Effect of heat treatment time on cycle performance of LiMn2O4 with “Nano Inclusion” for lithium ion batteries

Abstract

A LiMn₂O₄ cathode material with “Nano Inclusions” has been prepared by employing various heat treatment times. The effect of the heat treatment time on the electrochemical properties has been investigated. XRD powder pattern analysis and SEM observation indicated that LiMn₂O₄ formed at low temperature sintering collapsed at the initial stage of the heat treatment and LiMn₂O₄ particles with ZnMn₂O₄ “Nano Inclusions” grew in the subsequent heat treatment. HAADF-STEM images revealed that both the particle size of LiMn₂O₄ and that of the “Nano Inclusions” increased as the heat treatment time increased. While all the LiMn₂O₄ samples with “Nano Inclusions” exhibit a decreased initial discharge capacity in comparison with LiMn₂O₄ without “Nano Inclusions”, they show an improved discharge capacity retention rate. The sample heat-treated for 4 hours surpasses LiMn₂O₄ without “Nano Inclusions” in discharge capacity over the 31st cycle. The larger the size of the “Nano Inclusion”, the more the crack propagation was considered to be suppressed, but on the other hand, the larger the dead region increased. It is considered that an appropriate size of “Nano Inclusions” was formed by the 4 hour heat treatment.