Electrolyte additive, electrolyte and lithium ion battery
By introducing an electrolyte additive with an aminoboronic acid lactone structure containing BO and BN bonds into the electrolyte, the problem of iron ion dissolution in lithium iron phosphate batteries during high-temperature long-cycle operation was solved, thereby improving the battery's cycle performance and capacity retention.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BYD CO LTD
- Filing Date
- 2021-12-29
- Publication Date
- 2026-08-04
AI Technical Summary
During long-term cycling at high temperatures, iron ions in lithium iron phosphate batteries dissolve at the positive electrode and deposit on the negative electrode, leading to a decline in battery cycle performance.
An electrolyte additive with an aminoboronic acid lactone structure containing BO and BN bonds is used. Through hydrolysis, it generates weakly acidic phenylboronic acid and basic amines, which reduces the acidity of the electrolyte, reduces the amount of iron ions dissolved in the positive electrode material, and improves the battery cycle performance.
It significantly reduces the deposition of iron ions on the negative electrode, improves the cycle performance and capacity retention of lithium-ion batteries, and enhances the high-temperature long-cycle performance of the batteries.
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Figure CN116417669B_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of lithium-ion battery technology, specifically, this application relates to an electrolyte additive, an electrolyte, and a lithium-ion battery. Background Technology
[0002] In recent years, with my country's increasing efforts to promote new energy vehicles, pure electric vehicles, with their green and environmentally friendly characteristics, have become an inevitable trend in the future development of the automotive industry. They will gradually replace traditional fuel-powered buses as the daily transportation tool for ordinary people. As the power source for electric vehicles, the improvement of various performance aspects of lithium-ion batteries has always been a key focus of the industry.
[0003] Since their invention, lithium-ion batteries have been highly favored due to their advantages such as high energy density, stable discharge voltage, and long service life. Lithium iron phosphate (LFP) is widely used among common lithium-ion battery cathode materials. However, during high-temperature, long-cycle operation, iron ions at the cathode of LFP batteries tend to dissolve and deposit at the anode, leading to a decline in battery cycle performance. The electrolyte, as a crucial component of lithium-ion batteries, has a significant impact on their cycle performance.
[0004] In view of this, it is necessary to propose an electrolyte additive to improve the performance of the electrolyte, thereby improving the cycle performance of lithium-ion batteries. Summary of the Invention
[0005] One objective of this application is to provide a new technical solution for electrolyte additives, electrolytes, and lithium-ion batteries.
[0006] According to a first aspect of the embodiments of this application, an electrolyte additive is provided, the electrolyte additive comprising BO bonds and BN bonds, and the electrolyte additive having the structural formula shown in the following chemical formula a:
[0007]
[0008] R1 and R2 are selected from any one of alkyl, aryl and trimethylsilyl groups, respectively; R3, R4, R5 and R6 are selected from any one of hydrogen, alkyl, alkenyl, alkynyl and aryl groups, respectively; R7 and R8 are selected from any one of fluoroalkyl and sulfonyl groups, respectively.
[0009] Optionally, R1, R2, R3, R4, R5, and R6 are each independently selected from alkyl groups; and R7 and R8 are each independently selected from fluoroalkyl groups.
[0010] According to a second aspect of the embodiments of this application, an electrolyte is provided, the electrolyte comprising the electrolyte additives as described in the first aspect.
[0011] Optionally, the electrolyte additive has a mass percentage content of 0.1%-3% in the electrolyte.
[0012] Optionally, the electrolyte additive has a mass percentage content of 0.8-1.2% in the electrolyte.
[0013] Optionally, the electrolyte may further include lithium salt, solvent, and negative electrode film-forming additive.
[0014] Optionally, the lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium tetrafluoroborate; the concentration of the lithium salt is 0.9 mol / L to 1.5 mol / L.
[0015] Optionally, the solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, and ethylene carbonate.
[0016] Optionally, the negative electrode film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, methanemethylene disulfonate, lithium difluorophosphate, and lithium difluorooxalate borate.
[0017] Optionally, the mass of the negative electrode film-forming additive is 0.1%-5% of the mass of the solvent.
[0018] According to a third aspect of the embodiments of this application, a lithium-ion battery is provided, the lithium-ion battery comprising the electrolyte as described in the second aspect.
[0019] One technical advantage of the embodiments of this application is that:
[0020] This application provides an electrolyte additive with strong hydrolysis ability. It can undergo hydrolysis reaction with water in the electrolyte, and its hydrolysis products are weakly acidic phenylboronic acid, alcohol, and basic amine substances. After hydrolysis, the acidity of the electrolyte is reduced, the amount of iron ions dissolved in the positive electrode material is reduced, and the damage caused by iron ion deposition on the negative electrode is reduced, thereby improving the cycle performance of the battery. Detailed Implementation
[0021] Various exemplary embodiments of this application will now be described in detail. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values of the components and steps set forth in these embodiments do not limit the scope of this application.
[0022] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the scope of this application and its application or use.
[0023] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.
[0024] In all the examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.
[0025] This application provides an electrolyte additive, which includes BO bonds and BN bonds, and has the structural formula shown in chemical formula a:
[0026]
[0027] R1 and R2 are selected from any one of alkyl, aryl and trimethylsilyl groups, respectively; R3, R4, R5 and R6 are selected from any one of hydrogen, alkyl, alkenyl, alkynyl and aryl groups, respectively; R7 and R8 are selected from any one of fluoroalkyl and sulfonyl groups, respectively.
[0028] In one embodiment, R1, R2, R3, R4, R5, and R6 are each independently selected from alkyl groups; R7 and R8 are each independently selected from fluoroalkyl groups, wherein the fluoroalkyl groups include partially substituted fluoroalkyl groups and fully substituted fluoroalkyl groups, which can further improve the antioxidant capacity of the electrolyte additive.
[0029] The electrolyte additive provided in this application is a dehydrating additive with an aminoboron lactone structure. It contains a BO-bonded five-membered ring lactone structure and a BN-bonded structure, meaning the aminoboron lactone structure contains a five-membered ring lactone structure composed of boron, oxygen, and carbon. Simultaneously, an amino group is attached to the boron atom. Both of these structures have strong hydrolytic capabilities. Therefore, this aminoboron lactone structure has a strong hydrolytic ability and can undergo a hydrolysis reaction with water in the electrolyte. Its hydrolysis products are weakly acidic phenylboronic acid, alcohols, and basic amines. After hydrolysis, the acidity of the electrolyte is reduced, and the amount of iron ions dissolved in the positive electrode material is reduced, thereby reducing the damage caused by iron ion deposition on the negative electrode and improving the cycle performance of the battery. Furthermore, the amine substituent on the nitrogen atom in this aminoboron lactone structure is an electron-withdrawing group, enhancing the molecule's antioxidant properties.
[0030] This application also provides an electrolyte, which includes the electrolyte additives described above.
[0031] The electrolyte provided in this application embodiment contains the above-mentioned electrolyte additives, which significantly reduces its acidity and enhances its antioxidant capacity. This electrolyte can greatly reduce the amount of iron ions dissolved in the positive electrode material, thereby reducing the damage caused by iron ions deposited on the negative electrode and improving the cycle performance of the battery.
[0032] In one embodiment, the electrolyte additive further comprises 0.1%-3% by mass in the electrolyte.
[0033] The amount of electrolyte additive added affects its water removal capacity and the battery's cycle performance. Specifically, if the amount of electrolyte additive added is too low, the water removal effect will be poor; if the amount of electrolyte additive added is too high, it will have a negative impact on the battery's cycle performance. Therefore, in this specific example, the mass percentage content of the electrolyte additive in the electrolyte is set at 0.1%-3%, which ensures good water removal effect without negatively impacting the battery's cycle performance. Further, the mass percentage content of the electrolyte additive in the electrolyte is 0.8-1.2%.
[0034] In one embodiment, the electrolyte further includes lithium salt, solvent, and negative electrode film-forming additive.
[0035] In one embodiment, the lithium salt further comprises at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium tetrafluoroborate.
[0036] In one embodiment, the concentration of the lithium salt is further 0.9 mol / L to 1.5 mol / L.
[0037] In one embodiment, the solvent further includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and ethylene carbonate (EC).
[0038] In one embodiment, the negative electrode film-forming additive further includes at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), methanemethylene disulfonate (MMDS), lithium difluorophosphate (LiDFP), and lithium difluorooxalate borate (LiDFOB).
[0039] In one embodiment, the mass of the negative electrode film-forming additive is further 0.1%-5% of the mass of the solvent.
[0040] This application embodiment provides another lithium-ion battery, which includes the electrolyte as described above.
[0041] The present application will be further illustrated below through specific embodiments and comparative examples:
[0042] Example 1
[0043] S101. Use 100g of dimethoxymethyl ether as a solvent and add 0.1mol of bis(trifluoroethyl)amine to it. At the same time, continuously pass argon gas through it and slowly add n-butyllithium solution until no gas is generated. Obtain solid bis(trifluoroethyl)amine by vacuum distillation.
[0044] S102. Add 0.1 mol of 1-hydroxy-3,3-dimethyl-5,6,7,8-tetramethyl-1,2-benzoborone lactone to 100 g of CH2Cl2, and continuously bubble phosgene into the solution for 24 h. After the reaction is complete, add 0.1 mol of the solid bis(trifluoroethyl)aminolithium obtained in step S101. After refluxing for 24 h, 1-bis(trifluoroethyl)amino-3,3-dimethyl-5,6,7,8-tetramethyl-1,2-benzoborone lactone is obtained by vacuum distillation and column purification. Its chemical structural formula is as follows:
[0045] S103. Mix DMC, EMC, DEC, EC, and VC evenly, slowly add lithium hexafluorophosphate and stir evenly, then add 1-di(trifluoroethyl)amino-3,3-dimethyl-5,6,7,8-tetramethyl-1,2-benzoborone obtained in step S102 to obtain the electrolyte for lithium-ion batteries; wherein the mass percentage content of 1-di(trifluoroethyl)amino-3,3-dimethyl-5,6,7,8-tetramethyl-1,2-benzoborone is 0.8%.
[0046] Example 2
[0047] S101. Use 100g of dimethoxymethyl ether as a solvent and add 0.1mol of bis(trifluoroethyl)amine to it. At the same time, continuously pass argon gas through it and slowly add n-butyllithium solution until no gas is generated. Obtain solid bis(trifluoroethyl)amine by vacuum distillation.
[0048] S102. 0.1 mol of 1-hydroxy-3,3-dimethyl-1,2-benzoborone lactone was added to 100 g of CH2Cl2, and phosgene was continuously introduced for 24 h. After the reaction was complete, 0.1 mol of the bis(trifluoroethyl)aminolithium solid obtained in step S101 was added. The reaction was refluxed for 24 h, and then purified by vacuum distillation and column chromatography to obtain 1-bis(trifluoroethyl)amino-3,3-dimethyl-1,2-benzoborone lactone, whose chemical structural formula is [insert chemical formula here].
[0049] S103. Mix DMC, EMC, DEC, EC, and VC evenly, slowly add lithium hexafluorophosphate and stir evenly, then add 1-di(trifluoroethyl)amino-3,3-dimethyl-1,2-benzoborone obtained in step S102 to obtain the electrolyte for lithium-ion batteries; wherein, the mass percentage content of 1-di(trifluoroethyl)amino-3,3-dimethyl-1,2-benzoborone is 1%.
[0050] Example 3
[0051] S101. Use 100g of dimethoxymethyl ether as a solvent and add 0.1mol of bis(trifluoroethyl)amine to it. At the same time, continuously pass argon gas through it and slowly add n-butyllithium solution until no gas is generated. Obtain solid bis(trifluoroethyl)amine by vacuum distillation.
[0052] S102. 0.1 mol of 1-hydroxy-3,3-diethyl-1,2-benzoborone lactone was added to 100 g of CH2Cl2, and phosgene was continuously introduced for 24 h. After the reaction was complete, 0.1 mol of the bis(trifluoroethyl)aminolithium solid obtained in step S101 was added. The reaction was refluxed for 24 h, and then purified by vacuum distillation and column chromatography to obtain 1-bis(trifluoroethyl)amino-3,3-diethyl-1,2-benzoborone lactone, whose chemical structural formula is [insert chemical formula here].
[0053] S103. Mix DMC, EMC, DEC, EC, and VC evenly, slowly add lithium hexafluorophosphate and stir evenly, then add 1-di(trifluoroethyl)amino-3,3-diethyl-1,2-benzoborone obtained in step S102 to obtain the electrolyte for lithium-ion batteries; wherein, the mass percentage content of 1-di(trifluoroethyl)amino-3,3-diethyl-1,2-benzoborone is 1.2%.
[0054] Example 4
[0055] S101. 0.1 mol of 1-hydroxy-3,3-dimethyl-1,2-benzoborone lactone was added to 100 g of CH2Cl2, and phosgene was continuously introduced for 24 h. After the reaction was complete, 0.1 mol of lithium bis(methanesulfonamide)amide was added, and the reaction was refluxed for 24 h. Then, 1-di(methanesulfonyl)amino-3,3-dimethyl-1,2-benzoborone lactone was obtained by vacuum distillation and column purification. Its chemical structural formula is as follows:
[0056] S102. Mix DMC, EMC, DEC, EC, and VC evenly, slowly add lithium hexafluorophosphate and stir evenly, then add 1-di(methanesulfonyl)amino-3,3-dimethyl-1,2-benzoborone obtained in step S102 to obtain the electrolyte for lithium-ion batteries; wherein, the mass percentage content of 1-di(methanesulfonyl)amino-3,3-dimethyl-1,2-benzoborone is 0.8%.
[0057] Example 5
[0058] S101. 0.1 mol of 1-hydroxy-3,3-dimethyl-7-vinyl-1,2-benzoborone lactone was added to 100 g of CH2Cl2, and phosgene was continuously introduced for 24 h. After the reaction was complete, 0.1 mol of lithium bis(methanesulfonamide)amide was added, and the reaction was refluxed for 24 h. Then, 1-di(methanesulfonyl)amino-3,3-dimethyl-7-vinyl-1,2-benzoborone lactone was obtained by vacuum distillation and column purification. Its chemical structural formula is as follows:
[0059] S102. Mix DMC, EMC, DEC, EC, and VC evenly, slowly add lithium hexafluorophosphate and stir evenly, then add 1-di(methanesulfonyl)amino-3,3-dimethyl-7-vinyl-1,2-benzoborone obtained in step S102 to obtain the electrolyte for lithium-ion batteries; wherein, the mass percentage content of 1-di(methanesulfonyl)amino-3,3-dimethyl-7-vinyl-1,2-benzoborone is 0.8%.
[0060] Example 6
[0061] S101. 0.1 mol of 1-hydroxy-3,3-dimethyl-7-ethyl-1,2-benzoborone lactone was added to 100 g of CH2Cl2, and phosgene was continuously introduced for 24 h. After the reaction was complete, 0.1 mol of lithium bis(methanesulfonamide)amide was added, and the reaction was refluxed for 24 h. Then, 1-di(methanesulfonyl)amino-3,3-dimethyl-7-ethyl-1,2-benzoborone lactone was obtained by vacuum distillation and column purification. Its chemical structural formula is as follows:
[0062] S102. Mix DMC, EMC, DEC, EC, and VC evenly, slowly add lithium hexafluorophosphate and stir evenly, then add 1-di(methanesulfonyl)amino-3,3-dimethyl-7-ethyl-1,2-benzoborone obtained in step S102 to obtain the electrolyte for lithium-ion batteries; wherein, the mass percentage content of 1-di(methanesulfonyl)amino-3,3-dimethyl-7-ethyl-1,2-benzoborone is 3%.
[0063] Comparative Example 1
[0064] The electrolyte in Comparative Example 1 contains DMC, DEC, EMC, EC and VC, and the mass percentage content is DMC:DEC:EMC:EC:VC = 10:30:30:30:1.
[0065] Comparative Example 2
[0066] The electrolyte in Comparative Example 2 contains DMC, DEC, EMC, EC, VC and 1-di(trifluoroethyl)amino-3,3-dimethyl-5,6,7,8-tetramethyl-1,2-benzoborone lactone, and the mass percentage content of 1-di(trifluoroethyl)amino-3,3-dimethyl-5,6,7,8-tetramethyl-1,2-benzoborone lactone is 0.05%.
[0067] Comparative Example 3
[0068] The electrolyte in Comparative Example 3 contains DMC, DEC, EMC, EC, VC and 1-di(trifluoroethyl)amino-3,3-dimethyl-5,6,7,8-tetramethyl-1,2-benzoborone lactone, and the mass percentage content of 1-di(trifluoroethyl)amino-3,3-dimethyl-5,6,7,8-tetramethyl-1,2-benzoborone lactone is 5%.
[0069] Comparative Example 4
[0070] The electrolyte in Comparative Example 4 contains DMC, DEC, EMC, EC, VC and hexamethyldisilamine, and the mass percentage content is DMC:DEC:EMC:EC:VC:hexamethyldisilamine = 10:30:30:30:1:1.
[0071] Lithium-ion batteries were prepared using the electrolytes obtained in Examples 1-6 and Comparative Examples 1-4, respectively. The lithium-ion batteries prepared in Examples 1-6 were designated B1, B2, B3, B4, B5, and B6, respectively, and the lithium-ion batteries prepared in Comparative Examples 1-4 were designated C1, C2, C3, and C4, respectively. Performance tests were conducted on the above lithium-ion batteries. The specific test items and results are as follows:
[0072] 1) Battery cycle performance test
[0073] The battery was charged at 25°C with a constant current of 0.05C to 15% SOC, then charged at 0.25C to 3.8V, kept constant at 0.05C, and then discharged at 0.33C to 2.5V. It was then charged again at 1C to 3.8V, kept constant at 0.05C, and then discharged at 1C to 2.5V, marking the first cycle. This charge-discharge cycle was repeated 500 times. The discharge capacity of the 500th cycle was recorded, and the capacity retention rate (%) after 500 cycles was calculated as: (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%. The test results are shown in Table 1.
[0074] Table 1:
[0075]
[0076]
[0077] 2) Acid content test after battery storage and negative electrode iron content test after 500 cycles
[0078] The battery was stored at 45°C for four weeks before being disassembled, and the electrolyte was removed for testing of acid and iron content.
[0079] The battery was disassembled after being cycled 500 times at 45°C. After being soaked in DMC, the leachate was taken to test the Fe element and hydrofluoric acid content of the electrolyte. The Fe element of the negative electrode was also tested. The converted values of hydrofluoric acid and iron content in the electrolyte and iron content in the negative electrode are shown in Table 2 below.
[0080] Table 2:
[0081]
[0082] As can be seen from Tables 1 and 2, the amount of hydrofluoric acid and iron dissolved in the batteries prepared using the electrolytes obtained in Examples 1-6 is significantly lower than that in the comparative example, indicating that the electrolyte additives in this application have a significant inhibitory effect on the amount of hydrofluoric acid and iron dissolved in the batteries; furthermore, the iron content deposited on the negative electrode of the batteries prepared using the electrolytes obtained in Examples 1-6 is significantly reduced after 500 cycles; and the electrolyte additives in this application have a significant effect on improving the capacity retention rate of the batteries.
[0083] Furthermore, the electrolyte additives in Examples 1-3 contain fluorinated alkyl groups, so the corresponding batteries B1-B3 have a better capacity retention rate than batteries B4-B6 corresponding to Examples 4-6, and the iron content deposited on the negative electrode decreases more significantly after 500 cycles.
[0084] Although the electrolyte additive provided in this application was added in Comparative Example 2, the content of the electrolyte additive was too low, so the iron content deposited on the negative electrode of the corresponding battery C2 did not decrease well after 500 cycles. Although the electrolyte additive provided in this application was added in Comparative Example 3, the content of the electrolyte additive was too high, so although the iron content deposited on the negative electrode of the corresponding battery C3 decreased well after 500 cycles, the capacity retention rate of battery C3 was not good.
[0085] While specific embodiments of this application have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of this application. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of this application. The scope of this application is defined by the appended claims.
Claims
1. An electrolyte additive, characterized in that, The electrolyte additive includes BO bonds and BN bonds, and the electrolyte additive has the structural formula shown in chemical formula a: Chemical formula a; Among them, R3, R4, R5, and R6 are selected from any one of hydrogen, alkyl, and alkenyl groups, respectively, and R7 and R8 are selected from any one of fluoroalkyl and sulfonyl groups, respectively; R1 and R2 are each independently selected from alkyl groups.
2. The electrolyte additive according to claim 1, characterized in that, R3, R4, R5, and R6 are each independently selected from alkyl groups; R7 and R8 are each independently selected from fluoroalkyl groups.
3. An electrolyte, characterized in that, The electrolyte includes an electrolyte additive as described in any one of claims 1-2, wherein the electrolyte additive has a mass percentage content of 0.8%-3% in the electrolyte.
4. The electrolyte according to claim 3, characterized in that, The electrolyte additive has a mass percentage content of 0.8%-1.2% in the electrolyte.
5. The electrolyte according to claim 3, characterized in that, The electrolyte also includes lithium salt, solvent, and negative electrode film-forming additives.
6. The electrolyte according to claim 5, characterized in that, The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, and lithium tetrafluoroborate; the concentration of the lithium salt is 0.9 mol / L - 1.5 mol / L.
7. The electrolyte according to claim 5, characterized in that, The solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, and ethylene carbonate.
8. The electrolyte according to claim 5, characterized in that, The negative electrode film-forming additive includes at least one of vinylene carbonate, fluoroethylene carbonate, methanemethylene disulfonate, lithium difluorophosphate, and lithium difluorooxalate borate.
9. The electrolyte according to claim 5, characterized in that, The mass of the negative electrode film-forming additive is 0.1%-5% of the mass of the solvent.
10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 3-9.