Modification and deterioration mechanism of lithium manganese silicate as cathode material for lithium-ion batteries

Li2Mn1-xMgxSiO4/C cathode material for lithium-ion batteries was synthesized by a sol-gel method using LiCH3COO·2H2O, Mn(CH3COO)2·4H2O, Mg(CH3COO)2·4H2O, and Si(OC2H5)4 as starting materials under Ar/H2 atmosphere. The crystal structures and morphology of the as-prepared compounds were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy, respectively. The Li2MnSiO4 material maintains an orthorhombic structure with up to 10% (mass fraction) Mg doping on the Mn sites. The result obtained by electrochemical tests of the cathode materials reveals that Mg doping can improve the specific capacity of Li2MnSiO4. An initial specific discharge capacity of 212 mAh/g can be achieved for the Li2Mn1-xMgxSiO4/C (x = 0.1) cathode material at a current density of 16.65 mA/g. The deterioration mechanism was also discussed based on the results determined by XRD and X-ray photoelectronic spectroscopy. The poor capacity retention is mainly caused by the deterioration of the silicate crystal.