A Mechanochemical Route to Synthesize LiMn₂O₄ as a Cathode Material for Lithium Batteries

Abstract

Lithium manganate, LiMn2O4 , applicable as a cathode material for lithium batteries has been synthesized by a redox mechanochemistry route. Gamma-MnO2 shows an excellent reaction ability with LiOH under grinding and the amorphous ground product can be crystallized to LiMn2O4 at 400°C despite the requisition of the partial reduction of MnO2 to MnIIIMnIVO5. Contrary, Mn2O3 shows a poor reactivity. The dissociation of the edge-sharing chains of MnO6-octahedra in gamma- and beta-MnO2 and the increased reactivity of LiOH fused or activated under grinding is the proposed reaction mechanism. The ground products are slightly agglomerated by the moisture evolved from the hydroxide. However, the particle size can be controlled to be 300-500nm after the calcination at 800°C, when the grinding stress is limited not to be high. Unnecessarily high grinding stress induces the strong agglomeration to increase not only the size of agglomerates but the primary particle size. The synthesized LiMn2O4 with the particle size of 370nm and the crystallite of 48nm provides the good cyclic charge- discharge characteristics, while the rechargeability of LiMn2O4 with 500nm and 68nm degrades within 3 cycles.