Sulfur-containing additive, electrolyte and battery

Abstract

The invention belongs to the field of batteries, and particularly relates to a sulfur-containing additive, an electrolyte and a battery. Comprising a methylene methanedisulfonate compound # imgabs0 # as shown in a structural formula (I), wherein R1-R2 are independently selected from one of hydrogen or C1-C10 substituted or unsubstituted alkyl groups. According to the sulfur-containing additive in the technical scheme, the number of heterocycle substituted carbon atoms of a methylene methanedisulfonate (MMDS) compound is regulated and controlled, and the result shows that the sulfur-containing additive has an improvement effect on high-temperature performance and manganese dissolution of a lithium manganese iron phosphate battery.

Description

Technical Field

[0001] The invention belongs to the field of batteries, and in particular relates to a sulfur-containing additive, an electrolyte and a battery. Background Art

[0002] As the application and process development of lithium iron phosphate batteries become increasingly mature, it has become difficult to make greater breakthroughs in the energy density and capacity of the material. Therefore, researchers have turned their attention to lithium manganese iron phosphate materials with higher intrinsic capacity and voltage platform.

[0003] Lithium manganese iron phosphate is the product of the combination of lithium iron phosphate and lithium manganese phosphate. Theoretically, when the ratio of manganese to iron is 6:4, the performance can be improved by 10-15% compared to lithium iron phosphate, and the charging voltage can be increased from 3.4 V to 4.1 V. The high voltage platform brings higher energy density. In addition, lithium manganese iron phosphate materials also have the advantages of good safety and good cycle performance. However, the Jahn-Teller effect of manganese ions in lithium manganese iron phosphate can easily cause manganese to dissolve, which not only consumes the active components of the positive electrode and causes the battery's high-temperature cycle life to decay, but also deposits on the surface of the negative electrode, which will destroy the SEI film; at the same time, the acid produced by the decomposition of the electrolyte will further corrode the manganese ions in the lithium manganese iron phosphate, causing Mn 3+ The disproportionation produces Mn 2+ and Mn 4+ The process of Mn 2+ It also catalyzes PF6 − Decomposition into PF5, loss of electrolyte active ingredients, resulting in battery performance degradation, these factors limit the large-scale industrial production of lithium manganese iron phosphate. Therefore, adding electrolyte additives that inhibit the dissolution of manganese ions at the electrolyte end can effectively improve the high-temperature cycle performance and calendar life of lithium manganese iron phosphate batteries. Developing electrolytes that match lithium manganese iron phosphate batteries can accelerate the large-scale production and application of lithium manganese iron phosphate batteries. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a sulfur-containing additive, an electrolyte and a battery.

[0005] To achieve the above object, the technical solution adopted by the present invention is: A sulfur-containing additive, comprising a methylene disulfonate compound represented by structural formula (I); ; Wherein, R1-R2 are independently selected from hydrogen or C1-C 10 One of substituted or unsubstituted alkyl groups.

[0006] Preferably, R1 is selected from one of C1-C2 substituted or unsubstituted alkyl groups; and R2 is selected from one of C1-C4 substituted or unsubstituted alkyl groups.

[0007] Preferably, the methylene disulfonate compound is one of formula (1-1), (1-2), (1-3) or (1-4); .

[0008] Sulfur-containing additives also include vinyl sulfate compounds represented by structural formula (II); ; R3-R4 are independently selected from hydrogen or C1-C 10 One of substituted or unsubstituted alkyl groups.

[0009] Preferably, R3 is selected from one of C1-C2 substituted or unsubstituted alkyl groups, and preferably, R4 is selected from isopropyl group.

[0010] Preferably, the vinyl sulfate compound (II) is one of formula (2-1) or (2-2); .

[0011] The present invention also includes an electrolyte comprising a lithium salt, an organic solvent and an additive; the additive comprises the sulfur-containing additive; Preferably, the mass content of the sulfur-containing additive in the electrolyte is 1.5-3%; preferably 2%; preferably, the sulfur-containing additive is a mixture of methylene disulfonate compounds and vinyl sulfate compounds; preferably, the mass content of methylene disulfonate compounds in the electrolyte is 1-2%; more preferably 1.5%; the mass content of the vinyl sulfate compound in the electrolyte is 0.5%.

[0012] The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorobis(oxalate)phosphate and lithium bis(trifluoromethanesulfonyl)imide; The solvent includes one or more of carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, propyl propionate and butyl propionate, and carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, propylene carbonate and vinylene carbonate; The additives include sulfur-containing additives and other additives; the other additives are one or more of fluoroethylene carbonate, vinyl carbonate, 1,3-propylene sultone, tris(trimethylsilyl)phosphite, triphenyl phosphate, trimethyl phosphate, vinylene carbonate, p-phenylene diisocyanate, phenyl methanesulfonate, triallyl phosphate, succinonitrile, adiponitrile and succinic anhydride.

[0013] The lithium salt accounts for 12-15 parts by weight, the solvent accounts for 79.5-83.5 parts by weight, and the additive accounts for 4.5-5.5 parts by weight; The present invention also includes a lithium ion battery, including a positive electrode plate, a negative electrode plate, a separator and the electrolyte; the positive electrode active material of the positive electrode plate is lithium manganese iron phosphate material.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The sulfur-containing additives in the technical solution of this application regulate the number of heterocyclic carbon atoms of methylene disulfonate (MMDS) compounds. The results show that it has an improved effect on high temperature performance and manganese dissolution of lithium manganese iron phosphate batteries. Methylene disulfonate additives can undergo a ring-opening reaction during the first charge to form oligomers containing sulfate groups, and react with PF6 - The strong interaction between anions forms a cluster, and the cluster has a low oxidation potential, so that the methylene disulfonate additive is preferentially oxidized and decomposed on the positive electrode side to form a CEI film; at the same time, the methylene disulfonate additive can form a dense CEI and SEI film on the positive and negative electrodes through synergistic action with the vinyl sulfate additive, effectively inhibiting the dissolution of metal manganese ions in the positive electrode lithium manganese iron phosphate, while inhibiting the growth of negative electrode lithium dendrites and the generation of poorly conductive substances, and better protecting the electrode material. The additive combination provided by the present invention has a good application prospect in the field of lithium ion batteries.

[0015] Specifically, as the number of carbon atoms of the substituent groups R1 and R2 in the heterocyclic ring increases, the methylene disulfonate compound additive preferentially decomposes into an ultra-thin, strong sulfur-rich interface layer, preventing the manganese dissolved at high temperature from being adsorbed on the negative electrode surface, inhibiting the increase in impedance, significantly improving high-temperature performance, reducing the amount of manganese dissolved, and effectively improving the cycle characteristics; During the first charge, the sulfur-containing additives can undergo a solvation reaction between oxygen atoms and lithium ions in the electrolyte, inducing the sulfur-containing additives to open their rings and form oligomers containing sulfate groups (-S(=O)2-, -OS(=O)2- and -OS(=O)2O- groups), which can react with the transition metal Mn in the positive electrode material. 2+ / Mn 3+ Complexation, forming CEI film at the positive electrode and effectively inhibiting the dissolution of metallic manganese in the positive electrode material of lithium manganese iron phosphate battery; In addition, methylene disulfonate additives can be used with PF6 - The strong interaction between anions forms clusters, which have a low oxidation potential, so that the methylene disulfonate additive is preferentially oxidized and decomposed on the positive electrode side to form a CEI film. The sulfur additive of the present application has a lower LUMO value than the solvent molecule, can form a good SEI film at the negative electrode, inhibit the growth of negative electrode lithium dendrites and avoid the generation of high-impedance inactive substances, and better protect the electrode material. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with embodiments.

[0017] The sulfur-containing additives include methanedisulfonic acid methylene ester compounds shown in structural formula I, and preferably, vinyl sulfate compounds shown in structural formula II: ; wherein R1~R4 are independently selected from hydrogen or C1-C 10 One of substituted or unsubstituted alkyl groups.

[0018] R1 is selected from one of C1-C2 substituted or unsubstituted alkyl groups; R2 is selected from one of C1-C4 substituted or unsubstituted alkyl groups; R3 is selected from one of C1-C2 substituted or unsubstituted alkyl groups, preferably, R4 is selected from isopropyl group.

[0019] Methylene disulfonate compounds and vinyl sulfate compounds can be synthesized by equations (1) and (2): ; The preparation method of methylene disulfonate compounds comprises the following steps: using isooctane as a reaction solvent to synthesize methylene disulfonate compounds, dropping diiodoalkane compounds into isooctane of silver disulfonate compounds, and reflux the mixture for 4 hours. Then the reaction mixture is cooled, and the desired product is extracted with ethyl acetate. The extract is concentrated under reduced pressure. A crude product of methylene disulfonate compounds is obtained. After the crude product is dissolved in ethyl acetate, the solution is treated with activated carbon and then concentrated. N-hexane is added thereto, and the precipitate is filtered to obtain a precipitate, which is then dried under reduced pressure. The methylene disulfonate compounds are obtained in the form of white crystals.

[0020] The preparation method of vinyl sulfate compounds is characterized in that it comprises the following steps: under normal temperature conditions, dropping a substituted ethylene glycol compound into thionyl chloride, heating the temperature to 50-80°C and keeping the temperature for 24 hours after the dropping is completed, and then vacuumizing to obtain a reaction solution containing vinyl sulfite compounds; rectifying and purifying the reaction solution containing vinyl sulfite compounds under vacuum conditions to obtain vinyl sulfite compounds with a purity greater than 99.2%; dropping a sodium hypochlorite solution to carry out an oxidation reaction, the entire oxidation reaction temperature is controlled at 0-10°C, keeping the temperature for 1-1.5 hours, standing and separating the liquids to obtain a crude vinyl sulfate compound; and sequentially dehydrating, recrystallizing and drying the crude vinyl sulfate compound to obtain the vinyl sulfate compound.

[0021] ; The compounds of formula (1-1), (1-2), (1-3) or (1-4), (2-1) and (2-2) were prepared by the methods of formula (1) and (2) and applied to the following examples. Example 1

[0022] Preparation of positive electrode sheet: Mix the positive electrode active material lithium manganese iron phosphate, conductive agent carbon black, conductive agent carbon nanotubes, binder polyvinylidene fluoride (PVDF5130 and HSV900) and dispersant in a weight ratio of 96.5:8.5:0.8:0.5:0.8:1.2:0.2, add N-methylpyrrolidone (NMP), and stir under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; evenly coat the positive electrode slurry on the positive electrode current collector aluminum foil with a coating amount of 38 g / m 2 After drying at 85°C, cold pressing is performed, and trimming, cutting, and slitting are performed. After slitting, it is dried at 85°C under vacuum conditions for 4 hours, and the pole ears are welded to obtain the positive electrode sheet.

[0023] Preparation of negative electrode sheet: Mix the negative electrode active material graphite, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber in a weight ratio of 96.3:1:1.2:1.5, add deionized water, and obtain negative electrode slurry under the action of a vacuum mixer; evenly coat the negative electrode slurry on the negative electrode current collector copper foil with a coating amount of 17.8 g / m 2 After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and slitting are performed. After slitting, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the negative electrode sheet.

[0024] Preparation of isolation film: Ceramic dispensing with a thickness of 7+2+3 μm was selected.

[0025] The weight parts of each component in the electrolyte are: Lithium salt: lithium hexafluorophosphate 10.5%; Solvent: ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%; Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%; Sulfur additives: 1.5% ethylene glycol dimethyl disulfonate (Formula 1-1), 0.5% propylene sulfate (Formula 2-1). Example 2

[0026] Specific parameters including positive and negative electrode formula, foil, separator, solid content, coating amount, compaction density, tablet size and formation method are the same as those in Example 1, except that the weight parts of each component in the electrolyte are respectively: Lithium salt: lithium hexafluorophosphate 10.5%, Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%, Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%, Sulfur-containing additives: 1,5,2,4-dioxadithiooctane-2,2,4,4-tetraoxide (Formula 1-2) 1.5%, propylene sulfate 0.5%. Example 3

[0027] Specific parameters including positive and negative electrode formula, foil, separator, solid content, coating amount, compaction density, tablet size and formation method are the same as those in Example 1, except that the weight parts of each component in the electrolyte are respectively: Lithium salt: lithium hexafluorophosphate 10.5%, Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%, Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%, Sulfur-containing additives: 1,5,2,4-dioxadithiocyclononane-2,2,4,4-tetraoxide (Formula 1-3) 1.5%, propylene sulfate 0.5%. Example 4

[0028] Specific parameters including positive and negative electrode formula, foil, separator, solid content, coating amount, compaction density, tablet size and formation method are the same as those in Example 1, except that the weight parts of each component in the electrolyte are respectively: Lithium salt: lithium hexafluorophosphate 10.5%, Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%, Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%, Sulfur-containing additives: 1,6,2,5-dioxadithiocycloheptane-2,2,5,5-tetraoxide (Formula 1-4) 1.5%, propylene sulfate 0.5%. Example 5

[0029] Specific parameters including positive and negative electrode formula, foil, separator, solid content, coating amount, compaction density, tablet size and formation method are the same as those in Example 3, except that the weight parts of each component in the electrolyte are respectively: Lithium salt: lithium hexafluorophosphate 10.5%, Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%, Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%, Sulfur-containing additives: 1,5,2,4-dioxadithiacyclononane-2,2,4,4-tetraoxide (Formula 1-3) 2%. Example 6

[0030] Specific parameters including positive and negative electrode formula, foil, separator, solid content, coating amount, compaction density, tablet size and formation method are the same as those in Example 3, except that the weight parts of each component in the electrolyte are respectively: Lithium salt: lithium hexafluorophosphate 10.5%, Solvent: Ethylene carbonate 24.51%, dimethyl carbonate 8.17%, diethyl carbonate 12.255%, ethyl methyl carbonate 36.765%, vinylene carbonate 2.5%, Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%, Sulfur-containing additives: 1,5,2,4-dioxadithiocyclononane-2,2,4,4-tetraoxide (Formula 1-3) 1.0%, propylene sulfate 0.5%. Example 7

[0031] Specific parameters including positive and negative electrode formula, foil, separator, solid content, coating amount, compaction density, tablet size and formation method are the same as those in Example 3, except that the weight parts of each component in the electrolyte are respectively: Lithium salt: lithium hexafluorophosphate 10.5%, Solvent: Ethylene carbonate 24.21%, dimethyl carbonate 8.07%, diethyl carbonate 12.105%, ethyl methyl carbonate 36.315%, vinylene carbonate 2.5%, Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%, Sulfur-containing additives: 1,5,2,4-dioxadithiocyclononane-2,2,4,4-tetraoxide (Formula 1-3) 2.0%, propylene sulfate 0.5%. Comparative Example 1

[0032] Specific parameters including positive and negative electrode formula, foil, separator, solid content, coating amount, compaction density, tablet size and formation method are the same as those in Example 1, except that the weight parts of each component in the electrolyte are respectively: Lithium salt: lithium hexafluorophosphate 10.5%, Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%, Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%, Sulfur-containing additives: 1.5% methylene disulfonate, 0.5% propylene sulfate.

[0033] Comparative Example 2 Specific parameters including positive and negative electrode formula, foil, separator, solid content, coating amount, compaction density, tablet size and formation method are the same as those in Example 1, except that the weight parts of each component in the electrolyte are respectively: Lithium salt: lithium hexafluorophosphate 10.5%, Solvent: Ethylene carbonate 24.96%, dimethyl carbonate 8.32%, diethyl carbonate 12.48%, ethyl methyl carbonate 37.44%, vinylene carbonate 2.5%, Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%.

[0034] Based on the electrolytes of Examples 1-7 and Comparative Examples 1-2, electrical performance tests were performed on the prepared lithium ion batteries.

[0035] High temperature cycle performance test: In a high temperature oven at 45°C, the batteries prepared in Examples 1-4 and Comparative Example 1 were subjected to charge and discharge tests in a voltage range of 2.5-4.2V using a 1C / 1C charge and discharge cycle. First, the battery was charged at a rate of 1C. When the battery voltage reached 4.2 V, it was switched to constant voltage charging. When the charging current dropped to 0.05C, charging was stopped. After 10 minutes of dormancy, the battery was discharged at a rate of 1C with a constant current until the battery voltage dropped to 2.5 V. The battery was dormant for 10 minutes. The above charge and discharge steps were repeated, and the capacity retention rate of the battery after 500 cycles was recorded.

[0036] Manganese dissolution test: dissect the battery after 500 cycles, take out the negative electrode sheet, rinse the negative electrode sheet with DMC (dimethyl carbonate), soak the negative electrode sheet in deionized water after rinsing, let it stand, and filter and collect the negative electrode active material after the negative electrode active material falls off. Perform ICP test on manganese in negative electrode active material and electrolyte: accurately weigh 0.50 g of negative electrode active material or electrolyte in a beaker, slowly add 10 mL nitric acid, 10 mL sulfuric acid and 10 mL hydrochloric acid, heat until the sample is dissolved and cool, then filter with 50 μm filter paper, transfer to a volumetric flask to make up the volume, perform ICP test, and obtain the manganese content x1 in the negative electrode material and x2 in the electrolyte. The total dissolution of manganese is the manganese dissolution of the negative electrode sheet + the manganese dissolution in the electrolyte, that is, x1 + x2.

[0037] 60℃ storage performance test: After formation, the batteries prepared in Examples 1-4 and Comparative Example 1 were all charged at constant current to 4.2 V, then switched to constant voltage charging. Charging was stopped when the charging current dropped to 0.05C. The batteries were taken out and placed in a 60℃ oven for storage testing. The residual capacity and recovery capacity of each solution during two months of storage were counted.

[0038] ; From the 500-cycle capacity retention rate and manganese dissolution test results of Examples 1-7 and Comparative Examples 1-2 in Table 1, it can be seen that the addition of methanedisulfonic acid methylene ester compounds effectively improves the capacity retention rate under high-temperature cycles, and has a positive effect on improving battery performance; compared with the unsubstituted methanedisulfonic acid methylene ester in Comparative Example 1, as the number of carbon atoms of the substituent groups R1 and R2 in the heterocyclic ring increases, the high-temperature performance is significantly improved, the capacity retention rate is significantly improved, and the manganese dissolution amount is reduced; this may be attributed to the fact that the more carbon atoms of the substituent groups R1 and R2 in the heterocyclic ring, the corresponding PF6 - -MMDS clusters participate in the strong interaction of Li + The solvation structure is formed, and has a lower lowest unoccupied molecular orbital (LUMO) energy level, and preferentially decomposes into an ultra-thin, strong sulfur-rich interface layer, preventing the manganese dissolved at high temperature from being adsorbed on the surface of the negative electrode, inhibiting the rise of impedance, and effectively improving the cycle characteristics. In addition, by comparing Example 7 with Example 3, it can be seen that the methane disulfonic acid methylene ester additive can synergistically act with the vinyl sulfate additive to form a denser CEI and SEI film at the positive and negative electrodes, with stronger mechanical strength, effectively inhibiting the dissolution of metal manganese ions in the positive electrode lithium manganese iron phosphate, and effectively protecting the electrode material. Based on this, the effect of the content of methane disulfonic acid methylene ester additives on the 500-cycle cycle capacity retention rate and manganese dissolution amount was investigated (Examples 3, 6 and 7), and the results showed that the addition of 1.5wt% of 1,5,2,4-dioxadithiacyclononane-2,2,4,4-tetraoxide (Formula 1-3) was the optimal content.

[0039] ; From the test results of each embodiment and comparative example after high-temperature storage at 60°C in Table 2, it can be seen that as the number of heterocyclic carbon atoms of the methane disulfonic acid methylene ester compound additive increases, the residual capacity and recovery capacity after high-temperature storage are improved, and the attenuation of the battery capacity is delayed to a certain extent. This may be because the additives with larger heterocyclic rings can decompose on the surface of the positive and negative electrodes under high pressure to form stronger CEI and SEI films, which can prevent the oxidation of the lithium manganese iron phosphate positive electrode from causing manganese dissolution and inhibit its reduction deposition at the negative electrode, while ensuring that the transmission of lithium ions is not blocked, thereby slowing down the attenuation of the battery capacity. In addition, the storage performance of adding 1.5wt% of 1,5,2,4-dioxadithiocyclononane-2,2,4,4-tetraoxide (Formula 1-3) and 0.5wt% of propylene sulfate is better, further proving that this ratio is the optimal addition amount.

[0040] 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 principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A sulfur-containing additive, characterized in that: It includes methanedisulfonic acid methylene ester compounds represented by structural formula (I); ； Wherein, R1-R2 are independently selected from hydrogen or C1-C 10 One of substituted or unsubstituted alkyl groups.

2. The sulfur-containing additive according to claim 1, characterized in that: R1 is selected from one of C1-C2 substituted or unsubstituted alkyl groups; R2 is selected from one of C1-C4 substituted or unsubstituted alkyl groups.

3. The sulfur-containing additive according to claim 1, characterized in that: The methylene disulfonate compound is one of formula (1-1), (1-2), (1-3) or (1-4); 。 4. The sulfur-containing additive according to claim 1, characterized in that: Also included are vinyl sulfate compounds represented by structural formula (II); ； R3-R4 are independently selected from hydrogen or C1-C 10 One of substituted or unsubstituted alkyl groups.

5. The sulfur-containing additive according to claim 4, characterized in that: R3 is selected from one of C1-C2 substituted or unsubstituted alkyl groups, and preferably, R4 is selected from isopropyl group.

6. The sulfur-containing additive according to claim 4, characterized in that: The vinyl sulfate compound (II) is one of formula (2-1) or (2-2); 。 7. An electrolyte, characterized in that: It comprises a lithium salt, an organic solvent and an additive; the additive comprises the sulfur-containing additive according to any one of claims 1 to 3; Preferably, the mass content of the sulfur-containing additive in the electrolyte is 1.5-3%; preferably 2%; preferably, the sulfur-containing additive is a mixture of methylene disulfonate compounds and vinyl sulfate compounds; preferably, the mass content of methylene disulfonate compounds in the electrolyte is 1-2%; more preferably 1.5%; the mass content of the vinyl sulfate compound in the electrolyte is 0.5%.

8. The electrolyte according to claim 7, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium tetrafluorooxalate phosphate, lithium bis(oxalate)borate, lithium difluorooxalate borate, lithium difluorophosphate, lithium difluorobis(oxalate)phosphate and lithium bis(trifluoromethanesulfonyl)imide; The solvent includes one or more of carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, propyl propionate and butyl propionate, and dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, propylene carbonate and vinylene carbonate; The additives include sulfur-containing additives and other additives; the other additives are one or more of fluoroethylene carbonate, vinyl carbonate, 1,3-propylene sultone, tris(trimethylsilyl)phosphite, triphenyl phosphate, trimethyl phosphate, vinylene carbonate, p-phenylene diisocyanate, phenyl methanesulfonate, triallyl phosphate, succinonitrile, adiponitrile and succinic anhydride.

9. The electrolyte according to claim 8, characterized in that The lithium salt accounts for 12-15 parts by weight, the solvent accounts for 79.5-83.5 parts by weight, and the additive accounts for 4.5-5.5 parts by weight.

10. A lithium ion battery, characterized in that: It comprises a positive electrode plate, a negative electrode plate, a separator and the electrolyte according to claim 8 or 9; the positive electrode active material of the positive electrode plate is lithium manganese iron phosphate material.

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