Electrolyte, battery and electric equipment

Abstract

The invention discloses an electrolyte, a battery and electric equipment, the electrolyte comprises a first additive, a lithium salt and a solvent, and the first additive comprises at least one of thioimidazolidinone compounds containing carbon-carbon double bonds. The electrolyte comprises the first additive, and the first additive has multifunctional effects of positive and negative electrode film forming and transition metal ion complexing, so that an interfacial film formed by a positive electrode and a negative electrode has excellent ion conductivity and film forming stability, and DCR increase in the charging and discharging process can be effectively inhibited; meanwhile, dissolution and deposition of transition metal ions in the positive electrode material at high temperature / high pressure can be effectively inhibited, so that the high-temperature cycle performance and the storage performance of the battery are improved.

Description

Technical Field

[0001] The present application belongs to the field of batteries, and specifically relates to an electrolyte, a battery and an electrical device. Background Art

[0002] Lithium-ion secondary batteries are widely used in the fields of power systems and energy storage systems due to their high energy density, long cycle life, and no memory effect. With the continuous development of society and the continuous improvement of consumer demand, the demand for high energy density of lithium batteries is also increasing. In order to further improve the energy density of lithium batteries, it is necessary to innovate the lithium battery chemical system, especially the positive electrode material. The current mainstream solution is to increase the gram capacity of the positive electrode material and increase the operating voltage range of the battery. For example, based on the current mainstream power battery system lithium iron phosphate (LFP) and nickel cobalt manganese ternary (NCM) lithium battery, upgraded positive electrode materials have been developed - lithium iron manganese phosphate (LMFP) and NCM system with higher nickel content. The use of higher voltage can significantly improve the energy density of the battery. However, when LMFP or high-nickel NCM is used under high pressure, there is a serious problem of transition metal ion (Ni, Co, Mn, Fe, etc.) dissolution. Transition metal ions dissolve from the positive electrode (intensified under high temperature / high pressure), resulting in loss of positive electrode active materials, ion insertion and extraction are blocked, and they are transmitted through the electrolyte, pass through the diaphragm, and deposit on the negative electrode, destroying the SEI film, inducing electrolyte decomposition, resulting in continuous thickening of the SEI film, continuous consumption of electrolyte and active lithium, and increased impedance, which ultimately leads to rapid capacity loss and impedance growth. The above problems limit the practical application of the upgraded positive electrode materials mentioned above. Summary of the invention

[0003] The present application aims to solve at least one of the technical problems in the related art to a certain extent. To this end, one purpose of the present application is to provide an electrolyte, a battery and an electrical device. The electrolyte of the present application comprises a first additive, which has the multifunctional effect of forming a film of the positive and negative electrodes and complexing transition metal ions, so that the interface film formed by the positive and negative electrodes has excellent ion conductivity and film formation stability, and can also effectively inhibit the growth of DCR during the charge and discharge process, and can effectively inhibit the dissolution and deposition of transition metal ions in the positive electrode material under high temperature / high pressure, thereby improving the high temperature cycle performance and storage performance of the battery.

[0004] In a first aspect, the present application provides an electrolyte. According to an embodiment of the present application, the electrolyte includes a first additive, a lithium salt and a solvent, wherein the first additive includes at least one of thioimidazole ketone compounds containing a carbon-carbon double bond.

[0005] According to the electrolyte of the embodiment of the present application, the electrolyte includes a first additive, and the first additive has the multifunctional effect of forming a film on the positive and negative electrodes and complexing transition metal ions, so that the interface film formed by the positive and negative electrodes has excellent ion conductivity and film formation stability, and can also effectively inhibit the growth of DCR during the charging and discharging process, and at the same time can effectively inhibit the dissolution and deposition of transition metal ions in the positive electrode material under high temperature / high pressure, thereby improving the high temperature cycle performance and storage performance of the battery.

[0006] In addition, the electrolyte according to the above embodiment of the present application may also have the following additional technical features:

[0007] In some embodiments of the present application, the first additive is selected from at least one of the compounds represented by Formula I, Formula II and Formula III;

[0008]

[0009] Among them, R1 and R4 are respectively selected from hydrogen, halogen, C1-C8 alkyl, C1-C8 haloalkyl, C1-C4 alkenyl, C1-C4 alkynyl, amine, cyano or isocyanate, and R2 and R3 are respectively selected from hydrogen, C1-C8 alkyl, C1-C8 haloalkyl or alkylamine.

[0010] In some embodiments of the present application, the compound represented by formula I includes at least one of the following compounds:

[0011]

[0012] In some embodiments of the present application, the compound represented by formula II includes at least one of the following compounds:

[0013]

[0014] In some embodiments of the present application, the compound represented by formula III includes at least one of the following compounds:

[0015]

[0016] In some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.2% to 5%.

[0017] In some embodiments of the present application, the electrolyte further includes: a second additive, wherein the second additive includes a thermal initiator.

[0018] In some embodiments of the present application, the mass ratio of the first additive to the second additive is 100:(0.01-0.3); and / or, the thermal initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, lauroyl peroxide, and diisopropyl peroxydicarbonate.

[0019] In some embodiments of the present application, the electrolyte further includes: a third additive, wherein the third additive includes at least one of an S-containing additive, a double bond-containing additive, an F-containing additive, a B-containing additive, a P-containing additive, a CN-containing ester additive, and a lithium salt additive.

[0020] In some embodiments of the present application, the S-containing additive includes at least one of 1,3-propane sultone, propenyl-1,3-sultone, vinyl sulfate, and methylene disulfonate; and / or, the double bond-containing additive includes at least one of vinylene carbonate, vinyl ethylene carbonate, and triallyl phosphate; and / or, the F-containing additive includes at least one of fluoroethylene carbonate and tris(2,2,2-trifluoroethyl)phosphite; and / or, the B-containing additive includes at least one of lithium borate bis(oxalate), lithium borate bis(oxalate), and tris(trimethylsilyl)borate; and / or, the P-containing additive includes at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, lithium difluorophosphate, and lithium difluorobis(oxalate); and / or, the CN-containing ester additive includes at least one of hexanetrinitrile, succinonitrile, adiponitrile, 1,2-bis(cyanoethoxy)ethane, and tricyanoethoxypropane.

[0021] In some embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the third additive is 0.5% to 10%.

[0022] In some embodiments of the present application, the molar concentration of the lithium salt is 0.7 mol / L to 1.5 mol / L.

[0023] The second aspect of the present application provides a battery. According to an embodiment of the present application, the battery includes the electrolyte of the first aspect. As a result, the battery of the present application has good high-temperature cycle performance, high-temperature storage performance and dynamic performance, and can effectively suppress the DCR growth of the battery during the charge and discharge process.

[0024] In some embodiments of the present application, the battery includes a positive electrode active material, wherein the positive electrode active material includes at least one of lithium iron manganese phosphate and a nickel-cobalt-manganese ternary material with a high nickel content; the chemical formula of the lithium iron manganese phosphate is LiMn x Fe 1-x PO4, wherein x is 0.4 to 0.8; the chemical formula of the nickel-cobalt-manganese ternary material with a high nickel content is LiNi yCo z Mn 1-y-z O2, wherein y is 0.6 to 0.95, and z is 0.05 to 0.2.

[0025] In the third aspect of the present application, the present application proposes an electric device. According to an embodiment of the present application, the electric device has the battery described in the above embodiment. Therefore, the electric device has all the advantages of the battery, which will not be repeated here.

[0026] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. DETAILED DESCRIPTION

[0027] The embodiments of the present application are described in detail below, which are intended to be used to explain the present application but should not be construed as limiting the present application.

[0028] In the first aspect of the present application, an electrolyte is proposed. According to an embodiment of the present application, the above-mentioned electrolyte includes a first additive, a lithium salt and a solvent, and the first additive includes at least one of thioimidazole compounds containing a carbon-carbon double bond. Therefore, the electrolyte of the present application includes a first additive, and the first additive has the multifunctional effect of both positive and negative electrode film formation and complexing transition metal ions, so that the interface film formed by the positive and negative electrodes has excellent ion conductivity and film formation stability, and can also effectively inhibit the growth of DCR during charging and discharging, and can effectively inhibit the dissolution and deposition of transition metal ions in the positive electrode material under high temperature / high pressure, thereby improving the high temperature cycle performance and storage performance of the battery.

[0029] The following is a detailed description of the principle by which the electrolyte proposed in this application can achieve the above beneficial effects:

[0030] The present application provides a novel electrolyte, which includes a first additive, the first additive contains a thioimidazole heterocyclic group, which can be decomposed at the positive and negative electrodes to form a SEI / CEI interface film rich in various inorganic combinations (such as Li3N, Li2O, Li2S, etc.), and the inorganic substances with excellent ion-conducting properties and the presence of grain boundaries between different inorganic substances are conducive to the transmission of lithium ions at the interface, thereby effectively improving the ion transmission kinetics of the system; and the inorganic combination has good high-temperature stability, which can effectively inhibit the dissolution and decomposition of unstable components of SEI at high temperatures and inhibit the growth of DCR during charge and discharge. At the same time, the first additive also contains a lone pair of electron-containing N groups, which can effectively complex transition metal ions and inhibit the dissolution of positive transition metal ions. At the same time, the first additive also contains a strong electron-withdrawing S element, which gives the interface film a higher antioxidant performance and improves the high-voltage stability of the positive electrode interface film. Moreover, the first additive also contains carbon-carbon double bonds, so that the first additive can preferentially undergo redox reactions at the positive and negative electrodes, decompose and polymerize to form a uniform and dense organic flexible interface film, which can effectively adapt to the volume changes of the negative electrode material during the charge and discharge process, and enhance the resistance of SEI to the deposition and damage of transition metal ions. Therefore, the various functional groups contained in the first additive of the present application work together to make the formed interface film have both excellent ion conductivity and film-forming stability. At the same time, the first additive can complex transition metal ions, protect the positive and negative electrodes, avoid direct contact with the electrolyte, inhibit the side reactions of the electrolyte at the interface, effectively alleviate the dissolution and deposition of transition metal ions in the positive electrode material under high temperature / high pressure, and improve the high temperature cycle performance and storage performance of lithium batteries.

[0031] According to some specific embodiments of the present application, the first additive includes at least one of the compounds represented by Formula I, Formula II and Formula III;

[0032]

[0033] Among them, R1 is selected from hydrogen, halogen, C1-C8 alkyl, C1-C8 haloalkyl, alkenyl, alkynyl, amine, cyano or isocyanate, R2 and R3 are respectively selected from hydrogen, C1-C8 alkyl, C1-C8 haloalkyl or alkylamine, and R4 is selected from hydrogen, halogen, C1-C8 alkyl, C1-C8 haloalkyl, alkenyl, alkynyl, amine, cyano or isocyanate.

[0034] According to some further specific embodiments of the present application, the compound represented by formula I includes at least one of the following compounds:

[0035]

[0036] Therefore, the compound represented by formula I of the above structure further has the multifunctional effects of positive and negative electrode film formation and complexing transition metal ions, so that the formed interface film has both excellent ion conductivity and film formation stability, and can further effectively inhibit the dissolution and deposition of transition metal ions in the positive electrode material under high temperature / high pressure, thereby further improving the high temperature stability of the lithium battery.

[0037] According to some further specific embodiments of the present application, the compound represented by formula II includes at least one of the following compounds:

[0038]

[0039]

[0040] Therefore, the compound represented by Formula II of the above structure further has the multifunctional effects of positive and negative electrode film formation and complexing transition metal ions, so that the formed interface film has both excellent ion conductivity and film formation stability, and can further effectively inhibit the dissolution and deposition of transition metal ions in the positive electrode material under high temperature / high pressure, thereby further improving the high temperature stability of the lithium battery.

[0041] According to some further specific embodiments of the present application, the compound represented by formula III includes at least one of the following compounds:

[0042]

[0043] Therefore, the compound represented by formula III of the above structure further has the multifunctional effects of positive and negative electrode film formation and complexing transition metal ions, so that the formed interface film has both excellent ion conductivity and film formation stability, and can further effectively inhibit the dissolution and deposition of transition metal ions in the positive electrode material under high temperature / high pressure, thereby further improving the high temperature stability of the lithium battery.

[0044] According to some specific embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the first additive is 0.2% to 5%, preferably 0.5%-2%. As a result, the interface film formed by the positive and negative electrodes can further have both excellent ion conductivity and film-forming stability, and can further effectively inhibit the dissolution and deposition of transition metal ions in the positive electrode material under high temperature / high pressure, thereby further improving the high temperature stability of the lithium battery.

[0045] According to some other specific embodiments of the present application, the above-mentioned electrolyte also includes: a second additive, wherein the second additive includes a thermal initiator, which can effectively reduce the polymerization temperature of the first additive to form a SEI / CEI interface film at the positive electrode / negative electrode, thereby reducing the difficulty of preparation.

[0046] It should be noted that, by adding the above-mentioned first additive and the optional second additive to the electrolyte, injecting the electrolyte into the battery cell for packaging, and heating at high temperature for a certain period of time, a layer of artificial interface passivation film can be polymerized on the surface of the positive / negative electrode. When the electrolyte does not contain the second additive, the polymerization temperature of the SEI / CEI interface film formed at the positive / negative electrode is about 80°C or more, and when the electrolyte contains the second additive, the polymerization temperature of the SEI / CEI interface film formed at the positive / negative electrode is about 40°C to 60°C. It can be seen that the second additive can effectively reduce the polymerization temperature of the first additive to form the SEI / CEI interface film at the positive / negative electrode.

[0047] According to some further specific embodiments of the present application, the mass ratio of the first additive to the second additive is 100:(0.01-0.3), thereby further effectively reducing the polymerization temperature of the first additive in forming the SEI / CEI interface film at the positive electrode / negative electrode.

[0048] In the embodiments of the present application, the specific type of the above-mentioned thermal initiator is not particularly limited, and those skilled in the art can select it according to actual needs. As some preferred embodiments, the above-mentioned thermal initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, lauroyl peroxide, and diisopropyl peroxydicarbonate.

[0049] According to some other specific embodiments of the present application, the electrolyte further includes: a third additive, the third additive including at least one of an S-containing additive, a double bond-containing additive, an F-containing additive, a B-containing additive, a P-containing additive, an ester additive containing CN, and a lithium salt additive. The third additive is conducive to forming a SEI / CEI interface film at the positive / negative electrode, improving the film formation uniformity of the interface film, and improving the interface impedance.

[0050] In the embodiments of the present application, the specific type of the above-mentioned S-containing additive is not particularly limited. As some preferred embodiments, the S-containing additive includes at least one of 1,3-propane sultone (PS), propenyl-1,3-sultone (PST), diethylene sulfate (DTD), and methylene disulfonate (MMDS).

[0051] In the embodiments of the present application, the specific type of the above-mentioned double bond-containing additive is not particularly limited. As some preferred embodiments, the double bond-containing additive includes at least one of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and triallyl phosphate (TAP).

[0052] In the embodiments of the present application, the specific type of the above-mentioned F-containing additive is not particularly limited. As some preferred embodiments, the F-containing additive includes at least one of fluoroethylene carbonate (FEC) and tris(2,2,2-trifluoroethyl)phosphite (TTFP).

[0053] In the embodiments of the present application, the specific type of the above-mentioned B-containing additive is not particularly limited. As some preferred embodiments, the B-containing additive includes at least one of lithium dioxalatoborate (LiBOB), lithium dioxalatoborate (LiODFB), and tris(trimethylsilyl)borate (TMSB).

[0054] In the embodiments of the present application, the specific type of the above-mentioned P-containing additive is not particularly limited. As some preferred embodiments, the P-containing additive includes at least one of tris(trimethylsilyl)phosphate (TMSP), tris(trimethylsilyl)phosphite (TMSPi), lithium difluorophosphate (LiPO2F2), and lithium difluorobis(oxalate)phosphate (LiODFP).

[0055] In the embodiments of the present application, the specific type of the above-mentioned CN-containing ester additive is not particularly limited. As some preferred embodiments, the CN-containing ester additive includes at least one of hexanetrinitrile (HTCN), succinonitrile (SN), adiponitrile (ADN), 1,2-bis(cyanoethoxy)ethane (DENE), and tricyanoethoxypropane (TCP).

[0056] According to some other specific embodiments of the present application, based on the total mass of the electrolyte, the mass proportion of the third additive is 0.5% to 10%, which can further facilitate the formation of SEI / CEI interface film at the positive / negative electrode, further improve the film formation uniformity of the interface film, further improve the interface impedance, etc.

[0057] According to some specific embodiments of the present application, the molar concentration of the lithium salt in the electrolyte is 0.7 mol / L to 1.5 mol / L, so that the electrolyte has a higher ion conductivity. The organic solvent in the electrolyte is an important carrier for ion transmission, and when the electrolyte lithium salt is dissolved, it can have a higher electronic conductivity.

[0058] In the embodiments of the present application, the specific type of the above-mentioned solvent is not particularly limited. As some preferred embodiments, the above-mentioned solvent is selected from at least one of a carbonate solvent and a carboxylate solvent. The carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and various fluorinated cyclic and linear carbonates; the carboxylate solvent includes at least one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate and various fluorinated cyclic and linear carboxylates.

[0059] In the embodiments of the present application, the specific type of the above-mentioned lithium salt is not particularly limited. As some preferred embodiments, the above-mentioned lithium salt includes at least one of LiPF6, LiClO4, LiBF4, LiAsF6, LiBOB, LiODFB, LiFSI, LiTFSI, and LiTDI.

[0060] The second aspect of the present application provides a battery. According to an embodiment of the present application, the battery includes the electrolyte of the second aspect. As a result, the battery of the present application has good high-temperature cycle performance, high-temperature storage performance and dynamic performance, and can also effectively suppress the DCR growth of the battery during the charging and discharging process.

[0061] The battery type of the present application is not particularly limited, and can be a lithium-ion battery or a sodium-ion battery. The electrolyte additive of the present application is particularly suitable for lithium-ion batteries, which can effectively improve the ion conductivity and stability of the positive and negative electrode interface films of lithium-ion batteries, and can also effectively inhibit the growth of DCR during charging and discharging. At the same time, it can effectively inhibit the dissolution and deposition of transition metal ions in positive electrode materials (especially lithium iron manganese phosphate and nickel-cobalt-manganese ternary materials with high nickel content) under high temperature / high pressure, thereby improving the high temperature cycle performance and storage performance of the battery.

[0062] According to some specific embodiments of the present application, the battery includes a positive electrode active material, wherein the positive electrode active material includes at least one of lithium iron manganese phosphate and a nickel-cobalt-manganese ternary material with a high nickel content; the chemical formula of the lithium iron manganese phosphate is LiMn x Fe 1-x PO4, wherein x is 0.4 to 0.8; the chemical formula of the nickel-cobalt-manganese ternary material with a high nickel content is LiNi y Co z Mn 1-y-z O2, wherein y is 0.6 to 0.95, and z is 0.05 to 0.2.

[0063] Typically, a battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through.

[0064] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, wherein the positive active material layer includes a positive active material, which is preferably a lithium manganese iron phosphate material or a nickel-cobalt-manganese ternary material with a high nickel content.

[0065] In some embodiments of the present application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material base and a metal layer formed on at least one side of the polymer material base. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and other substrates).

[0066] In some embodiments of the present application, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0067] In some embodiments of the present application, the positive electrode active material layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0068] In some embodiments of the present application, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, and the binder are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0069] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0070] In some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0071] In some embodiments of the present application, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0072] In some embodiments of the present application, the negative electrode active material layer may further optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0073] In some embodiments of the present application, the negative electrode active material layer may further include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0074] In some embodiments of the present application, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0075] In some embodiments of the present application, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0076] The present application has no particular restrictions on the type of isolation membrane, and any known porous isolation membrane with good chemical stability and mechanical stability can be selected. In some embodiments of the present application, the isolation membrane may be made of at least one of glass fiber, non-woven fabric, polyethylene, polypropylene or polyvinylidene fluoride.

[0077] The battery of the present application may include a battery cell form, a battery module form and a battery pack form. In some embodiments, the battery cells can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module. In some embodiments, the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0078] The third aspect of the present application provides an electric device, which includes the battery of the second aspect, so that the electric device has excellent service life and safety performance.

[0079] Battery cells, battery modules, and battery packs can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0080] As an electrical device, a battery, a battery module or a battery pack can be selected according to its usage requirements.

[0081] As an embodiment, the electric device may be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electric device for high power and high energy density of the battery, a battery pack or a battery module may be used.

[0082] As another embodiment, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery cell may be used as a power source.

[0083] It should be noted that the features and advantages described above for the battery are also applicable to the electrical device and will not be repeated here.

[0084] The embodiments of the present application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. In addition, unless otherwise explicitly stated, all reagents used in the following embodiments are commercially available or can be synthesized according to this article or known methods, and the reaction conditions not listed are also easily available to those skilled in the art.

[0085] Example 1

[0086] 1) Preparation of positive electrode

[0087] The positive electrode active materials (LiNi 0.8 Co 0.1 Mn 0.1O2), conductive agent carbon black and binder polyvinylidene fluoride (PVDF) are dispersed in solvent N-methyl-2-pyrrolidone (NMP) and stirred under vacuum to obtain positive electrode slurry (solid content in the positive electrode slurry is 56%). The positive electrode slurry is evenly coated on both sides of the current collector aluminum foil, dried in an oven at 120°C for 8 hours, and then cold pressed. Then, the positive electrode sheets are made after trimming, cutting and stripping.

[0088] 2) Preparation of negative electrode sheet

[0089] The negative electrode active material graphite, the conductive agent carbon black, the binder styrene-butadiene rubber and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a mass ratio of 95:1.5:1.5:3, dispersed in deionized water, and the negative electrode slurry (the solid content in the negative electrode slurry is 55%) is obtained under vacuum stirring. The negative electrode slurry is evenly coated on both sides of the current collector copper foil, and the negative electrode sheet is made after drying, calendering and vacuum drying, and then cold pressing, trimming, cutting and stripping.

[0090] 3) Preparation of electrolyte

[0091] In a glove box with qualified water and oxygen content, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:70, and then lithium hexafluorophosphate (LiPF6) was added and stirred evenly to serve as the basic electrolyte. Based on the total mass of the basic electrolyte, the molar concentration of lithium hexafluorophosphate (LiPF6) was 1.0 mol / L.

[0092] The electrolyte functional additives shown in Table 1 were added to the above basic electrolyte.

[0093] 4) Isolation film

[0094] The diaphragm is a PE-coated ceramic diaphragm purchased from Xingyuan Materials with a thickness of 20 μm.

[0095] 5) Lithium-ion battery preparation

[0096] Stack the positive electrode sheet, isolation film, and negative electrode sheet in order, so that the isolation film is in the middle of the positive and negative electrode sheets to isolate the positive and negative electrodes, wind them to obtain a bare battery cell, weld the pole ears, place the bare battery cell in an outer package, inject the above-prepared electrolyte into the dried battery cell, and let it stand at 25°C for 24 hours after packaging to allow the electrolyte to fully infiltrate.

[0097] The battery is heated to 45-80°C and left to stand for 2.5 hours (specifically, the polymerization heating temperature of the battery is shown in Table 2) so that the first additive polymerizes at the positive electrode / negative electrode interface to form a SEI / CEI interface film. The battery is then subjected to conventional formation and capacity division, and the cells are taken offline for performance testing after capacity division.

[0098] Embodiments 2 to 20

[0099] The preparation methods of the lithium ion batteries of Examples 2 to 20 are the same as those of Example 1, except that the composition of the additives in the electrolyte is different, as shown in Table 1.

[0100] Comparative Example 1

[0101] The preparation method of the lithium ion battery of Comparative Example 1 is the same as that of Example 1, except that: the first additive is not added in Comparative Example 1.

[0102] Comparative Example 2

[0103] The preparation method of the lithium ion battery of Comparative Example 2 is the same as that of Example 19, except that: the first additive is not added in Comparative Example 2.

[0104] Table 1

[0105]

[0106]

[0107] The high temperature cycle, cycle DCR growth and cycle gas generation of the lithium ion batteries of Examples 1 to 20 and Comparative Examples 1 to 2 were tested respectively, and the results are shown in Table 2.

[0108] Performance Test:

[0109] The performance test was performed as follows, and the test results are shown in Table 2.

[0110] (1) High temperature cycle performance test: At 45°C, the battery was cycled and charged to 4.25V at 1C constant current, then charged at constant voltage until the current reached 0.05C. After half an hour of standing, it was discharged at 1C constant current to obtain the initial capacity of the first cycle of the battery and recorded as C1. After that, the charge and discharge cycle was repeated in the CCCV / DC mode of the first cycle. The capacity after the 400th cycle of discharge was recorded as C 400 , then the capacity retention rate after 400 cycles of high temperature cycling (%) = C 400 / C1×100%. Before and after the high temperature cycle of the battery cell, the DC internal resistance DCR value of the battery cell at 50% SOC is tested by the following current pulse method and recorded.

[0111] (2) DCR test: After cooling the cell before or after high temperature cycling to room temperature, charge it at 0.5C constant current to 4.25V, charge it at constant voltage to 0.05C, leave it for 1h, discharge it at 0.5C for 1h (50% SOC), leave it for another 1h, and record the voltage V1 at the end; then discharge it at 2C for 10s, and record the voltage V2 at the end. The DCR of the cell before or after cycling = (V1-V2) / (I 1C -I 0.1C), the unit is mΩ, and the DCR growth rate after cycling is (DCR 循环后 -DCR 循环前 ) / DCR 循环前 ×100%.

[0112] (3) Cyclic gas production test: After the battery cell before or after high-temperature cycling is cooled to room temperature, the battery volume is tested by the drainage method. The specific operation is as follows: Place a container filled with deionized water on an electronic scale, use a fixing clip to fix the pole ear on the upper end of the soft-pack battery, immerse the soft-pack battery completely in the liquid, and record the weight change displayed on the electronic scale. The volume of the soft-pack battery can be calculated by measuring the change in the volume of deionized water after the soft-pack battery is immersed in deionized water. The specific calculation formula is: V = (m1-m2) / ρ, where m1 is the weight of the soft-pack battery after it is completely immersed in deionized water, m2 is the weight of the soft-pack battery when it is not immersed in deionized water, and ρ is the density of deionized water (1g / L). The volume V before the cycle was measured respectively. 循环前 and the volume after the cycle V 循环后 , the cycle gas production is calculated by the following formula: (V 循环后- V 循环前 ) / V 循环前 ×100%.

[0113] Table 2

[0114]

[0115]

[0116] As can be seen from Table 2, compared with Comparative Example 1, the high temperature cycle performance cycle capacity retention rate of Examples 1 to 20 is increased by 2%-6%, the cycle DCR growth is reduced by 3%-15%, and the cycle gas production is reduced by 8%-20%. It can be seen that the first additive can effectively improve the high temperature cycle of the lithium-ion battery, inhibit the cycle DCR growth and inhibit the cycle gas production.

[0117] As can be seen from Table 2, compared with Comparative Example 2, the high temperature cycle performance cycle capacity retention rate of Example 19 is improved by 3.7%, the cycle DCR growth is reduced by 10.1%, and the cycle gas production is reduced by 14%. It can be seen that the first additive can effectively improve the high temperature cycle of the lithium-ion battery, inhibit the cycle DCR growth and inhibit the cycle gas production.

[0118] It can also be seen from Table 2 that compared with Example 1 and Examples 5 to 6, the high temperature cycle performance cycle capacity retention rate of Examples 2 to 4 is increased by 1.6%-4%, the cycle DCR growth is reduced by 1.6%-6.9%, and the cycle gas production is reduced by 1.5%-7%. It can be seen that based on the total mass of the electrolyte, the mass proportion of the first additive is preferably 0.5%-2%.

[0119] It can also be seen from Table 2 that compared with Examples 1 to 14, the polymerization heating temperature of the batteries of Examples 15 to 20 is significantly reduced. It can be seen that the second additive can effectively reduce the polymerization temperature of the first additive to form the SEI / CEI interface film at the positive / negative electrode, thereby reducing the difficulty of preparation.

[0120] It can also be seen from Table 2 that compared with Example 16, the high temperature cycle performance cycle capacity retention rate of Examples 18 to 20 is increased by 0.5%-1%, the cycle DCR growth is reduced by 1%-2.9%, and the cycle gas production is reduced by 1%-3.3%. It can be seen that the third additive can further improve the high temperature cycle of the lithium-ion battery, inhibit the cycle DCR growth and inhibit the cycle gas production.

[0121] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0122] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a first additive, a lithium salt and a solvent, wherein the first additive includes at least one thioimidazole ketone compound containing a carbon-carbon double bond.

2. The electrolyte according to claim 1, characterized in that The first additive is selected from at least one of the compounds represented by formula I, formula II and formula III; Among them, R1 and R4 are respectively selected from hydrogen, halogen, C1-C8 alkyl, C1-C8 haloalkyl, C1-C4 alkenyl, C1-C4 alkynyl, amine, cyano or isocyanate, and R2 and R3 are respectively selected from hydrogen, C1-C8 alkyl, C1-C8 haloalkyl or alkylamine.

3. The electrolyte according to claim 2, characterized in that The compound represented by formula I includes at least one of the following compounds:

4. The electrolyte according to claim 2, characterized in that The compound represented by formula II includes at least one of the following compounds:

5. The electrolyte according to claim 2, characterized in that The compound represented by formula III includes at least one of the following compounds:

6. The electrolyte according to claim 1, characterized in that Based on the total mass of the electrolyte, the mass proportion of the first additive is 0.2% to 5%.

7. The electrolyte according to any one of claims 1 to 6, characterized in that Also includes: A second additive, wherein the second additive comprises a thermal initiator.

8. The electrolyte according to claim 7, characterized in that The mass ratio of the first additive to the second additive is 100:(0.01-0.3); And / or, the thermal initiator includes at least one of azobisisobutyronitrile, azobisisoheptylnitrile, benzoyl peroxide, lauroyl peroxide, and diisopropyl peroxydicarbonate.

9. The electrolyte according to any one of claims 1 to 6, characterized in that Also includes: The third additive includes at least one of an S-containing additive, a double bond-containing additive, an F-containing additive, a B-containing additive, a P-containing additive, a CN-containing ester additive, and a lithium salt additive.

10. The electrolyte according to claim 9, characterized in that The sulfur-containing additive includes at least one of 1,3-propane sultone, propenyl-1,3-sultone, vinyl sulfate, and methylene methane disulfonate; And / or, the double bond-containing additive includes at least one of vinylene carbonate, vinyl ethylene carbonate, and triallyl phosphate; And / or, the F-containing additive includes at least one of fluoroethylene carbonate and tris(2,2,2-trifluoroethyl)phosphite; And / or, the B-containing additive includes at least one of lithium borate bis(oxalate), lithium borate bis(oxalate), and tris(trimethylsilyl)borate; And / or, the P-containing additive includes at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, lithium difluorophosphate, and lithium difluorobis(oxalate)phosphate; And / or, the CN-containing ester additive includes at least one of hexanetrinitrile, succinonitrile, adiponitrile, 1,2-bis(cyanoethoxy)ethane, and tricyanoethoxypropane.

11. The electrolyte according to claim 9, characterized in that Based on the total mass of the electrolyte, the mass proportion of the third additive is 0.5% to 10%.

12. The electrolyte according to any one of claims 1 to 6, characterized in that The molar concentration of the lithium salt in the electrolyte is 0.7 mol / L to 1.5 mol / L.

13. A battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 1 to 12.

14. The battery according to claim 13, characterized in that The battery comprises a positive electrode active material, wherein the positive electrode active material comprises at least one of lithium iron manganese phosphate and a nickel-cobalt-manganese ternary material with a high nickel content; The chemical formula of the lithium iron manganese phosphate is LiMn x Fe 1-x PO4, where x is 0.4 to 0.8; The chemical formula of the nickel-cobalt-manganese ternary material with high nickel content is LiNi y Co z Mn 1-y-z O2, wherein y is 0.6 to 0.95, and z is 0.05 to 0.

2.

15. An electrical equipment, characterized in that: A battery according to claim 13 or 14.

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