Sulfur-containing additives, electrolytes and batteries

Abstract

The present invention belongs to the field of batteries, and specifically relates to a sulfur-containing additive, an electrolyte, and a battery. The invention comprises a methanedisulfonic acid methylene ester compound represented by structural formula (I), wherein R1-R2 are independently selected from hydrogen or C1-C 10 The sulfur-containing additives in the technical solution of this application regulate the number of heterocyclic carbon atoms substituted in methylene disulfonate (MMDS) compounds. Results show that they improve high-temperature performance and manganese dissolution in lithium manganese iron phosphate batteries.

Description

Technical Field

[0001] The present 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 materials. 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+ disproportionation to produce Mn 2+ and Mn 4+ The process of Mn 2+ It also catalyzes PF6 − Decomposition into PF5, loss of active electrolyte components, and degradation of battery performance have limited the large-scale industrial production of lithium iron manganese phosphate. Therefore, adding electrolyte additives to the electrolyte to inhibit the dissolution of manganese ions can effectively improve the high-temperature cycle performance and calendar life of lithium iron manganese phosphate batteries. Developing electrolytes that match lithium iron manganese phosphate batteries can accelerate the large-scale production and application of lithium iron manganese 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:

[0006] A sulfur-containing additive, comprising a methylene disulfonate compound represented by structural formula (I);

[0007] ;

[0008] wherein R1-R2 are independently selected from hydrogen or C1-C 10 One of substituted or unsubstituted alkyl groups.

[0009] 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.

[0010] Preferably, the methylene disulfonate compound is one of formula (1-1), (1-2), (1-3) or (1-4);

[0011] .

[0012] Sulfur-containing additives also include vinyl sulfate compounds represented by structural formula (II);

[0013] ;

[0014] R3-R4 are independently selected from hydrogen or C1-C 10 One of substituted or unsubstituted alkyl groups.

[0015] Preferably, R3 is selected from one of C1-C2 substituted or unsubstituted alkyl groups, and preferably, R4 is selected from isopropyl group.

[0016] Preferably, the vinyl sulfate compound (II) is one of formula (2-1) or (2-2);

[0017] .

[0018] The present invention also includes an electrolyte comprising a lithium salt, an organic solvent and an additive; the additive comprises the sulfur-containing additive;

[0019] 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%.

[0020] The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium tetrafluorooxalatephosphate, lithium bis(oxalateborate), lithium difluorooxalateborate, lithium difluorophosphate, lithium difluorobis(oxalateborate) and lithium bis(trifluoromethanesulfonyl)imide;

[0021] 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;

[0022] The additives include sulfur-containing additives and other additives; the other additives are one or more of fluoroethylene carbonate, ethylene 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.

[0023] 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;

[0024] The present invention also includes a lithium-ion battery, comprising 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.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The sulfur-containing additives in the technical solution of this application regulate the number of carbon atoms substituted by the heterocyclic ring 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 clusters with a low oxidation potential, allowing the methylene disulfonate additive to preferentially oxidize and decompose on the positive electrode side to form a CEI film. Simultaneously, the methylene disulfonate additive can synergistically form dense CEI and SEI films at the positive and negative electrodes with the vinyl sulfate additive, effectively inhibiting the dissolution of metallic manganese ions from the positive electrode lithium manganese iron phosphate, while also suppressing the growth of lithium dendrites and the production of poorly conductive substances at the negative electrode, thereby better protecting the electrode material. The additive combination provided by the present invention has good application prospects in the field of lithium-ion batteries.

[0027] 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 manganese dissolved at high temperatures from being adsorbed on the negative electrode surface, suppressing the increase in impedance, significantly improving high-temperature performance, reducing the amount of manganese dissolved, and effectively improving cycle characteristics;

[0028] During the first charge, the sulfur-containing additives can react with the lithium ions in the electrolyte to form a solvation reaction, which can induce the sulfur-containing additives to open the ring and form oligomers containing sulfate (-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;

[0029] In addition, methylene disulfonate additives can be used with PF6 - The strong interaction between anions forms clusters, which have a low oxidation potential, causing the methylene disulfonate additive to preferentially oxidize and decompose on the cathode side to form a CEI film.

[0030] The sulfur additives of the present application have a lower LUMO value than solvent molecules, 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

[0031] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention is further described in detail below with reference to the embodiments.

[0032] The sulfur-containing additives include methylene disulfonate compounds shown in structural formula I, and preferably, vinyl sulfate compounds shown in structural formula II:

[0033] ; wherein R1~R4 are independently selected from hydrogen or C1-C 10 One of substituted or unsubstituted alkyl groups.

[0034] R1 is selected from a C1-C2 substituted or unsubstituted alkyl group; R2 is selected from a C1-C4 substituted or unsubstituted alkyl group; R3 is selected from a C1-C2 substituted or unsubstituted alkyl group, preferably, R4 is selected from an isopropyl group.

[0035] Methylene disulfonate compounds and vinyl sulfate compounds can be synthesized by equations (1) and (2):

[0036] ;

[0037] A method for preparing methylene methanedisulfonate compounds comprises the following steps: synthesizing a methylene methanedisulfonate compound using isooctane as a reaction solvent, dropwise adding a diiodoalkane compound to the isooctane solution of a silver methanedisulfonate compound, and reflux-reacting the mixture for 4 hours. The reaction mixture is then cooled, and the desired product is extracted with ethyl acetate. The extract is concentrated under reduced pressure. A crude product of the methylene methanedisulfonate compound is obtained. The crude product is dissolved in ethyl acetate, the solution is treated with activated carbon, and then concentrated. n-hexane is added, and the precipitate is filtered to obtain a precipitate, which is then dried under reduced pressure. The methylene methanedisulfonate compound is obtained as white crystals.

[0038] The preparation method of vinyl sulfate compounds is characterized by comprising the following steps: adding a substituted ethylene glycol compound dropwise to thionyl chloride at room temperature, heating the mixture to 50-80° C. and keeping the temperature for 24 hours after the addition is complete, and then vacuumizing the mixture 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%; adding a sodium hypochlorite solution dropwise to carry out an oxidation reaction, controlling the entire oxidation reaction temperature at 0-10° C., keeping the temperature for 1-1.5 hours, and allowing the mixture to stand for separation to obtain a crude vinyl sulfate compound; and sequentially dehydrating, recrystallizing, and drying the crude vinyl sulfate compound to obtain the vinyl sulfate compound.

[0039] ;

[0040] 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

[0041] Preparation of positive electrode sheet: 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 are mixed in a weight ratio of 96.5:8.5:0.8:0.5:0.8:1.2:0.2, and N-methylpyrrolidone (NMP) is added. Stir under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated 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 edge trimming, cutting, and striping are performed. After stripping, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the positive electrode sheet.

[0042] Preparation of negative electrode sheet: The negative electrode active material graphite, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber were mixed in a weight ratio of 96.3:1:1.2:1.5, and deionized water was added to obtain negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated 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 striping are performed. After stripping, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the negative electrode sheet.

[0043] Preparation of isolation film: ceramic dispensing with a thickness of 7+2+3 μm was selected.

[0044] The weight parts of each component in the electrolyte are:

[0045] Lithium salt: lithium hexafluorophosphate 10.5%;

[0046] Solvent: ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%;

[0047] Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%;

[0048] Sulfur additives: 1.5% ethylene glycol dimethyl disulfonate (Formula 1-1), 0.5% propylene sulfate (Formula 2-1). Example 2

[0049] Specific parameters including the positive and negative electrode formulations, foil materials, separators, solid content, coating amount, compaction density, tablet size, and formation process parameters are the same as those in Example 1, except that the weight parts of the components in the electrolyte are:

[0050] Lithium salt: lithium hexafluorophosphate 10.5%,

[0051] Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%,

[0052] Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%,

[0053] Sulfur-containing additives: 1,5,2,4-dioxadithiooctane-2,2,4,4-tetraoxide (Formula 1-2) 1.5%, propylene sulfate 0.5%. Example 3

[0054] Specific parameters including the positive and negative electrode formulations, foil materials, separators, solid content, coating amount, compaction density, tablet size, and formation process parameters are the same as those in Example 1, except that the weight parts of the components in the electrolyte are:

[0055] Lithium salt: lithium hexafluorophosphate 10.5%,

[0056] Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%,

[0057] Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%,

[0058] Sulfur-containing additives: 1,5,2,4-dioxadithiocyclononane-2,2,4,4-tetraoxide (Formula 1-3) 1.5%, propylene sulfate 0.5%. Example 4

[0059] Specific parameters including the positive and negative electrode formulations, foil materials, separators, solid content, coating amount, compaction density, tablet size, and formation process parameters are the same as those in Example 1, except that the weight parts of the components in the electrolyte are:

[0060] Lithium salt: lithium hexafluorophosphate 10.5%,

[0061] Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%,

[0062] Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%,

[0063] Sulfur-containing additives: 1,6,2,5-dioxadithioheptane-2,2,5,5-tetraoxide (Formula 1-4) 1.5%, propylene sulfate 0.5%. Example 5

[0064] Specific parameters including the positive and negative electrode formulations, foil materials, separators, solid content, coating amount, compaction density, tablet size, and formation process parameters are the same as those in Example 3, except that the weight parts of the components in the electrolyte are:

[0065] Lithium salt: lithium hexafluorophosphate 10.5%,

[0066] Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%,

[0067] Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%,

[0068] Sulfur-containing additives: 1,5,2,4-dioxadithiocyclononane-2,2,4,4-tetraoxide (Formula 1-3) 2%. Example 6

[0069] Specific parameters including the positive and negative electrode formulations, foil materials, separators, solid content, coating amount, compaction density, tablet size, and formation process parameters are the same as those in Example 3, except that the weight parts of the components in the electrolyte are:

[0070] Lithium salt: lithium hexafluorophosphate 10.5%,

[0071] Solvent: Ethylene carbonate 24.51%, dimethyl carbonate 8.17%, diethyl carbonate 12.255%, ethyl methyl carbonate 36.765%, vinylene carbonate 2.5%,

[0072] Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%,

[0073] Sulfur-containing additives: 1,5,2,4-dioxadithiocyclononane-2,2,4,4-tetraoxide (Formula 1-3) 1.0%, propylene sulfate 0.5%. Example 7

[0074] Specific parameters including the positive and negative electrode formulations, foil materials, separators, solid content, coating amount, compaction density, tablet size, and formation process parameters are the same as those in Example 3, except that the weight parts of the components in the electrolyte are:

[0075] Lithium salt: lithium hexafluorophosphate 10.5%,

[0076] Solvent: Ethylene carbonate 24.21%, dimethyl carbonate 8.07%, diethyl carbonate 12.105%, ethyl methyl carbonate 36.315%, vinylene carbonate 2.5%,

[0077] Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%,

[0078] 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

[0079] Specific parameters including the positive and negative electrode formulations, foil materials, separators, solid content, coating amount, compaction density, tablet size, and formation process parameters are the same as those in Example 1, except that the weight parts of the components in the electrolyte are:

[0080] Lithium salt: lithium hexafluorophosphate 10.5%,

[0081] Solvent: Ethylene carbonate 24.36%, dimethyl carbonate 8.12%, diethyl carbonate 12.18%, ethyl methyl carbonate 36.54%, vinylene carbonate 2.5%,

[0082] Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%,

[0083] Sulfur-containing additives: methylene methanedisulfonate 1.5%, propylene sulfate 0.5%.

[0084] Comparative Example 2

[0085] Specific parameters including the positive and negative electrode formulations, foil materials, separators, solid content, coating amount, compaction density, tablet size, and formation process parameters are the same as those in Example 1, except that the weight parts of the components in the electrolyte are:

[0086] Lithium salt: lithium hexafluorophosphate 10.5%,

[0087] Solvent: Ethylene carbonate 24.96%, dimethyl carbonate 8.32%, diethyl carbonate 12.48%, ethyl methyl carbonate 37.44%, vinylene carbonate 2.5%,

[0088] Other additives: lithium bis(fluorosulfonyl)imide 3%, 1,3-propylene sultone 0.5%, tris(trimethylsilyl) phosphate 0.3%.

[0089] Based on the electrolytes of Examples 1-7 and Comparative Examples 1-2, electrical performance tests were performed on the prepared lithium-ion batteries.

[0090] High-temperature cycling 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-discharge cycle. First, the battery was charged at a rate of 1C. When the battery voltage reached 4.2V, constant voltage charging was switched. Charging was stopped when the charging current dropped to 0.05C. After a 10-minute rest period, the battery was discharged at a constant current rate of 1C until the battery voltage dropped to 2.5V. Discharge was stopped and the battery rested for 10 minutes. The above charge and discharge steps were repeated, and the capacity retention rate of the battery after 500 cycles was recorded.

[0091] Manganese dissolution test: After 500 cycles, the battery was dissected, the negative electrode sheet removed, and rinsed with DMC (dimethyl carbonate). After rinsing, the negative electrode sheet was immersed in deionized water and allowed to stand. After the negative electrode active material fell off, the negative electrode active material was filtered and collected. ICP testing of manganese in the negative electrode active material and electrolyte was performed: 0.50 g of the negative electrode active material or electrolyte was accurately weighed into a beaker. 10 mL of nitric acid, 10 mL of sulfuric acid, and 10 mL of hydrochloric acid were slowly added to the mixture. The sample was heated until dissolved, cooled, and then filtered through 50 μm filter paper. The sample was then transferred to a volumetric flask, brought to volume, and subjected to ICP testing. The manganese content in the negative electrode material was calculated as x1, and the manganese content in the electrolyte was calculated as x2. The total manganese dissolution was calculated as the manganese dissolution from the negative electrode sheet plus the manganese dissolution from the electrolyte, i.e., x1 + x2.

[0092] 60°C storage performance test: After formation, the batteries prepared in Examples 1-4 and Comparative Example 1 were all charged with 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°C oven for storage testing. The residual capacity and recovery capacity of each solution during the two-month storage period were counted.

[0093] ;

[0094] From the 500-cycle capacity retention 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 under high-temperature cycling, and has a positive promoting effect on the improvement of 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 is significantly improved, and the manganese dissolution 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 higher the corresponding PF6 - -MMDS clusters participate in the strong interaction of Li + The solvated structure is formed with a lower lowest unoccupied molecular orbital (LUMO) energy level, preferentially decomposing into an ultra-thin, strong sulfur-rich interfacial layer. This prevents manganese dissolved at high temperatures from adsorbing on the negative electrode surface, suppressing the increase in impedance and effectively improving cycle performance. Furthermore, a comparison of Example 7 and Example 3 shows that the methylene disulfonate additive can synergize with the vinyl sulfate additive to form denser CEI and SEI films at both the positive and negative electrodes, resulting in greater mechanical strength. This effectively suppresses the dissolution of metallic manganese ions from the positive electrode lithium manganese iron phosphate, effectively protecting the electrode material. Based on this, the effect of the methylene disulfonate additive content on the 500-cycle capacity retention and manganese dissolution was investigated (Examples 3, 6, and 7). The results showed that the optimal content was 1.5 wt% of 1,5,2,4-dioxadithiacyclononane-2,2,4,4-tetraoxide (Formula 1-3).

[0095] ;

[0096] The test results of the Examples and Comparative Examples after high-temperature storage at 60°C in Table 2 show that as the number of heterocyclic substituted carbon atoms in the methanedisulfonic acid methylene ester additive increases, the residual capacity and recovery capacity after high-temperature storage both improve, significantly slowing the battery capacity decay. This is likely due to the fact that additives with larger heterocyclic rings can decompose under high pressure to form stronger CEI and SEI films on the positive and negative electrode surfaces. These films prevent the oxidation of the lithium manganese iron phosphate positive electrode, leading to manganese dissolution, and inhibit its reduction and deposition at the negative electrode, while also ensuring unimpeded lithium ion transport, thereby slowing the battery capacity decay. Furthermore, the addition of 1.5 wt% of 1,5,2,4-dioxadithiacyclononane-2,2,4,4-tetraoxide (Formula 1-3) and 0.5 wt% of propylene sulfate resulted in even better storage performance, further demonstrating that this ratio is the optimal addition amount.

[0097] 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 the scope of protection of the present invention.

Claims

1. A sulfur-containing additive, characterized in that: The invention comprises a methylene disulfonate compound represented by structural formula (I) and a vinyl sulfate compound represented by structural formula (II); the mass content of the sulfur-containing additive in the electrolyte is 1.5-3%; The methylene disulfonate compound is one of formula (1-1), (1-2), (1-3) or (1-4); ； The vinyl sulfate compound (II) is one of formula (2-1) or (2-2); 。 2. An electrolyte, characterized in that It comprises lithium salt, organic solvent and additives; the additives include the sulfur-containing additives according to claim 1.

3. The electrolyte according to claim 2, characterized in that The mass content of the sulfur-containing additive in the electrolyte is 2%.

4. The electrolyte according to claim 2, characterized in that The mass content of the methylene methanedisulfonate compound in the electrolyte is 1-2%; the mass content of the vinyl sulfate compound in the electrolyte is 0.5%.

5. The electrolyte according to claim 2, characterized in that The mass content of methylene disulfonate compounds in the electrolyte is 1.5%.

6. The electrolyte according to claim 2, characterized in that The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium tetrafluorooxalatephosphate, lithium bis(oxalateborate), lithium difluorooxalateborate, lithium difluorophosphate, lithium difluorobis(oxalateborate) and lithium bis(trifluoromethanesulfonyl)imide; The solvent includes carboxylic acid esters and carbonates; the carboxylic acid esters are one or more of methyl acetate, ethyl acetate, propyl acetate, propyl propionate and butyl propionate; the carbonates include one or more of 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, ethylene 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.

7. The electrolyte according to claim 2, 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.

8. A lithium-ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 2 to 7; the positive electrode active material of the positive electrode sheet is lithium manganese iron phosphate material.

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