Lithium ion battery electrolyte and application thereof

Abstract

The application provides a lithium ion battery electrolyte and application thereof. The electrolyte comprises a non-aqueous solvent, a lithium salt, and an additive, wherein the additive comprises a first additive and a second additive, the first additive has a structural formula of formula A, and the second additive is selected from a compound having a structural formula of formula B1 or formula B2; wherein n1 and n2 are each independently any natural number in 1-3, R1, R2, R3, R4 and R5 are each independently selected from -H, -F, C 1～6 alkyl, C 1～6 alkoxy, C 2～6 alkenyl, C 2～6 alkenyloxy, C 2～10 alkynyl, C 2～10 alkynyloxy, C 3～8 cycloalkyl, C 3～8 cycloalkoxy, C 6～12 aryl, C 6～12 heteroaryl or carbonyl, trifluoromethyl, and C 2～6 ester. The lithium ion battery electrolyte and application thereof can effectively inhibit gas production, and improve the fast-charging performance and high-low temperature performance of the lithium ion battery.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of power batteries, in particular to a lithium ion battery electrolyte and application thereof. BACKGROUND

[0002] With the increasing popularity of lithium ion secondary batteries in the fields of electric tools, electric vehicles and the like, people pursue higher endurance mileage, and at the same time, it is desired that the capacity of the loaded battery cell is higher under the condition of the same volume design. In some special application fields, lithium ion batteries are required to cope with more severe weather and have high and low temperature performance in a wider temperature range. In actual application, the carbonate solvent system generally has problems such as high viscosity, poor flowability, low ion conductivity and low diaphragm infiltration capacity, which seriously limit the high-rate discharge capacity of the system under low temperature conditions.

[0003] The positive active material with a phosphate structure has the advantages of high energy density, complete crystal structure, relatively uniform particle distribution, good thermal stability and high safety, meets the demand for high safety and high and low temperature performance in a wider temperature range, and is widely applied in modules such as electric vehicles, energy storage systems and electric tools. However, the positive active material with a phosphate structure has defects of low intrinsic electronic conductivity and low ion diffusion coefficient, and the fast charging rate and low temperature discharge capacity of the phosphate system need to be further improved. SUMMARY

[0004] The application provides a lithium ion battery electrolyte and application thereof, which can effectively inhibit gas production, improve the fast charging performance of the lithium ion battery, enhance the high and low temperature performance of the battery and improve the safety performance of the battery.

[0005] To solve the above technical problems, the application provides a lithium ion battery electrolyte, which at least comprises the following components:

[0006] a non-aqueous solvent;

[0007] a lithium salt; and

[0008] an additive, the additive comprising a first additive and a second additive, the first additive having a structural formula of Formula A, and the second additive being selected from a compound having a structural formula of Formula B1 or Formula B2;

[0009]

[0010] wherein n1 and n2 are each independently any natural number in 1-3, R1, R2, R3, R4 and R5 are each independently selected from -H, -F, C 1～6 alkyl, C 1～6 alkoxy, C 2～6 alkenyl, C 2～6alkenyl, C 2～10 alkynyl, C 2～10 alkynyl, C 3～8 cycloalkyl, C 3～8 cycloalkyl, C 6～12 aryl, C 6～12 heteroaryl or carbonyl, trifluoromethyl, and C 2～6 ester group or a combination of any one or several of the above.

[0011] In one embodiment of the present application, at least one of R1and R2comprises C 2～6 alkenyl, C 2～10 alkynyl, C 1～6 alkoxy, C 2～6 ester group or a combination of any one or several of the above.

[0012] In one embodiment of the present application, the first additive is selected from any one or a combination of several of the following compounds:

[0013]

[0014] In one embodiment of the present application, the second additive is selected from any one or a combination of several of the following compounds:

[0015]

[0016]

[0017] In one embodiment of the present application, the content of the first additive in the electrolyte is 2wt% to 10wt%.

[0018] In one embodiment of the present application, the content of the second additive in the electrolyte is 1wt% to 3wt%.

[0019] In one embodiment of the present application, the additive further comprises a third additive, and the third additive is selected from at least one or a combination of several of the following: vinyl carbonate, 1,3-propane sultone, 1,3-propene sultone, 2,4-butane sultone, methanedisulfonate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium difluorophosphate, lithium difluorophosphate, or vinyl sulfate.

[0020] In one embodiment of the present application, the non-aqueous solvent is selected from at least one or a combination of several of the following: ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, propylene carbonate, ethyl acetate, methyl acetate, ethyl formate, propyl formate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate.

[0021] In an embodiment of the present application, the lithium salt is selected from at least one or more of lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium bis-trifluoromethanesulfonimide, lithium perchlorate, lithium hexafluoroarsenate and lithium tetrafluoroborate, lithium bisoxalate borate or lithium difluorooxalate borate, and the content of the lithium salt in the electrolyte is 5wt% to 25wt%.

[0022] The present application also provides a lithium ion battery, comprising:

[0023] a positive electrode sheet comprising a lithium supplementing agent, the lithium supplementing agent comprising one or more of Li2NiO2, Li6CoO4 or Li5FeO4;

[0024] a negative electrode sheet;

[0025] a separator disposed between the positive electrode sheet and the negative electrode sheet;

[0026] an electrolyte selected from the lithium ion battery electrolyte described above.

[0027] In an embodiment of the present application, the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprising at least one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate and a composite material of lithium manganese iron phosphate and carbon.

[0028] The present application also provides an electronic device comprising the lithium ion battery described above.

[0029] In summary, the present application proposes a lithium ion battery electrolyte and its application. Through the joint use of the first additive and the second additive, the occurrence of oxidation side reactions at the solid-liquid interface can be reduced, the stability of the electrochemical window can be improved, the production of gas can be effectively inhibited, the viscosity of the electrolyte can be reduced, the fast charging performance and the low temperature discharge performance of the lithium ion battery can be improved. The direct current impedance of the lithium ion battery can be reduced, the loss of active lithium can be reduced, and the low temperature lithium precipitation window can be improved. The stability of the interface film can be improved, thereby improving the electrochemical performance. The charging and discharging efficiency and the energy density of the lithium ion battery can be improved, the high and low temperature performance of the battery can be enhanced, and the safety performance of the battery can be improved. DETAILED DESCRIPTION

[0030] The embodiments of the present application are described below through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the present specification. The present application can also be implemented or applied by different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0031] It is to be understood that the application can assume various alternative embodiments, and should not be construed as limited to the examples set forth herein. Rather, these examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

[0032] The technical solutions of the present application are further described in detail below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0033] The present application provides a lithium ion battery electrolyte, at least comprising a non-aqueous solvent, a lithium salt and an additive, wherein the additive comprises a first additive and a second additive, the structural formula of the first additive is formula A, and the second additive is selected from compounds with formula B1 or formula B2.

[0034]

[0035] wherein n1 and n2 are each independently any natural number from 1 to 3, R1, R2, R3, R4, R5 are each independently selected from -H, -F, C 1～6 alkyl, C 1～6 alkoxy, C 2～6 alkenyl, C 2～6 alkenyl, C 2～10 alkynyl, C 2～10 alkynyl, C 3～8 cycloalkyl, C 3～8 cycloalkyl, C 6～12 aryl, C 6～12 heteroaryl or carbonyl, trifluoromethyl, and C 2～6 ester, etc. In an embodiment of the present application, at least one of R1 and R2 comprises C 2～6 alkenyl, C 2～10 alkynyl, C 1～6 alkoxy, C 2～6The additive consists of one or more of the following: ester group or -F. The first additive exhibits high oxidation stability, enabling it to undergo ring-opening polymerization on the positive electrode side to form a film. It also possesses a high dielectric constant, acting as a solvent to partially replace the ethylene carbonate solvent, maintaining a high overall electrolyte conductivity. This reduces the oxidative decomposition of cyclic ethylene carbonate by active oxygen released from the lithium replenishment agent in the positive electrode, resulting in fewer oxidation side reactions at the solid-liquid interface and high electrochemical window stability. It effectively suppresses gas generation, reduces electrolyte viscosity, and improves the fast-charging and low-temperature discharge performance of lithium-ion batteries. The second additive is a boron-containing compound that readily adsorbs onto residual functional groups on the electrode material surface. After film formation, the interfacial film contains a significant amount of lithium borate, lithium fluoride, and lithium carbonate, further enhancing lithium-ion conductivity. The combined use of the second and first additives reduces the direct current resistance (DCR) of the lithium-ion battery, suppresses gas generation from the lithium replenishment agent, reduces active lithium loss, and improves the low-temperature lithium plating window.

[0036] In one embodiment of the present invention, the first additive is selected, for example, from any one or a combination of the following compounds:

[0037]

[0038] wait. In one embodiment of the present invention, the first additive is selected, for example, from any one or more of compounds A-2, A-3, A-4, or A-5. Since these compounds are all 5-membered or 6-membered ring structures, the ring structure has high stress and is relatively easy to open the ring to form a film. At the same time, the ortho position of the unsaturated functional group includes a fluorine-containing substituent, which makes it easier to undergo elimination reaction to produce a LiF-rich interfacial film, thereby improving the stability of the interfacial film and thus improving the electrochemical performance.

[0039] In one embodiment of the present invention, the second additive is selected, for example, from any one or a combination of the following compounds:

[0040]

[0041] wait. In one embodiment of the present invention, the second additive is selected, for example, from any one or more of compounds B-2, B-4 or B-5. Since the pyridine compounds with N-ortho-fluorine atom substitution in the structure of these compounds have good film-forming properties, they improve the low-temperature interface lithium plating performance of lithium-ion batteries.

[0042] In an embodiment of the present application, the content of the first additive in the electrolyte is, for example, 2wt% to 10wt%. The content of the second additive in the electrolyte is, for example, 1wt% to 3wt%. If the content of the first additive is too low, the conductivity of the electrolyte is low, the direct current impedance is large, and the quality of the interface film formed is poor, and the low-temperature interface lithium precipitation performance is poor. With the increase of the content of the first additive, the conductivity of the electrolyte increases, the quality of the interface film formed is improved, the direct current impedance decreases, and the low-temperature performance and gas production performance of the lithium ion battery are improved. If the content of the second additive is too low, the improvement of the direct current impedance is not obvious, and if the content of the second additive is too high, the improvement of the interface impedance and the low-temperature lithium precipitation of the lithium ion battery reaches a threshold. Therefore, the content of the first additive and the second additive is controlled so that the gas production performance, low-temperature performance, fast charging performance and low-temperature discharge performance of the lithium ion battery are within a better range.

[0043] In an embodiment of the present application, the additive further comprises a third additive, the third additive is selected from at least one or a combination of several of film-forming additives such as Ethylene Carbonate (EC), 1,3-Propanesultone (PS), Prop-1-ene-1,3-sultone (PST), 2,4-Butanesultone, Methylene Methanedisulfonate (MMDS), Lithium difluoro(oxalato)borate (LiODFB), Lithium bis(oxalato)borate (LiBOB), Lithium difluorophosphate (LiDFP), Lithium difluoro(oxalato)phosphate (LiDFOP) or 1,3,2-Dioxathiolane 2,2-dioxide (DTD), and the content of the third additive in the electrolyte is 0.1wt% to 5wt%. In an embodiment of the present application, the third additive is, for example, selected from any one or a combination of several of the following: Ethylene Carbonate with a content of 0.02wt% to 5wt%, 1,3-Propanesultone with a content of 0.02wt% to 3wt%, Prop-1-ene-1,3-sultone with a content of 0.02wt% to 3wt%, 2,4-Butanesultone with a content of 0.02wt% to 3wt%, Methylene Methanedisulfonate with a content of 0.02wt% to 3wt%, Lithium difluoro(oxalato)borate with a content of 0.02wt% to 3wt%, Lithium bis(oxalato)borate with a content of 0.02wt% to 3wt%, Lithium difluorophosphate with a content of 0.02wt% to 3wt%, Lithium difluoro(oxalato)phosphate with a content of 0.02wt% to 3wt%, or 1,3,2-Dioxathiolane 2,2-dioxide with a content of 0.02wt% to 3wt%. The third additive can synergize with the first additive and the second additive to further improve the integrity and density of the interface film, and improve the cycle performance and safety performance of the lithium ion battery.

[0044] In one embodiment of the present application, the lithium salt is, for example, selected from any one or more of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), and lithium tetrafluoroborate (LiBF4), lithium bisoxalate borate or lithium difluoro oxalate borate, etc., and the content of the lithium salt in the electrolyte is 5wt% to 25wt%, and is, for example, 10wt% to 15wt%. In one embodiment of the present application, the lithium salt is, for example, selected from lithium hexafluorophosphate and lithium bisfluorosulfonylimide, so as to improve the charge-discharge efficiency and energy density of the lithium ion battery, enhance the high and low temperature performance of the battery, and improve the safety performance of the battery.

[0045] In one embodiment of the present application, the non-aqueous solvent includes, for example, at least one or more combinations of ethylene carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), ethyl acetate (EA), methyl acetate (MA), ethyl formate (MEE), propyl formate (PF), propyl acetate (PA), methyl propionate (MP), ethyl propanoate (EP), or n-propyl propionate (PP), etc. Among them, ethylene carbonate and propylene carbonate are cyclic carbonates, and the rest are linear ester solvents.

[0046] In one embodiment of the present application, when the electrolyte is prepared, the non-aqueous solvent is mixed uniformly in a glove box with an inert gas atmosphere such as argon, with the moisture content and oxygen content being less than or equal to 0.1 ppm, respectively, the fully dried lithium salt is added to the non-aqueous solvent, and the additive is added, so as to prepare the lithium ion battery electrolyte. Among them, the content described in the present application is the weight percentage calculated based on the total weight of the electrolyte.

[0047] The present application provides a lithium ion battery, which comprises a shell and a bare cell arranged in the shell. The bare cell comprises positive electrode sheets, a separator and negative electrode sheets. The separator is arranged between the positive and negative electrode sheets to prevent short circuit of the positive and negative electrode sheets and allow lithium ions to pass through. The positive electrode sheets, the separator and the negative electrode sheets are stacked in sequence to ensure that the separator is arranged between any positive electrode sheet and negative electrode sheet. A multi-layered stack is obtained by winding or folding and is arranged in the battery shell as the bare cell. Finally, electrolyte is injected into the shell once or in multiple times to immerse the bare cell in the electrolyte. The electrolyte is selected from the above-mentioned electrolyte and serves to conduct ions between the positive and negative electrode sheets. In an embodiment of the present application, the lithium ion battery is a secondary battery, such as a soft pack battery, a square shell battery or a cylindrical battery. The present application does not specifically limit the type of lithium ion battery.

[0048] In an embodiment of the present application, the positive electrode sheet comprises a positive current collector and a positive active layer coated on one side surface of the positive current collector. The positive current collector is, for example, a metal foil or a composite current collector. The metal foil is, for example, a foil formed by surface treatment of nickel, nickel alloy, titanium, titanium alloy, aluminum, aluminum alloy, silver, silver alloy or stainless steel. The composite current collector comprises, for example, a polymer material base layer and a metal layer formed on one side surface of the polymer material base layer. The material of the polymer material base layer is, for example, at least one selected from polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE). The material of the metal layer is, for example, at least one selected from aluminum, aluminum alloy, nickel, nickel alloy, silver, silver alloy and titanium alloy.

[0049] In an embodiment of the present application, the positive active layer comprises a positive active material, a binder and a conductive agent. The positive active material comprises, for example, at least one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate and a composite material of lithium manganese iron phosphate and carbon. The positive active material is used to improve the safety, cycle performance and temperature adaptability of the lithium ion battery. The general formula of lithium manganese iron phosphate is LiMn x Fe 1-xPO4, x is in the range of 0 < x < 1. The binder is, for example, selected from any one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), ethylene tetrafluoroethylene-hexafluoropropylene (TFE-HFP-VDF), or tetrafluoroethylene-hexafluoropropylene copolymer (FEP). The conductive agent is, for example, selected from any one or more of conductive carbon black (Super P), acetylene black, or ketjen black.

[0050] In an embodiment of the present application, the positive active layer further comprises a lithium supplement agent, which is selected from one or more of Li2NiO2, Li6CoO4, or Li5FeO4, to improve the battery capacity, improve the cycle stability, slow down the SEI film formation consumption, and optimize the battery life. In the positive active layer, the mass ratio of the positive active material, the lithium supplement agent, the conductive agent, and the binder is, for example, (92-97):(1-2):(1-3):(1-3).

[0051] In an embodiment of the present application, the positive active material is, for example, lithium iron phosphate, the lithium supplement agent is, for example, selected from Li5FeO4, the binder is, for example, selected from polyvinylidene fluoride, and the conductive agent is, for example, selected from acetylene black. The positive active material, the lithium supplement agent, the conductive agent, and the binder are mixed in a mass ratio of, for example, 95.7:1.5:1:1.8, an organic solvent is added, and the system is stirred in a vacuum stirrer until it is uniform to obtain a positive electrode slurry. The organic solvent is, for example, selected from N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated on an aluminum foil, which is then transferred to an oven for drying after being dried at room temperature. The positive electrode sheet is obtained through processes such as cold pressing, edge cutting, piece cutting, and strip dividing. In other embodiments, the positive electrode sheet can also be obtained by selecting any other method for forming a positive electrode sheet.

[0052] In an embodiment of the present application, the negative electrode sheet comprises, for example, a negative current collector and a negative active layer coated on at least one side surface of the negative current collector. The negative current collector is, for example, a metal foil or a composite current collector. The metal foil is, for example, a copper foil. The composite current collector comprises, for example, a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer. The material of the polymer material base layer is, for example, selected from at least one of PP, PET, PBT, PS, or PE. The material of the metal layer is, for example, selected from at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy.

[0053] In an embodiment of the present application, the negative active layer includes a negative active material, a conductive agent, a binder, a thickening agent, and the like. Among them, the negative active material includes, for example, any one or a combination of two or more of artificial graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, or lithium titanate. Among them, the silicon-based material includes, for example, one or more of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, or a silicon alloy, and the tin-based material includes, for example, one or more of elemental tin, a sacrificial oxide compound, or a tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery negative active material can also be used. These negative active materials can be used alone or in combination of two or more.

[0054] In an embodiment of the present application, the binder is, for example, selected from at least one of polymerized styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylic amide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), or carboxymethyl chitosan (CMCS). The thickening agent is, for example, selected from carboxymethyl cellulose sodium (CMC-Na), and the conductive agent is, for example, selected from any one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers. The mass ratio of the negative active material, the conductive agent, the binder, and the thickening agent in the negative active layer is, for example, (94-97):(1-2):(1-2):(1-2).

[0055] In an embodiment of the present application, the negative active material is selected from, for example, graphite and silicon-carbon composite, and the mass ratio of the silicon-carbon composite and graphite is, for example, 2:98-5:95. By adding a small amount of silicon-carbon composite, the thickness of the negative active layer can be reduced, the fast charging window of the lithium ion battery can be improved, and the influence on the first discharge capacity can be reduced. The conductive agent is selected from, for example, conductive carbon black, the thickening agent is selected from, for example, sodium carboxymethyl cellulose, and the binder is selected from, for example, styrene-butadiene rubber. In an embodiment of the present application, the negative active material, the conductive agent, the thickening agent and the binder are mixed in a mass ratio of, for example, 96.5:1:1:1.5, deionized water is added, and the mixture is uniformly mixed under the action of a vacuum stirrer to obtain a negative slurry. The negative slurry is coated on a copper foil, then dried at room temperature, transferred to an oven for drying, and subjected to processes such as cold pressing, edge cutting, piece cutting and striping to obtain a negative electrode sheet. In other embodiments, the negative electrode sheet can also be obtained by selecting other any method for forming a negative electrode sheet.

[0056] In an embodiment of the present application, the separator is, for example, a ceramic separator, a polymer separator, a non-woven fabric or an inorganic-organic composite separator, etc., including but not limited to a single-layer polypropylene (PP) film, a single-layer polyethylene (PE) film, a double-layer PP / PE film, a double-layer PP / PP film and a three-layer PP / PE / PP film, etc.

[0057] In an embodiment of the present application, the above-mentioned positive electrode sheet, the separator and the negative electrode sheet are sequentially placed with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play a role of isolation, and a bare cell is obtained by winding or stacking. The bare cell is loaded into a shell, dried, and then sealed after injecting an electrolyte. At least processes such as vacuum packaging, standing, formation and shaping are performed to obtain a lithium ion battery.

[0058] The present application will be explained in more detail below by reference to examples, which should not be understood as limiting. Suitable modifications can be made within the scope consistent with the main idea of the present application, and all fall within the technical scope of the present application.

[0059] Example 1

[0060] Preparation of the electrolyte: In an argon glove box with an oxygen content of 0.1 ppm and a water content of 0.1 ppm, EC, EMC, DMC and compound A-1 were mixed in a mass ratio of 25:60:10:5 to obtain a mixed solvent, and then lithium hexafluorophosphate and lithium bisfluorosulfonylimide were added to the mixed solvent, the content of lithium hexafluorophosphate was 10wt%, and the content of lithium bisfluorosulfonylimide was 6wt%. Then 3wt% of ethylene carbonate, 1wt% of vinyl sulfate and 1wt% of compound B-1 were added and mixed uniformly to obtain the electrolyte.

[0061] Preparation of the positive electrode sheet: lithium iron phosphate, Li5FeO4, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 95.7:1.5:1:1.8, NMP was added, and the system was stirred to be uniform under the action of a vacuum stirrer to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated on an aluminum foil, then transferred to an oven for drying after drying at room temperature, and then subjected to the processes of cold pressing, edge cutting, sheet cutting, and striping to obtain a positive electrode sheet.

[0062] Preparation of the negative electrode sheet: the negative active material was graphite and silicon-carbon composite, and the mass ratio of the silicon-carbon composite and graphite was, for example, 3:97. The negative active material, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a mass ratio of 96.5:1:1:1.5, deionized water was added, and the mixture was uniformly mixed under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry was coated on a copper foil, then transferred to an oven for drying after drying at room temperature, and then subjected to the processes of cold pressing, edge cutting, sheet cutting, and striping to obtain a negative electrode sheet.

[0063] Selection of the separator: polyethylene with a thickness of 9 μm was used as the base film.

[0064] Preparation of the battery: the positive electrode sheet, the separator, and the negative electrode sheet were sequentially wound, so that the separator was between the positive electrode sheet and the negative electrode sheet to play a role of isolation, thereby obtaining a bare cell. The bare cell was then placed in an aluminum plastic film, dried, and then sealed after injecting an electrolyte. The battery was subjected to at least the processes of vacuum packaging, standing, formation, and shaping to obtain a lithium ion battery.

[0065] Example 2

[0066] In the electrolyte, the mass ratio of EC, EMC, DMC, and compound A-1 was 20:60:10:10, and the other steps were the same as those in Example 1.

[0067] Example 3

[0068] In the electrolyte, the mass ratio of EC, EMC, DMC, and compound A-1 was 20:60:10:10, and compound B-1 was replaced by compound B-2 and compound B-3, the content of compound B-2 was 0.5wt%, and the content of compound B-3 was 0.5wt%, and the other steps were the same as those in Example 1.

[0069] Example 4

[0070] In the electrolyte, the mass ratio of EC, EMC, DMC, and compound A-1 was 20:60:10:10, and compound B-1 was partially replaced by compound B-4, the content of compound B-1 was 0.5wt%, and the content of compound B-4 was 0.5wt%, and the other steps were the same as those in Example 1.

[0071] Example 5

[0072] In the electrolyte, the mass ratio of EC, EMC, DMC and compound A-1 is 20:60:10:10, the second additive is compound B-1 and compound B-4, the content of compound B-1 is 1.5wt%, the content of compound B-4 is 1.5wt%, and the other steps remain unchanged with example 1.

[0073] Example 6

[0074] In the electrolyte, the mass ratio of EC, EMC, DMC and compound A-1 is 20:60:10:10, the content of compound B-1 is 3wt%, and the other steps remain unchanged with example 1.

[0075] Example 7

[0076] In the electrolyte, the mass ratio of EC, EMC, DMC and compound A-1 is 20:60:10:10, the content of compound B-1 is 5wt%, and the other steps remain unchanged with example 1.

[0077] Example 8

[0078] In the electrolyte, compound A-1 is replaced by compound A-2, the mass ratio of EC, EMC, DMC and compound A-2 is 20:60:10:10, compound B-1 is replaced by compound B-2, and the content of compound B-2 is 1wt%, and the other steps remain unchanged with example 1.

[0079] Example 9

[0080] In the electrolyte, compound A-1 is replaced by compound A-3, the mass ratio of EC, EMC, DMC and compound A-3 is 20:60:10:10, compound B-1 is replaced by compound B-2, and the content of compound B-2 is 1wt%, and the other steps remain unchanged with example 1.

[0081] Example 10

[0082] In the electrolyte, compound A-1 is replaced by compound A-4, the mass ratio of EC, EMC, DMC and compound A-4 is 20:60:10:10, compound B-1 is replaced by compound B-2, and the content of compound B-2 is 1wt%, and the other steps remain unchanged with example 1.

[0083] Example 11

[0084] In the electrolyte, compound A-1 is replaced by compound A-5, the mass ratio of EC, EMC, DMC and compound A-5 is 20:60:10:10, compound B-1 is replaced by compound B-2, and the content of compound B-2 is 1wt%, and the other steps remain unchanged with example 1.

[0085] Example 12

[0086] In the electrolyte, compound A-1 was replaced by compound A-5 and compound A-6, the mass ratio of EC, EMC, DMC, compound A-5 and compound A-6 was 20:60:10:5:5, compound B-1 was replaced by compound B-2, the content of compound B-2 was 1wt%, and other steps were consistent with example 1.

[0087] Example 13

[0088] In the electrolyte, compound A-1 was replaced by compound A-4 and compound A-5, the mass ratio of EC, EMC, DMC, compound A-4 and compound A-5 was 20:60:10:5:5, compound B-1 was replaced by compound B-2, the content of compound B-2 was 1wt%, and other steps were consistent with example 1.

[0089] Example 14

[0090] In the preparation of the positive electrode sheet, the lithium supplement Li5FeO4 was replaced by Li2NiO2, and other steps were consistent with example 1.

[0091] Example 15

[0092] In the preparation of the positive electrode sheet, the lithium supplement Li5FeO4 was replaced by Li6CoO4, and other steps were consistent with example 1.

[0093] Comparative example 1

[0094] Preparation of electrolyte: in an argon glove box with oxygen content of 0.1ppm and water content of 0.1ppm, EC, EMC and DMC were mixed uniformly according to the mass ratio of 30:60:10 to obtain a mixed solvent, then lithium hexafluorophosphate and lithium bisfluorosulfonylimide were added to the mixed solvent, the content of lithium hexafluorophosphate was 10wt%, and the content of lithium bisfluorosulfonylimide was 6wt%. Then 3wt% of ethylene carbonate and 1wt% of ethylene sulfate were added and mixed uniformly to obtain the electrolyte.

[0095] In the preparation of the positive electrode sheet, the lithium supplement Li5FeO4 was replaced by Li2NiO2, and other steps were consistent with example 1.

[0096] Comparative example 2

[0097] Preparation of electrolyte: in an argon glove box with oxygen content of 0.1 ppm and water content of 0.1 ppm, EC, EMC and DMC were mixed uniformly at a mass ratio of 30:60:10 to obtain a mixed solvent, then lithium hexafluorophosphate and lithium bisfluorosulfonylimide were added to the mixed solvent, the content of lithium hexafluorophosphate was 10wt%, and the content of lithium bisfluorosulfonylimide was 6wt%. Then 3wt% of ethylene carbonate and 1wt% of vinyl sulfate were added and mixed uniformly to obtain the electrolyte. Other steps were consistent with Example 1.

[0098] Comparative Example 3

[0099] Preparation of electrolyte: in an argon glove box with oxygen content of 0.1 ppm and water content of 0.1 ppm, EC, EMC and DMC were mixed uniformly at a mass ratio of 30:60:10 to obtain a mixed solvent, then lithium hexafluorophosphate and lithium bisfluorosulfonylimide were added to the mixed solvent, the content of lithium hexafluorophosphate was 10wt%, and the content of lithium bisfluorosulfonylimide was 6wt%. Then 3wt% of ethylene carbonate and 1wt% of vinyl sulfate were added and mixed uniformly to obtain the electrolyte.

[0100] In the preparation of the positive electrode sheet, the lithium supplement Li5FeO4 was replaced by Li6CoO4, and other steps were consistent with Example 1.

[0101] Comparative Example 4

[0102] In the electrolyte, the second additive was not included, and other steps were consistent with Example 1.

[0103] Comparative Example 5

[0104] In the electrolyte, 1wt% of compound B-1 was included, and other steps were consistent with Comparative Example 2.

[0105] In the present application, in Examples 1-15 and Comparative Examples 1-5, the components of the electrolyte in the lithium ion battery are shown in Table 1, and different electrolytes are used to prepare lithium ion batteries, and the performance of the lithium ion batteries is tested, and the test results are shown in Table 2.

[0106] In an embodiment of the present application, the test method of low-temperature direct current impedance test is as follows: at 25℃, the lithium ion battery is charged at 1 / 3C constant current to 3.75V, and then charged at constant voltage until the current is 0.05C. Then the battery is discharged at 1 / 3C constant current to 2.5V. Repeat the above charging step once, and record the capacity of this charging as C0. The battery is discharged at 1 / 3C constant current to (50%*C0). Then the battery is placed at-20℃, and the initial voltage is recorded as U0. The battery is discharged at 1C constant current for 30s, and the end voltage is recorded as U1. DCR=(U0-U1) / (C0*1).

[0107] In one embodiment of the present application, the test method of normal temperature initial DCR test is as follows: at 25°C, the lithium ion battery is charged at 1 / 3C constant current to 3.75V, then charged at constant voltage until the current is 0.05C. Then the battery is discharged at 1 / 3C constant current to 2.5V. Repeat the above charging step, after recording the charging capacity as C0, record the next charging capacity as C1. The battery is discharged at 1 / 3C constant current to (50%*C1), and the initial voltage U2 is recorded. The battery is discharged at 1C constant current for 30s, and the end voltage U3 is recorded. Normal temperature initial DCR=(U2-U3) / (C1*1).

[0108] In one embodiment of the present application, the test method of high temperature storage test is as follows: at 60°C, the lithium ion battery is stored for 30 days (30D). Then the battery is discharged at 1 / 3C constant current to 2.5V at 25°C, and then charged at 1 / 3C constant current to 3.75V, then charged at constant voltage until the current is 0.05C. Then the battery is discharged at 1 / 3C constant current to 2.5V, and the discharge capacity C2 is recorded. The capacity recovery rate is (C2 / C1)*100%. Repeat the above charging step, and record the second charging capacity as C3. The battery is discharged at 1 / 3C constant current to (50%*C3), and the initial voltage U4 is recorded. The battery is discharged at 1C constant current for 30s, and the end voltage U5 is recorded. DCR=(U4-U5) / (C4*1). DCR growth rate=(DCR after 30 days of storage-initial DCR) / initial DCR*100%. At the same time, record the volume V1 of the lithium ion battery at 25°C before storage and the volume V2 at normal temperature after 30D storage at 60°C. Volume expansion rate=(V2-V1) / V1*100%. In this embodiment, the working voltage window of lithium iron phosphate system is 2.5V-3.75V, and in other embodiments, when other positive active materials are selected, the working voltage window is adjusted according to the positive active material.

[0109] In one embodiment of the present application, the lithium plating test (ALP) is as follows: the lithium ion batteries of Examples 1-15 and Comparative Examples 1-5 are placed in a thermostat at 25°C, then charged at a rate of 0.33C to 3.75V in the thermostat at 25°C, and then charged at a constant voltage to a current of 0.05C. The batteries are then discharged at a constant current of 1 / 3C to 2.5V, and then discharged at a rate of 0.1C to 2.0V, and the discharge capacity at this time is recorded as C6. Next, the batteries are charged at a rate of 0.33C to 3.75V in the thermostat at 25°C, and then discharged at a rate of 0.33C to 90%*C6. The temperature of the thermostat is adjusted to -20°C, and the batteries are left to stand for 3h. Then, the batteries are charged at a constant current of 1.2C to 70% of the battery capacity (State of Charge, SOC), and then adjusted to 80% SOC. Next, the batteries are charged at a rate of 0.33C to 3.75V, and then charged at a constant current of 0.05C to 3.75V. The temperature of the thermostat is adjusted to 25°C, and the batteries are left to stand for 3h. Finally, the batteries are discharged at a rate of 0.33C to 2.0V. The above lithium plating steps are repeated for 10 cycles, and finally the batteries are discharged at a rate of 0.33C to 2.0V. The batteries are then disassembled and the interface is observed for lithium plating.

[0110] Table 1, Components of the electrolyte in Examples 1-15 and Comparative Examples 1-5

[0111]

[0112] Table 2, Performance of the lithium ion batteries in Examples 1-15 and Comparative Examples 1-5

[0113]

[0114] As shown in Table 1 and Table 2, comparative example 1, comparative example 2, comparative example 4 and comparative example 5 can be known that when the electrolyte does not add the first additive and the second additive, the lithium ion battery has high low temperature and normal temperature impedance, high high temperature storage DCR growth rate, and large high temperature storage volume expansion rate, and there is lithium precipitation problem, which indicates that the safety of the lithium ion battery is poor. When the electrolyte adds the first additive and does not add the second additive, compared with comparative example 2, the lithium ion battery has low low temperature and normal temperature impedance, low high temperature storage DCR growth rate and high temperature storage volume expansion rate, and there is no lithium precipitation problem, which indicates that the first additive can effectively inhibit gas production, improve the fast charging performance and low temperature discharge performance of the lithium ion battery. When the electrolyte does not add the first additive and adds the second additive, compared with comparative example 2, the lithium ion battery has low low temperature and normal temperature impedance, low high temperature storage DCR growth rate, and large high temperature storage volume expansion rate, and there is no lithium precipitation problem, which indicates that the second additive can increase lithium borate, lithium fluoride and lithium carbonate substances in the interface film, improve the ability to conduct lithium ions, and reduce impedance. When the first additive and the second additive are used at the same time, the lithium ion battery has low low temperature and normal temperature impedance, low high temperature storage DCR growth rate, and large high temperature storage volume expansion rate, and there is no lithium precipitation problem, which indicates that the first additive and the second additive are used together, can reduce the direct current impedance of the lithium ion battery, inhibit the gas production caused by the lithium supplement agent, reduce the loss of active lithium, and improve the low temperature lithium precipitation window, and improve the high and low temperature performance of the lithium ion battery.

[0115] As shown in Table 1 and Table 2, comparative example 1-15 and comparative example 1-3 can be known that the lithium ion battery has low low temperature and normal temperature impedance, low high temperature storage DCR growth rate, and large high temperature storage volume expansion rate, and there is no lithium precipitation problem, which indicates that the first additive can be oxidized and ring-opening polymerized into a film on the positive electrode side, and at the same time has a high dielectric constant, replaces part of EC as a solvent, maintains the overall electrolyte conductivity at a high level, and to some extent reduces the oxidative decomposition of the active oxygen released by the lithium supplement agent in the positive electrode sheet. The second additive can reduce the high impedance caused by the first additive to some extent, and the synergistic effect improves the gas production in the lithium supplement agent and improves the low temperature lithium precipitation window.

[0116] As shown in Table 1 and Table 2, comparative example 1 and 2 can be known that when the content of the first additive is increased, the lithium ion battery has low low temperature and normal temperature impedance, low high temperature storage DCR growth rate, and large high temperature storage volume expansion rate, and there is no lithium precipitation problem, which indicates that the first additive replaces part of EC without affecting the overall conductivity, reduces the high viscosity of the electrolyte, and at the same time, the film forming consumption of the first additive is small. When the content of the first additive is greater than 5wt%, the content of lithium sulfonate in the film forming component of the first additive is high, which is helpful to reduce the interface impedance and other performances.

[0117] As shown in Tables 1 and 2, it can be seen from Comparative Examples 2-7 that the second additive with different structures can improve the performance of the lithium ion battery, and the improvement effect is close under the condition of the same content, which indicates that the second additive with different structures can improve the performance of the lithium ion battery. With the increase of the content of the second additive, the reduction of the interface impedance and the improvement of the low-temperature lithium precipitation reach a threshold value. In view of the above, the recommended maximum amount of the second additive is 5wt%.

[0118] As shown in Tables 1 and 2, it can be seen from Comparative Examples 7-13 that the first additive with different structures can improve the performance of the lithium ion battery, and the improvement effect is close under the condition of the same content, which indicates that the first additive with different structures can improve the performance of the lithium ion battery. As shown in Comparative Examples 1, 14-15, the first additive and the second additive process can effectively inhibit the gas production of the lithium supplement agent and improve the low-temperature lithium precipitation window.

[0119] The application further provides an electronic device comprising at least one lithium ion battery as described above for providing electric energy. The electronic device can be a vehicle, a mobile phone, a portable device, a notebook computer, a ship, a spacecraft, an electric toy, an electric tool, etc. In an embodiment of the application, the vehicle is a new energy vehicle, which can be a pure electric vehicle, a hybrid vehicle or a range extended vehicle, etc. The spacecraft includes an airplane, a rocket, a space shuttle and a spacecraft, etc. The electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy and an electric plane toy, etc. The electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool and a railway electric tool, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator and an electric planer, etc. The electronic device comprises the lithium ion battery as described above, and thus has the advantages of the lithium ion battery as described above, which will not be described herein.

[0120] In summary, the application provides a lithium ion battery electrolyte and its application. The combined use of the first additive and the second additive can reduce the oxidation side reaction at the solid-liquid interface, improve the electrochemical window stability, effectively inhibit the gas production, reduce the viscosity of the electrolyte, improve the fast charging performance and low temperature discharge performance of the lithium ion battery, reduce the direct current impedance of the lithium ion battery, reduce the loss of active lithium, and improve the low-temperature lithium precipitation window. The stability of the interface film is improved, thereby improving the electrochemical performance. The charging and discharging efficiency and energy density of the lithium ion battery are improved, the high and low temperature performance of the battery is enhanced, and the safety performance of the battery is improved.

[0121] The above description is only the preferred embodiment of the present application and the explanation of the technical principles applied, and those skilled in the art should understand that the inventive scope of the present application is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by the combinations of the above technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by the mutual replacement of the above features and the technical features disclosed in the present application (but not limited to) having similar functions.

[0122] In addition to the technical features described in the specification, the remaining technical features are known to those skilled in the art, and in order to highlight the innovative features of the present application, the remaining technical features will not be described here.

Claims

1. A lithium-ion battery electrolyte, characterized in that, It includes at least the following components: Non-aqueous solvents; Lithium salts; as well as The additive includes a first additive and a second additive, wherein the first additive has a structural formula of formula A and the second additive is selected from compounds having a structural formula of formula B1 or formula B2. Where n1 and n2 are each any natural number from 1 to 3, and R1, R2, R3, R4, and R5 are each independently selected from -H, -F, and C. 1～6 Alkyl, C 1～6 Alkoxy, C 2～6 alkenyl, C 2～6 alkenyloxy group, C 2～10 alkynyl group, C 2～10 Acryloxy group, C 3～8 cycloalkyl, C 3～8 Epoxyalkyl, C 6～12 Aryl, C 6～12 heteroaryl or carbonyl, trifluoromethyl, and C 2～6 Any one or a combination of several ester groups.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, At least one of R1 and R2 includes C. 2～6 alkenyl, C 2～10 alkynyl group, C 1～6 Alkoxy, C 2～6 Any one or a combination of ester groups or -F.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first additive is selected from any one or a combination of the following compounds:

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The second additive is selected from any one or a combination of the following compounds:

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of the first additive in the electrolyte is 2wt% to 10wt%.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of the second additive in the electrolyte is 1 wt% to 3 wt%.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The additive further includes a third additive selected from at least one or more combinations of ethylene carbonate, 1,3-propanesulfonyl lactone, 1,3-propenesulfonyl lactone, 2,4-butanesulfonyl lactone, methylene disulfonate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorophosphate, lithium difluorodioxalate phosphate, or ethylene sulfate.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that, The non-aqueous solvent is selected from at least one or more of ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, propylene carbonate, ethyl acetate, methyl acetate, ethyl formate, propyl formate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate.

9. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium di(oxalate)borate, or lithium di(oxalate)borate, and the content of the lithium salt in the electrolyte is 5 wt% to 25 wt%.

10. A lithium-ion battery, characterized in that, include: A positive electrode sheet, wherein the positive electrode sheet includes a lithium replenishing agent, the lithium replenishing agent including one or more of Li2NiO2, Li6CoO4 or Li5FeO4; Negative electrode plate; A diaphragm is disposed between the positive electrode and the negative electrode; The electrolyte is selected from the lithium-ion battery electrolyte according to any one of claims 1-9.

11. The lithium-ion battery according to claim 10, characterized in that, The positive electrode sheet includes a positive electrode active material, which includes at least one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

12. An electronic device, characterized in that, Includes the lithium-ion battery according to any one of claims 10-11.

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