In recent years Li-ion batteries have been the subject of an extensive research effort aimed at improving their performance for ever more demanding energy storage applications. (1, 2) The demands from consumer devices such as smartphones as well as electric vehicles have necessitated studies into the development of active materials with higher specific capacities and enhanced cycle-lives. With regards to anode materials three distinct classes of materials are being investigated namely, intercalation mode, alloying mode and conversion mode materials.(3-5) Conversion mode materials store charge via the transformation of a transition metal oxide (e.g. Co₃O₄, MnO etc.) to its parent metal and LiO₂ during charging, with the metal being oxidised during discharge (for anodes).(6) Higher specific capacity values can be facilitated from these reactions than typically seen for intercalation materials and consequently, there has been an increase in the interest in the development of conversion mode materials.

In this work, we present the formation of a carbon-coated honeycomb ternary Ni-Mn-Co-O inverse opal (IO) as a conversion mode anode material for Li-ion battery applications. Ni-Mn-Co-O (IO) samples are systemically structurally characterised via a combination of analytical techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, electron microscopy, electron diffraction, Raman spectroscopy and Energy-dispersive X-ray spectroscopy. This Ni-Mn-Co-O oxide material is unlike the classic lithiated NMC cathode material (LiNi_0.33Mn_0.33Co_0.33O₂) and functions as a conversion mode anode material.

The electrochemical performance of the Ni-Mn-Co-O material is evaluated through analysis of results obtained from cyclic voltammetry, rate capability testing and galvanostatic charging and discharging. The effect of ordering is investigated by comparing the performance of highly ordered, porous Ni-Mn-Co-O IO samples with disordered Ni-Mn-Co-O nanoparticles. We demonstrate that ordering and electrolyte additives have a profound influence of the specific capacity values and the capacity retention observed for our Ni-Mn-Co-O anode materials. In order to investigate the practical potential of C-coated Ni-Mn-Co-O IO anodes, they were tested in a full cell arrangement against a V₂O₅ IO cathode. Similar to our previous work, the Ni-Mn-Co-O IO anode was electrochemically pre-charged by a single charge against a Li metal counter electrode before being paired with a V₂O₅ IO cathode.(7) We demonstrate that the capacity values obtained the V₂O₅ IO/Ni-Mn-Co-O IO full cells are greater than previously reported values for V₂O₅ nanostructures cycled against Li in a half cell configuration.(8)

Acknowledgements

This work was also supported by Science Foundation Ireland (SFI) through an SFI Technology Innovation and Development Award under contract no. 13/TIDA/E2761. This research has received funding from the Seventh Framework Programme FP7/2007-2013 (Project STABLE) under grant agreement no. 314508. This publication has also emanated from research supported in part by a research grant from SFI under Grant Number 14/IA/2581.

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