Morphology and Interconnected Microstructure-Driven High-Rate Capability of Li-Rich Layered Oxide Cathodes

Abstract

A Li-rich layered oxide (LLO) cathode with morphology-dependent electrochemical performance with the composition Li_1.23Mn_0.538Ni_0.117Co_0.114O₂ in three different microstructural forms, namely, randomly shaped particles, platelets, and nanofibers, is synthesized through the solid-state reaction (SSR-LLO), hydrothermal method (HT-LLO), and electrospinning process (ES-LLO), respectively. Even though the cathodes possess different morphologies, structurally they are identical. The elemental dispersion studies using energy-dispersive X-ray spectroscopy mapping in scanning transmission electron microscopy show uniform distribution of elements. However, SSR-LLO and ES-LLO nanofibers show slight Co-rich regions. The electrochemical studies of LLO cathodes are evaluated in terms of charging/discharging, C-rate capability, and cyclic stability performances. A high reversible capacity of 275 mA h g^-1 is achieved in the fibrous LLO cathode which also demonstrates good high-rate capability (80 mA h g^-1 at 10 C-rate). These capacities and rate capabilities are superior to those of SSR-LLO [210.5 mA h g^-1 (0.1 C-rate) and 4 mA h g^-1 (3 C-rate)] and HT-LLO [242 mA h g^-1 (0.1 C-rate) and 22 mA h g^-1 (10 C-rate)] cathodes. The ES-LLO cathode exhibits 88% capacity retention after 100 cycles at 1 C-rate. A decrease in voltage on cycling is found to be common in all three cathodes; however, minimal voltage decay and capacity loss are observed in ES-LLO upon cycling. Well-connected small LLO particles constituting fibrous microstructural forms in ES-LLO provide an enhanced electrolyte/cathode interfacial area and reduced diffusion path length for Li⁺. This, in turn, facilitates superior electrochemical performance of the electrospun Co-low LLO cathode suitable for quick charge battery applications.