Fabrication of a Spinose Structure LiFePO4 Cathode Via Surface Etching to Improve the Rate Capability and Cycling Stability of Li-Ion Batteries

Abstract

Lithium iron phosphate (LiFePO4, LFP) has been demonstrated as a suitable cathode material for Li-ion batteries due to its relatively high theoretical capacity (170 mAh·g-1), cost effectiveness, long cycle life, good thermal stability, and environmental friendliness, However, key limitations of LFP are its low intrinsic electronic conductivity (10-9-10-10 S·cm-1) and limited lithium ion diffusion channel (one-dimensional path along the b-axis of the olivine structure), leading to poor rate capabilities and cycling stability in LFP batteries. To improve the rate capability of LFP cathode, the low electronic conductivity can be resolved by conductive material coating, heteroatomic doping, and downsizing of active materials. To improve the rate capability and cycling stability of LFP battery, we propose the surface treatment of LFP cathode material to increase the surface area. The surface area of LFP is controlled by the concentration of etching agents (0.5 M to 2.0 M), etching time (10 min to 360 min), and reaction temperatures (25 °C to 80 °C). The morphology of the etched LFP surface is characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specific surface area and crystal structure of surface etched LFP are characterized by Brunauer-Emmett-Teller (BET) and X-ray diffraction (XRD), respectively. To determine battery performance, coin-cells are assembled with cathodes containing various surface areas. Cycling testing is performed using an Arbin tester to measure the rate capability at different C-rates and cycling stability at same C-rate.