Synthesis of high-capacity Ti- and/or Fe-substituted Li_2MnO_3 positive electrode materials with high initial cycle efficiency by application of the carbothermal reduction method

摘要

Carbothermal reduction using sucrose was applied to Fe- and/or Ti-substituted Li_2MnO_3 positive electrode materials to improve their poor initial cycle efficiency (<60%) of 2.0-4.8 V. The initial cycle efficiency was improved from 53% to 68% for Li_(1+x)(Ti_(0.3)Mn_(0.6))_(1-x)O_2, 63%-72% for Li_(1+x)(Fe_(0.3)Mn_(0.7))_(1-x)O_2, or 62%-78% for Li_(1+x)(Fe_(0.2)Ti_(0.2)Mn_(0.6))_(1-x)O_2 by application of the carbothermal reduction process. All samples belong to 3.2 V class positive electrode material with high initial discharge capacity higher than 220 mAh g~(-1). The shape change of discharge curve with cycle progression was suppressed for all reduced samples. The compositional, transition metal valence state, and structural and powder property changes occurring before and after carbothermal reduction processing were examined to construct the material design concept of attractive Li_2MnO_2-based positive electrode candidates using only naturally abundant and cheap elements (Ti and Fe) as constituent metals.