Synthesis And Electrochemical Performance Of Silicates-based Polyanions Lithium Compounds For Lithium-ion Battery

Silicates based poly-anion lithium compounds, known for theirs structural stability, abundant resources and environmental friendliness, have drawn raising attention and been widely studied recent years. In this work, a new type of this class compound, LiFeSi2O6, was synthesised and its electrochemical property was studied for the first time. Further more, Li2FeSiO4has been synthesised through different ways (solid-state, liquid-phase and sol-gel). The synthesising conditions, composition, structure and electrochemical performance were investigated. At last, the synthesised Li2FeSiO4was applide in aqueous electrolyte battery system as anode for electrochemical performance testing for the first attempt.A new type of silicates based polyanions lithium compound LiFeSi2O6with high purity was synthesised and its Zn element dopped sample and electrochemical performance were also investigated. The as-synthesised LiFeSi2O6and LiFe1-xZnxSi2O6exhibit an initial discharging capacity of480and530mAh·g-1respectively, but the first discharging curves are much different form the following cycles. Both of samples suffer severe capacity attenuation over50%after first discharging process during which a structural transformation might has taken place. Further investigations of the mechanism of decay and means to improve cyclicity are necessary.Li2SiO3was synthesised and used as precursor for synthesising of Li2FeSiO4via different methods (solid-state, liquid-phase), to reduce reacting phases in order to generate better purified Li2FeSiO4. Sample synthesised via solid-state way shows relatively more impurity but much litter polarization with a carbon content of8.98wt%. It exhibits high capacity and good cycling performance with an initial discharging capacity of140mAh·g-1and cycling capcity around120mAh·g-1in organic electrolyte system. While sample producted by liquid-phase methode suffers an execrable property because of serious internal polarization caused by barely no carbon coating.synthesised via sol-gel method exhibits best performance in organic electrolyte system with a cycling capacity of140mAh·g-1. Then the same sample was used in aqueous electrolyte battery system as anode, layered oxide Li(Ni1-x-yCoxMny)O2as cathode and1M Li2SO4+0.1M LiOH aqueous as electrolyte. This aqueous electrolyte battery shows a cycling capacity approaching100mAh·g-1during the first30cycles. Indicating that Li2FeSiO4could be employed in aqueous electrolyte battery system and further investigations on optimizing the specific parameters are needed.