Electrochemically manipulating the redox state of 2,2′,5,5′-tetrahydroxybiphenyl as a new organic Li-rich cathode for Li-ion batteries

Abstract For the first time, a small organic molecule of 2,2′,5,5′-tetrahydroxybiphenyl (BP4OH) is synthesized as a new organic cathode for Li-ion batteries. After setting reduction in the 1st cycle in Li-ion half cells (reduction→oxidation), BP4OH can be in-situ transformed to its salt of lithium 2,2′-bis[benzene-1,4-bis(olate)] (BP4OLi) on Al foil. The resulting BP4OLi is a Li-rich organic cathode and exhibits very good cell performance. For example, the average capacity of ~155 mAh g−1 for the BP4OLi electrode is realized during 600 cycles (500 mA g−1). On the other hand, after setting oxidation in the 1st cycle (oxidation→reduction), BP4OH can be in-situ tuned to its oxidized state of 2,2′-bis(1,4-benzoquinone) (BBQ). Interestingly, the resulting BBQ can be still redox-active and show satisfactory cell performance. For instance, the average capacity of ~101 mAh g−1 for the BBQ electrode can be obtained for 600 cycles (500 mA g−1). This work reveals very interesting redox behaviors of organic electrodes.