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Research on New Type of High Pressure Electrolyte
2019-06-06
来源：亚科官网
Lithium battery has the advantages of long service life, high energy density, stable charge and discharge performance, etc. It has been widely used in everyday electronic products, and is also one of the main candidate power sources for many large mobile devices. Traditional carbonate electrolytes will continue to oxidize and decompose under high pressure conditions, which seriously restricts the development of high-voltage lithium batteries. Therefore, it is necessary to design, synthesize and screen new high-pressure electrolytes in combination with factors such as green, safety and economic benefits.
Traditional carbonate electrolyte
The conventional carbonate-based electrolyte is mainly composed of a carbonate-based organic solvent and a lithium salt (LiPF6, LiBF4, LiTFSI (diafluorotrimethanesulfonate), etc.) in a certain ratio. The electrolyte is stable in a wide temperature range, has a high electrical conductivity, (typically 3.0mS/cm), a high dielectric constant and a strong lithium salt solubility, and is 4.5V. It can be stable inside. Such a carbonate electrolyte has been widely used in the field of batteries, but when the voltage is higher than 4.5 V, the electrolyte is continuously oxidatively decomposed on the surface of the cathode, which seriously degrades the cycle stability of the battery.
New carbonate high pressure electrolyte
At present, it is mainly to improve the high-pressure performance of carbonate electrolyte from two aspects: one is improved carbonate, which improves the stability by changing the structure of carbonate; the other is to add other compounds to the carbonate electrolyte to optimize the electrolyte performance.
Improved
——Fluorocarbonate: Polyfluoroalkyl carbonate has the characteristics of strong chemical stability, hydrophobicity and oleophobicity, and can form a double-layer passivation film on the surface of the electrode to reduce the degradation of the electrode surface and the decomposition of the electrolyte. Moreover, the longer the carbon chain of the perfluorocarbon substituent, the stronger the nucleophilic ability, and the easier it is to form a passivation film on the surface of the electrode, but the intermolecular force is correspondingly increased, resulting in an increase in viscosity and a decrease in electrical conductivity.
Mixed mode
——Phosphorus-containing carbonate: Add appropriate amount of additives such as tris(2,2,2-trifluoroethyl)phosphite (TTFP) to the carbonate: a stable CEI passivation film can be formed on the cathode surface; TTFP center The phosphorus (III) atom has a pair of orphaned electrons, which can coordinate with PF6- in the electrolyte containing LiPF6 to form a stable lithium salt complex; the phosphorus (III) atom is not in the highest valence state and is easily oxidized. The soluble phosphate compound effectively inhibits the oxidative decomposition of the carbonate and further improves the cycle performance of the battery.
——Boron-containing carbonates: Boron-containing compounds can form stable CEI films on different cathode surfaces, which can improve the stability of other electrolytes on the electrode surface.
The new carbonate electrolyte can effectively improve the high pressure stability of the electrolyte, but how to improve the ignition point of the carbonate electrolyte, reduce the volatility, and further improve the safety performance of the battery, still need researchers to continue efforts.
Nitrile high pressure electrolyte
The aprotic aliphatic dinitrile compound NC-(CH)n-CN (n=3~8) has high pressure and safety characteristics as an electrolyte, and exhibits good electrochemical stability at a voltage of 7 to 8 V. High flash point and flash point. The addition of EC or DMC to the nitrile solvent can significantly improve the compatibility of the nitrile electrolyte with the graphite electrode and improve the solubility of the lithium salt. In addition, 1,3,6-hexane tricarbonitrile has great advantages in high voltage lithium battery electrolyte applications due to its good high temperature storage and cycle performance. However, how to reduce the toxicity and production cost of the nitrile solvent is still an urgent problem to be solved in the battery application.
Sulfone high pressure electrolyte
The sulfone organic compound has a dielectric constant of 40 or more and is in a stable state at a voltage of 5.5 V or less. For example, sulfolane (SL) is a common solvent with high dielectric constant, wide electrochemical window, and strong polarity. However, sulfone organic compounds have high viscosity, high melting point, and poor compatibility with graphite anode materials. It is often necessary to add an additive to lower the viscosity and increase the conductivity of the electrolyte. Therefore, improving the safety performance of sulfone electrolytes and reducing the viscosity of sulfones is still a research direction.
Ionic liquid high pressure electrolyte
Ionic liquids (ILs) are room temperature molten salts composed of anions and cations with high flash point, high ignition point, low volatility, high dielectric constant and wide electrochemical stability window. At present, the anion is determined to be TFSI-, which is easily reduced to an insoluble Li+ compound at a low potential, and forms a passivation film on the surface of the lithium and graphite anode. The pyrrole and piperidine electrolytes have good cycle stability at 2.5-4.8V, but the conductivity is relatively low and the resistance is high. The imidazole electrolyte has high conductivity, but its cycle stability is poor. Further improvements.
Star products of Yacoo
1,3,6-Hexanetrinitrile
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1,3,6-Hexanetrinitrile is superior in performance to other nitrile additives (adiponitrile, succinonitrile). It has good storage and circulation performance in high voltage electrolyte.
Suzhou Yacoo initiated a new process, completed the research and development of high-purity hexanetrinitrile, and obtained the national invention patent authorization (CN104387291B).
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Related links: 1,3,6-hexanetrinitrile
This article is edited by Suzhou Yake Technology Co., Ltd.
