An electrolyte based on propylene carbonate and a secondary battery using it.

Abstract

This invention provides an electrolyte based on propylene carbonate, comprising propylene carbonate, triphenyl phosphate, and difluoroethylene carbonate, with a mass ratio of difluoroethylene carbonate:triphenyl phosphate:propylene carbonate = 4.5–6:0.1–1:15–21; the mass percentage of propylene carbonate in the electrolyte is not less than 10%. In this design, PC, TPP, and DFEC are combined to participate in the composition of the electrolyte. The three components work synergistically to weaken the heat generated by the oxygen release reaction at the positive electrode and the heat generated by side reactions, and to reduce the flammable gases generated during the reduction at the negative electrode. Therefore, the electrolyte provided by this design can effectively reduce the heat generated by the reaction and the heat of combustion in the secondary battery, which helps prevent thermal runaway and provides a certain flame-retardant effect during the operation of the secondary battery, thus improving the safety performance of the secondary battery.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to an electrolyte based on propylene carbonate and a secondary battery using the same. Background Technology

[0002] 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. However, the development trend towards larger capacity and higher energy density increases the energy of thermal runaway in rechargeable battery cells, increasing the risk of flammability and explosion. These safety hazards have shaken users' confidence in using high-energy-density rechargeable batteries, becoming one of the main bottlenecks limiting the large-scale industrial application of high-energy-density rechargeable batteries. Summary of the Invention

[0003] In order to reduce the flammability and explosion risk of high-energy-density secondary batteries and improve their safety performance, this invention provides an electrolyte based on propylene carbonate and a secondary battery using the same electrolyte.

[0004] According to a first aspect of the present invention, an electrolyte based on propylene carbonate is provided, comprising propylene carbonate (PC), triphenyl phosphate (TPP), and difluoroethylene carbonate (DFEC), wherein the mass ratio of difluoroethylene carbonate:triphenyl phosphate:propylene carbonate is 4.5–6:0.1–1:15–21; and the mass percentage of propylene carbonate in the electrolyte is not less than 10%. In this solution, PC, TPP, and DFEC are combined to participate in the composition of the electrolyte, and the three components work synergistically to weaken the heat generated by the oxygen release reaction at the positive electrode and the heat generated by side reactions, and to reduce the flammable gases generated during the reduction at the negative electrode. Therefore, the electrolyte provided by this solution can effectively reduce the heat generated by the reaction and the heat of combustion in the secondary battery, which is beneficial to preventing thermal runaway in the secondary battery, and plays a certain role in flame retardancy during the operation of the secondary battery, thereby improving the safety performance of the secondary battery. The mass ratio of DFEC, TPP, and PC can be 4.5:0.1:15, 6:0.5:21, 4.5:0.1:21, 4.5:1:15, 6:0.1:21, etc., but is not limited to the listed values. Other unlisted values ​​within this range also apply.

[0005] Preferably, the TPP:PC ratio, calculated by mass, is 0.3–0.6:16–18. When the TPP:PC ratio meets the above range, it is more conducive to maintaining good cycle stability of the secondary battery. The TPP:PC mass ratio can be 0.3:16, 0.3:18, 0.6:16, 0.6:18, 0.5:17, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0006] Preferably, the electrolyte also includes vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0007] Preferably, the electrolyte also includes dimethyl carbonate (DMC), with the DMC comprising 50% to 60% of the electrolyte by mass percentage. Based on the applications of PC, DFEC, and TPP, DMC is further combined with the above materials to achieve a balance between the safety and cycle performance of the secondary battery using this electrolyte, thus ensuring the service life of the secondary battery using this electrolyte. The proportion of DMC in the electrolyte can be 50%, 52%, 55%, 58%, 60%, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0008] Preferably, the total mass percentage of PC, TPP, and DFEC in the electrolyte is 18% to 28%. The total mass percentage of PC, TPP, and DFEC in the electrolyte can be 18%, 20%, 22%, 24%, 26%, 28%, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0009] Preferably, the mass ratio of FEC:DMC:PC in the electrolyte is 7-11:50-60:15-21. Based on the application of PC, DFEC, and TPP, the composition of the organic solvent in the electrolyte is further optimized, thereby further improving the cycle performance of the electrolyte. The mass ratio of FEC, DMC, and PC, FEC:DMC:PC, can be 7:50:15, 11:60:21, 7:50:21, 7:60:15, 8:55:18, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0010] According to a second aspect of the present invention, a secondary battery is provided, the secondary battery comprising a positive electrode, a negative electrode and an electrolyte as described above.

[0011] Preferably, the positive electrode active material in the above-mentioned secondary battery includes a high-nickel positive electrode active material. In the high-nickel positive electrode active material, the total amount of metal elements other than lithium is A, and the amount of nickel is B, where 0.6 ≤ B / A < 1.

[0012] Preferably, the negative electrode active material in the above-mentioned secondary battery includes a silicon-based negative electrode active material. Attached Figure Description

[0013] Figure 1 The results of DSC tests on the pouch cell of the battery system using the electrolyte of formulation 1;

[0014] Figure 2 The results of DSC tests on the pouch cell using the D1 electrolyte formulation are shown. Detailed Implementation

[0015] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0016] Example 1

[0017] 1. Prepare the electrolyte

[0018] According to Table 1, this embodiment requires the preparation of electrolytes with formula numbers 1, 2, 3, 4, 5, 6, D1, D2, D3, D4, D5, D6, D7, D8, and D9 in Table 1. The materials are prepared according to the electrolyte formula composition shown in Table 1, where TPPi refers to triphenyl phosphite. 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.

[0019] Table 1. Electrolyte formulation required for Example 1

[0020]

[0021]

[0022] 2. Preparation of pouch cells

[0023] 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:

[0024] 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.

[0025] 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.

[0026] S3. Using a PE film with a ceramic coating as the separator, the pouch cell is fabricated by sequentially stacking the positive electrode, the separator, and the negative electrode. The resulting cell has a compaction density of 1.4 g / cm³. 3 .

[0027] 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.

[0028] 3. Performance Testing

[0029] (1) Needle penetration resistance test and high temperature resistance test

[0030] 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.

[0031] 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.

[0032] 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.

[0033] (2) DSC test

[0034] The soft-pack battery prepared in this embodiment is used as the test object for DSC testing.

[0035] The specific steps for DSC testing are as follows:

[0036] S1. Disassemble the fully charged pouch battery used as the test object and pour out the electrolyte for later use;

[0037] 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.

[0038] S3. Set the relevant test parameters of the DSC analyzer as follows: temperature range, 25-500℃; atmosphere, argon-Ar; heating rate, 5℃ / min.

[0039] 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.

[0040] S5. Place the positive electrode active material powder, negative electrode active material powder, and soft-pack battery into the aluminum crucible used in S4. Cover the open end of the aluminum crucible with the aluminum lid, press to seal, and then insert the hole. Perform DSC test under the test conditions set in S3, and record the heat release of the sample during the DSC test.

[0041] 4. Test Results

[0042] Test results are as follows Figure 2 As shown in the figure. Among the tested objects, most of the pouch batteries using electrolytes prepared with formulas D1, D2, D3, D4, D5, D6, D7, D8, and D9 caught fire in the nail penetration and high temperature resistance tests. DSC testing also showed that the heat release of the above pouch batteries reached a relatively high level. In contrast, the pouch batteries using electrolytes with formulas 1, 2, 3, 4, 5, and 6 had a significantly higher pass rate in the nail penetration and high temperature resistance tests, and their heat release in the DSC test was also significantly reduced.

[0043] Formulas 1, 2, 3, 4, 5, and 6 all contain PC, TPP, and DFEC. These three components can synergistically enhance the electrolyte system, weakening the heat generated by the oxygen release reaction at the positive electrode and the heat generated by the side reactions, and reducing the flammable gases generated during the reduction at the negative electrode. As a result, the electrolyte prepared using the above formulas can effectively reduce the heat generated by the battery reaction and the heat of combustion, which helps to prevent thermal runaway of the battery, plays a certain role in flame retardancy during the operation of the battery, and improves the safety performance of the secondary battery.

[0044] Formula D1 does not contain PC, TPP, or DFEC. Test results show that pouch batteries using Formula D1 electrolyte almost universally caught fire in both the nail penetration and high-temperature resistance tests, and also exhibited the highest heat release in the DSC test among all tested components. Formulas D2, D3, D5, D6, and D7 lack one or two of PC, TPP, and DFEC. Specifically, Formula D2 lacks both PC and DFEC, Formula D3 lacks PC, Formula D5 lacks DFEC, and Formulas D6 and D7 lack TPP. Comparing the test results for these electrolyte formulas with those for Formula D1 demonstrates that introducing one or two of PC, TPP, or DFEC into the electrolyte does not effectively improve battery safety or heat release. Compared to Formula 1, Formula D7 actually replaces TPP with TPPi, which has a similar structure to TPP. TPPi is used in conjunction with PC and DFEC. However, test results show that the fire rate in the nail penetration and high-temperature resistance tests of batteries using Formula D7 electrolyte did not show a significant decrease compared to batteries using Formula D1 electrolyte. Conversely, the fire rate in the nail penetration and high-temperature resistance tests of pouch batteries using Formula 1 electrolyte decreased significantly. This indicates that even though TPPi and TPP have similar structures, using TPPi in conjunction with PC and DFEC does not synergistically improve battery safety performance.

[0045] Although formulation D4 contains PC, TPP and DFEC, and the ratio of these three components is the same as that of formulation 1, the content of these three components in formulation D4 is relatively low. Under these conditions, it is still difficult to significantly suppress the heat released by the battery.

[0046] Formulas D8 and D9 also contain PC, TPP, and DFEC, and the total PC+DFEC+TPP content in these two formulas is the same as that in Formula 1. However, in Formula D8, the proportion of PC is lower and the proportion of DFEC is higher, while in Formula D9, the proportion of DFEC is lower and the proportion of PC is higher. Test results show that the fire rate in the nail penetration and high-temperature resistance tests of batteries using electrolytes D8 and D9 did not show a significant decrease compared to batteries using electrolyte D1. This indicates that when PC, TPP, and DFEC are used together as electrolyte components, the ratio of these three components is a crucial factor in their synergistic effect. Based on a mass ratio, when DFEC:TPP:PC = 4.5–6:0.1–1:15–21, the three components can synergistically suppress battery heat release.

[0047] As mentioned above, pouch batteries using electrolytes corresponding to formulations 1, 2, 3, 4, 5, and 6 all exhibit good safety performance. However, due to differences in the ratios of PC, TPP, and DFEC in the electrolyte formulations, there are certain variations in the test results of these pouch batteries. Among them, the pouch battery using electrolyte formulation 1 shows the best performance. Among the pouch batteries using the above-mentioned electrolyte formulations, the test results of the pouch battery using electrolyte formulation 6 are significantly worse than the other tested subjects. Compared to formulations 1, 4, 5, and 6, the DFEC content in the formulations is the same; the only difference lies in the ratio of PC to TPP. Formula 6 has a relatively higher PC content and a relatively lower TPP content, resulting in a slightly weaker suppression of heat release from the battery. By comparing the composition of the electrolyte formulations mentioned above, it can be seen that in electrolyte formulations that combine PC, TPP, and DFEC, a TPP to PC mass ratio of 0.3 to 0.6:16 to 18 is beneficial for better suppressing heat release from the battery, and thus for maintaining good cycle stability.

[0048] Figure 1 The paper presents the DSC test results of a pouch cell using electrolyte formulation 1. Figure 2 The DSC test results of the pouch cell using the D1 electrolyte formulation are presented.

[0049] Table 2. Statistical results of the needle penetration resistance test and high temperature resistance test of the soft-pack battery in Example 1

[0050]

[0051] Example 2

[0052] 1. Prepare the electrolyte

[0053] According to Table 3, this embodiment requires the preparation of electrolytes with formula numbers A, DA, B, and DB from 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 and D1 prepared in Example 1. The electrolyte formulas shown in Table 3 are grouped as follows: Group 1: Formula 1 and Formula D1; Group 2: Formula A and Formula DA; Group 3: Formula B and Formula DB. In Table 3, DEC refers to diethyl carbonate, and EMC refers to methyl ethyl carbonate. 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.

[0054] Table 3. Electrolyte formulation required for Example 2

[0055]

[0056] 2. Preparation of pouch cells

[0057] 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.

[0058] 3. Needle penetration resistance test and high temperature resistance test

[0059] 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.

[0060] 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.

[0061] 4. Cyclic performance test

[0062] The pouch cells prepared using electrolyte formula 1 and electrolyte formula D1 in Example 1, as well as the pouch cells prepared in this example, were used as test objects for cycle performance testing.

[0063] The cycle performance test method is as follows: The soft-pack battery to be tested is placed in a constant temperature chamber and charged to 4.2V at 1.0C at (25±2)℃. Then, the soft-pack battery is charged to 0.05C at a constant voltage. After resting for 10 minutes, it is discharged to 2.5V at 1.0C to prepare for room temperature cycle test. Before the room temperature cycle test of the soft-pack battery and during the cycle test, the capacity retention rate of the soft-pack battery to be tested is tested every 50 cycles.

[0064] 5. Test Results

[0065] The test results are shown in Table 4. For ease of comparison, Table 4 also displays 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. Comparing the test results of the pouch battery using electrolyte of formulation A and the pouch battery using electrolyte of formulation DA 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 Example 1 and this example, and comparing the test results of the pouch battery using electrolyte of formulation B and the pouch battery using electrolyte of formulation DB in this example, similar conclusions can be drawn. Based on the above comparison results, it is further demonstrated that using PC, TPP and DFEC in combination as electrolyte components can effectively improve the safety performance of the battery, and that using PC, TPP and DFEC in combination as electrolyte components can also improve the cycle stability of the battery.

[0066] The difference between Formula 1, Formula A, and Formula B lies in the different carbonate solvents contained in the electrolytes. Formula 1 contains DMC, Formula A contains DEC, and Formula B contains EMC. Based on these differences, the safety performance and cycle stability of pouch batteries using these three electrolyte formulas also differ. The pouch battery using Formula 1 electrolyte exhibits the best safety performance and cycle stability.

[0067] The difference between formulations D1, DA, and DB lies in the different carbonate solvents they contain. Formulation D1 contains DMC, formulation DA contains DEC, and formulation DB contains EMC. These differences result in variations in safety performance and cycle stability for pouch batteries using these three electrolyte formulations. However, the pouch battery using formulation D1 exhibits the worst safety performance and cycle stability.

[0068] The above comparison shows that, in electrolytes using PC, TPP, and DFEC in combination, further introduction of DMC is beneficial for obtaining electrolytes with higher safety performance and cycle stability. However, when the electrolyte does not simultaneously contain PC, TPP, and DFEC, using DMC as the organic solvent component of the electrolyte does not necessarily improve the safety performance and cycle stability of the electrolyte.

[0069] Table 4. Statistical analysis of performance test results of the pouch battery in Example 2

[0070]

[0071] Example 3

[0072] 1. Prepare the electrolyte

[0073] According to Table 5, this embodiment requires the preparation of electrolytes with formula numbers 7, 8, 9, 10, and 11 in Table 5. The materials are prepared according to the electrolyte formula composition shown in Table 5. For ease of comparison, Table 5 also shows the component composition of electrolytes formula 1 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.

[0074] Table 5. Electrolyte formulation required for Example 3

[0075] Formula number <![CDATA[LiPF6]]> VC FEC DMC PC DFEC TPP Formula 1 11 1 9 54 19 5.5 0.5 Formula 7 11 1 9 64 11.4 3.3 0.3 Formula 8 11 1 9 61 13.68 3.96 0.36 Formula 9 11 1 9 51 21.28 6.16 0.56 Formula 10 11 1 9 49 22.8 6.6 0.6 Formula 11 11 1 9 52 19 7.5 0.5

[0076] 2. Preparation of pouch cells

[0077] 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.

[0078] 3. Needle penetration resistance test and high temperature resistance test

[0079] 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.

[0080] 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.

[0081] 4. Cyclic performance test

[0082] The pouch cell prepared in this embodiment was used as the test object for cycle performance testing.

[0083] 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.

[0084] 5. Test Results

[0085] The test results are shown in Table 6. For ease of comparison, Table 6 also shows the nail penetration resistance and high temperature resistance test results of the pouch batteries using electrolyte formula 1 and electrolyte formula D1 in Example 1, and the cycle performance test results of the pouch batteries using electrolyte formula 1 in Example 2. In formulas 1, 7, 8, 9, and 10, the types of materials included in the components are the same, and the proportions of the core components PC, DFEC, and TPP are also the same. However, the total content of PC, DFEC, and TPP differs among the above formulas. Based on this difference, the safety performance and capacity retention of the pouch batteries using the above electrolyte formulas also differ. Based on the test results of this example, in electrolytes using PC, TPP, and DFEC in combination, a total content of PC, DFEC, and TPP of 18% to 28% in the electrolyte results in better safety performance and cycle stability.

[0086] Comparing Formula 1 and Formula 11, both electrolyte formulas contain the same types of materials, and the total content of the core components PC, DFEC, and TPP in the electrolyte is the same. However, the ratio of these three materials differs. Test results show that the ratio of PC, TPP, and DFEC in Formula 1 is more beneficial to improving the safety performance and cycle stability of the electrolyte.

[0087] Table 6. Statistical analysis of performance test results of the pouch battery in Example 3

[0088]

[0089] Example 4

[0090] 1. Prepare the electrolyte

[0091] According to Table 7, this embodiment requires the preparation of electrolytes with formula numbers X, DX, Y, and DY from Table 7. The materials are prepared according to the electrolyte formula composition shown in Table 7. For ease of comparison, Table 7 also shows the composition of the electrolyte prepared in Formula 1 of Example 1. The electrolyte formulas shown in Table 7 are grouped as follows: Group 1: Formula 1, Formula D1; Group 3: Formula X, Formula DX; Group 4: Formula Y, Formula DY. 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.

[0092] Table 7. Electrolyte formulation required for Example 4

[0093]

[0094] 2. Preparation of pouch cells

[0095] 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.

[0096] 3. Needle penetration resistance test and high temperature resistance test

[0097] 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.

[0098] 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.

[0099] 4. Cyclic performance test

[0100] The pouch cell prepared in this embodiment was used as the test object for cycle performance testing.

[0101] 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.

[0102] 5. Test Results

[0103] The test results are shown in Table 8. For ease of comparison, Table 8 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 X and the pouch battery using electrolyte of Formulation DX 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 Y and the pouch battery using electrolyte of Formulation DY in this example, similar conclusions can be drawn. Based on the above comparison results, it is further demonstrated that using PC, TPP and DFEC in combination as electrolyte components can effectively improve battery safety performance and improve battery cycle stability.

[0104] The difference between Formula 1, Formula X, and Formula Y lies in the different organic solvent components in the electrolyte. Compared to Formula 1, Formula X uses EC instead of FEC, thus eliminating FEC from the formula, while Formula Y has a lower FEC content. Based on these differences, the safety performance and cycle stability of pouch batteries using these three electrolyte formulas also differ. The pouch battery using Formula 1 electrolyte exhibits the best safety performance and cycle stability.

[0105] The differences between formulations D1, DX, and DY lie in the different organic solvent components in the electrolyte. Compared to formulation D1, formulation DX uses EC instead of FEC, resulting in an FEC-free formulation, while formulation DY has a lower FEC content. These differences lead to variations in safety performance and cycle stability for pouch batteries using these three electrolyte formulations; however, the pouch battery using formulation D1 exhibits the worst safety performance and cycle stability.

[0106] The above comparison shows that, in electrolytes using PC, TPP, and DFEC in combination, introducing a certain amount of FEC is beneficial for obtaining electrolytes with higher safety performance and cycle stability. However, if the electrolyte does not simultaneously contain PC, TPP, and DFEC, introducing a certain amount of FEC does not necessarily improve the safety performance and cycle stability of the electrolyte.

[0107] Table 8. Statistical analysis of performance test results of the pouch battery in Example 4

[0108]

[0109]

[0110] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. An electrolyte based on propylene carbonate, characterized in that: The electrolyte comprises propylene carbonate, triphenyl phosphate, and difluoroethylene carbonate (DFEC), with a mass ratio of DFEC:triphenyl phosphate:propylene carbonate = 4.5–6:0.1–1:15–21; propylene carbonate accounts for no less than 10% of the mass percentage in the electrolyte; and the total mass percentage of propylene carbonate, triphenyl phosphate, and difluoroethylene carbonate in the electrolyte is 18%–28%.

2. The propylene carbonate-based electrolyte as described in claim 1, characterized in that: Based on the mass ratio, triphenyl phosphate: propylene carbonate = 0.3~0.6: 16~18.

3. The propylene carbonate-based electrolyte as described in claim 1, characterized in that: The electrolyte also includes vinylene carbonate and fluoroethylene carbonate (FEC).

4. The propylene carbonate-based electrolyte as described in claim 3, characterized in that: The electrolyte also includes dimethyl carbonate, which accounts for 50% to 60% of the electrolyte by mass percentage.

5. The propylene carbonate-based electrolyte as described in claim 4, characterized in that: The electrolyte also includes at least one of ethylene ethylene carbonate (VEC) and diethyl carbonate (DEC).

6. The propylene carbonate-based electrolyte as described in claim 4, characterized in that: According to the mass ratio, in the electrolyte, the ratio of fluoroethylene carbonate: dimethyl carbonate: propylene carbonate is 7~11:50~60:15~21.

7. 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 6.

8. The secondary battery as described in claim 7, characterized in that: The positive electrode active material in the secondary battery includes a high-nickel positive electrode active material. In the high-nickel positive electrode active material, the total amount of metal elements other than lithium is A, and the amount of nickel is B, where 0.6 ≤ B / A < 1.

9. The secondary battery as described in claim 7, characterized in that: The negative electrode active material in the secondary battery includes silicon-based negative electrode active material.

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