Electrolyte additive composition, electrolyte and lithium ion battery

Abstract

The invention discloses an electrolyte additive composition, an electrolyte and a lithium ion battery, and relates to the technical field of lithium batteries. The electrolyte additive composition comprises an additive A as shown in a structural formula I and an additive B as shown in a structural formula II, the electrolyte comprises a lithium salt, an organic solvent, a conventional additive and the electrolyte additive composition disclosed by the invention, the lithium ion battery comprises a positive electrode, a negative electrode and the electrolyte added with the electrolyte additive composition disclosed by the invention. The additive A and the additive B in the electrolyte additive composition cooperate with each other, so that a layer of thin and stable interfacial film can be formed on the graphite surfaces of a high-nickel NCM positive electrode and a negative electrode, the direct contact between the electrode and the electrolyte at a high temperature is avoided, and the oxygenolysis reaction of the electrolyte is delayed; therefore, the capacity retention rate and the recovery rate of the battery in the high-temperature storage process are improved, meanwhile, by-products such as residual lithium compounds on the surfaces of the positive electrode and the negative electrode can be removed, and the ionic conductivity of an interfacial film is improved. # imgabs0 #

Description

Technical Field

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

[0002] Recently, lithium-ion batteries have become a new research hotspot and have received widespread attention. The electric vehicle field focuses on hybrid vehicles and mobile device power supplies, etc. This is due to its high energy density, environmental friendliness and economic benefits. It is well known that high temperature is an important factor affecting the performance, life and safety of lithium-ion batteries. Specifically, on the one hand, the aging of lithium-ion batteries is accelerated at high temperatures. On the other hand, the performance degradation of lithium-ion batteries is attributed to the poor thermal stability of lithium salts and organic solvents. In this case at high temperatures, the electrolyte will decompose and produce a large amount of gas, which can easily cause the battery to swell, thereby reducing its performance and safety. Therefore, it is urgent to develop an electrolyte that improves high temperature performance. Summary of the invention

[0003] To solve the above problems, the present invention provides an electrolyte additive composition and an electrolyte with improved high-temperature performance, which can form a thin and stable interface film on the surface of high-nickel positive and negative graphite, effectively isolating the electrodes from the electrolyte, and at the same time has the functions of removing water, reducing acid, and complexing, thereby greatly improving the conductivity of the interface film.

[0004] The electrolyte additive composition comprises an additive A as shown in structural formula I and an additive B as shown in structural formula II:

[0005]

[0006] R1 includes one of an alkoxy group, an amide group, and a halogen atom, and R2 is one of an alkenyl group or a halogen-substituted alkyl group.

[0007] Furthermore, R1 is selected from an alkyl group connected with an alkoxy group, an amide group substituted by an alkyl group, and a F atom; R2 is selected from a monoalkenyl group, and an alkyl group substituted by a F atom; wherein the number of carbon atoms of R1 and R2 are both integers between 0 and 8.

[0008] The additive A and the additive B in the electrolyte additive composition work synergistically, not only forming a thin and stable interface film on the surface of the high-nickel NCM positive electrode and negative electrode graphite, avoiding direct contact between the electrode and the electrolyte at high temperature, delaying the oxidative decomposition reaction of the electrolyte, thereby improving the capacity retention rate and recovery rate of the battery during high-temperature storage, but also removing by-products such as residual lithium compounds on the surface of the positive and negative electrodes, greatly improving the ionic conductivity of the interface film.

[0009] Further, the additive A is selected from at least one of compounds 1, 2, and 3, and the additive B is selected from at least one of compounds 4 and 5:

[0010]

[0011]

[0012] Compound 1, CAS: 118736-04-2, commercial source: Aladdin T161835;

[0013] Compound 2, CAS: 1337980-46-7, commercial source: Bidex Pharmaceuticals BD245939;

[0014] Compound 3, CAS: 113984-68-2, commercial source: Bidex Pharmaceuticals BD153099;

[0015] Compound 4, CAS: 16212-05-8, commercial source: Aladdin A475742;

[0016] Compound 5, CAS: 1535-65-5, commercial source: Aladdin D138285.

[0017] Furthermore, the electrolyte additive composition accounts for 0.1-3.0 wt % of the electrolyte by mass.

[0018] Furthermore, by mass, the electrolyte additive composition accounts for 0.5-3.0wt% of the electrolyte. As an example, it may be but not limited to 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.9wt%, 2.0wt%, 2.3wt%, 2.8wt%, and 3.0wt%.

[0019] Furthermore, the mass ratio of additive A to additive B is 1.0:0.2-5.0.

[0020] The present invention also provides an electrolyte comprising a lithium salt, an organic solvent and a conventional additive and the electrolyte additive composition.

[0021] The lithium salt is selected from at least one of a fluorinated lithium salt or a lithium oxalate salt;

[0022] The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium bis(fluorosulfonyl imide) salt or lithium bis(trifluoromethylsulfonyl imide).

[0023] Furthermore, the concentration of the lithium salt is 0.5-1.5 M, for example, but not limited to 0.50 M, 0.75 M, 1.00 M, 1.25 M, 1.50 M. The concentration of the lithium salt is limited to the above range, so that the battery can have both better electrochemical performance and room temperature cycle retention rate.

[0024] Furthermore, the organic solvent is selected from at least one of chain carbonate compounds, cyclic carbonate compounds or carboxylate compounds.

[0025] Further, the organic solvent is selected from at least one of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, propyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. The above additives are more compatible with this type of organic solvent, so that the battery can have both excellent electrochemical performance and capacity retention.

[0026] Furthermore, the conventional additive is selected from at least one of vinylene carbonate, vinyl sulfate, tris(trimethylsilyl)phosphite, diphenyl sulfone and methylene disulfonate.

[0027] Furthermore, the mass percentage of the conventional additive to the total mass of the lithium salt and the solvent is 0.1-2.0 wt %.

[0028] The present invention also provides a lithium ion battery, the lithium ion battery comprising a positive electrode, a negative electrode and a lithium ion battery electrolyte, wherein: the positive electrode is LiNi (1-x-y) Co x Mn y O2, 0≤x≤1, 0≤y≤1; the negative electrode is graphite; and the electrolyte is the aforementioned electrolyte.

[0029] Furthermore, in a preferred embodiment, the charging voltage of the lithium-ion battery is not higher than 4.8V, preferably 2.80-4.25V. DETAILED DESCRIPTION

[0030] Embodiment 1:

[0031] 1. Preparation of electrolyte:

[0032] Ethylene carbonate (EC), ethyl propionate (EP) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:EP:EMC=1:1:2, and after mixing, 0.7 mol of lithium hexafluorophosphate (LiPF6) and 0.3 mol of lithium bis(fluorosulfonyl)imide (LiFSI) are added. After the lithium salt is completely dissolved, 1 wt.% of compound 1 and 1% of compound 4, 0.5% of vinylene carbonate (VC) and 0.5% of vinyl sulfate (DTD) are added.

[0033] 2. Preparation of positive electrode:

[0034] The nickel-cobalt-lithium-manganese oxide ternary material LiNi 0.7 Co 0.1 Mn 0.2 O2, conductive agent Super P, adhesive PVDF and carbon nanotubes (CNT) are mixed evenly in a mass ratio of 97.5:0.5:1:1 to form a lithium-ion battery positive electrode slurry with a certain viscosity, which is coated on the aluminum foil for current collector. The coating amount is 360g / m 2 , dried at 85°C and then cold pressed; then striped and sliced, and then baked at 85°C in vacuum for 4 hours to make a lithium-ion battery positive electrode that meets the requirements.

[0035] 3. Preparation of negative electrode sheet:

[0036] Artificial graphite, conductive agent Super P, thickener CMC, and adhesive SBR (styrene-butadiene rubber latex) are mixed in a mass ratio of 95:1.5:1.0:2.5 to make a slurry, mix them evenly, apply the mixed slurry on both sides of the copper foil, dry and roll to obtain the negative electrode sheet, and then bake it at 85°C in vacuum for 4 hours to make a lithium-ion battery negative electrode sheet that meets the requirements.

[0037] 4. Preparation of lithium-ion batteries:

[0038] The positive electrode sheet, negative electrode sheet and separator prepared according to the above process are made into a lithium-ion battery with a thickness of 0.5 mm, a width of 8 mm, a length of 10 mm and a capacity of 3 Ah through a lamination process. They are vacuum-baked at 85°C for 48 hours, and the above electrolyte is injected to complete the battery production.

[0039] The electrolyte additives and their respective addition amounts in Examples 2-11 and Comparative Examples 1-6 are shown in Table 1. The preparation methods of the electrolyte, the positive electrode sheet, the negative electrode sheet, and the lithium-ion battery refer to Example 1.

[0040] Experimental Example 1

[0041] The 3Ah soft-pack lithium-ion batteries prepared in Examples 1 to 11 and Comparative Examples 1 to 6 were respectively subjected to the following tests, and the experimental results are shown in Table 1:

[0042] (1) Cycle performance test: Under the test condition of 45° C., the batteries in Examples 1 to 11 and Comparative Examples 1 to 6 were subjected to charge and discharge cycle performance tests at a charge and discharge rate of 1C, and the charge and discharge voltage range was set to 2.8 to 4.5 V;

[0043] (2) High temperature shelf test: The experimental battery was charged and discharged at a rate of 0.33C for 3 weeks at room temperature, and the average discharge capacity was taken as C1. It was then charged to 100% SOC, shelf at 60°C for 7 days, shelf at room temperature for 6 hours, discharged at a rate of 0.33C, and the discharge capacity was taken as C2. It was then charged and discharged for another 3 weeks, and the average discharge capacity was taken as C3. C2 divided by C1 is the capacity retention rate, and C3 divided by C1 is the capacity recovery rate.

[0044] The introduction of the combined additives of the present invention improves the ionic conductivity of the interface film by making the positive and negative electrode films more dense and stable, reducing the interface impedance of the positive and negative electrodes, and removing by-products on the surfaces of the positive and negative electrodes, thereby greatly improving the high temperature performance of the battery.

[0045] Table 1 Electrolyte composition and battery performance of Examples 1-11 and Comparative Examples 1-6

Claims

1. An electrolyte additive composition, characterized in that: The composition comprises an additive A as shown in structural formula I and an additive B as shown in structural formula II: Wherein, R1 is one of an alkoxy group, a substituted alkoxy group, an amide group, a substituted amide group and a halogen atom; R2 is one of an alkenyl group and a halogen-substituted alkyl group.

2. The electrolyte additive composition according to claim 1, characterized in that , wherein R1 is one of an alkyl-substituted alkoxy group, an alkyl-substituted amide group and a F atom; R2 is one of a monoalkenyl group and a F atom-substituted alkyl group; wherein the carbon number of R1 and R2 are both integers between 0 and 8.

3. The electrolyte additive composition according to claim 1 or 2, characterized in that: The additive A is selected from one of compound 1, compound 2 and compound 3:

4. The electrolyte additive composition according to claim 1 or 2, characterized in that: The additive B is selected from at least one of compound 4 and compound 5:

5. The electrolyte additive composition according to claim 1 or 2, characterized in that: The mass ratio of the additive A to the additive B is 1.0:0.2-5.

0.

6. An electrolyte, characterized in that: An electrolyte additive composition comprising the electrolyte additive composition according to any one of claims 1 to 5.

7. The electrolyte according to claim 6, characterized in that The composition accounts for 0.1-3.0 wt% of the total amount of the electrolyte.

8. The electrolyte according to claim 6 or 7, characterized in that The electrolyte further comprises a lithium salt, an organic solvent and conventional additives.

9. The electrolyte according to claim 8, characterized in that The lithium salt is selected from at least one of a fluorinated lithium salt and a lithium oxalate salt.

10. The electrolyte according to claim 9, characterized in that The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorooxalatophosphate, lithium bis(fluorosulfonyl imide) salt and lithium bis(trifluoromethylsulfonyl imide).

11. The electrolyte according to claim 8, characterized in that The concentration of the lithium salt is 0.5-1.5M.

12. The electrolyte according to claim 8, characterized in that The conventional additive is selected from at least one of vinylene carbonate, vinyl sulfate, tris(trimethylsilyl)phosphite, diphenyl sulfone and methylene disulfonate.

13. The electrolyte according to claim 8, characterized in that The organic solvent is selected from at least one of chain carbonate compounds, cyclic carbonate compounds and carboxylate compounds.

14. The electrolyte according to claim 13, characterized in that The organic solvent is selected from at least one of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, propyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate and ethyl butyrate.

15. A lithium ion battery comprising a positive electrode and a negative electrode, characterized in that: It also comprises the electrolyte additive composition according to any one of claims 1 to 5 or the electrolyte according to any one of claims 6 to 14.

16. The lithium ion battery according to claim 15, characterized in that: The charging voltage of the battery is no higher than 4.8V.

17. The lithium ion battery according to claim 15 or 16, characterized in that: The positive electrode includes a positive electrode material LiNi (1-x-y) Co x Mn y O2, where 0≤x≤1, 0≤y≤1, x+y<1.

18. The lithium ion battery according to claim 15 or 16, characterized in that: The negative electrode is graphite.

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