Electrochemical Properties of LiFePO₄ Cathodes: The Effect of Carbon Additives

Abstract

The influence of different conductive additives (carbon nanofibers (CNFs), carbon nanoplatelets, and pyrolytic carbon from sucrose (Sucr) or polyvinylidene fluoride) on the morphology, electron conductivity, and electrochemical performance of LiFePO4-based cathodes was investigated to develop the most efficient strategy for the fabrication of high-rate cathodes. Pyrolytic carbon effectively prevents the growth of LiFePO4 grains and provides contact between them, CNFs provide fast long-range conductive pathways, while carbon nanoplatelets can be embedded in carbon coatings as high-conductive “points” which enhance the rate capability and decrease the capacity fading of LFP. The LiFePO4/CSucr/CNF showed better performance than the other cathodes due to the synergy of the high-conductive CNF network (the electronic conductivity was 1.3 × 10−2 S/cm) and the shorter Li+ ion path (the lithium-ion diffusion coefficient was 2.1 × 10−11 cm2/s). It is shown that the formation of composites based on LFP and carbon nanomaterials via mortar grinding is a more promising strategy for electrode material manufacturing than ball milling.

Keywords

• cathode
• lithium-ion batteries
• LiFePO₄
• PVDF
• carbon nanofibers
• ball milling