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 the first additive comprises a carbodiimide cyclic compound. The lithium ion battery electrolyte and application thereof can improve the high-temperature storage and safety performance of the lithium ion battery.

Description

Technical Field

[0001] This invention relates to the field of power battery technology, specifically to a lithium-ion battery electrolyte and its application. Background Technology

[0002] Lithium-ion batteries have rapidly developed in fields such as electric vehicles, power tools, and electric bicycles, capturing a significant market share. While consumers experience numerous conveniences with the widespread application of lithium-ion batteries, higher demands are being placed on their safety. Typically, the positive electrode active material for higher energy density lithium-ion batteries is a nickel-cobalt-manganese ternary material (NCM). During charging and discharging, the volume of the lattice in the layered structure of the ternary positive electrode active material expands and contracts, and its oxygen release reaction intensifies. This inevitably leads to the thermal runaway safety risk caused by oxygen, resulting in safety anxiety for users and necessitating further improvements and solutions. Summary of the Invention

[0003] This invention proposes a lithium-ion battery electrolyte and its application. The lithium-ion battery electrolyte and its application provided by this invention can improve the high-temperature storage and safety performance of lithium-ion batteries.

[0004] To address the aforementioned technical problems, the present invention provides a lithium-ion battery electrolyte, comprising at least the following components:

[0005] Non-aqueous solvents;

[0006] Lithium salts; and

[0007] The additive includes a first additive, which comprises a carbodiimide cyclic compound.

[0008] In one embodiment of the present invention, the carbodiimide cyclic compound is selected from compounds having any one of formulas I-IV:

[0009]

[0010] Wherein, n1-n8 are each an independent integer from 0 to 3, X and Y are each independently selected from any one of the elements P, As, S, or Se, Z is selected from any one of the elements O, S, or Se, and R1, R2, R3, and R4 are each independently selected from H, C, and C. 1～6 Alkyl, C 1～6 Alkoxy, C 2～6 alkenyl, C 2～6 alkenyloxy group, C 2～10 alkynyl group, C 2～10 Acryloxy group, C 3～8 cycloalkyl, C 3～8 Epoxyalkyl, C 6～12Aryl, C 6～12 heteroaryl, carbonyl or C 2～6 Any one or a combination of several ester groups.

[0011] In one embodiment of the present invention, at least one of X and Y includes any one of P, S or Se, and at least one of Z includes an element atom of O or S.

[0012] In one embodiment of the present invention, the carbodiimide cyclic compound is selected from at least one or more combinations of the following compounds: In compound B, n3 is an integer between 0 and 3.

[0013] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.1wt% to 15wt%.

[0014] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.5 wt% to 5 wt%.

[0015] In one embodiment of the present invention, the additive further includes a second additive, the second additive being selected from at least one or more combinations of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonyl lactone, 1,3-propenesulfonyl lactone, 2,4-butanesulfonyl lactone, methanedisulfonate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, lithium difluorophosphate, or vinyl sulfate, and the content of the second additive in the electrolyte is 0.1 wt% to 3 wt%.

[0016] In one embodiment of the present invention, the non-aqueous solvent is selected from at least one or more combinations of ethylene carbonate, 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 invention, the lithium salt is selected from one or more combinations of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethyl)sulfonylimide, and the concentration of the lithium salt in the electrolyte is 0.3 mol / L to 2 mol / L.

[0018] The present invention also provides a lithium-ion battery, comprising:

[0019] Positive electrode sheet;

[0020] Negative electrode plate;

[0021] A diaphragm is disposed between the positive electrode and the negative electrode;

[0022] Electrolyte, the electrolyte being the lithium-ion battery electrolyte described above.

[0023] In one embodiment of the present invention, the positive electrode and / or the separator includes a first additive.

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

[0025] In summary, this invention proposes a lithium-ion battery electrolyte and its application. The first additive can oxidize and decompose on the electrode surface, generating a ring-opening polymerization reaction to form a complete, dense, and uniform passivation film. It also possesses a certain ability to neutralize reactive oxygen species. Under overcharge conditions, the interfacial film formed by the carbodiimide cyclic compound immediately blocks the reactive oxygen reaction, effectively solving the lithium battery safety problem of rapid heat release caused by interfacial side reactions triggered by the phase transition of the positive electrode active material and the resulting large amount of reactive oxygen. It can significantly reduce the further oxidation of solvents such as ethylene carbonate in the electrolyte by the large amount of reactive oxygen released from the positive electrode active material, effectively preventing the thermal release reaction of the lithium-ion battery from remaining at the thermal runaway trigger temperature T2 stage, thus widening the safe operating window of the lithium battery. Simultaneously, it does not significantly affect the fast charging and rate performance kinetics of the lithium battery. It can improve the integrity and density of the interfacial film, enhancing the high-temperature storage and safety performance of the lithium-ion battery. Detailed Implementation

[0026] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[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, which comprises a carbodiimide cyclic compound selected from compounds having any one of formulas I-IV.

[0030]

[0031] Where n1-n8 are each an independent integer from 0 to 3, X and Y are each independently selected from any one of the elements P, As, S, or Se, Z is selected from any one of the elements O, S, or Se, and R1, R2, R3, and R4 are each independently selected from H, C, and C. 1～6 Alkyl, C 1～6 Alkoxy, C 2～6 alkenyl, C 2～6 alkenyloxy group, C 2～10 alkynyl group, C 2～10 Acryloxy group, C 3～8 cycloalkyl, C 3～8 Epoxyalkyl, C 6～12 Aryl, C 6～12 heteroaryl, carbonyl or C 2～6 This refers to any combination of one or more of the following: ester groups, etc. Among them, carbodiimide cyclic compounds have lower film-forming potentials and are more easily oxidized and decomposed on the electrode surface, undergoing ring-opening polymerization to form a complete, dense, and uniform passivation film. The carbodiimide polar functional groups in their molecular formula are continuously reduced under high voltage. Simultaneously, this compound has a certain ability to neutralize reactive oxygen species. Under overcharge conditions, the interfacial film formed by the carbodiimide cyclic compound immediately blocks reactive oxygen species reactions, effectively solving the lithium battery safety problem caused by the rapid release of large amounts of heat due to the large amount of reactive oxygen species generated by the phase transition of the positive electrode active material under conditions such as high-potential overcharge and high-temperature thermal triggering. It can greatly reduce the further oxidation of solvents such as ethylene carbonate in the electrolyte by the large amount of reactive oxygen species released from the positive electrode active material, effectively preventing the thermal release reaction of lithium-ion batteries from remaining at the thermal runaway trigger temperature T2 stage, thus widening the safe operating window of lithium batteries. At the same time, it does not significantly affect the fast charging and rate performance kinetics of lithium batteries.

[0032] In one embodiment of the present invention, in the carbodiimide cyclic compound, at least one of X and Y includes any one of P, S, or Se, and at least one of Z includes an element atom such as O or S. In one embodiment of the present invention, at least one of X, Y, and Z includes an S element atom. The carbodiimide cyclic compound is selected from at least one or more combinations of the following compounds:

[0033] In compound B, n3 is an integer from 0 to 3. Cyclic compounds containing sulfur (S) are more prone to electron-free ring-opening polymerization to form films, resulting in interfacial films with greater flexibility and more stable spatial structures, capable of chemically neutralizing the large amounts of reactive oxygen species generated by overcharging. After film formation, the film contains more sulfonate or sulfate inorganic components, exhibiting stronger ion-conducting ability and further improving the performance of lithium-ion batteries.

[0034] In another embodiment of the invention, the carbodiimide cyclic compound is a compound whose ring contains, for example, one and / or two acyl groups. Specifically, the carbodiimide cyclic compound is selected from... wait.

[0035] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.1wt% to 15wt%, or for example, 0.5wt% to 5wt%. If the content of the first additive is too low, a dense interfacial film cannot be formed, resulting in a low pass rate of the high-voltage overcharge test of the lithium-ion battery, and the safety improvement of the lithium-ion battery is not significant. As the content of the first additive increases, a dense interfacial film can be formed, and all high-voltage overcharge tests of the lithium-ion battery pass. However, the high-temperature storage capacity and high-temperature storage gas generation of the lithium-ion battery do not improve further with further increases in content. Considering cost factors, the upper limit of the content of the first additive is controlled.

[0036] In one embodiment of the present invention, the additive further includes a second additive, which is selected from at least one or a combination of film-forming additives such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propanesultone (PS), 1,3-propene-1,3-sultone (PST), 2,4-butanesultone, methylenemethanedisulfonate (MMDS), lithium difluorooxalate borate (LiODFB), lithium dioxalate borate (LiBOB), lithium difluorobis(oxalate) phosphate (LiDFOB), lithium tetrafluorooxalate phosphate (LiOTFP), lithium difluorophosphate (LiDFP), or ethylene sulfate (1,3,2-Dioxathiolane 2,2-dioxide (DTD). The content of the second additive in the electrolyte is 0.1 wt% to 5 wt%. In one embodiment of the present invention, the second additive is selected, for example, from any one or a combination of several of the following: vinylene carbonate (0.02 wt% to 5 wt%), fluoroethylene carbonate (0.02 wt% to 3 wt%), 1,3-propanesulfonate lactone (0.02 wt% to 3 wt%), 1,3-propenesulfonate lactone (0.02 wt% to 3 wt%), 2,4-butanesulfonate lactone (0.02 wt% to 3 wt%), methanedisulfonate (0.02 wt% to 3 wt%), lithium difluorooxalate borate (0.02 wt% to 3 wt%), lithium dioxalate borate (0.02 wt% to 3 wt%), lithium difluorophosphate (0.02 wt% to 1 wt%), lithium difluorobis(oxalate) phosphate (0.02 wt% to 3 wt%), or vinyl sulfate (0.02 wt% to 3 wt%). The second additive can work synergistically with the first additive to further improve the integrity and density of the interfacial film, thereby enhancing the cycle performance and safety performance of lithium-ion batteries.

[0037] In one embodiment of the present invention, the lithium salt is selected from any one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethyl)sulfonylimide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium dioxalate borate, or lithium difluorooxalate borate, and the concentration of the lithium salt in the electrolyte is 0.1 mol / L to 2 mol / L, or for example, 0.5 mol / L to 1.3 mol / L.

[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), 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), and the mass content of the non-aqueous solvent in the electrolyte is 70 wt% to 85 wt%.

[0039] In one embodiment of the present invention, when preparing the electrolyte, in a glove box with an inert gas atmosphere such as argon containing a moisture content and an oxygen content of less than or equal to 0.1 ppm, a non-aqueous solvent is mixed evenly according to a mass ratio, and then a fully dried lithium salt is added to the non-aqueous solvent, along with additives, to prepare a lithium-ion battery electrolyte. The content described in this application is a weight percentage 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 plate 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 metal foil or a composite current collector, etc. The metal foil is, for example, a foil material formed after surface treatment of nickel, nickel alloy, titanium, titanium alloy, aluminum, aluminum alloy, silver, silver alloy, or stainless steel, etc. The composite current collector, for example, includes a polymer material base layer and a metal layer formed at least on one surface of the polymer material base layer. Among them, the material of the polymer material base layer is, for example, selected from at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE), etc. The material of the metal layer is, for example, selected from at least one of aluminum, aluminum alloy, nickel, nickel alloy, silver, silver alloy, or titanium alloy, etc.

[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 but is not limited to nickel-cobalt-manganese ternary material. The general formula of the nickel-cobalt-manganese ternary material is LiNi a Co b Mn 1-a-b O2, where the value ranges of a and b are 0 < a < 1 and 0 < b < 1. The binder is, for example, selected from any one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene terpolymer (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. In the positive electrode active layer, the mass ratio of the positive electrode active material, the conductive agent, and the binder is, for example, (90 - 98):(1 - 5):(1 - 5).

[0043] In an embodiment of the present invention, the positive electrode active material is, for example, LiNi 0.8 Co 0.1 Mn 0.1O2, a binder such as polyvinylidene fluoride, and a conductive agent such as acetylene black are used. The positive electrode active material, conductive agent, and binder are mixed in a mass ratio of 96.5:1.5:2. An organic solvent is added, and the mixture is stirred under vacuum until homogeneous to obtain a positive electrode slurry. The organic solvent is, for example, N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated onto aluminum foil, then air-dried at room temperature and transferred to an oven for drying. The positive electrode sheet is obtained through cold pressing, edge trimming, cutting, and slitting. In other embodiments, the positive electrode sheet can also be obtained by any other method of forming the positive electrode sheet.

[0044] In one embodiment of the present invention, the positive electrode sheet includes, for example, a first additive. Specifically, the positive active material, conductive agent, binder, and the first additive are mixed, for example, in a mass ratio of 97.3:1.5:1:0.2, and an organic solvent is added. The mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The organic solvent is, for example, selected from N-methylpyrrolidone. The positive electrode slurry is uniformly coated onto aluminum foil, then air-dried at room temperature and transferred to an oven for drying. The positive electrode sheet is obtained through processes such as cold pressing, edge trimming, cutting, and slitting. Adding the first additive to the positive electrode sheet improves the safety performance of the lithium-ion battery in a similar way to adding the first additive to the electrolyte.

[0045] 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, for example, a metal foil or a composite current collector. The metal foil is, for example, copper foil. The composite current collector includes, for example, a polymer material base layer and a metal layer formed at least on one surface of the polymer material base layer. The polymer material base layer is made of at least one material selected from PP, PET, PBT, PS, or PE, and the metal layer is made of at least one material selected from copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy.

[0046] 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 oxides, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys; the tin-based material includes, for example, one or more of elemental tin, sacrificial oxygen 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.

[0047] 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 is selected from, for example, sodium carboxymethyl cellulose (CMC-Na), and the conductive agent is selected from, for example, 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).

[0048] 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, 95:5 to 80:20. 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 before being 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.

[0049] In one embodiment of the present invention, the diaphragm is, for example, a ceramic diaphragm, a polymer diaphragm, a non-woven fabric or an inorganic-organic composite diaphragm, including but not limited to single-layer polypropylene (PP) membranes, single-layer polyethylene (PE) membranes, double-layer PP / PE membranes, double-layer PP / PP membranes and triple-layer PP / PE / PP membranes.

[0050] In one embodiment of the present invention, the separator includes a first additive. Specifically, a predetermined mass of the first additive is dissolved in a suspension containing ceramic particles and PVDF binder and stirred. The solution is then sprayed onto one or both sides of a PE or PP polymer separator. After drying, a composite layer is formed. The ceramic particles are, for example, alumina. The thickness of the composite layer is, for example, 2 μm to 4 μm, and the content of the first additive in the composite layer is, for example, 25 wt% to 35 wt%. The resulting separator, along with the positive / negative electrode sheets and electrolyte, can be used to fabricate a lithium-ion battery, which can also improve the safety performance of the lithium-ion battery.

[0051] 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.

[0052] 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.

[0053] Example 1

[0054] 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, EMC, and DMC were mixed uniformly at a mass ratio of 3:5:2 to obtain a mixed solvent. Then, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide were added to the mixed solvent, with the concentration of lithium hexafluorophosphate being 1 mol / L and the concentration of lithium bis(fluorosulfonyl)imide being 0.13 mol / L. Next, 1 wt% of 1,3-propanesulfonate lactone, 1 wt% of vinyl sulfate, and 0.1 wt% of compound A were added and mixed uniformly to obtain the electrolyte.

[0055] Preparation of positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 O2, acetylene black, and polyvinylidene fluoride were mixed in a mass ratio of 96.5:1.5:2, 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. After cold pressing, edge trimming, cutting, and slitting, the positive electrode sheet was obtained.

[0056] 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, for example, 85:15. 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.

[0057] Selection of diaphragm: 9μm thick polyethylene is used as the base membrane.

[0058] Battery fabrication: The positive electrode, separator, and negative electrode are sequentially wound, 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. It undergoes at least vacuum sealing, settling, formation, and shaping processes to obtain a lithium-ion battery.

[0059] Example 2

[0060] In the electrolyte, the content of compound A is 0.25 wt%, and the other steps are consistent with those in Example 1.

[0061] Example 3

[0062] In the electrolyte, the content of compound A is 0.5 wt%, and the other steps are consistent with those in Example 1.

[0063] Example 4

[0064] In the electrolyte, the content of compound A is 1 wt%, and the other steps are consistent with those in Example 1.

[0065] Example 5

[0066] In the electrolyte, the content of compound A was 2.5 wt%, and the other steps were consistent with those in Example 1.

[0067] Example 6

[0068] In the electrolyte, the content of compound A is 5 wt%, and the other steps are consistent with those in Example 1.

[0069] Example 7

[0070] In the electrolyte, the content of compound A is 15 wt%, and the other steps are consistent with those in Example 1.

[0071] Example 8

[0072] In the electrolyte, compound A was replaced with compound B, and the content of compound B was 2.5 wt%, while the other steps were the same as in Example 1.

[0073] Example 9

[0074] In the electrolyte, compound A was replaced with compound D, and the content of compound D was 2.5 wt%, while the other steps were the same as in Example 1.

[0075] Example 10

[0076] In the electrolyte, compound A was replaced with compound E, and the content of compound E was 2.5 wt%. The other steps were the same as in Example 1.

[0077] Example 11

[0078] In the electrolyte, compound A was replaced with compound F, and the content of compound F was 2.5 wt%. The other steps were the same as in Example 1.

[0079] Example 12

[0080] In the electrolyte, compound A was replaced with compound H, and the content of compound H was 2.5 wt%. The other steps were the same as in Example 1.

[0081] Example 13

[0082] In the electrolyte, the first additives are compound A and compound B, with compound A having a content of 1.5 wt% and compound B having a content of 1 wt%. Other steps are consistent with those in Example 1.

[0083] Example 14

[0084] In the electrolyte, compound A was replaced with compounds D and F, with compound D having a content of 1.5 wt% and compound F having a content of 1 wt%, while the other steps remained the same as in Example 1.

[0085] Example 15

[0086] In the electrolyte, all lithium salts are lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate is 1.13 mol / L. Compound A is replaced with compounds D and E, and the content of compound D is 1.5 wt% and the content of compound E is 1 wt%. Other steps are consistent with those in Example 1.

[0087] Example 16

[0088] In the electrolyte, the first additives are compound A and compound E, with compound A having a content of 2 wt% and compound E having a content of 0.5 wt%. Other steps are consistent with those in Example 1.

[0089] Example 17

[0090] In the electrolyte, compound A was replaced with compound B, and the content of compound B was 5 wt%, while the other steps were the same as in Example 1.

[0091] Example 18

[0092] In the electrolyte, compound A was replaced with compound E, and the content of compound E was 5 wt%, while the other steps were the same as in Example 1.

[0093] Example 19

[0094] In the electrolyte, compound A is replaced with compounds E and F, with compound E comprising 2.5 wt% and compound F comprising 2.5 wt%. Other steps are consistent with those in Example 1.

[0095] Example 20

[0096] 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, EMC, and DMC were mixed uniformly at a mass ratio of 3:5:2 to obtain a mixed solvent. Then, lithium hexafluorophosphate and lithium difluorosulfonylimide were added to the mixed solvent, with the lithium hexafluorophosphate concentration being 1 mol / L and the lithium difluorosulfonylimide concentration being 0.13 mol / L. Next, 1 wt% of 1,3-propanesulfonate lactone and 1 wt% of vinyl sulfate were added and mixed uniformly to obtain the electrolyte.

[0097] Membrane selection: Using 9μm thick polyethylene as the base membrane, a predetermined mass of compound A was dissolved in a suspension containing alumina particles and PVDF binder and stirred. The solution was then sprayed onto both sides of the polyethylene membrane and dried to form a composite layer. The ceramic particles were, for example, alumina. The composite layer thickness was 3μm, and the content of compound A in the composite layer was 30%. Other steps were consistent with those in Example 1.

[0098] Example 21

[0099] 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, EMC, and DMC were mixed uniformly at a mass ratio of 3:5:2 to obtain a mixed solvent. Then, lithium hexafluorophosphate and lithium difluorosulfonylimide were added to the mixed solvent, with the lithium hexafluorophosphate concentration being 1 mol / L and the lithium difluorosulfonylimide concentration being 0.13 mol / L. Next, 1 wt% of 1,3-propanesulfonate lactone and 1 wt% of vinyl sulfate were added and mixed uniformly to obtain the electrolyte.

[0100] Preparation of positive electrode: LiNi0.8 Co 0.1 Mn 0.1 O2, acetylene black, polyvinylidene fluoride, and compound A were mixed in a mass ratio of 97.3:1.5:1:0.2, and NMP was added. The mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto aluminum foil, then air-dried at room temperature before being transferred to an oven for drying. The positive electrode sheet was then obtained through cold pressing, edge trimming, cutting, and slitting processes. The other steps were consistent with those in Example 1.

[0101] Comparative Example 1

[0102] The electrolyte does not include the first additive, and the other steps are consistent with those in Example 1.

[0103] Comparative Example 2

[0104] The electrolyte does not include the first additive, and the other steps are consistent with those in Example 15.

[0105] In this invention, the electrolyte composition of the lithium-ion battery in Examples 1-21 and Comparative Examples 1-2 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.

[0106] In one embodiment of the present invention, the test method for low-temperature direct current resistance (DCR) is as follows: At 25°C, the lithium-ion battery is charged at a constant current of 1 / 3C to 4.25V, 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 2.8V. The above charging steps are repeated, and the capacity of the second 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. Low-temperature DCR = (U0 - U1) / (C0 * 1).

[0107] In one embodiment of the present invention, the test method for room temperature DCR is as follows: At 25°C, the lithium-ion battery is charged at a constant current of 1 / 3C to 4.25V, 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 2.8V. The above charging steps are repeated, and the capacity of the second charge 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. Room temperature DCR = (U2 - U3) / (C1 * 1).

[0108] 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 2.8V, then charged at a constant current of 1 / 3C to 4.25V, 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 2.8V, 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 record 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. Volume expansion rate = (V2 - V1) / V1 * 100%.

[0109] In one embodiment of the present invention, the overcharge test involves charging the lithium-ion batteries of Examples 1-21 and Comparative Examples 1-2 at 25°C with a constant current of 1 / 3C to 4.25V, followed by constant voltage charging to a current of 0.05C. The batteries are then discharged with a constant current of 1 / 3C to 2.8V. The initial discharge capacity of the battery is recorded. The lithium-ion batteries are then charged with a current of 0.33C0 for 236.4 minutes or with a constant current to 4.89V. The batteries are then placed in their original position in an explosion-proof box and observed for 1 hour for any opening of the explosion-proof valve or thermal runaway triggered by fire. If no such phenomena occur, the test is considered passed.

[0110] Table 1. Components of the electrolytes in Examples 1-21 and Comparative Examples 1-2

[0111]

[0112] Table 2 shows the performance of lithium-ion batteries in Examples 1-21 and Comparative Examples 1-2.

[0113]

[0114] Please refer to Tables 1 and 2. Comparing Examples 1-7 and Comparative Example 1, it can be seen that when the first additive is not added to the electrolyte, the high-temperature storage volume expansion rate of the lithium-ion battery is large, and all overcharge tests fail, indicating poor safety of the lithium-ion battery. With the increase of the first additive content, the high-temperature storage volume expansion rate can be reduced, and the pass rate of the high-voltage overcharge test of the lithium-ion battery increases until all tests pass. This indicates that with the increase of the first additive content, a dense interfacial film can be formed, and the carbodiimide polar functional group in the first additive molecular formula is continuously reduced under high voltage, possessing a certain ability to neutralize reactive oxygen species. Under overcharge conditions, the interfacial film formed by the first additive can block reactive oxygen species reactions immediately, improving the safety performance of lithium-ion batteries. However, the high-temperature storage capacity and high-temperature storage gas production of the lithium-ion battery do not further improve with further increases in content. Considering cost factors, the upper limit of the first additive content is controlled. However, the first additive also increases the thickness of the interfacial film to some extent, resulting in a slight increase in DC impedance.

[0115] Please refer to Tables 1 and 2. Comparing Examples 5 and 8-16, and Examples 6 and 17-19, it can be seen that when the content of the first additive is the same, the high-temperature storage and high-voltage overcharge pass rates of lithium-ion batteries are at the same level when different compounds or different combinations of compounds are selected as the first additive. This indicates that first additives with different structures can improve the safety performance and high-temperature storage performance of lithium-ion batteries. Among them, in Examples 11 and 12, in compounds F and H, the heterocyclic functional groups at both ends of the carbodiimide are single, with only one sulfone functional group. The degree of polymerization is relatively low, and its ring-opening polymerization ability is reduced. The mechanical properties of the formed interface film are worse, resulting in a slightly less improved high-temperature storage gas generation of the formed lithium-ion battery.

[0116] Please refer to Tables 1 and 2. Comparing Examples 2-6 and 20-21, it can be seen that when the first additive is applied to the separator or positive electrode, especially when applied to the separator, its improvement effect is limited, and high-voltage overcharge cannot be fully passed. However, when applied to the positive electrode, high-voltage overcharge can be fully passed, and the safety performance and high-temperature storage performance of the lithium-ion battery are better. In summary, when the first additive is an electrolyte additive and a positive electrode additive, the high-temperature storage improvement effect and high-voltage overcharge pass rate of the lithium-ion battery are higher, and its corresponding processability is also stronger.

[0117] Please refer to Table 1. Comparing Example 15 and Comparative Example 2, it can be seen that in a system where the electrolyte does not contain stable lithium salt LiFSI, the addition of the first additive can improve the high voltage overcharge pass rate and high temperature storage performance, thus also improving the performance of lithium-ion batteries.

[0118] 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.

[0119] In summary, this invention proposes a lithium-ion battery electrolyte and its application. The first additive can oxidize and decompose on the electrode surface, generating a ring-opening polymerization reaction to form a complete, dense, and uniform passivation film. It also possesses a certain ability to neutralize reactive oxygen species. Under overcharge conditions, the interfacial film formed by the carbodiimide cyclic compound immediately blocks the reactive oxygen reaction, effectively solving the lithium battery safety problem of rapid heat release caused by interfacial side reactions triggered by the phase transition of the positive electrode active material and the resulting large amount of reactive oxygen. It can significantly reduce the further oxidation of solvents such as ethylene carbonate in the electrolyte by the large amount of reactive oxygen released from the positive electrode active material, effectively preventing the thermal release reaction of the lithium-ion battery from remaining at the thermal runaway trigger temperature T2 stage, thus widening the safe operating window of the lithium battery. Simultaneously, it does not significantly affect the fast charging and rate performance kinetics of the lithium battery. It can improve the integrity and density of the interfacial film, enhancing the high-temperature storage and safety performance of the lithium-ion battery.

[0120] 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.

[0121] 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 additive includes a first additive, which comprises a carbodiimide cyclic compound; the carbodiimide cyclic compound is selected from compounds having any one of formulas I-IV: Wherein, n1-n8 are each an independent integer from 0 to 3, X and Y are each independently selected from any one of the elements P, As, S, or Se, Z is selected from any one of the elements O, S, or Se, and R1, R2, R3, and R4 are each independently selected from H, C, and C. 1～6 Alkyl, C 1～6 Alkoxy, C 2～6 alkenyl, C 2～6 alkenyloxy group, C 2～10 alkynyl group, C 2～10 Acryloxy group, C 3～8 cycloalkyl, C 3～8 Epoxyalkyl, C 6～12 Aryl, C 6～12 heteroaryl, carbonyl or C 2～6 Any one or more combinations of ester groups; The first additive is present in the electrolyte at a concentration of 0.1 wt% to 15 wt%.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, X and Y must each contain at least one of P, S or Se, and Z must contain at least one of O or S atoms.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The carbodiimide cyclic compound is selected from at least one or more combinations of the following compounds: In compound B, n3 is an integer between 0 and 3.

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% to 5 wt%.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The additive further includes a second additive selected from at least one or more combinations of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 2,4-butanesulfonate lactone, methanedisulfonate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorobis(oxalate) phosphate, lithium tetrafluorooxalate phosphate, lithium difluorophosphate, or vinyl sulfate, wherein the content of the second additive in the electrolyte is 0.1 wt% to 3 wt%.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The non-aqueous solvent is selected from at least one or more combinations of ethylene carbonate, 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.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is selected from one or more combinations of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethyl)sulfonylimide, and the concentration of the lithium salt in the electrolyte is 0.3 mol / L to 2 mol / L.

8. A lithium-ion battery, characterized in that, include: Positive electrode sheet; Negative electrode sheet; 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 1-7.

9. The lithium-ion battery according to claim 8, characterized in that, The positive electrode and / or the separator include a first additive.

10. An electronic device, characterized in that, Includes the lithium-ion battery as described in any one of claims 8-9.

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