A battery

Abstract

The application provides a battery, in particular a battery with fast charging performance and high safety performance. By optimizing the overhang of the diaphragm and the content of the carboxylic acid ester solvent in the electrolyte, the shrinkage rate of the diaphragm under high temperature environment is reduced; meanwhile, the compound shown in formula I is added in the electrolyte, which can not only form a dense and stable interface film on the negative electrode, but also can absorb heat when the temperature in the battery is relatively high, reduce the system temperature, reduce the risk of thermal runaway, thereby improving the fast charging performance and safety performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a battery with fast charging performance and high safety performance. BACKGROUND

[0002] With the attention to the exhaustion of non-renewable energy and environmental pollution, renewable clean energy has developed rapidly. Among them, lithium ion batteries have the characteristics of high energy density, long cycle life, low self-discharge rate, environmental friendliness, etc., and have been widely used in consumer electronics, new energy vehicles and other power battery products.

[0003] However, compared with gasoline vehicles, new energy electric vehicles have the problems of long charging time and safety, which limits the range and number of users, and the demand for fast charging is becoming more and more urgent. SUMMARY

[0004] It is found that the improvement of the conductivity of the electrolyte is beneficial to the improvement of the fast charging capacity of the battery, and the most common method to improve the conductivity of the electrolyte is to use carboxylate solvents. However, carboxylate solvents generally have low boiling points and poor high-temperature performance. While improving the conductivity of the electrolyte, it will also affect the shrinkage rate of the separator. In the case of large rate charge and discharge, overcharge and overdischarge, and high temperature, which may cause the surface temperature of the battery to rise in a short time, the shrinkage of the separator inside the battery will be aggravated, resulting in the contact of the positive and negative electrode sheets, causing short circuit and continued heat generation, the internal temperature increases sharply, leading to thermal runaway and causing safety accidents.

[0005] In order to solve the safety problems such as thermal runaway caused by the shrinkage of the separator of the battery with fast charging capacity, the present application provides a battery. The present application optimizes the overhang of the separator and the content of the carboxylate solvent in the electrolyte, ensures that the electrolyte has high conductivity, and reduces the influence of the carboxylate solvent on the shrinkage rate of the separator in high temperature environment; further, adding a compound represented by formula I to the electrolyte, which not only can form a dense and stable interface film at the negative electrode, but also can absorb heat when the internal temperature of the battery is high, reduce the system temperature, reduce the risk of thermal runaway, so as to realize the simultaneous improvement of the fast charging performance and safety performance of the battery.

[0006] The purpose of the present application is achieved by the following technical scheme:

[0007] A battery, the battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the electrolyte comprising a lithium salt, an organic solvent and an additive, the organic solvent comprising at least one carboxylate solvent;

[0008] The battery satisfies the following conditions:

[0009] 1.5≤A / B≤12;

[0010] Wherein, A is the overhang of the separator, unit: mm; B is the percentage of the mass of the carboxylic acid ester solvent in the total mass of the organic solvent in the electrolyte.

[0011] According to the embodiment of the present application, the overhang of the separator refers to the length of the single-side edge of the separator beyond the single-side edge of the negative electrode sheet.

[0012] According to the embodiment of the present application, A / B is 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or any point value in the range consisting of any two of the above endpoints.

[0013] When A / B < 1.5, the ratio of the overhang of the separator and the percentage of the mass of the carboxylic acid ester solvent in the total mass of the organic solvent in the electrolyte is small (the overhang of the separator is small or the percentage of the mass of the carboxylic acid ester solvent in the total mass of the organic solvent in the electrolyte is high), which can seriously degrade the heat box passing rate of the battery, because the small overhang of the separator shrinks seriously when heated, which can cause the positive and negative electrodes to contact, resulting in short circuit and continued heat generation, rapid increase of internal temperature, and thermal runaway. Moreover, with the increase of the percentage of the mass of the carboxylic acid ester solvent in the total mass of the organic solvent in the electrolyte, firstly, the shrinkage rate of the separator is increased, and secondly, the lithium ion kinetics in the electrolyte is significantly improved, and the fast charging capability of the battery is continuously improved, but at the same time, the internal reaction is intensified, the high temperature performance is deteriorated, and finally the heat box passing rate is significantly reduced. When A / B > 12, the percentage of the mass of the carboxylic acid ester solvent in the total mass of the organic solvent in the electrolyte is low, which cannot guarantee high conductivity, so 1.5 ≤ A / B ≤ 12 is controlled.

[0014] According to the embodiment of the present application, 1 ≤ A ≤ 2, for example, A is 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2. When 1 ≤ A ≤ 2, the shrinkage of the separator caused by too small overhang of the separator is avoided, which reduces the heat box passing rate, and the process difficulty of the separator caused by too large overhang of the separator is avoided, and the loss of the energy density of the battery is also avoided.

[0015] According to the embodiment of the present application, 0.20 ≤ B ≤ 0.80, for example, B is 0.20, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75 or 0.80. When 0.20 ≤ B ≤ 0.80, the fast charging capability can be guaranteed while the heat box passing rate of the battery is not reduced as much as possible. Within this range, with the increase of the percentage of the mass of the carboxylic acid ester solvent in the total mass of the organic solvent in the electrolyte, the deterioration of the heat box passing rate can be weakened by increasing the overhang of the separator and adding additives, etc.

[0016] According to an embodiment of the present application, the positive active material in the positive electrode sheet is at least one of lithium manganate, lithium iron phosphate, lithium nickel cobalt manganate ternary material, lithium nickel manganate, and lithium-rich manganese-based material.

[0017] According to an embodiment of the present application, the negative active material in the negative electrode sheet is at least one of artificial graphite, natural graphite, hard carbon, soft carbon, mesocarbon microbeads, silicon-based negative electrode material, and lithium-containing metal composite oxide material.

[0018] According to an embodiment of the present application, the lithium salt is at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium bisoxalate borate, and lithium difluoro oxalate borate.

[0019] According to an embodiment of the present application, the percentage of the mass of the lithium salt in the total mass of the electrolyte is 12wt% to 18wt%.

[0020] According to an embodiment of the present application, the carboxylic acid ester solvent is at least one of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate.

[0021] According to an embodiment of the present application, the organic solvent further includes at least one of the following compounds: propylene carbonate, ethyl methyl carbonate, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate, fluoroethylene carbonate, gamma-butyrolactone, and sulfolane.

[0022] According to an embodiment of the present application, the percentage of the mass of the organic solvent in the total mass of the electrolyte is 10wt% to 80wt%.

[0023] According to an embodiment of the present application, the additive includes a first additive selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), diethyl sulfite (DTD), 1,3-propane sultone (PS), ethylene sulfite (ES), tris(trimethylsilyl)borate (TMSB), and tris(trimethylsilyl)phosphate (TMSP).

[0024] According to an embodiment of the present application, the additive further includes a second additive selected from at least one of the compounds shown in Formula 1:

[0025]

[0026] wherein R1, R2, R3, R4, R5, the same or different, are independently selected from hydrogen, halogen, aldehyde group, substituted or unsubstituted alkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted alkynyl group; if substituted, the substituent is halogen, alkyl group, aldehyde group.

[0027] According to an embodiment of the present application, R1, R2, R3, R4, R5, the same or different, are independently selected from hydrogen, halogen, aldehyde group, substituted or unsubstituted C 1-6 alkyl group, substituted or unsubstituted C 2-6 alkenyl group, substituted or unsubstituted C 2-6 alkynyl group; if substituted, the substituent is halogen, C 1-6 alkyl group, aldehyde group.

[0028] According to an embodiment of the present application, R1, R2, R3, R4, R5, the same or different, are independently selected from hydrogen, halogen, aldehyde group, substituted or unsubstituted C 1-3 alkyl group, substituted or unsubstituted C 2-3 alkenyl group, substituted or unsubstituted C 2-3 alkynyl group; if substituted, the substituent is halogen, C 1-3 alkyl group, aldehyde group.

[0029] According to an embodiment of the present application, R1, R2, R3, R4, R5, the same or different, are independently selected from hydrogen, fluorine, -C(=O)H, substituted or unsubstituted C 1-3 alkyl group, substituted or unsubstituted C 2-3 alkenyl group, substituted or unsubstituted C 2-3 alkynyl group; if substituted, the substituent is fluorine, C 1-3 alkyl group, -C(=O)H.

[0030] According to an embodiment of the present application, the compound of formula 1 is selected from at least one of the following compounds I to IV:

[0031]

[0032] According to an embodiment of the present application, the first additive has a mass percentage of 0.5wt.% to 4wt.% of the total mass of the electrolyte, for example 0.5wt.%, 0.6wt.%, 0.7wt.%, 0.8wt.%, 0.9wt.%, 1wt.%, 1.2wt.%, 1.5wt.%, 1.8wt.%, 2wt.%, 2.2wt.%, 2.5wt.%, 2.8wt.%, 3wt.%, 3.2wt.%, 3.5wt.%, 3.6wt.%, 3.8wt.% or 4wt.%.

[0033] According to an embodiment of the present application, the second additive has a mass percentage of 0.5wt.% to 3wt.% in the total mass of the electrolyte, for example, 0.5wt.%, 0.6wt.%, 0.7wt.%, 0.8wt.%, 0.9wt.%, 1wt.%, 1.2wt.%, 1.5wt.%, 1.8wt.%, 2wt.%, 2.2wt.%, 2.5wt.%, 2.8wt.%, or 3wt.%.

[0034] According to an embodiment of the present application, the first additive and the second additive can be prepared by methods known in the art or purchased from commercial sources.

[0035] According to an embodiment of the present application, the charging cut-off voltage of the battery is 4.45V or higher.

[0036] According to an embodiment of the present application, the battery is a lithium ion battery.

[0037] Advantages of the present application:

[0038] The present application provides a battery, in particular a battery with fast charging performance and high safety performance. By optimizing the overhang of the separator and the content of carboxylate solvent in the electrolyte, the shrinkage rate of the separator under high temperature environment is reduced. At the same time, by adding a compound represented by Formula I to the electrolyte, not only a dense and stable interface film can be formed on the negative electrode, but also heat can be absorbed when the temperature inside the battery is high, thereby reducing the temperature of the battery system and reducing the risk of thermal runaway, thereby improving the fast charging performance and safety performance of the battery. DETAILED DESCRIPTION

[0039] The present application will be further described in detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology implemented based on the above description of the present application is encompassed within the scope of the present application.

[0040] In the following examples, the experimental methods used are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

[0041] In the description of the present application, it should be noted that the terms "first", "second", etc. are only for descriptive purposes, and do not indicate or imply relative importance.

[0042] Preparation of lithium ion battery

[0043] (1) Preparation of positive electrode sheet

[0044] The positive active material lithium nickel cobalt manganese oxide (NCM622), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed in a weight ratio of 96.5:2:1.5, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 7 μm; the coated aluminum foil is baked in an oven with 5 different temperature gradients, then dried in an oven at 120°C for 8 h, and then subjected to rolling and slitting to obtain a positive electrode sheet.

[0045] (2) Preparation of a negative electrode sheet

[0046] The negative active material artificial graphite, the thickening agent sodium carboxymethyl cellulose (CMC-Na), the binder styrene-butadiene rubber, the conductive agent acetylene black, and the conductive agent single-walled carbon nanotube (SWCNT) are mixed in a weight ratio of 95.9:1:2:1:0.1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a copper foil with a thickness of 6 μm; and the negative electrode sheet is obtained after drying (temperature: 85°C, time: 5 h), rolling, and die cutting.

[0047] (3) Preparation of an electrolyte

[0048] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), EC / DMC / EP / PP are mixed uniformly, wherein the sum of the mass of EP and PP is equal to the mass of the carboxylic acid ester solvent in the electrolyte, which accounts for the percentage content B of the organic solvent in the electrolyte; 14 wt% of LiPF6 and a certain amount of additives are quickly added to the mixed solution, and the mixture is stirred uniformly to obtain an electrolyte.

[0049] (4) Preparation of a separator

[0050] A 9 μm thick polyethylene separator is selected, and the separator is cut to have one side edge extending beyond the single side edge of the negative electrode sheet by a certain length, i.e., the overhang of the separator.

[0051] (5) Preparation of a lithium ion battery

[0052] The prepared positive electrode sheet, the separator, and the negative electrode sheet are wound to obtain a bare cell without electrolyte injection; the bare cell is placed in an outer packaging foil, the prepared electrolyte is injected into the dried bare cell, and the lithium ion battery is obtained after vacuum packaging, standing, formation, shaping, sorting, and other processes.

[0053] The test methods for the performance of the lithium ion batteries prepared in the various examples and comparative examples are as follows:

[0054] (1) Conductivity test: a conductivity meter is used for testing, a DSJ-1C platinum black electrode is used, and the conductivity of the prepared electrolyte at 25°C is tested.

[0055] (2) Hot box test: the prepared lithium ion battery was placed in a 135 °C constant temperature box for 120 min, and whether the battery caught fire or exploded was observed.

[0056] (3) Charging temperature rise test: the prepared lithium ion battery was placed in a 25 °C constant temperature box and charged at a rate of 5C, and the temperature rise of the battery surface relative to the uncharged battery was detected, that is, the temperature rise of the battery was equal to the temperature of the battery surface when the battery was charged at 5C minus the temperature of the battery surface when the battery was uncharged.

[0057] Comparative Example 1-2 and Example 1-7

[0058] The additives of Comparative Example 1-2 and Example 1-7 were 1 wt% of vinylene carbonate based on the total mass of the electrolyte, 1 wt% of fluoroethylene carbonate based on the total mass of the electrolyte, 2 wt% of ethylene sulfate based on the total mass of the electrolyte, and 2 wt% of 1,3-propane sultone based on the total mass of the electrolyte.

[0059] Table 1 Battery composition and performance test results of Comparative Example 1-2 and Example 1-7

[0060]

[0061] As can be seen from Comparative Example 2 and Examples 1-4, 7, as the content of low-boiling-point carboxylic acid ester solvents increases, the hot box pass rate of the battery decreases significantly, which may be because the increase of carboxylic acid ester solvents improves the shrinkage rate of the separator and the lithium ion kinetics in the electrolyte is significantly improved, the fast charging capacity of the lithium ion battery is continuously improved, but at the same time the internal reaction is intensified and the high temperature performance is deteriorated, ultimately leading to a significant decrease in the hot box pass rate, for example, the hot box pass rate of Example 4 is only 30%.

[0062] As can be seen from Example 2 and Examples 5-6, as the ratio of the overhang of the separator to the content of the carboxylic acid ester solvent decreases (the overhang of the separator decreases), the hot box pass rate also decreases, which is because at high temperatures, the carboxylic acid ester solvent significantly improves the shrinkage rate of the separator, thereby deteriorating the hot box performance, so control 1.5≤A / B≤12.

[0063] Examples 8-19

[0064] The additives of Examples 8-19 were 1 wt% of vinylene carbonate based on the total mass of the electrolyte, 1 wt% of fluoroethylene carbonate based on the total mass of the electrolyte, 2 wt% of ethylene sulfate based on the total mass of the electrolyte, 2 wt% of 1,3-propane sultone based on the total mass of the electrolyte, and a compound represented by Formula 1.

[0065] Table 2 Battery composition and performance test results of Examples 8-19

[0066]

[0067]

[0068] From Example 3 and Example 8, it can be seen that when the content of the compound shown in Formula 1 is less than 0.5%, the heat absorbed is limited, the surface temperature of the battery is high, the internal temperature of the battery cannot be effectively reduced, and the heat box passing rate is not obviously improved; from Example 3 and Example 9, it can be seen that when the content of the compound shown in Formula 1 is greater than 3%, although the reaction can occur to absorb heat, the internal impedance is increased, thereby resulting in a large surface temperature of the battery, and the internal temperature of the battery cannot be obviously reduced; from Examples 10-19, it can be seen that when the content of the compound shown in Formula 1 is in the range of 0.5%-3%, the reaction can occur to absorb internal heat, the heat box passing rate is obviously improved, and the temperature rise of the battery is small, indicating that the battery has good fast charging performance.

[0069] The embodiments of the present application are described above. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A battery, characterized by, The battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the electrolyte comprises a lithium salt, an organic solvent and an additive, the organic solvent comprises at least one carboxylic acid ester solvent; The battery satisfies the following conditions: 1.5≤A / B≤12; 1≤A≤2; 0.20≤B≤0.80; Wherein, A is the overhang of the separator, unit: mm; B is the mass percentage of the carboxylic acid ester solvent in the total mass of the organic solvent in the electrolyte; the overhang of the separator refers to the length of the single-side edge of the separator beyond the single-side edge of the negative electrode sheet; The charge cut-off voltage of the battery is 4.45 V or above.

2. The battery of claim 1, wherein, The carboxylic acid ester solvent is selected from at least one of the following: methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate (PP), butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate.

3. The battery of claim 1, wherein, The additive comprises a first additive selected from at least one of the following: vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), diethyl sulfate (DTD), 1,3-propane sultone (PS), ethylene sulfite (ES), tris(trimethylsilyl)borate (TMSB), tris(trimethylsilyl)phosphate (TMSP).

4. The battery according to any one of claims 1 to 3, characterized in that The additive further comprises a second additive selected from at least one of the compounds represented by Formula 1: Wherein, R1, R2, R3, R4, R5 are the same or different, and are independently selected from hydrogen, halogen, aldehyde group, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl; if substituted, the substituent is halogen, alkyl, aldehyde group.

5. The battery of claim 4, wherein, R1, R2, R3, R4, R5, are the same or different, independently of each other, selected from the group consisting of hydrogen, halogen, aldehyde, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 2-6 alkenyl, substituted or unsubstituted C 2-6 alkynyl; if substituted, the substituents are halogen, C 1-6 alkyl, aldehyde.

6. The battery of claim 5, wherein, R1, R2, R3, R4, R5, are the same or different, independently of each other, selected from the group consisting of hydrogen, halogen, aldehyde, substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 2-3 alkenyl, substituted or unsubstituted C 2-3 alkynyl; if substituted, the substituents are halogen, C 1-3 alkyl, aldehyde.

7. The battery of claim 6, wherein, R1, R2, R3, R4, R5, are the same or different, independently of each other, selected from the group consisting of hydrogen, fluorine, -C(=O)H, substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 2-3 alkenyl, substituted or unsubstituted C 2-3 alkynyl; if substituted, the substituents are fluorine, C 1-3 alkyl, -C(=O)H.

8. The battery of claim 7, wherein, The compound represented by Formula 1 is selected from at least one of the following compounds I-IV:

9. The battery of claim 3, wherein, The mass percentage of the first additive in the total mass of the electrolyte is 0.5wt%-4wt%.

10. The battery of claim 4, wherein, The mass percentage of the second additive in the total mass of the electrolyte is 0.5wt%-3wt%.

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