Reversible potassium vanadium bronze cathodes (K xV 6O 13+ y) with various potassium to vanadium ratios

Abstract

Electrodes composed of crystalline K x V 6O 13+ y , where 0.0 ⩽ x ⩽3.7 and 0.1 ⩽ y ⩽ 3.1, were prepared by thermal decomposition of electrochemically-deposited (NH 4) x K 4− x V 6O 16 phases at 300 to 350 °C. The reversible lithium insertion into these materials was measured under cyclic voltammetry and constant current conditions. Phase changes during discharge resembled those of V 2O 5 or V 6O 13 for similar vanadium oxidation states and small K/V ratios (⩽ 0.3). The reversible capacity decreased as the K/V ratios increased from 0.1 to 0.5 and was small above K/V = 0.5 (Li/V < 0.1). The reversible capacity of the bronzes improved for lower O/V ratios, but best cycle life was obtained for nonstoichiometric vanadium oxides with K/V ratios in the range of 0.05 to 0.3 for O/V ratios between 2.0 to 2.5. Over 50 cycles at the C-rate were obtained with 5 to 10% of the capacity lost at 0.4 e −/vanadium depth-of-discharge.