Lithium ion battery electrolyte and application thereof

Abstract

The application provides a lithium ion battery electrolyte and application thereof, and 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 structural formula of the first additive is formula A, and the structural formula of the second additive is formula B; R1 is selected from any one of the following: -H, -F, -SiF3, C1-6 alkyl and fluorinated C1-6 alkyl, C1-6 alkoxy and fluorinated C1-6 alkoxy, C2-6 alkenyl and fluorinated C2-6 alkenyl, C2-6 alkenyloxy and fluorinated C2-6 alkenyloxy, C2-10 alkynyl and fluorinated C2-10 alkynyl, C2-10 alkynyloxy and fluorinated C2-10 alkynyloxy, C3-8 cycloalkyl and fluorinated C3-8 cycloalkyl, C3-8 cycloalkyloxy and fluorinated C3-8 cycloalkyloxy, C6-12 aryl and fluorinated aryl, C6-12 heteroaryl and fluorinated heteroaryl, a carbonyl group, a sulfonyl group and a fluorine-containing sulfonyl group or a phosphonyl group; X is selected from one of O or S atoms, and n is selected from any natural number in 1-4. The lithium ion battery electrolyte and application thereof can obtain a wide-temperature-range fast-charging type high-kinetics electrolyte.

Description

TECHNICAL FIELD

[0001] The present 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 the application of lithium ion batteries in the fields of digital cameras, mobile phones, notebook computers, electric tools and electric vehicles, lithium ion batteries are developing towards higher working voltage, higher energy and power density. However, due to the material chemical properties of lithium ion batteries, their practical application in specific environments is greatly limited, for example, in cold northern environments and outer space environments with extremely low temperature, they face difficulties in starting, range anxiety, insufficient low-temperature discharge power and charging difficulties.

[0003] In a low-temperature environment, there are problems such as low lithium ion transmission kinetics of electrolyte, high viscosity of electrolyte at low temperature, poor wettability, very low diffusion capacity of positive / negative active material bulk phase, poor quality of solid electrolyte interface (SEI), and great limitation of the popularization and application of lithium ion batteries. SUMMARY

[0004] The present application provides a lithium ion battery electrolyte and application thereof, which can effectively reduce the direct current impedance of lithium ion batteries at low temperature, obtain a wide-temperature-range fast-charging high-kinetic electrolyte, and improve the high-temperature gas production performance and high-temperature cycle performance of lithium ion batteries.

[0005] To solve the above technical problems, the present 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 structural formula of the first additive being Formula A, and the structural formula of the second additive being Formula B;

[0009]

[0010] wherein R1is selected from -H, -F, -SiF3, C1-6alkyl and fluoro-C1-6alkyl, C1-6alkoxy and fluoro-C1-6alkoxy, C2-6alkenyl and fluoro-C2-6alkenyl, C2-6alkenyloxy and fluoro-C2-6alkenyloxy, C2-10alkynyl and fluoro-C2-10alkynyl, C2-10alkynyloxy and fluoro-C2-10alkynyloxy, C3-8cycloalkyl and fluoro-C3-8cycloalkyl, C3-8cycloalkoxy and fluoro-C3-8cycloalkoxy, C6-12aryl and fluoro-aryl, C6-12heteroaryl and fluoro-heteroaryl, carbonyl, sulfonyl and fluorine-containing sulfonyl or phosphonyl; X is selected from one of O or S element atom, and n is selected from any natural number between 1 and 4.

[0011] In one embodiment of the present application, the first additive is selected from at least one of the following compounds: Compound A1, Compound A2, Compound A3, or Compound A4.

[0012] In one embodiment of the present application, the second additive is selected from at least one of the following compounds:

[0013] Compound B1, Compound B2, Compound B3, Compound B4, or Compound B5.

[0014] In one embodiment of the present application, the content of the first additive in the electrolyte is 0.1wt% to 10wt%, and the content of the second additive in the electrolyte is 0.1wt% to 8wt%.

[0015] In one embodiment of the present application, the content of the first additive in the electrolyte is 0.5wt% to 5wt%, and the content of the second additive in the electrolyte is 0.4wt% to 5wt%.

[0016] In one embodiment of the present application, the non-aqueous solvent is selected from one or a combination of several of the following: ethylene carbonate, propylene carbonate, trifluoromethyl propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, ethyl acetate, methyl acetate, ethyl formate, propyl formate, propyl acetate, methyl propionate, ethyl propionate or propyl propionate.

[0017] In one embodiment of the present application, the lithium salt includes lithium hexafluorophosphate and lithium bisfluorosulfonylimide, the content of the lithium salt in the electrolyte is 8wt% to 20wt%, and the content of the lithium bisfluorosulfonylimide in the electrolyte is 0.2wt% to 5wt%.

[0018] In one embodiment of the present application, the additive further comprises a third additive selected from at least one of vinylene carbonate, 1,3-propane sultone, 1,3-propene sultone, 2,4-butane sultone, methylene methanedisulfonate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorophosphate, lithium difluorophosphate bis(oxalato), or ethylene sulfate.

[0019] The present application also provides a lithium ion battery comprising:

[0020] a positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising a material having a phosphate structure;

[0021] a negative electrode sheet;

[0022] a separator disposed between the positive electrode sheet and the negative electrode sheet;

[0023] an electrolyte selected from the lithium ion battery electrolyte described above.

[0024] The present application also provides an electronic device comprising the lithium ion battery described above.

[0025] In summary, the present application proposes a lithium ion battery electrolyte and its application. Through the combined use of the first additive and the second additive, a lithium ion rapid migration channel can be constructed, the liquid distance can be shortened, the interfacial concentration polarization can be reduced, etc. The high-dissociation lithium salt low-viscosity electrolyte can effectively reduce the direct current impedance of the lithium ion battery at low temperature, reduce the desolvation energy of the system at low temperature, and obtain a wide-temperature-range fast-charging high-kinetic electrolyte. The solid-liquid concentration polarization and electrochemical polarization of the electrode interface can be greatly reduced, and the fast-charging rate window of the lithium ion battery can be greatly improved. The interface film can be improved, the formed interface film is beneficial to the lithium ion shuttle interface, does not increase the interface transfer impedance, improves the cycle kinetics level, improves the high-temperature gas production performance of the lithium ion battery, improves the high-temperature cycle capacity retention rate, and can play a unique advantage in the phosphate system fast-charging long-life. DETAILED DESCRIPTION

[0026] The embodiments of the present application will be described in detail by specific examples below, and those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the specification. The present application can also be implemented or applied by different specific embodiments, and various modifications or changes can be made to the details in the specification based on different views and applications without departing from the spirit of the present application.

[0027] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0028] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention proposes a lithium-ion battery electrolyte, comprising at least a non-aqueous solvent, a lithium salt, and additives, wherein the additives include a first additive and a second additive. The first additive has the structural formula A, and the second additive has the structural formula B.

[0030] Wherein, R1 is selected from any one of -H, -F, -SiF3, C1-6 alkyl and fluorinated C1-6 alkyl, C1-6 alkoxy and fluorinated C1-6 alkoxy, C2-6 alkenyl and fluorinated C2-6 alkenyl, C2-6 alkenoxy and fluorinated C2-6 alkenoxy, C2-10 alkynyl and fluorinated C2-10 alkynyl, C2-10 alkynoxy and fluorinated C2-10 alkynoxy, C3-8 cycloalkyl and fluorinated C3-8 cycloalkyl, C3-8 epoxyalkyl and fluorinated C3-8 epoxyalkyl, C6-12 aryl and fluorinated aryl, C6-12 heteroaryl and fluorinated heteroaryl, carbonyl, sulfonyl and fluorinated sulfonyl or phosphoryl; X is selected from one of O or S elements, and n is selected from any natural number from 1 to 4. By using a first additive with high dissociation lithium salt and a second additive with low viscosity, a rapid lithium-ion migration channel can be constructed, shortening the liquid path distance and reducing interfacial concentration polarization. The electrolyte with high dissociation lithium salt and low viscosity can effectively reduce the direct current resistance (DCR) of lithium-ion batteries at low temperatures, reduce the desolvation energy of the system at low temperatures, and obtain a high-kinetic electrolyte with wide temperature range and fast charging capability.

[0031] In one embodiment of the present invention, the first additive is selected, for example, from any one or a combination of the following compounds:

[0032] Compound A1 Compound A2 Compound A3 or Compound A4, etc. The first additive is an asymmetric lithium salt, which has a low desolvation energy barrier and can significantly reduce solid-liquid concentration polarization and electrochemical polarization at the electrode interface, thereby greatly improving the fast charging rate window of lithium-ion batteries.

[0033] In one embodiment of the present invention, the second additive is selected, for example, from any one or a combination of the following compounds:

[0034] Compound B1, Compound B2 Compound B3, Compound B4 or Compound B5, etc. The second additive has a lower viscosity and, synergistically with the first additive, exhibits a higher lithium-ion migration coefficient, resulting in better kinetic performance of the system. It further reduces interfacial polarization and improves the high-temperature capacity cycle retention of lithium-ion batteries. Simultaneously, the second additive improves interfacial film formation, forming a film that facilitates lithium-ion shuttle movement without increasing interfacial transfer resistance, thus enhancing cycle kinetics, improving high-temperature gas generation performance, and increasing cycle capacity retention. It demonstrates unique advantages in the fast-charging and long-life characteristics of phosphate systems.

[0035] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.1 wt% to 10 wt%, or for example, 0.5 wt% to 5 wt%. The content of the second additive in the electrolyte is, for example, 0.1 wt% to 8 wt%, or for example, 0.4 wt% to 5 wt%. By controlling the content of the first additive and the second additive, multiple performance characteristics of the lithium-ion battery can be balanced, resulting in the optimal overall performance of the lithium-ion battery.

[0036] In one embodiment of the present invention, the additive further includes a third additive, which is selected from at least one of vinylene carbonate (VC), 1,3-propanesultone (PS), 1,3-propene-1,3-sultone (PST), 2,4-butanesultone, methylene methanedisulfonate (MMDS), lithium difluorooxalate borate (LiODFB), lithium bis(oxalate borate) (LiBOB), lithium difluorophosphate (LiDFP), lithium difluorodioxalate phosphate (LiDFOP), or ethylene sulfate (1,3,2-Dioxathiolane 2,2-dioxide (DTD). The total content of the third additive in the electrolyte is 0.1 wt% to 3 wt%. The third additive can synergistically improve the integrity and density of the interfacial film, and enhance the cycle performance and safety performance of the lithium-ion battery, in conjunction with the first and second additives.

[0037] In one embodiment of the present invention, the lithium salt is selected from any one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium dioxalate borate, or lithium difluorooxalate borate, and the content of the lithium salt in the electrolyte is 8 wt% to 20 wt%, or for example, 10 wt% to 15 wt%. In another embodiment of the present invention, the lithium salt is selected from lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the content of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.2 wt% to 5 wt%, in order to improve the charge and 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.

[0038] In one embodiment of the present invention, the non-aqueous solvent includes, for example, at least one or a combination of ethylene carbonate (EC), propylene carbonate (PC), trifluoromethyl propylene, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl acetate (EA), methyl acetate (MA), ethyl formate (MEE), propyl formate (PF), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), or n-Propyl propionate (PP).

[0039] In one embodiment of the present invention, when preparing the electrolyte, a non-aqueous solvent is uniformly mixed in a glove box with an inert gas atmosphere such as argon, where the moisture content and oxygen content are both less than or equal to 0.1 ppm. Sufficiently dried lithium salt is then added to the non-aqueous solvent, along with additives, to prepare a lithium-ion battery electrolyte. The contents described in this application are weight percentages calculated based on the total weight of the electrolyte.

[0040] This invention proposes a lithium-ion battery, comprising a casing and a bare cell disposed within the casing. The bare cell includes a positive electrode, a separator, and a negative electrode. The separator is placed between the positive and negative electrodes to prevent short circuits and allow lithium ions to pass through. The positive electrode, separator, and negative electrode are sequentially stacked to ensure that a separator is present between any positive and negative electrode. A multi-layered stack is obtained by winding or folding, and this stack is then inserted into the battery casing as the bare cell. Finally, an electrolyte is injected into the casing once or in multiple stages to completely immerse the bare cell in the electrolyte. The electrolyte, for example, is selected from the above-mentioned electrolytes and serves to conduct ions between the positive and negative electrodes. In one embodiment of this invention, the lithium-ion battery is, for example, a secondary battery, which may be, for example, a pouch battery, a prismatic battery, or a cylindrical battery. This invention does not specifically limit the type of lithium-ion battery.

[0041] In an embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer coated at least on one surface of the positive electrode current collector. Among them, the positive electrode current collector is, for example, a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, etc. In addition to the foil, the positive electrode current collector can also be used in any one or a combination of multiple forms such as film, mesh, porous, foam or non-woven fabric. Among them, the thickness of the positive electrode current collector is, for example, 8μm to 15μm. In this embodiment, the positive electrode current collector is, for example, aluminum foil, and the thickness of the aluminum foil is, for example, 13μm.

[0042] In an embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a binder, a conductive agent, etc. Among them, the positive electrode active material, for example, includes a material with a phosphate structure, specifically, for example, at least one or more of lithium iron phosphate or lithium manganese iron phosphate, etc., to improve the safety, cycle performance and temperature adaptability of the lithium-ion battery. Among them, the general formula of lithium manganese iron phosphate is LiMnFe 1-x PO4, and the value range of x is 0 < x < 1. The binder is, for example, selected from any one or more of polyvinylidene fluoride (Polyvinylidene Fluoride, PVDF), polytetrafluoroethylene (Polytetrafluoroethylene PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer (TFE-HFP-VDF) or tetrafluoroethylene-hexafluoropropylene copolymer (FEP), etc. The conductive agent is, for example, selected from any one or more of conductive carbon black (Super P), acetylene black or Ketjen black, etc. The mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode active layer is, for example, (90 to 97):(1 to 5):(2 to 5).

[0043] In an embodiment of the present invention, the positive electrode active material is, for example, lithium iron phosphate, the binder is, for example, selected from polyvinylidene fluoride, and the conductive agent is, for example, selected from acetylene black. After mixing the positive electrode active material, the conductive agent and the binder, for example, in a mass ratio of 97:1:2, an organic solvent is added, and the mixture is stirred under a vacuum mixer until the system becomes homogeneous to obtain a positive electrode slurry. Among them, the organic solvent is, for example, selected from N-methylpyrrolidone (N-Methylpyrrolidone, NMP). The positive electrode slurry is uniformly coated on the aluminum foil, then dried at room temperature and transferred to an oven for drying, and a positive electrode sheet is obtained through processes such as cold pressing, edge trimming, slicing and slitting. The present application does not limit the preparation method of the positive electrode sheet. In other embodiments, the positive electrode sheet can also be obtained by any other method of forming a positive electrode sheet.

[0044] In one embodiment of the present invention, the negative electrode sheet includes, for example, a negative electrode current collector and a negative electrode active layer coated at least on one surface of the negative electrode current collector. The negative electrode current collector is selected from, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector, and the thickness of the negative electrode current collector is, for example, 8 μm to 15 μm. In this embodiment, the negative electrode current collector is, for example, copper foil, and the thickness of the copper foil is, for example, 13 μm.

[0045] 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 negative electrode active material includes, for example, any one or more combinations of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, or lithium titanate. The silicon-based material includes, for example, one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys; the tin-based material includes, for example, one or more of elemental tin, tin oxide compounds, or tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0046] In one embodiment of the present invention, the binder is selected from at least one of the following: polymerized styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylic acid (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), or carboxymethyl chitosan (CMCS). The thickener includes, for example, sodium carboxymethyl cellulose (CMC-Na), and the conductive agent is selected from any one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers. The mass ratio of negative electrode active material, conductive agent, binder and thickener in negative electrode active layer is, for example, (94-97):(1-2):(1-2):(1-2).

[0047] In one embodiment of the present invention, the negative electrode active material is selected, for example, from graphite and silicon-carbon composite, and the mass ratio of silicon-carbon composite to graphite is, for example, 2:98 to 5:95. By adding a small amount of silicon-carbon composite, the thickness of the negative electrode active layer can be reduced, the fast-charging window of the lithium-ion battery can be improved, and the impact on the first discharge capacity can be reduced. The conductive agent is selected, for example, from conductive carbon black, the thickener is selected, for example, from sodium carboxymethyl cellulose, and the binder is selected, for example, from styrene-butadiene rubber. In one embodiment of the present invention, the negative electrode active material, conductive agent, thickener, and binder are mixed, for example, at a mass ratio of 96.5:1:1:1.5, deionized water is added, and the mixture is mixed evenly under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, and then dried at room temperature and transferred to an oven for drying. After cold pressing, edge trimming, cutting, and slitting, a negative electrode sheet is obtained. In other embodiments, the negative electrode sheet can also be obtained by any other method of forming a negative electrode sheet.

[0048] In one embodiment of the present invention, the separator is, for example, a ceramic separator, a polymer separator, a non-woven fabric or an inorganic-organic composite separator, including but not limited to single-layer polypropylene (PP) membrane, single-layer polyethylene (PE) membrane, double-layer PP / PE membrane, double-layer PP / PP membrane and triple-layer PP / PE / PP membrane, and the thickness of the separator is, for example, 9μm to 15μm.

[0049] In one embodiment of the present invention, the above-mentioned positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrode to provide isolation. A bare cell is obtained by winding or stacking the electrodes. The bare cell is then installed in a casing, dried, injected with electrolyte, and sealed. After at least vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0050] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the present invention, and all such modifications fall within the technical scope of the present invention.

[0051] Example 1

[0052] Electrolyte preparation: In an argon-filled glove box with an oxygen content of 0.1 ppm and a water content of 0.1 ppm, EC:PC:EMC:DMC were mixed in a mass ratio of 25:5:50:20 to obtain a mixed solvent. Lithium hexafluorophosphate and lithium difluorosulfonylimide were dissolved in the mixed solvent, and then compound A1 was added and mixed thoroughly to obtain the electrolyte. The electrolyte contained 10 wt% lithium hexafluorophosphate, 3 wt% lithium difluorosulfonylimide, and 0.2 wt% compound A1.

[0053] Preparation of the positive electrode sheet: Lithium iron phosphate, acetylene black, and polyvinylidene fluoride were mixed at a mass ratio of 97:1:2, and NMP was added. The mixture was stirred under vacuum until the system was homogeneous to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated onto aluminum foil, then air-dried at room temperature and transferred to an oven for drying. The positive electrode sheet was obtained through cold pressing, edge trimming, cutting, and slitting processes.

[0054] Preparation of negative electrode sheet: The negative electrode active material is a graphite and silicon-carbon composite, and the mass ratio of silicon-carbon composite to graphite is 3:97. The negative electrode active material, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 96.5:1:1:1.5. Deionized water is added and the mixture is mixed evenly under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is coated on copper foil, and then dried at room temperature and transferred to an oven for drying. After cold pressing, edge trimming, sheet cutting and slitting processes, the negative electrode sheet is obtained.

[0055] Selection of diaphragm: 9μm thick polyethylene is used as the base membrane.

[0056] Battery fabrication: The positive electrode, separator, and negative electrode are stacked sequentially and wound together, with the separator positioned between the positive and negative electrodes to act as a separator, resulting in a bare cell. The bare cell is then placed in an aluminum-plastic film, dried, injected with electrolyte, and sealed. After undergoing at least vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0057] Example 2

[0058] In the electrolyte, the content of compound A1 was 0.5 wt%, and the other steps were consistent with those in Example 1.

[0059] Example 3

[0060] In the electrolyte, the content of compound A1 is 1 wt%, and the other steps are consistent with those in Example 1.

[0061] Example 4

[0062] In the electrolyte, the content of compound A1 was 5 wt%, and the other steps were consistent with those in Example 1.

[0063] Example 5

[0064] In the electrolyte, the content of compound A1 is 5 wt%, and compound B1 is added at a content of 0.5 wt%. Other steps are consistent with those in Example 1.

[0065] Example 6

[0066] In the electrolyte, the content of compound A1 is 5 wt%, and compound B1 is added at a content of 3 wt%. Other steps are consistent with those in Example 1.

[0067] Example 7

[0068] In the electrolyte, the content of compound A1 is 5 wt%, and compound B1 is added at a content of 4 wt%. Other steps are consistent with those in Example 1.

[0069] Example 8

[0070] In the electrolyte, the content of compound A1 is 5 wt%, and compounds B2 and B4 are added at the same time, with the content of compound B2 being 1.5 wt% and the content of compound B4 being 1.5 wt%. Other steps are consistent with those in Example 1.

[0071] Example 9

[0072] In the electrolyte, the content of compound A1 is 5 wt%, and compounds B3 and B5 are added at the same time, with the content of compound B3 being 1.5 wt% and the content of compound B5 being 1.5 wt%. Other steps are consistent with those in Example 1.

[0073] Example 10

[0074] In the electrolyte, the content of compound A1 is 3 wt%, and compounds B3 and B5 are added at the same time, with the content of compound B3 being 1.5 wt% and the content of compound B5 being 1.5 wt%. Other steps are consistent with those in Example 1.

[0075] Example 11

[0076] In the electrolyte, the first additives are compounds A1 and A2, with compound A1 having a content of 2 wt% and compound A2 having a content of 3 wt%. Compound B4 is also added, with a content of 3 wt%. Other steps are consistent with those in Example 1.

[0077] Example 12

[0078] In the electrolyte, the first additives are compounds A1 and A2, with compound A1 having a content of 3 wt% and compound A2 having a content of 3 wt%. Compound B1 is also added, with a content of 3 wt%. Other steps are consistent with those in Example 1.

[0079] Example 13

[0080] In the electrolyte, the content of compound A1 is 5 wt%, and compound B3 is added at the same content of 5 wt%. Other steps are consistent with those in Example 1.

[0081] Example 14

[0082] In the electrolyte, the content of compound A1 is 5 wt%, and compound B3 is added at a content of 7 wt%. Other steps are consistent with those in Example 1.

[0083] Example 15

[0084] In the electrolyte, the first additive is compound A3, with a content of 5 wt%, and compound B2 is added at a content of 3 wt%. Other steps are consistent with those in Example 1.

[0085] Example 16

[0086] In the electrolyte, the first additives are compounds A1 and A3, with compound A1 having a content of 3 wt% and compound A3 having a content of 2 wt%. Compound B3 is also added, with a content of 3 wt%. All other steps remain unchanged and are consistent with those in Example 1.

[0087] Example 17

[0088] In the electrolyte, the first additives are compounds A3 and A4, with compound A3 having a content of 2 wt% and compound A4 having a content of 3 wt%. Compound B4 is also added, with a content of 3 wt%. Other steps are consistent with those in Example 1.

[0089] Example 18

[0090] In the electrolyte, the first additives are compounds A1 and A4, with compound A1 having a content of 2 wt% and compound A4 having a content of 3 wt%. Compound B5 is also added, with a content of 3 wt%. Other steps are consistent with those in Example 1.

[0091] Example 19

[0092] In the electrolyte, the first additives are compounds A2 and A4, with compound A2 having a content of 3 wt% and compound A4 having a content of 2 wt%. Compounds B2 and B5 are also added, with compound B2 having a content of 1.5 wt% and compound B5 having a content of 1.5 wt%. Other steps are consistent with those in Example 1.

[0093] Example 20

[0094] In the electrolyte, the first additives are compounds A1, A3, and A4, with compound A1 having a content of 2 wt%, compound A3 having a content of 2 wt%, and compound A4 having a content of 1 wt%. Simultaneously, compounds B1, B2, and B4 are added, with compound B1 having a content of 1 wt%, compound B2 having a content of 1 wt%, and compound B4 having a content of 1 wt%. Other steps are consistent with those in Example 1.

[0095] Example 21

[0096] PS was added to the electrolyte at a concentration of 1 wt%, and the other steps remained the same as in Example 6.

[0097] Example 22

[0098] PST was added to the electrolyte at a concentration of 1 wt%, and the other steps remained the same as in Example 6.

[0099] Example 23

[0100] LiODFB was added to the electrolyte at a concentration of 1 wt%, and the other steps were the same as in Example 6.

[0101] Comparative Example 1

[0102] In the electrolyte, neither the first nor the second additive is added, and the other steps are the same as in Example 1.

[0103] Comparative Example 2

[0104] Vitamin C was added to the electrolyte at a concentration of 0.5 wt%, while the other steps remained the same as in Comparative Example 1.

[0105] Comparative Example 3

[0106] Vitamin C was added to the electrolyte at a concentration of 35 wt%, while the other steps remained the same as in Comparative Example 1.

[0107] Comparative Example 4

[0108] Compound B1 was added to the electrolyte at a concentration of 0.5 wt%, while the other steps remained the same as in Comparative Example 1.

[0109] Comparative Example 5

[0110] Fluoroethylene carbonate (FEC) was added to the electrolyte at a concentration of 0.5 wt%, while the other steps remained the same as in Comparative Example 1.

[0111] In this invention, the electrolyte composition of the lithium-ion battery in Examples 1-23 and Comparative Examples 1-5 is shown in Table 1. Different electrolytes were used to prepare lithium-ion batteries, and the performance of the lithium-ion batteries was tested. The test results are shown in Table 2.

[0112] In one embodiment of the present invention, the test method for low-temperature DCR is as follows: At 25°C, the lithium-ion battery is charged at a constant current of 1 / 3C to 3.75V, 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 2.5V. The above charging steps are repeated once, and the capacity of this charge is recorded as C0. The battery is then discharged at a constant current of 1 / 3C to (50% * C0). The battery is then placed at -20°C, and the initial voltage is recorded as U0. The battery is discharged at a constant current of 1C for 30s, and the final voltage is recorded as U1. DCR = (U0 - U1) / (C0 * 1).

[0113] In one embodiment of the present invention, the test method for the initial DCR test at room temperature is as follows: At 25°C, the lithium-ion battery is charged at a constant current of 1 / 3C to 3.75V, 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 2.5V. The above charging steps are repeated, and after recording the charging capacity as C0, the next charging capacity is recorded as C1. The battery is discharged at a constant current of 1 / 3C to (50% * C1), and the initial voltage is recorded as U2. The battery is discharged at a constant current of 1C for 30s, and the final voltage is recorded as U3. The initial DCR at room temperature = (U2 - U3) / (C1 * 1).

[0114] In one embodiment of the present invention, the high-temperature storage test method is as follows: The lithium-ion battery is stored at 60°C for 30 days (30D). Then, the battery is discharged at 25°C with a constant current of 1 / 3C to 2.5V, then charged at a constant current of 1 / 3C to 3.75V, 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 2.5V, and the discharge capacity is recorded as C2. The capacity recovery rate is (C2 / C1)*100%. The above charging steps are repeated, and the second charge capacity is recorded as C3. The battery is discharged at a constant current of 1 / 3C to (50%*C3), and the initial voltage is recorded as U4. The battery is discharged at a constant current of 1C for 30s, and the final voltage is recorded as U5. DCR = (U4-U5) / (C3*1). DCR growth rate = (DCR after 30 days of storage - initial DCR) / initial DCR*100%. Simultaneously, the volume V1 of the lithium-ion battery at 25°C before storage and the volume V2 at room temperature after 30 days of storage at 60°C are recorded. The volume expansion rate is calculated as (V2 - V1) / V1 * 100%. In this embodiment, the operating voltage window of the lithium iron phosphate system is 2.5V to 3.75V. In other embodiments, when other positive electrode active materials are selected, the operating voltage window is adjusted according to the positive electrode active material.

[0115] In one embodiment of the present invention, the conductivity test method is as follows: the electrolytes of the examples and comparative examples are prepared and placed in a temperature chamber at 25±0.1℃ for 30 minutes. Then the electrolytes are placed in the sample cell, and data is read using a Mettler electrode 731-ISM. Each group is tested three times and the average value is recorded as the data.

[0116] In one embodiment of the present invention, the high-temperature cycling test method is as follows: The batteries obtained in the examples and comparative examples are placed in a 45°C chamber for 120 minutes, and then charged and discharged in a 45°C constant temperature chamber at a charge / discharge rate of 2C / 2C within a range of 2.8 to 3.75V. The initial discharge capacity of the battery and the discharge capacity after each cycle are recorded. After 600 cycles, the capacity retention rate is calculated as: discharge capacity per cycle / initial discharge capacity of the battery * 100%.

[0117] Table 1. Components and contents of additives in electrolytes in Examples 1-23 and Comparative Examples 1-5

[0118]

[0119] Table 2 shows the performance of lithium-ion batteries in Examples 1-23 and Comparative Examples 1-5.

[0120]

[0121] Please refer to Tables 1 and 2. Comparing Examples 1-4 and Comparative Example 1, it can be seen that when neither the first nor the second additive is added to the electrolyte, the electrolyte conductivity is low, the low-temperature DCR and room-temperature DCR of the lithium-ion battery are high, the high-temperature storage capacity recovery rate and high-temperature cycle capacity retention rate are low, and the high-temperature storage volume expansion rate is large, indicating poor performance of the lithium-ion battery. When only the first additive is added to the electrolyte, and the electrolyte conductivity increases with the increase of the content of the first additive, the room-temperature and low-temperature DCR are smaller. Because the desolvation barrier of this asymmetric lithium salt is low, it can significantly reduce the solid-liquid concentration polarization and electrochemical polarization at the electrode interface, greatly improving the fast charging rate window of the cell system.

[0122] Please refer to Tables 1 and 2. Comparing Examples 4-9 and Comparative Example 4, it can be seen that when only the second additive is added to the electrolyte, the conductivity of the electrolyte slightly increases, the low-temperature DCR and room-temperature DCR of the lithium-ion battery decrease, and the high-temperature storage volume expansion rate, high-temperature storage capacity recovery rate, and high-temperature cycle capacity retention are improved. This indicates that adding only the second additive improves the performance of the lithium-ion battery. Comparing Examples 4 and Examples 5-9, through the synergistic effect of the first and second additives, the interfacial polarization of the system can be further reduced. Compared with the first additive alone, the high-temperature capacity cycle retention rate of the lithium-ion battery is higher, and high-temperature storage gas generation is improved. This is because the asymmetric lithium salt and the low-viscosity second additive, through synergistic effect, have a higher lithium-ion migration coefficient, resulting in better kinetic performance of the system. Moreover, the second additive has the ability to form an interfacial film, which improves high-temperature gas generation compared to VC film formation, without causing excessively high initial interfacial impedance, and its cycle kinetics are also relatively high.

[0123] Please refer to Tables 1 and 2. Comparing Examples 5-7, it can be seen that when the content of the first additive is fixed and the content of the second additive is increased, the conductivity of the electrolyte can be improved, and the high-temperature storage volume expansion rate, high-temperature storage capacity recovery rate, and high-temperature cycle capacity are maintained and improved. However, further increases in content reduce the improvement. Therefore, controlling the amount of the first and second additives can improve the performance of lithium-ion batteries while reducing the use of additives and lowering costs. Comparing Examples 8-20, it can be seen that different combinations of the first and second additives can improve the performance of lithium-ion batteries, but the improvement in different performance aspects is slightly different. Therefore, different combinations of the first and second additives can be selected purposefully according to the intended use.

[0124] Please refer to Tables 1 and 2. By comparing with Comparative Examples 2-5, it can be seen that the second additive has the same film-forming ability as VC or FEC. The resulting interfacial film is conducive to lithium-ion shuttle interface, does not increase interfacial transfer impedance, improves cycle kinetics, and has a high cycle capacity retention rate. Through the combined use of the first and second additives, it can play a unique advantage in fast charging and long life of phosphate system.

[0125] Please refer to Tables 1 and 2. Comparing Examples 6 and 21-23, it can be seen that when the third additive is PS or PST, the resulting interfacial film is more resilient and has better high-temperature stability. It also works synergistically with the first and second additives to further improve the high-temperature storage performance of the lithium-ion battery, although the battery's discharge capacity (DCR) will increase slightly. The additive LiDFOB helps reduce interfacial impedance, resulting in an interfacial film with higher ion-conducting capacity, which further helps reduce interfacial impedance and increase discharge capacity.

[0126] This invention also provides an electronic device comprising at least one of the aforementioned lithium-ion batteries, which provides electrical energy. The electronic device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc. In one embodiment of this invention, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power 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 aforementioned lithium-ion battery, and therefore the advantages of including the aforementioned lithium-ion battery are not elaborated here.

[0127] In summary, this invention proposes a lithium-ion battery electrolyte and its application. Through the combined use of a first additive and a second additive, a rapid lithium-ion migration channel can be constructed, shortening the liquid path distance and reducing interfacial concentration polarization. The high-dissociation lithium salt and low-viscosity electrolyte effectively reduces the DC impedance of lithium-ion batteries at low temperatures, lowers the desolvation energy of the system at low temperatures, and obtains a high-kinetic electrolyte with a wide temperature range and fast charging capability. It can significantly reduce solid-liquid concentration polarization and electrochemical polarization at the electrode interface, greatly improving the fast-charging rate window of lithium-ion batteries. It can improve interfacial film formation; the formed interfacial film facilitates lithium-ion shuttle passage without increasing interfacial transfer impedance, improving cycle kinetics, enhancing the high-temperature gas generation performance of lithium-ion batteries, and increasing high-temperature cycle capacity retention. It can exert unique advantages in the fast-charging and long-life characteristics of phosphate systems.

[0128] The above description is merely a preferred embodiment of this 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 a 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. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0129] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail 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 additives include a first additive and a second additive, wherein the first additive has the structural formula of formula A and the second additive has the structural formula of formula B; Wherein, R1 is selected from any one of -H, -F, -SiF3, C1-6 alkyl and fluorinated C1-6 alkyl, C1-6 alkoxy and fluorinated C1-6 alkoxy, C2-6 alkenyl and fluorinated C2-6 alkenyl, C2-6 alkenoxy and fluorinated C2-6 alkenoxy, C2-10 alkynyl and fluorinated C2-10 alkynyl, C2-10 alkynoxy and fluorinated C2-10 alkynoxy, C3-8 cycloalkyl and fluorinated C3-8 cycloalkyl, C3-8 epoxyalkyl and fluorinated C3-8 epoxyalkyl, C6-12 aryl and fluorinated aryl, C6-12 heteroaryl and fluorinated heteroaryl, carbonyl, sulfonyl and fluorinated sulfonyl or phosphoryl; X is selected from one of O or S elements, and n is selected from any natural number from 1 to 4.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first additive is selected from at least one of the following compounds:

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The second additive is selected from at least one of the following compounds:

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first additive is present in the electrolyte at a concentration of 0.1 wt% to 10 wt%, and the second additive is present in the electrolyte at a concentration of 0.1 wt% to 8 wt%.

5. The lithium-ion battery electrolyte according to claim 4, characterized in that, The first additive is present in the electrolyte at a concentration of 0.5 wt% to 5 wt%, and the second additive is present in the electrolyte at a concentration of 0.4 wt% to 5 wt%.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The non-aqueous solvent is selected from one or a combination of several of ethylene carbonate, propylene carbonate, trifluoromethyl propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, ethyl acetate, methyl acetate, ethyl formate, propyl formate, propyl acetate, methyl propionate, ethyl propionate, or propyl propionate.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, the lithium salt in the electrolyte is 8 wt% to 20 wt%, and the lithium bis(fluorosulfonyl)imide in the electrolyte is 0.2 wt% to 5 wt%.

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

9. A lithium-ion battery, characterized in that, include: A positive electrode sheet, wherein the positive electrode sheet includes a positive active material, and the positive active material includes a material having a phosphate structure; 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 1-8.

10. An electronic device, characterized in that, Including the lithium-ion battery as described in claim 9.

Images