An electrolyte solution and a lithium-ion battery containing the same

Abstract

The present invention provides an electrolyte and a lithium-ion battery containing the same. The electrolyte includes an organic solvent, a lithium salt, and an additive, and the additive includes a bis(trimethylsilyl)boranyl sulfonic anhydride compound represented by Formula 1. The compound additive bis(trimethylsilyl)boranyl sulfonic anhydride compound in the electrolyte of the present invention has the ability to passivate the positive electrode interface and form a stable SEI protective film, thereby improving the high-temperature cycle, storage and other performances of the lithium-ion secondary battery, while taking into account the internal resistance.

Description

Technical Field

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

[0002] In recent years, with the development of new energy technologies, higher requirements have been put forward for the performance of lithium-ion power batteries for vehicles. In order to meet the long cruising range and wide temperature range environment of electric vehicles, it is necessary to develop lithium-ion secondary batteries with higher energy density, more excellent high-temperature cycle and storage performance. However, lithium-ion secondary batteries with high energy density usually use transition metal oxides with a relatively high nickel content (such as lithium nickel cobalt manganate). These materials are prone to interface deterioration, particle fragmentation, and oxidation of the electrolyte under high temperature and high pressure, resulting in a rapid decline in life at high temperature. Therefore, it is necessary to develop an electrolyte additive that can stabilize the cathode interface at high temperature.

[0003] CN 111276741A discloses an electrolyte for secondary batteries, which includes a lithium salt, a non-aqueous organic solvent, and a difluorophosphite olefin compound, and provides a lithium secondary battery including the electrolyte. The electrolyte can further stabilize the cathode structure, can only improve the high-temperature stability to a certain extent, and does not play a stabilizing role for the cathode interface.

[0004] CN 110838595A discloses a lithium-ion battery electrolyte and its application. A fluorine-containing non-ionic surfactant is added. The lithium-ion battery has high wettability, good high-temperature output characteristics, rate performance, and cycle performance, but the improvement of the high-temperature storage performance of the battery is not obvious.

[0005] Therefore, how to prepare an electrolyte with high-temperature cycle and storage performance is an important research direction in this field. Summary of the Invention

[0006] The purpose of the present invention is to provide an electrolyte and a lithium-ion battery containing the same, which solve the problem of life deterioration of lithium-ion batteries in the prior art during high-temperature cycling or storage.

[0007] To achieve the purpose of this invention, the following technical solutions are adopted:

[0008] One of the purposes of the present invention is to provide an electrolyte, which is characterized in that the electrolyte includes an organic solvent, a lithium salt, and an additive, and the additive includes a compound represented by Formula 1,

[0009] wherein, R is C n H 2n+1 、C n H 2n or Cn H 2n-1 Any one of them, where 1 ≤ n ≤ 8. The value of n can be 1, 2, 3, 4, 5, 6, 7, 8, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. R includes a saturated alkyl group or an unsaturated alkyl group. The unsaturated alkyl group includes a carbon-carbon double bond or a carbon-carbon triple bond. The alkyl group includes a linear alkyl group and / or a cyclic alkyl group. In the electrolyte additive compound of the present invention, there are two different functional groups. Among them, the trimethylsilyl group (-SiMe3) has the function of absorbing residual moisture and hydrofluoric acid in the electrolyte, reducing the internal resistance while reducing the side reaction between the electrolyte and the positive electrode. At the same time, -SO3 in the compound has the ability to form a stable interfacial film on the surface of the positive electrode, reducing the high-temperature interfacial side reaction and improving the cycling and storage performance of the battery at high temperatures. The compound additive in the electrolyte of the present invention has the ability to passivate the positive electrode interface and form a stable SEI protective film, thereby improving the high-temperature cycling, storage and other performances of the lithium-ion secondary battery, while taking into account the internal resistance.

[0010] As a preferred technical solution of the present invention, based on the mass fraction of the electrolyte being 100%, the mass fraction of the additive in the electrolyte is 0.01 - 3%. The mass fraction can be 0.01%, 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% or 3%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably 0.1 - 1%.

[0011] As a preferred technical solution of the present invention, the additive includes any one or a combination of at least two of the compounds represented by Formula 2 - Formula 6.

[0012]

[0013] As a preferred technical solution of the present invention, the additive further includes a high-temperature additive.

[0014] Preferably, the high-temperature additive includes any one or a combination of at least two of vinylene carbonate, vinyl ethyl carbonate, fluoroethylene carbonate, ethylene sulfate, 1,3-propane sultone, tris(trimethylsilyl) borate or tris(trimethylsilyl) phosphate. Typical but non-limiting examples of the combination are: a combination of vinylene carbonate and vinyl ethyl carbonate, a combination of vinyl ethyl carbonate and fluoroethylene carbonate, a combination of fluoroethylene carbonate and ethylene sulfate, a combination of ethylene sulfate and 1,3-propane sultone, a combination of 1,3-propane sultone and tris(trimethylsilyl) borate or a combination of tris(trimethylsilyl) borate and tris(trimethylsilyl) phosphate.

[0015] Preferably, the high-temperature additive includes vinylene sulfate.

[0016] Preferably, based on the mass fraction of the electrolyte being 100%, the mass fraction of the high-temperature additive in the electrolyte is 0.01 - 3%, where the mass fraction can be 0.01%, 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5% or 3%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably it is 0.1 - 2%.

[0017] Preferably, the lithium salt additive includes lithium difluorophosphate and lithium bis(fluorosulfonyl)imide.

[0018] Preferably, based on the mass fraction of the electrolyte being 100%, the mass fraction of lithium difluorophosphate in the electrolyte is 0.1 - 1.5%, where the mass fraction can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0019] Preferably, based on the mass fraction of the electrolyte being 100%, the mass fraction of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1 - 10%, where the mass fraction can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0020] As a preferred technical solution of the present invention, the organic solvent includes cyclic carbonates and chain carboxylic acid esters.

[0021] Preferably, the cyclic carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, butylene carbonate or γ-butyrolactone. Typical but non-limiting examples of the combination are: a combination of ethylene carbonate and propylene carbonate, a combination of propylene carbonate and butylene carbonate, a combination of butylene carbonate and γ-butyrolactone, or a combination of propylene carbonate and γ-butyrolactone, etc.

[0022] Preferably, the chain acid esters include any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate or ethyl butyrate. Typical but non-limiting examples of the combination are: the combination of dimethyl carbonate and diethyl carbonate, the combination of methyl ethyl carbonate and methyl propyl carbonate, the combination of ethyl propyl carbonate and methyl formate, the combination of methyl formate and ethyl formate, the combination of propyl formate and methyl acetate, the combination of ethyl acetate and propyl acetate, the combination of methyl propionate and ethyl propionate, the combination of propyl propionate and methyl butyrate or the combination of methyl butyrate and ethyl butyrate, etc.

[0023] In the present invention, the organic solvent can better avoid the damage of water to the electrolyte, and at the same time is conducive to promoting the more sufficient dissolution of each component in the electrolyte, thereby improving the synergy between the components and obtaining an electrolyte with excellent electrical properties.

[0024] As a preferred technical solution of the present invention, the volume ratio of the cyclic carbonate to the chain acid ester is (10 - 40):(60 - 90), where the mass ratio can be 10:90, 15:85, 20:80, 25:75, 30:70, 35:75 or 40:60, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably (15 - 40):(60 - 85).

[0025] Preferably, based on the mass fraction of the electrolyte being 100%, the mass fraction of the organic solvent in the electrolyte is 65.5 - 89.6%, where the mass fraction can be 65.5%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, 82%, 84%, 86%, 88% or 89.6%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0026] As a preferred technical solution of the present invention, the lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate, lithium bis(trifluoromethylsulfonyl)imide or lithium perchlorate. Typical but non-limiting examples of the combination are: the combination of lithium hexafluorophosphate and lithium tetrafluorophosphate, the combination of lithium tetrafluorophosphate and lithium bis(oxalato)borate, the combination of lithium difluoro(oxalato)borate and lithium difluorobis(oxalato)phosphate, the combination of lithium difluorobis(oxalato)phosphate and lithium bis(trifluoromethylsulfonyl)imide or the combination of lithium bis(trifluoromethylsulfonyl)imide and lithium perchlorate, etc.

[0027] Preferably, the lithium salt includes lithium hexafluorophosphate.

[0028] As an electrolyte for the electrolyte solution, lithium hexafluorophosphate can enhance the electrical conductivity, energy storage performance, and environmental friendliness of lithium-ion batteries.

[0029] As a preferred technical solution of the present invention, based on the mass fraction of the electrolyte solution being 100%, the mass fraction of the lithium hexafluorophosphate in the electrolyte solution is 10-20%, where the mass fraction can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] Preferably, based on the mass fraction of the electrolyte solution being 100%, the mass fraction of the lithium salt in the electrolyte solution is 10-20%, where the mass fraction can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable. The second object of the present invention is to provide a lithium-ion battery, and the lithium-ion battery includes the electrolyte solution as described in the first object.

[0031] The lithium-ion battery further includes a positive electrode plate and a negative electrode plate.

[0032] As a preferred technical solution of the present invention, the material of the positive electrode plate includes lithium transition metal oxides and / or lithium transition metal phosphate compounds.

[0033] Preferably, the lithium transition metal oxides include LiCoO2, LiNi x Co y Mn z O2, LiNi x Mn y O2, LiMn2O4, LiMnO2, Li2MnO4, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiMn 1-x M x O4 or Li2Mn 1-x O4, or any one or at least two combinations thereof, where typical but non-limiting examples of the combinations are: combinations of LiCoO2 and LiNi x Co y Mn z O2, combinations of LiNi x Mn y O2 and LiMn2O4, combinations of LiMnO2 and Li2MnO4, Li 1+a Mn 1-xM x a combination of O2 and LiCo 1-x M x a combination of O2 and LiMn 1-x M x a combination of O4 and Li2Mn 1-x O4, etc. Among them, 0 ≤ a < 0.2, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1. The value of a can be 0, 0.05, 0.1, 0.15 or 0.2. The value of x can be 0, 0.1, 0.2, 0.03, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1. The value of y can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1. The value of z can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc., but not limited to the listed values. Other unlisted values within the above numerical ranges are equally applicable.

[0034] Preferably, the lithium transition metal phosphate compound includes any one or a combination of at least two of LiFePO4, LiMnPO4, LiCoPO4 or LiFe 1- x M x PO4. Among them, typical but non-limiting examples of the combination are: a combination of LiFePO4 and LiMnPO4, a combination of LiMnPO4 and LiCoPO4, or a combination of LiCoPO4 and LiFe 1-x M x PO4, etc. Among them, M is selected from any one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, and 0 ≤ x ≤ 1. The value of x can be 0, 0.1, 0.2, 0.03, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0035] Preferably, the material of the negative electrode sheet includes any one or a combination of at least two of carbonaceous materials, alloy materials or lithium-containing metal composite materials. Among them, typical but non-limiting examples of the combination are: a combination of carbonaceous materials and alloy materials, a combination of alloy materials and lithium-containing metal composite materials, or a combination of carbonaceous materials and lithium-containing metal composite materials, etc.

[0036] Preferably, the material of the negative electrode sheet includes any one or a combination of at least two of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, silicon, silicon-carbon alloy or silicon-oxygen alloy. Typical but non-limiting examples of the combination include: the combination of natural graphite and artificial graphite, the combination of artificial graphite and soft carbon, the combination of soft carbon and hard carbon, the combination of hard carbon and lithium titanate, the combination of lithium titanate and silicon, the combination of silicon and silicon-carbon alloy, or the combination of silicon-carbon alloy and silicon-oxygen alloy, etc.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The electrolyte prepared by the present invention has excellent high-temperature storage performance and cycling performance when applied to a lithium-ion battery. At 60 °C for 30 days, the capacity retention rate can reach more than 95%, the gas generation expansion rate can be as low as less than 12%, and the cycling capacity retention rate at 45 °C for 800 cycles can reach more than 95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a comparison diagram of the cycling performance of Example 1 and Comparative Example 1 of the present invention at 45 °C. DETAILED DESCRIPTION OF THE INVENTION

[0040] The technical solution of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0041] Example 1

[0042] This example provides a lithium-ion battery electrolyte:

[0043] The lithium-ion battery electrolyte includes a lithium salt, an organic solvent and an additive;

[0044] Lithium salt: Based on the mass fraction of the electrolyte being 100%, lithium hexafluorophosphate accounting for 13% of the mass fraction of the electrolyte;

[0045] Organic solvent: Based on the mass fraction of the electrolyte being 100%, an organic solvent accounting for 81% of the mass fraction of the electrolyte, wherein the organic solvent includes ethylene carbonate, ethyl methyl carbonate and diethyl carbonate with a mass ratio of 30:50:20;

[0046] Additive: Based on the mass fraction of the electrolyte being 100%, a compound accounting for 0.5% of the mass fraction of the electrolyte as shown in Formula 2, vinylene sulfate accounting for 0.5% of the mass fraction of the electrolyte, lithium difluorophosphate accounting for 1% of the mass fraction of the electrolyte, and lithium bis(fluorosulfonyl)imide accounting for 4% of the mass fraction of the electrolyte,

[0047]

[0048] Among them, the synthesis method of the compound shown in Formula 2 is as follows:

[0049]

[0050] Example 2

[0051] This example provides a lithium-ion battery electrolyte:

[0052] The lithium-ion battery electrolyte includes a lithium salt, an organic solvent, and an additive;

[0053] Lithium salt: Based on the mass fraction of the electrolyte being 100%, lithium hexafluorophosphate accounting for 10% of the mass fraction of the electrolyte;

[0054] Organic solvent: Based on the mass fraction of the electrolyte being 100%, an organic solvent accounting for 89.6% of the mass fraction of the electrolyte, where the organic solvent includes propylene carbonate and ethyl propyl carbonate with a mass ratio of 40:60;

[0055] Additive: Based on the mass fraction of the electrolyte being 100%, the compound shown in Formula 3 accounting for 0.1% of the mass fraction of the electrolyte, vinylene sulfate accounting for 0.1% of the mass fraction of the electrolyte, lithium difluorophosphate accounting for 0.1% of the mass fraction of the electrolyte, and lithium bis(fluorosulfonyl)imide accounting for 0.1% of the mass fraction of the electrolyte,

[0056]

[0057] Among them, the synthesis method of the compound shown in Formula 3 is as follows:

[0058]

[0059] Example 3

[0060] This example provides a lithium-ion battery electrolyte:

[0061] The lithium-ion battery electrolyte includes a lithium salt, an organic solvent, and an additive;

[0062] Lithium salt: Based on the mass fraction of the electrolyte being 100%, lithium hexafluorophosphate accounting for 20% of the mass fraction of the electrolyte;

[0063] Organic solvent: Based on the mass fraction of the electrolyte being 100%, an organic solvent accounting for 65.5% of the mass fraction of the electrolyte, where the organic solvent includes γ-butyrolactone and methyl propionate with a mass ratio of 15:85;

[0064] Additive: Based on the mass fraction of the electrolyte being 100%, the compound shown in Formula 4 accounting for 1% of the mass fraction of the electrolyte, vinylene sulfate accounting for 2% of the mass fraction of the electrolyte, lithium difluorophosphate accounting for 1.5% of the mass fraction of the electrolyte, and lithium bis(fluorosulfonyl)imide accounting for 10% of the mass fraction of the electrolyte,

[0065]

[0066] Among them, the synthesis method of the compound shown in Formula 4 is as follows:

[0067]

[0068] Example 4

[0069] This example provides a lithium-ion battery electrolyte:

[0070] The lithium-ion battery electrolyte includes a lithium salt, an organic solvent, and an additive;

[0071] Lithium salt: Based on 100% of the mass fraction of the electrolyte, lithium hexafluorophosphate accounting for 13% of the mass fraction of the electrolyte;

[0072] Organic solvent: Based on 100% of the mass fraction of the electrolyte, an organic solvent accounting for 81.98% of the mass fraction of the electrolyte, where the organic solvent includes ethylene carbonate and diethyl carbonate with a mass ratio of 10:90;

[0073] Additive: Based on 100% of the mass fraction of the electrolyte, a compound accounting for 0.01% of the mass fraction of the electrolyte as shown in Formula 5, vinylene sulfate accounting for 0.01% of the mass fraction of the electrolyte, lithium difluorophosphate accounting for 1% of the mass fraction of the electrolyte, and lithium bis(fluorosulfonyl)imide accounting for 4% of the mass fraction of the electrolyte,

[0074] ;

[0075] Among them, the synthesis method of the compound shown in Formula 5 is as follows:

[0076]

[0077] Example 5

[0078] This example provides a lithium-ion battery electrolyte:

[0079] The lithium-ion battery electrolyte includes a lithium salt, an organic solvent, and an additive;

[0080] Lithium salt: Based on 100% of the mass fraction of the electrolyte, lithium hexafluorophosphate accounting for 13% of the mass fraction of the electrolyte;

[0081] Organic solvent: Based on 100% of the mass fraction of the electrolyte, an organic solvent accounting for 76% of the mass fraction of the electrolyte, where the organic solvent includes propylene carbonate, ethyl methyl carbonate, and diethyl carbonate with a mass ratio of 30:50:20;

[0082] Additives: Based on the electrolyte having a mass fraction of 100%, a compound accounting for 3% of the electrolyte mass fraction as shown in Formula 6, vinylene sulfate accounting for 3% of the electrolyte mass fraction, lithium difluorophosphate accounting for 1% of the electrolyte mass fraction, and lithium bis(fluorosulfonyl)imide accounting for 4% of the electrolyte mass fraction.

[0083]

[0084] The synthesis method of the compound shown in Formula 6 is as follows:

[0085]

[0086] Example 6

[0087] In this example, except that the compound accounting for 0.5% of the electrolyte mass fraction as shown in Formula 2 is replaced with: the compound accounting for 5% of the electrolyte mass fraction as shown in Formula 2, and the mass fraction of the organic solvent is replaced with 76.5%, other conditions are the same as those in Example 1.

[0088] Example 7

[0089] In this example, except that vinylene sulfate accounting for 0.5% of the electrolyte mass fraction is replaced with 1,3 - propane sultone accounting for 0.5% of the electrolyte mass fraction, other conditions are the same as those in Example 1.

[0090] Example 8

[0091] In this example, except that vinylene sulfate accounting for 0.5% of the electrolyte mass fraction is replaced with vinylene carbonate accounting for 0.5% of the electrolyte mass fraction, other conditions are the same as those in Example 1.

[0092] Example 9

[0093] In this example, except that lithium difluorophosphate accounting for 1% of the electrolyte mass fraction and lithium bis(fluorosulfonyl)imide accounting for 4% of the electrolyte mass fraction are not added, and the mass fraction of the organic solvent is replaced with 86%, other conditions are the same as those in Example 1.

[0094] Comparative Example 1

[0095] In this comparative example, except that the compound shown in Formula 2 is not added, other conditions are the same as those in Example 1.

[0096] The comparison of the cycling performance at 45 °C in Example 1 and Comparative Example 1 of the present invention is as Figure 1 described.

[0097] The electrolytes in Examples 1 - 9 and Comparative Example 1 are assembled into lithium - ion batteries. Among them, the preparation method of the battery is as follows:

[0098] (1) Preparation of the positive electrode sheet of the lithium - ion battery:

[0099] The cathode active material lithium nickel cobalt manganese oxide (LiNi 0.6 Co 0.1 Mn 0.3 O2), conductive agent Super-P, and binder PVDF are dissolved in the solvent N-methylpyrrolidone in a mass ratio of 96:2.0:2.0 and mixed evenly to form a cathode slurry. Then, the cathode slurry is evenly coated on the current collector aluminum foil with a coating amount of 18 mg / cm 2 . Subsequently, after drying at 85°C, cold pressing, trimming, slicing, and slitting are carried out, and then drying is performed under vacuum conditions at 85°C for 4 h, and the electrode tabs are welded to produce a cathode plate of a lithium-ion secondary battery that meets the requirements.

[0100] (2) Preparation of the anode plate of the lithium-ion battery:

[0101] The anode active material artificial graphite, conductive agent Super-P, thickening agent CMC, and binder SBR are dissolved in deionized water as the solvent in a mass ratio of 96.5:1.0:1.0:1.5 and mixed evenly to form an anode slurry. Then, the anode slurry is evenly coated on the current collector copper foil with a coating amount of 8.9 mg / cm 2 . Subsequently, after drying at 85°C, cold pressing, trimming, slicing, and slitting are carried out, and then drying is performed under vacuum conditions at 110°C for 4 h, and the electrode tabs are welded to produce an anode plate of a lithium-ion secondary battery that meets the requirements.

[0102] (3) Preparation of the lithium-ion battery:

[0103] The cathode plate, anode plate, and separator membrane (PE membrane) of the lithium-ion secondary battery prepared according to the foregoing process are made into a battery with a thickness of 8 mm, a width of 60 mm, and a length of 130 mm through a stacking process, and then vacuum baked at 85°C for 10 h, the electrolytes in Examples 1-9 and Comparative Example 1 are injected, and left standing for 24 h. Then, it is charged at a constant current of 0.1C (200 mA) to 4.35 V, then charged at a constant voltage of 4.35 V until the current drops to 0.05C (100 mA), and then discharged at a constant current of 0.1C (200 mA) to 2.8 V. The charge-discharge cycle is repeated 2 times, and finally charged at a constant current of 0.1C (200 mA) to 3.8 V, thus completing the preparation of the lithium-ion secondary battery.

[0104] The prepared lithium-ion batteries corresponding to Examples 1-9 and Comparative Example 1 are tested for high-temperature storage performance, cycling performance, and gas generation performance during high-temperature storage. The test results are shown in Table 1.

[0105] Among them, the test method for the high-temperature storage performance of the lithium-ion battery is as follows: At 25°C, first charge the lithium-ion secondary batteries prepared in Examples 1-9 and Comparative Example 1 at a constant current of 1C to 4.35V, and then charge at a constant voltage of 4.35V until the current is 0.05C. Then discharge the lithium-ion secondary battery at a constant current of 1C to 2.8V. The discharge capacity at this time is the discharge capacity of the lithium-ion secondary battery before high-temperature storage. Then charge the lithium-ion secondary battery at a constant current of 1C to 4.35V, place the lithium-ion secondary battery at 60°C for 30 days of storage. After the storage is completed, place the lithium-ion secondary battery in a 25°C environment, and then discharge the lithium-ion secondary battery at a constant current of 0.5C to 2.8V. Then charge the lithium-ion secondary battery at a constant current of 1C to 4.35V, further charge at a constant voltage of 4.35V until the current is 1C, and then discharge the lithium-ion secondary battery at a constant current of 1C to 2.8V. The discharge capacity of the last time is the discharge capacity of the lithium-ion secondary battery after high-temperature storage. The capacity retention rate (%) of the lithium-ion secondary battery after high-temperature storage = [discharge capacity of the lithium-ion secondary battery after high-temperature storage / discharge capacity of the lithium-ion secondary battery before high-temperature storage] × 100%.

[0106] Test method for the high-temperature cycling performance of the lithium-ion battery: Test the high-temperature cycling performance of the lithium-ion secondary batteries prepared in Examples 1-9 and Comparative Example 1 respectively. The specific method is as follows: At 45°C, first charge the lithium-ion secondary battery at a constant current of 1C to 4.35V, then charge at a constant voltage of 4.35V until the current is 0.05C, and then discharge the lithium-ion secondary battery at a constant current of 1C to 2.8V. This is a charge-discharge cycle process, and the discharge capacity at this time is the discharge capacity of the first cycle. Perform cyclic charge-discharge tests on the lithium-ion secondary battery in the above manner, and take the discharge capacity of the 800th cycle.

[0107] Test for the gas generation performance of the lithium-ion battery during high-temperature storage: At 25°C, first charge the lithium-ion secondary batteries prepared in Examples 1-9 and Comparative Example 1 at a constant current of 1C to 4.35V, then charge at a constant voltage of 4.35V until the current is 0.05C, and then discharge the lithium-ion secondary battery at a constant current of 1C to 2.8V. The discharge capacity at this time is the discharge capacity of the lithium-ion secondary battery before high-temperature storage. Then charge the lithium-ion secondary battery at a constant current of 1C to 4.35V, charge at a constant voltage of 4.35V until the current is 0.05C, and fully charge the lithium-ion battery. Use the drainage method to measure the volume of the battery, and use a micrometer to measure the thickness of the battery.

[0108] Afterwards, the lithium-ion battery was stored at 60 °C for 30 days. After the storage ended, the secondary lithium-ion battery was placed in an environment of 25 °C, and the volume of the battery was measured by the drainage method, and the thickness of the battery was measured with a micrometer. Then, the secondary lithium-ion battery was discharged to 2.8 V at a constant current of 0.5 C, and then charged to 4.35 V at a constant current of 1 C. Further, it was charged at a constant voltage of 4.35 V until the current reached 1 C, and then discharged to 2.8 V at a constant current of 1 C. The discharge capacity of the last time was the discharge capacity of the secondary lithium-ion battery after high-temperature storage.

[0109] Battery volume expansion rate = (volume after storage / volume before storage - 1) %.

[0110] Table 1

[0111]

[0112]

[0113] It can be obtained from the above table that from the comparison between Example 1 and Comparative Example 1, it can be seen that compared with the battery without adding bis(trimethylsilyl)borane sulfonic anhydride compounds, with the addition of bis(trimethylsilyl)borane sulfonic anhydride compounds, the capacity retention rate of the secondary lithium-ion battery during storage at 60 °C increases, the gas generation during storage decreases, and the cycle capacity retention rate improves.

[0114] It can be seen from the comparison between Examples 7-8 and Example 1 that 1,3-propanesultone, or vinylene carbonate in combination with bis(trimethylsilyl)borane sulfonic anhydride compounds can also obtain excellent high-temperature performance slightly lower than that of adding ethylene sulfate.

[0115] It can be seen from the comparison between Example 9, Example 1 and Comparative Example 1 that the additives lithium difluorophosphate and lithium bis(fluorosulfonyl)imide in combination with bis(trimethylsilyl)borane sulfonic anhydride compounds can obtain excellent high-temperature performance.

[0116] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes an organic solvent, a lithium salt, and an additive, and the additive includes a compound represented by Formula 1. Among them, R is C n H 2n+1 、C n H 2n or C n H 2n-1 Any one of them, 1 ≤ n ≤ 8, R includes a saturated alkyl group or an unsaturated alkyl group, the unsaturated alkyl group includes a carbon-carbon double bond or a carbon-carbon triple bond, and the alkyl group includes a linear alkyl group and / or a cyclic alkyl group.

2. The electrolyte according to claim 1, wherein Based on the mass fraction of the electrolyte being 100%, the compound represented by Formula 1 accounts for 0.01 - 3% of the electrolyte by mass fraction.

3. The electrolyte according to claim 2, wherein Based on the mass fraction of the electrolyte being 100%, the compound represented by Formula 1 accounts for 0.1 - 1% of the electrolyte by mass fraction.

4. The electrolyte according to claim 1, wherein The additive includes any one or a combination of at least two of the compounds represented by Formula 2 - Formula 6.

5. The electrolyte according to claim 1, wherein The additive further includes a high-temperature additive and a lithium salt additive.

6. The electrolyte according to claim 5, characterized in that, The high-temperature additive includes any one or a combination of at least two of vinylene carbonate, vinyl ethyl carbonate, fluoroethylene carbonate, ethylene sulfate, 1,3 - propanesultone, tris(trimethylsilyl) borate, or tris(trimethylsilyl) phosphate.

7. The electrolyte according to claim 5, wherein The high-temperature additive includes ethylene sulfate.

8. The electrolyte according to claim 5, characterized in that, Based on the mass fraction of the electrolyte being 100%, the high-temperature additive accounts for 0.01 - 3% of the electrolyte by mass fraction.

9. The electrolyte according to claim 8, characterized in that, Based on the mass fraction of the electrolyte being 100%, the high-temperature additive accounts for 0.1 - 2% of the electrolyte by mass fraction.

10. The electrolyte according to claim 5, characterized in that, The lithium salt additive includes lithium difluorophosphate and lithium bis(fluorosulfonyl)imide.

11. The electrolyte according to claim 10, wherein Based on the mass fraction of the electrolyte being 100%, lithium difluorophosphate accounts for 0.1 - 1.5% of the electrolyte by mass fraction.

12. The electrolyte according to claim 10, characterized in that, Based on the mass fraction of the electrolyte being 100%, lithium bis(fluorosulfonyl)imide accounts for 0.1 - 10% of the electrolyte by mass fraction.

13. The electrolyte according to claim 1, characterized in that, The organic solvent includes a cyclic carbonate and a chain carbonate.

14. The electrolyte according to claim 13, characterized in that, The cyclic carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, butylene carbonate, or γ - butyrolactone.

15. The electrolyte according to claim 13, wherein, The chain carbonate includes any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, or ethyl butyrate.

16. The electrolyte according to claim 13, wherein, The volume ratio of the cyclic carbonate to the chain carbonate is (10 - 40):(60 - 90).

17. The electrolyte according to claim 16, characterized in that, The volume ratio of the cyclic carbonate to the chain carbonate is (15 - 40):(60 - 85).

18. The electrolyte according to claim 1, characterized in that, Based on the mass fraction of the electrolyte being 100%, the organic solvent accounts for 65.6 - 89.6% of the electrolyte by mass fraction.

19. The electrolyte according to claim 1, characterized in that, The lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate, lithium bis(trifluoromethylsulfonyl)imide, or lithium perchlorate.

20. The electrolyte according to claim 1, wherein The lithium salt includes lithium hexafluorophosphate.

21. The electrolyte according to claim 20, wherein Based on the mass fraction of the electrolyte being 100%, lithium hexafluorophosphate accounts for 10 - 20% of the electrolyte by mass fraction.

22. The electrolyte according to claim 1, characterized in that, Based on the mass fraction of the electrolyte being 100%, the lithium salt accounts for 10 - 20% of the electrolyte by mass fraction.

23. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte according to any one of claims 1 - 22. The lithium-ion battery further includes a positive electrode plate and a negative electrode plate.

24. The lithium ion battery according to claim 23, wherein, The material of the positive electrode sheet includes lithium transition metal oxides and / or lithium transition metal phosphate compounds.

25. The lithium-ion battery according to claim 24, characterized in that, The transition metal oxides of lithium include LiCoO2, LiNi x Co y Mn z O2, LiNi x Mn y O2, LiMn2O4, LiMnO2, Li2MnO4, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiMn 1-x M x O4 or Li2Mn 1-x O4, where any one or a combination of at least two of them are included, and 0 ≤ a < 0.2, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1.

26. The lithium ion battery according to claim 24, wherein, The lithium transition metal phosphate compound includes any one or a combination of at least two of LiFePO4, LiMnPO4, LiCoPO4 or LiFe 1-x M x PO4, wherein M is selected from any one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, and 0 ≤ x ≤ 1.

27. The lithium ion battery according to claim 23, characterized in that, The material of the negative electrode sheet includes any one or a combination of at least two of carbonaceous materials, alloy materials, or metal composite materials containing lithium.

28. The lithium ion battery according to claim 23, characterized in that, The material of the negative electrode sheet includes any one or a combination of at least two of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, silicon, silicon-carbon alloy, or silicon-oxygen alloy.

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