Ni-B/RGO anode material for efficient and stable Li-ion batteries

Abstract

Lithium ion batteries (LIBs) are considered as main sources of power for portable electronic devices due to high energy density and long durability and they are deployed for power supply in hybrid electric and electric vehicles. Conventional anodes for LIBs use graphite, however it has limited capacities (372 mAh g-1) to satisfy the demands for high capacity applications. Therefore, conversion-type anodes with higher capacities are being magnified as promising anodes. Among them, boron with light weight has the highest theoretical capacity by forming up to five bonding with lithium ions in theory. Nevertheless, boron materials have not received attention due to their inertness, leading to difficulties in reacting directly with lithium. To overcome the problems, we design Ni-B/RGO composites as anode materials, which combine merits of Ni and RGO. The Ni can activate boron materials by helping to accommodate lithium ions and RGO can prevent the agglomerations of particles and alleviate volume expansions, resulting in improved stability of electrode. The Ni-B/RGO composite is successfully synthesized via a simple chemical reduction and it shows that Ni, B nanoparticles are uniformly distributed on RGO. The cycling performance of Ni-B/RGO exhibits high capacity with good reversibility and it is attributed to redox mechanisms of B2O3, NiO, and B. Especially, long-term cyclic capacity of Ni-B/RGO reaches up to 1200 mAh g-1 at 400 mA g-1. It is because B from reduction of B2O3 is dispersed well, and then enhances reactions with lithium ions, contributing to increase in capacities gradually. After long cycles, Ni-B/RGO is maintained without volume changes in addition to uniform dispersions of elements. Therefore, Ni-B/RGO keeps the high stability during long cycles and it leads to high reversibility.