Electrolyte additive, electrolyte, and lithium-ion battery

Abstract

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 represented by formula I, and the second additive is a compound represented by 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 0.05≤A / B≤20. By means of the synergistic effect of the first additive and the second additive, SEI and CEI films having good film formation uniformity and structural stability can be obtained, effectively suppressing gas generation during battery cycling, and reducing battery impedance, thereby effectively improving the fast-charging cycle performance and high-temperature performance of batteries.

Description

Electrolyte additive, electrolyte and lithium ion battery

[0001] This application claims priority to the Chinese patent application No. 202411334085.7, filed on September 24, 2024, and entitled "Electrolyte additive, electrolyte and lithium ion battery", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] 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

[0003] A lithium ion battery is a kind of secondary battery relying on the movement of lithium ions (Li + ) between the positive electrode and the negative electrode 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 due to its high specific energy, long cycle life, small self-discharge and other advantages, and is distributed in every corner of our life. 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.

[0004] Increasing the specific capacity of the positive electrode 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 electrode active material and the charging voltage (≥4.2V) of the battery will bring a series of problems, such as poor structure stability of the positive electrode active material, micro-cracks, increased irreversible phase transition, transition metal dissolution, gas precipitation, etc., leading to 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

[0005] 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:

[0006] 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;

[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] The second aspect of the present application provides an electrolyte, which comprises a non-aqueous organic solvent, an electrolyte, and the electrolyte additive provided by the first aspect of the present application.

[0009] The third aspect of the present application provides a lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte provided by the second aspect of the present application. DETAILED DESCRIPTION

[0010] To make the objectives, technical solutions, and advantages of the present application clearer, the following embodiments are provided for further detailed description of the present application. Obviously, the described embodiments are only a part 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 belong to the scope of protection of the present application.

[0011] 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;

[0012] 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 composed of any two of the above values.

[0013] 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 inventors found that 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, and 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 positive electrode surface, reduce the impedance of the lithium ion battery, and the free radicals generated by the P-O break diffuse to the positive electrode surface 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 positive electrode surface, 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 negative electrode surface, further improving the stability of the SEI film. The inventors further found that when the second additive is added alone in the ternary system, the gas production of the lithium ion battery increases, and when the first additive is added simultaneously, the gas production is significantly reduced, because the second additive will decompose into strong acid or strong base substances, which will corrode the negative electrode and destroy the SEI film on the negative electrode side, causing the electrolyte to decompose at the negative electrode and increase the gas production, when the first additive is added, the structure of the first additive is relatively stable, and the first additive can react with the decomposition products of the second additive to reduce the corrosion of the positive and negative electrodes. 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. With the increase of nickel content in the ternary system, it is easy to cause the dissolution of transition metals to the negative electrode, destroy the SEI film components of the negative electrode, and reduce the performance of the lithium ion battery. However, compared with the addition of the first additive and the second additive, the content of Ni and Mn at the negative electrode is found to decrease significantly by ICP. This is because the dense organic-inorganic composite CEI film formed by the first additive and the second additive at the positive electrode can significantly reduce the dissolution of Ni and Mn.In particular, the positive electrode has a Ni content of 50%-80%. The composite CEI film formed by the first additive and the second additive can better stabilize the positive electrode and improve the stability of the CEI film of the positive electrode. However, for the positive electrode with a Ni content lower than 50%, although the first additive and the second additive still have effects, the performance of the lithium ion battery in this system and its stability are improved after the addition, but the performance is not improved as obviously as the lithium ion battery with a Ni content in the range of 50%-80%. For the positive electrode with a Ni content higher than 80%, the CEI film formed by the first additive and the second additive can also protect the positive electrode, but the performance of the 9-series positive electrode is prone to diving in the later cycle stage, which may be due to the high Ni content. The first additive and the second additive can reduce the dissolution of transition metals and thus delay the diving node, but the improvement is still relatively poor compared with the lithium ion battery with a Ni content in the range of 50%-80%. Therefore, the preferred range of the positive active material of the lithium ion battery is set as a Ni content of 50%-80%. The above Ni content refers to the mass percentage of Ni based on the mass of transition metals in the positive active material, for example, the Ni content of 50%-80% refers to the mass percentage of Ni of 50%-80% based on the mass of transition metals in the positive active material. 4+ The first additive and the second additive can reduce the dissolution of transition metals and thus delay the diving node, but the improvement is still relatively poor compared with the lithium ion battery with a Ni content in the range of 50%-80%. Therefore, the preferred range of the positive active material of the lithium ion battery is set as a Ni content of 50%-80%. The above Ni content refers to the mass percentage of Ni based on the mass of transition metals in the positive active material, for example, the Ni content of 50%-80% refers to the mass percentage of Ni of 50%-80% based on the mass of transition metals in the positive active material.

[0014] In some embodiments of the present application, the mass percentage of the first additive is A and the mass percentage 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 formed by any two of the values.

[0015] By 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, the SEI film and the CEI film with better film uniformity and structural stability can be obtained through the synergistic effect of the first additive and the second additive, the generation of gas is further inhibited, and the impedance of the ion battery is reduced, thereby effectively improving the fast-charging cycle performance and high-temperature performance of the battery.

[0016] In some embodiments of the present application, the electrolyte additive further comprises a third additive, and the third additive is a compound shown in formula III.

[0017] wherein the mass percentage of the third additive is C, and 0.05≤A / C≤20, based on the total mass of the electrolyte additive. For example, the value of A / C can be 0.05, 0.5, 1, 2, 5, 10, 12, 15, 20, or a range defined by any two of these values.

[0018] The SEI film formed by the first additive at the negative electrode contains lithium carbonate, which helps to improve the uniformity and stability of the SEI film. However, lithium carbonate is easily corroded by HF, and the electrolyte will then decompose at the negative electrode to increase gas production, destroy the SEI film on the surface of the negative active material, and further introduce the third additive of the present application on the basis of the first additive and the second additive. The third additive will promote the film formation of the first additive after ring opening, and reduce the lithium carbonate content in the SEI film, while Li2SO4 and its over-lithiated products (lithium oxide and amorphous Li x S and Li x O) will sandwich the lithium carbonate in the middle, limit the decomposition of lithium carbonate by HF in the electrolyte and the thickening of the SEI film, and further reduce the impedance of the lithium ion battery. Therefore, the further introduction of the third additive in the electrolyte additive and the adjustment of the A / C ratio within the range of the present application can further reduce the impedance of the lithium ion battery, improve the cycle performance and reduce gas production.

[0019] In some embodiments of the present 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 defined by any two of these values. Controlling the mass percentage of the first additive, the second additive and the third additive of the present application within the above range can further reduce the impedance of the battery, reduce gas production, and improve the cycle performance of the battery.

[0020] The second aspect of the present application provides an electrolyte comprising a non-aqueous organic solvent, an electrolyte and an electrolyte additive provided by the first aspect of the present application.

[0021] 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. For example, W1 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range formed by any two of them, and W2 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range formed by any two of them. By controlling the first additive and the second additive in the electrolyte within the above range, the SEI film and the CEI film with better film uniformity and structural stability can be obtained through the synergistic effect of the first additive and the second additive. In addition, the electrolyte additive can also effectively inhibit the generation of gas during the battery cycle process, while reducing the battery impedance to effectively improve the fast charging cycle performance and high temperature performance of the battery.

[0022] 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. For example, W1 can be 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 0.9%, 1%, or a range formed by any two of them, and W2 can be 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 0.9%, 1%, or a range formed by any two of them. By controlling the content of the first additive and the second additive in the electrolyte within the range of the present application, the SEI film and the CEI film with better film uniformity and structural stability can be obtained through the synergistic effect of the first additive and the second additive, further inhibiting the generation of gas, while reducing the impedance of the ion battery to effectively improve the fast charging cycle performance and high temperature performance of the battery.

[0023] In some embodiments of the present application, the electrolyte further comprises a third additive, and the third additive is a compound represented by formula III:

[0024] 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≤1.5%. For example, W3 can be 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range formed by any two of them.

[0025] The SEI film formed by the first additive on the negative electrode contains lithium carbonate, which is easily corroded by HF, and the electrolyte is then decomposed at the negative electrode to increase gas production and reduce the stability of the SEI film. On the basis of the first additive and the second additive, the third additive of the present application is further introduced, and the values of W1, W2 and W3 are controlled within the range of the present application. After ring opening of the third additive, the first additive film is promoted, the lithium carbonate content in the SEI film is reduced, the decomposition of lithium carbonate by HF in the electrolyte and the thickening of the SEI film are limited, the impedance of the lithium ion battery is further reduced, the cycle performance is improved, and the gas production is reduced.

[0026] In some embodiments of the present application, the electrolyte further comprises a fourth additive selected from at least one of triphenyl phosphite, triphenyl phosphate, pentafluoroethoxy phosphazene and bis-cyclohexyl carbimide; the mass percentage content W4 of the fourth additive satisfies: 0.01%≤W4≤0.1%, based on the total mass of the electrolyte. For example, W4 can be 0.01%, 0.02%, 0.03%, 0.05%, 0.07%, 0.08%, 0.09%, 0.1%, or a range formed by any two of them. By adding the fourth additive to the electrolyte and controlling the mass percentage content of the fourth additive within the range of the present application, the storage stability of the electrolyte can be improved, which helps to keep the properties of the electrolyte stable during storage and transportation, and reduces the deterioration caused by changes in external environment.

[0027] 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. For example, W5 can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or a range formed by any two of them. By adding the fifth additive to the electrolyte and controlling the mass percentage content of the fifth additive within the range of the present application, the uniformity of SEI film formation can be improved.

[0028] The third aspect of the present application provides a lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte provided by the second aspect of the present application.

[0029] In some embodiments of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode material layer comprises a positive electrode active material; the positive electrode active material satisfies the general formula Li a Ni b Co c M1 d M2 e Of 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, 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). The positive electrode active material of the present application can further improve the specific capacity of the positive electrode active material and reduce the cost of the positive electrode active material.

[0030] In the present application, the electrolyte includes a non-aqueous organic solvent. The non-aqueous organic solvent, as a main component of the electrolyte, should have a high solubility of lithium salt, so that the electrolyte has a high ionic conductivity. The non-aqueous organic solvent, as an important carrier of ion transmission, can have a high electronic conductivity after the electrolyte is dissolved, thereby improving the cycle life, charge-discharge rate, high-temperature performance, low-temperature performance and energy density of the battery. The non-aqueous organic solvent is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the non-aqueous organic solvent can include, but is not limited to, at least one of a carbonate compound, a carboxylic ester compound, an ether compound or other organic solvents. The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound or a cyclic carbonate compound. The chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate or methyl ethyl carbonate. The cyclic carbonate can include, but is not limited to, at least one of vinyl carbonate, propylene carbonate (PC) or butylene carbonate. The carboxylic ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone or capro-lactone. The ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The other organic solvents can include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The content of the non-aqueous organic solvent in the electrolyte is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the mass percentage of the non-aqueous organic solvent can be 78% to 91% based on the total mass of the electrolyte.

[0031] In some embodiments of the present application, the solvent can include vinyl carbonate, methyl ethyl carbonate and dimethyl carbonate in a mass ratio of 1:(0.5-2):(0.5-2).

[0032] In the present application, the electrolyte solution includes an electrolyte. The electrolyte can release lithium ions after being dissolved in the solvent of the electrolyte solution, and the lithium ions form a solvated structure with the solvent, which is conducive to the rapid migration of lithium ions. The electrolyte is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the electrolyte can 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, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. The content of the electrolyte in the electrolyte solution is not particularly limited in the present application as long as the purpose of the present application can be achieved.

[0033] In some embodiments of the present application, the electrolyte can be selected from at least one of LiPF6, LiFSI, LiBF4, and LiTFSI.

[0034] In some embodiments of the present application, the mass percentage of the electrolyte is 8% to 18% based on the total mass of the electrolyte solution. For example, the mass percentage of the electrolyte can be 8%, 10%, 12%, 14%, 16%, 18%, or a range formed by any two of the above values based on the total mass of the electrolyte solution. Controlling the mass percentage of the electrolyte within the range of the present application can make the electrolyte fully dissolved in the non-aqueous organic solvent, while the electrolyte solution has high ionic conductivity and low manufacturing cost.

[0035] The lithium ion battery of the present application also comprises a positive electrode sheet, which comprises a positive current collector and a positive material layer disposed on at least one surface of the positive current collector. In the present application, the positive material layer can be disposed on one surface in the thickness direction of the positive current collector, or on both surfaces in the thickness direction of the positive current collector. The positive current collector of the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the positive current collector can comprise a metal foil or a composite current collector, etc. The metal foil is, for example, an aluminum foil. The composite current collector can comprise a polymer material base layer and a metal material layer disposed on at least one surface of the polymer material base layer. The material of the metal material layer can comprise at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver or silver alloy, for example. The polymer material base layer can comprise at least one of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene or polyethylene. The thickness of the positive current collector and the positive material layer of the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the positive current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm. The thickness of the single-sided positive material layer is 30 μm to 120 μm. The positive material layer of the present application can also comprise a conductive agent and a binder, which are not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the conductive agent can comprise, but is not limited to, at least one of Super P, acetylene black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The binder can comprise, but is not limited to, at least one of polyvinyl chloride, polyvinyl alcohol, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer or fluorine-containing acrylic ester resin.

[0036] The lithium ion battery of the present application comprises a negative electrode sheet, which comprises a negative current collector and a negative material layer disposed on at least one surface of the negative current collector. In the present application, the negative material layer can be disposed on one surface in the thickness direction of the negative current collector, or on both surfaces in the thickness direction of the negative current collector. The negative current collector of the present application is not particularly limited, and any negative current collector known in the art can be used as long as the purpose of the present application can be achieved. For example, the negative current collector can comprise at least one of an aluminum foil, a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, and a foamed copper. In the present application, the thickness of the negative current collector and the negative material layer is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the negative current collector is 4 μm to 15 μm, and the thickness of the single-sided negative material layer is 30 μm to 150 μm. Optionally, the negative active material comprises a thickening agent, which can include but is not limited to sodium carboxymethyl cellulose. The negative material layer of the present application can further comprise a conductive agent and a binder. The conductive agent and the binder of the present application are not particularly limited, as long as the purpose of the present application can be achieved. For example, the binder and the conductive agent can include but are not limited to at least one of the optional substances of the positive material layer described above.

[0037] The negative material layer of the present application comprises a negative active material. The type of negative active material of the present application is not particularly limited, and any negative active material known in the art can be used as long as the purpose of the present application can be achieved. For example, the negative active material can comprise at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon-based material, tin-based material, and lithium titanate. The silicon-based material described above can include but is not limited to at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, or silicon alloy; and the tin-based material described above can include at least one of elemental tin, tin oxide compound, or tin alloy.

[0038] The lithium ion battery of the present application further comprises a separator, which separates the positive electrode sheet and the negative electrode sheet, prevents internal short circuit of the battery, allows free passage of electrolyte ions, and does not affect the electrochemical charging and discharging process. The type of separator of the present application is not particularly limited, and any porous structure separator with good chemical stability and mechanical stability can be selected. For example, the material of the separator can comprise at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The type of separator can include but is not limited to at least one of woven membrane, non-woven membrane (non-woven fabric), microporous membrane, composite membrane, calendered membrane, or spunlaid membrane. The separator can be a single-layer thin film or a multi-layer composite thin film. In the present application, the thickness of the separator is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness can be 5 μm to 20 μm.

[0039] The lithium ion battery of the present application also comprises a packaging bag for containing the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art, which are not limited by the present application. The packaging bag is not particularly limited by the present application, and can be a packaging bag known in the art as long as the purpose of the present application can be achieved. For example, an aluminum plastic film packaging bag can be used.

[0040] The preparation process of the lithium ion battery of the present application is well known to those skilled in the art, and is not particularly limited by the present application, for example, can include but is not limited to the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and winding or folding them as needed to obtain a wound structure of the electrode assembly, placing the electrode assembly into the packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the lithium ion battery; or stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, then fixing the four corners of the entire stack structure with adhesive tape to obtain a stack structure of the electrode assembly, placing the electrode assembly into the packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain the lithium ion battery. In addition, the overcurrent prevention element, the guide plate, etc. can also be placed in the packaging bag as needed, so as to prevent the pressure inside the lithium ion battery from rising and overcharging and discharging.

[0041] The battery of the present application can include battery monomers, battery modules, and battery packs. The battery monomers can be assembled into battery modules, and the number of battery monomers contained in the battery modules can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module. The battery module of the present application can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0042] Examples

[0043] Hereinafter, examples and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are mass-based.

[0044] Test methods and equipment:

[0045] Normal temperature cycle performance test

[0046] The lithium ion battery was placed in a 25°C environment for 2h, charged at 0.5C constant current to 4.2V, and then charged at 4.2V constant voltage to the cutoff current 0.05C, and then discharged at 0.5C constant current to 2.5V, which was one charge-discharge cycle process, and the first discharge capacity was recorded as C1. The above charge-discharge cycle process was repeated for 600 times, and the discharge capacity C 600 of the 600th week was recorded. Normal temperature cycle capacity retention rate = (C 600 / C1) x 100%.

[0047] High temperature cycle performance test

[0048] The lithium ion battery was placed in a 45℃ environment for 2h, charged at 0.5C constant current to 4.2V, charged at 4.2V constant voltage to the cutoff current 0.05C, and then discharged at 0.5C constant current to 2.5V, which was one charge-discharge cycle process, and the first discharge capacity was recorded as C1'. The above charge-discharge cycle process was repeated for 600 times, and the discharge capacity C 600 ' of the 600th week was recorded, and the high temperature cycle capacity retention rate was (C 600 ' / C1 ') x 100%.

[0049] High temperature storage for 30 days gas production test

[0050] The lithium ion battery was placed in a 25℃ constant temperature environment, charged at 1C constant current to 4.2V, and charged at 4.2V constant voltage to the cutoff current 0.05C. The lithium ion battery was suspended by a fine wire and immersed in a container filled with water, and the reading of the balance at this time was recorded as m1. After the lithium ion battery was placed in a 45℃ explosion-proof oven for 30 days, the lithium ion battery was again suspended by a fine wire and immersed in a container filled with water, and the reading of the balance was recorded as m2.

[0051] The gas production AV was measured by the drainage method, AV = (m2-m1) / p, where p is the density of liquid water.

[0052] Direct current resistance (DCR) test

[0053] The lithium ion battery was placed in a 25℃ environment for 30 minutes to reach a constant temperature. Discharged at 1C constant current to the cutoff voltage 2.5V, stand for 5min, then charged at 1C constant current to the upper limit voltage 4.2V, charged at 4.2V constant voltage to the cutoff current 0.05C. The battery was discharged at 1C constant current for 30min, adjusted to 50% SOC (SOC refers to the state of charge of the battery), and the voltage value of the battery was recorded as V0 after standing for 5min at 25℃. The battery was discharged at 2C corresponding current I 2C for 30s, and the voltage value of the battery was recorded as V1.

[0054] The direct current resistance at 50% SOC is calculated as follows: DCR (mΩ) = (V0-V1) / I 2C x 1000.

[0055] Normal temperature rate cycle performance test

[0056] The lithium ion battery was placed in a 25°C environment for 2h, discharged at 1C constant current to the cut-off voltage 2.5V, rested for 5min, charged to the upper limit voltage 4.2V at 1.6C constant current, and charged to the cut-off current 0.05C at 4.2V constant voltage. This was one charge-discharge cycle process. The above charge-discharge cycle process was repeated 600 times, and the discharge capacity of the first cycle was recorded as C 600 ”, and the room temperature rate cycle capacity retention rate = (C 600 ” / C1”) x 100%.

[0057] Example 1-1

[0058] Preparation of electrolyte

[0059] In an argon atmosphere glove box with moisture <10ppm and oxygen <1ppm, ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 3:5:2 to obtain a base solvent. Sufficiently dried lithium hexafluorophosphate, a first additive, and a second additive were added to the base solvent. The mass percentage of lithium hexafluorophosphate in the electrolyte was 12.5%, the mass percentage of the first additive in the electrolyte was 0.1%, the mass percentage of the second additive in the electrolyte was 0.6%, and the rest was the base solvent.

[0060] Preparation of positive electrode sheet

[0061] The positive electrode active material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2), the binder polyvinylidene fluoride (PVDF), the conductive agent acetylene black, and the carbon nanotube were mixed in a mass ratio of 93:2.3:2:0.7, N-methyl pyrrolidone (NMP) was added, and the mixture was stirred uniformly under the action of a vacuum stirrer until the mixture became a positive electrode slurry with uniform fluidity, obtaining a positive electrode slurry with a solid content of 68.5wt%. The positive electrode slurry was uniformly coated on one surface of a positive current collector aluminum foil with a thickness of 16μm, and the coating amount was 35g / m 2 After drying at 85°C, a single-sided positive electrode material layer was obtained. The above steps were repeated on the other surface of the positive current collector aluminum foil, and a double-sided positive electrode material layer was obtained. After drying under vacuum at 85°C, cold pressing, edge cutting, sheet cutting, striping, sheet making, and welding tab pasting were performed, and a positive electrode sheet with a specification of 70mm x 54mm was obtained. The thickness of the double-sided positive electrode material layer was 113μm.

[0062] Preparation of negative electrode sheet

[0063] The negative active material graphite, conductive agent acetylene black, thickening agent carboxymethyl cellulose sodium (CMC-Na), binder styrene-butadiene rubber were mixed according to the mass ratio of 95:1.5:1:2.5, deionized water was added, and the mixture was stirred uniformly under the action of a vacuum stirrer to obtain a negative electrode slurry with a solid content of 49wt%. The negative electrode slurry was uniformly coated on a negative electrode current collector copper foil with a thickness of 9μm, and the coating amount was 20g / m 2 After drying at 85℃, a negative electrode sheet with a single-sided coated negative electrode material layer was obtained. The above steps were repeated on the other surface of the negative electrode current collector copper foil, i.e. a negative electrode sheet with a double-sided coated negative electrode material layer was obtained. After drying under vacuum at 85℃, the negative electrode sheet was obtained after cold pressing, edge cutting, sheet cutting, striping, sheet making, and welding tab pasting. The specification of the negative electrode sheet was 74mm×58mm. The thickness of the double-sided negative electrode material layer was 164μm.

[0064] <Preparation of the separator>

[0065] The separator was SP312J3020H separator purchased from Xingyuan Material.

[0066] <Preparation of the lithium ion battery>

[0067] The separator, the positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet and the negative electrode sheet were separated, and then the positive electrode sheet and the negative electrode sheet were wound, the positive tab was connected to the positive electrode sheet, and the negative tab was connected to the negative electrode sheet, to obtain an electrode assembly. The electrode assembly was placed in an aluminum foil packaging bag, and the positive tab and the negative tab were led out from the inside space of the packaging bag to the outside space of the packaging bag. After drying at 85℃ for 48 hours to remove water, the packaging bag was heat-sealed to obtain an electrode core to be injected with electrolyte. The above-prepared electrolyte was injected into the dried electrode core, and the electrode core was subjected to vacuum packaging, standing, formation, shaping, and capacity grading processes to obtain a lithium ion battery. The formation conditions were as follows: the lithium ion battery was charged at 0.1C constant current to 3.4V, and then charged at 0.2C constant current to 3.9V.

[0068] Examples 1-2 to 1-15

[0069] Except that the parameters in <Preparation of the electrolyte> were adjusted according to Table 1, the rest was the same as in Example 1-1. When the values of W1 and W2 in the electrolyte changed, the mass percentage content of the base solvent changed accordingly, and the mass percentage content of the electrolyte remained unchanged.

[0070] Examples 1-16 to 1-28

[0071] The rest is the same as Example 1-1 except that the mass percentage contents W1, W2 and W3 of the first additive, the second additive and the third additive are adjusted according to Table 1 in the preparation of the electrolyte. Among them, when the values of W1, W2 and W3 in the electrolyte change, the mass percentage content of the base solvent changes accordingly, and the mass percentage content of the electrolyte remains unchanged.

[0072] Examples 2-1 to 2-4

[0073] The rest is the same as Example 1-1 except that the mass percentage contents W1, W2 and W3 of the first additive, the second additive and the third additive are adjusted according to Table 2 in the preparation of the electrolyte, and the type of positive active material is changed according to Table 2 in the preparation of the positive electrode sheet. Among them, when the values of W1, W2 and W3 in the electrolyte change, the mass percentage content of the base solvent changes accordingly, and the mass percentage content of the electrolyte remains unchanged.

[0074] Examples 3-1 to 3-19

[0075] The rest is the same as Example 1-3 except that the third additive, the fourth additive and the fifth additive are added and the mass percentage contents W3, W4 and W5 of the third additive, the fourth additive and the fifth additive are adjusted according to Table 3 in the preparation of the electrolyte. Among them, when the values of W1, W2, W3, W4 and W5 in the electrolyte change, the mass percentage content of the base solvent changes accordingly, and the mass percentage content of the electrolyte remains unchanged.

[0076] Comparative Examples 1 to 5

[0077] The rest is the same as Example 1-1 except that only one of the first additive and the second additive is not added or added in the preparation of the electrolyte, and the mass percentage contents of the first additive and the second additive are adjusted according to Table 1. Among them, when the values of W1 and W2 in the electrolyte change, the mass percentage content of the base solvent changes accordingly, and the mass percentage content of the electrolyte remains unchanged.

[0078] Comparative Examples 6 to 9

[0079] The rest is the same as Example 1-1 except that the mass percentage contents W1 and W2 of the first additive and the second additive are adjusted according to Table 1 in the preparation of the electrolyte. Among them, when the values of W1 and W2 in the electrolyte change, the mass percentage content of the base solvent changes accordingly, and the mass percentage content of the electrolyte remains unchanged.

[0080] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 3.

[0081] Table 1

[0082] Note: " / " in Table 1 means that the corresponding preparation parameter or substance does not exist.

[0083] As can be seen from Examples 1-1 to 1-15 and Comparative Examples 1 to 9, the electrolyte includes the first additive and the second additive, and the values of W1 and W2 are regulated within the range of the present application. Through the synergistic effect of the first additive and the second additive, the lithium ion battery has high capacity retention rate at room temperature, high capacity retention rate at high temperature, and high capacity retention rate at room temperature under rate, and low gas production amount at high temperature storage and low direct current impedance, indicating that the lithium ion battery has good cycle performance at high temperature and room temperature. The electrolyte of the lithium ion battery in Comparative Examples 1 to 5 does not include the first additive and the second additive at the same time, and the values of W1 and W2 in the electrolyte of the lithium ion battery in Comparative Examples 6 to 9 exceed the range of the present application. The lithium ion battery has low capacity retention rate at room temperature, low capacity retention rate at high temperature, and low capacity retention rate at room temperature under rate, and high gas production amount at high temperature storage and high direct current impedance. It is indicated that the addition of one of the first additive and the second additive, and the values of W1 and W2 exceeding the range of the present application, the cycle performance and rate performance of the lithium ion battery at room temperature and high temperature are poor.

[0084] The SEI film formed by the first additive at the negative electrode contains lithium carbonate, which is easy to be corroded by HF, and then the electrolyte will decompose at the negative electrode to increase gas production and reduce the stability of the SEI film. The third additive promotes the film formation of the first additive after ring opening, while reducing the content of lithium carbonate in the SEI film, limiting 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 the cycle performance and reducing the gas production. As can be seen from Examples 1-17 to 1-22, 1-24 to 1-28 and Examples 1-16 and 1-23, on the basis of the first additive and the second additive, further introducing the third additive of the present application, and regulating the values of W1, W2 and W3 within the range of the present application, the lithium ion battery has high capacity retention rate at room temperature, high capacity retention rate at high temperature, and high capacity retention rate at room temperature under rate, and low gas production amount at high temperature storage and low direct current impedance, indicating that the lithium ion battery has good cycle performance and rate performance at high temperature and room temperature.

[0085] Table 2

[0086] Note: " / " in Table 2 means that the corresponding preparation parameter or substance does not exist.

[0087] As can be seen from Example 2-1 to Example 2-4, the electrolyte additive of the present application is used in the positive electrode active material system of the present application, which can make the lithium ion battery have higher capacity retention rate at room temperature, high-temperature cycle capacity retention rate and room-temperature rate cycle capacity retention rate, and lower high-temperature storage gas production and direct current impedance, indicating that the lithium ion battery has good cycle performance and rate performance at high temperature and room temperature.

[0088] Table 3

[0089] Note: " / " in Table 3 indicates that there is no corresponding preparation parameter or substance.

[0090] Further adding a fourth additive in the electrolyte can improve the storage stability of the electrolyte, which helps the electrolyte to maintain stable properties during storage and transportation. As can be seen from Example 3-1 to Example 3-9, adding the fourth additive in the electrolyte and controlling the mass percentage content of the fourth additive within the range of the present application can make the lithium ion battery have higher capacity retention rate at room temperature, high-temperature cycle capacity retention rate and room-temperature rate cycle capacity retention rate, and lower high-temperature storage gas production and direct current impedance, indicating that the lithium ion battery has good cycle performance and rate performance at high temperature and room temperature. Adding a fifth additive in the electrolyte can improve the uniformity of SEI film formation. As can be seen from Example 3-10 to Example 3-19, adding the fifth additive in the electrolyte and controlling the mass percentage content of the fifth additive within the range of the present application can make the lithium ion battery have higher capacity retention rate at room temperature, high-temperature cycle capacity retention rate and room-temperature rate cycle capacity retention rate, and lower high-temperature storage gas production and direct current impedance, further improving the cycle performance and rate performance of the lithium ion battery at high temperature and room temperature.

[0091] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrolyte additive comprising a first additive and a second additive; the first additive is a compound of Formula I, and the second additive is a compound of Formula II; wherein A and B satisfy 0.05≤A / B≤20, based on the total mass of the electrolyte additives.

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

3. The electrolyte additive according to claim 1, wherein, The electrolyte additive further comprises a third additive, which is a compound represented by Formula III; C, based on the total mass of the electrolyte additives.

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 the electrolyte additive according to any one of claims 1 to 4.

6. The electrolyte of claim 5, wherein, W1 and W2 satisfy 0.1%≤W1≤2% and 0.1%≤W2≤2%, based on the total mass of the electrolyte.

7. The electrolyte of claim 6, wherein, 0.1%≤W1≤1% and 0.1%≤W2≤1%.

8. The electrolyte of claim 5, further comprising a third additive, the third additive being a compound of Formula III; wherein W3 satisfies 0.1%≤W3≤2%, based on the total mass of the electrolyte.

9. The electrolyte of claim 8, wherein, 0.1％≤W3≤1.5％。 10. The electrolyte of any one of claims 5-9, wherein, The electrolyte further comprises a fourth additive selected from at least one of triphenyl phosphite, triphenyl phosphate, pentafluoroethoxy phosphazene and bis-cyclohexyl carbodiimide; W4 satisfies 0.01%≤W4≤0.1%, based on the total mass of the electrolyte.

11. The electrolyte of any one of claims 5-9, wherein, The electrolyte further comprises a fifth additive selected from at least one of vinylene carbonate, fluoroethylene carbonate and vinyl ethylene carbonate; W5 satisfies 0.5%≤W5≤2%, based on the total mass of the electrolyte.

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

13. The lithium-ion battery of claim 12, wherein, 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.

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