Electrolyte additive, electrolyte and battery

Abstract

Disclosed are an electrolyte additive, an electrolyte and a battery. The electrolyte additive comprises a first additive and a second additive. The first additive comprises a compound containing a silicon element and an unsaturated hydrocarbon group. The second additive comprises a compound represented by formula 1, where X1, X2, X3 and X4 are each independently selected from N or CH, R is selected from a 5-6 membered aryl, a 5-6 membered aryl substituted with R0, a 5-6 membered heteroaryl, a 5-6 membered heteroaryl substituted with R0, a C1-8 alkyl, a C1-8 alkyl substituted with R0, a C2-8 alkenyl, a C2-8 alkenyl substituted with R0, a C0-8 alkylsilane, or a C0-8 alkylsilane substituted with R0, and R0 is selected from a C1-6 alkyl, a C1-6 alkoxy or halogen.

Description

Electrolyte additives, electrolytes and batteries

[0001] Priority information

[0002] This application claims priority and benefits to patent application No. 202410990690.3, filed with the China National Intellectual Property Administration on July 23, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application belongs to the field of batteries, specifically relating to an electrolyte additive, an electrolyte, and a battery. Background Technology

[0004] In recent years, the rapid development and widespread application of various portable electronic devices, new energy electric vehicles, and energy storage systems have created an increasingly urgent demand for rechargeable batteries with high energy density, long cycle life, safe use, and good rate performance.

[0005] However, the cathode materials in secondary batteries (such as sodium-ion batteries) may suffer from instability. High-temperature performance is particularly important for secondary batteries, which are prone to poor storage performance, poor cycle performance, and gas generation at high temperatures during operation. One significant reason is the poor thermal stability of lithium hexafluorophosphate (LiPF6), a commercially available lithium salt. Under high temperatures, it is susceptible to decomposition reactions and reactions with trace impurities in the electrolyte, leading to a rapid increase in electrolyte acidity. This deteriorates electrolyte quality, causes severe gas generation at high temperatures, and ultimately worsens the battery's cycle performance, storage performance, and safety performance at high temperatures.

[0006] Existing rechargeable batteries typically incorporate various additives into the electrolyte, which can form an organic passivation film on the surface of the active materials to improve battery performance, including cycle life and high-temperature storage. However, the passivation film formed by conventional additives on the surface of the active materials has high internal resistance, and this passivation film is unable to suppress the continuous decomposition of the electrolyte on the negative electrode active material during battery cycling. This leads to a continuous increase in the thickness of the passivation film, resulting in a continuous increase in the internal resistance of the rechargeable battery during cycling. At the same time, conventional additives cannot solve the problem of electrolyte stability at high temperatures, which seriously affects the battery's performance in high-temperature cycling and storage, and also impacts battery safety.

[0007] Given the above shortcomings, it is essential to develop an electrolyte that can significantly improve the cycle performance and high-temperature storage performance of secondary batteries. Summary of the Invention

[0008] This application aims to at least partially address one of the technical problems in the related art. Therefore, one objective of this application is to provide an electrolyte additive, an electrolyte, and a battery, wherein adding the electrolyte additive to a secondary battery can improve the cycle performance and storage performance of the secondary battery at high temperatures.

[0009] The first aspect of this application discloses an electrolyte additive, which includes a first additive and a second additive, wherein the first additive includes a compound containing silicon and an unsaturated hydrocarbon group, and the second additive includes a compound represented by Formula 1:

[0010] Wherein, X1, X2, X3, and X4 are independently selected from N or CH; R is selected from 5-6 aryl, 5-6 aryl substituted with R0, 5-6 heteroaryl, 5-6 heteroaryl substituted with R0, and C. 1-8 Alkyl groups, C substituted with R0 1-8 Alkyl, C 2-8 Alkenyl, C substituted with R0 2-8 alkenyl, C 0-8 Alkyl silyl or C substituted with R0 0-8 Alkylsilyl; R0 is selected from C 1-6 Alkyl, C 1-6 Alkoxy or halogen.

[0011] The combined use of the first and second additives can form a protective layer with a three-dimensional network on the negative electrode of the battery, providing a cross-linking protective layer and forming an SEI film with high electrical conductivity and high thermal stability. This effectively reduces the formation of secondary particles aggregated at the battery interface, reduces the thickness of the SEI film, and improves the high-temperature storage performance of the battery.

[0012] In some implementations, at least one of X1, X2, X3, and X4 is N, and the rest are CH.

[0013] In some embodiments, the mass ratio of the first additive to the second additive is (1-50):(1-50). Therefore, by keeping the mass ratio of the first additive and the second additive within the above range, they can work together more effectively to form an excellent SEI film on the negative electrode of the battery, reducing the impedance of the negative electrode during battery recycling and improving the battery's high-temperature cycle performance and high-temperature storage performance.

[0014] In some embodiments, the first additive comprises at least one of the compounds shown in Formula 2 and Formula 3:

[0015] Among them, R1, R2, R3, R4, R5, R6, R7, R8, R9 and R 10Each of the following is independently selected from H, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkoxy, and C2-C5 alkenyloxy, and R1, R2, R3, R4, R5, R6, R7, R8, R9 and R 10 At least one of them is an unsaturated hydrocarbon group.

[0016] In some embodiments, the first additive includes at least one selected from tetravinylsilane, tetramethyldivinyldisiloxane, vinyltrimethoxysilane, and allyloxytrimethylsilane. Thus, the first additive can form a stable SEI film on the negative electrode surface of the battery, and works in conjunction with the second additive to improve the battery's high-temperature cycle performance and high-temperature storage performance.

[0017] In some embodiments, the second additive includes at least one of the following substances:

[0018] Therefore, the second additive can form an SEI film with high lithium-ion conductivity on the negative electrode surface, and work together with the first additive to improve the battery's high-temperature cycle performance and high-temperature storage performance.

[0019] In some embodiments, the electrolyte additive further includes a third additive, which comprises fluoroethylene carbonate. Therefore, the addition of the third additive can enhance the antioxidant capacity of the electrolyte and reduce the probability of electrolyte decomposition at the active sites of the negative electrode.

[0020] In some embodiments, the mass ratio of the first additive, the second additive, and the third additive is (1-50):(1-50):(2-50). Therefore, the combined effects of the first, second, and third additives can be fully utilized, not only to form an SEI with high conductivity and high thermal stability, but also to improve the antioxidant properties of the electrolyte, ensuring the quality of the electrolyte at high temperatures while enhancing the cycle performance and storage performance of the secondary battery at high temperatures.

[0021] The second aspect of this application discloses an electrolyte comprising the electrolyte additives described in the first aspect. Thus, when this electrolyte is added to a secondary battery, an SEI film with a cross-linked protective network can be formed, which can improve the battery's high-temperature cycle performance and high-temperature storage performance, reduce the phenomenon of expansion and gas generation in the secondary battery under high-temperature environments, and solve the problem of continuously increasing internal resistance during cycling.

[0022] In some embodiments, the mass percentage of the first additive is 0.1%-5%, optionally 0.1%-3%, based on the total mass of the electrolyte. Thus, within the aforementioned mass percentage range, the first additive can generate a stable SEI film on the negative electrode surface, and simultaneously combine with the sulfone functional groups of the second additive to form an SEI film with a cross-linked protective network, thereby improving the battery's high-temperature cycle performance and high-temperature storage performance.

[0023] In some embodiments, the second additive accounts for 0.1%-5% of the total mass of the electrolyte, optionally 0.1%-3%. Thus, within the aforementioned mass percentage range, the second additive can generate an SEI film with high conductivity on the negative electrode surface, while simultaneously inhibiting further thickening of the SEI film formed by the first additive, reducing the phenomenon of continuously increasing battery internal resistance, and improving the battery's high-temperature cycle performance and high-temperature storage performance.

[0024] In some embodiments, the third additive accounts for 0.2%-5% of the total mass of the electrolyte, and optionally 0.5%-2%. Thus, within the aforementioned mass percentage range, the third additive can enhance the electrolyte's antioxidant capacity and improve the battery's high-temperature cycle performance.

[0025] A third aspect of this application discloses a battery comprising the electrolyte described in the second aspect. Consequently, this battery exhibits excellent high-temperature cycling performance and high-temperature storage performance.

[0026] In some embodiments, the positive electrode active material includes 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.

[0027] In some embodiments, the battery includes a positive electrode active material, the positive electrode active material including Na X1 M1O2, Na X2At least one of M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3, Na2M4(SO4)2·2H2O, where 0 < x1 ≤ 1, M1 includes at least one of Ni, Co, Mn, Fe, and Cu, 0 < x2 < 6, M2 includes at least one of Ni, Fe, and Mn, M3 includes at least one of Fe and Mn, and M4 includes at least one of Fe, Co, Mn, and Cu.

[0028] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Detailed implementation manners

[0029] The embodiments of the present application are described in detail below, aiming to explain the present application and should not be construed as a limitation to the present application.

[0030] Referring to "embodiment" herein means that the specific features, structures, or characteristics described in connection with the embodiment can be included in at least one embodiment of the present application. The phrase appears at various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0031] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "comprising" and "having" and any variations thereof in the specification and claims of the present application and the above accompanying drawings are intended to cover non-exclusive inclusion. <00001​​​​It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0035] Terminology Explanation

[0036] The term "alkyl" refers to a saturated hydrocarbon containing a primary (normal) carbon atom, or a secondary carbon atom, or a tertiary carbon atom, or a quaternary carbon atom, or a combination thereof. Phrases containing this term include, for example, "C". 1-8 "Alkyl" refers to an alkyl group containing 1 to 8 carbon atoms. Suitable examples include, but are not limited to: methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s- Bu, s-butyl, -CH(CH3)CH2CH3), 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3), 1-pentyl (n-pentyl, -CH2CH2CH2CH2CH3), 2-pentyl (-CH(CH3)CH2CH2CH3), 3-pentyl (-CH(CH2CH3)2), 2-methyl-2-butyl (-C(CH3)2CH2CH3), 3-methyl-2-butyl (-CH(CH3)CH(CH3)2), 3- Methyl-1-butyl (-CH2CH2CH(CH3)2), 2-methyl-1-butyl (-CH2CH(CH3)CH2CH3), 1-hexyl (-CH2CH2CH2CH2CH2CH3), 2-hexyl (-CH(CH3)CH2CH2CH2CH3), 3-hexyl (-CH(CH2CH3)(CH2CH2CH3)), 2-methyl-2-pentyl (-C(CH3)2CH2CH2CH3), 3-methyl-2-pentyl (-CH(CH2CH2CH3)) 3) CH(CH3)CH2CH3), 4-methyl-2-pentyl (-CH(CH3)CH2CH(CH3)2), 3-methyl-3-pentyl (-C(CH3)(CH2CH3)2), 2-methyl-3-pentyl (-CH(CH2CH3)CH(CH3)2), 2,3-dimethyl-2-butyl (-C(CH3)2CH(CH3)2), 3,3-dimethyl-2-butyl (-CH(CH3)C(CH3)3 and octyl-(CH2)7CH3).

[0037] "Alkenyl" refers to a group containing at least one unsaturated site, i.e., carbon-carbon sp. 2 Hydrocarbons with double bonds consisting of a positive, secondary, tertiary carbon atom, or a cyclic carbon atom. Phrases containing this term, such as "C". 2-8 "Alkenyl" refers to an alkenyl group containing 2 to 8 carbon atoms. Suitable examples include, but are not limited to: vinyl (-CH=CH2), propenyl (-CH2CH=CH2), cyclopentenyl (-C5H7), and 5-hexenyl (-CH2CH2CH2CH2CH=CH2).

[0038] The term "aryl" can be used alone or as a part of "aranyl," "aranalkoxy," or "aranoxyalkyl," referring to a monocyclic, bicyclic, or tricyclic carbocyclic system containing 6-14 membered rings, wherein at least one ring system is aromatic, and each ring system contains 3-7 membered rings with one or more attachment sites connected to the rest of the molecule. The term "aryl" can be used interchangeably with the term "aromatic ring," as aromatic rings can include phenyl, naphthyl, and anthracene. Furthermore, the aryl group can be substituted or unsubstituted, wherein the substituent can be, but is not limited to, deuterium, hydroxyl, amino, halogen, cyano, aryl, heteroaryl, alkoxy, alkylamino, alkyl, alkenyl, alkynyl, heterocyclic, mercapto, nitro, aryloxy, hydroxy-substituted alkoxy, hydroxy-substituted alkyl-C(=O)-, alkyl-C(=O)-, alkyl-S(=O)2-, hydroxy-substituted alkyl-S(=O)-, hydroxy-substituted alkyl-S(=O)2-, carboxyl-substituted alkoxy, etc.

[0039] The term "heteroaryl" can be used alone or as a part of "heteroarylalkyl" or "heteroarylalkoxy" to indicate monocyclic, bicyclic, and tricyclic systems containing 5-14 membered rings, wherein at least one ring system is aromatic, and at least one ring system contains one or more heteroatoms, wherein the heteroatoms have the meaning described in this invention, wherein each ring system contains 3-7 membered rings and has one or more attachment sites connected to the remainder of the molecule. The term "heteroaryl" may be used interchangeably with the terms "aromatic heterocyclic" or "heteroaromatic compound". Furthermore, the heteroaryl group can be substituted or unsubstituted, wherein the substituent can be, but is not limited to, deuterium, hydroxyl, amino, halogen, cyano, aryl, heteroaryl, alkoxy, alkylamino, alkyl, alkenyl, alkynyl, heterocyclic, mercapto, nitro, aryloxy, hydroxy-substituted alkoxy, hydroxy-substituted alkyl-C(=O)-, alkyl-C(=O)-, alkyl-S(=O)2-, hydroxy-substituted alkyl-S(=O)-, hydroxy-substituted alkyl-S(=O)2-, carboxyl-substituted alkoxy, etc.

[0040] “C 0-8 "Alkylsilyl" refers to In this context, R represents C. 0-8 Alkyl, understandably, when R is C0 alkyl, indicates In this case, R does not contain carbon atoms, meaning all R atoms are H, which is equivalent to...

[0041] The term "alkoxy" indicates that an alkyl group is attached to the remainder of the molecule by an oxygen atom, wherein the alkyl group has the meaning as described in this invention. Unless otherwise specified, the alkoxy group contains 2-5 carbon atoms. In one embodiment, the alkoxy group contains 1-4 carbon atoms; in another embodiment, the alkoxy group contains 1-3 carbon atoms. The alkoxy group may optionally be substituted by one or more substituents described in this invention.

[0042] The term "alkenyloxy group" means that an alkenyl group is attached to the rest of the molecule by an oxygen atom, wherein the alkenyl group has the meaning as described in this invention.

[0043] "Halogen" or "halogen atom" refers to F, Cl, Br and I.

[0044] Although the amount of electrolyte additives used is only a small portion of the electrolyte in a secondary battery, appropriate amounts of additives can form an SEI (Solid Electrolyte Interface) film on the surface of the negative electrode active material and a CEI (Cathode Electrolyte Interface) film on the surface of the positive electrode active material. The SEI and CEI films formed on the surfaces of the negative and positive electrode active materials, respectively, reduce the problem of side reactions occurring after direct contact between the active materials and the electrolyte.

[0045] However, under high temperature or high pressure environments, the cycle performance and storage performance of batteries are prone to significant degradation. Existing rechargeable batteries typically incorporate various additives into the electrolyte, which can form SEI and CEI on the surface of the active materials to improve cycle performance and high-temperature storage. However, the SEI and CEI formed by conventional additives on the surface of the active materials have high internal resistance, and these SEI and CEI are insufficient to suppress the continuous decomposition of the electrolyte on the positive electrode active material during battery cycling. This leads to a continuous increase in the thickness of the SEI and CEI, resulting in a continuous increase in the internal resistance of the rechargeable battery during cycling. Furthermore, this does not solve the problem of poor thermal stability of lithium hexafluorophosphate (LiPF6), which is currently widely used in commercial batteries. It is prone to decomposition reactions at high temperatures, degrading electrolyte quality and causing severe gas generation in the battery under high-temperature conditions. These factors seriously affect the battery's cycle and storage performance at high temperatures, thus impacting battery safety.

[0046] In view of this, the first aspect of this application provides an electrolyte additive, the electrolyte additive comprising a first additive and a second additive, wherein the first additive comprises a compound containing silicon and an unsaturated hydrocarbon group, and the second additive comprises a compound represented by Formula 1:

[0047] Wherein, X1, X2, X3, and X4 are independently selected from N or CH; R is selected from 5-6 aryl, 5-6 aryl substituted with R0, 5-6 heteroaryl, 5-6 heteroaryl substituted with R0, and C. 1-8 Alkyl groups, C substituted with R0 1-8 Alkyl, C 2-8 Alkenyl, C substituted with R0 2-8 alkenyl, C 0-8 Alkyl silyl or C substituted with R0 0-8 Alkylsilyl; R0 is selected from C 1-6 Alkyl, C 1-6 Alkoxy or halogen.

[0048] The first additive generates an SEI film containing unsaturated bonds in an organic polymer on the negative electrode surface. This polymer component improves the stability of the SEI film; however, with high-temperature cycling, the polymer component thickens continuously, significantly increasing the SEI film impedance. The second additive generates an SEI film containing lithium alkyl sulfonate (RSO3Li) on the negative electrode surface. The presence of lithium alkyl sulfonate not only improves the lithium-ion conductivity of the SEI film but also inhibits further thickening of the unsaturated organic polymer SEI film generated by the first additive. Therefore, the combined effect of both additives forms a three-dimensional network protective layer on the negative electrode, providing cross-linking protection and creating an SEI film with high conductivity and high thermal stability. This effectively reduces the formation of secondary particles aggregated at the battery interface, decreases the SEI film thickness, and reduces SEI film resistance. This not only extends the battery's cycle life at high temperatures but also suppresses the expansion and gas generation of the secondary battery under high-temperature conditions and the continuous increase in internal resistance during cycling, improving the battery's high-temperature cycling and storage performance.

[0049] Furthermore, the nitrogen-containing five-membered heterocycle in the second additive contains a nitrogen atom with a lone pair of electrons, making the compound exhibit weak Lewis basicity in the electrolyte. It can form a six-ligand complex with phosphorus pentafluoride (PF5) in the electrolyte, reducing the Lewis acidity and reactivity of PF5, thereby effectively suppressing the rise in electrolyte acidity and stabilizing electrolyte quality. However, the second additive also contains an imidazole group. At high temperatures, the imidazole group readily attacks solvents in the electrolyte, such as cyclic carbonates (EC), leading to severe gas production. The first additive can suppress this negative impact because it contains unsaturated bonds and has higher reactivity, preferentially capturing the imidazole group on the second additive to prevent it from undergoing side reactions with the electrolyte solvent and producing gas.

[0050] In some embodiments of this application, R0 is selected from C. 1-4 Alkyl or halogen; further, R0 is selected from halogen; further, R0 is selected from fluorine.

[0051] In some embodiments of this application, R in the compound represented by Formula 1 may be selected from: phenyl, thienyl, imidazolyl, pyridyl, fluorophenyl, fluorothienyl, fluoroimidazolyl, fluoropyridine, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, fluoromethyl, fluoroethyl, fluoro-1-propyl, fluoro-2-propyl, fluoro-1-butyl, fluoro-2-methyl-1-propyl, fluoro-2-butyl, vinyl, propenyl, butenyl, fluorovinyl, fluoropropenyl, fluorobutenyl.

[0052] In some embodiments of this application, R in the compound represented by Formula 1 is selected from: phenyl, fluorophenyl, imidazolyl, methyl, vinyl, or trifluoromethyl.

[0053] In some embodiments of this application, the mass ratio of the first additive to the second additive is (1-50):(1-50). For example, the mass ratio of the first additive to the second additive can be 1:1, 1:5, 1:10, 1:20, 1:25, 1:30, 1:40, 1:50, 3:50, 2:5, 5:2, 50:1, 25:1, 50:3, 10:1, 5:1, etc., or can be a range of any of the above values. Therefore, by controlling the mass ratio of the first additive to the second additive within the above range, the functions of the first additive and the second additive can be fully utilized to form a protective layer with a three-dimensional network on the negative electrode of the battery, providing cross-linking protective layers, forming an SEI with high conductivity and high thermal stability, effectively reducing the formation of secondary particles aggregated at the battery interface, reducing the thickness of the SEI, reducing SEI impedance, avoiding high-temperature gas generation, ensuring the quality of the electrolyte at high temperatures while improving the cycle performance and storage performance of the secondary battery at high temperatures. In other embodiments of this application, the mass ratio of the first additive, the second additive and the third additive is (1-30):(1-30), (1-20):(1-20), (1-10):(1-10).

[0054] In some embodiments of this application, the first additive includes at least one of the compounds shown in Formula 2 and Formula 3:

[0055] Among them, R1, R2, R3, R4, R5, R6, R7, R8, R9 and R 10 Each of the following is independently selected from H, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkoxy, and C2-C5 alkenyloxy, and R1, R2, R3, R4, R5, R6, R7, R8, R9 and R 10 At least one of them is an unsaturated hydrocarbon group.

[0056] As an example, when R1, R2, R3, R4, R5, R6, R7, R8, R9 and R 10 When each alkyl group is independently selected from C1-C5, the number of carbon atoms can be 1-5, 2-4, 3-4, etc. When R1, R2, R3, R4, R5, R6, R7, R8, R9 and R 10 When each is independently selected from any one of the C2-C5 alkenyl, C2-C5 alkynyl, or C2-C5 alkoxy groups, the number of carbon atoms can be 2-5, 3-5, 3-4, 4-5, etc.

[0057] In some embodiments of this application, the first additive includes at least one of tetravinylsilane, tetramethyldivinyldisiloxane, vinyltrimethoxysilane, and allyloxytrimethylsilane.

[0058] Specifically, the structural formula of the above-mentioned additive is as follows:

[0059] Tetravinylsilane (CAS: 1112-55-6) Tetramethyldivinyldisiloxane (CAS: 2627-95-4)

[0060] Vinyltrimethoxysilane (CAS: 2768-02-7) Allyloxytrimethylsilane (CAS: 18146-00-4)

[0061] Specifically, when the first additive uses at least one of the aforementioned substances, it possesses a high HOMO energy level and can preferentially form an organic polymer film with Si-C as the main component at the interface of the negative electrode active material, prioritizing the formation of the solvent in the electrolyte. This reduces direct contact between the negative electrode active material and the electrolyte, effectively reducing the decomposition and gas generation of other components in the electrolyte at the negative electrode interface under high temperature and high voltage. Simultaneously, it can work synergistically with the second additive to form a three-dimensional network protective layer on the negative electrode of the battery, creating an SEI with high conductivity and high thermal stability. This reduces the thickness and impedance of the SEI, prevents high-temperature gas generation, and improves the cycle performance and storage performance of the secondary battery at high temperatures.

[0062] In some embodiments of this application, the second additive includes at least one of the following substances:

[0063] Specifically, when the second additive uses at least one of the above substances, the nitrogen atom containing a lone pair of electrons in the five-membered heterocycle can make the compound exhibit weak Lewis basicity in the electrolyte, thereby effectively suppressing the rise of electrolyte acidity, stabilizing the quality of the electrolyte under high temperature conditions, and suppressing battery gas production. In addition, the second additive can not only form an SEI film with high lithium-ion conductivity on the negative electrode surface, but also inhibit the further thickening of the SEI film formed by the organic polymer of the first additive, reduce the thickness of the SEI film, and reduce the SEI film resistance.

[0064] By adding a first and a second additive to the electrolyte, a SEI film with high conductivity and high thermal stability was formed at the negative electrode. Further investigation revealed that adding fluoroethylene carbonate (FEC) as a third additive not only enhances the electrolyte's antioxidant capacity but also significantly improves the battery's cycle performance under high-temperature conditions, thereby optimizing the overall performance and stability of the battery.

[0065] Fluorinated ethylene carbonate (FEC) has an additional fluorine (-F) substituent group compared to EC. This group has a strong electron-withdrawing ability and undergoes a reduction decomposition reaction at higher potentials. The resulting fluorine-containing product first occupies the active sites on the graphite electrode surface, effectively inhibiting the decomposition of the electrolyte solvent at lower potentials, thereby widening the electrochemical stability window of the electrolyte and reducing electrolyte decomposition at the active sites of the negative electrode. In addition, FEC can form a fluorine-rich inorganic SEI film on the negative electrode, which can significantly reduce the impedance of the negative electrode during battery recycling. Therefore, the addition of FEC can improve the electrolyte's oxidation resistance and the battery's high-temperature cycle performance. However, FEC is prone to releasing HF during high-temperature storage, causing gas generation in the battery and affecting its high-temperature storage performance. The addition of the first and second additives can suppress this negative impact. This is because the silicon-containing first additive can act as an alkaline electron donor, effectively complexing HF, PF5, and H2O, thereby stabilizing the electrolyte's stability at high temperatures; the Lewis alkaline second additive can further capture HF, thereby improving the cell's high-temperature storage performance.

[0066] In some embodiments of this application, the mass ratio of the first additive, the second additive, and the third additive is (1-50):(1-50):(2-50). For example, the mass ratio of the first additive, the second additive, and the third additive can be 1:1:2, 1:1:5, 2:5:10, 1:1:15, 10:10:1, 10:10:3, 1:1:1, 2:2:1, etc., or can be any range of the above values. Therefore, by controlling the mass ratio of the first additive, the second additive, and the third additive within the above range, the effects of the first additive, the second additive, and the third additive can be fully utilized, achieving an effect of 1+1+1>3. This not only forms a three-dimensional network protective layer on the negative electrode of the battery, providing cross-linking protective layers and forming an SEI with high conductivity and high thermal stability, but also improves the antioxidant performance of the electrolyte, reduces the probability of the electrolyte being decomposed at the negative electrode, and improves the cycle performance and storage performance of the secondary battery at high temperatures while ensuring the quality of the electrolyte at high temperatures. In some other embodiments of this application, the mass ratio of the first additive, the second additive and the third additive is (1-30):(1-30):(2-20), (1-30):(1-30):(5-20), (1-20):(1-20):(5-20), (1-10):(1-10):(5-20).

[0067] The second aspect of this application discloses an electrolyte comprising the electrolyte additives described in the first aspect. Therefore, this electrolyte possesses all the features and advantages of the aforementioned electrolyte additives, which will not be repeated here. In general, adding this electrolyte to a secondary battery suppresses expansion and gas generation at high temperatures and the increase in internal resistance during cycling, thereby improving the battery's high-temperature cycling performance and high-temperature storage performance.

[0068] In some embodiments of this application, the mass percentage of the first additive is 0.1%-5% based on the total mass of the electrolyte. For example, it can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5%, or any range of the above values. Therefore, by keeping the content of the first additive within the above range, it is beneficial for the first additive to form an organic polymer SEI film on the negative electrode surface of the battery, capturing the imidazole groups in the second additive. Simultaneously, it can also complex the HF generated by the third additive during high-temperature storage, preventing it from reacting with the electrolyte solvent to produce gas, thereby improving the stability of the electrolyte at high temperatures and the high-temperature storage performance of the battery cell. In other embodiments of this application, the mass percentage of the first additive is 0.1%-3% based on the total mass of the electrolyte, for example, 0.1%-2%.

[0069] In some embodiments of this application, the mass percentage of the second additive is 0.1%-5% based on the total mass of the electrolyte. For example, it can be 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5%, or any range of the above values. Therefore, by keeping the content of the second additive within the above range, it is beneficial for the second additive to form an SEI film with high lithium-ion conductivity on the negative electrode surface of the battery, while effectively suppressing the thickening of the SEI film formed by the first additive and the increase in electrolyte acidity, stabilizing electrolyte quality, and improving the cycle performance and storage performance of the secondary battery at high temperatures. In other embodiments of this application, the mass percentage of the second additive is 0.1%-3% based on the total mass of the electrolyte, for example, 0.1%-2%.

[0070] In some embodiments of this application, the mass percentage of the third additive is 0.2%-5% based on the total mass of the electrolyte. For example, it can be 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range of the above values. Therefore, by keeping the content of the third additive within the above range, it is beneficial for the third additive to form a fluorine-rich SEI film on the negative electrode surface, while simultaneously improving the antioxidant properties of the electrolyte, inhibiting the decomposition of the electrolyte solvent at lower potentials, and improving the stability of the electrolyte. In other embodiments of this application, the mass percentage of the second additive is 0.5%-2% based on the total mass of the electrolyte.

[0071] In some embodiments of this application, the electrolyte further includes a solvent comprising at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, phenyl acetate, 1,4-butylsulfonyl lactone, 3,3,3-trifluoropropylene carbonate, dimethyl carbonate, ethyl methyl 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. Using at least one of the aforementioned substances as the solvent in the electrolyte is beneficial for promoting the combined effect of the first, second, and third additives. This facilitates the formation of an SEI with high conductivity and high thermal stability at the negative electrode of the battery, reduces the thickness and resistance of the SEI film, suppresses the expansion and gas generation of the secondary battery under high-temperature conditions, and inhibits the continuous increase in internal resistance during cycling. It also improves the electrolyte's antioxidant properties and enhances the cycling and storage performance of the secondary battery at high temperatures. In other embodiments of this application, the solvent includes at least one of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0072] In some embodiments of this application, the solvent accounts for 65%-87% of the total mass of the electrolyte. For example, 65%, 67%, 70%, 72%, 75%, 80%, 85%, 87%, etc. By controlling the solvent content within the above range, it is beneficial to further promote the synergistic effect of the first additive, the second additive, and the third additive, forming an SEI with high conductivity and high thermal stability at the battery negative electrode, reducing the thickness of the SEI film, reducing the SEI film resistance, suppressing the phenomenon of expansion and gas generation of the secondary battery under high temperature environment and the continuous increase of internal resistance during cycling, improving the oxidation resistance of the electrolyte, and enhancing the cycling performance and storage performance of the secondary battery at high temperature.

[0073] In some embodiments of this application, the electrolyte further includes a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium difluorooxalate phosphate, and lithium bis(trifluoromethanesulfonyl)imide.

[0074] In some embodiments of this application, the mass percentage of the lithium salt is 5%-20% based on the total mass of the electrolyte, for example, it can be 5%, 10%, 15%, 20%, etc.

[0075] A third aspect of this application discloses a battery. According to an embodiment of this application, the battery includes the electrolyte described in the second aspect.

[0076] Therefore, in batteries containing this electrolyte, the simultaneous use of the first, second, and third additives during battery formation and cycling allows them to work synergistically, mitigating their individual drawbacks and achieving a synergistic effect greater than the sum of its parts (1+1+1>3). Specifically, the first additive generates an SEI (Sediment Injection) of an organic polymer containing unsaturated bonds on the negative electrode surface. The second additive generates an SEI containing alkyl sulfonate (RSO3Li) on the negative electrode surface. The presence of alkyl sulfonate increases the lithium-ion conductivity of the SEI and also reacts with the unsaturated organic polymer SEI generated by the first additive, inhibiting further thickening of the organic polymer SEI film. Simultaneously, the third additive forms a film on the negative electrode, reducing the impedance of the negative electrode during battery recycling, improving the electrolyte's antioxidant properties, and enhancing the battery's cycle performance and storage performance at high temperatures.

[0077] Typically, a battery cell includes a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active metal ions repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, acting as a conductor for the active metal ions, lies between the positive and negative electrodes.

[0078] [Positive electrode plate]

[0079] In some embodiments of this application, the positive electrode includes a positive current collector, which may be a metal foil, a foamed metal, or a composite current collector. For example, as a metal foil, silver-treated aluminum or stainless steel, stainless steel, copper, aluminum, nickel, carbon electrodes, carbon, or titanium may be used. The composite current collector may include a polymer material substrate and a metal layer. The foamed metal may be foamed nickel, foamed copper, foamed aluminum, foamed alloy, etc. The composite current collector can be formed by forming a metal material (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, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0080] In some embodiments of this application, the positive electrode sheet may further include a positive electrode active material layer, which includes a positive electrode active material. The specific type of the positive electrode active material is not limited, and any active material known in the art that can be used for the positive electrode of a battery can be used. Those skilled in the art can select according to actual needs.

[0081] In some embodiments of this application, when the battery is a lithium-ion battery, the positive electrode active material includes 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.

[0082] 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, etc.

[0083] Understandable, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2 and LiFe 1-x M xIn 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 mutually exclusive and do not affect each other; they can be the same or different.

[0084] In other embodiments of this application, the positive electrode active material includes lithium iron phosphate-based positive electrode active materials (LiFePO4, LiFe...). 1-x M x Specifically, compared to other positive electrode active materials (such as ternary materials), lithium iron phosphate positive electrode active materials have a lower voltage plateau and better stability. This allows the battery of this application to be charged and discharged at low voltage. At high temperature and low pressure, lithium iron phosphate positive electrode active materials, when matched with the additives of this application, can further reduce the probability of SEI decomposition of the three-dimensional network, reduce battery gas production, and improve the battery's cycle performance and storage performance at high temperature.

[0085] When the battery is a sodium-ion battery, the positive electrode active material may include at least one of the following materials:

[0086] Na x MO2, wherein M includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, and 0 < x ≤ 1.

[0087] Polyanionic compounds: NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' includes at least one of V, Fe, Mn and Ni) and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0088] Prussian blue compounds: Na a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0089] In some embodiments, the positive electrode active material includes Na. X1 M1O2, Na X2At least one of M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3, Na2M4(SO4)2·2H2O, where 0 < x1 ≤ 1, M1 includes at least one of Ni, Co, Mn, Fe, and Cu, 0 < x2 < 6, M2 includes at least one of Ni, Fe, and Mn, M3 includes at least one of Fe and Mn, and M4 includes at least one of Fe, Co, Mn, and Cu. The above-mentioned positive electrode active material has a high working voltage. When combined with the electrolyte additive of the embodiment of the present application, it can better generate a three-dimensional network SEI. At high voltages, the SEI has strong stability, which can reduce gas generation in the battery and improve the cycling performance and storage performance of the battery at high temperatures.

[0090] In some embodiments of the present application, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some embodiments of the present application, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0092] In some embodiments of the present application, the positive electrode plate can be prepared by the following method: Dispersing the above-mentioned components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, and binder, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; Coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0093] [[ID=1 (12]] [Negative electrode plate]

[0094] The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material.

[0095] In some embodiments of the present application, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer 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 substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0096] In some embodiments of this application, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: 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.

[0097] In some embodiments of this application, the negative electrode active material layer may optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0098] In some embodiments of this application, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments of this application, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0100] In some embodiments of this application, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0101] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0102] In some embodiments of this application, the material of the separator may include at least one of glass fiber, non-woven fabric, polyolefin membrane, aromatic polyamide membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane.

[0103] In some embodiments of this application, the thickness of the separator can be 10μm-12μm, for example, 10μm, 11μm, 12μm, etc.

[0104] The embodiments of the present invention are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known to others. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0105] Example 1

[0106] 1. Preparation of positive electrode sheet

[0107] Lithium iron phosphate (purchased from Defang Nano), carbon black, carbon nanotubes, and polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone solvent at a mass ratio of 94.5:3.5:0.5:1.5 to obtain a positive electrode active material slurry. The positive electrode active material slurry was uniformly coated on the surface of the positive electrode current collector aluminum foil. After drying, rolling, baking, slitting, and spot welding of tabs, a positive electrode sheet was obtained with a total thickness of 90 μm.

[0108] 2. Preparation of negative electrode sheet

[0109] The negative electrode active material graphite (purchased from Jiangxi Zichen), conductive agent carbon black, binder polyvinylidene fluoride and sodium carboxymethyl cellulose were dispersed in deionized water at a mass ratio of 94.5:2:2:1.5 and stirred evenly to obtain a negative electrode active material layer slurry. The negative electrode active material layer slurry was uniformly coated on the surface of the negative electrode current collector copper foil. After drying, rolling, baking, slitting and spot welding of electrode tabs, a negative electrode sheet was obtained with a total thickness of 128 μm.

[0110] 3. Preparation of electrolyte

[0111] EC and EMC were mixed at a mass ratio of 3:7. After mixing, lithium salt, the first additive, and the second additive were added according to the molar concentration and mass fraction of each component, and the mixture was stirred evenly to obtain the electrolyte. The organic solvents included ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 3:7; the lithium salt included LiPF6, and the molar concentration of lithium salt in the electrolyte was 1 mol / L; the first additive included tetravinylsilane at 0.2% of the total mass of the electrolyte; the second additive was compound 1-1, with a mass of 0.5% of the total mass of the electrolyte.

[0112] 4. Separating membrane

[0113] A 10μm polyethylene film was used as the separator.

[0114] 5. Lithium-ion battery manufacturing

[0115] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain a bare cell. The tabs are welded on, and the bare cell is placed in an outer package. The electrolyte prepared above is injected into the dried cell. The cells are then encapsulated, left to stand, formed, and shaped to complete the preparation of the lithium-ion battery.

[0116] The lithium-ion battery preparation methods of Examples 2-31 and Comparative Examples 1-5 are the same as those of Example 1, except that the composition of additives in the electrolyte is different, as shown in Table 1.

[0117] Table 1

[0118] Example 32

[0119] The lithium-ion battery was prepared using essentially the same method as in Example 1, except that the positive electrode active material in this example was selected from lithium cobalt oxide (LiCoO2) and purchased from Xiamen Tungsten New Energy Materials Co., Ltd.

[0120] The lithium-ion battery preparation methods in Examples 33-34 are basically the same as those in Example 32, except that the positive electrode active materials of the lithium-ion batteries are different. Both were purchased from Xiamen Tungsten New Energy Materials Co., Ltd., as shown in Table 2.

[0121] The lithium-ion battery preparation methods in Examples 35-37 are basically the same as those in Examples 32-34, except that the composition of additives in the electrolyte is different, as shown in Table 2.

[0122] Table 2

[0123] Example 38

[0124] 1. Preparation of positive electrode sheet

[0125] 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 are dispersed in N-methylpyrrolidone solvent at a mass ratio of 94.5:3.5:0.5:1.5 to obtain a positive electrode active material layer slurry. The positive electrode active material layer slurry is uniformly coated on the surface of the positive electrode current collector aluminum foil. After drying, rolling, baking, slitting, and spot welding of electrode tabs, a positive electrode sheet is obtained with a total thickness of 90 μm.

[0126] 2. Preparation of negative electrode sheet

[0127] The negative electrode active material graphite (purchased from Jiangxi Zichen), conductive agent carbon black, binder polyvinylidene fluoride and sodium carboxymethyl cellulose were dispersed in deionized water at a mass ratio of 94.5:2:2:1.5 and stirred evenly to obtain a negative electrode active material layer slurry. The negative electrode active material layer slurry was uniformly coated on the surface of the negative electrode current collector copper foil. After drying, rolling, baking, slitting and spot welding of electrode tabs, a negative electrode sheet was obtained with a total thickness of 128 μm.

[0128] 3. Preparation of electrolyte

[0129] EC and EMC were mixed at a mass ratio of 3:7. After mixing, sodium salt, first additive, and second additive were added according to the molar concentration and mass fraction of each component, and the mixture was stirred until homogeneous to obtain the electrolyte. The organic solvents included ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a mass ratio of 3:7; the sodium salt included NaPF6, and the molar concentration of sodium in the electrolyte was 1 mol / L; the first additive included tetravinylsilane at 0.2% of the total mass of the electrolyte; and the second additive was compound 1-1, with a mass of 0.5% of the total mass of the electrolyte.

[0130] 4. Separating membrane

[0131] A 10μm polyethylene film was used as the separator.

[0132] 5. Sodium-ion battery preparation

[0133] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain a bare cell. The tabs are welded on, and the bare cell is placed in an outer package. The electrolyte prepared above is injected into the dried cell. The cell is then encapsulated, left to stand, formed, and shaped to complete the preparation of the sodium-ion battery.

[0134] The sodium-ion batteries in Examples 39-45 are prepared in the same way as those in Example 38, except that the composition of the additives in the electrolyte is different, as shown in Table 3.

[0135] Table 3

[0136] The high-temperature storage performance and high-temperature cycling performance of the secondary batteries obtained in Examples 1-31, 32-37 and Comparative Examples 1-5 were characterized, and the characterization results are shown in Tables 4 and 5.

[0137] 1. At 45℃, the battery is cycled 800 times to test its capacity retention.

[0138] At 45℃, charge to 3.65V with 1C constant current and constant voltage, let stand for 5 minutes, and then discharge to 2.0V with 1C constant current. After 800 cycles, calculate the capacity retention rate. The calculation method is: capacity retention rate (%) = (1500th discharge capacity / 1st discharge capacity) × 100%, see Table 3.

[0139] 2. High-temperature storage performance test:

[0140] Expansion rate test: At 25℃, charge to 3.65V with 1C constant current and constant voltage, measure the initial thickness of the lithium-ion battery at this time, and then store at 60℃ for 30 days to test the thickness of the lithium-ion battery. Calculate the battery expansion rate according to the formula: Expansion rate (%) = (Thickness after storage - Initial thickness) / Initial thickness × 100%.

[0141] Cyclic performance test: After high-temperature storage, the lithium-ion battery is discharged to 2.0V at 1C, and the capacity retention rate of the battery is measured and calculated. The calculation formula is as follows: Capacity retention rate (%) = Retained capacity / Initial capacity × 100%.

[0142] DCR growth rate test: Secondary battery DC resistance (DCR) test: DCR test before storage: At an ambient temperature of 25℃, the battery is charged at a constant current of 1.0C to 3.65V, then at a constant voltage of 3.65V until the cutoff current is 0.05C. The battery is then left to rest for 30 minutes, followed by discharge at 1.0C for 30 minutes (adjusted to 50% SOC). The ending voltage V1 is recorded. After resting for 1 hour, the battery is discharged at 2.0C for 10 seconds, and the ending voltage V2 is recorded. The DCR1 before storage is (V1-V2) / (2.0C-1.0C). Storage at 60℃ for 30 minutes... The DCR test was conducted as follows: At an ambient temperature of 25°C, the stored battery was charged at a constant current of 1.0C to 3.65V, then at a constant voltage of 3.65V until the cutoff current reached 0.05C. The battery was then left to rest for 30 minutes, followed by a discharge at 1.0C for 30 minutes (adjusted to 50% SOC). The ending voltage V3 was recorded. After resting for 1 hour, the battery was discharged at 2.0C for 10 seconds, and the ending voltage V4 was recorded. The DCR2 after storage was calculated as (V3-V4) / (2.0C-1.0C); the DCR growth rate was calculated as (DCR2-DCR1) / DCR1×100%.

[0143] Table 4

[0144] Table 5

[0145] As shown in Table 4, in Examples 1-10 of this application, the first and second additives work together to reduce battery gas production, improve the battery's high-temperature cycle performance and high-temperature storage performance, and suppress the increase in battery impedance (DCR). When the third additive is added, in Examples 11-31, it can be seen that the improvement in the battery's high-temperature cycle performance and high-temperature storage performance is more significant, and the effect of suppressing the increase in battery impedance (DCR) is also more pronounced.

[0146] Compared to Examples 11-31, Comparative Examples 1-4 did not simultaneously add the first additive, the second additive, and the third additive. The resulting batteries exhibited significantly lower gas generation performance, high-temperature cycle performance, and high-temperature storage performance, and a significantly higher impedance (DCR). This demonstrates that the electrolyte additives proposed in this application enable the first additive, the second additive, and the third additive to work together. Adding them together to a secondary battery can reduce battery gas generation, improve the battery's high-temperature cycle performance and high-temperature storage performance, and suppress the increase in battery impedance.

[0147] The high-temperature cycling performance, high-temperature storage gas generation performance, capacity retention rate and DCR growth rate of the batteries in the other embodiments of Examples 1-5 are significantly better than those of Example 5. This is because the amount of the first additive added in Example 5 (5%) is higher than that in the other embodiments. The possible reason is that the excessive use of the first additive causes the additive itself to continuously undergo film decomposition, resulting in an increase in impedance and the occurrence of side reactions that generate gas, thereby degrading the battery performance.

[0148] The batteries in the other embodiments of Examples 6-10 have significantly better high-temperature cycling performance, high-temperature storage gas generation performance, capacity retention rate and DCR growth rate than those in Example 10. This is because the amount of the second additive added in Example 10 (5%) is higher than in the other embodiments. The possible reason is that the use of excessive second additive will lead to an increase in electrolyte viscosity, and the additive itself will undergo side reactions to generate gas, thereby degrading battery performance.

[0149] The batteries in the other embodiments of Examples 11-16 have significantly better high-temperature cycling performance, high-temperature storage gas generation performance, capacity retention rate and DCR growth rate than those in Example 16. This is because the amount of the third additive added in Example 16 (5%) is higher than in the other embodiments. The possible reason is that the use of excessive third additive will lead to its own decomposition, generating HF and thus degrading the cell performance.

[0150] As shown in Table 5, adding either the first and second additives, or the first, second, and third additives, to different lithium-ion battery systems can reduce battery gas production, improve high-temperature cycle performance and high-temperature storage performance, and suppress battery impedance growth. The combination of the first, second, and third additives shows better results, which is consistent with the conclusions for battery systems using lithium iron phosphate as the positive electrode active material. This indicates that the electrolyte additives of this application are applicable to different lithium-ion battery systems.

[0151] The high-temperature storage performance and high-temperature cycling performance of the secondary batteries obtained in Examples 38-45 were characterized, and the characterization results are shown in Table 6.

[0152] 1. At 45℃, the battery is cycled 300 times to test its capacity retention.

[0153] The capacity retention rate of sodium-ion batteries after 300 cycles at high temperature (45℃) under 1C charge-discharge conditions was tested. Sodium-ion batteries with their capacity determined by the upper clamp were placed in a preset temperature environment and charged at a constant current and constant voltage of 1C to the upper limit cutoff voltage (cutoff current was 0.05C). Then, they were discharged at a constant current of 1C / 1C to the lower limit cutoff voltage. This cycle was repeated, and the discharge capacity of the battery in the first and last cycles was recorded. The capacity retention rate was calculated using the following formula: Capacity retention rate = (Discharge capacity in the last cycle / Discharge capacity in the first cycle) × 100%.

[0154] 2. High-temperature storage performance test:

[0155] Expansion rate test: At 25℃, charge the sodium-ion battery to the upper limit cutoff voltage using 1C constant current and constant voltage, measure the initial thickness of the sodium-ion battery at this time, and then store it at 60℃ for 30 days to test the thickness of the sodium-ion battery. Calculate the battery expansion rate according to the formula: Expansion rate (%) = (Thickness after storage - Initial thickness) / Initial thickness × 100%.

[0156] Cycle performance test: After the sodium-ion battery with the upper clamp has been capacity-graded, the clamp is removed and the battery is placed in a 25°C environment. It is charged at a constant current and constant voltage of 1C to the upper limit cutoff voltage, with a cutoff current of 0.05C. Then, it is discharged at a constant current of 1C to the lower limit cutoff voltage, and the discharge capacity at this point is recorded as C0. The battery is then charged again at a constant current and constant voltage of 1C to the upper limit cutoff voltage, with a cutoff current of 0.05C. The fully charged battery is then placed in a 60°C constant temperature oven for 30 days. After that, the battery is removed and placed in a 25°C environment for 2 hours. Then, it is discharged at a constant current of 1C to the lower limit cutoff voltage in a 25°C environment, and the discharge capacity at this point is recorded as C1. Capacity retention rate = (C1 / C0) × 100%.

[0157] DCR growth rate test: Test DCR1 before storage and DCR2 after storage. Calculate the DCR growth rate according to the formula (DCR2-DCR1) / DCR1×100%.

[0158] Table 6

[0159] As shown in Table 6, in Examples 38-45 of this application, compared to adding only the first and second additives, the addition of the third additive can more significantly reduce battery gas production, improve the high-temperature cycle performance and high-temperature storage performance of the battery, and suppress the increase in battery impedance (DCR). Therefore, the electrolyte additives in the embodiments of this application are also applicable to sodium-ion batteries, and can improve the high-temperature cycle performance and high-temperature storage performance of sodium-ion batteries, and suppress the increase in battery impedance (DCR).

[0160] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0161] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. An electrolyte additive, characterized in that, The electrolyte additive includes a first additive and a second additive, wherein the first additive includes a compound containing silicon and an unsaturated hydrocarbon group, and the second additive includes a compound represented by Formula 1: Among them, X1, X2, X3 and X4 are independently selected from N or CH; R is selected from 5-6 aryl, 5-6 aryl substituted with R0, 5-6 heteroaryl, 5-6 heteroaryl substituted with R0, and C. 1-8 Alkyl groups, C substituted with R0 1-8 Alkyl, C 2-8 Alkenyl, C substituted with R0 2-8 alkenyl, C 0-8 Alkyl silyl or C substituted with R0 0-8 Alkylsilyl; R0 is selected from C 1-6 Alkyl, C 1-6 Alkoxy or halogen.

2. The electrolyte additive according to claim 1, characterized in that, The mass ratio of the first additive to the second additive is (1-50):(1-50).

3. The electrolyte additive according to claim 1 or 2, characterized in that, The first additive includes at least one of the compounds shown in Formula 2 and Formula 3: Among them, R1, R2, R3, R4, R5, R6, R7, R8, R9 and R 10 Each of the following is independently selected from H, C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkoxy, and C2-C5 alkenyloxy, and R1, R2, R3, R4, R5, R6, R7, R8, R9 and R 10 At least one of them is an unsaturated hydrocarbon group.

4. The electrolyte additive according to any one of claims 1-3, characterized in that, The first additive includes at least one of tetravinylsilane, tetramethyldivinyldisiloxane, vinyltrimethoxysilane, and allyloxytrimethylsilane.

5. The electrolyte additive according to any one of claims 1-4, characterized in that, The second additive includes at least one of the following substances:

6. The electrolyte additive according to any one of claims 1-5, characterized in that, Further includes: The third additive includes fluoroethylene carbonate.

7. The electrolyte additive according to claim 6, characterized in that, The mass ratio of the first additive, the second additive, and the third additive is (1-50):(1-50):(2-50).

8. An electrolyte, characterized in that, The electrolyte additive includes any one of claims 1-7.

9. The electrolyte according to claim 8, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the first additive is 0.1%-5%, optionally 0.1%-3%; And / or, based on the total mass of the electrolyte, the mass percentage of the second additive is 0.1%-5%, optionally 0.1%-3%; And / or, based on the total mass of the electrolyte, the mass percentage of the third additive is 0.2%-5%, optionally 0.5%-2%.

10. A battery, characterized in that, The electrolyte includes any one of claims 8-9.

11. The battery according to claim 10, characterized in that, The battery includes a positive electrode active material, which includes 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 battery includes a positive electrode active material, and the positive electrode active material includes Na X1 M1O2, Na X2 at least one of M2[M3(CN)6], NaFePO4, Na3V2(PO4)3, Na2M4P2O7, Na2Fe2(SO4)3, and Na2M4(SO4)2·2H2O, where 0 < x1 ≤ 1, M1 includes at least one of Ni, Co, Mn, Fe, and Cu, 0 < x2 < 6, M2 includes at least one of Ni, Fe, and Mn, M3 includes at least one of Fe and Mn, and M4 includes at least one of Fe, Co, Mn, and Cu.

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