High-voltage-resistant solvent, high-voltage-resistant electrolyte and application

Abstract

The invention provides a high-voltage-resistant solvent, a high-voltage-resistant electrolyte and reference, the high-voltage-resistant solvent has a structure as shown in a formula I. In the formula I, R1 and R2 are independently selected from hydrogen, halogen and substituted or unsubstituted C1-C12 alkyl. According to the invention, DMDOHD (dimethyl 2, 5-dioxaadipate) is used as a basic structure, but the dissociation capability of lithium salt of the solvent is poor, the conductivity of the electrolyte is reduced, and the low-temperature and rate performance is deteriorated. An SEI film formed by the solvent on an electrode interface is large in film impedance and poor in stability, an electrode cannot be effectively passivated, and transmission of lithium ions is affected, a specific functional group is introduced into the dimethyl 2, 5-dioxaadipate, the dissociation capacity of lithium salt can be improved while the oxidizability of the solvent is improved, and the service life of the solvent is prolonged. And the influence of low conductivity on low temperature and rate capability is optimized.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and in particular relates to a high-voltage resistant solvent, a high-voltage resistant electrolyte and applications. Background Art

[0002] Traditional lithium battery electrolytes are composed of solvents, lithium salts and additives. Under high-voltage systems, some components of the electrolyte are unstable and easy to decompose. They continue to react at the electrode-electrolyte interface, consume active lithium, and cause battery capacity decay. Battery decay is more serious under high temperatures. Under high voltage, the positive electrode interface problem is a key factor affecting battery performance.

[0003] To solve the above problems, high-voltage resistant solvents are usually added when designing the electrolyte. Commonly used high-voltage resistant solvents include nitrile solvents, sulfone solvents, ionic liquids, etc. Nitrile and sulfone solvents have poor compatibility with the negative electrode and increase the risk of negative electrode impedance. Ionic liquids have high viscosity and high price, and are relatively less used. Summary of the invention

[0004] The purpose of the present invention is to provide a high-pressure resistant solvent, a high-pressure resistant electrolyte and applications. The high-pressure resistant solvent in the present invention has high oxidation stability and thermal stability, and can effectively improve the high-voltage and high-temperature cycle performance of the battery.

[0005] The present invention provides a high pressure resistant solvent having a structure shown in Formula I:

[0006]

[0007] In formula I, R1 and R2 are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C12 alkyl.

[0008] Preferably, R1 and R2 are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C5 alkyl.

[0009] Preferably, the high pressure resistant solvent has a structure shown in any one of Formula I-1 to Formula I-4:

[0010]

[0011] The present invention provides a high-voltage resistant electrolyte, comprising a lithium salt, a first solvent and a second solvent;

[0012] The first solvent includes two or more of polycarbonate, propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone;

[0013] The second solvent is the high-voltage resistant solvent; the mass fraction of the second solvent in the high-voltage resistant electrolyte is 5-15%.

[0014] Preferably, the high-voltage resistant electrolyte further includes a fluorinated solvent, and the fluorinated solvent includes one or more of fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane; the mass fraction of the fluorinated solvent in the high-voltage resistant electrolyte is 2 to 15%.

[0015] Preferably, the first solvent includes a mixed solvent of at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate and other solvents; the other solvents include one or more of polycarbonate, propylene carbonate, ethylene carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone.

[0016] Preferably, the high-voltage resistant electrolyte further includes a low-internal-resistance film-forming additive; the low-internal-resistance film-forming additive includes one or more of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, pentafluorocyclophosphazene, 4,5-dicyano-2-trifluoromethyl-imidazole lithium, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium difluorooxalatophosphate, vinyl sulfate, vinyl fluorosulfate, vinyl disulfate and vinyl disulfite; the mass fraction of the low-internal-resistance film-forming additive in the high-voltage resistant electrolyte is 0.1 to 8%.

[0017] Preferably, the lithium salt includes one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate and lithium tetrafluoroborate; and the concentration of the lithium salt in the high-voltage resistant electrolyte is 0.5 to 2.0 mol / L.

[0018] The present invention provides a lithium ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the high-voltage resistant electrolyte described above.

[0019] The present invention provides the use of the high-voltage resistant solvent or the high-voltage resistant electrolyte described above in a high-voltage battery system;

[0020] The charging cut-off voltage in the high-voltage battery system is greater than 4.6V.

[0021] The present invention provides a high-pressure resistant solvent having a structure shown in Formula I, wherein R1 and R2 are independently selected from hydrogen, halogen, substituted or unsubstituted C1-C12 alkyl. The present invention is based on 2,5-dioxadipic acid dimethyl ester (DMDOHD), but the solvent has poor lithium salt dissociation ability, reduces electrolyte conductivity, and deteriorates low temperature and rate performance. In addition, the SEI film formed by the solvent at the electrode interface has a large film impedance and poor stability, and cannot effectively passivate the electrode, affecting the transmission of lithium ions. In the present invention, a specific functional group is introduced into 2,5-dioxadipic acid dimethyl ester, which can improve the solvent oxidizability while improving the lithium salt dissociation ability, and optimize the effect of low conductivity on low temperature and rate performance.

[0022] The present invention introduces the structural high-pressure solvent into the electrolyte, which generates free radicals to participate in the formation of the SEI film. The regulation of the solvent on the interface reduces the generation of protons H by the oxidation of the solvent at the positive electrode, and inhibits the reduction of protons H generated by the decomposition of the solvent at the negative electrode, thereby reducing the gas production of the battery and improving the safety performance of the battery. DETAILED DESCRIPTION

[0023] The present invention provides a high pressure resistant solvent having a structure shown in Formula I:

[0024]

[0025] In formula I, R1 and R2 are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C12 alkyl.

[0026] In the present invention, R1 and R2 are independently selected from hydrogen, -Cl, -F, -Br, -I, substituted or unsubstituted C1~C5 alkyl. Preferably, R1 and R2 are independently selected from hydrogen, -Cl, -F, -Br, substituted or unsubstituted C1~C3 alkyl. More preferably, R1 and R2 are independently selected from one or more of hydrogen, -Cl, -F, -Br, methyl, ethyl and propyl.

[0027] In the present invention, the high pressure resistant solvent preferably has a structure shown in any one of Formula I-1 to Formula I-4:

[0028]

[0029] In the present invention, the high-pressure resistant solvent may be any one of the compounds having the structure of Formula I used alone as a high-pressure solvent, or may be a mixture of multiple compounds having the structure of Formula I used, and the present invention does not impose any particular limitation on this.

[0030] In the present invention, the high pressure resistant solvent is preferably prepared according to the steps shown in the following formula II, wherein a chlorosulfonamide compound and 2-carboxyloxyethyl methyl carbonate undergo a nucleophilic addition reaction in the presence of a catalyst to generate a high pressure solvent shown in formula I.

[0031]

[0032] In the present invention, the types of R1 and R2 are consistent with the types of R1 and R2 described above, and the present invention will not be repeated here.

[0033] In the present invention, the molar ratio of the chlorosulfonamide compound to 2-carboxyoxyethyl methyl carbonate is preferably 1:(0.9-1.1), more preferably 1:(1-1.1); the catalyst is preferably sodium methoxide; the molar ratio of the catalyst to the chlorosulfonamide compound is preferably (0.1-0.5):1, more preferably (0.2-0.4):1, and most preferably 0.3:1.

[0034] In the present invention, the reaction temperature is preferably 50-80°C, more preferably 60-75°C, and most preferably 65-70°C; the reaction time is preferably 3-8 hours, more preferably 4-7 hours, and most preferably 5-6 hours; the reaction is preferably carried out in an alcohol solvent, more preferably methanol, and most preferably ultra-dry methanol. The reaction is preferably carried out under reflux conditions. After the reaction is completed, a transparent liquid is obtained by reduced pressure distillation, which is the compound shown in Formula I.

[0035] The present invention also provides a high-voltage resistant electrolyte, comprising a lithium salt, a first solvent and a second solvent;

[0036] The first solvent includes two or more of polycarbonate, propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone;

[0037] The second solvent is the high-voltage resistant solvent described above; the mass fraction of the second solvent in the high-voltage resistant electrolyte is 5-15%.

[0038] In the present invention, the lithium salt preferably includes one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate and lithium tetrafluoroborate; the concentration of the lithium salt in the high voltage resistant electrolyte is preferably 0.5-2.0 mol / L, more preferably 1-1.5 mol / L, such as 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, preferably a range value with any of the above values ​​as the upper or lower limit.

[0039] In the present invention, the first solvent preferably includes two or more of polycarbonate, propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone; more preferably, it is a mixed solvent of low-viscosity carbonate and the above-mentioned other solvents, and the low-viscosity carbonate is preferably at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; the other solvents are the remaining solvents in the first solvent except the low-viscosity carbonate, that is, the other solvents include one or more of polycarbonate, propylene carbonate, ethylene carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone; the mass fraction of the first solvent in the electrolyte is preferably 65-75%, such as 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, preferably a range value with any of the above values ​​as the upper or lower limit.

[0040] The present invention preferably uses low-viscosity carbonates, especially dimethyl carbonate (DMC), in the electrolyte, which can take into account both high-voltage oxidation stability and low viscosity, and can effectively reduce the viscosity of the electrolyte, improve electrode wettability, and reduce battery polarization.

[0041] In the present invention, the second solvent is preferably the high-pressure resistant solvent having the structure shown in Formula I as described above, and the mass fraction of the second solvent in the electrolyte is preferably 5-15%, more preferably 10-12%, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, preferably a range value with any of the above values ​​as the upper or lower limit.

[0042] In the present invention, the high-voltage electrolyte preferably further comprises a fluorinated solvent, the fluorinated solvent having a high electrochemical window, and can form a fluorinated polymer on the electrode surface to reduce the gas production of the battery. The fluorinated solvent is preferably one or more of fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane; the mass fraction of the fluorinated solvent in the high-voltage electrolyte is preferably 2 to 10%, more preferably 5 to 8%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, preferably a range value with any of the above values ​​as the upper or lower limit.

[0043] In the present invention, the high-voltage resistant electrolyte preferably also includes a low internal resistance film-forming additive; the low internal resistance film-forming additive includes one or more of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, pentafluorocyclophosphazene, 4,5-dicyano-2-trifluoromethyl-imidazole lithium, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium difluorooxalatophosphate, vinyl sulfate, vinyl fluorosulfate, vinyl disulfate and vinyl disulfite; the mass fraction of the low internal resistance film-forming additive in the high-voltage resistant electrolyte is preferably 0.1-8%, more preferably 1-7%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, preferably a range value with any of the above values ​​as the upper or lower limit.

[0044] The present invention uses fluorinated solvents and film-forming additives in a high-voltage resistant electrolyte to form an inorganic interface rich in L3N, L2S, and LiF and an organic component of a fluorinated polymer, an organic-inorganic composite interface, which has stronger oxidation resistance and inhibits the continuous growth of the interface film impedance, so as to further improve the high-voltage cycle stability.

[0045] The present invention also provides a lithium ion battery, a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is preferably the high voltage resistant electrolyte described above.

[0046] In the present invention, the types of the positive electrode, negative electrode and separator can all be the positive electrode, negative electrode and separator commonly used in the art. In the present invention, the positive electrode active material in the positive electrode is preferably lithium cobalt oxide, nickel manganese cobalt oxide or lithium-rich manganese-based positive electrode material; the negative electrode active material is selected from graphite, silicon carbon, silicon carbon composite material or metallic lithium.

[0047] The present invention also provides an application of the high-voltage resistant solvent or the high-voltage resistant electrolyte described above in a high-voltage battery system. In the present invention, the high-voltage battery system is a high-voltage and high-temperature battery system, and the charging cut-off voltage is preferably >4.6V, more preferably >4.7V.

[0048] The invention provides a sulfonamide-modified high-pressure solvent, which has excellent high-pressure stability and thermal stability, can effectively improve the electrochemical window of the electrolyte, and enhance the high-voltage room-temperature cycle stability and high-voltage cycle stability of the battery. Meanwhile, the introduction of sulfonamide can improve the dissociation ability of the lithium salt and improve the conductivity of the electrolyte, thereby avoiding the disadvantages of high viscosity and poor dissociation of the lithium salt of 2,5-dioxaadipate.

[0049] The present invention introduces the structural high-pressure solvent into the electrolyte to generate free radicals to participate in the formation of SEI film. The sulfonamide functional group regulates the components in the SEI film to generate an interface film component rich in Li3N and Li2S, Li2SO3 and Li2SO4, which is beneficial to Li +Transfer, the regulation of the solvent on the interface effectively inhibits the continuous reduction and decomposition of the low LUMO energy level of the fluorinated solvent at the negative electrode, increasing the membrane impedance. In addition, the regulation of the interfacial film composition can effectively reduce the oxidation of the solvent at the positive electrode to generate protons H, and inhibit the reduction of protons H generated by the decomposition of the solvent at the negative electrode, while achieving the optimization of the interface on both sides of the positive and negative electrodes, reducing battery gas production and thus improving battery safety performance.

[0050] Furthermore, the present invention introduces high-pressure solvents and fluorinated solvents into the high-pressure resistant electrolyte, and uses them in combination with low internal resistance film-forming additives to form inorganic interface film components rich in L3N, L2S, and LiF and fluorinated polymer organic components. By regulating the positive electrode film-forming additives, the fluorinated polymer content is optimized and the organic components such as polyphosphazene and BOB are increased. The organic-inorganic composite interface has stronger oxidation resistance, which inhibits the continuous growth of membrane impedance and further improves the long cycle performance.

[0051] In addition, the present invention introduces DMC into the electrolyte to take into account both high-voltage oxidation stability and low viscosity, which can effectively reduce the viscosity of the electrolyte, improve electrode wettability, reduce battery polarization, and reduce lithium plating.

[0052] In order to further illustrate the present invention, a high-voltage resistant solvent, a high-voltage resistant electrolyte and applications provided by the present invention are described in detail below in conjunction with embodiments, but it should not be understood as limiting the scope of protection of the present invention.

[0053] Example 1 Preparation of Compound of Formula I-1

[0054] Under nitrogen atmosphere, 100 mL of ultra-dry methanol was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor, and then 0.1 mol of N, N-dimethylaminosulfonylethyl chloride and 0.11 mol of 2-carboxyloxyethyl methyl carbonate were added, and magnetic stirring was turned on to fully dissolve them. 0.03 mol of catalyst sodium methoxide was added, and heating was turned on. The reaction temperature was controlled at 65 ° C., heated to reflux for 6 h, cooled, and a transparent liquid was obtained by vacuum distillation, which is a compound of formula I-1. TOF-SIMS (m / z): calcd.forC8H 15 O8NS[M+1] + ,285.27,found 285.09.

[0055] Example 2 Preparation of Compound of Formula I-2

[0056] Under nitrogen atmosphere, 100 mL of ultra-dry methanol was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor, and then 0.1 mol of N, N-diethylaminosulfonylethyl chloride and 0.11 mol of 2-carboxyloxyethyl methyl carbonate were added, and magnetic stirring was turned on to fully dissolve them. 0.03 mol of catalyst sodium methoxide was added, and heating was turned on. The reaction temperature was controlled at 65 ° C., heated to reflux for 6 h, cooled, and a transparent liquid was obtained by reduced pressure distillation, which is the compound of formula I-2. TOF-SIMS (m / z): calcd.forC 10 H 19 O8NS[M+1] + ,313.32,found 313.11.

[0057] Example 3 Preparation of Compound of Formula I-3

[0058] Under nitrogen atmosphere, 100 mL of ultra-dry methanol was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor, and then 0.1 mol of N-methyl-N-ethylaminosulfonylethyl chloride and 0.111 mol of 2-carboxyloxyethyl methyl carbonate were added, and magnetic stirring was turned on to fully dissolve it. 0.03 mol of catalyst sodium methoxide was added, and heating was turned on. The reaction temperature was controlled at 65 ° C., heated to reflux for 6 h, cooled, and a transparent liquid was obtained by reduced pressure distillation, which is a compound of formula I-3. TOF-SIMS (m / z): calcd. for C9H 17 O8NS[M+1] + ,299.29,found 299.20.

[0059] Example 4 Preparation of Compound of Formula I-4

[0060] The specific steps for preparing compound (I) are as follows:

[0061] Under nitrogen atmosphere, 100 mL of ultra-dry methanol was added to a clean and dry 250 mL three-necked flask equipped with a magnetic rotor, and then 0.1 mol of N-methyl-N-propylaminosulfonylethyl chloride and 0.11 mol of 2-carboxyloxyethyl methyl carbonate were added, and magnetic stirring was turned on to fully dissolve them, and 0.03 mol of catalyst sodium methoxide was added, and heating was turned on. The reaction temperature was controlled at 65 ° C, heated to reflux for 6 h, cooled and filtered, and a transparent liquid was obtained by vacuum distillation, which is a compound of formula I-4. TOF-SIMS (m / z): calcd. for C9H 16 O8NS[M+1] + ,298.29,found 298.03.

[0062] Examples 5 to 7 Preparation of high voltage resistant electrolyte

[0063] In a glove box filled with argon (water <0.1 ppm, oxygen <0.1 ppm), the electrolyte was prepared. The formulations of the embodiments and comparative examples are shown in Table 1.

[0064] Table 1 Formulas of high voltage resistant electrolytes in the embodiments of the present invention and the comparative examples (with the total mass of the electrolyte as 100%)

[0065]

[0066]

[0067] Application Examples

[0068] The lithium-ion battery electrolytes of the above-mentioned embodiments and comparative examples are respectively made into soft-pack lithium-ion batteries with a capacity of 2000 mAh. The lithium-ion batteries include a positive electrode plate, a negative electrode plate, a separator, an electrolyte and battery auxiliary materials. The positive electrode active material is 5V spinel nickel lithium manganese oxide, and the negative electrode active material is graphite.

[0069] The preparation process is as follows: the positive electrode sheet, the separator and the negative electrode sheet are wound together into a core, which is sealed with an aluminum-plastic film and then baked so that the moisture content of the electrode meets the requirements. After baking, the battery cell is injected with electrolyte, and the finished soft-pack battery cell is obtained through the steps of standing, forming, capacity separation and aging.

[0070] Battery Test

[0071] 1. Cycle test

[0072] The Xinwei test program is set up as follows: at a certain temperature, the battery is charged at a constant current of 0.5C to a charge cut-off voltage of 4.85V, then charged at a constant voltage until the current drops to 0.05C, and then discharged at a constant current of 1C to 3.0V to obtain the capacity retention rate of different formulas.

[0073] Capacity retention rate = discharge capacity in the last week / initial discharge capacity * 100%.

[0074] 2. High temperature storage performance test

[0075] The battery was charged and discharged at 0.5C / / 1C for one cycle at 25°C with a voltage range of (3.0-4.85V). The discharge capacity was recorded. The battery was then charged at a constant current of 0.5C until it reached 100% SOC. The battery was placed in an explosion-proof oven at 45°C and stored for 30 days. After the storage, it was discharged at 1C and the capacity retention rate, capacity recovery rate and gas production were calculated.

[0076] Capacity retention rate = discharge capacity in the first cycle after high-temperature storage / discharge capacity in the last week before high-temperature storage * 100%;

[0077] Capacity recovery rate = discharge capacity in the second cycle after high-temperature storage / discharge capacity in the last week before high-temperature storage * 100%.

[0078] 3. Low temperature performance test: At a specific temperature, 0.1C charge and discharge cycle for one week, the voltage range is (3.0-4.85V) and the discharge capacity is recorded. 0.1C full charge, the battery is placed in a low temperature environment, and it is left still for 6 hours. It is discharged at a rate of 0.1C and the discharge capacity is recorded.

[0079] Low-temperature discharge capacity retention rate: discharge capacity in the second cycle after high-temperature storage / discharge capacity in the last week before high-temperature storage*100%.

[0080] The test results are shown in Table 2.

[0081] Table 2 Performance test data of batteries in embodiments and comparative examples

[0082]

[0083] It can be seen from the results of the examples and comparative examples that the sulfonamide-modified 2,5-dioxadipic acid dimethyl ester high-voltage electrolyte solvent provided in this patent shows better high-voltage cycle stability than 2,5-dioxadipic acid dimethyl ester, and the normal temperature and high temperature cycles are significantly improved. The introduction of the sulfonamide group regulates the composition of the positive and negative electrode interface film, reduces the oxidation of the solvent under high pressure and the reduction on the negative electrode surface, thereby reducing gas production.

[0084] From the results of Example 6 and Comparative Example 3, it can be seen that the introduction of sulfonic acid amine improves the dissociation ability of lithium salts, improves the conductivity of the electrolyte, and improves the low-temperature discharge performance while increasing the oxidation potential of the solvent. Compared with DMDOHD with sulfonamide additives, the introduction of functional groups can increase the concentration of effective groups and improve the cycle performance. From the results of Example 6 and Comparative Examples 4 and 5, it can be seen that compared with other modified 2,5-dioxadipic acid dimethyl ester solvents, the sulfonamide-modified solvent is more effective in improving battery circulation and inhibiting battery gas production, which can greatly improve the safety of high-temperature operation of the battery.

[0085] It can be seen from the results of Examples 6, 7, 8 and 9 that the shorter the sulfonamide substituent, the better the high pressure performance.

[0086] By comparing Example 6 with Example 10, Example 11 and Example 12, it is found that the high-pressure solvent is used in combination with a fluorinated solvent and a positive electrode film-forming additive to form an inorganic interface film component rich in L3N, L2S, and LiF and a fluorinated polymer organic component. By regulating the positive electrode film-forming additive, the fluorinated polymer content is optimized and the organic components such as polyphosphazene and BOB are increased. The organic-inorganic composite interface has stronger oxidation resistance, which inhibits the continuous growth of membrane impedance, improves the cycle coulomb efficiency, and further improves the long cycle performance.

[0087] Table 3 Low temperature performance of batteries in Examples and Comparative Examples

[0088] Electrolyte Conductivity 0℃ Capacity retention rate % -20℃ Capacity retention rate % Example 5 7.10 95.2 90.2 Example 6 7.52 97.9 92.6 Example 7 7.34 96.3 91.9 Example 8 7.43 97.3 92.1 Example 9 7.31 96.4 91.5 Comparative Example 6 6.79 93.3 90.7

[0089] From the low temperature performance of the batteries in Examples 5 and 6, it can be seen that DMC has higher oxidation stability than other linear carbonates, and can reduce electrolyte viscosity, improve electrode wetting, and reduce battery polarization while improving the high voltage performance of the battery.

[0090] By comparing Example 5, Example 6, Example 7, Example 8, Example 9 and Comparative Example 6, it is found that the solvent can improve the high-voltage performance compared with the fluorocarbonate, indicating that the modified solvent can form a more stable SEI and CEI film, inhibit the circulation and storage side reactions. It also has higher conductivity and improves low-temperature performance.

[0091] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A high pressure resistant solvent having a structure shown in Formula I: In Formula I, R 1 and R 2 Independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C12 alkyl.

2. The high pressure resistant solvent according to claim 1, It is characterized in that The R 1 and R 2 Independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C5 alkyl.

3. The high pressure resistant solvent according to claim 1, It is characterized in that The high pressure resistant solvent has a structure shown in any one of Formula I-1 to Formula I-4:

4. A high voltage resistant electrolyte comprising a lithium salt, a first solvent and a second solvent; The first solvent includes two or more of polycarbonate, propylene carbonate, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone; The second solvent is the high-voltage resistant solvent according to any one of claims 1 to 3; the mass fraction of the second solvent in the high-voltage resistant electrolyte is 5 to 15%.

5. The high voltage resistant electrolyte according to claim 4, It is characterized in that The high-voltage resistant electrolyte also includes a fluorinated solvent, which includes one or more of fluoroethylene carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,3,3,3-pentafluoropropyl-2,2,2-trifluoroethyl ether and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane; the mass fraction of the fluorinated solvent in the high-voltage resistant electrolyte is 2 to 15%.

6. The high voltage electrolyte according to claim 4, It is characterized in that The first solvent includes a mixed solvent of at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate and other solvents; the other solvents include one or more of polycarbonate, propylene carbonate, ethylene carbonate, ethyl acetate, propyl acetate, propyl propionate, methyl butyrate, methyl acetate, ethyl propionate and γ-butyrolactone.

7. The high voltage electrolyte according to claim 4, It is characterized in that The high-voltage resistant electrolyte also includes a low-internal-resistance film-forming additive; the low-internal-resistance film-forming additive includes one or more of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, pentafluorocyclophosphazene, 4,5-dicyano-2-trifluoromethyl-imidazole lithium, lithium difluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium difluorooxalatophosphate, vinyl sulfate, vinyl fluorosulfate, vinyl disulfate and vinyl disulfite; the mass fraction of the low-internal-resistance film-forming additive in the high-voltage resistant electrolyte is 0.1 to 8%.

8. The high voltage electrolyte according to claim 4, It is characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate and lithium tetrafluoroborate; the concentration of the lithium salt in the high-voltage resistant electrolyte is 0.5-2.0 mol / L.

9. A lithium ion battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the high voltage resistant electrolyte according to any one of claims 4 to 8.

10. Use of the high-voltage resistant solvent according to any one of claims 1 to 3 or the high-voltage resistant electrolyte according to any one of claims 4 to 8 in a high-voltage battery system; The charging cut-off voltage in the high-voltage battery system is greater than 4.6V.

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