In-situ modification of polyimide anode materials in dual-ion batteries

•A metal free battery is constructed based on polyimide anode, graphite cathode and pure ionic liquid electrolyte.•NaCl participated in the redox reaction of carbonyl group due to adsorption of cations by anode.•By in-situ modification, NaCl instead of EMIm+cation in electrochemical reactions alleviates the capacity fading.•A high capacity of 79 mAh g − 1 is provided as well as good rate performance. Low conductivity severely limits the application of polymer materials in dual-ion batteries (DIBs), which results in high voltage drop and capacity degradation. In this paper, a strategy of in-situ modification is proposed, which utilize the adsorption of Na+ by polyimide (PI) anode to destroy the symmetric conjugation effect, thus the cycle performance is greatly improved. In this dual-ion battery (PI/NaCl-DIB), polyimide material mixed with trace amounts of NaCI (PI/NaCl), natural graphite (NG) and 1-ethyl-3-methylimidazolium bis(trimethylmethane sulfonyl)imide salt (EMImTFSI) pure ionic liquid are used as anode, cathode and electrolyte, respectively. Due to the addition of NaCI in electrochemical process, the storage mechanism of cations on polyimide anode is changed, and capacity performance is also improved. PI/NaCl-DIB has a maximum capacity of 79 mAh g − 1 at 1 C and still discharges 45 mAh g − 1 at a large rate of 5 C after 300 cycles, with a capacity retention of 96%, while the battery with pure polyimide (PI-DIB) only has 25.0 mAh g − 1 at 1 C. The mechanism of NaCI in the polyimide anode materials is investigated by SEM, XRD, XPS, and CV, and the in-situ modification model is constructed for PI/NaCI anode in DIB.