Lithium ion battery electrolyte and lithium ion battery
By combining fluorocyclopropyl compounds with other additives, a low-impedance SEI film is formed, which solves the problem of limited life of lithium-ion batteries and achieves a lithium-ion battery with longer life and excellent performance.
Patent Information
- Application Number
- CN202510434051.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-08
- Publication Date
- 2025-07-04
AI Technical Summary
The circulation and storage life of existing lithium-ion batteries is limited by the density and impedance of the SEI film. The amount of conventional additives cannot further improve the battery life. At the same time, the dense SEI film causes interfacial lithium-ion analysis problems and deteriorates battery performance.
Fluorocyclopropyl compounds are used as additives and combined with fluorovinyl carbonate, vinyl sulfate, lithium difluorooxalate borate, etc. to form a low-impedance three-dimensional mesh SEI film to improve the stability of the electrode interface.
Significantly improve the cycle life, calendar life and rate performance of lithium-ion batteries, avoid deterioration of high and low temperature performance, and achieve long-life and high-performance lithium-ion batteries.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a lithium-ion battery electrolyte and a lithium-ion battery. Background Art
[0002] Lithium-ion batteries have advantages such as higher energy density, faster charge and discharge rates, and no memory effect compared with other chemical energy storage devices. Therefore, they are widely used in fields such as mobile phones, laptop computers, fuel vehicles, new energy vehicles, and industrial energy storage. However, in some specific application scenarios, such as grid energy storage systems, remote monitoring devices, or space exploration, etc., the battery needs to work stably for a long time. These application scenarios usually require the battery to have high reliability and an extremely long service life. At the same time, in a highly competitive market environment, such as the fields of electric vehicles and renewable energy storage, products with a longer life can enable enterprises to occupy a favorable position in the market. Therefore, researching lithium-ion batteries with a longer life is not only the key to solving current technical and market challenges, but also the key to expanding the application fields of lithium-ion batteries.
[0003] Improving the life of a lithium-ion battery specifically refers to increasing the cycle life and calendar life of the lithium-ion battery. The cycle life refers to the number of times the battery is charged and discharged at a certain current. When a lithium-ion battery is charged and discharged, the volume of the negative electrode changes, resulting in the rupture of the SEI film at the interface, exposing the surface of the negative electrode. The electrolyte will undergo electrochemical decomposition at the exposed place and consume the lithium-ion content of the battery, resulting in a decrease in the total lithium content of the battery, that is, a decrease in the discharge capacity and a shortening of the cycle life. During the charge and discharge cycle, in addition to the changes at the interface, the crystal structure and electrical contact performance of the material also change, ultimately affecting the cycle life. The calendar life refers to the change in the capacity of the lithium-ion battery after standing for a certain period of time, mainly reflected by the change in the discharge capacity. The calendar life is also affected by the stability of the SEI film. When the SEI film swells, the electrolyte enters the inside of the SEI film, and the electrolyte reacts with the lithium in the negative electrode, resulting in a decrease in the active lithium content, thereby reducing the calendar life.
[0004] How to improve the cycle and storage life of lithium-ion batteries? A commonly used method in the electrolyte industry is to increase the addition amount of vinylene carbonate or fluoroethylene carbonate. Since vinylene carbonate or fluoroethylene carbonate can form a dense SEI film at the electrode interface, reducing the probability of direct contact between the electrolyte and the negative electrode interface, reducing the decomposition of the electrolyte and the consumption of active lithium, thereby improving the cycle and storage life of lithium-ion batteries. However, the dense SEI film will lead to an increase in interfacial polarization and a decrease in the interfacial potential. When the interfacial potential drops below 0V, the problem of lithium deposition at the interface will occur, and the side reaction between the deposited lithium and the electrolyte is stronger, resulting in further decomposition of the electrolyte and consumption of active lithium, which instead deteriorates the life of lithium-ion batteries. Therefore, the addition amount of vinylene carbonate or fluoroethylene carbonate cannot be continuously increased. Generally, after exceeding 5%, the cycle performance of the battery core deteriorates rapidly.
[0005] Although the use of conventional additives can improve the life of lithium-ion batteries, due to the relatively large film-forming impedance of these additives, the addition amount of the additives is limited, thereby limiting the improvement range of the life of lithium-ion batteries. Summary of the Invention
[0006] The object of the present invention is to provide an electrolyte that can improve the life of lithium-ion batteries and take into account the rate performance; another object of the present invention is to provide a lithium-ion battery with a longer life and excellent rate performance.
[0007] The present invention discloses a lithium-ion battery electrolyte, comprising a lithium salt, an organic solvent, and an additive; the additive comprises a fluorocyclopropyl compound having the structural formula (I): (I); Wherein, A is a carbonate group, a phosphate group, a sulfonate group, a sulfate group, a borate group, a siloxy group, or a sulfite group.
[0008] Further, A is one of a carbonate group, a sulfite group, and a sulfate group.
[0009] The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium difluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium hexafluoroarsenate.
[0010] The organic solvents include one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, vinylene carbonate, ethylene sulfite, methyl acetate, ethyl acetate, ethyl propionate, propyl propionate, methyl propionate, propyl formate, fluorobenzene, xylene, toluene, fluoroethylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, trimethyl phosphite, triethyl phosphite, tripropyl phosphite, tetrahydrofuran, acetonitrile, sulfolane, dimethyl sulfoxide, 1,2-dimethoxyethane.
[0011] The additives include 1,3-propane sultone, ethylene sulfate, methylene methanedisulfonate, propylene sultone, tris(trimethylsilyl) phosphate, propylene sulfate, tris(trimethylsilyl) borate, lithium bis(oxalato)borate, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium difluorophosphate, lithium difluoro(oxalato)phosphate, fluoroethylene carbonate, ethylene fluoroethylene carbonate, lithium difluoro(oxalato)phosphate, etc. One to four of these additives are selected and used in combination with the fluorocyclopropyl compound.
[0012] Furthermore, the mass of the lithium salt accounts for 8-12% of the mass of the electrolyte; the mass of the organic solvent accounts for 75-85% of the mass of the electrolyte; the mass of the additive accounts for 5-15% of the mass of the electrolyte.
[0013] Furthermore, the mass of the fluorocyclopropyl compound accounts for 7-12% of the mass of the electrolyte.
[0014] Furthermore, the additive also includes one or more of fluoroethylene carbonate (FEC), ethylene sulfate (DTD), lithium difluoro(oxalato)borate (LiDFOB).
[0015] The fluorocyclopropyl film-forming additive has a synergistic effect with fluoroethylene carbonate, ethylene sulfate, and lithium difluoro(oxalato)borate, and can further improve the life, high and low temperature performance, and rate performance of the lithium-ion battery.
[0016] Furthermore, the mass of the fluoroethylene carbonate accounts for 0.8-1.2% of the mass of the electrolyte, the mass of the ethylene sulfate accounts for 0.5-1% of the mass of the electrolyte, and the mass of the lithium difluoro(oxalato)borate accounts for 0.3-0.5% of the mass of the electrolyte.
[0017] Furthermore, the organic solvent includes one or more of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.
[0018] Furthermore, the mass ratio of ethylene carbonate:ethyl methyl carbonate:dimethyl carbonate is 3:4:3.
[0019] Furthermore, the lithium salt includes lithium hexafluorophosphate.
[0020] The present invention also discloses a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and the lithium-ion battery electrolyte as described above.
[0021] The active material of the positive electrode sheet includes one or more of lithium cobaltate, lithium manganate, lithium nickelate, lithium iron phosphate, lithium manganese iron phosphate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, and lithium-rich manganese.
[0022] The active material of the negative electrode sheet includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, silicon carbon, silicon monoxide, and lithium titanate.
[0023] The present invention does not strictly limit the selection range of the separator, and common separators all meet the requirements of the present invention. For example: polypropylene separator (PP), polyethylene separator (PE), polyethylene / polypropylene double-layer composite film, polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene three-layer composite separator (PP / PE / PP), ceramic separator, PVDF-coated separator, etc.
[0024] The lithium-ion battery electrolyte provided by the present invention adds a fluorocyclopropyl-based film-forming additive. After the film-forming additive gains electrons at the electrode interface, cyclopropyl ring cleavage and recombination polymerization occur, forming a three-dimensional network structure, which improves the stability of the SEI film. Since the molecular weight of this additive is relatively large and the film-forming density is lower than that of vinylene carbonate and fluorinated carbonate, the SEI film formed by this additive has a lower impedance. In addition to the low film-forming density of the new additive, the new additive can form anionic groups with a weak binding ability to lithium ions, which is also one of the reasons for the lower impedance of the SEI film. Therefore, the lithium-ion battery prepared by using the lithium-ion battery electrolyte provided in this application not only has a long lifespan, but also does not deteriorate the high and low temperature performance and rate performance. Specific Embodiments
[0025] To make the technical solutions of the present invention clearer, the following further describes the present invention in detail with specific embodiments.
[0026] In the lithium-ion battery positive electrode sheets prepared in the examples and comparative examples of the present invention, lithium iron phosphate is used as the positive electrode active material, and lithium iron phosphate, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95.5:2:2.5. The specific preparation method is as follows: First, lithium iron phosphate, conductive carbon black, and PVDF are dispersed in an appropriate amount of N-methylpyrrolidone, and then they are fully stirred evenly according to the homogenization step. The uniformly dispersed positive electrode slurry is evenly coated on aluminum foil, and after baking, rolling, slitting, and punching, the positive electrode sheet is obtained.
[0027] In the examples and comparative examples of the present invention, artificial graphite is used as the negative active material for the lithium-ion battery negative electrode sheet. Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are put into a homogenizing tank according to a mass ratio of 96:1:2:1, and a uniformly dispersed negative electrode slurry is prepared according to the pulping process. Then, the negative electrode slurry is uniformly coated on a copper foil, and after baking, rolling, slitting, and punching, a negative electrode sheet is obtained.
[0028] After the positive electrode sheet and the negative electrode are punched, the positive electrode is baked in an oven at 110 - 140°C, and the negative electrode is baked in an oven at 90 - 100°C for 20 - 30 h. When the moisture of the electrode sheet meets the requirements, the positive electrode sheet, the negative electrode sheet, and the separator are placed in a stacker to form a bare battery, and then the bare battery is encapsulated into a stamped aluminum-plastic film bag. After the encapsulated dry battery is dried at 80 - 95°C for 8 - 15 h, the electrolyte of the present invention is injected into the dry battery. After the battery is left standing, pre-charged, aged at high temperature, degassed, formed, aged at high temperature, and sorted, a lithium-ion battery is obtained.
[0029] Fluorocyclopropyl compounds are mainly synthesized from (2-fluorocyclopropane-1,1-diyl) dimethanol and ester compounds. The specific synthesis steps are as follows: 。
[0030] The fluorocyclopropyl compounds selected in the examples are 1,1-fluorocyclopropane dimethanol carbonate (T1), 1,1-fluorocyclopropane dimethanol sulfite (T2), and 1,1-fluorocyclopropane dimethanol sulfate (T3).
[0031] The specific synthesis method is as follows: The synthesis method of T1 is: 。
[0032] The synthesis method of T2 is: 。
[0033] The synthesis method of T3 is: 。 Example 1
[0034] The electrolyte in this example is prepared by the following steps: Control the moisture content in the glove box to be below 10 ppm and control the moisture content of the solvent to be below 10 ppm. Use a percentile balance to accurately weigh 30 grams of ethylene carbonate, 40 grams of ethyl methyl carbonate, and 30 grams of dimethyl carbonate, and pour them into an aluminum bottle. After stirring well, place it in a constant temperature box at 0°C and freeze for 1 h. Then add 13 grams of lithium hexafluorophosphate while stirring. Finally, add 12.6 grams of T1 reagent and stir evenly.
[0035] Inject the electrolyte into a lithium-ion dry battery for energy storage, and then place it in an environment at 25°C for soaking for 48 hours. After the electrolyte has fully soaked the battery, pre-charge formation and grading are started. The pre-charge step is to charge at a constant current of 0.01C to 10% SOC, and then change to a constant current of 0.02C to charge to 30% SOC. After pre-charging, it is aged in an environment at 45°C for 48 hours, and then vacuumed. After aging, it is charged at a constant current and voltage of 0.1C to 3.65V, left standing for 10 minutes and then discharged to 2.5V to determine the initial charge-discharge efficiency. Next, continue aging at 45°C for 24 hours. After completing aging, grading is carried out by charging at a constant current and voltage of 0.1C to 3.65V and discharging at a constant current and voltage of 0.1C to 2.5V, and finally a finished lithium-ion battery is obtained. Example 2
[0036] The electrolyte in this example is prepared by the following steps: Control the moisture content in the glove box to be below 10 ppm and control the moisture content of the solvent to be below 10 ppm. Use a percentile balance to accurately weigh 30 grams of ethylene carbonate, 40 grams of ethyl methyl carbonate, and 30 grams of dimethyl carbonate, and pour them into an aluminum bottle. After stirring well, place it in a constant temperature oven at 0°C and freeze for 1 h. Then add 13 grams of lithium hexafluorophosphate while stirring. Finally, add 12.6 grams of T2 reagent and stir evenly.
[0037] Inject the electrolyte into a lithium-ion dry battery for energy storage, and then place it in an environment at 25°C for soaking for 48 hours. After the electrolyte has fully soaked the battery, pre-charge formation and grading are started. The pre-charge step is to charge at a constant current of 0.01C to 10% SOC, and then change to a constant current of 0.02C to charge to 30% SOC. After pre-charging, it is aged in an environment at 45°C for 48 hours, and then vacuumed. After aging, it is charged at a constant current and voltage of 0.1C to 3.65V, left standing for 10 minutes and then discharged to 2.5V to determine the initial charge-discharge efficiency. Next, continue aging at 45°C for 24 hours. After completing aging, grading is carried out by charging at a constant current and voltage of 0.1C to 3.65V and discharging at a constant current and voltage of 0.1C to 2.5V, and finally a finished lithium-ion battery is obtained. Example 3
[0038] The electrolyte in this example is prepared by the following steps: Control the moisture content in the glove box to be below 10 ppm and control the moisture content of the solvent to be below 10 ppm. Use a percentile balance to accurately weigh 30 grams of ethylene carbonate, 40 grams of ethyl methyl carbonate, and 30 grams of dimethyl carbonate, and pour them into an aluminum bottle. After stirring well, place it in a constant temperature oven at 0°C and freeze for 1 h. Then add 13 grams of lithium hexafluorophosphate while stirring. Finally, add 12.6 grams of T3 reagent and stir evenly.
[0039] Inject the electrolyte into the lithium-ion dry battery for energy storage, and then place it in an environment at 25°C for infiltration for 48 hours. After the electrolyte fully infiltrates the battery, pre-charge formation and grading are started. The pre-charge step is to charge at a constant current of 0.01C to 10% SOC, and then change to a constant current of 0.02C to charge to 30% SOC. After pre-charging, age at 45°C for 48 hours, and then evacuate with a vacuum pump. After aging, charge at a constant current and voltage of 0.1C to 3.65V, let it stand for 10 minutes and then discharge to 2.5V to determine the first charge-discharge efficiency. Next, continue to age at 45°C for 24 hours. After completing the aging, perform grading by charging at a constant current and voltage of 0.1C to 3.65V and discharging at a constant current and voltage of 0.1C to 2.5V, and finally obtain the finished lithium-ion battery. Example 4
[0040] The electrolyte in this example is prepared by the following steps: Control the moisture content in the glove box to be below 10 ppm and control the moisture content of the solvent to be below 10 ppm. Accurately weigh 30 grams of ethylene carbonate, 40 grams of ethyl methyl carbonate, and 30 grams of dimethyl carbonate using a percentile balance, and pour them into an aluminum bottle. After stirring evenly, place it in a constant temperature oven at 0°C and freeze for 1 hour. Then add 13 grams of lithium hexafluorophosphate while stirring. Finally, add 12.6 grams of T1 reagent, 1.3 grams of FEC, 1 gram of DTD, and 0.4 grams of LiDFOB, and stir evenly.
[0041] Inject the electrolyte into the lithium-ion dry battery for energy storage, and then place it in an environment at 25°C for infiltration for 48 hours. After the electrolyte fully infiltrates the battery, pre-charge formation and grading are started. The pre-charge step is to charge at a constant current of 0.01C to 10% SOC, and then change to a constant current of 0.02C to charge to 30% SOC. After pre-charging, age at 45°C for 48 hours, and then evacuate with a vacuum pump. After aging, charge at a constant current and voltage of 0.1C to 3.65V, let it stand for 10 minutes and then discharge to 2.5V to determine the first charge-discharge efficiency. Next, continue to age at 45°C for 24 hours. After completing the aging, perform grading by charging at a constant current and voltage of 0.1C to 3.65V and discharging at a constant current and voltage of 0.1C to 2.5V, and finally obtain the finished lithium-ion battery. Example 5
[0042] The electrolyte in this example is prepared by the following steps: Control the moisture content in the glove box to be below 10 ppm and control the moisture content of the solvent to be below 10 ppm. Accurately weigh 30 grams of ethylene carbonate, 40 grams of ethyl methyl carbonate, and 30 grams of dimethyl carbonate using a percentile balance, and pour them into an aluminum bottle. After stirring evenly, place it in a constant temperature oven at 0°C and freeze for 1 hour. Then add 13 grams of lithium hexafluorophosphate while stirring. Finally, add 12.6 grams of T2 reagent, 1.3 grams of FEC, 1 gram of DTD, and 0.4 grams of LiDFOB, and stir evenly.
[0043] Inject the electrolyte into the lithium-ion dry battery for energy storage, and then place it in an environment of 25°C for infiltration for 48 hours. After the electrolyte fully infiltrates the battery, start the pre-charge formation and grading. The pre-charge step is to charge at a constant current of 0.01C to 10% SOC, and then change to a constant current of 0.02C to charge to 30% SOC. After pre-charging, age at 45°C for 48 hours, and then evacuate the air under vacuum. After aging, charge at a constant current and voltage of 0.1C to 3.65V, wait for 10 minutes and then discharge to 2.5V to determine the first charge-discharge efficiency. Next, continue to age at 45°C for 24 hours. After completing the aging, perform grading by charging at a constant current and voltage of 0.1C to 3.65V and discharging at a constant current and voltage of 0.1C to 2.5V, and finally obtain the finished lithium-ion battery. Example 6
[0044] The electrolyte in this example is prepared by the following steps: control the water content in the glove box to be less than 10 ppm and the water content of the solvent to be less than 10 ppm. Use a percentile balance to accurately weigh 30 grams of ethylene carbonate, 40 grams of ethyl methyl carbonate, and 30 grams of dimethyl carbonate, and pour them into an aluminum bottle. After stirring evenly, place it in a constant temperature box at 0°C and freeze for 1 h. Then add 13 grams of lithium hexafluorophosphate while stirring. Finally, add 12.6 grams of T3 reagent, 1.3 grams of FEC, 1 gram of DTD, and 0.4 gram of LiDFOB, and stir evenly.
[0045] Inject the electrolyte into the lithium-ion dry battery for energy storage, and then place it in an environment of 25°C for infiltration for 48 hours. After the electrolyte fully infiltrates the battery, start the pre-charge formation and grading. The pre-charge step is to charge at a constant current of 0.01C to 10% SOC, and then change to a constant current of 0.02C to charge to 30% SOC. After pre-charging, age at 45°C for 48 hours, and then evacuate the air under vacuum. After aging, charge at a constant current and voltage of 0.1C to 3.65V, wait for 10 minutes and then discharge to 2.5V to determine the first charge-discharge efficiency. Next, continue to age at 45°C for 24 hours. After completing the aging, perform grading by charging at a constant current and voltage of 0.1C to 3.65V and discharging at a constant current and voltage of 0.1C to 2.5V, and finally obtain the finished lithium-ion battery. Comparative Example
[0046] The electrolyte in this embodiment is prepared by the following steps: controlling the water content in the glove box to be less than 10 ppm and controlling the water content of the solvent to be less than 10 ppm. Accurately weigh 30 grams of ethylene carbonate, 40 grams of ethyl methyl carbonate, and 30 grams of dimethyl carbonate using a percentile balance, and pour them into an aluminum bottle. After stirring well, place it in a constant temperature oven at 0 °C and freeze for 1 h. Then add 13 grams of lithium hexafluorophosphate while stirring. Finally, add 1.3 grams of FEC, 1 gram of DTD, and 0.4 gram of LiDFOB, and stir evenly.
[0047] Inject the electrolyte into a lithium-ion dry battery for energy storage, and then place it in an environment at 25 °C for infiltration for 48 hours. After the electrolyte fully infiltrates the battery, start the pre-charge formation and grading. The pre-charge process is to charge at a constant current of 0.01C to 10% SOC, and then change to a constant current of 0.02C to charge to 30% SOC. After pre-charging, age at 45 °C for 48 hours, and then evacuate with a vacuum pump. After aging, charge at a constant current and voltage of 0.1C to 3.65V, let it stand for 10 minutes and then discharge to 2.5V to determine the first charge-discharge efficiency. Next, continue to age at 45 °C for 24 hours. After completing the aging, perform grading by charging at a constant current and voltage of 0.1C to 3.65V and discharging at a constant current and voltage of 0.1C to 2.5V, and finally obtain the finished lithium-ion battery. Performance test:
[0048] The electrolytes and lithium-ion batteries of the examples and comparative examples are tested and compared for performance differences by the following methods: (1)45 °C cycle test of lithium-ion batteries The examples and comparative examples in this patent are subjected to a 45 °C cycle test according to the following steps. The detailed steps are as follows: Take a fixed-volume lithium-ion battery, place it in a constant temperature oven at 45 °C, and let it stand for more than 1 hour to ensure that the internal temperature of the battery is close to 45 °C. Then charge at a constant current and voltage of 1C, with a cut-off voltage of 3.65V and a cut-off current of 0.05C. Then discharge at a constant current of 1C to 2.5V. Charge and discharge the battery according to the above steps, and record the discharge capacity retention rate after 1000 cycles. The calculation method of the discharge capacity retention rate of the battery after 1000 cycles is the discharge capacity after cycling divided by the discharge capacity of the first cycle. The specific test data are shown in Table 1.
[0049] Table 1 45 °C cycle performance test results of lithium-ion batteries
[0050] (2)25 °C rate test of lithium-ion batteries The batteries in the embodiments and comparative examples of this patent were tested for rate performance at 25 °C according to the following steps. The battery was placed in a constant temperature cabinet at 25 °C and allowed to stand for 6 hours before charging and discharging began. First, it was charged at a constant current and constant voltage of 0.1C and discharged at a constant current of 0.1C, that is, the battery was volume-fixed. Then, the discharge rate was changed, and the battery was discharged to 2.5V at 0.3C, 0.5C, and 1C respectively, and the discharge capacities at different rates were obtained. The discharge capacities at different rates were divided by the discharge capacity at 0.1C to obtain the capacity retention rates at different rates. The test results of the 25 °C rate are shown in Table 2.
[0051] Table 2 Test Results of the Rate Performance of Lithium-Ion Batteries at 25 °C
[0052] (3)60 °C Storage Test of Lithium-Ion Batteries The steps for testing the high-temperature storage performance of the batteries in the embodiments and comparative examples of this patent are as follows: The volume-fixed battery was discharged at a constant current of 1C to 2.5V, left to stand for 5 minutes, and then charged at a constant current and constant voltage of 1C to 3.65V, with a cut-off current of 0.05C. The battery was placed in a constant temperature oven at 60 °C and stored for 30 days, 60 days, 90 days, 120 days, and 150 days respectively. After the battery was stored for the specified number of days, it was taken out. The battery was connected to the test cabinet, discharged at a constant current of 1C to 2.5V, and then charged at a constant current and constant voltage of 1C. The process of discharging at a constant current of 1C was repeated for charging and discharging 3 times. Finally, the discharge capacity recovery rate of the battery was obtained, and the relevant test results are shown in Table 3.
[0053] Table 3 Test Results of the 60 °C Storage of Lithium-Ion Batteries
[0054] As shown in Table 1, from the data comparison between Examples 1-3 and the comparative examples, it can be seen that only adding fluorocyclopropyl compounds can also significantly improve the cycle performance. This is related to the excellent film-forming performance of fluorocyclopropyl compounds and sufficient addition amounts. By comparing Examples 1-3, it was found that T2 has better cycle performance, which should be related to the ability of sulfite groups to form a SEI film with lower impedance. When the T1-T3 additives are used in combination with FEC, DTD, and LiDFOB, the cycle performance of lithium-ion batteries is significantly improved. It may be that the conventional additives and the fluorocyclopropyl compound additives have a synergistic effect, further optimizing the cycle performance of the battery.
[0055] As shown in Table 2, when only T1, T2 or T3 is added to the electrolyte, the rate performance of the lithium-ion battery is better than that of the comparative example. This is related to the fact that the SEI film formed by the novel additive is less dense than that of the conventional additive. Among T1, T2 and T3, the best rate performance is T2, which is related to the fact that the T2 additive can form lithium organosulfite, because the lithium-ion dissociation energy of lithium organosulfite is lower, reducing the desolvation energy. Based on the T1, T2 and T3 additives, after adding the additives of the control group, the rate performance of Examples 4 and 5 is less affected by the conventional additive, while the rate performance of Example 6 is more affected by the conventional additive. It may be related to the synergistic effect between T1, T2 and the conventional additive.
[0056] As shown in Table 3, Table 3 lists the high-temperature storage performance data of the examples and the comparative examples. Only one additive, namely T1, T2 and T3, was added in Examples 1 to 3. Compared with the comparative examples using conventional additives, Examples 1 to 3 have higher capacity recovery rates in high-temperature storage, indicating that T1, T2 and T3 can improve the high-temperature storage performance of lithium-ion batteries. This is related to the fact that the novel additive can form a stable and thick SEI film layer at the electrode interface. Among T1, T2 and T3, the T3 additive has greater advantages in improving high-temperature storage, which is related to the fact that the sulfate group can form stable lithium sulfate. Although the effect of the T2 additive used alone is not as good as that of T1 and T3, the effect of T2 combined with FEC, DTD, and LiDFOB is better than that of T1 and T3. This may be related to the sulfite group of the T2 additive. The sulfite group interacts with the carbonate group and the sulfate group of the conventional additive, and this interaction optimizes the high-temperature storage performance.
[0057] Combining the data of 45°C cycling, room-temperature rate and high-temperature storage, Example 5 has the best performance in terms of cycle life, calendar life and room-temperature rate.
[0058] The present invention proposes a fluorocyclopropyl compound additive, which can form a stable but moderately dense SEI film, keeping the impedance of the battery at a low level. The low-impedance performance provides the possibility to increase the addition amount of the additive, and its addition amount can exceed 10%, significantly improving the cycle life and calendar life.
[0059] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.
Claims
1. A lithium-ion battery electrolyte, characterized in that, It includes a lithium salt, an organic solvent, and an additive; the additive includes a fluorocyclopropyl compound having the structural formula (I): （I）； Wherein, A is a carbonate group, a phosphate group, a sulfonate group, a sulfate group, a borate group, a siloxy group, or a sulfite group.
2. The electrolyte for a lithium-ion battery according to claim 1, wherein A is one of a carbonate group, a sulfite group, and a sulfate group.
3. The electrolyte of a lithium-ion battery according to claim 1, characterized in that, The mass of the lithium salt accounts for 8-12% of the mass of the electrolyte; the mass of the organic solvent accounts for 75-85% of the mass of the electrolyte; the mass of the additive accounts for 5-15% of the mass of the electrolyte.
4. A lithium-ion battery electrolyte according to claim 1, characterized in that, The mass of the fluorocyclopropyl compound accounts for 7-12% of the mass of the electrolyte.
5. A lithium-ion battery electrolyte according to claim 1, characterized in that, The additive further includes one or more of fluoroethylene carbonate, vinylene sulfate, and lithium difluoro(oxalato)borate.
6. The electrolyte of a lithium-ion battery according to claim 4, characterized in that, The mass of the fluoroethylene carbonate accounts for 0.8-1.2% of the mass of the electrolyte, the mass of the vinylene sulfate accounts for 0.5-1% of the mass of the electrolyte, and the mass of the lithium difluoro(oxalato)borate accounts for 0.3-0.5% of the mass of the electrolyte.
7. An electrolyte for a lithium-ion battery according to claim 3, characterized in that, The organic solvent includes one or more of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.
8. The electrolyte of a lithium-ion battery according to claim 7, wherein The mass ratio of the ethylene carbonate: the ethyl methyl carbonate: the dimethyl carbonate is 3:4:
3.
9. The electrolyte of a lithium-ion battery according to claim 3, characterized in that, The lithium salt includes lithium hexafluorophosphate.
10. A lithium-ion battery, characterized in that, It includes a positive electrode sheet, a negative electrode sheet, a separator, and a lithium-ion battery electrolyte as described in any one of claims 1-9.