Direct Synthesis of Low-Crystalline Li ₂ MnO ₃ with Cation-Disordered NaCl-Type Structure by a Mechanochemical Process and Its Electrochemical Properties

Low-crystalline Li 2 MnO 3 with cation-disordered NaCl-type structure (space group F m 3 ̅ m ) was synthesized by a one-step mechanochemical milling process directly from Li 2 O and MnO 2 in an attempt to apply as a cathode material in a lithium battery. The obtained Li 2 MnO 3 (LMO-MM) reversibly converted into layered monoclinic Li 2 MnO 3 ( C 2/ m ) by heat treatment at 900 °C. The LMO-MM sample showed electrochemical Li + extraction/insertion reactions in the cells with liquid electrolyte, and its discharge capacity ( ca . 230 mAh·g −1 ) was increased by forming composites with fine-grained carbon (LMO-MM-AB sample; ca . 340 mAh·g −1 ), due mainly to the improvement of the electronic conductivity. XAFS analyses demonstrated that the LMO-MM-AB exhibited the redox reaction of Mn 3+/4+ as well as O 2−/− during electrochemical charging/discharging. With cycling, there was an increase in the low-valence Mn components (<3+), as well as an extensive distortion of MnO 6 octahedral coordination and its irregular disordering, which would be responsible for the cycle degradation of the LMO-MM-AB sample cells.