Long Cycle-life Organic Electrode Material based on an Ionic Naphthoquinone Derivative for Rechargeable Batteries

The applicability of the redox reactions of 5,8-dihydroxy-1,4-naphthoquinone (1) and its lithium salt, 5,8-dihydroxy-1,4-naphthoquinone dilithium salt (2), as positive electrode active materials for rechargeable lithium batteries was investigated. The prepared electrodes showed initial discharge capacities of 170 mAh g(1)−1 with an average voltage of 2.2 V vs. Li+/Li, and 247 mAh g(2)−1 with an average voltage of 2.1 V vs. Li+/Li for 1 and 2, respectively. The obtained discharge capacities correspond to their two-electron redox behaviors. While the electrode using 1 suffered from a poor cycle-stability, the one using 2 underwent many cycles; i.e., after a small drop in the capacity at the first cycle, the capacity of the latter electrode hardly decayed during the subsequent 100 cycles. The effects of the introduction of ionic groups on the physical properties including the cycle stability were discussed along with quantum chemistry calculation results.