A battery

Abstract

The application provides a battery, and the synergistic effect of positive and negative active materials and an aluminum salt compound (i.e. a compound shown in formula 1 and / or a compound shown in formula 2) in an electrolyte can effectively improve the low-temperature performance, high-temperature cycle, high-temperature storage and safety performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and relates to a battery, specifically a high-voltage lithium-ion battery with excellent high and low temperature performance. Background Technology

[0002] In recent years, lithium-ion batteries have been widely used in smartphones, tablets, smart wearables, power tools, and electric vehicles. As the application of lithium-ion batteries becomes increasingly widespread, consumers' demands for the operating environment and performance of these batteries are constantly rising. This requires lithium-ion batteries to maintain high safety while also achieving good performance at high and low temperatures.

[0003] Currently, lithium-ion batteries pose safety hazards during use. For example, under extreme conditions such as continuous high temperatures, they are prone to serious accidents such as fires or even explosions. The main reason for these problems is that the positive electrode material is structurally unstable under high temperatures and high voltages. Metal ions easily dissolve from the positive electrode and are reduced and deposited on the surface of the negative electrode, damaging the SEI film structure on the negative electrode surface. This causes the negative electrode impedance and battery thickness to increase continuously, leading to a continuous rise in cell temperature. When the accumulated heat cannot be released, a safety accident occurs.

[0004] To overcome the aforementioned technical problems, the main approach currently is to add flame retardants (such as trimethyl phosphate) to the electrolyte to improve the battery's high-temperature and safety performance. However, the use of these flame retardants often leads to severe degradation of battery performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a battery in which the electrolyte contains an aluminum salt compound. This aluminum salt compound can more effectively form a passivation coating protective layer rich in Al2O3 and AlF3 on the surface of the positive electrode, providing efficient protection for the positive electrode active material, inhibiting the decomposition of electrolyte side reactions catalyzed by metal ion dissolution, and effectively improving the battery's high-temperature storage and safety performance. Simultaneously, it can also more effectively reduce the surface tension of the electrolyte and inhibit lithium dendrite growth, reduce the contact angle between the electrolyte and the negative electrode, improve electrolyte wettability, increase ion transport rate, and enhance the battery's low-temperature discharge performance. Thus, a battery with high safety while also exhibiting good high-temperature storage performance, high-temperature cycle performance, and low-temperature discharge performance is obtained.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode comprises a positive active material, and the negative electrode comprises a negative active material; the electrolyte comprises an organic solvent, additives, and an electrolyte salt, wherein the electrolyte salt comprises at least one compound of Formula 1 and / or at least one compound of Formula 2.

[0008]

[0009] In Formula 1, R1, R2, R3, and R4 may be the same or different, and are independently selected from substituted or unsubstituted alkyl groups; the substituents are halogens, halogen-substituted or unsubstituted alkyl groups;

[0010] In Formula 2, R5, R6, R7, and R8 may be the same or different, and are independently selected from -C(=O)-, substituted or unsubstituted alkylene groups; the substituents are halogens, halogen-substituted or unsubstituted alkyl groups;

[0011] The battery satisfies the following condition: the ratio of (A+B) to C is 10 to 1000;

[0012] Where A is the specific surface area of ​​the positive electrode active material, in m². 2 / g; B is the specific surface area of ​​the negative electrode active material, in m². 2 / g; C is the percentage of the mass of the compound shown in Formula 1 and / or the compound shown in Formula 2 in the total mass of the electrolyte.

[0013] According to the present invention, the ratio of (A+B) to C is 10, 50, 100, 150, 200, 250, 300, 400, 450, 500, 550, 600, 700, 800, 900, 1000, or any value within the range of the two endpoints mentioned above. When the ratio of (A+B) to C is between 10 and 1000, the compound shown in Formula 1 and / or the compound shown in Formula 2 (i.e., aluminum salt compound) can more fully form a passivation coating protective layer rich in Al2O3 and AlF3 on the positive electrode surface, providing efficient protection for the positive electrode active material, inhibiting the decomposition of side reactions of the electrolyte catalyzed by metal ion dissolution, and effectively improving the high-temperature storage and safety performance of the battery; furthermore, the compound shown in Formula 1 and / or the compound shown in Formula 2 can more fully reduce the surface tension of the electrolyte and inhibit the growth of lithium dendrites, reduce the contact angle between the electrolyte and the negative electrode, improve the wettability of the electrolyte, improve the ion transport rate, and improve the low-temperature discharge performance of the battery. Compounds of Formula 1 and / or Formula 2 with a (A+B) to C ratio in the range of 10 to 1000 can more fully cooperate with the positive and negative electrode active materials to achieve synergistic effects, improve battery interface compatibility, effectively suppress side reactions between electrodes and electrolytes, and thus comprehensively improve the battery cell performance.

[0014] According to the present invention, the specific surface area A of the positive electrode active material is between 0.05 and 1 m². 2 The range is preferably 0.1–0.4 m / g. 2 / g, for example, 0.05m 2 / g, 0.1m 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g or 1m 2 / g.

[0015] According to the present invention, the specific surface area B of the negative electrode active material is between 0.5 and 5 m². 2 The value is preferably between 0.9 and 2 m in the range of / g. 2 / g, for example, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g、1m 2 / g, 1.5m 2 / g, 1.8m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g, 3.5m 2 / g、4m 2 / g, 4.5m 2 / g or 5m 2 / g.

[0016] According to the present invention, in Formula 1, R1, R2, R3, and R4 may be the same or different, and are independently selected from substituted or unsubstituted C. 1-6 Alkyl groups; C substituents are halogenated, halogenated, or unsubstituted. 1-6 Alkyl groups.

[0017] According to the present invention, in Formula 1, R1, R2, R3, and R4 may be the same or different, and are independently selected from substituted or unsubstituted C. 1-3 Alkyl groups; C substituents are halogenated, halogenated, or unsubstituted. 1-3 Alkyl groups.

[0018] According to the present invention, in Formula 1, R1, R2, R3, and R4 may be the same or different, and are independently selected from substituted methyl, substituted ethyl, and substituted propyl groups; the substituents are fluorine, fluorinated or unsubstituted methyl, fluorinated or unsubstituted ethyl groups.

[0019] According to the present invention, in Formula 2, R5, R6, R7, and R8 may be the same or different, and are independently selected from -C (=O)-, substituted or unsubstituted C. 1-6 Alkylene; substituents are halogenated, halogenated, or unsubstituted C. 1-6 Alkyl groups.

[0020] According to the present invention, in Formula 2, R5, R6, R7, and R8 may be the same or different, and are independently selected from -C (=O)-, substituted or unsubstituted C. 1-3 Alkylene; substituents are halogenated, halogenated, or unsubstituted C. 1-3 Alkyl groups.

[0021] According to the present invention, in Formula 2, R5, R6, R7, and R8 may be the same or different, and are independently selected from -C(=O)-, substituted or unsubstituted methylene, substituted or unsubstituted ethylene; the substituents are fluorine, fluorinated or unsubstituted methyl, fluorinated or unsubstituted ethyl.

[0022] According to the present invention, the compound represented by Formula 1 is selected from the compounds represented by Formula T1 below:

[0023]

[0024] According to the present invention, the compound represented by Formula 2 is selected from at least one of the compounds represented by Formulas T2 to T4:

[0025]

[0026] According to the present invention, the compound shown in Formula 1 and / or the compound shown in Formula 2 accounts for 0.1-16 wt% of the total mass of the electrolyte, preferably 0.2-12 wt%, for example, 0.2 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, or 16 wt%.

[0027] According to the present invention, the mass of the electrolyte salt accounts for 10 wt% to 20 wt% of the total mass of the electrolyte.

[0028] According to the present invention, the electrolyte salt further includes a lithium salt.

[0029] According to the present invention, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate.

[0030] According to the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer coated on one or both surfaces of the positive current collector. The positive active material layer includes a positive active material, a conductive agent, and a binder. The positive active material is selected from lithium cobalt oxide or lithium cobalt oxide doped with two or more elements selected from Al, Mg, Mn, Cr, Ti, and Zr. The chemical formula of the lithium cobalt oxide doped with two or more elements selected from Al, Mg, Mn, Cr, Ti, and Zr is Li. x Co 1-y1-y2-y3-y4 A y1 B y2 C y3 D y4 O2; 0.95≤x≤1.05, 0.01≤y1≤0.1, 0.01≤y2≤0.1, 0≤y3≤0.1, 0≤y4≤0.1, A, B, C, and D are selected from two or more elements among Al, Mg, Mn, Cr, Ti, and Zr.

[0031] According to the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material is selected from one or more of artificial graphite, natural graphite, hard carbon, mesophase carbon microspheres, lithium titanate, silicon carbide, and silicon suboxide.

[0032] According to the present invention, the electrolyte further comprises 1-ethyl-3-methylimidazolium aluminate (CAS No. 87587-77-7).

[0033] According to the present invention, the 1-ethyl-3-methylimidazolium aluminate accounts for 0.1-2 wt% of the total mass of the electrolyte, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2 wt%.

[0034] According to the present invention, the electrolyte further comprises one or more of nitrile compounds, sulfur-containing compounds, and carbonate compounds; preferably, the nitrile compounds are selected from one or more of succinic anionyl nitrile, glutaronitrile, adiponitrile, heptanonitrile, octanoic anionyl nitrile, triglycerides, ethoxypentafluorophosphazene, and 1,3,6-hexanetrionitrile; preferably, the sulfur-containing compounds are selected from one or more of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, and vinylene sulfate; preferably, the carbonate compounds are one or more of ethylene carbonate, fluoroethylene carbonate, and ethylene ethylene carbonate.

[0035] According to the present invention, the organic solvent is selected from at least one of carbonates, carboxylic esters, and fluoroethers, wherein the carbonate is selected from one or more combinations of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and methyl propyl carbonate; the carboxylic ester is selected from one or more combinations of ethyl propionate and propyl propionate; and the fluoroether is selected from 1,1,2,3-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0036] According to the present invention, the charging cut-off voltage of the battery is 4.45V or higher.

[0037] The beneficial effects of this invention are as follows:

[0038] This invention provides a battery. Through dedicated research, the inventors of this application have discovered that the synergistic effect of the positive and negative electrode active materials and the aluminum salt compounds in the electrolyte (i.e., the compounds described in Formula 1 and / or the compounds shown in Formula 2) can effectively improve the battery's low-temperature performance, high-temperature cycling, high-temperature storage, and safety performance.

[0039] In this invention, the aluminum salt compound in the electrolyte and the positive and negative electrodes have a better synergistic effect. Specifically, the aluminum salt compound can form a passivation coating protective layer rich in Al2O3 and AlF3 on the surface of the positive electrode, providing efficient protection for the positive electrode active material, inhibiting the decomposition of side reactions in the electrolyte catalyzed by metal ion dissolution, and effectively improving the battery's high-temperature storage and safety performance. Simultaneously, the aluminum salt compound can reduce the surface tension of the electrolyte and inhibit lithium dendrite growth, reduce the contact angle between the electrolyte and the negative electrode, improve electrolyte wettability, increase ion transport rate, and enhance the battery's low-temperature discharge performance. The aluminum salt compound can improve the battery interface compatibility and effectively suppress side reactions between the electrodes and the electrolyte, resulting in a comprehensive improvement in the battery cell performance.

[0040] Furthermore, the 1-ethyl-3-methylimidazolium aluminate in the electrolyte can participate in film formation on the negative electrode surface to form a robust SEI film, effectively inhibiting the reduction and decomposition of the electrolyte on the negative electrode surface, reducing side reactions at the negative electrode interface, and significantly improving the cycle performance of the cell. The cooperative combination of the positive and negative electrodes and the electrolyte is beneficial for the cell to take into account high-temperature storage performance, cycle performance, low-temperature discharge performance and safety performance. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0042] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0043] Comparative Examples 1-3 and Examples 1-11

[0044] The lithium-ion batteries of Comparative Examples 1-3 and Examples 1-11 were all prepared according to the following preparation method, the only difference being the selection of positive and negative electrode active materials with different specific surface areas and electrolytes, as shown in Table 1.

[0045] (1) Preparation of positive electrode

[0046] The positive electrode active material LiCoO2 (specific surface area shown in Table 1), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were mixed in a weight ratio of 98.2:1.1:0.7. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until a uniform and fluid positive electrode slurry was formed. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 12 μm. The coated aluminum foil was baked in ovens with five different temperature gradients, and then dried in an oven at 120°C for 8 hours. After that, it was rolled and slit to obtain the different positive electrode sheets required.

[0047] (2) Preparation of negative electrode sheet

[0048] A slurry was prepared by wet process using artificial graphite (specific surface area shown in Table 1) as the negative electrode active material (96.5% by mass), single-walled carbon nanotube (SWCNT) conductive agent (0.2% by mass), conductive carbon black (SP) conductive agent (1% by mass), sodium carboxymethyl cellulose (CMC) binder (1% by mass), and styrene-butadiene rubber (SBR) binder (1.3% by mass). The slurry was coated on the surface of copper foil as the negative electrode current collector, and then dried (temperature: 85℃, time: 5h), rolled, and die-cut to obtain the different negative electrode sheets required.

[0049] (3) Electrolyte preparation

[0050] In an argon-filled glove box (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), and ethyl propionate (EP) are mixed uniformly in a mass ratio of 2:1:5:2. Lithium hexafluorophosphate, aluminum salt compounds (i.e., compounds shown in Formula 1 and / or Formula 2), and additives (specific amounts and selections are shown in Table 1) are slowly added to the mixed solution and stirred until homogeneous to obtain the electrolyte.

[0051] (4) Preparation of the diaphragm

[0052] A polyethylene diaphragm with a thickness of 7–9 μm is selected.

[0053] (5) Preparation of lithium-ion batteries

[0054] The prepared positive electrode sheet, separator, and negative electrode sheet are wound together to obtain a bare cell without electrolyte injection. The bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, shaping, and sorting, the desired lithium-ion battery is obtained.

[0055] Table 1. Lithium-ion batteries prepared in Comparative Examples 1-3 and Examples 1-11

[0056]

[0057] The electrochemical performance of the batteries obtained in the comparative examples and embodiments above was tested, and the relevant explanations are as follows:

[0058] (1) 45℃ Cyclic Experiment: The batteries obtained in the above examples and comparative examples were placed in an environment of (45±2)℃ and left to stand for 2-3 hours. When the battery body reached (45±2)℃, the battery was charged at a constant current of 1C with a cutoff current of 0.05C. After the battery was fully charged, it was left to stand for 5 minutes, and then discharged at a constant current of 0.7C to the cutoff voltage of 3.0V. The highest discharge capacity of the first 3 cycles was recorded as the initial capacity Q. When the cycle reached 500 times, the discharge capacity Q1 of the last cycle of the battery was recorded. The results are shown in Table 2.

[0059] The calculation formula used is as follows: Capacity retention rate (%) = Q1 / Q × 100%.

[0060] (2) 85℃ High-Temperature Storage Experiment: The batteries obtained in the above examples and comparative examples were placed at room temperature and subjected to three charge-discharge cycles at a charge-discharge rate of 0.5C. Then, they were charged to full capacity at a rate of 0.5C, and the highest discharge capacity Q2 of the first three 0.5C cycles was recorded. The fully charged batteries were stored at 85℃ for 8 hours, and the 0.5C discharge capacity Q3 of the batteries after 4 hours was recorded. The capacity retention rate and gas generation of the batteries during high-temperature storage were calculated, and the results are shown in Table 2.

[0061] The calculation formulas used are as follows:

[0062] Capacity retention rate (%) = Q3 / Q2 × 100%;

[0063] (3) Overcharge test: The batteries obtained in the above examples and comparative examples were charged to 5V at a constant current of 3C rate at an ambient temperature of 25±3℃. The battery status was recorded and the results are shown in Table 2.

[0064] (4) Low-temperature discharge experiment: The batteries obtained in the above examples and comparative examples were discharged at 0.2C to 3.0V at an ambient temperature of 25±3℃ and left to stand for 5 minutes. They were then charged at 0.7C. When the cell terminal voltage reached the charging limit voltage, constant voltage charging was switched until the charging current was less than or equal to the cutoff current. Charging was stopped, and the batteries were left to stand for 5 minutes. Then, the batteries were discharged at 0.2C to 3.0V, and the discharge capacity was recorded as the room temperature capacity Q4. The cells were then charged at 0.7C. When the cell terminal voltage reached the charging limit voltage, constant voltage charging was switched until the charging current was less than or equal to the cutoff current. The fully charged batteries were left to stand at -10±2℃ for 4 hours and then discharged at 0.4C to the cutoff voltage of 3.0V. The discharge capacity Q5 was recorded. The low-temperature discharge capacity retention rate was calculated, and the results are shown in Table 2.

[0065] The calculation formula used is as follows: Low-temperature discharge capacity retention rate (%) = Q5 / Q4 × 100%.

[0066] Table 2 shows the battery test results obtained from Comparative Examples 1-5 and Examples 1-8.

[0067]

[0068]

[0069] As can be seen from the results in Table 2, the comparative examples and embodiments show that lithium-ion batteries can effectively improve their long-cycle performance, high-temperature storage performance, low-temperature discharge performance, and safety performance through the synergistic effect of positive and negative electrode active materials and aluminum salt compounds in the electrolyte, as well as the addition of 1-ethyl-3-methylimidazolium aluminate additive to the electrolyte.

[0070] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode includes a positive active material, and the negative electrode includes a negative active material; the electrolyte includes an organic solvent, additives, and an electrolyte salt, wherein the electrolyte salt includes at least one compound of Formula 1 and / or at least one compound of Formula 2. Formula 1 Formula 2 In Equation 1, R1, R2, R3, and R4 may be the same or different, and are independently selected from substituted or unsubstituted C. 1-6 Alkyl groups; C substituents are halogenated, halogenated, or unsubstituted. 1-6 Alkyl groups; In Equation 2, R5, R6, R7, and R8 may be the same or different, and are independently selected from -C(=O)-, substituted or unsubstituted C. 1-6 Alkylene; substituents are halogenated, halogenated, or unsubstituted C. 1-6 Alkyl groups; The battery satisfies the following condition: the ratio of (A+B) to C is 10~1000; Where A is the specific surface area of ​​the positive electrode active material, in m². 2 / g; B is the specific surface area of ​​the negative electrode active material, in m². 2 / g; C is the percentage of the mass of the compound shown in Formula 1 and / or the compound shown in Formula 2 in the total mass of the electrolyte; The specific surface area A of the positive electrode active material is in the range of 0.05~1 m². 2 The specific surface area B of the negative electrode active material is between 0.5 and 5 m² / g. 2 The mass of the compound shown in Formula 1 and / or the compound shown in Formula 2 accounts for 0.1-16 wt% of the total mass of the electrolyte.

2. The battery according to claim 1, characterized in that, The compound represented by Formula 1 is selected from the compound represented by Formula T1 below: T1。 3. The battery according to claim 1, characterized in that, The compound represented by Formula 2 is selected from at least one of the compounds represented by Formulas T2 to T4 below: T2； T3； T4。 4. The battery according to any one of claims 1-3, characterized in that, The electrolyte salt also includes a lithium salt, which is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium hexafluorophosphate.

5. The battery according to any one of claims 1-3, characterized in that, The electrolyte also includes 1-ethyl-3-methylimidazolium aluminate, wherein the mass of 1-ethyl-3-methylimidazolium aluminate accounts for 0.1-2 wt% of the total mass of the electrolyte.

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