Fe-rich and Mn-rich nanodomains in Li1.2Mn0.4Fe0.4O2 positive electrode materials for lithium-ion batteries

The authors investigated the distribution and local valence states of transition metal ions in a positive electrode material for lithium-ion batteries, Li1.2Mn0.4Fe0.4O2 nanoparticles, by electron energy-loss spectroscopy combined with scanning transmission electron microscopy. The experiments clarified the coexistence of Mn-rich and Fe-rich nanodomains in each single particle, and it is found that Fe-rich nanodomains contain Mn3+ ions which should be active in a redox reaction in spite of previous views of inactive Mn4+ ions in this material. The authors discuss a redox mechanism associated with the nanodomains.