Electrolyte and lithium battery containing same

Abstract

The present invention relates to an electrolyte and a lithium battery containing same. In order to solve the problem of poor electrochemical performance of lithium batteries at high voltage, the present invention provides an electrolyte, comprising an organic solvent, a lithium salt, and an additive, wherein the additive comprises fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane, and an acid anhydride compound. The electrolyte in the present invention has simple components, and by means of the synergistic effect of fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane, and the acid anhydride compound, the electrolyte can effectively inhibit the swelling, cycle attenuation and thickness increase of the lithium battery under high voltage (4.5 V and above) and high temperature conditions, improving the rate performance of the battery.

Description

Electrolyte and lithium battery containing the same Technical Field

[0001] The present invention relates to an electrolyte and a lithium battery containing the electrolyte. Background Art

[0002] With the emergence of emerging consumer sectors such as mobile phones, tablets, smart wearables, and ETC, lithium-ion batteries have demonstrated significant advantages with their high energy density and long cycle life. However, as the functions of these devices continue to diversify and the power consumption of power-consuming modules continues to rise, conventional lithium-ion batteries are no longer able to meet user needs. To improve the user experience, the development direction of lithium-ion batteries has become increasingly clear: to maximize energy density or achieve rapid charging while maintaining safety.

[0003] To increase energy density, the industry is currently pursuing three main development approaches. First, new material systems are being explored, such as cathode materials like lithium cobalt oxide, lithium-rich manganese-based batteries, and ternary high-nickel batteries, and anode materials like silicon-carbon. Second, the cutoff charge voltage of existing materials is being increased, such as for lithium cobalt oxide batteries exceeding 4.5V and ternary batteries exceeding 4.4V. Third, battery manufacturing processes are being modified to increase both areal and compaction densities, or by using thinner current collectors, adhesive tapes, and aluminum-plastic casings. To achieve rapid charging, fast-charging lithium-ion batteries have emerged, initially with 0.2C charging rates, later increasing to 2C and even 5C.

[0004] In the digital field, which demands high volumetric energy density, the design concept for lithium batteries is high-voltage lithium cobalt oxide and silicon-carbon negative electrodes. The voltage of commercial lithium cobalt oxide batteries has gradually increased from the initial 4.2V to 4.5V and above. However, as the voltage increases, existing lithium cobalt oxide batteries have shown certain negative effects. For example, the presence of dangling bonds and unsaturated coordination relationships on the surface of the material makes its reaction activity significantly higher than that of the bulk phase. When charging a lithium cobalt oxide battery, the following reaction process occurs:

[0005] (1) The cathode material begins to remove lithium from the surface;

[0006] (2) After delithiation occurs, the oxygen atoms in the Li layer lose their barrier and repel each other, resulting in unstable surface structure;

[0007] (3) Continuous lithium removal promotes gas overflow from surface lattice activity;

[0008] (4) The outflow of gas causes the surface Co atoms to become less stable and dissolve;

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

[0010] Side reactions at the solid-liquid interface are an inevitable issue in the development of lithium batteries. The chemical window of currently used electrolytes is typically below 4.5V. When the charge cutoff voltage rises above 4.5V, the electrolyte undergoes oxidative decomposition on the battery surface, causing a sharp drop in battery capacity. Furthermore, the oxidative decomposition products coat the electrode material surface, increasing the battery's internal resistance. Free transition metal elements catalyze the separation of surface side reaction products, causing the electrode material to maintain a highly active state, posing a potential risk.

[0011] Therefore, it is necessary to develop an electrolyte with good electrochemical performance at high voltage.

[0012] Summary of the Invention

[0013] The object of the present invention is to provide an electrolyte having good high temperature stability and cycle performance under high voltage.

[0014] A second object of the present invention is to provide a lithium battery comprising the electrolyte.

[0015] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0016] An electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the additive comprises fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane and an acid anhydride compound.

[0017] Preferably, the mass of the 1,2,3,4,5-penta(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 the present invention, the 1,2,3,4,5-penta(cyanoethoxy)pentane can be prepared by mixing xylitol and sodium ethoxide and then adding acrylonitrile to react; wherein the reaction temperature is preferably 80-100°C.

[0018] Preferably, the acid anhydride compound is a cyclic carboxylic acid anhydride.

[0019] Further preferably, the acid anhydride compound is selected from the compound represented by structural formula A and / or the compound represented by 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. The alkyl group having 1 to 3 carbon atoms may be, for example, a methyl group, an ethyl group or a propyl group.

[0020] More preferably, the acid anhydride compound is selected from the compound represented by structural formula B, wherein structural formula B is R3 and R4 are each independently selected from H, an alkyl group having 1 to 3 carbon atoms, or a phenyl group. The alkyl group having 1 to 3 carbon atoms may be, for example, a methyl group, an ethyl group, or a propyl group.

[0021] In some specific embodiments, the acid anhydride compound is selected from one or more of 2-methylmaleic anhydride, 2,3-dimethylmaleic anhydride, phenylmaleic anhydride, and succinic anhydride.

[0022] Preferably, the mass of the acid anhydride compound accounts for 0.1-1% of the total mass of the electrolyte, more preferably 0.3-0.5%, for example 0.3%, 0.35%, 0.4%, 0.45% or 0.5%.

[0023] Preferably, the mass of the fluoroethylene carbonate accounts for 0.1-10% of the total mass of the electrolyte, more preferably 2-8%, for example 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc.

[0024] Preferably, the organic solvent is a mixture of cyclic esters and chain esters, the cyclic ester is one or more of γ-butyrolactone, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; the chain ester is one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl 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 fluoroacetate.

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

[0026] Further preferably, the organic solvent further comprises ethyl fluoroacetate, and ethyl fluoroacetate may be, for example, 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, and the lithium salt additive is one or more of lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate, lithium trifluoromethylsulfonate, and lithium bis(fluorosulfonyl)imide.

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

[0031] According to one embodiment, the additive consists of fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane and an acid anhydride compound.

[0032] According to another embodiment, the additive consists of fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane, an acid anhydride compound and a lithium salt additive.

[0033] A second object of the present invention is to provide a lithium battery comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte as described above.

[0034] Preferably, the active material of the positive electrode sheet is lithium cobalt oxide, and the charging cut-off voltage of the lithium battery can reach 4.5V or above.

[0035] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0036] The electrolyte components of the present invention are simple. Through the synergistic combination of fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane and anhydride compounds, it can effectively suppress the bloating, cycle attenuation and thickness increase of lithium batteries under high voltage (4.5V and above) and high temperature conditions, thereby improving the battery's rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is the C NMR spectrum of 1,2,3,4,5-penta(cyanoethoxy)pentane;

[0038] Figure 2 is the H NMR spectrum of 1,2,3,4,5-penta(cyanoethoxy)pentane. DETAILED DESCRIPTION

[0039] The present invention is further described below with reference to the following examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples may be further adjusted according to the specific requirements of the application. Unspecified implementation conditions are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention may be combined with each other as long as they do not conflict with each other.

[0040] In the present invention, the structural formula of 1,2,3,4,5-penta(cyanoethoxy)pentane is as follows:

[0041] 1,2,3,4,5-penta(cyanoethoxy)pentane can be prepared by mixing xylitol and sodium ethoxide and then adding acrylonitrile to the mixture.

[0042] As a preferred example, the preparation method of 1,2,3,4,5-penta(cyanoethoxy)pentane is as follows:

[0043] 152 g of xylitol and 6.8 g of sodium ethoxide were mixed and heated to 90° C. and stirred for 2 hours. 477 g of acrylonitrile was then slowly added dropwise and stirred. The mixture was reacted for 12 hours. After cooling to room temperature, 6000 g of ethanol was added and stirred evenly. The mixture was filtered to obtain a residue. The residue was recrystallized and purified using ethyl acetate and n-hexane to obtain a finished product with a purity of >99%. The NMR spectra are shown in Figures 1 and 2.

[0044] Unless otherwise specified, the reagents used in the Examples and Comparative Examples of the present invention are commercially available products. In the Examples and Comparative Examples of the present invention, diethyl carbonate is referred to as DEC, ethylene carbonate is referred to as EC, propylene carbonate is referred to as PC, ethyl propionate is referred to as EP, propyl propionate is referred to as PP, and 2,2-difluoroethyl acetate is referred to as DFEA.

[0045] Example 1

[0046] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.1wt% of succinic anhydride were added to the electrolyte to prepare an electrolyte.

[0047] Example 2

[0048] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of succinic anhydride were added to the electrolyte to prepare an electrolyte.

[0049] Example 3

[0050] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.5wt% of succinic anhydride were added to the electrolyte to prepare an electrolyte.

[0051] Example 4

[0052] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 1wt% of succinic anhydride were added to the electrolyte to prepare an electrolyte.

[0053] Example 5

[0054] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.5wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0055] Example 6

[0056] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.5wt% of 2,3-dimethylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0057] Example 7

[0058] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.5wt% of phenyl maleic anhydride were added to the electrolyte to prepare an electrolyte.

[0059] Example 8

[0060] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 1wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0061] Example 9

[0062] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0063] Example 10

[0064] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 5wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0065] Example 11

[0066] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate, 7wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0067] Example 12

[0068] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 1wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0069] Example 13

[0070] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 2wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0071] Example 14

[0072] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 8wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0073] Example 15

[0074] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 10wt% of fluoroethylene carbonate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0075] Example 16

[0076] In an argon-filled glove box (H2O content <10ppm), DFEA, DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:1:2:1:2:3, 1.2 mol / L LiPF6 was added to the mixed solution, and then 4 wt% of fluoroethylene carbonate, 3 wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3 wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0077] Example 17

[0078] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 0.5% lithium difluorooxalatoborate, 4wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0079] Comparative Example 1

[0080] In an argon-filled glove box (H2O content <10 ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, and 1.2 mol / L LiPF6 was added to the mixed solution to prepare an electrolyte.

[0081] Comparative Example 2

[0082] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate and 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane were added to the electrolyte to prepare an electrolyte.

[0083] Comparative Example 3

[0084] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed 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 succinic anhydride were added to the electrolyte to prepare an electrolyte.

[0085] Comparative Example 4

[0086] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate and 0.3wt% of succinic anhydride were added to the electrolyte to prepare an electrolyte.

[0087] Comparative Example 5

[0088] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 4wt% of fluoroethylene carbonate and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0089] Comparative Example 6

[0090] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed 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 an electrolyte.

[0091] Application Example Group A

[0092] Preparation of lithium cobalt oxide graphite battery:

[0093] (1) Positive electrode active material: lithium cobalt oxide

[0094] (2) Negative electrode active material: artificial graphite

[0095] (3) Diaphragm: PP / PE / PP (polypropylene / polyethylene / polypropylene) composite film

[0096] The electrolytes prepared in the above Examples 1 to 17 and Comparative Examples 1 to 6 were respectively assembled with the positive electrode sheet, the negative electrode sheet and the separator to form a lithium cobalt oxide graphite battery. The assembly method refers to the prior art and is not specifically limited in the present invention.

[0097] Performance testing:

[0098] (1) Capacity retention and battery swelling rate after 4 hours at 85°C

[0099] The lithium cobalt oxide graphite battery was charged to 4.5V at 1C under constant current / constant voltage (CC / CV) conditions at 25°C, then placed in an oven at 85°C for 4 hours, and then discharged to 3.0V at 1C. The capacity and thickness of the battery after 4 hours at 85°C were tested. The capacity and thickness of the battery after charging under the same conditions, not being placed at high temperature, and then discharged under the same conditions were tested. The capacity retention rate of the battery after 4 hours at 85°C was equal to the capacity after 4 hours at high temperature divided by the capacity before high temperature placement. The swelling rate of the battery after 4 hours at 85°C was equal to the difference between the thickness of the battery after placement and the thickness of the battery before placement divided by the thickness of the battery before placement.

[0100] (2) 45℃ 200-cycle capacity retention

[0101] At 45°C, constant current / constant voltage (CC / CV) conditions, the battery was charged to 4.5V at 1C, 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 measured. The 200-cycle capacity retention rate at 45°C is equal to the battery capacity after 200 cycles of charge and discharge divided by the battery capacity after the first charge and discharge.

[0102] (3) 50% SCO, 2C10s DCR

[0103] The DCR test method for 50% SCO and 2C10s is: the ratio of the voltage difference to the current when the battery is discharged at a constant current of 2C for 10S at a 50% SCO state of charge.

[0104] The relevant performance test data of the above-mentioned lithium cobalt oxide graphite battery are shown in Table 1 below.

[0105] Table 1

[0106] Example 18

[0107] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 0.5% lithium difluorooxalatoborate, 2wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0108] Example 19

[0109] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 0.5% lithium difluorooxalatoborate, 4wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0110] Example 20

[0111] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 0.5% lithium difluorooxalatoborate, 6wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0112] Example 21

[0113] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 0.5% lithium difluorooxalatoborate, 8wt% fluoroethylene carbonate, 3wt% 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0114] Comparative Example 7

[0115] In an argon-filled glove box (H2O content <10ppm), DEC, EC, PC, EP and PP were mixed in a volume ratio of 1:2:1:3:3, 1.2mol / L LiPF6 was added to the mixed solution, and then 0.5% lithium difluorooxalatoborate, 3wt% of 1,2,3,4,5-penta(cyanoethoxy)pentane and 0.3wt% of 2-methylmaleic anhydride were added to the electrolyte to prepare an electrolyte.

[0116] Application Example Group B

[0117] Preparation of lithium cobalt oxide silicon oxygen carbon battery:

[0118] (1) Positive electrode active material: lithium cobalt oxide

[0119] (2) Negative electrode active material: silicon oxide carbon, capacity is 450mAh / g

[0120] (3) Diaphragm PP / PE / PP composite film

[0121] The electrolytes prepared in Examples 18 to 21 and Comparative Example 7 are respectively assembled with the positive electrode sheet, the negative electrode sheet and the separator to form a lithium cobalt oxide silicon oxygen carbon battery. The assembly method refers to the prior art and is not specifically limited in the present invention.

[0122] The performance test data of the above-mentioned lithium cobalt oxide silicon oxygen carbon battery can be found in Table 2. The performance test method is the same as that of Application Example Group A and will not be repeated here.

[0123] Table 2

[0124] By comparing Examples 1 to 17 and Comparative Examples 1 to 5, it was found that the combined use of three additives with different functions, namely, fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane and acid anhydride, enables the high-voltage LCO system lithium-ion battery to have better high-temperature stability and cycle performance at high temperatures, and can avoid the use of strictly controlled substances such as 1-propylphosphoric acid cyclic anhydride.

[0125] Comparison of Examples 1 to 4 revealed that, when fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane, and succinic anhydride were added simultaneously, the high-temperature shelf capacity retention and cycle retention of the battery first increased and then decreased with increasing succinic anhydride dosage, while the high-temperature shelf swelling ratio and battery internal resistance (DCR) first decreased and then increased. Overall, the battery performance was better when the succinic anhydride dosage was 0.1-1wt%, and even better when the succinic anhydride dosage was 0.3-0.5wt%.

[0126] By comparing Example 3 with Examples 5 to 7, it was found that when fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane and acid anhydride were added simultaneously and the content of each component was the same, the battery with the addition of 2-methylmaleic anhydride, 2,3-dimethylmaleic anhydride or phenylmaleic anhydride had better high-temperature shelf capacity retention and cycle retention than the battery with the addition of succinic anhydride, but the battery swelling rate and battery internal resistance with the addition of 2,3-dimethylmaleic anhydride or phenylmaleic anhydride were higher than those with the addition of succinic anhydride.

[0127] Comparison of Examples 8 to 11 revealed that when fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane, and 2-methylmaleic anhydride were added simultaneously, the battery's high-temperature shelf capacity retention and cycle retention first increased and then decreased with increasing 1,2,3,4,5-penta(cyanoethoxy)pentane dosage. The battery's swelling rate also showed a downward trend, while the battery's internal resistance showed an upward trend. Overall, the battery performed better when the 1,2,3,4,5-penta(cyanoethoxy)pentane dosage was 1-7 wt%, and even better when the 1,2,3,4,5-penta(cyanoethoxy)pentane dosage was 3-5 wt%.

[0128] By comparing Example 9 with Examples 12 to 15, it was found that when fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane, and 2-methylmaleic anhydride were added simultaneously, as the amount of fluoroethylene carbonate increased, the battery's high-temperature shelf capacity retention and cycle retention first increased and then decreased, the battery's swelling first decreased and then increased, and the battery's internal resistance first decreased and then increased. Overall, the battery performance was better when the amount of fluoroethylene carbonate was 1-10wt%, and even better when the amount of fluoroethylene carbonate was 2-8wt%.

[0129] By comparing Example 9 and Example 16, it was found that the addition of DFEA can improve the electrochemical performance of the battery.

[0130] By comparing Example 9 and Example 17, it is found that the addition of lithium difluorooxalatoborate can improve the swelling rate of the battery, but slightly increases the internal resistance, and has little effect on the high-temperature storage capacity retention rate and cycle retention rate of the battery.

[0131] By comparing Examples 18 to 21 and Comparative Example 7, it was found that when three additives with different functions, namely, fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane and acid anhydride, were present at the same time, the addition of lithium difluorooxalatoborate had a better effect, and as the amount of lithium difluorooxalatoborate added increased, the high-temperature shelf capacity retention rate and cycle retention rate of the battery increased, and the swelling rate and battery internal resistance decreased.

[0132] The above detailed description of the present invention is intended to enable persons familiar with the art to understand the contents of the present invention and implement them. It does not limit the scope of protection of the present invention. Any equivalent changes or modifications made based on the spirit of the present invention should be included in the scope of protection of the present 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(cyanoethoxy)pentane and anhydride compounds.

2. The electrolyte according to claim 1, characterized in that: The mass of the 1,2,3,4,5-penta(cyanoethoxy)pentane accounts for 0.1-7% of the total mass of the electrolyte.

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

4. The electrolyte according to claim 1, characterized in that: The acid anhydride compound is a cyclic carboxylic acid anhydride.

5. The electrolyte according to claim 4, characterized in that: The acid anhydride compound is selected from the compound represented by structural formula A and / or the compound represented by 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.

6. The electrolyte according to claim 4 or 5, characterized in that: The acid anhydride compound is selected from one or more of 2-methylmaleic anhydride, 2,3-dimethylmaleic anhydride, phenyl maleic anhydride, and succinic anhydride; and / or, The mass of the acid anhydride compound accounts for 0.1-1% of the total mass of the electrolyte.

7. The electrolyte according to claim 4 or 5, characterized in that: The mass of the acid anhydride compound accounts for 0.3-0.5% of the total mass of the electrolyte.

8. The electrolyte according to claim 1, characterized in that: The mass of the fluoroethylene carbonate accounts for 0.1-10% of the total mass of the electrolyte.

9. The electrolyte according to claim 1, characterized in that: The organic solvent is a mixture of cyclic esters and chain esters, the cyclic ester is one or more of γ-butyrolactone, ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; the chain ester is one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl 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 fluoroacetate.

10. The electrolyte according to claim 1, characterized in that: The organic solvent is ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate and propyl propionate; or, the organic solvent is ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate and 2,2-difluoroethyl acetate.

11. 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 to 3 mol / L.

12. The electrolyte according to claim 1, characterized in that: The additives also include lithium salt additives, which are one or more of lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorooxalatoborate, lithium difluorophosphate, lithium trifluoromethylsulfonate, and lithium bis(fluorosulfonyl)imide; and / or, the lithium salt additives account for 0.1 to 5% of the total mass of the electrolyte.

13. The electrolyte according to any one of claims 1 to 12, characterized in that: The additive consists of fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane and an acid anhydride compound; or, the additive consists of fluoroethylene carbonate, 1,2,3,4,5-penta(cyanoethoxy)pentane, an acid anhydride compound and a lithium salt additive.

14. A lithium battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The electrolyte is the electrolyte according to any one of claims 1 to 13.

15. The lithium battery according to claim 14, characterized in that: The active material of the positive electrode sheet is lithium cobalt oxide, and the charging cut-off voltage of the lithium battery can reach 4.5V or above.

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