Optimizing discharge product morphology with hetero-nanostructured NiCoP/NiCo2O4 for enhanced sustainability in Li–O2 battery performance

Abstract

Progress in Li–O₂ battery (LOB) research is crucial for achieving the ambitious goal of full electrification in transportation. However, one of the major challenges that continues to hinder advancements in LOB technology is the difficulty in effectively catalyzing the slow oxygen kinetics. This study addresses this issue by synthesizing a groundsel flower-like hierarchical microsphere network of NiCoP/NiCo₂O₄ (NCP@NCO/Ni) in situ, grafted onto nickel foam as a high-performance oxygen cathode for LOBs. The presence of heterogeneous NiCoP and NiCo₂O₄ significantly enhances oxygen reduction and evolution reactions by promoting efficient surface electron transfer. The assembled LOB cells exhibit an exceptional cycle life, sustaining over 400 cycles at a high current density of 800 mA g⁻¹. They also achieve impressive discharge and charge capacities of 15 710 mA h g⁻¹ and 14 632 mA h g⁻¹, respectively, at a rate of 100 mA g⁻¹, with low charging overpotentials. This performance is attributed to the rapid charge transfer across the heterostructure interface. Notably, even after the charge rate increases sixfold, the discharge capacity only decreases by 10%, to 14 092 mA h g⁻¹, while the capacities of pure metal phosphide and metal oxide cathodes degrade significantly. Additionally, the cell's reversibility and performance are improved by the efficient decomposition of the sheet-like Li₂O₂, acting as a parallel array of resistors with lower impedance, overcoming the limitations exhibited by other Li₂O₂ morphologies.