Li / Li1 + x  V 3 O 8 Secondary Batteries: III . Further Characterization of the Mechanism of Li+ Insertion and of the Cycling Behavior

The reduction mechanism of the bronze in nonaqueous Li cells has been elucidated. Upon Li + insertion, a solid solution is formed with an upper composition of . 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 , 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.