Electrolyte additive, electrolyte and battery

Abstract

The present application provides an electrolyte additive, an electrolyte and a battery, wherein the electrolyte additive includes a first additive and a second additive; the first additive includes a compound represented by formula I: R1, R2 and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkane, R4 substituted phenyl and R5 substituted benzyl; R4 and R5 are each independently selected from H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, C 2‑ Any one of a C4 fluoroalkenyl group and a C2-C4 fluoroalkynyl group; the second additive comprises an isocyanate compound. The electrolyte additive of the present application forms an interfacial film on the electrode surface that is highly stable, smooth, uniform in thickness, flexible, highly conductive, and corrosion-resistant, resulting in excellent cycling stability and high-temperature storage performance under high-voltage conditions.

Description

Technical Field

[0001] The present application relates to the field of material preparation, and in particular, to an electrolyte additive, an electrolyte, and a battery. Background Art

[0002] With the development of energy storage technology, secondary batteries, especially lithium-ion batteries, have become the preferred power source for portable electronic devices, electric vehicles, and large-scale energy storage systems due to their high energy density, long cycle life, and environmental friendliness. However, the performance stability of lithium-ion batteries under high voltage and high temperature conditions remains a technical challenge. The battery's electrolyte easily undergoes side reactions with the electrode materials, leading to interfacial instability, increasing the battery's internal resistance, and reducing its cycling stability and safety. Summary of the Invention

[0003] This application aims to at least partially address one of the technical problems in the related art. To this end, this application proposes an electrolyte additive, an electrolyte, and a battery. The electrolyte additive forms an interfacial film on the electrode surface that is highly stable, smooth, uniform in thickness, flexible, highly conductive, and corrosion-resistant, resulting in the battery having excellent cycling stability and high-temperature storage performance under high-voltage conditions.

[0004] In a first aspect, the present application provides an electrolyte additive, wherein the electrolyte additive includes a first additive and a second additive;

[0005] The first additive includes a compound represented by formula I:

[0006] R1, R2 and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkane, R4 substituted phenyl and R5 substituted benzyl;

[0007] R4 and R5 are each independently selected from any one of H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, C2-C4 fluoroalkenyl and C2-C4 fluoroalkynyl;

[0008] The second additive includes an isocyanate compound.

[0009] The electrolyte additive of the present application has excellent film-forming properties. The interface film formed on the surface of the electrode is stable, smooth, uniform, flexible, highly conductive and corrosion-resistant, which enables the battery to have excellent cycle stability and high-temperature storage performance under high voltage conditions.

[0010] According to an embodiment of the present application, the first additive includes at least one of the compounds having the structures shown in Formulas 1-1 to 1-22:

[0011]

[0012]

[0013] According to an embodiment of the present application, the isocyanate compound includes at least one of hexamethylene diisocyanate, p-phenylene diisocyanate, toluene-2,4-diisocyanate and 4,4-diisocyanate dicyclohexylmethane.

[0014] According to an embodiment of the present application, the mass ratio of the first additive to the second additive is (0.06-50):1.

[0015] In a second aspect, the present application provides an electrolyte, which includes: the electrolyte additive described in the first aspect.

[0016] According to an embodiment of the present application, the added amount of the first additive accounts for 0.05% to 5% of the total mass of the electrolyte.

[0017] According to an embodiment of the present application, the added amount of the second additive accounts for 0.03% to 1% of the total mass of the electrolyte.

[0018] According to an embodiment of the present invention, the electrolyte further comprises lithium salt, and the amount of the lithium salt added accounts for 8% to 20% of the total mass of the electrolyte.

[0019] According to an embodiment of the present invention, the lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2 and LiPF4C2O4.

[0020] According to an embodiment of the present invention, the lithium salt further includes a non-aqueous organic solvent; the added amount of the non-aqueous organic solvent accounts for 70% to 92% of the total mass of the electrolyte.

[0021] According to an embodiment of the present invention, the non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, cyclopentane, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl acetate, and methyl-(2,2,2-trifluoroethyl) carbonate.

[0022] In a third aspect, the present application provides a battery, comprising: the electrolyte additive described in the first aspect or the electrolyte described in the second aspect.

[0023] According to an embodiment of the present application, the battery further comprises: a positive electrode sheet, a negative electrode sheet and a separator; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer provided on at least one side surface of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material;

[0024] The positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, LiNi x Co y Mn z M 1-x-y-z O2、Li 1+a Mn 1-x M x O2、LiCo 1-x M x O2、LiFe 1-x M x PO4, Li2Mn 1-x O4、Na m At least one of AO2, polyanionic compounds, and Prussian blue compounds; wherein M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, A includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, 0≤a<0.2, 0≤x<1, and 0<m≤1.

[0025] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. DETAILED DESCRIPTION

[0026] The following embodiments of the technical solution of the present application are described in detail. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only used as examples and are not intended to limit the scope of protection of the present application.

[0027] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0028] " scope " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and selected lower limit and upper limit define the boundary of special range.The scope that this mode limits can be to include end value, and can be combined arbitrarily, and promptly any lower limit can form a scope with any upper limit combination.For example, if the scope of 60-120 and 80-110 is listed for specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5.In the present application, unless otherwise specified, numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers, and the scope that this mode limits can be to include end value a and b. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0030] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0031] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0032] In a first aspect, the present application provides an electrolyte additive, wherein the electrolyte additive includes a first additive and a second additive;

[0033] The first additive includes a compound represented by formula I:

[0034] R1, R2 and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkane, R4 substituted phenyl and R5 substituted benzyl;

[0035] R4 and R5 are each independently selected from any one of H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, C2-C4 fluoroalkenyl and C2-C4 fluoroalkynyl;

[0036] The second additive includes an isocyanate compound.

[0037] The electrolyte additive of the present application has excellent film-forming properties. The interface film formed on the surface of the electrode is stable, smooth, uniform, flexible, highly conductive and corrosion-resistant, thereby enabling the battery to have excellent cycle stability and high-temperature storage performance under high voltage conditions.

[0038] The following is a detailed description of the principle by which this application can achieve the above beneficial effects:

[0039] The silicon-based fluorophosphate compound (first additive) in the electrolyte additive of the present application can form a stable CEI (positive electrode electrolyte interface) film and SEI (negative electrode electrolyte interface) film on the surface of the positive electrode and the negative electrode, effectively preventing the interface side reaction between the electrode material and the electrolyte, and having strong corrosion resistance, thereby protecting the electrode material and the electrolyte. At the same time, it helps to optimize the transmission of ions, reduce the interface impedance, improve the conductivity, and significantly improve the cycle stability and high temperature performance of the battery. In addition, the organic group in the silicon-based fluorophosphate compound provides good flexibility, so that the interface film can adapt to the deformation of the electrode material when the volume expands and contracts during the charge and discharge process of the battery, reduce the generation of cracks, and maintain the integrity of the film.

[0040] However, the lithium salt LiPF6 in the electrolyte can be decomposed into phosphorus pentafluoride, and phosphorus pentafluoride undergoes the following reaction PF5+H2O→POF3+HF. The HF in the electrolyte will react with silicon-based fluorophosphate to produce fluorosilane-like gas, causing the battery to produce serious gas after a period of storage or circulation, resulting in a diving phenomenon. Therefore, the second additive-isocyanate compound is introduced. The isocyanate functional group is an electron donor that can attract phosphorus pentafluoride to form a complex, thereby stabilizing and inactivating phosphorus pentafluoride, reducing the generation of HF, and effectively reducing the generation of fluorosilane-like gas during storage or circulation of silicon-based fluorophosphate compounds. However, the isocyanate compound itself will reduce and polymerize to form an amide compound, which will reduce the ion transfer rate while improving the stability of the SEI film. The first additive has a high reactivity and can be reduced before the isocyanate additive to form lithium fluoride, lithium phosphate and Li x PO y F z etc. to improve SEI film components that improve ion transport, thereby reducing the negative effects of isocyanates.

[0041] In summary, the silicon-based fluorophosphate compound and the isocyanate compound complement each other, jointly promoting the formation of a uniform and stable interfacial film while maintaining low interfacial impedance. As a result, the battery has excellent cycle stability and storage performance under high voltage and high temperature conditions.

[0042] According to an embodiment of the present application, the first additive includes at least one of the compounds having the structures shown in Formulas 1-1 to 1-22:

[0043]

[0044]

[0045] Among them, the CAS numbers of formulas 1-1 to 1-17 are:

[0046] 1-1: 2708941-25-5; 1-2: 4419-25-9; 1-3: 13683-39-1; 1-4: 4414-27-1; 1-5: 4414-26-0; 1-6: 4480-02-8; 1-7: 2577172-95-1; 1-8: 13683-40-4; 1-9: 2577172-93 -9; 1-10: 2708941-27-7; 1-11: 2287283-36-5; 1-12: 6231-57-8; 1-13: 1386-54-9; 1-14: 2708941-26-6; 1-15: 6231-58-9; 1-16: 6231-59-0; 1-17: 2577172-94-0

[0047] The synthesis method of 1-18 to 1-22 is prepared by referring to the preparation method of Example 14 in patent CN114728992A. Specifically, the raw materials shown below are used to replace the chlorodimethylphenylsilane in the reference document.

[0048] The raw material is trivinylchlorosilane (1871-21-2)

[0049] The raw material is dimethyl butyl chlorosilane (2069196-19-4)

[0050] The raw material is dimethyl (trifluoropropylene) chlorosilane (89705-02-2)

[0051] The raw material is tris(pentafluoroethyl)chlorosilane (1620665-21-5)

[0052] The raw material is dimethyl (p-methylbenzyl) chlorosilane (1833-28-9)

[0053] The first additive exhibits excellent film-forming properties, forming an interfacial film on the electrode surface that combines excellent stability, corrosion resistance, and flexibility, protecting the electrode material and electrolyte. Furthermore, its high ion transport rate, low interfacial impedance, and high electrical conductivity effectively offset the negative effects of isocyanate compounds, further improving battery stability under high-temperature and high-voltage conditions.

[0054] According to an embodiment of the present application, the isocyanate compound includes at least one of hexamethylene diisocyanate, p-phenylene diisocyanate, toluene-2,4-diisocyanate, and 4,4-diisocyanate dicyclohexylmethane. These isocyanate compounds can further improve the excessive acidity and severe battery gassing caused by silicon-based fluorophosphate compounds under high voltage and high temperature conditions, thereby further improving the stability of the battery under high temperature and high pressure conditions.

[0055] According to an embodiment of the present application, the mass ratio of the first additive to the second additive is (0.06-50):1, for example, it can be 0.06:1, 0.1:1, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 20:1, 50:1. The first additive and the second additive meet the above conditions and can form an interface film with good stability, corrosion resistance and flexibility on the surface of the pole piece, while having a high ion transfer rate, low interface impedance and high conductivity. In addition, it can further improve the situation of excessive acidity and severe battery gas production caused by silicon-based fluorophosphate compounds under high voltage and high temperature conditions, thereby further improving the stability of the battery under high temperature and high pressure conditions.

[0056] A second aspect of the present application provides an electrolyte comprising the electrolyte additive described in the first aspect. This electrolyte thus possesses all the characteristics and advantages of the aforementioned electrolyte additive, which are not further elaborated herein. In general, the interface film formed at least on the electrode surface exhibits strong stability, smoothness, uniform thickness, good flexibility, high conductivity, and corrosion resistance, thereby enabling the battery to exhibit excellent cycling stability and high-temperature storage performance under high-voltage conditions.

[0057] According to some embodiments of the present application, the amount of the first additive added is 0.05% to 5% of the total mass of the electrolyte, for example, it can be 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%. The amount of the first additive added meets the above conditions and can have better film-forming properties. It can form an interface film with good stability, corrosion resistance, and flexibility on the surface of the electrode, which plays a protective role on the electrode material and the electrolyte. At the same time, the ion transfer rate is high, the interface impedance is low, and the conductivity is high, which can better offset the negative effects of isocyanate compounds, thereby further improving the stability of the battery under high temperature and high pressure conditions.

[0058] According to some embodiments of the present application, the amount of the second additive added is 0.03% to 1% of the total mass of the electrolyte, for example, 0.05%, 0.1%, 0.5%, or 1.0%. When the amount of the second additive meets the above conditions, it can further improve the excessive acidity and severe battery gassing caused by the silicon-based fluorophosphate compound under high voltage and high temperature conditions, thereby further improving the stability of the battery under high temperature and high pressure conditions.

[0059] According to some embodiments of the present application, the electrolyte further includes: a lithium salt, the amount of the lithium salt added accounts for 8% to 20% of the total mass of the electrolyte, for example, 8%, 10%, 12%, 15%, 18%, or 20%. As a result, the lithium salt meets the above conditions, and the efficient migration and stable transmission of ions in the electrolyte improves the charge and discharge efficiency and power density of the battery. In addition, it helps to maintain the chemical stability of the electrolyte and reduce side reactions during high-voltage charging, such as decomposition of the electrolyte and gas generation, which helps to extend the cycle life of the battery and improve its safety.

[0060] As an example, the lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2 and LiPF4C2O4.

[0061] According to some embodiments of the present application, the electrolyte further includes: a non-aqueous organic solvent, and the amount of the non-aqueous organic solvent added accounts for 70% to 92% of the total mass of the electrolyte, for example, it can be 70%, 72%, 75%, 78%, 80%, 82%, 85%, 87%, 90%, 92%. The non-aqueous organic solvent meets the above conditions and can enable ions to migrate efficiently and be evenly distributed in the electrolyte, thereby improving the charge and discharge efficiency and cycle stability of the battery. In addition, it helps to form a stable SEI film, reduce the decomposition of the electrolyte and the dissolution of transition metals, and extend the service life of the battery. At the same time, it can also optimize the thermal stability and safety of the battery, reduce the risk of side reactions and overheating under high temperature conditions, and enable the battery to maintain excellent performance under various operating conditions.

[0062] As an example, the non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, cyclopentane, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl acetate, and methyl-(2,2,2-trifluoroethyl) carbonate.

[0063] A third aspect of this application provides a battery comprising the electrolyte additive described in the first aspect or the electrolyte described in the second aspect. This battery thus possesses all the characteristics and advantages of the aforementioned electrolytes, which are not further elaborated here. In general, it exhibits at least low internal resistance, low gassing, excellent cycling stability under high voltage conditions, and high-temperature storage performance.

[0064] According to some embodiments of the present application, the battery further includes: a positive electrode sheet, a negative electrode sheet, and a separator. During the battery's charge and discharge process, active ions are intercalated and released back and forth between the positive and negative electrode sheets. The electrolyte between the positive and negative electrode sheets acts as an ion conductor. The separator is disposed between the positive and negative electrode sheets, primarily preventing a short circuit between the positive and negative electrodes while allowing ions to pass through.

[0065] According to some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one side surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material; the positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, LiNi x Co y Mn z M 1-x-y-z O2、Li 1+a Mn 1-x M x O2、LiCo 1-x M x O2、LiFe 1-x M x PO4, Li2Mn 1-x O4、Na m At least one of AO2, polyanionic compounds, and Prussian blue compounds; wherein M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, and F, and A includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, 0≤a<0.2, 0≤x<1, and 0<m≤1.

[0066] According to 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 layer and a metal layer formed on at least one side surface of the polymer material base layer. For example, the composite positive 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), etc.).

[0067] According to 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.

[0068] According to some embodiments of the present application, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0069] According to 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.

[0070] According to some embodiments of the present application, the negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes a binder.

[0071] According to some embodiments of the present application, 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).

[0072] According to some embodiments of the present application, the negative electrode active material may be a negative electrode active material for batteries known in the art. For example, the negative electrode active material may include at least one of the following materials: soft carbon, hard carbon, silicon-based materials, tin-based materials, etc. Soft carbon includes graphite. 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.

[0073] According to 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] According to some embodiments of the present application, the negative electrode active material layer may optionally further include other auxiliary agents, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0075] According to some embodiments of the present application, the negative electrode sheet includes a negative electrode current collector, and the negative electrode active material layer is provided on at least one side surface of the negative electrode current collector.

[0076] According to some embodiments of the present application, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum or copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (aluminum, copper, copper alloy, nickel, nickel alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0077] According to 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 current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0078] The present application has no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0079] According to some embodiments of the present application, the material of the separator may include one or more of polyolefin, aromatic polyamide, polytetrafluoroethylene, and polyethersulfone. Furthermore, the separator may include one or both of polyethylene and polypropylene. Furthermore, the separator may be formed by sequentially stacking multiple layers of materials. For example, the separator may include a polypropylene layer, a polyethylene layer, and a polypropylene layer stacked sequentially.

[0080] According to some embodiments of the present application, the thickness of the isolation film may be 9 μm-12 μm, for example, 9 μm, 10 μm, 11 μm, 12 μm, etc.

[0081] Below in conjunction with embodiment, the scheme of the application will be explained. Those skilled in the art will appreciate that the following examples are merely for illustration of the application and should not be considered as limiting the scope of the application. Where specific techniques or conditions are not indicated in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product specifications. Reagents used or instruments not indicated by the manufacturer are conventional products that can be obtained commercially.

[0082] Example 1

[0083] 1. Preparation of electrolyte: The electrolyte of this embodiment is prepared with the following components according to mass fraction: 12.5% ​​LiPF6,

[0084] 1.0% of the compound of formula 1, 0.3% of hexamethylene diisocyanate, and a non-aqueous organic solvent (the mass ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) is 3:5:2) to make up to 100%.

[0085] 2. Positive electrode preparation: LiNi 0.6 Co 0.2 Mn 0.2 The O2 positive electrode material (NCM523), conductive agent SuperP (conductive carbon black), conductive agent CNT (carbon nanotube), and adhesive PVDF (polyvinylidene fluoride) were mixed uniformly in a mass ratio of 96.3:2:0.5:1.2, and vacuum stirred until the fluidity was uniform. The slurry was then evenly coated on the front and back of the aluminum foil, dried at 85°C, cold pressed, trimmed, cut, stripped, and vacuum dried at 85°C for 12 hours. After welding the tabs, the surface density was 33 mg / cm 2 The positive electrode.

[0086] 3. Negative electrode preparation: Graphite negative electrode material, conductive agent Super P (conductive carbon black), thickener CMC (sodium carboxymethyl cellulose), and adhesive SBR (styrene-butadiene rubber emulsion) are fully mixed into a uniform slurry at a mass ratio of 96:1.5:1.5:2. After coating on both sides of the copper foil, it is dried at 85°C, then cold pressed, trimmed, cut into pieces, and slit. Finally, it is dried under vacuum conditions at 85°C for 12 hours. The electrode tab is welded to obtain a surface density of 19.3 mg / cm 2 The negative electrode.

[0087] 4. Diaphragm: A 9 μm thick polyethylene porous polymer film is used as the substrate, and a 2 μm adhesive coating is applied on both sides of the substrate.

[0088] 5. Lithium-ion battery preparation:

[0089] The positive electrode sheet, separator, and negative electrode sheet are stacked sequentially and wound into a bare cell with a theoretical capacity of 1600 mAh. The bare cell is then placed in aluminum foil and vacuum-baked at 75°C for 10 hours before the electrolyte is injected. After vacuum packaging, standing, formation, aging, and capacity grading, the lithium-ion battery is complete.

[0090] The preparation methods of Examples 1 to 42 and Comparative Examples 1 to 9 are the same as those of Example 1, and the differences are detailed in Table 1.

[0091] Test Case

[0092] The lithium-ion batteries prepared in Examples 1 to 42 and Comparative Examples 1 to 9 were respectively subjected to impedance, cycle and high and low temperature performance tests. The testing method for the NCM523 battery is as follows. The difference between the testing method for the lithium cobalt oxide (LiCoO2) battery and the NCM523 battery is that the charge cut-off voltage is 4.48V and the discharge cut-off voltage is 3.0V. The difference between the testing method for the lithium iron phosphate (LiFePO4) battery and the NCM523 battery is that the charge cut-off voltage is 3.65V and the discharge cut-off voltage is 2.0V.

[0093] 25℃ normal temperature cycle test: At 25℃, charge the battery to 4.4V at a constant current of 1.0C, charge at a constant voltage of 4.4V to a cut-off current of 0.05C, and then discharge the battery to 2.75V at a constant current of 1.0C. Repeat the charge and discharge steps for 1000 cycles. The discharge capacity of the 1000th cycle and the discharge capacity of the 1st cycle are recorded and the capacity retention rate is obtained by dividing the two.

[0094] 45℃ high temperature cycle test: Charge at 45℃ with a constant current of 1.0C to 4.4V, charge at a constant voltage of 4.4V to a cut-off current of 0.05C, and then discharge at a constant current of 1.0C to 2.75V. Repeat the charge and discharge steps for 800 cycles. The discharge capacity of the 800th cycle and the discharge capacity of the first cycle are recorded and the capacity retention rate is obtained by dividing the two.

[0095] 60℃ high temperature 30-day storage test: At 25℃, charge to 4.4V at 1.0C constant current, charge to 4.4V at constant voltage to a cutoff current of 0.05C, then discharge to 2.75V at 1.0C constant current, and record the discharge capacity as C1. At 25℃, charge to 4.4V at 1.0C constant current, charge to 4.4V at constant voltage to a cutoff current of 0.05C, then transfer the battery to 60℃ and let it sit for 30 days, then discharge to 2.75V at 1.0C constant current, and record the discharge capacity as C2. Capacity retention rate of 30-day storage at 60℃ = C2 / C1*100%.

[0096] Initial DCIR test: Charge the lithium-ion battery at 25°C at a constant current of 1.0C to 4.4V, then charge at a constant voltage of 4.4V to a cutoff current of 0.05C. Then discharge the battery at a constant current of 1.0C for 30 minutes. After standing for 1 hour, discharge it at a constant current of 2.0C for 10 seconds. Calculate the DCIR impedance value of the battery at 50% SOC.

[0097] The results are shown in Table 1.

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105] It can be seen that the overall performance of the lithium-ion batteries prepared in Examples 1 to 42 is superior to that of the lithium-ion batteries prepared in Comparative Examples 1 to 5. By compounding the first additive and the second additive and adding them to the lithium-ion battery, the present application can significantly improve the room temperature cycle, high temperature cycle stability, and storage performance of the battery, and can effectively reduce the initial DCR value.

[0106] Comparative Examples 1, 3, 6, and 8 show that without the addition of isocyanate compounds, silicon-based fluorophosphate compounds can easily cause abnormal changes in electrolyte acidity, resulting in uneven thickness of the formed interface film, prone to abnormal gas generation, and a relatively rough surface of the electrode material and high interfacial impedance, leading to poor battery cycle performance and high-temperature storage performance under high voltage, room temperature, and high temperature conditions. Examples 1, 39, and 40, by adding isocyanate compounds, can effectively improve the excessive acidity and severe battery gas production caused by silicon-based fluorophosphate compounds under high voltage and high temperature conditions, thereby improving the battery's cycle performance and high-temperature storage performance under high voltage, room temperature, and high temperature conditions.

[0107] Comparative Examples 2, 4, 7, and 9 show that without the addition of a silicon-based fluorophosphate compound, the isocyanate compound reduces the lithium ion transport rate, resulting in higher battery impedance and a poor cycle life. Examples 1, 39, and 40, by adding a silicon-based fluorophosphate compound, effectively improve lithium ion transport, offsetting the negative effects of the isocyanate compound, resulting in improved battery cycling performance under high-temperature, high-voltage conditions and improved high-temperature storage performance.

[0108] As can be seen from Comparative Example 5, although the addition of tris(trimethylsilyl)phosphine can slightly improve the cycle and storage performance of the battery, the magnitude is far less than that of the compound of Formula I, and tris(trimethylsilyl)phosphine fails to reduce the initial impedance value of the battery.

[0109] It can be seen from Examples 2, 32 and 33 that when the content of the first additive is too little, the degree of improvement is very limited; when the content of the first additive is too much, the SEI film formed is too thick, which cannot reduce the DCR and improve the cycle.

[0110] It can be seen from Examples 2, 34 and 35 that if the content of the second additive is too little, the water removal and acid inhibition effect of the second additive is difficult to exert, resulting in no obvious performance improvement; if the content of the second additive is too much, the impedance will increase rapidly, reducing the transmission efficiency of lithium ions, which is manifested as a significant increase in impedance.

[0111] It can be seen from Examples 26-38 that the mass ratio of the first additive to the second additive is too small, and the silicon-based fluorophosphate additive is difficult to offset the negative impact of the isocyanate additive, resulting in still large impedance and poor cycle life; the mass ratio of the first additive to the second additive is too large, and the isocyanate additive is difficult to eliminate the problem of easy hydrolysis and gas production of the silicon-based fluorophosphate additive, resulting in unsatisfactory cycle life.

[0112] 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 additive, characterized in that including a first additive and a second additive; The first additive includes a compound represented by formula I: Formula I; R1, R2 and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkane, R4 substituted phenyl and R5 substituted benzyl; R4 and R5 are each independently selected from any one of H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, C2-C4 fluoroalkenyl and C2-C4 fluoroalkynyl; The second additive includes an isocyanate compound; The isocyanate compound includes at least one of hexamethylene diisocyanate, p-phenylene diisocyanate, toluene-2,4-diisocyanate and 4,4-diisocyanate dicyclohexylmethane; The mass ratio of the first additive to the second additive is (0.06~50):

1.

2. The electrolyte additive according to claim 1, characterized in that The first additive includes at least one compound having a structure shown in Formula 1-1 to 1-22: (Formula 1-1), (Formula 1-2), (Formula 1-3), (Formula 1-4), (Formula 1-5), (Formula 1-6), (Formula 1-7), (Formula 1-8), (Formula 1-9), (Formula 1-10), (Formula 1-11), (Formula 1-12), (Formula 1-13), (Formula 1-14), (Formula 1-15), (Formula 1-16), (Formula 1-17), (Formula 1-18), (Formula 1-19), (Formula 1-20), (Formula 1-21), (Formula 1-22).

3. An electrolyte, characterized in that include: The electrolyte additive according to any one of claims 1 to 2.

4. The electrolyte according to claim 3, characterized in that The amount of the first additive added accounts for 0.05% to 5% of the total mass of the electrolyte.

5. The electrolyte according to claim 3, characterized in that The amount of the second additive added is 0.03% to 1% of the total mass of the electrolyte.

6. The electrolyte according to claim 4, characterized in that The electrolyte further comprises lithium salt, wherein the amount of the lithium salt added accounts for 8% to 20% of the total mass of the electrolyte.

7. The electrolyte according to claim 6, characterized in that The lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiSO3CF3, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2 and LiPF4C2O4.

8. The electrolyte according to claim 3, characterized in that It further comprises a non-aqueous organic solvent; the amount of the non-aqueous organic solvent added accounts for 70% to 92% of the total mass of the electrolyte.

9. The electrolyte according to claim 8, characterized in that The non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, cyclopentane, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl acetate, and methyl-(2,2,2-trifluoroethyl) carbonate.

10. A battery, characterized in that: The electrolyte additive according to claim 1 or 2 or the electrolyte according to any one of claims 3 to 9.

11. The battery according to claim 10, characterized in that Further including: A positive electrode sheet, a negative electrode sheet and a separator; the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one side surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material; The positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-x M x O2、LiCo 1-x M x O2、LiFe 1-x M x PO4, Li2Mn 1-x O4、Na m At least one of AO2, polyanionic compounds, and Prussian blue compounds; wherein M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, A includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, 0≤a<0.2, 0≤x<1, and 0<m≤1.

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