Electrolyte and use thereof

Abstract

An electrolyte and a use thereof, belonging to the technical field of new energy. Raw materials for preparing the electrolyte comprise a solvent, an additive, and a lithium salt. The solvent comprises a fluoroether solvent. The additive comprises p-benzoquinone, an acid anhydride and isocyanate, the mass proportions of the p-benzoquinone, the acid anhydride and the isocyanate in the electrolyte being x%, y% and z%, respectively, such that 0.1≤x+y-2z≤1, 0.2≤x / y≤1.5, 0.1≤x / z≤2, and 0.5≤y / z≤2.5. The electrolyte can be effectively adapted to high-voltage lithium cobalt oxide, high-silicon negative electrodes, and lithium supplementing material systems of 4.53 V or above. The additive can absorb residual alkali, singlet oxygen and water, improve the adaptability of the electrolyte, and broaden the working voltage window of the electrolyte. The energy density, cycle performance and safety performance of lithium ion batteries comprising the electrolyte are also improved.

Description

An electrolyte and its application Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to an electrolyte and applications thereof. Background Art

[0002] With the advancement of electronic technology, portable devices have increasingly higher requirements for energy sources, that is, batteries. While meeting cycle life requirements, they also need to take into account high-rate charge and discharge performance, and even more importantly, increase the volume energy density of lithium-ion batteries. Currently, there are two effective ways to increase the energy density of lithium-ion batteries: one is to increase the battery voltage, and the other is to increase the gram capacity of the positive and negative active materials. Specifically:

[0003] Replacing existing graphite materials with higher gram capacity negative electrode materials is an effective way to improve energy density. Among various new negative electrode materials with certain application prospects, silicon stands out due to its excellent comprehensive performance and has become the next generation negative electrode material most likely to be applied on a large scale. However, the initial efficiency of silicon materials is low, so lithium replenishment technology needs to be used in silicon negative electrode systems. Lithium ferrite (Li5FeO4, abbreviated as LFO) is a lithium replenisher with excellent performance, but it requires the addition of excessive lithium carbonate Li2CO3 during its production process, which is difficult to remove by water washing and other methods; at the same time, LFO will release singlet oxygen during the cycle, which will cause oxidation of the electrolyte; that is, in a lithium replenishment system containing LFO, residual alkali and singlet oxygen are prone to occur.

[0004] Using high-gram capacity cathode materials is also a way to increase energy density. Compared to other types of cathode materials, high-nickel cathode materials have higher gram-to-gram capacity. However, as the nickel content increases, the residual alkali on the cathode material surface becomes more difficult to remove. In other words, high residual alkali is more likely to occur in high-nickel systems.

[0005] Increasing the battery's charge cut-off voltage can also increase energy density to a certain extent. However, after increasing the voltage, the electrolyte is also easily oxidized by the positive electrode.

[0006] In summary, there is an urgent need to develop an electrolyte that can reduce the impact of residual alkali on the electrochemical system, while absorbing singlet oxygen, reducing its side reactions on the electrolyte, reducing gas production and improving cycle performance.

[0007] Summary of the Invention

[0008] The present invention aims to address at least one of the technical problems existing in the prior art. To this end, the present invention provides an electrolyte compatible with lithium ferrite, a lithium supplement, to alleviate the oxygen release problem that occurs during subsequent discharge of the lithium ferrite, thereby improving the cycle performance and service life of lithium-ion batteries with silicon anode systems.

[0009] The present invention also provides a lithium ion battery comprising the electrolyte.

[0010] According to an embodiment of the first aspect of the present invention, there is provided an electrolyte, wherein raw materials for preparing the electrolyte include a solvent, an additive, and a lithium salt;

[0011] The solvent includes a fluoroether solvent;

[0012] The additives include p-benzoquinone, acid anhydride and isocyanate;

[0013] The structural formula of the isocyanate is shown in Formula VIII:

[0014] The mass proportion of the p-benzoquinone in the electrolyte is x%, the mass proportion of the acid anhydride in the electrolyte is y%, and the mass proportion of the isocyanate in the electrolyte is z%; the relationship is satisfied: 0.1≤x+y-2z≤1; 0.2≤x / y≤1.5; 0.1≤x / z≤2; 0.5≤y / z≤2.5; and the value of x is 0.1~3; the value of y is 0.1~5; and the value of z is 0.1~5.

[0015] The electrolyte according to the embodiment of the present invention has at least the following beneficial effects:

[0016] The electrolyte provided by the present invention uses p-benzoquinone, acid anhydride and isocyanate as a combination additive in a fluorinated solvent and is controlled within the above-mentioned mass range. The electrolyte system is compatible with the high-silicon negative electrode / lithium supplement material system. P-benzoquinone can absorb singlet oxygen, and acid anhydride can reduce the amount of residual alkali by neutralizing residual alkali, thereby reducing the gas production caused by residual alkali. Isocyanate can absorb water produced by the neutralization reaction of acid anhydride and residual alkali. The two work synergistically to absorb moisture in the lithium-ion battery system, inhibit lithium salt decomposition and high-voltage gas production caused by trace moisture, and improve the cycle life of the lithium-ion battery. Further, usually, the residual alkali (mainly referring to the residual alkali on the surface of the lithium supplement agent) content is usually 500 to 5000 ppm. In the present invention, the amount of isocyanate added is an excess component relative to the water content. When the isocyanate is excessive, only biuret compounds will be generated, and no gas will be generated. It can be seen from this that in the electrolyte provided by the present invention, the energy density, operating voltage, cycle performance and safety performance of the lithium-ion battery including the electrolyte can be significantly improved by matching the additives.

[0017] In the electrolyte provided by the present invention, by adding a specific type of solvent, the oxidation resistance of the electrolyte can be improved while improving the solvation structure; the solvent and the additive can work together to improve the comprehensive performance of the obtained electrolyte. Specifically, the oxidation resistance of the electrolyte is significantly improved, and it can adapt to high-voltage LiCoO2 (positive electrode) of 4.53V and above, high-silicon negative electrode / lithium supplement material system, and improve the high-voltage cycle performance, high-temperature storage performance and hot box performance of lithium-ion batteries.

[0018] In summary, in the electrolyte provided by the present invention, by adopting specific types of solvents and additives and limiting the dosage relationship of the additives, the obtained electrolyte can be well adapted to high-voltage lithium cobalt oxide, high-silicon negative electrode and lithium-supplementing material systems of 4.53V and above, and the energy density, cycle performance and safety performance of lithium-ion batteries including the electrolyte are also improved.

[0019] According to some embodiments of the present invention, the structural formula of the fluoroether in the fluoroether solvent is as shown in Formula I;

[0020] In formula I, R1 to R2 are independently selected from one of a C1 to C10 unsubstituted alkyl group and a C1 to C10 substituted alkyl group.

[0021] According to some embodiments of the present invention, in Formula I, the C1-C10 substituted alkyl group is a C1-C10 alkyl group substituted with F, or a C1-C10 alkyl group substituted with a heterocycle, wherein the heterocycle contains S or N. More specifically, the heterocycle may be a pyridine ring.

[0022] According to some embodiments of the present invention, the fluoroether solvent is one of the compounds represented by Formula II to Formula III:

[0023] In fluoroether solvents, after H is replaced by F, F has a strong electron-withdrawing effect, which can reduce the energy of the solvent's HOMO orbital, making it more difficult for the electrons in its HOMO orbital to be captured. Therefore, after fluorination, the solvent's oxidation resistance can be significantly improved, thereby extending the battery's cycle life. At the same time, fluoroether solvents can undergo reduction decomposition on the negative electrode surface to form a solid electrolyte interface film (SEI) rich in LiF. The interface film has a higher Young's modulus, which can effectively suppress the SEI film rupture caused by the volume effect of the silicon negative electrode during charge and discharge, and has a higher ionic conductivity, which can effectively suppress the formation of lithium dendrites. At the same time, organic fluorine compounds have good flame retardant properties, and therefore can significantly improve the battery's cycle performance, high temperature performance, and hot box performance. That is, the fluoroether solvents selected by the present invention can improve the cycle performance, high temperature resistance, and high voltage resistance of the electrolyte.

[0024] According to some embodiments of the present invention, the mass percentage of the fluoroether solvent in the electrolyte is 1 to 25%.

[0025] According to some embodiments of the present invention, the mass percentage of the fluoroether solvent in the electrolyte is 2.5-12%, more specifically about 11%.

[0026] According to some embodiments of the present invention, the solvent further comprises at least two of chain carbonates, cyclic carbonates and carboxylic acid ester compounds.

[0027] According to some embodiments of the present invention, the chain carbonate includes at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0028] According to some embodiments of the present invention, the cyclic carbonate includes at least one of propylene carbonate (PC) and ethylene carbonate (EC).

[0029] According to some embodiments of the present invention, the carboxylate compound includes at least one of ethyl propionate (EP) and ethyl acetate (EA).

[0030] According to some embodiments of the present invention, the nitrile compound includes at least one of acetonitrile and propionitrile.

[0031] According to some embodiments of the present invention, the solvent is a mixture of the fluoroether solvent, cyclic carbonate, chain carbonate and carboxylate.

[0032] The mass ratio of the fluoroether solvent to the cyclic carbonate is 1:0.8 to 1.2, for example, about 1:1.

[0033] The mass ratio of the fluoroether solvent to the chain carbonate is 1:1.5 to 2.5, for example, about 1:2.

[0034] The mass ratio of the fluoroether solvent to the carboxylic acid ester is 1:1.5 to 2.5, for example, about 1:2.

[0035] According to some embodiments of the present invention, the mass percentage of p-benzoquinone (CAS: 106-51-4) in the electrolyte is 0.3-2%, more specifically about 1% or 1.5%.

[0036] According to some embodiments of the present invention, the structural formula of the acid anhydride is shown in Formula IV:

[0037] In formula IV, R4 and R5 are independently selected from one of a C1-C10 unsubstituted hydrocarbon group and a C1-C10 substituted hydrocarbon group; and R4 and R5 exist independently or form a ring.

[0038] According to some embodiments of the present invention, in Formula IV, when R4 and R5 are selected from C1-C10 substituted hydrocarbon groups, the C1-C10 substituted hydrocarbon groups contain at least one heteroatom selected from F, N, S and Si.

[0039] According to some embodiments of the present invention, the acid anhydride comprises at least one of the compounds represented by Formula V to Formula VII:

[0040] (CAS:71016-95-0, cyclopentanecarboxylic anhydride),

[0041] (CAS: 4744-50-7, 2,3-pyrazine dianhydride),

[0042] (CAS: 6007-85-8, 3,4-thiophenedicarboxylic anhydride);

[0043] In formula IV, R4 is selected from one of C1-C10 unsubstituted alkyl and C1-C10 substituted alkyl;

[0044] According to some embodiments of the present invention, the acid anhydride is one of the compounds represented by Formula V to Formula VII.

[0045] According to some embodiments of the present invention, the mass percentage of the acid anhydride in the electrolyte is 0.2-4%, for example, about 1.5%, 2%, 2.5% or 3%.

[0046] According to some embodiments of the present invention, in Formula VIII, R6 is selected from C1 to C 15 Hydrocarbon group.

[0047] According to some embodiments of the present invention, in Formula VIII, when R6 is a substituted hydrocarbon group, the substituted hydrocarbon group contains at least one of F, N, S and Si heteroatoms.

[0048] According to some embodiments of the present invention, the isocyanate includes a compound represented by Formula IX or Formula X:

[0049] (CAS: 101-68-8, 4,4'-methylenebis(phenyl isocyanate)),

[0050] (CAS: 584-84-9, toluene-2,4-diisocyanate).

[0051] According to some embodiments of the present invention, the mass percentage of the isocyanate in the electrolyte is 0.3-3%, for example, about 1%, 1.5%, 2% or 2.5%.

[0052] According to some embodiments of the present invention, 0.3≤x+y-2z≤0.8, and more specifically approximately equal to 0.5.

[0053] According to some embodiments of the present invention, 0.5≤x / y≤1, and more specifically approximately equal to 0.75.

[0054] According to some embodiments of the present invention, 0.8≤x / z≤1.2, and more specifically approximately equal to 1.

[0055] According to some embodiments of the present invention, 1≤y / z≤1.5, more specifically 1.3-1.4.

[0056] According to some embodiments of the present invention, the additive further includes a film-forming additive.

[0057] According to some embodiments of the present invention, the film-forming additive includes at least one of 1,3-propane sultone (PS), diethylene sulfate (DTD), fluoroethylene carbonate (FEC), tris(trimethylsilyl) borate (TMSB) and tris(trimethylsilyl) phosphate (TMSP).

[0058] When the film-forming additive includes the fluoroethylene carbonate, the film-forming additive and other additives, as well as the solvent, act synergistically to form a SEI film with stable structure and high electronic conductivity on the surface of the negative electrode, which can inhibit the growth of lithium dendrites and weaken the side effects caused by the volume change of the negative electrode active material, ultimately significantly improving the cycle performance, high temperature performance and hot box performance of the electrolyte.

[0059] According to some embodiments of the present invention, the mass percentage of the film-forming additive in the electrolyte is 8-20%, for example, about 10%, 12%, 15%, 17% or 20%.

[0060] According to some embodiments of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiODFP), lithium tetrafluorooxalatophosphate (LiOTFP), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) and lithium bis(fluorosulfonyl imide) (LiFSI).

[0061] According to some embodiments of the present invention, the lithium salt accounts for 8-25% by mass of the electrolyte, for example, about 10%, 12%, 14%, 15%, 17% or 20%.

[0062] According to some embodiments of the present invention, raw materials for preparing the electrolyte include a solvent, an additive, and a lithium salt;

[0063] The solvent is a mixture of the fluoroether solvent, cyclic carbonate, chain carbonate and carboxylate in a mass ratio of 1:0.8-1.2:1.5-2.5:1.5-2.5; the mass percentage of the fluoroether solvent in the electrolyte is 1-25%;

[0064] Measured by mass percentage of the electrolyte, the additives include:

[0065] According to an embodiment of the second aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator separated from the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are infiltrated by the electrolyte, and the positive electrode comprises a positive electrode current collector and a positive electrode coating provided on the surface of the positive electrode current collector.

[0066] Because the lithium-ion battery utilizes all of the technical solutions of the electrolyte of the aforementioned embodiment, it exhibits at least all of the beneficial effects of the technical solutions of the aforementioned embodiment. Specifically, when using the same positive and negative electrodes, the lithium-ion battery utilizing the electrolyte of the present invention exhibits higher energy density, can be charged and discharged at higher voltages, and exhibits improved cycle performance and safety.

[0067] According to some embodiments of the present invention, the positive electrode current collector includes aluminum foil.

[0068] According to some embodiments of the present invention, the positive electrode coating includes a lithium supplement.

[0069] According to some embodiments of the present invention, the lithium supplement includes at least one of Li5FeO4, LiNiO2 and Li2O.

[0070] According to some embodiments of the present invention, the lithium supplement accounts for 0.5-5% by mass of the positive electrode coating, for example, about 1%, 1.5% or about 2%.

[0071] According to some embodiments of the present invention, the positive electrode coating further includes a positive electrode active material, a positive electrode binder and a conductive agent.

[0072] in:

[0073] The positive electrode active material includes at least one of a polyanion material, a layered material, and a spinel material. The layered material has a general formula of LiMO2, where M comprises at least one of nickel, cobalt, and manganese. More specifically, the layered material is lithium cobalt oxide, or lithium manganese oxide containing nickel, cobalt, and any combination thereof.

[0074] When the positive electrode active material includes lithium cobalt oxide, since the charging voltage of lithium cobalt oxide is generally high, when the voltage is higher than 4.50V, the crystal structure of lithium cobalt oxide tends to be unstable, and the structure is more likely to collapse during the cycle, resulting in the dissolution of metal ions in the lattice, leading to electrolyte oxidation and increased impedance, thereby deteriorating the cycle performance. During the cycle of the positive electrode active material LiCoO2, since the energy bands of Co and O in the lattice partially overlap, when Co loses electrons and is oxidized during the charging process, O will also participate in the charge transfer, resulting in O being converted into singlet oxygen. 1 O2, 1 O2 will subsequently be converted into active oxygen. Both have extremely strong oxidizing properties, causing the electrolyte to oxidize, generating gas that causes battery bloating and deterioration of cycle performance. However, p-benzoquinone has the function of forming a film on the surface of the positive electrode, forming a dense CEI, preventing the dissolution of transition metal ions, and at the same time, it can use its own unsaturated structure to absorb singlet oxygen. 1 O2, to avoid the release of lithium supplements 1 O2 causes oxidation of the electrolyte, thereby improving the battery's cycle performance and high-temperature storage performance.

[0075] The positive electrode conductive agent includes at least one of graphene, conductive carbon black (SP), and carbon nanotubes.

[0076] The positive electrode binder includes polyvinylidene fluoride (PVDF).

[0077] According to some embodiments of the present invention, the mass ratio of the positive electrode active material to the positive electrode conductive agent is 60 to 70:1, for example, about 63:1, 65:1, or about 64:1.

[0078] According to some embodiments of the present invention, the mass ratio of the positive electrode conductor to the positive electrode binder is 1:0.6-0.7.

[0079] According to some embodiments of the present invention, the negative electrode includes a negative electrode current collector and a negative electrode coating disposed on a surface of the negative electrode current collector.

[0080] According to some embodiments of the present invention, the negative electrode current collector includes copper foil.

[0081] According to some embodiments of the present invention, the negative electrode coating comprises a negative electrode active material.

[0082] According to some embodiments of the present invention, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, tin-based materials and silicon-based negative electrode materials. The silicon-based material includes silicon oxide materials (abbreviated as SiO x ) and at least one of silicon carbon material (abbreviated as SiC).

[0083] According to some embodiments of the present invention, the mass ratio of the graphite to the silicon-based negative electrode material is 3 to 5:1, for example, about 4:1.

[0084] According to some embodiments of the present invention, the negative electrode coating further comprises a negative electrode conductive agent, a thickener and a negative electrode binder.

[0085] The negative electrode conductive agent includes at least one of carbon nanotubes and graphene. The mass ratio of the negative electrode conductive agent to the negative electrode binder is 0.3 to 0.35:1. For example, it can be 0.32 to 0.33:1.

[0086] The thickener includes sodium carboxymethyl cellulose (CMC). The mass ratio of the thickener to the negative electrode binder is 0.25 to 0.35:1. For example, the mass ratio can be about 0.3:1.

[0087] The negative electrode binder includes at least one of polyacrylic acid (PAA) and styrene-butadiene rubber (SBR). The mass ratio of the negative electrode active material to the negative electrode binder is 20 to 25:1. For example, it can be 23 to 24:1.

[0088] According to some embodiments of the present invention, the lithium-ion battery further includes a separator, which is disposed between the positive electrode and the negative electrode.

[0089] In a lithium-ion battery system in which the positive electrode includes a lithium replenisher (especially Li5FeO4) and the negative electrode active material includes a silicon-based material: p-benzoquinone can absorb the singlet oxygen generated by the lithium replenisher, the acid anhydride can remove the residual alkali on the surface of the lithium replenisher through a neutralization reaction, reduce the amount of residual alkali on its surface, and reduce the gas production caused by the residual alkali, and the isocyanate can absorb the water produced by the neutralization reaction between the acid anhydride and the residual alkali. The two work synergistically to absorb the moisture in the lithium replenisher, inhibit the decomposition of lithium salts and high-voltage gas production caused by trace moisture, and improve the cycle life of the lithium-ion battery. Overall, the lithium-ion battery using the electrolyte can significantly inhibit the side effects of the lithium replenisher, improve the stability of the silicon-based negative electrode material, inhibit the occurrence of cracks on the surface of the silicon material particles during the cycle, and at the same time improve the stability of the positive electrode material surface and inhibit the dissolution of transition metal ions, thereby improving the battery's room temperature / high temperature cycle performance, high temperature storage performance and hot box performance.

[0090] According to some embodiments of the present invention, the charging cut-off voltage of the lithium-ion battery is ≥4.5V, for example, approximately 4.53V.

[0091] According to some embodiments of the present invention, the lithium-ion battery has a capacity retention rate of ≥86% over 400 cycles under the conditions of a charge cut-off voltage of 4.53V, a temperature of 25°C, and a charge / discharge rate of 0.7C / 0.5C. Specifically, the capacity retention rate may be approximately 87%.

[0092] According to some embodiments of the present invention, the lithium-ion battery has a capacity retention rate of ≥85% over 300 cycles under the conditions of a charge cut-off voltage of 4.53V, a temperature of 45°C, and a charge / discharge rate of 0.7C / 0.5C. Specifically, the capacity retention rate may be approximately 86%.

[0093] According to some embodiments of the present invention, the lithium-ion battery is maintained at 135±2° C. for 60 minutes, and the pass rate of not catching fire or exploding is 100%.

[0094] According to some embodiments of the present invention, the thickness expansion rate of the lithium-ion battery in a fully charged state after being stored at 85° C. for 24 hours is ≤3%, for example, approximately 2%, 2.3%, or approximately 2.5%.

[0095] According to some embodiments of the present invention, the capacity retention rate of the lithium-ion battery in a fully charged state after being stored at 85° C. for 24 hours is ≥86%, for example, approximately 87% or approximately 88%.

[0096] According to some embodiments of the present invention, the capacity recovery rate of the lithium-ion battery in a fully charged state after being stored at 85° C. for 24 hours is ≥90%, for example, approximately 91% or approximately 92%.

[0097] Unless otherwise specified, the term “about” in the present invention actually means that the error is allowed to be within the range of ±2%, for example, about 100 actually means 100±2%×100.

[0098] Unless otherwise specified, “between” in the present invention includes the number itself, for example, “between 2 and 3” includes the endpoint values ​​2 and 3.

[0099] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0100] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0101] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0102] Example 1

[0103] In this example, an electrolyte was prepared. The raw materials used are shown in Table 1. The specific steps are as follows:

[0104] In an argon-filled glove box, lithium salt was dissolved in a solvent;

[0105] The resulting mixture is mixed with additives.

[0106] Examples 2 to 5 and Comparative Examples 1 to 16 respectively prepared an electrolyte, which differed from Example 1 in that some of the preparation raw materials were different. The specific preparation raw materials are shown in Table 1.

[0107] Table 1 Raw materials for preparing electrolytes in Examples 1 to 5 and Comparative Examples 1 to 16

[0108] In Table 1, all ratios are mass ratios, and all percentages are mass percentages.

[0109] Application Examples

[0110] This example provides a lithium-ion battery, specifically:

[0111] Electrolyte: from Examples 1 to 5 and Comparative Examples 1 to 16. The obtained lithium-ion batteries are numbered according to the source of the electrolyte used.

[0112] Positive electrode: The preparation process is to mix the positive electrode active material lithium cobalt oxide LiCoO2 (Xiamen Tungsten New Energy), conductive agent Super P, binder polyvinylidene fluoride PVDF, and lithium supplement agent Li5FeO4 in a weight ratio of 96:1.5:1:1.5, and add them to N-methylpyrrolidone (NMP) to prepare the positive electrode slurry: the positive electrode slurry is coated on the positive electrode current collector aluminum foil, dried at 85°C and cold pressed, and then trimmed, cut and stripped, and dried at 85°C under vacuum conditions for 4 hours, and the pole ears are welded.

[0113] Negative electrode: The preparation process is to mix the anode active material graphite (Shenzhen Beterry) and silicon oxide SiOx, the conductive agent carbon nanotubes CNT, the thickener sodium carboxymethyl cellulose (CMC) and the binder polyacrylic acid (PAA) in a weight ratio of 93.5:1.3:1.2:4, wherein the mass ratio of graphite and silicon oxide in the anode active material is 4:1; deionized water is added to the obtained mixture and mixed evenly to prepare the negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, dried at 85°C, and then trimmed, cut into pieces, and striped, and then dried at 85°C under vacuum conditions for 12 hours.

[0114] The diaphragm was purchased from Shenzhen Xingyuan.

[0115] Preparation of lithium-ion batteries: stack the positive electrode, separator, and negative electrode in order, with the separator placed between the positive and negative electrode sheets, and wind them to obtain a bare cell; place the bare cell in an aluminum-plastic film outer package, inject the electrolyte obtained in the example or comparative example into the dried cell, encapsulate, let it stand, form, shape, and divide the capacity to complete the preparation of lithium-ion soft-pack batteries.

[0116] In the lithium-ion battery, the cell design capacity is 4500mAh, the N / P ratio is 1.05, the liquid filling coefficient is 1.8g / Ah, and the liquid retention coefficient is 1.3g / Ah.

[0117] Test Case

[0118] This example tests the electrochemical performance of the lithium-ion battery obtained in the application example. Specifically:

[0119] (1) Normal temperature cycle performance test: In a 25°C environment, the divided battery is charged to 4.53V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. After 400 cycles of charge and discharge, the capacity retention rate at the 400th week is calculated. The calculation formula is as follows:

[0120] 400th cycle capacity retention rate (%) = (400th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0121] The first cycle discharge capacity refers to the discharge capacity of the first cycle after formation and capacity separation are completed.

[0122] (2) High temperature cycle performance test: In a 45°C environment, the divided battery is charged to 4.53V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. After 300 cycles of charge and discharge, the capacity retention rate at the 300th week is calculated. The calculation formula is as follows:

[0123] 300th cycle capacity retention rate (%) = (300th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0124] (3) 85℃ / 24h high temperature storage test: The divided battery is placed at room temperature and charged and discharged once at 0.5C (4.53V-3.0V), and the discharge capacity C0 of the battery before storage is recorded. Then the battery is charged to 4.53V (100% SOC) at 1C constant current and constant voltage. The thickness d1 of the battery before high temperature storage is measured using a PPG battery thickness gauge (600g). The battery is placed in an 85℃ constant temperature box and stored for 24h. After the storage is completed, the battery is taken out and the thermal thickness d2 of the battery after storage is measured. The thickness expansion rate of the battery after storage at 85℃ for 24h is calculated. After the battery is cooled at room temperature for 24h, the battery is again discharged at 0.5C constant current to 3.0V, and then charged to 4.53V at 0.5C constant current and constant voltage. The discharge capacity C1 and charge capacity C2 of the battery after storage are recorded. The capacity remaining rate and recovery rate of the battery after storage at 85℃ for 24h are calculated as follows:

[0125] Thickness expansion ratio after storage at 85℃ for 24h = (d2-d1) / d1*100%;

[0126] After storage at 85℃ for 24h, the remaining capacity is C1 / C0*100%.

[0127] After storage at 85°C for 24 hours, the capacity recovery rate = C2 / C0*100%.

[0128] (4) Thermal shock performance: Under 25°C ambient conditions, discharge the battery to 3.0V at a given current of 0.2C; place it aside for 5 minutes; charge it to 4.53V at a charging current of 0.2C. When the cell voltage reaches 4.53V, change it to 4.53V constant voltage charging until the charging current ≤ the cut-off current of 0.05C; place it aside for 1 hour, then place the cell in an oven, and increase the oven temperature to 135±2°C at a rate of 5±2°C / min, and keep it for 60 minutes before stopping. The judgment standard is that the cell does not catch fire or explode. Six parallel tests are carried out for each group, and the number of cells that pass is recorded. For example, 6 / 6 means that six parallel tests were carried out, and all six cells did not catch fire or explode.

[0129] In the above electrical performance tests, the rate parameter is 1C=4500mA.

[0130] The results of the above performance tests are shown in Table 2.

[0131] Table 2 Electrochemical properties of lithium ion batteries including the electrolytes obtained in Examples 1 to 5 and Comparative Examples 1 to 16

[0132] According to Examples 1-5 and Comparative Examples 1-16, by introducing fluoroether solvents to partially replace conventional solvents, and introducing additives such as benzoquinone, acid anhydride and isocyanate, the synergistic effect between them effectively reduces the residual alkali content on the surface of the lithium replenisher particles, reduces the gas production caused by it in the later cycle process, and improves the oxidation resistance of the electrolyte. This makes the electrolyte adaptable to high-voltage LiCoO2+ high-silicon negative electrode / lithium replenisher material systems of 4.53V and above, thereby improving the high-voltage cycle performance, high-temperature storage performance and hot box performance of the battery.

[0133] Fluorinated ether solvents can significantly improve the oxidation resistance of the electrolyte system, thereby extending the cycle life of the battery. Fluorinated ether solvents can also undergo reduction and decomposition on the negative electrode surface, forming a LiF-rich solid electrolyte interface (SEI) film. This effectively inhibits the SEI film rupture caused by the volume effect of the silicon negative electrode during charge and discharge. Fluorinated organic compounds also have good flame retardant properties, thus significantly improving the battery's cycle performance, high-temperature performance, and hot box performance.

[0134] Benzoquinone has the function of forming a film on the surface of the positive electrode, forming a dense CEI, preventing the dissolution of transition metal ions, and at the same time can use its own unsaturated structure to absorb singlet oxygen 1 O2, to avoid the release of lithium supplements 1 O2 causes oxidation of the electrolyte, thereby improving the battery's cycle performance and high-temperature storage performance.

[0135] The interaction of electrolyte components improves the high-voltage, high-temperature, cycling, and safety performance of the high-voltage lithium cobalt oxide + high-silicon anode + cathode lithium supplement system. The resulting lithium-ion battery is expected to find widespread application in energy storage, power batteries, and the consumer electronics (3C) sector.

[0136] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. An electrolyte, characterized in that: The raw materials for preparing the electrolyte include solvent, additives and lithium salt; The solvent includes a fluoroether solvent; The additives include p-benzoquinone, acid anhydride and isocyanate; The structural formula of the isocyanate is shown in Formula VIII: In formula VIII, R6 is selected from substituted or unsubstituted hydrocarbon groups; The mass proportion of the p-benzoquinone in the electrolyte is x%, the mass proportion of the acid anhydride in the electrolyte is y%, and the mass proportion of the isocyanate in the electrolyte is z%; the relationship is satisfied: 0.1≤x+y-2z≤1; 0.2≤x / y≤1.5; 0.1≤x / z≤2; 0.5≤y / z≤2.5; and the value of x is 0.1~3; the value of y is 0.1~5; and the value of z is 0.1~5.

2. The electrolyte according to claim 1, characterized in that The structural formula of the fluoroether in the fluoroether solvent is shown in Formula I; In Formula I, R1 to R2 are independently selected from one of C1 to C10 unsubstituted alkyl and C1 to C10 substituted alkyl; Preferably, in the formula I, the C1-C10 substituted alkyl group is a C1-C10 alkyl group substituted with F, or a C1-C10 alkyl group substituted with a heterocycle; preferably, the fluoroether solvent is at least one of the compounds represented by formula II to formula III:

3. The electrolyte according to claim 1, characterized in that The solvent further comprises at least one of chain carbonate, cyclic carbonate, carboxylate and nitrile compound.

4. The electrolyte according to claim 1 or 3, characterized in that The mass percentage of the fluoroether solvent in the electrolyte is 1 to 25%.

5. The electrolyte according to claim 1, characterized in that The structural formula of the acid anhydride is shown in Formula IV: In formula IV, R4 and R5 are independently selected from one of a C1-C10 unsubstituted hydrocarbon group and a C1-C10 substituted hydrocarbon group; and R4 and R5 exist independently or form a ring; Preferably, in formula IV, when R4 and R5 are selected from C1-C10 substituted hydrocarbon groups, the C1-C10 substituted hydrocarbon groups contain at least one heteroatom selected from F, N, S and Si; Preferably, the acid anhydride comprises at least one of the compounds represented by Formula V to Formula VII:

6. The electrolyte according to claim 1, characterized in that In formula VIII, when R6 is a substituted hydrocarbon group, the substituted hydrocarbon group contains at least one heteroatom selected from the group consisting of F, N, S, and Si; Preferably, the isocyanate comprises a compound represented by formula IX or formula X:

7. The electrolyte according to claim 1, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, bistrifluoromethanesulfonyl imide lithium salt and lithium bisfluorosulfonyl imide; preferably, the lithium salt accounts for 8 to 25% by mass of the electrolyte; preferably, the additive further includes a film-forming additive; preferably, the film-forming additive includes at least one of 1,3-propane sultone, vinyl sulfate, fluoroethylene carbonate, tris(trimethylsilyl)borate and tris(trimethylsilyl)phosphate; preferably, the film-forming additive accounts for 8 to 20% by mass of the electrolyte.

8. A lithium-ion battery comprising a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are soaked in the electrolyte, characterized in that: The electrolyte is the electrolyte according to any one of claims 1 to 7; the positive electrode includes a positive electrode current collector and a positive electrode coating provided on the surface of the positive electrode current collector.

9. The lithium-ion battery according to claim 8, characterized in that The positive electrode coating includes a lithium supplement; preferably, the lithium supplement includes at least one of Li5FeO4, LiNiO2 and Li2O.

10. The lithium-ion battery according to claim 8, characterized in that The negative electrode includes a negative electrode current collector and a negative electrode coating arranged on the surface of the negative electrode current collector; preferably, the negative electrode coating includes a negative electrode active material; preferably, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, tin-based materials and silicon-based negative electrode materials.

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