X-ray absorption spectroscopy and energy storage of Ni-doped cobalt nitride, (Ni0.33Co0.67)N, prepared by a simple synthesis route

Abstract

Metal nitride (Ni_0.33Co_0.67)N nanoparticles are prepared by nitridation using NiCo₂O₄ as a precursor material by heating at 335 °C for 2 h in flowing NH₃ + N₂ gas and characterized by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high resolution-transmission electron microscopy (HR-TEM), along with selective area electron diffraction (SAED) and X-ray absorption spectroscopy (XAS) techniques. The X-ray absorption near edge structure (XANES) at the Co K-edge showed that the oxidation state of cobalt is close to 3+. The (Ni_0.33Co_0.67)N showed a shift in edge energy towards lower values due to Ni-doping to cobalt site. The Li-storage behaviour of (Ni_0.33Co_0.67)N nanoparticles was evaluated by galvanostatic cycling and cyclic voltammetry in the cells with Li-metal as counter electrode in the voltage range of 0.005–3.0 V at ambient temperature. When cycled at 250 mA g⁻¹, the first-cycle reversible capacity of 700 (±5) mA h g⁻¹ (∼1.9 moles of Li) is obtained. It showed an initial decrease in capacity until the 10^th cycle and a stable capacity of 400 (±5) mA h g⁻¹ (∼1.09 moles of Li) is observed at the end of the 50^th cycle. Excellent rate capability is also shown when cycling at 500 mA g⁻¹ (up to 50 cycles). The materials showed excellent Li-ion insertion/extraction, with the coulombic efficiency reaching almost 99% in the range of 10–50 cycles. The average charge and discharge potentials are ∼2.03 and ∼1.0 V, respectively for the decomposition/formation of Li₃N as determined by electroanalytical techniques.