Nanomanufacturing Transition Metal Oxide Composite Electrode Architectures Via Electrodeposition

Abstract

Electrode architectures that combine a conductive carbon material and a high capacity active material have the potential to close the gap between batteries and capacitors. Going forward, more research efforts need to be focused on developing robust manufacturing and processing methods for hierarchical electrode architectures. In this work, we have used cyclic voltammetry to electrodeposit orthorhombic molybdenum trioxide (α-MoO3) onto a free-standing carbon nanotube foam (CNTF). The porous carbon mesostructure provides sufficient ion diffusion and electrical conduction throughout electrodes with high active material loading. Furthermore, α-MoO3 has a layered structure that is capable of intercalating up to 1.5 Li ions per mole of molybdenum (280 mAh/g), while having fast charge/discharge kinetics since the Li ions are intercalating into the interlayers instead of causing slow phase transformations in the active material. Electrodeposition of the α-MoO3 was carried out using an acidified disodium molybdate dihydrate aqueous precursor solution, in a process that only took ~3 to ~30 minutes depending on the user-defined parameters. This work investigated the effect of concentration and pH of the precursor and post-synthesis heat treatment on the morphology and electrochemical performance of the resulting electrodes. Scanning electron microscopy showed that the as deposited sample formed a smooth, conformal coating on the surface of the CNTs, while a faceted microstructure formed upon heat treatment. Raman spectroscopy confirmed that the as-deposited materials was an amorphous hydrated molybdate structure, in agreement with electrochemical results, while the heat treated material was α-MoO3. Electrochemical characterization was performed in a three-electrode configuration with a Li counter and reference electrode, α-MoO3/CNTF working electrode and a 1M LiClO4 in PC electrolyte. Cyclic voltammetry showed that electrodes with high active material loading (>4 mg cm-2) maintained similar rate capability to electrodes with low active material loading (~1 mg cm-2). Overall, this work has demonstrated that electrodeposition can be used as a robust synthesis technique for layered TMOs for high energy and high power density electrodes, and it revealed the effects of various synthesis parameters on the morphology and electrochemical performance of electrodeposited α-MoO3 on CNTFs.