Non-aqueous electrolyte and high-voltage lithium ion battery

Abstract

The application discloses a nonaqueous electrolyte and a high-voltage lithium ion battery, wherein the nonaqueous electrolyte comprises a lithium salt, an organic solvent and an additive, the structure of the additive is shown in formula 1 or formula 2, and R1-R5 are each independently selected from a methyl group, a hydroxyl group, hydrogen, a halogen or a cyano group. The nonaqueous electrolyte can significantly improve the fast-charging capacity, high-temperature cycle performance and reduce the internal resistance of the high-voltage lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a non-aqueous electrolyte and a high-voltage lithium-ion battery. Background Technology

[0002] With the rapid development of the new energy industry, the market share of electric vehicles is gradually increasing. However, the two major considerations of battery range and charging time have greatly limited consumers' desire to buy pure electric vehicles. Therefore, achieving fast charging of lithium-ion batteries has become a technical problem that urgently needs to be solved for the commercialization of new energy vehicles.

[0003] To improve the fast-charging capability of lithium-ion batteries, it is necessary to control their kinetic performance. From the electrolyte perspective, during fast charging, the battery's internal resistance tends to rise sharply, leading to lithium plating due to poor kinetic performance. Simultaneously, the higher the charging cut-off voltage of the positive electrode material, the more highly oxidized active sites are on the positive electrode surface, resulting in more intense electrolyte oxidation and decomposition. This leads to increased cell impedance and decreased cycle performance at high temperatures. Therefore, developing lithium-ion battery electrolyte formulations that significantly improve the fast-charging performance, high-temperature cycle performance, and reduce the internal resistance of high-voltage lithium-ion batteries is currently a key focus.

[0004] Therefore, there is an urgent need for a non-aqueous electrolyte and high-voltage lithium-ion battery to address the shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a non-aqueous electrolyte that can significantly improve the fast charging capability, high-temperature cycle performance, and reduce the internal resistance of high-voltage lithium-ion batteries.

[0006] Another object of the present invention is to provide a lithium-ion battery that has excellent fast charging capability, high-temperature cycle performance and low internal resistance.

[0007] To achieve the above objectives, the present invention also provides a non-aqueous electrolyte, comprising a lithium salt, an organic solvent, and an additive, wherein the structure of the additive is shown in Formula 1 or Formula 2.

[0008] R1 to R5 are each independently selected from methyl, hydroxyl, hydrogen, halogen or cyano groups.

[0009] Compared to existing technologies, the additive of this invention contains dissociable lithium ions, which increases the concentration of lithium ions in the electrolyte, improves the electrolyte conductivity, and thus enhances the lithium ion transport speed, thereby improving fast-charging performance and reducing the overall internal resistance of the battery. Furthermore, the additive optimizes the cathode / electrolyte interface, reduces electrode surface activity, and inhibits electrolyte oxidative decomposition, allowing the electrolyte to maintain SEI stability during prolonged high-temperature cycling. Simultaneously, the amide structure further enables the additive to maintain a good interfacial SEI under high temperature and high voltage conditions, further improving interfacial stability and thus enhancing high-temperature cycling performance.

[0010] Preferably, the additive of the present invention is selected from at least one of compounds 1 to 6:

[0011] .

[0012] Preferably, the additive of the present invention has a mass percentage of 0.1-3% in the non-aqueous electrolyte. The specific additive content may be, but is not limited to, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, or 3%.

[0013] Preferably, the organic solvent of the present invention is selected from at least one of chain carbonates, cyclic carbonates, carboxylic acid esters, fluorocarbonates and fluorocarboxylic acid esters.

[0014] Preferably, the organic solvent of the present invention is selected from at least one of ethylene carbonate (EC), dimethyl carbonate, diethyl carbonate (DEC), methyl ethyl carbonate (EMC), propylene carbonate (PC), butyl acetate (BA), γ-butyrolactone, propyl propionate, ethyl propionate (EP), ethyl butyrate, ethyl fluorocarbonate, fluoroethylene carbonate, methyl fluoroacetate, propyl fluoropropionate, and tetrafluoroethyl tetrafluoropropyl ether.

[0015] Preferably, the lithium salt of the present invention is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate)borate (LiBOB), lithium difluorophosphate, lithium difluorooxalateborate, lithium difluorodioxalate phosphate, and lithium bis(fluorosulfonyl)imide.

[0016] Preferably, the non-aqueous electrolyte of the present invention further includes an additive selected from at least one of vinylene carbonate (VC), 1,3-propanesulfonic acid lactone (1,3-PS), succinate (SN), adiponitrile (ADN), fluoroethylene carbonate (FEC), maleic anhydride, 1-propylphosphonic anhydride, and triphenyl phosphite. The additive can further reduce battery impedance and improve the battery's high-temperature cycle performance and fast-charging performance. Specifically, the additive of the present invention has a mass percentage of 0.1% to 6% in the non-aqueous electrolyte, specifically, but not limited to, 0.1%, 0.5%, 1%, 1.2%, 1.8%, 2%, 2.5%, 2.8%, 3%, 3.5%, 4%, 4.4%, 5%, 5.2%, 5.5%, and 6%.

[0017] Preferably, the concentration of the lithium salt in this invention is 0.5~1.5M; specifically, it can be, but is not limited to, 0.5M, 0.8M, 1.0M, 1.2M, or 1.5M.

[0018] To achieve the above objectives, the present invention also provides a lithium-ion battery, including a positive electrode material, a negative electrode material, and the aforementioned non-aqueous electrolyte, and a maximum charging voltage of 4.5V.

[0019] Compared with existing technologies, the lithium-ion battery of the present invention includes an additive shown in Formula 1 or Formula 2. This additive contains dissociable lithium ions, which can increase the concentration of lithium ions in the electrolyte, improve the electrolyte conductivity, and thus improve the lithium-ion transport speed, thereby improving fast-charging performance and reducing the overall internal resistance of the battery. Furthermore, the additive can optimize the positive electrode / electrolyte interface, reduce the surface activity of the electrode, and thus inhibit the oxidative decomposition of the electrolyte, allowing the electrolyte to maintain SEI stability during long-term high-temperature cycling. Simultaneously, the amide structure further enables the additive to maintain a good interface SEI under high temperature and high voltage, further improving interface stability and thus improving high-temperature cycling performance. Therefore, the lithium-ion battery of the present invention has excellent fast-charging capability, high-temperature cycling performance, and low battery internal resistance.

[0020] Preferably, the cathode material of the present invention is a layered oxide or lithium cobalt oxide (LiCoO2), and the chemical formula of the layered oxide is LiNi. x Co y Mn z M (1-x-y-z) O2, wherein M is independently selected from at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, and Ti, 0 <x<1,0<y<1,0<z<1,x+y+z≤1。

[0021] Preferably, the negative electrode material of the present invention is selected from at least one of graphite, artificial graphite, hard carbon, natural graphite, silicon oxide, and silicon. Detailed Implementation

[0022] 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.

[0023] The sources of all raw materials used in this invention are not particularly limited; they can be purchased from the market or prepared using conventional methods well known to those skilled in the art. The purity of all raw materials used in this invention is not particularly limited; however, analytical grade or conventional purity levels common in the field of lithium-ion battery electrolytes are preferred.

[0024] Furthermore, compounds 1, 2, 3, and 6 of the present invention can be prepared by referring to the following route:

[0025] Example 1 (1) Preparation of non-aqueous electrolyte In an argon-filled glove box (O2 < 1 ppm, H2O < 1 ppm), ethylene carbonate (EC), butyl acetate (BA), and ethyl propionate (EP) were mixed in a weight ratio of EC: Ba: EP = 1:4:5 to prepare 86.5 g of non-aqueous organic solvent. Then, 1 g of compound 1 was added, dissolved, and stirred thoroughly. After that, 12.5 g of lithium hexafluorophosphate (LiPF6) was added and mixed evenly to obtain a non-aqueous electrolyte.

[0026] (2) Preparation of positive electrode sheet Lithium cobalt oxide, binder PVDF and conductive agent SuperP are mixed evenly at a mass ratio of 95:1:4 to prepare a lithium-ion battery positive electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of aluminum foil, dried and rolled to obtain the positive electrode sheet.

[0027] (3) Preparation of negative electrode sheet Artificial graphite, conductive agent SuperP, and binder PVDF are mixed in a mass ratio of 97:1:2 to form a slurry. The mixture is then coated on both sides of a copper foil, dried, and rolled to obtain the negative electrode sheet.

[0028] (4) Preparation of lithium-ion batteries The positive electrode, separator, and negative electrode are wound together to form a square soft-pack battery cell, which is then packaged with polymer and filled with the non-aqueous electrolyte for lithium-ion batteries prepared above. After formation, capacity testing, and other processes, a lithium-ion battery with a capacity of 2000mAh is produced.

[0029] The non-aqueous electrolyte formulations of Examples 1-11 and Comparative Example 1 are shown in Table 1. The steps for preparing the electrolyte, positive electrode, negative electrode and lithium-ion battery in Examples 2-11 are the same as in Example 1.

[0030] Table 1 Formulation of non-aqueous electrolyte

[0031] The lithium-ion batteries prepared in Examples 1-11 and Comparative Example 1 were subjected to high-temperature cycling tests, high-temperature cycling constant current charge ratio tests, and internal resistance tests. The specific test conditions are as follows, and the results are shown in Table 2.

[0032] High temperature cycling test The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 60 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 3C to a voltage of 4.5V, followed by constant voltage charging at 4.5V to a current of 0.05C, and finally discharged at a constant current of 1C to a voltage of 3V. This constitutes one charge-discharge cycle. The initial battery capacity C0 was recorded. Then, 300 cycles of 3C / 1C charge-discharge were performed at 45°C, and the discharge capacity C1 of the 300th cycle was recorded.

[0033] Capacity retention rate = C1 / C0 * 100% High-temperature cyclic constant current charge ratio test The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 60 minutes to allow it to reach a constant temperature. It was then charged at a 3C constant current until the voltage reached 4.5V, followed by a 1C constant current discharge until the voltage reached 3V. Next, it was charged at a 4.5V constant voltage until the current reached 0.05C, and then discharged at a 1C constant current until the voltage reached 3V. This constitutes one charge-discharge cycle. Then, 300 cycles of 3C / 1C charge-discharge were performed at 45°C. The capacity C0 during the constant current charging phase and the capacity C1 during the constant voltage phase were recorded during the 300th cycle.

[0034] Constant current injection ratio = C0 / (C0 + C1) * 100% Internal resistance test After capacity testing, the lithium-ion batteries were placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow them to reach a constant temperature. They were then charged at a constant current of 1C until the voltage reached 4.5V, followed by constant voltage charging at 4.5V until the current reached 0.05C. Next, they were discharged at a constant current of 1C until the voltage reached 3V. The first discharge capacity of the battery was recorded as C0. This constitutes one charge-discharge cycle. Then, at 25°C, the batteries were charged and discharged at 1C / 1C for three cycles. The batteries were discharged to 0.5C0, and the DC internal resistance R was measured.

[0035] Table 2. Performance test results of lithium-ion batteries

[0036] As shown in Table 2, the high-voltage lithium-ion batteries of all embodiments exhibit excellent fast-charging capability, high-temperature cycling performance, and low internal resistance. This indicates that the additive of the present invention contains dissociable lithium ions, which can increase the concentration of lithium ions in the electrolyte, improve the electrolyte conductivity, and thus enhance the lithium-ion transport speed, thereby improving fast-charging performance and reducing the overall internal resistance of the battery. Furthermore, the additive optimizes the cathode / electrolyte interface, reduces the surface activity of the electrode, and inhibits the oxidative decomposition of the electrolyte, allowing the electrolyte to maintain SEI stability during long-term high-temperature cycling. Simultaneously, the amide structure further enables the additive to maintain a good interfacial SEI under high temperature and high voltage, further improving interfacial stability and thus enhancing high-temperature cycling performance.

[0037] Comparing Example 1 with Examples 10-11, it can be seen that the non-aqueous electrolyte may also include additives. The introduction of additives can further improve the fast charging capability and high-temperature cycle performance of lithium-ion batteries, as well as further reduce the internal resistance of the battery.

[0038] 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, 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 non-aqueous electrolyte, comprising a lithium salt, an organic solvent, and additives, characterized in that, The structure of the additive is shown in Formula 1 or Formula 2. R1 to R5 are each independently selected from methyl, hydroxyl, hydrogen, halogen or cyano groups.

2. The non-aqueous electrolyte as described in claim 1, characterized in that, The additive is selected from at least one of compounds 1 to 6:

3. The non-aqueous electrolyte as described in claim 1, characterized in that, The additive constitutes 0.1% to 3% of the mass of the non-aqueous electrolyte.

4. The non-aqueous electrolyte as described in claim 1, characterized in that, The organic solvent is selected from at least one of chain carbonates, cyclic carbonates, carboxylic acid esters, fluorocarbonates, and fluorocarboxylic acid esters.

5. The non-aqueous electrolyte as described in claim 1, characterized in that, The organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, ethyl propionate, ethyl butyrate, ethyl fluoroacetate, fluoroethylene carbonate, methyl fluoroacetate, propyl fluoropropionate, and tetrafluoroethyl tetrafluoropropyl ether.

6. The non-aqueous electrolyte as described in claim 1, characterized in that, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate-borate), lithium difluorophosphate, lithium difluorooxalate-borate, lithium difluorodioxalate-phosphate, and lithium bis(oxalate-imide).

7. The non-aqueous electrolyte as described in claim 1, characterized in that, It also includes an additive selected from at least one of vinylene carbonate, 1,3-propanesulfonic acid lactone, succinate, adiponitrile, fluoroethylene carbonate, maleic anhydride, 1-propylphosphonic anhydride, and triphenyl phosphite.

8. The non-aqueous electrolyte as described in claim 1, characterized in that, The concentration of the lithium salt is 0.5–1.5 M.

9. A lithium-ion battery, comprising a positive electrode material and a negative electrode material, characterized in that, It also includes the non-aqueous electrolyte as described in any one of claims 1 to 8, and the maximum charging voltage is 4.5V.

10. The lithium-ion battery as described in claim 9, characterized in that, The cathode material is a layered oxide or lithium cobalt oxide, and the chemical formula of the layered oxide is LiNi. x Co y Mn z M (1-x-y-z) O2, wherein M is independently selected from at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, and Ti, 0 <x<1,0<y<1,0<z<1,x+y+z≤1。

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