Additive for electrolyte, electrolyte containing additive and lithium ion battery

Abstract

The invention provides an additive for an electrolyte, the electrolyte containing the additive and a lithium ion battery. The additive for the electrolyte provided by the invention has a structure as shown in a formula (a), wherein R1, R2, R3, R4, R5, RA, RB, RC, RD and RE are respectively and independently selected from at least one of H, F, NH2, CN, C1-C10 alkyl, fluorine-containing alkyl and nitrogen-containing alkyl. The additive for the electrolyte provided by the invention not only can block a path (reaction formula: anhydride + H2O-carboxylic acid) for hydrolyzing LiPF6 to generate HF and inhibit the dissolution of transition metal by utilizing the reaction between an anhydride group (-CO-O-CO-) and trace water in the electrolyte, but also can generate sacrificial oxidation on the surface of a positive electrode, form a stable CEI layer and inhibit the solvent decomposition, so that the electrolyte can be used for the lithium ion battery. And thus, the structural stability and safety of the positive electrode material in the high-voltage circulation process are improved. Formula (a)

Description

Technical Field

[0001] This application relates to the field of electrolyte additives, and more specifically, to an electrolyte additive, an electrolyte containing the additive, and a lithium-ion battery. Background Technology

[0002] Electrolyte engineering is the simplest and most cost-effective strategy to change the stability of the electrolyte and electrodes by using additives to adjust the composition of the electrolyte.

[0003] Lithium-ion batteries (LIBs) are the core power source for portable electronic devices, electric vehicles, and large-scale energy storage systems, and improving their performance and lifespan has always been a goal pursued by the research and industry communities. Especially for electric vehicle applications, the demand for high-voltage, high-energy-density batteries is increasing, and nickel-manganese-cobalt (NMC) cathode materials have become one of the preferred choices for high-voltage lithium-ion batteries due to their high specific capacity and relatively stable performance. However, NMC cathode materials face several challenges during high-voltage cycling, including transition metal dissolution, cathode structure degradation, negative electrode interface side reactions, and lithium dendrite formation. These problems can significantly reduce the cycle life and safety of the battery.

[0004] To address these issues, researchers have explored various methods, such as cathode surface coating, elemental doping, and improved electrolyte formulations. Cathode surface coating materials (e.g., ZnO, AlF3) can enhance the interfacial stability of cathode materials, but these methods are often complex and costly. Elemental doping can improve the structural stability of cathode materials, but it also cannot completely solve the interfacial problems. In contrast, methods to improve battery performance through electrolyte engineering have attracted considerable attention due to their ease of operation and cost-effectiveness. The introduction of electrolyte additives, such as boron- and phosphorus-containing compounds, has been shown to improve the stability of the electrode / electrolyte interface, but they each have limitations. For example, an excessively thick interfacial layer can hinder lithium-ion transport, or it may have limited buffering capacity for LiPF6 hydrolysis products, failing to completely prevent the dissolution of transition metals.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The main objective of this application is to provide an electrolyte additive, an electrolyte containing the additive, and a lithium-ion battery, in order to solve the problems in the prior art where the introduction of boron- and phosphorus-containing compounds into the electrolyte to improve the stability of the electrode / electrolyte interface has limitations, hindering lithium-ion transport or having limited buffering capacity against LiPF6 hydrolysis products.

[0007] To achieve the above objectives, according to one aspect of this application, an electrolyte additive is provided, which has the structure shown in formula (a) below:

[0008] Equation (a)

[0009] R1, R2, R3, R4, R5, R A R B R C R D R E Each is independently selected from at least one of H, F, NH2, CN, C1-C10 alkyl, fluorinated alkyl, and nitrogen-containing alkyl; wherein the fluorinated alkyl is a substituted C1-C10 alkyl, and at least one hydrogen atom is substituted by F; the general formula of the nitrogen-containing alkyl is R6-NR7 (R8), where R6 is a direct bond or a C1-C6 alkylene, and R7 and R8 are each independently H or C1-C6 alkyl.

[0010] Furthermore, R1, R2, R3, R4, R5, R A R B R C R D R E Each is independently selected from at least one of H, F, NH2, CN, C1-C6 alkyl, fluorinated alkyl, and nitrogen-containing alkyl; wherein the fluorinated alkyl is a substituted C1-C6 alkyl, and at least one hydrogen atom is substituted by F; the general formula of the nitrogen-containing alkyl is R6-NR7 (R8), where R6 is a direct bond or methylene, and R7 and R8 are each independently H or C1-C3 alkyl.

[0011] Furthermore, the fluorinated alkyl group is CF3, CH2CF3, CF2CF3, CH2CH2CF3, CH(CF3)2, CF(CF3)2, or C(CF3)3.

[0012] Furthermore, the nitrogen-containing alkyl group is N(CH3)2, N(CH2CH3)2, NHCH3, NHCH2CH3, CH2N(CH3)2, or CH2N(CH2CH3)2.

[0013] Furthermore, the electrolyte additive is selected from at least one of the following compounds:

[0014] , , , , , , .

[0015] In a second aspect of this application, an electrolyte is also provided, which includes a lithium salt, a solvent, and an additive. The additive includes the electrolyte additive provided in the first aspect above, and the mass content of the electrolyte additive is 0.3%-1%, preferably 0.4%-0.6%.

[0016] Furthermore, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium dioxoborate, lithium tetrafluoroborate, lithium hexachloroate, lithium bis(trifluoromethanesulfonyl)imide, lithium methanesulfonate, and lithium trifluoromethanesulfonate.

[0017] Furthermore, the electrolyte contains 15-35% lithium salt by mass.

[0018] Furthermore, the solvent is an organic solvent, including at least one of ester solvents, amine solvents, sulfone solvents, and nitrile solvents.

[0019] Furthermore, the ester solvent includes at least one of ethylene carbonate, propylene carbonate, butene carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propyl acetate.

[0020] Furthermore, the amine solvents include at least one of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide.

[0021] Furthermore, sulfone solvents include at least one of dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, and dipropyl sulfone.

[0022] Furthermore, nitrile solvents include at least one of acetonitrile, butadiene nitrile, adiponitrile, and glutaronitrile.

[0023] Furthermore, the electrolyte also includes conventional additives, including at least one of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and trimethylsilyl phosphate.

[0024] Furthermore, the electrolyte includes vinylene carbonate, and the mass content of vinylene carbonate is 2%-5%.

[0025] Furthermore, the electrolyte includes fluoroethylene carbonate, and the mass content of fluoroethylene carbonate is 1%-2%.

[0026] Furthermore, the electrolyte includes 1,3-propanesulfonate lactone, and the mass content of 1,3-propanesulfonate lactone is 0.3%-1%.

[0027] Furthermore, the electrolyte includes trimethylsilyl phosphate, and the mass content of trimethylsilyl phosphate is 0.2%-0.5%.

[0028] According to a third aspect of this application, a lithium-ion battery is also provided, which includes the electrolyte additive provided in the first aspect or the electrolyte provided in the second aspect.

[0029] By applying the technical solution of this application, the electrolyte additive provided by this application can not only utilize the reaction of acid anhydride groups (-CO-O-CO-) with trace amounts of water in the electrolyte to block the pathway of LiPF6 hydrolysis to generate HF (reaction formula: acid anhydride + H2O → carboxylic acid) and inhibit the dissolution of transition metals, but also undergo sacrificial oxidation on the positive electrode surface to form a stable CEI layer, inhibiting solvent decomposition, thereby improving the structural stability and safety of the positive electrode material during high-voltage cycling. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0031] As analyzed in the background section of this application, cathode materials face various challenges in terms of stability and safety during high-voltage cycling, making the improvement of the structural stability of cathode materials through electrolyte engineering a significant focus. Currently, adding boron- or phosphorus-containing compounds as additives to the electrolyte has been shown to improve the stability of the electrode / electrolyte interface, but limitations exist. For example, an excessively thick interface layer can hinder lithium-ion transport, or it has limited buffering capacity for LiPF6 hydrolysis products, failing to completely prevent the dissolution of transition metals. To address at least one of the aforementioned problems, this application provides an electrolyte additive, an electrolyte comprising the additive, and a lithium-ion battery.

[0032] In a first typical embodiment of this application, an electrolyte additive is provided, having the structure shown in formula (a):

[0033] Equation (a)

[0034] Among them, R1, R2, R3, R4, R5, R A R B R C R D R E Each is independently selected from at least one of H, F, NH2, CN, C1-C10 alkyl, fluorinated alkyl, and nitrogen-containing alkyl; wherein the fluorinated alkyl is a substituted C1-C10 alkyl, and at least one hydrogen atom is substituted by F; the general formula of the nitrogen-containing alkyl is R6-NR7 (R8), where R6 is a direct bond or a C1-C6 alkylene, and R7 and R8 are each independently H or C1-C4 alkyl.

[0035] In this application, the term "C1-C10 alkyl" means having 1 to 10 alkyl groups, which are straight chains or branched chains with one or more branches, such as butyl, such as n-butyl, sec-butyl, isobutyl, tert-butyl; propyl, such as n-propyl or isopropyl; ethyl or methyl; and more particularly, methyl, isopropyl or tert-butyl.

[0036] Furthermore, the term "C1-C10 alkyl" means that the group has 1-10 carbon atoms. Unless otherwise specified, the number of carbon atoms generally does not include the number of carbon atoms of the substituents, and the range of carbon atoms can be extended from the lower limit to the upper limit. For example, C1-C10 means that the number of carbon atoms can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0037] The electrolyte additive provided in this application can not only utilize the reaction of acid anhydride groups (-CO-O-CO-) with trace amounts of water in the electrolyte to block the pathway of LiPF6 hydrolysis to generate HF (reaction formula: acid anhydride + H2O → carboxylic acid) and inhibit the dissolution of transition metals, but also undergo sacrificial oxidation on the cathode surface to form a stable CEI layer, inhibiting solvent decomposition, thereby improving the structural stability and safety of the cathode material during high-voltage cycling.

[0038] When R1, R2, R3, R4, R5, R A R B R C R D R E When at least one of the additives is selected from F or fluorinated alkyl groups, the above-mentioned electrolyte additives can decompose to generate LiF during charge and discharge, forming a LiF-rich interface, significantly increasing the LiF content of the CEI / SEI film, thereby significantly improving the mechanical strength of the CEI / SEI film and effectively suppressing interface rupture caused by volume changes in the electrode material; at the same time, taking advantage of LiF's large band gap and high electronic conductivity (~1), The characteristics of L (S / cm) and a wide electrochemical window (~0-5.5 V) promote L Rapid transport, suppression of electron tunneling (reducing side reactions), and optimization of electrode / electrolyte interface kinetics.

[0039] When R1, R2, R3, R4, R5, R A R B R C R D R E When at least one is selected from NH2 or a nitrogen-containing alkyl group, the nitrogen atom interacts with a transition metal ion (such as Ni) through the lone pair electrons of the nitrogen atom. / Mn Formation of coordination bonds and formation of Li3N / LiN-rich compounds x O yThe conductive interface layer (CEI) effectively suppresses the dissolution of transition metals in the cathode material under high voltage, improves the structural stability of the cathode material during cycling, and extends the cycle life of the battery.

[0040] In some embodiments of this application, R1, R2, R3, R4, R5, R A R B R C R D R E Each is independently selected from at least one of H, F, NH2, CN, C1-C6 alkyl, fluorinated alkyl, and nitrogen-containing alkyl; wherein the fluorinated alkyl is a substituted C1-C6 alkyl, and at least one hydrogen atom is replaced by F; the general formula of the nitrogen-containing alkyl is R6-NR7 (R8), where R6 is a direct bond or methylene, and R7 and R8 are independently H or C1-C3 alkyl, which is more conducive to utilizing the reaction efficiency of the anhydride group (-CO-O-CO-) with trace amounts of water in the electrolyte, further blocking the pathway of LiPF6 hydrolysis to generate HF, forming a more stable CEI layer, inhibiting solvent decomposition, and further improving the stability of the electrode / electrolyte interface.

[0041] In some embodiments of this application, when the fluorinated alkyl group is CF3, CH2CF3, CF2CF3, CH2CH2CF3, CH(CF3)2, CF(CF3)2, or C(CF3)3, the above-mentioned electrolyte additives are more conducive to the decomposition and generation of LiF during charge and discharge, increasing the LiF content of the CEI / SEI film, further improving the mechanical strength of the EI / SEI film, more effectively suppressing the volume change of the electrode material, improving the cycle stability of the electrode material, and also more conducive to promoting Li + Rapid transport further optimizes the kinetics of the electrode / electrolyte interface.

[0042] In some embodiments of this application, when the nitrogen-containing alkyl group is N(CH3)2, N(CH2CH3)2, NHCH3, NHCH2CH3, CH2N(CH3)2, or CH2N(CH2CH3)2, the above-mentioned electrolyte additives are more conducive to the interaction of nitrogen atom lone pair electrons with transition metal ions (such as Ni). / Mn This forms coordination bonds, creating a conductive interface layer (CEI) with high Li3N content. This further suppresses the dissolution of transition metals in the cathode material under high voltage, improves the structural stability of the cathode material during charge and discharge, and extends the cycle life of the battery.

[0043] In some embodiments of this application, the electrolyte additive is selected from at least one of the following compounds:

[0044] , , , , , , .

[0045] When the electrolyte additive is selected from any one or more of the above compounds, it not only improves the reaction efficiency between the additive and trace amounts of water in the electrolyte, further blocking the hydrolysis of LiPF6 to generate HF; but also promotes the preferential oxidation on the positive electrode surface to form a more stable CEI layer, inhibiting solvent decomposition, further improving the stability of the electrode / electrolyte interface, and thus more effectively improving the cycle stability and safety of the positive electrode material during charge and discharge.

[0046] In a second typical embodiment of this application, an electrolyte is provided, which includes a lithium salt, a solvent and an additive. The additive includes the electrolyte additive provided in the first typical embodiment above, and the mass content of the electrolyte additive is 0.2%-1.5%.

[0047] The electrolyte provided in this application, by adding the electrolyte additives provided in the first typical embodiment, can not only utilize the anhydride groups (-CO-O-CO-) in the electrolyte additives to react with trace amounts of water in the electrolyte, blocking the pathway of LiPF6 hydrolysis to generate HF (reaction formula: anhydride + H2O → carboxylic acid), and inhibiting the dissolution of transition metals, but also utilize the electrolyte additives to undergo sacrificial oxidation on the positive electrode surface to form a stable CEI layer, inhibiting solvent decomposition, thereby improving the structural stability and safety of the positive electrode material during high-voltage cycling.

[0048] In the electrolyte provided in this application, the mass content of the electrolyte additive is 0.2%-1.5%, which is more conducive to improving the structural stability and safety of the cathode material during cycling. Specifically, in the electrolyte provided in this application, the mass content of the electrolyte additive is 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any range of two values.

[0049] In the electrolyte provided in this application, if the mass content of the electrolyte additive is too low, it is not conducive to sufficient reaction with trace water in the electrolyte, and thus not conducive to fully blocking the pathway of LiPF6 hydrolysis to HF. If the mass content of the electrolyte additive is too high, not only will the cost increase, but excessive fluoride may also generate additional HF byproducts, corroding the electrode and leading to a decline in electrical performance.

[0050] In some preferred embodiments of this application, the above-mentioned electrolyte additive has a mass content of 0.4%-1% in the electrolyte, which is more conducive to improving the structural stability and safety of the cathode material during high-voltage cycling.

[0051] In some embodiments of this application, the lithium salt is a lithium salt commonly used in the art, including but not limited to any one or more of lithium hexafluorophosphate, lithium dioxoborate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium methanesulfonate, and lithium trifluoromethanesulfonate.

[0052] In some embodiments of this application, the lithium salt content in the electrolyte is 15%-35% by mass, which is more conducive to improving the lithium-ion transport performance of the lithium-ion battery. Specifically, the lithium salt content is 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, or any range of two values.

[0053] In some specific embodiments of this application, the lithium salt in the electrolyte includes lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonate)imide, and the mass ratio of the two is (10-20):(10-20), which is more conducive to improving the electron transport properties of the electrolyte.

[0054] Specifically, in the electrolyte, the mass ratio of lithium hexafluorophosphate to lithium bis(trifluoromethanesulfonate)imine is 10:10, 10:12, 10:15, 10:18, 10:20, 11.5:14, 11.5:15, 11.5:18, 11.5:20, 15:10, 15:12, 15:18, 15:20, 18:10, 18:12, 18:15, 18:20, or any range of two values.

[0055] In the electrolyte provided in this application, the solvent is a commonly used organic solvent in the art, including but not limited to at least one of ester solvents, amine solvents, sulfone solvents and nitrile solvents.

[0056] In some specific embodiments of this application, the ester solvent is a commonly used ester solvent in the art, including but not limited to any one or more mixed solvents selected from ethylene carbonate, propylene carbonate, butene carbonate, γ-butyrolactone, dipropyl carbonate, dimethyl sulfite, vinylene carbonate, methyl propyl carbonate, ethyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propyl acetate.

[0057] In some specific embodiments of this application, the amine solvent is a commonly used amine solvent in the art, including but not limited to any one or more mixed solvents of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide.

[0058] In some embodiments of this application, the sulfone solvent is a commonly used sulfone solvent in the art, including but not limited to any one or more mixed solvents selected from dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, and dipropyl sulfone.

[0059] In some specific embodiments of this application, the nitrile solvent is a commonly used nitrile solvent in the art, including but not limited to any one or more mixed solvents of acetonitrile, succinic anhydride, adiponitrile, and glutaronitrile.

[0060] In some embodiments of this application, the solvent is a mixed solution of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate, with a volume ratio of 1:1:(1~3), which is more conducive to improving the wettability of the electrolyte and the stability during the cycling process. Specifically, the volume ratio of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate in the solvent is 1:1:1, 1:1:2, 1:1:1:3, or any range of two values.

[0061] In some embodiments of this application, the electrolyte also includes conventional additives, which are additives for electrolytes different from those provided in the first typical embodiment, including but not limited to any one or more of vinylene carbonate, fluoroethylene carbonate, 1,3-propanesulfonate lactone, and trimethylsilyl phosphate.

[0062] In some specific embodiments of this application, the electrolyte includes vinylene carbonate, and the mass content of vinylene carbonate is 2%-5%. Specifically, the mass content of vinylene carbonate in the electrolyte is 2%, 2.5%, 3%, 4%, 5%, or any two of these values.

[0063] In some specific embodiments of this application, the electrolyte includes fluoroethylene carbonate, and the mass content of fluoroethylene carbonate is 1%-2%. Specifically, the mass content of fluoroethylene carbonate in the electrolyte is 1%, 1.2%, 1.5%, 1.8%, 2%, or any combination of two values.

[0064] In some embodiments of this application, the electrolyte includes 1,3-propanesulfonate lactone, and the mass content of 1,3-propanesulfonate lactone is 0.3%-1%. Specifically, the mass content of 1,3-propanesulfonate lactone in the electrolyte is 0.3%, 0.5%, 0.6%, 0.8%, 1%, or any combination of two values.

[0065] In some embodiments of this application, the electrolyte comprises trimethylsilyl phosphate, and the mass content of trimethylsilyl phosphate is 0.2%-0.5%. Specifically, the mass content of trimethylsilyl phosphate is 0.2%, 0.3%, 0.4%, 0.5%, or any range of two values.

[0066] In a third typical embodiment of this application, a lithium-ion battery is provided, which includes an electrolyte, the electrolyte being the electrolyte provided in the second typical embodiment described above.

[0067] The lithium-ion battery provided in this application, by using an electrolyte containing the electrolyte additive provided in the first typical embodiment, can not only utilize the anhydride groups (-CO-O-CO-) in the electrolyte additive to react with trace amounts of water in the electrolyte, blocking the pathway of LiPF6 hydrolysis to generate HF (reaction formula: anhydride + H2O → carboxylic acid), and inhibiting the dissolution of transition metals, but also utilize the electrolyte additive to undergo sacrificial oxidation on the positive electrode surface to form a stable CEI layer, inhibiting solvent decomposition, thereby improving the structural stability and safety of the positive electrode material during high-voltage cycling.

[0068] In some embodiments of this application, the lithium-ion battery further includes a positive electrode material, which is a nickel-cobalt-manganese positive electrode material, to further improve the battery capacity.

[0069] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0070] Example 1

[0071] This application provides an electrolyte comprising a lithium salt, a solvent, an electrolyte additive, and conventional additives. The electrolyte additive is a compound represented by formula (A) and has a mass content of 0.5% in the electrolyte. The lithium salt comprises lithium hexafluorophosphate (LiPF6) and lithium bis(trifluoromethanesulfonyl)imide (LiFSI), with lithium hexafluorophosphate comprising 11.5% of the electrolyte and lithium bis(trifluoromethanesulfonyl)imide comprising 14% of the electrolyte. The conventional additives include vinylene carbonate (VC), fluorine... The mixture comprises ethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), and trimethylsilyl phosphate (TMSP), wherein the mass percentages of ethylene carbonate are 3%, fluoroethylene carbonate is 1.2%, 1,3-propanesulfonate lactone is 0.5%, and trimethylsilyl phosphate is 0.3%; the solvent is a mixed solution of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:2.

[0072] Formula (A)

[0073] Example 2

[0074] The difference between this embodiment and Example 1 is that the mass content of the compound shown in formula (A) in the electrolyte is 0.4%.

[0075] Example 3

[0076] The difference between this embodiment and Example 1 is that the mass content of the compound shown in formula (A) in the electrolyte is 0.6%.

[0077] Example 4

[0078] The difference between this embodiment and Example 1 is that the mass content of the compound shown in formula (A) in the electrolyte is 0.3%.

[0079] Example 5

[0080] The difference between this embodiment and Example 1 is that the mass content of the compound shown in formula (A) in the electrolyte is 1%.

[0081] Example 6

[0082] The difference between this embodiment and Embodiment 1 is that the compound shown in Formula (A) is replaced by the compound shown in Formula (B).

[0083] Formula (B)

[0084] Example 7

[0085] The difference between this embodiment and Example 1 is that the compound shown in formula (A) is replaced by the compound shown in formula (C).

[0086] Formula (C)

[0087] Example 8

[0088] The difference between this embodiment and Embodiment 1 is that the compound shown in Formula (D) is replaced by the compound shown in Formula (D).

[0089] Equation (D)

[0090] Example 9

[0091] The difference between this embodiment and Example 1 is that the compound shown in Formula (A) is replaced by the compound shown in Formula (E).

[0092] Equation (E)

[0093] Example 10

[0094] The difference between this embodiment and Example 1 is that the compound shown in Formula (A) is replaced by the compound shown in Formula (F).

[0095] Formula (F)

[0096] Example 11

[0097] The difference between this embodiment and Embodiment 1 is that the compound shown in Formula (A) is replaced by the compound shown in Formula (G).

[0098] Formula (G)

[0099] Example 12

[0100] The difference between this embodiment and Example 1 is that the compound shown in formula (A) is replaced by the compound shown in formula (H).

[0101] Formula (H)

[0102] Example 13

[0103] The difference between this embodiment and Example 1 is that the compound shown in Formula (A) is replaced by the compound shown in Formula (I).

[0104] Formula (I)

[0105] Example 14

[0106] The difference between this embodiment and Example 1 is that the compound shown in formula (A) is replaced by the compound shown in formula (J).

[0107] Formula (J)

[0108] Comparative Example 1

[0109] The difference between this comparative example and Example 1 is that the compound shown in formula (A) was not added to the electrolyte.

[0110] Comparative Example 2

[0111] The difference between this comparative example and Example 1 is that the compound shown in formula (A) is replaced by the compound shown in formula (K).

[0112] Formula (K)

[0113] Comparative Example 3

[0114] The difference between this embodiment and Example 1 is that the mass content of the compound shown in formula (A) in the electrolyte is 2%.

[0115] Comparative Example 4

[0116] The difference between this embodiment and Example 1 is that the mass content of the compound shown in formula (A) in the electrolyte is 0.2%.

[0117] Test case

[0118] The electrolytes provided in the above embodiments and comparative examples were assembled into 5Ah soft-pack cells, and their electrochemical performance was tested. The results are shown in Table 1 below.

[0119] Among them, (1) the soft-pack battery cell includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte provided in the examples or comparative examples; wherein, the positive electrode sheet includes an aluminum foil and a positive active material layer attached to the surface of the aluminum foil, the positive active material layer includes a positive electrode material (NCM622), a positive electrode conductive agent (acetylene black) and a positive electrode binder (polyvinylidene fluoride), and the mass ratio of the three is 96:2:2; the separator is a polypropylene (PP) separator; the negative electrode sheet includes a copper foil and a negative active material layer attached to the surface of the copper foil, the negative active material layer includes a negative electrode material (artificial graphite), a negative electrode conductive agent (acetylene black), a negative electrode binder (styrene-butadiene rubber) and a thickener (sodium carboxymethyl cellulose), and the mass ratio of the four is 96:2:1:1.

[0120] The preparation process is as follows: the positive electrode, separator and negative electrode are wound together into a core, sealed with aluminum-plastic film and then baked to meet the requirements of electrode moisture content. After baking, the cell is injected with electrolyte and then subjected to standing, formation, capacity testing and aging processes to obtain the finished soft-pack cell. The core height of the soft-pack cell is 7.6cm and the thickness is 7.3mm.

[0121] (2) The specific steps of the cyclic test at room temperature (25℃) are as follows: At room temperature (25℃), charge the soft-pack battery cell at a constant current of 0.5C to 4.4V, then charge it at a constant current and voltage until the cutoff current is 0.05C, and let it stand for five minutes. Discharge it at a constant current of 0.5C to 2.8V, and record the first cycle discharge capacity. After 800 cycles of charging and discharging, record the discharge capacity after 800 cycles.

[0122] Based on the capacity measured at room temperature (25℃) during the first cycle and the capacity after 800 cycles, the capacity retention rate after 800 cycles at room temperature (25℃) was calculated.

[0123] (3) The specific steps of the high-temperature 45℃ cycle test are as follows: At room temperature of 45℃, charge the soft-pack battery cell at a constant current of 0.5C to 4.4V, then charge it at a constant current and constant voltage until the cutoff current is 0.05C, and let it stand for five minutes. Discharge it at a constant current of 0.5C to 2.8V, and record the first cycle discharge capacity. After 500 cycles of charging and discharging, record the discharge capacity after 500 cycles.

[0124] Based on the capacity measured at room temperature (45℃) during the first cycle and the capacity after 500 cycles, the capacity retention rate after 500 cycles at room temperature (25℃) was calculated.

[0125] (4) The test method for the retention rate and recovery rate of the lithium-ion battery after 30 days of storage at 60℃ is as follows: Under normal temperature (25℃) conditions, the soft-pack battery cell is charged and discharged at 0.5C / 0.5C (the discharge capacity is recorded as C0), and then the lithium-ion battery is charged at a constant current of 0.5C to 4.4V; the battery is placed in a 60℃ heat preservation box for 30 days, and after being taken out, it is cooled to normal temperature conditions and discharged at 0.5C to 3.0V (the discharge capacity is recorded as C1); finally, the soft-pack battery cell is charged and discharged at 0.5C / 0.5C at normal temperature (the discharge capacity is recorded as C2), and the capacity retention rate and capacity recovery rate of the lithium-ion battery under high temperature conditions are calculated using the following formulas: Capacity retention rate = (C1 / C0) × 100% Capacity recovery rate = (C2 / C0) × 100%.

[0126] Table 1

[0127]

[0128] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0129] As can be seen from the comparison of the data of Examples 1-14 and Comparative Examples 1-4 in Table 1, the electrolyte provided in this application, by adding an electrolyte additive with the structure shown in formula (a) and controlling its mass content to be 0.3%-1%, can not only utilize the anhydride group (-CO-O-CO-) in the electrolyte additive to react with trace amounts of water in the electrolyte, blocking the path of LiPF6 hydrolysis to generate HF (reaction formula: anhydride + H2O → carboxylic acid), and inhibiting the dissolution of transition metals, but also utilize the electrolyte additive to undergo sacrificial oxidation on the positive electrode surface to form a stable CEI layer, inhibiting solvent decomposition, thereby improving the structural stability and safety of the positive electrode material during high-voltage cycling.

[0130] A comparison of Examples 1-14 with Comparative Examples 1-2 shows that when no electrolyte additive of the structure shown in Formula (a) is added to the electrolyte, the structural stability and cycle stability of the electrolyte are significantly reduced.

[0131] A comparison of Examples 1-14 with Comparative Examples 3-4 shows that the electrolyte provided in this application, by controlling the mass content of the electrolyte additive in the structure shown in Formula (a) to be 0.3%-1%, is not only more conducive to reducing costs, but also more conducive to improving electrical performance.

[0132] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An additive for electrolytes, characterized in that, The electrolyte additive has the structure shown in formula (a): Equation (a) The R1, R2, R3, R4, R5, R A R B R C R D R E Each is independently selected from at least one of H, F, NH2, CN, C1-C10 alkyl, fluorinated alkyl, and nitrogen-containing alkyl; wherein the fluorinated alkyl is a substituted C1-C10 alkyl, and at least one hydrogen atom is substituted by F; the general formula of the nitrogen-containing alkyl is R6-NR7 (R8), where R6 is a direct bond or a C1-C6 alkylene bond, and R7 and R8 are each independently H or C1-C6 alkyl.

2. The electrolyte additive according to claim 1, characterized in that, The R1, R2, R3, R4, R5, R A R B R C R D R E Each is independently selected from at least one of H, F, NH2, CN, C1-C6 alkyl, fluorinated alkyl, and nitrogen-containing alkyl; wherein the fluorinated alkyl is a substituted C1-C6 alkyl, and at least one hydrogen atom is substituted by F; the general formula of the nitrogen-containing alkyl is R6-NR7 (R8), where R6 is a direct bond or methylene, and R7 and R8 are each independently H or C1-C3 alkyl.

3. The electrolyte additive according to claim 1 or 2, characterized in that, The fluorinated alkyl group is CF3, CH2CF3, CF2CF3, CH2CH2CF3, CH(CF3)2, CF(CF3)2, or C(CF3)3; And / or, the nitrogen-containing alkyl group is N(CH3)2, N(CH2CH3)2, NHCH3, NHCH2CH3, CH2N(CH3)2, or CH2N(CH2CH3)2.

4. The electrolyte additive according to claim 1, characterized in that, The electrolyte additive is selected from at least one of the following compounds: 、 、 、 、 、 、 。 5. An electrolyte, characterized in that, The electrolyte comprises lithium salt, solvent and additives, wherein the additives include the electrolyte additives according to any one of claims 1 to 4, and the mass content of the electrolyte additives is 0.3%-1%, preferably 0.4-0.6%.

6. The electrolyte according to claim 5, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium dioxoborate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium methanesulfonate, and lithium trifluoromethanesulfonate. And / or, the electrolyte contains 15-35% lithium salt by mass.

7. The electrolyte according to claim 5, characterized in that, The solvent is an organic solvent, which includes at least one of ester solvents, amine solvents, sulfone solvents, and nitrile solvents.

8. The electrolyte according to claim 7, characterized in that, The ester solvents include at least one of ethylene carbonate, propylene carbonate, butenyl carbonate, γ-butyrolactone, dipropyl carbonate, methyl propyl carbonate, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propyl acetate. And / or, the amine solvent includes at least one of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide; And / or, the sulfone solvents include at least one of dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, and dipropyl sulfone; And / or, the nitrile solvents include at least one of acetonitrile, succinic anhydride, adiponitrile, and glutaronitrile.

9. The electrolyte according to any one of claims 5 to 8, characterized in that, The electrolyte also includes conventional additives, which include at least one of vinylene carbonate, fluorovinyl carbonate, 1,3-propanesulfonate lactone, and trimethylsilyl phosphate. Preferably, the electrolyte comprises vinylene carbonate, and the mass content of vinylene carbonate is 2%-5%; Preferably, the electrolyte comprises fluoroethylene carbonate, and the mass content of fluoroethylene carbonate is 1%-2%; Preferably, the electrolyte comprises 1,3-propanesulfonate lactone, and the mass content of 1,3-propanesulfonate lactone is 0.3%-1%; Preferably, the electrolyte comprises trimethylsilyl phosphate, and the mass content of trimethylsilyl phosphate is 0.2%-0.5%.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte additive according to any one of claims 1 to 4 or the electrolyte according to any one of claims 5 to 9.

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