Investigation of In-Situ Carbon Coated LiFePO₄ as a Superior Cathode Material for Lithium Ion Batteries.

Abstract

In the present study, we have developed a simple and cost-effective approach for the synthesis of carbon coated LiFePO₄ wherein different carbon precursors were used to find out the suitable precursor for carbon coating. Initially, the appropriate amount of Li, Fe, and P precursors and carbon source (glucose/sucrose/fructose) were dissolved in ethanol solution followed by hydrothermal treatment at 180 °C to obtain carbon coated LiFePO₄. The structure and morphological analysis of In-Situ carbon coated LiFePO₄ revealed the formation of thin and homogeneous carbon layer on crystalline single-phase LiFePO₄ particles with fructose used as carbon precursor. Raman analysis confirms the presence of more ordered graphitic carbon and the ID/IG ratio is 1.01, 0.69 and 0.87 for C-LFP-S, C-LFP-F and C-LFP-G respectively, indicating that fructose assisted In-Situ carbon coating leads to the formation of more ordered carbon coating on LiFePO₄ with high graphitization degree in comparison with carbon coating by glucose and sucrose. HR-TEM results revealed the presence of uniform carbon distribution, which encapsulates the crystalline LiFePO₄ particles forming a core-shell structure in the presence of fructose as carbon precursor. C-LFP-S delivered a capacity of 125 mAh/g at 0.1 C rate but then due to non-uniform carbon layer distribution, the capacity faded out completely when tested at higher C-rates. Whereas C-LFP-F delivered a discharge capacity of 98 mAh/g at 0.1 C and 48 mAh/g at 1 C, which is promising compared to the LiFePO₄ carbon coated using sucrose and glucose. It is concluded that LiFePO₄ carbon coated using monosacrides as carbon precursors showed better electro-chemical performance in terms of capacity and cyclic stability when compared to LiFePO₄ carbon coated using dissacrides, attributing that uniform, thin layer, and highly ordered graphitic carbon coverage on nano sized LiFePO₄ particles greatly reduces the polarization resistance and hence improving the electrochemical performance of C-LFP-F.