Lithium ion battery electrolyte and application thereof

Abstract

The application provides a lithium ion battery electrolyte and application thereof, and the electrolyte comprises at least the following components: a lithium salt, a solvent and an additive, wherein the additive comprises a first additive, and the structural general formula of the first additive is: wherein n1 and n2 are each independently any natural number selected from 0-5, X and Y are each selected from one of O, S, Se or Te, R1 and R2 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, carbonyl or C 2～6 ester, Z and Q are each independently selected from one of O, S, CH or CH2. The lithium ion battery electrolyte and application thereof can improve the fast charging rate, low-temperature discharge capacity, cycle performance and high-temperature storage performance of the battery, and can also reduce the amount of the additive in the electrolyte, thereby saving the preparation cost of the electrolyte.

Description

Technical Field

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

[0002] As lithium-ion batteries are increasingly used in fields such as power tools and electric vehicles, the demand for high-performance lithium-ion batteries is growing. Among them, phosphate-structured positive electrode active materials have the advantages of complete crystal structure, relatively uniform particle distribution, good thermal stability and safety, and are widely used in fields such as electric vehicles, energy storage systems and power tools. However, in the actual application of phosphate-structured positive electrode active materials, there are defects such as low intrinsic electronic conductivity and low ion diffusion coefficient, which greatly restrict the fast charge rate performance and low-temperature discharge capacity of the system. Therefore, how to improve the fast charge rate and low-temperature discharge capacity of the phosphate system is an urgent problem to be solved.

[0003] Electrolyte composition is one of the most effective ways to improve the fast charge rate and low-temperature discharge capabilities of phosphate-based systems. However, carbonate solvent systems in electrolytes suffer from high viscosity, poor fluidity, low ionic conductivity, and poor separator wetting ability. These issues severely limit the battery's high-rate discharge capability at low temperatures and prevent it from improving the phosphate-based system. Summary of the Invention

[0004] The present invention proposes a lithium-ion battery electrolyte and its application. The lithium-ion battery electrolyte and its application provided by the present invention can improve the battery's fast charge rate, low-temperature discharge capability, cycle performance and high-temperature storage performance, and can also reduce the amount of additives in the electrolyte, thereby saving the preparation cost of the electrolyte.

[0005] To solve the above technical problems, the present invention provides a lithium-ion battery electrolyte comprising at least the following components:

[0006] lithium salts;

[0007] solvents; and

[0008] Additives, wherein the additives include a first additive, and the general structural formula of the first additive is:

[0009]

[0010] Wherein, n1 and n2 are each independently selected from any natural number between 0 and 5, X and Y are each independently selected from one of O, S, Se or Te, R1 and R2 are each selected from H, F, C 1～6 Alkyl, C 1～6 Alkoxy, C 2～6 Alkenyl, C 2～6 Alkenyloxy, C2～10 Alkynyl, C 2～10 Alkynyloxy, C 3～8 Cycloalkyl, C 3～8 Epoxyalkyl, C 6～12 Aryl, C 6～12 Heteroaryl, carbonyl or C 2～6 At least one of the ester groups, Z and Q are each independently selected from one of O, S, CH or CH2.

[0011] In one embodiment of the present invention, at least one of R1 and R2 includes F, C 1～6 Alkoxy, C 2～6 Alkenyl, C 2～10 Alkynyl or C 2～6 One or more ester groups.

[0012] In one embodiment of the present invention, the first additive is selected from:

[0013]

[0014]

[0015]

[0016] At least one of .

[0017] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.5 wt %-6 wt %.

[0018] In one embodiment of the present invention, the solvent includes cyclic esters and chain esters, the cyclic esters are selected from at least one of ethylene carbonate or propylene carbonate, the chain esters are selected from at least one of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, ethyl acetate, methyl acetate, ethyl formate, propyl formate, propyl acetate, methyl propionate, ethyl propionate or propyl propionate, and the mass ratio of the cyclic esters to the chain esters is (0.15-1):1.

[0019] In one embodiment of the present invention, the lithium salt includes a first lithium salt, the first lithium salt is a fluorine-containing sulfonyl imide lithium salt, the fluorine-containing sulfonyl imide lithium salt is selected from at least one of lithium bis(fluorosulfonyl imide) or lithium bis(trifluoromethylsulfonyl imide), and the content of the first lithium salt in the electrolyte is 5wt%-12wt%.

[0020] In one embodiment of the present invention, the lithium salt further includes a second lithium salt, and the second lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalatoborate) or lithium difluorooxalatoborate.

[0021] In one embodiment of the present invention, the additive further includes a second additive, the second additive being selected from at least one of vinylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, 2,4-butane sultone, methanedisulfonic acid methylene ester, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorobisoxalatophosphate or vinyl sulfate, and the mass ratio of the first additive to the second additive is (0.2-0.9):1.

[0022] In one embodiment of the present invention, the mass ratio of the first additive to the second additive is (0.3-0.5):1.

[0023] The present invention also provides a lithium ion battery, comprising at least:

[0024] A positive electrode plate, comprising a positive electrode active layer, wherein the positive electrode active layer comprises a positive electrode active material, wherein the positive electrode active material comprises an olivine-structured lithium-phosphate material, wherein the olivine-structured lithium-phosphate material is selected from at least one 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 iron manganese phosphate, or a composite material of lithium iron manganese phosphate and carbon;

[0025] negative electrode;

[0026] a separator, disposed between the positive electrode sheet and the negative electrode sheet; and

[0027] The electrolyte is selected from the lithium-ion battery electrolyte described above.

[0028] In summary, the present invention proposes a lithium-ion battery electrolyte and its application. By improving the components of the electrolyte, the dielectric constant and lithium ion migration constant of the electrolyte can be increased. The electrolyte can also have the advantages of selective film formation, few high-temperature interfacial side reactions, low low-temperature viscosity and high electrochemical stability, thereby greatly improving the fast charge rate and low-temperature discharge capacity of the phosphate system. The amount of the second additive in the electrolyte can be reduced, thereby saving the preparation cost of the electrolyte. The battery cycle performance can be improved, and the increase of impedance during high-temperature storage can be effectively suppressed, thereby improving the high-temperature storage performance of the battery. DETAILED DESCRIPTION

[0029] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0030] 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.

[0031] The technical solutions of the present application are further described in detail below in conjunction with the embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0032] The present application provides a lithium ion battery electrolyte, at least comprising lithium salt, additives and solvents, wherein the additives comprise a first additive, and the structural general formula of the first additive is:

[0033] wherein n1 and n2 are each independently selected from any natural number in 0-5, X and Y are each independently selected from one of O, S, Se or Te, R1 and R2 are each selected from at least one of 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, carbonyl or C 2～6 ester, Z and Q are each independently selected from one of O, S, CH or CH2. In the lithium ion battery electrolyte provided by the present application, the first additive not only has a high dielectric constant and lithium ion migration coefficient, but also has the advantages of selective film formation, less high-temperature interface side reaction, low low-temperature viscosity and high electrochemical stability, thereby greatly improving the fast charging rate and low-temperature discharge capacity of the lithium ion battery. Moreover, since the first additive has a high selective film formation capacity, the content of the second additive in the electrolyte can be greatly reduced, thereby reducing the preparation cost of the electrolyte.

[0034] In one embodiment of the present invention, the first additive is, for example, a bridged ring organic compound containing heteroatoms X and Y, wherein n1 and n2 are, for example, independently selected from any natural number between 1 and 3. The first additive has the advantages of high dielectric constant, high lithium ion migration constant, selective film-forming ability, few high-temperature interface side reactions, low low-temperature viscosity and high electrochemical stability, thereby improving the fast charge rate and low-temperature discharge capability of the lithium-ion battery. Specifically, in the first additive, the heteroatoms X and Y have high electron-donating coordination ability, can form an electrolyte with high lithium ion conductivity, and reduce the interfacial transfer impedance of lithium ion transmission. Moreover, during the charge and discharge process of the lithium-ion battery, the first additive is very likely to undergo electrochemical catalytic reactions on the electrode surface to form a uniform, dense and passivated protective film. Moreover, the introduction of side chains R1 and R2 containing unsaturated bonds such as double bonds or triple bonds on the bridge ring of the first additive can further effectively construct an interface film with a three-dimensional spatial network, and use it as a spatial three-dimensional channel for lithium ion conduction.

[0035] In one embodiment of the present invention, in formula B1, at least one of R1 and R2 includes F, C 1～6 Alkoxy, C 2～6 Alkenyl, C 2～10 Alkynyl or C 2～6 One or more of the following: ester groups, etc. Furthermore, in this embodiment, the number of carbon atoms in the R1 and R2 substituents is, for example, less than or equal to 3. By limiting the number of carbon atoms in the R1 and R2 substituents, the chain length of the substituents on the bridge ring in the first additive can be shortened, thereby reducing the steric hindrance of the interface film formed by the first additive, improving the density and continuity of the interface film, and thus extending the cycle life of the battery.

[0036] In one embodiment of the present invention, in Formula B1, at least one of R1 and R2 contains F. Specifically, at least one of R1 and R2 is F, an alkoxy group substituted with an F atom, or an alkyl group containing F. By limiting R1 and R2 to contain F, the interfacial film formed with the F-containing first additive contains more inorganic LiF, which helps reduce interfacial impedance, extend the cycle life of the lithium-ion battery, and improve the battery's dynamic performance.

[0037] In one embodiment of the present invention, the first additive is selected from

[0038]

[0039]

[0040] Further, the first additive is for example selected from at least one of B2, B3, B4, B5, B6, B7, B8, B9, B10, B11, B13, B14 or B15, and the like, and further, the first additive is for example selected from at least one of B2, B3, B6, B8, B10, B13 or B15, and the like. The content of the first additive in the electrolyte is for example 0.5wt%-20wt%, and further for example 0.5wt%-6wt%, 1wt%-10wt% or 2wt%-10wt%, and the like, and further, and further for example 2wt%-5wt%. By controlling the content of the first additive in the electrolyte, the effect of the first additive can be exerted while the amount of the first additive is reduced as much as possible, thereby reducing the preparation cost of the electrolyte.

[0041] In one embodiment of the present invention, the additive further includes a second additive, and the second additive is selected from at least one of vinylene carbonate (VC), 1,3-propane sultone (PS), 1,3-propylene sultone, 2,4-butane sultone, methylene disulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate or lithium difluorobisoxalatophosphate and vinyl sulfate (DTD). The content of the second additive in the electrolyte is, for example, 0.1wt%-5wt%. Further, the content of the second additive in the electrolyte is, for example, in the range of any two of 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%. Specifically, the content of each second additive in the electrolyte may be different, and the content of VC in the electrolyte may be, for example, 0.02 wt%-5 wt%, the content of PS in the electrolyte may be, for example, 0.02 wt%-3 wt%, the content of 1,3-propylene sultone in the electrolyte may be, for example, 0.02 wt%-3 wt%, the content of 2,4-butane sultone in the electrolyte may be, for example, 0.02 wt%-3 wt%, the content of methylene methanedisulfonate in the electrolyte may be, for example, 0.02 wt%-3 wt%. For example, the content of lithium difluorooxalatoborate in the electrolyte is 0.02wt%-3wt%, the content of lithium dioxalatoborate in the electrolyte is 0.02wt%-3wt%, the content of lithium difluorophosphate in the electrolyte is 0.02wt%-1wt%, the content of lithium difluorobisoxalatophosphate in the electrolyte is 0.02wt%-3wt%, and the content of DTD in the electrolyte is 0.02wt%-3wt%. In this embodiment, the second additive is, for example, VC. By adding the second additive with low impedance, the low-temperature discharge capacity and power of the battery can be greatly improved, thereby improving the low-temperature discharge capability of the battery. Moreover, the second additive can synergize with the first additive to further improve the cycle performance of the battery and effectively suppress the increase of impedance during high-temperature storage, thereby improving the high-temperature storage performance of the battery.

[0042] In one embodiment of the present invention, the mass ratio of the first additive to the second additive is, for example, (0.2-0.9):1, or another example, (0.3-0.5):1. Since both the first additive and the second additive have selective film-forming capabilities, controlling the mass ratio of the first additive to the second additive can significantly reduce the content of the second additive in the electrolyte, thereby achieving the goal of reducing costs and increasing efficiency.

[0043] In one embodiment of the present invention, the additive further includes a third additive selected from at least one of PS, 1,3-propylene sultone, 2,4-butane sultone, methylene disulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorobis(oxalatophosphate), or DTD. The third additive is present in the electrolyte in an amount of, for example, 1 wt% to 5 wt%. The third additive and the second additive act synergistically to improve the battery's cycling performance and high-temperature storage performance.

[0044] In one embodiment of the present invention, the solvent includes cyclic esters and chain esters, wherein the cyclic ester is selected from at least one of ethylene carbonate (EC) or propylene carbonate (PC), and the chain ester is selected from at least one of ethyl methyl carbonate (EMC), diethyl carbonate, dimethyl carbonate (DMC), ethyl acetate, methyl acetate, ethyl formate, propyl formate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The mass ratio of the cyclic ester to the chain ester is, for example, (0.15-1):1, and another example is (0.3-0.5):1. By controlling the content of the solvent, while the performance of the electrolyte is maximized, it is possible to prevent the solvent content from being too high, resulting in excessive viscosity of the electrolyte, thereby reducing the ionic conductivity and wettability of the electrolyte.

[0045] In one embodiment of the present invention, the lithium salt includes a first lithium salt, which is, for example, a fluorinated sulfonyl imide lithium salt, which is selected from at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide, and the content of the first lithium salt in the electrolyte is, for example, 5 wt%-12 wt%, and for example, 6 wt%.

[0046] In one embodiment of the present invention, the lithium salt further includes a second lithium salt, and the second lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalatoborate), and lithium difluorooxalatoborate. The total content of the first lithium salt and the second lithium salt in the electrolyte is, for example, 5 wt% to 25 wt%, or, for example, 10 wt% to 15 wt%.

[0047] In one embodiment of the present invention, when preparing the electrolyte, in a glove box with a stable gas atmosphere such as argon, the solvents are uniformly mixed according to a mass ratio, and then a fully dried lithium salt is added to the solvent. Furthermore, a first additive, a second additive, and a third additive are added to prepare a lithium-ion battery electrolyte. The moisture content in the glove box is, for example, less than 1 ppm.

[0048] The application further provides a lithium ion battery, which comprises a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. The separator is arranged between the positive electrode sheet and the negative electrode sheet to prevent short circuit between the positive electrode sheet and the negative electrode sheet, and the lithium ion can pass through. The electrolyte is filled between the positive electrode sheet, the separator and the negative electrode sheet, and the electrolyte is the lithium ion battery electrolyte described above, which plays a role of ion conduction. The lithium ion battery is, for example, a primary battery or a secondary battery, and the secondary battery is, for example, a soft package battery, a hard shell battery or a cylindrical battery, and the application does not specifically limit the type and category of the lithium ion battery.

[0049] In an embodiment of the application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active layer coated on at least one side surface of the positive electrode current collector. The positive electrode current collector is, for example, a metal foil or a composite current collector, and 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 at least 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), and 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.

[0050] In an embodiment of the application, the positive electrode active layer comprises a positive electrode active material, a conductive agent and a binder. The ratio of the positive electrode active material, the conductive agent and the binder can be selected according to actual needs. The positive electrode active material is, for example, a lithium-containing phosphoric acid material with an olivine structure, and the lithium-containing phosphoric acid material with an olivine structure is, for example, at least one selected from 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 or a composite material of lithium manganese iron phosphate and carbon. The chemical formula of the lithium manganese iron phosphate is LiMnxFe1-xPO4, 0 x Fe 1-x PO4, 0

[0051] In one embodiment of the present invention, the conductive agent is, for example, selected from at least one of conductive carbon black (SuperP), acetylene black, carbon nanotubes or graphene, and the binder is, for example, selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer or tetrafluoroethylene-hexafluoropropylene copolymer.

[0052] In one embodiment of the present invention, the positive electrode current collector is, for example, aluminum foil, the positive electrode active material is, for example, lithium iron phosphate, the conductive agent is, for example, conductive carbon black, and the binder is, for example, polyvinylidene fluoride. The positive electrode active material, the conductive agent, and the binder are mixed, for example, in a mass ratio of 97:1:2, and an organic solvent is added. The mixture is stirred in a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on the aluminum foil, and then dried at room temperature and then transferred to an oven for drying. The positive electrode sheet is obtained through processes such as cold pressing, trimming, cutting, and slitting. The organic solvent is, for example, N-methylpyrrolidone (NMP).

[0053] In one embodiment of the present invention, the negative electrode plate includes, for example, a negative electrode current collector and a negative electrode active layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector may be, for example, a metal foil or a composite current collector, such as copper foil. The composite current collector may include, for example, a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The polymer base layer may be made of, for example, at least one selected from PP, PET, PBT, PS, or PE, and the metal layer may be made of, for example, at least one selected from copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, or a silver alloy.

[0054] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode active material, a conductive agent, a binder, and a thickener. The ratio of the negative electrode active material, conductive agent, binder, and thickener can be selected based on actual needs. The negative electrode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, or lithium titanate. Specifically, the silicon-based material is selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys. The tin-based material is selected from at least one of elemental tin, tin oxide compounds, or tin alloys.

[0055] In one embodiment of the present invention, the binder is selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylic amide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The thickener is selected from at least one of carboxymethyl cellulose (CMC). The conductive agent is selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0056] In one embodiment of the present invention, the negative electrode current collector is, for example, copper foil, the negative electrode active material includes, for example, a silicon-carbon composite and artificial graphite, with the mass ratio of the silicon-carbon composite to the artificial graphite being, for example, 90:10, the conductive agent is, for example, conductive carbon black, the thickener is, for example, CMC, and the binder is, for example, styrene-butadiene rubber. Specifically, the artificial graphite, conductive agent, thickener, and binder carbon are mixed in a mass ratio of 96.5:1:1:1.5, deionized water is added as a solvent, and then the mixture is thoroughly stirred and mixed in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is then coated on copper foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing, trimming, cutting, and slitting, the negative electrode sheet is obtained.

[0057] In one embodiment of the present invention, the diaphragm is, for example, a conventional diaphragm, a ceramic diaphragm, a polymer diaphragm, a non-woven fabric or an inorganic-organic composite diaphragm, and specifically, the diaphragm is, for example, a single-layer PP film, a single-layer PE film, a double-layer PP / PE film, a double-layer PP / PP film or a three-layer PP / PE / PP film.

[0058] In one embodiment of the present invention, the aforementioned positive electrode sheet, separator, and negative electrode sheet are sequentially placed, with the separator positioned between the positive and negative electrode sheets to provide isolation. The electrode assembly is then wound or laminated to form an electrode assembly. The electrode assembly is then placed in an outer packaging shell, dried in a vacuum oven, and then injected with the aforementioned lithium-ion battery electrolyte. The soft-pack lithium-ion battery is then produced through vacuum packaging, standing, hot and cold pressing, formation, fixture assembly, and capacity sizing.

[0059] Hereinafter, the present invention will be explained in more detail by citing examples, which should not be construed as limiting. Appropriate modifications may be made within the scope consistent with the gist of the present invention, all of which fall within the technical scope of the present invention.

[0060] Example 1

[0061] Preparation of positive electrode sheets: Lithium iron phosphate, conductive carbon black and polyvinylidene fluoride are mixed in a mass ratio of 97:1:2, NMP is added, and stirred under the action of a vacuum mixer until the system becomes uniform to obtain a positive electrode slurry. The positive electrode slurry is then evenly coated on aluminum foil, and then dried at room temperature and transferred to an oven for drying. The positive electrode sheets are obtained through processes such as cold pressing, trimming, cutting and slitting.

[0062] Preparation of the negative electrode sheet: Silicon-carbon composite and artificial graphite are mixed in a mass ratio of 90:10 to obtain the negative electrode active material. The negative electrode active material, conductive carbon black, CMC, and styrene-butadiene rubber are mixed in a mass ratio of 96.5:1:1:1.5, and deionized water is added. The mixture is then thoroughly stirred in a vacuum mixer to obtain a negative electrode slurry. The slurry is coated on copper foil, dried at room temperature, and then transferred to an oven for drying. After cold pressing, trimming, cutting, and slitting, the negative electrode sheet is obtained.

[0063] Preparation of the electrolyte: In an argon atmosphere glove box with a moisture content of less than 1 ppm, EC, PC, EMC, and DMC were mixed in a mass ratio of 20:10:50:20 to obtain a solvent. The fully dried first lithium salt LiFSI and second lithium salt LiPF6 were then added to the solvent. The first additive B2, the second additive VC, and the third additive DTD were also added and mixed to prepare a lithium-ion battery electrolyte. The contents of LiPF6, LiFSI, VC, DTD, and B2 in the electrolyte were 10wt%, 6wt%, 3wt%, 1wt%, and 2wt%, respectively.

[0064] Selection of diaphragm: Choose single-layer PP film as the diaphragm.

[0065] Battery Preparation: The positive electrode sheet, separator, and negative electrode sheet are placed in sequence and wound or stacked to form an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried in a vacuum oven, and then the prepared lithium-ion battery electrolyte is injected. After vacuum packaging, static standing, hot and cold pressing, formation, fixture, and capacity division, a soft-pack lithium-ion battery is obtained.

[0066] Example 2

[0067] The first additives are B2 and B3, and the contents of B2 and B3 in the electrolyte are both 1 wt %. Other steps are the same as those in Example 1.

[0068] Example 3

[0069] The first additives are B2 and B6, and the contents of B2 and B6 in the electrolyte are both 1 wt %. Other steps are the same as those in Example 1.

[0070] Example 4

[0071] The first additives are B3 and B8, and the contents of B3 and B8 in the electrolyte are both 1 wt %. Other steps are the same as those in Example 1.

[0072] Example 5

[0073] The content of the first additive B2 in the electrolyte is 5 wt %. Other steps are the same as those in Example 1.

[0074] Example 6

[0075] The first additive is B10, and the content of B10 in the electrolyte is 2 wt %. Other steps are the same as those in Example 1.

[0076] Example 7

[0077] The first additives are B2 and B10, and the contents of B2 and B10 in the electrolyte are 2 wt % and 3 wt % respectively. Other steps are the same as those in Example 1.

[0078] Example 8

[0079] The first additive is B15, and the content of B15 in the electrolyte is 5 wt %. Other steps are the same as those in Example 1.

[0080] Example 9

[0081] The first additive is B11, and the content of B11 in the electrolyte is 2 wt %. Other steps are the same as those in Example 1.

[0082] Example 10

[0083] The first additive is B17, and the content of B17 in the electrolyte is 2 wt %. Other steps are the same as those in Example 1.

[0084] Example 11

[0085] The content of the first additive B2 in the electrolyte is 0.5 wt %. Other steps are the same as those in Example 1.

[0086] Example 12

[0087] The first additive is B19, and the content of B19 in the electrolyte is 2 wt %. Other steps are the same as those in Example 1.

[0088] Example 13

[0089] The first additive is B15, the content of B15 in the electrolyte is 5 wt %, and there is no VC in the electrolyte. The other steps are the same as those in Example 1.

[0090] Example 14

[0091] The content of the second lithium salt LiPF6 in the electrolyte is 14.9 wt %, and the electrolyte does not contain the first lithium salt LiFSI. The other steps are the same as those in Example 1.

[0092] Example 15

[0093] The first additive is B8, and the content of B8 in the electrolyte is 5 wt %. The other steps are the same as those in Example 14.

[0094] Example 16

[0095] There is no VC in the electrolyte, and the other steps are the same as Example 15.

[0096] Example 17

[0097] The first additives are B17 and B18, and the contents of B17 and B18 in the electrolyte are 2 wt % and 3 wt % respectively. The other steps are the same as those in Example 14.

[0098] Example 18

[0099] There was no VC in the electrolyte, and the other steps were the same as those in Example 6.

[0100] Example 19

[0101] The content of VC in the electrolyte was 1 wt %. Other steps were the same as those in Example 6.

[0102] Example 20

[0103] The positive electrode active material is LiNi 0.6 Co 0.1 M 0.3 O2, the mass ratio of the positive electrode active material, the conductive carbon black and the polyvinylidene fluoride is 97.5:1.5:1, and the first additives are B2 and B10, and the contents of B2 and B10 in the electrolyte are 2wt% and 3wt% respectively. The other steps are the same as those in Example 1.

[0104] Example 21

[0105] There was no DTD in the electrolyte, and the other steps were the same as those in Example 1.

[0106] Example 22

[0107] The content of DTD in the electrolyte was 3 wt %. Other steps were the same as those in Example 1.

[0108] Example 23

[0109] The content of DTD in the electrolyte was 5 wt %. Other steps were the same as those in Example 1.

[0110] Example 24

[0111] The content of B2 in the electrolyte is 3.2 wt %. Other steps are the same as those in Example 1.

[0112] Example 25

[0113] No VC and DTD were added to the electrolyte, and the other steps were the same as in Example 1.

[0114] Comparative Example 1

[0115] B10 was not added, and the other steps were the same as in Example 19.

[0116] Comparative Example 2

[0117] B2 was not added, and the other steps were the same as in Example 14.

[0118] Comparative Example 3

[0119] B2 was not added, and the other steps were the same as in Example 1.

[0120] Comparative Example 4

[0121] No VC was added to the electrolyte, and other steps were the same as those in Comparative Example 2.

[0122] Comparative Example 5

[0123] The B1 compound is added to the electrolyte, and the other steps are the same as Example 20.

[0124] Comparative Example 6

[0125] There is no B2 in the electrolyte, and the other steps are the same as Example 25.

[0126] The raw material component contents and raw material mass ratios required for the electrolytes prepared in the examples and comparative examples are shown in Table 1. The content of each component is the mass percentage calculated based on the total mass of the electrolyte.

[0127] Table 1. Composition of the electrolyte in Examples 1-25 and Comparative Examples 1-6

[0128]

[0129]

[0130] In the present invention, performance tests were conducted on the lithium-ion batteries prepared using different ratios in Examples 1-25 and Comparative Examples 1-6. The test results are shown in Table 2.

[0131] In one embodiment of the present invention, for example, a low-temperature Direct Current Resistance (DCR) test is performed on a lithium-ion battery. Specifically, at 25°C, the lithium-ion battery is charged to the upper limit voltage at a constant current of 1 / 3C, and then charged at a constant voltage to a current of 0.05C. The battery is then discharged to the lower limit voltage at a constant current of 1 / 3C. Repeat the above charging steps, record the charging capacity as C0, and then discharge the battery to (50%*C0) at a constant current of 1 / 3C. The battery is then placed at -20°C, and the initial voltage is recorded as U0. The battery is then discharged at a constant current of 1C for 30s, and the terminal voltage is recorded as U1. Finally, the low-temperature DCR is calculated based on C0, U1, and U0. Among them, in Examples 1-19, Examples 21-25 and Comparative Examples 1-4, the upper limit voltage is 3.75V and the lower limit voltage is 2.5V, while in Example 20 and Comparative Example 5, the upper limit voltage is 4.35V and the lower limit voltage is 2.8V. The low temperature DCR is calculated according to the following formula:

[0132] Low temperature DCR = (U0-U1) / (C0*1).

[0133] In one embodiment of the present invention, for example, a room temperature DCR test is performed on a lithium-ion battery. Specifically, at 25°C, the lithium-ion battery is charged to the upper limit voltage at a constant current of 1 / 3C, and then charged to a current of 0.05C at a constant voltage. The battery is then discharged to the lower limit voltage at a constant current of 1 / 3C. Repeat the above charging steps, record the charging capacity as C1, and then discharge the battery to (50%*C1) at a constant current of 1 / 3C, and record the initial voltage as U2. The battery is then discharged at a constant current of 1C for 30s, and the terminal voltage is recorded as U3. Finally, the room temperature DCR is calculated based on C1, U2 and U3. Among them, in Examples 1-19, Examples 21-25 and Comparative Examples 1-4, the upper limit voltage is 3.75V and the lower limit voltage is 2.5V, while in Example 20 and Comparative Example 5, the upper limit voltage is 4.35V and the lower limit voltage is 2.8V. The room temperature DCR is calculated according to the following formula:

[0134] DCR at room temperature = (U2-U3) / (C1*1).

[0135] In one embodiment of the present invention, for example, a high-temperature storage test is performed on a lithium-ion battery. Specifically, the lithium-ion battery is stored at 60°C for 30 days. The battery is then placed at 25°C and discharged at a constant current of 1 / 3C to 2.5V. The battery is then charged at a constant current of 1 / 3C to the upper limit voltage, and then charged at a constant voltage to a current of 0.05C. The battery is then discharged at a constant current of 1 / 3C to the lower limit voltage, and the discharge capacity is recorded as C3 and the capacity recovery rate is calculated. The above charging steps are repeated, and the charge capacity is recorded as C4. The battery is discharged at a constant current of 1 / 3C to (50%*C4), and the initial voltage is recorded as U4. The battery is discharged at a constant current of 1C for 30s, and the terminal voltage is recorded as U5. The DCR and DCR growth rate after storage for 30 days are calculated. At the same time, the volume V1 of the lithium-ion battery at 25°C before storage and the volume V2 at room temperature after storage at 60°C for 30D are recorded, and the volume expansion rate is calculated. Among them, in Examples 1-19 and Comparative Examples 1-4, the upper limit voltage is 3.75 V and the lower limit voltage is 2.5 V, while in Example 20 and Comparative Example 5, the upper limit voltage is 4.35 V and the lower limit voltage is 2.8 V. The capacity recovery rate, DCR after storage for 30 days, DCR growth rate and volume expansion rate are calculated according to the following formula:

[0136] Capacity recovery rate = (C3 / C2)*100%;

[0137] After 30 days of storage, DCR = (U4-U5) / (C4*1);

[0138] DCR growth rate = (DCR after 30 days of storage - initial DCR) / initial DCR * 100%;

[0139] Volume expansion rate Gas = (V2-V1) / V1*100%;

[0140] Among them, the initial DCR refers to the room temperature DCR data obtained by directly performing the room temperature DCR test after the battery cell is manufactured without performing other tests.

[0141] In one embodiment of the present invention, for example, a lithium-ion battery is subjected to a cycle test. Specifically, the batteries of Examples 1-25 and Comparative Examples 1-6 are respectively placed in a 45°C incubator for 120 minutes, and then subjected to a charge-discharge cycle test in a 45°C incubator at a charge-discharge rate of 1C / 1C within the operating voltage window. The initial discharge capacity of the battery and the discharge capacity after each cycle are recorded. The cycle is repeated for 600 times, and the capacity retention rate is calculated according to the following formula:

[0142] Capacity retention rate = discharge capacity per cycle / battery first discharge capacity * 100%.

[0143] Among them, in the positive electrode active material provided by the present invention, the operating voltage window of the lithium iron phosphate system is 2.5V~3.75V, the operating voltage window of the ternary material system is 2.8V~4.35V, and the operating voltage window of the lithium manganese iron phosphate system is 2.5V~4.3V.

[0144] Table 2. Performance test results of lithium-ion batteries in Examples 1-25 and Comparative Examples 1-6

[0145]

[0146]

[0147] Please refer to Table 1 and Table 2. By comparing Examples 1-11 and Comparative Example 3, as well as Example 25 and Comparative Example 6, it can be seen that when the first additive is added to the electrolyte, the low-temperature DCR, room-temperature DCR, DCR growth rate and volume expansion rate of the battery are significantly reduced, and the capacity recovery rate and capacity retention rate are significantly increased, indicating that the first additive, as a special type of heteroatom-containing bridge-ring organic matter, is very easy to undergo electrochemical catalytic reactions on the electrode surface during the charge and discharge process of the lithium-ion battery, thereby forming a uniform and dense passivation protective film. At the same time, the introduction of side chains containing unsaturated bonds such as double bonds or triple bonds on the bridge ring of the first additive can further effectively construct an interface film with a three-dimensional spatial network, which serves as a spatial three-dimensional channel for lithium ion conduction. At the same time, the heteroatoms in the first additive have a high electron-donating coordination ability, which can form an electrolyte with a high lithium ion conductivity, further reducing the interfacial transfer impedance of lithium ion transmission. Therefore, the first additive improves the cycle dynamics and high-temperature storage performance of the lithium-ion battery.

[0148] As shown in Tables 1 and 2, by comparing Examples 1, 5, and 11, it can be seen that when the B2 content increases from 0.5wt% to 2wt%, the low-temperature DCR, room-temperature DCR, DCR growth rate, and volume expansion rate of the battery are significantly reduced, while the capacity recovery rate and capacity retention rate are significantly increased. This indicates that when the B2 content increases from 0.5wt% to 2wt%, the battery's kinetic performance, cycling performance, and high-temperature storage performance are significantly improved. When the B2 content continues to increase from 2wt% to 5wt%, although the battery's room-temperature DCR continues to decrease, the low-temperature DCR, DCR growth rate, and volume expansion rate increase, while the capacity recovery rate and capacity retention rate decrease. This indicates that when the B2 content continues to increase from 2wt% to 5wt%, although the battery's room-temperature kinetic performance can be improved, the battery's low-temperature kinetic performance, cycling performance, and high-temperature storage performance deteriorate. Therefore, by controlling the content of the first additive, it is possible to balance the battery's kinetic performance, cycling performance, and high-temperature storage performance.

[0149] Referring to Table 1 and Table 2, it can be seen from the comparison between Example 8 and Example 13, Example 15 and Example 16, and Example 18 and Example 19 that when the second additive VC and the first additive are both present in the electrolyte, although the low-temperature DCR and room-temperature DCR of the battery increase, the DCR growth rate and volume expansion rate of the battery decrease, and the capacity recovery rate and capacity retention rate increase, indicating that the second additive and the first additive can act synergistically to further improve the cycle performance of the battery, effectively inhibit the increase of impedance during high-temperature storage, and improve the high-temperature storage performance of the battery.

[0150] Please refer to Table 1 and Table 2. By comparing Example 1 and Example 24, it can be seen that when the mass ratio of the first additive B2 to the second additive VC increases from 2:3 to 3.2:3, although the room temperature DCR of the battery decreases, the low temperature DCR, DCR growth rate and volume expansion rate increase, and the capacity recovery rate and capacity retention rate decrease. This shows that: with the increase of the mass ratio of the first additive to the second additive, the low temperature kinetic performance, high temperature storage performance and cycle performance of the battery deteriorate, but the room temperature kinetic performance of the battery is improved.

[0151] Referring to Table 1 and Table 2, a comparison of Example 5 and Example 8, Example 6 and Example 10, Example 6 and Example 12, and Examples 1, 10, and 12 shows that when the ortho position of the heteroatom X or Y in the first additive B1 is replaced by a fluorine atom, the room-temperature DCR of the battery is lower. This indicates that when the ortho position of the heteroatom X or Y in the first additive B1 contains a fluorine atom, the selective film-forming ability of the electrolyte can be improved, and the interface film formed with the participation of the first additive B1 has a higher content of inorganic LiF, which helps to reduce the interfacial impedance, extend the cycle life, and improve the kinetic performance of the lithium-ion battery.

[0152] As shown in Tables 1 and 2, by comparing Example 1 and Comparative Example 3, Example 14 and Comparative Example 2, and Example 16 and Comparative Example 4, it can be seen that the addition of the first additive to electrolytes composed of different lithium salts can improve the capacity recovery rate and capacity retention rate of the battery, and reduce the DCR growth rate, volume expansion rate, low-temperature DCR, and room-temperature DCR of the battery, thereby indicating that the first additive can improve the kinetic performance, cycle performance, and high-temperature storage performance of the battery in different lithium salt systems.

[0153] Please refer to Table 1 and Table 2. By comparing Example 1 and Comparative Example 3, as well as Example 20 and Comparative Example 5, it can be seen that when the positive electrode active material is a ternary system, the synergistic effect of the first additive and the second additive VC can also reduce the low-temperature DCR, room-temperature DCR, DCR growth rate and volume expansion rate of the battery, and improve the capacity retention rate of the battery. However, the improvement of the first additive and the second additive VC for the battery composed of the ternary system is less than the improvement for the battery composed of the lithium iron phosphate system, which shows that for the ternary system battery and the lithium iron phosphate system battery, the synergistic use of the first additive and the second additive can improve the battery's kinetic performance, high-temperature storage performance and cycle performance, but the improvement effect of the first additive and the second additive on the lithium iron phosphate system battery is more obvious.

[0154] As shown in Tables 1 and 2, by comparing Example 1 and Example 25, it can be seen that when the electrolyte contains both the second additive VC and the third additive DTD, although the low-temperature DCR and room-temperature DCR of the battery increase, the capacity recovery rate and capacity retention rate increase significantly, and the DCR growth rate and volume expansion rate decrease significantly, indicating that the second additive and the third additive work synergistically to improve the cycle performance and high-temperature storage performance of the battery.

[0155] As shown in Tables 1 and 2, a comparison of Example 1 and Example 21 shows that when the electrolyte contains the third additive DTD, although the battery's capacity recovery rate and capacity retention rate decrease, and the volume expansion rate and room-temperature DCR increase, the DCR growth rate and low-temperature DCR decrease. This indicates that the DTD third additive can help form an interfacial film with a certain degree of ion conductivity on the positive electrode side, helping to slightly improve the battery's low-temperature impedance and enhance low-temperature kinetic performance. Therefore, by adding the third additive to the electrolyte, the battery's low-temperature kinetic performance can be improved.

[0156] Please refer to Table 1 and Table 2. Comparing Example 1 and Examples 22-23, it can be seen that when the content of the third additive DTD in the electrolyte increases from 1wt% to 3wt% and 5wt%, the low-temperature DCR, DCR growth rate and volume expansion rate of the battery increase, and the capacity recovery rate and capacity retention rate decrease, but the room-temperature DCR shows a decreasing trend, indicating that as the content of the third additive DTD in the electrolyte increases from 1wt% to 3wt% and 5wt%, the interfacial impedance of the battery decreases, and the room-temperature impedance performance and room-temperature kinetic performance are improved.

[0157] The present invention also provides an electronic device, which includes at least one of the above-mentioned lithium-ion batteries, and the lithium-ion battery is used to provide electrical energy. The electronic device may be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, and an electric tool, etc. In one embodiment of the present invention, the vehicle is, for example, a new energy vehicle, which may be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, etc. The spacecraft includes airplanes, rockets, space shuttles, and spacecraft, etc. The electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. The electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the above-mentioned lithium-ion battery, and therefore includes the advantages of the above-mentioned lithium-ion battery, which will not be elaborated on here.

[0158] In summary, the present invention proposes a lithium-ion battery electrolyte and its application. By introducing a first additive into the electrolyte, the first additive has a higher dielectric constant and lithium ion migration constant, and also has the advantages of selective film formation, less high-temperature interface side reactions, low low-temperature viscosity and high electrochemical stability, thereby greatly improving the fast charge rate and low-temperature discharge capability of the phosphate system. Moreover, since the first additive has the advantage of selective film formation, the amount of the second additive in the electrolyte can be reduced, thereby saving the preparation cost of the electrolyte. Moreover, the synergistic effect of the first additive and the additive in the electrolyte can improve the cycle performance of the battery, and effectively suppress the growth of impedance during high-temperature storage, thereby improving the high-temperature storage performance of the battery.

[0159] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned 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-mentioned features with (but not limited to) technical features with similar functions disclosed in this application.

[0160] Except for the technical features described in the specification, the remaining technical features are known technologies to those skilled in the art. In order to highlight the innovative features of the present invention, the remaining technical features will not be described here in detail.

Claims

1. A lithium ion battery electrolyte, characterized in that At least the following components: lithium salts; solvents; as well as Additives, wherein the additives include a first additive, and the general structural formula of the first additive is: Wherein, n1 and n2 are each independently selected from any natural number between 0 and 5, X and Y are each independently selected from one of O, S, Se or Te, R1 and R2 are each 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 Epoxyalkyl, C 6～12 Aryl, C 6～12 Heteroaryl, carbonyl or C 2～6 At least one of the ester groups, Z and Q are each independently selected from one of O, S, CH or CH2.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that At least one of R1 and R2 includes F, C 1～6 Alkoxy, C 2～6 Alkenyl, C 2～10 Alkynyl or C 2～6 One or more ester groups.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that The first additive is selected from: At least one of .

4. The lithium-ion battery electrolyte according to claim 1, characterized in that The content of the first additive in the electrolyte is 0.5 wt%-6 wt%.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that The solvent includes cyclic esters and chain esters, the cyclic esters are selected from at least one of ethylene carbonate or propylene carbonate, the chain esters are selected from at least one of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, ethyl acetate, methyl acetate, ethyl formate, propyl formate, propyl acetate, methyl propionate, ethyl propionate or propyl propionate, and the mass ratio of the cyclic esters to the chain esters is (0.15-1):

1.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that The lithium salt includes a first lithium salt, which is a fluorine-containing sulfonyl imide lithium salt, selected from at least one of lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethylsulfonyl imide), and the content of the first lithium salt in the electrolyte is 5wt%-12wt%.

7. The lithium-ion battery electrolyte according to claim 6, characterized in that The lithium salt further includes a second lithium salt, and the second lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalatoborate) or lithium difluorooxalatoborate.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that The additives also include a second additive, which is selected from at least one of vinylene carbonate, 1,3-propane sultone, 1,3-propylene sultone, 2,4-butane sultone, methylene disulfonate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorophosphate, lithium difluorobisoxalatophosphate or vinyl sulfate, and the mass ratio of the first additive to the second additive is (0.2-0.9):

1.

9. The lithium-ion battery electrolyte according to claim 8, characterized in that The mass ratio of the first additive to the second additive is (0.3-0.5):

1.

10. A lithium ion battery, characterized in that: At least: A positive electrode plate, comprising a positive electrode active layer, wherein the positive electrode active layer comprises a positive electrode active material, wherein the positive electrode active material comprises an olivine-structured lithium-phosphate material, wherein the olivine-structured lithium-phosphate material is selected from at least one 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 iron manganese phosphate, or a composite material of lithium iron manganese phosphate and carbon; negative electrode; a separator, disposed between the positive electrode sheet and the negative electrode sheet; and The electrolyte is selected from the lithium ion battery electrolyte according to any one of claims 1 to 9.

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