Electrolyte and battery

Abstract

The invention discloses an electrolyte and a battery. The electrolyte comprises a solvent, a lithium salt and an additive, the solvent comprises acetonitrile and carboxylic ester, the additive comprises a first additive, a second additive and a third additive, the first additive is at least one of phosphate, borate, fluorophosphate and fluoborate with a film-forming potential of 1.3-2V, and the third additive is at least one of lithium salt and fluoborate with a film-forming potential of 1.3-2V. The second additive is at least one of a sulfur-containing additive, a boron-containing additive and a phosphorus-containing additive, and the third additive is a negative electrode film-forming additive; and Y is more than 0.025 and less than 60. According to the invention, a solvent system and an interface film forming mechanism of the electrolyte are synergistically regulated and controlled, so that the core problem of violent side reaction between the acetonitrile-based electrolyte and the negative electrode is solved, and meanwhile, the combination of high energy density and ultrafast charging performance is realized. The electrolyte is suitable for high-energy-density, wide-temperature-range and fast-charging type lithium iron phosphate batteries.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to an electrolyte and a battery. Background Art

[0002] With the global emphasis on environmental protection and sustainable development, the electric vehicle industry has entered a period of rapid development. However, concerns about range and charging remain key factors hindering the further adoption of electric vehicles. To meet consumer demand for long driving range and fast charging, power batteries (such as lithium iron phosphate batteries) must continuously improve their energy density and charge rate.

[0003] CN 116207347 A discloses an electrolyte for a lithium ion secondary battery and the lithium ion secondary battery. The electrolyte contains: an organic solvent, an electrolyte lithium salt and an additive. The additive contains compound A. The compound A is shown in the following structural formula a: Wherein, in the above structural formula a, R1 and R2 are each independently selected from the group consisting of a halogen atom, a C1-C20 alkyl group substituted or unsubstituted by halogen, a C3-C20 cycloalkyl group substituted or unsubstituted by halogen, a phenyl group substituted or unsubstituted by halogen, a C1-C20 olefin group substituted or unsubstituted by halogen, an unsubstituted biphenyl group, a C6-C26 phenylalkyl group substituted or unsubstituted by halogen, a C6-C26 condensed ring aromatic hydrocarbon group substituted or unsubstituted by halogen, and a blank bond. By using this electrolyte, the cycle performance and charge rate of the lithium ion secondary battery at high energy density can be improved.

[0004] CN 117276538 A discloses a secondary battery and a battery pack, comprising a positive electrode plate, an electrolyte and a separator, and further comprising: a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises graphite; wherein the non-Faraday capacitance of the negative electrode plate is CdlnF / g, 50≤Cdl≤250; the electrolyte comprises a sulfur-containing additive, and the content of the sulfur-containing additive is A%, 0.05≤Cdl×A%≤12.5 based on the mass of the electrolyte. Sulfur-containing additives have high stability and high ionic conductivity, which ensure the number of electrochemically active sites on the surface of the negative electrode, are beneficial to the contact between the negative electrode and the electrolyte, accelerate the ion-electron conduction rate, reduce the side reactions of the electrolyte components themselves and the reactions between them and the negative electrode materials, reduce the impedance of the SEI film, and thus extend the life of the secondary battery, reduce the charge transfer resistance, and can effectively increase the charging rate of the secondary battery and improve the fast charging performance. At the same time, it can increase the current density of the negative electrode and increase the energy density of the secondary battery, so that the secondary battery has excellent kinetic performance and cycle performance, and has good application prospects.

[0005] Acetonitrile has the advantages of low viscosity (0.35mPa·s, 25°C), high dielectric constant and wide liquid range (boiling point approximately 81.6°C, melting point approximately -45.7°C). These advantages enable acetonitrile-based electrolytes to achieve ultra-high conductivity (>20mS / cm), accelerate the internal transfer rate of lithium ions, and enhance the electrolyte's charging capacity. Furthermore, the low viscosity property increases the electrolyte's ability to wet the positive and negative electrode systems, enabling its application in high-area-density fast-charging batteries (e.g., rates of 4C to 8C).

[0006] Although acetonitrile-based electrolytes have shown many advantages, they face serious interfacial stability issues in practical applications. The LUMO (lowest unoccupied molecular orbital) energy level of acetonitrile molecules is relatively low. During battery charging, especially in the strong reducing environment on the negative electrode surface, acetonitrile molecules can easily obtain electrons and undergo reduction and decomposition reactions, producing a large amount of gaseous byproducts such as methane (CH4) and ethane (C2H6). This causes the gas pressure inside the battery cell to increase, causing swelling and deformation, destroying the mechanical integrity of the battery, and also producing inorganic solid products, forming an uneven passivation film on the negative electrode surface, which greatly increases the interfacial impedance of the battery. Especially in high temperature environments, the kinetics of the side reactions between acetonitrile and the negative electrode are significantly accelerated, resulting in a decrease in the electrochemical performance of the battery (such as fast charging performance).

[0007] Therefore, providing an acetonitrile-based electrolyte that utilizes the advantages of acetonitrile while overcoming its poor interfacial stability, so that the electrolyte has high conductivity, reduces pre-charging gas production of the battery cell, and improves the fast charging performance of the battery is a technical problem that needs to be solved urgently. Summary of the Invention

[0008] In view of the above technical problems existing in the prior art, the object of the present invention is to provide an electrolyte and a battery.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides an electrolyte, comprising a solvent, a lithium salt, and an additive, wherein the solvent comprises acetonitrile and a carboxylic acid ester, the additive comprises a first additive, a second additive, and a third additive, wherein the first additive is at least one of a phosphate, a borate, a fluorophosphate, and a fluoroborate having a film-forming potential between 1.3 V and 2 V, the second additive is at least one of a sulfur-containing additive, a boron-containing additive, and a phosphorus-containing additive, and the third additive is a negative electrode film-forming additive;

[0011] Based on the total volume of the electrolyte being 100 vol%, the volume fraction of the acetonitrile is A vol%, and the volume fraction of the carboxylic acid ester is B vol%;

[0012] Based on the total mass of the electrolyte being 100 wt.%, the mass fraction of the first additive is c wt.%, the mass fraction of the second additive is d wt.%, and the mass fraction of the third additive is ewt.%;

[0013]

[0014] The present invention adopts a gradient film-forming strategy to design the composition of the electrolyte, wherein the first additive is at least one of phosphates, borates, fluorophosphates and fluoroborates with a film-forming potential between 1.3V and 2V, and its decomposition potential is before acetonitrile, and can form an inorganic SEI film rich in LiF, boron-containing compounds or phosphorus-containing compounds, isolate the acetonitrile solvent, suppress the side reactions, and prevent gas production in the pre-charging stage of the battery cell. The second additive is a sulfur-containing additive, which decomposes in the middle stage of charging (for example, between the reduction potential of 2V and 2.5V) to produce lithium sulfate and lithium sulfonate inorganic components with better thermal stability, so that the second additive is always present in the subsequent electrolyte, continuously suppressing the decomposition of acetonitrile and reducing gas production. The third additive is a conventional negative electrode film-forming additive. During the cycle, the SEI film is in a dynamic process of continuous rupture and repair. The negative electrode film-forming additive repairs the SEI film in situ and improves the stability of the electrolyte interface.

[0015] In the electrolyte of the present invention, there is a synergistic effect between the components. The electrolyte can have high conductivity and excellent fast charging performance. Among them, Y represents the interfacial stability of the electrolyte. The higher the A or B value, the higher the electrolyte conductivity and the better the fast charging ability. However, too high a content leads to a high proportion of unstable solvents in the electrolyte, increased side reactions, and deteriorated performance. The higher the values ​​of c, d, and e, the better the film quality. The acetonitrile and carboxylic acid ester solvents are more compatible with the positive and negative electrodes. However, an increase in their content means excessive film formation reactions and increased interfacial resistance. Therefore, the solvent content and the additive content synergistically affect the Y value. The higher the solvent content, the higher the electrolyte reaction activity. The lower the additive content, the insufficient film protection, the lowest electrolyte stability, and the smaller the Y value; the lower the solvent content, the lower the electrolyte conductivity. The higher the additive content, the increased interfacial resistance. The larger the Y value, the lower the electrolyte charging capacity. In summary, by regulating the volume fraction of acetonitrile, the volume fraction of carboxylic acid ester, the mass fraction of the first additive, the mass fraction of the second additive, and the mass fraction of the third additive, the following conditions are met: The electrolyte has the best stability, high conductivity, and good fast charging performance.

[0016] To address the strong reactivity of acetonitrile electrolytes and the problems they present at various stages, this invention enhances electrolyte stability by synergistically regulating the electrolyte's solvent system and interfacial film-forming mechanism, resolving the core issue of vigorous side reactions between acetonitrile-based electrolytes and the negative electrode. This electrolyte offers the advantages of high conductivity, high wettability, and a wide liquid range, exhibiting excellent compatibility with both positive and negative electrode systems, while simultaneously achieving a combination of high energy density and ultra-fast charging performance.

[0017] The electrolyte of the present invention solves the problems of pre-charging gas generation and poor fast-charging performance of the battery cell, and is suitable for high-energy-density, wide-temperature-range, fast-charging lithium iron phosphate batteries.

[0018] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0019] Preferably, 0<A<60, for example, can be 0.01, 0.03, 0.05, 0.08, 0.1, 0.3, 0.6, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 20, 22, 23, 25, 26, 27, 28, 30, 32, 33, 35, 37, 38, 40, 42, 43, 44, 45, 46, 47, 49, 50, 51, 53, 55, 56, 57, 58, 59 or 59.5, preferably 11≤A≤48. In the present invention, acetonitrile has the characteristics of low viscosity and high dielectric constant, which provides a good cutoff environment for ion transport and lithium salt dissociation. If its content is too low, the conductivity of the electrolyte cannot be significantly improved; if its content is too high, the electrolyte will be highly reactive and a large number of side reactions will occur.

[0020] 61, 62, 63, 64, 65, 66, 67, 68, 69 or 69.5, and preferably 10≤B≤58. In the present invention, the carboxylate and acetonitrile form a mixed solvent system, which can improve the conductivity of the electrolyte, thereby maximizing the electrolyte's charging capacity. It maintains the advantages of low viscosity and high conductivity even at extremely low temperatures, while also improving the electrolyte's wettability for electrode materials. If the carboxylate content is too low, the electrolyte's advantages of low viscosity and high wettability cannot be fully realized; if the carboxylate content is too high, there is a risk of electrolyte instability.

[0021] Preferably, 0.4≤c≤1.7, for example, it can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 or 1.7, etc. In the present invention, if the content of the first additive is too low, uniform initial SEI interface protection cannot be formed; if the content of the first additive is too high, it cannot be completely consumed after the pre-charge is completed and continues to decompose, resulting in increased interface impedance.

[0022] Preferably, 0.9≤d≤2.8, for example, it can be 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7 or 2.8, etc. In the present invention, if the content of the second additive is too low, the second additive cannot be always present in the subsequent electrolyte to continuously inhibit the decomposition of acetonitrile; if the content of the second additive is too high, the interfacial impedance will increase, thereby deteriorating the fast charging performance.

[0023] Preferably, 5≤e≤9, for example, it can be 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5 or 9. In the present invention, if the content of the third additive is too low, the third additive cannot be always present in the subsequent electrolyte to continuously repair the SEI film; if the content of the third additive is too high, the interfacial impedance will increase, deteriorating the fast charging performance.

[0024] Preferably, 0.1≤Y≤3, for example, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, 0.76, 0.78, 0.8, 0.82, 0.85, 0.88, 0.9, 0.93, 0.94, 0.95, 0.96, 0.98, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.28, 1.31, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3, etc.

[0025] Preferably, the carboxylic acid ester comprises ethyl acetate and / or methyl acetate.

[0026] As a preferred technical solution of the electrolyte of the present invention, the first additive includes at least one of lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOP), lithium dioxalatoborate (LiBOB), lithium difluorooxalatophosphate (LiDFOB) and lithium tetrafluoroborate (LiBF4).

[0027] Preferably, the second additive includes at least two of sulfates, sulfonates, thiophene-based sulfur-containing additives, phosphates, and borates.

[0028] Preferably, the second additive includes at least one of ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), benzo[1,2-b:4,5-b']dithiophene-4,8-dione (BDTD), 1,3-propane sultone (PS) tris(trimethylsilyl)phosphate (TMSP) and bis(trimethylsilyl)borate (TMSB).

[0029] Preferably, the third additive includes fluoroethylene carbonate (FEC) and / or ethylene carbonate (VC).

[0030] Preferably, the lithium salt includes lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide (LiFSI).

[0031] Preferably, the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 2 mol / L, for example, it can be 0.8 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L.

[0032] In a second aspect, the present invention provides a battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the electrolyte described in the first aspect;

[0033] The positive electrode is a lithium iron phosphate positive electrode.

[0034] The electrolyte provided by the present invention is used in lithium iron phosphate batteries. Through the synergy of the high conductivity solvent and the "gradient film-forming" composite additive in the electrolyte, a high energy density, long life, wide temperature range, and fast-charging battery is achieved.

[0035] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0036] Compared with the existing technology, the present invention has the following beneficial effects:

[0037] (1) The present invention solves the core problem of acetonitrile-based electrolytes’ intense side reactions with negative electrodes by synergistically regulating the electrolyte’s solvent system and interfacial film-forming mechanism, while simultaneously achieving a combination of high energy density and ultra-fast charging performance. The electrolyte of the present invention is suitable for high-energy-density, wide-temperature-range, fast-charging lithium iron phosphate batteries.

[0038] (2) The electrolyte conductivity of the battery of the present invention is high, at 13.7 mS / cm, preferably at or above 16.5 mS / cm. The battery of the present invention has a 4C cycle number (80% SOH) of more than 420 cycles, preferably more than 680 cycles; a 6C cycle number (80% SOH) of more than 300 cycles, preferably more than 490 cycles. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0040] The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] Example 1

[0042] This embodiment provides an electrolyte, comprising a solvent, a lithium salt, and an additive. The lithium salt is 1 mol / L LiPF6. The solvent comprises acetonitrile (ACN), a carboxylate, ethyl methyl carbonate, and ethylene carbonate in a volume ratio of 30:30:20:20, and the carboxylate is ethyl acetate (EA). The additives include a first additive, a second additive, and a third additive. The first additive is a mixture of lithium difluorooxalatoborate (LiDFOP) and lithium difluorooxalatophosphate (LiDFOB) in a mass ratio of 1:1, and the mass fraction of the first additive in the electrolyte is 1%. The second additive is a mixture of ethylene sulfate (DTD) and 1,3-propane sultone (PS) in a mass ratio of 2:1, and the mass fraction of the second additive in the electrolyte is 1.5%. The third additive is a mixture of fluoroethylene carbonate (FEC) and ethylene carbonate (VC) in a mass ratio of 2:1, and the mass fraction of the third additive in the electrolyte is 6%.

[0043] The preparation method of the electrolyte of this embodiment is as follows: in an argon glove box, acetonitrile, ethyl acetate, ethyl methyl carbonate, and ethylene carbonate are mixed uniformly in a volume ratio of 30:30:20:20, and then lithium salt, a first additive, a second additive, and a third additive are added, and stirred until the mixture is uniform to obtain an electrolyte.

[0044] Based on the total volume of the electrolyte being 100 vol%, the volume fraction of the acetonitrile is A vol%, the volume fraction of the carboxylic acid ester is B vol%. Based on the total mass of the electrolyte being 100 wt.%, the mass fraction of the first additive is c wt.%, the mass fraction of the second additive is d wt.%, and the mass fraction of the third additive is ewt.%. In this embodiment, A is 30, B is 30, c is 1, d is 1.5, and e is 7. According to the formula The calculated value of Y is 0.94. See Table 1.

[0045] The conductivity of the electrolyte of this embodiment was tested. See Table 1.

[0046] This embodiment also provides a battery, the preparation method of which includes the following steps:

[0047] (1) Preparation of positive electrode sheet:

[0048] LiFePO4, conductive carbon black (SP), and polyvinylidene fluoride (PVDF) were mixed in a solvent, N-methylpyrrolidone, at a weight ratio of 97:1:2 and stirred evenly to produce a positive electrode slurry. Aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was coated on the positive electrode current collector. The cathode was then baked at 120°C for 1 hour, followed by cold pressing, cutting, and slitting to produce the positive electrode sheets.

[0049] (2) Preparation of negative electrode sheet:

[0050] Artificial graphite, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in deionized water at a weight ratio of 96:1:1.5:1.5 and stirred evenly to produce a negative electrode slurry. Copper foil was used as the negative electrode current collector, and the slurry was coated on the negative electrode current collector. The negative electrode sheet was then baked at 120°C for 1 hour, followed by cold pressing, cutting, and slitting.

[0051] (3) Battery assembly:

[0052] The positive electrode sheet, separator, and negative electrode sheet are arranged in sequence and assembled into a button battery, which is pre-charged and then formed for fast charging performance testing. The pre-charging condition is: 0.1C charging to 60% SOC.

[0053] Fast charging performance test:

[0054] 4C cycle times (80% SOH): test temperature 25°C, voltage range 2-3.8V, charge is step charge, average charge rate is 4C, discharge is 1C, constant current discharge.

[0055] 6C cycle times (80% SOH): test temperature 25°C, voltage range 2-3.8V, charge is step charge, average charge rate is 6C, discharge is 1C, constant current discharge.

[0056] Examples 2 to 20

[0057] The difference from Example 1 lies in the values ​​of A, B, c, d, and e. Note that the proportions of the first, second, and third additives are the same as those in Example 1.

[0058] Example 21

[0059] The difference from Example 1 is that the first additive is a mixture of lithium difluorophosphate (LiPO 2 F 2 ) and lithium difluorooxalophosphate (LiDFOB), and the mass ratio of LiPO 2 F 2 to LiDFOB is 1:1.

[0060] Example 22

[0061] The difference from Example 1 is that the second additive is a mixture of methylene methanedisulfonate (MMDS) and DTD, and the mass ratio of MMDS to DTD is 1:1.

[0062] Example 23

[0063] The difference from Example 1 is that the first additive is a mixture of LiPO2F2 and LiDFOB, and the mass ratio of LiPO2F2 to LiDFOB is 1:1; the second additive is a mixture of MMDS and tris(trimethylsilyl) phosphate (TMSP), and the mass ratio of MMDS to TMSP is 1:1.

[0064] Comparative Example 1

[0065] Provided is an electrolyte, and a preparation method thereof comprises the following steps: in an argon glove box, uniformly mixing acetonitrile, ethyl methyl carbonate, and ethylene carbonate in a volume ratio of 30:40:30, and adding 1 mol / L lithium salt LiPF6 and 2 wt.% VC.

[0066] Comparative Example 2

[0067] The difference from Example 1 is that the first additive is not added.

[0068] Comparative Example 3

[0069] The difference from Example 1 is that no second additive is added.

[0070] Comparative Example 4

[0071] The difference from Example 1 is that the third additive is not added.

[0072] The conductivity of the electrolyte and the fast charging performance of the battery were tested in the same manner as in Example 1. The results are shown in Table 1.

[0073] Table 1

[0074]

[0075] Comparative Examples 1 to 4 do not have data on fast-charging performance due to pre-charging and gas production.

[0076] In summary, in the electrolyte of the present invention, there is a synergistic effect between the components. The electrolyte can have high conductivity and excellent fast charging performance.

[0077] By comparing Examples 1 to 5, it can be seen that the volume fraction Avol% of acetonitrile affects the fast charging performance of the battery, 0<A<60, preferably 11≤A≤48. Compared with Example 1, the volume fraction of acetonitrile in Example 5 is 50vol%, which is too large, and the electrolyte reaction activity is strong, resulting in a decrease in fast charging performance. The volume fraction of acetonitrile in Example 3 is 10vol%, which is too small, and the conductivity of the electrolyte is low, resulting in a decrease in fast charging performance.

[0078] A comparison of Examples 6 to 10 shows that a carboxylate volume fraction of B vol% affects the fast-charging performance of the battery, preferably 0 < B < 70, and more preferably 10 ≤ B ≤ 58. Compared with Example 1, the carboxylate content in Example 10 is 60 vol%, which is too high, resulting in an excessively high proportion of unstable solvents in the electrolyte, which deteriorates the fast-charging performance of the battery cell.

[0079] A comparison of Examples 11 to 13 shows that the mass fraction c wt.% of the first additive affects the fast-charging performance of the battery, preferably 0.4 ≤ c ≤ 1.7. In Example 13, the first additive content was 1.8 wt.%, which was too high, resulting in a thick SEI formed by the film-forming reaction, increasing the cell impedance and reducing the fast-charging performance.

[0080] A comparison of Examples 14 to 17 shows that the mass fraction d wt.% of the second additive affects the fast-charging performance of the battery, preferably 0.9 ≤ d ≤ 2.8. The content of the second additive in Example 17 is 3 wt.%, which is too high, resulting in a thick SEI formed by the film-forming reaction, increasing the cell impedance and reducing the fast-charging performance.

[0081] A comparison of Examples 18 to 20 shows that the mass fraction e wt.% of the third additive affects the fast-charging performance of the battery, preferably 5 ≤ e ≤ 9. The content of the third additive in Example 20 is 10 wt.%, which is too high, resulting in a thick SEI formed by the film-forming reaction, increasing the cell impedance and reducing the fast-charging performance.

[0082] In Comparative Example 1, no carboxylate, first additive, and second additive were added, the content of the third additive VC was too low, and the electrolyte was not optimized for additives for gradient film formation, so severe gas generation occurred during the pre-charging stage.

[0083] In Comparative Example 2, the first additive was not added, and the SEI formed in the pre-filling film-forming stage was not strong enough, resulting in the decomposition of the acetonitrile solvent and the generation of a large amount of gas.

[0084] In Comparative Example 3, no second additive was added, and no residue remained during the subsequent testing process, and the gas production could not be continuously reduced.

[0085] In Comparative Example 4, the third additive was not added, and the SEI could not be repaired dynamically and continuously, resulting in the negative electrode interface being exposed to the acetonitrile electrolyte, and continuously reacting and producing gas.

[0086] The applicant states that the present invention is intended to illustrate the detailed methods of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed methods, that is, it does not mean that the present invention must rely on the above-described detailed methods in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for various raw materials in the products of the present invention, addition of auxiliary ingredients, and selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a solvent, a lithium salt and an additive, the solvent includes acetonitrile and a carboxylic acid ester, the additive includes a first additive, a second additive and a third additive, the first additive is at least one of phosphate, borate, fluorophosphate and fluoroborate having a film-forming potential between 1.3V and 2V, the second additive is at least one of a sulfur-containing additive, a boron-containing additive and a phosphorus-containing additive, and the third additive is a negative electrode film-forming additive; Based on the total volume of the electrolyte being 100 vol%, the volume fraction of the acetonitrile is A vol%, and the volume fraction of the carboxylic acid ester is B vol%; Based on the total mass of the electrolyte being 100 wt.%, the mass fraction of the first additive is c wt.%, the mass fraction of the second additive is d wt.%, and the mass fraction of the third additive is ewt.%; 2. The electrolyte according to claim 1, characterized in that 0<A<60, preferably 11≤A≤48; Preferably, 0<B<70, preferably 10≤B≤58.

3. The electrolyte according to claim 1 or 2, characterized in that 0.4≤c≤1.7； Preferably, 0.9≤d≤2.8; Preferably, 5≤e≤9.

4. The electrolyte according to any one of claims 1 to 3, characterized in that 0.1≤Y≤3。 5. The electrolyte according to any one of claims 1 to 4, characterized in that The carboxylic acid ester includes ethyl acetate and / or methyl acetate.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The first additive includes at least one of lithium difluorophosphate LiPO2F2, lithium difluorooxalatoborate LiDFOP, lithium dioxalatoborate LiBOB, lithium difluorooxalatophosphate LiDFOB, and lithium tetrafluoroborate LiBF4.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The second additive includes at least two of sulfates, sulfonates, thiophene sulfur-containing additives, phosphates, and borates; Preferably, the second additive includes at least one of ethylene sulfate DTD, methylene methanedisulfonate MMDS, benzo[1,2-b:4,5-b']dithiophene-4,8-dione BDTD, 1,3-propane sultone PS, tris(trimethylsilyl)phosphate TMSP and bis(trimethylsilyl)borate TMSB.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The third additive includes fluoroethylene carbonate FEC and / or ethylene carbonate VC.

9. The electrolyte according to any one of claims 1 to 8, characterized in that The lithium salt includes lithium hexafluorophosphate and / or lithium bis(fluorosulfonyl)imide LiFSI; Preferably, the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 2 mol / L.

10. A battery comprising a positive electrode, a negative electrode, a separator and an electrolyte, characterized in that: The electrolyte is the electrolyte according to any one of claims 1 to 9; The positive electrode is a lithium iron phosphate positive electrode.

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