LiFePO4(LFP) nanobars,microplates and nanorods have been selectively synthesized via a solvothermal method in a water-ethylene glycol(EG) binary solvent with H3PO4,LiOH·H2O,and FeSO4·7H2O as starting materials.The morphology and size of the as-obtained LFP products can be deliberately controlled by varying the volume ratio of EG to water.The formation mechanism and electrochemical properties of different LFP morphologies have been investigated.With carbon coating,the Li-ion diffusion coefficients of LFP nanorods,nanobars and micro-plates are 2.58×10-9,2.91×10-10,and 7.22×10-10 cm2 s-1,respectively.For the carbon-coated nanorods,excellent rate capability and cyclability were attained.At 5 C,the capacity was 141 mAh g-1 for the first cycle and maintained 120 mAh g-1 after 100 cycles;at 10 C,the capacity was still as high as 132 mAh g-1.
Oxalic-acid-based co-precipitation method was employed to prepare LiNi2/3Mn1/3O2 sample with a high-ordered structure. Li+,Ni2+ and Mn2+ acetates were used as starting materials. The influence of the amount of lithium source in the starting materials on Li+ content,disorder of Li+-Ni2+ ions,and electrochemical performance has been investigated. Rietveld refinement shows that the sample prepared with 20% excess Li-source in the starting materials exhibits a perfect ordered structure. A specific discharge capacity is as high as 172 mAh/g at C/20 in the voltage range of 4.35?2.7 V. However,the cyclability is not satisfactory:about 25.3% fade in capacity was observed over 50 cycles. Chemically stable SiO2 was coated on the surface of LiNi2/3Mn1/3O2 particles. A significant improvement in cyclability was attained with 3 wt% SiO2 coating,which is ascribable to the protection of LiNi2/3Mn1/3O2 particles from being dissolved into the electrolyte.
