Electrolyte and secondary battery using same

Abstract

An electrolyte. The electrolyte comprises a fluorine-containing ester additive. The ratio of the fluorine-containing ester additive in the electrolyte is 2-9% by mass percentages. The fluorine-containing ester additive comprises 2,2-difluoroethyl acetate, difluoroethylene carbonate and trifluoroethyl methyl carbonate.

Description

An electrolyte and a secondary battery using the same.

[0001] This application claims priority to Chinese Patent Application No. 2024118602288, filed with the Chinese Patent Office on December 16, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery materials technology, specifically to an electrolyte and a secondary battery using the same. Background Technology

[0003] In recent years, rechargeable battery technology has developed rapidly, gradually becoming a core driving force leading the electrification of automobiles and new energy storage. Consequently, users have placed higher demands on the energy density of rechargeable batteries. To improve the energy density of rechargeable batteries, the industry has made various attempts, such as innovating positive and negative electrode active materials. The application of high-nickel positive electrode active materials and silicon-based negative electrode active materials are effective ways to improve the energy density of rechargeable batteries. Technical issues

[0004] The trend towards larger capacity and higher energy density increases the energy of thermal runaway in secondary battery cells, raising the risk of flammability and explosion. Technical solutions

[0005] According to a first aspect of this application, an electrolyte is provided, the electrolyte comprising fluorinated ester additives, wherein the fluorinated ester additives account for 2% to 9% of the electrolyte by mass percentage, and the fluorinated ester additives include ethyl 2,2-difluoroacetate (DFEA), difluoroethylene carbonate (DFEC), and trifluoroethyl methyl carbonate (FEMC).

[0006] According to a second aspect of this application, a secondary battery is provided, the secondary battery comprising a positive electrode, a negative electrode and the electrolyte as described above. Beneficial effects

[0007] In this application, DFEA, DFEC, and FEMC are combined to participate in the composition of the electrolyte, thereby enabling the electrolyte provided by this application to effectively reduce the reaction heat between the electrolyte and the positive / negative active materials, effectively reduce the reaction heat and combustion heat of the secondary battery, help prevent thermal runaway of the secondary battery, play a certain flame-retardant role in the operation of the secondary battery, and improve the safety performance of the secondary battery. Attached Figure Description

[0008] Figure 1 shows the DSC test results of the pouch cell using the electrolyte formulation D1.

[0009] Figure 2 shows the DSC test results of the pouch cell using the electrolyte of formulation 1;

[0010] Figure 3 shows the DSC test results of the pouch cell using the electrolyte of formulation 2. Embodiments of the present invention

[0011] In some embodiments, the proportion of fluorinated ester additives in the electrolyte can be 2%, 4%, 5%, 7%, 9%, etc., by mass percentage, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0012] In some implementations, the mass ratio of DFEA:DFEC:FEMC in the electrolyte is 0.5–3:1–3:1–3. The ratio of DFEA, DFEC, and FEMC is optimized to improve safety. The mass ratio of DFEA:DFEC:FEMC can be 0.5:1:1, 3:1:1, 1:1:1, 2:1.5:1.5, 0.5:3:3, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0013] In some embodiments, the mass ratio of DFEA:DFEC:FEMC in the electrolyte is 1.2–1.8:1.2–1.8:0.8–1.1. By optimizing the ratio of DFEA, DFEC, and FEMC in the electrolyte provided by this solution, the heat generated by the reaction between the electrolyte and the positive and negative electrode active materials can be reduced, thereby fully leveraging the advantages of the electrolyte provided by this solution in improving the safety performance of secondary batteries. The mass ratio of DFEA, DFEC, and FEMC (DFEA:DFEC:FEMC) can be 1.2:1.2:0.8, 1.8:1.8:1.1, 1.5:1.5:1, 1.5:1.2:0.8, 1.2:1.8:0.8, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0014] In some embodiments, the proportion of fluorinated ester additives in the electrolyte is 2% to 5% by mass percentage. The proportion of fluorinated ester additives in the electrolyte can be 2%, 3%, 4%, 4.5%, 5%, etc., by mass percentage, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0015] In some embodiments, the electrolyte also includes vinylene carbonate (VC).

[0016] In some embodiments, the electrolyte also includes an organic solvent, including dimethyl carbonate (DMC), which comprises 52% to 59% by mass. Based on the application of DFEA, DFEC, and FEMC, DMC is used in combination with the above materials to achieve a balance between the safety and cycle performance of the secondary battery using this electrolyte, thus ensuring the lifespan of the secondary battery using this electrolyte. The mass percentage of DMC in the electrolyte can be 52%, 54%, 55%, 57%, 59%, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0017] In some embodiments, in the electrolyte, the mass ratio of DMC to fluorinated ester additives is 55-60:2-5. The mass ratio of DMC to fluorinated ester additives can be 55:2, 60:2, 55:5, 60:5, 57:4, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0018] In some embodiments, the organic solvent also includes propylene carbonate (PC) and fluoroethylene carbonate (FEC). Based on the application of DFEA, DFEC, and FEMC, the composition of the organic solvent in the electrolyte is selected to improve the electrolyte's cycle performance.

[0019] In some embodiments, the mass ratio of PC:FEC:DMC in the electrolyte is 11–20:5–15:52–59. The mass ratio of PC:FEC:DMC can be 11:5:52, 20:15:59, 11:15:52, 11:5:59, 20:5:52, 15:10:55, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0020] In some embodiments, the above-mentioned secondary battery satisfies at least one of the following a and b: a. The positive electrode active material in the secondary battery includes a high-nickel positive electrode active material, wherein in the high-nickel positive electrode active material, the total amount of metal elements other than lithium is A, the amount of nickel is B, and 0.6 ≤ B / A < 1; b. The negative electrode active material in the secondary battery includes a silicon-based negative electrode active material.

[0021] Example 1

[0022] 1. Prepare the electrolyte

[0023] According to Table 1, this embodiment requires the preparation of electrolytes with formula numbers 1, 2, D1, D2, D3, D4, D5, D6, and D7 in Table 1. Materials are prepared according to the electrolyte formula components shown in Table 1. After preparation, the required materials are mixed in the specified amounts according to the different formulas and fully dissolved to form a homogeneous solution, thus completing the electrolyte preparation.

[0024] Table 1. Electrolyte formulation required for Example 1

[0025]

[0026] 2. Preparation of pouch cells

[0027] Using the electrolyte prepared in this embodiment, soft-pack batteries with a capacity of 3.3 Ah were prepared. The specific operations are as follows:

[0028] S1. Prepare materials according to the mass ratio of ternary material NCM811: binder polyvinylidene fluoride (PVDF): conductive agent = 97:1.6:1.4. Use the above materials to prepare positive electrode slurry. Use aluminum foil as positive electrode current collector. Coat the surface of the aluminum foil with positive electrode slurry and dry it to transform the positive electrode slurry coating into a positive electrode active material layer, thereby obtaining a soft-pack positive electrode.

[0029] S2. Prepare materials according to the mass ratio of silicon-carbon anode material (silicon doping ratio 20wt.%): aqueous binder: conductive agent = 96:3:1. Use the above materials to prepare a negative electrode slurry. Use copper foil as the negative electrode current collector. Coat the surface of the copper foil with the negative electrode slurry and dry it to transform the negative electrode slurry coating into a negative electrode active material layer (negative electrode specific capacity of 600mAh / g). Thus, the negative electrode of the soft pack battery is obtained.

[0030] S3. Using a PE film with a ceramic coating on its surface as a separator, the soft-pack positive electrode, the separator, and the soft-pack negative electrode are stacked in sequence to make a battery cell. The compaction density of the battery cell obtained in this way is 1.4 g / cm³.

[0031] S4. The battery cell obtained in S3 is placed into a soft-pack casing, and the electrolyte obtained in this embodiment is injected. After vacuum sealing, standing, formation, shaping and other processes, a soft-pack battery is obtained.

[0032] 3. Needle penetration resistance test and high temperature resistance test

[0033] The pouch cell prepared in this embodiment was used as the test object for the nail penetration resistance test and the high temperature resistance test. Based on the differences in the composition of the electrolytes used, 50 replicates were set for each type of pouch cell, with each replicate consisting of one pouch cell. The specific test methods for the nail penetration resistance test and the high temperature resistance test are described below.

[0034] (1) Testing method

[0035] Needle penetration test: After fully charging the test object, use a Φ3mm high-temperature resistant steel needle (with a cone angle of 45-60° at the needle tip, and a smooth surface free of rust, oxide layer and oil) to penetrate the soft-pack battery from a direction perpendicular to the battery plate at a speed of (25±5)mm / s. The penetration position should be close to the geometric center of the pierced surface. The steel needle remains in the soft-pack battery for 1 hour. Observe the fire situation of the test object and count and calculate the number of test objects that caught fire.

[0036] High temperature resistance test: The test object is placed in a hot oven at 150℃ for 30 minutes, the ignition of the test object is observed, and the number of test objects that ignite is counted and calculated.

[0037] (2) Test results

[0038] The test results are shown in Table 2. As can be seen from the results in Table 2, only the pouch batteries using electrolyte formula 1 and electrolyte formula 2 achieved a 0% percentage of battery content in both the needle penetration test and the high temperature resistance test. Pouch batteries using electrolyte formulas D1, D2, D3, D4, D5, D6, and D7 all experienced fires during the tests.

[0039] Formula D1 does not contain DFEA, DFEC, or FEMC. Test results show that pouch batteries using formula D1 electrolyte almost universally caught fire in both the nail penetration and high-temperature resistance tests. Formulas D5, D6, and D7 contain only one of DFEA, DFEC, and FEMC. Comparing the test results for these electrolyte formulas with those for formula D1 demonstrates that introducing one or two of DFEA, DFEC, and FEMC into the electrolyte does not effectively improve battery safety or heat release.

[0040] Formulas D2, D3, and D4 lack one of DFEA, DFEC, and FEMC, respectively. Compared to pouch cells using electrolytes D1, D5, D6, and D7, the percentage of pouch cells using electrolytes D2, D3, and D4 that caught fire in the nail penetration and high temperature resistance tests has decreased to some extent; however, the percentage of pouch cells that caught fire in these tests remains relatively high.

[0041] In summary, the test results in Table 2 show that using DFEA, DFEC, and FEMC together as fluorinated ester additives in the preparation of electrolyte can significantly improve the safety performance of pouch batteries.

[0042] Table 2. Statistical results of the needle penetration resistance test and high temperature resistance test of the soft-pack battery in Example 1

[0043]

[0044] 4. DSC Test

[0045] In the pouch cells prepared in this embodiment, pouch cells using electrolyte formulation 1, electrolyte formulation 2, and electrolyte formulation D1 respectively were used as test objects for DSC testing.

[0046] (1) Testing method

[0047] The specific steps for DSC testing are as follows:

[0048] S1. Disassemble the fully charged pouch battery used as the test subject and pour out the electrolyte for later use;

[0049] S2. Separate the positive and negative electrodes, clean them separately with DMC and then dry them. Then use a ceramic knife to scrape the positive and negative active material layers to obtain positive / negative active material powder for later use.

[0050] S3. Set the relevant test parameters of the DSC analyzer as follows: temperature range: 25-500℃; atmosphere: argon (Ar); heating rate: 5℃ / min;

[0051] S4. Record the mass of the empty aluminum crucible used to load the sample to be tested, and then put the aluminum crucible into the DSC tester and perform DSC test under the test conditions set in S3 to obtain the reference curve of the empty crucible.

[0052] S5. The positive electrode active material powder, the negative electrode active material powder, and the soft-pack battery are loaded into the aluminum crucible used in S4. The aluminum lid of the aluminum crucible is used to cover the open end of the aluminum crucible, and then the opening is pressed to seal it. Then, the DSC test is performed under the test conditions set in S3.

[0053] (2) Test results

[0054] Figure 1 shows the DSC test results of the pouch cell using electrolyte formulation D1, with a heat release of 2114 J / g. Figure 2 shows the DSC test results of the pouch cell using electrolyte formulation 1, with a heat release of 1276 J / g. Figure 3 shows the DSC test results of the pouch cell using electrolyte formulation 2, with a heat release of 1328 J / g. Clearly, compared to electrolyte formulation D1, the reaction heat generated between electrolyte formulation 1 and electrolyte formulation 2 and the positive and negative electrode active materials is significantly lower. Therefore, the pouch cells using electrolyte formulation 1 and electrolyte formulation 2 exhibit better safety performance, consistent with the test results of the needle penetration and high-temperature resistance tests described in this embodiment.

[0055] Example 2

[0056] 1. Prepare the electrolyte

[0057] According to Table 3, this embodiment requires the preparation of electrolytes with formula numbers 3, 4, 5, 6, 7, and 8 in Table 3. The materials are prepared according to the electrolyte formula composition shown in Table 3. For ease of comparison, Table 3 also shows the component composition of electrolytes formula 1, formula 2, and formula D1 prepared in Example 1. After the materials are prepared, the required materials are mixed in the specified amounts according to the different formulas and fully dissolved to form a homogeneous solution, thus completing the electrolyte preparation.

[0058] Table 3. Electrolyte formulation required for Example 2

[0059]

[0060] 2. Preparation of pouch cells

[0061] Using the electrolyte prepared in this embodiment, pouch batteries with a capacity of 3.3Ah were prepared. Except for the difference in the electrolyte used, the operation of preparing pouch batteries in this embodiment is consistent with the relevant operation of preparing pouch batteries in Example 1.

[0062] 3. Needle penetration resistance test and high temperature resistance test

[0063] The pouch cell prepared in this embodiment was used as the test object for the nail penetration test and the high temperature resistance test. Based on the difference in the composition of the electrolyte used, 50 replicates were set for each type of pouch cell, and each replicate was a pouch cell.

[0064] (1) Testing method

[0065] Apart from the difference in the test objects, the specific test methods for the needle penetration test and high temperature resistance test in this embodiment are consistent with the relevant operations for the needle penetration test and high temperature resistance test in Embodiment 1.

[0066] (2) Test results

[0067] The test results are shown in Table 4. For easy comparison, Table 4 also shows the test results of the needle penetration test and high temperature resistance test of the soft pack batteries using electrolyte formula 1, electrolyte formula 2 and electrolyte formula D1 respectively in Example 1.

[0068] In this embodiment, the pouch batteries using electrolytes Formula 1, Formula 2, and Formula 3 did not ignite during the needle penetration and high-temperature resistance tests, indicating that all three electrolytes have good safety performance. Formula 1 and Formula 3 contain the same ratio of DFEA, DFEC, and FEMC. Similarly, Formula 8 contains the same ratio of DFEA, DFEC, and FEMC. However, because Formula 8 contains a relatively lower total amount of DFEA, DFEC, and FEMC, the pouch battery using Formula 8 is less safe than those using Formula 1 and Formula 3.

[0069] Comparing electrolyte formulations 2, 3, 4, 5, 6, and 7, we found that these formulations contain the same total amounts of DFEA, DFEC, and FEMC; the difference lies in the ratio of these three materials. Test results of soft-pack batteries using these electrolytes show that when the mass ratio of DFEA, DFEC, and FEMC in the electrolyte formulation meets the criteria of DFEA:DFEC:FEMC = 0.5–3:1–3:1–3, it is beneficial to improve the battery's safety performance.

[0070] Table 4. Statistical results of the needle penetration resistance test and high temperature resistance test of the soft-pack battery in Example 2

[0071]

[0072] 4. Cyclic performance test

[0073] The soft-pack batteries based on electrolyte formulations 1, 2, 3, 8, and D1 were used as the test objects for cycle performance testing.

[0074] (1) Testing method

[0075] The pouch cell battery used as the test subject was placed in a constant temperature chamber and charged to 4.2V at 1.0C at (25±2)℃. Then, it was charged to 0.05C at a constant voltage and allowed to rest for 10 minutes before being discharged to 2.5V at 1.0C, ready for room temperature cycle testing. Before and during the cycle test, the capacity retention rate of the pouch cell battery was tested every 50 cycles.

[0076] (2) Test results

[0077] As shown in Table 5, under the same test conditions, among the test subjects participating in the cycle performance test, the pouch battery using electrolyte formula 1 showed the highest cycle capacity retention. As mentioned above, the electrolyte formulas 1, 3, and 8 contain the same ratio of DFEA, DFEC, and FEMC; the difference lies in the total content of DFEA, DFEC, and FEMC in the electrolyte. The cycle performance test results of pouch batteries using the above three electrolytes show that as the total content of DFEA, DFEC, and FEMC in the electrolyte increases, the cycle stability of the pouch battery exhibits a trend of first improving and then deteriorating. Among the three electrolytes, electrolyte formula 1, with a total content of 4% DFEA, DFEC, and FEMC, showed the best cycle stability in the pouch battery tested.

[0078] Furthermore, as mentioned above, both electrolyte formulations 2 and 3 contain the same total amount of DFEA, DFEC, and FEMC. The difference lies in the ratio of these three materials. Based on the test results shown in Table 5, electrolyte formulation 3, with a mass ratio of DFEA:DFEC:FEMC of 1.5:1.5:1, exhibits better battery cycle stability.

[0079] Table 5. Statistical analysis of cycle performance test results of the pouch battery in Example 2

[0080]

[0081] Example 3

[0082] 1. Prepare the electrolyte

[0083] According to Table 6, this embodiment requires the preparation of electrolytes with formula numbers 9, D9, 10, and D10 in Table 6. The materials are prepared according to the electrolyte formula composition shown in Table 6. For ease of comparison, Table 6 also shows the component composition of electrolytes 1 and D1 prepared in Example 1. To facilitate comparison, the electrolyte formulas shown in Table 6 are grouped as follows: Group 1: Formulas 1 and D1; Group 2: Formulas 9 and D9; Group 3: Formulas 10 and D10. In Table 6, DEC refers to diethyl carbonate, and EMC refers to methyl ethyl carbonate. After preparation, the required materials are mixed in the appropriate amounts according to the different formulas and fully dissolved to form a homogeneous solution, thus completing the electrolyte preparation.

[0084] Table 6. Electrolyte formulation required for Example 3

[0085]

[0086] 2. Preparation of pouch cells

[0087] Using the electrolyte prepared in this embodiment, pouch batteries with a capacity of 3.3Ah were prepared. Except for the difference in the electrolyte used, the operation of preparing pouch batteries in this embodiment is consistent with the relevant operation of preparing pouch batteries in Example 1.

[0088] 3. Needle penetration resistance test and high temperature resistance test

[0089] The pouch cell prepared in this embodiment was used as the test object for the nail penetration test and the high temperature resistance test. Based on the difference in the composition of the electrolyte used, 50 replicates were set for each type of pouch cell, and each replicate was a pouch cell.

[0090] Apart from the difference in the test objects, the specific test methods for the needle penetration test and high temperature resistance test in this embodiment are consistent with the relevant operations for the needle penetration test and high temperature resistance test in Embodiment 1.

[0091] 4. Cyclic performance test

[0092] The pouch cell prepared in this embodiment was used as the test object for cycle performance testing.

[0093] Apart from the difference in the test objects, the specific test method for the loop performance test in this embodiment is consistent with the relevant operations for the loop performance test in Embodiment 2.

[0094] 5. Test Results

[0095] The test results are shown in Table 7. For easy comparison, Table 7 also shows the test results of the needle penetration test and high temperature resistance test of the soft pack batteries using Formulation 1 electrolyte and Formulation D1 electrolyte respectively in Example 1, and the cycle performance test results of the soft pack batteries using Formulation 1 electrolyte and Formulation D1 electrolyte respectively in Example 2.

[0096] Comparing the test results of the pouch cell using electrolyte formula 9 and the pouch cell using electrolyte formula D9 in this embodiment, the former showed a significantly lower proportion of pouch cells catching fire in the nail penetration and high temperature resistance tests. Furthermore, in the cycle capacity retention test, under the same cycle conditions, the former exhibited a higher cycle capacity retention rate, indicating that it possesses superior safety performance and cycle stability. Comparing the test results of the pouch cell using electrolyte formula 1 and the pouch cell using electrolyte formula D1 in Examples 1 and 2, and comparing the test results of the pouch cell using electrolyte formula 10 and the pouch cell using electrolyte formula D10 in this embodiment, similar conclusions were reached. Based on the above comparison results, it is further demonstrated that using DFEA, DFEC, and FEMC in combination as electrolyte components can effectively improve battery safety performance, and also that using DFEA, DFEC, and FEMC in combination as electrolyte components can improve battery cycle stability.

[0097] The difference between Formulas 1, 9, and 10 lies in the different carbonate solvents contained in the electrolytes. Formula 1 contains DMC, Formula 9 contains DEC, and Formula 10 contains EMC. Based on these differences, the pouch cells using these three electrolyte formulas exhibit varying cycle stability, with the pouch cell using Formula 1 showing the best cycle stability.

[0098] The difference between formulations D1, D9, and D10 lies in the different carbonate solvents they contain. Formulation D1 contains DMC, formulation D9 contains DEC, and formulation D10 contains EMC. These differences result in variations in cycle stability for pouch cells using these three electrolyte formulations; however, the safety performance and cycle stability of pouch cells using formulation D1 are not optimal.

[0099] The above comparison shows that introducing DMC into the electrolyte, which uses DFEA, DFEC, and FEMC in combination, is beneficial for obtaining an electrolyte with higher cycle stability. However, if the electrolyte does not simultaneously contain DFEA, DFEC, and FEMC, using DMC as the organic solvent component of the electrolyte does not necessarily improve the cycle stability of the electrolyte.

[0100] Table 7. Statistical analysis of performance test results of the pouch battery in Example 3

[0101]

[0102] Example 4

[0103] 1. Prepare the electrolyte

[0104] According to Table 8, this embodiment requires the preparation of electrolytes with formula numbers 11, D11, 12, and D12 in Table 8. The materials are prepared according to the electrolyte formula composition shown in Table 8. For ease of comparison, Table 8 also shows the component composition of electrolytes 1 and D1 prepared in Example 1. To facilitate comparison, the electrolyte formulas shown in Table 8 are grouped as follows: Group 1: Formula 1, Formula D1; Group 4: Formula 11, Formula D11; Group 5: Formula 12, Formula D12. In Table 8, EC refers to ethylene carbonate. After preparation, the required materials are mixed in the appropriate amounts according to the different formulas and fully dissolved to form a homogeneous solution, thus completing the electrolyte preparation.

[0105] Table 8. Electrolyte formulation required for Example 4

[0106]

[0107] 2. Preparation of pouch cells

[0108] Using the electrolyte prepared in this embodiment, pouch batteries with a capacity of 3.3Ah were prepared. Except for the difference in the electrolyte used, the operation of preparing pouch batteries in this embodiment is consistent with the relevant operation of preparing pouch batteries in Example 1.

[0109] 3. Needle penetration resistance test and high temperature resistance test

[0110] The pouch cell prepared in this embodiment was used as the test object for the nail penetration test and the high temperature resistance test. Based on the difference in the composition of the electrolyte used, 50 replicates were set for each type of pouch cell, and each replicate was a pouch cell.

[0111] Apart from the difference in the test objects, the specific test methods for the needle penetration test and high temperature resistance test in this embodiment are consistent with the relevant operations for the needle penetration test and high temperature resistance test in Embodiment 1.

[0112] 4. Cyclic performance test

[0113] The pouch cell prepared in this embodiment was used as the test object for cycle performance testing.

[0114] Apart from the difference in the test objects, the specific test method for the loop performance test in this embodiment is consistent with the relevant operations for the loop performance test in Embodiment 2.

[0115] 5. Test Results

[0116] The test results are shown in Table 9. For ease of comparison, Table 9 also shows the test results of the nail penetration resistance test and high temperature resistance test for the pouch batteries using electrolytes of Formulation 1 and Formulation D1 respectively in Example 1, and the cycle performance test results for the pouch batteries using electrolytes of Formulation 1 and Formulation D1 respectively in Example 2. Comparing the test results of the pouch battery using electrolyte of Formulation 11 and the pouch battery using electrolyte of Formulation D11 in this example, the former shows a significantly lower proportion of pouch batteries catching fire in the nail penetration resistance test and high temperature resistance test. In the cycle capacity retention test, under the same cycle conditions, the former shows a higher cycle capacity retention rate, indicating that the former has higher safety performance and cycle stability. Comparing the test results of the pouch battery using electrolyte of Formulation 1 and the pouch battery using electrolyte of Formulation D1 in Examples 1 and 2, and comparing the test results of the pouch battery using electrolyte of Formulation 12 and the pouch battery using electrolyte of Formulation D12 in this example, similar conclusions can be drawn. Based on the above comparison results, it is further demonstrated that using DFEA, DFEC and FEMC in combination as electrolyte components can effectively improve battery safety performance and improve battery cycle stability.

[0117] The difference between Formula 1, Formula 11, and Formula 12 lies in the different organic solvent components contained in the electrolyte. Compared to Formula 1, Formula 11 uses PC instead of FEC, thus eliminating FEC, while Formula 12 uses EC instead of PC, eliminating PC. Based on these differences, the safety performance and cycle stability of pouch batteries using the three electrolyte formulas also differ. The pouch battery using Formula 1 electrolyte exhibits the best cycle stability.

[0118] The difference between formulations D1, D11, and D12 lies in the different organic solvent components in the electrolyte. Compared to formulation D1, formulation D11 uses PC instead of FEC, thus eliminating FEC, while formulation D12 uses EC instead of PC, eliminating PC. Based on these differences, the safety performance and cycle stability of pouch batteries using these three electrolyte formulations also differ. However, the cycle stability of pouch batteries using formulation D1 electrolyte is not optimal.

[0119] The above comparison shows that in electrolytes using DFEA, DFEC, and FEMC in combination, introducing a certain amount of FEC and PC into the electrolyte is beneficial for obtaining an electrolyte with higher cycle stability. However, if the electrolyte does not simultaneously contain DFEA, DFEC, and FEMC, introducing a certain amount of FEC and PC into the electrolyte does not necessarily improve the cycle stability of the electrolyte.

[0120] Table 9. Statistical analysis of performance test results of the pouch battery in Example 4

[0121]

Claims

1. An electrolyte comprising fluorinated ester additives, wherein the fluorinated ester additives account for 2% to 9% of the electrolyte by mass percentage, and the fluorinated ester additives include ethyl 2,2-difluoroacetate, difluoroethylene carbonate, and trifluoroethyl methyl carbonate.

2. The electrolyte as described in claim 1, wherein: In the electrolyte, the mass ratio of ethyl 2,2-difluoroacetate to ethylene difluorocarbonate to trifluoroethyl methyl carbonate is 0.5–3:1–3:1–3.

3. The electrolyte as described in claim 2, wherein: In the electrolyte, the mass ratio of ethyl 2,2-difluoroacetate: ethylene difluorocarbonate: trifluoroethyl methyl carbonate is 1.2–1.8: 1.2–1.8: 0.8–1.

1.

4. The electrolyte as described in claim 1, wherein: The fluorinated ester additives account for 2% to 5% of the electrolyte by mass percentage.

5. The electrolyte of claim 1, wherein the electrolyte further comprises other additives, the other additives comprising at least one of vinylene carbonate, ethylene ethylene carbonate, and fluoroethylene carbonate.

6. The electrolyte according to any one of claims 1 to 5, wherein the electrolyte further comprises an organic solvent, wherein the organic solvent comprises dimethyl carbonate, and the proportion of dimethyl carbonate in the electrolyte is 52% to 59% by mass percentage.

7. The electrolyte as described in claim 6, wherein: In the electrolyte, the mass ratio of dimethyl carbonate to the fluorinated ester additive is 55-60:2-5.

8. The electrolyte of claim 6, wherein the organic solvent further comprises propylene carbonate and fluoroethylene carbonate.

9. The electrolyte as described in claim 8, wherein: In the electrolyte, the mass ratio of propylene carbonate: fluoroethylene carbonate: dimethyl carbonate is 11-20: 5-15: 52-59.

10. A secondary battery, the secondary battery comprising a positive electrode, a negative electrode and an electrolyte as described in any one of claims 1 to 9.

11. The secondary battery as claimed in claim 10, wherein, The secondary battery satisfies at least one of the following a and b: a. The positive electrode active material in the secondary battery includes a high-nickel positive electrode active material, wherein in the high-nickel positive electrode active material, the total amount of metal elements other than lithium is A, the amount of nickel is B, and 0.6 ≤ B / A < 1. b. The negative electrode active material in the secondary battery includes silicon-based negative electrode active material.

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