Electrolyte and secondary battery using the same

Abstract

The application provides an electrolyte, which comprises a fluorine-containing ester additive, wherein the fluorine-containing ester additive accounts for 2-9% of the electrolyte in terms of mass percentage, and the fluorine-containing ester additive comprises 2,2-difluoroacetic acid ethyl ester, difluoroethylene carbonate and trifluoroethyl methyl carbonate. In the scheme, the DFEA, the DFEC and the FEMC are matched to participate in the component construction of the electrolyte, so that the electrolyte provided by the scheme can effectively reduce the reaction heat between the electrolyte and the positive active material / negative active material, can effectively reduce the reaction heat and the combustion heat of the secondary battery, is beneficial to preventing the thermal runaway of the secondary battery, plays a certain flame-retardant role in the working process of the secondary battery, and improves the safety performance of the secondary battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of battery materials, and particularly relates to an electrolyte and a secondary battery using the same. BACKGROUND

[0002] In recent years, secondary battery technology has developed rapidly and gradually become the core driving force leading the electrification of automobiles and new energy storage. With this, users have higher requirements for the energy density of secondary batteries. In order to improve the energy density of secondary batteries, various attempts have been made in the industry, such as through innovation of positive and negative active materials, application of high-nickel positive active materials and silicon-based negative active materials, which are effective ways to improve the energy density of secondary batteries. However, the development direction of large capacity and high energy density increases the energy of thermal runaway of secondary battery cells and increases the risk of flammability and explosion of the cells. The safety hazard of flammability and explosion shakes the user's confidence in using high-energy-density secondary batteries, and has become one of the main bottlenecks restricting the industrialization and large-scale application of high-energy-density secondary batteries. SUMMARY

[0003] In order to reduce the flammable and explosive risk of high-energy-density secondary batteries and improve the safety performance of secondary batteries, the present application provides an electrolyte and a secondary battery using the same.

[0004] According to a first aspect of the present application, an electrolyte is provided, which comprises a fluorine-containing ester additive, the proportion of the fluorine-containing ester additive in the electrolyte is 2% to 9% calculated in terms of mass percentage, and the fluorine-containing ester additive comprises 2,2-difluoroethyl acetate (DFEA), difluoroethylene carbonate (DFEC) and trifluoroethyl methyl carbonate (FEMC). In this scheme, DFEA, DFEC and FEMC are used to participate in the component construction of the electrolyte, so that the electrolyte provided by this scheme can effectively reduce the reaction heat between the electrolyte and the positive active material / negative active material, effectively reduce the reaction heat and combustion heat of the secondary battery, and be beneficial to prevent the secondary battery from thermal runaway, play a certain flame-retardant role in the working process of the secondary battery, and improve the safety performance of the secondary battery. The proportion of the fluorine-containing ester additive in the electrolyte can be 2%, 4%, 5%, 7%, 9% and the like calculated in terms of mass percentage, but is not limited to the listed values, and other values not listed in this range are also applicable.

[0005] Preferably, in the electrolyte, the mass ratio of DFEA:DFEC:FEMC is 0.5-3:1-3:1-3. The ratio of DFEA, DFEC and FEMC is optimized for the purpose of improving safety performance. 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, and other values not listed within the range are also applicable.

[0006] Preferably, in the electrolyte, the mass ratio of DFEA:DFEC:FEMC is 1.2-1.8:1.2-1.8:0.8-1.1. By further optimizing the ratio of DFEA, DFEC and FEMC in the electrolyte provided in the present solution, the heat generated by the reaction between the electrolyte and the positive active material and the negative active material can be further reduced, thereby fully exerting the advantages of the electrolyte provided in the present solution in improving the safety performance of the secondary battery. The mass ratio of 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, and other values not listed within the range are also applicable.

[0007] Preferably, the content of the fluorine-containing ester additive in the electrolyte is 2%-5% by mass. The content of the fluorine-containing ester additive in the electrolyte can be 2%, 3%, 4%, 4.5%, 5%, etc., by mass, but is not limited to the listed values, and other values not listed within the range are also applicable.

[0008] Preferably, the electrolyte further comprises vinylene carbonate (VC).

[0009] Preferably, the electrolyte further comprises an organic solvent, and the organic solvent comprises dimethyl carbonate (DMC), and the content of dimethyl carbonate in the electrolyte is 52%-59% by mass. Based on the application of DFEA, DFEC and FEMC, DMC is further used in combination with the above-mentioned materials to achieve the effect of taking into account the safety performance and cycle performance of the secondary battery using the electrolyte, thereby ensuring the service life of the secondary battery using the electrolyte. The content of DMC in the electrolyte can be 52%, 54%, 55%, 57%, 59%, etc., by mass, but is not limited to the listed values, and other values not listed within the range are also applicable.

[0010] Preferably, in the electrolyte, the mass ratio of DMC:fluorine-containing ester additive is 55-60:2-5. The mass ratio of DMC:fluorine-containing ester additive can be 55:2, 60:2, 55:5, 60:5, 57:4, etc., but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0011] Preferably, the organic solvent further includes propylene carbonate (PC) and fluoroethylene carbonate (FEC). Based on the application of DFEA, DFEC, and FEMC, the composition of the organic solvent of the electrolyte is further optimized, thereby achieving the effect of further improving the cycle performance of the electrolyte.

[0012] Preferably, in the electrolyte, the mass ratio of PC:FEC:DMC 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, and other values not listed in the value range are also applicable.

[0013] According to a second aspect of the present application, a secondary battery is provided, which includes a positive electrode, a negative electrode, and the above electrolyte.

[0014] Preferably, the above secondary battery satisfies at least one of the following a and b: a. the positive active material in the secondary battery includes a high-nickel positive active material, in which the total amount of the substance of metal elements other than lithium elements is A, and the amount of substance of nickel elements is B, 0.6≤B / A<1; b. the negative active material in the secondary battery includes a silicon-based negative active material. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 DSC test results of soft package batteries of battery systems using electrolyte formula D1;

[0016] Figure 2 DSC test results of soft package batteries of battery systems using electrolyte formula 1;

[0017] Figure 3 DSC test results of soft package batteries of battery systems using electrolyte formula 2. DETAILED DESCRIPTION

[0018] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all.

[0019] Example 1

[0020] 1. Formulation of electrolyte

[0021] According to Table 1, the electrolyte formulations with formulation numbers of Formulation 1, Formulation 2, Formulation D1, Formulation D2, Formulation D3, Formulation D4, Formulation D5, Formulation D6, and Formulation D7 in Table 1 need to be prepared according to the electrolyte formulation components shown in Table 1. After the preparation is completed, the required materials are mixed according to different formulations, and are dissolved sufficiently to form a uniform solution, thereby completing the preparation of the electrolyte.

[0022] Table 1. Formulations of electrolytes required in Example 1

[0023]

[0024] 2. Preparation of soft package battery

[0025] The electrolyte prepared in this example is used to prepare a soft package battery with a capacity of 3.3 Ah, and the specific operation is as follows:

[0026] S1. The materials are prepared according to the mass ratio of ternary material NCM811: binder polyvinylidene fluoride (PVDF): conductive agent = 97:1.6:1.4, and the positive electrode slurry is prepared using the above materials. The aluminum foil is used as the positive electrode current collector, and the positive electrode slurry is coated on the surface of the aluminum foil and dried, so that the positive electrode slurry coating is converted into a positive electrode active material layer, thereby preparing a soft package positive electrode.

[0027] S2. The materials are prepared according to the mass ratio of silicon-carbon negative electrode material (20wt.% of silicon doping): water-based binder: conductive agent = 96:3:1, and the negative electrode slurry is prepared using the above materials. The copper foil is used as the negative electrode current collector, and the negative electrode slurry is coated on the surface of the copper foil and dried, so that the negative electrode slurry coating is converted into a negative electrode active material layer (negative electrode specific capacity of 600 mAh / g), thereby preparing a soft package negative electrode.

[0028] S3. The PE film with a ceramic coating on the surface is used as a separator, and the soft package positive electrode, the separator, and the soft package negative electrode are stacked in sequence to form a battery cell, and the compact density of the battery cell obtained is 1.4 g / cm³.

[0029] S4. The battery cell prepared in S3 is placed in a soft package shell, and the electrolyte prepared in this example is injected. After vacuum packaging, standing, formation, shaping, and other processes, a soft package battery is prepared.

[0030] 3. Needle puncture resistance test and high temperature resistance test

[0031] The soft package battery prepared in the example is taken as the test object of the needle penetration resistance test and the high temperature resistance test. Based on the difference between the electrolytes used, 50 repetitions are set for each soft package battery. The specific test methods of the needle penetration resistance test and the high temperature resistance test are described below.

[0032] (1) Test method

[0033] Needle penetration resistance test: after the test object is fully charged, a Φ3mm high-temperature-resistant steel needle (the conical angle of the needle tip is 45-60°, the needle surface is smooth, free of rust, oxidation layer and oil stains) is used to penetrate the soft package battery from the direction perpendicular to the electrode plate at a speed of (25±5) mm / s. The penetration position is preferably close to the geometric center of the punctured surface. The steel needle stays in the soft package battery for 1 hour. The ignition of the test object is observed, and the number of ignited test objects is counted and calculated.

[0034] High temperature resistance test: the test object is placed in a 150°C hot box for 30 minutes. The ignition of the test object is observed, and the number of ignited test objects is counted and calculated.

[0035] (2) Test results

[0036] The test results are shown in Table 2. From the test results shown in Table 2, it can be seen that in the needle penetration resistance test and the high temperature resistance test, only the soft package batteries using the electrolyte of formula 1 and formula 2 have a measured soft package battery ratio of 0%. The soft package batteries prepared by using the electrolytes of formula D1, formula D2, formula D3, formula D4, formula D5, formula D6 and formula D7 all ignited during the test.

[0037] Formula D1 does not contain DFEA, DFEC and FEMC. From the test results, it can be seen that the soft package battery using the electrolyte of formula D1 basically ignited in the needle penetration resistance test and the high temperature resistance test. Formulas D5, D6 and D7 only contain one of DFEA, DFEC and FEMC. By comparing the test results of the electrolytes corresponding to the above formulas with the test results of the electrolyte of formula D1, the results show that the introduction of one or two of DFEA, DFEC and FEMC into the electrolyte cannot effectively improve the safety performance and heat release of the battery.

[0038] The soft package battery using the electrolyte of the formula D2, the electrolyte of the formula D3, or the electrolyte of the formula D4 is respectively lack of one of DFEA, DFEC, and FEMC. Relative to the soft package battery using the electrolyte of the formula D1, the electrolyte of the formula D5, the electrolyte of the formula D6, or the electrolyte of the formula D7, the proportion of the ignited soft package battery in the needle-penetration test and the high-temperature test of the soft package battery using the electrolyte of the formula D2, the electrolyte of the formula D3, or the electrolyte of the formula D4 has been reduced to a certain extent, but the proportion of the ignited soft package battery in the needle-penetration test and the high-temperature test is still relatively high.

[0039] In summary, the test results in Table 2 show that using DFEA, DFEC, and FEMC together as fluorine-containing ester additives to participate in the preparation of the electrolyte can significantly improve the safety performance of the soft package battery.

[0040] Table 2. Statistics of the needle-penetration test results and the high-temperature test results of the soft package battery of Example 1

[0041]

[0042] 4. DSC test

[0043] In the soft package battery prepared in this example, the soft package battery using the electrolyte of the formula 1, the electrolyte of the formula 2, or the electrolyte of the formula D1 is taken as the test object of the DSC test.

[0044] (1) Test method

[0045] The specific operation of the DSC test is as follows:

[0046] S1. Disassemble the full-charge soft package battery as the test object, and pour out the electrolyte for standby;

[0047] S2. Separate the positive electrode and the negative electrode, clean them respectively with DMC, and then dry them. Then, use a ceramic knife to scrape the positive active material layer and the negative active material layer to obtain positive / negative active material powder for standby;

[0048] S3. Set the related test parameters of the DSC tester as follows: temperature range: 25-500℃; atmosphere: argon-Ar; heating rate: 5℃ / min;

[0049] S4. Record the empty crucible mass of the aluminum crucible used for loading the sample to be tested, and then put the aluminum crucible into the DSC tester to perform the DSC test under the test conditions set in S3 to obtain the reference curve of the empty crucible;

[0050] S5. Put the positive active material powder, the negative active material powder, and the soft package battery into the aluminum crucible used in S4, cover the opening of the aluminum crucible with the aluminum cover of the aluminum crucible, press to seal, and then insert the hole to perform the DSC test under the test conditions set in S3.

[0051] (2) Test results

[0052] Figure 1 The DSC test results of the soft package battery of the battery system using the electrolyte of formula D1 are shown, and the DSC test releases 2114 J / g of heat. Figure 2 The DSC test results of the soft package battery of the battery system using the electrolyte of formula 1 are shown, and the DSC test releases 1276 J / g of heat. Figure 3 The DSC test results of the soft package battery of the battery system using the electrolyte of formula 2 are shown, and the DSC test releases 1328 J / g of heat. Obviously, compared with the electrolyte of formula D1, the reaction heat generated between the electrolyte of formula 1, the electrolyte of formula 2 and the positive active material and the negative active material is obviously lower, and based on this, the safety performance of the soft package battery using the electrolyte of formula 1 and the soft package battery using the electrolyte of formula 2 is better, which is consistent with the test results of the above-mentioned needle puncture test and high temperature test in this embodiment.

[0053] Example 2

[0054] 1. Preparation of electrolyte

[0055] According to Table 3, the electrolytes of formula 3, formula 4, formula 5, formula 6, formula 7 and formula 8 in Table 3 need to be prepared in this embodiment, and the raw materials are prepared according to the electrolyte formula components shown in Table 3. In order to facilitate comparison, the component compositions of formula 1 electrolyte, formula 2 electrolyte and formula D1 electrolyte prepared in Example 1 are also shown in Table 3. After the preparation of raw materials is completed, the required materials are mixed according to different formulas, and are dissolved to form a uniform solution, and the preparation of electrolyte is completed.

[0056] Table 3. Electrolyte formula prepared in Example 2

[0057]

[0058] 2. Preparation of soft package battery

[0059] The soft package battery with a capacity of 3.3 Ah is prepared by using the electrolyte prepared in this embodiment. Except for the difference in the electrolyte used, the operation of preparing the soft package battery in this embodiment is consistent with the related operation of preparing the soft package battery in Example 1.

[0060] 3. Needle puncture test and high temperature test

[0061] The soft package battery prepared in this embodiment is used as the test object of the needle puncture test and the high temperature test. Based on the difference between the electrolytes used, 50 repetitions are set for each soft package battery for each test.

[0062] (1) Test method

[0063] The specific test methods of the needle-penetration resistance test and the high-temperature resistance test in this embodiment are consistent with the related operations of performing the needle-penetration resistance test and the high-temperature resistance test in Embodiment 1, except for the difference in the test objects.

[0064] (2) Test results

[0065] The test results are shown in Table 4. For ease of comparison, the test results of the needle-penetration resistance test and the high-temperature resistance test of the soft package batteries using the electrolyte of Formula 1, the electrolyte of Formula 2, and the electrolyte of Formula D1 in Embodiment 1 are also shown in Table 4.

[0066] The soft package batteries using the electrolyte of Formula 1, the electrolyte of Formula 2, and the electrolyte of Formula 3 did not catch fire in the needle-penetration resistance test and the high-temperature resistance test involved in this embodiment, indicating that the safety performance of the above three electrolytes is good. The ratio of DFEA, DFEC, and FEMC in the electrolyte of Formula 1 and the electrolyte of Formula 3 is the same, and the ratio of DFEA, DFEC, and FEMC in the electrolyte of Formula 8 is also the same as that in the above two electrolytes. However, the total amount of DFEA, DFEC, and FEMC in the electrolyte of Formula 8 is relatively low, which makes the safety performance of the soft package battery using the electrolyte of Formula 8 worse than that of the soft package battery using the electrolyte of Formula 1 or the electrolyte of Formula 3.

[0067] Comparing the electrolyte of Formula 2, the electrolyte of Formula 3, the electrolyte of Formula 4, the electrolyte of Formula 5, the electrolyte of Formula 6, and the electrolyte of Formula 7, the total amount of DFEA, DFEC, and FEMC in these formulas is the same, and the difference lies in the ratio of the above three materials. From the test results of the soft package batteries using the above electrolytes, when the mass ratio of DFEA, DFEC, and FEMC in the electrolyte formula satisfies DFEA:DFEC:FEMC = 0.5-3:1-3:1-3, it is beneficial to further improve the safety performance of the battery.

[0068] Table 4. Statistics of the needle-penetration resistance test results and the high-temperature resistance test results of the soft package batteries in Embodiment 2

[0069]

[0070] 4. Cycle performance test

[0071] The soft package batteries based on the electrolyte of Formula 1, the electrolyte of Formula 2, the electrolyte of Formula 3, the electrolyte of Formula 8, and the electrolyte of Formula D1 were used as the test objects for the cycle performance test.

[0072] (1) Test method

[0073] The soft package battery as the test object was placed in a thermostat, and charged at 1.0C to 4.2V at a temperature of (25±2)℃, then the soft package battery was charged at constant voltage to 0.05C, and after 10min, discharged at 1.0C to 2.5V, and prepared for normal temperature cycle test. The capacity retention rate test was carried out on the soft package battery as the test object before the normal temperature cycle test of the soft package battery, and every 50 cycles during the cycle test of the soft package battery.

[0074] (2) Test results

[0075] As shown in Table 5, under the same test conditions, among the test objects participating in the cycle performance test, the cycle capacity retention rate of the soft package battery using the electrolyte of formula 1 was the highest. As described above, the proportions of DFEA, DFEC and FEMC in the electrolyte of formula 1, formula 3 and formula 8 are the same, and the difference among the three is the total content of DFEA, DFEC and FEMC in the electrolyte. From the cycle performance test results of the soft package batteries using the above three electrolytes respectively, it can be seen that with the increase of the total content of DFEA, DFEC and FEMC in the electrolyte, the cycle stability of the soft package battery shows a trend of first getting better and then getting worse. Among the above three electrolytes, the cycle stability of the soft package battery corresponding to the electrolyte of formula 1 with the total content of DFEA, DFEC and FEMC in the electrolyte reaching 4% is the best.

[0076] In addition, as described above, the total amount of DFEA, DFEC and FEMC contained in the electrolyte of formula 2 and formula 3 is the same, and the difference is the proportion among the above three materials. Based on the test results shown in Table 5, among the above two electrolytes, the cycle stability of the battery corresponding to the electrolyte of formula 3 with the mass ratio of DFEA, DFEC and FEMC reaching DFEA:DFEC:FEMC=1.5:1.5:1 is better.

[0077] Table 5. Cycle performance test results of soft package batteries of Example 2

[0078]

[0079] Example 3

[0080] 1. Preparation of electrolyte

[0081] According to Table 6, the electrolyte formulations No. 9, No. D9, No. 10 and No. D10 in Table 6 need to be prepared in this embodiment. For the convenience of comparison, the component compositions of the electrolyte formulation No. 1 and No. D1 prepared in Example 1 are also shown in Table 6. For the convenience of comparison, the electrolyte formulations shown in Table 6 are grouped as follows: Group 1, No. 1 and No. D1; Group 2, No. 9 and No. D9; Group 3, No. 10 and No. D10. In Table 6, DEC refers to diethyl carbonate, and EMC refers to ethyl methyl carbonate. After the preparation of the materials, the required materials are mixed according to different formulations, and are dissolved sufficiently to form a uniform solution, thereby completing the preparation of the electrolyte.

[0082] Table 6. Electrolyte formulations required to be prepared in Example 3

[0083]

[0084] 2. Preparation of soft package batteries

[0085] Soft package batteries with a capacity of 3.3 Ah are prepared using the electrolytes prepared in this embodiment. Except for the difference in the electrolytes used, the operations for preparing the soft package batteries in this embodiment are consistent with the relevant operations for preparing the soft package batteries in Example 1.

[0086] 3. Needle-penetration resistance test and high-temperature resistance test

[0087] The soft package batteries prepared in this embodiment are used as the test objects for the needle-penetration resistance test and the high-temperature resistance test. Based on the difference in the electrolytes used, 50 repetitions are set for each of the soft package batteries tested.

[0088] Except for the difference in the test objects, the specific test methods for the needle-penetration resistance test and the high-temperature resistance test in this embodiment are consistent with the relevant operations for performing the needle-penetration resistance test and the high-temperature resistance test in Example 1.

[0089] 4. Cycle performance test

[0090] The soft package batteries prepared in this embodiment are used as the test objects for the cycle performance test.

[0091] Except for the difference in the test objects, the specific test methods for the cycle performance test in this embodiment are consistent with the relevant operations for performing the cycle performance test in Example 2.

[0092] 5. Test results

[0093] The test results are shown in Table 7. For ease of comparison, the test results of the soft package battery using the electrolyte of Formula 1 and the electrolyte of Formula D1 in the needle-penetration resistance test and the high-temperature resistance test in Example 1 are also shown in Table 7. In addition, the test results of the soft package battery using the electrolyte of Formula 1 and the electrolyte of Formula D1 in the cycle performance test in Example 2 are also shown.

[0094] The soft package battery using the electrolyte of Formula 9 and the soft package battery using the electrolyte of Formula D9 are compared in terms of the test results in the present example. The proportion of the soft package battery on fire in the needle-penetration resistance test and the high-temperature resistance test is significantly reduced for the former, and the cycle capacity retention rate measured under the same cycle conditions is higher for the former in the cycle capacity retention rate test. Therefore, it is indicated that the former has higher safety performance and cycle stability. Similar conclusions can be obtained by comparing the test results of the soft package battery using the electrolyte of Formula 1 and the electrolyte of Formula D1 in Example 1 and Example 2, and by comparing the test results of the soft package battery using the electrolyte of Formula 10 and the electrolyte of Formula D10 in the present example. Based on the above comparison results, it is again indicated that the use of DFEA, DFEC and FEMC as electrolyte components can effectively improve the safety performance of the battery, and it is also indicated that the use of DFEA, DFEC and FEMC as electrolyte components can also improve the cycle stability of the battery.

[0095] The difference between Formula 1, Formula 9 and Formula 10 is that the carbonate solvents contained in the electrolytes are different. The carbonate solvent contained in Formula 1 is DMC, the carbonate solvent contained in Formula 9 is DEC, and the carbonate solvent contained in Formula 10 is EMC. Based on the above difference, the cycle stability of the soft package battery using the electrolyte of the above three formulas is different, and the cycle stability of the soft package battery using the electrolyte of Formula 1 is the best.

[0096] The difference between Formula D1, Formula D9 and Formula D10 is also that the carbonate solvents contained in the electrolytes are different. The carbonate solvent contained in Formula D1 is DMC, the carbonate solvent contained in Formula D9 is DEC, and the carbonate solvent contained in Formula D10 is EMC. Based on the above difference, the cycle stability of the soft package battery using the electrolyte of the above three formulas is also different, and the safety performance and cycle stability of the soft package battery using the electrolyte of Formula D1 are not the best.

[0097] It can be shown by the above comparison that, in the electrolyte in which DFEA, DFEC and FEMC are used in combination, further introducing DMC into the electrolyte is conducive to obtaining an electrolyte with higher cycle stability. However, without the simultaneous presence of DFEA, DFEC and FEMC in the electrolyte, selecting DMC as the organic solvent component of the electrolyte does not necessarily have the effect of improving the cycle stability of the electrolyte.

[0098] Table 7. Statistics of soft pack battery performance test results of Example 3

[0099]

[0100] Example 4

[0101] 1. Preparation of electrolyte

[0102] According to Table 8, the electrolytes with formulation numbers of Formulation 11, Formulation D11, Formulation 12 and Formulation D12 in Table 8 need to be prepared in this example, and the materials are prepared according to the electrolyte formulation components shown in Table 8. In order to facilitate comparison, the component compositions of Formulation 1 electrolyte and Formulation D1 electrolyte prepared in Example 1 are also shown in Table 8. In order to facilitate comparison, the electrolyte formulations shown in Table 8 are grouped, and the specific grouping is as follows: Group 1, Formulation 1, Formulation D1; Group 4, Formulation 11, Formulation D11; Group 5, Formulation 12, Formulation D12. In Table 8, EC refers to ethylene carbonate. After the preparation of materials is completed, the required materials are mixed according to different formulations, and dissolved sufficiently to form a uniform solution, thereby completing the preparation of the electrolyte.

[0103] Table 8. Electrolyte formulations required to be prepared in Example 4

[0104]

[0105] 2. Preparation of soft pack battery

[0106] The soft pack batteries with a capacity of 3.3 Ah are prepared using the electrolytes prepared in this example. Except for the difference in the electrolytes used, the operation for preparing the soft pack batteries in this example is consistent with the relevant operation for preparing the soft pack batteries in Example 1.

[0107] 3. Needle puncture resistance test and high temperature resistance test

[0108] The soft pack batteries prepared in this example are used as the test objects for the needle puncture resistance test and the high temperature resistance test. Based on the difference between the electrolytes used, 50 repetitions are set for each of the soft pack batteries tested.

[0109] The specific test method of the needle-penetration resistance test and the high-temperature resistance test in this embodiment is consistent with the related operation of performing the needle-penetration resistance test and the high-temperature resistance test in Embodiment 1, except that the test objects are different.

[0110] 4. Cycle performance test

[0111] The soft package battery prepared in this embodiment is taken as the test object of the cycle performance test.

[0112] The specific test method of the cycle performance test in this embodiment is consistent with the related operation of performing the cycle performance test in Embodiment 2, except that the test objects are different.

[0113] 5. Test results

[0114] The test results are shown in Table 9. In order to facilitate comparison, the test results of the needle-penetration resistance test and the high-temperature resistance test of the soft package battery using the electrolyte of Formula 1 and the electrolyte of Formula D1 in Embodiment 1 are also shown in Table 9, and the cycle performance test results of the soft package battery using the electrolyte of Formula 1 and the electrolyte of Formula D1 in Embodiment 2 are also shown in Table 9. Comparing the test results of the soft package battery using the electrolyte of Formula 11 and the electrolyte of Formula D11 in this embodiment, the proportion of the soft package battery on fire in the needle-penetration resistance test and the high-temperature resistance test corresponding to the former is obviously reduced, and under the same cycle conditions, the cycle capacity retention rate measured by the former is higher in the cycle capacity retention rate test, which indicates that the former has higher safety performance and cycle stability. Comparing the test results of the soft package battery using the electrolyte of Formula 1 and the electrolyte of Formula D1 in Embodiment 1 and Embodiment 2, and comparing the test results of the soft package battery using the electrolyte of Formula 12 and the electrolyte of Formula D12 in this embodiment, similar conclusions can be obtained. Based on the above comparison results, it is again indicated that by using DFEA, DFEC and FEMC as electrolyte components, the safety performance of the battery can be effectively improved, and the cycle stability of the battery can also be improved.

[0115] The difference between Formula 1, Formula 11 and Formula 12 is that the organic solvent components contained in the electrolyte are different. Compared with Formula 1, Formula 11 uses PC instead of FEC so that Formula 11 does not contain FEC, and Formula 12 uses EC instead of PC so that Formula 12 does not contain PC. Based on the above difference, the safety performance and cycle stability of the soft package battery using the electrolyte of the above three formulas are also different, and the cycle stability of the soft package battery using the electrolyte of Formula 1 is the best.

[0116] The difference between the formula D1, the formula D11, the formula D12 is that the organic solvent component contained in the electrolyte is different, wherein, compared with the formula D1, the formula D11 uses PC instead of FEC, so that the formula D11 does not contain FEC, and the formula D12 uses EC instead of PC, so that the formula D12 does not contain PC. Based on the above-mentioned difference, the soft package battery using the above-mentioned three kinds of electrolyte respectively also makes a difference in safety performance and cycle stability, but the cycle stability of the soft package battery using the formula D1 electrolyte is not the best.

[0117] The above comparison shows that in the electrolyte using DFEA, DFEC and FEMC in combination, further introducing a certain amount of FEC, PC into the electrolyte is beneficial to obtain an electrolyte with higher cycle stability. However, without meeting the condition that the electrolyte contains DFEA, DFEC and FEMC at the same time, introducing a certain amount of FEC, PC into the electrolyte does not necessarily have the effect of improving the cycle stability of the electrolyte.

[0118] Table 9. Soft package battery performance test result statistics of example 4

[0119]

[0120] 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 above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents, but these modifications or replacements are within the protection scope of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte includes fluorinated ester additives, and the proportion of the fluorinated ester additives in the electrolyte is 2% to 9% by mass percentage. The fluorinated ester additives include ethyl 2,2-difluoroacetate, difluoroethylene carbonate, and trifluoroethyl methyl carbonate. 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.

2. The electrolyte as described in claim 1, characterized in that: 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.

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

4. The electrolyte as described in claim 1, characterized in that: The electrolyte also includes other additives, including at least one of vinylene carbonate, ethylene ethylene carbonate, and fluoroethylene carbonate.

5. The electrolyte according to any one of claims 1 to 4, characterized in that: The electrolyte also includes an organic solvent, which includes dimethyl carbonate, and the proportion of dimethyl carbonate in the electrolyte is 52% to 59% by mass percentage.

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

7. The electrolyte as described in claim 5, characterized in that: The organic solvents also include propylene carbonate and fluoroethylene carbonate.

8. The electrolyte as described in claim 7, characterized in that: In the electrolyte, the mass ratio of propylene carbonate: fluoroethylene carbonate: dimethyl carbonate is 11-20: 5-15: 52-59.

9. A secondary battery, characterized in that: The secondary battery includes a positive electrode, a negative electrode, and an electrolyte as described in any one of claims 1 to 8.

10. The secondary battery as described in claim 9, characterized in that, 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.

Images