Journal of Power Sources, Vol.293, 613-625, 2015
Carbon coating on the current collector and LiFePO4 nanoparticles -Influence of sp(2) and sp(3)-like disordered carbon on the electrochemical properties
The charging/discharging cycles, rate capabilities, cyclic voltammetry and electrochemical impedance spectra (EIS) of sol gel prepared C-coated LiFePO4 (C-LFP-SG) and a commercial LiFePO4 (LFP-comm), in combination with two different current collectors, viz. Al foil and C-coated Al foil (Al-C) are studied. A flat voltage profile at similar to 3.4 V was seen during the charging/discharging cycle of C-LFP-SG/Al. However, C-LFP-SG/Al C showed a continuous decrease in voltage during discharging and an increase during charging cycles. On contrary, LFP-comm/Al-C showed a constant flat voltage profile, whereas LFP-comm/Al shows a slight decrease during the discharge. C-LFP-SG/Al and LFP-comm/Al-C-Cells exhibit better electrochemical performance compared to C-LFP-SG/Al-C and LFP-comm/Al respectively. This is also reflected from a direct correlation between the flat potential behavior and their rate capabilities. From EIS measurements, we discuss the effect of C-coating on the charge-transfer resistances of LFP nano-particles and current collectors. Raman analysis of carbon modes in all the cathodes and current collectors reveal that a large contribution from sp(2) bonded carbon gives better electrochemical properties. Increasing sp(3)-like disordered carbon at the C-C interface leads to large polarization effects during the charging and discharging cycles. (C) 2015 Elsevier B.V. All rights reserved.