Synthesis and Electrode Properties of Metastable Li[sub 2]Mn[sub 4]O[sub 9−δ] Spinel Oxides

spinel oxides with 0.36 < δ < 0.46 were synthesized by oxidation of aqueous with hydrogen peroxide or lithium peroxide in the presence of lithium carbonate or lithium hydroxide followed by firing the precursor in air at 300–400°C spinel is metastable and disproportionates at about 500°C to give a lithium‐rich spinel and . The disproportionation temperature and the amount of impurity formed depended on the synthesis procedure and raw materials used. Use of lithium peroxide and lithium hydroxide in the solution‐based oxidation procedure produced the least amount of impurity at intermediate temperatures. However, the value of x in the lithium‐rich spinel decreased with a further increase in firing temperature, and the stoichiometric spinel without impurity was formed at 800°C. Phase analysis as a function of firing temperature for a wider range of Li/Mn ratios in the system (0.7 ≤ y ≤1.33) also revealed that single‐phase spinel could be formed for the entire firing temperature range 300 ≤ T ≤ 800°C only for a narrow value of 1.05 ≤ y ≤ 1.25. The lithium‐intercalation properties of the metastable spinel were influenced by the firing temperaturfe deltae. A sample formed at an optimum temperature of 400°C showed a capacity of 130 mAh/g in the range 3.8–2.0 V with excellent cyclability. © 2000 The Electrochemical Society. All rights reserved.