Electrolyte additive, electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte additive, an electrolyte and a lithium ion battery, the electrolyte additive comprises a first additive and a second additive; the first additive is a compound as shown in a formula I, and the second additive is a compound as shown in a formula II; wherein based on the total mass of the electrolyte additive, the mass percentage content of the first additive is A, the mass percentage content of the second additive is B, and A / B is larger than or equal to 0.05 and smaller than or equal to 20. Through the synergistic effect of the first additive and the second additive, an SEI film and a CEI film with relatively excellent film forming uniformity and structural stability can be obtained, the gas production phenomenon in the battery cycle process is effectively inhibited, and the battery impedance is reduced, so that the fast charge cycle performance and the high-temperature performance of the battery are effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to an electrolyte additive, an electrolyte and a lithium ion battery. BACKGROUND

[0002] A lithium ion battery is a secondary battery that relies on the movement of lithium ions (Li + ) between the positive and negative electrodes to achieve the purpose of charging and discharging. In recent years, it has been widely used in mobile phones, tablet computers, notebook computers, smart watches, unmanned aerial vehicles, electric bicycles, electric vehicles and other types of electric tools, and is distributed in every corner of our lives. With the increasing demand for lithium ion battery endurance time of consumer electronic products, it is urgent to further improve the volumetric energy density of the battery.

[0003] Increasing the specific capacity of the positive active material and the charging voltage of the battery is a common method to improve the energy density of the battery. However, in actual use, increasing the nickel content of the positive active material and the charging voltage (≥4.2V) of the battery will cause a series of problems, such as poor structure stability of the positive active material, micro-cracks, increased irreversible phase transition, transition metal dissolution, gas precipitation, etc., resulting in increased cycle impedance of the battery, rapid decline in cycle performance and high-temperature storage performance. Therefore, how to solve the problems of cycle impedance growth, poor cycle stability and large gas production of lithium ion batteries during high-voltage fast charging has become one of the difficulties and bottlenecks in the design of lithium ion batteries. SUMMARY

[0004] The purpose of the present application is to provide an electrolyte additive, an electrolyte and a lithium ion battery to solve the problems of cycle impedance growth, poor cycle stability and large gas production of lithium ion batteries during high-voltage fast charging. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides an electrolyte additive, which comprises a first additive and a second additive; the first additive is a compound represented by Formula I, and the second additive is a compound represented by Formula II;

[0006]

[0007] wherein, based on the total mass of the electrolyte additive, the mass percentage of the first additive is A, and the mass percentage of the second additive is B, 0.05≤A / B≤20.

[0008] In some embodiments of the present application, based on the total mass of the electrolyte additive, the mass percentage of the first additive is A, and the mass percentage of the second additive is B, 0.1≤A / B≤10.

[0009] In some embodiments of the present application, the electrolyte additive comprises a third additive, which is a compound represented by Formula III;

[0010]

[0011] wherein the mass percentage content of the third additive is C, and 0.05≤A / C≤20, based on the total mass of the electrolyte additive.

[0012] In some embodiments of the present application, 0.1≤A / C≤10.

[0013] A second aspect of the present application provides an electrolyte, which comprises a non-aqueous organic solvent, an electrolyte, and an electrolyte additive of the present application.

[0014] In some embodiments of the present application, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy: 0.1%≤W1≤2%, 0.1%≤W2≤2%, based on the total mass of the electrolyte.

[0015] In some embodiments of the present application, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy: 0.1%≤W1≤1%, 0.1%≤W2≤1%, based on the total mass of the electrolyte.

[0016] In some embodiments of the present application, the electrolyte comprises a third additive, which is a compound represented by Formula III;

[0017]

[0018] wherein the mass percentage content W3 of the third additive satisfies: 0.1%≤W3≤2%, based on the total mass of the electrolyte.

[0019] In some embodiments of the present application, the mass percentage content W3 of the third additive satisfies: 0.1%≤W3≤1%, based on the total mass of the electrolyte.

[0020] In some embodiments of the present application, the electrolyte further comprises a fourth additive, which is selected from at least one of triphenyl phosphite, triphenyl phosphate, pentafluoroethoxy phosphazene, and dicyclohexyl carbodiimide; and the mass percentage content W4 of the fourth additive satisfies: 0.01%≤W4≤0.1%, based on the total mass of the electrolyte.

[0021] In some embodiments of the present application, the electrolyte further comprises a fifth additive selected from at least one of vinylene carbonate, fluoroethylene carbonate and vinyl ethylene carbonate; the mass percentage content W5 of the fifth additive satisfies: 0.5%≤W5≤2%, based on the total mass of the electrolyte.

[0022] The third aspect of the present application provides a lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte provided by the second aspect of the present application.

[0023] In some embodiments of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the positive electrode material layer comprising a positive electrode active material; the positive electrode active material satisfies the general formula Li a Ni b Co c M1 d M2 e O f R g , wherein 1≤a≤1.2, 0<b<1, 0<c<1, 0<d<1, 0≤e≤0.2, b+c+d+e=1, 1≤f≤2, 0≤g≤1, f+g=2; M1 is selected from at least one of Mn and Al, M2 is selected from at least one of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W and Nb, and R is selected from at least one of N, F, S and Cl.

[0024] Advantages of the present application:

[0025] The present application provides an electrolyte additive, comprising a first additive and a second additive; the first additive is a compound shown in formula I, and the second additive is a compound shown in formula II; wherein the mass percentage content of the first additive is A and the mass percentage content of the second additive is B, based on the total mass of the electrolyte additive, 0.05≤A / B≤20. Through the synergistic effect of the first additive and the second additive, SEI film and CEI film with better film uniformity and structural stability can be obtained. In addition, the electrolyte additive can also effectively inhibit the increase of cycle impedance and the generation of gas during the high-voltage fast charging process of the lithium ion battery, thereby effectively improving the cycle performance of the battery.

[0026] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application shall fall within the scope of the present application.

[0028] The first aspect of the present application provides an electrolyte additive, which comprises a first additive and a second additive; the first additive is a compound shown in formula I, and the second additive is a compound shown in formula II;

[0029]

[0030] wherein, based on the total mass of the electrolyte additive, the mass percentage of the first additive is A, and the mass percentage of the second additive is B, 0.05≤A / B≤20. For example, the value of A / B can be 0.05, 0.5, 1, 2, 5, 10, 12, 15, 20 or a range formed by any two of the above values.

[0031] The first additive and the second additive are used in combination in the present application, and through the synergistic effect of both, the problems of cycle impedance growth, poor cycle stability and large gas production of lithium ion batteries during high-voltage fast charging can be solved. Among them, the oxidation and reduction potentials of the first additive are both before the electrolyte solvent, and during the pre-charging process of the battery, the first additive is preferentially oxidized at the positive electrode and reduced at the negative electrode, then a stable and high-ionic-conductivity CEI film (Chemical-electrochemical Interface) is constructed at the positive electrode, and a stable and high-ionic-conductivity SEI film (Solid electrolyte Interface) is constructed at the negative electrode surface, effectively reducing the decomposition of electrolyte during the cycle process, thereby improving the cycle stability of lithium ion batteries. The CEI film formed by the first additive at the positive electrode contains lithium carbonate, and if the content of lithium carbonate is too high, it is easy to be corroded by HF, causing the CEI film to thicken, thereby causing the impedance of the lithium ion battery to increase. Therefore, the second additive is further introduced, the second additive can form inorganic matter rich in F and Li on the surface of the positive electrode, reduce the impedance of the lithium ion battery, and the free radicals generated by the P-O break diffuse to the surface of the positive electrode and are oxidized to form CEI film components, which can stabilize the positive electrode active material, avoid direct contact between the electrolyte and the positive electrode, and P-O-M (M=Ni, Co, Mn) complexation can occur on the surface of the positive electrode, reducing the dissolution of transition metals and improving the cycle performance of lithium ion batteries; in addition, the second additive can also form a phosphorus-containing oligomer and a SEI film component rich in P-O, LiF and other groups on the surface of the negative electrode, further improving the stability of the SEI film. The electrolyte includes the first additive and the second additive, and the synergistic effect of both can obtain SEI film and CEI film with better film uniformity and structural stability, effectively inhibiting the generation of gas during the cycle process of the lithium ion battery, while reducing the impedance of the lithium ion battery, thereby effectively improving the fast-charging cycle performance and high-temperature performance of the lithium ion battery.

[0032] In some embodiments of the present application, the mass percentage content of the first additive is A and the mass percentage content of the second additive is B based on the total mass of the electrolyte additive, and 0.1≤A / B≤10. For example, the value of A / B can be 0.1, 0.5, 1, 2, 3, 5, 7, 8, 9, 10 or a range composed of any two of the above values.

[0033] Using the electrolyte additive of the present application and controlling the content of the first additive and the second additive within the range of the present application, through the synergistic effect of the first additive and the second additive, SEI film and CEI film with better film uniformity and structural stability can be obtained, further inhibiting the generation of gas, while reducing the impedance of the ion battery, thereby effectively improving the fast-charging cycle performance and high-temperature performance of the battery.

[0034] In some embodiments of this application, the additive includes a third additive, which is a compound of formula III;

[0035]

[0036] Wherein, based on the total mass of the electrolyte additives, the mass percentage content of the third additive is C, where 0.05 ≤ A / C ≤ 20. For example, the value of A / C can be 0.05, 0.5, 1, 2, 5, 10, 12, 15, 20, or a range of any two of these values.

[0037] The first additive forms an SEI film containing lithium carbonate at the negative electrode, which helps improve the uniformity and stability of the SEI film. However, lithium carbonate is easily corroded by HF, leading to electrolyte decomposition at the negative electrode, increasing gas production and damaging the SEI film on the surface of the negative electrode active material. Based on the first and second additives, a third additive of this application is further introduced. After ring opening, the third additive promotes the film formation of the first additive and reduces the lithium carbonate content in the SEI film, while simultaneously generating Li₂SO₄ and its over-lithium products (lithium oxide and amorphous Li₂). x S and Li x By sandwiching lithium carbonate in the middle, the decomposition of lithium carbonate by HF in the electrolyte and the thickening of the SEI film are limited, further reducing the impedance of the lithium-ion battery. Therefore, by further introducing a third additive into the electrolyte additive and adjusting the A / C ratio within the range of this application, the impedance of the lithium-ion battery can be further reduced, the cycle performance improved, and gas production reduced.

[0038] In some embodiments of this application, 0.1 ≤ A / C ≤ 10. For example, the value of A / C can be 0.1, 0.5, 1, 2, 3, 5, 7, 8, 9, 10, or a range of any two of these values. By controlling the mass percentage content of the first, second, and third additives of this application within the above range, battery impedance can be further reduced, gas production can be reduced, and battery cycle performance can be improved.

[0039] A second aspect of this application provides an electrolyte comprising a non-aqueous organic solvent, an electrolyte, and the electrolyte additives of this application.

[0040] In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy the following: 0.1% ≤ W1 ≤ 2%, 0.1% ≤ W2 ≤ 2%. For example, W1 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range of any two of these values, and W2 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range of any two of these values. By controlling the first and second additives in the electrolyte within the above ranges, SEI films and CEI films with superior film uniformity and structural stability can be obtained through the synergistic effect of the first and second additives. In addition, this electrolyte additive can effectively suppress the generation of gas during battery cycling, while reducing battery impedance, thereby effectively improving the fast-charging cycle performance and high-temperature performance of the battery.

[0041] In some embodiments of this application, based on the total mass of the electrolyte, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy: 0.1% ≤ W1 ≤ 1%, 0.1% ≤ W2 ≤ 1%. For example, W1 can be 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 0.9%, 1%, or a range of any two values ​​therein, and W2 can be 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 0.9%, 1%, or a range of any two values ​​therein. By controlling the content of the first and second additives in the electrolyte within the range specified in this application, through the synergistic effect of the first and second additives, SEI films and CEI films with superior film uniformity and structural stability can be obtained, further suppressing gas generation and reducing the impedance of the ion battery, thereby effectively improving the fast-charging cycle performance and high-temperature performance of the battery.

[0042] In some embodiments of this application, the electrolyte includes a third additive, which is a compound of formula III;

[0043]

[0044] Wherein, based on the total mass of the electrolyte, the mass percentage content W3 of the third additive satisfies: 0.1% ≤ W3 ≤ 2%, preferably 0.1% ≤ W3 ≤ 1%. For example, W3 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range of any two of these values.

[0045] The SEI film formed by the first additive at the negative electrode contains lithium carbonate, which is easily corroded by HF. Consequently, the electrolyte decomposes at the negative electrode, increasing gas production and reducing the stability of the SEI film. Based on the first and second additives, a third additive of this application is further introduced, and the values ​​of W1, W2, and W3 are adjusted within the range of this application. After the third additive opens its ring, it promotes the film formation of the first additive, while simultaneously reducing the lithium carbonate content in the SEI film. This limits the decomposition of lithium carbonate by HF in the electrolyte and the thickening of the SEI film, further reducing the impedance of the lithium-ion battery, improving cycle performance, and reducing gas production.

[0046] In some embodiments of this application, the electrolyte further includes a fourth additive, which is selected from at least one of triphenyl phosphite, triphenyl phosphate, pentafluoroethoxyphosphazene, and dicyclohexylcarbamate; based on the total mass of the electrolyte, the mass percentage W4 of the fourth additive satisfies: 0.01% ≤ W4 ≤ 0.1%. For example, W4 can be 0.01%, 0.02%, 0.03%, 0.05%, 0.07%, 0.08%, 0.09%, 0.1%, or a range of any two of these values. By adding a fourth additive to the electrolyte and controlling its mass percentage within the range specified in this application, the storage stability of the electrolyte can be improved, helping the electrolyte maintain its properties during storage and transportation, and reducing deterioration caused by changes in the external environment.

[0047] In some embodiments of this application, the electrolyte further includes a fifth additive, which is selected from at least one of vinylene carbonate, fluoroethylene carbonate, and ethylene ethylene carbonate; based on the total mass of the electrolyte, the mass percentage W5 of the fifth additive satisfies: 0.5% ≤ W5 ≤ 2%. For example, W5 can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range of any two of these values. By adding a fifth additive to the electrolyte and controlling the mass percentage of the fifth additive within the range specified in this application, the film uniformity of the SEI can be improved.

[0048] A third aspect of this application provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte of this application.

[0049] In some embodiments of this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, the positive electrode material layer including a positive electrode active material; the positive electrode active material satisfies the general formula Li a Ni b Co c M1 d M2 e O f Rg , where 1 ≤ a ≤ 1.2, 0 < b < 1, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, b + c + d + e = 1, 1 ≤ f ≤ 2, 0 ≤ g ≤ 1, f + g = 2; M1 is selected from at least one of Mn and Al, M2 is selected from at least one of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W and Nb, and R is selected from at least one of N, F, S and Cl. For example, the positive electrode active material can be NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2), NCM523 (LiNi 0.5 Co 0.2 Mn 0.3 O2), NCM712 (LiNi 0.7 Co 0.1 Mn 0.2 O2), NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O2), NCM111 (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2). Selecting the positive electrode active material of the present application can further increase the specific capacity per gram of the positive electrode active material and reduce the cost of the positive electrode active material.

[0050] In this application, the electrolyte includes a non-aqueous organic solvent. As the main component of the electrolyte, the non-aqueous organic solvent should have high lithium salt solubility to ensure high ionic conductivity. As an important carrier for ion transport, the non-aqueous organic solvent can exhibit high electronic conductivity after the electrolyte dissolves, improving battery cycle life, charge / discharge rate, high-temperature performance, low-temperature performance, and energy density. This application does not impose any particular limitation on the non-aqueous organic solvent, as long as it achieves the purpose of this application. For example, the non-aqueous organic solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds or cyclic carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate, propylene carbonate (PC), or butylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous organic solvents in the electrolyte, as long as the purpose of this application is achieved. For example, based on the total mass of the electrolyte, the mass percentage of non-aqueous organic solvents can be 78% to 91%.

[0051] In some embodiments of this application, the solvent may include ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 1:(0.5-2):(0.5-2).

[0052] In this application, the electrolyte includes an electrolyte. After dissolving in the solvent of the electrolyte, the electrolyte releases lithium ions. The lithium ions form a solvated structure with the solvent, which facilitates the rapid migration of lithium ions. This application does not impose any particular limitation on the electrolyte, as long as it achieves the purpose of this application. For example, the electrolyte may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, LiFSI, lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. This application does not impose any particular limitation on the content of the electrolyte in the electrolyte, as long as it achieves the purpose of this application.

[0053] In some embodiments of this application, the electrolyte may be selected from at least one of LiPF6, LiFSI, LiBF4, and LiTFSI.

[0054] In some embodiments of this application, the mass percentage of the electrolyte is 8% to 18% based on the total mass of the electrolyte. For example, the mass percentage of the electrolyte can be 8%, 10%, 12%, 14%, 16%, 18%, or a range of any two of these values, based on the total mass of the electrolyte. Controlling the mass percentage of the electrolyte within the range specified in this application allows the electrolyte to dissolve sufficiently in non-aqueous organic solvents, while simultaneously providing the electrolyte with both high ionic conductivity and low manufacturing cost.

[0055] The lithium-ion battery of this application further includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. In this application, the positive electrode material layer may be disposed on one surface or on two surfaces in the thickness direction of the positive current collector. This application does not have any particular limitation on the positive current collector, as long as it can achieve the purpose of this application. For example, the positive current collector may include a metal foil or a composite current collector. For example, the metal foil may be aluminum foil. The composite current collector may include a polymer material base layer and a metal material layer disposed on at least one surface of the polymer material base layer. For example, the material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy. The polymer material base layer may include at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, or polyethylene. This application does not have any particular limitation on the thickness of the positive current collector and the positive electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive electrode material layer is 30 μm to 120 μm. The positive electrode material layer of this application may also contain a conductive agent and a binder. This application does not have any particular limitations on the conductive agent and binder, as long as they can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of superconducting carbon (Super P), acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binder may include, but is not limited to, at least one of polyvinyl chloride, polyacrylamide, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin.

[0056] The lithium-ion battery of this application includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. In this application, the negative electrode material layer may be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. This application does not impose any particular limitation on the negative electrode current collector; any negative electrode current collector known in the art can be used, as long as it achieves the purpose of this application. For example, the negative electrode current collector may comprise at least one of aluminum foil, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, and copper foam. In this application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm, and the thickness of the single-sided negative electrode material layer is 30 μm to 150 μm. Optionally, the negative electrode active material includes a thickener, which may include, but is not limited to, sodium carboxymethyl cellulose. The negative electrode material layer of this application may also include a conductive agent and a binder. This application does not impose any particular limitations on the conductive agent and the binder, as long as they can achieve the purpose of this application. For example, the binder and conductive agent may include, but are not limited to, at least one of the optional materials for the positive electrode material layer described above.

[0057] The negative electrode material layer of this application includes a negative electrode active material. This application does not particularly limit the type of negative electrode active material; any negative electrode active material known in the art can be used, as long as it achieves the purpose of this application. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon-based materials, tin-based materials, and lithium titanate. The aforementioned silicon-based materials may include, but are not limited to, at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys; the aforementioned tin-based materials may include at least one of elemental tin, tin oxide compounds, or tin alloys.

[0058] The lithium-ion battery of this application also includes a separator to separate the positive electrode and the negative electrode, prevent internal short circuits, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the type of separator; any porous separator with good chemical and mechanical stability can be selected. For example, the separator material can include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator type can include, but is not limited to, at least one of woven membrane, nonwoven membrane (nonwoven fabric), microporous membrane, composite membrane, rolled membrane, or spun membrane. The separator can be a single-layer thin film or a multi-layer composite thin film. In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application; for example, the thickness can be from 5 μm to 20 μm.

[0059] The lithium-ion battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application. For example, an aluminum-plastic film packaging bag can be used.

[0060] The manufacturing process of the lithium-ion battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and winding and folding them as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a lithium-ion battery; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain a lithium-ion battery. In addition, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent the internal pressure of the lithium-ion battery from rising and overcharging / discharging.

[0061] The battery of this application may be in the form of a single battery cell, a battery module, or a battery pack. A single battery cell can be assembled into a battery module, and a battery module may contain one or more battery cells; the specific number can be selected by those skilled in the art based on the application and capacity of the battery module. The battery modules of this application can also be assembled into a battery pack, and a battery pack may contain one or more battery modules; the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0062] Example

[0063] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0064] Test methods and apparatus:

[0065] ambient temperature cycling performance test

[0066] The lithium-ion battery was placed in a 25°C environment and left to stand for 2 hours. It was then charged at a constant current of 0.5C to a voltage of 4.2V, and then charged at a constant voltage of 4.2V until the cutoff current reached 0.05C. Finally, it was discharged at a constant current of 0.5C to 2.5V. This constitutes one charge-discharge cycle, and the initial discharge capacity was recorded as C1. This charge-discharge cycle was repeated for 600 cycles, and the discharge capacity C1 on the 600th cycle was recorded. 600 Room temperature cycling capacity retention rate = (C 600 / C1)×100%.

[0067] High-temperature cycling performance test

[0068] The lithium-ion battery was placed in a 45℃ environment and left to stand for 2 hours. It was then charged at a constant current of 0.5C to a voltage of 4.2V, and then charged at a constant voltage of 4.2V until the cutoff current reached 0.05C. Finally, it was discharged at a constant current of 0.5C to 2.5V. This constitutes one charge-discharge cycle, and the initial discharge capacity was recorded as C1. This charge-discharge cycle was repeated for 600 cycles, and the discharge capacity C on the 600th cycle was recorded. 600 High-temperature cycling capacity retention rate = (C 600 / C1)×100%.

[0069] Gas production test after 30 days of high-temperature storage

[0070] The lithium-ion battery was placed in a constant temperature environment at 25℃ and charged at a constant current of 1C until the voltage reached 4.2V. Then, it was charged at a constant voltage at 4.2V until the cutoff current reached 0.05C. The lithium-ion battery was suspended by a thin thread and immersed in a container of water. The balance reading at this point was recorded as m1. After storing the lithium-ion battery in a 45℃ explosion-proof oven for 30 days, it was again suspended by a thin thread and immersed in a container of water. The balance reading was recorded as m2.

[0071] The gas production ΔV is measured using the water displacement method, where ΔV = (m2 - m1) / ρ, and ρ is the density of liquid water.

[0072] DC Impedance (DCR) Test

[0073] The lithium-ion battery was placed in a 25°C environment and left to stand for 30 minutes to reach a constant temperature. It was then discharged at a constant current of 1C to the cutoff voltage of 2.5V, left to stand for 5 minutes, and subsequently charged at a constant current of 1C to the upper limit voltage of 4.2V. It was then charged at a constant voltage of 4.2V until the cutoff current was 0.05C. The battery was discharged at a constant current of 1C for 30 minutes to adjust to 50% SOC (SOC refers to the battery's state of charge), left to stand at 25°C for 5 minutes, and the battery voltage value V0 was recorded. The battery was then charged at the current I corresponding to 2C. 2C The battery was discharged under constant current for 30 seconds, and the voltage value V1 was recorded.

[0074] The formula for calculating DC impedance at 50% SOC is as follows: DCR(mΩ)=(V0-V1) / I 2C ×1000.

[0075] Room temperature rate cycling performance test

[0076] The lithium-ion battery was placed in a 25°C environment and left to stand for 2 hours. It was then discharged at a constant current of 1C to the cutoff voltage of 2.5V, left to stand for 5 minutes, and then charged at a constant current of 1.6C to the upper limit voltage of 4.2V. Finally, it was charged at a constant voltage of 4.2V to the cutoff current of 0.05C. This constitutes one charge-discharge cycle. This charge-discharge cycle was repeated 600 times. The discharge capacity of the first cycle was recorded as C1, and the discharge capacity of the 600th cycle was recorded as C2. 600 Room temperature rate cycling capacity retention = (C 600 / C1)×100%.

[0077] Example 1-1

[0078] <Preparation of Electrolyte>

[0079] In an argon-atmosphere glove box with moisture content <10 ppm and oxygen content <1 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed uniformly at a mass ratio of 3:5:2 to obtain a base solvent. Thoroughly dried lithium hexafluorophosphate, a first additive, and a second additive were added to the base solvent. The electrolyte contained 12.5% ​​lithium hexafluorophosphate by mass, 0.1% of the first additive by mass, and 0.6% of the second additive by mass, with the remainder being the base solvent.

[0080] <Preparation of the positive electrode>

[0081] The positive electrode active material NCM811(LiNi) 0.8 Co 0.1 Mn 0.1 O2), polyvinylidene fluoride (PVDF) binder, acetylene black conductive agent, and carbon nanotubes were mixed in a mass ratio of 93:2.3:2:0.7. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum until a homogeneous and fluid positive electrode slurry was obtained, yielding a positive electrode slurry with a solid content of 68.5 wt%. The positive electrode slurry was then uniformly coated onto one surface of a 16 μm thick aluminum foil current collector, with a coating weight of 35 g / m². 2 After drying at 85℃, a positive electrode sheet with a single-sided coating of positive electrode material is obtained. The above steps are repeated on the other surface of the positive current collector aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying under vacuum at 85℃, the sheet undergoes cold pressing, edge trimming, cutting, slitting, sheet making, and electrode tab welding and adhesive bonding processes to obtain a positive electrode sheet with dimensions of 70mm × 54mm. The thickness of the double-sided positive electrode material layer is 113μm.

[0082] <Preparation of Negative Electrode Sheets>

[0083] Graphite (negative electrode active material), acetylene black (conductive agent), sodium carboxymethyl cellulose (CMC-Na) (thickener), and styrene-butadiene rubber (binder) were mixed in a mass ratio of 95:1.5:1:2.5. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry with a solid content of 49 wt%. The negative electrode slurry was then uniformly coated onto a 9 μm thick copper foil for the negative electrode current collector, with a coating weight of 20 g / m². 2 After drying at 85℃, a negative electrode sheet with a single-sided coating of negative electrode material is obtained. The above steps are repeated on the other surface of the negative electrode current collector copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying under vacuum at 85℃, the sheet undergoes cold pressing, edge trimming, cutting, slitting, sheet making, and welding of tabs with adhesive to obtain a negative electrode sheet with dimensions of 74mm × 58mm. The thickness of the double-sided negative electrode material layer is 164μm.

[0084] <Preparation of the diaphragm>

[0085] The diaphragm is SP312J3020H diaphragm purchased from Xingyuan Material.

[0086] <Preparation of Lithium-ion Batteries>

[0087] The separator, positive electrode, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to isolate them. They are then wound, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, thus obtaining the electrode assembly. The electrode assembly is placed in an aluminum foil packaging bag, with the positive and negative tabs extended from the inside to the outside of the bag. After drying at 85°C for 48 hours to remove moisture, it is heat-sealed to obtain the cell ready for electrolyte injection. The prepared electrolyte is then injected into the dried cell. Following vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion battery is obtained. The formation conditions are: charging the lithium-ion battery at a constant current of 0.1C to 3.4V, and then charging it at a constant current of 0.2C to 3.9V.

[0088] Examples 1-2 to Examples 1-15

[0089] Except for adjusting the relevant parameters according to Table 1 in the section on <Preparation of Electrolyte>, the rest is the same as in Example 1-1. When the values ​​of W1 and W2 in the electrolyte change, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged.

[0090] Examples 1-16 to Examples 1-28

[0091] Except for adjusting the mass percentages W1, W2, and W3 of the first, second, and third additives according to Table 1 in the <Preparation of Electrolyte> section, the rest is the same as in Example 1-1. When the values ​​of W1, W2, and W3 in the electrolyte change, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged.

[0092] Examples 2-1 to 2-4

[0093] Except for adjusting the mass percentages W1, W2, and W3 of the first, second, and third additives according to Table 2 in the <Preparation of Electrolyte> section, and changing the type of positive electrode active material according to Table 2 in the <Preparation of Positive Electrode> section, the rest is the same as in Examples 1-1. When the values ​​of W1, W2, and W3 in the electrolyte change, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged.

[0094] Examples 3-1 to 3-19

[0095] Except for the addition of the third, fourth, and fifth additives according to Table 3 in the <Preparation of Electrolyte> section, and the adjustment of the mass percentages W3, W4, and W5 of the third, fourth, and fifth additives, the rest is the same as in Examples 1-3. When the values ​​of W1, W2, W3, W4, and W5 in the electrolyte change, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged.

[0096] Comparative Examples 1 to 5

[0097] Except for the fact that in the <Preparation of Electrolyte>, only one of the first and second additives is added or omitted, and the mass percentages of the first and second additives are adjusted according to Table 1, the rest is the same as in Examples 1-1. When the values ​​of W1 and W2 in the electrolyte change, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged.

[0098] Comparative Examples 6 to 9

[0099] Except for adjusting the mass percentages W1 and W2 of the first and second additives according to Table 1 in the <Preparation of Electrolyte> section, the rest is the same as in Example 1-1. When the values ​​of W1 and W2 in the electrolyte change, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged.

[0100] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0101] Table 1

[0102]

[0103]

[0104] Note: In Table 1, " / " indicates that the corresponding preparation parameters or substances do not exist.

[0105] As can be seen from Examples 1-1 to 1-15 and Comparative Examples 1 to 9, the electrolyte includes a first additive and a second additive, and W1 and W2 are regulated within the scope of this application. Through the synergistic effect of the first and second additives, the lithium-ion battery can exhibit high room temperature cycle capacity retention, high temperature cycle capacity retention, and room temperature rate cycle capacity retention, as well as low high temperature storage gas generation and DC resistance. This indicates that the lithium-ion battery has good cycle performance at both high and room temperatures. However, the lithium-ion battery electrolytes in Comparative Examples 1 to 5 did not simultaneously include the first and second additives. In Comparative Examples 6 to 9, W1 and W2 in the lithium-ion battery electrolytes are outside the scope of this application, resulting in lithium-ion batteries with low room temperature cycle capacity retention, high temperature cycle capacity retention, and room temperature rate cycle capacity retention, as well as high high temperature storage gas generation and DC resistance. This demonstrates that without the addition of the first additive or only one of the second additive, and with W1 and W2 being outside the scope of this application, the lithium-ion battery exhibits poor cycle performance and rate performance at both room and high temperatures.

[0106] The SEI film formed by the first additive at the negative electrode contains lithium carbonate, which is easily corroded by HF. Consequently, the electrolyte decomposes at the negative electrode, increasing gas production and reducing the stability of the SEI film. The third additive, after ring-opening, promotes the film formation of the first additive while reducing the lithium carbonate content in the SEI film. This limits the decomposition of lithium carbonate by HF in the electrolyte and the thickening of the SEI film, further reducing the impedance of the lithium-ion battery, improving cycle performance, and reducing gas production. As can be seen from Examples 1-17 to 1-22, Examples 1-24 to 1-28, and Examples 1-16 and 1-23, by further introducing the third additive of this application based on the first and second additives, and adjusting the values ​​of W1, W2, and W3 within the range of this application, the lithium-ion battery can exhibit high room temperature cycle capacity retention, high temperature cycle capacity retention, and room temperature rate cycle capacity retention, as well as low high-temperature storage gas production and DC impedance. This demonstrates that the lithium-ion battery has good cycle performance and rate performance at both high and room temperatures.

[0107] Table 2

[0108]

[0109] Note: In Table 2, " / " indicates that the corresponding preparation parameters or substances do not exist.

[0110] As can be seen from Examples 2-1 to 2-4, using the electrolyte additive of this application in the positive electrode active material system of this application can enable the lithium-ion battery to have a high room temperature cycle capacity retention rate, high temperature cycle capacity retention rate and room temperature rate cycle capacity retention rate, as well as a low high temperature storage gas generation and DC resistance, indicating that the lithium-ion battery has good cycle performance and rate performance at both high temperature and room temperature.

[0111] Table 3

[0112]

[0113]

[0114] Note: In Table 3, " / " indicates that the corresponding preparation parameters or substances do not exist.

[0115] Adding a fourth additive to the electrolyte can improve its storage stability, helping it maintain stable properties during storage and transportation. As seen in Examples 3-1 to 3-9, adding a fourth additive to the electrolyte and controlling its mass percentage within the range specified in this application results in higher room temperature cycle capacity retention, higher high temperature cycle capacity retention, and higher room temperature rate cycle capacity retention for the lithium-ion battery, as well as lower high-temperature storage gas generation and DC resistance. This indicates that the lithium-ion battery exhibits good cycle performance and rate performance at both high and room temperatures. Adding a fifth additive to the electrolyte can improve the uniformity of SEI film formation. As seen in Examples 3-10 to 3-19, adding a fifth additive to the electrolyte and controlling its mass percentage within the range specified in this application results in higher room temperature cycle capacity retention, higher high temperature cycle capacity retention, and higher room temperature rate cycle capacity retention for the lithium-ion battery, as well as lower high-temperature storage gas generation and DC resistance. This further improves the cycle performance and rate performance of the lithium-ion battery at both high and room temperatures.

[0116] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrolyte additive, comprising a first additive and a second additive; the first additive being a compound of formula I, and the second additive being a compound of formula II; in, Based on the total mass of the electrolyte additives, the mass percentage of the first additive is A, the mass percentage of the second additive is B, and 0.05 ≤ A / B ≤ 20.

2. The electrolyte additive according to claim 1, wherein, 0.1≤A / B≤10.

3. The electrolyte additive according to claim 1, wherein, The electrolyte additive includes a third additive, which is a compound of formula III. Wherein, based on the total mass of the electrolyte additives, the mass percentage of the third additive is C, and 0.05≤A / C≤20.

4. The electrolyte additive according to claim 3, wherein, 0.1≤A / C≤10.

5. An electrolyte comprising a non-aqueous organic solvent, an electrolyte, and an electrolyte additive according to any one of claims 1 to 4.

6. The electrolyte according to claim 5, wherein, Based on the total mass of the electrolyte, the mass percentage content W1 of the first additive and the mass percentage content W2 of the second additive satisfy: 0.1% ≤ W1 ≤ 2%, 0.1% ≤ W2 ≤ 2%.

7. The electrolyte according to claim 6, wherein, 0.1% ≤ W1 ≤ 1%, 0.1% ≤ W2 ≤ 1%.

8. The electrolyte according to claim 5, wherein the electrolyte comprises a third additive, the third additive being a compound of formula III; in, Based on the total mass of the electrolyte, the mass percentage W3 of the third additive satisfies: 0.1% ≤ W3 ≤ 2%.

9. The electrolyte according to claim 8, wherein, 0.1％≤W3≤1％。 10. The electrolyte according to any one of claims 5 to 9, wherein, The electrolyte further includes a fourth additive, which is selected from at least one of triphenyl phosphite, triphenyl phosphate, pentafluoroethoxyphosphazene, and dicyclohexylcarboimide; based on the total mass of the electrolyte, the mass percentage W4 of the fourth additive satisfies: 0.01% ≤ W4 ≤ 0.1%.

11. The electrolyte according to any one of claims 5 to 9, wherein, The electrolyte further includes a fifth additive, which is selected from at least one of vinylene carbonate, fluoroethylene carbonate, and ethylene ethylene carbonate; based on the total mass of the electrolyte, the mass percentage W5 of the fifth additive satisfies: 0.5% ≤ W5 ≤ 2%.

12. A lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte according to any one of claims 5 to 11.

13. The lithium-ion battery according to claim 12, wherein, The positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector, wherein the positive electrode material layer includes a positive electrode active material; The positive electrode active material satisfies the general formula Li a Ni b Co c M1 d M2 e O f R g , where 1 ≤ a ≤ 1.2, 0 < b < 1, 0 < c < 1, 0 < d < 1, 0 ≤ e ≤ 0.2, b + c + d + e = 1, 1 ≤ f ≤ 2, 0 ≤ g ≤ 1, f + g = 2; M1 is selected from at least one of Mn and Al, M2 is selected from at least one of Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, Sr, Sb, Y, W, and Nb, and R is selected from at least one of N, F, S, and Cl.

Images