using the electrolyte of Comparative Example 5 (FEC additive) shows the reduction peak of FEC, and in the battery using the electrolyte of Example 5 (additive A-1 of the present invention), the reduction peaks of both A-1 and FEC appear, which means that the additive of the present invention can fluorinate EC in the electrolyte into FEC, thereby further proving that the use of the additive of the present invention can reduce the amount of FEC used.

[0079] In summary, by using the additive for lithium ion battery electrolyte, the electrolyte and lithium ion secondary battery containing the same according to the present invention, the amount of film-forming additives such as FEC used is reduced while improving the capacity retention rate of the battery.

[0080] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An additive for lithium ion battery electrolyte, characterized in that: The additive comprises a compound having the structure of the following formula (1): Wherein R1 and R2 are respectively an alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted aryl group containing heteroatoms, and Rf is fluorine or a fluorine-substituted alkyl group having 1 to 10 carbon atoms.

2. The additive according to claim 1, characterized in that In formula (1), R1 and R2 are substituted or unsubstituted phenyl groups, and Rf is fluorine or a fluorinated alkyl group.

3. The additive according to claim 1 or 2, characterized in that The compound of the structure of formula (1) is selected from any one of the following: Best A-1： A-2: or A-3： 4. An electrolyte for a lithium ion battery, characterized in that: The electrolyte comprises the additive according to any one of claims 1 to 3, an organic solvent and a lithium salt.

5. The electrolyte according to claim 4, characterized in that The amount of the additive is in the range of 0.1 parts by weight to 2.0 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt.

6. The electrolyte according to claim 4, characterized in that The organic solvent includes cyclic carbonate, linear carbonate or a combination thereof.

7. The electrolyte according to claim 6, characterized in that The organic solvent includes ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate or any combination thereof.

8. The electrolyte according to claim 4, characterized in that The lithium salt is selected from the group consisting of LiCl, LiBr, LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiAlCl4, Li2SiF6 or a combination thereof.

9. The electrolyte according to claim 4, characterized in that The electrolyte further includes a fluorine-substituted cyclic carbonate compound.

10. A lithium ion secondary battery, characterized in that: include: Positive electrode, Negative electrode, Diaphragm, and The electrolyte according to any one of claims 4 to 9.

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