High-temperature-resistant lithium ion battery electrolyte

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a high-temperature-resistant lithium ion battery electrolyte. Aiming at the problems of battery capacity attenuation, short service life and the like caused by the defects of the traditional lithium ion battery electrolyte, the invention provides the following technical scheme: the lithium ion battery electrolyte is prepared from the following components in percentage by mass: 0.3 to 1 percent of first additive, 0.3 to 3 percent of second additive, 0.01 to 15 percent of lithium salt and 80 to 95 percent of organic solvent; the first additive and the second additive are used for inhibiting high-temperature decomposition of the lithium salt and strengthening the thermal stability and the mechanical strength of the interfacial film. According to the working effect of the sulfur-containing and silane additive, the lithium salt and the organic solvent system are matched and optimized, and the adaptive pole piece and the ceramic diaphragm are combined, so that the generation of HF is inhibited, the performance of an interfacial film is strengthened, the high temperature resistance of the battery is improved, the cycle life is prolonged, the safety is improved, the energy storage requirement is met, and the process is feasible.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a high-temperature resistant lithium-ion battery electrolyte. Background Technology

[0002] Traditional lithium-ion battery electrolytes exhibit significant drawbacks at high temperatures. Specifically, the conventional LiPF6 lithium salt in the electrolyte readily decomposes above 60°C, generating HF. HF in the electrolyte affects both the interfacial chemistry and interfacial phase chemistry of the positive and negative electrodes. On the positive electrode side, it primarily leads to transition metal dissolution and capacity decay; on the negative electrode side, HF participates in the formation and evolution of the solid electrolyte interphase (SEI). Furthermore, commonly used carbonate solvents, such as EC and DMC, have low boiling points, all below 150°C. Under high-temperature conditions, these solvents readily volatilize and can trigger oxidation side reactions, producing gases such as CO and H2, significantly increasing the risk of gas generation in the battery and impacting its stability and safety.

[0003] During high-temperature cycling, the insufficient mechanical strength of the SEI / CEI film on the battery electrode surface becomes apparent. Due to the poor strength of the film, repeated rupture and repair occur during battery charge-discharge cycles. This process consumes a large amount of active lithium, ultimately leading to increased internal impedance and a significant decrease in battery life. Furthermore, traditional electrolytes are flammable and can easily trigger a chain exothermic reaction at high temperatures. Once triggered, this poses a serious threat to the safety of the entire battery system and may even cause a safety accident. Therefore, this invention proposes a high-temperature resistant lithium-ion battery electrolyte. Summary of the Invention

[0004] The purpose of this invention is to address the problems of lithium salt decomposition producing HF, solvent evaporation producing gas, easy rupture of SEI / CEI film, and flammability of electrolyte in traditional lithium-ion battery electrolytes at high temperatures, which lead to battery capacity decay, shortened lifespan, and insufficient safety. This invention proposes a high-temperature resistant lithium-ion battery electrolyte.

[0005] The technical solution of this invention is as follows: A high-temperature resistant lithium-ion battery electrolyte, composed of a first additive, a second additive, a lithium salt, and an organic solvent, wherein the mass percentage of each component is: 0.3%-1% for the first additive, 0.3%-3% for the second additive, 0.01%-15% for the lithium salt, and 80%-95% for the organic solvent;

[0006] The first additive is a sulfur-containing film-forming additive, and the second additive is a silane-based additive. The first and second additives are used to inhibit the high-temperature decomposition of lithium salts and enhance the thermal stability and mechanical strength of the interface film.

[0007] Optionally, the mass percentage of each component is as follows: 0.6% for the first additive, 2.2% for the second additive, 7.5% for the lithium salt, and 89.7% for the organic solvent.

[0008] Optionally, the first additive includes at least one of FPS, TMS, SPA, PS, ES, DES, PES, DMS, and DTD;

[0009] The double bonds or carbonyl groups contained in the molecular structure of the first additive are used to reduce chemical hardness and form an SEI layer with a thickness of 5-20 nm and a porosity of ≤15% on the electrode surface, thereby inhibiting the consumption of active lithium and the continuous decomposition of the electrolyte.

[0010] Optionally, the second additive is selected from at least one of γ-mercaptopropyltrimethoxysilane, methyltriethoxysilane, and phenyltrimethoxysilane.

[0011] Optionally, the lithium salt is selected from one or more of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium dioxaborate, and lithium difluorooxaborate.

[0012] Optionally, the organic solvent is at least one selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, difluoroethyl acetate, trifluoroethyl acetate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, diethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and ethylene glycol dimethyl ether.

[0013] Optionally, the organic solvent is a combination of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate, wherein ethylene carbonate accounts for 20%-30% of the total mass of the organic solvent;

[0014] The organic solvent includes 0.5%-2% by mass of fluoroethylene carbonate or trifluoroethyl methyl carbonate.

[0015] The present invention also proposes a long-life, high-temperature resistant lithium-ion energy storage battery using the above-mentioned electrolyte, wherein the energy storage battery further includes a positive electrode, a negative electrode and a separator.

[0016] The positive electrode, separator, and negative electrode are stacked and packaged in an aluminum-plastic film bag, and then sealed after being injected with electrolyte to form a battery cell.

[0017] Optionally, the preparation of the positive electrode sheet includes the following steps: mixing the positive electrode material lithium iron phosphate, conductive carbon black and the binder polyvinylidene fluoride in a mass ratio of 92±3:2±1:1±0.5;

[0018] The cathode slurry was obtained by dispersing it in N-methyl-2-pyrrolidone.

[0019] The slurry is evenly coated onto carbon-coated aluminum foil, dried, rolled, and finally slit to obtain the positive electrode sheet;

[0020] The preparation of the negative electrode sheet includes the following steps: artificial graphite, conductive carbon black and carboxymethyl cellulose are uniformly mixed and dispersed in deionized water at a mass ratio of 92±3:2±1:1±0.5, and stirred evenly to obtain a negative electrode slurry.

[0021] The negative electrode slurry is coated onto copper foil, dried, and then cold-pressed and slit to obtain the negative electrode sheet;

[0022] The diaphragm is an Al2O3 or ZrO2 ceramic diaphragm with a coating thickness of 1-3 μm and a mass ratio of ceramic diaphragm to binder of 9-9.05:1-1.02.

[0023] In summary, this application includes at least one of the following beneficial technical effects:

[0024] This invention effectively suppresses the reaction pathway of high-temperature decomposition of traditional LiPF6 lithium salt to produce HF through the synergistic effect of sulfur-containing film-forming additives and silane additives, thereby reducing the erosion of positive and negative electrodes by HF; it also reduces the dissolution rate of transition metals on the positive electrode side to alleviate capacity decay; and it regulates the formation process of the SEI layer on the negative electrode side to avoid abnormal evolution of the SEI film caused by HF, thus ensuring the chemical stability of the electrode interface.

[0025] Furthermore, the chemical hardness can be reduced by the double bonds or carbonyl groups in the sulfur-containing additive molecules, and the Si-O bonds contained in silane additives are preferentially reduced to form a high mechanical strength SEI / CEI composite film. The composite film can avoid repeated cracking and repair during charge and discharge cycles, reduce the consumption of active lithium, reduce the rate of increase of battery internal resistance, and significantly extend battery cycle life.

[0026] Furthermore, by using organic solvents to enhance the boiling point and antioxidant properties of the solvent, and in conjunction with additives to inhibit electrolyte decomposition, the evaporation of solvents and the generation of gases such as CO and H2 at high temperatures are reduced, thereby reducing the risk of battery gas expansion and improving the stability of the battery at high temperatures.

[0027] The phenyl structure of silane additives and the molecular characteristics of sulfur-containing additives improve the flammability defects of traditional electrolytes, reduce the probability of chain exothermic reactions at high temperatures, and, together with the thermal stability protection of Al2O3 or ZrO3 ceramic separators, further enhance the battery's high temperature resistance, fire resistance and safety performance, and prevent safety accidents.

[0028] It ensures ionic conductivity and interface compatibility under high temperature conditions. Combined with the adaptability design of carbon-coated aluminum foil positive current collector and artificial graphite negative electrode, the battery maintains excellent capacity retention after high temperature cycling, while also taking into account low temperature ion transport efficiency, thus expanding the applicable temperature range of the battery and meeting the wide temperature range application needs of energy storage systems.

[0029] In summary, the working effect of the sulfur-containing and silane additives in this invention, combined with the optimized lithium salt and organic solvent system, and the appropriate electrode and ceramic separator, suppresses HF generation, enhances the performance of the interface film, improves the battery's high temperature resistance, cycle life and safety, meets energy storage requirements and the process is feasible. Detailed Implementation

[0030] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0031] Example 1

[0032] This invention proposes a high-temperature resistant lithium-ion battery electrolyte, composed of a first additive, a second additive, a lithium salt, and an organic solvent, with the following mass percentage content for each component:

[0033] First additive: Fluorophenyl thiophosphate, mass percentage 0.3±0.1%;

[0034] Second additive: γ-mercaptopropyltrimethoxysilane, mass percentage 0.8±0.2%;

[0035] Lithium salt: Lithium difluorophosphate, 7.5% by mass;

[0036] Organic solvents: Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are mixed in a mass ratio of 2:3:5, and 1% fluoroethylene carbonate is added. The total mass percentage of organic solvents is 89.4%.

[0037] Example 2

[0038] A high-temperature resistant lithium-ion battery electrolyte is composed of a first additive, a second additive, a lithium salt, and an organic solvent, with the following mass percentages for each component:

[0039] First additive: Trimethyl thiophosphate, mass percentage 0.4±0.2%;

[0040] Second additive: Methyltriethoxysilane, mass percentage 0.7±0.1%;

[0041] Lithium salt: Lithium difluorosulfonylimide, 7.5% by mass;

[0042] Organic solvents: Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are mixed in a mass ratio of 2:3:5, and 1% (by mass) of trifluoroethyl methyl carbonate is added, resulting in a total organic solvent mass percentage of 89.4%.

[0043] Example 3

[0044] A high-temperature resistant lithium-ion battery electrolyte is composed of a first additive, a second additive, a lithium salt, and an organic solvent, with the following mass percentages for each component:

[0045] First additive: Triphenyl thiophosphate, mass percentage 1±0.2%;

[0046] Second additive: phenyltrimethoxysilane, mass percentage 2±0.3%;

[0047] Lithium salt: Lithium dioxalatoborate, 7.5% by mass;

[0048] Organic solvent: Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are mixed in a mass ratio of 2:3:5, and 1% fluoroethylene carbonate is added. The total mass percentage of organic solvent is 89.5%.

[0049] Comparative Example

[0050] A conventional lithium-ion battery electrolyte, without the addition of the first and second additives, with the following mass percentage of the remaining components:

[0051] Lithium salt: Lithium hexafluorophosphate, 7.5% by mass;

[0052] Organic solvent: Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate are mixed in a mass ratio of 2:3:5, with a mass percentage of 92.5%.

[0053] Based on the electrolyte formulations of Examples 1-3 and the comparative examples, a long-life, high-temperature resistant lithium-ion energy storage battery is proposed, specifically including the following steps:

[0054] Positive electrode preparation: Lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride are mixed in a mass ratio of 92:3:5 and dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry; the slurry is coated on the surface of carbon-coated aluminum foil, dried, rolled and cut to obtain the positive electrode sheet.

[0055] Negative electrode preparation: Artificial graphite, conductive carbon black, and carboxymethyl cellulose are mixed in a mass ratio of 92:3:5 and dispersed in deionized water to prepare a negative electrode slurry; the slurry is coated on the surface of copper foil, dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0056] The battery cell assembly involves arranging the positive electrode, Al2O3 ceramic separator, and negative electrode in a stacked manner, welding tabs, and then sealing them in an aluminum-plastic film packaging bag. The electrolytes from Examples 1-3 and the comparative examples are then injected, and the cells are sealed to produce lithium-ion battery cells.

[0057] The performance of the batteries prepared in Examples 1-3 and the comparative examples was tested.

[0058] Test conditions:

[0059] Cyclic performance: 1000 cycles at 25℃ and 45℃ temperature environments and 1C charge / discharge current;

[0060] High-temperature gas production rate: After standing at 60℃ for 72 hours, the cell volume change rate was tested;

[0061] Rate of change of internal resistance: Initial internal resistance (R0) before test cycle and internal resistance (R) after 1000 cycles. 1000 ), calculate the rate of change = (R 1000 -R0) / R0×100%;

[0062] The test results are shown in Table 1 below:

[0063] Table 1 Battery performance test results data table

[0064] Case types Capacity retention rate at 25℃ (%) Capacity retention rate at 45℃ (%) Gas production rate at 60℃ (%) Rate of change of internal resistance after 1000 cycles (%) Example 1 96.11 85.58 3.2 18.5 Example 2 95.49 84.79 3.5 19.2 Example 3 96.71 85.33 3.1 17.8 Comparative Example 92.35 80.65 6.8 32.7

[0065] As can be seen from Table 1 above, the batteries of Embodiments 1-3 of the present invention exhibit significant advantages:

[0066] Cyclic performance: Capacity retention rate ≥95% after 1000 cycles at 25℃ and ≥84% at 45℃, which is 3%-4% and 4%-5% higher than the comparative examples (92.35% and 80.65%), respectively, demonstrating the effect of additives in enhancing the stability of the interfacial film.

[0067] High-temperature gas production: The gas production rate after standing at 60℃ for 72 hours was only 3.1%-3.5%, far lower than the 6.8% of the comparative example, proving that the optimized electrolyte can effectively suppress solvent volatilization and oxidation side reactions, and reduce the risk of gas production;

[0068] Internal resistance control: The internal resistance change rate after 1000 cycles is ≤19.2%, which is significantly lower than that of the comparative example (32.7%). This is attributed to the fact that the dense SEI / CEI film reduces the consumption of active lithium and the increase in interface impedance.

[0069] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A high-temperature resistant lithium-ion battery electrolyte, characterized in that, It is composed of a first additive, a second additive, a lithium salt, and an organic solvent, with the following mass percentages: first additive 0.3%-1%, second additive 0.3%-3%, lithium salt 0.01%-15%, and organic solvent 80%-95%. The first additive is a sulfur-containing film-forming additive, and the second additive is a silane-based additive. The first and second additives are used to inhibit the high-temperature decomposition of lithium salts and enhance the thermal stability and mechanical strength of the interface film.

2. The high-temperature resistant lithium-ion battery electrolyte according to claim 1, characterized in that, The mass percentage of each component is as follows: first additive 0.4%, second additive 2.7%, lithium salt 7.5%, and organic solvent 89.4%.

3. The high-temperature resistant lithium-ion battery electrolyte according to claim 1, characterized in that, The first additive includes at least one of FPS, TMS, SPA, PS, ES, DES, PES, DMS, and DTD; The double bonds or carbonyl groups contained in the molecular structure of the first additive are used to reduce chemical hardness and form an SEI layer with a thickness of 5-20 nm and a porosity of ≤15% on the electrode surface, thereby inhibiting the consumption of active lithium and the continuous decomposition of the electrolyte.

4. The high-temperature resistant lithium-ion battery electrolyte according to claim 1, characterized in that, The second additive is selected from at least one of γ-mercaptopropyltrimethoxysilane, methyltriethoxysilane, and phenyltrimethoxysilane.

5. The high-temperature resistant lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is selected from one or more of lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium dioxaborate, and lithium difluorooxaborate phosphate.

6. The high-temperature resistant lithium-ion battery electrolyte according to claim 1, characterized in that, The organic solvent is at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl butyl carbonate, propylene carbonate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, difluoroethyl acetate, trifluoroethyl acetate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, diethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and ethylene glycol dimethyl ether.

7. The high-temperature resistant lithium-ion battery electrolyte according to claim 1, characterized in that, The organic solvent is a combination of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate, wherein ethylene carbonate accounts for 20%-30% of the total mass of the organic solvent; The organic solvent includes 0.5%-2% by mass of fluoroethylene carbonate or trifluoroethyl methyl carbonate.

8. A long-life, high-temperature resistant lithium-ion energy storage battery using the electrolyte described in any one of claims 1-7, characterized in that, The energy storage battery also includes a positive electrode, a negative electrode, and a separator; The positive electrode, separator, and negative electrode are stacked and packaged in an aluminum-plastic film bag, and then sealed after being injected with electrolyte to form a battery cell.

9. A long-life, high-temperature resistant lithium-ion energy storage battery according to claim 8, characterized in that, The preparation of the positive electrode sheet includes the following steps: The positive electrode material lithium iron phosphate, conductive carbon black and binder polyvinylidene fluoride are mixed in a mass ratio of 92±3:2±1:1±0.5; The cathode slurry was obtained by dispersing it in N-methyl-2-pyrrolidone. The slurry is evenly coated onto carbon-coated aluminum foil, dried, rolled, and finally slit to obtain the positive electrode sheet; The preparation of the negative electrode sheet includes the following steps: artificial graphite, conductive carbon black and carboxymethyl cellulose are uniformly mixed and dispersed in deionized water at a mass ratio of 92±3:2±1:1±0.5, and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, dried, and then cold-pressed and slit to obtain the negative electrode sheet.

10. A long-life, high-temperature resistant lithium-ion energy storage battery according to claim 9, characterized in that, The diaphragm is an Al2O3 or ZrO2 ceramic diaphragm with a coating thickness of 1-3 μm and a mass ratio of ceramic diaphragm to binder of 9-9.05:1-1.02.