We investigated the influence of the anions in ionic liquid electrolytes on the electrochemical performance of a silicon (Si) negative electrode for a lithium-ion battery. While the electrode exhibited poor cycle stability in tetrafluoroborate-based and propylene carbonate-based electrolytes, better cycle performance was achieved in bis(fluorosulfonyl)amide (FSA -)-and bis(trifluoromethanesulfonyl)amide (TFSA -)-based electrolytes, in which the discharge capacity of a Si electrode was more than 1000 mA h g -1 at the 100th cycle. It is considered that a surface film derived from FSA --and TFSA --based electrolytes effectively suppressed continuous decomposition of the electrolyte. In a capacity limitation test, a discharge capacity of 1000 mA h g -1 was maintained even after about the 1600th cycle in the FSA --based electrolyte, which corresponds to a cycle life almost twice as long as that in TFSA --based electrolyte. This result should be explained by the high structural stability of FSA --derived surface film. In addition, better rate capability with a discharge capacity of 700 mA h g -1 was obtained at a high current rate of 6 C (21 A g -1 ) in FSA --based electrolyte, which was 7-fold higher than that in TFSA --based electrolyte. These results clarified that FSA --based ionic liquid electrolyte is the most promising candidate for Si-based negative electrodes.

Ionic liquids consisted of 1-((2-methoxyethoxy)methyl)-1-methylpiperidinium (PP1MEM) or 1-hexyl-1-methylpiperidinium (PP16) and bis(trifluoromethanesulfonyl)amide (TFSA) were applied to an electrolyte for Li-ion battery. The effect of their cation structure on anode properties of Si electrodes were investigated through the use of thick film prepared by gas-deposition without any binder and conductive additive. The Si electrode in PP1MEM-TFSA exhibited an initial reversible capacity of 2670 mA h g −1 , which is larger than that in PP16-TFSA by ca. 900 mA h g −1 . Moreover, a comparatively high capacity of 1150 mA h g −1 at a high current density of 4200 mA g −1 is achieved in PP1MEM-TFSA whereas the Si electrode in PP16-TFSA showed the capacity of only 210 mA h g −1 . Raman analysis and electrochemical impedance measurements revealed that PP1MEM cation played a role reducing the interaction between Li ion and TFSA anions, and that Li-ion transfer at the electrode−electrolyte interface in PP1MEM-TFSA was remarkably improved compared with PP16-TFSA. These results indicate that the excellent performances obtained in PP1MEM-TFSA originate from a smooth Li-insertion into Si electrode. It was suggested that introduction of ether functional group into cation is valid to enhance the electrode performance.Li-ion battery (LIB) has been utilized in large-scale battery systems such as power supply of electric vehicles in recent years. Unfortunately, the conventional LIB using graphite anode has insufficient energy density to satisfy the growing demand. Silicon is one of promising candidates of anode materials for next-generation LIB due to its huge theoretical capacity compared with that of graphite practically used. Si and Li form several Li-rich binary alloy phases such as Li 15 Si 4 at room temperature and Li 22 Si 5 at a high temperature of 415 • C, which offers extremely high theoretical capacities of 3580 and 4200 mA h g −1 , respectively. 1-3 The volume of Si is, however, significantly changed during alloying/dealloying reactions. The volumetric change ratios per Si atom from Si to Li 15 Si 4 and Li 22 Si 5 correspond to 380% and 410%, which results in a generation of high stress and large strain in the active material. The strain accumulated by repeating charge−discharge cycle causes a disintegration of Si electrodes, leading to a rapid capacity fading and a poor cycle stability. In addition, Si has disadvantages of a low electrical conductivity and a low diffusion coefficient of Li + in it (D Li+ , 10 −14 to 10 −12 cm 2 s −1 ). 4-6 For these reasons, a practical application of Si electrodes has been hindered. To overcome these problems, considerable attempts have been carried out. Many researchers have studied composite materials consisted of carbon, with mechanically soft property and good electrical conductivity, and pure Si. 7-10 We have recently demonstrated that composite electrodes prepared by using LaSi 2 /Si and Ni−P/Si exhibit a high anode performance because LaSi 2 and Ni−P effectively compensate for silico...

A simple microreactor system has been utilized for the continuous flow synthesis of novel ionic liquids having a (2-meth­oxy­ethoxy)methyl or methoxy­methyl substituent. Conversion rates of N-bases and tributylphosphine in the microreactor system are faster than those in the batch system because of less diffusion distance in the tube reactor. This method allows us to prepare ionic liquids in efficient yields with high purity.