Electrolyte, lithium ion battery and vehicle

Abstract

The invention relates to the technical field of electrolyte, in particular to electrolyte, a lithium ion battery and a vehicle. The electrolyte comprises an organic solvent, fluorine-containing lithium salt and a first additive; the organic solvent comprises carboxylic ester and carbonic ester; the first additive comprises a combination of 1, 3-propane sultone and methylene methanedisulfonate; in terms of the total mass of the electrolyte being 100%, the content of the carboxylic ester is S1, the content of the 1, 3-propane sultone is W1, the content of the methylene methanedisulfonate is W2, and S1, W1 and W2 meet (S1 / 120) lt; (W1 + W2) lt; (S1 / 20). According to the electrolyte provided by the invention, through the synergistic effect of the organic solvent, the fluorine-containing lithium salt and the additive, the low-temperature conductivity is greatly improved, and the charging time of the battery at a low temperature is effectively shortened, so that the prepared lithium ion battery has excellent fast charging performance and low-temperature performance on the premise of not losing high-temperature performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and in particular to an electrolyte, a lithium-ion battery and a vehicle. Background Art

[0002] Lithium-ion batteries have been widely used in various electronic products, electric vehicles, various electric tools, energy storage devices, etc. in recent years due to their high capacity, high voltage, high cycle stability, environmental friendliness and other advantages. In particular, they are increasingly widely used in electric vehicles. However, conventional lithium-ion batteries have a narrow applicable temperature range, either with low low-temperature discharge rates or poor high-temperature storage. Therefore, research on lithium-ion batteries that can take into account both low-temperature and high-temperature performance is of great practical significance.

[0003] Compared with ternary positive electrode materials, lithium iron phosphate materials have a slower lithium ion diffusion rate, poor electronic conductivity, and are prone to polarization, which is particularly evident at low temperatures. Since the characteristics of the electrolyte itself and the interface formed with the positive and negative electrodes largely affect the high and low temperature performance of the battery, it is hoped to provide an electrolyte that can take into account both the low temperature performance and high temperature performance of lithium-ion batteries. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an electrolyte, a lithium-ion battery and a vehicle.

[0005] In a first aspect, the present invention provides an electrolyte, the electrolyte comprising an organic solvent, a fluorine-containing lithium salt and a first additive;

[0006] The organic solvent includes carboxylic acid esters and carbonate esters;

[0007] The first additive includes a combination of 1,3-propane sultone (PS) and methylene methane disulfonate (MMDS);

[0008] Taking the total mass of the electrolyte as 100%, the content of the carboxylic acid ester is S 1 , the content of 1,3-propane sultone is W 1 , the content of methylene methane disulfonate is W 2 , S 1 , W 1 and W 2 Satisfaction 1 / 120)<(W 1 +W 2 )<(S 1 / 20).

[0009] As a preferred technical solution of the present invention, S 1 Satisfy 20%≤S 1 ≤65%.

[0010] As a preferred technical solution of the present invention, W 1 Satisfy 0.05%≤W 1 ≤1%.

[0011] As a preferred technical solution of the present invention, W 2 Satisfy 0.05%≤W 2 ≤1%.

[0012] As a preferred technical solution of the present invention, the carboxylic acid ester includes any one or more of ethyl acetate (EA), ethyl propionate (EP), methyl propionate (MP) or methyl acetate (MA).

[0013] As a preferred technical solution of the present invention, the carbonate includes any one or more of ethyl methyl carbonate (EMC), ethylene carbonate (EC) or dimethyl carbonate (DMC).

[0014] As a preferred technical solution of the present invention, the fluorine-containing lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI). Based on the total mass of the electrolyte being 100%, the content of the lithium bis(fluorosulfonyl)imide is 1-8%.

[0015] As a preferred technical solution of the present invention, the fluorine-containing lithium salt also includes lithium hexafluorophosphate (LiPF6).

[0016] As a preferred technical solution of the present invention, based on the total mass of the electrolyte being 100%, the content of the fluorine-containing lithium salt is 10-18%.

[0017] As a preferred technical solution of the present invention, the electrolyte also includes a second additive, and the second additive includes any one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl vinyl carbonate (VEC), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), lithium difluorooxalatoborate (LiODFB), vinyl sulfate (DTD) or lithium difluorophosphate (LiPO2F2).

[0018] As a preferred technical solution of the present invention, based on the total mass of the electrolyte being 100%, the content of the second additive is 1-5%.

[0019] In a second aspect, the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the electrolyte described in the first aspect.

[0020] As a preferred technical solution of the present invention, the lithium-ion battery further includes a positive electrode sheet, a negative electrode sheet and a separator.

[0021] As a preferred technical solution of the present invention, the positive electrode material in the positive electrode plate includes lithium iron phosphate positive electrode material.

[0022] As a preferred technical solution of the present invention, the negative electrode material in the negative electrode plate includes graphite.

[0023] As a preferred technical solution of the present invention, the charging cut-off voltage of the lithium-ion battery is ≤3.75V.

[0024] In a third aspect, the present invention provides a vehicle, comprising the lithium-ion battery according to the second aspect.

[0025] The technical solution provided by the embodiment of the present invention has the following advantages compared with the prior art:

[0026] The electrolyte provided by the present invention has greatly improved low-temperature conductivity through the synergistic effect of organic solvents, fluorine-containing lithium salts and additives, effectively shortening the charging time of the battery at low temperatures, while overcoming the problem of poor compatibility between carboxylic acid esters and graphite negative electrodes, taking into account high-temperature performance, so that the prepared lithium-ion battery has excellent fast charging performance and low-temperature performance without sacrificing high-temperature performance. DETAILED DESCRIPTION

[0027] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0030] Compared with ternary positive electrode materials, lithium iron phosphate materials have a slower lithium ion diffusion rate, poor electronic conductivity, and are prone to polarization, which is particularly evident at low temperatures. Since the characteristics of the electrolyte itself and the interface formed with the positive and negative electrodes largely affect the high and low temperature performance of the battery, it is hoped to provide an electrolyte that can take into account both the low temperature performance and high temperature performance of lithium-ion batteries.

[0031] In a first aspect, an embodiment of the present invention provides an electrolyte, wherein the electrolyte includes an organic solvent, a fluorine-containing lithium salt, and a first additive;

[0032] The organic solvent includes carboxylic acid esters and carbonate esters;

[0033] The first additive includes a combination of 1,3-propane sultone (PS) and methylene methane disulfonate (MMDS);

[0034] Taking the total mass of the electrolyte as 100%, the content of the carboxylic acid ester is S 1 , the content of 1,3-propane sultone is W 1 , the content of methylene methane disulfonate is W 2 , S 1 , W 1 and W 2 Satisfaction 1 / 120)<(W 1 +W 2 )<(S 1 / 20).

[0035] The electrolyte provided in the embodiment of the present invention has a synergistic effect of an organic solvent, a fluorine-containing lithium salt and a first additive, and its low-temperature conductivity is greatly improved, which effectively shortens the charging time of the battery at low temperatures, so that the prepared lithium-ion battery has both excellent fast charging performance and low-temperature performance without sacrificing high-temperature performance. Specifically:

[0036] The electrolyte provided by the embodiment of the present invention includes an organic solvent, a fluorine-containing lithium salt and a first additive. First, the organic solvent carboxylic acid ester has low viscosity and high dielectric constant, which can effectively improve the ion transmission rate of the electrolyte, thereby improving the fast charging performance of the battery at low temperature; at the same time, due to the poor compatibility of the carboxylic acid ester with the graphite negative electrode, it is difficult to form a stable SEI film, which will lead to poor capacity retention performance of the battery after high-temperature cycling and high-temperature storage, and will also cause the battery to be easily bloated at high temperature, affecting the safety performance of the battery. Therefore, the present invention introduces a fluorine-containing lithium salt into the electrolyte, and the fluorine-containing lithium salt can generate a LiF-rich component. The interface film improves the ionic conductivity of the interface film and reduces the initial impedance, improves the compatibility of the carboxylate system with the negative electrode, and enhances the film-forming stability of the SEI film, thereby greatly improving the high-temperature performance of the battery; and the additive 1,3-propane sultone generates alkyl sulfonates and sulfonate compounds containing unsaturated bonds (C=C) during battery formation, which can effectively inhibit the further reaction of the carboxylate solvent with the graphite negative electrode and improve the interface stability of the SEI film. Methylene disulfonate is a sulfur-based additive that can be reduced preferentially before carboxylate, has a good film-forming effect, can inhibit the dissolution of transition metals at high temperatures, and improves the high-temperature performance of the battery.

[0037] The embodiment of the present invention creatively finds that the content of carboxylic acid ester in the electrolyte is S 1, 1,3-propane sultone content W 1 , the content of methylene methane disulfonate W 2 The interaction between them, when (S 1 / 120)<(W 1 +W 2 )<(S 1 / 20), the problem of poor compatibility between carboxylic acid ester and graphite negative electrode can be overcome, while taking into account fast charging and low temperature performance, so that the battery has excellent low temperature performance without losing high temperature performance. Specifically:

[0038] The present invention finds that when the contents of carboxylic acid ester, 1,3-propane sultone and methylene disulfonate in the electrolyte satisfy the above relationship, when the content of carboxylic acid ester increases, the low temperature performance of the battery can be improved and the impedance can be reduced. However, the degree of side reaction between carboxylic acid ester and graphite increases, which will cause the cycle performance of the battery to decrease. Therefore, more first additives (1,3-propane sultone and methylene disulfonate) are required to participate in the film formation at the negative electrode interface and inhibit the occurrence of negative electrode side reactions. At the same time, the increase in the content of carboxylic acid ester compensates for the increase in 1,3-propane sultone and methylene disulfonate on the fast charging performance and low temperature performance of the battery. That is, when the content of carboxylic acid ester increases, the content of the first additive needs to be increased at the same time. Correspondingly, when the content of carboxylic acid ester decreases, the content of the first additive needs to be reduced at the same time to satisfy the relationship. Therefore, the embodiment of the present invention achieves a balanced low temperature performance and high temperature performance of the obtained battery through the synergistic effect of carboxylic acid ester, 1,3-propane sultone and methylene disulfonate in the electrolyte. If S 1 Too big, W 1 +W 2 If S is small, the low temperature performance and fast charging performance of the battery will be improved, but the protective effect of the interface film will be reduced, the interface side reaction will be aggravated, the interface film will be decomposed, and the battery's cycle performance and storage performance will be reduced. 1 Too small, W 1 +W 2 The electrolyte viscosity increases, the ion migration rate decreases, the film formation impedance increases, the battery cycle and storage performance improves, but the battery's low temperature performance and fast charging performance decrease.

[0039] In some embodiments of the present invention, S 1 Satisfy 20%≤S 1 ≤65%, for example, it may be 20%, 30%, 40%, 50%, 60%, 65%, etc. However, the present invention is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0040] When the content of the carboxylate is within the scope of the present invention, the low-temperature conductivity of the electrolyte can be more effectively improved. If the content of the carboxylate is too low, the conductivity of the electrolyte decreases, resulting in a decrease in low-temperature performance. If the content of the carboxylate is too high, it may cause a decrease in the cycle performance of the battery.

[0041] In some embodiments of the present invention, W 1 Satisfy 0.05%≤W 1 ≤1%, for example, it may be 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, etc. However, the present invention is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0042] When the content of 1,3-propane sultone is within this range, it can more effectively inhibit the further reaction of the carboxylate solvent and the graphite negative electrode, thereby improving the interface stability of the SEI film.

[0043] In some embodiments of the present invention, W 2 Satisfy 0.05%≤W 2 ≤1%, for example, it may be 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, etc. However, the present invention is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0044] When the content of methylene methanedisulfonate is within this range, the dissolution of transition metals can be more effectively suppressed at high temperatures, thereby improving the high temperature performance of the battery.

[0045] In some embodiments of the present invention, the carboxylic acid ester includes any one or more of ethyl acetate (EA), ethyl propionate (EP), methyl propionate (MP) or methyl acetate (MA). In the embodiments of the present invention, the carboxylic acid ester can significantly improve the low-temperature conductivity of the electrolyte and effectively shorten the charging time of the battery at low temperatures.

[0046] In some embodiments of the present invention, the carboxylic acid ester is selected from ethyl acetate.

[0047] In some embodiments of the present invention, the carbonate includes any one or more of ethyl methyl carbonate (EMC), ethylene carbonate (EC) or dimethyl carbonate (DMC).

[0048] In some embodiments of the present invention, the fluorine-containing lithium salt includes lithium bis(fluorosulfonyl)imide. In the embodiments of the present invention, lithium bis(fluorosulfonyl)imide can generate an interface film rich in LiF components, improve the ionic conductivity of the interface film and reduce the initial impedance, improve the compatibility of the carboxylate system with the graphite negative electrode, and enhance the film formation stability of the SEI film, thereby greatly improving the high temperature performance of the battery.

[0049] In some embodiments of the present invention, based on the total mass of the electrolyte being 100%, the content of the lithium bis(fluorosulfonyl)imide is 1-8%, for example, 1%, 2%, 4%, 6%, 8%, etc. However, the present invention is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0050] When the content of lithium bis(fluorosulfonyl)imide is within the above range, the compatibility of the carboxylate system with the graphite negative electrode can be more effectively improved.

[0051] In some embodiments of the present invention, the fluorine-containing lithium salt further comprises lithium hexafluorophosphate.

[0052] In some embodiments of the present invention, based on the total mass of the electrolyte being 100%, the content of the fluorine-containing lithium salt is 10-18%, for example, 10%, 12%, 14%, 16%, 18%, etc. However, the present invention is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0053] When the content of fluorine-containing lithium salt is within this range, the ionic conductivity of the electrolyte can be more effectively improved, thereby improving the low-temperature fast charging performance of the battery. If the content of fluorine-containing lithium salt is too high or too low, it may cause the ionic conductivity of the electrolyte to decrease, and even cause lithium precipitation during low-temperature charging.

[0054] In some embodiments of the present invention, the electrolyte further comprises a second additive, wherein the second additive comprises any one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl vinyl carbonate (VEC), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), lithium difluorooxalatoborate (LiODFB), vinyl sulfate (DTD) or lithium difluorophosphate (LiPO2F2). The present invention can add the second additive according to actual conditions.

[0055] In some embodiments of the present invention, based on the total mass of the electrolyte being 100%, the content of the second additive is 1-5%, for example, 1%, 2%, 3%, 4%, 5%, etc. However, the present invention is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0056] In a second aspect, an embodiment of the present invention provides a lithium-ion battery, wherein the lithium-ion battery comprises the electrolyte described in the first aspect.

[0057] The lithium-ion battery provided by the embodiment of the present invention has excellent high temperature performance, cycle performance, low temperature fast charging performance and safety.

[0058] In some embodiments of the present invention, the lithium-ion battery further includes a positive electrode sheet, a negative electrode sheet and a separator.

[0059] In some embodiments of the present invention, the positive electrode material in the positive electrode plate includes a lithium iron phosphate positive electrode material.

[0060] The electrolyte provided by the present invention can be applied to lithium iron phosphate positive electrode lithium ion batteries, can solve the polarization problem during low temperature charging, and ensure the high temperature performance and low temperature performance of the lithium ion battery.

[0061] In some embodiments of the present invention, the negative electrode material in the negative electrode plate includes graphite.

[0062] In some embodiments of the present invention, the charging cut-off voltage of the lithium-ion battery is ≤3.75V.

[0063] The electrolyte provided by the present invention is suitable for a graphite negative electrode lithium ion battery, is compatible with the graphite negative electrode, and ensures the high temperature performance and low temperature performance of the lithium ion battery.

[0064] In a third aspect, an embodiment of the present invention provides a vehicle, comprising the lithium-ion battery according to the second aspect.

[0065] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail in conjunction with the embodiments below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its applications. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0066] If no specific techniques or conditions are specified in the examples, the conventional techniques or conditions in the art, or the techniques or conditions described in the literature, or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0067] Examples & Comparative Examples

[0068] The embodiment and the comparative example respectively provide an electrolyte, and the composition of the electrolyte is specifically shown in Table 1.

[0069] Table 1

[0070]

[0071]

[0072]

[0073] Application Examples

[0074] The electrolyte provided in the examples and comparative examples is used to assemble a battery, as follows:

[0075] (1) Preparation of electrolyte

[0076] In a glove box or a dry room, carbonate and carboxylate are mixed according to the mass ratio in Table 1, and then the substances shown in Table 1 are added and mixed evenly to prepare an electrolyte. The content of each substance shown in Table 1 is the mass percentage based on the total mass of the electrolyte.

[0077] (2) Preparation of positive electrode sheet

[0078] The positive electrode material LiFePO 4 The binder PVDF and the conductive agent acetylene black were mixed in a mass ratio of 94:3:3, and N-methylpyrrolidone (NMP) solvent was added until the system became uniform and transparent. The positive electrode slurry was prepared by stirring with a vacuum mixer, and then evenly coated on the current collector aluminum foil (thickness of 12 μm), dried at room temperature, transferred to a 120°C oven for drying for 1 h, and then cold pressed (compacted density of 2.5 g / cm 3 ) and cut to obtain the positive electrode sheet.

[0079] (3) Preparation of negative electrode sheet

[0080] The negative electrode material graphite, thickener sodium carboxymethyl cellulose (CMC) solution, and binder styrene butadiene rubber latex were mixed in a mass ratio of graphite: sodium carboxymethyl cellulose: styrene butadiene rubber of 96:2:2, and deionized water solvent was added. After stirring with a vacuum mixer, the negative electrode slurry was prepared, and then evenly coated on the current collector copper foil (thickness of 8 μm), dried at room temperature, transferred to a 120 ° C oven for 1 h, and then cold pressed (compacted density 1.6 g / cm 3 ) and cut to obtain the negative electrode sheet.

[0081] (4) Assembly of lithium-ion batteries

[0082] The positive electrode sheet, the negative electrode sheet and the polypropylene separator are wound, wrapped with an aluminum-plastic film, baked to remove water, and then injected with the above-mentioned electrolyte and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a soft-pack lithium-ion battery is prepared.

[0083] It should be noted that the above-mentioned test lithium-ion battery is only an example listed for testing the performance of the electrolyte, and the present invention is not limited to this kind of battery, wherein the raw materials (except the electrolyte), proportions, parameters and processes can be replaced with other conventional raw materials, proportions, parameters and processes in the art, thereby forming a battery different from the test lithium-ion battery.

[0084] Performance Testing

[0085] The performance tests were performed on the electrolytes prepared in the examples and comparative examples and the lithium-ion batteries assembled:

[0086] (1) Electrolyte conductivity test

[0087] The electrolytes of the embodiment and the comparative example were placed in a constant temperature water bath at 25°C for 30 min, and then the conductivity was tested with a conductivity meter.

[0088] (2) Low temperature fast lithium charging test

[0089] At -10°C, the lithium ion batteries of the embodiment and comparative example were first discharged at 1C to 2.0V, then charged at 0.5C constant current to 3.75V, and after 10 cycles of charge and discharge, they were charged at 1C constant current to 3.75V, and then charged at a constant voltage to a current of 0.05C, and then disassembled in a drying room to inspect the negative electrode interface.

[0090] (3) 25℃4C cycle performance test

[0091] At 25°C, the lithium ion batteries of the embodiment and the comparative example were first discharged at 1C to 2.0V and then subjected to a cycle test. The test process was to first charge at 4C constant current to 3.75V, then charge at constant voltage to a current of 0.05C, and then discharge at 1C constant current to 2.0V, and then cycle charge / discharge in this way to calculate the capacity retention rate of the lithium ion battery after 1000 cycles of 4C / 1C at 25°C.

[0092] (4) 60℃ storage performance test

[0093] At 25°C, the lithium ion batteries of the embodiment and the comparative example were first discharged at 1C to 2.0V, then charged at 1C constant current to 3.75V, then charged at constant voltage to a current of 0.05C, and then discharged at 1C constant current to 2.0V. The discharge capacity was recorded as C. 放1 The battery cell is then charged to 3.75V at 1C constant current, and then charged to 0.05C at constant voltage. The battery cell is stored in a 60℃ oven for 60 days, and then placed at room temperature, first discharged to 2.0V at 1C, then charged to 3.75V at 1C constant current, then charged to 0.05C at constant voltage, and then discharged to 2.0V at 1C constant current. The discharge capacity is recorded as C. 放2 . C 放2 / C 放1 =Capacity retention rate.

[0094] The test results are shown in Table 2:

[0095] Table 2

[0096]

[0097]

[0098] It can be found from Table 2 that the electrolyte provided by the present invention has a higher electrical conductivity, and the lithium ion battery prepared using the electrolyte provided by the present invention has excellent low-temperature fast charging performance, high-temperature storage performance and cycle performance compared to traditional electrolyte systems.

[0099] By comparing Example 1 with the traditional electrolyte system (Comparative Example 1), it can be found that the low-temperature charging capability of the battery cell can be greatly improved without deteriorating the cycle and high-temperature performance.

[0100] From the comparison between Example 1 and Comparative Example 2, it can be found that by introducing additives PS and MMDS, the 60°C storage performance and 25°C 4C cycle capacity retention rate are greatly improved without deteriorating the degree of lithium precipitation at -10°C 0.5C charging, indicating that PS can generate alkyl sulfonates and sulfonate compounds containing unsaturated bonds (C=C), which can effectively inhibit the further reaction of carboxylate solvents with graphite negative electrodes and improve the interface stability of SEI film; while methylene disulfonate is a sulfur additive, which can be reduced preferentially over carboxylate, has a good film-forming effect, can inhibit the dissolution of transition metals at high temperatures, and improve the high temperature performance of the battery. The synergistic effect of the two can greatly improve the interface stability of the carboxylate system electrolyte.

[0101] From the comparison between Examples 1 and 2, it can be found that the storage performance at 60°C decreases with decreasing PS content, while the 25°C 4C cycle capacity retention rate is not much different, indicating that the protective effect of 0.05% PS on the negative electrode interface is relatively poor, and 0.5% PS can more effectively inhibit the further reaction of the carboxylate solvent and the graphite negative electrode, thereby improving the high-temperature interface stability of the SEI film.

[0102] From the comparison between Examples 1 and 3, it can be found that the storage performance at 60°C and the cycle capacity retention rate at 25°C 4C are slightly improved by increasing the PS content, but there is slight lithium deposition during -10°C 0.5C charging, indicating that the increase in PS content improves the interface stability of the SEI film at high temperatures while causing poor low-temperature performance.

[0103] From the comparison between Examples 1 and 4-5, it can be found that the high-temperature storage performance of the battery is slightly worsened by reducing the amount of MMDS, and there is moderate lithium precipitation when charging at -10℃ 0.5C by increasing the amount of MMDS, indicating that adding an appropriate amount of MMDS can improve the high-temperature cycle performance and storage performance while taking into account the low-temperature fast charging performance;

[0104] From the comparison between Examples 1 and 6, it can be found that by reducing the EA content, the conductivity of the electrolyte decreases, lithium deposition is slight during charging at -10°C 0.5C, and high-temperature storage and cycling are significantly improved;

[0105] From the comparison between Examples 1 and 7, it can be found that increasing the EA content increases the conductivity of the electrolyte. In order to ensure the interface stability, it is necessary to increase the contents of MMDS and PS at the same time to ensure that high-temperature storage and cycling will not deteriorate significantly.

[0106] From the comparison between Examples 1 and 8-9, it can be found that when EP replaces EA, the high-temperature storage is slightly improved, and there is slight lithium deposition at -10℃ 0.5C charging; when MA replaces EA, the high-temperature storage and cycle deteriorate;

[0107] From the comparison between Examples 1 and 10, it can be found that EP partially replaces EA, the high temperature storage is slightly improved, and there is slight lithium deposition during -10℃ 0.5C charging;

[0108] From the comparison between Examples 1 and 11, it can be found that the total lithium salt content is reduced, the electrolyte conductivity is reduced, and there is slight lithium precipitation when charging at -10℃ 0.5C;

[0109] From the comparison between Examples 1 and 12, it can be found that the total lithium salt content increases, the electrolyte conductivity decreases, and there is moderate lithium precipitation when charging at -10℃ and 0.5C;

[0110] From the comparison between Examples 1 and 13-19, it can be found that the addition of additives such as FEC, VEC, TMSP, LiODFB, DTD, TMSP, LiPO2F2, etc., respectively, has a slight effect on the cycle and storage, and can be added according to the actual application situation.

[0111] By comparing Comparative Example 2 with Comparative Example 1 (traditional electrolyte system), it can be found that the degree of lithium precipitation at -10℃0.5C charging and the low-temperature charging time are significantly reduced, but due to the large degree of side reaction between carboxylate EA and the graphite negative electrode, the 60℃ storage performance and 25℃4C cycle capacity retention rate are greatly reduced, indicating that although carboxylate EA can improve the low-temperature performance of the battery, its high-temperature cycle and storage performance are poor.

[0112] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0113] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments described herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises an organic solvent, a fluorine-containing lithium salt and a first additive; The organic solvent includes carboxylic acid esters and carbonate esters; The first additive includes a combination of 1,3-propane sultone and methylene methane disulfonate; Based on the total mass of the electrolyte as 100%, the content of the carboxylic acid ester is S1, the content of the 1,3-propane sultone is W1, the content of the methylene disulfonate is W2, and S1, W1 and W2 satisfy (S1 / 120)<(W1+W2)<(S1 / 20).

2. The electrolyte according to claim 1, characterized in that S1 satisfies 20%≤S1≤65%.

3. The electrolyte according to claim 1 or 2, characterized in that W1 satisfies 0.05%≤W1≤1%; And / or, W2 satisfies 0.05%≤W2≤1%.

4. The electrolyte according to claim 1 or 2, characterized in that The carboxylic acid ester includes any one or more of ethyl acetate, ethyl propionate, methyl propionate or methyl acetate; And / or, the carbonate includes any one or more of ethyl methyl carbonate, ethylene carbonate or dimethyl carbonate.

5. The electrolyte according to claim 1 or 2, characterized in that: The fluorine-containing lithium salt includes lithium bis(fluorosulfonyl)imide. Based on the total mass of the electrolyte being 100%, the content of the lithium bis(fluorosulfonyl)imide is 1-8%.

6. The electrolyte according to claim 5, characterized in that The fluorine-containing lithium salt also includes lithium hexafluorophosphate.

7. The electrolyte according to claim 6, characterized in that Based on the total mass of the electrolyte being 100%, the content of the fluorine-containing lithium salt is 10-18%.

8. The electrolyte according to claim 1 or 2, characterized in that: The electrolyte also includes a second additive, which includes any one or more of vinylene carbonate, fluoroethylene carbonate, vinyl vinyl carbonate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, lithium difluorooxalatoborate, vinyl sulfate or lithium difluorophosphate.

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

10. A vehicle, characterized in that: The vehicle includes the lithium-ion battery of claim 9.

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