Electrolyte additive, electrolyte containing electrolyte additive and lithium ion secondary battery

Abstract

The invention discloses an electrolyte additive, an electrolyte containing the electrolyte additive and a lithium ion secondary battery. The electrolyte additive comprises a substance as shown in a formula (1), and in the formula (1), R1, R3 and R4 are respectively and independently hydrogen, substituted or unsubstituted phenyl, halogen, C1-6 alkoxy or cyano; r2 is phenyl substituted or unsubstituted by C1-6 alkyl groups, hydrogen, C1-10 alkyl groups, silyl groups, alkoxy groups, ester groups or alkoxy alkylene groups; with the proviso that when R1, R3 and R4 are all hydrogen, R2 is not phenyl. By using the electrolyte additive disclosed by the invention, the cycle performance of the battery is obviously improved, and the impedance and gas production of the battery are obviously reduced. # imgabs0 #

Description

Technical Field

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

[0002] As various electronic devices such as mobile phones have become widely used, there is a strong demand for miniaturization, weight reduction, and longer life of these electronic devices. Therefore, development of small, lightweight, and high-energy-density secondary batteries as power sources is underway.

[0003] Secondary batteries are not limited to electronic devices, but are also being studied for other uses, such as battery packs that can be detachably mounted on electronic devices, electric vehicles such as electric cars, power storage systems such as home power servers, and electric tools such as electric drills.

[0004] Compared with traditional lead-acid batteries and zinc-manganese batteries, lithium-ion batteries have the advantages of long service life, high output voltage, high energy density, low self-discharge, low environmental pollution and no memory effect. Nowadays, they have been widely used in portable electronic devices, electric vehicles, power tools and other fields. As one of the important components of lithium-ion batteries, the composition of electrolyte has an important influence on the overall performance of the battery.

[0005] Therefore, various studies have been conducted in the art on the composition of the electrolyte. For example, CN110945705A discloses a five-membered ring structure However, since the five-membered ring structure contains more fluorine atoms, it will decompose during the battery charging and discharging process to form excessive inorganic lithium salts such as LiF, resulting in increased battery impedance. In addition, compounds with more fluorine substitution have lower boiling points and are more volatile. Summary of the invention

[0006] The main purpose of the present invention is to provide an electrolyte additive, an electrolyte containing the same and a lithium ion secondary battery, so as to solve the problems of poor battery cycle performance, high battery impedance and high battery gas production in the prior art.

[0007] In order to achieve the above object, according to one aspect of the present invention, there is provided an electrolyte additive, the additive comprising a substance represented by the following formula (1):

[0008]

[0009] wherein R1, R3 and R4 are each independently hydrogen, substituted or unsubstituted phenyl, halogen, C 1-6 Alkoxy or cyano;

[0010] R2 is C 1-6 Alkyl substituted or unsubstituted phenyl, hydrogen, C1-10 Alkyl, silyl, alkoxy, ester or alkoxyalkylene;

[0011] Provided that when R1, R3 and R4 are all hydrogen, R2 is not phenyl.

[0012] Further, in the above electrolyte additive, provided that when R3 and R4 are hydrogen, R1 is hydrogen, substituted or unsubstituted phenyl, halogen, C 1-6 Alkoxy or cyano.

[0013] Further, in the above electrolyte additive, there is a proviso that when R1 is hydrogen, R3 and R4 are each independently halogen.

[0014] Furthermore, in the above electrolyte additive, R2 is C 1-6 Alkyl substituted or unsubstituted phenyl, hydrogen, C 1-6 alkyl, silyl, trimethylsilyl, triethylsilyl, tripropylsilyl or 2-methoxyethoxymethyl.

[0015] Furthermore, in the above electrolyte additive, the substance of formula (1) is selected from any one of the following items:

[0016]

[0017] According to another aspect of the present invention, an electrolyte is provided, comprising an organic solvent, a lithium salt and the electrolyte additive described in the present invention.

[0018] Further, in the above electrolyte, the amount of the electrolyte additive is in the range of 0.1 parts by weight to 5.0 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt.

[0019] Furthermore, in the above electrolyte, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate.

[0020] According to another aspect of the present invention, a lithium-ion secondary battery is provided, comprising: a positive electrode, a negative electrode, a separator, and the electrolyte described in the present invention.

[0021] By using the electrolyte additive of the present invention, since the asymmetric difluorocyclopropene structure has high reaction activity during the cycle of battery charge and discharge, it is easier to decompose and form a stable solid electrolyte interface (SEI) film, which can protect the electrode material and prevent the electrolyte from directly contacting the electrode, and the asymmetric difluorocyclopropene structure can participate in the reaction at the positive and negative electrodes of the battery at the same time, and the generated SEI and positive electrode electrolyte interface (CEI) impedance are small, which significantly improves the battery cycle performance. In addition, the functional groups on both sides of the asymmetric difluorocyclopropene structure are different, compared with the compounds of symmetrical structures, the solubility of the electrolyte additive in non-aqueous electrolyte can be effectively improved. And the reaction product of the asymmetric difluorocyclopropene structure does not contain gas, so the gas production of the battery can be significantly reduced. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0023] As described in the background art, only five-membered unsaturated cyclic compounds are proposed as electrolyte additives in the prior art. However, since the five-membered unsaturated cyclic compound contains more fluorine atoms, it will decompose to form excessive inorganic lithium salts such as LiF during the battery charge and discharge process, resulting in increased battery impedance, and compounds with more fluorine substitution have lower boiling points and are volatile. Therefore, it is still necessary to develop an electrolyte additive that can overcome the problems in the prior art. In view of the problems in the prior art, according to a typical embodiment of the present invention, an electrolyte additive is provided, which comprises a substance represented by the following formula (1):

[0024]

[0025] wherein R1, R3 and R4 are each independently hydrogen, substituted or unsubstituted phenyl, halogen, C 1-6 Alkoxy or cyano;

[0026] R2 is C 1-6 Alkyl substituted or unsubstituted phenyl, hydrogen, C 1-10 Alkyl, silyl, alkoxy, ester or alkoxyalkylene;

[0027] Provided that when R1, R3 and R4 are all hydrogen, R2 is not phenyl.

[0028] By using the electrolyte additive of the present invention, since the asymmetric difluorocyclopropene structure has high reaction activity during the cycle of battery charge and discharge, it is easier to decompose and form a stable solid electrolyte interface (SEI) film, which can protect the electrode material and prevent the electrolyte from directly contacting the electrode, and the asymmetric difluorocyclopropene structure can participate in the reaction at the positive and negative electrodes of the battery at the same time, and the generated SEI and positive electrode electrolyte interface (CEI) impedance are small, which significantly improves the battery cycle performance. In addition, the functional groups on both sides of the difluorocyclopropene structure are different, and compared with the compounds of symmetrical structures, the solubility of the electrolyte additive in the non-aqueous electrolyte can be effectively improved. And the reaction product of the asymmetric difluorocyclopropene structure does not contain gas, so the gas production of the battery can be significantly reduced.

[0029] definition

[0030] Alkoxy refers to a group formed by connecting an alkyl group to an oxygen atom (RO-), such as methoxy, ethoxy, propoxy, etc.

[0031] Phenyl is a hydrophobic aromatic functional group obtained from benzene (C6H6) with the molecular formula -C6H5.

[0032] Alkyl is the part of an alkane molecule that has one hydrogen atom removed. n H 2n+1 , such as methyl, ethyl, propyl, etc.

[0033] Alkoxyalkylene is a compound having the chemical formula (C n H 2n+1 O) m C n H 2n -structure, wherein m is greater than or equal to 1 and n is greater than or equal to 1.

[0034] Preferred R1

[0035] R1 is preferably hydrogen, phenyl, alkoxy-substituted phenyl, halogen (e.g., F, Cl, Br or I), C 1-6 More preferably, R1 is hydrogen, phenyl, C 1-6 Alkoxy-substituted phenyl, C 1-6 Most preferably, R1 is hydrogen, phenyl, methoxy or cyano.

[0036] Preferred R3

[0037] R3 is preferably hydrogen, phenyl, alkoxy-substituted phenyl, halogen (e.g., F, Cl, Br or I), C 1-6 More preferably, R3 is hydrogen, phenyl, C 1-6 Alkoxy substituted phenyl, halogen, C 1-6Most preferably, R3 is hydrogen or halogen (most preferably F).

[0038] Preferred R4

[0039] R4 is preferably hydrogen, phenyl, alkoxy-substituted phenyl, halogen (e.g., F, Cl, Br or I), C 1-6 More preferably, R4 is hydrogen, phenyl, C 1-6 Alkoxy substituted phenyl, halogen, C 1-6 Most preferably, R4 is hydrogen or halogen (most preferably F).

[0040] Preferably, in formula (1), provided that when R3 and R4 are hydrogen, R1 is hydrogen, substituted or unsubstituted phenyl, halogen (e.g., F, Cl, Br or I), C 1-6 By using a substance represented by formula (1) that satisfies this condition, the battery impedance can be further reduced and the battery gas generation can be significantly reduced. R1 is preferably hydrogen, phenyl, C 1-6 Alkoxy-substituted phenyl, C 1-6 Alkoxy or cyano (-CN). Most preferably, R1 is hydrogen, phenyl, methoxy or cyano.

[0041] Preferably, in formula (1), when R1 is hydrogen, R3 and R4 are each independently a halogen. By using a substance represented by formula (1) that satisfies this condition, the battery impedance can be further reduced and the battery gas generation can be significantly reduced. The halogen is preferably F, Cl, Br or I, and most preferably F.

[0042] Preferably, in formula (1), R2 is C 1-6 Alkyl substituted or unsubstituted phenyl, hydrogen, C 1-6 alkyl, silyl, trimethylsilyl, triethylsilyl, tripropylsilyl or 2-methoxyethoxymethyl. By using the substance represented by formula (1) that satisfies this condition, the battery impedance can be further reduced and the battery gas generation can be significantly reduced. R2 is preferably C 1-6 Alkyl substituted or unsubstituted phenyl, hydrogen, C 1-6 More preferably, R2 is C 1-6 Alkyl-substituted phenyl, hydrogen, C 1-6 alkyl, trimethylsilyl or 2-methoxyethoxymethyl.

[0043] Preferably, the substance of formula (1) is selected from any one of the following:

[0044]

[0045] By using the substances shown, the battery impedance can be further reduced and the battery gassing can be significantly reduced.

[0046] According to another aspect of the present invention, an electrolyte is provided, comprising an organic solvent, a lithium salt and the electrolyte additive described in the present invention.

[0047] By using the electrolyte additive of the present invention in the electrolyte, since the asymmetric difluorocyclopropene structure has high reaction activity during the battery charge and discharge cycle, it is easier to decompose and form a stable solid electrolyte interface (SEI) film, which can protect the electrode material and prevent the electrolyte from directly contacting the electrode, and the asymmetric difluorocyclopropene structure can participate in the reaction at the positive and negative electrodes of the battery at the same time, and the generated SEI and positive electrode electrolyte interface (CEI) impedance are small, which significantly improves the battery cycle performance. In addition, the functional groups on both sides of the difluorocyclopropene structure are different, and compared with the compounds of the symmetrical structure, the solubility of the electrolyte additive in the non-aqueous electrolyte can be effectively improved. In addition, the reaction product of the asymmetric difluorocyclopropene structure does not contain gas, so the gas production of the battery can be significantly reduced.

[0048] Preferably, in the above electrolyte, based on 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 to 5.0 parts by weight. Preferably, the amount of the electrolyte additive is in the range of 0.1 to 4.0 parts by weight. Preferably, the amount of the electrolyte additive is in the range of 0.1 to 2.0 parts by weight. Within this range, the electrolyte additive can be well dissolved in the organic solvent, thereby further reducing the battery impedance and significantly reducing the battery gas production.

[0049] Specifically, in the above-mentioned electrolyte, based on 100 parts by weight of the organic solvent and the lithium salt, the amount of the electrolyte additive can be 0.1 parts by weight, 0.5 parts by weight, 1.0 parts by weight, 1.1 parts by weight, 1.5 parts by weight, 2.0 parts by weight, 2.1 parts by weight, 2.5 parts by weight, 3.0 parts by weight, 3.1 parts by weight, 3.5 parts by weight, or 4.0 parts by weight.

[0050] Preferably, in the above-mentioned electrolyte, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate. The above is only an example of the organic solvent used in the present invention, but is not limited to this. Those skilled in the art can select suitable organic solvent according to actual needs.

[0051] The present invention does not impose any limitation on lithium salts, and any lithium salt commonly used in the art can be used in the present invention.

[0052] According to another aspect of the present invention, a lithium ion secondary battery is provided, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte described in the present invention. The present invention does not impose any restrictions on the positive electrode, the negative electrode, and the separator, and the positive electrode, the negative electrode, and the separator commonly used in the art can be used in the present invention.

[0053] By using the electrolyte additive of the present invention in a lithium ion secondary battery, since the asymmetric difluorocyclopropene structure has high reaction activity during the battery charge and discharge cycle, it is easier to decompose and form a stable solid electrolyte interface (SEI) film, which can protect the electrode material and prevent the electrolyte from directly contacting the electrode, and the asymmetric difluorocyclopropene structure can participate in the reaction at the positive and negative electrodes of the battery at the same time, and the generated SEI and positive electrode electrolyte interface (CEI) impedance are small, which significantly improves the battery cycle performance. In addition, the functional groups on both sides of the difluorocyclopropene structure are different, and compared with the compounds of the symmetrical structure, the solubility of the electrolyte additive in the non-aqueous electrolyte can be effectively improved. And the reaction product of the asymmetric difluorocyclopropene structure does not contain gas, so the gas production of the battery can be significantly reduced.

[0054] Example

[0055] Preparation of positive electrode

[0056] 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) were mixed to obtain a positive electrode mixture, and the positive electrode mixture was dispersed in N-methylpyrrolidone to obtain a positive electrode mixture slurry. Then, the positive electrode mixture slurry was uniformly coated on a positive electrode collector made of aluminum foil, which was dried and stamped to form a positive electrode sheet.

[0057] Preparation of negative electrode

[0058] A mixture of silicon oxide and graphite powder (95.85 g, where the weight ratio of silicon oxide to graphite is 9:1) of negative electrode active material, conductive carbon black (1.00 g), binder carboxymethyl cellulose and styrene butadiene latex (3.15 g) 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.

[0059] Preparation of basic electrolyte

[0060] Ethylene carbonate (20.00 g), dimethyl carbonate (62.00 g), and lithium hexafluorophosphate (18.00 g) were mixed to prepare a basic electrolyte.

[0061] Preparation of the electrolyte of Examples 1-11

[0062] Add 0.5 g of electrolyte additives C1-C11 to the basic electrolyte respectively, mix well and set aside.

[0063] Preparation of the electrolyte of Examples 12-16

[0064] The preparation of the electrolytes of Examples 12 to 16 was the same as that of Example 9, except that the amounts of the electrolyte additives were changed to 0.01 g, 1.0 g, 1.5 g, 2.0 g, and 4.0 g, respectively.

[0065] Preparation of the electrolyte of Comparative Example 1

[0066] The preparation of the electrolyte of Comparative Example 1 is the same as that of the basic electrolyte.

[0067] Preparation of the electrolyte of Comparative Example 2

[0068] The preparation of the electrolyte of Comparative Example 2 is the same as that of the electrolyte of Examples 1-11, except that the electrolyte additive of the present invention is replaced by fluoroethylene carbonate FEC.

[0069] Preparation of the electrolyte of Comparative Example 3

[0070] The preparation of the electrolyte of Comparative Example 3 is the same as that of the electrolyte of Examples 1-11, except that the electrolyte additive of the present invention is replaced by P1, wherein P1 is

[0071] Preparation of the electrolyte of Comparative Example 4

[0072] The preparation of the electrolyte of Comparative Example 4 is the same as that of the electrolyte of Examples 1-11, except that the electrolyte additive of the present invention is replaced by P2, wherein P2 is

[0073] Battery Assembly

[0074] Assemble CR2016 button cells in a dry laboratory. Use the positive electrode sheet obtained in the above steps as the positive electrode, the negative electrode sheet as the negative electrode, and the electrolyte prepared in the embodiment and the comparative example as the electrolyte. Assemble the positive electrode, the negative electrode, the separator and the battery shell of the button cell and inject the electrolyte. After the battery is assembled, let it stand for 12 hours to age and obtain an NCA button cell.

[0075] Battery performance test

[0076] 1. Use a charge and discharge instrument to test the battery's cycle performance and impedance.

[0077] The batteries in the embodiments and comparative examples were first subjected to a 0.1C charge and discharge cycle test at 23°C once, and the first discharge capacity (discharge capacity of the first cycle) was measured. Then, a cycle test of 0.5C charge and 5C discharge was performed 100 times at 60°C, and the discharge capacity of the 100th cycle was measured. Based on the following formula: Capacity retention rate after 100 cycles [%] = (discharge capacity of the 100th cycle / discharge capacity of the 1st cycle) × 100%, the capacity retention rate after 100 cycles (%) was calculated using the discharge capacity of the 1st cycle and the discharge capacity of the 100th cycle. Finally, a charge test at a rate of 0.5C was performed once at 60°C to determine the impedance value of the battery.

[0078] 2. Gas production test

[0079] After completing a 0.1C charge-discharge cycle test at 23°C, the volume of each battery was recorded through water as the initial volume; after performing a 0.5C charge and 5C discharge cycle test at 60°C for 100 times, the volume of each battery was recorded through water again as the final volume. The difference between the two volumes is the amount of gas generated by the battery.

[0080] The performance test results of the batteries of Examples 1-11 and Comparative Examples 1-4 are shown in Table 1 below.

[0081] Table 1

[0082] serial number Additive Type Additive content (wt%) Capacity retention rate (%) Impedance (Ohms) Gas production (mL) Example 1 C1 0.5 71.1 17.0 0.160 Example 2 C2 0.5 71.3 17.0 0.161 Example 3 C3 0.5 72.0 16.5 0.166 Example 4 C4 0.5 72.5 16.0 0.160 Example 5 C5 0.5 71.63 18.17 0.162 Example 6 C6 0.5 72.05 17.52 0.167 Example 7 C7 0.5 72.20 17.11 0.166 Example 8 C8 0.5 72.35 17.31 0.170 Example 9 C9 0.5 72.90 18.73 0.163 Example 10 C10 0.5 73.5 17.0 0.160 Embodiment 11 C11 0.5 73.5 15.0 0.162 Comparative Example 1 / / 70.00 18.26 0.217 Comparative Example 2 FEC 0.5 71.41 21.83 0.269 Comparative Example 3 P1 0.5 71.58 22.85 0.169 Comparative Example 4 P2 0.5 72.64 21.96 0.178

[0083] Note: The additive content is the weight percentage based on the total weight of the basic electrolyte.

[0084] It can be seen from the test results in Table 1 that the above embodiments of the present invention achieve the following technical effects:

[0085] Compared with Comparative Example 1, Examples 1 to 11 show that the electrolyte additives C1 to C11 of the present invention can significantly improve the cycle performance of the battery and reduce the impedance and gas production of the battery;

[0086] Compared with Comparative Example 2, when the cycle performance of the batteries of Examples 1 to 11 is equal to or better than that of Comparative Example 2, the electrolyte additives C1-C11 of the present invention can significantly reduce the impedance and gas production of the batteries;

[0087] Compared with Examples 1 to 11 and Comparative Examples 3-4, when the cycle performance and gas production of the batteries of Examples 1 to 11 are equivalent to or better than those of Comparative Examples 3-4, the electrolyte additives C1-C11 of the present invention can significantly reduce the impedance of the battery.

[0088] The performance test results of the batteries of Examples 9, 12-16 are shown in Table 2 below.

[0089] Table 2

[0090] serial number Additive Type Additive content (wt%) Capacity retention rate (%) Gas production (mL) Example 12 C9 0.01 70.05 0.213 Example 9 C9 0.5 72.90 0.163 Embodiment 13 C9 1.0 76.43 0.151 Embodiment 14 C9 1.5 75.17 0.143 Embodiment 15 C9 2.0 73.40 0.130 Example 16 C9 4.0 71.0 0.120

[0091] It can be seen from the test results in Table 2 that the above embodiments of the present invention achieve the following technical effects:

[0092] Compared with Comparative Example 1, Examples 12 to 16 show that the electrolyte additive C9 of the present invention can significantly improve the cycle performance of the battery and reduce the gas production of the battery;

[0093] Compared with Comparative Example 2, when the cycle performance of the batteries of Examples 12 to 16 is equal to or better than that of Comparative Example 2, the electrolyte additive C9 of the present invention can significantly reduce the gas production of the battery;

[0094] Compared with Comparative Examples 3-4, when the cycle performance of the batteries of Examples 12-16 is equivalent to or better than that of Comparative Examples 3-4, the electrolyte additive C9 of the present invention can significantly reduce the gas production of the battery.

[0095] Compared with Examples 12 and 16, when the amount of the electrolyte additive C9 was in the range of 0.5 parts by weight to 2.0 parts by weight, Examples 9 and 13-15 further improved the capacity retention rate and further reduced the gas generation of the battery.

[0096] It can be seen from the above battery performance test results that the electrolyte additive of the present invention effectively improves the cycle performance of the lithium ion secondary battery and reduces the impedance and gas production of the lithium ion secondary battery.

[0097] The above description is only the 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 electrolyte additive, characterized in that: The additive comprises a substance represented by the following formula (1): wherein R1, R3 and R4 are each independently hydrogen, substituted or unsubstituted phenyl, halogen, C 1-6 Alkoxy or cyano; R2 is C 1-6 Alkyl substituted or unsubstituted phenyl, hydrogen, C 1-10 Alkyl, silyl, alkoxy, ester or alkoxyalkylene; Provided that when R1, R3 and R4 are all hydrogen, R2 is not phenyl.

2. The electrolyte additive according to claim 1, characterized in that: Provided that when R3 and R4 are hydrogen, R1 is hydrogen, substituted or unsubstituted phenyl, halogen, C 1-6 Alkoxy or cyano.

3. The electrolyte additive according to claim 1, characterized in that: Provided that when R1 is hydrogen, R3 and R4 are each independently halogen.

4. The electrolyte additive according to claim 1, characterized in that: R2 is C 1-6 Alkyl substituted or unsubstituted phenyl, hydrogen, C 1-6 alkyl, silyl, trimethylsilyl, triethylsilyl, tripropylsilyl or 2-methoxyethoxymethyl.

5. The electrolyte additive according to claim 1, characterized in that: The substance of formula (1) is selected from any one of the following: 6 . An electrolyte comprising an organic solvent, a lithium salt and the electrolyte additive according to any one of claims 1 to 5.

7. The electrolyte according to claim 6, characterized in that The amount of the electrolyte additive is in the range of 0.1 parts by weight to 5.0 parts by weight based on 100 parts by weight of the organic solvent and the lithium salt.

8. The electrolyte according to claim 6 or 7, characterized in that The organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, ethyl methyl carbonate, methylpropyl carbonate and propyl propionate.

9. A lithium ion secondary battery, characterized in that: include: positive electrode, negative electrode, Diaphragm, and The electrolyte according to any one of claims 6 to 8.

Images