Electrolyte and battery

Abstract

The application relates to the technical field of batteries, in particular to an electrolyte and a battery comprising the electrolyte. The electrolyte comprises an organic solvent, an electrolyte salt and an additive; wherein the organic solvent comprises ethyl propionate, the electrolyte salt comprises lithium tetrafluoroborate, and the additive comprises a first additive with a structure of formula (I) and / or a structure of formula (II), wherein R1 is selected from C1-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkoxy, C6-C24 aryl and a null bond; R2 and R3 are each independently selected from C1-C20 alkyl, C1-C20 alkoxy, C2-C20 alkenyl, C2-C20 alkynyl and C6-C12 aryl; and R4 is selected from hydrogen, fluorine, cyano, C1-10 alkyl, C2-10 alkenyl and C6-12 aryl. The electrolyte of the application can resist high voltage, has high lithium ion migration rate and high conductivity; the battery of the application can resist high voltage, has good kinetic performance and low internal resistance, thereby having good long cycle performance, better high and low temperature performance and higher safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to an electrolyte and a battery comprising the electrolyte. BACKGROUND

[0002] Since commercialization, lithium ion batteries have been widely used in digital, energy storage, power, military aerospace and communication equipment fields due to high specific energy and good cycle performance. With the wide application of lithium ion batteries, consumers' demand for the use environment of lithium ion batteries is continuously improved, which requires lithium ion batteries to have high and low temperature performance. However, there are serious safety problems in the use of lithium ion batteries. When the battery is overcharged, overdischarged or in some extreme use conditions, it is easy to cause safety hazards, and even fire or explosion.

[0003] As an important part of lithium ion batteries, electrolyte has a great influence on the performance of the battery. In order to solve the above problems, by adding overcharge protection additives (such as diphenyl, cyclohexylbenzene, etc.) to the electrolyte, the safety performance can be improved, but the capacity of these additives is limited when the amount is small, and the performance of the battery is seriously deteriorated when the amount is large.

[0004] Therefore, it is very important to invent a battery that can withstand high pressure and has high and low temperature performance and safety performance. SUMMARY

[0005] The purpose of the present application is to overcome the above-mentioned problems existing in the prior art, and to provide an electrolyte and a battery comprising the electrolyte. The electrolyte of the present application can generate a cross-linked high-strength composite interface protection film on the surface of the positive and negative electrodes, and can improve the wettability of the electrolyte, realize the effect of high pressure resistance, high lithium ion migration rate and high conductivity; the battery obtained by the electrolyte of the present application can withstand high voltage, has good kinetic performance and low internal resistance, so as to have good long cycle performance, better high and low temperature performance and higher safety performance.

[0006] The inventors of the present application found that by improving the performance of the positive and negative electrode surface protection film and improving the wettability of the electrolyte, the internal resistance of the battery can be reduced, the long cycle performance of the battery can be improved, and the high pressure resistance, high and low temperature performance and safety performance of the battery can be improved.

[0007] The inventors of the present application found that in order to improve the performance of the positive and negative electrode surface protection film and improve the wettability of the electrolyte, a specific substance group can be added to the electrolyte to form a protection film with better performance on the surface of the positive and negative electrodes, and the electrolyte has high wettability. The inventors of the present application have screened out a specific substance group which can improve the performance of the positive and negative electrode surface protection film and improve the wettability of the electrolyte through a large number of in-depth researches.

[0008] To achieve the above object, the first aspect of the present application provides an electrolyte, the electrolyte comprising an organic solvent, an electrolyte salt and an additive; wherein the organic solvent comprises ethyl propionate, the electrolyte salt comprises lithium tetrafluoroborate, and the additive comprises a first additive having a structure of formula (I) and / or a structure of formula (II),

[0009]

[0010] wherein R1 is selected from C1-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkoxy, C6-C24 aryl and a bond;

[0011] R2 and R3 are each independently selected from substituted or unsubstituted C1-C20 alkyl, C1-C20 alkoxy, C2-C20 alkenyl, C2-C20 alkynyl, C6-C12 aryl, the substituent being selected from halogen and C6-C12 aryl;

[0012] R4 is selected from hydrogen, fluorine, cyano, substituted or unsubstituted C1-10 alkyl, C2-10 alkenyl, C6-12 aryl, the substituent being selected from halogen.

[0013] The second aspect of the present application provides a battery, the electrolyte of the battery being the electrolyte according to the first aspect of the present application.

[0014] Compared with the prior art, the present application has at least the following advantages:

[0015] (1) The electrolyte of the present application has good wettability;

[0016] (2) The lithium ion migration speed in the electrolyte of the present application is high, and the conductivity is high;

[0017] (3) The battery of the present application has low internal resistance;

[0018] (4) The battery of the present application can withstand a voltage of 4.48V and above;

[0019] (5) The battery of the present application has good long cycle performance;

[0020] (6) The battery of the present application has good high and low temperature performance;

[0021] (7) The battery of the present application has high safety.

[0022] Other features and advantages of the present application will be described in detail in the following specific embodiments. DETAILED DESCRIPTION

[0023] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application.

[0024] The first aspect of the present application provides an electrolyte, the electrolyte comprising an organic solvent, an electrolyte salt and an additive; wherein the organic solvent comprises ethyl propionate, the electrolyte salt comprises lithium tetrafluoroborate, and the additive comprises a first additive having a structure of formula (I) and / or a structure of formula (II),

[0025]

[0026] wherein R1 is selected from C1-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkoxy, C6-C24 aryl and a bond;

[0027] R2 and R3 are each independently selected from substituted or unsubstituted C1-C20 alkyl, C1-C20 alkoxy, C2-C20 alkenyl, C2-C20 alkynyl, C6-C12 aryl, and the substituent is selected from halogen and C6-C12 aryl;

[0028] R4 is selected from hydrogen, fluorine, cyano, substituted or unsubstituted C1-10 alkyl, C2-10 alkenyl, C6-12 aryl, and the substituent is selected from halogen.

[0029] By adding the above-mentioned specific structure of the substance group to the electrolyte, the electrolyte has been able to achieve higher lithium ion migration rate, higher conductivity and high pressure resistance effect than the prior art. In order to further improve the effect, one or more technical features can be further optimized.

[0030] The electrolyte comprises an organic solvent, an electrolyte salt and an additive; wherein the organic solvent comprises ethyl propionate, the electrolyte salt comprises lithium tetrafluoroborate, and the additive comprises a first additive having a structure of formula (I) and / or a structure of formula (II), specifically, the electrolyte comprises ethyl propionate, lithium tetrafluoroborate and a first additive having a structure of formula (I) and / or a structure of formula (II).

[0031] The first additive can have a structure represented by formula (I), or a structure represented by formula (II), or a compound having a structure of formula (I) and a structure of formula (II).

[0032] wherein R1 can be selected from C1-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkoxy, C6-C24 aryl and a bond.

[0033] The structure of the first additive is shown in formula (I) and / or (II), and it can be seen that R1 is linked to the phosphorus group and the carbon-carbon double bond containing the substituent R4 on both sides, so the C1-C20 alkyl, C2-C20 alkenyl, C2-C20 alkynyl, C1-C20 alkoxy, C6-C24 aryl and empty bond selected for R1 can satisfy the structure of formula (I) and (II). For example, R1 is a methyl group, and the structure of the methyl group is -CH2-.

[0034] When R1 is an empty bond, it means that R1 is absent, and the P on one side is directly connected to the -C=CR4 on the other side.

[0035] According to a specific embodiment, R1 is selected from C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C1-C10 alkoxy, C6-C12 aryl and an empty bond.

[0036] According to a preferred embodiment, R1 is selected from C1-C5 alkyl, C1-C5 alkoxy, phenyl and an empty bond.

[0037] R2 and R3 can be the same or different, and each is independently selected from substituted or unsubstituted C1-C20 alkyl, C1-C20 alkoxy, C2-C20 alkenyl, C2-C20 alkynyl, C6-C12 aryl.

[0038] In the present application, the expression of substituted or unsubstituted means, for example, "substituted or unsubstituted C1-C20 alkyl", which means that the alkyl group can be substituted with a substituent, or can not be substituted with any substituent.

[0039] The substituent can be selected from halogen and C6-C12 aryl. For example, when the alkyl group is substituted with halogen, one H in the alkyl group can be substituted with halogen, or multiple Hs can be substituted with halogen, or all Hs can be substituted with halogen.

[0040] In the present application, the halogen substituent can be F, Cl, Br or I.

[0041] According to a specific embodiment, R2 and R3 are each independently selected from substituted or unsubstituted C1-C10 alkyl, C1-C10 alkoxy, C2-C10 alkenyl, C2-C10 alkynyl, C6-C12 aryl, and the substituent is selected from halogen and C6-C12 aryl.

[0042] According to a preferred embodiment, R2 and R3 are each independently selected from C1-C5 alkyl, C2-C5 alkenyl and phenyl.

[0043] R4may be selected from the group consisting of hydrogen, fluorine, cyano, substituted or unsubstituted C1-10alkyl, C2-10alkenyl, C6-12aryl, the substituents being selected from the group consisting of halogen.

[0044] According to a specific embodiment, R4is selected from the group consisting of hydrogen, fluorine, cyano, substituted or unsubstituted C1-5alkyl, C2-5alkenyl, C6-8aryl, the substituents being selected from the group consisting of halogen.

[0045] According to a preferred embodiment, R4is selected from the group consisting of hydrogen, cyano, phenyl.

[0046] In one example, R1is selected from the group consisting of C1-C10alkyl, C2-C10alkenyl, C2-C10alkynyl, C1-C10alkoxy, C6-C12aryl, and a bond; R2and R3are each independently selected from the group consisting of substituted or unsubstituted C1-C10alkyl, C1-C10alkoxy, C2-C10alkene, C2-C10alkyne, C6-C12aryl, the substituents being selected from the group consisting of halogen, C6-C12aryl; R4is selected from the group consisting of hydrogen, fluorine, cyano, substituted or unsubstituted C1-10alkyl, C2-10alkenyl, C6-12aryl, the substituents being selected from the group consisting of halogen.

[0047] In one example, R1is selected from the group consisting of C1-C5alkyl, C1-C5alkoxy, phenyl, and a bond; R2and R3are each independently selected from the group consisting of C1-C5alkyl, C2-C5alkene, phenyl; R4is selected from the group consisting of hydrogen, cyano, phenyl.

[0048] In one example, the first additive is selected from one or more of the following structures:

[0049]

[0050]

[0051] According to a specific embodiment, the weight content of the first additive is 0.1-2wt% (e.g., 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.7wt%, 2wt%) based on the total weight of the electrolyte, the weight content of the ethyl propionate is 5-70wt% (e.g., 5wt, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%), the weight content of the lithium tetrafluoroborate is 0.1-1.5wt% (e.g., 0.1wt%, 0.2wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%).

[0052] In one example, based on the total weight of the electrolyte, the weight content of the first additive is 0.2-1.2 wt %, the weight content of the ethyl propionate is 15-55 wt %, and the weight content of the lithium tetrafluoroborate is 0.2-0.8 wt %.

[0053] According to a specific embodiment, the additive further comprises ethoxypentafluorophosphazene.

[0054] In one example, based on the total weight of the electrolyte, the weight content of the ethoxypentafluorophosphazene is 0.1-2 wt % (e.g., 0.1 wt %, 0.2 wt %, 0.5 wt %, 0.8 wt %, 1 wt %, 1.2 wt %, 1.5 wt %, 1.7 wt %, 2 wt %).

[0055] In one embodiment, based on the total weight of the electrolyte, the weight content of the ethoxy pentafluorophosphazene is 0.2-1 wt %.

[0056] According to a specific embodiment, the electrolyte salt further includes one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate.

[0057] In one example, based on the total weight of the electrolyte, the weight content of the electrolyte salt is 13-20 wt % (e.g., 13 wt %, 14 wt %, 15 wt %, 16 wt %, 17 wt %, 18 wt %, 19 wt %, 20 wt %).

[0058] According to a specific embodiment, the additive further includes a nitrile compound and a sulfur-containing compound.

[0059] In one example, the nitrile compound is selected from one or more of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, glycerol trinitrile and 1,3,6-hexane trinitrile.

[0060] In one example, the sulfur-containing compound is selected from one or more of 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, and vinylene sulfate.

[0061] According to a specific embodiment, the organic solvent further comprises one or more of carbonate, carboxylate and fluoroether.

[0062] In one embodiment, the carbonate is selected from one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, vinyl ethylene carbonate, diethyl carbonate and methyl propyl carbonate.

[0063] In one example, the carboxylic acid ester is selected from one or more of ethyl fluoropropionate, propyl propionate and propyl acetate.

[0064] In one example, the fluoroether is selected from one or more of 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0065] The second aspect of the present application provides a battery, the electrolyte of which is the electrolyte according to the first aspect of the present application.

[0066] The materials and preparation methods of the battery, except for the electrolyte, can be carried out in the manner of the art, and can achieve the effects of low-temperature resistance, good cycle stability and high safety performance.

[0067] The battery is preferably a lithium ion battery.

[0068] According to a specific embodiment, the battery further comprises a positive electrode sheet, a negative electrode sheet and a separator.

[0069] The positive electrode sheet can be a conventional positive electrode sheet in the art, for example, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a conductive agent and a binder.

[0070] In one example, the positive electrode active material is selected from lithium cobaltate, lithium cobaltate subjected to doping and coating treatment with two or more elements selected from Al, Mg, Mn, Cr, Ti and Zr, the chemical formula of the lithium cobaltate subjected to doping and coating treatment with two or more elements selected from Al, Mg, Mn, Cr, Ti and Zr being Li x Co 1-y1-y2-y3-y4 A y1 B y2 C y3 D y4 O2; 0.95≤x≤1.05, 0.01≤y1≤0.1, 0.01≤y2≤0.1, 0≤y3≤0.1, 0≤y4≤0.1, A, B, C, D are selected from two or more elements selected from Al, Mg, Mn, Cr, Ti and Zr.

[0071] In one example, the content of the positive electrode active material is 80-99.8 wt%, the content of the conductive agent is 0.1-10 wt% and the content of the binder is 0.1-10 wt%, based on the total weight of the positive electrode active material layer.

[0072] Preferably, the content of the cathode active material is 90-99.6 wt%, the content of the conductive agent is 0.2-5 wt% and the content of the binder is 0.2-5 wt% based on the total weight of the cathode active material layer.

[0073] The negative electrode sheet can be a conventional negative electrode sheet in the art, for example, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder.

[0074] In an example, the negative electrode active material is selected from one or more of graphite, SiO x / C (0 < x < 2), Si / C.

[0075] In an example, the conductive agent is selected from one or more of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube and metal powder.

[0076] In an example, the binder is selected from one or more of sodium carboxymethyl cellulose, styrene butadiene latex, polytetrafluoroethylene and polyethylene oxide.

[0077] In an example, the content of the negative electrode active material is 80-99.8 wt%, the content of the conductive agent is 0.1-10 wt% and the content of the binder is 0.1-10 wt% based on the total weight of the negative electrode active material layer.

[0078] Preferably, the content of the negative electrode active material is 90-99.6 wt%, the content of the conductive agent is 0.2-5 wt% and the content of the binder is 0.2-5 wt% based on the total weight of the negative electrode active material layer.

[0079] In an example, the charge cut-off voltage of the battery is 4.48 V and above.

[0080] The battery of the present application has low internal resistance, good long cycle performance, good high and low temperature performance and high safety performance due to containing the electrolyte of the present application.

[0081] The present application will be described in detail below by way of examples. The examples described in the present application are only a part of the examples of the present application, but not all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0082] The following examples are used to illustrate the electrolyte of the present application.

[0083] Example 1

[0084] (1) Preparation of components

[0085] First additive: first additive having the structure of formula (I-4) 0.5 parts by weight;

[0086] Electrolyte salt: lithium tetrafluoroborate 0.3 parts by weight;

[0087] Other additive: 1,3-propylene sulfite 3 parts by weight;

[0088] Ethyl propionate 20 parts by weight;

[0089] Other organic solvent: ethylene carbonate (EC) 11.4 parts by weight, propylene carbonate (PC) 11.4 parts by weight, propyl propionate (PP) 34.4 parts by weight, fluoroethylene carbonate 5 parts by weight;

[0090] Other electrolyte lithium salt: lithium hexafluorophosphate (LiPF6) 14 parts by weight.

[0091] (2) Preparation of electrolyte

[0092] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP) were mixed uniformly, LiPF6, fluoroethylene carbonate, 1,3-propylene sulfite, first additive, lithium tetrafluoroborate and ethyl propionate were slowly added into the mixed solution, and stirred uniformly to obtain the electrolyte.

[0093] Examples 2-14

[0094] On the basis of Example 1, the components and / or contents were changed respectively, see Table 1.

[0095] Comparative Example 1

[0096] Example 1 was carried out, except that no first additive was added in the electrolyte, see Table 1.

[0097] Comparative Example 2

[0098] Example 1 was carried out, except that no lithium tetrafluoroborate was added in the electrolyte, see Table 1.

[0099] Comparative Example 3

[0100] Example 1 was carried out, except that no ethyl propionate was added in the electrolyte, see Table 1.

[0101] Table 1

[0102]

[0103] Preparation Example

[0104] The electrolyte obtained in the examples and the comparative example was used to prepare a battery in the following manner, respectively:

[0105] (1) Preparation of positive electrode sheet

[0106] The positive electrode active material LiCoO2, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were mixed in a weight ratio of 97:2:1, N-methyl pyrrolidone (NMP) was added, and the mixture was stirred in a vacuum stirrer until the mixture became a positive electrode slurry with uniform fluidity. The positive electrode slurry was uniformly coated on an aluminum foil with a thickness of 9-12 μm. The coated aluminum foil was baked in an oven with five different temperature gradients, then dried in an oven at 120°C for 8 h, and then subjected to rolling and slitting to obtain the desired positive electrode sheet.

[0107] (2) Preparation of negative electrode sheet

[0108] A negative electrode material of artificial graphite with a mass fraction of 96.5%, a single-walled carbon nanotube (SWCNT) conductive agent with a mass fraction of 0.2%, a conductive carbon black (SP) conductive agent with a mass fraction of 1%, a sodium carboxymethyl cellulose (CMC) binder with a mass fraction of 1%, and a butadiene-styrene rubber (SBR) binder with a mass fraction of 1.3% were mixed to form a slurry by a wet process, which was coated on the surface of a negative electrode current collector copper foil, and then subjected to drying (temperature: 85°C, time: 5 h), rolling, and slitting to obtain a negative electrode sheet.

[0109] (3) Preparation of electrolyte

[0110] The electrolyte obtained in each of the above examples and the comparative example was used.

[0111] (4) Preparation of separator

[0112] A composite layer of a mixture of titanium oxide and polyvinylidene fluoride-hexafluoropropylene copolymer with a thickness of 2 μm was coated on a polyethylene separator with a thickness of 7 μm.

[0113] (5) Preparation of lithium ion battery

[0114] The positive electrode sheet, the separator, and the negative electrode sheet prepared above were wound to obtain a bare cell without electrolyte injection; the bare cell was placed in an outer packaging foil, and the electrolyte prepared above was injected into the dried bare cell, which was subjected to vacuum packaging, standing, formation, shaping, sorting, and other processes to obtain the desired lithium ion battery.

[0115] Test example

[0116] The batteries obtained in the examples and the comparative example were tested in the following manner, respectively:

[0117] (1) 45°C cycle test

[0118] The batteries obtained in the above examples and comparative examples were placed in a (45±2)°C environment and left to stand for 2-3 hours. When the battery body reached (45±2)°C, the battery was charged at a 1C constant current with a cutoff current of 0.05C. After the battery was fully charged, it was left for 5 minutes and then discharged at a 0.5C constant current to a cutoff voltage of 3.0V. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q. When the cycle reached the required number of times, the last discharge capacity Q1 of the battery was recorded. The recording results are shown in Table 2.

[0119] The calculation formula is as follows: Capacity retention rate (%) = Q1 / Q*100%.

[0120] (2) Low temperature discharge test

[0121] The batteries obtained in the above examples and comparative examples were first discharged at 0.2C to 3.0V at an ambient temperature of (25±3)°C and left for 5 minutes. They were then charged at 0.7C. When the cell terminal voltage reached the charge limit voltage, constant voltage charging was switched to continued until the charging current ≤ the cutoff current, at which point charging was stopped. After 5 minutes of waiting, the batteries were discharged at 0.2C to 3.0V, and the discharge capacity at this time was recorded as the room temperature capacity Q2. The batteries were then charged at 0.7C. When the cell terminal voltage reached the charge limit voltage, constant voltage charging was switched to continued until the charging current was less than or equal to the cutoff current, at which point charging was stopped. The fully charged batteries were left at (-10±2)°C for 4 hours, and then discharged at 0.4C to a cutoff voltage of 3.0V. The discharge capacity Q3 was recorded, and the low temperature discharge capacity retention rate was calculated. The recorded results are shown in Table 2.

[0122] The low-temperature discharge capacity retention rate of the battery (%) = Q3 / Q2*100%.

[0123] (3) 150℃ thermal shock test

[0124] The batteries obtained in the above examples and comparative examples were heated using convection or a circulating hot air oven at a starting temperature of (25±3)°C at a temperature ramp rate of (5±2)°C / min to (150±2)°C. The temperature was maintained for 60 minutes before the test was terminated. If the battery did not catch fire or explode, it passed. If the battery caught fire and / or exploded, it failed. The test was performed five times, and the battery status results were recorded and shown in Table 2.

[0125] (4) Overcharge test

[0126] The batteries obtained in the above examples and comparative examples were charged at a constant current rate of 3C to 5V, and the battery status was recorded. If the battery did not catch fire or explode, it was considered passed. If the battery caught fire and / or exploded, it was considered failed. The test was performed five times, and the results were recorded as shown in Table 2.

[0127] (5) Acupuncture test

[0128] The battery obtained in the above examples and comparative examples is punctured by a high-temperature-resistant steel needle with a diameter of 5-8 mm (the conical angle of the needle tip is 45-60°, the surface of the needle is smooth without rust, oxidation layer and oil stain) at a speed of (25±5) mm / s from the direction perpendicular to the electrode plate, and the puncture position is close to the geometric center of the punctured surface (the steel needle stays in the battery). When 1 hour or the maximum temperature of the battery surface drops to 10°C or less than the peak temperature, the test is stopped and the battery state is recorded. If the battery does not catch fire and explode, it is indicated that it passes, and if the battery catches fire and / or explodes, it is indicated that it fails. Five tests are performed, and the results are shown in Table 2.

[0129] Table 2

[0130]

[0131]

[0132] As can be seen from Table 1, it can be seen from the comparative examples and examples that the high and low temperature performance of the battery prepared from the electrolyte of the examples is significantly improved, the long cycle performance is significantly improved, and the safety is significantly improved, which indicates that the introduction of the specific structure of the substance group of the application improves the performance of the positive and negative electrode surface protection film, thereby improving the long cycle performance of the battery, and improving the high and low temperature performance and safety performance of the battery.

[0133] The preferred embodiments of the application are described in detail above, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the application and fall within the protection scope of the application.

Claims

1. A lithium-ion battery, characterized in that: The lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector. The positive electrode active material layer comprises a positive electrode active material selected from one or more of lithium cobalt oxide and lithium cobalt oxide doped and coated with two or more elements of Al, Mg, Mn, Cr, Ti and Zr. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material selected from graphite. The electrolyte comprises an organic solvent, an electrolyte salt and an additive; wherein the organic solvent comprises ethyl propionate, the electrolyte salt comprises lithium tetrafluoroborate, and the additive comprises a first additive having a structure of formula (I) and / or a structure of formula (II). (Ⅰ)、 (Ⅱ)， wherein R1 is selected from a C1-C20 alkyl group, a C2-C20 alkene group, a C2-C20 alkyne group, a C6-C24 aryl group, and a null bond; R2 and R3 are each independently selected from a C1-C20 alkoxy group; R4 is selected from hydrogen, fluorine, cyano, substituted or unsubstituted C1-10 alkyl, C2-10 alkenyl, C6-12 aryl, and the substituent is selected from halogen; Based on the total weight of the electrolyte, the weight content of the first additive is 0.2-1.2 wt %, the weight content of the ethyl propionate is 15-55 wt %, and the weight content of the lithium tetrafluoroborate is 0.2-0.8 wt %.

2. The lithium-ion battery according to claim 1, wherein R1 is selected from C1-C10 alkyl, C2-C10 alkene, C2-C10 alkyne, C6-C12 aryl and a null bond; R2 and R3 are each independently selected from C1-C10 alkoxy.

3. The lithium ion battery according to claim 1, wherein R1 is selected from C1-C5 alkyl, phenyl and empty bond; R4 is selected from hydrogen, cyano and phenyl.

4. The lithium ion battery according to claim 1, wherein The first additive is selected from one or more of the following structures: (Ⅰ-4)、 (Ⅰ-5)、 (Ⅱ-1)、 (Ⅱ-3)。 5. The lithium-ion battery according to any one of claims 1 to 4, wherein: The electrolyte also includes ethoxypentafluorophosphazene.

6. The lithium ion battery according to claim 5, wherein Based on the total weight content of the electrolyte, the weight content of the ethoxy pentafluorophosphazene is 0.1-2 wt %.

7. The lithium ion battery according to claim 6, wherein Based on the total weight content of the electrolyte, the weight content of the ethoxy pentafluorophosphazene is 0.2-1 wt %.

8. The lithium-ion battery according to claim 1, wherein The additives further include nitrile compounds and sulfur-containing compounds; the nitrile compounds are selected from one or more of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, glycerol trinitrile and 1,3,6-hexane trinitrile; and / or, The sulfur-containing compound is selected from one or more of 1,3-propane sultone, 1,3-propylene sultone and vinylene sulfate.

9. The lithium ion battery according to claim 1, wherein The organic solvent further comprises one or more of carbonates, carboxylates and fluoroethers; wherein the carbonates are selected from one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, ethylene carbonate, ethylene ethylene carbonate, diethyl carbonate and methyl propyl carbonate; the carboxylates are selected from one or more of ethyl fluoropropionate, propyl propionate and propyl acetate; the fluoroethers are selected from one or more of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

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