Poly(5-amino-1,4-naphthoquinone), a novel lithium-inserting electroactive polymer with high specific charge

The monomer 5-amino-1,4-naphthoquinone can be polymerized electrochemically or chemically to form a redox polymer in which the quinone/hydroquinone redox couple can be electrochemically oxidized and reduced in aqueous and organic electrolytes. The polymer exchanges cations for the charge-compensating process. In LiClO4/acetonitrile electrolyte lithium ions can be inserted and expelled reversibly. Cyclic voltammograms and galvanostatic experiments show that the charge storage capacity of this polymer is very close to its theoretical value of 290 Ah/kg. The redox potential is about 2.6 V more positive than that of the Li/Li+ couple. If the electrode potential is kept within the window from -1.25 to -0.20 V vs. Ag/AgCl the stability of poly(5-amino-1,4-naphthoquinone) (PANQ) is reasonable, and an acceptable cycle life can be reached. However, at lower potentials irreversible electrochemical reactions proceed, and the cycle life of PANQ is shortened. Hence, PANQ is an interesting electrode material for lithium metal or lithium-ion batteries. From potential-jump experiments on porous composite PANQ electrodes an overall diffusion coefficient at least 1.10(-7) cm(2)/s was estimated for the lithium deinsertion. Assuming a thin-layer cell with a LiC6 negative and a PANQ positive electrode (using common dimensions for the current collectors and battery housing, and accounting for the electrolyte necessary to fill the pores in the electrode and separator), we estimated that a battery having a specific energy of up to 125 Wh/kg at very low charge/discharge rates could be realized. For the 1 h discharge rate about 100 Wh/kg should be possible. (C) 1999 The Electrochemical Society. S0013-4651(98)10-099-X. All rights reserved.