Electrolyte, battery, battery pack and electric equipment

Abstract

The invention provides an electrolyte, a battery, a battery pack and electric equipment. The electrolyte comprises a first additive and a second additive, wherein the first additive is a bicyclic compound, each cyclic group of the bicyclic compound comprises a sulfur-containing functional group, and the second additive comprises a silane group. According to the design of the electrolyte, the first additive and the second additive are introduced, and under the synergistic cooperation of the first additive and the second additive, the battery impedance is reduced, and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to an electrolyte, in particular to an electrolyte, a battery, a battery pack and an electrical device, belonging to the field of secondary batteries. Background Art

[0002] Secondary batteries (also known as rechargeable batteries) occupy an important position in the field of modern energy storage due to their reusability, high energy density and environmental protection characteristics.

[0003] However, current secondary batteries still have certain drawbacks in practical applications. For one thing, limitations in battery components, such as electrode materials and electrolytes, result in high impedance, which in turn leads to energy loss and limits the battery's power output. Furthermore, after repeated charge and discharge cycles, the capacity of secondary batteries gradually decays, resulting in a short cycle life, which limits the battery's service life and economic viability.

[0004] Therefore, developing a battery system that can reduce battery impedance and increase battery life has become an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] The present invention provides an electrolyte. The electrolyte is designed by introducing a first additive and a second additive. Through the synergistic cooperation of the first additive and the second additive, the battery impedance is reduced and the battery cycle life is increased.

[0006] The present invention also provides a battery, which comprises the above electrolyte and thus has good charge and discharge efficiency and cycle stability.

[0007] The present invention also provides a battery pack, which includes the battery and has excellent performance.

[0008] The present invention also provides an electrical device, which includes the battery or battery pack and has good performance.

[0009] In one aspect, the present invention provides an electrolyte comprising a first additive and a second additive;

[0010] The first additive is a bicyclic compound, each cyclic group of the bicyclic compound includes a sulfur-containing functional group, and the second additive includes a silane group.

[0011] In the electrolyte as described above, the sulfur-containing functional group includes at least one of a sulfonyl group, a sulfinyl group, and a thioether group.

[0012] In the electrolyte described above, the first additive is selected from at least one of the compounds represented by Formula 1-1, Formula 1-2, Formula 1-3, and Formula 1-4:

[0013]

[0014] Wherein, X, X', X1, X1', X2, X2', and X3 are each independently selected from a sulfonyl group, a sulfinyl group, and a thioether group;

[0015] R1, R2, R5, R6, R7, R8, R 11 、R 12 , R1', R2', R5', R6', R7', R8', R 11 '、R 12 'Each independently selected from one of oxygen atoms, C1-C10 alkylene, and C1-C10 alkoxyalkylene; R3, R4, R 10 、R 13 、R 14 Each independently selected from a hydrogen atom, a C1-C10 alkyl group, and a halogen atom; R 15 An alkylene group selected from C0 to C10.

[0016] In the electrolyte as described above, the bicyclic compound is a five-membered ring or a six-membered ring.

[0017] In the electrolyte described above, the second additive is selected from at least one of the compounds represented by Formula 2-1, Formula 2-2, and Formula 2-3:

[0018]

[0019] Wherein, Y is selected from at least one of a phosphate group, a phosphite group, a borane group, and a nitrogen group; Y' is selected from at least one of an oxygen group and a C1-C10 alkoxyalkylene group; and Y" is selected from at least one of a C1-C10 alkyl group, a C1-C10 alkoxy group, and a C1-C10 haloalkyl group.

[0020] In the electrolyte as described above, the mass ratio of the first additive to the second additive is 1:(0.5-2).

[0021] In the electrolyte as described above, the mass percentage of the first additive in the electrolyte is 0.1% to 4%.

[0022] In the electrolyte as described above, the mass percentage of the second additive in the electrolyte is 0.1% to 4%.

[0023] In another aspect, the present invention provides a battery comprising the electrolyte described above.

[0024] In another aspect, the present invention provides a battery pack comprising the battery described above.

[0025] In another aspect, the present invention provides an electrical device comprising the battery or the battery pack as described above.

[0026] The electrolyte provided by the present invention includes a first additive having a specific group and a second additive having a methylsilane group. Under the synergistic effect of the first additive and the second additive, it can not only remove H2O and HF, but also produce components such as Si(CH3)3 and SiOH on the positive and negative electrode sides, and can form a densified SEI film, inhibit the decomposition of the electrolyte during the cycle, improve the interface dynamics, promote the electrode capacity, reduce the risk of metal dissolution, and significantly extend the cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 TOF-SIMS characterization of the SEI films of the positive and negative electrodes of the battery prepared with the electrolyte provided in Example 1 of the present invention after 50 cycles;

[0028] Figure 2 TOF-SIMS characterization of the SEI films of the positive and negative electrodes of the battery prepared with the electrolyte provided in Comparative Example 1 of the present invention after 50 cycles;

[0029] Figure 3 TOF-SIMS characterization of the SEI films of the positive and negative electrodes of the battery prepared with the electrolyte provided in Comparative Example 2 of the present invention after 50 cycles. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0031] During the actual use of secondary batteries, electrolyte decomposition or side reactions in electrode materials can generate non-conductive byproducts, which in turn increase impedance and affect ion transmission efficiency. Furthermore, side reactions between electrode materials and electrolytes can generate gas, which accelerates electrode material degradation and interfacial side reactions, thereby shortening the battery's cycle life.

[0032] By using more stable electrolytes and inhibiting electrolyte decomposition, gas production can be effectively reduced and battery performance and safety can be improved.

[0033] In one aspect, the present invention provides an electrolyte comprising a first additive and a second additive;

[0034] The first additive is a bicyclic compound, each cyclic group of the bicyclic compound includes a sulfur-containing functional group, and the second additive includes a silane group.

[0035] Specifically, the bicyclic compound in the electrolyte provided by the present invention refers to a first additive comprising two cyclic groups, wherein a cyclic group refers to a chemical group having a cyclic structure formed by atoms connected by covalent bonds. The two cyclic groups can be connected by bridging or direct bonding. Each cyclic group including a sulfur-containing functional group means that each cyclic group includes a functional group composed of heteroatom sulfur atoms. The bicyclic compound provides more cross-linking sites during the formation of the SEI film, can form a complex polymer network structure, and improve the stability of the SEI film.

[0036] The present invention does not limit the specific type of the sulfur-containing functional group, and the sulfur-containing functional group can be selected according to actual needs. For example, in one embodiment, the sulfur-containing functional group includes at least one of a sulfonyl group, a sulfinyl group, and a thioether group.

[0037] For example, in one embodiment, both cyclic groups of the first additive include sulfonyl groups. In another embodiment, one of the two cyclic groups of the first additive includes a sulfinyl group, and the other includes a thioether group.

[0038] The second additive of the present invention includes silane groups, wherein the present invention does not limit the number of silane groups. For example, the number of silane groups in the second additive is 1 to 3.

[0039] The specific type of silane group may be selected according to actual needs, such as a methylsilane group.

[0040] The electrolyte provided by the present invention can be used in battery systems to significantly improve the battery's cycling stability and reduce battery impedance. This is because during the process of forming the SEI film, the first additive decomposes to form a more complex cross-linked polymer network structure between molecules or with cyclic solvent molecules, resulting in a more stable and dense SEI film polymer layer. In addition, the sulfur-containing functional groups in the first additive and the silane groups in the second additive can undergo free radical reactions to form stable silicon-oxygen bonds or other derivatives, further stabilizing the SEI film, homogenizing ion deposition, reducing interfacial impedance, and improving the battery's cycling performance.

[0041] Furthermore, in a specific embodiment, the first additive is selected from at least one of the compounds represented by Formula 1-1, Formula 1-2, Formula 1-3, and Formula 1-4:

[0042]

[0043] Wherein, X, X', X1, X1', X2, X2', and X3 are each independently selected from a sulfonyl group, a sulfinyl group, and a thioether group;

[0044] R1, R2, R5, R6, R7, R8, R 11 、R 12 , R1', R2', R5', R6', R7', R8', R 11 '、R 12 'Each independently selected from one of oxygen atoms, C1-C10 alkylene, and C1-C10 alkoxyalkylene; R3, R4, R 10 、R 13 、R 14 Each independently selected from a hydrogen atom, a C1-C10 alkyl group, and a halogen atom; R 15 An alkylene group selected from C0 to C10.

[0045] Among them, when R 15 When the alkyl group is selected from C0, that is, there is no alkylene group, it means that the cyclic group including X3 and the cyclic group including X3' are directly bonded.

[0046] Furthermore, in one embodiment, the bicyclic compound is a five-membered ring or a six-membered ring.

[0047] Specifically, the number N of ring elements in the two cyclic groups in the bicyclic compound can be the same or different. For example, in one embodiment, one cyclic group in the bicyclic compound is a five-membered ring and the other cyclic group is a six-membered ring; in another embodiment, both cyclic groups in the bicyclic compound are five-membered rings.

[0048] Furthermore, in a specific embodiment, the second additive is selected from at least one of the compounds represented by Formula 2-1, Formula 2-2, and Formula 2-3:

[0049]

[0050] Wherein, Y is selected from at least one of a phosphate group, a phosphite group, a borane group, and a nitrogen group; Y' is selected from at least one of an oxygen group and a C1-C10 alkoxyalkylene group; and Y" is selected from at least one of a C1-C10 alkyl group, a C1-C10 alkoxy group, and a C1-C10 haloalkyl group.

[0051] A haloalkyl group is an organic compound in which one or more hydrogen atoms in an alkyl group (a chain or cyclic group composed of carbon and hydrogen) are replaced by a halogen (fluorine, chlorine, bromine, or iodine). During the formation of the SEI film, the haloalkyl group decomposes to form the inorganic component NaX (X = F, Cl, Br, I), which enhances the thermal and electrochemical stability of the SEI film and ensures long-term cycling performance.

[0052] Furthermore, in a specific embodiment, the mass ratio of the first additive to the second additive is 1:(0.5-2).

[0053] In detail, the mass ratio of the first additive to the second additive includes but is not limited to 1:0.5, 1:0.6, 1:0.8, 1:1.0, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2 or a range between any two thereof.

[0054] When the mass ratio of the first additive to the second additive is within the above range, the first additive forms a stable solid electrolyte interface film (SEI film) on the electrode surface through its sulfur-containing functional groups (such as sulfonyl groups and sulfinyl groups), thereby inhibiting the decomposition of the electrolyte. The second additive can remove trace amounts of H2O and HF in the electrolyte through silane groups (such as methylsilane groups), promote the density of the film, and at the same time, the silane groups react with the above sulfur-containing functional groups to form a complex cross-linked network structure, thereby improving the density and stability of the SEI film. The appropriate mass ratio enables the two additives to work synergistically, significantly improving the overall chemical stability of the electrolyte, and enabling the battery to maintain a high capacity retention rate and low capacity attenuation during long-term cycling.

[0055] Furthermore, in a specific embodiment, the mass percentage of the first additive in the electrolyte is 0.1% to 4%.

[0056] In detail, the mass percentage of the first additive in the electrolyte includes but is not limited to 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or a range between any two thereof.

[0057] When the first additive is present in the electrolyte at a concentration of 0.1% to 4% by weight, it not only forms an effective protective layer but also creates an interfacial film of suitable thickness, ensuring internal resistance within a suitable range and improving battery performance. Furthermore, within this concentration range, the first additive improves the electrolyte's ionic conductivity and the compatibility of the electrode / electrolyte interface without significantly increasing the electrolyte's viscosity.

[0058] In another specific embodiment, the mass percentage of the second additive in the electrolyte is 0.1% to 4%.

[0059] In detail, the mass percentage of the second additive in the electrolyte includes but is not limited to 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or a range between any two thereof.

[0060] Silane groups have the function of removing H2O and HF, which can reduce the risk of electrolyte deterioration and battery gas production. An addition amount of 0.1% to 4% is sufficient to play the role of removing H2O and HF, while avoiding the negative impact of excessive addition on other properties of the electrolyte. Moreover, the second additive can form a dense and stable protective film on the surface of the electrode, inhibiting the side reactions between the electrolyte and the electrode material, and reducing the corrosion and degradation of the electrode material. Additives within this content range can effectively improve the interface stability, while avoiding excessive addition that causes the interface film to be too thick, thereby increasing the internal resistance of the battery.

[0061] It is understandable that the electrolyte provided by the present invention may further include an electrolyte salt and a solvent in addition to the first additive and the second additive mentioned above.

[0062] The present invention does not limit the battery system to which the electrolyte is applicable. The electrolyte provided by the present invention can be used in lithium-ion batteries, sodium-ion batteries or other battery systems.

[0063] In a specific embodiment, the electrolyte provided by the present invention is used for a sodium ion battery, and the electrolyte salt is a sodium salt, such as sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), sodium bis(fluorosulfonyl)imide (NaFSI), sodium trifluoromethanesulfonate (NaCF3SO3), sodium difluorooxalatoborate (NaDFOB), sodium bisoxalatoborate (NaBOB), sodium hexafluoroarsenate (NaAsF6), sodium tetrafluoroborate (NaBF4), sodium nitrate (NaNO3), and sodium chloride (NaCl). One or more.

[0064] In another specific embodiment, the electrolyte provided by the present invention is used for a lithium ion battery, and the electrolyte salt is a lithium salt, such as lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium difluorophosphate (LiPO2F2), lithium nitrate (LiNO3), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), and lithium perchlorate (LiClO4). One or more.

[0065] The present invention is not limited to the specific type of solvent, and common solvents in the art can be selected, such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, dimethyl sulfoxide, tetrahydrofuran, acetonitrile, N,N-dimethylformamide, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and one or more of bis(2,2,2-trifluoroethyl) ether.

[0066] In order to improve the comprehensive performance of the electrolyte, conventional additives may also be added to the electrolyte, such as one or more of fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, ethoxy (pentafluoro) cyclotriphosphazene, N,N-dimethyltrifluoroacetamide, trimethoxyboroxine, biphenyl, succinonitrile, adiponitrile, and 1,2,3-tris(2-cyano)propane.

[0067] The mass percentages of the electrolyte salt, solvent, and conventional additives in the electrolyte can be adjusted according to actual needs. For example, in one specific embodiment, the mass percentage of the electrolyte salt in the electrolyte is 1% to 20%, the mass percentage of the solvent in the electrolyte is 67% to 98.8%, and the mass percentage of the conventional additives in the electrolyte is 0 to 5%.

[0068] In another aspect, the present invention provides a battery comprising the electrolyte described above.

[0069] Since the battery provided by the present invention includes the above electrolyte, it has low impedance and good cycle performance during actual use.

[0070] It is understood that the battery provided by the present invention includes, in addition to the above-mentioned solid electrolyte, a positive electrode sheet, a negative electrode sheet, and a separator. During the battery's charge and discharge process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte acts as an ion conductor between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, primarily to prevent short circuits between the positive and negative electrodes while allowing ions to pass through.

[0071] The present invention does not strictly limit the positive electrode active material used in the positive electrode sheet. Taking lithium-ion batteries as an example, commonly used positive electrode active materials can be selected, such as at least one composite oxide of lithium and a metal selected from the group consisting of cobalt, manganese, nickel, and combinations thereof. Specifically, the active material can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate (LFP), lithium nickel manganese oxide, and lithium-rich manganese-based materials.

[0072] Taking sodium ion batteries as an example, the positive electrode active material can be at least one of layered metal oxides (NaCoO2, NaNiO2 and NaFeO2, etc.), polyanion compounds (sodium iron phosphate (NaFePO4), sodium vanadium phosphate (Na3V2(PO4)3), etc.), and Prussian blue materials.

[0073] The present invention is not strictly limited to the negative electrode active material in the negative electrode sheet, and can be at least one of the currently commonly used negative electrode active materials, such as graphite, hard carbon, soft carbon, mesophase carbon microbeads, silicon-based negative electrode materials (mainly including silicon monoxide, silicon-carbon negative electrode), tin-based negative electrode materials (mainly including tin, tin alloy), etc.

[0074] Another aspect of the present invention provides a battery pack comprising the battery as described above, thereby having good ion conductivity and cycle stability.

[0075] In another aspect, the present invention provides an electrical device comprising the battery or the battery pack as described above.

[0076] The present invention is not limited to the specific types of electrical equipment, and can include large energy storage cabinets, electric vehicles, mobile phones, smart homes, robots, drones, electronic cigarettes, speakers, and any other equipment that requires batteries to power it.

[0077] The electrical equipment provided by the present invention includes the above-mentioned battery or battery pack, and thus has good performance.

[0078] Hereinafter, the electrolyte provided by the present invention will be described in detail through specific examples.

[0079] Example 1

[0080] The preparation method of the electrolyte provided in this embodiment includes the following steps:

[0081] First, propylene carbonate (PC), ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a mass ratio of 20:10:70 to prepare an electrolyte mother liquor, and the water in the mother liquor is removed by molecular sieve. 1 mol / L sodium hexafluorophosphate is added in batches to the dry and anhydrous electrolyte mother liquor while stirring. After cooling, 2 wt% of a first additive (4,4'-di(1,3,2-dioxathiolane)]-2,2'-dioxide, BDTD) and 1 wt% of a second additive (tris(trimethylsilyl) phosphate, TMSP) are added. The mass ratio of the first additive to the second additive is 1:0.5, and a clear, colorless and transparent electrolyte is finally obtained.

[0082] Example 2

[0083] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0084] The first additive is replaced by bis(vinyl disulfate) (BTDT), and the mass ratio of the first additive to the second additive is 1:0.5.

[0085] Example 3

[0086] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0087] The first additive was replaced with dihydro-1,3,2-dioxazolo[1,3,2]dioxane-2,2,5,5-tetraoxide (DDDT, CAS: 496-45-7), and the mass ratio of the first additive to the second additive was 1:0.5.

[0088] Example 4

[0089] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0090] The second additive was replaced with tris(trimethylsilyl)borate (TMSB), and the mass ratio of the first additive to the second additive was 1:0.5.

[0091] Example 5

[0092] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0093] The second additive was replaced with (trifluoromethyl)trimethylsilane (TFMTMS), and the mass ratio of the first additive to the second additive was 1:0.5.

[0094] Example 6

[0095] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0096] The mass percentage of the first additive is 4%, and the mass ratio of the first additive to the second additive is 1:0.25.

[0097] Example 7

[0098] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0099] The mass percentage of the second additive is 4%, and the mass ratio of the first additive to the second additive is 1:2.

[0100] Example 8

[0101] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0102] The mass percentage content of the first additive is 0.1%, the mass percentage content of the second additive is 4%, and the mass ratio of the first additive to the second additive is 1:40.

[0103] Example 9

[0104] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0105] The mass percentage of the first additive is 4.5%, and the mass ratio of the first additive to the second additive is 1:0.22.

[0106] Example 10

[0107] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0108] The mass percentage of the second additive is 4.5%, and the mass ratio of the first additive to the second additive is 1:2.5.

[0109] Example 11

[0110] The preparation method of the electrolyte provided in this embodiment is basically the same as that in Example 1, except that:

[0111] The mass percentage of the second additive is 0.1%, and the mass ratio of the first additive to the second additive is 1:0.05.

[0112] Comparative Example 1

[0113] The preparation method of the electrolyte provided in this comparative example comprises the following steps:

[0114] First, PC, EC and DEC were mixed in a mass ratio of 20:10:70 to prepare an electrolyte mother liquor. The water in the mother liquor was removed with a molecular sieve. 1 mol / L sodium hexafluorophosphate was added in batches to the dry and anhydrous electrolyte mother liquor while stirring. After cooling, 2 wt% 4,4'-di(1,3,2-dioxathiolane)-2,2'-dioxide (BDTD) was added to finally obtain a clear, colorless and transparent electrolyte.

[0115] Comparative Example 2

[0116] The preparation method of the electrolyte provided in this comparative example is basically the same as that of comparative example 1, except that:

[0117] 2 wt% BDTD was replaced with 1 wt% tris(trimethylsilyl)phosphate (TMSP).

[0118] Comparative Example 3

[0119] The preparation method of the electrolyte provided in this comparative example is basically the same as that in Example 1, except that:

[0120] BDTD was replaced by diethyl sulfate (DTD).

[0121] Comparative Example 4

[0122] The preparation method of the electrolyte provided in this comparative example is basically the same as that of Example 1, except that the first additive and the second additive are not included.

[0123] The electrolytes provided in all the examples and comparative examples were used in sequence to prepare a battery, comprising the following steps:

[0124] The positive electrode material sodium iron pyrophosphate (NFPP), polyvinylidene fluoride (PVDF) binder, and acetylene black (SuperP) conductive agent are mixed in a ratio of 8:1:1, and a certain amount of N-methylpyrrolidone (NMP) is added to prepare the positive electrode slurry. The solid content of the slurry is adjusted to about 50%. After degassing and sieving, the slurry is evenly coated on the surface of aluminum foil, and then dried, rolled, and cut to obtain the positive electrode sheet.

[0125] Hard carbon negative electrode material (HC), styrene-butadiene rubber (SBR) / carboxymethyl cellulose (CMC) composite binder and SuperP conductive agent are mixed in a ratio of 8:1:1 and added with deionized water to prepare negative electrode slurry. The solid content is adjusted to about 45%. After degassing and sieving, it is evenly coated on the surface of aluminum foil. The negative electrode sheet is obtained after drying, rolling and cutting.

[0126] The negative electrode sheet, separator, and positive electrode sheet are stacked in sequence to form a battery cell, which is then encapsulated in an aluminum-plastic shell. After the battery cell is baked to remove moisture, the prepared electrolyte is injected into the soft-pack battery. After aging, formation, aging, and capacity separation, a soft-pack sodium-ion battery is obtained.

[0127] 1. DC impedance test

[0128] The battery was adjusted to 50% SOC at a current of 0.2C according to the battery capacity. The positive and negative ears of the battery were clamped respectively using a battery internal resistance tester to read the battery DC impedance test results. The specific test results are shown in Table 1.

[0129] 2. Cycle capacity retention test

[0130] The test temperature is 25℃, and the battery is charged to 3.6V at a constant current of 1C, then charged to 3.6V at a constant voltage of 0.05C, and then discharged to 1.5V at a discharge rate of 1C. Repeat this charge and discharge cycle 500 times to measure the discharge capacity Q1 at the first cycle and the discharge capacity Q at the 500th cycle. 500The capacity retention rate Q after 500 cycles is calculated according to the following formula: Capacity retention rate Q = Q 500 / Q1*100%, see Table 1 for specific test results.

[0131] Table 1

[0132]

[0133] After 50 cycles of the batteries prepared with the electrolytes provided in Example 1, Comparative Example 1, and Comparative Example 2, the batteries were disassembled and the positive and negative SEI films were characterized by TOF-SIMS. The C2HO signal in TOF-SIMS characterization is generally considered to be a decomposition product of carbonate solvents. The stronger the signal intensity, the higher the product content. Figure 1-Figure 3 The TOF-SIMS characterization diagrams of Example 1 and Comparative Examples 1-2 are respectively. It can be seen that when TMSP or BDTD is used alone, the signal intensity of C2HO on the negative electrode side is strong, indicating that the electrolyte continues to decompose during the cycle; however, when the two are used together, the signal intensity of C2HO on the negative electrode side is significantly weakened, indicating that the combination of TMSP and BDTD can significantly inhibit the decomposition of the electrolyte and improve the cycle stability, which is consistent with the cycle data results in Table 1.

[0134] By comparing the impedance and cycle performance of batteries prepared with the electrolytes provided in Example 1, Example 6, Example 8 and Example 9, it can be seen that the electrolyte provided by Example 1 has the best cycle performance, and Example 1, Example 6 and Example 8 are all better than Example 9, indicating that the effect is better when the mass percentage of the first additive in the electrolyte is 0.1% to 4%.

[0135] By comparing the impedance and cycle performance of batteries prepared with the electrolytes provided in Example 1, Example 7, and Example 10, the electrolyte provided in Example 1 has the best cycle performance, and both Example 1 and Example 7 are better than Example 10, indicating that the effect is better when the mass percentage of the second additive in the electrolyte is 0.1% to 4%.

[0136] The performance of batteries prepared with the electrolytes provided in Examples 1-11 is superior to that of Comparative Examples 1-3. This is because during the formation of the SEI film by the first additive, a more complex cross-linked polymer network structure is formed between molecules or with cyclic solvent molecules during the decomposition process. The SEI film polymer layer formed by the bicyclic compound provided by the first additive is more stable and dense, while the monocyclic sulfate compound can only form a low-molecular-weight chain polymer network structure, resulting in relatively poor SEI film stability. In addition, the first additive can also react with the second additive compound containing methyl silane groups to produce free radicals, further stabilizing the SEI film. Therefore, when the first additive and the second additive are used together, the stability of the SEI film is significantly improved, and the decomposition process of the electrolyte can be effectively inhibited, achieving lower interfacial impedance and better cycle performance.

[0137] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that including a first additive and a second additive; The first additive is a bicyclic compound, each cyclic group of the bicyclic compound includes a sulfur-containing functional group, and the second additive includes a silane group.

2. The electrolyte according to claim 1, characterized in that The sulfur-containing functional group includes at least one of a sulfonyl group, a sulfinyl group, and a thioether group.

3. The electrolyte according to claim 1 or 2, characterized in that The first additive is selected from at least one of the compounds represented by Formula 1-1, Formula 1-2, Formula 1-3, and Formula 1-4: Wherein, X, X', X1, X1', X2, X2', and X3 are each independently selected from a sulfonyl group, a sulfinyl group, and a thioether group; R1, R2, R5, R6, R7, R8, R 11 、R 12 , R1', R2', R5', R6', R7', R8', R 11 '、R 12 'Each independently selected from one of oxygen atoms, C1-C10 alkylene, and C1-C10 alkoxyalkylene; R3, R4, R 10 、R 13 、R 14 Each independently selected from a hydrogen atom, a C1-C10 alkyl group, and a halogen atom; R 15 An alkylene group selected from C0 to C10.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The bicyclic compound is a five-membered ring or a six-membered ring.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The second additive is selected from at least one of the compounds represented by Formula 2-1, Formula 2-2, and Formula 2-3: Wherein, Y is selected from at least one of a phosphate group, a phosphite group, a borane group, and a nitrogen group; Y' is selected from at least one of an oxygen group and a C1-C10 alkoxyalkylene group; and Y" is selected from at least one of a C1-C10 alkyl group, a C1-C10 alkoxy group, and a C1-C10 haloalkyl group.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The mass ratio of the first additive to the second additive is 1:(0.5-2).

7. The electrolyte according to any one of claims 1 to 6, characterized in that The mass percentage of the first additive in the electrolyte is 0.1% to 4%.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The mass percentage of the second additive in the electrolyte is 0.1% to 4%.

9. A battery, characterized in that: The electrolyte comprises the electrolyte according to any one of claims 1 to 8.

10. A battery pack, characterized in that: A battery comprising the battery of claim 9.

11. An electrical device, characterized in that: Comprising the battery according to claim 9 or the battery pack according to claim 10.

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