Anode performances of LaSi2/Si composite thick-films were investigated in ionic liquids as Li-ion battery electrolytes containing cations of N-methyl-N-propylpiperidinium (PP13) or 1-ethyl-3-methylimidazolium and anions of bis(fluorosulfonyl)amide (FSA) or bis(trifluoromethanesulfonyl) amide. The LaSi2/Si electrode exhibited much better performance in PP13-FSA compared with the other electrolytes including a conventional organic solvent one: the reversible capacity at the 250th cycle and its retention were 800 mA h g−1 and 80%. The excellent performance is attributed to a higher stability of PP13 cations against a cathodic decomposition and an easier desolvation of Li ions and FSA anions at the electrode/electrolyte interface. This result offers a promising applicability of ionic liquid electrolyte to various Si-based anodes with high performances by architecture of cation and anion structures.