Lithium ion battery electrolyte and lithium ion battery

Abstract

The application relates to a lithium ion battery electrolyte and a lithium ion battery. In order to solve the problem that high-voltage lithium ion batteries cannot simultaneously consider battery voltage drop and battery cycle performance in the prior art, the application provides a lithium ion battery electrolyte which comprises a non-aqueous organic solvent, a lithium salt and an additive, wherein the additive comprises a silicon-based phosphate ester compound and a sulfonate compound. The lithium ion battery electrolyte can significantly improve the voltage drop of the battery under normal temperature conditions, improve the normal temperature and high-low temperature cycle performance of the battery, and inhibit the swelling of the battery during high-temperature storage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a lithium ion battery electrolyte and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have developed rapidly in the fields of mobile devices, electric vehicles and energy storage due to their high capacity, high energy density and environmental friendliness, and their further development has become a consensus in the scientific community. The electrolyte is composed of non-aqueous organic solvents, lithium salts and additives, among which the commonly used lithium salt is lithium hexafluorophosphate, which is very unstable in the electrolyte and will react with a small amount of water to generate hydrofluoric acid (HF). On the one hand, it consumes the effective lithium ions in the electrolyte, and on the other hand, HF will cause the transition metal oxide material in the positive electrode to dissolve in the electrolyte, destroying the structure of the positive electrode material, causing the capacity of the battery to decay, and this phenomenon is more pronounced at high temperatures.

[0003] Improving the voltage is an important means to obtain high-capacity batteries, but the oxidation potential of conventional carbonate-based electrolytes is about 4.6V, and under high-temperature and high-concentration salt conditions, the HUMO energy level of the solvent molecules further increases, and the oxidation potential of the electrolyte will be lower than that under normal conditions. Therefore, the increase of the voltage of the material will cause the oxidative decomposition of the electrolyte, greatly affecting the effective life of the battery. In addition to replacing the battery material and modifying the coating of the material, additives are widely used as a simple and effective method to improve the stability of the electrolyte and the cycle performance of the battery, because the additives can form a solid interface film on the surface of the positive and negative electrodes during the pre-charging process of the battery, preventing direct contact between the electrode material and the electrolyte, and avoiding more invalid side reactions in the battery.

[0004] The patent with application number CN114566712A discloses a high-voltage lithium ion battery electrolyte containing lithium difluorophosphate, its preparation method and a lithium ion battery. It selects high-concentration LiPO2F2 as an additive to improve the high-voltage performance of the battery, but the solubility of LiPO2F2 in conventional mixed solvents of cyclic carbonates and chain carbonates and chain carboxylic acid esters is not high, usually about 1%, and decreases with the increase of lithium salt concentration. Therefore, improving the solubility of LiPO2F2 in the electrolyte is an important link to further enhance the high-voltage performance of the battery.

[0005] The patent with authorization number CN111740163B discloses a high-voltage lithium ion battery electrolyte and a lithium ion battery using the electrolyte. The tris(trimethylsilyl) phosphite used in the patent can effectively meet the safety requirements of the electrolyte, and the P-containing additive can be used to improve the cycle performance of the battery at high voltage. However, tris(trimethylsilyl) phosphite will generate a certain amount of gas under high-temperature conditions, which may cause the battery to swell and affect the use of the battery.

[0006] But in order to solve the above-mentioned problems in the battery, usually need to synergistic effect between multiple additives, not only bring higher cost, and the internal resistance of the battery is not easy to control, therefore, the urgent need to find a multiple consideration of additives to solve the above-mentioned problems encountered in the battery. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application provides a high-voltage lithium ion battery electrolyte and a battery using the same, which effectively solves the problems of large voltage drop at room temperature, poor room temperature and high-low temperature cycle performance, and swelling during high-temperature storage of lithium ion batteries.

[0008] To solve the above technical problems, the application adopts the following technical solutions:

[0009] The first object of the present application is to provide a lithium ion battery electrolyte, comprising a non-aqueous organic solvent, a lithium salt and an additive, the additive comprising a silicon-based phosphate compound represented by formula (I) and a sulfonate compound represented by formula (II), the structure of the silicon-based phosphate compound represented by formula (I) and the sulfonate compound represented by formula (II) being as follows:

[0010]

[0011] In formula (I), R1 and R2 are each independently selected from one of halogen atom, alkyl, haloalkyl, unsaturated hydrocarbon group, aryl, haloaryl, alkoxy or haloalkoxy; R3-R5 in formula (II) are each independently carbon atom or oxygen atom, and at least one of R3-R5 is oxygen atom.

[0012] Preferably, in formula (I), R1 and R2 are each independently selected from one of fluorine atom, alkyl with carbon atom number of 1-3, fluoroalkyl with carbon atom number of 1-3, unsaturated hydrocarbon group with carbon atom number of 2-3, aryl, fluoroaryl, alkoxy with carbon atom number of 1-3 or fluoroalkoxy with carbon atom number of 1-3.

[0013] Preferably, the sulfonate compound represented by formula (II) is selected from methylene methylenedisulfonate (MMDS) and / or 1,3-propanedisulfonic anhydride (ODTO), and the structure of MMDS and ODTO is as follows:

[0014]

[0015] Preferably, the silicon-based phosphate compound represented by formula (I) is selected from one or more of the following substances:

[0016]

[0017] Preferably, the silicon-based phosphate compound represented by formula (I) is selected from one or more of the following substances:

[0018] Preferably, the mass ratio of the silane-based phosphate compound of formula (I) in the electrolyte is 0.05% to 5%, such as 0.1%, 0.8%, 1.4%, 1.8%, 2.2%, 3.2%, 3.8%, 4.2%, 4.8%, etc.

[0019] Further preferably, the mass ratio of the silane-based phosphate compound of formula (I) in the electrolyte is 0.05% to 3%.

[0020] More preferably, the mass ratio of the silane-based phosphate compound of formula (I) in the electrolyte is 0.1% to 3%.

[0021] Preferably, the mass ratio of the sulfonate compound of formula (II) in the electrolyte is 0.1% to 5%, such as 0.3%, 1.2%, 1.4%, 1.6%, 2.2%, 2.6%, 3%, 3.5%, 4%, 4.5%, etc.

[0022] Further preferably, the mass ratio of the sulfonate compound of formula (II) in the electrolyte is 0.1% to 2%.

[0023] More preferably, the mass ratio of the sulfonate compound of formula (II) in the electrolyte is 0.3% to 2%.

[0024] According to specific embodiments, the sulfonate compound of formula (II) is 1,3-propanedisulfonic anhydride, and the mass ratio thereof in the electrolyte is 0.5% to 2%.

[0025] Preferably, the additive further comprises other additives, which are one or more selected from butanedinitrile (SN), adiponitrile (ADN), fluoroethylene carbonate (FEC), vinylene carbonate (VC), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP), tris(trimethylsilyl)phosphite (TMSPi), vinyl ethylene carbonate (VEC), maleic anhydride, glutaric anhydride, triallyl isocyanurate, and tetra-vinylsilane.

[0026] According to specific embodiments, the other additives are one or more selected from butanedinitrile (ADN), fluoroethylene carbonate (FEC), and tris(trimethylsilyl)phosphite (TMSPi).

[0027] Preferably, the mass ratio of the other additives in the electrolyte is 0.05% to 5%, such as 0.1%, 0.8%, 1.4%, 1.8%, 2.2%, 3.2%, 3.8%, 4.2%, 4.8%, etc.

[0028] Further preferably, the mass ratio of the other additives in the electrolyte is 0.1% to 3%.

[0029] Preferably, the non-aqueous organic solvent is selected from one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethylene carbonate, methyl formate, ethyl acetate, methyl butyrate, methyl acrylate, N-methyl pyrrolidone, N-methyl formamide, N-methyl acetamide, acetonitrile, N,N-dimethyl formamide, sulfolane, dimethyl sulfoxide, methyl sulfide, gamma-butyrolactone, and tetrahydrofuran.

[0030] Further preferably, the non-aqueous organic solvent is ethylene carbonate, propylene carbonate, and methyl ethyl carbonate, and the mass ratio of the three is (15-30):(0-10):(60-85), such as 20:5:75, 23:4:73, 28:6:66, etc.

[0031] According to a specific embodiment, the mass ratio of the ethylene carbonate, propylene carbonate, and methyl ethyl carbonate is (20-28):(3-8):(65-75).

[0032] Preferably, the lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium hexafluorophosphate, lithium carbonate, lithium sulfate, lithium sulfite, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, and lithium difluorobis(oxalato)phosphate.

[0033] Further preferably, the molar concentration of the lithium salt in the electrolyte is 0.5M to 3.0M, such as 0.6M, 1.3M, 1.8M, 2.2M, 2.5M, 2.8M.

[0034] According to a specific embodiment, the lithium salt is lithium hexafluorophosphate, and the molar concentration of the lithium salt in the electrolyte is 0.8M to 1.2M.

[0035] A second object of the present application is to provide a lithium ion battery using the above electrolyte, which comprises a positive electrode sheet, a negative electrode sheet, a separator between the positive electrode sheet and the negative electrode sheet, and an electrolyte, wherein the electrolyte is the above lithium ion battery electrolyte.

[0036] Preferably, the positive electrode sheet comprises a positive electrode material, the positive electrode material being one or more of lithium transition metal composite oxides, or compounds obtained by doping or coating lithium transition metal composite oxides with other transition metals or non-transition metals.

[0037] Preferably, the negative electrode sheet comprises a negative electrode material, the negative electrode material being selected from one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compounds, silicon-carbon composites, lithium titanate, and metals capable of forming alloys with lithium.

[0038] Preferably, the lithium transition metal composite oxide is selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0039] Preferably, the upper limit charging voltage of the lithium ion battery is not less than 4.35 V.

[0040] Thanks to the use of the above technical solutions, the present application has the following advantages compared with the prior art:

[0041] The high-voltage lithium ion battery electrolyte provided by the present application reduces the generation of HF during electrolyte storage by adding a certain concentration of silicon-based phosphate compounds and sulfonate compounds to the electrolyte, greatly reduces the internal resistance of the battery, and thus improves the voltage drop under normal temperature conditions, the cycle performance under normal temperature and high and low temperature conditions, and inhibits the swelling during high-temperature storage. DETAILED DESCRIPTION

[0042] The present application will be further described below in conjunction with examples. However, the present application is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to different specific requirements, and the implementation conditions not specified are the conventional conditions in the industry. The technical features involved in each embodiment of the present application can be combined with each other as long as there is no conflict. Unless otherwise specified, "%" represents mass percentage.

[0043] With the expansion of the application scenarios of lithium batteries and the improvement of environmental protection requirements, it is necessary to improve the electrolyte of lithium ion secondary batteries to achieve the effects of reducing the voltage drop under normal temperature conditions, improving the cycle performance of the battery under normal temperature and high and low temperature conditions, and inhibiting the swelling during high-temperature storage. Therefore, the inventors of the present application have conducted in-depth research and a large number of experiments, and finally proposed an electrolyte and a lithium ion battery using the electrolyte.

[0044] The lithium battery electrolyte provided by the present application comprises multiple components, and particularly, a certain mass fraction of silicon-based phosphate compounds and sulfonate compounds are added. Under the synergistic effect of the components in the electrolyte, the voltage drop of the lithium-rich manganese-based battery is obviously relieved, and the cycle performance under normal temperature and high and low temperature conditions is also significantly improved, and the swelling during high-temperature storage is also effectively inhibited. The reasons are as follows: 1) the silicon-based phosphate compounds have a lower HOMO electron orbital and a higher LUMO orbital, so that the additive can form an interface film on the positive and negative electrode surfaces, preventing the direct contact of the active material with the electrolyte and reducing the decomposition of the electrolyte; 2) the introduction of the silane group can consume the moisture existing in the electrolyte, block the reaction link of the reaction of the moisture with lithium hexafluorophosphate to generate HF, avoid the corrosion of HF on the positive electrode material and the dissolution of the transition metal ions therein, and thus improve the service life of the battery; 3) as the silicon-based phosphate compounds have lone pair electrons in the heteroatoms such as P, when the two elements participate in the formation of the solid interface film, the transmission rate of the electrons in the interface can be improved, the battery interface resistance is reduced, and the cycle efficiency of the battery is improved; 4) the existence of F in the silicon-based phosphate compounds can increase the existence of inorganic substances such as LiF, Li x PO y F z in the solid interface film, improve the rigidity of the interface film, and the SEI film formed by the sulfonate compounds has better toughness, so that the swelling and shrinkage of the SEI film during the charging and discharging process become more stable, which is beneficial to the improvement of the cycle performance of the battery.

[0045] In the present application, the preparation method of the compound 2 is as follows: 4.26g of vinyl difluorophosphite (CAS No. 18133-42-1) is added into 6.1g of hexamethyldisiloxane under the protection of nitrogen, and the system is reacted at 75-80℃ for 2h, and then the temperature of the system is increased to 95℃, so that the compound 2 can be obtained.

[0046] Example 1

[0047] Preparation of the electrolyte: vinyl carbonate (EC), propylene carbonate (PC) and methyl ethyl carbonate (EMC) are mixed in a mass ratio of 25:5:70, 1M lithium salt LiPF6 is fully dissolved, and then the compound 1 and 1,3-propanedisulfonic anhydride are added, and the weight fraction of the compound 1 and 1,3-propanedisulfonic anhydride in the electrolyte is 0.5% and 0.5%, respectively.

[0048] Preparation of the positive electrode sheet: lithium-rich manganese (Li-Rich) positive electrode active material, conductive agent acetylene black and polyvinylidene fluoride (PVDF) are added into an N-methyl pyrrolidone solvent system in a mass ratio of 95:3:2, and then the mixture is fully stirred and uniformly mixed, coated on an aluminum foil positive electrode current collector, and then dried and cold-pressed to obtain a positive electrode sheet, wherein the PVDF is used as a binder.

[0049] Preparation of negative electrode sheet: the negative electrode active material graphite, conductive agent acetylene black, butadiene rubber (SBR), carboxymethyl cellulose sodium (CMC-Na) were added into the deionized water solvent system according to the mass ratio of 95:2:2:1, and after being fully stirred and mixed uniformly, coated on the negative electrode current collector Cu foil, dried and cold-pressed to obtain the negative electrode sheet, wherein SBR was used as the binder and CMC-Na was used as the thickening agent.

[0050] Preparation of separator: a PE porous polymer film was used as the separator.

[0051] Preparation of lithium ion battery: the prepared positive electrode sheet, separator and negative electrode sheet were stacked in order, with the separator between the positive and negative electrode sheets to play a separating role, and after being wound, a bare cell was obtained. The bare cell was placed in an outer package, and the above prepared electrolyte was injected, and after packaging, a lithium ion battery was obtained. The design capacity of the obtained lithium ion battery was 740 mAh, and the charge and discharge interval of the battery was 3.0 V-4.6 V.

[0052] Example 2

[0053] The electrolyte and lithium ion battery were prepared according to the same method as in Example 1, except that the mass fraction of 1,3-propanedisulfonic anhydride in the electrolyte of this example was 1%.

[0054] Example 3

[0055] The electrolyte and lithium ion battery were prepared according to the same method as in Example 1, except that the mass fraction of 1,3-propanedisulfonic anhydride in the electrolyte of this example was 2%.

[0056] Example 4

[0057] The electrolyte and lithium ion battery were prepared according to the same method as in Example 1, except that the mass fraction of compound 1 in the electrolyte of this example was 1%, and the mass fraction of 1,3-propanedisulfonic anhydride in the electrolyte was 1%.

[0058] Example 5

[0059] The electrolyte and lithium ion battery were prepared according to the same method as in Example 1, except that the mass fraction of compound 1 in the electrolyte of this example was 2%, and the mass fraction of 1,3-propanedisulfonic anhydride in the electrolyte was 1%.

[0060] Example 6

[0061] The electrolyte and lithium ion battery were prepared according to the same method as in Example 1, except that the mass fraction of compound 1 in the electrolyte of this example was 3%, and the mass fraction of 1,3-propanedisulfonic anhydride in the electrolyte was 1%.

[0062] Example 7

[0063] The electrolyte and lithium ion battery were prepared according to the same method as in Example 4, except that no compound 1 was added to the electrolyte of this example, but compound 2 was added, which accounted for 1% of the mass fraction of the electrolyte.

[0064] Example 8

[0065] The electrolyte and lithium ion battery were prepared according to the same method as in Example 4, except that no compound 1 was added to the electrolyte of this example, but compound 3 was added, which accounted for 2% of the mass fraction of the electrolyte.

[0066] Example 9

[0067] The electrolyte and lithium ion battery were prepared according to the same method as in Example 4, except that no compound 1 was added to the electrolyte of this example, but compound 4 was added, which accounted for 1% of the mass fraction of the electrolyte.

[0068] Example 10

[0069] The electrolyte and lithium ion battery were prepared according to the same method as in Example 5, except that tris(trimethylsilyl) phosphite (TMSPi) was also added to the electrolyte of this example, which accounted for 1% of the mass fraction of the electrolyte.

[0070] Example 11

[0071] The electrolyte and lithium ion battery were prepared according to the same method as in Example 7, except that adiponitrile was also added to the electrolyte of this example, which accounted for 1% of the mass fraction of the electrolyte.

[0072] Example 12

[0073] The electrolyte and lithium ion battery were prepared according to the same method as in Example 5, except that fluoroethylene carbonate (FEC) was also added to the electrolyte of this example, which accounted for 1% of the mass fraction of the electrolyte.

[0074] Comparative Example 1

[0075] The electrolyte and lithium ion battery were prepared according to the same method as in Example 2, except that no compound 1 was added to the electrolyte of this example, but LiPO2F2 was added, wherein LiPO2F2 accounted for 0.5% of the mass fraction of the electrolyte.

[0076] Comparative Example 2

[0077] The electrolyte and lithium ion battery were prepared according to the same method as in Example 2, except that compound 1 was not added in the electrolyte of the present comparative example, but tris(trimethylsilyl) phosphate (TMSP) was added, wherein the mass fraction of TMSP in the electrolyte was 1%.

[0078] Comparative Example 3

[0079] The electrolyte and lithium ion battery were prepared according to the same method as in Example 2, except that compound 1 was not added in the electrolyte of the present comparative example, but FEC was added, wherein the mass fraction of FEC in the electrolyte was 2%.

[0080] Comparative Example 4

[0081] The electrolyte and lithium ion battery were prepared according to the same method as in Example 2, except that compound 1 was not added in the electrolyte of the present comparative example, but adiponitrile was added, wherein the mass fraction of adiponitrile in the electrolyte was 1%.

[0082] The voltage drop, room temperature and high-low temperature cycle performance, and swelling during high-temperature storage of the batteries prepared in Examples 1-12 and Comparative Examples 1-4 were tested according to the following method.

[0083] (1) Full-state storage voltage drop test

[0084] The fresh electrolyte prepared in Examples 1-12 and Comparative Examples 1-4 above was injected into the battery, which was subjected to 0.1C formation, two-sealing, and then 0.2C cycle for 10 weeks, and then charged to 4.6V at 1C constant current and constant voltage, with a cutoff current of 0.05C. After 4 days of room temperature storage, the battery voltage drop (ΔV) condition was observed. The test results of the battery voltage drop (ΔV) after room temperature storage are shown in Table 1.

[0085] Table 1

[0086] AV (mV) Example 1 171 Example 2 163 Example 3 165 Example 4 122 Example 5 80 Example 6 85 Example 7 64 Example 8 94 Example 9 76 Example 10 61 Example 11 59 Example 12 63 Comparative Example 1 186 Comparative Example 2 203 Comparative Example 3 265 Comparative Example 4 237

[0087] From the results of Table 1, it can be seen that, compared with Comparative Examples 1-4, the present application can significantly reduce the voltage drop of the battery by adding the silicon-based phosphate compound and the sulfonate compound. The results of Examples 4-6 show that, as the mass fraction of Compound 1 increases, its ability to alleviate the voltage drop also increases, but when the mass fraction is greater than 2%, the voltage drop of the battery actually increases, so the mass ratio of the silicon-based phosphate compound and the sulfonate compound to the electrolyte needs to be within a certain range to achieve the best effect of reducing the voltage drop. Among them, the optimal mass ratio of Compound 1 to the electrolyte is 2%, the optimal mass ratio of Compound 2 to the electrolyte is 1%, the optimal mass ratio of Compound 3 to the electrolyte is 2%, the optimal mass ratio of Compound 4 to the electrolyte is 1%, and the optimal mass ratio of 1,3-propanedisulfonic anhydride to the electrolyte is 1%. The results of Examples 5-9 show that, among the four compounds, Compound 2 has the strongest effect on reducing the voltage drop. This is because Compound 2 contains an ethylene group, and during the redox reaction of the battery, the additive itself will undergo a certain polymerization reaction to form a polymer with a larger molecular weight, making the solid interface film more integrated and increasing the crack resistance of the solid interface film, thereby reducing the occurrence of self-discharge of the battery. The results of Comparative Examples 1-4 show that LiPO2F2, TMSP, and adiponitrile have a certain effect on reducing the voltage drop of the battery during storage, with LiPO2F2 being the best and nitriles being the worst, but their effects are far inferior to those of the present application.

[0088] (2) Normal temperature cycle performance test

[0089] At 25°C, the battery was subjected to 400 cycles of charge and discharge under the conditions of 1C / 1C charge and discharge, and the charge and discharge voltage interval was 3.0V-4.6V. The discharge capacity of the first cycle and the 400th cycle was recorded respectively. The 400th cycle capacity retention rate was calculated, and the formula was: 400th cycle capacity retention rate (%) = 400th cycle discharge capacity / first cycle discharge capacity*100%, and the calculation results are shown in Table 2.

[0090] (3) High temperature cycle test

[0091] At 45°C, the battery was subjected to 200 cycles of charge and discharge under the conditions of 1C / 1C charge and discharge, and the charge and discharge voltage interval was 3.0V-4.6V. The discharge capacity of the first cycle and the 200th cycle was recorded respectively. The 200th cycle capacity retention rate was calculated, and the formula was: 200th cycle capacity retention rate (%) = 200th cycle discharge capacity / first cycle discharge capacity*100%, and the calculation results are shown in Table 2.

[0092] (4) High temperature swelling test

[0093] Firstly, the formed battery is charged and discharged at room temperature for 3 times at 1C, the charge and discharge voltage interval is 3.0V-4.6V, then the battery is charged at 1C to 4.6V with constant current and constant voltage, the cut-off current is 0.05C, the initial thickness of the battery is measured and recorded as t1, then the battery is stored at 60℃ for 7 days, after the battery is completely cooled, the thickness of the battery is measured again and recorded as t2, the thickness change rate is calculated, the formula is: thickness change rate = (t2-t1) / t1*100%, the calculation result is shown in Table 2.

[0094] (5) Low-temperature cycle performance test

[0095] The battery is tested for 200 cycles of charge and discharge at 0℃ under the condition of 0.5C / 1C charge and discharge, the charge and discharge voltage interval is 3.0V-4.6V, and the discharge capacity of the first week and the 200th week is recorded respectively. The 200th week capacity retention rate is calculated, the formula is: the 200th week capacity retention rate (%) = the 200th week discharge capacity / first week discharge capacity*100%, the result is shown in Table 2.

[0096] Table 2

[0097]

[0098] From Table 2, it can be seen that LiPO2F2 and TMSP both play a certain role in the cycle stability of the battery in the high-voltage system, while 1,3-propanedisulfonic anhydride and adiponitrile have a limited effect. From Examples 5-12, it can be seen that after adding a certain mass fraction of silicon-based phosphate compounds, sulfonate compounds and other additives in the application, the cycle performance of the lithium-rich manganese-based battery under normal temperature and high-low temperature conditions is greatly improved, and the swelling during high-temperature storage is also effectively inhibited. The reasons are as follows: first, the silicon-based phosphate compound in the application can be regarded as a combination of LiPO2F2 and TMSP, the silicon-based phosphate compound in the application includes a silicon-based phosphate functional group and a lithium fluorophosphate functional group, the combination of the two functional groups further improves the HOMO orbital energy level and reduces the LUMO orbital energy level, so that a stable solid interface film can be formed on the positive and negative electrode surfaces; second, the silicon-based phosphate compound in the application contains a silicon-based group, which can consume trace amounts of water in the battery, reduce the swelling of the battery during high-temperature storage, and the P element in the film component has a lone pair of electrons, which also reduces the impedance of the interface film to a certain extent and improves the cycle performance of the battery; finally, the F element in the silicon-based phosphate compound decomposes to produce more LiF and Li x PO y F z substances during the formation of the solid interface film, which increases the mechanical strength of the interface film and is beneficial to improving the high-temperature performance of the battery.

[0099] In summary, after adding the compound 1 with a mass fraction of 2%, 1,3-propanedisulfonic anhydride with a mass fraction of 1%, and other additives, especially tris(trimethylsilyl) phosphite with a mass fraction of 1%, the voltage drop of the battery is significantly reduced, the cycle performance under normal temperature and high and low temperature conditions is greatly improved, and the swelling during high-temperature storage is effectively inhibited.

[0100] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. A lithium ion battery electrolyte comprising a nonaqueous organic solvent, a lithium salt, and an additive, characterized in that, The additive comprises a silicon-based phosphate compound shown in formula (I) and a sulfonate compound shown in formula (II), and the structural formulae of the silicon-based phosphate compound shown in formula (I) and the sulfonate compound shown in formula (II) are as follows: In formula (I), R1 and R2 are each independently selected from a fluorine atom, an alkyl group with 1-3 carbon atoms, a fluorinated alkyl group with 1-3 carbon atoms, and an unsaturated hydrocarbon group with 2-3 carbon atoms; and in formula (II), R3-R5 are each independently a carbon atom or an oxygen atom, and at least one of R3-R5 is an oxygen atom.

2. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The sulfonate compound shown in formula (II) is selected from methylenedisulfonic acid dimethyl ester and / or 1,3-propanedisulfonic anhydride.

3. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The silicon-based phosphate compound shown in formula (I) is selected from one or more of the following substances:

4. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The mass ratio of the silicon-based phosphate compound shown in formula (I) in the electrolyte is 0.05%-5%, and the mass ratio of the sulfonate compound shown in formula (II) in the electrolyte is 0.1%-5%.

5. The electrolyte for lithium-ion batteries according to claim 4, characterized in that, The mass ratio of the silicon-based phosphate compound shown in formula (I) in the electrolyte is 0.05%-3%, and the mass ratio of the sulfonate compound shown in formula (II) in the electrolyte is 0.1%-2%.

6. The electrolyte for lithium-ion batteries according to any one of claims 1 to 5, characterized in that, The additive further comprises other additives, the other additives are one or more selected from butanedinitrile, hexanedinitrile, fluorinated ethylene carbonate, vinylene carbonate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, ethylene vinylene carbonate, maleic anhydride, glutaric anhydride, triallyl isocyanurate, and tetra-vinylsilane; and / or, the mass ratio of the other additives in the electrolyte is 0.05%-5%.

7. The electrolyte for lithium-ion batteries according to claim 1, characterized in that, The non-aqueous organic solvent is selected from one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethylene carbonate, methyl formate, ethyl acetate, methyl butyrate, methyl acrylate, N-methyl pyrrolidone, N-methyl formamide, N-methyl acetamide, acetonitrile, N,N-dimethyl formamide, sulfolane, dimethyl sulfoxide, methyl sulfide, gamma-butyrolactone, and tetrahydrofuran.

8. The electrolyte for lithium ion batteries according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium perchlorate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium hexafluorophosphate, lithium carbonate, lithium sulfate, lithium sulfite, lithium nitrate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, and lithium difluorobis(oxalato)phosphate.

9. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator between the positive electrode sheet and the negative electrode sheet, and an electrolyte, characterized by, The electrolyte is a lithium ion battery electrolyte according to any one of claims 1-8.

10. The lithium-ion battery of claim 9, wherein, The positive electrode sheet comprises a positive electrode material, and the positive electrode material is one or more of a lithium transition metal composite oxide, or a compound obtained by doping or coating the lithium transition metal composite oxide with other transition metals or non-transition metals; and / or, the negative electrode sheet comprises a negative electrode material, and the negative electrode material is selected from one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compounds, silicon-carbon composites, lithium titanate, and metals capable of forming alloys with lithium.

11. The lithium-ion battery of claim 10, wherein, The lithium transition metal composite oxide is selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide.

12. The lithium-ion battery of claim 9, wherein, The upper limit voltage of the lithium ion battery is not less than 4.35 V.

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