دانلود Effect of first-stage temperature on the hydrothermal synthesis of flower-like lithium iron phosphate

Abstract

A controllable synthesis of flower-like lithium iron phosphate LiFePO4 (LFP) was obtained via a two-stage heating during hydrothermal process. In the first stage, the temperature was held at 105 °C (LFP1), 120 °C (LFP2), 150 °C (LFP3) and 190 °C (LFP4) for  5  h.  In  the  final  stage,  the  temperature  was  held  constant  at  400  °C  under  H2/N2 atmosphere for 4 h. To increase the electrochemical reversibility and electronic conductivity, LFP is treated with polyethylene glycol (PEG) as the templating agent and carbon sources for the as-prepared materials. This is to obtain a  modified LFP  cathode with optimum electrical contact  between  the  electroactive  materials  and  the  carbon-filled  electrode  matrix  which  is found  to  be  effective  in  terms  of  raising  the  electrochemical  performance  of  the  Li-ion batteries.  Results  show  that  as  the  first-stage  temperature  increased,  the  corresponding electrochemical performance of the resulting sample has been  increased up to a  temperature of 150 °C. Galvanostatic charge-discharge test indicates that flower-like LiFePO4/C composite,  LFP3,  exhibits  initial  discharge  capacity  of  118  mAh  g-1  at  0.1C  rates.  The performance  improvement was attributed to a reduction of the thickness and particle  size of the  flower-like  LiFePO4  particles.  Results  of  X-ray  diffraction  (XRD)  revealed  that  the structure of the latter represents phase of the ordered olivine structure without any impurities. Cyclic voltammetry indicates that the improvement in redox cycling could be attributed to an increase of the electrochemical active surface area (ECSA) and the related increase in microporosity as evidenced by SEM analysis.