Electrolyte additive, electrolyte and secondary battery

Abstract

The invention provides an electrolyte additive, an electrolyte and a secondary battery. The electrolyte additive comprises a first component and a second component, wherein the first component is selected from a compound as shown in a formula I; and the second component is selected from a compound as shown in a formula II. The synergistic effect of the first component and the second component in the electrolyte additive can improve the rate capability, the high-temperature storage performance and the high-temperature cycle performance of the secondary battery.

Description

TECHNICAL FIELD

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

[0002] In recent years, the rapid development and wide application of various portable electronic devices, new energy electric vehicles and energy storage systems have made the demand for secondary batteries with high energy density, long cycle life, safe use and good rate characteristics increasingly urgent. However, the positive material of the secondary battery (such as lithium ion battery, sodium ion battery) may have problems such as insufficient stability, and the high temperature performance and rate performance of the secondary battery are particularly important. The secondary battery is prone to have problems such as poor storage performance at high temperature, poor cycle performance and gas production during operation. One of the important reasons is that the currently commercially used lithium salt (such as lithium hexafluorophosphate) and sodium salt (sodium hexafluorophosphate) have poor thermal stability, and are prone to decomposition reaction at high temperature, and react with trace impurities in the electrolyte, thereby causing rapid increase of electrolyte acidity, deteriorating electrolyte quality, causing serious gas production problem of the secondary battery under high temperature conditions, and thus deteriorating the cycle performance, storage performance and safety performance of the secondary battery at high temperature. At the same time, because the conventional electrolyte system has problems such as high viscosity and low conductivity, it is difficult for the secondary battery to have high rate and fast charging performance.

[0003] The existing secondary battery usually adds various additives in the electrolyte, which can form an organic passivation film on the surface of the active material to improve the high temperature storage performance, high temperature cycle performance and high rate performance of the secondary battery. However, the conventional additives are difficult to solve the stability problem of the electrolyte at high temperature, which seriously affects the cycle and storage performance of the secondary battery at high temperature, and also cannot guarantee the rate performance of the secondary battery. Therefore, it is an urgent technical problem for those skilled in the art to develop an electrolyte that can significantly improve the rate performance, high temperature storage performance and high temperature cycle performance of the secondary battery. SUMMARY

[0004] The purpose of the present application is to provide an electrolyte additive, an electrolyte and a secondary battery to improve the rate performance, high temperature storage performance and high temperature cycle performance of the secondary battery. The specific technical solutions are as follows:

[0005] The first aspect of the present application provides an electrolyte additive, which comprises a first component and a second component;

[0006]

[0007]

[0008] The second component is selected from the compound shown in formula II;

[0009] ​

[0010] wherein X1, X2, X3and X4are each independently selected from N or CH, and one of them is selected from N;

[0011] R is selected from unsubstituted or substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl; a substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl; 12 substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl; a substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl; 12 substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl; a substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl; a substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl; a are each independently selected from C1-C6alkyl or halogen; the heteroatoms in the heteroaryl are each independently selected from O, S or N;

[0012] R1, R2and R3are each independently selected from C1-C4alkyl or C3-C6cycloalkyl. 10 substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl; 10 substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl;

[0013] In one embodiment of the present application, the mass ratio of the first component and the second component is 0.02 to 50:1, preferably 0.03 to 30:1.

[0014] In one embodiment of the present application, R is selected from unsubstituted or fluorine-substituted C6-C10aryl, unsubstituted or fluorine-substituted C3-C6heteroaryl, unsubstituted or fluorine-substituted C1-C4alkyl, unsubstituted or fluorine-substituted C2-C4alkenyl. 12 substituted C6-C10aryl, unsubstituted or substituted C3-C6heteroaryl, unsubstituted or substituted C1-C4alkyl, unsubstituted or substituted C2-C4alkenyl;

[0015] R1, R2and R3are each independently selected from C1-C4alkyl or C3-C6cycloalkyl.

[0016] In one embodiment of the present application, the first component is selected from at least one of the following compounds:

[0017]

[0018] In one embodiment of the present application, the second component is selected from at least one of the following compounds:

[0019]

[0020] The second aspect of the present application provides an electrolyte, which comprises the electrolyte additive of the first aspect of the present application; the mass percentage of the electrolyte additive in the electrolyte is 0.2% to 10%, preferably 0.2% to 6%, based on the mass of the electrolyte.

[0021] In an embodiment of the present application, the mass percentage of the first component is A, 0.1%≤A≤5%, and the mass percentage of the second component is B, 0.1%≤B≤5%, based on the mass of the electrolyte; preferably, the mass percentage of the first component is A, 0.1%≤A≤3%, and the mass percentage of the second component is B, 0.1%≤B≤3%, based on the mass of the electrolyte.

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

[0023] In an embodiment of the present application, the positive electrode sheet comprises a positive electrode active material, the positive electrode active material being selected from at least one of LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4 and Li2Mn 1-x O4, M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, 0≤a<0.2, 0≤x<1; or,

[0024] The positive electrode active material is selected from at least one of Na x1 M1O2, Na x2 M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3 and Na2M4(SO4)2·2H2O, wherein 0

[0025] The beneficial effects of the present application are:

[0026] The application provides an electrolyte additive, an electrolyte and a secondary battery. The electrolyte additive of the application comprises a first component and a second component. When applied to the electrolyte, the first component can effectively inhibit the increase of electrolyte acidity, and avoid the protonation of the second component. The anion with a larger spatial structure in the second component can stabilize the imidazole and other nitrogen-containing heterocyclic groups of the first component, and at the same time, regulate the solvation ability of the electrolyte, and further improve the solvent decomposition gas problem of the electrolyte at high temperature. In addition, the difluorophosphine group in the second component can effectively improve the stability of the positive and negative electrode interface structure of the secondary battery containing the electrolyte, inhibit the release of metal ions in the positive electrode material at high voltage and high temperature, and prevent the damage of transition metal ions to the negative electrode interface. At the same time, the unsaturated bond-containing sulfonic acid group in the second component further modifies the dense SEI on the basis of the first component reducing to form a relatively sparse solid electrolyte interface (SEI), and the lithium alkyl sulfate produced by the decomposition of the above compound introduces S element into the SEI, increases the ionic conductivity, forms a low-impedance dense SEI, and thus can meet the large-rate charge-discharge characteristics of the secondary battery. The synergistic effect of the first component and the second component can ensure the quality of the electrolyte under high temperature conditions, so that the electrolyte has both thermal stability and kinetic performance. At the same time, the SEI with high conductivity and high thermal stability is formed on the negative electrode of the secondary battery, and the positive electrode-electrolyte interface film (Cathode Electrolyte Interface Interface, CEI) with stable high voltage and high temperature metal ion release in the positive electrode material is formed on the positive electrode, thereby meeting the large-rate charge-discharge characteristics of the secondary battery, and effectively inhibiting the swelling and gas production of the secondary battery in a high temperature environment, and improving the high temperature storage performance and high temperature cycle performance of the secondary battery.

[0027] Of course, implementing any product or method of the application does not necessarily require achieving all the advantages described above at the same time. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the application, not all the embodiments. All other embodiments obtained by those skilled in the art based on the application belong to the scope of protection of the application.

[0029] Electrolyte additives account for only a small portion of the electrolyte, but appropriate amounts of functional additives can effectively ensure electrolyte quality and form SEI on the surface of the negative electrode active material and CEI on the surface of the positive electrode active material. SEI and CEI form films on the surfaces of the negative and positive electrode active materials, respectively, reducing side reactions that occur after direct contact between the active materials and the electrolyte. However, under high temperature or high pressure environments, the electrolyte itself may deteriorate in quality, such as undergoing thermal decomposition, failing to maintain kinetic performance, leading to a significant reduction in the cycle and storage performance of the secondary battery, thus failing to achieve high-rate performance. Existing secondary batteries typically add various additives to the electrolyte, which can form SEI and CEI on the surface of the active materials to improve cycle and high-temperature storage performance. However, the SEI and CEI formed by conventional additives on the surface of the active materials have high internal resistance, and this cannot solve the problems of poor thermal stability and poor electrolyte kinetic performance of currently commercially available lithium salts (e.g., lithium hexafluorophosphate) or sodium salts (e.g., sodium hexafluorophosphate). These factors severely impact the performance of secondary batteries in high-temperature cycling and storage, as well as their high-rate performance.

[0030] In view of this, a first aspect of this application provides an electrolyte additive comprising a first component and a second component;

[0031] The first component is selected from the compounds shown in Formula I;

[0032]

[0033] The second component is selected from the compounds shown in Formula II;

[0034]

[0035] Among them, X1, X2, X3 and X4 are each independently selected from N or CH, and one of them is selected from N;

[0036] R is selected from unsubstituted or R-selected. a Replacement C6-C 12 aryl, unsubstituted or R a Replacement C3-C 12 heteroaryl, unsubstituted or R a Substituted C1-C8 alkyl, unsubstituted or R a Substituted C2-C8 alkenyl groups; substituent R a Each of the heteroatoms is independently selected from C1-C6 alkyl or halogen; each heteroatom in the heteroaryl group is independently selected from O, S or N;

[0037] R1, R2, and R3 are each independently selected from C1-C 10 Alkyl or C3-C 10 Cycloalkyl.

[0038] The first component is the compound shown in Formula I. The nitrogen-containing five-membered heterocycle of Formula I contains nitrogen atoms with lone pairs of electrons, making the compound exhibit weak Lewis basicity in the electrolyte. It can form a six-ligand complex with phosphorus pentafluoride produced by the decomposition of lithium hexafluorophosphate or sodium hexafluorophosphate, reducing the Lewis acidity and reactivity of phosphorus pentafluoride, thereby effectively inhibiting the rise in electrolyte acidity, stabilizing electrolyte quality, and ensuring electrolyte stability under high-temperature conditions. Simultaneously, the first component has film-forming properties, capable of being reduced to form an SEI at the negative electrode, thus improving the high-temperature storage performance of the secondary battery. However, due to the presence of sterically hindered imidazole and other nitrogen-containing heterocyclic groups in the first component, the electrolyte viscosity increases, deteriorating kinetic performance. During cyclic storage, it promotes solvent decomposition and gas generation. Furthermore, the SEI formed as a film-forming additive has high impedance, failing to simultaneously achieve high-rate performance of the secondary battery.

[0039] The second component is the compound shown in Formula II, which is an ionic liquid additive containing multiple functional groups. The introduction of the second component significantly increases the ion transport number in the electrolyte, resulting in higher conductivity. This helps improve the ion transport rate of the electrolyte. Its addition enhances the thermal and electrochemical stability of the electrolyte and improves the interfacial stability between the electrolyte and the electrode. While improving the high-temperature performance of the secondary battery, it also ensures high-rate performance, enabling the secondary battery to achieve fast charging capabilities. However, the anions of the second component are sensitive to acid and easily protonated, leading to anion decomposition and inactivation. This is because under high-temperature storage conditions, the increased acidity makes it difficult for the second component to function effectively.

[0040] The electrolyte additive of this application includes both a first component and a second component, which can fully leverage the synergistic effect of the first and second components. The first component effectively inhibits the rise in electrolyte acidity and prevents the second component from being protonated. The anions with larger spatial structures in the second component can stabilize the nitrogen-containing heterocyclic groups such as imidazole in the first component, while also regulating the solvation ability of the electrolyte and further improving the problem of solvent decomposition and gas generation at high temperatures. In addition, the difluorophosphoxy group in the second component can effectively improve the stability of the positive and negative electrode interface structure of the secondary battery containing this electrolyte, inhibit the extraction of metal ions from the positive electrode material at high voltage and high temperature, and prevent the damage of the negative electrode interface by transition metal ions. At the same time, the sulfonic acid groups containing unsaturated bonds, based on the relatively sparse SEI formed by the reduction of the first component, further modify the film to form a dense SEI. Moreover, the alkylated lithium sulfate produced by the decomposition of the above compounds introduces sulfur elements into the SEI, increasing the ionic conductivity and forming a low-impedance dense SEI, thereby meeting the high-rate charge and discharge characteristics of the secondary battery. The synergistic effect of the first and second components ensures the quality of the electrolyte under high-temperature conditions, enabling the electrolyte to balance thermal stability and kinetic performance. Simultaneously, an SEI with high conductivity and high thermal stability is formed on the negative electrode of the secondary battery, while a CEI with stable high voltage and high-temperature metal ion extraction from the positive electrode material is formed. This satisfies the high-rate charge-discharge characteristics of the secondary battery, while effectively suppressing expansion and gas generation under high-temperature conditions, thus improving the secondary battery's high-temperature storage and cycling performance.

[0041] In one embodiment of this application, the mass ratio of the first component to the second component is 0.02 to 50:1, preferably 0.03 to 30:1. For example, the mass ratio of the first component to the second component can be 0.02:1, 0.05:1, 0.1:1, 0.5:1, 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, or a range consisting of any two of these values. When the mass ratio of the first component to the second component is within the above range, the synergistic effect of the first and second components can be more fully utilized, further improving the rate performance, high-temperature storage performance, and high-temperature cycle performance of the secondary battery.

[0042] In this application, the term "halogen" refers to a fluorine, chlorine, bromine, or iodine atom.

[0043] In this application, the dashed lines in the compounds shown in Formula II represent conjugated π bonds.

[0044] In one embodiment of this application, R is selected from unsubstituted or fluorinated C6-C. 12The electrolyte comprises aryl, unsubstituted or fluorinated C3-C6 heteroaryl, unsubstituted or fluorinated C1-C4 alkyl, and unsubstituted or fluorinated C2-C4 alkenyl; R1, R2, and R3 are each independently selected from C1-C4 alkyl or C3-C6 cycloalkyl. When the electrolyte comprising the above-mentioned first and second components is applied to a secondary battery, the synergistic effect of the first and second components can better improve the rate performance, high-temperature storage performance, and high-temperature cycling performance of the secondary battery.

[0045] In one embodiment of this application, R is selected from unsubstituted or fluorinated phenyl, unsubstituted or fluorinated C3-C6 nitrogen-containing heteroaryl, unsubstituted or fluorinated C1-C4 alkyl, and unsubstituted or fluorinated C2-C4 alkenyl; preferably, R is selected from phenyl, thiophene, imidazolyl, pyridinyl, fluorophenyl, fluorothiophene, fluoroimidazolyl, fluoropyridine, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, fluoromethyl, fluoroethyl, fluoro1-propyl, fluoro2-propyl, fluoro1-butyl, fluoro2-methyl-1-propyl, fluoro2-butyl, vinyl, propenyl, butenyl, fluorovinyl, fluoropropenyl, or fluorobutenyl; more preferably, R is selected from phenyl, fluorophenyl, imidazolyl, methyl, vinyl, or trifluoromethyl.

[0046] In one embodiment of this application, R1, R2 and R3 are each independently selected from C1-C4 alkyl or C3-C6 cycloalkyl; preferably, R1, R2 and R3 are each independently selected from methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, cyclopropane, cyclobutane, cyclopentane or cyclohexane.

[0047] When an electrolyte comprising the first and second components is applied to a secondary battery, the synergistic effect of the first and second components can further improve the rate performance, high-temperature storage performance, and high-temperature cycling performance of the secondary battery.

[0048] In one embodiment of this application, the first component is selected from at least one of the following compounds;

[0049]

[0050] Applying an electrolyte containing the first component to a secondary battery can effectively suppress the rise in electrolyte acidity, stabilize the quality of the electrolyte at high temperatures, and suppress gas production. At the same time, it can work synergistically with the second component to form an SEI with high conductivity and high thermal stability at the negative electrode of the secondary battery, thereby improving the cycle performance and storage performance of the secondary battery at high temperatures.

[0051] In one embodiment of this application, the second component is selected from at least one of the following compounds;

[0052]

[0053] Applying the electrolyte containing the second component to a secondary battery effectively improves the stability of the positive and negative electrode interface structure of the secondary battery containing the electrolyte, suppresses the extraction of metal ions from the positive electrode material under high voltage and high temperature, and prevents the damage of the negative electrode interface by transition metal ions. The sulfonic acid groups containing unsaturated bonds further modify the SEI to form a dense SEI based on the relatively sparse SEI formed by the reduction of the first component. The alkylated lithium sulfate produced by the decomposition of the above compounds introduces S element into the SEI, increases the ionic conductivity, and forms a low-resistance dense SEI, thereby meeting the high-rate charge and discharge characteristics of the secondary battery.

[0054] In summary, the electrolyte additive of this application includes both the first component and the second component, which can give full play to the synergistic effect of the first component and the second component, thereby improving the rate performance, high-temperature storage performance and high-temperature cycling performance of the secondary battery.

[0055] This application does not impose any particular limitation on the preparation method of the electrolyte additive, as long as the purpose of this invention is achieved. For example, the two components can be directly mixed. The preparation method of the compounds used in this application is not particularly limited; they can be prepared using methods known in the art or purchased directly from the market.

[0056] The second aspect of this application provides an electrolyte comprising the electrolyte additive described in the first aspect of this application; based on the mass of the electrolyte, the mass percentage of the electrolyte additive is 0.2% to 10%, preferably 0.2% to 6%. For example, based on the mass of the electrolyte, the mass percentage of the electrolyte additive can be 0.2%, 0.5%, 1%, 3%, 5%, 8%, 10%, or a range consisting of any two of these values. The electrolyte of this application, comprising the electrolyte additive described in the first aspect of this application, enables the electrolyte to balance thermal stability and kinetic performance. Furthermore, when the amount of electrolyte additive is within the aforementioned range, the secondary battery can exhibit higher rate performance, high-temperature storage performance, and high-temperature cycling performance.

[0057] In one embodiment of this application, based on the mass of the electrolyte, the mass percentage of the first component is A, 0.1% ≤ A ≤ 5%, and the mass percentage of the second component is B, 0.1% ≤ B ≤ 5%. Preferably, based on the mass of the electrolyte, the mass percentage of the first component is A, 0.1% ≤ A ≤ 3%, and the mass percentage of the second component is B, 0.1% ≤ B ≤ 3%. For example, based on the mass of the electrolyte, the mass percentage A of the first component can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two values; the mass percentage B of the second component can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two values. When the contents of the first and second components are within the above-mentioned range, the synergistic effect of the first and second components can be better utilized, further enabling the secondary battery to have higher rate performance, high-temperature storage performance and high-temperature cycle performance.

[0058] In one embodiment of this application, the electrolyte further includes other additives selected from vinylene carbonate (VC).

[0059] In one embodiment of this application, the mass percentage of the other additives is 0.1% to 5%, preferably 0.5% to 3%, based on the total mass of the electrolyte. For example, based on the mass of the electrolyte, the mass percentage of the other additives can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two of these values.

[0060] In one embodiment of this application, the electrolyte further includes a lithium salt or a sodium salt. This application does not impose any particular limitation on the lithium salt or sodium salt, as long as it achieves the purpose of this application. For example, the lithium salt may be selected from, but is not limited to, at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, and lithium bis(trifluoromethanesulfonyl)imide; for example, the sodium salt may be selected from, but is not limited to, at least one of sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide.

[0061] This application does not impose any particular limitation on the content of lithium or sodium salts in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of lithium or sodium salts is 5% to 20%, preferably 10% to 15%. For example, based on the mass of the electrolyte, the mass percentage of lithium or sodium salts can be 5%, 8%, 10%, 13%, 15%, 18%, 20%, or a range of any two of these values.

[0062] In one embodiment of this application, the electrolyte further includes a non-aqueous solvent. This application does not have any particular limitation on the non-aqueous solvent, as long as it achieves the purpose of this application. For example, the non-aqueous solvent may be selected from, but is not limited to, ethylene carbonate, propylene carbonate, γ-butyrolactone, phenyl acetate, 1,4-butylsulfonyl lactone, 3,3,3-trifluoropropylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, (2,2,2)-trifluoroethyl carbonate, 2,2-difluoroethyl acetate, 2,2-difluoroethyl propionate, and 2,2-difluoroethyl methyl carbonate. Preferably, the non-aqueous solvent may be selected from, but is not limited to, at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Using at least one of the above substances as the non-aqueous solvent in the electrolyte helps to form an electrolyte that balances thermal stability and kinetic performance, promotes the synergistic effect of the first and second components, and forms an SEI with high conductivity and high thermal stability, thereby improving the storage performance and high-rate performance of the secondary battery at high temperatures.

[0063] This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of non-aqueous solvents is 65% to 94%, preferably 76% to 89%. For example, based on the mass of the electrolyte, the mass percentage of non-aqueous solvents can be 65%, 67%, 70%, 72%, 75%, 80%, 85%, 87%, 90%, 94%, or a range of any two of these values. A non-aqueous solvent content within the above range is more conducive to forming an electrolyte that balances thermal stability and kinetic performance, and is beneficial to promoting the synergistic effect of the first and second components, forming an SEI with higher conductivity and higher thermal stability, thereby improving the storage performance and high-rate performance of the secondary battery at high temperatures.

[0064] This application does not impose any particular restrictions on the preparation method of the electrolyte, as long as it can achieve the purpose of this application. For example, various non-aqueous solvents in the electrolyte can be mixed, and then electrolyte lithium salt or sodium salt and electrolyte additives can be added and mixed evenly.

[0065] A third aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte described in the second aspect of this application.

[0066] In 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 phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that "surface" here can refer to the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0067] This application does not impose any particular limitation on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the positive electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, aluminum foil, aluminum alloy foil, or carbon-coated aluminum foil can be used. The composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0068] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular restrictions on the positive electrode active material, as long as it can achieve the purpose of this application.

[0069] In one embodiment of this application, the positive electrode active material is selected from LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4 and Li2Mn 1-xAt least one of O4, M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, 0 ≤ a < 0.2, 0 ≤ x < 1. For example, 0 ≤ a ≤ 0.19, 0.05 ≤ a ≤ 0.15, 0.08 ≤ a ≤ 0.13, 0.1 ≤ a ≤ 0.12; 0 ≤ x ≤ 0.9, 0.1 ≤ x ≤ 0.8, 0.2 ≤ x ≤ 0.7, 0.3 ≤ x ≤ 0.6, 0.4 ≤ x ≤ 0.5.

[0070] It should be noted that Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2 and LiFe 1-x M x In PO4, the choice of M in each chemical formula is independent and does not affect each other; they can be the same or different. Similarly, in the list of positive electrode active materials above, the choices of a and x are also independent and do not affect each other; they can be the same or different.

[0071] In one embodiment of this application, the positive electrode active material is selected from lithium iron phosphate positive electrode active materials, such as LiFePO4 and LiFe 1-x M x At least one of PO4. Lithium iron phosphate cathode active materials have a lower voltage plateau and better stability, thus enabling the secondary battery of this application to be charged and discharged at low voltage. At high temperature and low pressure, the lithium iron phosphate cathode active material, matched with the electrolyte additive of this application, can further reduce the probability of SEI decomposition of the three-dimensional network, reduce gas production in the secondary battery, and improve the storage performance and high-rate performance of the secondary battery at high temperature.

[0072] In one embodiment of this application, the positive electrode active material is selected from at least one of the following materials: Na x MO2, where M is selected from at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, 0 < x ≤ 1; polyanionic compounds, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F, and Na3(VO y )2(PO4)2F 3-2y At least one of the following, wherein M' is selected from at least one of V, Fe, Mn, and Ni, 0 ≤ y ≤ 1; Prussian blue compounds: Na a Me b Me' c(CN)6, where Me and Me’ are each independently selected from at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0073] In one embodiment of the present application, the positive electrode active material is selected from x1 Na x2 M1O2, Na

[0074] M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3, and Na2M4(SO4)2·2H2O, where 0 < x1 ≤ 1, M1 is selected from at least one of Ni, Co, Mn, Fe, and Cu, 0 < x2 < 6, M2 is selected from at least one of Ni, Fe, and Mn, M3 is selected from at least one of Fe and Mn, and M4 is selected from at least one of Fe, Co, Mn, and Cu. The above positive electrode active materials have a higher working voltage. In combination with the electrolyte additive of the present application, at high voltage, the SEI stability is stronger, which can reduce the gas generation of the secondary battery and further improve the cycling performance and high-rate performance of the secondary battery at high temperature.

[0075] The present application does not particularly limit the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 10 μm to 16 μm, and the thickness of the single-sided positive electrode material layer is 40 μm to 200 μm.

[0076] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer. For example, the conductive agent may be selected from, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may be selected from, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0077] This application does not impose any particular limitation on the preparation method of the positive electrode sheet, as long as it can achieve the purpose of this application. For example, the components used to prepare the positive electrode sheet, such as the positive electrode active material, conductive agent, and binder, are dispersed in a solvent to form a positive electrode slurry with a solid content of 50-70 wt%; the positive electrode slurry is coated on the positive electrode current collector, and after drying, rolling and other processes, the positive electrode sheet can be obtained.

[0078] In this application, the secondary battery further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0079] This application does not impose any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the negative electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, copper foil or aluminum alloy foil can be used. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a polypropylene, polyethylene terephthalate, polybutylene terephthalate, etc. substrate).

[0080] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material can be selected from, but is not limited to, at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nano carbon, elemental silicon, silicon oxide, silicon-carbon composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy and lithium titanate.

[0081] In some embodiments of this application, the negative electrode material layer may further include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the conductive agent may be selected from, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may be selected from, but is not limited to, at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0082] In some embodiments of this application, the negative electrode material layer may further include a conductive agent, a binder, and a thickener. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the conductive agent may be selected from, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binder may be selected from, but is not limited to, at least one of polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan. The thickener may be selected from, but is not limited to, at least one of sodium carboxymethyl cellulose (CMC-Na) and lithium carboxymethyl cellulose (CMC-Li). This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0083] This application does not impose any particular limitations on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 12 μm, and the thickness of the single-sided negative electrode material layer is 40 μm to 200 μm.

[0084] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer. For example, the conductive agent may be selected from, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may be selected from, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0085] This application does not impose any particular limitation on the preparation method of the negative electrode sheet, as long as it can achieve the purpose of this application. For example, the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and thickener, are dispersed in a solvent to form a negative electrode slurry with a solid content of 45-55 wt%; the negative electrode slurry is coated on the negative electrode current collector, and after drying, rolling and other processes, the negative electrode sheet can be obtained.

[0086] In this application, the secondary battery also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material can be selected from, but is not limited to, at least one of glass fiber, non-woven fabric, polyolefin membrane, aromatic polyamide membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane. This application does not impose any particular limitation on the number of layers in the separator, as long as it achieves the purpose of this application; for example, the separator can be a single-layer thin film or a multi-layer composite thin film.

[0087] In some embodiments of this application, the diaphragm may include a substrate layer and a surface treatment layer. This application does not impose any particular limitation on the substrate layer, as long as it achieves the purpose of this application. For example, the substrate layer may be selected from, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, and polyacrylonitrile.

[0088] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. This application does not impose any particular limitation on the surface treatment layer, as long as it achieves the purpose of this application. For example, the surface treatment layer may be selected from, but is not limited to, conductive carbon, alumina, and Li. 6.4 La3Zr 1.4 Ta 0.6 O 12 At least one of (LLZTO).

[0089] In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be 10μm to 12μm, such as 10μm, 11μm, 12μm, etc.

[0090] The secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as an aluminum-plastic film or a steel-plastic film.

[0091] The preparation process of the secondary battery in this application is well known to those skilled in the art, and this application has no particular limitations. For example, the preparation process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in sequence, and winding, folding and other operations as needed to obtain the wound electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing, standing, formation, aging, and resealing to obtain the secondary battery.

[0092] A fourth aspect of this application provides an electronic device comprising the secondary battery described in the third aspect of this application.

[0093] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0094] Example

[0095] 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.

[0096] Test methods and apparatus:

[0097] High-temperature cycling performance test

[0098] High-temperature cycle performance test of lithium-ion batteries:

[0099] The lithium-ion battery was placed in a 45°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 3C to 3.65V, followed by constant voltage charging at 3.65V until the cutoff current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 2V, and this discharge capacity was recorded as C1. This process was repeated for 800 cycles, and the discharge capacity C2 after 800 cycles was recorded. The cycle capacity retention rate of the lithium-ion battery was calculated. High-temperature cycle capacity retention rate = C2 / C1 × 100%.

[0100] High-temperature cycle performance test of sodium-ion batteries:

[0101] The sodium-ion battery was placed in a 45°C constant-temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1C to 4V, followed by constant voltage charging at 4V until the cutoff current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 2.5V, and this discharge capacity was recorded as C1. This process was repeated for 300 cycles, and the discharge capacity C2 after 300 cycles was recorded. The cycle capacity retention rate of the sodium-ion battery was calculated. High-temperature cycle capacity retention rate = C2 / C1 × 100%.

[0102] High-temperature storage performance test

[0103] High-temperature storage performance test of lithium-ion batteries:

[0104] The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1C to 3.65V, followed by constant voltage charging at 3.65V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 2V, and the discharge capacity was recorded as C3. It was then charged again at a constant current of 1C to 3.65V, followed by constant voltage charging at 3.65V until the cutoff current was 0.05C. The lithium-ion battery was removed, and its thickness was measured and recorded as h1. The lithium-ion battery was then transferred to 60°C and left to stand for 30 days. The thickness was measured and recorded as h2. The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 2 hours to allow it to reach a constant temperature. It was then discharged at a constant current of 1C to 2V, and the discharge capacity was recorded as C4. High-temperature storage capacity retention rate = C4 / C3 × 100%, high-temperature storage thickness expansion rate = (h2 - h1) / h1 × 100%.

[0105] High-temperature storage performance test of sodium-ion batteries:

[0106] The sodium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to reach a constant temperature. It was then charged at a constant current of 1C to 4V, followed by constant voltage charging at 4V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 2.5V, and the discharge capacity was recorded as C3. It was then charged again at a constant current of 1C to 2.5V, followed by constant voltage charging at 4V until the cutoff current was 0.05C. The sodium-ion battery was removed, and its thickness was measured and recorded as h1. The sodium-ion battery was then transferred to 60°C and left to stand for 30 days. The thickness was measured and recorded as h2. The sodium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 2 hours to reach a constant temperature. It was then discharged at a constant current of 1C to 2.5V, and the discharge capacity was recorded as C4. High-temperature storage capacity retention rate = C4 / C3 × 100%, high-temperature storage thickness expansion rate = (h2 - h1) / h1 × 100%.

[0107] Battery rate performance test

[0108] Lithium-ion battery rate performance test:

[0109] The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 3C to the rated voltage of 3.65V, then charged at a constant voltage of 3.65V until the cutoff current was 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 1C to 2V. This discharge capacity was recorded as C5. The battery was then charged at a constant current of 0.5C to the rated voltage of 3.65V, then charged at a constant voltage of 3.65V until the cutoff current was 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 1C to 2V. This constituted one charge-discharge cycle, which was repeated 3 times. The battery was then charged at a constant current of 1C to the rated voltage of 3.65V, then charged at a constant voltage of 3.65V until the cutoff current was 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 1C to 2V. This constituted one charge-discharge cycle, which was repeated 3 times. Finally, the battery was charged at a constant current of 2C to the rated voltage of 3.65V, then discharged at a constant current of 1C to 2V. This constituted one charge-discharge cycle, which was repeated 3 times. Charge at 3.65V until the cutoff current is 0.05C, let stand for 5 minutes, then discharge at 1C constant current to 2V, let stand for 5 minutes. This is one charge-discharge cycle. Repeat the charge-discharge steps 3 times. Then charge at 3C constant current to the rated voltage 3.65V, then charge at 3.65V until the cutoff current is 0.05C, let stand for 5 minutes, then discharge at 1C constant current to 2V, let stand for 5 minutes. This is one charge-discharge cycle. Repeat the charge-discharge steps 3 times. The constant current charging capacity of the last cycle at 3C rate is recorded as C6. The 3C constant current charging ratio = (C6 / C5) × 100%.

[0110] Sodium-ion battery rate performance test:

[0111] The sodium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 3C to the rated voltage of 4V, followed by constant charging at 4V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 2.5V, and this was recorded as the discharge capacity C5. The battery was then charged again at a constant current of 0.5C to the rated voltage of 4V, followed by constant charging at 4V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 2.5V and left to stand for 5 minutes. This constituted one charge-discharge cycle, which was repeated 3 times. The battery was then charged again at a constant current of 1C to the rated voltage of 4V, followed by constant charging at 4V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1C to 2.5V and left to stand for 5 minutes. This constituted one charge-discharge cycle, which was repeated 3 times. Finally, it was charged again at a constant current of 2C to the rated voltage of 4V, followed by constant charging at 4V... Charge to the cutoff current of 0.05C, let stand for 5 minutes, then discharge at a constant current of 1C to 2.5V, let stand for 5 minutes. This is one charge-discharge cycle. Repeat the charge-discharge steps 3 times. Then charge at a constant current of 3C to the rated voltage of 4V, then charge at a constant voltage of 4V to the cutoff current of 0.05C, let stand for 5 minutes, then discharge at a constant current of 1C to 2.5V, let stand for 5 minutes. This is one charge-discharge cycle. Repeat the charge-discharge steps 3 times. The constant current charging capacity of the last cycle at 3C rate is recorded as C6. The 3C constant current charging ratio = (C6 / C5) × 100%.

[0112] Example 1-1

[0113] <Preparation of the positive electrode>

[0114] Lithium iron phosphate (LiFePO4, purchased from Shenzhen Defang Nanotechnology Co., Ltd.), carbon black, carbon nanotubes, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 94.5:3.5:0.5:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 68 wt%. After vacuum stirring, the slurry was obtained. The slurry was uniformly coated onto one surface of a 16 μm thick aluminum foil current collector. After drying at 110℃, rolling, and baking at 95℃ for 8 hours, a single-sided coated positive electrode sheet was obtained. After slitting and spot welding of tabs, positive electrode sheets with dimensions of 70 mm × 54 mm were obtained for later use. The compaction density of the positive electrode layer was 2.5 g / cm³. 3 The thickness of the single-sided positive electrode material layer is 160 μm.

[0115] <Preparation of Negative Electrode Sheets>

[0116] Artificial graphite (purchased from Jiangxi Zichen Technology Co., Ltd.), conductive carbon black, polyvinylidene fluoride (PVDF) binder, and sodium carboxymethyl cellulose (CMC) thickener were mixed in a mass ratio of 94.5:2:2:1.5. Deionized water was added as a solvent to prepare a slurry with a solid content of 49 wt%. After vacuum stirring, the slurry was obtained. The slurry was uniformly coated on one surface of a 9 μm thick copper foil current collector. After drying at 110°C, rolling, and baking at 95°C for 8 hours, a single-sided coated negative electrode sheet was obtained. After slitting and spot welding of tabs, negative electrode sheets with a size of 74 mm × 58 mm were obtained for later use. The compaction density of the negative electrode material layer was 1.6 g / cm³. 3 The thickness of the single-sided negative electrode material layer is 122 μm.

[0117] <Preparation of Electrolyte>

[0118] In an argon-atmospheric glove box (water content <10ppm, oxygen content <1ppm), non-aqueous solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a mass ratio of 3:7. Then, lithium salt LiPF6, other additives VC, first component compound 1-1, and second component compound 2-1 were added and mixed uniformly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of other additives VC was 2.5%, the mass percentage of first component compound 1-1 was 0.1%, the mass percentage of second component compound 2-1 was 5%, and the mass percentage of lithium salt LiPF6 was 12.5%.

[0119] <Preparation of the diaphragm>

[0120] 10μm polyethylene (purchased from Shenzhen Xingyuan Material Technology Co., Ltd.) was used as the diaphragm.

[0121] <Preparation of Lithium-ion Batteries>

[0122] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. They are then wound, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, resulting in an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film, with the positive and negative tabs extended from the interior to the exterior of the film. Moisture is removed at 85°C, and the electrolyte prepared above is injected. The process involves vacuum sealing, standing for 24 hours, constant current charging at 0.05C to 60% SOC for formation, aging in a formation cabinet at 45°C for 24 hours after formation, and a second sealing process to obtain a lithium-ion battery.

[0123] Examples 1-2 to 1-27

[0124] Except for adjusting the types and mass percentages of the first and second components according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the non-aqueous solvent accordingly, and keeping the mass percentage of the lithium salt unchanged, the rest is the same as in Example 1-1.

[0125] Comparative Example 1

[0126] Except that the first and second components are not added in the <Preparation of Electrolyte>, the mass percentage of non-aqueous solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0127] Comparative Example 2

[0128] Except for the omission of the first component in the <Preparation of Electrolyte>, the adjustment of the mass percentage of the second component according to Table 1, the change in the mass percentage of the non-aqueous solvent, and the unchanged mass percentage of the lithium salt, the rest is the same as in Example 1-1.

[0129] Comparative Example 3

[0130] Except that the second component is not added in the <Preparation of Electrolyte>, the mass percentage of the first component is adjusted according to Table 1, the mass percentage of the non-aqueous solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0131] Example 2-1

[0132] <Preparation of the positive electrode>

[0133] The positive electrode active material Na(Ni) 0.33 Fe 0.33 Mn 0.33 O2, conductive carbon black, conductive carbon nanotubes, and binder polyvinylidene fluoride were mixed in a mass ratio of 94.5:3.5:0.5:1.5, with N-methylpyrrolidone added as a solvent to prepare a slurry with a solid content of 50 wt%. After vacuum stirring, a positive electrode slurry was obtained. This slurry was then uniformly coated onto one surface of a 16 μm thick aluminum foil used as a positive electrode current collector. After drying at 110℃, rolling, and baking at 95℃ for 8 hours, a positive electrode sheet with a single-sided coating of positive electrode material was obtained. After slitting and spot welding of tabs, positive electrode sheets with dimensions of 70 mm × 54 mm were obtained for later use. The compaction density of the positive electrode material layer was 1.9 g / cm³. 3 The thickness of the single-sided positive electrode material layer is 158 μm.

[0134] <Preparation of Negative Electrode Sheets>

[0135] Artificial graphite (purchased from Jiangxi Zichen Technology Co., Ltd.), conductive carbon black, polyvinylidene fluoride (PVDF) binder, and sodium carboxymethyl cellulose (CMC) thickener were mixed in a mass ratio of 94.5:2:2:1.5. Deionized water was added as a solvent to prepare a slurry with a solid content of 49 wt%. After vacuum stirring, the slurry was obtained. The slurry was uniformly coated onto one surface of a 9 μm thick copper foil current collector. After drying at 110°C, rolling, and baking at 95°C for 8 hours, a negative electrode sheet with a single-sided coating of negative electrode material was obtained. After slitting and spot welding of tabs, negative electrode sheets with a size of 74 mm × 58 mm were obtained for later use. The compaction density of the negative electrode material layer was 0.95 g / cm³. 3 The thickness of the single-sided negative electrode material layer is 135μm.

[0136] <Preparation of Electrolyte>

[0137] In an argon-atmospheric glove box (water content <10ppm, oxygen content <1ppm), non-aqueous solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed uniformly at a mass ratio of 3:7. Then, sodium salt NaPF6, other additives VC, first component compound 1-1, and second component compound 2-1 are added and mixed uniformly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of other additives VC is 2.5%, the mass percentage of first component compound 1-1 is 0.5%, the mass percentage of second component compound 2-1 is 5%, and the mass percentage of sodium salt NaPF6 is 12.5%.

[0138] <Preparation of the diaphragm>

[0139] 10μm polyethylene (purchased from Shenzhen Xingyuan Material Technology Co., Ltd.) was used as the diaphragm.

[0140] <Preparation of Sodium-ion Batteries>

[0141] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. They are then wound, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, resulting in an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film, with the positive and negative tabs extended from the interior to the exterior of the film. Moisture is removed at 85°C, and the electrolyte prepared above is injected. The process involves vacuum sealing, standing for 24 hours, constant current charging at 0.05C to 60% SOC for formation, aging in a formation cabinet at 45°C for 24 hours after formation, and a second sealing process to obtain a sodium-ion battery.

[0142] Examples 2-2 to 2-5

[0143] Except for adjusting the types and mass percentages of the first and second components according to Table 2 in the <Preparation of Electrolyte>, changing the mass percentage of the non-aqueous solvent accordingly, and keeping the mass percentage of the sodium salt unchanged, the rest is the same as in Example 2-1.

[0144] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0145]

[0146]

[0147] As can be seen from Examples 1-1 to 1-27 and Comparative Examples 1 to 3, electrolytes without the first and second components, or with only the first or second component, when applied to lithium-ion batteries, result in lower high-temperature cycle capacity retention, higher high-temperature storage capacity retention, and lower 3C constant current charge-in ratio, as well as higher high-temperature storage thickness expansion rate. When electrolytes with both the first and second components are added simultaneously are applied to lithium-ion batteries, the batteries exhibit higher high-temperature cycle capacity retention, higher high-temperature storage capacity retention, and higher 3C constant current charge-in ratio, as well as lower high-temperature storage thickness expansion rate. These results demonstrate that the combined use of the first and second components can improve the rate performance, high-temperature storage performance, and high-temperature cycle performance of lithium-ion batteries.

[0148] As can be seen from Examples 2-1 to 2-5, when the electrolyte with both the first and second components is applied to sodium-ion batteries, the sodium-ion batteries exhibit higher high-temperature cycle capacity retention, higher high-temperature storage capacity retention, and a higher 3C constant current charge-in ratio, as well as lower high-temperature storage thickness expansion rate. These results demonstrate that the combined use of the first and second components can improve the rate performance, high-temperature storage performance, and high-temperature cycle performance of sodium-ion batteries.

[0149] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0150] 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 component and a second component; The first component is selected from the compounds shown in Formula I; The second component is selected from the compounds shown in Formula II; in, X1, X2, X3, and X4 are each independently selected from N or CH, with one of them selected from N; R is selected from unsubstituted or R-selected. a Replacement C6-C 12 aryl, unsubstituted or R a Replacement C3-C 12 heteroaryl, unsubstituted or R a Substituted C1-C8 alkyl, unsubstituted or R a Substituted C2-C8 alkenyl groups; substituent R a Each of the heteroatoms is independently selected from C1-C6 alkyl or halogen; each heteroatom in the heteroaryl group is independently selected from O, S or N; R1, R2, and R3 are each independently selected from C1-C 10 Alkyl or C3-C 10 Cycloalkyl.

2. The electrolyte additive according to claim 1, wherein, The mass ratio of the first component to the second component is 0.02 to 50:1, preferably 0.03 to 30:

1.

3. The electrolyte additive according to claim 1, wherein, R is selected from unsubstituted or fluorinated C6-C. 12 Aryl, unsubstituted or fluorinated C3-C6 heteroaryl, unsubstituted or fluorinated C1-C4 alkyl, unsubstituted or fluorinated C2-C4 alkenyl; R1, R2, and R3 are each independently selected from C1-C4 alkyl or C3-C6 cycloalkyl.

4. The electrolyte additive according to claim 1, wherein, The first component is selected from at least one of the following compounds; 5. The electrolyte additive according to claim 1, wherein, The second component is selected from at least one of the following compounds; 6. An electrolyte comprising the electrolyte additive according to any one of claims 1 to 5; wherein the electrolyte additive comprises, based on the mass of the electrolyte, 0.2% to 10% by mass, preferably 0.2% to 6%.

7. The electrolyte according to claim 6, wherein, Based on the mass of the electrolyte, the mass percentage of the first component is A, 0.1% ≤ A ≤ 5%, and the mass percentage of the second component is B, 0.1% ≤ B ≤ 5%.

8. The electrolyte according to claim 6, wherein, Based on the mass of the electrolyte, the mass percentage of the first component is A, 0.1% ≤ A ≤ 3%, and the mass percentage of the second component is B, 0.1% ≤ B ≤ 3%.

9. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte according to any one of claims 6 to 8.

10. The secondary battery according to claim 9, wherein, The positive electrode includes a positive electrode active material, which is selected from LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1- x M x PO4 and Li2Mn 1-x At least one of O4, M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, 0 ≤ a < 0.2, 0 ≤ x < 1; or, The positive electrode active material is selected from Na x1 M1O2, Na x2 M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3, and Na2M4(SO4)2·2H2O, where 0 < x1 ≤ 1, M1 is selected from at least one of Ni, Co, Mn, Fe, and Cu, 0 < x2 < 6, M2 is selected from at least one of Ni, Fe, and Mn, M3 is selected from at least one of Fe and Mn, and M4 is selected from at least one of Fe, Co, Mn, and Cu.

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