Electrolyte and battery comprising the same

Abstract

The present invention provides an electrolyte and a battery comprising the electrolyte. The electrolyte comprises an organic solvent, an electrolyte salt and a functional additive, wherein the functional additive comprises at least one compound represented by formula 1 and / or at least one compound represented by formula 2: #imgabs0# The compound represented by formula 1 in the electrolyte has a high affinity with silicon alloys and a low reaction energy barrier, which helps to preferentially form a layer of SEI film on the surface of the negative electrode, increase the thickness of the SEI film on the surface of the negative electrode, reduce the consumption of lithium salt in the electrolyte, and effectively increase the initial charge and discharge efficiency of the silicon negative electrode. The compound represented by formula 2 is conducive to complexing with anions in the electrolyte, thereby effectively improving the conductivity of the electrolyte. It can significantly improve the initial charge and discharge efficiency and normal high temperature cycle performance of batteries (especially silicon negative electrode batteries).

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to an electrolyte and a battery comprising the electrolyte. Background Art

[0002] Lithium-ion batteries, with their advantages of high specific energy density and long cycle life, are widely used in various electronic products. In recent years, they have also been widely used in electric vehicles, various power tools, and energy storage devices. With the improvement of people's living standards and the yearning for a better life, higher requirements are being placed on battery energy density. Traditional batteries use graphite as the negative electrode material. Silicon-based materials, as an emerging negative electrode material, have a gram capacity several times higher than graphite negative electrodes and are one of the main directions for the development of next-generation high-energy-density batteries.

[0003] However, during the cycling process of silicon-based anodes, unstable SEI can seriously reduce the initial coulombic efficiency of the battery and produce dead lithium, leading to battery failure. At the same time, uneven lithium deposition can produce dendrites, which can pierce the separator and cause a short circuit in the battery, causing serious safety issues. Summary of the Invention

[0004] To address the deficiencies of the prior art, the present invention provides an electrolyte and a battery comprising the electrolyte. The use of the electrolyte can significantly improve the initial charge and discharge efficiency and normal high-temperature cycle performance of batteries (particularly silicon anode batteries), thereby avoiding serious safety issues.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] An electrolyte comprising an organic solvent, an electrolyte salt, and a functional additive, wherein the functional additive comprises at least one compound represented by Formula 1 and / or at least one compound represented by Formula 2:

[0007]

[0008] In Formula 1, R1, R2, R3, R4, R5, R6, R7, and R8 are the same or different and are independently selected from halogen, -CHO, -COOH, -NO2, -CN, and substituted alkyl; if substituted, the substituent is halogen, -CHO, -COOH, -NO2, or -CN.

[0009] In formula 2, X is selected from halogen, substituted or unsubstituted alkoxy; R9, R 10 are the same or different and are independently selected from substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl; if substituted, the substituent is halogen, alkyl or cycloalkyl.

[0010] According to the present invention, the electrolyte is used for silicon negative electrode, preferably, for silicon negative electrode battery.

[0011] According to the present invention, in Formula 1, R1, R2, R3, R4, R5, R6, R7, and R8 are the same or different and are independently selected from halogen, -CHO, -COOH, -NO2, -CN, substituted C 1-6 Alkyl; if substituted, the substituent is halogen, -CHO, -COOH, -NO2 or -CN.

[0012] According to the present invention, in Formula 1, R1, R2, R3, R4, R5, R6, R7, and R8 are the same or different and are independently selected from -F, -Cl, -Br, -CHO, -COOH, -NO2, -CN, substituted C 1-3 Alkyl; if substituted, the substituent is -F, -CHO, -COOH, -NO2 or -CN.

[0013] According to the present invention, in Formula 1, R1, R2, R3, R4, R5, R6, R7, and R8 are the same or different and are independently selected from -F, -Cl, -Br, -CHO, -COOH, -NO2, -CN, and -CF3.

[0014] According to the present invention, when the R1, R2, R3, R4, R5, R6, R7, and R8 groups are selected from or contain electron-withdrawing groups, it helps to generate S free radicals more stably, thereby further improving the performance of the battery.

[0015] According to the present invention, the compound represented by Formula 1 is specifically selected from at least one of the compounds represented by the following Formula 1-1:

[0016]

[0017] According to the present invention, in Formula 2, X is selected from -F, -Cl, -Br, substituted or unsubstituted C 1-6 Alkoxy, R9, R 10 The same or different, independently selected from substituted or unsubstituted C 1-6 Alkyl, substituted or unsubstituted C 2-6 Cycloalkyl.

[0018] According to the present invention, in Formula 2, X is selected from -F, -Cl, -Br, substituted or unsubstituted C 1-3 Alkoxy, R9, R 10 The same or different, independently selected from substituted or unsubstituted C 1-3 Alkyl, substituted or unsubstituted C 2-3 Cycloalkyl.

[0019] According to the present invention, the compound represented by Formula 2 is specifically selected from at least one of the compounds represented by the following Formula 2-1:

[0020]

[0021] According to the present invention, the compound represented by Formula 1 and the compound represented by Formula 2 can be prepared by methods known in the art, or can be purchased through commercial channels.

[0022] According to the present invention, the mass of the compound represented by Formula 1 accounts for 0.1-2wt% of the total mass of the electrolyte, for example, 0.1wt%, 0.2wt%, 0.5wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.7wt%, 1.8wt%, and 2wt%.

[0023] According to the present invention, the mass of the compound represented by Formula 2 accounts for 0.1-2wt% of the total mass of the electrolyte, for example, 0.1wt%, 0.2wt%, 0.5wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.7wt%, 1.8wt%, or 2wt%.

[0024] According to the present invention, the electrolyte salt is selected from an electrolyte lithium salt, and the electrolyte lithium salt is selected from one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethylsulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluoroborate, lithium bisoxalatoborate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methyllithium or lithium bis(trifluoromethylsulfonyl)imide.

[0025] According to the present invention, the mass of the electrolyte salt accounts for 11-18 wt% of the total mass of the electrolyte, for example, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, or 18 wt%.

[0026] According to the present invention, the electrolyte may further include one or more of the following additives: vinylene carbonate, vinyl carbonate, fluoroethylene carbonate, vinyl sulfite, methylene methanedisulfonate, vinyl sulfate, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, sunflower dinitrile, 1,3,6-hexanetrinitrile, 1,2-bis(2-cyanoethoxy)ethane, 3-methoxypropionitrile, 1,3-propane sultone, and propenyl-1,3-sultone.

[0027] According to the present invention, the organic solvent is selected from carbonates and / or carboxylates, the carbonates are selected from one or more of the following fluorinated or unsubstituted solvents: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate; the carboxylates are selected from one or more of the following fluorinated or unsubstituted solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl n-butyrate.

[0028] The present invention also provides a battery, comprising the above-mentioned electrolyte.

[0029] According to an embodiment of the present invention, the battery is a lithium-ion battery. Preferably, the battery is a silicon negative electrode lithium-ion battery.

[0030] According to an embodiment of the present invention, the battery further includes a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a separator.

[0031] According to an embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one or both sides of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0032] According to an embodiment of 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 sides of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0033] According to an embodiment of the present invention, the mass percentage of each component in the positive electrode active material layer is: 80-99.8 wt % of positive electrode active material, 0.1-10 wt % of conductive agent, and 0.1-10 wt % of binder.

[0034] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90-99.6 wt % of positive electrode active material, 0.2-5 wt % of conductive agent, and 0.2-5 wt % of binder.

[0035] According to an embodiment of the present invention, the mass percentages of the components in the negative electrode active material layer are: 80-99.8 wt % of the negative electrode active material, 0.1-10 wt % of the conductive agent, and 0.1-10 wt % of the binder.

[0036] Preferably, the mass percentage of each component in the negative electrode active material layer is: 90-99.6 wt % of negative electrode active material, 0.2-5 wt % of conductive agent, and 0.2-5 wt % of binder.

[0037] According to an embodiment of the present invention, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0038] According to an embodiment of the present invention, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0039] According to an embodiment of the present invention, the positive electrode active material is selected from at least one of transition metal lithium oxides, lithium iron phosphate, lithium iron manganese phosphate compounds, nickel cobalt manganese ternary materials, etc.; the chemical formula of the transition metal lithium oxide is Li 1+x Co z M 1-z O2, where, -0.1 ≤ x ≤ 1, 0 < z ≤ 1; M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr; the chemical formula of the lithium iron manganese phosphate compound is LiFe x Mn 1-x PO4, where, -0.1 ≤ x ≤ 1, M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr; the chemical formula of the nickel cobalt manganese ternary material is LiNi x Co y Mn z O2, 0 < x, 0 < y, 0 < z, x + y + z = 1.

[0040] According to an embodiment of the present invention, the negative electrode active material includes a silicon-based negative electrode material.

[0041] According to an embodiment of the present invention, the negative electrode active material may further include a carbon-based negative electrode material.

[0042] According to an embodiment of the present invention, the silicon-based negative electrode material is selected from at least one of nano-silicon, silicon oxide negative electrode material (SiOx(0 < x < 2)), or silicon-carbon negative electrode material.

[0043] According to an embodiment of the present invention, the carbon-based negative electrode material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0044] According to an embodiment of the present invention, in the negative electrode active material, the mass ratio of the silicon-based negative electrode material to the carbon-based negative electrode material is 10:0 to 1:19, for example, 1:19, 1:18, 1:17, 1:16, 1:15, 1:14, 1:13, 1:12, 1:11, 1:10, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, or 10:0.

[0045] According to an embodiment of the present invention, the charging cut-off voltage of the battery is 4.45V or above.

[0046] Beneficial effects of the present invention:

[0047] The present invention provides an electrolyte and a battery comprising the electrolyte. The compound represented by Formula 1 in the electrolyte has a high affinity with silicon alloys and a low reaction energy barrier, which helps to preferentially form a SEI film on the surface of the negative electrode, increase the thickness of the SEI film on the surface of the negative electrode, reduce the consumption of lithium salts in the electrolyte, and effectively increase the initial charge and discharge efficiency of the silicon negative electrode. In addition, because the compound represented by Formula 1 has a strong complexing ability with the metal ions on the surface of the positive electrode, it can effectively inhibit the oxidative decomposition of the electrolyte and the dissolution of transition metals, thereby effectively enhancing the cycle stability of the electrolyte. The compound represented by Formula 2 is conducive to complexing with the anions in the electrolyte, thereby effectively improving the conductivity of the electrolyte. When the two additives are added to the electrolyte at the same time, the compound shown in Formula 1 preferentially forms a more uniform SEI film with the negative electrode, thereby reducing the consumption of lithium salts in the electrolyte and preventing the first efficiency from decreasing. At the same time, a better SEI film can make the deposition of lithium ions at the negative electrode more uniform, which helps the lithium ions to deposit on the negative electrode surface. The compound shown in Formula 2 is beneficial for complexing with the anions in the electrolyte. During the cycle, the electronic conductivity of the electrolyte does not decrease as the cycle progresses, so that the electrolyte maintains excellent electronic conductivity during the cycle, thereby ensuring stable cycle performance. A synergistic effect is generated between the two, which can significantly improve the first charge and discharge efficiency and normal high temperature cycle performance of the battery (especially the silicon negative electrode battery). DETAILED DESCRIPTION

[0048] The present invention will be described in further detail below with reference to specific examples. It should be understood that the following examples are merely illustrative and explanations 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 encompassed within the scope of protection that the present invention is intended to protect.

[0049] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the reagents, materials, etc. used in the following examples are all commercially available unless otherwise specified.

[0050] The batteries used in the following examples were prepared by the following method:

[0051] Preparation of the positive electrode: The positive electrode active materials lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), SP (super-P) and carbon nanotubes (CNT) are mixed in a mass ratio of 96:2:1.5:0.5, N-methylpyrrolidone (NMP) is added, and the mixture is stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode active slurry with uniform fluidity; the positive electrode active slurry is evenly coated on both surfaces of the aluminum foil; the coated aluminum foil is dried, and then rolled and cut to obtain the required positive electrode sheet.

[0052] Preparation of the negative electrode: The negative electrode active materials artificial graphite, silicon oxide, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 79.5:15:2.5:1.5:1:0.5, deionized water was added, and the negative electrode active slurry was obtained under the action of a vacuum mixer; the negative electrode active slurry was evenly coated on both surfaces of the copper foil; the coated copper foil was dried at room temperature, then transferred to an 80°C oven for drying for 10 hours, and then cold pressed and cut to obtain the negative electrode sheet.

[0053] Preparation of electrolyte:

[0054] In an argon-filled glove box (H2O <0.1ppm, O2 <0.1ppm), EC / PC / DME were mixed uniformly in a mass ratio of 25 / 35 / 40, and then 1 mol / L of fully dried lithium hexafluorophosphate (LiPF6) was quickly added thereto. After dissolution, 10 wt% of fluoroethylene carbonate, 1 wt% of succinonitrile, and the compound represented by Formula 1-1 and / or the compound represented by Formula 2-1 (specific amounts are described in Table 1) based on the total mass of the electrolyte were added, stirred uniformly, and after passing the moisture and free acid tests, the desired electrolyte was obtained.

[0055] Preparation of the battery:

[0056] The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to form a battery cell. The battery cell is placed in an outer aluminum foil package, and the electrolyte from step 3) is injected into the outer packaging. The battery is vacuum packaged, allowed to stand, formed, shaped, and sorted to obtain a battery. The battery of the present invention has a charge and discharge range of 3.0-4.45V.

[0057] 1) 25℃ cycle performance test

[0058] The battery in Table 1 was charged and discharged for 1000 cycles at a rate of 1C within the charge and discharge cut-off voltage range at 25°C. The discharge capacity in the first week of the test was calculated as x1mAh, and the discharge capacity in the Nth week was calculated as y1mAh. The capacity in the Nth week was divided by the capacity in the first week to obtain the cycle capacity retention rate R1 = y1 / x1 in the Nth week. When the cycle capacity retention rate R1 was 80%, the number of cycles was recorded.

[0059] 2) 45℃ cycle performance test

[0060] The battery in Table 1 was charged and discharged for 1000 cycles at a rate of 1C within the charge and discharge cut-off voltage range at 45°C. The discharge capacity in the first week of the test was calculated as x2mAh, and the discharge capacity in the Nth week was calculated as y2mAh. The capacity in the Nth week was divided by the capacity in the first week to obtain the cycle capacity retention rate R2 = y2 / x2 in the Nth week. When the cycle capacity retention rate R2 was 80%, the number of cycles was recorded.

[0061] 3) First charge and discharge efficiency test of the battery

[0062] The battery in Table 1 was subjected to a charge and discharge cycle test at 45°C at a rate of 1C within the charge and discharge cut-off voltage range. The discharge capacity of the first cycle was calculated as x3mAh, and the discharge capacity of the first cycle was calculated as y3mAh; the charge capacity of the first cycle was divided by the discharge capacity of the first cycle, and the first charge and discharge efficiency = y3 / x3.

[0063] Table 1 Electrolyte compositions of Examples and Comparative Examples

[0064]

[0065]

[0066] Table 2 Performance test results of batteries of Examples and Comparative Examples

[0067] First charge and discharge efficiency 25℃ cycle capacity retention rate 45℃ cycle capacity retention rate Comparative Example 1 83.0％ 722 615 Example 1 83.6％ 764 648 Example 2 84.3％ 782 721 Example 3 85.2％ 677 653 Example 4 83.1％ 782 642 Example 5 83.05％ 643 571 Example 6 84.7％ 852 821

[0068] As can be seen from Table 2, the number of cycles at 25°C of Comparative Example 1, which does not contain additives of the compound represented by Formula 1-1 and / or the compound represented by Formula 2-1, is significantly lower than that of Examples 1 to 2 and Example 6, which contain additives of the compound represented by Formula 1-1 that can form an SEI film. This demonstrates that the compound represented by Formula 1-1 that can form an SEI film has a significant effect on improving the cycle performance of the silicon-containing negative electrode.

[0069] Furthermore, it can be seen from Examples 1 to 3 that as the amount of the additive of the compound represented by Formula 1-1 that can form an SEI film increases, the improvement in its room temperature and high temperature cycle performance first becomes stronger and then weakens. This shows that adding an appropriate amount of the compound represented by Formula 1-1 that can form an SEI film is beneficial to the improvement of the battery cycle performance, and side effects such as increased impedance caused by excessive addition begin to become more significant.

[0070] As can be seen from Table 2, the initial charge and discharge efficiency of Comparative Example 1, which did not include the compound represented by Formula 1-1 and / or the compound represented by Formula 2-1, was significantly lower than that of Examples 1 to 3 and Example 6, which included the compound represented by Formula 1-1 capable of forming an SEI film. This demonstrates that the compound represented by Formula 1-1 capable of forming an SEI film replaces the lithium salt in forming the SEI film, allowing more lithium ions to be embedded in the negative electrode, thereby increasing the initial charge and discharge efficiency of the battery. Furthermore, as the amount of additive increases, the initial charge and discharge efficiency significantly improves.

[0071] At the same time, it can be seen that the number of cycles at 25°C in Comparative Example 1, which does not add the compound represented by Formula 1-1 and / or the compound represented by Formula 2-1, is significantly less than that in Examples 4 and 6, which add the compound represented by Formula 2-1 that can form an SEI film. The addition of the compound represented by Formula 2-1 can improve its cycle performance because the viscosity of the electrolyte increases with the progress of the cycle, while affecting its conductivity. A certain amount of the compound represented by Formula 2-1 can improve the cycle performance of the electrolyte. Furthermore, from Example 5, it can be seen that excessive addition is not conducive to the cycle of the battery.

[0072] The above describes the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that The electrolyte includes an organic solvent, an electrolyte salt, and a functional additive, wherein the functional additive includes at least one compound represented by Formula 2: In formula 2, X is selected from halogen, substituted or unsubstituted alkoxy; R9, R 10 are the same or different and are independently selected from substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl; if substituted, the substituent is halogen, alkyl or cycloalkyl; The mass of the compound represented by Formula 2 accounts for 0.1-2 wt % of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that The electrolyte is used for silicon negative electrode.

3. The electrolyte according to claim 1, characterized in that The functional additive further comprises at least one compound represented by Formula 1: In Formula 1, R1, R2, R3, R4, R5, R6, R7, and R8 are the same or different and are independently selected from halogen, -CHO, -COOH, -NO2, -CN, and substituted alkyl; if substituted, the substituent is halogen, -CHO, -COOH, -NO2, or -CN.

4. The electrolyte according to claim 3, characterized in that In formula 1, R1, R2, R3, R4, R5, R6, R7, and R8 are the same or different and are independently selected from halogen, -CHO, -COOH, -NO2, -CN, substituted C 1-6 Alkyl; if substituted, the substituent is halogen, -CHO, -COOH, -NO2 or -CN.

5. The electrolyte according to claim 4, characterized in that The compound represented by Formula 1 is specifically the compound represented by Formula 1-1:

6. The electrolyte according to claim 1, characterized in that In formula 2, X is selected from -F, -Cl, -Br, substituted or unsubstituted C 1-6 Alkoxy, R9, R 10 The same or different, independently selected from substituted or unsubstituted C 1-6 Alkyl, substituted or unsubstituted C 2-6 Cycloalkyl.

7. The electrolyte according to claim 6, characterized in that The compound represented by Formula 2 is specifically the compound represented by Formula 2-1:

8. The electrolyte according to claim 3, characterized in that The mass of the compound represented by Formula 1 accounts for 0.1-2 wt % of the total mass of the electrolyte.

9. A battery, characterized in that: The battery comprises the electrolyte according to any one of claims 1 to 8.

10. The battery according to claim 9, characterized in that The charging cut-off voltage of the battery is 4.45V or above.

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