An electrolyte and a lithium-ion battery comprising the electrolyte.

Abstract

This invention discloses an electrolyte and a lithium-ion battery containing the same. The electrolyte comprises a lithium salt, an organic solvent, and a multifunctional six-membered heterocyclic compound additive as shown in the following formula: wherein R1 and R2 are each independently selected from any one of substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C1-C10 alkynyl, substituted or unsubstituted phenyl, substituted or unsubstituted carbonyl, substituted or unsubstituted carboxylic ester, substituted or unsubstituted alkylsilyl, cyano, isocyano, or isothiocyano. Compared with the prior art, the multifunctional electrolyte additive of this invention can participate in the film-forming reaction on the surface of the lithium-ion battery electrode material, decomposing to generate various film-forming products containing silicon, sulfur, and phosphorus, promoting the formation of a dense, stable, and low-resistance solid electrolyte interface film, thereby simultaneously improving the normal, high-cycle, and low-temperature discharge performance of the lithium-ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to an electrolyte and a lithium-ion battery containing the electrolyte. Background Technology

[0002] Lithium-ion batteries are widely used due to their high operating voltage, high specific energy, long cycle life, and lack of memory effect. For example, lithium-ion batteries are now widely used in 3C consumer electronics products, and with the development of new energy vehicles, they are also widely used in power and energy storage fields. As a result, higher demands are being placed on the various performance characteristics of lithium-ion batteries.

[0003] Lithium-ion battery electrolytes are one of the four main materials in lithium-ion batteries. They exist between the positive and negative electrode materials and in the pores of the separator, playing a crucial role in lithium-ion transport and significantly impacting the battery's cycle life, rate capability, safety, and other performance characteristics. Currently, commercially available electrolytes consist of lithium salts, solvents, and additives. While additives are added in relatively small quantities, they form a solid electrolyte interface film on the electrode material surface, playing a vital role in suppressing ongoing side reactions between the electrode material and the electrolyte and aiding in lithium-ion desolvation. A wide variety of electrolyte additives are currently under research, including phosphorus-containing phosphate esters, boron-containing borate esters, and sulfur-containing sulfate esters. To improve the overall performance of lithium-ion batteries, various additives with different functional groups are typically added to the electrolyte. However, this process is costly, involves complex optimization and screening, and makes it difficult to leverage the synergistic effects between different functional groups. Therefore, exploring novel multifunctional electrolyte additives is more conducive to achieving synergistic effects between different functional groups, improving the efficiency of additive combination screening, and ultimately enhancing the overall electrochemical performance of lithium-ion batteries. Summary of the Invention

[0004] Based on the technical problems existing in the background art, the purpose of this invention is to provide an electrolyte and a lithium-ion battery containing the electrolyte. The electrolyte uses a multifunctional six-membered heterocyclic compound as an electrolyte additive for lithium-ion batteries, which can improve the efficiency of electrolyte additive combination optimization and achieve comprehensive electrochemical performance improvement of lithium-ion batteries, such as normal and high cycle performance and low temperature discharge performance.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] An electrolyte comprising a lithium salt, an organic solvent, and a multifunctional six-membered heterocyclic compound additive, the chemical structural formula of which is as follows:

[0007]

[0008] Wherein: R1 and R2 are each independently selected from any one of substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C1-C10 alkynyl, substituted or unsubstituted phenyl, substituted or unsubstituted carbonyl, substituted or unsubstituted carboxylic ester, substituted or unsubstituted alkylsilyl, cyano, isocyano or isothiocyano.

[0009] In a further embodiment, the multifunctional six-membered heterocyclic compound additive comprises at least one of the compounds shown in formulas (1) to (6):

[0010]

[0011] Preferably, the organic solvent is selected from at least one of cyclic or linear carbonates, cyclic or linear carboxylic esters, and cyclic or linear ethers. More preferably, the organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl methyl carbonate, propyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, ethyl propionate, methyl butyrate, butyl acetate, methyl propionate, propyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, and 1,3-dioxolane.

[0012] Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0013] Preferably, the electrolyte contains 5-30 wt% lithium salt; the electrolyte contains 0.5-20% polyfunctional six-membered heterocyclic compound additives; and the electrolyte contains 60-85% organic solvents.

[0014] The present invention also discloses a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte described above.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] 1) The multifunctional six-membered heterocyclic compound additive proposed in this invention can participate in the film-forming reaction on the surface of lithium-ion battery electrode materials, decompose to produce a variety of film-forming products containing silicon, sulfur, and phosphorus, promote the formation of a dense, stable, and low-impedance solid electrolyte interface film, thereby simultaneously improving the normal, high-cycle, and low-temperature discharge performance of lithium-ion batteries.

[0017] 2) The multifunctional six-membered heterocyclic compound additive proposed in this invention contains multiple functional groups such as phosphate esters, borate esters and sulfonates, which avoids the tedious screening work of combining and optimizing multiple additives containing single functional groups, and can better achieve the synergistic effect between different functional groups. Detailed Implementation

[0018] The present invention will be further described below with reference to the embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. The raw materials and reagents used in the following embodiments and comparative examples are all commercially available products.

[0019] Example 1

[0020] A lithium-ion battery electrolyte includes a lithium salt, an organic solvent, and an additive, wherein the additive is a multifunctional six-membered heterocyclic compound of compound 1 as shown in formula (1).

[0021]

[0022] The electrolyte was prepared as follows: In an inert atmosphere glove box with water / oxygen levels both <0.1 ppm, LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a mass ratio of 3:2:5. The LiPF6 concentration was 1.0 mol / L. After the LiPF6 was completely dissolved, 4% (by mass) of compound 1 (as an additive) was added to the electrolyte mixture. The mixture was then stirred until homogeneous to obtain the lithium-ion battery electrolyte sample.

[0023] A lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the lithium-ion battery electrolyte sample prepared above.

[0024] The preparation method of this lithium-ion battery is as follows: Artificial graphite (negative electrode material), conductive substrate (SP), binder (CMC), and dispersant (SBR) are mixed with an appropriate amount of deionized water at a mass ratio of 96:1:1.5:1.5 to form a uniform paste. This paste is then uniformly coated onto a copper foil serving as a 12μm negative electrode current collector and baked at 100℃ for 12 hours to obtain the negative electrode sheet. The positive electrode material is LiNi... 0.33 Co 0.33 Mn 0.33 O2, conductive agent SP, and binder PVDF were mixed with an appropriate amount of NMP solvent at a mass ratio of 96:2:2 to form a uniform paste. This paste was then evenly coated onto a 15μm aluminum foil serving as the positive electrode current collector and baked at 110℃ for 12 hours to obtain the positive electrode sheet. The positive electrode sheet, separator, and negative electrode sheet were then stacked sequentially to obtain a lithium-ion battery cell. The battery prepared in this experiment was a 2Ah soft-pack battery. After drying the cell, 8g of electrolyte sample was injected to obtain the corresponding battery sample.

[0025] Example 2

[0026] A lithium-ion battery electrolyte and battery are prepared in the same way and with the same steps as in Example 1. The only difference is that compound 2, as shown in formula (2), is used instead of compound 1. The rest is the same as in Example 1 and will not be repeated.

[0027]

[0028] Example 3

[0029] A lithium-ion battery electrolyte and battery are prepared in the same way and with the same steps as in Example 1. The only difference is that compound 3, as shown in formula (3), is used instead of compound 1. The rest is the same as in Example 1 and will not be repeated.

[0030]

[0031] Example 4

[0032] A lithium-ion battery electrolyte and battery are prepared in the same way and with the same steps as in Example 1. The only difference is that compound 4, as shown in formula (4), is used instead of compound 1. The rest is the same as in Example 1 and will not be repeated.

[0033]

[0034]

[0035] Example 5

[0036] A lithium-ion battery electrolyte and battery are prepared in the same way and with the same steps as in Example 1. The only difference is that compound 5, as shown in formula (5), is used instead of compound 1. The rest is the same as in Example 1 and will not be repeated.

[0037]

[0038] Example 6

[0039] A lithium-ion battery electrolyte and battery are prepared in the same way and with the same steps as in Example 1. The only difference is that compound 6, as shown in formula (6), is used instead of compound 1. The rest is the same as in Example 1 and will not be repeated.

[0040]

[0041] Example 7

[0042] A lithium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1, except that 2% of compound 1 and 2% of compound 2 are used instead of 4% of compound 1. The rest are the same as in Example 1 and will not be repeated here.

[0043] Comparative Example 1

[0044] A lithium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1. The only difference is that the additives contain only 4% vinylene carbonate. The rest are the same as in Example 1 and will not be described again.

[0045] Comparative Example 2

[0046] A lithium-ion battery electrolyte and battery are prepared using the same method and steps as in Example 1. The only difference is that 4% of Compound 1 in Example 1 is replaced with a mixture of 1% vinylene carbonate, 1% vinyl sulfate, 1% tris(trimethylsilyl)phosphate and 1% tris(trimethylsilyl)borate. The rest is the same as in Example 1 and will not be repeated here.

[0047] Test methods: The batteries prepared in the above examples and comparative examples were subjected to room temperature cycling tests, high temperature cycling tests and low temperature discharge performance tests, respectively.

[0048] (I) Room temperature cycling test

[0049] The batteries from Examples 1-7 and Comparative Examples 1-2 were charged to 4.2V using a constant current and constant voltage of 0.2C at 25°C, with a cutoff current of 0.05C. They were then discharged to 2.5V using a constant current of 0.2C, and their initial discharge capacity Q0 was recorded as the initial discharge capacity. After 100 cycles of the same charge-discharge cycle while maintaining a constant ambient temperature, the discharge capacity Q0 on the 300th cycle was recorded. 300 Then the room temperature discharge capacity retention rate = Q 300 / Q0*100%.

[0050] (II) High-Temperature Cycling Performance Test

[0051] The high-temperature cycling performance test method is the same as the normal-temperature cycling test method, the only difference being that the ambient temperature for the cycling test is set to 45℃.

[0052] (III) Low-temperature discharge performance test at -20℃

[0053] The lithium-ion batteries of Examples 1-7 and Comparative Examples 1-2 were charged to 4.2V at 25℃ using a constant current and constant voltage of 0.2C, with a cutoff current of 0.05C; then discharged to 2.0V using a constant current of 0.2C, and their discharge capacity Q0 was recorded as the initial discharge capacity. The battery was charged to 4.2V using a constant current and constant voltage of 0.2C, with a cutoff current of 0.05C; subsequently, the sample was placed at -20℃ for 3 hours to reach temperature equilibrium, and then the experimental cell was discharged to 2.0V using a constant current of 0.2C, and its discharge capacity Q1 was recorded. This process was repeated for three parallel experimental batteries, and the average value was taken. The low-temperature discharge capacity retention rate was calculated as Q1 / Q0*100%.

[0054] The test results are shown in Table 1.

[0055] Table 1. Test results of battery samples from the examples and comparative examples.

[0056]

[0057]

[0058] The test data from Comparative Examples 1-2 show that using only vinylene carbonate additive results in poor low-temperature performance of the electrolyte, with a discharge capacity retention rate of less than 60% at -20℃. Even though Comparative Example 2 combined multiple additives such as vinyl sulfate, tris(trimethylsilyl)phosphate, and tris(trimethylsilyl)borate, the improvement in various electrochemical properties was still worse than that of the multifunctional six-membered heterocyclic compound additives in the examples. The main reason is that the synergistic effect of different additives could not be achieved, resulting in poor film stability and severe side reactions between the electrolyte and electrode materials.

[0059] In contrast, the test data from Examples 1-7 show that using one or a combination of the multifunctional six-membered heterocyclic compounds 1-7 as additives can leverage the synergistic effect of different functional groups, promote the formation of a dense and stable solid electrolyte interface film, and significantly improve cycle performance. The capacity retention rate after 300 cycles at room temperature is >94%, and the capacity retention rate after 300 cycles at room temperature is >85.9%. Simultaneously, it exhibits significant improvement in low-temperature discharge performance, with a capacity retention rate of >70.9% at -20°C. Therefore, the multifunctional six-membered heterocyclic compound additive proposed in this invention avoids the tedious screening process of optimizing combinations of multiple additives containing single functional groups, and can better achieve the synergistic effect between different functional groups.

[0060] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises a lithium salt, an organic solvent, and a multifunctional six-membered heterocyclic compound additive, wherein the multifunctional six-membered heterocyclic compound additive comprises at least one of the compounds shown in formulas (1) to (6): （1） （2） （3） （4） （5） （6）。 2. The electrolyte according to claim 1, characterized in that: The organic solvent is selected from at least one of cyclic or chain carbonates, cyclic or linear carboxylic esters, and cyclic or linear ethers.

3. The electrolyte according to claim 2, characterized in that: The organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl methyl carbonate, propyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, ethyl propionate, methyl butyrate, butyl acetate, methyl propionate, propyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, and 1,3-dioxolane.

4. The electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

5. The electrolyte according to any one of claims 1 to 4, characterized in that: The electrolyte contains 5-30 wt% lithium salt.

6. The electrolyte according to any one of claims 1 to 4, characterized in that: The electrolyte contains 0.5-20% polyfunctional six-membered heterocyclic compound additives.

7. The electrolyte according to any one of claims 1 to 4, characterized in that: The content of organic solvent in the electrolyte is 60-85%.

8. A lithium-ion battery, characterized in that: It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the electrolyte as described in any one of claims 1 to 7.

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