Effect of conductive carbon additives and negative/positive capacity ratio on graphite/LiFePO4 full-cells performance

Abstract

In this article, we study two factors (carbon additive, N/P ratio) affecting the performance of Li-ion cells using LiFePO4 (LFP) synthesized via the hydrothermal method. X-ray diffraction (XRD) results show that the synthesized LFP material is pure and within the single phase of the orthorhombic lattice. The electrochemical properties of synthesized LFP cathode (physically mixed with different carbon C65 and CNTs) were studied by cyclic voltammetry (CV) and galvanostatically cycling. The diffusion coefficients of LFP-CNTs and LFP-C65 were calculated using the Randles-Sevcik equation and reached 8.350.10−10 cm2 s−1 and 1.620.10−10 cm2 s−1, respectively. In a rate capability tests, LFP-CNTs based cell demonstrates an excellent cyclability with a discharge capacity (CapDis) of 147.9 mAh g−1 at 0.1C and 84.0 mAh g−1 at 5.0C, whereas LFP-C65 completely lost capacity at 2.0C. In addition, the investigation of negative/positive capacity ratios (N/P ratios) at 1.18 and 1.23 reveals high specific capacity (Capspe), high-capacity retention, and an excellent charge/discharge efficiency (EC/DC) at different C-rates.