Preparation, Optimization And Characterization Of Spinel LiMn₂O₄ For Lithium Ion Batteries

LiMrn2O4 spinel, which theoretic cycle capacity is 148 mAh.g-1, is considered as the most promising cathode materials for Lithium Ion battery for its highlights of low cost, easily prepared and environment free. However, the serious capacity fading upon cycling especially at surroundings over 55# hampered its immediately commercial application.The stoichiometric LiMn2O4 spinel was prepared by carbonate wet method using Li2CO3, Mn(CH3COO)2-4H20 and CO2 as raw materials. The products were measured by TG/DTA, XRD, IR. The results Showed that the sample calcined at 800 # for 10h was well crystallized monophase product, and its initial cycling capacity can reach 111 mAh.g-1.The value of Mn in LiMn2O4 spinel is mixed value of Mn[III] and Mn[IV], it is Mn[III] that reacts in electrochemical process. LiMn204 spinel can fully resolve in 4 mol-L-1 H4P2O7+4mol/L H2S04 mixture, based on the Lambert-Beer law, we put forward a new method to determine the contents of Mn[III] and Mn[IV] in LiMn2O4 spinel simultaneously by spectrophotometric analysis with pyrophosphoric acid.There are two possible theory of capacity fading of LiMn204 spinel. The two Mn-O bonds of [MnO6] unit along the c-axis in LiMn204 spinel are prolonged because of Jahn-Teller distortion, resulting in the weaken of Mn-O bonds and structural break of LiMn2O4 spinel. The doping of LiMn2O4 spinel with elements of Co, Ni,Cr et al can restrain the Jahn-Teller distortion and improve the stability of material. In our experiment, the Ni-doped sample LiMn1.95Ni0.05O4 exhibited theexcellent capacity of 120mAh.g-1 in the third cycle. The other major reason of capacity fading of LiMn2O4 spinel is the Mn dissolution into electrolyte. By surface coated with Li4SiO4, Li2PO4 and LiCoO2, the Mn dissolution of LiMn2O4 spinel can be effectively suppressed, exhibited improved capability.