Additive for lithium ion battery, lithium ion battery, and electric device

Abstract

The application discloses an additive for a lithium ion battery, the lithium ion battery and an electric device, wherein the lithium ion battery comprises a negative electrode sheet, a positive electrode sheet, a diaphragm and a nonaqueous electrolyte, and at least one of the positive electrode sheet, the diaphragm or the nonaqueous electrolyte comprises a compound described in formula I, formula IIa or formula IIb. The application adds the compound described in formula I, formula IIa or formula IIb in the positive electrode sheet, the electrolyte or the diaphragm, the compound is a polyboron atom oxide or halide, and an electrochemical passivation reaction is easily preferentially generated on the positive electrode surface in the charging and discharging process of the lithium ion battery to form a uniform, dense and stable passivation protective layer rich in BF3 or containing fluorine borate, and the formed passivation film can effectively inhibit corrosion of the positive electrode sheet.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to lithium-ion batteries and electrical devices using additives for lithium-ion batteries. Background Technology

[0002] In recent years, electrochemical components, especially as power sources for small electronic devices such as mobile phones and laptops, as well as for electric vehicles and energy storage, have been widely accepted and used. Gradually, lithium-ion rechargeable batteries with various special properties have entered our daily lives, and their convenience and practicality are increasingly recognized.

[0003] At the same time, there is an urgent need to further address the high demands of people for lithium-ion batteries, such as long battery life, high capacity, fast charging, and a wide operating temperature range, so that lithium-ion rechargeable batteries can be more widely used in people's lives and provide greater convenience and experience.

[0004] Lithium-ion batteries are mainly composed of positive and negative electrode materials that can insert and extract lithium, and a non-aqueous electrolyte containing lithium salts and non-aqueous solvents. Typically, non-aqueous solvents include carbonates such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), and propylene carbonate (PC), and additives are usually ethylene sulfate (DTD), vinylene carbonate (VC), 1,3-propanesulfonate lactone (1,3-PS), etc.

[0005] Using highly crystallized materials such as natural or artificial graphite as the negative electrode offers the advantage of a lower operating voltage. This allows for the formation of lithium-ion secondary batteries with higher output voltages when combined with positive electrode materials containing metal oxides such as Ni / Co / Mn. However, due to the low potential of graphite, additives and solvents in the electrolyte easily form an SEI passivation film on the graphite surface, effectively preventing further reduction and decomposition of the lithium-intercalated graphite and the electrolyte. While the SEI's lithium-ion-conducting properties enable normal charging and discharging of lithium-ion secondary batteries, traditional electrolytes are continuously oxidized under high plateau voltage conditions. This oxidation, accompanied by the precipitation of transition metal ions in the positive electrode material, causes structural damage, resulting in lower coulombic efficiency and poor cycle life for lithium batteries. Consequently, the oxidation and decomposition problem of conventional electrolytes under high voltage becomes increasingly prominent, and this bottleneck urgently needs further resolution.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide additives for lithium-ion batteries, lithium-ion batteries, and electrical devices.

[0008] This invention is implemented as follows:

[0009] In a first aspect, the present invention provides an additive for lithium-ion batteries, comprising at least one of a compound of formula I, a compound of formula II-a, and a compound of formula II-b, wherein the compound of formula I has the following structure;

[0010]

[0011] In Formula I, R1 is selected from hydrogen, Li, Be, Na, Mg, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Rb, Cs, NH4, N(R3)4, alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alynyl, haloalkyl, haloalkenyl, haloalkynyl, and aryl and benzyl with 6 to 10 carbon atoms;

[0012] The structure of the compound of formula II-a is as follows;

[0013]

[0014] In formula II-a, n is a positive integer ≥1, and R2 is independently selected from H, F, Cl, Br, I, Li, Be, Na, Mg, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Rb, Cs, alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alynyl, haloalkyl, haloalkenyl, haloalkynyl, and aryl and benzyl groups having 6 to 10 carbon atoms;

[0015] The structure of compound II-b is as follows;

[0016]

[0017] In equation II-b, n1 is a positive integer ≥1, and X is C, Si, N, P, As, O, S, or Se;

[0018] When X is C or Si, n2 = 3, and R3 is selected from H, alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alkenyl, haloalkyl, haloalkenyl, haloalkynyl, and aryl and benzyl with 6 to 10 carbon atoms.

[0019] When X is N, P or As, n2 = 2, and R3 is selected from H, alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alkenyl, haloalkyl, haloalkenyl, haloalkynyl, and aryl and benzyl with 6 to 10 carbon atoms.

[0020] When X is O, S, or Se, n2 = 1, and R3 is selected from H, Li, Be, Na, Mg, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Rb, Cs, alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alkenyl, haloalkyl, haloalkenyl, haloalkynyl, and aryl and benzyl with 6 to 10 carbon atoms.

[0021] In an optional embodiment, in the compound represented by Formula I, R1 is Li, alkyl, alkenyl, alkynyl, haloalkyl, haloalkenyl, haloalkynyl, phenyl, or benzyl.

[0022] In the compound represented by formula II-a, R2 is F, alkyl, alkenyl, alkynyl, haloalkyl, haloalkenyl, haloalkynyl, phenyl or benzyl;

[0023] In the compound shown in formula II-b, R3 is Li, alkyl, alkenyl, alkynyl, haloalkyl, haloalkenyl, haloalkynyl, phenyl, benzyl, halophenyl, or halobenzyl.

[0024] In a second aspect, the present invention provides a lithium-ion battery containing the aforementioned additives for lithium-ion batteries, comprising a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein at least one of the positive electrode, separator, or non-aqueous electrolyte comprises at least one of the compounds of formula I, formula II-a, and formula II-b.

[0025] Preferably, the surface of the positive electrode sheet is rich in a passivation protective layer containing BF3 or fluorinated borate.

[0026] In an optional embodiment, the content of the compound of formula I, formula II-a or formula II-b in the non-aqueous electrolyte is 0.01wt% to 15wt%.

[0027] Preferably, the content of the compound of formula I, formula II-a or formula II-b is 0.05wt% to 6wt%.

[0028] In an optional embodiment, the non-aqueous electrolyte further includes an additive, the concentration of which is 0.1 wt% to 3 wt%. The additive includes at least one of vinyl sulfate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, 1-propylene-1,3-sulfonate lactone, methanedisulfonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, and tris(trimethylsilyl) borate.

[0029] In an optional embodiment, the non-aqueous electrolyte further includes a lithium salt, such as LiFSI or C4BLi3O. 11 LiPF 6-n (CF3)n , LiN[(FSO2C6F4)(CF3SO2)], LiSO3CF3, LiTFSI, LiCH(SO2CF3)2, LiTFSM, LiPF6, LiBF4, LiBOB, LiDFOB, LiAsF6, LiPO2F2, LiN(CF3SO2)2, LiCF3SO3, LiClO4 and LiN(C x F 2x+1 SO2)(C y F 2y+1 At least one of SO2, where n is an integer from 0 to 6, and x and y are both natural numbers;

[0030] The molar concentration of lithium ions in the non-aqueous electrolyte is 0.1–3 mol / L, calculated as lithium ions.

[0031] Preferably, the molar concentration of lithium ions in the non-aqueous electrolyte is 0.2–2 mol / L, calculated as lithium ions.

[0032] In an optional embodiment, the concentration of lithium bisfluorosulfonylimide or lithium bistrifluoromethanesulfonylimide in the non-aqueous electrolyte is 0.01 wt% to 23 wt%.

[0033] Preferably, the content of lithium bisfluorosulfonylimide or lithium bistrifluoromethanesulfonylimide in the non-aqueous electrolyte is 0.2wt% to 18.4wt%.

[0034] In an optional embodiment, the non-aqueous electrolyte further includes an organic solvent, wherein the organic solvent is at least one selected from carbonates, carboxylic acid esters, sulfates, phosphates, amides, nitriles, and ethers.

[0035] Preferably, the organic solvent is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, acid anhydride, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, sulfolane, dimethyl sulfoxide, ethylene sulfite, propylene sulfite, triethyl phosphate, methyl ethyl phosphite, dimethyl sulfide, diethyl sulfite, dimethyl sulfite, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, fluorinated cyclic organic esters, and sulfur-containing cyclic organic esters.

[0036] Preferably, the organic solvent content in the non-aqueous electrolyte is 60wt% to 85wt%.

[0037] Thirdly, the present invention provides an electrical device including the lithium-ion battery described in the foregoing embodiments.

[0038] The present invention has the following beneficial effects:

[0039] The present invention adds a compound of formula I, IIa or IIb to the positive electrode, electrolyte or separator. The compound is an oxide with multiple boron atoms and readily undergoes an electrochemical passivation reaction on the surface of the positive electrode during the charging and discharging process of the lithium-ion battery to form a uniform, dense and stable passivation protective layer rich in BF3 or containing fluorinated borate. The passivation film formed can effectively inhibit the corrosion of the positive electrode.

[0040] When the cathode material is a low-cobalt ternary cathode material, the passivation film on the cathode surface further covers the highly active sites on the surface of the low-cobalt (Co%) ternary cathode material in the high-voltage (≥4.1V) system. This improves the strong oxidation, poor structural order and instability, poor conductivity and kinetic performance of the material, and the tendency of the bulk phase of the material to undergo Li+ oxidation caused by the low cobalt content. + / Ni 2+ Mixed arrangement leads to defects such as rock salt phase transformation. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 The image shows the passivation CP (x1000) of aluminum foil after high-temperature cycling in Example 11, when the electrolyte contains 1M LiFSI + 1% Li2B4O7.

[0043] Figure 2 For Comparative Example 3, the aluminum foil was severely corroded after high-temperature cycling when the electrolyte contained 1M LiFSI (CP diagram, x1000). Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0045] This application provides an additive for lithium-ion batteries, comprising at least one of a compound of formula I, a compound of formula II-a, and a compound of formula II-b, wherein the compound of formula I has the following structure;

[0046]

[0047] In Formula I, R1 is selected from one of hydrogen, NH4, N(R3)4, alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alkynyl, haloalkyl, haloalkenyl, haloalkynyl, aryl and benzyl with 6 to 10 carbon atoms, or at least one of metal atoms such as Li, Be, Na, Mg, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Rb or Cs;

[0048] The structure of the compound of formula II-a is as follows;

[0049]

[0050] In formula II-a, n is a positive integer ≥1, and R2 is independently selected from halogen atoms such as H, F, Cl, Br, I, and alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alkenyl, haloalkyl, haloalkenyl, haloalkynyl, and aryl and haloaryl with 6 to 10 carbon atoms.

[0051] The structure of the compound of formula II-b is as follows;

[0052]

[0053] In equation II-b, n1 is a positive integer ≥1, and X is C, Si, N, P, As, O, S, or Se;

[0054] When X is C or Si, n2 = 3, and R3 is selected from H, alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alkenyl, haloalkyl, haloalkenyl, haloalkynyl, and aryl and benzyl with 6 to 10 carbon atoms.

[0055] When X is N, P or As, n2 = 2, and R3 is selected from H, alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alkenyl, haloalkyl, haloalkenyl, haloalkynyl, and aryl and benzyl with 6 to 10 carbon atoms.

[0056] When X is an atom such as O, S or Se, n2 = 1, and R3 is selected from H, Li, Be, Na, Mg, K, Ca, Mn, Fe, Co, Ni, Cu, Zn, Rb, Cs, alkyl, cyclic alkyl, alkenyl, cyclic alkenyl, alkynyl, cyclic alkynyl, haloalkyl, haloalkenyl, haloalkynyl, and aryl and benzyl with 6 to 10 carbon atoms.

[0057] In some embodiments of this application, in the compound represented by Formula I, R1 is Li, alkyl, alkenyl, alkynyl, haloalkyl, haloalkenyl, haloalkynyl, phenyl or benzyl.

[0058] In the compound shown by formula II-a, R2 is F, alkyl, alkenyl, alkynyl, haloalkyl, haloalkenyl, haloalkynyl, phenyl or benzyl, halophenyl, halobenzyl;

[0059] In the compound shown in formula II-b, R3 is Li, alkyl, alkenyl, alkynyl, haloalkyl, haloalkenyl, haloalkynyl, phenyl, benzyl, halophenyl, or halobenzyl.

[0060] In some embodiments, the additive is a compound having one of the following structures:

[0061]

[0062]

[0063]

[0064] Another embodiment of this application provides a lithium-ion battery containing the aforementioned lithium-ion battery additive, including a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode, separator, or non-aqueous electrolyte includes at least one of the compounds of formula I, formula II-a, and formula II-b.

[0065] Preferably, the surface of the positive electrode is rich in a passivation protective layer containing BF3 or fluorinated borate, which has special electrical properties.

[0066] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0067] In some embodiments, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the opposite surfaces of the negative electrode current collector. The negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0068] In some embodiments, the negative electrode active material may be one or a combination of several of the following: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, with a particle size D value ≥ 0.1 μm. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys; the tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0069] In some embodiments, the negative electrode film layer may optionally include an adhesive. The adhesive may be selected from 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).

[0070] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0071] In some embodiments, the positive electrode includes a positive current collector and a layer of positive active material disposed on at least one surface of the positive current collector. For example, the positive current collector includes two opposing surfaces in its thickness direction, and the positive active material is stacked on either or both of the two surfaces of the positive current collector.

[0072] In some embodiments, the positive electrode sheet includes a positive electrode active material, and the general structural formula of the positive electrode active material includes Li. a Ni x Co y M z O2, wherein 0.1≤a≤1.2, 0≤x≤1.0, y≤0.2, x+y+z=1, and M includes one or both of Al and Mn; or the general structural formula of the positive electrode active material includes Li a Mn x Fe y PO4, where 0.1≤a≤1.2, 0≤x≤1.0, 0≤y≤1.0, and x+y=1, the cathode material includes LiFePO4 and LiMn. x Fe y PO4.

[0073] In some embodiments, the lithium metal battery of the present invention does not have particular limitations on the separator, and can use known porous structure separators with electrochemical and chemical stability, such as one or more single-layer or multi-layer films of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP) and polyvinylidene fluoride (PVDF).

[0074] The present invention adds at least one of the compounds shown in Formula I, Formula II-a and Formula II-b to the positive electrode, electrolyte or separator. The compound is an oxide with multiple boron atoms and readily undergoes an electrochemical passivation reaction on the positive electrode surface during the charging and discharging process of a lithium-ion battery to form a uniform, dense and stable passivation protective layer rich in BF3 or containing fluorinated borate. The formed passivation film can effectively inhibit the corrosion of the positive electrode.

[0075] When the cathode material is a low-cobalt ternary cathode material, the passivation film on the cathode surface further covers the highly active sites on the surface of the low-cobalt (Co%) ternary cathode material in the high-voltage (≥4.1V) system. This improves the strong oxidation, poor structural order and instability, poor conductivity and kinetic performance of the material, and the tendency of the bulk phase of the material to undergo Li+ oxidation caused by the low cobalt content. + / Ni 2+ Mixed arrangement leads to defects such as rock salt phase transformation.

[0076] In some embodiments of this application, the surface of the positive electrode sheet has a passivation protective layer rich in BF3 or fluorinated borate substances.

[0077] In some embodiments of this application, the content of the compound of formula I, formula II-a, or formula II-b in the non-aqueous electrolyte is 0.01 wt% to 15 wt%.

[0078] Preferably, the content of the compound of formula I, formula II-a or formula II-b is 0.05wt% to 6wt%.

[0079] When the content of the compounds shown in Formula I, Formula II-a, and Formula II-b is less than 0.01%, their concentration is too low to effectively form a uniform and dense passivation film on the surface of the positive electrode aluminum foil. This cannot improve the strong oxidation corrosion of the aluminum foil caused by high concentration (≥0.3MLiFSI), and cannot fundamentally improve the problems of excessively rapid decay of high-temperature cycle life and high-temperature storage capacity. When the content of the compounds shown in Formula I, Formula II-a, and Formula II-b is >6%, they have a significant improvement effect on the strong oxidation corrosion of aluminum foil in high-concentration LiFSI electrolyte. At the same time, the high cost of electrolyte caused by high content of Formula I, Formula II-a, and Formula II-b compounds is significantly increased. The content of Formula I, Formula II-a, and Formula II-b compounds is 0.05wt% to 6wt%.

[0080] In some embodiments of this application, the non-aqueous electrolyte further includes additives, the concentration of which is 0.1 wt% to 3 wt%. The additives include at least one of vinyl sulfate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, 1-propylene-1,3-sulfonate lactone, methanedisulfonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, and tris(trimethylsilyl) borate.

[0081] In some embodiments of this application, the lithium salt includes LiFSI and C4BLi3O. 11 LiPF 6-n (CF3) n , LiN[(FSO2C6F4)(CF3SO2)], LiSO3CF3, LiTFSI, LiCH(SO2CF3)2, LiTFSM, LiPF6, LiBF4, LiBOB, LiDFOB, LiAsF6, LiPO2F2, LiN(CF3SO2)2, LiCF3SO3, LiClO4 and LiN(C x F 2x+1 SO2)(C y F 2y+1 The lithium salt is selected from at least one of the following: (SO2), where n is an integer from 0 to 6, and x and y are natural numbers; considering the energy density, power characteristics, and cycle life of the battery, the preferred lithium salts are LiPF6, LiN(SO2F)2, and LiBF4.

[0082] The molar concentration of lithium ions in the non-aqueous electrolyte is 0.1–3 mol / L, calculated as lithium ions.

[0083] Preferably, the lithium ion molar concentration in the non-aqueous electrolyte is 0.2–2 mol / L, based on lithium ions. A higher lithium salt concentration makes the lithium salt less prone to dissociation in the solvent system; a lower lithium salt concentration results in fewer dissociated Li+ ions and lower conductivity.

[0084] In some embodiments of this application, the concentration of lithium bisfluorosulfonylimide or lithium bistrifluoromethanesulfonylimide in the non-aqueous electrolyte is 0.01wt% to 23wt%.

[0085] Preferably, the content of lithium bisfluorosulfonylimide or lithium bistrifluoromethanesulfonylimide in the non-aqueous electrolyte is 0.2wt% to 18.4wt%.

[0086] Lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide have high lithium-ion conductivity and exhibit good high-temperature cycling performance and low-temperature discharge capability when applied to non-aqueous electrolytes.

[0087] On the other hand, lithium bisfluorosulfonylimide can cause corrosion of the positive electrode, especially at higher concentrations, easily leading to strong oxidative corrosion of the positive electrode current collector, such as aluminum foil. Therefore, lithium-ion batteries are prone to cycle drops and accelerated capacity decay in the later stages of cycling.

[0088] This invention introduces compounds of formulas I, II-a, and II-b into lithium-ion batteries, which preferentially form a passivation protective film on the positive electrode surface, inhibiting the corrosion of aluminum foil by lithium bis(fluorosulfonyl)imide, thereby further improving the high-temperature cycle life and high-temperature storage life of the electrolyte system, while also taking into account low-temperature discharge capability. It is important to emphasize that the compounds of formulas I, II-a, and II-b in this patent application can participate in chemical or electrochemical reactions in high-concentration LiFSI electrolytes to generate substances rich in BF3 or fluorinated borates. These substances preferentially passivate and form a film on the surface of the positive electrode aluminum foil, preventing the oxide protective layer on the aluminum foil surface from further reacting with the LiFSI components to continuously generate Al(FSI)3 dissolved in the electrolyte, thus causing continuous corrosion of the aluminum foil and deterioration of the electrochemical performance of the lithium battery. This passivation protection mechanism differs from the disclosed mechanisms that act on the negative electrode to reduce and generate LiF or borate substances to enhance the toughness of the negative electrode interface film, and the starting point for improvement is also different.

[0089] When the concentration of LiFSI compounds is below 0.1%, the improvement in electrolyte conductivity is minimal, and it cannot significantly improve the high-temperature cycling kinetics and low-temperature discharge performance of the battery cell. When its concentration reaches 1.2 mol / L, the improvement in high-temperature cycling performance reaches a high level, and it has excellent low-temperature discharge performance. At the same time, as the concentration of LiFSI increases, the improvement in high-temperature cycling and low-temperature discharge of lithium-ion batteries is limited. Considering the cost of electrolytes, a system with a higher concentration of LiFSI is usually not adopted.

[0090] In some embodiments of this application, the non-aqueous electrolyte further includes an organic solvent, which is at least one selected from carbonates, carboxylic esters, sulfates, phosphates, amides, nitriles, and ethers.

[0091] Preferably, the organic solvent is at least one selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, ethyl acetate, acid anhydride, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, sulfolane, dimethyl sulfoxide, ethylene sulfite, propylene sulfite, triethyl phosphate, methyl ethyl phosphite, dimethyl sulfide, diethyl sulfite, dimethyl sulfite, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, fluorinated cyclic organic esters, and sulfur-containing cyclic organic esters.

[0092] Preferably, the organic solvent content in the non-aqueous electrolyte is 60wt% to 85wt%.

[0093] In some embodiments, the carbonate may be a cyclic carbonate or a chain carbonate. The cyclic carbonate may be at least one of ethylene carbonate (EC), fluoroethylene carbonate (FEC), and propylene carbonate (PC); the chain carbonate may be at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0094] Secondly, the present invention provides an electrical device including the lithium-ion battery described in the foregoing embodiments.

[0095] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0096] Examples 1-32

[0097] The electrolytes in Examples 1-33 were prepared as follows: In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), organic solvents (ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate (mass ratio 3:2:5)) were weighed into a sample bottle. 15.3% (1 M) of LiFSI (1.2 M in Example 24) and 1% (1 M) of vinylene carbonate (VC) were added to the sample bottle. Then, the compounds shown in Formula I, Formula IIa, or Formula IIb were added and mixed thoroughly to obtain the prepared electrolyte.

[0098] The preparation methods of the electrolytes in Examples 1 to 32 are as follows:

[0099] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), weigh organic solvent (ethylene carbonate, diethyl carbonate, methyl ethyl carbonate (mass ratio 3:2:5)) into a sample bottle. Add LiFSI (1M and 1.2M) and 1% vinylene carbonate (VC) in different proportions of the total mass to the sample bottle. Then add the compound shown in Formula I, Formula IIa, or Formula IIb and mix well to obtain the prepared electrolyte.

[0100] Examples 1-32 also provide a series of batteries, prepared by the following methods:

[0101] Preparation of positive electrode sheet:

[0102] LiNi, the positive electrode active material 0.68 Co 0.03 Mn 0.29O2 (lithium nickel cobalt manganese oxide) and conductive agent acetylene black (SuperP) are mixed evenly in a mixing tank. Then, N-methylpyrrolidone (NMP) and binder polyvinylidene fluoride (PVDF) are added and stirred evenly to obtain a black slurry. This slurry is coated on aluminum foil, baked, rolled, and cut into sheets to obtain the positive electrode sheet. The mass ratio of the positive electrode active material, conductive agent, and binder is (96.5:2:1.5).

[0103] The preparation methods for the series of batteries in Examples 33-38 are as follows:

[0104] LiNi, the positive electrode active material 0.68 Co 0.03 Mn 0.29 O2 (lithium nickel cobalt manganese oxide) and conductive agent acetylene black (SuperP) are mixed evenly in a mixing tank. Then, N-methylpyrrolidone (NMP), binder polyvinylidene fluoride adhesive (PVDF), and polyborate / polyborate ester are added to the mixture in a certain mass ratio and stirred evenly to obtain a black slurry. This slurry is coated on aluminum foil, baked, rolled, and cut to obtain a positive electrode sheet. The mass ratio of conductive agent to binder is 2% and 1.5% or more.

[0105] Negative electrode preparation (Examples 1-38 series of batteries):

[0106] The negative electrode active material graphite and the conductive agent acetylene black (Super P) are mixed evenly in a mixing tank. Then, the binder SBR and deionized water are added and stirred evenly to obtain a black slurry. This slurry is coated on copper foil, baked, rolled, and cut into sheets to obtain the negative electrode sheet. The ratio of active material, conductive agent and binder is (96.5:2:1.5).

[0107] Battery cell manufacturing:

[0108] The obtained positive electrode sheet, negative electrode sheet, and separator are stacked in the order of positive electrode, separator, and negative electrode. After winding, hot pressing and shaping, and electrode tab welding, a bare cell is obtained. The top and side are sealed with aluminum-plastic film. After completion, the cell is placed in an oven at 85±10℃ for 24h±12h to ensure that the water content of the electrode sheet is qualified. Then, electrolyte is injected. After depressurization packaging, standing, formation, shaping and other processes, the battery is obtained.

[0109] The battery performance obtained in Examples 1 to 33 was tested using the following methods, and the results are shown in Table 1.

[0110] I. Loop Testing:

[0111] Room temperature cycling: The batteries of Examples 1-38 and Comparative Examples 1-5 were subjected to charge-discharge cycle tests at 25°C with a charge-discharge rate of 1C / 1C in the range of 2.8-4.40V. The initial discharge capacity and the discharge capacity after each cycle were recorded. The cycle was 1000 cycles. The capacity retention rate was calculated as (discharge capacity per cycle / initial discharge capacity of the battery) * 100%. The cycle termination condition was 80% SOC. The recorded data are shown in Table 1.

[0112] High-temperature cycling: The batteries of Examples 1-38 and Comparative Examples 1-5 were placed in a 45°C chamber for 120 minutes, and then subjected to charge-discharge cycle tests in a 45°C constant temperature chamber at a charge / discharge rate of 1C / 1C within the range of 2.8-4.40V. The initial discharge capacity and the discharge capacity after each cycle were recorded. The cycle was 500 times. The capacity retention rate was calculated as (discharge capacity per cycle / initial discharge capacity of the battery) * 100%. The cycle termination condition was 80% SOC. The recorded data are shown in Table 1.

[0113] II. High-temperature storage:

[0114] The batteries from Examples 1-38 and Comparative Examples 1-5 were fully charged and stored in a 60°C constant temperature chamber. Every 10 days, they were removed, fully charged again, and stored in the 60°C constant temperature chamber for another 120 days. Their recoverable capacity was then tested. The method for testing the recoverable capacity is as follows:

[0115] 1. Discharge at a constant current of 1C to 2.8V, then let stand for 10 minutes;

[0116] 2. Charge the 1C CC-CV to 4.40V, with a cutoff current of 0.05C, and let it stand for 10 minutes;

[0117] 3. Discharge at a constant current of 1C to 2.8V, and record the discharged capacity as the recoverable capacity.

[0118] Capacity retention rate = recoverable capacity after storage / recoverable capacity of fresh battery * 100%, and the recorded data is shown in Table 1.

[0119] III. Volume expansion experiment: The batteries of Examples 1-38 and Comparative Examples 1-5 were charged to 4.40V at 1C and their volumes were tested by the water displacement method. The initial volume and the volume after 7 days of storage at 85°C were recorded. The volume expansion rate was calculated as (volume after 7 days of storage at 85°C - initial volume) / initial volume * 100%. The storage termination condition was 80% SOC. The results are shown in Table 1.

[0120] IV. Constant voltage leakage current test:

[0121] The batteries from Examples 1-38 and Comparative Examples 1-5 were charged to 4.40V at 1C CC-CV with a cutoff current of 0.05C, and then charged at 0.05C capacity at constant voltage for 36 hours. The leakage current of the lithium-ion secondary batteries was then continuously observed and recorded at 25°C to complete the test. The recorded results are shown in Tables 1 to 3.

[0122] Table 1. Composition of the electrolytes in Examples 1-17 and test results of the resulting batteries (lithium borate).

[0123]

[0124] Table 2. Composition of the electrolytes in Examples 18-25 and test results of the resulting batteries (borate esters)

[0125]

[0126] Note: FB3O4 is mixture ② of the compound of formula II in the claims, and its specific structure is described in the specific examples above.

[0127] Examples 26-32

[0128] The only difference between Examples 26-32 and Example 2 is that the types of compounds represented by Formula I, Formula IIa, or Formula IIb are different; all other components and concentrations are the same. The resulting batteries were tested, and the results are shown in Table 3.

[0129] Table 3 shows the composition of the electrolyte and the test results of the batteries obtained in Examples 26-32.

[0130]

[0131] Remark: Example 32 uses a 1.2M LiFSI electrolyte solution.

[0132] Comparative Examples 1-5

[0133] The only difference between Comparative Examples 1-5 and Examples 1-32 is the electrolyte. The preparation method of the electrolyte in Comparative Examples 1-5 is as follows:

[0134] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), organic solvents (ethylene carbonate, diethyl carbonate, and methyl ethyl carbonate (mass ratio 3:2:5)) were weighed into sample vials. LiPF6 + LiFSI in different mass ratios (total concentration 1.0 M or 1.2 M) and 1% vinylene carbonate (VC) were added to the sample vials, followed by the compound shown in Formula I. The mixture was thoroughly mixed to obtain the prepared electrolyte. The composition of the electrolyte and the test results of the battery performance are shown in Table 4.

[0135] Table 4 shows the composition of the electrolytes in Comparative Examples 1-5 and the test results of the resulting batteries.

[0136]

[0137] Examples 33-38

[0138] The only difference from Comparative Example 3 is that FB3O4 was mixed into the positive electrode or the membrane material instead of the electrolyte solution, and the results are shown in Table 5.

[0139] Table 5 shows the composition of the positive electrode or separator in Examples 33-38 and the test results of the resulting batteries.

[0140]

[0141] Note: In Examples 33 / 35 / 37, the amount of FB3O4 added is 1% / 3% / 5% of the active material content of the positive electrode, respectively; in Examples 34 / 36 / 38, the amount of FB3O4 added is 1% / 3% / 5% of the membrane mass, respectively, and FB3O4 is added as a slurry to the formulation and is attached to one or both sides of the membrane by spraying / rolling.

[0142] As can be seen from the data of Examples 1-38 and Comparative Examples 1-5, the boron-containing compounds of Formula I, IIa, or IIb undergo an electrochemical oxidation reaction on the surface of the positive electrode aluminum foil during the charging and discharging process of a high-voltage 4.4V lithium-ion battery to form a uniform and dense passivation film (see [link to relevant documentation] for specific aluminum foil passivation effects and corrosion phenomena). Figure 1 and Figure 2This material prioritizes the passivation effect of lithium salts such as LiFSI or LiTFSI, effectively preventing the severe gas generation and rapid capacity decay caused by strong oxidation corrosion of aluminum foil due to high concentrations of LiFSI or LiTFSI. It also effectively reduces side reactions such as high leakage current and accelerated capacity decay at high temperatures caused by high concentrations of LiFSI. At the same time, the passivation film formed by boron-containing substances in the electrolyte greatly reduces the solid-liquid interface impedance, avoids large polarization factors during charging and discharging, and thus improves the rapid increase in cell impedance caused by high-voltage system cell high-temperature cycling and high-temperature storage. Comparative analysis of the experimental results in Examples 1-4 and 5-9 leads to the conclusion that: when the boron-containing additive is lithium metaborate, if the electrolyte addition amount is <1.5% or the content of polyborate / ester additive is <0.1%, the additive content is low, and correspondingly, the number of boron functional groups in its compound is relatively small, making it difficult to form an effective, dense, and uniform passivation film. Therefore, the effect of improving room temperature cycling and leakage current is not significant. When the content is >6%, the interface film formed by the electrochemical oxidation reaction of high-concentration boron-containing substances or polyborates on the surface of the positive electrode aluminum foil is rich in BF3, boron-containing fluorides, etc. The inorganic components effectively prevent severe corrosion of aluminum foil caused by high-concentration LiFSI, improving the electrochemical kinetics performance of lithium batteries. Simultaneously, the positive electrode passivation film formed on the positive electrode surface enhances lithium-ion conductivity, thus significantly mitigating the rapid increase in polarization and severe lithium plating at the negative electrode caused by high-rate fast charging. Comparison of the results of Examples 8 and 9 shows that after the borate content exceeds 6%, unilaterally increasing the borate content does not significantly improve the cycle and storage performance of lithium-ion batteries. Considering cost factors, excessive addition is not recommended. Comparison of Examples 6-9 with different addition amounts concludes that different proportions of compounds of formula I, IIa, or IIb can significantly improve the cycle and storage performance of lithium-ion batteries.

[0143] A comparison of the performance data from Examples 18-32 and Comparative Example 3 shows that, compared with LiB3O5 (content 1%) in Example 6, compounds (6-14) containing fluorine atoms, alkylphosphine, alkylthiol, and silane substituents exhibit stronger nucleophilicity in their additive molecules. This results in stronger polar boron-heteroatom bonds, making the nucleophilic substituents more easily oxidized and broken, thus forming a more uniform and dense passivation film on the surface of the high-voltage positive electrode aluminum foil. This significantly improves the cycle life of lithium-ion batteries and reduces leakage current. In contrast, the substituents on the B atoms in compounds (12) and (13) have weaker nucleophilicity, and the resulting BX heteroatom polar bonds cannot be well oxidized and broken into films at the interface of the high-voltage positive electrode aluminum foil. Consequently, their effect on improving the strong oxidation corrosion of aluminum foil is relatively poor. For compounds of formula IIa and IIb, polyboronic esters and lithium polyboronate have the same passivation improvement effect on strong oxidative corrosion of aluminum foil containing high concentrations of LiFSI system, and have the same improvement level in room temperature / high temperature cycle life. Given the solubility and easy high temperature storage characteristics of polyboronic esters, they are easy to dissolve in electrolyte and transport over long distances. Compared with the synthesis cost of lithium polyboronate, polyboronic esters have many advantages.

[0144] Comparison of the performance data of Examples 33-38 and the comparative examples shows that compound FB3O4, as both an electrode additive and a separator additive, can improve the cycle life of lithium-ion batteries and reduce leakage current.

[0145] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that, Includes negative electrode, positive electrode, diaphragm, and non-aqueous electrolyte; The non-aqueous electrolyte includes a lithium salt, wherein the molar concentration of lithium ions in the non-aqueous electrolyte is 0.2~2 mol / L; the lithium salt includes lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide; the content of lithium bis(fluorosulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide in the non-aqueous electrolyte is 0.2 wt%~18.4 wt%; The non-aqueous electrolyte also includes at least one of compounds of formula II-a and formula II-b; The compound of formula II-a is a compound having one of the following structures: The formula II-b is a compound having one of the following structures: ； In the non-aqueous electrolyte, the content of the compound of formula II-a or formula II-b is 0.01 wt% to 15 wt%; During the charging and discharging process of the lithium-ion battery, a passivation protective layer rich in BF3 or containing fluorinated borate is formed on the surface of the positive electrode.

2. The lithium-ion battery according to claim 1, characterized in that, The content of the compound of formula II-a or formula II-b is 0.05 wt% to 6 wt%.

3. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte also includes the following additives, the concentration of which is 0.1 wt% to 3 wt%. The additives include at least one of vinyl sulfate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, 1-propylene-1,3-sulfonate lactone, methanedisulfonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphite, and tris(trimethylsilyl) borate.

4. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The non-aqueous electrolyte also includes an organic solvent, which is at least one of carbonates, carboxylic esters, sulfates, phosphates, amides, nitriles, and ethers.

5. The lithium-ion battery according to claim 4, characterized in that, The organic solvent is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl formate, ethyl formate, ethyl propionate, methyl propionate, ethyl butyrate, ethyl acetate, acid anhydride, N. Methylpyrrolidone, N Methylformamide, N Methylacetamide, acetonitrile, sulfolane, dimethyl sulfoxide, ethylene sulfite, propylene sulfite, triethyl phosphate, methyl ethyl phosphite, dimethyl sulfide, diethyl sulfite, dimethyl sulfite, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3 At least one of dioxolane, tetrahydrofuran, fluorinated cyclic organic esters, and sulfur-containing cyclic organic esters.

6. The lithium-ion battery according to claim 5, characterized in that, In the non-aqueous electrolyte, the content of the organic solvent is 60 wt% to 85 wt%.

7. An electrical appliance, characterized in that, Includes the lithium-ion battery as described in any one of claims 1-6.

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