Electrolyte functional additive composition and electrolyte and lithium battery using same

Abstract

The application provides an electrolyte functional additive composition and an electrolyte and a lithium ion battery using the same, the functional additive composition comprising a cyclic sulfate, the chemical structure of the cyclic sulfate being shown as formula (1), wherein X is selected from any one of a vinyl group, a propenyl group, an alkyne propyl group, an ethyl cyanide group, a propyl cyanide group, a monofluoromethyl group, a difluoromethyl group and a trifluoromethyl group. The functional additive composition provided by the application can form a uniform and dense CEI film on the positive electrode under high voltage conditions, blocks the contact between the positive electrode material and the electrolyte, thereby reducing the positive electrode interface side reaction; on the other hand, the functional additive composition can also form a uniform and dense SEI film on the negative electrode, prevents transition metal sulfide (TMs) metal ions from being deposited on the negative electrode surface, makes the SEI more stable in the cycle process, and reduces the loss of active lithium.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of materials, and particularly relates to an electrolyte functional additive composition and an electrolyte and a lithium ion battery using the same. BACKGROUND

[0002] In recent years, new energy power vehicles have developed rapidly, but some deficiencies have also appeared, for example, slow charging, short endurance, low actual mileage in severe cold regions, etc. Endurance mileage has become the focus of attention, and developing a new high-voltage battery system or increasing the charging cutoff voltage has become a research hotspot of high-energy-density lithium batteries, and increasing the working voltage of the positive electrode material is the main means to improve the energy density of lithium ion batteries.

[0003] At present, high-voltage positive electrode materials such as spinel lithium nickel manganese oxide (LNMO), high-voltage ternary, high-voltage lithium cobaltate, and layered lithium-rich oxide (LLO) have become research hotspots. With the continuous increase of the voltage of lithium ion batteries, the electrolyte interface reaction will be more intense, and with the continuous charging and discharging cycles of the battery, the internal resistance of the battery gradually increases, thereby leading to the decline or even failure of the battery performance. Especially under high voltage and high temperature conditions, Mn 4+ in the positive electrode material will undergo disproportionation reaction and dissolve into the electrolyte in the form of Mn 2 + .

[0004] Researchers mainly overcome the existing drawbacks by coating and element doping of the positive electrode material. However, the material doping and coating method is complex and high in cost. By introducing electrolyte additives, the composition of the positive and negative electrode films can be adjusted to effectively reduce the interface side reaction and achieve the purpose of improving the battery performance. SUMMARY

[0005] In order to improve the capacity attenuation and excessive metal dissolution problems in the cycle process of high-voltage positive electrode material system battery, the present application provides an electrolyte functional additive composition and an electrolyte and a lithium ion battery using the same.

[0006] According to a first aspect of the present application, a cyclic sulfate is provided, the chemical structure of which is shown as formula (1), wherein X is selected from any one of a vinyl group, a propenyl group, an alkyne propyl group, an ethyl cyanide group, a propyl cyanide group, a monofluoromethyl group, a difluoromethyl group, and a trifluoromethyl group.

[0007] The unsaturated functional group X contained in the cyclic sulfate structure provided by this invention can be oxidized and reduced to form a uniform and dense CEI film at the positive electrode, blocking the contact between the positive electrode material and the electrolyte, thereby reducing side reactions at the positive electrode interface. On the other hand, this cyclic sulfate can also form a uniform and dense SEI film at the negative electrode, preventing transition metal sulfide (TMS) ions from depositing on the negative electrode surface, making the SEI film more stable during cycling and reducing the loss of active lithium. Thus, the cyclic sulfate provided by this invention can participate in the film formation of both positive and negative electrodes, easily forming a dense and uniform CEI film, and effectively inhibiting the dissolution of TMS metal ions and the release of oxygen, thereby reducing interfacial side reactions.

[0008] Preferably, the cyclic sulfate is selected from at least one of the compounds shown in formulas (2) to (9).

[0009]

[0010] According to a second aspect of the present invention, a method for preparing the cyclic sulfate ester as described above is provided, the method comprising the following steps: using oxothiazine as a raw material, obtaining a crude product by at least one of the following reaction methods: cyclization reaction, chlorination reaction, fluorination reaction, oxidation reaction, and elimination reaction, and then obtaining the cyclic sulfate ester by recrystallization treatment.

[0011] According to a third aspect of the present invention, an electrolyte functional additive composition is provided, the functional additive composition comprising the cyclic sulfates as described above.

[0012] Preferably, the functional additive composition further includes at least one of a fluorocarboxylic acid ester polymer, a lithium salt additive, a sulfur-containing additive, and a carbonate additive; wherein the fluorocarboxylic acid ester polymer includes fluoroethylene carbonate.

[0013] Ester (FEC); lithium salt additives include at least one of lithium difluorosulfonylimide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium dioxalatoborate (LiBOB), and lithium difluorooxalatoborate (LiODFB); sulfur-containing additives include at least one of 1,3-propanesulfonyl lactone (PS), 1-propylene-1,3-sulfonyl lactone (PST), and vinyl sulfate (DTD); carbonate additives include vinylene carbonate (VC).

[0014] The electrolyte functional additive composition provided by this invention further incorporates fluorocarboxylic acid ester polymers, lithium salt additives, sulfur-containing additives, and carbonate additives, which can promote the formation of stable CEI and SEI films in the positive and negative electrodes, thereby enhancing the electrical performance of the battery.

[0015] Preferably, the functional additive composition further includes fluorocarboxylic acid ester polymers, lithium salt additives, sulfur-containing additives, and carbonate additives.

[0016] Preferably, the mass ratio of cyclic sulfate: fluorocarboxylate polymer: lithium salt additive: sulfur-containing additive: carbonate additive is (0.3-1) : (0.1-5) : (0.5-1) : (0.5-3).

[0017] According to a fourth aspect of the present application, an electrolyte is provided, which comprises an organic solvent, a lithium salt, and the functional additive composition as described above. Thus, the electrolyte provided by the present application can improve the capacity decay and excessive metal dissolution of high-voltage cathode material system batteries during cycling, and further improve the performance of the batteries at high voltage, due to the use of the functional additive composition provided by the present application.

[0018] Preferably, the mass fraction of the cyclic sulfate in the electrolyte is 0.3-1.5%.

[0019] Preferably, the mass fraction of the fluorocarboxylate polymer in the electrolyte is 1-5%.

[0020] Preferably, the mass fraction of the lithium salt additive in the electrolyte is 0.5-1%. The lithium salt additive can participate in the formation of the positive and negative electrodes, and an insufficient amount cannot form a dense SEI film, and an excessive amount cannot be completely dissolved.

[0021] Preferably, the mass fraction of the sulfur-containing additive in the electrolyte is 0.5-3%. The sulfur-containing additive can assist in the formation of the positive and negative electrodes, has high thermal stability, an insufficient amount cannot form a dense SEI film in the negative electrode, and an excessive amount can form excessive films with large impedance, resulting in a decrease in cycle performance.

[0022] Preferably, the mass fraction of the carbonate additive, vinylene carbonate, in the electrolyte is 0.1-1%.

[0023] Preferably, the mass fraction of the organic solvent in the electrolyte is 70-90%, and the organic solvent comprises a cyclic carbonate, a chain carbonate, and a chain fluorinated ester. The mass ratio of the cyclic carbonate: chain carbonate: chain fluorinated ester is 1-15: 20-70: 5-20.

[0024] Preferably, the cyclic carbonate comprises at least one of ethylene carbonate (EC) and propylene carbonate (PC).

[0025] Preferably, the chain carbonate comprises at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0026] Preferably, the chain fluorinated ester comprises at least one of fluoroethylene carbonate (FEC) and fluoropropylene carbonate (FPC).

[0027] Preferably, the chain fluorinated ester includes at least one of bis(2,2,2-trifluoroethyl) carbonate, ethyl trifluoroethyl carbonate, methyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl difluoroethyl carbonate, bis(2,2-difluoroethyl) carbonate, 2,2-difluoroethyl-2,2,2-trifluoroethyl carbonate, 2,2,3,3-tetrafluoropropyl methyl carbonate, 2,2,3,3,3-pentafluoropropyl ethyl carbonate, methyl fluoroacetate, ethyl fluoroacetate, acetic acid-2-fluoroethyl ester, acetic acid-2,2-difluoroethyl ester, acetic acid-2,2,2-trifluoroethyl ester, ethyl 2-fluoropropionate, trifluoroacetic acid-2,2,2-trifluoroethyl ester, trifluoroacetic acid-2,2-difluoroethyl ester, trifluoroacetic acid-2-fluoroethyl ester, trifluoroacetic acid ethyl ester, trifluoroacetic acid methyl ester, difluoroacetic acid ethyl ester, difluoroacetic acid methyl ester, fluoroacetic acid methyl ester, ethyl 2-fluoropropionate.

[0028] According to a third aspect of the present application, there is provided a lithium ion battery comprising the electrolyte as described above. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 Formula of the cyclic sulfate;

[0030] Figure 2 Flow chart for preparing cyclic sulfate for Treatment Group 1A of Example 1;

[0031] Figure 3 Flow chart for preparing cyclic sulfate for Treatment Group 2A of Example 1;

[0032] Figure 4 Flow chart for preparing cyclic sulfate for Treatment Group 3A of Example 1. DETAILED DESCRIPTION

[0033] In order to make the personnel in the technical field better understand the technical solutions in the present application, the technical solutions of the present application will be described clearly and completely in combination with the drawings of the embodiments and examples of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person of ordinary skill in the art without making creative labor should belong to the protection scope of the present application.

[0034] Example 1

[0035] Treatment Group 1A

[0036] 1. Preparation of cyclic sulfate

[0037] The flow chart for preparing cyclic sulfate for Treatment Group 1A is as follows Figure 2The raw material used in the present process group is ethylene sulfite (CAS No. 3741-38-6), which is obtained by chlorination, oxidation, fluorination and recrystallization treatment.

[0038] 2. Composition of electrolyte

[0039] The specific materials for the composition of the electrolyte are shown in Table 1. Among them, the organic solvent is configured by ethylene carbonate, diethyl carbonate and 2,2-difluoroethyl acetate, and the mass ratio of ethylene carbonate: diethyl carbonate: 2,2-difluoroethyl acetate is 15:65:20; the cyclic sulfate is selected from the material with the chemical structure shown in formula (5).

[0040] Table 1. Materials for the composition of the electrolyte

[0041]

[0042] 3. Preparation of electrolyte

[0043] Under an argon atmosphere, the formula amount of VC, PS, LiPO2F2 and cyclic sulfate with the chemical structure shown in formula (5) is added to the organic solvent, and then lithium salt is added. The mixture is stirred at a temperature of 10°C to obtain the electrolyte.

[0044] 4. Preparation of lithium ion battery

[0045] The negative electrode material graphite, conductive agent acetylene black and binder CMC, SBR are prepared into a slurry with a mass percentage of 94:1:2:3, which is coated on a copper foil current collector, vacuum dried to obtain a negative electrode sheet.

[0046] The positive electrode material 0.25Li2MnO3·0.75LiMn 0.375 Ni 0.375 Co 0.25 O2, conductive agent acetylene black and binder PVDF are prepared into a slurry with a mass ratio of 94:3:3, which is coated on an aluminum foil current collector, vacuum dried to obtain a positive electrode sheet.

[0047] The positive electrode sheet, the negative electrode sheet, the Celgard2400 separator and the electrolyte prepared above are assembled into a soft package battery.

[0048] The treatment groups 2A-3A of Example 1 and the comparative groups 1A-5A were used to prepare electrolyte solutions according to the formulation and method provided in the treatment group 1A of Example 1, with the material of the cyclic sulfate used in the formulation as a variable. The variables used in the treatment groups 2A-3A of Example 1 and the comparative groups 1A-5A to prepare the electrolyte solutions are shown in Table 2. Except for the above-mentioned differences, the operation steps for preparing the electrolyte solutions and lithium ion batteries in the treatment groups 2A-3A of Example 1 and the comparative groups 1A-5A were strictly consistent with those in the treatment group 1A of Example 1.

[0049] The preparation method of the cyclic sulfate in the treatment group 2A of Example 1 is as follows: 1,2,4-butanetriol (CAS No. 3068-00-6) is used as a raw material, and the cyclic sulfate is obtained through ring formation reaction, chlorination reaction, fluorination reaction, oxidation reaction, and elimination reaction, followed by recrystallization treatment. The specific synthesis path is shown in Figure 3 .

[0050] The preparation method of the cyclic sulfate in the treatment group 3A of Example 1 is as follows: propylene glycol (CAS No. 57-55-6) is used as a raw material, and the cyclic sulfate is obtained through ring formation reaction, chlorination reaction, fluorination reaction, oxidation reaction, and elimination reaction, followed by recrystallization treatment. The specific synthesis path is shown in Figure 4 .

[0051] The comparative groups 1A-5A are existing materials, and their chemical structural formulas are shown in formulas (10)-(14).

[0052] Table 1. Variables for preparing ternary positive electrode materials in Examples 1-5

[0053]

[0054]

[0055] Comparative group 6A

[0056] This comparative group was used to prepare electrolyte solutions and batteries according to the formulation and method provided in the treatment group 1A of Example 1. With reference to the treatment group 1A of Example 1, the difference between this comparative group and the treatment group 1A of Example 1 is that no cyclic sulfate is added to prepare the electrolyte solution in this comparative group. Specifically, the mass fraction of an organic solvent is used to replace the cyclic sulfate, and the organic solvent maintains a mass ratio of ethylene carbonate: diethyl carbonate: 2,2-difluoroacetic acid = 15:65:20. Except for the above-mentioned difference, the operation for preparing the electrolyte solutions and batteries in this comparative group is strictly consistent with that in the treatment group 1A of Example 1.

[0057] Test Example 1

[0058] 1. Test object

[0059] The electrolytes provided in the various embodiments and comparative examples were applied to lithium-ion batteries, and performance tests were conducted using lithium-ion batteries. Electrochemical tests were performed using the Xinwei charge-discharge test cabinet.

[0060] 2. Testing Methods

[0061] (1) Room temperature cycle performance test: At 25℃, the lithium-ion battery was charged at a constant current of 0.5C (nominal capacity) to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current ≤0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to a cutoff voltage of 2.5V. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 1000 charge-discharge cycles at 25℃ under the above conditions. The capacity retention rate was calculated according to formula (1), and the average voltage was calculated according to formula (2).

[0062]

[0063]

[0064] (2) High-temperature cycle performance test: At 45℃, the lithium-ion battery is subjected to a constant current of 1.0C (nominal capacity).

[0065] Charge the battery to 4.6V, then charge it at a constant voltage of 4.6V until the current is ≤0.05C. After resting for 10 minutes, discharge it at a constant current of 1C until the cutoff voltage is 2.5V. This constitutes one charge-discharge cycle. Perform 800 charge-discharge cycles at 45℃ under the above conditions. The capacity retention rate is calculated according to equation (1), and the average voltage is calculated according to equation (2).

[0066] (3) Mn dissolution: The lithium-ion battery after the corresponding cycle test is discharged at a constant current of 0.5C (nominal capacity) to the cutoff voltage of 2.5V. Then the battery is disassembled, the negative electrode is removed and the negative electrode powder attached to the copper current collector is scraped off with a ceramic blade, and ICP-OES test is performed.

[0067] 3. Test Results and Analysis

[0068] The test results of the present test example are shown in Table 3, wherein the influence of different structures of cyclic sulfate on the performance of the prepared lithium ion battery is mainly explored in the present test example. In the comparative group 6A of Example 1, no cyclic sulfate is added, and it can be found that when no cyclic sulfate is added, the lithium ion battery using it has a serious TMs metal ion dissolution problem, which further leads to a lower capacity retention performance at different temperatures. In the treatment groups 1A-3A, the cyclic sulfate provided by the present application is used, and compared with the comparative group 6A, the TMs metal ion dissolution problem is obviously improved. In the comparative groups 1A-4A, although the existing materials contain the same X functional group, the improvement of the TMs metal ion dissolution problem is not as obvious as the cyclic sulfate provided by the present application. This is because the fluorine atom on the ring can prevent the TMs metal ion from depositing on the negative electrode surface. The material used in the comparative group 5A has no fluorine atom group and X group, and its effect on improving the TMs metal ion dissolution is poor.

[0069] The above experiments show that the cyclic sulfate provided by the present application, through the complementary of the fluorine atom group and the X group on the ring, can form a uniform and dense CEI film on the positive electrode, and also form a stable SEI film in the negative electrode, improve the TMs dissolution problem, and further improve the cycle performance of the lithium ion battery in the high temperature and high pressure environment.

[0070] Table 3. Test results of Test Example 1

[0071]

[0072]

[0073] Example 2

[0074] In the present example, the treatment group 1B is set according to the treatment group 1A of Example 1.

[0075] In addition, the treatment groups 2B-7B of the present example refer to the formulation for preparing the electrolyte of the treatment group 1B, and the matching of the content of the cyclic sulfate, FEC, VC, LiPO2F2 and PS in the formulation is used as a variable to set different treatment groups. The additive composition for preparing the electrolyte of each treatment group of the present example is shown in Table 4. Among them, the content change of the cyclic sulfate, FEC, VC, LiPO2F2 and PS is adjusted by increasing or decreasing the mass fraction of the organic solvent in the electrolyte, wherein the organic solvent maintains the ratio of ethylene carbonate: diethyl carbonate: 2,2-difluoroacetic acid = 15:65:20. In addition to the above differences, the operation of preparing the electrolyte and the lithium ion battery of the treatment groups 2B-11B of the present example is strictly consistent with that of the treatment group 1B of Example 2.

[0076] Table 4. Additive compositions used in the preparation of electrolytes for the treatment groups 1B to 1 IB of this example

[0077] Group Cyclic sulfate FEC VC LiPO2F2 PS Treatment group 1B 1％ 5％ 0.5％ 0.5％ 1％ Treatment group 2B 0.5％ 5％ 0.5％ 0.5％ 1％ Treatment group 3B 0.3％ 5％ 0.5％ 0.5％ 1％ Treatment group 4B 1.5％ 5％ 0.5％ 0.5％ 1％ Treatment group 5B 1％ 0 0.5％ 0.5％ 1％ Treatment group 6B 1％ 5％ 0 0.5％ 1％ Treatment group 7B 1％ 5％ 0.5％ 0 1％ Treatment group 8B 1％ 5％ 0.5％ 0.5％ 0

[0078] The treatment groups 9B to 1 IB of this example were prepared according to the formulation of the treatment group 1 B of Example 2, with the lithium salt additive, sulfur-containing additive materials used in the electrolyte functional additive composition as variables, as shown in Table 5. Except for the above-mentioned differences, the operations for preparing electrolytes and batteries in the treatment groups 9B to 1 IB of this example were strictly consistent with the treatment group 1 B of Example 2.

[0079] Table 5. Additive compositions used in the preparation of electrolytes for the treatment groups 9B to 1 IB of this example

[0080]

[0081]

[0082] Test Example 2

[0083] 1. Test objects

[0084] The batteries prepared in the treatment groups 1 B to 14B of Example 2 were subjected to electrochemical tests using a new Wei charge-discharge test cabinet.

[0085] 2. Test methods

[0086] This test example was tested according to the method provided in Test Example 1.

[0087] 3. Test results and analysis

[0088] The test results of this test example are shown in Table 6, in which the effects of the contents of the cyclic sulfate, fluorinated carboxylate polymer, lithium salt additive, sulfur-containing additive, and vinylene carbonate added in the additives on the performance of the prepared lithium ion batteries were mainly explored in this test example.

[0089] First, in the treatment groups 1 B to 4B, the effects of the contents of the cyclic sulfate added on the performance of the prepared lithium ion batteries were explored. From the test results, the content of the cyclic sulfate added would affect the TMs metal ion dissolution, and with the increase of the content of the cyclic sulfate, the dissolution of the TMs metal ion showed a trend of first decreasing and then increasing. This indicates that when the content of the cyclic sulfate added is too low, the improvement of the TMs metal ion dissolution problem is weak; when the content of the cyclic sulfate added is too high, due to the interface side reaction, it is not conducive to improving the cycle performance of the battery.

[0090] By comparing the test results of the treatment group 1B, the treatment group 5B and the comparison group 6A, it can be concluded that, with the cycle, TMs are continuously dissolved from the positive electrode and reduced and deposited in the negative electrode, thereby continuously destroying the SEI film, and the FEC can continuously repair the damaged SEI film, thereby improving the cycle performance.

[0091] By comparing the test results of the treatment group 1B and the treatment group 6B, it can be concluded that, since the VC can form an organic film in the negative electrode, thereby enhancing the stability of the SEI film, and further improving the cycle stability of the lithium ion battery using the same.

[0092] By comparing the test results of the treatment group 1B and the treatment group 7B, it can be concluded that LiPO2F2 can participate in the film forming process of the positive and negative electrodes, and further enhance the cycle performance of the lithium ion battery. In combination with the test results of the treatment groups 9B and 11B, the compactness of the SEI film formed by different lithium salt additives is different, which will affect the cycle performance of the lithium ion battery using the same.

[0093] By comparing the test results of the treatment group 1B and the treatment group 8B, it can be concluded that the introduction of PS can assist in film forming in the positive and negative electrodes, and due to its high thermal stability, it can further promote the effect of assisting in film forming in the positive and negative electrodes at high temperature. In combination with the test results of the treatment groups 10B-11B, the different sulfur-containing additives provide different effects of assisting in film forming, which will affect the high-temperature cycle performance of the lithium ion battery using the same.

[0094] Therefore, through the present test example, it can be proved that by matching the fluorocarboxylic acid ester polymer, the lithium salt additive, the sulfur-containing additive and the carbonate additive to adjust the electrolyte formula, the problem of rapid cycle capacity decay and voltage decay of the high-voltage positive electrode material system battery can be solved to different degrees.

[0095] Table 6. Test results of test example 2

[0096]

[0097] Example 3

[0098] In this example, the treatment group 1C is set according to the treatment group 1A of example 1. In addition, the formulations of the treatment groups 2C-3C of this example for preparing electrolyte are referred to the treatment group 1C, and the mass ratio of ethylene carbonate, diethyl carbonate and acetic acid-2,2-difluoroethyl ester in the organic solvent in the formulation is used as a variable to set different treatment groups, and the additive composition of each treatment group of this example for preparing electrolyte is shown in Table 7. In this example, the mass fraction of the organic solvent in the electrolyte is kept at 77%. Furthermore, each treatment group of this example is used to prepare the electrolyte and the lithium battery by referring to the treatment group 1A of example 1.

[0099] Table 7. Additive composition for preparing electrolyte in processing group 2C-3C of the present example

[0100]

[0101]

[0102] Processing group 5C

[0103] The present processing group prepares electrolyte and battery according to the formulation and method provided by processing group 1C of Example 3, and the difference between the present processing group and processing group 1A of Example 1 is that the present processing group does not add diethyl carbonate to prepare electrolyte, specifically, equal parts of ethylene carbonate: 2,2-difluoroethyl acetate = 15:20 by mass ratio are used to replace ethylene carbonate to prepare electrolyte. Except for the above difference, the operation of preparing electrolyte and battery in the present processing group is strictly consistent with processing group 1C of Example 3.

[0104] Processing group 6C

[0105] The present processing group prepares electrolyte and battery according to the formulation and method provided by processing group 1C of Example 3, and the difference between the present processing group and processing group 1A of Example 1 is that the present processing group does not add diethyl carbonate to prepare electrolyte, specifically, equal parts of ethylene carbonate: 2,2-difluoroethyl acetate = 15:20 by mass ratio are used to replace ethylene carbonate to prepare electrolyte. Except for the above difference, the operation of preparing electrolyte and battery in the present processing group is strictly consistent with processing group 1C of Example 3.

[0106] Test Example 3

[0107] 1. Test object

[0108] The batteries prepared by processing groups 1C-6C of Example 3 are subjected to electrochemical tests using a new Wei charge-discharge test cabinet.

[0109] 2. Test method

[0110] The present test example is tested according to the method provided by Test Example 1.

[0111] 3. Test results and analysis

[0112] The test results of the test example 3 are shown in Table 8, wherein in the test example 3, the effects of the ratio of the cyclic carbonate, the chain carbonate and the chain fluorinated ester added in the organic solvent and the material on the performance of the prepared lithium ion battery are mainly explored respectively. In the processing groups 5C-6C of Example 3, no diethyl carbonate and no difluoroacetic acid ethyl ester are added respectively, which causes different degrees of reduction in the cycle performance of the lithium ion battery using the same. In the processing groups 1C-4C of Example 3, the effects of the mass ratio of different vinyl carbonate, diethyl carbonate and difluoroacetic acid ethyl ester on the performance of the lithium ion battery using the same are explored. It can be seen from the test results that the cycle performance of the battery can be further improved when the cyclic carbonate: chain carbonate: chain fluorinated ester = 1-15: 20-70: 5-20.

[0113] Table 8. Test results of test example 3

[0114]

[0115] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A cyclic sulfate characterized in that, The chemical structure of the cyclic sulfate ester is shown in formula (1). Equation (1) Wherein, X is selected from any one of vinyl, propenyl, propargyl, acetocyano, propanyl, monofluoromethyl, difluoromethyl, and trifluoromethyl.

2. A process for the preparation of the cyclic sulfate according to claim 1, characterized in that, The method includes the following steps: The cyclic sulfate ester is obtained from ethylene sulfite as a raw material through chlorination, oxidation, fluorination, and recrystallization; or, Using 1,2,4-butanetriol as a raw material, the cyclic sulfate ester is obtained through cyclization, chlorination, fluorination, oxidation, and elimination reactions, followed by recrystallization; or, The cyclic sulfate ester is obtained by using propylene glycol as a raw material through cyclization reaction, chlorination reaction, fluorination reaction, oxidation reaction, and then recrystallization.

3. An electrolyte functional additive composition, characterized by: The functional additive composition includes the cyclic sulfate ester as described in claim 1.

4. The functional aid composition according to claim 3, wherein The functional additive composition further includes at least one of fluorocarboxylic acid ester polymers, lithium salt additives, sulfur-containing additives, and carbonate additives; The fluorocarboxylic acid ester polymer is fluoroethylene carbonate; The lithium salt additive is selected from at least one of lithium difluorosulfonylimide, lithium difluorophosphate, lithium dioxaborate, and lithium difluorooxaborate. The sulfur-containing additive is selected from at least one of 1,3-propanesulfonate lactone, 1-propylene-1,3-sulfonate lactone, and vinyl sulfate. The carbonate additive is vinylene carbonate.

5. The functional additive composition according to claim 4, characterized in that, The functional additive composition further includes the fluorocarboxylic acid ester polymer, the lithium salt additive, the sulfur-containing additive, and the carbonate additive.

6. The functional additive composition according to claim 5, characterized in that, The mass ratio of the cyclic sulfate ester to the fluorocarboxylic acid ester polymer to the lithium salt additive to the sulfur-containing additive to the carbonate additive is (0.3~1): (0.1~5): (0.5~1): (0.5~3).

7. An electrolyte, characterized in that, The electrolyte comprises an organic solvent, a lithium salt, and a functional additive composition as described in any one of claims 3 to 5.

8. The electrolyte as described in claim 7, characterized in that, The organic solvent accounts for 70% to 90% of the mass fraction of the electrolyte, and the organic solvent includes cyclic carbonates, chain carbonates, and chain fluorinated esters; calculated by mass ratio, the cyclic carbonate : chain carbonate : chain fluorinated ester = 1~15 : 20~70 : 5~20.

9. The electrolyte as described in claim 8, characterized in that, The chain-like fluoroester is selected from at least one of bis(2,2,2-trifluoroethyl) carbonate, ethyl trifluoroethyl carbonate, methyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl difluoroethyl carbonate, bis(2,2-difluoroethyl) carbonate, 2,2-difluoroethyl-2,2,2-trifluoroethyl carbonate, 2,2,3,3-tetrafluoropropyl methyl carbonate, 2,2,3,3,3-pentafluoropropyl ethyl carbonate, methyl fluoroacetate, ethyl fluoroacetate, 2-fluoroethyl acetate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, ethyl 2-fluoropropionate, 2,2,2-trifluoroethyl trifluoroacetate, 2,2-difluoroethyl trifluoroacetate, 2-fluoroethyl trifluoroacetate, ethyl trifluoroacetate, methyl trifluoroacetate, ethyl difluoroacetate, methyl difluoroacetate, methyl fluoroacetate, and ethyl 2-fluoropropionate.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 7 to 9.

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