Lithium ion battery and fast charging electrolyte thereof

Abstract

The invention relates to the technical field of batteries, and discloses a lithium ion battery and a fast charging electrolyte thereof, the electrolyte comprises a first injection electrolyte and a second injection electrolyte, and the volume ratio of the first injection electrolyte to the second injection electrolyte is (95: 5)-(50: 50); the first injection of electrolyte comprises a high-boiling-point solvent, a low-concentration high-thermal-stability lithium salt and a film-forming additive, the concentration of the low-concentration high-thermal-stability lithium salt is 0.5-1 mol / L, and the volume ratio of the high-boiling-point solvent to the low-concentration high-thermal-stability lithium salt to the film-forming additive is (75-85): (8-15): (2-5); the secondary injection electrolyte comprises a low-viscosity solvent, a high-concentration lithium salt, a film-forming repairing agent and a surfactant, the concentration of the high-concentration lithium salt is 1.5-3 mol / L, and the volume ratio of the low-viscosity solvent to the high-concentration lithium salt to the film-forming repairing agent to the surfactant is (75-85): (15-40): (0.5-20): (0.1-2). The electrolyte provided by the invention can reduce the film-forming internal resistance, improve the fast charging performance, improve the thermal decomposition temperature of the electrolyte, and improve the high-temperature storage and cycle performance.

Description

Technical Field

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

[0002] With the increasing breakthroughs in energy density of new energy batteries, it is crucial to develop batteries with fast charging performance. Such batteries mainly include the use of electrode materials with high lithium ion migration speed, the use of high porosity and air-permeable diaphragms, and the use of high conductivity and high wetting electrolytes.

[0003] In order to meet the fast charging performance, the current fast charging electrolyte usually uses a large amount of low boiling point solvents, such as lipid solvents (ethylene ethylene carbonate) and carbonate solvents (dimethyl carbonate). However, due to the large charging current density of the fast charging battery, the temperature rise is higher than other batteries, which leads to the poorer high temperature performance of the fast charging battery under the low boiling point solvent electrolyte. In order to solve this problem, the electrolyte secondary injection process is usually adopted. Generally, the electrolyte of the secondary injection process is two different electrolytes, among which one injection of electrolyte is a low viscosity and high conductivity electrolyte, and the second injection of electrolyte is a long cycle electrolyte.

[0004] In the related art, when applying the secondary injection process, the electrolyte viscosity is reduced by excluding electrolyte lithium salt in the second injection electrolyte to improve the wetting performance, low temperature performance and power performance. However, this solution does not pay attention to the high temperature problem caused by temperature rise, which reduces the high temperature storage and cycle performance. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems in the related art to a certain extent. To this end, the first purpose of the present invention is to provide a fast-charging electrolyte for lithium-ion batteries, which not only reduces the internal resistance of film formation and improves the fast-charging performance by combining two electrolytes with different components and different lithium salt concentrations, but also improves the thermal decomposition temperature of the electrolyte and the stability of the solid electrolyte interface film, thereby improving the high-temperature storage and cycle performance.

[0006] A second objective of the present invention is to provide a lithium-ion battery.

[0007] To achieve the above-mentioned purpose, the first embodiment of the present invention proposes a lithium-ion battery fast-charging electrolyte, comprising: one injection of electrolyte and two injections of electrolyte, the volume ratio of the one injection of electrolyte to the two injections of electrolyte is (95:5) to (50:50); the one injection of electrolyte comprises a high boiling point solvent, a low concentration and high thermal stability lithium salt and a film-forming additive, wherein the concentration of the low concentration and high thermal stability lithium salt is 0.5 to 1 mol / L, and the volume ratio of the high boiling point solvent, the low concentration and high thermal stability lithium salt and the film-forming additive is (75 to 85): (8 to 15): (2 to 5); the two injections of electrolyte comprise a low viscosity solvent, a high concentration lithium salt, a film-forming repair agent and a surfactant, wherein the concentration of the high concentration lithium salt is 1.5 to 3 mol / L, and the volume ratio of the low viscosity solvent, the high concentration lithium salt, the film-forming repair agent and the surfactant is (75 to 85): (15 to 40): (0.5 to 20): (0.1 to 2).

[0008] In addition, the lithium-ion battery fast-charge electrolyte according to the above embodiment of the present invention may also have the following additional technical features:

[0009] According to some embodiments of the present invention, the high boiling point solvent is at least one or more of carbonates, chain ethers, sulfones, and alkanones.

[0010] According to some embodiments of the present invention, the carbonate includes at least one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, and butylene carbonate; the chain ether includes ethylene glycol dimethyl ether and / or ethylene glycol diethyl ether; the sulfones include bis(4-nitrophenyl); and the alkanones include N-methyl-2-pyrrolidone and / or N-ethylpyrrolidone.

[0011] According to some embodiments of the present invention, the low-concentration high-thermal-stability lithium salt is at least one or more of lithium tetrafluoroborate, lithium hexafluoroarsenate, anhydrous lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorobisoxalate phosphate, lithium difluorophosphate, lithium trifluoromethylsulfonate, lithium difluorobisoxalate phosphate, lithium monooxalate bisfluoroborate, and lithium bis(trifluorosulfonyl)imide.

[0012] According to some embodiments of the present invention, the film-forming additive is at least one or more of vinyl carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl carbonate, vinyl acetate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(oxalatoboratefluorophosphate), lithium difluorophosphate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), lithium bis(oxalatodifluorophosphate), 1,3-propane sultone, vinyl sulfite, bis(vinyl sulfone), propylene sultone, dimethylthiomethane, vinyl vinyl sulfite, vinyl sulfate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, 3-fluoro-1,3-propane sultone, propylene sulfate, propylene sultone, siloxane, polyether polyol, acrylate, and styrene.

[0013] According to some embodiments of the present invention, the low viscosity solvent is at least one or more of dimethyl carbonate, methyl vinyl carbonate, dimethyltetrahydrofuran, tetrahydrofuran, 1,3-dioxolane, 1,2-dimethoxyethane, methyl acetate, methyl formate, methyl propionate, ethyl acrylate, and phenyl ether silane derivative solvents.

[0014] According to some embodiments of the present invention, the film-forming repair agent is an unsaturated ester additive, and the unsaturated ester additive is at least one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl carbonate, vinyl ethylene carbonate, and vinyl acetate.

[0015] According to some embodiments of the present invention, the surfactant is at least one or more of hydrofluoroether, polydimethylsiloxane, sodium dodecyl sulfate, trifluoromethylbenzene, silicone surfactant, and polyvinyl alcohol.

[0016] According to some embodiments of the present invention, one injection of electrolyte is used to be injected before the battery is formed to form a stable solid electrolyte interface film on the electrode surface; the second injection of electrolyte is used to be injected after the battery is formed and before aging to repair the solid electrolyte interface film.

[0017] According to an embodiment of the present invention, the lithium-ion battery fast-charge electrolyte comprises one injection of electrolyte and two injections of electrolyte, and the volume ratio of the one injection of electrolyte to the two injections of electrolyte is (95:5) to (50:50); the one injection of electrolyte comprises a high boiling point solvent, a low concentration of high thermal stability lithium salt and a film-forming additive, wherein the concentration of the low concentration of high thermal stability lithium salt is 0.5 to 1 mol / L, and the volume ratio of the high boiling point solvent, the low concentration of high thermal stability lithium salt and the film-forming additive is (75 to 85): (8 to 15): (2 to 5); the two injections of electrolyte comprise a low viscosity solvent, a high concentration of lithium salt, a film-forming repair agent and a surfactant, wherein the concentration of the high concentration of lithium salt is 1.5 to 3 mol / L, and the volume ratio of the low viscosity solvent, the high concentration of lithium salt, the film-forming repair agent and the surfactant is (75 to 85): (15 to 40): (0.5 to 20): (0.1 to 2). Therefore, the present electrolyte, through the combined use of two electrolytes with different compositions and different lithium salt concentrations, not only reduces the internal resistance of film formation and improves the fast charging performance, but also improves the thermal decomposition temperature of the electrolyte and the stability of the solid electrolyte interface film, thereby improving high-temperature storage and cycle performance.

[0018] To achieve the above object, a second embodiment of the present invention provides a lithium-ion battery, which is composed of a positive electrode, a negative electrode, a separator and the above-mentioned lithium-ion battery fast-charge electrolyte.

[0019] According to the lithium-ion battery of the embodiment of the present invention, by using two electrolytes with different components and different lithium salt concentrations in combination, not only the internal resistance of film formation is reduced and the fast charging performance is improved, but also the thermal decomposition temperature of the electrolyte and the stability of the solid electrolyte interface film are improved, thereby improving high-temperature storage and cycle performance.

[0020] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic diagram of a lithium-ion battery fast-charge electrolyte according to some embodiments of the present invention;

[0022] Figure 2 is a schematic diagram of the structural formula of a phenyl ether silane derivative solvent according to some embodiments of the present invention;

[0023] Figure 3 is a schematic diagram of the structural formula of 5,5-methyl-3,3-trimethylphenyl ether silane according to some embodiments of the present invention;

[0024] Figure 4 Schematic diagram of the structural formula of 5,5-hydroxy-3,3-trimethylphenyl ether silane according to some embodiments of the present invention. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0026] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the embodiments of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0027] As mentioned in the background technology section, with the increasing breakthroughs in energy density of new energy batteries, it is crucial to develop batteries with fast charging performance. Such batteries mainly include the use of electrode materials with high lithium ion migration speed, the use of high porosity and air-permeable diaphragms, and the use of high conductivity and high wetting electrolytes.

[0028] In order to meet the fast charging performance, the current fast charging electrolyte usually uses a large amount of low boiling point solvents, such as lipid solvents (ethylene ethylene carbonate) and carbonate solvents (dimethyl carbonate). However, due to the large charging current density of the fast charging battery, the temperature rise is higher than other batteries, which leads to the poorer high temperature performance of the fast charging battery under the low boiling point solvent electrolyte. In order to solve this problem, the electrolyte secondary injection process is usually adopted. Generally, the electrolyte of the secondary injection process is two different electrolytes, among which one injection of electrolyte is a low viscosity and high conductivity electrolyte, and the second injection of electrolyte is a long cycle electrolyte.

[0029] In the process of realizing the present invention, the applicant discovered that in the related art, when applying the secondary injection process, the electrolyte viscosity is reduced by not including electrolyte lithium salt in the second injection electrolyte to improve the wetting performance, low temperature performance and power performance, but this solution does not pay attention to the high temperature problem caused by temperature rise, thereby reducing the high temperature storage and cycle performance.

[0030] The lithium ion battery fast-charging electrolyte and the lithium ion battery provided in the embodiments of the present invention are described below with reference to the accompanying drawings.

[0031] refer to Figure 1 , is a schematic diagram of a lithium-ion battery fast-charge electrolyte according to some embodiments of the present invention.

[0032] The lithium-ion battery fast-charge electrolyte of the embodiment of the present invention includes a first-injection electrolyte and a second-injection electrolyte, and the volume ratio of the first-injection electrolyte to the second-injection electrolyte is (95:5) to (50:50).

[0033] Preferably, the volume ratio of the first injection electrolyte to the second injection electrolyte is (90:10) to (80:20).

[0034] It should be noted that the volume ratio of the first injection of electrolyte and the second injection of electrolyte is only the volume ratio indicated by the most preferred embodiment. In specific implementations, the range of the volume ratio can be flexibly set according to actual needs.

[0035] One injection of electrolyte is used to be injected before the battery is formed to form a stable solid electrolyte interface film on the electrode surface; the second injection of electrolyte is used to be injected after the battery is formed and before aging to repair the solid electrolyte interface film.

[0036] The electrolyte can be injected by negative pressure injection, ultrasonic injection, and temperature difference injection. Among them, negative pressure injection refers to the formation of negative pressure inside the battery so that the electrolyte enters the battery cell under the pressure difference. Isobaric injection is to first inject the electrolyte using the differential pressure principle, and then move the battery cell to a high-pressure container for static circulation to increase the electrolyte infiltration rate. Ultrasonic injection is a method that uses ultrasonic energy to promote the infiltration of electrolyte inside the battery. Ultrasonic waves can produce tiny bubbles. When these bubbles collapse, they will produce strong local shock waves, which will help break the gas barrier inside the battery and allow the electrolyte to penetrate into every corner of the battery more evenly. This method can improve the injection efficiency and battery consistency. Temperature difference injection is a method that uses temperature differences to promote electrolyte infiltration. By controlling the temperature of the injection environment, the viscosity of the electrolyte can be reduced and its fluidity can be increased, thereby accelerating the diffusion rate of the electrolyte inside the battery. For example, injecting at a higher temperature and then letting the battery stand in a low temperature environment can use the temperature gradient to promote the penetration and distribution of the electrolyte.

[0037] It should be explained that during the injection operation, the injection amount needs to be strictly controlled to ensure that the battery capacity meets expectations. If the injection amount is insufficient, the battery capacity may be reduced and the expected discharge platform cannot be reached. In addition, too high an injection temperature may cause an abnormal increase in the internal temperature of the battery and even cause thermal runaway. Therefore, it is necessary to check the heating and cooling systems to ensure their normal operation, and adjust the temperature control parameters or replace faulty components if necessary. Pressure control during the injection process is also very important. Abnormal pressure may be caused by blockage in the injection pipeline or malfunction of the pump. The injection system needs to be checked to ensure that there is no blockage or leakage, and the cleanliness of the pipeline should be checked at the same time.

[0038] An electrolyte includes a high boiling point solvent, a low concentration of a high thermal stability lithium salt and a film-forming additive, wherein the boiling point of the high boiling point solvent is greater than 100°C, the concentration of the low concentration of a high thermal stability lithium salt is 0.5 to 1 mol / L, and the thermal decomposition temperature of the low concentration of a high thermal stability lithium salt is greater than 100°C, and the volume ratio of the high boiling point solvent, the low concentration of a high thermal stability lithium salt and the film-forming additive is (75 to 85):(8 to 15):(2 to 5).

[0039] The high boiling point solvent includes, but is not limited to, at least one or more of carbonates, chain ethers, sulfones, and alkanones.

[0040] Wherein, carbonate comprises at least one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (EMC), butylene carbonate (BC). Chain ether comprises at least one or two of ethylene glycol dimethyl ether (DME) and ethylene glycol diethyl ether (DEE). Sulfone comprises bis(4-nitrophenyl) (DNPC). Alkanone comprises at least one or two of N-methyl-2-pyrrolidone (NMP) and N-ethylpyrrolidone (NEP).

[0041] Low-concentration, high-thermal-stability lithium salts include, but are not limited to, at least one or more of lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), anhydrous lithium perchlorate (LiClO4), lithium bis(trifluoromethylsulfonyl)imide (LiNTf2), lithium difluorobis(oxalate)phosphate (LiODFP), lithium difluorophosphate (LiPF2), lithium trifluoromethylsulfonate (LiCF3SO3), lithium difluorobis(oxalate)phosphate (LiODFP), lithium monooxalatobis(fluoroborate) (LiDFOB), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0042] Film-forming additives include vinyl carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), vinyl carbonate (CC), vinyl acetate (VA), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium bis(oxalatoborate) fluorophosphate (LiTFOP), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), lithium bis(fluorosulfonyl imide) (LiFSI), lithium bis(oxalatodifluorophosphate) (LiBODFP), 1,3-propane sultone (PS), At least one or more of vinyl sulfate (ES), bisvinyl sulfone (DES), propene sultone (PES), dimethylthiomethane (DMS), vinyl vinyl sulfite (VES), vinyl sulfate (DTD), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), 3-fluoro-1,3-propane sultone (FPS), propene sulfate (SPA), propene sultone (PTS), siloxane (SiOx), polyether polyol (PPG), acrylate (Ac), and styrene (St).

[0043] The second injection electrolyte includes a low-viscosity solvent, a high-concentration lithium salt, a film-forming repair agent and a surfactant, which is mainly used to improve the performance of the electrolyte, improve the cycle stability, safety and low-temperature performance of the battery, and can effectively improve the performance of the battery. Among them, the viscosity value of the low-viscosity solvent is less than 0.7mPa·s (40°C), the concentration of the high-concentration lithium salt is 1.5~3mol / L, and the volume ratio of the low-viscosity solvent, high-concentration lithium salt, film-forming repair agent and surfactant is (75~85): (15~40): (0.5~20): (0.1~2).

[0044] The low viscosity solvent includes at least one or more of dimethyl carbonate (DMC), ethylene methyl carbonate (EMC), dimethyltetrahydrofuran (DMTHF), tetrahydrofuran (THF), 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DME), methyl acetate (MA), methyl formate (MF), methyl propionate (MP), ethyl acrylate (EA), and phenyl ether silane derivative solvents, wherein reference Figure 2 , is a schematic diagram of the structural formula of a phenyl ether silane derivative solvent according to some embodiments of the present invention, wherein R1 and R2 are independently selected from hydrogen, halogen elements (fluorine, chlorine, bromine), alkenyl groups, cyano groups, phosphate groups, and the like.

[0045] The film-forming repair agent includes unsaturated ester additives, and the unsaturated ester additives include at least one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), vinyl carbonate (CC), vinyl ethylene carbonate (AEC), and vinyl acetate (VA).

[0046] The surfactant includes, but is not limited to, at least one or more of hydrofluoroether (HFE), polydimethylsiloxane (PDMS), sodium dodecyl sulfate (SDS), trifluoromethylbenzene (BTF), silicone surfactant, and polyvinyl alcohol (PVA).

[0047] As a first specific example, the effect of phenyl ether silane solvent derivatives on the performance of the battery cell is compared. Figure 3 and Figure 4 , respectively, are schematic diagrams of the structural formula of 5,5-methyl-3,3-trimethylphenyl ether silane according to some embodiments of the present invention and schematic diagrams of the structural formula of 5,5-hydroxy-3,3-trimethylphenyl ether silane according to some embodiments of the present invention, and two solvents, 5,5-methyl-3,3-trimethylphenyl ether silane and 5,5-hydroxy-3,3-trimethylphenyl ether silane, are synthesized respectively, and the synthesis method thereof is as follows:

[0048] Reference Table 1 shows the formula and injection ratio of electrolyte 1, electrolyte 2, and electrolyte 3. Using chlorotoluene and 3-methylcresol as raw materials, 3,3'-trimethylphenyl ether is prepared by WiIIiamm reaction, and then 5,5-methyl-3,3-trimethylphenyl ether silane is prepared by reacting trimethylsilane bromide with 3,3'-trimethylphenyl ether at 35-65°C. Under the action of a catalyst, 5,5-methyl-3,3-trimethylphenyl ether silane is hydrolyzed into 5,5-methyl-3,3-trimethylphenyl ether silane by hydrolysis. Among them, the WiIIiamm reaction is an organic chemical reaction used to prepare ether compounds.

[0049] The four electrolyte formulations in Table 1 were prepared respectively, among which formulation 1 was a one-shot electrolyte formulation; 5,5-methyl-3,3-trimethylphenyl ether silane solvent was added to formulation 3 and formulated with formulation 2 to form electrolyte 2, which was a two-shot electrolyte; 5,5-hydroxy-3,3-trimethylphenyl ether silane solvent was added to formulation 4 and formulated with formulation 2 to form electrolyte 3, which was a two-shot electrolyte.

[0050] Then, the three electrolytes were respectively injected into the 10Ah lithium iron phosphate / graphite soft pack battery system in proportion, and the two-injection electrolyte formula 3 and formula 4 were injected after the formation process. After aging and capacity separation, the three groups of batteries were respectively subjected to 2.5C constant current and constant voltage charging, mixed power pulse characteristics, and 60°C high temperature storage for 30 days. Refer to Table 2 for the performance test results of electrolyte 1, electrolyte 2, and electrolyte 3. The results show that the two-injection method, using the developed 5,5-methyl-3,3-trimethylphenyl ether silane solvent and 5,5-hydroxy-3,3-trimethylphenyl ether silane solvent, can not only improve the constant current charging ratio under fast charging, but also improve high temperature storage and cycle performance.

[0051] Table 1

[0052]

[0053] Table 2

[0054]

[0055] As a second specific embodiment, the effect of the dispersant on the performance of the battery cell is compared. Referring to Table 3, the formulas and injection ratios of electrolyte 4 and electrolyte 5 are shown, and the electrolytes of the three formulas in Table 3 are prepared respectively. Among them, formula 5 and formula 6 are combined to form electrolyte 4 (two injections of electrolyte); formula 5 and formula 7 are combined to form electrolyte 5 (two injections of electrolyte). Formula 7 adds 0.3% hydrofluoroether dispersant relative to formula 6.

[0056] Then, the two electrolytes were respectively injected into the 150Ah nickel manganese cobalt oxide lithium / graphite square shell battery system according to the proportion. Formula 6 and Formula 7 in the second injection electrolyte were injected after the formation process. After aging and capacity separation, the three groups of batteries were subjected to 2.5C constant current and constant voltage charging, mixed power pulse characteristics, 55℃ high temperature storage for 7 days, and 45℃ cycle test results as shown in Table 4. The results show that the addition of dispersants helps to reduce internal resistance, improve fast charging, and improve high temperature cycling and storage.

[0057] Table 3

[0058]

[0059]

[0060] Table 4

[0061]

[0062] As a third specific example, the effect of the content of 5,5-methyl-3,3-trimethylphenyl ether silane on the performance of the battery cell was verified. Formula 2 was one injection of electrolyte, and Formulas 8, 9, and 10 were prepared respectively. The three formulas with MP:5,5-methyl-3,3-trimethylphenyl ether silane in the ratio of 3:7, 4:6, and 5:5 were two injections of electrolyte. The other ingredients of the two injections of electrolyte are detailed in Table 5, which is the formula and injection ratio of Electrolyte 7, Electrolyte 8, and Electrolyte 9.

[0063] Then, the three electrolytes were respectively injected into the 10Ah lithium iron phosphate / graphite soft pack battery system in proportion, and the second electrolyte formulation 8, formulation 9, and formulation 10 were injected after the formation process. After aging and capacity separation, the three groups of batteries were subjected to 4C constant current and constant voltage charging, mixed power pulse characteristics, and 60°C high temperature storage for 30 days. The test results are shown in Table 6, which are the test results of the performance of electrolyte 6, electrolyte 7, and electrolyte 8. The results show that the increase in the content of 5,5-methyl-3,3-trimethylphenyl ether silane is conducive to fast charging and reduces the internal resistance to a certain extent, but has little effect on high temperature storage and cycling.

[0064] Table 5

[0065]

[0066]

[0067] Table 6

[0068]

[0069] As a fourth specific embodiment, the effect of different lithium salt concentrations of two injections of electrolyte on the performance of the battery cell is verified. Formula 2 is one injection of electrolyte, and Formula 11, Formula 12, Formula 13, and Formula 14 are prepared respectively, and their lithium salt concentrations are 1 mol / L, 1.5 mol / L, 2 mol / L, and 2.5 mol / L, respectively, which are two injections of electrolyte. For other ingredients, see Table 7, which is the formula and injection ratio of electrolyte 12, electrolyte 13, electrolyte 14, and electrolyte 6.

[0070] Then, the four electrolytes were injected into the 10Ah lithium iron phosphate / graphite soft pack battery system in proportion. After aging and capacity separation, the three groups of batteries were subjected to 4C constant current and constant voltage charging, mixed power pulse characteristics, 60℃ high temperature storage for 30 days, and -20℃ low temperature discharge retention rate test results. Table 8 shows the performance test results of electrolyte 9, electrolyte 10, electrolyte 11, and electrolyte 12. The results show that the increase in the lithium salt concentration of the two injected electrolytes is conducive to fast charging, and high temperature storage and cycling are improved, but the internal resistance increases slightly.

[0071] Table 7

[0072]

[0073]

[0074] Table 8

[0075]

[0076] As a fifth specific embodiment, the effects of different boiling point solvents in an electrolyte on the high temperature performance of the battery cell are compared (Table 9 shows the boiling points of different solvents). Electrolytes with different boiling point solvents are prepared, namely, Formula 15, Formula 16, and Formula 17. The detailed explanation of the formulas is shown in Table 10, which is the formula and injection ratio of Electrolyte 13, Electrolyte 14, and Electrolyte 15.

[0077] Then, the prepared electrolyte was injected into the 10Ah lithium iron phosphate / graphite soft pack battery system at an injection ratio of 85%. After the capacity was divided, the two batteries were respectively injected with 15% of the electrolyte of formula 3. After aging and capacity division, the three groups of batteries were subjected to mixed power pulse characteristics, 60℃ high temperature storage for 30 days, 45℃ 1C / 1C cycle, -20℃ low temperature discharge retention rate. The results showed that after adding a solvent below 100℃ to a shot of electrolyte, the high temperature storage recovery rate was lower, the high temperature cycle was worse, and the lower the boiling point, the worse the high temperature performance, and the solvent with a high boiling point had little effect on low temperature and internal resistance. The specific data is shown in Table 11, which is the performance test results of electrolyte 9, electrolyte 10, electrolyte 11, and electrolyte 12.

[0078] Table 9

[0079]

[0080] Table 10

[0081]

[0082] Table 11

[0083]

[0084]

[0085] In summary, the lithium-ion battery fast-charging electrolyte according to an embodiment of the present invention includes one injection of electrolyte and two injections of electrolyte, and the volume ratio of the one injection of electrolyte to the two injections of electrolyte is (95:5) to (50:50); the one injection of electrolyte includes a high boiling point solvent, a low concentration of high thermal stability lithium salt and a film-forming additive, wherein the concentration of the low concentration of high thermal stability lithium salt is 0.5 to 1 mol / L, and the volume ratio of the high boiling point solvent, the low concentration of high thermal stability lithium salt and the film-forming additive is (75 to 85): (8 to 15): (2 to 5); the two injections of electrolyte include a low viscosity solvent, a high concentration of lithium salt, a film-forming repair agent and a surfactant, wherein the concentration of the high concentration of lithium salt is 1.5 to 3 mol / L, and the volume ratio of the low viscosity solvent, the high concentration of lithium salt, the film-forming repair agent and the surfactant is (75 to 85): (15 to 40): (0.5 to 20): (0.1 to 2). Therefore, the present electrolyte, through the combined use of two electrolytes with different compositions and different lithium salt concentrations, not only reduces the internal resistance of film formation and improves the fast charging performance, but also improves the thermal decomposition temperature of the electrolyte and the stability of the solid electrolyte interface film, thereby improving high-temperature storage and cycle performance.

[0086] Corresponding to the above embodiment, the present invention further proposes a lithium-ion battery, which is composed of a positive electrode, a negative electrode, a separator and the above lithium-ion battery fast-charge electrolyte.

[0087] According to the lithium-ion battery of the embodiment of the present invention, by using two electrolytes with different components and different lithium salt concentrations in combination, not only the internal resistance of film formation is reduced and the fast charging performance is improved, but also the thermal decomposition temperature of the electrolyte and the stability of the solid electrolyte interface film are improved, thereby improving high-temperature storage and cycle performance.

[0088] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the embodiments of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0089] Although the spirit and principle of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the disclosed specific embodiments, and the division of various aspects does not mean that the features in these aspects cannot be combined to benefit, and this division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the attached claims. The scope of the attached claims conforms to the broadest interpretation, thereby including all such modifications and equivalent structures and functions.

Claims

1. A lithium ion battery fast charge electrolyte, characterized in that: The method comprises a first injection of electrolyte and a second injection of electrolyte, wherein the volume ratio of the first injection of electrolyte to the second injection of electrolyte is (95:5) to (50:50); The electrolyte comprises a high boiling point solvent, a low concentration lithium salt with high thermal stability and a film-forming additive, wherein the concentration of the low concentration lithium salt with high thermal stability is 0.5-1 mol / L, and the volume ratio of the high boiling point solvent, the low concentration lithium salt with high thermal stability and the film-forming additive is (75-85): (8-15): (2-5); The second injection electrolyte includes a low-viscosity solvent, a high-concentration lithium salt, a film-forming repair agent and a surfactant, wherein the concentration of the high-concentration lithium salt is 1.5-3 mol / L, and the volume ratio of the low-viscosity solvent, the high-concentration lithium salt, the film-forming repair agent and the surfactant is (75-85): (15-40): (0.5-20): (0.1-2).

2. The lithium ion battery fast charge electrolyte according to claim 1, characterized in that: The high boiling point solvent is at least one or more of carbonates, chain ethers, sulfones, and alkanones.

3. The lithium ion battery fast charge electrolyte according to claim 2, characterized in that: The carbonate includes at least one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, and butylene carbonate; the chain ether includes ethylene glycol dimethyl ether and / or ethylene glycol diethyl ether; the sulfones include bis(4-nitrophenyl); and the alkanones include N-methyl-2-pyrrolidone and / or N-ethylpyrrolidone.

4. The lithium ion battery fast charge electrolyte according to claim 1, characterized in that: The low-concentration, high-thermal-stability lithium salt is at least one or more of lithium tetrafluoroborate, lithium hexafluoroarsenate, anhydrous lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium difluorobisoxalate phosphate, lithium difluorophosphate, lithium trifluoromethylsulfonate, lithium difluorobisoxalate phosphate, lithium monooxalate bisfluoroborate, and lithium bis(trifluorosulfonyl)imide.

5. The lithium ion battery fast charge electrolyte according to claim 1, characterized in that: The film-forming additive is at least one or more of vinyl carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl carbonate, vinyl acetate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(oxalatoboratefluorophosphate), lithium difluorophosphate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide), lithium bis(oxalatodifluorophosphate), 1,3-propane sultone, vinyl sulfite, bis(vinyl sulfone), propylene sultone, dimethylthiomethane, vinyl vinyl sulfite, vinyl sulfate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate, 3-fluoro-1,3-propane sultone, propylene sulfate, propylene sultone, siloxane, polyether polyol, acrylate, and styrene.

6. The lithium ion battery fast charge electrolyte according to claim 1, characterized in that: The low viscosity solvent is at least one or more of dimethyl carbonate, methyl vinyl carbonate, dimethyltetrahydrofuran, tetrahydrofuran, 1,3-dioxolane, 1,2-dimethoxyethane, methyl acetate, methyl formate, methyl propionate, ethyl acrylate, and phenyl ether silane derivative solvents.

7. The lithium ion battery fast charge electrolyte according to claim 1, characterized in that: The film-forming repair agent is an unsaturated ester additive, and the unsaturated ester additive is at least one or more of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl carbonate, vinyl ethylene carbonate, and vinyl acetate.

8. The lithium ion battery fast charge electrolyte according to claim 1, characterized in that: The surfactant is at least one or more of hydrofluoroether, polydimethylsiloxane, sodium dodecyl sulfate, trifluoromethylbenzene, an organic silicon surfactant, and polyvinyl alcohol.

9. The lithium ion battery fast charge electrolyte according to any one of claims 1 to 8, characterized in that: The first injection of electrolyte is used to be injected before the battery is formed to form a stable solid electrolyte interface film on the electrode surface; the second injection of electrolyte is used to be injected after the battery is formed and before aging to repair the solid electrolyte interface film.

10. A lithium ion battery, characterized in that: The invention is composed of a positive electrode, a negative electrode, a separator and the lithium ion battery fast-charge electrolyte according to any one of claims 1 to 9.

Images