Electrolyte and Lithium-Ion Battery

Abstract

The present invention provides an electrolyte and a lithium-ion battery. The electrolyte includes a lithium salt, an organic solvent, and an additive, and the additive includes a first additive. The first additive includes a cyclic sulfonamide derivative represented by Formula 1, Formula 1, wherein R1 and R2 are each independently selected from a first substituent having an unsaturation degree of 0 to 6, 0 to 2 halogen atoms, and 1 to 15 carbon atoms. The first substituent is selected from any one of an alkyl group, an alkenyl group, an ester group, an amino group, a silicon group, or an aryl group. R3 and R4 are each independently selected from H or a second substituent having an unsaturation degree of 0 to 4 and 0 to 7 carbon atoms. The second substituent is selected from any one of an alkyl group, a carbonyl group, or a pyridyl group. The present invention selects a cyclic sulfonamide derivative as an electrolyte additive, effectively improving the surface properties of the lithium-ion battery and inhibiting the growth of lithium dendrites.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and relates to an electrolyte and a lithium-ion battery. Background Art

[0002] At present, lithium-ion batteries have been widely used in technical products such as automobiles and mobile phones. Commercial lithium-ion batteries use graphite as the negative electrode material, and their capacity utilization has approached the theoretical value of graphite (372 mAh / g). It is very difficult to significantly improve the capacity of lithium-ion batteries by treating graphite. Those skilled in the art have noticed that the theoretical specific capacity of lithium metal is as high as 3860 mAh / g, and the electrode potential is as low as -3.04 V. Therefore, the development of lithium-ion batteries with metallic lithium as the negative electrode has gradually become the future development direction.

[0003] However, there are two factors restricting the development of lithium-ion batteries with lithium metal negative electrodes: (1) Lithium dendrites are easily generated on the lithium metal electrode during the cycling process. Lithium dendrites are likely to pierce the separator of the battery cell, resulting in a short circuit phenomenon in the battery; (2) Lithium metal has a large surface area and high activity, and it is easy to react violently with the electrolyte, resulting in continuous reorganization of the SEI film on the surface of metallic lithium, consuming the electrolyte and active lithium, which will lead to a reduction in the cycling efficiency and shorten the battery cycle life. Therefore, how to effectively improve the surface properties of the lithium metal electrode and inhibit the growth of lithium dendrites is an urgent problem to be solved in the development of lithium-ion batteries using lithium metal negative electrodes. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, one of the purposes of the present invention is to provide an electrolyte, the electrolyte includes a lithium salt, an organic solvent and an additive, the additive includes a first additive, and the first additive includes a cyclic sulfonamide derivative represented by formula (1).

[0005]

[0006] Wherein, R1 and R2 are each independently selected from a first substituent with an unsaturation degree of 0 to 6, a halogen atom of 0 to 2 and a carbon atom number of 1 to 15. The first substituent is selected from any one of an alkyl group, an alkenyl group, an ester group, an amino group, a silicon group or an aryl group. R3 and R4 are each independently selected from H or a second substituent with an unsaturation degree of 0 to 4 and a carbon atom number of 0 to 7. The second substituent is selected from any one of an alkyl group, a carbonyl group or a pyridyl group.

[0007] Another purpose of the present invention is to provide a lithium-ion battery, the lithium-ion battery includes a positive electrode, a negative electrode and the electrolyte as described in purpose one.

[0008] Compared with the existing technology, the beneficial effects of the present invention are:

[0009] The present invention selects a cyclic sulfonamide derivative as an electrolyte additive, effectively improving the surface properties of the lithium metal electrode and inhibiting the growth of lithium dendrites. The cycling performance and storage performance of the lithium-ion battery are improved. The capacity retention rate can be as high as over 92% after 500 cycles at 45 °C, and the volume expansion rate can be as low as below 4.1% after storing for 30 days at 60 °C. Detailed implementation mode

[0010] The present invention provides an electrolyte, which comprises a lithium salt, an organic solvent and an additive. The additive comprises a first additive, and the first additive comprises a cyclic sulfonamide derivative represented by formula (1).

[0011]

[0012] Wherein, R1 and R2 are each independently selected from a first substituent having an unsaturation degree of 0 to 6 (where the unsaturation degree can be 0, 1, 2, 3, 4, 5 or 6, etc.), a halogen atom of 0 to 2 and a carbon atom number of 1 to 15. The carbon atom number can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15. The first substituent is selected from any one of an alkyl group, an alkenyl group, an ester group, an amino group, a silicon group or an aryl group. R3 and R4 are each independently selected from H or a second substituent having an unsaturation degree of 0 to 4 and a carbon atom number of 0 to 7. Wherein, the unsaturation degree can be 0, 1, 2, 3 or 4, etc., and the carbon atom number can be 0, 1, 2, 3, 4, 5, 6 or 7, etc. The second substituent is selected from any one of an alkyl group, a carbonyl group or a pyridyl group. Other unlisted values within the above numerical ranges are equally applicable.

[0013] The present invention adopts a cyclic sulfonamide derivative represented by formula 1. During the battery cycling, the cyclic sulfonamide derivative can generate Li3N and Li2S. Compared with the SEI film composed of organic polymers, the inorganic salts have excellent mechanical properties and better expansion and contraction properties of the SEI film during the battery cycling process. Therefore, it has an improving effect on the performance of the lithium-ion battery.

[0014] As a preferred technical solution of the present invention, the first additive comprises any combination of one or more of the compounds represented by formula 1 to formula 8.

[0015] Typical but non-limiting examples of the combination include: the combination of the compounds represented by formula 2 and formula 3, the combination of the compounds represented by formula 3 and formula 4, the combination of the compounds represented by formula 4 and formula 5, the combination of the compounds represented by formula 5 and formula 6, the combination of the compounds represented by formula 6 and formula 7, the combination of the compounds represented by formula 7 and formula 8, or the combination of formula 8 and formula 9, etc.

[0016]

[0017] Preferably, it is any one or a combination of at least two of the compounds represented by Formula 2, the compounds represented by Formula 4, or the compounds represented by Formula 5. Typical but non-limiting examples of the combination include: the combination of the compound represented by Formula 2 and the compound represented by Formula 4, the combination of the compound of Formula 4 and the compound represented by Formula 5, or the combination of the compound represented by Formula 2 and the compound represented by Formula 5, etc.

[0018] As a preferred technical solution of the present invention, based on the mass of the electrolyte being 100%, the mass fraction of the first additive in the electrolyte is 0.2% to 15%. The mass fraction can be 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, or 12%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 0.2% to 10%.

[0019] For the lithium-ion battery according to the present invention, if the mass percentage of the first additive in the electrolyte is too low, the content of SO2 gas generated during the operation of the lithium-ion battery is low, and the properties of the lithium metal electrode surface cannot be effectively improved; while if the content of additive (I) is too high, the viscosity of the electrolyte system will increase, affecting the lithium-ion conduction inside the battery.

[0020] As a preferred technical solution of the present invention, the additive further includes a second additive, and the second additive includes cyclic ester additives.

[0021] The cyclic ester additives include any one or a combination of at least two of cyclic carbonate additives, cyclic sulfonic acid lactone additives, or cyclic sulfate additives. Typical but non-limiting examples of the combination include: the combination of cyclic carbonate additives and cyclic sulfonic acid lactone additives, the combination of cyclic sulfonic acid lactone additives and cyclic sulfate additives, or the combination of cyclic carbonate additives and cyclic sulfate additives, etc.

[0022] The cyclic carbonate additives include any one or a combination of at least two of vinylene carbonate, fluoroethylene carbonate, or ethylene ethylene carbonate. Typical but non-limiting examples of the combination include: the combination of vinylene carbonate and fluoroethylene carbonate, the combination of fluoroethylene carbonate and ethylene ethylene carbonate, or the combination of vinylene carbonate and ethylene ethylene carbonate, etc.

[0023] The cyclic sulfonic acid lactone additives include 1,3-propane sultone and / or 1,3-propene sultone.

[0024] The cyclic sulfate additives include ethylene sulfate and / or propylene sulfate.

[0025] Based on the mass of the electrolyte being 100%, the mass fraction of the second additive in the electrolyte is 0.05% to 20%, where the mass fraction can be 0.05%, 0.1%, 0.5%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18% or 20%, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0026] As a preferred technical solution of the present invention, the organic solvent includes any one or a combination of at least two of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate or diethyl carbonate. Typical but non-limiting examples of the combination are: a combination of ethylene carbonate and dimethyl carbonate, a combination of dimethyl carbonate and ethyl methyl carbonate, a combination of ethyl methyl carbonate and propylene carbonate, or a combination of propylene carbonate and diethyl carbonate, etc.

[0027] Based on the mass of the electrolyte being 100%, the mass fraction of the organic solvent in the electrolyte is 60% to 85%, where the mass fraction can be 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84% or 85%, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0028] As a preferred technical solution of the present invention, the lithium salt includes any one or a combination of at least two of LiPF6, LiBF4, LiFSI, LiTFSI, LiBOB, LiODFP, LiODFB, LiPO2F2 or CF3SO3Li. Typical but non-limiting examples of the combination are: a combination of LiPF6 and LiBF4, a combination of LiBF4 and LiFSI, a combination of LiFSI and LiTFSI, a combination of LiTFSI and LiBOB, a combination of LiODFP and LiODFB, a combination of LiODFB and LiPO2F2, or a combination of LiPO2F2 and CF3SO3Li, etc.

[0029] The concentration of the lithium salt in the electrolyte is 0.1 mol / L to 2 mol / L, where the concentration can be 0.1 mol / L, 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] The present invention provides a method for preparing an electrolyte as described in one of the purposes, and the preparation method includes:

[0031] After mixing sulfonyl chloride and ethylenediamine in a solvent, sodium bicarbonate is added, followed by extraction. After purification, the product is dissolved in a DMF solution, sodium carbonate and the corresponding substituted halide are added, and the mixture is heated at 60 °C for 8 hours. After the reaction is completed, the excess DMF solvent is removed by rotary evaporation, and extraction is carried out using dichloromethane and water. The extract is distilled to obtain the first additive.

[0032] As a preferred technical solution of the present invention, the solvent includes dichloromethane.

[0033] The equivalent ratio of the sulfonyl chloride to the ethylenediamine is 1:(1 to 1.5), where the equivalent ratio can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, or 1:1.5, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0034] The mixing includes heating, and the heating temperature is 55 °C to 65 °C, where the temperature can be 55 °C, 56 °C, 57 °C, 58 °C, 59 °C, 60 °C, 61 °C, 62 °C, 63 °C, 64 °C, or 65 °C, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0035] The heating time is 10 h to 15 h, where the time can be 10 h, 11 h, 12 h, 13 h, 14 h, or 15 h, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0036] The extraction solvent used for the extraction is dichloromethane and water.

[0037] The extract is the dichloromethane component.

[0038] The distillation can be rotary evaporation.

[0039] The present invention also provides a lithium-ion battery, which includes a positive electrode, a negative electrode, and an electrolyte as described above.

[0040] As a preferred technical solution of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material coated on the positive electrode current collector. The positive electrode active material includes any one or at least two combinations of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. Typical but non-limiting examples of the combinations include: a combination of lithium cobalt oxide and lithium nickel oxide, a combination of lithium nickel oxide and lithium manganese oxide, a combination of lithium manganese oxide and lithium nickel manganese oxide, a combination of lithium nickel manganese oxide and lithium nickel cobalt manganese oxide, or a combination of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, etc.

[0041] The negative electrode includes a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector, and the negative electrode active material includes a lithium alloy sheet layer and / or a metallic lithium sheet layer.

[0042] The lithium alloy sheet layer includes any one or a combination of at least two of Li-Sn alloy, Li-Sn-O alloy, Li-Mg alloy, Li-B alloy, or Li-Al alloy. Typical but non-limiting examples of the combination include: the combination of Li-Sn alloy and Li-Sn-O alloy, the combination of Li-Sn-O alloy and Li-Mg alloy, the combination of Li-Mg alloy and Li-B alloy, or the combination of Li-B alloy and Li-Al alloy, etc.

[0043] The numerical ranges described in the present invention not only include the point values exemplified above, but also include any point values between the above numerical ranges not exemplified. Due to space limitations and for the sake of brevity, the specific point values included in the scope of the present invention are not exhaustively listed herein.

[0044] The technical solution of the present invention will be further described below through specific embodiments.

[0045] Example 1

[0046] This example provides an electrolyte, which includes an organic solvent, a lithium salt, and an additive.

[0047] Among them, the organic solvents are ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate, and the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate is 3:5:2.

[0048] The lithium salt is lithium hexafluorophosphate, and the concentration is 1 mol / L.

[0049] The additive includes a cyclic sulfonamide derivative and a cyclic ester additive. Among them, the cyclic sulfonamide derivative is as shown in Formula 2.

[0050]

[0051] The cyclic ester additives are vinylene carbonate, 1,3-propane sultone, and ethylene sulfate. Based on the mass of the electrolyte being 100%, the mass fraction of the cyclic sulfonamide derivative as shown in Formula 2 is 0.5%, the mass fraction of vinylene carbonate is 2.5%, the mass fraction of 1,3-propane sultone is 2.5%, and the mass fraction of ethylene sulfate is 5%.

[0052] Among them, the preparation method of the cyclic sulfonamide derivative as shown in Formula 2 is as follows:

[0053] After mixing sulfonyl chloride and ethylenediamine in a solvent, sodium bicarbonate is added. After extraction, the extract is distilled to obtain the additive shown in Formula 2 above as the first additive. After mixing sulfonyl chloride and ethylenediamine in a solvent, sodium bicarbonate is added, followed by extraction. After purification, the product is dissolved in a DMF solution, sodium carbonate and the corresponding substituted halide (methyl iodide CAS: 74-88-4 and tert-butyl chloroformate CAS: 24608-52-4, in an equivalent ratio of 1:1) are added, and the mixture is heated at 60 °C for 8 hours. After the reaction is completed, the excess DMF solvent is rotary evaporated, and extraction is carried out using dichloromethane and water. The extract is distilled to obtain the first additive shown in Formula 2.

[0054] Example 2

[0055] This example provides an electrolyte, which also includes an organic solvent, a lithium salt, and an additive.

[0056] Among them, the organic solvent includes ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate. Among them, the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate is 3:5:2.

[0057] The lithium salt is lithium hexafluorophosphate, and the concentration is 0.5 mol / L.

[0058] The additive includes a cyclic sulfonamide derivative and a cyclic ester additive. Among them, the cyclic sulfonamide derivative is shown in Formula 4.

[0059]

[0060] The cyclic ester additive is vinylene carbonate and 1,3-propane sultone. Based on the mass of the electrolyte being 100%, the mass fraction of the cyclic sulfonamide derivative shown in Formula 4 is 0.01%, the mass fraction of vinylene carbonate is 0.025%, and the mass fraction of 1,3-propane sultone is 0.025%.

[0061] The preparation method of the cyclic sulfonamide derivative containing the one shown in Formula 4 is as follows:

[0062] After mixing sulfonyl chloride and ethylenediamine in a solvent, sodium bicarbonate is added. After extraction, the extract is distilled to obtain the above additive as the first additive. After mixing sulfonyl chloride and ethylenediamine in a solvent, sodium bicarbonate is added, followed by extraction. After purification, the product is dissolved in a DMF solution, sodium carbonate and acetaldehyde CAS: 75-07-0 are added, and the mixture is heated at 60 °C for 8 hours. After the reaction is completed, the excess DMF solvent is rotary evaporated, and extraction is carried out using dichloromethane and water. The extract is distilled to obtain the first additive shown in Formula 4.

[0063] Example 3

[0064] This embodiment provides a lithium-ion battery electrolyte, which also includes an organic solvent, a lithium salt, and an additive.

[0065] Among them, the organic solvent includes ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate, and the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate is 3:5:2.

[0066] The lithium salt is lithium hexafluorophosphate, and the concentration is 2 mol / L.

[0067] The additive includes a cyclic sulfonamide derivative and a cyclic ester additive. Among them, the cyclic sulfonamide derivative is shown in Formula 5.

[0068]

[0069] The cyclic ester additive is vinylene carbonate and 1,3-propane sultone. Based on the mass of the electrolyte being 100%, the mass fraction of the cyclic sulfonamide derivative shown in Formula 5 is 15%, the mass fraction of vinylene carbonate is 5%, the mass fraction of 1,3-propane sultone is 10%, and the mass fraction of ethylene sulfate is 5%.

[0070] Among them, the preparation method of the cyclic sulfonamide derivative shown in Formula 5 is as follows:

[0071] After mixing sulfonyl chloride and ethylenediamine in a solvent, sodium bicarbonate is added. After extraction, the extract is distilled to obtain the above additive as the first additive. After mixing sulfonyl chloride and ethylenediamine in a solvent, sodium bicarbonate is added, extracted, and purified. Then the product is dissolved in a DMF solution, sodium carbonate and trimethylchlorosilane CAS: 75-77-4 are added, and heated at 60 °C for 8 hours. After the reaction is completed, the excess DMF solvent is rotary evaporated, and extracted with dichloromethane and water. The extract is distilled to obtain the first additive.

[0072] Example 4

[0073] In this embodiment, except that the mass fraction of the cyclic sulfonamide derivative shown in Formula 2 is replaced by 0.3%, and the amount of the non-aqueous solvent is adaptively adjusted so that the total amount of the electrolyte is 100%, other conditions are the same as those in Example 1.

[0074] Example 5

[0075] In this embodiment, except that the mass fraction of the cyclic sulfonamide derivative shown in Formula 2 is replaced by 5%, and the amount of the non-aqueous solvent is adaptively adjusted so that the total amount of the electrolyte is 100%, other conditions are the same as those in Example 1.

[0076] Example 6

[0077] In this example, except that the mass fraction of the cyclic sulfonamide derivative shown in Formula 2 is replaced by 10%, and the amount of the non-aqueous solvent is adaptively adjusted so that the total amount of the electrolyte is 100%, other conditions are the same as those in Example 1.

[0078] Example 7

[0079] In this example, except that the mass fraction of the cyclic sulfonamide derivative shown in Formula 2 is replaced by 18%, and the amount of the non-aqueous solvent is adaptively adjusted so that the total amount of the electrolyte is 100%, other conditions are the same as those in Example 1.

[0080] Example 8

[0081] In this example, except that no cyclic ester additive is added, and the amount of the non-aqueous solvent is adaptively adjusted so that the total amount of the electrolyte is 100%, other conditions are the same as those in Example 1.

[0082] Comparative Example 1

[0083] In this comparative example, except that the cyclic sulfonamide derivative shown in Formula 2 is not added, and the amount of the non-aqueous solvent is adaptively adjusted so that the total amount of the electrolyte is 100%, other conditions are the same as those in Example 1.

[0084] Comparative Example 2

[0085] In this comparative example, except that the cyclic sulfonamide derivative shown in Formula 2 is replaced by a compound having only one N substituent on the ring shown in Formula 10, other conditions are the same as those in Example 1.

[0086]

[0087] The preparation methods of the electrolytes in Examples 1 to 8 and Comparative Examples 1 to 2 are as follows:

[0088] The electrolyte is prepared in a glove box where the nitrogen content is 99.999% and the actual oxygen content is 0.1 ppm and the moisture content is 0.1 ppm. Based on the total mass of the non-aqueous electrolyte being 100%, ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate battery-grade organic solvents with a mass ratio of 3:5:2 are mixed evenly, and then the fully dried lithium salt is added to the above non-aqueous solvent, and additives are added to adjust the concentration of the lithium salt to prepare the non-aqueous electrolytes for lithium-ion batteries corresponding to Examples 1 to 8 and Comparative Examples 1 to 3.

[0089] The preparation method of the lithium-ion battery is as follows:

[0090] The positive electrode active material LiNi 0.5 Mn 1.5O4, acetylene black as the conductive agent, and polyvinylidene fluoride as the binder were fully stirred and mixed evenly in an N-methylpyrrolidone solvent system at a mass ratio of 95:3:2, then coated on aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet with a tap density of 3.5 g / cm 3 .

[0091] The negative active material graphite, acetylene black as the conductive agent, styrene-butadiene rubber as the binder, and sodium carboxymethyl cellulose as the thickening agent were fully stirred and mixed evenly in a deionized water solvent system at a mass ratio of 96:2:1:1, then coated on copper foil, dried, and cold-pressed to obtain a negative electrode sheet with a tap density of 1.65 g / cm 3 .

[0092] A separator was obtained by using a 9-μm-thick polyethylene as the base film and coating a 3-μm-thick nano-aluminum oxide coating on the base film.

[0093] The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence, with the separator placed in the middle between the positive electrode sheet and the negative electrode sheet to play a role in isolation, and a bare battery cell was obtained by stacking.

[0094] The bare battery cell was placed into an aluminum-plastic film, then baked at 80 °C to remove water, and then injected with the corresponding electrolytes of Examples 1 to 8 and Comparative Examples 1 to 2 and sealed. After that, through processes such as standing, hot and cold pressing, formation, clamping, and grading, the finished soft-packaged lithium-ion secondary batteries corresponding to Examples 1 to 8 and Comparative Examples 1 to 2 were obtained.

[0095] Then, the following performance tests were carried out on each example and comparative example.

[0096] I. Capacity retention rate during high-temperature cycling at 45 °C

[0097] At 45 °C, the lithium-ion battery was charged at a constant current of 1C to 5V, then charged at a constant voltage of 5V until the current was less than 0.05C. After standing for 10 min, it was discharged at a constant current of 1C to 2.8V, and the discharge capacity of the lithium-ion battery at this time was measured as the discharge capacity of the first cycle; the battery was cycled multiple times under the above conditions, and the capacity retention rate of the battery after 1000 cycles was calculated respectively. The capacity retention rate relative to the capacity after cycling was calculated according to the following formula.

[0098] Capacity retention rate (%) = (Discharge capacity corresponding to 1000 cycles / Discharge capacity of the first cycle) × 100%.

[0099] II. Volume expansion rate after storing at 60 °C for 30 days

[0100] At 25°C, charge the lithium-ion battery at a constant current of 1C to 5V, then charge it at a constant voltage until the current reaches 0.05C, measure the volume of the lithium-ion battery and record it as V0. Then place the fully charged battery in an oven at 60°C for 30 days, measure the volume after storage and record it as V1, and calculate the volume expansion rate of the lithium-ion battery relative to before storage according to the following formula.

[0101] Volume expansion rate (%) = (V1 - V0) / V0 × 100%.

[0102] For the lithium-ion secondary batteries prepared in Examples 1 to 8 and Comparative Examples 1 to 2, the capacity retention rate during high-temperature cycling at 45°C and the volume expansion rate during high-temperature storage at 60°C for 30 days were tested, and the test results are shown in the following table:

[0103] Table 1

[0104] Capacity retention rate after 500 cycles at 45℃ Volume expansion rate after storage at 60℃ for 30 days Example 1 90.2％ 4.3 Example 2 92.3％ 4.1％ Example 3 89.1％ 5.6％

[0105] It can be seen from Table 1 that: by adding 0.2% to 15% of the compound of formula (1) to the electrolyte of the present invention, the interfacial properties of the lithium metal electrode can be effectively improved, the growth of lithium dendrites can be inhibited, and the high-temperature cycling performance and high-temperature storage performance of the lithium-ion battery can be enhanced.

[0106] Table 2

[0107] Capacity retention rate after 500 cycles at 45℃ Volume expansion rate after storage at 60℃ for 30 days Example 1 90.2％ 4.3％ Example 4 87.4％ 7.8％ Example 5 89.9％ 7.3％ Example 6 85.2％ 9.6％ Example 7 82.3％ 10.8％

[0108] It can be seen from Table 2 that: as the addition amount of the cyclic sulfonamide derivative increases, the performance of the lithium-ion battery will first increase and then decrease. When the addition amount of the cyclic sulfonamide derivative is too much, the performance of the lithium-ion battery will deteriorate further.

[0109] Table 3

[0110] Capacity retention rate after 500 cycles at 45℃ Volume expansion rate after storage at 60℃ for 30 days Example 1 90.2％ 4.3％ Example 8 86.1％ 6.5％

[0111] It can be seen from Table 3 that: when the cyclic ester additive is not added, the cycle capacity retention rate of the battery will decrease, and the volume expansion rate during storage will also increase. It shows that the combined use of the cyclic sulfonamide derivative and the cyclic ester additive can comprehensively improve the high-temperature cycling performance and high-temperature storage performance of the battery cell, and the two need to be used in combination to improve the performance of the lithium-ion battery.

[0112] Table 4

[0113] Capacity retention rate after 500 cycles at 45℃ Volume expansion rate after storage at 60℃ for 30 days Example 1 90.2％ 4.3％ Comparative Example 1 80.3％ 12.6％ Comparative Example 2 79.8％ 17.4％

[0114] It can be seen from Table 4 that without adding the cyclic sulfonamide derivative, the cycling and storage performance of the battery will decrease significantly, indicating the important role of the cyclic sulfonamide derivative in performance improvement and the stable construction of the SEI film. When the cyclic sulfonamide derivative is replaced with a compound having only one N substituent on the benzene ring, both the cycling performance and the storage performance of the battery decrease. On the one hand, because the hydrogen of the amino group on the ring has weak acidity, which is disadvantageous to the system. On the other hand, the inorganic components that can effectively form Li3N and Li2S are less, and the performance is inferior to that of the cyclic sulfonamide.

[0115] The specific embodiments described above further elaborate on the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, 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, characterized in that, The electrolyte includes a lithium salt, an organic solvent, and an additive. The additive includes a first additive, and the first additive includes a cyclic sulfonamide derivative represented by formula (1). Wherein, R1 and R2 are each independently selected from a first substituent having an unsaturation degree of 0 to 6, 0 to 2 halogen atoms, and 1 to 15 carbon atoms. The first substituent is selected from any one of alkyl, alkenyl, ester group, amino group, silicon group, or aryl group. R3 and R4 are each independently selected from H or a second substituent having an unsaturation degree of 0 to 4 and 0 to 7 carbon atoms. The second substituent is selected from any one of alkyl, carbonyl group, or pyridyl group.

2. The electrolyte according to claim 1, characterized in that, The first additive includes any combination of one or more of the compounds represented by formula 2 to formula 9.

3. The electrolyte according to claim 1, characterized in that, Based on the mass of the electrolyte being 100%, the mass fraction of the first additive in the electrolyte is 0.2% to 15%.

4. The electrolyte according to any one of claims 1 to 3, characterized in that, The additive further includes a second additive. The second additive includes a cyclic ester additive. The cyclic ester additive includes any one or a combination of at least two of cyclic carbonate additives, cyclic sultone additives, or cyclic sulfate additives. Based on the mass of the electrolyte being 100%, the mass fraction of the second additive in the electrolyte is 0.05% to 20%.

5. The electrolyte according to any one of claims 1 to 3, characterized in that The organic solvent includes any one or a combination of at least two of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, or diethyl carbonate. Based on the mass of the electrolyte being 100%, the mass fraction of the organic solvent in the electrolyte is 60% to 85%.

6. The electrolyte according to any one of claims 1 to 3, characterized in that, The lithium salt includes any one or a combination of at least two of LiPF6, LiBF4, LiFSI, LiTFSI, LiBOB, LiODFP, LiODFB, LiPO2F2, or CF3SO3Li. The concentration of the lithium salt in the electrolyte is 0.1 mol / L to 2 mol / L.

7. A lithium-ion battery, characterized in that, The lithium ion battery includes a positive electrode, a negative electrode, and the electrolyte according to any one of claims 1 to 6.

8. The lithium ion battery according to claim 7, characterized in that, The positive electrode includes a positive electrode current collector and a positive electrode active material coated on the positive electrode current collector. The positive electrode active material includes any one or a combination of at least two of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. The negative electrode includes a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector. The negative electrode active material includes a lithium alloy sheet layer and / or a metallic lithium sheet layer. The lithium alloy sheet layer includes any one or a combination of at least two of Li-Sn alloy, Li-Sn-O alloy, Li-Mg alloy, Li-B alloy, or Li-Al alloy.

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