Sol–gel synthesis and impedance characteristics of networked nanocrystalline olivine cathode for Li-ion full cells

Abstract

A sol–gel synthesis using adipic acid yielded small particles of around 20 nm in size of olivine LiFePO₄/C cathode materials. In the characterization of cathode system(s), solid state impedance spectra of the pristine LiFePO₄/C cathode revealed clear localization of charge through charge build-up. When networked with MWCNT, this material facilitates enhancement in charge mobility, eventually explaining the capacity enhancement of the LiFePO₄/C–MWCNT electrode, which yields a high capacity of 163 mA h g⁻¹ at C/10. On the other hand, the lower capacity of 125 mA h g⁻¹ found for the pristine LiFePO₄/C electrode material can be explained in terms of charge becoming localized/trapped in the vicinity of inter- and intra-granular regions of the cathode particles. To get a broader view of the application potential (in terms of cell voltages of ∼3 V, 2 V, and safety aspects) of the networked cathode materials, two kinds of Li-ion full cells using mesocarbon microbeads (MCMB) and Li₄Ti₅O₁₂ as anodes were fabricated, which yielded capacities of 1.94 and 2.1 mA h respectively.