Mellitic Triimides Showing Three One‐Electron Redox Reactions with Increased Redox Potential as New Electrode Materials for Li‐Ion Batteries

The mellitic triimide (MTI) bearing three imide groups on a benzene core with C3 symmetry is proposed as a new building block for organic electrode materials in lithium‐ion batteries. MTI was anticipated to deliver a higher theoretical specific capacity of up to 282 mAh g −1 with increased reduction potentials compared with the well‐known pyromellitic diimide building block bearing two imide groups because the additional imide group can accept one more electron and provide an electron‐withdrawing effect. A model compound, ethyl‐substituted mellitic triimide (ETTI), shows three well distinguished and reversible one‐electron redox reactions at −0.97, −1.62, and −2.34 V versus Ag/Ag + in 0.1  m tetrabutylammonium hexafluorophosphate electrolyte, but the redox potentials were increased in 2  m lithium bis(trifluoromethanesulfonyl)imide electrolyte: −0.60 V, −0.86 V, and −1.42 V vs. Ag/Ag + . The DFT calculations revealed that the unique C3 symmetric structural design leads to the higher reduction potential of MTI in the Li‐based electrolyte by formation of a stable 7‐membered ring with a Li ion and the two carbonyl oxygen atoms from the adjacent imide groups. In a Li‐ion coin cell, the ETTI electrode delivered a specific capacity of 176 mAh g −1 , corresponding to 81 % of capacity utilization, with three clear voltage plateaus. The higher average discharge voltage (2.41 V vs. Li/Li + ) of ETTI allows it to deliver one of the highest specific energies (421 Wh kg −1 ) among reported diimide‐based electrode materials. Finally, its redox mechanism was investigated by ex situ FTIR measurements and DFT calculations.