Lithium ion battery and application thereof

Abstract

The invention provides a lithium ion battery and application thereof, the lithium ion battery comprises: a positive pole piece comprising a positive pole material, the positive pole material comprising a positive pole active substance and elemental sulfur coating the surface of the positive pole active substance; a negative pole piece; the diaphragm is arranged between the positive pole piece and the negative pole piece; the electrolyte comprises an additive, the additive comprises a first additive, and the structural formula of the first additive is as shown in formula (I); formula (I); wherein R1, R2, R3 and R4 are respectively selected from at least one of H, substituted or unsubstituted alkyl with the carbon atom number of 1-12, substituted or unsubstituted alkenyl with the carbon atom number of 2-12 or substituted or unsubstituted alkoxy with the carbon atom number of 3-12, and during substitution, the substituent is halogen or alkyl with the carbon atom number of 1-12. According to the lithium ion battery and the application thereof provided by the invention, self-discharge at a high temperature can be reduced, and the capacity loss of the battery is reduced.

Description

Technical Field

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

[0002] Lithium-ion batteries play an increasingly important role in modern society, with widespread applications in energy storage systems, portable energy storage, satellites, aerospace, and electronic devices. They demonstrate the enormous potential of energy storage batteries across various fields, not only improving energy efficiency but also promoting sustainable development and environmental protection. With technological advancements, the demand for lithium-ion batteries is growing rapidly. Although lithium battery technology is relatively mature, issues related to safety, lifespan, and energy density still need to be addressed. Summary of the Invention

[0003] This invention proposes a lithium-ion battery and its application. By controlling the composition of the electrolyte and the structure of the cathode material, a three-dimensional network CEI film is formed, which improves the float charge capability of the battery cell, reduces self-discharge at high temperatures, reduces capacity loss during storage, and improves the cycle performance of the battery.

[0004] To solve the above-mentioned technical problems, the present invention provides a lithium-ion battery, comprising:

[0005] A positive electrode sheet, wherein the positive electrode sheet includes a positive electrode material, wherein the positive electrode material includes a positive electrode active material and elemental sulfur coated on the surface of the positive electrode active material; Negative electrode plate; A diaphragm is disposed between the positive electrode and the negative electrode; and An electrolyte, the electrolyte comprising additives, the additives comprising a first additive having a structural formula of formula (Ⅰ); Formula (Ⅰ); wherein R1, R2, R3 and R4 are each selected from at least one of H, substituted or unsubstituted alkyl with 1 to 12 carbon atoms, substituted or unsubstituted alkenyl with 2 to 12 carbon atoms, or substituted or unsubstituted alkoxy with 3 to 12 carbon atoms, and when substituted, the substituent is a halogen or an alkyl with 1 to 12 carbon atoms.

[0006] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.1wt% to 2wt%.

[0007] In one embodiment of the present invention, the content of elemental sulfur in the cathode material is 0.1 wt% to 2 wt%.

[0008] In one embodiment of the present invention, in the lithium-ion battery, the mass ratio of the first additive to the elemental sulfur is 1:30 to 5:3.

[0009] In one embodiment of the present invention, the electrolyte further includes a lithium salt selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethyl)sulfonylimide, lithium dioxolane borate, lithium difluorodioxolane phosphate, lithium difluorooxolane borate, lithium difluorophosphate, or lithium trifluoromethylsulfonate.

[0010] In one embodiment of the present invention, the lithium salt includes lithium hexafluorophosphate and lithium difluorosulfonylimide, wherein the content of lithium hexafluorophosphate in the electrolyte is 11wt% to 15wt%, and the content of lithium difluorosulfonylimide in the electrolyte is 0.5wt% to 3wt%.

[0011] In one embodiment of the present invention, the electrolyte further includes a non-aqueous solvent, which is selected from at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents.

[0012] In one embodiment of the present invention, the additive includes a second additive, the second additive including vinyl disulfate, and the content of the second additive in the electrolyte is 0.1wt% to 2wt%.

[0013] In one embodiment of the present invention, the positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

[0014] The present invention also provides an electronic device comprising the lithium-ion battery described above.

[0015] In summary, this invention proposes a lithium-ion battery and its application. By controlling the composition of the electrolyte and the structure of the cathode material, elemental sulfur is coated onto the surface of the cathode material. A first additive is added to the electrolyte. During the first charge of the lithium-ion battery, when a CEI film is formed, the elemental sulfur undergoes a sulfur cross-linking reaction with the first additive, forming a three-dimensional network structure CEI film, effectively increasing the protection area. Furthermore, after cross-linking, the elemental sulfur can still absorb active oxygen released from the cathode, reducing gas production in the cell and improving its safety performance. Simultaneously, it increases the polymerization degree of the organic layer of the CEI film, effectively reducing the dissolution and regeneration of the CEI film at high temperatures, improving the cell's float charge capability, reducing self-discharge at high temperatures, minimizing capacity loss during storage, and improving the battery's cycle performance. Detailed Implementation

[0016] 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.

[0017] 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.

[0018] 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.

[0019] This invention proposes a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive electrode material, which comprises a positive electrode active material and elemental sulfur coated on the surface of the positive electrode active material. The electrolyte includes additives, including a first additive with the structural formula (Ⅰ): Formula (I); wherein R1, R2, R3, and R4 are each selected from at least one of H, substituted or unsubstituted alkyl groups with 1 to 12 carbon atoms, substituted or unsubstituted alkenyl groups with 2 to 12 carbon atoms, or substituted or unsubstituted alkoxy groups with 3 to 12 carbon atoms. When substituted, the substituent is a halogen or an alkyl group with 1 to 12 carbon atoms. By controlling the composition of the electrolyte and the structure of the positive electrode material, a three-dimensional network positive electrode electrolyte interface (CEI) film can be formed, which greatly increases the degree of polymerization of the CEI film, effectively reduces the dissolution and regeneration of the CEI film at high temperatures, improves the float charge capability of the battery cell, and reduces self-discharge at high temperatures.

[0020] In one embodiment of the present invention, the lithium-ion battery is, for example, a primary battery or a secondary battery. A secondary battery is, for example, a pouch battery, a hard-case battery, or a cylindrical battery. The present invention does not specifically limit the type of lithium-ion battery. In this embodiment, a pouch battery is used as an example to illustrate the lithium-ion battery.

[0021] 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 after 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-like, mesh-like, porous, foam-like or non-woven fabric. Among them, the thickness of the positive electrode current collector is, for example, 8 μm to 20 μm. In this embodiment, the positive electrode current collector is, for example, an aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm.

[0022] In an embodiment of the present invention, the positive electrode active layer is disposed on either one or both surfaces of the positive electrode current collector, and the positive electrode active layer includes a positive electrode material, a positive electrode binder, a positive electrode conductive agent, etc. Among them, the positive electrode material includes a positive electrode active substance and sulfur单质coated on the surface of the positive electrode active substance. The positive electrode active substance is, for example, selected from at least one of lithium iron phosphate (LiFePO4), lithium manganese iron phosphate (LiFe x Mn1 x PO4, 0 < x < 1), lithium cobalt oxide (‌LiCoO2‌), lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide (LiNi X Mn 2-x O4, 0 < x < 1), lithium nickel cobalt manganese oxide (NCM) or lithium nickel cobalt aluminum oxide (NCA), etc. In the positive electrode material, the content of sulfur单质is 0.1 wt% to 2 wt%. By coating sulfur单质on the surface of the positive electrode material, when the lithium-ion battery forms a CEI film during the first charge, sulfur单质reacts with the first additive to form a CEI film with a three-dimensional network structure, effectively increasing the protection area. In addition, after sulfur单质crosslinks, it can still absorb the active oxygen released by the positive electrode, reduce the gas generation of the battery cell, and improve the safety performance of the battery cell.

[0023] In one embodiment of the present invention, to obtain the cathode material, elemental sulfur is dissolved in a nonpolar solution such as carbon disulfide (CS2) to obtain a sulfur solvent. The cathode active material is then immersed in the sulfur solution and thoroughly wetted by stirring or sonication. Under a fume hood or inert atmosphere, the solvent, such as carbon disulfide, is slowly evaporated at 30°C to 40°C, causing sulfur to precipitate on the surface of the cathode active material. Then, vacuum drying is performed at 60°C to 80°C to remove residual solvent, obtaining the cathode material. In other embodiments, after vacuum drying, heat treatment is performed at 180°C to 200°C to make the distribution of elemental sulfur on the surface of the cathode material more uniform. In this application, the concentration of elemental sulfur in the nonpolar solution is controlled to control the sulfur content in the cathode material. In this embodiment, based on the total mass of the cathode material as 100%, the sulfur content in the cathode material is, for example, 0.1 wt% to 2 wt%. By controlling the content of elemental sulfur in the cathode material, a high-quality three-dimensional CEI film can be formed.

[0024] In one embodiment of the present invention, the positive electrode binder is selected from at least one of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate (PAcr), polyvinyl ether (PVE), polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), or polyhexanefluoropropylene (PHFP). The positive electrode conductive agent is selected from one or a combination of two or more of conductive carbon black (Super P), Ketjen black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, or porous carbon in any proportion. The mass ratio of the positive electrode material, the positive electrode conductive agent, and the positive electrode binder in the positive electrode active layer is, for example, (90 to 98):(1 to 5):(1 to 5).

[0025] In one embodiment of the present invention, the positive electrode material is, for example, selected from sulfur-coated LiNi. 0.8 Co 0.1 Mn 0.1O2, positive electrode conductive agent (e.g., acetylene black), and positive electrode binder (e.g., polyvinylidene fluoride). The positive electrode material, positive electrode conductive agent, and positive electrode binder are mixed in a mass ratio of 95:3:2, and an organic solvent is added. The mixture is then thoroughly stirred and homogenized under vacuum 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 before being transferred to an oven for drying. The positive electrode sheet is then obtained through cold pressing, edge trimming, cutting, and slitting processes.

[0026] In one embodiment of the present invention, the electrolyte includes, for example, a non-aqueous solvent, a lithium salt, and additives. The additives include a first additive, which is a compound containing conjugated unsaturated bonds. This first additive reacts with elemental sulfur to form a three-dimensional network structure CEI film, significantly increasing the degree of polymerization of the organic layer of the CEI film. This effectively reduces the dissolution and regeneration of the CEI film at high temperatures, improves the float charge capability of the battery cell, reduces self-discharge at high temperatures, reduces capacity loss during storage, and improves the cycle performance of the battery.

[0027] In one embodiment of the present invention, the content of the first additive in the electrolyte is, for example, 0.1 wt% to 2 wt%, or, for example, 0.1 wt% to 0.5 wt%. In one embodiment of the present invention, in the lithium-ion battery, the mass ratio of the first additive to elemental sulfur is, for example, 1:30 to 5:3, or, for example, 1:2 to 2.5:1. If the mass ratio of the first additive to elemental sulfur is small, the content of the first additive is low, and a three-dimensional network structure cannot be formed. If the mass ratio of the first additive to elemental sulfur is large, excessive cross-linking occurs, resulting in a dense three-dimensional network structure that cannot effectively transport lithium ions. This leads to an increase in the direct current resistance (DCR) of the lithium-ion battery, affecting the efficiency of the lithium-ion battery, and may also cause a decrease in the cycle performance of the lithium-ion battery. Therefore, controlling the content and mass ratio of the first additive and elemental sulfur is crucial to forming a high-quality CEI film and improving the performance of the lithium-ion battery.

[0028] In one embodiment of the present invention, the additive further includes a second additive, which includes sulfur-containing additives such as ethylene disulfide (BIDTD), and the content of the second additive in the electrolyte is, for example, 0.1 wt% to 2 wt%. The second additive can synergistically improve the stability of the CEI film with the first additive, thereby improving the performance of the lithium-ion battery.

[0029] In one embodiment of the present invention, the lithium salt includes, for example, one or a combination of at least two of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethyl)sulfonylimide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), lithium dioxolaneborate (LiBOB), lithium difluorodioxolane phosphate (LiDFOP), lithium difluorooxolaneborate (LiDFOB), lithium difluorophosphate (LiPF2O2), or lithium trifluoromethylsulfonate (CF3SO3Li), and the content of the lithium salt in the electrolyte is, for example, 10 wt% to 20 wt%. In a specific embodiment of the present invention, the lithium salt is, for example, selected from lithium hexafluorophosphate and lithium bis(fluorosulfonylimide), and the content of lithium hexafluorophosphate in the electrolyte is greater than the content of lithium bis(fluorosulfonylimide) in the electrolyte. The content of lithium hexafluorophosphate in the electrolyte is, for example, 11 wt% to 15 wt%, and the content of lithium bis(fluorosulfonylimide) in the electrolyte is, for example, 0.5 wt% to 3 wt%. To improve the ionic conductivity of the electrolyte, thereby increasing the charge-discharge efficiency and energy density of lithium-ion batteries, and to control the content of lithium bisfluorosulfonylimide, thereby improving the safety performance of the battery.

[0030] In one embodiment of the present invention, the non-aqueous solvent includes, for example, one or a combination of at least two of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents, and the content of the non-aqueous solvent in the electrolyte is, for example, 75 wt% to 85 wt%. The carbonate solvent includes, for example, at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC). Carboxylic acid ester solvents are selected from at least one of methyl formate (MF), ethyl formate (EF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), butyl acetate (BA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), or ethyl butyrate (EB). Ether solvents are selected from at least one of ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), diethylene glycol dimethyl ether (Diglyme), or 1,3-dioxolane. Nitrile solvents are selected from at least one of acetonitrile (ACN), adiponitrile (ADN), glutaronitrile (GLN), and succinonitrile (SN).

[0031] In one embodiment of the present invention, when preparing the electrolyte, a non-aqueous solvent is selected and mixed uniformly 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 1 ppm, to obtain a mixed solvent. Lithium salt and additives are then added to the mixed solvent and mixed uniformly 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.

[0032] 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, for example, from foils treated with nickel, titanium, gold, silver, chromium, molybdenum, copper, stainless steel, or carbon. Besides foils, the negative electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or nonwoven fabric. The thickness of the negative electrode current collector is, for example, 6 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, 8 μm.

[0033] In one embodiment of the present invention, the negative electrode active layer is disposed on any one or both surfaces of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode active material is selected from at least one of carbon materials, elemental silicon, silicon oxide compounds, or silicon-carbon composite materials. In one embodiment of the present invention, the negative electrode active material includes, for example, a first negative electrode active component and a second negative electrode active component. The first negative electrode active component is selected from at least one of elemental silicon, silicon oxide compounds, or silicon-carbon composite materials, and the second negative electrode active component is selected from at least one of soft carbon, hard carbon, artificial graphite, or natural graphite. The mass ratio of the first negative electrode active component and the second negative electrode active component is not specifically limited. The negative electrode binder is selected from, for example, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), sodium carboxymethyl cellulose (CMC-Na), or lithium carboxymethyl cellulose (CMC-Li). The negative electrode conductive agent is selected from, for example, one of conductive carbon black, Ketjen black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, or porous carbon, or a combination of two or more in any proportion. The mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode active layer is, for example, (94 to 98):(1 to 3):(1 to 3).

[0034] In one embodiment of the present invention, the negative electrode active material is selected from, for example, artificial graphite; the negative electrode conductive agent is selected from, for example, acetylene black; and the negative electrode binder is selected from, for example, sodium carboxymethyl cellulose. The negative electrode active material, negative electrode conductive agent, and negative electrode binder are mixed, for example, at a mass ratio of 96:2:2, deionized water is added, and the mixture is thoroughly stirred and homogenized under vacuum to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, then air-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.

[0035] In one embodiment of the present invention, the lithium-ion battery further includes a separator, such as a conventional separator, a ceramic separator, a polymer separator, a non-woven fabric separator, or an inorganic-organic composite separator, and the thickness of the separator is, for example, 9 μm to 15 μm. Specifically, the separator is, for example, a single-layer polypropylene (PP) membrane, a single-layer polyethylene (PE) membrane, a double-layer PP / PE membrane, a double-layer PP / PP membrane, or a triple-layer PP / PE / PP membrane. In one embodiment of the present invention, the separator is, for example, selected as an 8 μm to 10 μm polyethylene base membrane, and a 2 μm to 4 μm thick nano-alumina coating is coated on at least one side of the base membrane.

[0036] In one embodiment of the present invention, the positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to act as a separator while allowing lithium ions to pass through. The electrode assembly is obtained by winding or stacking. The electrode assembly is then placed in an aluminum-plastic film and baked at 80°C to 100°C to remove moisture. The aforementioned electrolyte is then injected into the aluminum-plastic film once or in multiple stages, followed by sealing. The electrolyte, for example, is selected from the above-mentioned electrolytes and acts as a conductor for ions between the positive and negative electrodes. After subsequent processes such as settling, hot and cold pressing, formation, clamping, and capacity testing, a soft-pack lithium-ion battery is obtained.

[0037] 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 invention and all such modifications fall within the technical scope of the invention. Unless otherwise stated, the raw materials and reagents used in the following embodiments are commercially available or can be prepared by conventional methods in the art, and the instruments used in the embodiments are also commercially available.

[0038] Example 1 Electrolyte preparation: In an argon glove box with an oxygen content of 1 ppm and a water content of 1 ppm, ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed uniformly at a mass ratio of 3:5:2 to obtain a mixed solvent. Dried LiPF6, LiFSI, and the first additive were added to the mixed solvent and mixed uniformly to obtain the lithium-ion battery electrolyte. In the first additive, R1, R2, R3, and R4 are all H. Based on the total mass of the lithium-ion battery electrolyte (100%), the content of LiPF6 is 13.7 wt%, the content of LiFSI is 1.5 wt%, and the content of the first additive is 0.1 wt%.

[0039] Preparation of the positive electrode: The positive active material was selected as LiNi. 0.8 Co 0.1 Mn 0.1 O2, through 9.9g of LiNi0.8 Co 0.1 Mn 0.1 O2 was immersed in a carbon disulfide solution containing elemental sulfur (0.1 g of sulfur). The carbon disulfide was slowly evaporated at 35°C in a fume hood. Then, it was vacuum dried at 70°C to remove residual solvent, yielding the positive electrode material. The sulfur content in the positive electrode material was 1 wt%. The positive electrode conductive agent was selected from acetylene black, and the positive electrode binder was selected from polyvinylidene fluoride. The positive electrode material, positive electrode conductive agent, and positive electrode binder were mixed in a mass ratio of 95:3:2, and NMP was added. The mixture was thoroughly stirred and homogenized under vacuum 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. After cold pressing, edge trimming, cutting, and slitting, positive electrode sheets were obtained.

[0040] Preparation of negative electrode sheet: Artificial graphite, acetylene black and sodium carboxymethyl cellulose are mixed in a mass ratio of 96:2:2, deionized water is added, and the mixture is thoroughly stirred and mixed 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, cutting and slitting, the negative electrode sheet is obtained.

[0041] Selection of diaphragm: A 12μm thick polypropylene membrane was selected as the diaphragm.

[0042] Battery fabrication: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. This stacking process yields an electrode assembly. The electrode assembly is then encased in an aluminum-plastic film, baked at 80°C to remove moisture, injected with electrolyte, sealed, and subjected to formation to obtain a soft-pack lithium-ion battery. In this lithium-ion battery, by controlling the mass of the positive electrode active layer on the positive electrode and the amount of electrolyte injected, the mass ratio of the first additive to elemental sulfur is maintained at 1:10.

[0043] Example 2 In the electrolyte, the content of the first additive is 0.5 wt%. In the lithium-ion battery, the mass ratio of the first additive to elemental sulfur is 1:2. Other steps are consistent with those in Example 1.

[0044] Example 3 In the electrolyte, the content of the first additive is 1 wt%. In the lithium-ion battery, the mass ratio of the first additive to elemental sulfur is 1:1. Other steps are consistent with those in Example 1.

[0045] Example 4 In the electrolyte, the content of the first additive is 2 wt%. In the lithium-ion battery, the mass ratio of the first additive to elemental sulfur is 2:1. Other steps are consistent with those in Example 1.

[0046] Example 5 In the electrolyte, the content of the first additive is 2.5 wt%. In the lithium-ion battery, the mass ratio of the first additive to elemental sulfur is 2.5:1. Other steps are consistent with those in Example 1.

[0047] Example 6 In preparing the cathode material, the content of elemental sulfur in the cathode material is 0.1 wt%. In the lithium-ion battery, the mass ratio of the first additive to elemental sulfur is 5:1. Other steps are consistent with those in Example 2.

[0048] Example 7 In preparing the cathode material, the content of elemental sulfur in the cathode material is 0.5 wt%. In the lithium-ion battery, the mass ratio of the first additive to elemental sulfur is 1:1. Other steps are consistent with those in Example 2.

[0049] Example 8 In preparing the cathode material, the content of elemental sulfur in the cathode material is 2 wt%. In the lithium-ion battery, the mass ratio of the first additive to elemental sulfur is 1:4. Other steps are consistent with those in Example 2.

[0050] Example 9 In preparing the cathode material, the content of elemental sulfur in the cathode material is 2.5 wt%. In the lithium-ion battery, the mass ratio of the first additive to elemental sulfur is 1:5. Other steps are consistent with those in Example 2.

[0051] Example 10 A second additive, BIDTD, was added to the electrolyte at a content of 0.1 wt%, and the other steps were the same as in Example 2.

[0052] Example 11 A second additive, BIDTD, was added to the electrolyte at a concentration of 0.5 wt%, and the other steps remained the same as in Example 2.

[0053] Example 12 A second additive, BIDTD, was added to the electrolyte at a content of 1 wt%, and the other steps remained the same as in Example 2.

[0054] Example 13 A second additive, BIDTD, was added to the electrolyte at a content of 2 wt%, and the other steps remained the same as in Example 2.

[0055] Example 14 A second additive, BIDTD, was added to the electrolyte at a concentration of 2.5 wt%, and the other steps remained the same as in Example 1.

[0056] Comparative Example 1 In the electrolyte, no first additive is added, the positive electrode material is not coated with elemental sulfur, and the other steps are consistent with those in Example 1.

[0057] Comparative Example 2 In the electrolyte, no first additive was added, and in the positive electrode material, the content of elemental sulfur was 0.5 wt%. Other steps were consistent with those in Example 1.

[0058] Comparative Example 3 In the electrolyte, the content of the first additive is 0.5 wt%, the positive electrode material is not coated with elemental sulfur, and the other steps are consistent with those in Example 1.

[0059] Comparative Example 4 In the electrolyte, the first additive is not added, but 0.5 wt% of the second additive BIDTD is added. The positive electrode material is not coated with elemental sulfur. Other steps are consistent with those in Example 1.

[0060] In this invention, lithium-ion batteries were prepared in Examples 1 to 14 and Comparative Examples 1 to 4 using different electrolytes and cathode materials. The formulations of some electrolytes and cathode materials are shown in Table 1.

[0061] Table 1. Partial characteristics of the electrolytes and lithium-ion batteries in Examples 1 to 14 and Comparative Examples 1 to 4

[0062] In one embodiment of the present invention, the float charge test involves placing the lithium-ion battery in a constant temperature chamber at 45°C, charging the lithium-ion battery at a constant current of 1 / 3C to 4.35V, and then charging it at a constant voltage until the current is 0.0001C. The float charge duration T is recorded.

[0063] In one embodiment of the present invention, the DC impedance (DCR) test is performed at 25°C by charging the lithium-ion battery at a constant current of 1 / 3C to 4.35V, then charging it at a constant voltage to a current of 0.05C, and finally discharging it at a constant current of 1 / 3C to 2.5V. This charging process is repeated, and the capacity of the third charge is recorded as C1. The battery is then discharged at a constant current of 1 / 3C to (50%). C1), record the initial voltage as V1. Discharge the battery at a constant current of 1C1 for 30s, and record the final voltage as V2. DCR = (V1 - V2) / C1.

[0064] In one embodiment of the present invention, the self-discharge test is performed by charging the lithium-ion battery to 3.8V at a constant current of 1 / 3C at 25°C, and then storing it at 45°C for 24 hours, recording the measured voltage as U1. Then, after storing the lithium-ion battery at 45°C for 48 hours, the measured voltage is U2, and the self-discharge K = (U1 - U2) / 48.

[0065] Table 2 shows the performance of lithium-ion batteries in Examples 1 to 14 and Comparative Examples 1 to 4.

[0066] Please refer to Tables 1 and 2. Comparing Example 1 and Comparative Examples 1 to 3, it can be seen that when the electrolyte does not contain the first additive and the cathode material does not contain elemental sulfur, the lithium-ion battery has a high DC resistance, a long float charge time, and a large self-discharge. Adding the first additive alone or adding elemental sulfur to the cathode material slightly improves the DC resistance, float charge time, and self-discharge, but the improvement is not significant. This is because the first additive reacts with elemental sulfur to form a three-dimensional network CEI film, effectively reducing the dissolution and regeneration of the CEI film at high temperatures, improving the float charge capability of the cell, and reducing self-discharge at high temperatures. When the first additive and / or elemental sulfur are lacking, the formed CEI film is easily dissolved and regenerated at high temperatures, reducing the performance of the lithium-ion battery.

[0067] Please refer to Tables 1 and 2. Comparing Examples 1 to 5, it can be seen that as the content of the first additive increases, the mass ratio of the first additive to elemental sulfur in the lithium-ion battery increases, and the DC resistance of the lithium-ion battery continuously increases. However, the float charge time and self-discharge decrease. When the content of the first additive reaches 0.5 wt%, increasing the content of the first additive alone no longer improves the float charge time and self-discharge. Therefore, controlling the content of the first additive, thereby controlling the thickness and quality of the CEI film, can effectively facilitate lithium-ion transport and improve the performance of the lithium-ion battery.

[0068] Please refer to Tables 1 and 2. Comparing Examples 2, 6 to 9, it can be seen that as the mass of elemental sulfur in the cathode material gradually increases, the mass ratio of the first additive to elemental sulfur in the lithium-ion battery decreases. The float charge time of the lithium-ion battery first decreases and then increases, and the self-discharge first decreases and then increases. When the sulfur content in the cathode material increases to 1 wt%, the float charge time and self-discharge no longer change. However, if the sulfur content continues to increase, the DC impedance of the battery continues to increase. Therefore, by controlling the content of the first additive and the mass of elemental sulfur in the cathode material, thereby controlling the mass ratio of the first additive to elemental sulfur, a high-quality CEI film can be formed, effectively enabling lithium-ion transport and improving the float charge performance and self-discharge performance of the lithium-ion battery while controlling the DC impedance.

[0069] Please refer to Tables 1 and 2. Comparing Examples 2, 10 to 14, it can be seen that, under the premise of the same mass ratio of the first additive to elemental sulfur, adding a second additive to the electrolyte can further reduce the float charge time and self-discharge of the lithium-ion battery. As the content of the second additive increases, after the content of the second additive increases to 0.5 wt%, the float charge time and self-discharge no longer continue to decrease, but the DC resistance continues to increase. This is because the second additive can synergistically improve the stability of the CEI film with the first additive, thereby improving the performance of the lithium-ion battery. However, when the content of the second additive is too high, the thickness of the formed CEI film is large, which hinders the transport of lithium ions and increases the DC resistance of the lithium-ion battery. Comparing Examples 11, 1, and 4, it can be seen that when the second additive is added alone, the DC resistance, float charge time, and self-discharge of the lithium-ion battery are slightly improved, but the improvement is not significant.

[0070] 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.

[0071] In summary, this invention proposes a lithium-ion battery and its application. By controlling the composition of the electrolyte and the structure of the cathode material, elemental sulfur is coated onto the surface of the cathode material. A first additive is added to the electrolyte. During the initial charging of the lithium-ion battery, when a CEI film is formed, the elemental sulfur undergoes a sulfur cross-linking reaction with the first additive, forming a three-dimensional network structure CEI film, effectively increasing the protection area. Furthermore, after cross-linking, the elemental sulfur can still absorb active oxygen released from the cathode, reducing gas production in the cell and improving its safety performance. Simultaneously, it increases the polymerization degree of the organic layer of the CEI film, effectively reducing the dissolution and regeneration of the CEI film at high temperatures, improving the cell's float charge capability, reducing self-discharge at high temperatures, minimizing capacity loss during storage, and improving the battery's cycle performance. The addition of a second additive synergistically enhances the stability of the CEI film, thereby improving the performance of the lithium-ion battery.

[0072] 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.

[0073] 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, characterized in that, include: A positive electrode sheet, wherein the positive electrode sheet includes a positive electrode material, wherein the positive electrode material includes a positive electrode active material and elemental sulfur coated on the surface of the positive electrode active material; Negative electrode plate; A diaphragm is disposed between the positive electrode and the negative electrode; and An electrolyte, the electrolyte comprising additives, the additives comprising a first additive having a structural formula of formula (Ⅰ); Formula (Ⅰ); wherein R1, R2, R3 and R4 are each selected from at least one of H, substituted or unsubstituted alkyl with 1 to 12 carbon atoms, substituted or unsubstituted alkenyl with 2 to 12 carbon atoms, or substituted or unsubstituted alkoxy with 3 to 12 carbon atoms, and when substituted, the substituent is a halogen or an alkyl with 1 to 12 carbon atoms.

2. The lithium-ion battery according to claim 1, characterized in that, The first additive is present in the electrolyte at a concentration of 0.1 wt% to 2 wt%.

3. The lithium-ion battery according to claim 1, characterized in that, In the cathode material, the content of elemental sulfur is from 0.1 wt% to 2 wt%.

4. The lithium-ion battery according to claim 1, characterized in that, In the lithium-ion battery, the mass ratio of the first additive to the elemental sulfur is 1:30 to 5:

3.

5. The lithium-ion battery according to claim 1, characterized in that, The electrolyte further includes a lithium salt selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethyl)sulfonylimide, lithium dioxolane borate, lithium difluorodioxolane phosphate, lithium difluorooxolane borate, lithium difluorophosphate, or lithium trifluoromethylsulfonate.

6. The lithium-ion battery according to claim 5, characterized in that, The lithium salt includes lithium hexafluorophosphate and lithium difluorosulfonyl imide, wherein the content of lithium hexafluorophosphate in the electrolyte is 11wt% to 15wt%, and the content of lithium difluorosulfonyl imide in the electrolyte is 0.5wt% to 3wt%.

7. The lithium-ion battery according to claim 1, characterized in that, The electrolyte also includes a non-aqueous solvent, which is selected from at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents.

8. The lithium-ion battery according to claim 1, characterized in that, The additive includes a second additive, which includes vinyl disulfate, and the content of the second additive in the electrolyte is from 0.1 wt% to 2 wt%.

9. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

10. An electronic device, characterized in that, Includes the lithium-ion battery according to any one of claims 1-9.

Images