Electrolyte and lithium ion battery containing same

Abstract

The invention provides an electrolyte and a lithium ion battery containing the same. According to the electrolyte disclosed by the invention, the first additive and the second additive are introduced and have a synergistic effect, so that the stability between the negative electrode side and the carboxylic ester is improved, the side reaction between active lithium and the carboxylic ester is reduced, and many problems caused by introduction of the carboxylic ester are solved; and by limiting the contents of the carboxylic ester, the first additive and the second additive and the conductivity of the electrolyte, the low-temperature fast charging performance of the lithium ion battery is effectively improved under the condition that other performances of the lithium ion battery are not influenced, and the lithium ion battery has a relatively good application prospect.

Description

Technical Field

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

[0002] Compared with ternary cathode materials, lithium iron phosphate materials have a lower lithium ion diffusion rate and poor electronic conductivity, which makes LFP batteries (lithium iron phosphate batteries) prone to polarization during low-temperature and normal-temperature charging, greatly limiting their application in the field of fast charging. In order to improve the fast charging ability of LFP cells, it is necessary to enhance the kinetics of liquid-phase transport of the electrolyte. Currently, carboxylic ester solvents with low viscosity and high conductivity at low temperature are usually selected to reduce the viscosity. However, carboxylic esters have high reactivity and are extremely likely to react with active lithium, resulting in a significant drop in the cycle performance of the cell at low temperature and seriously deteriorating the performance and safety performance of the battery.

[0003] Therefore, for electrolytes containing carboxylic esters, how to reduce their side reactions with active lithium without affecting other performance of lithium-ion batteries, so as to improve the low-temperature fast charging performance of lithium-ion batteries has become an urgent problem to be solved. Summary of the Invention

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

[0005] In a first aspect, the present invention provides an electrolyte, comprising a solvent, a lithium salt, a first additive, and a second additive:

[0006] The solvent includes a carboxylic ester solvent; the first additive is a compound represented by Formula I; the second additive is vinylene carbonate;

[0007]

[0008] In the electrolyte, the content of the carboxylic ester solvent is 10-65 wt%; the content of the first additive is 0.05-2 wt%, and the content of the second additive is 0.4-4.8 wt%;

[0009] The content of the carboxylic ester solvent, the content of the first additive, and the content of the second additive satisfy the following relationship:

[0010] (S 1 / 26.3)<(1.58×A 1 +A 2 )<(S 1 / 7.96)

[0011] Wherein, S 1 is the content of the carboxylic ester solvent;

[0012] A 1 is the content of the first additive;

[0013] A 2 is the content of the second additive;

[0014] The electrolyte has a conductivity of 11.8 - 18.7 mS / cm at 25°C.

[0015] In some embodiments of the present invention, the carboxylic ester solvent includes one or two of ethyl acetate, ethyl propionate, methyl acetate, or methyl propionate.

[0016] In some embodiments of the present invention, the carboxylic ester solvent is ethyl acetate or methyl acetate.

[0017] In some embodiments of the present invention, the solvent further includes a carbonate solvent;

[0018] The carbonate solvent includes one or more of ethyl methyl carbonate, ethylene carbonate, or dimethyl carbonate.

[0019] In some embodiments of the present invention, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, or lithium tetrafluoro(oxalato)phosphate.

[0020] In some embodiments of the present invention, in the electrolyte, the content of the lithium salt is 10 - 18 wt%.

[0021] In some embodiments of the present invention, the electrolyte further includes a third additive;

[0022] The third additive includes one or more additives such as tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, lithium difluoro(oxalato)borate, or lithium difluorophosphate.

[0023] In some embodiments of the present invention, in the electrolyte, the content of the third additive is 0.3 - 1.5 wt%.

[0024] In a second aspect, the present invention provides a lithium-ion battery, including a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte as described in the first aspect.

[0025] In some embodiments of the present invention, the negative electrode sheet contains a negative electrode active material, and the negative electrode active material includes graphite.

[0026] In some embodiments of the present invention, the positive electrode sheet contains a positive electrode active material, and the positive electrode active material includes lithium iron phosphate.

[0027] In a third aspect, the present invention also provides a vehicle, which includes the lithium-ion battery as described in the second aspect.

[0028] The technical solutions provided by the embodiments of the present invention have the following advantages compared with the prior art:

[0029] (1) Aiming at the problems of large side reactions between the lithium-ion battery electrolyte and active lithium caused by the introduction of carboxylic esters, resulting in a sharp decline in cycling at low temperatures and poor high-temperature performance, the present invention introduces a first additive and a second additive, which play a synergistic role to inhibit the interaction between the α-H of carboxylic esters and active lithium, reduce the damage of carboxylic esters to the negative electrode interface, and improve the stability between the negative electrode side and carboxylic esters;

[0030] (2) The present invention also effectively reduces the interfacial impedance and improves the low-temperature fast charging performance of the lithium-ion battery by limiting the contents of carboxylic esters, the first additive, the second additive, and the conductivity of the electrolyte, and has good application prospects without affecting other performances of the lithium-ion battery. Detailed Embodiments

[0031] In order to more clearly understand the above-mentioned objects, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0032] Many specific details are set forth in the following description to facilitate a thorough understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled 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.

[0034] In a first aspect, the present invention provides an electrolyte, which includes a solvent, a lithium salt, a first additive, and a second additive:

[0035] The solvent includes a carboxylic ester solvent; the first additive is a compound represented by Formula I; the second additive is vinylene carbonate;

[0036]

[0037] In the electrolyte, the content of the carboxylic ester solvent is 10-65 wt%; the content of the first additive is 0.05-2 wt%, and the content of the second additive is 0.4-4.8 wt%;

[0038] The content of the carboxylic acid ester solvent, the content of the first additive, and the content of the second additive satisfy the following relational expressions:

[0039] (S 1 / 26.3) < (1.58 × A 1 + A 2 ) < (S 1 / 7.96)

[0040] Wherein, S 1 is the content of the carboxylic acid ester solvent;

[0041] A 1 is the content of the first additive;

[0042] A 2 is the content of the second additive;

[0043] The conductivity of the electrolyte at 25 °C is 11.8 - 18.7 mS / cm.

[0044] Wherein, the content of the carboxylic acid ester solvent is such as 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt% or 65 wt%, etc.; the content of the first additive is such as 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1.0 wt%, 1.5 wt% or 2 wt%, etc.; the content of the second additive is such as 0.4 wt%, 0.45 wt%, 0.6 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 4.8 wt%, etc., but is not limited to the listed values, and other unlisted values within the above ranges are equally applicable.

[0045] The conductivity of the electrolyte at 25 °C is such as 11.8 mS / cm, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm or 18.7 mS / cm, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0046] In the present invention, by adding two different additives, the stability between the negative electrode side and the carboxylic acid ester is improved, the side reaction between the active lithium and the carboxylic acid ester is reduced, and the diving phenomenon during the cycling of the battery at low temperature is improved. Among them, the first additive can react preferentially with the carboxylic acid ester on the negative electrode side to form a multi-layer dense and uniform SEI film; in this compound, the sulfate ester structure can form with Li 2 SO 4As the main component, a thin and dense SEI film can be formed with a carbonate structure containing Li 2 CO 3 As the main component, a stable SEI film is formed, thus forming a multi-layer uniform SEI film to inhibit the reaction between active lithium and carboxylate on the negative electrode side; while the second additive can form a relatively thick polymer film to improve the influence of Fe dissolution in the LFP battery on the negative electrode interface. The two additives work synergistically, thus effectively solving the problem of poor low-temperature fast charging performance of lithium-ion batteries caused by using carboxylate as the electrolyte.

[0047] Furthermore, the present invention more effectively improves the low-temperature fast charging performance of lithium-ion batteries by controlling the contents of carboxylate, the first additive, the second additive, and the conductivity of the electrolyte, while ensuring that other performances of the lithium-ion battery do not deteriorate. When the content of carboxylate solvent in the electrolyte increases, the degree of side reaction between carboxylate and the negative electrode increases, and more first additive and second additive are needed to participate in the film formation at the negative electrode interface to inhibit the occurrence of negative electrode side reactions. At the same time, the increase in carboxylate content can also compensate for the impact on low-temperature fast charging performance caused by the increase in the first additive and the second additive. However, the contents of carboxylate, the first additive, and the second additive should not exceed the upper limit of the defined range. If the contents of carboxylate, the first additive, and the second additive increase synchronously to exceed their defined upper limits, resulting in the relationship result also exceeding its defined upper limit, it will lead to a large film formation impedance in the battery cell, making it difficult for the improvement in kinetics brought about by the concentration polarization caused by the increase in carboxylate to offset the impact of the increase in film formation impedance, thereby significantly deteriorating the fast charging performance of the battery cell; when the carboxylate content is too low, the degree of side reaction between carboxylate and the negative electrode decreases, and the contents of the first additive and the second additive need to be reduced to lower the interface impedance. However, the contents of carboxylate, the first additive, and the second additive should not be lower than the lower limit of the defined range. If the contents of carboxylate, the first additive, and the second additive decrease synchronously to be lower than their defined lower limits, resulting in the relationship result also being lower than its defined lower limit, it will lead to a poor film formation effect, making it difficult to inhibit the side reactions caused by carboxylate. At the same time, a low carboxylate content will also result in insufficient fast charging ability of the battery cell, ultimately leading to no competitive advantage compared with traditional electrolytes.

[0048] When the content of carboxylic ester solvents in the electrolyte is large while the contents of the first additive and the second additive are small (i.e., when the result of the relational expression is lower than the lower limit value of the relational expression), although the low-temperature performance and fast-charging performance of the lithium-ion battery are improved, the protective effect of the interface film decreases, the interface side reactions intensify, which will exacerbate the decomposition of the interface film, thus leading to a decline in the cycle performance and storage performance of the battery. When the content of carboxylic ester solvents in the electrolyte is small while the contents of the first additive and the second additive are large (i.e., when the result of the relational expression exceeds the upper limit value of the relational expression), the viscosity of the electrolyte increases, the ion migration rate decreases, and the film-forming impedance increases. Although the cycle and storage performances of the battery are improved, it will lead to a decline in the low-temperature performance and fast-charging performance of the lithium-ion battery.

[0049] In addition, the present invention also controls the appropriate conductivity of the electrolyte in a coordinated manner, making the liquid-phase mass transfer in the battery cell a non-rate-limiting step during the fast-charging process, so that the battery cell has good fast-charging ability. If the conductivity is too small, it will cause the liquid-phase mass transfer to be a rate-limiting step during high-rate charging, resulting in lithium deposition in the battery cell during high-rate charging, intensifying side reactions, and loss of active lithium.

[0050] In summary, through the overall design of the solvent content, additive content, and electrolyte conductivity in the electrolyte, the present invention enables the electrolyte to overcome the problem of large side reactions between carboxylic esters and active lithium, so that the lithium-ion battery has excellent low-temperature fast-charging ability without sacrificing high-temperature performance, cycle life, and calendar life.

[0051] In some embodiments of the present invention, the carboxylic ester solvents include one or two of ethyl acetate (EA), ethyl propionate (EP), methyl acetate (MA), or methyl propionate (MP).

[0052] In some embodiments of the present invention, the carboxylic ester solvent is ethyl acetate (EA) or methyl acetate (MA).

[0053] In some embodiments of the present invention, the solvent further includes carbonate solvents;

[0054] The carbonate solvents include one or more of ethyl methyl carbonate (EMC), ethylene carbonate (EC), or dimethyl carbonate (DMC).

[0055] In some embodiments of the present invention, the lithium salts include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate.

[0056] In some embodiments of the present invention, the content of the lithium salt in the electrolyte is 10-18 wt%, such as 10 wt%, 12 wt%, 14 wt%, 15 wt% or 18 wt%, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0057] In the embodiments of the present invention, an appropriate lithium salt concentration helps to improve the conductivity of the electrolyte and the fast charging ability of the battery cell. If the lithium salt concentration is too low, although it will significantly reduce the viscosity of the electrolyte, it will also reduce the conductivity of the electrolyte, resulting in an increase in the concentration polarization of the electrolyte, thereby affecting the fast charging performance; if it is too high, it will cause an increase in the viscosity of the electrolyte and a decrease in the viscosity of the electrolyte, which will also affect the fast charging performance of the battery cell.

[0058] In some embodiments of the present invention, the electrolyte further includes a third additive.

[0059] The third additive includes one or more additives selected from tris(trimethylsilyl) phosphate ((TMSP)), tris(trimethylsilyl) borate (TMSB), lithium difluorooxalate borate ((LiODFB)) or lithium difluorophosphate (LiPO 2 F 2 )).

[0060] In some embodiments of the present invention, the content of the third additive in the electrolyte is 0.3-1.5 wt%, such as 0.3 wt%, 0.6 wt%, 0.9 wt%, 1.2 wt% or 1.5 wt%, etc., and is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0061] In a second aspect, the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte as proposed in the first aspect.

[0062] In some embodiments of the present invention, the negative electrode sheet contains a negative electrode active material; the negative electrode active material includes graphite.

[0063] In some embodiments of the present invention, the positive electrode sheet contains a positive electrode active material; the positive electrode active material includes lithium iron phosphate.

[0064] In a third aspect, the present invention provides a vehicle, comprising the lithium-ion battery as proposed in the second aspect.

[0065] 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 below in conjunction with embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way constitutes a limitation on the present invention and its application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0066] For those not specified in the embodiments regarding specific techniques or conditions, follow the conventional techniques or conditions in the art, or those described in the literature, or the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0067] Examples 1-11 and Comparative Examples 1-7 respectively provide an electrolyte, and the specific parameters are shown in Table 1, all in weight percentages.

[0068] Table 1

[0069]

[0070]

[0071] Continued Table 1

[0072] Conductivity (mS / cm) at 25 °C <![CDATA[S 1 / 26.3]]> <![CDATA[1.58×A 1 +A 2 > <![CDATA[S 1 / 7.96]]> Example 1 14.4 0.015 0.038 0.050 Example 2 11.8 0.004 0.005 0.013 Example 3 16.7 0.025 0.080 0.082 Example 4 18.7 0.015 0.038 0.050 Example 5 12.2 0.015 0.038 0.050 Example 6 13.9 0.015 0.038 0.050 Example 7 13.3 0.015 0.038 0.050 Example 8 13.5 0.015 0.038 0.050 Example 9 14.5 0.015 0.038 0.050 Example 10 14.6 0.015 0.038 0.050 Example 11 14.3 0.015 0.038 0.050 Comparative Example 1 10.2 0 0 0 Comparative Example 2 14.5 0.015 0.062 0.050 Comparative Example 3 14.3 0.015 0.011 0.050 Comparative Example 4 14.6 0.015 0 0.050 Comparative Example 5 14.7 0.015 0.035 0.050 Comparative Example 6 14.5 0.015 0.032 0.050 Comparative Example 7 10.7 0.004 0.005 0.013

[0073] Among them, the test method for conductivity is as follows:

[0074] Put the electrolytes of Examples 1-11 and Comparative Examples 1-7 into a constant temperature water bath at 25 °C for 30 min, and then measure the conductivity with a conductivity meter.

[0075] Performance Test

[0076] 1. Preparation of a lithium-ion battery for testing

[0077] Electrolyte: In a glove box, mix the solvent, various additives and lithium salt according to the ratio in Table 1, and after stirring evenly, prepare the electrolyte;

[0078] Preparation of the positive electrode sheet: Use the positive electrode active material (LiFePO 4) The positive electrode slurry is prepared by mixing a binder (PVDF), a conductive agent (acetylene black) in a mass ratio of 96.5:2.5:1, adding an N-methylpyrrolidone (NMP) solvent until the system becomes uniformly transparent, and stirring with a vacuum mixer. Then it is uniformly coated on a current collector aluminum foil (with a thickness of 13 μm), air-dried at room temperature and then transferred to an oven at 120 °C for drying for 1 h. After that, it is cold-pressed (the compaction density is 2.6 g / cm 3 , and the areal density is 400 g / m 2 ), and then cut to obtain the positive electrode plate;

[0079] Preparation of the negative electrode plate: The negative electrode active material (graphite), a thickening agent (sodium carboxymethyl cellulose, CMC) solution, and a binder (styrene-butadiene rubber emulsion) are mixed in a mass ratio of 97:2:1, deionized water is added, and the mixture is stirred with a vacuum mixer to obtain the negative electrode slurry. Then it is uniformly coated on a current collector copper foil (with a thickness of 6 μm), air-dried at room temperature and then transferred to an oven at 120 °C for drying for 1 h. After that, it is cold-pressed (the compaction density is 1.6 g / cm 3 , and the density is 180 g / m 2 ), and then cut to obtain the negative electrode plate;

[0080] Separator: A polypropylene separator is selected.

[0081] The above positive electrode plate, negative electrode plate, and separator are wound, wrapped with an aluminum-plastic film, baked to remove water, then the above electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, grading and other processes, a soft-pack lithium-ion battery is prepared.

[0082] It should be noted that the above lithium-ion battery for testing is only an example listed for testing the performance of the electrolyte. The present invention is not limited to this kind of battery, and the raw materials (except the electrolyte), ratios, parameters, and processes can all be replaced with other conventional raw materials, ratios, parameters, and processes in the art, so as to form a battery different from this lithium-ion battery for testing.

[0083] 2. Lithium plating test during charging at 0.8C at -10 °C

[0084] At -10 °C, the lithium-ion batteries for testing in Examples 1-11 and Comparative Examples 1-7 are first discharged to 2.0V at 0.33C, and then cyclic tests are carried out. The cyclic test process includes: first charging at a constant current of 0.8C to 3.75V, then charging at a constant voltage until the current is 0.05C, and then discharging at a constant current of 0.33C to 2.0V. After such cyclic charging / discharging 20 times, at 25 °C, it is charged at 1C to 3.75V, then charged at a constant voltage until the current is 0.05C, and the cell is disassembled to observe the disassembly interface situation and record the data.

[0085] 3. 6C cyclic test at 25 °C

[0086] At 25 °C, the test lithium-ion batteries of Examples 1-11 and Comparative Examples 1-7 were first discharged at 1C to 2.0V, and then subjected to a cycle test. The cycle test process includes: first charging at a constant current of 6C to 3.75V, then charging at a constant voltage until the current is 0.05C, and then discharging at a constant current of 1C to 2.0V. Such cyclic charging / discharging was carried out, and the capacity retention rate of the lithium-ion battery at 25 °C with 6C discharge for 500 cycles was calculated.

[0087] 4. 60 °C Storage Test

[0088] At 25 °C, the test lithium-ion batteries of Examples 1-11 and Comparative Examples 1-7 were first discharged at 1C to 2.0V, then charged at a constant current of 1C to 3.75V, then charged at a constant voltage until the current was 0.05C, and then discharged at a constant current of 1C to 2.0V. The discharge capacity was denoted as C 1 ;

[0089] Then the lithium battery was charged at a constant current of 1C to 3.75V, and then charged at a constant voltage until the current was 0.05C. The lithium battery was placed in an oven at 60 °C for 60 days, and then placed at room temperature. First, it was discharged at 1C to 2.0V, then charged at a constant current of 1C to 3.75V, then charged at a constant voltage until the current was 0.05C, and then discharged at a constant current of 1C to 2.0V. The discharge capacity was denoted as C 2 . C 2 / C 1 ×100% = Capacity Retention Rate.

[0090] The results of the above performance tests are shown in Table 2.

[0091] Table 2

[0092]

[0093]

[0094] Compared with Example 1, the contents of the first additive, the second additive, and the carboxylic acid ester in Example 2 were synchronously reduced (the relational result was close to the lower limit value). Due to the reduction in the contents of the first additive and the second additive, the interfacial impedance was reduced. Therefore, no lithium precipitation occurred during 0.8C charging at -10 °C, and the high-temperature storage and 6C cycling performance at 25 °C deteriorated slightly.

[0095] Compared with Example 1, the contents of the first additive, the second additive, and the carboxylic acid ester in Example 3 were synchronously increased (the relational result was close to the upper limit value). Due to the increase in the contents of the first additive and the second additive, the interfacial impedance was increased. Therefore, no lithium precipitation occurred during 0.8C charging at -10 °C, and at the same time, the high-temperature storage was slightly improved, but the 6C cycling performance at 25 °C deteriorated slightly.

[0096] Compared with Example 1, in Examples 4, 5, and 6, MA, EP, and MP are used to replace EA respectively. EP and MP will affect the kinetics, so there is slight lithium plating during the low-temperature fast charging test.

[0097] Compared with Example 1, in Example 7, the content of the lithium salt is reduced, the viscosity is reduced, there is no lithium plating during low-temperature fast charging, and the high-temperature storage performance is slightly affected.

[0098] Compared with Example 1, in Example 8, the content of the lithium salt is appropriately increased, but the performance in all aspects is not much different.

[0099] Compared with Example 1, in Examples 9, 10, and 11, the effects of third additives such as TMSP, TMSB, LiODFB, and LiPO 2 F 2 on low-temperature fast charging, 6C cycle performance at 25°C, and high-temperature storage performance are slightly affected, but the overall impact is not significant and can be introduced according to the actual application situation.

[0100] Compared with Comparative Example 1 (traditional electrolyte system), the liquid-phase transport ability of the electrolyte obtained in Example 1 is greatly improved, the kinetics is good, there is no lithium plating during 0.8C charging at -10°C. At the same time, due to the synergistic effect of the first additive and the second additive, the side reaction of carboxylic acid ester (EA) on active lithium at high temperature is effectively inhibited. Therefore, the high-temperature storage can be maintained at the same level as the traditional electrolyte (as can be seen from the 60°C storage test results). In addition, by further controlling the contents of carboxylic acid ester, the first additive, the second additive, and the conductivity of the electrolyte, the low-temperature fast charging performance of the lithium-ion battery is effectively improved. In Comparative Example 1, due to insufficient kinetics, serious lithium plating occurred during the 6C cycle, the loss of active lithium was aggravated, resulting in a voltage drop of the battery cell.

[0101] Compared with Example 1, in Comparative Example 2, the content of the first additive is increased, making 1.58×A 1 +A 2 exceed the upper limit value, resulting in serious lithium plating in the low-temperature fast charging test of the battery cell. This is because the film-forming impedance of the battery cell becomes larger, and at the same time, the liquid-phase transport ability is not improved, seriously affecting the kinetics.

[0102] Compared with Example 1, in Comparative Example 3, the contents of the first additive and the second additive are both reduced, but the carboxylic acid ester is not reduced, making 1.58×A 1 +A 2 lower than the lower limit value, resulting in the side reaction between the carboxylic acid ester and the active lithium not being well inhibited. Therefore, the 6C cycle performance at 25°C deteriorates significantly.

[0103] Compared with Example 1, in Comparative Example 4, the first additive and the second additive were not added, resulting in the reaction between carboxylic acid ester (EA) and active lithium, causing the cycle performance of the battery cell to drop significantly at low temperature, the high-temperature storage performance to deteriorate severely, and the cycle performance at room temperature to also drop, seriously deteriorating the safety performance of the battery.

[0104] Compared with Example 1, in Comparative Example 5, although the contents of the second additive and the carboxylic acid ester as a whole satisfy the relational expression proposed by the present invention, since the first additive was not added, it was impossible to exert a synergistic effect with the second additive, resulting in a low retention rate of the high-temperature storage capacity of the battery cell and an aggravation of the high-temperature side reaction.

[0105] Compared with Example 1, in Comparative Example 6, although the contents of the first additive and the carboxylic acid ester as a whole satisfy the relational expression proposed by the present invention, since the second additive was not added, it was impossible to exert a synergistic effect with the first additive, resulting in lithium deposition during low-temperature cycling of the battery cell, and its high-temperature storage performance and 6C cycle performance at 25°C were affected.

[0106] In Comparative Example 7, although the contents of each raw material in the electrolyte all satisfy the defined range of the present application and the result of the relational expression also satisfies, due to the low conductivity, the liquid-phase transfer ability of the electrolyte is insufficient, lithium deposition occurs during low-temperature cycling of the electrolyte, and the retention rate of the 6C cycle capacity at 25°C is severely low, making it difficult to meet the fast-charging requirement.

[0107] 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 actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0108] The above are only specific embodiments of the present invention, enabling those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can 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 these embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrolyte, characterized in that: Including solvent, lithium salt, first additive and second additive: The solvent includes a carboxylic acid ester solvent; the first additive is a compound represented by formula I; the second additive is vinylene carbonate; In the electrolyte, the content of the carboxylate solvent is 10-65wt%; the content of the first additive is 0.05-2wt%; the content of the second additive is 0.4-4.8wt%; The content of the carboxylate solvent, the content of the first additive, and the content of the second additive satisfy the following relationship: (S1 / 26.3)<(1.58×A1+A2)<(S1 / 7.96) Wherein, S1 is the content of the carboxylate solvent; A1 is the content of the first additive; A2 is the content of the second additive; The conductivity of the electrolyte at 25° C. is 11.8-18.7 mS / cm.

2. The electrolyte according to claim 1, characterized in that The carboxylic acid ester solvent includes one or two of ethyl acetate, ethyl propionate, methyl acetate or methyl propionate.

3. The electrolyte according to claim 1, characterized in that The solvent also includes carbonate solvents; The carbonate solvent includes one or more of ethyl methyl carbonate, ethylene carbonate or dimethyl carbonate.

4. The electrolyte according to claim 1, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorobis(oxalatophosphate) or lithium tetrafluorooxalatophosphate.

5. The electrolyte according to claim 1, characterized in that In the electrolyte, the content of the lithium salt is 10-18wt%.

6. The electrolyte according to claim 1, characterized in that The electrolyte further includes a third additive; The third additive includes one or more additives selected from tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, lithium difluorooxalatoborate or lithium difluorophosphate; In the electrolyte, the content of the third additive is 0.3-1.5wt%.

7. A lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte as claimed in any one of claims 1 to 6.

8. The lithium-ion battery according to claim 7, characterized in that: The negative electrode sheet contains a negative electrode active material, and the negative electrode active material includes graphite.

9. The lithium-ion battery according to claim 7, characterized in that: The positive electrode plate contains a positive electrode active material, and the positive electrode active material includes lithium iron phosphate.

10. A vehicle, characterized in that: The vehicle comprises a lithium-ion battery as claimed in any one of claims 7 to 9.

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