The piperidinium ionic liquid is a compound containing piperidinium ions (Figure. 1). Typical anions are chloride, bromide, acetate, diethylphosphate, triflate, dicyanamide, tetrafluoroborate, hexafluorophosphate, and the very important bis(trifluoromethylsulfonyl)imide (= bistriflimide) ion. Piperidinium ionic liquids attract considerable interest due to their superior performance in terms of high ionic conductivity, wide electrochemical window, low volatility and low flammability. One of the most important applications of piperidinium ionic liquids is its application in electrolyte systems. Some ionic liquids contains 1-methyl-1-propyl piperidinium [MPPip]+, 1-methyl-1-butyl piperidinium [MBPip]+, and 1-methyl-1-octyl piperidinium [MOPip]+ cations，and these piperidinium ionic liquids provide a new alternative to pyridinium and imidazolium ionic liquids. The high thermal stability of ionic liquids increases the safety of applications such as rechargeable lithium-ion batteries and other electrochemical devices.
Figure 1. The structure of piperidinium ionic liquids
The ionic liquid based on piperidinium TFSI molten salt and amorphous silicon can be used as high capacity anode material for a rechargeable lithium battery. The Si-Li electrode exhibits a stable cyclic behavior in this system. The Si-Li electrode has a high capacity of 3000 mA h g-1, which is about an order of magnitude higher than the capacity of most commonly used graphite anodes. At the same time, these electrodes have good safety performance and are significantly better than Li metal anodes. The high anode stability of ionic liquid may allow the development of extremely high energy density systems based on Si-Li anodes and 5V cathodes, which will also have excellent safety characteristics.
Ionic liquids based on ether groups and piperidinium are also used in battery systems. Lithium plating and striping on the Ni electrode can be observed, and these ionic electrolytes also exhibit good chemical stability to lithium metal. Li / LiFePO4 cells using these additive-freeIonic liquid electrolytes have good capacity and cycle property at a current rate of 0.1C.
1. Baranchugov, V.; et al. (2007). “Amorphous silicon thin films as a high capacity anodes for Li-ion batteries in ionic liquid electrolytes.” Electrochemistry Communications 9(4), 796–800.
2. Salminen, J.; et al. (2007). “Physicochemical properties and toxicities of hydrophobic piperidinium and pyrrolidinium ionic liquids.” Fluid Phase Equilibria 261(1-2), 421–426.