Micron‐sized was prepared in a single‐step solid‐state reaction involving and , and its electrochemical behavior was evaluated in Li and Li‐ion cells containing a polyacrylonitrile (PAN)‐based solid polymer electrolyte. The usefulness of was demonstrated for three distinctive applications: (i) cathode of a 1.5 V rechargeable Li battery, (ii) auxiliary electrode for investigating the electrochemistry of Li insertion cathode materials, and (iii) anode of a Li‐ion cell in conjunction with a high voltage cathode, e.g., cubic spinel . The micron‐sized exhibit ed a capacity of 160 mAh/g at C/20–C/30 rates which is about 7% better than the capacity exhibited by this material prepared according to a previously published procedure. More importantly, the micron‐sized oxide showed significantly better high rate capability, yielding 25–50% larger capacity at the 3C to 8C rates. Li/solid polymer electrolyte// cells underwent extended, full‐depth, charge/discharge cycling at ⩾1C rates with virtually no capacity fade. The auxiliary electrode concept was demonstrated in (x ∼ 1.2)//solid polymer electrolyte// cells. At a 1C discharge rate more than 150 cycles were demonstrated in these cells with a capacity fade rate of about 0.1% per cycle and an end utilization of ∼90 mAh/g for spinel . Balanced //solid polymer electrolyte// cells of slightly cathode‐limited configuration showed full‐depth extended cycling capability at a utilization of ∼90 mAh/g for at 1C rate and a capacity fade rate of about 0.08% per cycle. The capacity fade in the ‐containing cells appears to come from this cathode. When fully packaged, specific energy of the Li//PAN electrolyte// cell would be about 57 Wh/kg and that of the //PAN electrolyte// cell is about 60 Wh/kg.