Electrolyte additive, nonaqueous electrolyte, and lithium ion battery

Abstract

This invention provides an electrolyte additive comprising a compound having the structure shown in Formula 1, wherein R1 represents at least one of a hydrogen atom, a substituted or unsubstituted C1-C6 alkyl group, a carboxyl group, an amino group, or a sulfonic acid group. The electrolyte additive of this invention comprises a compound having Formula 1, which contains various types of unsaturated double bonds. During the formation stage, this compound can regulate the SEI composition, improve ion mobility, and thus achieve high-temperature fast-charging cycle performance of the battery cell. Furthermore, the compound contains various types of nitrogen elements, which can provide a large number of lone pairs of electrons, attracting the dissolution of cobalt ions under high voltage, thus mitigating the damage of dissolved cobalt ions to the effective solvent in the electrolyte and inhibiting the oxidative decomposition of the non-aqueous electrolyte, thereby improving the high-temperature storage performance of lithium-ion batteries under high-voltage systems. This invention also provides a non-aqueous electrolyte and a lithium-ion battery.

Description

Technical Field

[0001] This invention relates to the field of secondary batteries, specifically to an electrolyte additive, a non-aqueous electrolyte, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are widely used in 3C digital products, power tools, aerospace, energy storage, and electric vehicles due to their advantages such as high specific energy, no memory effect, and long cycle life. With the rapid development of electronic information technology and consumer products, higher demands are being placed on the high voltage and high energy density of lithium-ion batteries, especially in portable mobile devices. To meet the needs of portable mobile devices, the development of high-capacity lithium-ion batteries has become urgent. The most common method is to increase the voltage of lithium-ion batteries, such as by using lithium cobalt oxide cathode materials. However, all high-voltage cathode materials face a common problem: electrolyte decomposition occurs at high voltages, especially when the upper limit voltage exceeds 4.5V. This problem becomes more pronounced because the oxidation potential of conventional carbonate electrolytes is around 5V, making them highly susceptible to oxidation and decomposition reactions on the surface of the battery cathode at high voltages. This oxidation and decomposition is further accelerated under high-temperature cycling conditions, producing gases (including CO and CO2), which pose safety hazards to lithium-ion batteries. Furthermore, when the operating voltage of the lithium cobalt oxide cathode material is greater than 4.5V, it means that more lithium ions need to be extracted and inserted (>0.6V). The extraction of more lithium ions will bring about a phase change in the structure of the lithium cobalt oxide cathode material, changing from a hexagonal layered structure to a rock salt phase structure. Compared with the hexagonal phase, the rock salt phase structure can accommodate fewer oxygen atoms, causing oxygen atoms to escape to the surface of the cathode material as active oxygen. The active oxygen on the surface of the lithium cobalt oxide cathode material will further oxidize the solvent in the electrolyte, causing the electrolyte to undergo oxidative decomposition, thereby affecting the capacity performance of the lithium-ion battery itself. Summary of the Invention

[0003] One of the objectives of this invention is to provide an electrolyte additive that can inhibit the oxidative decomposition of non-aqueous electrolytes and improve the high-temperature storage performance and high-temperature fast-charge cycle performance of lithium-ion batteries under high voltage (greater than 4.5V, especially 4.53V) systems.

[0004] The second objective of this invention is to provide a non-aqueous electrolyte containing the above-mentioned electrolyte additives.

[0005] The third objective of this invention is to provide a lithium-ion battery containing the aforementioned non-aqueous electrolyte.

[0006] To achieve the above objectives, the first aspect of the present invention provides an electrolyte additive comprising having a structure

[0007] The compound shown in Formula 1,

[0008]

[0009] Wherein, R1 represents at least one of hydrogen atom, substituted or unsubstituted C1-C6 alkyl, carboxyl, amino, and sulfonic acid groups.

[0010] Compared with the prior art, the electrolyte additive of the present invention contains a compound having structural formula 1, which contains various types of unsaturated double bonds (such as C=O, C=C, C=N). During the formation stage, it can regulate the SEI composition and improve ion mobility, thereby achieving high-temperature fast-charging cycle performance of the battery cell. able Furthermore, the compound contains various types of nitrogen elements, which can provide a large number of lone pairs of electrons. This has a certain attraction effect on the dissolution of cobalt ions under high voltage, which slows down the destruction of the effective solvent in the electrolyte by the dissolved cobalt ions. This suppresses the oxidative decomposition of non-aqueous electrolytes, thereby improving the high-temperature storage performance of lithium-ion batteries under high voltage (especially at 4.53V) systems.

[0011] Preferably, the compound represented by structural formula 1 is selected from at least one of compounds one through four:

[0012]

[0013] A second aspect of the present invention provides a non-aqueous electrolyte, comprising a lithium salt, a non-aqueous organic solvent, and the aforementioned electrolyte additives.

[0014] Preferably, the electrolyte additive is present in the non-aqueous electrolyte at a weight percentage of 0.1% to 2%, specifically 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0015] Preferably, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium bis(oxalateborate)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorooxalateborate (LiODFB), lithium difluorodioxalate phosphate (LiPF2(C2O4)2), and lithium bis(fluorosulfonyl)imide.

[0016] Preferably, the lithium salt content accounts for 5% to 25% of the weight percentage of the non-aqueous electrolyte, specifically 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, and 25%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0017] Preferably, the non-aqueous organic solvent is selected from at least one of carbonates and carboxylic esters. Further, the carbonate is selected from at least one of linear carbonates or cyclic carbonates. More preferably, the non-aqueous organic solvent is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl acetate (PE), γ-butyrolactone (GBL), propyl propionate (PP), ethyl propionate (EP), and ethyl butyrate (EB).

[0018] Preferably, the non-aqueous organic solvent accounts for 60-85% of the weight percentage of the non-aqueous electrolyte, specifically 60%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 80%, 81%, 82%, 83%, 84%, and 85%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0019] A third aspect of the present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and the aforementioned non-aqueous electrolyte.

[0020] Preferably, the active material of the positive electrode is selected from lithium cobalt oxide.

[0021] Lithium cobalt oxide can be pure LCO, doped and / or coated LCO.

[0022] Preferably, the active material of the negative electrode is selected from any one of artificial graphite, natural graphite, lithium titanate, silicon-carbon composite material, and silicon suboxide. Detailed Implementation

[0023] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be considered as specific limitations of the invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0024] Example 1

[0025] (1) Preparation of non-aqueous electrolyte: In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed evenly at a mass ratio of 1:1:1 to obtain 87 g of non-aqueous organic solvent. Then, 0.5 g of compound 1 was added to obtain a mixed solution. The mixed solution was sealed and packaged and frozen in a freezer (-4℃) for 2 hours. After being removed, 12.5 g of lithium hexafluorophosphate was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After mixing evenly, the non-aqueous electrolyte was prepared.

[0026] (2) Preparation of positive electrode: Lithium cobalt oxide (LCO) material, binder PVDF and conductive agent SuperP are mixed evenly at a mass ratio of 95:1:4 to prepare a lithium-ion battery positive electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of aluminum foil, dried and rolled to obtain the positive electrode sheet.

[0027] (3) Preparation of negative electrode: Artificial graphite, conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber emulsion) are mixed in a mass ratio of 95:1.5:1.0:2.5 to form a slurry. The mixture is then coated on both sides of copper foil, dried, and rolled to obtain the negative electrode sheet.

[0028] (4) Preparation of lithium-ion battery: The positive electrode, separator and negative electrode are stacked to form a square cell, which is packaged with polymer and filled with the non-aqueous electrolyte of lithium-ion battery prepared above. After formation, capacity testing and other processes, a lithium-ion battery with a capacity of 1000mAh is made.

[0029] The non-aqueous electrolyte formulations for Examples 2-6 and Comparative Example 1 are shown in Table 1. The steps for preparing the non-aqueous electrolyte and lithium-ion battery are the same as in Example 1.

[0030] Table 1. Non-aqueous electrolyte formulations for lithium-ion batteries

[0031]

[0032] The lithium-ion batteries prepared in Examples 1-6 and Comparative Example 1 were subjected to high-temperature fast-charge cycle performance and high-temperature storage performance tests. The test conditions are as follows, and the test results are shown in Table 2.

[0033] High-temperature storage performance test

[0034] Under normal temperature (25℃) conditions, a lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle (battery discharge capacity recorded as C0), with an upper limit voltage of 4.53V. The battery was then placed in a 60℃ oven for 7 days, removed, and placed in a 25℃ environment for a 0.3C discharge, with the discharge capacity recorded as C1. Finally, the lithium-ion battery was subjected to one 0.3C / 0.3C charge and discharge cycle (battery discharge capacity recorded as C2). The capacity retention rate and capacity recovery rate of the lithium-ion battery were calculated using the following formulas:

[0035] Capacity retention rate = C1 / C0 * 100%

[0036] Capacity recovery rate = C2 / C0 * 100%

[0037] High-temperature fast charging cycle performance test

[0038] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 2C until the voltage reached 4.53V, followed by constant voltage charging at 4.53V until the current reached 0.05C. Finally, it was discharged at a constant current of 1C until the voltage reached 3.0V. The first discharge capacity was recorded as C0. This constitutes one charge-discharge cycle. Then, 300 cycles of 2C / 1C charging and discharging were performed at 45°C, and the discharge capacity was recorded as C1.

[0039] Capacity retention rate = C1 / C0 * 100%

[0040] Table 2. Performance test results of lithium-ion batteries

[0041]

[0042]

[0043] As shown in Table 2, Comparative Example 1, which does not contain a compound with Formula 1, exhibits unsatisfactory high-temperature storage and high-temperature fast-charge cycle performance. In contrast, Examples 1-6, which use compounds with Formula 1 as additives, demonstrate superior high-temperature storage and high-temperature fast-charge cycle performance. The mechanism of action is not fully understood and requires further investigation. However, the inventors speculate that compounds with Formula 1 contain various types of unsaturated double bonds (such as C=O, C=C, and C=N), which can regulate the SEI composition during the formation stage, improve ion mobility, and thus achieve high-temperature fast-charge cycle performance of the battery cell. Furthermore, the compound contains various types of nitrogen elements, which can provide a large number of lone pairs of electrons, attracting the dissolution of cobalt ions under high voltage. This mitigates the damage of dissolved cobalt ions to the effective solvent in the electrolyte, inhibiting the oxidative decomposition of non-aqueous electrolytes and improving the high-temperature storage performance of lithium-ion batteries under high voltage (especially at 4.53V).

[0044] The data from Example 3 also shows that its high-temperature fast-charging cycle performance is relatively excellent. The possible reason is that the structure contains amino groups with symmetrical structures, which increases the stability of the electron cloud. After participating in the interfacial reaction, the organic matter formed has a stable compound structure and is not easily dissolved in high-voltage solvents, thus resulting in excellent high-temperature fast-charging cycle performance.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, and a separator, characterized in that, It also includes a non-aqueous electrolyte, wherein the active material of the positive electrode is selected from lithium cobalt oxide, the upper limit voltage is 4.53V, and the non-aqueous electrolyte comprises: Lithium salts; Non-aqueous organic solvents; and An electrolyte additive, wherein the non-aqueous organic solvent is selected from at least one of carbonates and carboxylic acid esters, and the electrolyte additive comprises a compound having the structure shown in Formula 1. Wherein, R1 represents at least one of hydrogen atom, substituted or unsubstituted C1-C6 alkyl, carboxyl, amino, and sulfonic acid groups.

2. The lithium-ion battery as described in claim 1, characterized in that, The compound shown in structural formula 1 is selected from at least one of compounds one through four: 。 3. The lithium-ion battery as described in claim 1, characterized in that, The electrolyte additive is present in the non-aqueous electrolyte at a weight percentage of 0.1% to 2%.

4. The lithium-ion battery as described in claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate)borate, lithium difluorophosphate, lithium difluorooxalateborate, lithium difluorodioxalate phosphate, and lithium bis(fluorosulfonyl)imide.

5. The lithium-ion battery as described in claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, and ethyl butyrate.

6. The lithium-ion battery as described in claim 1, characterized in that, The active material of the negative electrode is selected from any one of artificial graphite, natural graphite, lithium titanate, silicon-carbon composite material, and silicon suboxide.

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