Lithium ion battery electrolyte and lithium ion battery thereof

Abstract

The application discloses a lithium ion battery electrolyte and a lithium ion battery. The lithium ion battery electrolyte comprises a lithium salt, a non-water organic solvent and an additive, the additive comprises a first additive and a second additive, the first additive is selected from at least one of ethylene carbonate, fluoroethylene carbonate and vinyl sulfate, and the second additive comprises a compound A shown in a structural formula I. The lithium ion battery electrolyte comprises the first additive and the second additive, and the two are used in combination, so that the damage of water and hydrofluoric acid to the battery can be effectively inhibited, and the cycle life of the battery is improved. The structural formula I is shown in the figure.

Description

Technical Field

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

[0002] Because lithium-ion battery electrolytes contain trace amounts of water and hydrofluoric acid, these trace amounts of water can react with lithium salts in the electrolyte to form hydrofluoric acid. This further increases the hydrofluoric acid content in the electrolyte. Hydrogen ions can damage the positive and negative electrode interfaces of the lithium-ion battery, leading to the shedding of active materials from both electrodes. This reduces the battery's lifespan and, in severe cases, can cause a short circuit, fire, or explosion. Therefore, there is an urgent need for a lithium-ion battery electrolyte and a lithium-ion battery thereof to address the shortcomings of existing technologies. Summary of the Invention

[0003] In view of the above problems, the purpose of this invention is to provide a lithium-ion battery electrolyte and a lithium-ion battery thereof. The lithium-ion battery electrolyte contains a first additive and a second additive. When used in combination, the two additives can effectively inhibit the damage of water and hydrofluoric acid to the battery and improve the cycle life of the battery.

[0004] To achieve the above objectives, the present invention provides a lithium-ion battery electrolyte comprising a lithium salt, a non-aqueous organic solvent, and additives. The additives include a first additive and a second additive. The first additive is selected from at least one of ethylene carbonate, fluoroethylene carbonate, and ethylene sulfate. The second additive comprises compound A as shown in structural formula 1.

[0005] Structure 1 (CAS No.: 1520-22-5).

[0006] Compared with the prior art, the lithium-ion battery electrolyte of the present invention includes a first additive and a second additive. The second additive contains an N=C=S structure that can react with trace amounts of water and hydrofluoric acid in the lithium-ion battery electrolyte, thereby inhibiting the damage of water and hydrofluoric acid to the battery. Furthermore, the second additive can synergistically cooperate with the first additives, ethylene carbonate, fluoroethylene carbonate, and / or ethylene sulfate, to form an SEI film and a CEI film at the positive and negative electrode interfaces, thereby improving the interfacial stability of the positive and negative electrodes of the lithium-ion battery and effectively improving the cycle life of the lithium-ion battery.

[0007] Specifically, the reaction mechanism of compound A with water and acid is shown below.

[0008] .

[0009] Furthermore, the first additive of the present invention accounts for 0.1% to 5% of the total mass of the lithium-ion battery electrolyte. Specifically, the first additive accounts for 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5% of the total mass of the lithium-ion battery electrolyte, but is not limited thereto, and other values ​​not listed within the scope of the present invention are also applicable.

[0010] Further, the second additive of the present invention accounts for 0.1% to 5% of the total mass of the lithium-ion battery electrolyte. Preferably, the second additive accounts for 0.1% to 3% of the total mass of the lithium-ion battery electrolyte, more preferably, the second additive accounts for 0.5% to 2% of the total mass of the lithium-ion battery electrolyte. Specifically, the second additive accounts for 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5% of the total mass of the lithium-ion battery electrolyte, but is not limited thereto, and other values ​​not listed within the scope of the present invention are also applicable.

[0011] Furthermore, the lithium salt of the present invention is at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethylsulfonylimide (LiTFSI), lithium difluorooxalate borate (LiDFOB), and lithium tetrafluoroborate (LiBF4).

[0012] Furthermore, the lithium salt of the present invention accounts for 10% to 20% of the total mass of the lithium-ion battery electrolyte. Specifically, the lithium salt of the present invention accounts for 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20% of the total mass of the lithium-ion battery electrolyte.

[0013] Furthermore, the non-aqueous organic solvent of the present invention is selected from at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0014] Furthermore, the non-aqueous organic solvent of the present invention is selected from ethylene carbonate (EC), propylene carbonate (PCA), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), γ-butyrolactone (GBL), γ-valerolactone (GVL), δ-valerolactone (DVL), methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate (BAC), and propyl propionate (PP). At least one of the following: butyl propionate (PRB), 1,3-dioxolane (DOL), 1,4-dioxolane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), 2-trifluoromethyltetrahydrofuran (2-CF3-THF), dimethoxymethane (DMM), diethoxymethane (DEM), ethoxymethoxymethane (DCE), ethylene glycol di-n-butyl ether (EDB), and diethylene glycol dimethyl ether (DEGME).

[0015] Another aspect of the present invention provides a lithium-ion battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, wherein the electrolyte is the aforementioned lithium-ion battery electrolyte.

[0016] Furthermore, the cathode material includes at least one of lithium cobalt oxide, lithium iron phosphate, and nickel cobalt manganese oxide. Specifically, the lithium iron phosphate material can be lithium iron phosphate (LiFePO4) or doped and modified lithium iron phosphate; the lithium manganese iron phosphate material can be lithium manganese iron phosphate or doped and modified lithium manganese iron phosphate; the lithium cobalt oxide material is lithium cobalt oxide (LiCoO2) or doped and modified lithium cobalt oxide; and the nickel cobalt manganese oxide has the chemical formula LiNi. x Co y Mn z M (1-x-y-z) O2, wherein M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, 0 <x<1,0<y<1,0<z<1,x+y+z≤1 Furthermore, the negative electrode material includes at least one of artificial graphite, natural graphite, lithium titanate, silicon-carbon composite material, and silicon suboxide. Preferably, the negative electrode material of the present invention is selected from artificial graphite. Detailed Implementation

[0017] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0018] Example 1 1.1 Preparation of electrolyte: In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 10 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 2:3 to obtain a non-aqueous organic solvent. Then, 1 g of ethylene carbonate (VC) and 1 g of compound A were added to obtain a mixed solution. The mixed solution was sealed and packaged, then frozen in a freezer (-4°C) for 2 hours. After removal, 14 g of lithium hexafluorophosphate was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), and mixed thoroughly to prepare the electrolyte.

[0019] 1.2 Preparation of lithium iron phosphate cathode: Lithium iron phosphate, conductive agent SuperP, and binder PVDF are mixed evenly at a mass ratio of 96:2:2 to prepare a lithium-ion battery positive electrode slurry of a certain viscosity. The slurry is coated on aluminum foil for current collectors with a coating amount of 324 g / m2. After drying at 120℃, it is cold-pressed. Then, it is trimmed, cut into sheets, and slit. After slitting, it is dried at 85℃ for 4 hours under vacuum conditions. The tabs are then welded to produce a lithium-ion battery positive electrode sheet that meets the requirements.

[0020] 1.3 Preparation of the negative electrode: Artificial graphite, SBR (styrene-butadiene rubber latex) binder, and SuperP conductive agent were mixed in a mass ratio of 96:3:1 to form a slurry. After being thoroughly mixed, the slurry was coated on both sides of a copper foil, dried at 90°C, and rolled to obtain the negative electrode sheet, thus producing a lithium-ion battery negative electrode sheet that meets the requirements. 1.4 Preparation of lithium-ion batteries: The positive electrode, negative electrode and separator prepared according to the above process are stacked to form a lithium-ion battery with a thickness of 4.7 mm, a width of 55 mm and a length of 60 mm. The battery is then vacuum baked at 75°C for 10 h, injected with the above electrolyte, and then packaged, formed and tested to complete the production of the lithium-ion battery.

[0021] The composition and content of the electrolytes in Examples 1-12 and Comparative Examples 1-6 are shown in Table 1. The preparation processes of the lithium-ion battery electrolytes, positive electrode sheets, negative electrode sheets, and lithium-ion batteries in Examples 2-12 and Comparative Examples 1-6 are the same as those in Example 1.

[0022] Example 13 The difference between this embodiment and Embodiment 1 lies in the preparation of the positive electrode sheet. In this embodiment, the preparation of the lithium cobalt oxide positive electrode sheet includes: mixing lithium cobalt oxide, conductive agent SuperP, and binder PVDF at a mass ratio of 96:2:2 to form a lithium-ion battery positive electrode slurry of a certain viscosity, and coating it onto aluminum foil for current collectors, with a coating amount of 324 g / m². 2After drying at 120°C, the material is cold-pressed; then trimmed, cut into sheets, and slit. After slitting, the material is dried at 85°C for 4 hours under vacuum, and then the tabs are welded to produce a lithium-ion battery positive electrode sheet that meets the requirements. The rest is the same as in Example 1.

[0023] The composition and content of the electrolytes in Examples 13-21 and Comparative Examples 7-9 are shown in Table 1. The preparation processes of the lithium-ion battery electrolytes, positive electrode sheets, negative electrode sheets, and lithium-ion batteries in Examples 14-21 and Comparative Examples 7-9 are the same as those in Example 13.

[0024] Table 1. Composition of the electrolytes in the examples and comparative examples

[0025] The structures of compound 1 and compound 2 in the comparative examples in Table 1 are shown below:

[0026] Compound 1

[0027] Compound 2 The lithium-ion batteries prepared in Examples 1-21 and Comparative Examples 1-14 were subjected to high-temperature cycling tests, low-temperature cycling tests, and acid value and moisture content tests of the non-aqueous electrolyte after high-temperature cycling tests. The test conditions are as follows, and the test results are shown in Table 2.

[0028] High-temperature cycling test: Under high-temperature (45℃) conditions, the lithium-ion battery is charged and discharged at 1.0C / 1.0C (the average discharge capacity of the first three cycles is C0), with a charging cut-off current of 0.05C and a discharging cut-off current of 3.0V. After 500 cycles of 1.0C / 1.0C charging and discharging at 45℃ (battery discharge capacity is C1), the capacity retention rate is calculated using the following formula: Capacity retention rate = (C1 / C0) × 100% Low-temperature cycling test: Under low-temperature (15℃) conditions, the lithium-ion battery is charged and discharged at 1.0C / 1.0C (the average discharge capacity of the first three cycles is C0), with a charging cut-off current of 0.05C and a discharging cut-off current of 3.0V. After 500 cycles of 1.0C / 1.0C charging and discharging at 15℃ (battery discharge capacity is C1), the capacity retention rate is calculated using the following formula: Capacity retention rate = (C1 / C0) × 100% Acid value test of non-aqueous electrolyte: After calibrating the potentiometric titrator according to section 4.5.1 of SJ / T 11723-2018 Electrolytes for Lithium-ion Batteries, accurately weigh 10.00g of electrolyte sample (circulated at 45℃ for 500 cycles), add it to 50mL of anhydrous ethanol, and titrate with a 0.01mol / L weak organic base. Record the titration volume, and the instrument will automatically calculate the free acid content (calculated as HF) in the electrolyte.

[0029] Moisture content testing of non-aqueous electrolytes: Refer to section 4.5.2 of SJ / T 11723-2018, "Determination of Moisture in Electrolytes for Lithium-ion Batteries," for standard method. A Karl Fischer titration method is used. The Fischer coulometric moisture analyzer, under dry nitrogen protection, accurately weighs 2.00g of electrolyte sample after 500 cycles at 45℃ and injects it into the anode chamber of the moisture analyzer. The instrument automatically completes the titration and displays the moisture content, with the result expressed in ppm.

[0030] Table 2 Performance test results of lithium-ion batteries

[0031] Please refer to Table 2 for the test results. By comparing Examples 1-12 with Comparative Examples 1-6, and Examples 13-21 with Comparative Examples 9-12, it can be seen that when the non-aqueous electrolyte contains both the first additive and the second additive of this application, both lithium iron phosphate batteries and lithium cobalt oxide batteries exhibit superior high and low temperature cycle performance. This may be because the second additive contains an N=C=S structure that can react with trace amounts of water and hydrofluoric acid in the lithium-ion battery electrolyte, thereby inhibiting the damage of water and hydrofluoric acid to the battery. Furthermore, the second additive can synergistically cooperate with the first additive, ethylene carbonate, fluoroethylene carbonate, and / or ethylene sulfate, to form SEI and CEI films at the positive and negative electrode interfaces, improving the interfacial stability of the positive and negative electrodes of the lithium-ion battery, thereby effectively improving the cycle life of the lithium-ion battery.

[0032] Further comparisons with Examples 1-9 and Examples 13-21 show that, compared with lithium cobalt oxide batteries, the first additive and the second additive exhibit superior high and low temperature cycle performance improvement effects in lithium iron phosphate batteries.

[0033] Further comparisons with Examples 1 and 7-8, and with Examples 13 and 13-14, show that replacing Compound A with Compound 1 or Compound 2 does not significantly improve the high and low temperature cycling performance. This may be because Compound 1 lacks vinyl conjugated double bonds that can participate in film formation, and cannot synergistically crosslink with the first additive to form a stable and dense interfacial film. The film strength and resistance to high and low temperatures are insufficient, making it difficult to suppress electrolyte decomposition and electrode corrosion for a long time. Therefore, the improvement in the high and low temperature cycling performance of the battery is not significant. Although Compound 2 also contains vinyl double bonds, the presence of methylene structures between the vinyl double bonds and the carbon-nitrogen double bonds significantly weakens the conjugation effect between them, reducing the reactivity and the stability of the formed interfacial film, thus limiting the improvement in high and low temperature cycling performance.

[0034] 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, it is not limited to those listed in the 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 electrolyte, comprising a lithium salt, a non-aqueous organic solvent, and additives, characterized in that, The additive includes a first additive and a second additive, wherein the first additive is selected from at least one of ethylene carbonate, fluoroethylene carbonate, and ethylene sulfate, and the second additive includes compound A as shown in structural formula one. Structure 1.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first additive accounts for 0.1% to 5% of the total mass of the lithium-ion battery electrolyte.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The second additive accounts for 0.1% to 5% of the total mass of the lithium-ion battery electrolyte.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt is at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium difluorooxalateborate, and lithium tetrafluoroborate.

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

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

7. The lithium-ion battery electrolyte according to claim 6, characterized in that, The non-aqueous organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, γ-butyrolactone, γ-valerolactone, δ-valerolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, propyl propionate, butyl propionate, 1,3-dioxolane, 1,4-dioxane, crown ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2-trifluoromethyltetrahydrofuran, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether.

8. A lithium-ion battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized in that, The electrolyte is the lithium-ion battery electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that, The cathode material includes at least one of lithium cobalt oxide, lithium iron phosphate, and nickel cobalt manganese oxide.

10. The lithium-ion battery according to claim 8, characterized in that, The negative electrode material includes at least one of artificial graphite, natural graphite, lithium titanate, silicon-carbon composite material, and silicon suboxide.

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