An electrolyte additive containing trithiane hexaoxide structure, electrolyte and lithium ion battery thereof

Abstract

The present invention provides an electrolyte additive containing a trithiane hexaoxide structure. The wetting additive described in the present invention comprises two characteristic groups, a non-polar trithiane group and a polar R group; the synergistic effect of the two groups can significantly reduce the surface tension of the battery cell, improve the wetting characteristics of the battery cell, and thus can match the high-density positive electrode sheet, which provides the necessary conditions for obtaining a high-energy-density lithium-ion battery. The trithiane group can form a sulfur-rich film on the surface of the battery cell. The film is tough and has high strength. It can block harmful reactions between the electrode sheet and the electrolyte during the cycle. Moreover, the film has high ion conductivity and will not hinder the conduction of lithium ions, significantly improving the first effect and cycle performance of the battery cell. A non-aqueous electrolyte containing a small amount of the additive of the present invention can significantly improve the wetting characteristics of the battery cell, and at the same time can form a tough film on the electrode surface to protect the electrode sheet and reduce side reactions.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to an electrolyte additive containing a trithiane hexaoxide structure, an electrolyte thereof, and a lithium ion battery. Background Art

[0002] With the increasing popularity of electronic products such as electric vehicles and portable devices, the demand for high-energy-density lithium-ion batteries is becoming increasingly urgent. This type of battery has broad application prospects in fields such as energy storage and aerospace, and how to increase the energy density of lithium-ion batteries has become a research focus for scholars.

[0003] Using positive and negative electrode materials with higher compaction density can maximize the space utilization of the battery. However, as the compaction density of the positive and negative electrode materials increases, the problem of difficulty in cell wetting arises. The use of conventional electrolytes will make it difficult for the electrode to absorb liquid and increase the wetting aging time, thereby lengthening the battery production cycle and reducing production efficiency. Poor consistency in electrode absorption will lead to deterioration of the performance of the problem battery cell and even cause lithium plating at the negative electrode, causing safety problems.

[0004] The essence of wetting additives is surfactants. Such wetting agents have the advantages of high surface activity, low flammability and high chemical stability. After adding wetting agents to the electrolyte, they can reduce the surface tension of the liquid, improve the wetting ability and penetration ability of the electrolyte to the electrode, thereby improving the electrochemical performance of the battery. The development of matching wetting electrolytes has broad market prospects.

[0005] Commonly used wetting additives have two mechanisms of action. One is to reduce the surface tension of the electrolyte and improve the wettability of the electrolyte by combining the polar groups of the electrolyte solvent with the non-polar groups of the electrode. This type of wetting improvement additive only has a good improvement effect on the wettability of the battery cell. It does not participate in the formation of the positive and negative electrode membrane structures during the cycle stage, and has limited effect on the electrochemical improvement of the battery cell, such as fluorobenzene and its derivatives.

[0006] The other type is an organic compound with a special structure and properties. This type of additive generally contains two groups with different properties. One end is a long-chain hydrophobic group or hydrophobic group. This hydrophobic group is generally a long-chain hydrocarbon, and sometimes also an organic fluorine, organic silicon, organic phosphorus, organic tin chain, etc.; the other end is a hydrophilic group or hydrophilic group, which ensures that the entire surfactant can be dissolved in water and has the necessary solubility. This type of wetting additive has a high film-forming impedance, increases the internal resistance of the battery cell, and is not conducive to the circulation. The addition amount is generally less than 0.5wt%.

[0007] Therefore, it is a problem to be solved to provide a battery additive that has good wetting performance on battery cells, can effectively improve the electrochemical performance of battery cells, and significantly improve the initial efficiency and cycle performance of battery cells. Summary of the Invention

[0008] In view of this, the technical problem to be solved by the present invention is to provide an electrolyte additive containing a trithiane hexaoxide structure, an electrolyte and a lithium-ion battery thereof. The electrolyte prepared by the battery additive provided by the present invention has good wetting performance on the battery cell, can effectively improve the electrochemical performance of the battery cell, and significantly improve the first efficiency and cycle performance of the battery cell.

[0009] The present invention provides an electrolyte additive containing a trithiane hexaoxide structure, which has a structure shown in Formula I:

[0010]

[0011] In formula I, 1≤n≤3, and R is a group having electron-withdrawing properties.

[0012] Preferably, R is selected from one of trifluoromethane, pentafluoroethane, cyano, nitro, amino, sulfonic acid, maleimide, vinyl or acetylene.

[0013] The present invention also provides a method for preparing the electrolyte additive, comprising the following steps:

[0014] In the presence of an inert gas and a catalyst, trithiane hexaoxide reacts with a compound having a structure represented by Formula II to obtain an electrolyte additive having a structure represented by Formula I;

[0015]

[0016] R is a group with electron-withdrawing properties, preferably one of trifluoromethane, pentafluoroethane, cyano, nitro, amino, sulfonic acid, maleimide, vinyl or acetylene.

[0017] Preferably, the molar ratio of trithiane hexaoxide to the compound having the structure represented by Formula II is (1-1.05):1.

[0018] Preferably, the reaction temperature is 60-80° C. and the reaction time is 8-12 h.

[0019] Preferably, the solution environment of the reaction is an N,N-dimethylamide solution of sodium methoxide, and the concentration of sodium methoxide is 0.5 to 1 mol / L.

[0020] The present invention also provides an electrolyte comprising a lithium salt, the electrolyte additive and an organic solvent, wherein the electrolyte additive accounts for 0.05% to 3% by mass of the electrode solution.

[0021] Preferably, the lithium salt includes a mixture of one or more of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium difluorooxalatoborate, and lithium bis(oxalatoborate), and the concentration of the lithium salt in the electrolyte is 0.5M to 2M.

[0022] Preferably, the organic solvent includes one or more of carbonate solvents, carboxylate solvents, amine solvents, sulfone solvents and nitrile solvents;

[0023] The carbonate solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, methyl propyl carbonate, butylene carbonate, methyl butyl carbonate, and dibutyl carbonate;

[0024] The carboxylate solvent includes one or more of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and methyl propionate;

[0025] The amine solvent includes one or more of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide;

[0026] The sulfone solvent includes one or more of dimethyl sulfide, dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, dipropyl sulfone, dimethyl sulfite, diethyl sulfite, and tetramethyl sulfoxide;

[0027] The nitrile solvent includes one or more of acetonitrile, succinonitrile, adiponitrile, 3-methoxypropionitrile, 3-ethoxypropionitrile, and 1,3,6-hexanetrinitrile.

[0028] The present invention also provides a lithium-ion battery comprising the above electrolyte.

[0029] Compared with the prior art, the present invention provides an electrolyte additive containing a trithiane hexaoxide structure. The wetting additive described in the present invention contains two characteristic groups, a non-polar trithiane group and a polar R group; the synergistic effect of the two groups can significantly reduce the surface tension of the battery cell, improve the wetting characteristics of the battery cell, and then match the high-density positive electrode sheet, which provides the necessary conditions for obtaining a high-energy density lithium-ion battery. The trithiane group can form a sulfur-rich film on the surface of the battery cell. The film is tough and has high strength. It can block the harmful reaction between the electrode sheet and the electrolyte during the cycle. Moreover, the ion conductivity of the film is high and will not hinder the conduction of lithium ions, significantly improving the first effect and cycle performance of the battery cell. The non-aqueous electrolyte containing a small amount of the additive of the present invention can significantly improve the wetting characteristics of the battery cell, and at the same time can form a tough film on the electrode surface to protect the electrode sheet and reduce side reactions. DETAILED DESCRIPTION

[0030] The present invention provides an electrolyte additive containing a trithiane hexaoxide structure, which has a structure shown in Formula I:

[0031]

[0032] In Formula I, 1≤n≤3, R is an electron-withdrawing group. Preferably, R is selected from one of trifluoromethane, pentafluoroethane, cyano, nitro, amino, sulfonic acid, maleimide, vinyl, or ethynyl.

[0033] In the present invention, 1≤n≤3, such as n is 1, 2 or 3. When n is greater than 3, the longer carbon chain will cause the electron-withdrawing properties of the R group to fail to act on trithiane hexaoxide, making it difficult to optimize the electron cloud distribution of trithiane hexaoxide and unable to further enhance the additive's ability to improve wetting.

[0034] The present invention selects a derivative of trithiane hexaoxide as an electrolyte additive. Trithiane hexaoxide is a symmetrical non-polar group, and the introduced R group is a polar group with electron-withdrawing ability. The combination of the polar group and the non-polar group reduces the surface tension of the electrolyte and improves the wetting effect. The properties of the surfactant are not only related to the size and shape of the non-polar group, but also mainly to the polar group. Trithiane hexaoxide (15.99*10 -24 cm 3 ) has a larger diameter than the benzene ring (10.40*10 -24 cm 3 ) has a larger polarizability, which makes trithiane hexaoxide less polar to polar groups, and the difference between the polar end and the non-polar end is more obvious, so it has a better wetting improvement effect than fluorobenzene and its derivatives.

[0035] The trithiane structure of the present invention can form a dense sulfur-containing film structure on the surface of the positive and negative electrodes, effectively protecting the active materials from corrosion by the electrolyte and significantly improving the initial efficiency and cycle stability of the battery cell, which is a feature not possessed by fluorobenzene and its derivative additives.

[0036] The present invention also provides a method for preparing the electrolyte additive, comprising the following steps:

[0037] In the presence of an inert gas and a catalyst, trithiane hexaoxide reacts with a compound having a structure represented by Formula II to obtain an electrolyte additive having a structure represented by Formula I;

[0038]

[0039] In formula II, 1≤n≤3, and R is selected from one of trifluoromethane, pentafluoroethane, cyano, nitro, amino, sulfonic acid, maleimide, vinyl or acetylene.

[0040] In the present invention, the chemical reaction formula of the above preparation method is as follows:

[0041]

[0042] Wherein, the inert gas is selected from one of nitrogen and argon.

[0043] The molar ratio of the trithiane hexaoxide to the compound having the structure represented by Formula II is (1-1.05):1, and can be 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, or any value between (1-1.05):1.

[0044] The reaction temperature is 60-80°C, which can be 60, 65, 70, 75, 80, or any value between 60-80°C; the reaction time is 8-12h, which can be 8, 9, 10, 11, 12, or any value between 8-12h.

[0045] The solution environment of the reaction is an N,N-dimethylamide solution of sodium methoxide, and the concentration of sodium methoxide is 0.5-1 mol / L, which can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any value between 0.5 and 1 mol / L.

[0046] The present invention also provides an electrolyte comprising a lithium salt, the above electrolyte additive, and an organic solvent. The electrolyte additive accounts for 0.05% to 3% by mass of the electrode solution, and may be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, or any value between 0.05% and 3%. Preferably, the electrolyte additive accounts for 0.1% to 1%.

[0047] The lithium salt includes a mixture of one or more of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium difluorooxalatoborate, and lithium bis(oxalatoborate). In the electrolyte, the concentration of the lithium salt is 0.5M to 2M, and can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or any value between 0.5M and 2M.

[0048] The organic solvent includes one or more of carbonate solvents, carboxylate solvents, amine solvents, sulfone solvents and nitrile solvents;

[0049] The carbonate solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, methyl propyl carbonate, butylene carbonate, methyl butyl carbonate, and dibutyl carbonate;

[0050] The carboxylate solvent includes one or more of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and methyl propionate;

[0051] The amine solvent includes one or more of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide;

[0052] The sulfone solvent includes one or more of dimethyl sulfide, dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, dipropyl sulfone, dimethyl sulfite, diethyl sulfite, and tetramethyl sulfoxide;

[0053] The nitrile solvent includes one or more of acetonitrile, succinonitrile, adiponitrile, 3-methoxypropionitrile, 3-ethoxypropionitrile, and 1,3,6-hexanetrinitrile.

[0054] The organic solvent accounts for 70% to 90% of the total mass of the electrolyte, and can be 70%, 75%, 80%, 85%, 90%, or any value between 70% and 90%.

[0055] The electrolyte provided by the present invention is a high-voltage electrolyte and is also a wetting electrolyte, which can significantly reduce the infiltration time of the electrolyte and has a certain improvement effect on the electrochemical performance of the battery cell.

[0056] The present invention also provides a lithium-ion battery comprising the above electrolyte, a positive electrode, a negative electrode and a separator.

[0057] Wherein, the positive electrode includes a positive electrode current collector and a positive electrode material layer arranged on the surface of the positive electrode current collector. The material of the positive electrode current collector is selected from aluminum, titanium or stainless steel. The positive electrode material layer includes a positive electrode active material, a conductive agent and a binder. The positive electrode active material includes lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), medium-high nickel ternary materials and composite positive electrode materials thereof. The conductive agent includes a carbon material, preferably one or more of carbon black, conductive polymer, acetylene black, carbon fiber, carbon nanotubes and graphite. The binder is selected from one or more of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), fluorine-based rubber, ethylene propylene diene monomer rubber and styrene butadiene rubber (SBR).

[0058] The negative electrode includes a negative electrode current collector and a negative electrode material layer on the surface of the negative electrode current collector. The negative electrode current collector is made of copper, nickel, or stainless steel. The negative electrode material layer includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes metallic lithium, a lithium-intercalated carbon material, or a lithium alloy. The conductive agent and binder used in the negative electrode are selected from the same types as those used in the positive electrode.

[0059] The isolation membrane is selected from polypropylene (PP), polyethylene (PE), a composite material of polypropylene (PP) and polyethylene (PE), glass fiber felt, and a composite membrane formed by welding or bonding a wettable polyolefin microporous membrane.

[0060] The wetting additive described in the present invention comprises two characteristic groups, a non-polar trithiane group and a polar R group; the synergistic effect of the two groups can significantly reduce the surface tension of the battery cell, improve the wetting characteristics of the battery cell, and thus can match the high-density positive electrode sheet, which provides the necessary conditions for obtaining a high-energy-density lithium-ion battery. The trithiane group can form a sulfur-rich film on the surface of the battery cell. The film is tough and has high strength. It can block harmful reactions between the electrode sheet and the electrolyte during the cycle. Moreover, the ion conductivity of the film is high and will not hinder the conduction of lithium ions, significantly improving the first effect and cycle performance of the battery cell. A non-aqueous electrolyte containing a small amount of the additive of the present invention can significantly improve the wetting characteristics of the battery cell, and at the same time can form a tough film on the electrode surface to protect the electrode sheet and reduce side reactions.

[0061] In order to further understand the present invention, the electrolyte additive containing trithiane hexaoxide structure, the electrolyte and the lithium ion battery provided by the present invention are described below with reference to the examples. The protection scope of the present invention is not limited by the following examples.

[0062] Example 1:

[0063] 0.1 mol of trithiane hexaoxide and 0.1 mol of 3-chloropropionitrile were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 1 mol / L) and stirred at 60°C for 8 h under an argon atmosphere. After the reaction was complete, the mixed solution was separated by flash chromatography to obtain compound A. GC-MS (m / z): calculated for C6H9O6NS3[M+1] + , 286.96, found287.32.

[0064]

[0065] In a glove box, 30w% EC, 30w% DMC, and 26w% EMC were mixed to form a uniform solution. 13w% LiPF6 was added to the mixed solution and stirred until fully dissolved to form a mixed salt solution. 1w% Compound A was further added to the mixed salt solution, and the resulting mixed solution was used as the electrolyte. The resulting electrolyte was then subjected to a wetting test.

[0066] Example 2:

[0067] 0.1 mol of trithiane hexaoxide and 0.1 mol of ethylchloroamine were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 0.6 mol / L) and stirred at 65°C under argon atmosphere for 8 h. After the reaction was complete, the mixed solution was separated by flash chromatography to obtain compound B. GC-MS (m / z): calculated for C4H9NO6S3[M+1] + ,262.96,found263.30.

[0068]

[0069] In a glove box, 30w% EC, 30.5w% DMC, and 26w% EMC were stirred evenly to form a mixed solution; 13w% LiPF6 was added to the mixed solution and stirred to fully dissolve to obtain a mixed salt solution; 0.5w% compound B was further added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte.

[0070] Example 3:

[0071] 0.1 mol of trithiane hexaoxide and 0.101 mol of 2-chloroethylsulfonic acid were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 1 mol / L) and stirred at 80°C for 8 h under argon atmosphere. After the reaction was completed, the mixed solution was separated by flash chromatography to obtain compound C. GC-MS (m / z): calcd. for C5H 10 O9S4[M+1] + , 341.92, found342.37.

[0072]

[0073] In a glove box, 30w% EC, 30.9w% DMC, and 26w% EMC were stirred evenly to form a mixed solution; 13w% LiPF6 was added to the mixed solution and stirred to fully dissolve to obtain a mixed salt solution; 0.1w% compound C was further added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte.

[0074] Example 4:

[0075] 0.105 mol of trithiane hexaoxide and 0.105 mol of chlorotrifluoroethane were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 1 mol / L) and stirred at 60°C for 8 h under a nitrogen atmosphere. After the reaction was complete, the mixed solution was separated by flash chromatography to obtain compound D. GC-MS (m / z): calculated for C5H7F3O6S3[M+1] + , 315.94, found 316.28.

[0076]

[0077] In a glove box, 30w% EC, 30.6w% DMC, and 26w% EMC were stirred to form a mixed solution; 13w% LiPF6 was added to the mixed solution and stirred to fully dissolve to obtain a mixed salt solution; 0.2w% of structural formula D and 0.2w% of structural formula A were further added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte.

[0078] Example 5:

[0079] 0.101 mol of trithiane hexaoxide and 0.1 mol of chloropentafluoropropane were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 1 mol / L) and stirred at 65°C for 8 h under an argon atmosphere. After the reaction was complete, the mixed solution was separated by flash chromatography to obtain compound E. GC-MS (m / z): calculated for C6H7F5O6S3[M+1] + ,365.93,found366.29.

[0080]

[0081] In a glove box, 30w% EC, 30.95w% DMC, and 26w% EMC were stirred to form a mixed solution; 13w% LiPF6 was added to the mixed solution and stirred to fully dissolve to obtain a mixed salt solution; 0.05w% of structural formula E was further added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte.

[0082] Example 6:

[0083] 0.103 mol of trithiane hexaoxide and 0.1 mol of 1-(chloromethyl)-1H-pyrrole-2,5-dione were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 1 mol / L) and stirred at 70°C for 8 h under a nitrogen atmosphere. After the reaction was completed, the mixed solution was separated by flash chromatography to obtain compound F. GC-MS (m / z): calculated for C8H9NO8S3[M+1] + , 342.95, found 343.34.

[0084]

[0085] In a glove box, 30w% EC, 29w% DMC, and 26w% EMC were stirred to form a mixed solution; 13w% LiPF6 was added to the mixed solution and stirred to fully dissolve to obtain a mixed salt solution; 1.5w% of structural formula F and 0.5w% of structural formula C were further added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte.

[0086] Example 7:

[0087] 0.105 mol of trithiane hexaoxide and 0.1 mol of 3-chloronitropropane were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 1 mol / L) and stirred at 60 ° C for 8 h under argon atmosphere. After the reaction was completed, the mixed solution was separated by flash chromatography to obtain compound G. GC-MS (m / z): calcd. for C6H 11 O8NS3[M+1] + ,320.96,found321.39.

[0088]

[0089] In a glove box, 30w% EC, 28w% DMC, and 26w% EMC were stirred evenly to form a mixed solution; 13w% LiPF6 was added to the mixed solution and stirred to fully dissolve to obtain a mixed salt solution; 3w% of structural formula G was further added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte.

[0090] Example 8

[0091] 0.105 mol of trithiane hexaoxide and 0.1 mol of 4-chloro-1-butene were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 1 mol / L) and stirred at 60°C for 8 h under an argon atmosphere. After the reaction was completed, the mixed solution was separated by flash chromatography to obtain compound H. GC-MS (m / z): calculated for C7H 12O6S3[M+1] + , 287.98, found288.55.

[0092]

[0093] In a glove box, 30w% EC, 30.5w% DMC, and 26w% EMC were stirred to form a mixed solution; 13w% LiPF6 was added to the mixed solution and stirred to fully dissolve to obtain a mixed salt solution; 0.5w% of structural formula H was further added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte.

[0094] Example 9

[0095] 0.105 mol of trithiane hexaoxide and 0.1 mol of 4-chloro-1-butyne were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 1 mol / L) and stirred at 60 ° C for 8 h under argon atmosphere. After the reaction was completed, the mixed solution was separated by flash chromatography to obtain compound I. GC-MS (m / z): calcd. for C7H 10 O6S3[M+1] + , 285.96, found286.33.

[0096]

[0097] In a glove box, 30w% EC, 30.5w% DMC, and 26w% EMC were stirred to form a mixed solution; 13w% LiPF6 was added to the mixed solution and stirred to fully dissolve to obtain a mixed salt solution; 0.5w% of structural formula I was further added to the mixed salt solution, and the obtained mixed solution was used as an electrolyte.

[0098] Comparative Example 1

[0099] In a glove box, 30w% EC, 30w% DMC, and 26w% EMC were mixed to form a uniform solution. 13w% LiPF6 was added to the mixed solution and stirred until fully dissolved, resulting in a mixed salt solution. 1w% fluorobenzene was further added to the mixed salt solution, and the resulting mixed solution was used as the electrolyte. The resulting electrolyte was then subjected to a wetting test.

[0100] Comparative Example 2

[0101] In a glove box, 30w% EC, 30w% DMC, and 26w% EMC were mixed to form a uniform solution. 13w% LiPF6 was added to the mixed solution and stirred until fully dissolved to form a mixed salt solution. 1w% trithiane hexaoxide was further added to the mixed salt solution, and the resulting mixed solution was used as the electrolyte. The resulting electrolyte was then subjected to a wetting test.

[0102] Comparative Example 3

[0103] In a glove box, 30w% EC, 31w% DMC, and 26w% EMC were stirred evenly to form a mixed solution; 13w% LiPF6 was added to the mixed solution and stirred to fully dissolve to obtain a mixed salt solution; the obtained mixed solution was used as an electrolyte.

[0104] Comparative Example 4

[0105] 0.1 mol of trithiane hexaoxide and 0.1 mol of 3-chlorovaleronitrile were placed in 15 ml of N,N-dimethylformamide solution (CH3ONa; 1 mol / L) and stirred at 60°C for 8 h under argon atmosphere. After the reaction was completed, the mixed solution was separated by flash chromatography to obtain compound J. GC-MS (m / z): calcd. for C8H 13 O6NS3[M+1] + ,314.99,found315.82.

[0106]

[0107] In a glove box, 30w% EC, 30w% DMC, and 26w% EMC were stirred to form a mixed solution. 13w% LiPF6 was added to the mixed solution and stirred until fully dissolved to form a mixed salt solution. 1w% Compound J was further added to the mixed salt solution, and the resulting mixed solution was used as the electrolyte. The resulting electrolyte was then subjected to a wetting test.

[0108] Test Case

[0109] 1. Preparation of batteries:

[0110] 95.5wt% LiFePO4, 2wt% PVDF and 2.5wt% conductive carbon black were mixed and dispersed in NN dimethyl pyrrolidone to form a slurry, which was evenly coated on aluminum foil and cut into pieces; 94.8w% artificial graphite, 1.7w% CMC, 2.5w% SBR and 1wt% conductive carbon black were mixed and dispersed in pure water to form a slurry, which was evenly coated on copper foil and rolled (surface density was 2.6g / cm 3 ) pieces. A 2032 button cell was assembled in the order of negative electrode shell - negative electrode sheet - polypropylene separator - positive electrode sheet - gasket - spring - positive electrode shell, and then the electrolyte described in Examples 1-9 and Comparative Examples 1-4 was injected.

[0111] 2. Battery performance test

[0112] (1) The button battery cycle test is 0.2C constant current constant voltage to 3.7V, and 0.2C constant current discharge to 2.5V.

[0113] (2) The wetting balance method was used to test the amount of washing liquid per unit area of ​​the positive electrode within a certain period of time to characterize the improvement effect of electrolyte additives on the wetting of the LFP positive electrode.

[0114] The test results are shown in Table 1, which shows the performance test results of the batteries prepared in the examples and comparative examples.

[0115] Table 1 Performance test results of batteries prepared in Examples and Comparative Examples

[0116]

[0117] By comparing Example 1 with Comparative Example 1, it can be found that the structure described in the present invention can significantly improve the wetting characteristics of the electrolyte under the same electrolyte system and the same addition amount, and at the same time has a more excellent wetting improvement effect than fluorobenzene.

[0118] By comparing Examples 1-7 with Comparative Example 3, it can be found that the additives described in the present invention can form a sulfur-rich SEI film on the surface of the active material, significantly improving the first efficiency and cycle stability of the battery cell, while also having a certain improvement effect on the rate performance.

[0119] By comparing Examples 1-7 with Comparative Example 2, it can be found that due to the interaction between the two characteristic groups, the introduction of the R group into trithiane hexaoxide has a good wetting improvement effect, and at the same time has a further improvement effect on the capacity retention rate, first efficiency and rate performance of the battery cell.

[0120] By comparing Example 1 with Comparative Example 4, it can be found that when the carbon chain is long (n>3), the electron-withdrawing group cannot optimize the electron cloud distribution of trithiane hexaoxide and will not play a role in improving the wetting effect.

[0121] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An electrolyte additive containing a trithiane hexaoxide structure, characterized in that: Having the structure shown in formula I: Formula I In formula I, 1≤n≤3, and R is selected from one of trifluoromethane, pentafluoroethane, cyano, nitro, amino, sulfonic acid, maleimide, vinyl or acetylene.

2. A method for preparing the electrolyte additive according to claim 1, characterized in that: The following steps are involved: In the presence of an inert gas and a catalyst, trithiane hexaoxide reacts with a compound having a structure represented by Formula II to obtain an electrolyte additive having a structure represented by Formula I; Formula II R is selected from one of trifluoromethane, pentafluoroethane, cyano, nitro, amino, sulfonic acid, maleimide, vinyl or acetylene.

3. The preparation method according to claim 2, characterized in that The molar ratio of the trithiane hexaoxide to the compound having the structure represented by Formula II is (1-1.05):

1.

4. The preparation method according to claim 2, characterized in that The reaction temperature is 60-80° C. and the reaction time is 8-12 hours.

5. The preparation method according to claim 2, characterized in that The reaction solution is a sodium methoxide N,N-dimethylamide solution, and the concentration of sodium methoxide is 0.5-1 mol / L.

6. An electrolyte, characterized in that The electrolyte solution comprises a lithium salt, the electrolyte additive according to claim 1 and an organic solvent, wherein the electrolyte additive accounts for 0.05% to 3% by mass of the electrode solution.

7. The electrolyte according to claim 6, characterized in that The lithium salt is selected from a mixture of one or more of lithium perchlorate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium trifluoromethylsulfonate, lithium difluorooxalatoborate, and lithium bis(oxalatoborate). In the electrolyte, the concentration of the lithium salt is 0.5M~2M.

8. The electrolyte according to claim 6, characterized in that The organic solvent is selected from one or more of carbonate solvents, carboxylate solvents, amine solvents, sulfone solvents and nitrile solvents; The carbonate solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, methyl propyl carbonate, butylene carbonate, methyl butyl carbonate, and dibutyl carbonate; The carboxylate solvent is selected from one or more of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and methyl propionate; The amine solvent is selected from one or more of N-methylacetamide, N-methylformamide, dimethylformamide, and diethylformamide; The sulfone solvent is selected from one or more of dimethyl sulfide, dimethyl sulfoxide, sulfolane, diphenyl sulfoxide, thionyl chloride, dipropyl sulfone, dimethyl sulfite, diethyl sulfite, and tetramethyl sulfoxide; The nitrile solvent is selected from one or more of acetonitrile, succinonitrile, adiponitrile, 3-methoxypropionitrile, 3-ethoxypropionitrile and 1,3,6-hexanetrinitrile.

9. A lithium-ion battery, characterized in that: The electrolyte according to any one of claims 6 to 8.

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