Ammonia- and lithia-doped manganese dioxide for 3 V lithium batteries

Specific discharge capacities in excess of 200 mAh/g and good reversible cycling behavior between 3.8 and 2.0 V has been observed in a lithium cell for alpha -MnO2 phases with the hollandite structure. A combination of Lithia (Li2O) doping and ammonia (NH3) treatment of the active material powder having the composition alpha-[0.143Li(2)O .0.007NH(3)]. MnO2 gave the best electrochemical performance in liquid organic electrolyte (1:1 EC:DMC, 1 M LiPF6) coin cells, with metallic Li as the negative electrode. The added lithia forms a defect close-packed array of oxide anions and stabilizes the interior of the 2 x 2 tunnel of the hollandite structure by partially filling the crystallographic position (0,0,0.5) of the tetragonal unit cell (I4/m) with O2- from the added Li2O. Ammonia treatment is hypothesized to partially fill other lattice vacancies still available within the 2 x 2 tunnel with the nitrogen atoms from NH3 taking the same position as the oxide anion in the array. The NH3 can further stabilize the cell during lithium insertion/extraction because of its favorable hydrogen bonding ability and Lewis base characteristics. (C) 2001 Elsevier Science B.V. All rights reserved.