Electrolyte and lithium-ion battery using same

Abstract

An electrolyte and a lithium-ion battery using same. The electrolyte comprises a first additive; the mass ratio of the first additive in the electrolyte is 2.5-5.5%; the first additive comprises trimethyl phosphate and pentafluoro ethoxy cyclotriphosphazene; upon calculation, the mass ratio of trimethyl phosphate to pentafluoro ethoxy cyclotriphosphazene is equal to 0.5-2:2-3.5.

Description

Electrolyte and lithium ion battery using same

[0001] The present application claims priority to the Chinese patent application No. 202410675302.2, filed on May 28, 2024, to the Chinese Patent Office, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of lithium ion batteries, in particular to an electrolyte and a lithium ion battery using the same. BACKGROUND

[0003] The continuous prosperity of computers, communications and consumer electronics has brought rapid development of the lithium ion battery industry, especially in recent years, the rise of new energy vehicles not only promotes the development of power lithium ion batteries, but also puts forward higher requirements for energy density and safety performance.

[0004] The application of high-nickel ternary materials and silicon-based materials is an effective way for lithium ion batteries to achieve high energy density. However, the poor safety of high-nickel / high-silicon systems and the high-temperature storage gas production problem have become one of the main bottlenecks restricting their large-scale industrial application. SUMMARY

[0005] The main reason for the flammability and explosiveness of the battery is the production of flammable gas by thermal runaway of the battery cell, and the flammable gas mainly comes from the reduction and decomposition of organic solvents in the electrolyte. Therefore, the existing high-nickel / high-silicon lithium ion batteries are difficult to simultaneously consider high energy density and high safety performance. Therefore, there is an urgent need to develop an electrolyte that can improve the safety performance of lithium ion batteries.

[0006] The present application provides an electrolyte, which comprises a first additive, the mass fraction of the first additive in the electrolyte is 2.5-5.5%; the first additive comprises trimethyl phosphate (TMP) and pentafluoroethoxy cyclotriphosphazene (PFPN); the mass ratio of trimethyl phosphate to pentafluoroethoxy cyclotriphosphazene is 0.5-2:2-3.5.

[0007] The present application also provides a lithium ion battery, which comprises the above-mentioned electrolyte. ADVANTAGEOUS EFFECTS

[0008] The electrolyte provided in the application adds a first additive containing trimethyl phosphate and pentafluoroethoxy cyclotriphosphazene, both of which have the characteristic of low heat of combustion. Under the synergistic effect of phosphorus in trimethyl phosphate and fluorine in pentafluoroethoxy cyclotriphosphazene, the electrolyte exhibits excellent flame retardant effect and has good thermal stability and electrochemical stability. When the electrolyte is applied to a lithium ion battery, the first additive will release a large amount of free radicals that can capture combustion free radicals (H•, O2* and HO•) in the gas phase during the heating process, thereby achieving the effect of flame retardant. The nitrogen element in pentafluoroethoxy cyclotriphosphazene can form a protective layer by generating N2 and ammonia during the combustion process, thereby inhibiting the supply of oxygen. Through the above effects, the introduction of the first additive in the electrolyte not only reduces the risk of flammable and explosive lithium ion batteries due to the reduction and decomposition of the electrolyte to produce more combustible gas, improves the safety performance of the lithium ion battery, but also improves the high-temperature storage gas production problem of the lithium ion battery and improves the high-temperature storage performance of the lithium ion battery. Embodiments of the application

[0009] In order to solve the existing problems of poor safety and high-temperature storage gas production of high-nickel / high-silicon lithium ion batteries, improve the high-temperature storage gas production problem of lithium ion batteries, and improve the safety performance of lithium ion batteries, the embodiments of the application provide an electrolyte and a lithium ion battery containing the same.

[0010] The embodiments provide an electrolyte, which includes a first additive, and the mass fraction of the first additive in the electrolyte is 2.5-5.5%; the first additive includes trimethyl phosphate (TMP) and pentafluoroethoxy cyclotriphosphazene (PFPN); and the mass ratio of trimethyl phosphate to pentafluoroethoxy cyclotriphosphazene is 0.5-2:2-3.5.

[0011] The electrolyte provided in the application adds the first additive containing trimethyl phosphate and pentafluoroethoxy cyclotriphosphazene, the trimethyl phosphate and the pentafluoroethoxy cyclotriphosphazene both have the characteristic of low heat of combustion, the electrolyte shows excellent flame retardant effect under the synergistic effect of the phosphorus element in the trimethyl phosphate and the fluorine element in the pentafluoroethoxy cyclotriphosphazene, and has good thermal stability and electrochemical stability, the electrolyte is applied to a lithium ion battery, when the lithium ion battery is in thermal runaway, the first additive releases a large amount of free radicals capable of capturing combustion free radicals (H•, O2*, HO•) in the gas phase in the heating process, so that the flame retardant effect is achieved, and the nitrogen element in the pentafluoroethoxy cyclotriphosphazene can form a protective layer by generating N2 and ammonia in the combustion process, so as to inhibit the supply of oxygen, through the action, the introduction of the first additive in the electrolyte can not only reduce the risk of flammable and explosive lithium ion batteries due to the reduction and decomposition of the electrolyte to produce more combustible gas, improve the safety performance of the lithium ion battery, but also improve the high-temperature storage gas production problem of the lithium ion battery and improve the high-temperature storage performance of the lithium ion battery.

[0012] In some embodiments, the electrolyte further comprises a second additive, the mass ratio of the second additive in the electrolyte is 1.05-1.65%; the second additive comprises lithium difluorophosphate (LiPO2F2) and tripropargyl phosphate (TPP); according to the mass ratio, lithium difluorophosphate: tripropargyl phosphate = 1-1.5: 0.05-0.15.

[0013] Although the addition of the first additive containing trimethyl phosphate and pentafluoroethoxy cyclotriphosphazene in the electrolyte and the application of the electrolyte to the lithium ion battery can improve the high-temperature storage gas production problem of the lithium ion battery and improve the safety performance of the lithium ion battery, the addition of the first additive will cause the electrochemical performance and cycle performance of the lithium ion battery to decrease.

[0014] On the basis of adding the first additive containing trimethyl phosphate and pentafluoroethoxy cyclotriphosphazene in the electrolyte, the second additive containing lithium difluorophosphate and tripropargyl phosphate is further added in the electrolyte, the tripropargyl phosphate has a lower HOMO-LUMO energy level, can preferentially form a film on the positive and negative electrodes, inhibit gas production, improve high-temperature storage and safety, and the lithium difluorophosphate and the tripropargyl phosphate both have the effect of low impedance, can effectively reduce the impedance and the loss of active lithium, improve the lithium intercalation capacity, and improve the performance of the lithium ion battery, through the action, the introduction of the second additive in the electrolyte can not only improve the high-temperature storage gas production problem of the lithium ion battery and improve the safety performance of the lithium ion battery, but also improve the electrochemical performance and cycle performance of the lithium ion battery to a certain extent, which is conducive to improving the cycle life of the lithium ion battery.

[0015] In some embodiments, the electrolyte further comprises an organic solvent, and the mass percentage of the organic solvent in the electrolyte is 84-88%; the organic solvent comprises at least one of propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) and vinylene carbonate (VC).

[0016] In some embodiments, the organic solvent comprises propylene carbonate and dimethyl carbonate; the mass percentage of the propylene carbonate in the electrolyte is 5-15%; and the mass percentage of the dimethyl carbonate in the electrolyte is 10-20%.

[0017] By greatly reducing the content of the high-calorific-value solvents propylene carbonate and dimethyl carbonate in the electrolyte and applying them in the lithium ion battery, the high-temperature storage gas production problem of the lithium ion battery can be further improved, and the safety performance of the lithium ion battery can be improved.

[0018] In some embodiments, the organic solvent further comprises fluoroethylene carbonate, ethyl methyl carbonate and vinylene carbonate; the mass percentage of the fluoroethylene carbonate in the electrolyte is 8-9%; the mass percentage of the ethyl methyl carbonate in the electrolyte is 50-52%; and the mass percentage of the vinylene carbonate in the electrolyte is 1-2%.

[0019] In some embodiments, the electrolyte comprises the following components in terms of mass percentage: 1% trimethyl phosphate, 3.2% pentafluoroethoxy cyclotriphosphazene, 1.2% lithium difluorophosphate, 0.10% tripropargyl phosphate, 10% propylene carbonate, 15% dimethyl carbonate, 8.5% fluoroethylene carbonate, 50.2% ethyl methyl carbonate and 1.5% vinylene carbonate.

[0020] In some embodiments, the electrolyte further comprises a lithium salt, and the mass percentage of the lithium salt in the electrolyte is 9-9.5%; the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate and lithium tetrafluoroborate.

[0021] In some embodiments, the lithium salt in the electrolyte is lithium hexafluorophosphate.

[0022] The embodiment provides a lithium ion battery, which comprises the electrolyte.

[0023] The electrolyte provided by the application can be applied to a lithium ion battery, so that the high-temperature storage gas production problem of the lithium ion battery can be improved, and the safety performance of the lithium ion battery can be improved.

[0024] In some embodiments, the lithium ion battery further comprises a cathode sheet, the cathode sheet comprising a cathode current collector and a cathode active coating layer disposed on at least one surface of the cathode current collector, the cathode active coating layer containing a ternary material LiNi x Co y M 1-x-y O2, wherein 0.6≤x<1, 0

[0025] In some embodiments, the lithium ion battery further comprises an anode sheet, the anode sheet comprising an anode current collector and an anode active coating layer disposed on at least one surface of the anode current collector, the anode active coating layer containing a silicon-based material; the silicon content in the silicon-based material is 5-30 t%.

[0026] Embodiments of the present application are further illustrated by the following.

[0027] Examples 1-6 and Comparative Example 1

[0028] Examples 1-6 and Comparative Example 1 provide a lithium ion battery, which is prepared by the following steps:

[0029] 1. Preparation of the cathode sheet

[0030] The ternary material LiNi 0.8 Co 0.1 Mn 0.1 O2, a binder polyvinylidene fluoride (PVDF) and a conductive agent acetylene black are mixed in a mass ratio of 97:1.6:1.4 and then added to a solvent N-methyl pyrrolidone (NMP), and uniformly mixed to prepare a cathode slurry with a solid content of 45%. The cathode slurry is coated on both surfaces of a cathode current collector aluminum foil (thickness of 12 μm) to form a cathode active coating layer. After vacuum drying, a cathode sheet is prepared.

[0031] 2. Preparation of the anode sheet

[0032] The silicon-based material, a binder sodium carboxymethyl cellulose (CMC) and a conductive agent conductive carbon black (SP) are mixed in a mass ratio of 96:3:1 and then added to a solvent deionized water, and uniformly mixed to prepare an anode slurry with a solid content of 45%. The anode slurry is coated on both surfaces of an anode current collector copper foil (thickness of 6 μm) to form an anode active coating layer. After vacuum drying, an anode sheet is prepared.

[0033] 3. Preparation of the separator

[0034] A polyethylene (PE) film containing a ceramic layer (thickness of 12 μm) is used as the separator.

[0035] 4. Preparation of the electrolyte

[0036] The specific components of the electrolyte are shown in Table 1. The electrolyte is prepared by the following steps: dissolving a lithium salt in an organic solvent to prepare a lithium salt solution, adding an additive to the lithium salt solution, and mixing uniformly to prepare the electrolyte.

[0037] Table 1. Specific components of the electrolyte of the lithium ion battery of Examples 1-6 and Comparative Examples 1

[0038]

[0039] 5. Assembly and formation of the lithium ion battery

[0040] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order with the separator between the positive and negative electrode sheets to serve as a separator, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with the electrolyte. After vacuum packaging, standing, formation, and shaping, the lithium ion battery is obtained.

[0041] Comparative Examples 2-6

[0042] Comparative Examples 2-6 provide a lithium ion battery. Compared with Example 1, the difference is that the components of the electrolyte are different, as shown in Table 2.

[0043] Table 2. Specific components of the electrolyte of the lithium ion battery of Example 1 and Comparative Examples 2-6

[0044]

[0045] In addition to the differences shown in Table 2, the materials, formulation ratios, and preparation operations used in Comparative Examples 2-6 are strictly consistent with those of Example 1.

[0046] Examples 7-11

[0047] Examples 7-11 provide a lithium ion battery. Compared with Example 4, the difference is that the components of the electrolyte are different, as shown in Table 3.

[0048] Table 3. Specific components of the electrolyte of the lithium ion battery of Example 4 and Examples 7-11

[0049]

[0050] In addition to the differences shown in Table 3, the materials, formulation ratios, and preparation operations used in Examples 7-11 are strictly consistent with those of Example 4.

[0051] Examples 12-15

[0052] Examples 12-15 provide a lithium ion battery. Compared with Example 4, the difference is that the components of the electrolyte are different, as shown in Table 4.

[0053] Table 4. Specific components of the electrolytes for the lithium-ion batteries in Examples 4 and 12-15.

[0054]

[0055] Except for the differences shown in Table 4, the materials, formulation ratios, and preparation operations used in Examples 12-15 are strictly consistent with those in Example 4.

[0056] Test case

[0057] 1. Participants

[0058] This test example uses the lithium-ion batteries prepared in Examples 1-15 and Comparative Examples 1-6 as test objects to conduct relevant performance tests.

[0059] 2. Test Content

[0060] (1) Storage performance test at 60℃

[0061] The lithium-ion batteries, after capacity testing, were charged to 4.2 V at 0.5 C, then switched to constant voltage charging to 0.05 C. After reaching full charge, the batteries were left at room temperature for 2 hours before the voltage was tested. The cell volume of the lithium-ion batteries was measured in silicone oil using Archimedes' principle. Subsequently, the batteries were stored in a 60℃ oven for 28 days. The composition of the stored gas, the amount and rate of gas production, the ACR increase, the capacity retention rate, and the capacity recovery rate were measured before and after storage.

[0062] ACR refers to contact resistance, which is tested using a voltage resistance meter. The formula for calculating the ACR increment is as follows: ACR increment = (resistance value of the lithium-ion battery in a fully charged state after storage - resistance value of the lithium-ion battery in a fully charged state before storage) / resistance value of the lithium-ion battery in a fully charged state before storage × 100%;

[0063] Capacity retention rate refers to the capacity retention rate of a lithium-ion battery before and after storage. The calculation formula is as follows: Capacity retention rate = Discharge capacity of the lithium-ion battery after storage at 0.1C to 2.5V (0% SOC) / Discharge capacity of the lithium-ion battery before storage at 0.33C × 100%;

[0064] Capacity recovery rate refers to the ratio between the discharge capacity of a lithium-ion battery after its capacity has been recovered from storage and the discharge capacity value calibrated at 0.33C before storage. The calculation formula is as follows: Capacity recovery rate = Discharge capacity value of the lithium-ion battery after storage (discharged to 2.5V at 0.1C and then charged and discharged at 0.1C) / Discharge capacity value calibrated at 0.33C before storage × 100%.

[0065] (2) Safety performance test

[0066] ① Needle puncture resistance test

[0067] The main principle of the needle penetration test is to create a short circuit between the positive and negative electrodes by piercing the separator, thus artificially creating a short circuit point inside the lithium-ion battery and simulating the short circuit phenomenon caused by excess conductive material inside the battery. The needle penetration test is the most complex safety test because the energy of the entire lithium-ion battery is rapidly released through the internal short circuit point in a short period (up to 70% of the energy can be released within one minute), causing a sharp rise in temperature and triggering a chain reaction that leads to thermal runaway. Factors affecting the results of the lithium-ion battery needle penetration test mainly include the diameter of the steel needle, the penetration speed, the capacity of the lithium-ion battery, and the material system (positive and negative electrode materials, separator, electrolyte).

[0068] The following steps were taken to conduct a needle penetration test on the lithium-ion battery: After the single lithium-ion battery was fully charged, a Φ3mm high-temperature resistant steel needle (with a cone angle of 45-60° at the tip, and a smooth surface free of rust, oxide layer and oil) was used to penetrate the battery from a direction perpendicular to the lithium-ion 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 remained in the lithium-ion battery for 1 hour. The fire situation of the lithium-ion battery was observed, and the number of lithium-ion batteries that caught fire was counted and calculated.

[0069] ②High temperature resistance test

[0070] The lithium-ion batteries were baked in a 150°C hot box for 30 minutes. The ignition of the lithium-ion batteries was observed, and the number of lithium-ion batteries that caught fire was counted and calculated.

[0071] (3) Cyclic performance test

[0072] After capacity testing, the lithium-ion batteries were placed in a constant temperature chamber and charged at 1.0 C to 4.2 V at 25±2℃. Then, they were charged at constant voltage to 0.05 C and left to stand for 10 min. Finally, they were discharged at 1.0 C to 3.0 V for room temperature and high temperature cycle tests. The discharge DC internal resistance (DCR) was tested before the room temperature (25℃) and high temperature (60℃) cycle tests and after every 500 cycles.

[0073] 3. Experimental Results

[0074] Table 5. Gas composition test results of lithium-ion batteries after storage at 60℃ for 28 days

[0075]

[0076] The gas composition test results of lithium-ion batteries after being stored at 60°C for 28 days are shown in Table 5.

[0077] Compared to Comparative Examples 1-6, the electrolytes of the lithium-ion batteries provided in Examples 1-15 contain 2.5-5.5 wt% of a first additive, which is a mixture of TMP and PEPN in a mass ratio of 0.5-2:2-3.5. The test results show that the amount of gas produced and the amount of total combustible gas in the lithium-ion batteries provided in Examples 1-15 after being stored at 60°C for 28 days are lower than those in Comparative Examples 1-6.

[0078] Compared with Example 1, the electrolytes of the lithium-ion batteries provided in Examples 4 to 6 also contain 1.05 to 1.65 wt% of a second additive. The second additive is a mixture of LiPO2F2 and TPP in a mass ratio of 1 to 1.5: 0.05 to 0.15. The test results show that the amount of gas produced and the amount of total combustible gas in the lithium-ion batteries provided in Examples 4 to 6 after being stored at 60°C for 28 days are both lower than those in Example 1.

[0079] Table 6 Performance test results of lithium-ion batteries after storage at 60°C for 28 days

[0080] Group ACR Increment (%) Capacity Retention Rate (%) Capacity Recovery Rate (%) Example 1 16.46 91.97 95.42 Example 2 17.16 90.07 95.42 Example 3 16.89 0.27 95.82 Example 4 12.21 94.90 98.65 Example 5 13.21 93.47 97.97 Example 6 13.66 93.47 97.06 Example 7 15.39 1.99 6.22 Example 8 15.45 91.79 6.02 Example 9 14.89 1.47 96.82 Example 10 15.83 91.4 596.85 Example 11 14.89 91.26 96.62 Example 12 18.28 9.09 4.22 Example 13 19 88.59 3.99 Example 14 19.58 8.19 3.4 Example 15 19.68 8.09 3.2 Comparative Example 1 28.29 85.11 89.86 Comparative Example 2 23.26 87.11 92.86 Comparative Example 3 23.16 86.29 1.89 Comparative Example 4 20.74 87.22 92.9 Comparative Example 5 25.23 87.51 91.88 Comparative Example 6 21.18 86.12 90.76

[0081] The performance test results of lithium-ion batteries after being stored at 60°C for 28 days are shown in Table 6.

[0082] Compared to Comparative Examples 1-6, the electrolytes of the lithium-ion batteries provided in Examples 1-15 contain 2.5-5.5 wt% of a first additive, which is a mixture of TMP and PEPN in a mass ratio of 0.5-2:2-3.5. The test results show that the ACR increment of the lithium-ion batteries provided in Examples 1-15 after being stored at 60°C for 28 days is lower than that of Comparative Examples 1-6, while the capacity retention rate and capacity recovery rate are higher than those of Comparative Examples 1-6.

[0083] Compared with Example 1, the electrolytes of the lithium-ion batteries provided in Examples 4 to 6 also contain 1.05 to 1.65 wt% of a second additive. The second additive is a mixture of LiPO2F2 and TPP in a mass ratio of 1 to 1.5: 0.05 to 0.15. The test results show that the ACR increment of the lithium-ion batteries provided in Examples 4 to 6 after being stored at 60°C for 28 days is lower than that of Example 1, while the capacity retention rate and capacity recovery rate are higher than those of Example 1.

[0084] Table 7 Safety performance test results of lithium-ion batteries

[0085] Group Needle penetration test Heat chamber 150℃, 30 min Example 1 30% ignition 30% ignition Example 2 35% ignition 30% ignition Example 3 30% ignition 35% ignition Example 4 0% ignition 0% ignition Example 5 10% ignition 10% ignition Example 6 5% ignition 5% ignition Example 7 20% ignition 20% ignition Example 8 25% ignition 25% ignition Example 9 20% ignition 20% ignition Example 10 25% ignition 20% ignition Example 11 20% ignition Example 1: 20% ignition rate; Example 2: 35% ignition rate; Example 3: 40% ignition rate; Example 4: 40% ignition rate; Example 5: 20% ignition rate; Example 6: 20% ignition rate; Example 7: 70% ignition rate; Example 8: 70% ignition rate; Example 9: 90% ignition rate; Example 10: 100% ignition rate; Example 11: 100% ignition rate; Example 12: 80% ignition rate; Example 13: 80% ignition rate; Example 14: 20% ignition rate; Example 15: 70% ignition rate; Example 16: 70% ignition rate; Example 17: 75% ignition rate; Example 18: 70% ignition rate; Example 19: 70% ignition rate; Example 10: 70% ignition rate; Example 10: 70% ignition rate; Example 10: 70% ignition rate; Example 10: 70% ignition rate; Example 11: 100% ignition rate; Example 19: 100% ignition rate; Example 10: 80% ignition rate; Example 10: 80% ignition rate; Example 19: 85% ignition rate; Example 10: 85% ignition rate; Example 10: 70% ignition rate; Example 10: 70% ignition rate; Example 10: 70% ignition rate; Example 10: 70% ignition rate; Example 11: 70% ignition rate; Example 12: 35% ignition rate; Example 13: 40% ignition rate; Example 19: 40% ignition

[0086] The performance test results of lithium-ion batteries after being stored at 60°C for 28 days are shown in Table 7.

[0087] Compared to Comparative Examples 1-6, the electrolytes of the lithium-ion batteries provided in Examples 1-15 contain 2.5-5.5 wt% of a first additive, which is a mixture of TMP and PEPN in a mass ratio of 0.5-2:2-3.5. The test results show that the safety performance of the lithium-ion batteries provided in Examples 1-15 is better than that of Comparative Examples 1-6.

[0088] Table 8. Test results of kinetic and cycle performance of lithium-ion batteries

[0089]

[0090] The test results of the kinetic and cycle performance of the lithium-ion battery are shown in Table 8.

[0091] Compared to Comparative Example 1, the lithium-ion batteries provided in Examples 1-3, after introducing a first additive containing TMP and PEPN into the electrolyte, showed significantly lower gas production and total combustible gas content after storage at 60°C for 28 days. However, the DCR values ​​of the lithium-ion batteries provided in Examples 1-3 were higher than those of Comparative Example 1, and their cycle capacity retention rates were lower than those of Comparative Example 1. In contrast, the lithium-ion batteries provided in Examples 4-6, after introducing a second additive into the electrolyte, showed significantly lower gas production and total combustible gas content after storage at 60°C for 28 days, and their DCR values ​​were lower than those of Comparative Example 1, while their cycle capacity retention rates were higher than those of Comparative Example 1. The reason for this result is that while adding a first additive containing trimethyl phosphate and pentafluoroethoxycyclotriphosphazene to the electrolyte and applying this electrolyte to lithium-ion batteries can improve the high-temperature storage gas generation problem and enhance the safety performance of lithium-ion batteries, the addition of the first additive will reduce the electrochemical performance and cycle performance of the lithium-ion battery. Therefore, further adding a second additive containing lithium difluorophosphate and tripropynyl phosphate to the electrolyte is necessary. Alkyne esters have lower HOMO-LUMO energy levels, allowing them to preferentially form films on both positive and negative electrodes, suppressing gas generation and improving high-temperature storage and safety. Lithium difluorophosphate and tripropynyl phosphate both have low impedance, which can effectively reduce impedance and loss of active lithium, increase lithium intercalation capacity, and improve the performance of lithium-ion batteries. Through this effect, the introduction of a second additive into the electrolyte can not only improve the gas generation problem during high-temperature storage and enhance the safety performance of lithium-ion batteries, but also improve the electrochemical performance and cycle performance of lithium-ion batteries to a certain extent, which is beneficial to improving the cycle life of lithium-ion batteries.

Claims

1. An electrolyte comprising a first additive, wherein the first additive comprises 2.5% to 5.5% by mass in the electrolyte; The first additive includes trimethyl phosphate and pentafluoroethoxycyclotriphosphazene; The mass ratio of the trimethyl phosphate to the pentafluoroethoxycyclotriphosphazene is 0.5~2:2~3.

5.

2. The electrolyte as described in claim 1, wherein the electrolyte further comprises a second additive, the second additive comprising 1.05~1.65% by mass in the electrolyte; The second additive includes lithium difluorophosphate and tripropynyl phosphate; The mass ratio of lithium difluorophosphate to tripropynyl phosphate is 1~1.5:0.05~0.

15.

3. The electrolyte as described in claim 2, wherein the electrolyte further comprises an organic solvent, and the organic solvent accounts for 84-88% by mass in the electrolyte; The organic solvent includes at least one of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, methyl ethyl carbonate, and vinylene carbonate.

4. The electrolyte as described in claim 3, wherein: The organic solvents include propylene carbonate and dimethyl carbonate; The propylene carbonate in the electrolyte comprises 5-15% by mass. The mass percentage of dimethyl carbonate in the electrolyte is 10-20%.

5. The electrolyte as described in claim 4, wherein: The organic solvents also include fluoroethylene carbonate, methyl ethyl carbonate and vinylene carbonate; The fluoroethylene carbonate accounts for 8-9% of the mass of the electrolyte; The methyl ethyl carbonate in the electrolyte comprises 50-52% by mass. The mass percentage of the vinylene carbonate in the electrolyte is 1-2%.

6. The electrolyte of claim 5, wherein the electrolyte comprises the following components by mass percentage: 1% trimethyl phosphate, 3.2% pentafluoroethoxycyclotriphosphazene, 1.2% lithium difluorophosphate, 0.10% tripropynyl phosphate, 10% propylene carbonate, 15% dimethyl carbonate, 8.5% fluoroethylene carbonate, 50.2% methyl ethyl carbonate, and 1.5% vinylene carbonate.

7. The electrolyte according to any one of claims 1-6, wherein the electrolyte further comprises a lithium salt, and the lithium salt accounts for 9-9.5% of the mass of the electrolyte; The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium di(oxalato)borate, lithium di(fluorooxalato)borate, and lithium tetrafluoroborate.

8. A lithium-ion battery, the lithium-ion battery comprising the electrolyte as described in any one of claims 1 to 7.

9. The lithium-ion battery of claim 8, further comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active coating disposed on at least one surface of the positive current collector, the positive active coating containing a ternary material LiNi. x Co y M 1-x-y O2, where, 0.6≤x<1, 0<y<0.4, where M is selected from Mn and Al.

10. The lithium-ion battery of claim 8 or 9, further comprising a negative electrode sheet, the negative electrode sheet comprising a negative current collector and a negative active coating disposed on at least one surface of the negative current collector, the negative active coating comprising a silicon-based material; The silicon content in the silicon-based material is 5-30 wt%.

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