LiFePO4/Carbon Nanomaterial Composites for Cathodes of High-Power Lithium Ion Batteries

Abstract

Using a simple and technological approach, we have fabricated composites based on a lithium iron phosphate (LFP) with the olivine structure and a carbon coating containing 5–10% carbon nanotubes (CNTs) or nanoflakes. Materials prepared with the use of mechanochemical activation have a slightly smaller particle size. At the same time, their electrical conductivity is higher by several orders of magnitude, reaching 8.7 × 10–2 S/cm for the best samples. Moreover, the synthesized materials demonstrate a considerable increase in their reversible capacity, especially at high battery charge/discharge rates. The composites containing carbon nanotubes show the best performance. In particular, the discharge capacity of the LFP/C/10CNT-500 composite is 120, 97, 78, and 57 mAh/g at current densities of 200, 800, 1600, and 3200 mA/g, respectively, whereas the discharge capacity of the pristine LFP/C is 70, 63, 43, and 30 mAh/g. This effect is due to a decrease in particle size and the formation of a network of high-conductive contacts between particles of the cathode material. No clear correlation has been found between the electrochemical capacity of the composites and their specific surface area or electrical conductivity.