Abstract
having a defect spinel‐framework structure 
was prepared and examined in non‐aqueous lithium cells. 
(white in color) was reduced to 
(dark blue) at a voltage of 1.55 V and the reaction was highly reversible. X‐ray diffraction measurements indicated that the lattice dimension did not change during the reaction
Since the reaction consists of lithium ion and electron insertion into/extraction from the solid matrix without a noticeable change in lattice dimension, called a zero‐strain insertion reaction, capacity failure due to the damage to the solid matrix was not observed even after 100 cycles. Feasibility of zero‐strain insertion materials for advanced batteries is discussed based on the experimental results.