Lithium ion battery electrolyte containing thioether cyano compound and application of lithium ion battery electrolyte

Abstract

The invention discloses an electrolyte additive containing a thioether cyano compound and an electrolyte containing the additive. The structural general formula of the additive is NC-S-R1-R2, R1 is selected from methyl, ethyl, propyl or butyl, and R2 is cyano or alkenyl. The invention further discloses application of the additive, the electrolyte containing the thioether cyano compound additive is applied to the lithium ion battery, especially the high-voltage lithium ion battery, and the electrolyte can be better than the electrolyte to form a stable CEI film on the surface of a positive electrode in the charging and discharging process; the additive is added into the high-voltage lithium ion battery, side reaction caused by dissolution of metal ions and direct contact with electrolyte in the charge-discharge process of the positive electrode material of the high-voltage lithium ion battery of over 4.5 V is avoided, and the additive participates in construction of a low-impedance SEI film, so that the interface charge transfer resistance is reduced, and the cycle and high-temperature performance of the high-voltage lithium ion battery is improved.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemistry, and specifically relates to lithium ion battery electrolyte technology, in particular to a high-voltage lithium ion battery electrolyte and its application. Background Art

[0002] With the increasing demand for energy density in new energy vehicles and portable electronic devices, the development of high-voltage (≥4.5V) lithium-ion batteries has become a key research direction. However, traditional carbonate-based electrolytes have significant defects under high voltage:

[0003] 1. Oxidative decomposition problem: When the charging voltage is ≥4.5V, the organic solvents in the electrolyte (such as EC, DEC) are prone to irreversible oxidation on the surface of the positive electrode, resulting in gas production, increased impedance and capacity attenuation.

[0004] 2. Insufficient interface stability: High-voltage positive electrode materials (such as lithium cobalt oxide) are prone to transition metal ion dissolution, which reacts with the electrolyte to generate by-products, destroying the stability of the electrode / electrolyte interface and exacerbating the growth of SEI film impedance.

[0005] 3. Limitations of Additives: While existing additives (such as FEC and VC) can improve some performance, they struggle to balance positive electrode protection at high voltages with negative electrode SEI film regulation. For example, sulfur-containing additives (such as DTD) can enhance oxidation resistance but may increase interfacial side reactions; while cyano compounds can stabilize the positive electrode, they lack compatibility with the negative electrode.

[0006] Current research indicates that designing dual-action additives that combine positive electrode CEI formation with negative electrode SEI regulation is a key path to overcoming the high-voltage bottleneck. To address this issue, the present invention proposes a high-voltage lithium-ion battery electrolyte containing a thioether cyano compound. Summary of the Invention

[0007] The purpose of the present invention is to propose a dual-effect additive containing a thioether cyano compound in view of the above-mentioned problems of the prior art, which has both the ability to form a positive electrode CEI film and the function of regulating the negative electrode SEI film. It is used as an additive to form an electrolyte containing a thioether cyano compound and is applied to high-voltage lithium-ion batteries.

[0008] The technical solutions adopted by the present invention are specifically as follows.

[0009] The present invention first provides an electrolyte additive, wherein the electrolyte additive is a thioether cyano compound, and the general structure of the compound is as follows:

[0010] NC-S-R1-R2

[0011] wherein R1 is selected from methyl, ethyl, propyl or butyl, and R2 is selected from cyano or alkenyl.

[0012] The present invention also provides an electrolyte solution, which comprises an electrolyte salt, a solvent and the electrolyte additive described above.

[0013] Furthermore, the mass percentage of the electrolyte additive in the electrolyte is 0.5-3%.

[0014] Furthermore, the electrolyte salt is one or a combination of lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, and lithium bis(trifluoromethanesulfonyl)imide. Preferably, the electrolyte salt is composed of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. More preferably, the molar ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 1:0.2-0.6.

[0015] Furthermore, the solvent includes one or more of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, vinylene carbonate, propylene sulfite, vinyl sulfate, propylene sultone, lithium difluorophosphate and triphenyl phosphite. Preferably, the solvent includes ethylene carbonate.

[0016] The present invention also provides a lithium-ion battery comprising a positive electrode, a negative electrode and the electrolyte as described above.

[0017] Furthermore, the lithium-ion battery particularly refers to a high-voltage lithium-ion battery, that is, a lithium-ion battery with an output voltage ≥4.5V.

[0018] The present invention provides a battery electrolyte containing a thioether cyano compound for use in lithium-ion batteries, especially high-voltage lithium-ion batteries. The thioether cyano compound is used as an electrolyte additive. During the charge and discharge process, it can be superior to the electrolyte in oxidizing on the positive electrode surface to form a stable CEI film, thereby avoiding the dissolution of metal ions in the ≥4.5V positive electrode material during the charge and discharge process and the occurrence of side reactions caused by direct contact with the electrolyte. In addition, the additive participates in the construction of a low-impedance SEI film, reduces the interfacial charge transfer resistance, and improves the cycle and high-temperature performance of the high-voltage lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a hydrogen nuclear magnetic spectrum test chart of the thioether cyano compound having structure 2 used in the examples of the present invention.

[0020] Figure 2 This is a hydrogen nuclear magnetic spectrum test chart of the thioether cyano compound having structure 6 used in the examples of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below in conjunction with the embodiments, but this does not constitute any limitation to the present invention. Any limited modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0022] In order to explain the technical content of the present invention in detail, further description will be given below in conjunction with the embodiments.

[0023] An electrolyte additive comprises a thioether cyano compound having the following general structure:

[0024] NC-S-R1-R2

[0025] wherein R1 is selected from methyl, ethyl, propyl or butyl, and R2 is selected from cyano or alkenyl. Specifically, the compound has any one or more of the following structural formulas: Structure 1 to Structure 8:

[0026] Structure 1:

[0027] Structure 2:

[0028] Structure 3:

[0029] Structure 4:

[0030] Structure 5:

[0031] Structure 6:

[0032] Structure 7:

[0033] Structure 8:

[0034] The electrolyte additives used in each embodiment of the present invention are thioether cyano compounds of Structures 1 to 8. The inventors prepared the thioether cyano compounds used in the present invention using the following method. However, this preparation method does not limit the use of the thioether cyano compounds of the present invention as electrolyte additives. The inventors have repeatedly verified that the compounds of Structures 1 to 8 used in the present invention are not limited by their preparation method or preparation process parameters. When using the thioether cyano compounds of the above-mentioned formulas, it is recommended that their purity be ≥99.9% and their water content be ≤50 ppm. This is because the lower the impurity content in the product, the less impact it has on the results. However, excessive water content may increase the occurrence of side reactions and may affect the observed effects. However, the recommended purity and water content are not necessary to achieve the objectives of the present invention.

[0035] The electrolyte additive thioether cyano compounds having the above-mentioned 8 structures used in the following embodiments of the present invention are synthesized according to the following method, as follows.

[0036] Raw materials 1 and 2 were added to the reaction solvent in a molar ratio, and the reaction was completed by reflux at 125° C. for 2-3 hours under nitrogen atmosphere. The reaction was then completed by extraction with an organic solvent, the aqueous phase was separated, and the organic phase was evaporated to dryness. Finally, water was removed to obtain the product thioether cyanide compound with a moisture content of ≤50 ppm. The purity was measured by gas chromatography to be ≥99.9%.

[0037] In the synthesis method, raw material 2 is potassium thiocyanate, raw material 1 is as shown in Table 1 below, the molar ratio of raw material 1 to raw material 2 is 2:3, the reaction solvent is DMF solvent, the organic solvent for extraction is ethyl acetate solvent, and the reaction conditions for preparing each thioether cyano compound are shown in Table 1. The thioether cyano compounds finally prepared were all tested by nuclear magnetic hydrogen spectrum to determine the structure of each product, confirming that the thioether cyano compounds of the above-mentioned structures 1 to 8 were obtained respectively. As shown in the attached Figure 1 This is the H NMR spectrum test diagram of the prepared thioether cyano compound having the above structure 2, as can be seen in the figure: 1 H-NMR (400MHz,CDCl3):δ5.75-5.84(m,1H),5.17-5.24(m,2H),3.01-3.05(m,2H),2.56-2.62(m,2H); Figure 2 This is the H NMR spectrum test diagram of the prepared thioether cyano compound having the above structure 6, as can be seen in the figure: 1H-NMR (400 MHz, CDCI3): δ 3.22 (m, 2H), 2.95 (m, 2H).

[0038] Table 1. Reaction conditions for obtaining thioether cyano compounds having structures 1 to 8 and information on the obtained products (purity and water content)

[0039] Compound structure Raw material 1 Product purity (%) Moisture content (ppm) Structure 1 3-Bromo-1-propene 99.95 14 Structure 2 4-Bromo-1-butene 99.91 7 Structure 3 5-Bromo-1-pentene 99.96 11 Structure 4 6-Bromo-1-hexene 99.95 8 Structure 5 2-Bromoacetonitrile 99.96 19 Structure 6 3-Bromopropionitrile 99.97 5 Structure 7 4-Bromobutyronitrile 99.95 14 Structure 8 5-Bromovaleronitrile 99.94 8

[0040] Example 1

[0041] In a closed environment with a moisture content of ≤10 ppm, organic solvents (ethylene carbonate, diethyl carbonate and methyl vinyl carbonate) were evenly mixed in a volume ratio of 3:3:4, and lithium salts (lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide) were added to the organic solvent in a molar ratio of 1:0.2 to prepare a 1.3 mol / L electrolyte. Finally, 0.5% by mass of the thioether cyanide compound having structure 1 prepared above was added as an electrolyte additive, and the mixture was stirred evenly to obtain the desired lithium-ion battery electrolyte.

[0042] Example 2 to Example 3

[0043] The preparation conditions, methods and steps of the lithium ion battery electrolyte in Examples 2-3 are the same as those in Example 1, except that the mass fraction of the structure 1 additive is different. The mass fractions of the structure 1 additive in the electrolyte of Examples 2-3 are 1.5% and 3%, respectively.

[0044] Example 4 to Example 6

[0045] The preparation conditions, methods and steps of the lithium-ion battery electrolytes in Examples 4-6 are the same as those in Example 1, except that the type and content of the additives are different. The additive is the thioether cyano compound having structure 5 prepared above as the electrolyte additive. The mass fractions of the structure 5 additive in the electrolyte in Examples 4-6 are 0.5%, 1.5% and 3%, respectively.

[0046] Comparative Example 1

[0047] In a closed environment with a moisture content of ≤10ppm, organic solvents (ethylene carbonate, diethyl carbonate and methyl vinyl carbonate) are evenly mixed in a volume ratio of 3:3:4, and lithium salts (lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide) are added to the organic solvent in a molar ratio of 1:0.2 to prepare a 1.3 mol / L lithium-ion battery basic electrolyte.

[0048] Performance Testing

[0049] The lithium ion battery electrolytes configured in Examples 1-6 and Comparative Example 1 were injected into a high-voltage lithium ion battery, wherein a 4.5V lithium cobalt oxide positive electrode material was selected for the positive electrode and a graphite material was selected for the negative electrode to prepare a 1000mAh lithium cobalt oxide battery. The capacity retention rate after 200 cycles, the capacity recovery rate after 7 days of high-temperature storage, the gas production, and the SEI film impedance were tested. After 200 cycles at room temperature, the nitrogen element analysis on the positive electrode surface was performed using EDS. The nitrogen element content can be used to understand the adhesion of the -CN group. The specific test method and test data are as follows:

[0050] 1. Normal temperature cycle test:

[0051] At a test temperature of 25°C, charge the battery to 4.5V at a constant current and constant voltage of 1C, cut off the current rate to 0.05C, leave it for 10 minutes, and then discharge it to 3.0V at a constant current of 1C. This is recorded as the initial discharge capacity. Repeat the charge and discharge for 200 cycles, and record the discharge capacity at the 200th cycle.

[0052] Capacity retention rate after 200 cycles = discharge capacity at 200th cycle / initial capacity * 100%

[0053] 2. Nitrogen element test on the positive electrode surface

[0054] After 200 cycles at room temperature, the battery was disassembled, the lithium cobalt oxide positive electrode was cleaned and dried, and the surface nitrogen atomic percentage was analyzed by EDS surface scanning. Five areas (10×10μm 2 ) and take the average value.

[0055] 3. SEI film impedance test

[0056] A button battery was assembled in the order of graphite negative electrode sheet / electrolyte / diaphragm / electrolyte / lithium metal. After charging and discharging at 0.1C three times, the battery was adjusted to 50% SOC. The AC impedance test was performed using an electrochemical workstation with a frequency range of 500,000 Hz–0.03 Hz and an amplitude of 10 mV. The AC impedance was tested and the impedance data of the SEI film was recorded.

[0057] 4. High temperature storage test

[0058] At the test temperature of 25℃, charge to 4.5V at a constant current and constant voltage of 0.33C, cut off the current rate at 0.05C, and let it sit for 10 minutes. Then discharge to 3.0V at a constant current of 0.33C, which is recorded as the initial capacity. Then charge to 4.5V at a constant current and constant voltage of 0.33C, cut off the current rate at 0.05C. Store the fully charged battery at a test environment of 60℃ for 7 days. After high-temperature storage, measure the internal gas volume of the battery by the drainage gas collection method. Then charge and discharge at 0.33C for 3 times at the test temperature of 25℃, and record the highest discharge capacity.

[0059] Capacity recovery rate after storage = (maximum discharge capacity after storage / initial capacity) × 100%.

[0060] The test results of the above-mentioned various properties of the above embodiments and comparative examples are shown in Table 2 below.

[0061] Table 2. Test data of Examples 1-6 and Comparative Example 1

[0062]

[0063] In the cycle test, the capacity retention rate of comparative example 1 is the lowest, indicating that the electrolyte is easily decomposed at a high voltage of 4.5V without additives, resulting in loss of active materials and capacity decay. After adding structure 1, the capacity retention rate is improved. For example, the capacity retention rate of Example 1 is 91.5%, the capacity retention rate of Example 2 is 98.1%, and the capacity retention rate of Example 3 is 96.3%. The performance of structure 5 is similar to that of structure 1. When such additives are present, the battery cycle performance is greatly improved, and the performance is best when the additive content is 1.5%. This is because the cyanide group has a strong electronegativity and is easily adsorbed on the positive electrode surface. It can better oxidize the electrolyte on the positive electrode surface to form a stable CEI film, avoiding the dissolution of metal ions in the positive electrode material during the charge and discharge process and the occurrence of side reactions caused by direct contact with the electrolyte.

[0064] After 200 cycles, nitrogen content was measured on the positive electrode surface. Comparative Example 1 had the lowest nitrogen content, reaching a background value of 0.09%, indicating that no cyanide groups adhered to the positive electrode surface in the absence of the additive. After adding Structures 1 and 5, higher additive levels correlated with higher nitrogen content on the positive electrode surface, indicating more cyanide groups adsorbed on the positive electrode surface and more complete surface coverage. However, at high concentrations, such as in Examples 3 and 6, where the additive content reached 3.0%, uneven deposition led to localized excess nitrogen, resulting in a decrease in capacity. This also indirectly illustrates the variation in cycle capacity retention when the additive content ranged from 0.5% to 3.0%.

[0065] SEI film impedance testing revealed that the SEI film in Comparative Example 1 had the highest impedance, at 25Ω. Adding additives of Structure 1 and Structure 5 reduced the impedance. This is because during the initial charge and discharge process of the battery, the electrolyte decomposes to form the SEI film. The additives contain cyano groups, thioether groups (-S-), and alkenyl groups that are reduced on the negative electrode surface. EDS surface scanning analysis of the negative electrode surfaces of Example 2 and Comparative Example 1 revealed nitrogen and sulfur elements. The nitrogen content on the surface of the negative electrode in Example 2 was 1.45%, and the sulfur content was 1.30%. The nitrogen content on the surface of the negative electrode in Comparative Example 1 was 0.05%, and the sulfur content was 0.03%. Due to the high electronegativity of cyano and thioether groups, they enhance their attraction to lithium ions, generating N-Li and S-Li compounds during reduction on the negative electrode surface, which improves ionic conductivity. Therefore, the addition of additives of Structure 1 and Structure 5 in each example reduced the impedance of the SEI film. However, if the additive content is too high, excessive polymerization may occur at the negative electrode, leading to an increase in the SEI film impedance.

[0066] In the high-temperature storage test, it was found that the capacity recovery rate and gas production of Examples 1-6 were better than those of Comparative Example 1. This is because the cyanide group in the additive is adsorbed on the surface of the positive electrode to participate in the construction of the CEI film, which avoids direct contact between the positive electrode material and the electrolyte in the fully charged state, and inhibits electrolyte oxidation and gas production at high temperatures. In addition, the additive participates in the construction of a low-impedance SEI film, reduces the interfacial charge transfer resistance, and improves the capacity recovery rate after storage. From the data, it was found that at 1.5%, the impedance was the lowest, the recovery rate was the highest, and the gas production was the least; when the additive content was 3.0%, the gas production increased, and the capacity recovery rate after storage decreased. This is because too much additive content will make the SEI film too thick, increase the impedance, and lead to more side reactions.

[0067] As can be seen from the test data of Examples 1-6 and the comparative example, the performance is optimal when the additive content is 1.5%. During their exploration, the inventors discovered that the additives of the other six structural formulas also achieved similar results. The following only lists the examples with the optimal percentage by mass of each structural additive in the electrolyte of 1.5% and the test analysis results. In the following examples, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are used as the electrolyte lithium salts. Lithium bis(fluorosulfonyl)imide has a much higher degree of dissociation and lower viscosity than lithium hexafluorophosphate. Lithium hexafluorophosphate easily decomposes to produce HF at high temperatures, which corrodes the electrode. The addition of lithium bis(fluorosulfonyl)imide consumes HF. Therefore, in the subsequent lithium salts, the molar ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is increased to 1:0.6.

[0068] Example 7

[0069] In a closed environment with a moisture content of ≤10ppm, organic solvents (ethylene carbonate, diethyl carbonate and methyl vinyl carbonate) are evenly mixed in a volume ratio of 3:3:4, and lithium salts (lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide) are added to the organic solvent in a molar ratio of 1:0.6 to prepare a 1.3 mol / L electrolyte. Finally, a 1.5% mass fraction of structure 1 additive is added and stirred evenly to obtain the desired lithium-ion battery electrolyte.

[0070] Example 8 to Example 14

[0071] The preparation conditions, methods and steps of the lithium-ion battery electrolytes in Examples 8-14 are the same as those in Example 7, except that the types of additives are different. The additive structures corresponding to Examples 8-14 are Structure 2, Structure 3, Structure 4, Structure 5, Structure 6, Structure 7 and Structure 8, respectively.

[0072] Comparative Example 2

[0073] In a closed environment with a moisture content of ≤10ppm, organic solvents (ethylene carbonate, diethyl carbonate and methyl vinyl carbonate) are evenly mixed in a volume ratio of 3:3:4, and lithium salts (lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide) are added to the organic solvent in a molar ratio of 1:0.6 to prepare a 1.3 mol / L lithium-ion battery basic electrolyte.

[0074] Performance Testing

[0075] The lithium-ion battery electrolytes configured in Examples 7-14 and Comparative Example 2 were subjected to an electrochemical stability window test and injected into a lithium-ion battery, wherein a 4.5V lithium cobalt oxide positive electrode material was selected as the positive electrode and a graphite material was selected as the negative electrode to prepare a 1000mAh lithium cobalt oxide battery. The capacity retention rate after 800 cycles at room temperature and 500 cycles at a high temperature of 45°C were tested. The specific test method and test data are as follows:

[0076] Electrochemical stability window test

[0077] Electrochemical stability window test was performed by linear sweep voltammetry, using platinum as working electrode, lithium metal as counter electrode, scan rate of 0.5 mV / s, and scan voltage range of 3-6 V.

[0078] Normal temperature cycle test

[0079] The initial capacity was recorded by charging at 1 C current rate to 4.5 V, cutting off at 0.05 C current rate, resting for 10 min, and then discharging at 1 C current rate to 3.0 V. The discharge capacity at the 800th cycle was recorded after 800 cycles of repeated charging and discharging.

[0080] Normal temperature 800-cycle capacity retention rate = discharge capacity at the 800th cycle / initial capacity * 100%.

[0081] High temperature cycle test

[0082] The initial capacity was recorded by charging at 1 C current rate to 4.5 V, cutting off at 0.05 C current rate, resting for 10 min, and then discharging at 1 C current rate to 3.0 V. The discharge capacity at the 500th cycle was recorded after 500 cycles of repeated charging and discharging.

[0083] High temperature 500-cycle capacity retention rate = discharge capacity at the 500th cycle / initial capacity * 100%.

[0084] The test results of the above properties of Examples 7-14 and Comparative Example 2 are shown in Table 3 below.

[0085] Table 3. Test data of Examples 7-14 and Comparative Example 2

[0086]

[0087] Electrochemical stability window test

[0088] Generally, for high-voltage lithium cobalt oxide batteries, the electrochemical stability window should be no less than 0.8 V higher than the maximum working voltage of the lithium cobalt oxide battery to inhibit the oxidative decomposition of the electrolyte. The electrochemical stability window of Comparative Example 2 is 4.8 V, indicating that the base electrolyte is more prone to oxidative decomposition at high voltage (4.5 V). After adding the additive, the electrochemical stability window is improved to 5.5-5.8 V. The window of all additive groups is higher than 5.5 V, meeting the requirements of 4.5 V high-voltage lithium ion batteries.

[0089] Normal temperature cycle and high temperature cycle test

[0090] The 800-week retention rate of Comparative Example 2 is only 62.5% at room temperature, and 51.5% at high temperature for 500 weeks, indicating that the capacity is severely attenuated during the cycle. After adding the additive, the capacity retention rate at room temperature reaches 90.6-94.5%, and the high-temperature retention rate reaches 81.8-89.1%. This is because the CEI film formed by the cyanide group at the positive electrode inhibits the dissolution of metal ions and the side reaction of the positive electrode N content data, and the additive constructs a low-impedance SEI at the negative electrode to reduce capacity attenuation. The positive electrode N content data and impedance data tested by the inventor are equivalent to those in Table 2 above, which also confirms these. Under high-temperature 45°C cycling, the high-temperature gas production data test results equivalent to those in Table 2 also confirm that the additive has achieved the effect of inhibiting electrolyte decomposition and gas production.

[0091] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications derived therefrom remain within the scope of protection of the present invention.

Claims

1. An electrolyte additive, characterized in that The electrolyte additive is a compound containing a thioether cyano group, and the general structure of the compound is as follows: NC-S-R1-R2; wherein R1 is selected from methyl, ethyl, propyl or butyl, and R2 is selected from cyano or alkenyl.

2. An electrolyte, characterized in that: The electrolyte solution comprises an electrolyte salt, a solvent, and the electrolyte additive according to claim 1 .

3. An electrolyte according to claim 2, characterized in that: The mass percentage of the electrolyte additive in the electrolyte is 0.5-3%.

4. An electrolyte according to claim 2, characterized in that: The electrolyte salt is one or a combination of lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate and lithium bis(trifluoromethanesulfonyl)imide.

5. An electrolyte according to claim 4, characterized in that: The electrolyte salt is composed of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the molar ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 1:0.2-0.

6.

6. An electrolyte according to claim 2, characterized in that: The solvent includes one or a combination of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, vinylene carbonate, propylene sulfite, vinyl sulfate, propylene sultone, lithium difluorophosphate and triphenyl phosphite.

7. An electrolyte according to claim 6, characterized in that: The solvent comprises ethylene carbonate.

8. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, and the electrolyte according to any one of claims 2 to 7 and / or the electrolyte additive according to claim 1.

9. A lithium-ion battery according to claim 8, characterized in that: The lithium-ion battery is a high-voltage lithium-ion battery, that is, a lithium-ion battery with an output voltage ≥ 4.5V.

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