An ionic liquid, N-allyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide PP13*TFSI has been successfully tested as a solid electrolyte interface (SEI) forming agent for graphite composite anode at elevated temperature of 55°C in a purely ionic liquid-based electrolyte: 0.5m LiTFSI in a mixture of PP13*TFSI–PP13TFSI (20–80wt.%) The reversible discharge capacity was 340–350mAhg−1 with only a small irreversible capacity loss per cycle. The electrochemical polymerisation of the allylic double bond participates on the SEI formation on the graphite surface. In the absence of unsaturated ionic liquid, the piperidinium cation is co-intercalated into graphite and causes its exfoliation with permanent loss of capacity. The electrolyte is thermally stable up to 320°C and reasonably conductive (2.4mScm−1 at 55°C).