Solvothermal Synthesis Of Nanoplate LiFePO₄and Its Electrochemical Properties

As a kind of cathode material for Lithium-ion battery, LiFePO4has manyadvantages, such as low cost in raw materials, excellent cycling stability and high safety.However, its drawbacks of low electronic conductivity and lithium ion diffusivity havesignificantly restricted the commercial application in power batteries. In order to solvethe problem, a solvothermal method was developed to synthesize nanoplate LiFePO4with CH3COOLi, Fe(CH3COO)2, NH4H2PO4as starting materials, tetraethylene glycol(TTEG) or ethylene glycol (EG) as a solvent. The parameters of temperature, time andpressure on the structure and electrochemical properties were discussed carefully in theexperiments.In synthesis of nanoplate LiFePO4with TTEG, the parameters of temperature, timeand the viscosity of hydroxide radicals should be controlled strictly. When using0.01mol starting materials,100ml TTEG and controlling the temperature as300℃,time as10h, the method yielded well crystallized nanoparticles with plateletmorphology. The size of nanoplates was about500nm in length and30nm in thickness.And the nanoplates stacked on top of each other in face-by-face format andconstructed the structure of sandwich.When the nanoplate LiFePO4was synthesized by EG, the parameters oftemperature, time, pressure and the cooling progress were important to the formation ofnanoplate morphology. When the temperature was controlled as270℃, the time as8hand the pressure as3~4MPa, furthermore the cooling progress shoud be controlledslowely, then well crystallized nanoplates could be got. The size of naoplates was about500nm in length and40nm in thickness. And the initially formed nanoplates assembledout-of-order and constructed the hierarchical architectures.Comparing the two kinds of nanoplates with each other, the latter with nanoplatesstacked out-of-order provided more rooms and larger specific surface area. And itsnanoplates possessed better crystallization. At low rate performance of0.2C and1C,there seemed no difference in their capacity. However at high rate of10C,20C and30C,the nanoplates synthesized by EG performed better than the nanoplates synthesized byTTEG. The nanoplates by EG could maintain100mAh·g-1,90mAh·g-1and80mAh·g-1in capacity, while the nanoplates by TTEG could only maintain100mAh·g-1,75mAh·g-1and58mAh·g-1. The nanoplates synthesized by EG exhibited higherperformance in high rate performance than commercial LiFePO40.The formation of nanoplate LiFePO4lay on the hydroxide radicals’ selectiveadsorption onto LiFePO4nuclei. The selective adsorption reduced the surface energy ofthe certain panel and restricted the growth in its direction. And the other panels couldgrow as usual. With reaction time longer, the LiFePO4nuclei began to form nanoplate LiFePO4. There were four steps in the nucleation and growth of nanoplate LiFePO4:(1)Formation of starting precursor;(2) Formation of LiFePO4nuclei and selectiveadsorption of hydroxide radicals;(3) Formation and growth of nanoplates;(4)Self-assembly of nanoplates.