真空辅助法合成Fe_3(PO_4)_2·8H_2O及对LiFePO_4/C结构、形貌和电化学性能的影响(英文)

Vacuum-Assisted Synthesis of Fe_3(PO_4)_2·8H_2O and Its Influence on Structure, Morphology and Electrochemical Performance of LiFePO_4/C

采用了一种真空辅助沉淀法制备Fe3(PO4)2·8H2O,并以此进一步合成粒径尺寸在400 nm左右LiFePO4颗粒.研究了Fe3(PO4)2·8H2O对于磷酸铁锂的形貌、结构、电化学性能的影响.X射线衍射(XRD)结果表明,真空辅助制备的Fe3(PO4)2·8H2O具有高纯度,以此制备的LiFePO4具有高结晶度和纯度.扫描电子显微镜(SEM)结果表明,真空辅助制备的Fe3(PO4)2·8H2O具有未完全发育的颗粒,以此制备的LiFePO4均匀无硬团聚.透射电子显微镜(TEM)结果显示真空辅助制备的LiFePO4包覆一层均匀的碳.真空制备的LiFePO4显示了优异的电化学性能,在1C、10C、20C倍率下的容量分别为140、113、100 mAh·g-1.真空制备的LiFePO4的循环伏安曲线显示了小的极化电压和尖锐的氧化峰.充放电平台曲线表明真空对LiFePO4高倍率性能起到重要作用.电化学阻抗谱(EIS)计算结果显示,真空和非真空制备的LiFePO4的锂离子扩散系数分别为1.42×10-13和4.22×10-14cm2·s-1,说明真空辅助能够提高LiFePO4的扩散系数.

A vacuum-assisted precipitation method was used to synthesize Fe3（PO4）2·8H2O（FP）. The FP was then used to synthesize carbon-coated LiFePO4 （LFP/C） particles. The influence of FP on the structure, morphology, and electrochemical performance of LFP was investigated. The X-ray diffraction （XRD） patterns and molar ratio of Fe to P showed that the FP which was produced using a vacuum-assisted method was of high purity and gave highly crystalline, impurity-free LFP. Scanning electron microscopy （SEM） showed that the FP contained undeveloped particles. The undeveloped FP results in uniform LFP/C particles, without agglomeration. Transmission electron microscopy （TEM） showed that the LFP particles were coated with a homogeneous carbon layer. The LFP/C showed excellent discharge capacities of 140,113, and 100 mAh-g-1 at 1 C, 10C, and 20C rates, respectively. The cyclic voltammograms （CVs） of LFP showed a low polarization voltage and sharp redox peaks. The charge-discharge platform curves showed that LFP had an excellent high-rate capability. Electrochemical impedance spectroscopy （EIS） tests showed that the lithium-ion diffusion coefficients of LFP/C produced with and without vacuum assistance were 1.42× 10^-13 and 4.22× 10^-14 cm2. s-1, respectively,proving that vacuum assistance can improve the diffusion coefficients of LFP/C.