Electrolyte and lithium battery comprising the same

Abstract

The present application relates to a kind of electrolyte and the lithium battery comprising the electrolyte. To solve the problem of poor electrochemical performance of lithium battery under high voltage, the present application provides a kind of electrolyte, including organic solvent, lithium salt and additive, additive includes fluoroethylene carbonate, 1,2,3,4,5-penta (2-cyanoethoxyl) pentane and acid anhydride compound.The electrolyte component of the present application is simple, through the synergistic cooperation of fluoroethylene carbonate, 1,2,3,4,5-penta (2-cyanoethoxyl) pentane and acid anhydride compound, can effectively inhibit the gas expansion, cycle attenuation and thickness increase of lithium battery under high voltage (4.5V and above) and high temperature condition, improve the rate capability of battery.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrolyte and a lithium battery comprising the same. BACKGROUND

[0002] With the emergence of new consumer fields such as mobile phones, tablets, smart wear and ETC, lithium ion batteries have shown great advantages due to their high energy density and long cycle life. However, with the continuous diversification of the functions of the corresponding devices and the continuous rise of the power consumption of the power modules, conventional lithium ion batteries have been difficult to meet the user's use requirements. In order to improve the user experience, the development direction of lithium ion batteries has become increasingly clear, that is, to improve the energy density as much as possible or to achieve fast charging under safe conditions.

[0003] In order to improve the energy density, the industry is currently developing in three aspects. One is to seek new material systems, such as lithium cobaltate, lithium-rich manganese-based, ternary high-nickel positive electrode materials, silicon-carbon negative electrode materials, etc.; the second is to improve the cut-off charging voltage of existing materials, such as 4.5V or higher lithium cobaltate batteries, 4.4V or higher ternary batteries, etc.; the third is to improve the areal density and the green density by changing the battery process or using thinner current collectors, tapes and aluminum plastic shells, etc. In order to achieve fast charging, fast charging type lithium ion batteries have emerged, from the initial 0.2C charging, to the later 2C charging, and even 5C charging.

[0004] In the digital field with high requirements for volume energy density, the design idea of lithium battery is high-voltage lithium cobaltate & silicon-carbon negative electrode. The voltage of commercial lithium cobaltate battery has been gradually increased from the initial 4.2V to 4.5V and above, but with the increase of voltage, the existing lithium cobaltate battery shows certain negative effects, such as the material surface due to the existence of dangling bonds and unsaturated coordination relationship will make its reaction activity significantly higher than the bulk. When the lithium cobaltate battery is charged, the following reaction process will occur:

[0005] (1) The positive electrode material starts to delithiate from the surface;

[0006] (2) After delithiation, the oxygen atoms between the Li layers lose the barrier and produce repulsion, resulting in unstable surface structure;

[0007] (3) Continuous delithiation promotes the surface lattice activity to produce gas overflow;

[0008] (4) The overflow gas causes the surface Co atom to become unstable and dissolve;

[0009] (5) The dissolved high-valence Co element will also oxidize the electrolyte and participate in the electrolyte chemical reaction.

[0010] Solid-liquid interface side reactions are an unavoidable problem in the development of lithium batteries. Currently used electrolytes typically have a chemical window below 4.5V. When the charging cutoff voltage exceeds 4.5V, the electrolyte undergoes oxidative decomposition on the battery surface, causing a sharp drop in battery capacity. Simultaneously, the products of oxidation decomposition also coat the electrode material surface, increasing the battery's internal resistance. Furthermore, the catalytic action of free transition metal elements on the boundary of surface side reaction products poses a potential risk in maintaining the electrode material in a high-activity state.

[0011] Therefore, it is necessary to develop an electrolyte with good electrochemical performance under high voltage. Summary of the Invention

[0012] The purpose of this invention is to provide an electrolyte with good high-temperature stability and cycling performance under high voltage.

[0013] A second objective of the present invention is to provide a lithium battery containing the electrolyte.

[0014] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0015] An electrolyte comprising an organic solvent, a lithium salt, and additives, said additives including fluoroethylene carbonate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and acid anhydride compounds.

[0016] Preferably, the 1,2,3,4,5-penta(2-cyanoethoxy)pentane accounts for 0.1-7% of the total mass of the electrolyte, more preferably 0.5-5%, and even more preferably 3-5%, for example 3%, 3.5%, 4%, 4.5%, or 5%. In this invention, 1,2,3,4,5-penta(2-cyanoethoxy)pentane can be prepared by mixing xylitol and sodium ethoxide, followed by the addition of acrylonitrile; wherein the reaction temperature is preferably 80-100°C.

[0017] Preferably, the acid anhydride compound is a cyclic carboxylic anhydride.

[0018] More preferably, the acid anhydride compound is selected from the compound shown in structural formula A and / or the compound shown in structural formula B, wherein structural formula A is... Structural formula B is R1, R2, R3, and R4 are each independently selected from H, an alkyl group having 1 to 3 carbon atoms, or a phenyl group. An alkyl group having 1 to 3 carbon atoms can be, for example, methyl, ethyl, or propyl.

[0019] In some specific embodiments, the anhydride compound is selected from one or more of 2-methylmaleic anhydride, 2,3-dimethylmaleic anhydride, phenylmaleic anhydride, and succinic anhydride.

[0020] Preferably, the acid anhydride compound accounts for 0.1% to 1% of the total mass of the electrolyte, more preferably 0.3% to 0.5%, for example 0.3%, 0.35%, 0.4%, 0.45% or 0.5%.

[0021] Preferably, the fluoroethylene carbonate accounts for 0.1% to 10% of the total mass of the electrolyte, more preferably 2% to 8%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc.

[0022] Preferably, the additive further includes other additives, including one or more of the following: ethylene carbonate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, adiponitrile, succinic anion, 1,2-di(2-cyanoethoxy)ethane, 1,4-dicyano-2-butene, 1,2,3-tris(2-cyanoethoxy)propane, decanonitrile, and 2-methylglutaronitrile.

[0023] Preferably, each of the other additives accounts for 0.1% to 8% of the total mass of the electrolyte.

[0024] Preferably, the organic solvent is a mixture of cyclic esters and chain esters, wherein the cyclic ester is one or more selected from γ-butyrolactone, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; and the chain ester is one or more selected from dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl acetate, ethyl acetate, propyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl fluoropropionate, ethyl fluoropropionate, and ethyl fluoropropionate.

[0025] In some embodiments, the organic solvent is ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, and propyl propionate. Conventional carbonate solvents are prone to catalytic decomposition under high voltage conditions. This invention, through the synergistic effect of the above-mentioned additives, effectively inhibits the catalytic decomposition of carbonate solvents, thereby reducing battery gas production and metal ion dissolution.

[0026] More preferably, the organic solvent further includes ethyl fluoroacetate, such as 2,2-difluoroethyl acetate.

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

[0028] Preferably, the concentration of the lithium salt is 0.8 to 3 mol / L.

[0029] Preferably, the additive further includes a lithium salt additive, which is one or more of lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium di(trifluoromethanesulfonyl)imide, lithium difluorophosphate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, and lithium difluorosulfonylimide.

[0030] More preferably, the lithium salt additive accounts for 0.1% to 5% of the total mass of the electrolyte.

[0031] A second objective of the present invention is to provide a lithium battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described above.

[0032] Preferably, the active material of the positive electrode is lithium cobalt oxide, and the charging cut-off voltage of the lithium battery can reach 4.5V or higher.

[0033] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0034] The electrolyte of this invention has a simple composition. Through the synergistic effect of fluoroethylene carbonate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane and acid anhydride compounds, it can effectively suppress the gas expansion, cycle decay and thickness increase of lithium batteries under high voltage (4.5V and above) and high temperature conditions, thereby improving the rate performance of the battery. Attached Figure Description

[0035] Figure 1 The NMR C-NMR spectrum of 1,2,3,4,5-penta(2-cyanoethoxy)pentane;

[0036] Figure 2 The NMR spectrum of 1,2,3,4,5-penta(2-cyanoethoxy)pentane. Detailed Implementation

[0037] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0038] In this invention, the structural formula of 1,2,3,4,5-penta(2-cyanoethoxy)pentane is shown below.

[0039]

[0040] 1,2,3,4,5-penta(2-cyanoethoxy)pentane can be prepared by mixing xylitol and sodium ethoxide, followed by the addition of acrylonitrile.

[0041] As a preferred example, the preparation method of 1,2,3,4,5-penta(2-cyanoethoxy)pentane is as follows:

[0042] 152g xylitol and 6.8g sodium ethoxide were mixed and heated to 90℃ with stirring for 2 hours. Then, 477g acrylonitrile was slowly added dropwise and stirred. The mixture was reacted for 12 hours. After cooling to room temperature, 6000g ethanol was added and stirred until homogeneous. The mixture was filtered, and the residue was purified by recrystallization from ethyl acetate and n-hexane to obtain a product with a purity >99%. See the NMR spectrum for details. Figure 1 and Figure 2 .

[0043] Unless otherwise specified, all reagents used in the embodiments and comparative examples of this invention are commercially available products. In the embodiments or comparative examples of this invention, diethyl carbonate is abbreviated as DEC, ethylene carbonate as EC, propylene carbonate as PC, ethyl propionate as EP, propyl propionate as PP, and 2,2-difluoroethyl acetate as DFEA.

[0044] Example 1

[0045] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.1wt% succinic anhydride were added to the electrolyte to prepare the electrolyte.

[0046] Example 2

[0047] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.3wt% succinic anhydride were added to the electrolyte to prepare the electrolyte.

[0048] Example 3

[0049] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.5wt% succinic anhydride were added to the electrolyte to prepare the electrolyte.

[0050] Example 4

[0051] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 1wt% succinic anhydride were added to the electrolyte to prepare the electrolyte.

[0052] Example 5

[0053] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.5wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0054] Example 6

[0055] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 4 wt% fluoroethylene carbonate, 3 wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.5 wt% 2,3-dimethylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0056] Example 7

[0057] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.5wt% phenyl maleic anhydride were added to the electrolyte to prepare the electrolyte.

[0058] Example 8

[0059] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0060] Example 9

[0061] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 4 wt% fluoroethylene carbonate, 3 wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3 wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0062] Example 10

[0063] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 5wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0064] Example 11

[0065] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 7wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0066] Example 12

[0067] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 1wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0068] Example 13

[0069] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 2wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0070] Example 14

[0071] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 8 wt% fluoroethylene carbonate, 3 wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3 wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0072] Example 15

[0073] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 10wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0074] Example 16

[0075] In an argon-filled glove box (H2O content <10ppm), DFEA, DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:1:2:1:2:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 4 wt% fluoroethylene carbonate, 3 wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3 wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0076] Example 17

[0077] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 0.5% lithium difluorooxalate borate, 4 wt% fluoroethylene carbonate, 3 wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3 wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0078] Comparative Example 1

[0079] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was then added to the mixed solution to prepare the electrolyte.

[0080] Comparative Example 2

[0081] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% fluoroethylene carbonate and 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane were added to the electrolyte to obtain the electrolyte solution.

[0082] Comparative Example 3

[0083] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution, and then 3wt% of 1,2,3,4,5-penta(2-cyanoethoxy)pentane and 0.3wt% of succinic anhydride were added to the electrolyte to prepare the electrolyte.

[0084] Comparative Example 4

[0085] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% fluoroethylene carbonate and 0.3wt% succinic anhydride were added to the electrolyte to obtain the electrolyte.

[0086] Comparative Example 5

[0087] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% fluoroethylene carbonate and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to obtain the electrolyte.

[0088] Comparative Example 6

[0089] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 4wt% fluoroethylene carbonate, 1wt% 1,2,3,4-tetratetra(cyanoethoxy)butane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0090] Comparative Example 7

[0091] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution, and then 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0092] Application example A group

[0093] Preparation of lithium cobalt oxide graphite batteries:

[0094] (1) Positive electrode active material: 4.5V lithium cobalt oxide

[0095] (2) The active material of the negative electrode is artificial graphite.

[0096] (3) PP / PE / PP (polypropylene / polyethylene / polypropylene) composite membrane

[0097] The electrolytes prepared in Examples 1 to 17 and Comparative Examples 1 to 7 were assembled with positive electrode plates, negative electrode plates and separators to form lithium cobalt oxide graphite batteries. The assembly method is in accordance with the prior art, and the present invention does not impose specific limitations.

[0098] Performance testing:

[0099] (1) Capacity retention rate and battery swelling rate after being placed at 85℃ for 4 hours

[0100] The aforementioned lithium cobalt oxide graphite batteries were charged to 4.5V at 1C under constant current / constant voltage (CC / CV) conditions at 25℃, then placed in an oven at 85℃ for 4 hours, and then discharged to 3.0V at 1C. The capacity and battery thickness after being placed at 85℃ for 4 hours were tested. The capacity and battery thickness of the batteries after being charged under the same conditions and discharged under the same conditions without high-temperature placement were also tested. The capacity retention rate of the batteries after being placed at 85℃ for 4 hours is equal to the capacity after 4 hours of high-temperature placement divided by the capacity without high-temperature placement. The battery swelling rate after being placed at 85℃ for 4 hours is equal to the difference between the battery thickness after placement and the battery thickness before placement divided by the battery thickness before placement.

[0101] (2) Capacity retention rate after 200 cycles at 45℃

[0102] Under constant current / constant voltage (CC / CV) conditions at 45℃, the battery was charged to 4.5V at 1C and then discharged to 3.0V at 1C. The battery capacity after the first charge and discharge and after 200 cycles of charge and discharge were tested respectively. The battery capacity retention rate after 200 cycles at 45℃ is equal to the battery capacity after 200 cycles of charge and discharge divided by the battery capacity after the first charge and discharge.

[0103] (3) DCR of 50% SCO and 2C10s

[0104] The DCR test method for 50% SCO and 2C10s is as follows: the ratio of the voltage difference to the current when the battery is discharged at 2C constant current for 10s under 50% SCO charge.

[0105] The relevant performance test data of the above-mentioned lithium cobalt oxide graphite battery are shown in Table 1 below.

[0106] Table 1

[0107]

[0108]

[0109] Example 18

[0110] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 0.5% lithium difluorooxalate borate, 2wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0111] Example 19

[0112] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 0.5% lithium difluorooxalate borate, 4 wt% fluoroethylene carbonate, 3 wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3 wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0113] Example 20

[0114] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2mol / L LiPF6 was added to the mixed solution. Then, 0.5% lithium difluorooxalate borate, 6wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0115] Example 21

[0116] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 0.5% lithium difluorooxalate borate, 8 wt% fluoroethylene carbonate, 3 wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3 wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0117] Comparative Example 8

[0118] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP, and PP were mixed uniformly in a volume ratio of 1:2:1:3:3. 1.2 mol / L LiPF6 was added to the mixed solution. Then, 0.5% lithium difluorooxalate borate, 3 wt% 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 0.3 wt% 2-methylmaleic anhydride were added to the electrolyte to prepare the electrolyte.

[0119] Application Example Group B

[0120] Preparation of lithium cobalt oxide silicon-oxygen-carbon batteries:

[0121] (1) Positive electrode active material: 4.5V lithium cobalt oxide

[0122] (2) The active material of the negative electrode is silicon-oxygen-carbon, with a capacity of 450mAh / g.

[0123] (3) PP / PE / PP composite membrane

[0124] The electrolytes prepared in Examples 18 to 21 and Comparative Example 8 were assembled with the positive electrode, negative electrode and separator to form a lithium cobalt oxide silicon oxygen carbon battery. The assembly method is in accordance with the prior art and is not specifically limited in this invention.

[0125] The performance test data of the above-mentioned lithium cobalt oxide silicon oxygen carbon battery are shown in Table 2. The performance test methods are as described above and will not be repeated here.

[0126] Table 2

[0127]

[0128] Comparative Examples 1 to 17 and Comparative Examples 1 to 5 revealed that the combined use of three additives with different functions—fluoroethylene carbonate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and acid anhydride—enables high-voltage LCO lithium-ion batteries to exhibit superior high-temperature stability and cycle performance at high temperatures.

[0129] Comparative studies of Examples 1 to 4 revealed that, when fluoroethylene carbonate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and succinic anhydride were added simultaneously, the high-temperature storage capacity retention and cycle retention initially increased and then decreased with increasing succinic anhydride content, while the high-temperature storage swelling rate and internal resistance (DCR) initially decreased and then increased. Overall, the battery performance was best when the succinic anhydride content was 0.1–1 wt%, and even better when the succinic anhydride content was 0.3–0.5 wt%.

[0130] Comparison of Examples 3 and 5 to 7 revealed that, when fluoroethylene carbonate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and anhydride were added simultaneously with the same content of each component, batteries with the addition of 2-methylmaleic anhydride, 2,3-dimethylmaleic anhydride, or phenylmaleic anhydride exhibited better high-temperature storage capacity retention and cycle retention compared to batteries with the addition of succinic anhydride. However, batteries with the addition of 2,3-dimethylmaleic anhydride or phenylmaleic anhydride had higher swelling rates and internal resistance than those with the addition of succinic anhydride.

[0131] Comparative studies of Examples 8 to 11 revealed that, when fluoroethylene carbonate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 2-methylmaleic anhydride were added simultaneously, with increasing amounts of 1,2,3,4,5-penta(2-cyanoethoxy)pentane, the high-temperature storage capacity retention and cycle retention of the battery initially increased and then decreased, while the battery swelling rate showed a decreasing trend, but the battery internal resistance showed an increasing trend. In summary, the battery performance was better when the amount of 1,2,3,4,5-penta(2-cyanoethoxy)pentane was 1–7 wt%, and even better when the amount of 1,2,3,4,5-penta(2-cyanoethoxy)pentane was 3–5 wt%.

[0132] Comparative analysis of Examples 9 and 12-15 revealed that, when fluoroethylene carbonate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and 2-methylmaleic anhydride were added simultaneously, with increasing fluoroethylene carbonate content, the battery's high-temperature storage capacity retention and cycle life initially increased and then decreased; battery swelling initially decreased and then increased; and battery internal resistance initially decreased and then increased. Overall, the battery performance was best when the fluoroethylene carbonate content was 1–10 wt%, and even better when the content was 2–8 wt%.

[0133] A comparison of Examples 9 and 16 revealed that the addition of DFEA can improve the electrochemical performance of the battery.

[0134] Comparing Examples 9 and 17, it was found that the addition of lithium difluorooxalate borate can improve the swelling rate of the battery, but it will slightly increase the internal resistance, and has little effect on the battery's high-temperature storage capacity retention rate and cycle retention rate.

[0135] Comparative Examples 18 to 21 and Comparative Example 8 revealed that when three additives with different functions—fluoroethylene carbonate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and acid anhydride—are present simultaneously, the addition of lithium difluorooxalate borate has the best effect. Furthermore, with the increase of the amount of lithium difluorooxalate borate added, the high-temperature storage capacity retention rate and cycle retention rate of the battery are improved, while the swelling rate and internal resistance of the battery decrease.

[0136] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. An electrolyte comprising an organic solvent, a lithium salt, and an additive, characterized in that: The additives include fluoroethylene carbonate, 1,2,3,4,5-penta(2-cyanoethoxy)pentane, and acid anhydride compounds, wherein the 1,2,3,4,5-penta(2-cyanoethoxy)pentane accounts for 0.1-7% of the total mass of the electrolyte; the acid anhydride compounds are selected from one or more of 2-methylmaleic anhydride, 2,3-dimethylmaleic anhydride, and phenylmaleic anhydride, and the acid anhydride compounds account for 0.1-1% of the total mass of the electrolyte; and the fluoroethylene carbonate accounts for 0.1-10% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that: The 1,2,3,4,5-penta(2-cyanoethoxy)pentane comprises 1 to 5% of the total mass of the electrolyte.

3. The electrolyte according to claim 1, characterized in that: The acid anhydride compounds account for 0.3 to 0.5% of the total mass of the electrolyte.

4. The electrolyte according to claim 1, characterized in that: The organic solvent is a mixture of cyclic esters and chain esters. The cyclic esters are one or more of γ-butyrolactone, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. The chain esters are one or more of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl acetate, ethyl acetate, propyl acetate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl fluoropropionate, ethyl fluoropropionate, and ethyl fluoropropionate.

5. The electrolyte according to claim 1, characterized in that: The lithium salt is lithium hexafluorophosphate; and / or the concentration of the lithium salt is 0.8~3 mol / L.

6. The electrolyte according to claim 1, characterized in that: The additive further includes lithium salt additives, wherein the lithium salt additives are one or more selected from lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium difluorophosphate, lithium trifluoromethanesulfonate, and lithium difluorosulfonylimide; and / or, The lithium salt additive accounts for 0.1-5% of the total mass of the electrolyte.

7. A lithium battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that: The electrolyte is the electrolyte according to any one of claims 1 to 6.

8. The lithium battery according to claim 7, characterized in that: The active material of the positive electrode is lithium cobalt oxide, and the charging cut-off voltage of the lithium battery can reach 4.5V or higher.

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