Electrolyte and use thereof

Abstract

This invention provides an electrolyte and its application. The electrolyte comprises an organic solvent and a lithium salt. The organic solvent comprises a first solvent and a second solvent. The first solvent comprises a cyclic sulfite solvent. The second solvent comprises a chain carbonate solvent and / or a chain carboxylic acid ester solvent. The lithium salt comprises lithium hexafluorophosphate. In this invention, the electrolyte, while meeting the battery's rate discharge performance and cycle performance requirements, can improve battery safety performance, and is particularly suitable for lithium-ion batteries containing high-nickel cathode materials, avoiding the problem of thermal runaway leading to violent combustion or even explosion.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to an electrolyte and its application. Background Technology

[0002] Long-range electric vehicles require lithium-ion batteries with higher energy density (>300Wh / kg). Currently, the feasible technical approach is to use silicon-containing anodes and high-nickel cathodes. However, using conventional electrolytes containing cyclic carbonates and bis(fluorosulfonyl)imide lithium salts can lead to serious safety hazards in such high-energy-density lithium-ion batteries. Under conditions of electric vehicle malfunction or accident, thermal runaway can easily occur, resulting in violent combustion or even explosion. One reason for this result is that the electrolyte reacts with the positive and negative electrodes at high temperatures, releasing more heat. When the temperature exceeds 200°C, high-nickel materials undergo a violent exothermic reaction with the electrolyte, especially cyclic carbonate solvents in the electrolyte, which are more prone to this violent exothermic reaction with high-nickel materials (Yu Wu, et al, High-Voltage and High-Safety Practical Lithium Batteries with Ethylene Carbonate-Free Electrolyte, Adv. Energy Mater. 2021, 11:2102299). Secondly, although lithium bis(fluorosulfonyl)imide (LiFSI) has good dissociation ability in solvents and can provide excellent ionic conductivity, and is widely used as the main salt or additive in electrolytes, it reacts violently with the charged negative electrode material, releasing a large amount of heat and seriously compromising battery safety. Therefore, its role needs to be re-evaluated in electrolyte formulation design (Hao Jia, et al, Is Nonflammability of Electrolyte Overrated in the Overall Safety Performance of Lithium Ion Batteries (A Sobering Revelation from a Completely Nonflammable Electrolyte, 2022, Adv. Energy Mater. 2023, 13, 2203144); In addition, high-nickel materials release oxygen at high temperatures, and carbonate solvents are highly flammable. Under the influence of high temperature and oxygen, they can burn violently or even explode, further deteriorating the safety performance of the battery.

[0003] The common drawback of existing technologies is that conventional electrolytes have poor safety performance, especially for high-energy-density lithium-ion batteries using high-nickel cathode materials, which pose serious safety hazards. Under conditions of electric vehicle malfunction or accident, thermal runaway can easily occur, leading to violent combustion or even explosion.

[0004] Therefore, developing an electrolyte that improves the safety performance of lithium-ion batteries while ensuring their rate performance and cycle performance, especially for lithium-ion batteries using high-nickel cathode materials, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an electrolyte and its applications. This electrolyte, while meeting the requirements for high-rate discharge performance and cycle performance, can improve battery safety, and is particularly suitable for lithium-ion batteries containing high-nickel cathode materials.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides an electrolyte comprising an organic solvent and a lithium salt; the organic solvent comprising a first solvent and a second solvent; the first solvent comprising a cyclic sulfite solvent; the second solvent comprising a chain carbonate solvent and / or a chain carboxylic acid ester solvent; and the lithium salt comprising lithium hexafluorophosphate.

[0008] In this invention, cyclic sulfite solvents possess certain flame-retardant properties and exhibit low reactivity with the positive and negative electrodes of lithium-ion batteries at high temperatures, resulting in minimal exothermic reactions and good safety. Furthermore, as organic solvents, they demonstrate strong salt dissociation capabilities, and some solvents also participate in SEI formation. These solvents serve as the electrolyte solvent throughout the entire lifespan of the battery cell. Chain carbonate or carboxylic acid ester solvents have low viscosity and provide a certain degree of lithium salt dissociation capability, ensuring excellent ion conduction capacity of the electrolyte and improving rate discharge performance. Lithium hexafluorophosphate (LiPF6)... The high solubility in the solvent and relative stability between the active materials of the same electrode, coupled with lower exothermic reaction than other main salts (such as LiFSI), ensures battery safety characteristics. Furthermore, the electrolyte using cyclic sulfite solvents and LiPF6 exhibits high conductivity, meeting the rate discharge requirements of lithium-ion batteries. In summary, this invention breaks with conventional limitations by using cyclic sulfites and chain carboxylic esters, commonly used as additives, as organic solvents. This not only ensures the safety performance of lithium-ion batteries but also meets the requirements for rate discharge and cycle performance, making it particularly suitable for high-nickel lithium-ion batteries.

[0009] In an optional embodiment of the present invention, the mass percentage of the first solvent in the electrolyte is 5% to 50%, for example, it can be 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 42%, 44%, 45%, 46%, 48%, 50%, etc.; preferably 10% to 40%.

[0010] As an optional embodiment of the present invention, the cyclic sulfite solvent includes any one or a combination of at least two of vinyl sulfite (ES), butylene sulfite (BS), 1,3-propanediol sulfite (TMS), or 1,2-propanediol sulfite (MES).

[0011] As an optional embodiment of the present invention, the cyclic sulfite solvent includes a combination of vinyl sulfite and 1,3-propanediol sulfite; or, the cyclic sulfite solvent includes a combination of vinyl sulfite and 1,2-propanediol sulfite; or, the cyclic sulfite solvent includes a combination of butenyl sulfite and 1,3-propanediol sulfite; or, the cyclic sulfite solvent includes a combination of butenyl sulfite and 1,2-propanediol sulfite.

[0012] As an optional embodiment of the present invention, the mass ratio of vinyl sulfite to 1,3-propanediol sulfite is 1:(0.2-1); or, the mass ratio of vinyl sulfite to 1,2-propanediol sulfite is 1:(0.2-1); or, the mass ratio of butene sulfite to 1,3-propanediol sulfite is 1:(0.2-1); or, the mass ratio of the combination of butene sulfite and 1,2-propanediol sulfite is 1:(0.2-1); wherein, the specific value of (0.2-1) can be, for example, 0.2, 0... 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.34, 0.36, 0.38, 0.4, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64, 0.66, 0.68, 0.7, 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, 1, etc.

[0013] In an optional embodiment of the present invention, the mass percentage of the second solvent in the electrolyte is 20% to 80%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 42%, 44%, 45%, 46%, 48%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 68%, 70%, 72%, 74%, 76%, 78%, 80%, etc.; preferably 40% to 75%.

[0014] As an optional embodiment of the present invention, the chain carbonate solvent includes any one or a combination of at least two of dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC).

[0015] As an optional embodiment of the present invention, the chain carboxylic acid ester solvent includes any one or a combination of at least two of ethyl acetate (EA), propyl acetate (PA), butyl acetate (BA), methyl propionate (MP), ethyl propionate (EP), or propyl propionate (PP).

[0016] As an optional embodiment of the present invention, the mass percentage of lithium salt in the electrolyte is 10% to 30%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc.

[0017] As an optional embodiment of the present invention, the electrolyte satisfies at least one of the following conditions a to d:

[0018] a. The electrolyte also includes additives;

[0019] b. The mass percentage of the additive in the electrolyte is 0.1% to 10%, for example, it can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.;

[0020] c. The additives include any one or a combination of at least two of the following: fluorocarbonates, unsaturated cyclic carbonates, cyclic sulfonates, cyclic sulfates, or lithium salt additives.

[0021] d. The additives include any one or a combination of at least two of the following: fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propanesulfonate lactone (1,3-PS), vinyl sulfate (DTD), 1,3-propenesulfonate lactone (RPS), lithium difluorophosphate, lithium difluorooxalate borate, or lithium difluorobis(oxalate) phosphate.

[0022] In this invention, the method for preparing the electrolyte includes the following steps:

[0023] The electrolyte is obtained by mixing an organic solvent and a lithium salt.

[0024] As an optional embodiment of the present invention, the mixing process further includes a step of mixing the first solvent and the second solvent and removing water; the water removal device includes an activated 3A molecular sieve; and the water content of the mixed solvent is less than 20 ppm after water removal.

[0025] As an optional embodiment of the present invention, the organic solvent and lithium salt are mixed in a glove box; the dew point of the glove box is below -40°C.

[0026] As an optional embodiment of the present invention, the mixed materials further include additives; after the organic solvent and lithium salt are mixed, additives are added to the mixture to obtain the electrolyte.

[0027] In a second aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the electrolyte according to the first aspect.

[0028] In this invention, the lithium-ion battery further includes a positive electrode, a negative electrode, and a separator.

[0029] In this invention, the positive electrode material includes a positive electrode slurry and a positive electrode current collector; the positive electrode slurry includes a positive electrode active material, a conductive agent, a binder, and a solvent; the mass ratio of the positive electrode active material, the conductive agent, and the binder is 96-97:1-2:2; and the solid content of the positive electrode slurry is 60-70%.

[0030] As an optional embodiment of the present invention, the positive electrode active material of the lithium-ion battery includes any one or a combination of at least two of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, or lithium manganese iron phosphate, preferably lithium nickel cobalt manganese oxide.

[0031] In this invention, the conductive agent in the positive electrode slurry includes, but is not limited to, carbon black; the binder includes, but is not limited to, polyvinylidene fluoride (PVDF); the solvent includes, but is not limited to, N-methylpyrrolidone (NMP); and the positive electrode current collector includes aluminum foil.

[0032] In this invention, the negative electrode material includes a negative electrode slurry and a negative electrode current collector; the negative electrode slurry includes a negative electrode active material, a conductive agent, a binder, and a solvent; the mass ratio of the negative electrode active material, the conductive agent, and the binder is 96-98:1.5:0.5-2.5; and the solid content of the negative electrode slurry is 40-60%.

[0033] As an optional embodiment of the present invention, the negative electrode active material of the lithium-ion battery includes any one or a combination of at least two of graphite, silicon suboxide-carbon composite material, or silicon-carbon composite material.

[0034] In this invention, the conductive agent in the negative electrode slurry includes, but is not limited to, carbon black; the binder includes, but is not limited to, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR); the solvent includes, but is not limited to, water; and the negative electrode current collector includes copper foil.

[0035] In this invention, the diaphragm includes a base membrane and a ceramic coating applied to both surfaces of the base membrane.

[0036] As an optional embodiment of the present invention, the base film includes, but is not limited to, a porous polyethylene membrane; the thickness of the base film is 8 to 10 μm.

[0037] As an optional embodiment of the present invention, the ceramic coating includes, but is not limited to, a boehm stone coating; the single-layer thickness of the ceramic coating is 1 to 3 μm.

[0038] Thirdly, the present invention provides an electrical device comprising an electrolyte according to the first aspect or a lithium-ion battery according to the second aspect.

[0039] Lithium-ion batteries can be used as a power source for electrical devices or as an energy storage unit for electrical devices. Electrical devices can be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0040] Electrical devices can choose the specific type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0041] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] The electrolyte provided by this invention uses cyclic sulfites, chain carbonates and / or chain carboxylic acids as organic solvents, and lithium hexafluorophosphate as the lithium salt. This can improve the safety performance of lithium-ion batteries, especially for high-energy-density lithium-ion batteries using high-nickel cathode materials, reduce safety hazards, avoid thermal runaway leading to violent combustion or even explosion, and ensure excellent rate discharge performance and cycle performance of lithium ions. Attached Figure Description

[0044] Figure 1 The DSC test spectra of the electrolytes provided in Examples 1-3 and Comparative Example 1;

[0045] Figure 2 The exothermic peak area data are shown for the DSC test spectra of the electrolytes provided in Examples 1-3 and Comparative Example 1. Detailed Implementation

[0046] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0047] Examples 1-14, Comparative Examples 1-2

[0048] Examples 1-14 and Comparative Examples 1-2 each provide an electrolyte, the specific formulation of which is shown in Table 1 by mass percentage; wherein, EC represents ethylene carbonate; the preparation method of the electrolyte includes:

[0049] After the first solvent and the second solvent are mixed evenly in a set ratio, the mixed solvent is dehydrated using an activated 3A molecular sieve to reduce the water content of the mixed solvent to less than 20 ppm. Then, in a glove box with a dew point below -40°C, the prescribed amount of lithium hexafluorophosphate (LiPF6) is dissolved in the mixed solvent to prepare an electrolyte of a set concentration. Then, according to the prescribed amount, additives are added to it to obtain the electrolyte of the present invention. In Table 1, " / " indicates that the substance is not in the formula.

[0050] Table 1

[0051]

[0052] Application examples

[0053] A lithium-ion battery, wherein the electrolyte of the lithium-ion battery comprises the electrolytes provided in Examples 1-14 and Comparative Examples 1 and 2, respectively; the preparation method of the lithium-ion battery includes:

[0054] (1) Preparation of the positive electrode

[0055] Lithium nickel cobalt manganese oxide (LiNi) is used as the positive electrode active material.0.8 Co 0.1 Mn 0.1 O2 (S8303 from Hubei Rongbai Lithium Battery Materials Co., Ltd.), carbon black conductive agent (TIMCAL Super) Li), PVDF adhesive (SOLVAY) 5130) was mixed in a weight ratio of 96.5:1.5:2 and added to a double planetary mixer. N-methylpyrrolidone (NMP) was added, and the mixture was thoroughly stirred and then filtered through a filter screen to obtain a slurry with a solid content of 65%. The slurry was then coated onto both sides of a 12μm thick aluminum foil using an extrusion coating machine. After baking and hot rolling, a positive electrode plate was obtained. The areal density of the coating on one side of the positive electrode plate was 20 mg / cm³. 2 The single-sided coating thickness is 60μm. The obtained positive electrode plate is dried in a vacuum oven at 120℃ for more than 24 hours to obtain the positive electrode.

[0056] (2) Preparation of negative electrode

[0057] The negative electrode active material is artificial graphite (Jiangxi Zichen Technology Co., Ltd. G49), and the carbon black conductive agent is TIMCALSuper. Li and sodium carboxymethyl cellulose (CMC) (DAICEL CMC2200) were mixed at a weight ratio of 97:1.5:1.5 and then added to a double planetary mixer. Deionized water (DIW) was added, and the solid content was set to 50%. After thorough mixing, styrene-butadiene rubber latex (SBR) (ZEON BM-451B, solid content 40%), accounting for 1% of the total solid weight of the negative electrode slurry, was added and slowly mixed until homogeneous. The mixture was then filtered through a filter screen to obtain the slurry. The slurry was then coated onto both sides of an 8μm thick copper foil using an extrusion coating machine. After baking and hot rolling, the negative electrode plate was obtained. The areal density of the single-sided coating of the negative electrode plate was 13 mg / cm³. 2 The single-sided coating thickness is 80μm. The resulting negative electrode plate is dried in a vacuum oven at 100℃ for more than 24 hours to obtain the negative electrode.

[0058] (3) Preparation of dry cell

[0059] The aforementioned positive electrode, negative electrode, and separator (a 9μm thick polyethylene porous membrane coated with a 2μm boehmite coating on both sides) are cut into specific shapes. The active material region on the positive electrode is 48mm × 44mm, the active material region on the negative electrode is 52mm × 46mm, and the separator is 56mm × 50mm. Current collectors are provided on both the positive and negative electrodes. The electrodes are then stacked layer by layer in the order of negative electrode, separator, positive electrode, separator, and negative electrode, resulting in a total of 18 positive electrodes and 19 negative electrodes, with the outermost layer being the negative electrode. The current collectors of the positive electrodes are then welded together using an ultrasonic welder, and positive electrode tabs are welded on. Similarly, the current collectors of the negative electrodes are welded together using an ultrasonic welder, and negative electrode tabs are welded on. This yields the stacked body.

[0060] The aforementioned stacked bodies are placed into a packaging bag made of aluminum-plastic film after being stamped on both sides, and the hot melt adhesive on the tabs is fused to the packaging bag by hot melting. The tabs are led out of the packaging bag, and an air bladder and liquid injection port are left on one side of the packaging bag, thus obtaining a dry cell.

[0061] (4) Battery manufacturing

[0062] In a glove box with a dew point below -40°C, the electrolytes provided in Examples 1-14 and Comparative Examples 1 and 2 of this invention are injected into the dry cell through the injection port. After standing for 24 hours, the injection port outside the air bag is sealed with a vacuum heat sealer, and the gas in the cell is extracted to obtain the battery.

[0063] (5) Battery formation and capacity testing

[0064] The battery is formed using a charging and discharging device. First, it is charged at a constant current of 0.05C to 3.6V. Then, a vacuum heat sealer is used to evacuate and seal the gasket and cut off the gas. Next, it is charged at a constant current of 0.33C to 4.2V. Then, it is charged at a constant voltage until the current drops to 0.05C. Finally, it is discharged at a constant current of 0.33C to 3.0V, thus obtaining a well-capacitated battery cell, which is the lithium-ion battery of the present invention.

[0065] Performance testing

[0066] 1. Thermal stability test of electrolyte / electrode system

[0067] A DSC instrument was used to test the thermal stability of the electrolyte / electrode system, specifically lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1Taking O2 (NCM811) positive electrode as an example, the specific method is as follows: In a glove box with a dew point below -40℃, after disassembling a fully charged battery, take out an NCM811 positive electrode sheet and immerse it in a large amount of dimethyl carbonate (DMC) solvent. After 30 minutes, replace it with fresh DMC solvent and repeat the immersion process twice. Then, remove the positive electrode sheet and dry it thoroughly. Next, use a belt punch to cut out a positive electrode sheet with a diameter of 4.5 mm. The weight of the active material in the positive electrode sheet is controlled to be ~3.2 mg. Place the positive electrode sheet in a special gold crucible, add 0.5 μL of electrolyte, and tighten and seal it with a special tool. Then, place the special gold crucible in a DSC device for testing. The test conditions are a temperature range of 30–350℃ (N2 atmosphere), a heating rate of 10℃ / min, and natural cooling.

[0068] Taking Examples 1-3 and Comparative Example 1 as examples, their DSC test results are as follows: Figure 1 As shown; by Figure 1 It can be seen that the use of a high-safety electrolyte in Examples 1-3 effectively suppressed the exothermic reaction between the electrolyte and the charged positive electrode, and the exothermic onset temperature was significantly delayed to a higher temperature; the corresponding heat of exothermic reaction was also reduced to 49.9%, 60.6%, and 77.4% of that in the comparative examples, respectively (see Figure 2 ).

[0069] 2. Battery testing

[0070] 2.1 Rate Discharge Performance Test

[0071] At room temperature, the battery was charged at a constant current of 1C to 4.2V, then charged at a constant voltage until the current dropped to 0.05C. It was then discharged at a constant current of 1C to 3.0V, and the first 1C constant current discharge capacity was recorded. After resting for 10 minutes, the battery was charged again at a constant current of 1C to 4.2V, then charged at a constant voltage until the current dropped to 0.05C, and finally discharged at a constant current of 3C to 3.0V, and the second 3C constant current discharge capacity was recorded. The second 3C constant current discharge capacity was compared with the first 1C constant current discharge capacity to calculate the 3C / 1C discharge capacity retention rate.

[0072] 2.2 Charge-discharge cycle test

[0073] At room temperature, the battery is charged at a constant current of 1C to 4.2V, then charged at a constant voltage until the current drops to 0.05C, and then discharged at a constant current of 1C to 3.0V. This cycle is repeated for 1000 cycles. The discharge capacity retention rate is calculated by comparing the discharge capacity of the last discharge with that of the first discharge.

[0074] 2.3 Hot Box Test

[0075] The battery heating safety test was conducted in accordance with GB 38031-2020. The battery was placed in a high-temperature chamber and the ambient temperature was raised to 130°C at a rate of 5°C / min. This temperature was maintained for 30 minutes. If the battery did not catch fire, the temperature was raised by 5°C and maintained for 30 minutes until the battery caught fire. The ignition temperature of the battery was recorded.

[0076] The specific test results are shown in Table 2:

[0077] Table 2

[0078]

[0079]

[0080] As shown in the table above, the electrolyte provided by this invention uses a specific amount and type of cyclic sulfite solvent combined with chain carbonates and / or chain carboxylic acids, and lithium hexafluorophosphate is used as the lithium salt, which makes the electrolyte safe with an ignition temperature ≥150℃; the discharge capacity retention rate at 3C / 1C is ≥89.0%, and the capacity retention rate after 1000 cycles at room temperature is ≥93.3%.

[0081] A comparison of Example 1 and Example 12 shows that the first solvent exceeds the further preferred range, and the content of the second solvent is lower than the further preferred range. As a result, the ignition temperature of the battery is reduced, the safety performance is slightly worse, the capacity retention rate of the rate discharge performance is reduced, and the cycle performance is also reduced.

[0082] A comparison of Example 1 and Example 13 shows that when the content of the first solvent is below the further preferred range and the content of the second solvent exceeds the further preferred range, the ignition temperature of the battery decreases, the safety performance deteriorates, the capacity retention rate of the rate discharge performance decreases, and the cycle performance also decreases.

[0083] A comparison of Example 1 and Example 14 shows that without additives that form a film, the battery's ignition temperature decreases and its safety performance deteriorates.

[0084] As can be seen from the comparison between Example 1 and Comparative Example 1, the electrolyte system is not specific to this invention. Comparative Example 1 uses cyclic carbonate solvent EC, which is incompatible with the high-nickel material system cell, resulting in a lower ignition temperature, worse safety performance, lower capacity retention rate during rate discharge, and reduced cycle performance.

[0085] As can be seen from the comparison between Example 1 and Comparative Example 2, the electrolyte system is not specific to this invention. The lithium salt used in Comparative Example 2 includes LiPF6 and LiFSI. LiFSI is prone to react with the negative electrode material, which reduces the ignition temperature of the battery and worsens its safety performance.

[0086] In summary, the electrolyte provided by this invention avoids the use of conventional ethylene carbonate solvent, instead using cyclic sulfite esters, chain carbonates, and / or chain carboxylic acid esters as organic solvents. By selecting specific types of organic solvents and specific types of lithium salts, the safety performance of lithium-ion batteries can be improved. In particular, for high-energy-density lithium-ion batteries using high-nickel cathode materials, this invention helps to reduce safety hazards, avoid thermal runaway leading to violent combustion or even explosion, and ensure that lithium-ion batteries have excellent cycle performance.

[0087] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises an organic solvent and a lithium salt; The organic solvent includes a first solvent and a second solvent; the first solvent includes cyclic sulfite solvents; the second solvent includes chain carbonate solvents and / or chain carboxylic acid ester solvents; The lithium salt includes lithium hexafluorophosphate.

2. The electrolyte according to claim 1, characterized in that, The mass percentage of the first solvent in the electrolyte is 5-50%, preferably 10-40%.

3. The electrolyte according to claim 1 or 2, characterized in that, The cyclic sulfite solvents include any one or a combination of at least two of vinyl sulfite, 1,3-propanediol sulfite, or 1,2-propanediol sulfite.

4. The electrolyte according to any one of claims 1 to 3, characterized in that, The mass percentage of the second solvent in the electrolyte is 20-80%, preferably 40-75%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that, The chain carbonate solvents include any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate. And / or, the chain carboxylic acid ester solvent includes any one or a combination of at least two of ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, or propyl propionate.

6. The electrolyte according to any one of claims 1 to 5, characterized in that, The electrolyte contains 10-30% lithium salt by mass.

7. The electrolyte according to any one of claims 1 to 6, characterized in that, It satisfies at least one of the following conditions a to d: a. The electrolyte also includes additives; b. The mass percentage of the additive in the electrolyte is 0.1% to 10%; c. The additives include any one or a combination of at least two of the following: fluorocarbonates, unsaturated cyclic carbonates, cyclic sulfonates, cyclic sulfates, or lithium salt additives. d. The additives include any one or a combination of at least two of the following: fluoroethylene carbonate, vinylene carbonate, vinyl ethylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, 1,3-propenesulfonate lactone, lithium difluorophosphate, lithium difluorooxalate borate, or lithium difluorobis(oxalate) phosphate.

8. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that, The positive electrode active material of the lithium-ion battery includes any one or a combination of at least two of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, or lithium manganese iron phosphate. And / or, the negative electrode active material of the lithium-ion battery includes any one or a combination of at least two of graphite, silicon suboxide-carbon composite material, or silicon-carbon composite material.

10. An electrical device, characterized in that, The electrical device includes the electrolyte according to any one of claims 1 to 7 or the lithium-ion battery according to claim 8 or 9.

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