Electrochemical study of intercalated vanadyl phosphate

A detailed electrochemical study of Li intercalation/deintercalation in VOPO 4 compounds with various inserted molecules (H 2 O, HCOOH and CH 3 COOH) is presented. For VOPO 4 ·2H 2 O, water oxidation is responsible for capacity fading. In order to improve the cyclability, the electrochemical behavior of other intercalated VOPO 4 compounds, such as VOPO 4 ·H 2 O, VOPO 4 ·HCOOH and VOPO 4 ·0.78CH 3 COOH, has been studied. For all these materials, the intercalation (deintercalation) takes place in several steps. The electrochemical study of the monohydrate indicates that the vanadium-coordinated water molecule is more stable than the second water molecule towards cycling. The highest initial specific capacity values (approximately 100 mAh/g) are obtained for the compounds with the largest interlayer space. Upon cycling, the pillaring molecules are destroyed by a high-potential oxidation process, yielding a collapse of the 2D structure and thus a loss of crystallinity. As a result, the observed specific capacity is the same for all the materials after a long cycling. This capacity is higher than the anhydrous one.