Binder-Free ZnO Cathode synthesized via ALD by Direct Growth of Hierarchical ZnO Nanostructure on Current Collector for High-Performance Rechargeable Aluminium-Ion Batteries

Abstract

Nanoscale ZnO, directly grown on current collector through ALD, shows high electrochemical performance as a binder-free cathode for rechargeable Al-ion batteries (AIBs). Al coin cell fabricated using binder-free ALD grown ZnO cathode (ZnO-ALD-E) manifests an initial discharge capacity of 2563 mAh g-1, and remains at 245 mAh g-1 at a current rate of 400 mA g-1 after 50 cycles with almost 95% Coulombic efficiency. Distinct and consistent plateaus in discharge/charge curves reveal the Al-ion insertion/extraction process and electrochemical stability of the battery. The delivered discharge capacity of the battery with ZnO-ALD-E cathode is significantly higher (1000%) than that of batteries fabricated using a conventional ZnO cathode composed of ZnO powder (nanoparticles or bulk) and binder with conductive carbon. Ex-situ XRD and Photoluminescence spectroscopy in different discharge/charge states of Al/ZnO-ALD-E battery reveal the structural information of ZnO-ALD-E, upon Al-ion intercalation/deintercalation. Such remarkable electrochemical performance is attributed to the binder-free, well-defined textured nanostructures of ALD grown ZnO cathode with c-axis orientation along the surface normal, facilitating good electrical contact and enhanced pathways for electron/ion transfer/transport kinetics. First principle based DFT calculations explain the Al-ion intercalation phenomena in the framework of c-axis oriented ZnO. The proposed concept provides a strategy for transitioning to next-generation AIBs with a binder-free cathode. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim