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Synthesis and phase transition of Li-Mn-O spinels with high Li/Mn ratio by thermo-decomposition of LiMnC2O4(Ac)
Authors:Xin-Cun Tang  Cheng-Kui Jiang  Bo-Yun Huang
Affiliation:a College of Chemistry & Chemical Engineering, Central South University, Changsha, Hunan 410083, PR China
b State Key Laboratory of Powder Metallurgy, Central South University, Changsha, Hunan 410083, PR China
Abstract:LiMnC2O4(Ac) precursor in which Li+ and Mn2+ were amalgamated in one molecule was prepared by solid-state reaction at room-temperature using manganese acetate, lithium hydroxide and oxalic acid as raw materials. By thermo-decomposition of LiMnC2O4(Ac) at various temperatures, a series of Li1+y[Mn2−xLix]16dO4 spinels were prepared with Li2MnO3 as impurities. The structure and phase transition of these spinels were investigated by XRD, TG/DTA, average oxidation state of Mn and cyclic voltammeric techniques. Results revealed that the Li-Mn-O spinels with high Li/Mn ratio were unstable at high temperature, and the phase transition was associated with the transfer of Li+ from octahedral 16c sites to 16d sites. With the sintering temperature increasing from 450 to 850 °C, the phase structure varied from lithiated-spinel Li2Mn2O4 to Li4Mn5O12-like to LiMn2O4-like and finally to rock-salt LiMnO2-like. A way of determining x with average oxidation state of Mn and the content of Li2MnO3 was also demonstrated.
Keywords:Lithium manganese oxide   Phase transition   LiMnC2O4(Ac)   Room-temperature solid-state reaction   Lithium-ion batteries
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