An electrolyte and a lithium ion battery comprising the same

Abstract

The application relates to a non-aqueous electrolyte solution comprising an organic solvent, a lithium salt and an additive, wherein the additive contains a substituted or unsubstituted catechol sulfite and optionally a cyano or cyanoalkoxy-substituted alkane. The application also relates to a lithium ion battery comprising the non-aqueous electrolyte solution. The application can make the lithium ion battery have good high-voltage stability, high-temperature performance and low-temperature performance.

Description

Technical Field

[0001] This application relates to the field of lithium-ion batteries, and in particular to a non-aqueous electrolyte and a lithium-ion battery containing the electrolyte. Background Technology

[0002] In line with the global trend of green and low-carbon development, lithium-ion batteries, as a clean energy source, have been widely used in digital products, electronic devices, and energy storage. In recent years, with the rapid development of intelligent electronic products, short battery life has impacted user experience, making the improvement of battery life a major concern in the industry. Currently, there are two main strategies to improve user experience: the development of fast-charging technology and the development of high-energy-density batteries.

[0003] For the development of high-energy-density batteries, increasing the upper voltage limit of the cathode material can effectively improve energy density. However, increasing the upper voltage limit of the cathode material leads to two problems: firstly, the structural stability of the cathode material deteriorates, making it more prone to releasing reactive oxygen species, which oxidize the electrolyte and release gases. Secondly, transition metal elements in the cathode material (such as nickel, cobalt, and manganese) undergo reduction reactions and dissolve, depositing onto the SEI film on the negative electrode surface, causing SEI film damage and further degrading the battery's electrochemical performance. Therefore, developing electrolytes with high voltage stability helps to alleviate or solve this problem. Summary of the Invention

[0004] The purpose of this application is to provide a non-aqueous electrolyte and a lithium-ion battery containing the non-aqueous electrolyte. This electrolyte can operate normally for a long time under high voltage and ensure the battery's excellent high-temperature storage performance, cycle performance, and low-temperature performance.

[0005] To achieve the above objectives, the first aspect of this application provides a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and an additive, wherein the additive comprises a first additive and a second additive.

[0006] Furthermore, the first additive is selected from cyclic sulfite compounds having the structure of formula (I), and the second additive is a cyano-substituted alkane and / or a cyanoalkoxy-substituted alkane.

[0007] Formula (I):

[0008] In formula (I): R9-R 12 Each of the following can be independently H, halogen, hydroxyl, cyano, sulfonyl, fluorosulfonyl, sulfonic acid, fluorosulfonic acid, 1-10 carbon atoms of saturated or unsaturated alkyl, 1-10 carbon atoms of saturated or unsaturated haloalkyl, 1-10 carbon atoms of alkoxy or 1-10 carbon atoms of fluoroalkoxy.

[0009] Furthermore, in the non-aqueous electrolyte, the content of the first additive by weight is 0.01%-10%, preferably 0.01%-3%, more preferably 0.3%-2%; and the content of the second additive is 0.01%-10%, preferably 1%-5%, more preferably 1%-3%.

[0010] Further, the first additive is selected from one or more of compounds 1-1 to 1-5:

[0011]

[0012]

[0013] Further, the second additive is selected from one or more of acetonitrile, propionitrile, butyronitrile, succinic anhydride, glutaritrile, adiponitrile, heptanitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane, 1,2-bis(3-cyanopropoxy)ethane, 1,3,6-hexanetrionitrile, 1,2,3-propanetrionitrile, 1,3,5-pentanetrionitrile, 3,3-bis(cyanomethyl)glutaritrile, 3,3-bis(cyanomethyl)adiponitrile, and 1,2,3-tris(2-cyanoethoxy)propane.

[0014] Further, the organic solvent is selected from carbonates and / or carboxylic esters, wherein the carbonate is selected from one or more of the following solvents, substituted or unsubstituted: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and the carboxylic ester is selected from one or more of the following solvents, substituted or unsubstituted: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, and ethyl butyrate.

[0015] Further, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluorosulfonyl, lithium bis(trifluoromethylsulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide. The lithium salt content, by weight, is 9-20%.

[0016] Furthermore, the non-aqueous electrolyte also contains vinylene carbonate and fluoroethylene carbonate, wherein the vinylene carbonate and fluoroethylene carbonate account for 0.1%-20% of the total mass of the non-aqueous electrolyte.

[0017] Furthermore, the non-aqueous electrolyte also contains 1,3-propanesulfonyl lactone, which accounts for 0.1%-5% of the total mass of the non-aqueous electrolyte.

[0018] A second aspect of this application provides a lithium-ion battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, wherein the electrolyte is the aforementioned non-aqueous electrolyte.

[0019] Furthermore, the positive electrode material includes lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, ternary materials, etc.; the negative electrode material includes soft carbon, hard carbon, carbon fiber, graphitized carbon microspheres, artificial graphite, natural graphite, silicon, silicon carbide, silicon-carbon composite materials, etc.

[0020] Through the above technical solution, the synergistic effect of the first additive and the second additive in this application enables the lithium-ion battery to have good high voltage stability, high temperature performance, and low temperature performance.

[0021] Other features and advantages of this application will be described in detail in the following detailed description section. Detailed Implementation

[0022] The specific embodiments of this application are described in detail below. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0023] The first aspect of this application provides a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and an additive, wherein the additive contains a first additive and a second additive.

[0024] Specifically, the first additive is selected from cyclic sulfite compounds having the structure of formula (I), and the second additive is a cyano-substituted alkane and / or a cyanoalkoxy-substituted alkane.

[0025] Formula (I):

[0026] In formula (I): R9-R 12 Each of the following can be independently H, halogen, hydroxyl, cyano, sulfonyl, fluorosulfonyl, sulfonic acid, fluorosulfonic acid, 1-10 carbon atoms of saturated or unsaturated alkyl, 1-10 carbon atoms of saturated or unsaturated haloalkyl, 1-10 carbon atoms of alkoxy or 1-10 carbon atoms of fluoroalkoxy.

[0027] In the non-aqueous electrolyte, the content of the first additive, by weight, is 0.01%-10%, preferably 0.1%-2%, more preferably 0.3%-2%; the content of the second additive is 0.01%-10%, preferably 0.1%-6%, more preferably 2%-4%. When the content of the first additive is preferably 0.3%-2% and the content of the second additive is 2%-4%, it achieves excellent modification effects on the positive and negative electrode interfaces, enabling the SEI film to provide better protection without increasing impedance due to excessive thickness, thus preventing hindering lithium-ion transport at the interface. Therefore, the battery can achieve better high-voltage stability and balanced high-temperature and low-temperature performance.

[0028] The second additive is selected from one or more of the following: acetonitrile, propionitrile, butyronitrile, succinic anhydride, glutaritrile, adiponitrile, heptanitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane, 1,2-bis(3-cyanopropoxy)ethane, 1,3,6-hexanetrionitrile, 1,2,3-propanetrionitrile, 1,3,5-pentanetrionitrile, 3,3-bis(cyanomethyl)glutaritrile, 3,3-bis(cyanomethyl)adiponitrile, and 1,2,3-tris(2-cyanoethoxy)propane.

[0029] The first additive, due to its lower LUMO orbital, is the first to gain electrons and be reduced, forming a stable, uniform, and thin SEI film on the negative electrode surface of the energy storage device. This inhibits solvent embedding into the negative electrode and reduction decomposition in the electrolyte. Furthermore, after reduction, this additive generates alkylated lithium sulfate (ROSO2Li) and lithium sulfite (Li2SO3), introducing sulfur (S) into the SEI film, improving its ionic conductivity and reducing the battery's DC internal resistance. Additionally, the unsaturated bonds in the unsaturated sulfite compound passivate the positive electrode surface, inhibiting the dissolution of transition metal ions and preventing direct contact and oxidative decomposition of the electrolyte with the positive electrode active material, thereby improving the stability of the lithium-ion battery under high-temperature conditions. The cyano group in the second additive can complex with transition metal ions on the positive electrode surface and also combine with HF, reducing the corrosion of the positive electrode surface by HF. Therefore, the second additive can effectively improve the stability of the positive electrode interface, thereby improving the high-temperature performance of the lithium-ion battery; the synergistic effect of the first and second additives ensures that the negative electrode SEI film has a low impedance and the positive electrode interface is stable, thus enabling the lithium-ion battery to have good high voltage stability and low-temperature performance.

[0030] The organic solvent is selected from carbonates and / or carboxylic esters, wherein the carbonate is selected from one or more of the following solvents, substituted or unsubstituted: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate; and the carboxylic ester is selected from one or more of the following solvents, substituted or unsubstituted: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate.

[0031] The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluorosulfonyl, lithium bis(trifluoromethylsulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide.

[0032] Preferably, the lithium salt content in the non-aqueous electrolyte is 9-20% by weight. The lithium salt concentration is controlled at around 1 mol / L, at which point the electrolyte conductivity is at a relatively high value. It can also be adjusted according to specific cost and usage requirements. 9-20% is a relatively wide range, basically covering the lithium salt concentration in common formulations.

[0033] According to a preferred embodiment of this application, the electrolyte comprises: ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), catechol cyclic sulfite, and lithium hexafluorophosphate. The electrolyte composition is EC:EMC+DEC = 20%-40%:60%-80% (total mass ratio 100%). In this preferred embodiment, lithium hexafluorophosphate has good dissociation ability, resulting in good conductivity of the electrolyte, and the viscosity of the electrolyte is also suitable.

[0034] According to a preferred embodiment of this application, the non-aqueous electrolyte further contains vinylene carbonate and / or fluoroethylene carbonate, wherein the vinylene carbonate and / or fluoroethylene carbonate account for 0.1%-20% of the total mass of the non-aqueous electrolyte, preferably 0.2-10%.

[0035] According to a preferred embodiment of this application, the non-aqueous electrolyte further contains 1,3-propanesulfonyl lactone, which accounts for 0.1%-5% of the total mass of the non-aqueous electrolyte, preferably 1-4%.

[0036] This application also provides a lithium-ion battery, including a positive electrode material, a negative electrode material, and the non-aqueous electrolyte as described above.

[0037] In one embodiment of this application, the positive electrode material includes lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, ternary materials, etc.; the negative electrode material includes soft carbon, hard carbon, carbon fiber, graphitized carbon microspheres, artificial graphite, natural graphite, silicon, silicon carbide, silicon-carbon composite materials, etc.

[0038] Particularly preferably, the electrolyte contains a first additive, a second additive, vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propane sulpholactone (PS); under this preferred condition, the battery can achieve better high voltage stability, as well as high temperature and low temperature performance.

[0039] The present application will be further illustrated below with comparative examples and embodiments, but the present application is not limited thereto.

[0040] Comparative Example 1

[0041] Preparation of the non-aqueous electrolyte: The non-aqueous electrolyte uses 13.5 wt% lithium hexafluorophosphate (LiPF6) as the lithium salt, and a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) as the non-aqueous organic solvent, mixed in a mass percentage of EC:EMC:DEC = 30:30:40. Adiponitrile (ADN) was added at a mass percentage of 3.0%.

[0042] Preparation of positive electrode sheet: The positive electrode active material LiCoO2, conductive agent CNT, and binder polyvinylidene fluoride (PVDF) are mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97.6:0.8:1.6 to prepare a positive electrode slurry. The slurry is coated on the current collector aluminum foil and dried at 85°C. After cold pressing, the slurry is then trimmed, cut into sheets, and slit. Finally, it is dried under vacuum at 85°C for 4 hours and the tabs are welded to form the positive electrode sheet.

[0043] Preparation of negative electrode sheet: The negative electrode active material graphite, conductive agent Super-P, thickener CMC, and binder SBR are mixed with deionized water at a mass ratio of 96.6:1.0:1.2:1.2 to prepare a negative electrode slurry. The slurry is coated on the current collector copper foil and dried at 85°C. After cold pressing, the slurry is trimmed, cut, and slit. It is then dried under vacuum at 110°C for 4 hours. The tabs are then welded to form the negative electrode sheet.

[0044] Preparation of lithium-ion batteries: A porous PE polymer film is used as the separator; the prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator between the positive and negative electrodes, and wound to obtain a bare cell; the bare cell is placed in an outer packaging, and the above-prepared non-aqueous electrolyte (the prepared electrolyte has a water content of less than 20 ppm and an acidity of less than 30 ppm) is injected into the dried bare cell, followed by encapsulation, standing, formation (0.02C constant current charging to 3.4V, then 0.1C constant current charging to 3.9V), shaping, and capacity testing to complete the preparation of a soft-pack lithium-ion battery (the soft-pack lithium-ion battery has a thickness of 4.3 mm, a width of 6.3 mm, and a length of 8.3 mm).

[0045] Comparative Examples 2-7

[0046] Comparative Examples 2 to 7 are used to illustrate the electrolyte, battery and preparation method disclosed in this application, including the operation steps of Comparative Example 1, the difference being that: electrolyte additives as shown in Comparative Examples 2 to 7 in Table I are used.

[0047] Examples 1-18

[0048] Examples 1-18 are used to compare and illustrate the electrolyte, battery and preparation method disclosed in this application, including the operation steps of Comparative Example 1, the difference being that the electrolyte additives shown in Examples 1-18 in Table I are used.

[0049] Table I. Additive composition and dosage of the non-aqueous electrolytes in Comparative Examples 1-7 and Examples 1-18

[0050]

[0051] Performance testing

[0052] The performance of the lithium-ion batteries prepared in Comparative Examples 1-7 and Examples 1-18 was tested.

[0053] Low-temperature discharge performance: The formed lithium-ion battery was charged at room temperature using a constant current and constant voltage of 0.7C to 4.40V, with a cutoff at 0.05C. Then, it was discharged at a constant current of 0.2C to 3.0V, repeated twice. The capacity of the second discharge was recorded as the initial capacity at room temperature. The lithium-ion battery was then charged at room temperature using a constant current and constant voltage of 0.7C to 4.40V, with a cutoff at 0.05C. The battery was then placed in a -20℃ constant temperature chamber for 4 hours, followed by a constant current discharge at 0.2C to 3.0V. The capacity retention rate of the lithium-ion battery was tested (discharge capacity at -20℃ / initial capacity at room temperature × 100%).

[0054] High-temperature storage performance: The formed lithium-ion battery was charged at room temperature using a constant current and constant voltage of 0.7C to 4.40V, cut off at 0.05C, and then discharged at a constant current of 0.2C to 3.0V. This cycle was repeated twice, and the capacity of the second discharge was recorded as the initial capacity at room temperature. The lithium-ion battery was then charged at room temperature using a constant current and constant voltage of 0.7C to 4.40V, cut off at 0.05C, and the thickness at full charge was recorded (tested using constant force PPG). The fully charged lithium-ion battery was stored in a 60℃ constant temperature chamber for 28 days, and the thickness expansion rate after 28 days of storage was recorded as ((28-day storage thickness - initial full charge thickness) / initial full charge thickness × 100%). The battery was then discharged at 0.5C to 3.0V, and the capacity retention rate of the lithium-ion battery was tested as (discharge capacity after 28 days of storage / initial capacity at room temperature × 100%).

[0055] High-temperature cycling performance: After formation, the lithium-ion battery was placed in a 45°C constant-temperature chamber for 2 hours, then charged at a constant current and constant voltage of 1.3C to 4.20V, with a cutoff at 0.7C; then charged at a constant current and constant voltage of 0.7C to 4.40V, with a cutoff at 0.05C. After resting for 5 minutes, it was discharged at a constant current of 0.7C to 3.0V. This constitutes one cycle. After 600 such cycles, the capacity retention rate of the lithium-ion battery was recorded.

[0056] The test results are shown in Table II:

[0057] Table II

[0058]

[0059]

[0060] As shown in Table II, when the content of the first additive is preferably 0.3%-2% and the content of the second additive is 2%-4%, the battery can achieve better high voltage stability, high temperature performance, and low temperature performance. When the electrolyte preferably contains the first additive, the second additive, vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propane sulpholactone (PS), the battery can achieve even better high voltage stability, high temperature performance, and low temperature performance.

[0061] The preferred embodiments of this application have been described in detail above. However, this application is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this application, various simple modifications can be made to the technical solution of this application, and these simple modifications all fall within the protection scope of this application.

[0062] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not describe the various possible combinations separately.

[0063] Furthermore, various different implementations of this application can be combined in any way, as long as they do not violate the spirit of this application, they should also be regarded as the content disclosed in this application.

Claims

1. A non-aqueous electrolyte, comprising an organic solvent, a lithium salt, and an additive, characterized in that: The additive contains a first additive and a second additive, wherein the first additive is a cyclic sulfite compound having the structure shown in formula (I), and the second additive is a cyano-substituted alkane and / or a cyanoalkoxy-substituted alkane. Equation (I): In formula (I): R9-R 12 Each of the following can be independently H, halogen, hydroxyl, cyano, sulfonyl, fluorosulfonyl, sulfonic acid, fluorosulfonic acid, 1-10 carbon atoms of saturated or unsaturated alkyl, 1-10 carbon atoms of saturated or unsaturated haloalkyl, 1-10 carbon atoms of alkoxy or 1-10 carbon atoms of fluoroalkoxy. Of which, by weight, the non-aqueous electrolyte contains, The content of the first additive is 0.01%-10%; the content of the second additive is 0.01%-10%.

2. The non-aqueous electrolyte according to claim 1, wherein, By weight, the non-aqueous electrolyte contains, The content of the first additive is 0.01%-3%; the content of the second additive is 1%-6%.

3. The non-aqueous electrolyte according to claim 2, wherein, By weight, the non-aqueous electrolyte contains, The content of the first additive is 0.3%-2%; the content of the second additive is 2%-4%.

4. The non-aqueous electrolyte according to claim 1, wherein, The first additive is selected from one or more of compounds 1-1 to 1-5: Compound 1-1, Compound 1-2, Compound 1-3 Compounds 1-4 and 1-5.

5. The non-aqueous electrolyte according to claim 1, wherein, The second additive is selected from one or more of acetonitrile, propionitrile, butyronitrile, succinic anhydride, glutaritrile, adiponitrile, heptanitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,2-bis(2-cyanoethoxy)propane, 1,2-bis(3-cyanopropoxy)ethane, 1,3,6-hexanetrionitrile, 1,2,3-propanetrionitrile, 1,3,5-pentanetrionitrile, 3,3-bis(cyanomethyl)glutaritrile, 3,3-bis(cyanomethyl)adiponitrile, and 1,2,3-tris(2-cyanoethoxy)propane.

6. The non-aqueous electrolyte according to any one of claims 1-5, wherein, The organic solvent is selected from carbonates and / or carboxylic esters, wherein the carbonate is selected from one or more of the following solvents, substituted or unsubstituted: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate; and the carboxylic ester is selected from one or more of the following solvents, substituted or unsubstituted: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate.

7. The non-aqueous electrolyte according to any one of claims 1-5, wherein, The lithium salt content in the non-aqueous electrolyte is 9-20% by weight.

8. The non-aqueous electrolyte according to claim 7, wherein, The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium trifluorosulfonyl, lithium bis(trifluoromethylsulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide.

9. The non-aqueous electrolyte according to any one of claims 1-5, wherein, The non-aqueous electrolyte also contains vinylene carbonate and / or fluoroethylene carbonate, wherein the vinylene carbonate and / or fluoroethylene carbonate account for 0.1%-20% of the total mass of the non-aqueous electrolyte.

10. The non-aqueous electrolyte according to any one of claims 1-5, wherein, The non-aqueous electrolyte also contains 1,3-propanesulfonyl lactone, which accounts for 0.1%-5% of the total mass of the non-aqueous electrolyte.

11. A lithium-ion battery, characterized in that, The electrolyte in the lithium-ion battery is the non-aqueous electrolyte according to any one of claims 1-10.

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