Li/ Li1+xV3O8 secondary batteries. III°. Further characterization of the mechanism of Li+ insertion and of the cycling behaviour.

The reduction mechanism of the bronze Li1.2V3O8 in nonaqueous Li cells has been elucidated. Upon Li+ insertion, a solid solution is formed with an upper composition of Li3V3O8. Within this composition range, Li+ progressively fills the tetrahedral sites available in the unit cell. Four such sites are supposed to be filled at the upper composition limit. Beyond this, a new phase is nucleated to accommodate excess Li+, this resulting in a constant cell's OCV. Li+ insertions not greater than 3.0 eq/mol are reversible, as shown by the cycling behavior and the x-ray patterns. Owing to the outstanding structure stability and to the high speed of Li+ diffusion in Li1.2V3O8, extended cycling at high rates is achievable with cells based on this bronze. 445 cycles at discharge rates variable in the range of 2-10 mA/cm 2 have been obtained