Positive electrode materials for lithium batteries based on VOPO4

A detailed electrochemical study of Li insertion in the alpha -form of VOPO4 and the optimization of the cycling performance are presented. The redox process occurs in one step close to 3.76 V, along with a phase transition. In order to improve the intercalation kinetics, the electronic conductivity was optimized by introducing a mixed valency, and the ionic conductivity was favored by introducing 'pillaring' molecules or ions in the interlayer space. In this way, the electrochemical behaviors of alpha -VOPO4 . 2H(2)O, alpha -NaxVOPO4, alpha -KxVOPO4 and alpha -MgxVOPO4 (0 less than or equal to x less than or equal to 1) have been studied: the hydrate compound shows a good specific capacity (100 mA h/g at a C/5 regime), but a poor cyclability was mainly because of water oxidation. The inserted large alkaline ions improved the cyclability up to 80 cycles (Na+) or over 100 cycles (K+). Enhancements of the VOPO4 specific capacity have been obtained as well by mechanical ball-millings. (C) 2001 Elsevier Science B.V. All rights reserved.