A high-nickel ternary lithium-ion battery electrolyte and lithium-ion battery

Abstract

The invention discloses an electrolyte for a high-nickel ternary lithium-ion battery and a lithium-ion battery, comprising an organic solvent, a lithium salt and an additive, wherein the additive comprises a film-forming additive and a water-removing and acid-inhibiting additive, wherein the film-forming additive can preferentially form a dense and uniform phosphorus-rich CEI film on the surface of a positive electrode to inhibit oxidative decomposition of the electrolyte, and the added water-removing and acid-inhibiting additive can effectively reduce the generation of HF in the electrolyte, inhibit the dissolution of transition metal ions, and thus improve the cycle and high-temperature storage performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery electrolytes, and in particular to an electrolyte for a high-nickel ternary lithium ion battery and a lithium ion battery. Background Art

[0002] As the demand for power batteries continues to increase, the requirements for battery energy density are also getting higher and higher. Ternary materials are gradually developing from low nickel to high nickel to improve the energy density of batteries while also reducing the cost of batteries. Therefore, high nickel ternary materials have gradually become the key research direction of lithium-ion batteries.

[0003] The capacity of high-nickel ternary materials increases with the increase of nickel content, but the surface stability of high-nickel materials will also decrease with the increase of nickel content. Since the tetravalent nickel ions in high nickel have high catalytic activity, they will catalyze the oxidation and decomposition of the electrolyte, affecting the battery life. In addition, the surface residual alkali content will increase with the increase of nickel content. The surface residual alkali will promote the decomposition of the electrolyte and produce more HF. HF can corrode high-nickel materials and accelerate the dissolution of transition metal ions, which will reduce the material capacity and lead to reduced cycle performance and storage performance of high-nickel ternary materials. Summary of the invention

[0004] The purpose of the present invention is to provide an electrolyte for a high-nickel ternary lithium-ion battery and a lithium-ion battery, wherein the electrolyte can solve the problems of circulation and high-temperature storage performance of commercial high-nickel ternary positive electrode lithium-ion batteries.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] An electrolyte for a high-nickel ternary lithium-ion battery, comprising an organic solvent, a lithium salt and an additive, wherein the additive comprises a film-forming additive and a water-removing and acid-suppressing additive, and the film-forming additive is at least one of the compounds shown in structural formula 1:

[0007]

[0008] Wherein, R1, R2, R3, R4 and R5 are each independently selected from hydrogen, a saturated hydrocarbon group having 1 to 4 carbon atoms or an unsaturated hydrocarbon group having 1 to 4 carbon atoms.

[0009] A further technical solution is that the film-forming additive accounts for 0.1 to 3% of the total mass of the electrolyte.

[0010] A further technical solution is that the water-removing and acid-inhibiting additive is selected from one or more of 2,2,2-trifluoroethyl butyrate, 4,4,4-trifluoroethyl butyrate, N,N-tetraethylsulfonamide, and 2-thiophenesulfonamide.

[0011] A further technical solution is that the water-removing and acid-inhibiting additive accounts for 0.01% to 2% of the total mass of the electrolyte.

[0012] A further technical solution is that the lithium salt is a lithium salt system composed of two lithium salts, lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide, and the lithium salt system accounts for 10% to 18% of the total mass of the electrolyte.

[0013] A further technical solution is that the molar concentration of the lithium salt system in the electrolyte is 0.9-1.4 mol / L, wherein the lithium bis(trifluoromethylsulfonyl)imide accounts for 0.5%-5% of the total lithium salt.

[0014] A further technical solution is that the solvent system is selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate.

[0015] A further technical solution is that the solvent system accounts for 75-90% of the total mass of the electrolyte.

[0016] The present invention also provides a lithium ion battery, wherein the electrolyte of the lithium ion battery is the electrolyte for the high-nickel ternary lithium ion battery.

[0017] Compared with the prior art, the present invention has the following beneficial effects: the film-forming additive used in the present invention has a higher HOMO (highest electron occupied orbital) energy level through the first calculation principle, is easy to lose electrons, and can preferentially form a dense and stable CEI film on the positive electrode surface. 4+ The CEI film formed with strong oxidizing property can effectively inhibit the oxidative decomposition of electrolyte on the positive electrode surface, improve the battery's cycle and high-temperature storage performance. In addition, the residual alkali content on the surface of high-nickel ternary materials is relatively high. The surface residual alkali reacts with lithium hexafluorophosphate to generate HF, which can corrode the positive electrode so that metal ions on the positive electrode side are dissolved, resulting in structural damage. At the same time, by adding water-removing and acid-inhibiting additives, the generation of HF in the electrolyte can be effectively inhibited, the dissolution of transition metal ions can be inhibited, and the battery's cycle and high-temperature storage performance can be improved. The lithium salt is composed of lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide. Lithium bis(trifluoromethylsulfonyl)imide can form a fluorine-rich CEI film on the positive electrode surface, reduce the impedance of the high-nickel ternary positive electrode, and improve the cycle life of the lithium-ion battery. DETAILED DESCRIPTION

[0018] In order to make the technical problems, technical solutions and advantages solved by the present invention clearer, the present invention is described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] Example 1

[0020] Preparation steps of electrolyte: An electrolyte for high nickel ternary lithium ion battery, including organic solvent, lithium salt, film-forming additive and water-removing and acid-inhibiting additive. The specific steps of preparing the electrolyte in a glove box filled with argon are as follows: 1. Prepare a mixed solvent, the organic solvent includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), diethyl carbonate (DEC) and dimethyl carbonate (DMC), and mix the solvents in a mass ratio of EC: PC: DEC = 2.5: 0.5: 7; 2. Add lithium salt to the mixed solvent, the lithium salt includes lithium hexafluorophosphate and lithium bistrifluoromethylsulfonyl imide, add lithium hexafluorophosphate (LiPF6) to a molar concentration of 1.0 mol / L, and then add lithium bistrifluoromethylsulfonyl imide to account for 0.5% of the total lithium salt molar ratio, and fully dissolve; 3. Add 0.5% of the film-forming additive structure 1 and 0.5% of 2,2,2-trifluoroethyl butyrate to remove water and acid-inhibiting additive.

[0021]

[0022] Example 2

[0023] Example 1 was repeated, except that the mass ratio of the organic solvent was EC:PC:EMC=2.5:0.5:7, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1.0 mol / L, the added lithium bis(trifluoromethylsulfonyl)imide accounted for 1.0% of the total lithium salt molar ratio, the film-forming additive structural formula 1 accounted for 1% of the total mass of the electrolyte, and the water-removing and acid-inhibiting additive 4,4,4-trifluorobutyric acid ethyl ester accounted for 1.0% of the total mass of the electrolyte.

[0024]

[0025] Example 3

[0026] Example 1 was repeated, except that the mass ratio of the organic solvents was EC:PC:EMC:DEC=2:1:3.5:3.5, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1.1 mol / L, the added lithium bis(trifluoromethylsulfonyl)imide accounted for 2.0% of the total lithium salt molar ratio, the film-forming additive structural formula 2 accounted for 2% of the total mass of the electrolyte, and the water-removing and acid-suppressing additive N,N-tetraethylsulfonamide accounted for 2% of the total mass of the electrolyte.

[0027]

[0028] Example 4

[0029] Example 1 was repeated, except that the mass ratio of the organic solvent was EC:PC:DMC=2.5:0.5:7, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1.2 mol / L, the added lithium bis(trifluoromethylsulfonyl)imide accounted for 1.5% of the total lithium salt molar ratio, the film-forming additive structural formula 2 accounted for 1.0% of the total mass of the electrolyte, and the water-removing and acid-inhibiting additive 2,2,2-trifluoroethyl butyrate accounted for 0.01% of the total mass of the electrolyte.

[0030]

[0031] Example 5

[0032] Example 1 was repeated, except that the mass ratio of the organic solvent was EC:EMC:DEC=3:4:4, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 0.9 mol / L, the added lithium bis(trifluoromethylsulfonyl)imide accounted for 5.0% of the total lithium salt molar ratio, the film-forming additive structural formula 3 accounted for 2% of the total mass of the electrolyte, and the water-removing and acid-inhibiting additive 2-thiophenesulfonamide accounted for 0.01% of the total mass of the electrolyte.

[0033]

[0034] Example 6

[0035] Example 1 was repeated, except that the mass ratio of the organic solvent was EC:EMC:DMC=3:4:4, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1.0 mol / L, the added lithium bis(trifluoromethylsulfonyl)imide accounted for 1.5% of the total lithium salt molar ratio, the film-forming additive structural formula 3 accounted for 3.0% of the total mass of the electrolyte, and the water-removing and acid-suppressing N,N-tetraethylsulfonamide additive accounted for 1.5% of the total mass of the electrolyte.

[0036]

[0037] Example 7

[0038] Example 1 was repeated, except that the mass ratio of the organic solvent was EC:DEC=2:8, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1.05 mol / L, the added lithium bis(trifluoromethylsulfonyl)imide accounted for 1.0% of the total lithium salt molar ratio, the film-forming additive structural formula 4 accounted for 1.0% of the total mass of the electrolyte, and the water-removing and acid-inhibiting additives included 0.5% of 2,2,2-trifluoroethyl butyrate and 0.5% of N,N-tetraethylsulfonamide.

[0039]

[0040] Example 8

[0041] Example 1 was repeated, except that the mass ratio of the organic solvent was EC:DEC=3.5:6.5, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1.0 mol / L, the added lithium bis(trifluoromethylsulfonyl)imide accounted for 2.0% of the total lithium salt molar ratio, the film-forming additive structural formula 4 accounted for 0.1% of the total mass of the electrolyte, and the water-removing and acid-inhibiting additives included 1.0% of ethyl 4,4,4-trifluorobutyrate and 1.0% of 2-thiophenesulfonamide.

[0042]

[0043] Comparative Example 1

[0044] The comparative example is an embodiment in publication number CN109687023A (Chinese patent), and the specific steps are as follows: electrolyte for high-nickel ternary positive electrode material system battery and lithium-ion battery, the preparation process of the electrolyte: in a glove box filled with argon, the mixed solvent mass ratio is configured according to FEC:DEC:EMC=3:2:5, and after mixing evenly, LiPF6 is added to a molar concentration of 1.0 mol / L, and the mixture is fully stirred and mixed, and 0.5% triphenylborate (TPB) and 1.0% 5-nitrile-1,3-benzodithiol (BSN) are added and mixed evenly.

[0045] The above embodiments and comparative examples are all tested using a lithium-ion battery with a positive electrode of LiNi0.85Co0.1Mn0.5, a negative electrode of artificial graphite, a nominal capacity of 3Ah, and a battery injection volume of 10g.

[0046] The battery performance tests were carried out on the above-mentioned embodiments and comparative examples, and the normal temperature cycle performance and high temperature storage performance were tested respectively. The battery cells after capacity conversion were tested for the following electrical properties:

[0047] Room temperature cycle performance test: At 25°C, charge to 4.2V at 1C constant current and constant voltage, with a current less than 0.03A. After leaving for 5 minutes, discharge to 3.0V at 1C constant current. Follow this step for 400 cycles, and record the first cycle 1C discharge capacity C1 and the 400th cycle discharge capacity C2 step by step. The room temperature capacity retention rate is calculated as C2 / C1*100%.

[0048] High temperature storage performance test: At 25°C, first charge and discharge once at 0.5C and record the battery discharge capacity C3, then charge to 4.2V at 0.5C constant current and constant voltage, put the battery into a 60°C high temperature oven, store at high temperature for 7 days and then take it out, after the battery returns to room temperature, discharge to 3.0V at 0.5C constant current and record the battery discharge capacity C4, then charge and discharge the battery once at 0.5C and record the battery discharge capacity C5, the capacity retention rate at 60°C / 7d = C4 / C3*100%, the capacity recovery rate at 60°C / 7d = C5 / C3*100%

[0049] The test results of the capacity retention rate after 400 cycles at room temperature and the capacity retention rate and capacity recovery rate at 60°C / 7d for the above embodiments and comparative examples are shown in Table 1.

[0050] Table 1 Test results of embodiments and comparative examples

[0051]

[0052]

[0053] According to the data of the embodiment and the comparative example in Table 1, the embodiment of the present invention has higher room temperature cycle performance and high temperature storage performance than the comparative example. Therefore, the high nickel ternary lithium ion battery electrolyte in the present invention can significantly improve the room temperature cycle performance of the high nickel ternary lithium ion battery, and at the same time has good high temperature storage performance.

[0054] Although the present invention is described herein with reference to the illustrative embodiments of the present invention, the above embodiments are only preferred embodiments of the present invention, and the embodiments of the present invention are not limited to the above embodiments. It should be understood that those skilled in the art can design many other modifications and embodiments, which will fall within the scope and spirit of the principles disclosed in this application.

Claims

1. An electrolyte for a high-nickel ternary lithium-ion battery, comprising an organic solvent, a lithium salt and an additive, characterized in that: The additives include film-forming additives and water-removing and acid-inhibiting additives, wherein the water-removing and acid-inhibiting additives are selected from one or more of 2,2,2-trifluoroethyl butyrate, 4,4,4-trifluoroethyl butyrate, N,N-tetraethylsulfonamide, and 2-thiophenesulfonamide; and the film-forming additive is at least one of the compounds shown in structural formula 1: Wherein, R1, R2, R3, R4 and R5 are each independently selected from hydrogen, a saturated hydrocarbon group having 1 to 4 carbon atoms or an unsaturated hydrocarbon group having 1 to 4 carbon atoms.

2. The high nickel ternary lithium ion battery electrolyte according to claim 1, characterized in that: The film-forming additive accounts for 0.1 to 3% of the total mass of the electrolyte.

3. The electrolyte for high nickel ternary lithium ion battery according to claim 1, characterized in that: The water-removing and acid-suppressing additive accounts for 0.01% to 2% of the total mass of the electrolyte.

4. The electrolyte for high-nickel ternary lithium-ion battery according to claim 1, characterized in that: The lithium salt is a lithium salt system composed of two lithium salts, lithium hexafluorophosphate and lithium bis(trifluoromethylsulfonyl)imide, and the lithium salt system accounts for 10% to 18% of the total mass of the electrolyte.

5. The electrolyte for high-nickel ternary lithium-ion battery according to claim 4, characterized in that: The molar concentration of the lithium salt system in the electrolyte is 0.9-1.4 mol / L, wherein the lithium bis(trifluoromethylsulfonyl)imide accounts for 0.5%-5% of the total molar number of lithium salt.

6. The electrolyte for high nickel ternary lithium ion battery according to claim 1, characterized in that: The solvent system is selected from one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate.

7. The electrolyte for high-nickel ternary lithium-ion battery according to claim 6, characterized in that: The solvent system accounts for 75-90% of the total mass of the electrolyte.

8. A lithium ion battery, characterized in that: The electrolyte of the lithium-ion battery is the electrolyte for a high-nickel ternary lithium-ion battery as described in any one of claims 1 to 7.

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