Template-assisted molten-salt synthesis of hierarchical lithium-rich layered oxide nanowires as high-rate and long-cycling cathode materials

Abstract

Lithium-rich layered oxides are promising cathode materials for next-generation lithium-ion batteries (LIBs) used in electric vehicles, due to their high specific capacity over 250 mAh g−1 and high energy density of ∼900 Wh Kg−1. However, the poor rate performance and inferior cycling stability of current lithium-rich layered oxides have greatly hindered their practical applications in vehicular LIBs, mostly due to the ineffectiveness of conventional synthesis methods in controlling the materials size and morphology. Herein, one-dimensional (1D) hierarchical lithium-rich layered oxide (Li1.15Mn0.54Co0.08Ni0.23O2) nanowires were successfully synthesized by a template-assisted molten-salt method that used α-MnO2 nanotubes as both the manganese source and template. The prepared lithium-rich layer oxide nanowires were ∼60–80 nm in diameter and ∼0.5–1 μm in length, and each nanowire was composed of homogeneous and interconnected primary nanoparticles (5–20 nm). Electrochemical characterization showed that the 1D lithium-rich layered oxide nanowires exhibited impressively high-rate performance, long cycle life, and excellent capacity retention as cathode materials for LIBs. For example, the cathode delivered a high initial discharge capacity of 304.5 mAh g−1 with a Columbic efficiency of 81.2%, and maintained a discharge capacity of 253.3 mAh g−1, 241 mAh g−1, 222 mAh g−1, and 203 mAh g−1 after 100 cycles, at 0.5C, 1C, 2C and 5C, respectively. Moreover, at an even high rate of 10C, 20C and 30C, the lithium-rich layered oxide nanowires could still deliver a discharge capacity of 149 mAh g−1, 121 mAh g−1, and 65 mAh g−1 respectively for 1000 cycles, without any capacity decay. Post-cycling structural analysis showed that the 1D nanowire morphology of lithium-rich layered oxide was well preserved after prolonged charge/discharge cycling at 10C for 1000 cycles. The excellent electrochemical performance can be ascribed to the good structural stability of 1D nanowires, primary nanosized particles, high crystallinity of the 1D Li1.15Mn0.54Co0.08Ni0.23O2 nanowires. This work developed a new strategy to synthesize manganese-based cathodes with controlled morphology and high crystallinity by the combination of suitable manganese source and molten salt.