A high-temperature resistant lithium-ion battery electrolyte

Abstract

The present invention discloses a high-temperature resistant lithium-ion battery electrolyte, which comprises a lithium salt, a non-aqueous solvent, a high-temperature improvement additive and other functional additives; the high-temperature improvement additive comprises a phenylboronic acid pinacol ester compound, and the phenylboronic acid pinacol ester compound is a compound represented by formula (I), a compound represented by formula (II) or a combination thereof. The battery using the electrolyte of the present invention has good stability and high safety at high temperatures, and can effectively improve the high-temperature performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly to a high-temperature resistant electrolyte for lithium-ion batteries. Background Art

[0002] Recently, lithium-ion batteries have become a research hotspot and received extensive attention. Due to their advantages of high energy density, environmental friendliness, and good economy, they have high application potential in hybrid vehicles and mobile device power supplies in the field of electric vehicles. As is well known, high temperature is an important factor affecting the performance, lifespan, and safety of lithium-ion batteries. Specifically, on the one hand, lithium-ion batteries will age rapidly at high temperatures, affecting their service life; on the other hand, the lithium salts and organic solvents in the electrolyte of lithium-ion batteries have poor thermal stability, resulting in a decline in their performance at high temperatures. The electrolyte will also decompose at high temperatures and generate a large amount of gas, which is likely to cause the battery to expand, thereby reducing its service performance and safety. Therefore, it is urgent to develop an electrolyte for lithium-ion batteries with good stability, high safety, and long service life at high temperatures. Summary of the Invention

[0003] Based on the technical problems existing in the background art, the present invention proposes a high-temperature resistant electrolyte for lithium-ion batteries.

[0004] A high-temperature resistant electrolyte for lithium-ion batteries proposed by the present invention includes a lithium salt, a non-aqueous solvent, a high-temperature improvement additive, and other functional additives;

[0005] The high-temperature improvement additive includes phenylboronic acid pinacol esters, and the phenylboronic acid pinacol esters are compounds represented by formula (I), compounds represented by formula (II), or a combination thereof:

[0006]

[0007]

[0008] In formula (I), R1 to R4 are each independently selected from any one of H, a halogen atom, an ester group, a substituted or unsubstituted C 1～3 alkyl group, a substituted or unsubstituted C 1～3 alkoxy group, wherein the substituent of the substituted one is one or more of halogen atoms;

[0009]

[0010] In formula (II), R5 to R8 are each independently selected from any one of H, a halogen atom, an ester group, a substituted or unsubstituted C 1～3 alkyl group, a substituted or unsubstituted C 1～3 alkoxy group, wherein the substituent of the substituted one is one or more of halogen atoms.

[0011] Preferably, the compound represented by formula (I) is selected from Compound 1 to Compound 3:

[0012]

[0013] Among them, Compound 1 is 3-acetoxy-4-methoxycarbonylphenylboronic acid pinacol ester, Compound 2 is 3-fluoro-4-methoxycarbonylphenylboronic acid pinacol ester, and Compound 3 is 2-methyl-4-methoxycarbonylphenylboronic acid pinacol ester.

[0014] Preferably, the compound represented by formula (II) is selected from Compound 4 to Compound 6:

[0015]

[0016] Among them, Compound 4 is 5-(tert-butyldimethylsilyloxy)-2,3-difluorophenylboronic acid pinacol ester, Compound 5 is 3-bromo-5-(tert-butyldimethylsilyloxy)phenylboronic acid pinacol ester, and Compound 6 is 3-(tert-butyldimethylsilyloxy)-5-(methoxycarbonyl)phenylboronic acid pinacol ester.

[0017] Preferably, the phenylboronic acid pinacol ester compound is composed of the compound represented by formula (I) and the compound represented by formula (II) in a mass ratio of 0.5 - 1.5:1.5 - 2.5.

[0018] Preferably, the mass of the phenylboronic acid pinacol ester compound accounts for 0.1 - 10 wt% of the total mass of the electrolyte; preferably, the mass of the phenylboronic acid pinacol ester compound accounts for 0.5 - 5 wt% of the total mass of the electrolyte.

[0019] Preferably, the lithium salt is at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluoro(oxalato)phosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0020] Preferably, the mass of the lithium salt accounts for 10 - 20% of the total mass of the electrolyte; preferably, the mass of the lithium salt accounts for 13.5% of the total mass of the electrolyte.

[0021] Preferably, the other functional additives include at least one of a cycling additive, a low-temperature additive, and an overcharge prevention additive.

[0022] Preferably, the other functional additives include at least one of fluoroethylene carbonate, ethylene sulfate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) phosphate, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, and tris(hexafluoroisopropyl) phosphate.

[0023] Preferably, the mass of the other functional additives accounts for 1-5% of the total mass of the electrolyte.

[0024] Preferably, the non-aqueous solvent includes at least one of chain carbonate solvents, cyclic carbonate solvents, and carboxylic acid ester solvents; the cyclic carbonate solvents include at least one of ethylene carbonate (EC), fluoroethylene carbonate (FEC), and propylene carbonate (PC); the chain carbonate solvents include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC); the carboxylic acid ester solvents include at least one of propyl acetate (PA), ethyl acetate (EA), and propyl propionate (PP).

[0025] The beneficial effects of the present invention are as follows:

[0026] The present invention uses phenylboronic acid pinacol esters containing ester groups and siloxy functional groups or combinations thereof as additives. Among them, the phenylboronic acid pinacol ester containing an ester group has a relatively high redox potential, which can effectively inhibit side reactions in the battery, thereby improving the cycle life and safety of the battery. It can also form a stable complex with lithium ions, thereby improving the ionic conductivity of the electrolyte; the siloxy functional group can form a network group structure composed of alternating silicon-oxygen bonds and carbon-oxygen-silicon bonds on the surface of the negative electrode, which can avoid direct contact between the electrode and the electrolyte at high temperatures and effectively improve the stability of the negative electrode material. Moreover, the silicon-carbon bond is easily broken and combined with trace amounts of HF in the electrolyte, which can play a role in removing water and acid; the two additives have a synergistic effect and can form a stable passivation film on the surfaces of the positive and negative electrodes of the battery. This passivation film can effectively inhibit the direct contact between the electrolyte and the positive and negative electrode materials and has good lithium ion migration kinetics characteristics, thereby significantly improving the high-temperature storage performance of the battery. Detailed implementation manners

[0027] Next, the technical solutions of the present invention will be described in detail through specific examples.

[0028] Example 1

[0029] Prepare an electrolyte:

[0030] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed according to a mass ratio of EC:EMC = 3:7 to obtain a solvent; lithium hexafluorophosphate (LiPF6) is slowly added to the solvent. After lithium hexafluorophosphate is completely dissolved, VC (vinylene carbonate) and Compound 1 are added to obtain the electrolyte.

[0031] Among them, the raw materials of the electrolyte are composed of components with the following mass percentages: 13.5% lithium hexafluorophosphate (LiPF6), 2.0% vinylene carbonate (VC), 0.5% of Compound 1, and the solvent is made up to 100%.

[0032] Prepare the positive electrode sheet:

[0033] Mix the active material lithium nickel cobalt manganese oxide (NCM811), the conductive agent Super P (SP), and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1:2 in the solvent N-methyl-2-pyrrolidone, and stir well to mix evenly. Then, coat the obtained slurry on the current collector Al foil, and obtain the positive electrode sheet after slitting, die-cutting, and rolling. Its compaction density is 3.45 g / cm 3 .

[0034] Prepare the negative electrode sheet:

[0035] Mix the silicon-carbon negative electrode (SiOC600), the conductive agent Super P (SP), the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) in a mass ratio of 95:1:2:2 in the solvent deionized water, and stir well to mix evenly. Then, coat the obtained slurry on the current collector Cu foil, and obtain the negative electrode sheet after slitting, rolling, and die-cutting. Its compaction density is 1.6 g / cm 3 .

[0036] Prepare the lithium-ion battery:

[0037] Stack the positive electrode sheet, the separator (the separator used is a polypropylene PP film coated with a nano-aluminum oxide coating, where the thickness of the PP film is 12 μm and the thickness of the nano-aluminum oxide coating is 4 μm), and the negative electrode sheet in sequence, and obtain a bare battery cell according to the process of the stacked battery. Then, place the bare battery cell in an aluminum-plastic film for pre-packaging, inject the prepared electrolyte, and then package it to obtain the required soft-pack battery.

[0038] Example 2

[0039] Prepare the electrolyte:

[0040] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), mix ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of EC:EMC = 3:7 to obtain a solvent; slowly add lithium hexafluorophosphate (LiPF6) to the solvent. After the lithium hexafluorophosphate is completely dissolved, add VC (vinylene carbonate) and Compound 1 to obtain it.

[0041] Among them, the raw materials of the electrolyte are composed of components with the following mass percentages: 13.5% lithium hexafluorophosphate (LiPF6), 2.0% vinylene carbonate (VC), 1.0% of Compound 1, and the solvent is made up to 100%.

[0042] The preparation methods of the positive electrode sheet, negative electrode sheet and battery in Example 2 are the same as those in Example 1.

[0043] Example 3

[0044] Prepare the electrolyte solution:

[0045] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed according to a mass ratio of EC:EMC = 3:7 to obtain a solvent; lithium hexafluorophosphate (LiPF6) is slowly added to the solvent, and after lithium hexafluorophosphate is completely dissolved, VC (vinylene carbonate) and Compound 1 are added to obtain the electrolyte solution.

[0046] Among them, the raw materials of the electrolyte solution are composed of the following components by mass percentage: 13.5% of lithium hexafluorophosphate (LiPF6), 2.0% of vinylene carbonate (VC), 3.0% of Compound 1, and the solvent is made up to 100%.

[0047] The preparation methods of the positive electrode sheet, negative electrode sheet and battery in Example 3 are the same as those in Example 1.

[0048] Example 4

[0049] Prepare the electrolyte solution:

[0050] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed according to a mass ratio of EC:EMC = 3:7 to obtain a solvent; lithium hexafluorophosphate (LiPF6) is slowly added to the solvent, and after lithium hexafluorophosphate is completely dissolved, VC (vinylene carbonate) and Compound 5 are added to obtain the electrolyte solution.

[0051] Among them, the raw materials of the electrolyte solution are composed of the following components by mass percentage: 13.5% of lithium hexafluorophosphate (LiPF6), 2.0% of vinylene carbonate (VC), 0.5% of Compound 5, and the solvent is made up to 100%.

[0052] The preparation methods of the positive electrode sheet, negative electrode sheet and battery in Example 4 are the same as those in Example 1.

[0053] Example 5

[0054] Prepare the electrolyte solution:

[0055] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:EMC = 3:7 to obtain a solvent; lithium hexafluorophosphate (LiPF6) was slowly added to the solvent, and after LiPF6 was completely dissolved, VC (vinylene carbonate) and Compound 5 were added to obtain the electrolyte;

[0056] Among them, the raw materials of the electrolyte consisted of the following components by mass percentage: 13.5% of lithium hexafluorophosphate (LiPF6), 2.0% of vinylene carbonate (VC), 3.0% of Compound 5, and the solvent was made up to 100%.

[0057] The preparation methods of the positive electrode sheet, negative electrode sheet and battery in Example 5 were the same as those in Example 1.

[0058] Example 6

[0059] Prepare the electrolyte:

[0060] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:EMC = 3:7 to obtain a solvent; lithium hexafluorophosphate (LiPF6) was slowly added to the solvent, and after LiPF6 was completely dissolved, VC (vinylene carbonate) and Compound 5 were added to obtain the electrolyte;

[0061] Among them, the raw materials of the electrolyte consisted of the following components by mass percentage: 13.5% of lithium hexafluorophosphate (LiPF6), 2.0% of vinylene carbonate (VC), 5.0% of Compound 5, and the solvent was made up to 100%.

[0062] The preparation methods of the positive electrode sheet, negative electrode sheet and battery in Example 6 were the same as those in Example 1.

[0063] Example 7

[0064] Prepare the electrolyte:

[0065] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:EMC = 3:7 to obtain a solvent; lithium hexafluorophosphate (LiPF6) was slowly added to the solvent, and after LiPF6 was completely dissolved, VC (vinylene carbonate), Compound 1 and Compound 5 were added to obtain the electrolyte;

[0066] Among them, the raw materials of the electrolyte are composed of components with the following mass percentages: 13.5% of lithium hexafluorophosphate (LiPF6), 2.0% of vinylene carbonate (VC), 0.5% of Compound 1, 2.5% of Compound 5, and the solvent is made up to 100%.

[0067] The preparation methods of the positive electrode sheet, negative electrode sheet and battery in Example 7 are the same as those in Example 1.

[0068] Example 8

[0069] Prepare the electrolyte:

[0070] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed according to a mass ratio of EC:EMC = 3:7 to obtain a solvent; lithium hexafluorophosphate (LiPF6) is slowly added to the solvent, and after the lithium salt is completely dissolved, VC (vinylene carbonate), Compound 1 and Compound 5 are added to obtain it.

[0071] Among them, the raw materials of the electrolyte are composed of components with the following mass percentages: 13.5% of lithium hexafluorophosphate (LiPF6), 2.0% of vinylene carbonate (VC), 1% of Compound 1, 2% of Compound 5, and the solvent is made up to 100%.

[0072] The preparation methods of the positive electrode sheet, negative electrode sheet and battery in Example 8 are the same as those in Example 1.

[0073] Example 9

[0074] Prepare the electrolyte:

[0075] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed according to a mass ratio of EC:EMC = 3:7 to obtain a solvent; lithium hexafluorophosphate (LiPF6) is slowly added to the solvent, and after the lithium hexafluorophosphate is completely dissolved, VC (vinylene carbonate), Compound 1 and Compound 5 are added to obtain it.

[0076] Among them, the raw materials of the electrolyte are composed of components with the following mass percentages: 13.5% of lithium hexafluorophosphate (LiPF6), 2.0% of vinylene carbonate (VC), 1.5% of Compound 1, 1.5% of Compound 5, and the solvent is made up to 100%.

[0077] The preparation methods of the positive electrode sheet, negative electrode sheet and battery in Example 9 are the same as those in Example 1.

[0078] Comparative Example 1

[0079] The difference between the electrolyte of Comparative Example 1 and that of Example 1 is only that it does not contain Compound 1. The other raw materials and preparation methods are the same as those of Example 1.

[0080] Comparative Example 2

[0081] Preparation of electrolyte:

[0082] In a glove box filled with argon (moisture < 0.1 ppm, oxygen content < 0.1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed according to a mass ratio of EC:EMC = 3:7 to obtain a solvent; lithium hexafluorophosphate (LiPF6) was slowly added to the solvent, and after the lithium salt was completely dissolved, VC (vinylene carbonate) and pinacol phenylborate were added to obtain the electrolyte.

[0083] Among them, the raw materials of the electrolyte are composed of the following components by mass percentage: 13.5% of lithium hexafluorophosphate (LiPF6), 2.0% of vinylene carbonate (VC), 0.5% of pinacol phenylborate, and the solvent is made up to 100%.

[0084] The preparation methods of the positive electrode sheet, negative electrode sheet and battery of Comparative Example 2 are the same as those of Example 1.

[0085] Test Example

[0086] (1) 60°C high-temperature storage test

[0087] After the experimental batteries in Examples 1-9 and Comparative Examples 1-2 were formed and volume-adjusted, they were placed in a constant-temperature oven at 60°C for 28 days in a fully charged state, and the discharge capacity and volume of the batteries before and after storage were measured, and the capacity retention rate, recovery rate and volume expansion rate after 28 days were calculated. The test results are shown in Table 1:

[0088] Table 1: Performance comparison of Examples and Comparative Examples after 28 days of high-temperature storage

[0089]

[0090] Comparing Examples 1-3 with Comparative Example 1, it can be seen that adding 1% of Compound 1 additive can significantly improve the retention rate and recovery rate of the battery after high-temperature storage, and at the same time reduce the volume expansion, improving the high-temperature performance of the battery. This is because the ester-based phenylborate has a relatively high redox potential, which can effectively inhibit the side reactions in the battery, reduce the gas generation amount, and can also form a stable complex with lithium ions, thereby improving the ionic conductivity of the electrolyte.

[0091] Similarly, comparing Examples 4 to 6 with Comparative Example 1, it can be found that when the content of Compound 5 additive is 2%, the capacity retention rate and recovery rate after 28 days of high-temperature storage are improved most significantly. This is attributed to the fact that the siloxy functional group can form a network group structure on the surface of the negative electrode, which is formed by the interlaced combination of silicon-oxygen bonds and carbon-oxygen-silicon bonds. This can prevent the direct contact between the electrode and the electrolyte at high temperatures, effectively improving the stability of the negative electrode material. Moreover, the silicon-carbon bond is easily broken and combines with trace amounts of HF in the electrolyte, which can play a role in removing water and acid.

[0092] The difference between Comparative Example 1 and Comparative Example 2 is that 0.5% of pinacol phenylborate is added in Comparative Example 2. It can be seen that pinacol phenylborate can slightly improve the high-temperature storage performance. Comparing Examples 1 and 4 with Comparative Example 2, on the basis of pinacol phenylborate, an ester group or a siloxy group is added, and both the high-temperature storage performance and the gas generation of the battery are improved. The combined effect is further verified below.

[0093] Examples 7 to 9 are the combined use of two additives. It can be seen that the capacity retention rate and recovery rate are further improved after 28 days of high-temperature storage, indicating that the two additives have a synergistic effect and can form a stable passivation film on the surfaces of the positive and negative electrodes of the battery. This passivation film can effectively inhibit the direct contact between the electrolyte and the positive and negative electrode materials and has good lithium-ion migration kinetics characteristics, thereby significantly improving the high-temperature storage performance of the battery.

[0094] Comparing Examples 7 to 9 with Example 5, the same amount of additives is used, but the difference is that the combination of Compound 1 and Compound 5 is used. It can be seen that after the combination of the two compounds in different ratios, the improvement effects of the capacity retention rate and recovery rate after 28 days of high-temperature storage are better than those of a single compound. And when the mass ratio of Compound 1 to Compound 5 is 1:1, the performance is the best. The capacity retention rate after 28 days is increased by 6.3% compared with Compound 5, and the recovery rate is increased by 5.5%. At the same time, gas generation is further inhibited. It can be seen that only by continuously optimizing the content and ratio between the two types of additives can the synergistic effect be maximized.

[0095] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A high temperature resistant lithium ion battery electrolyte, characterized in that: Including lithium salts, non-aqueous solvents, high temperature improvement additives and other functional additives; The high temperature improvement additive comprises a phenylboronic acid pinacol ester compound, wherein the phenylboronic acid pinacol ester compound is composed of a compound represented by formula (I) and a compound represented by formula (II) in a mass ratio of 0.5 to 1.5:1.5 to 2.5: In formula (I), R1 to R4 are each independently selected from H, a halogen atom, an ester group, a substituted or unsubstituted C 1～3 Alkyl, substituted or unsubstituted C 1～3 Any of the alkoxy groups, wherein the substituted substituent is one or more of the halogen atoms; In formula (II), R5 to R8 are each independently selected from H, a halogen atom, an ester group, a substituted or unsubstituted C 1～3 Alkyl, substituted or unsubstituted C 1～3 Any of the alkoxy groups, wherein the substituents substituted are one or more of the halogen atoms.

2. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The compound represented by formula (I) is selected from compound 1 to compound 3:

3. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The compound represented by formula (II) is selected from compound 4 to compound 6:

4. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The mass of the phenylboronic acid pinacol ester compound accounts for 0.1 to 10 wt % of the total mass of the electrolyte.

5. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The mass of the phenylboronic acid pinacol ester compound accounts for 0.5-5wt% of the total mass of the electrolyte.

6. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium difluorooxalatephosphate, lithium bis(fluorosulfonyl)imide salt, and lithium bis(trifluoromethyl)sulfonylimide.

7. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The mass of the lithium salt accounts for 10-20% of the total mass of the electrolyte.

8. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The mass of the lithium salt accounts for 13.5% of the total mass of the electrolyte.

9. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The other functional additives include at least one of a circulation additive, a low-temperature additive, and an anti-overcharge additive.

10. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The other functional additives include at least one of fluoroethylene carbonate, vinyl sulfate, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphate, tris(pentafluorophenyl)borane, lithium difluorophosphate, 3-hexylthiophene, hexafluorocyclotriphosphazene, and tris(hexafluoroisopropyl)phosphate.

11. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The mass of the other functional additives accounts for 1-5% of the total mass of the electrolyte.

12. The high temperature resistant lithium ion battery electrolyte according to claim 1, characterized in that: The non-aqueous solvent includes at least one of a chain carbonate solvent, a cyclic carbonate solvent, and a carboxylate solvent; the cyclic carbonate solvent includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate; the chain carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; the carboxylate solvent includes at least one of propyl acetate, ethyl acetate, and propyl propionate.

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