Development of Lithium/Sodium-Ion Battery Electrodes Based on Solvent Engineered Tin(II) Oxide Nanomaterials

With the global economy pushing towards a greener and cleaner energy future for the world, renewable energy storage technologies must continue to develop and improve to allow for a seamless transition from the ways of the past to a carbon neutral future. To this end, renewable battery technology and in particular that of the capacity of the anode must be improved. Furthermore these improvements must be made across various battery technologies (Lithium/Sodium-ion) and be cost-effective to allow for its widespread implementation and use worldwide.<br/><br/>In this work, Tin(II) Oxide (SnO)/single wall carbon nanotube (SWCNT) composite electrodes are analysed as a possible alternative anode material for both lithium (LIB) and sodium-ion batteries (NIB). The LIB is limited by the current commercial anode material of graphite with a relatively low theoretical capacity of 372 mAh g^-1whilst NIB’s use hard carbon with a capacity of roughly 300 mAh g^-1. Alloy/de-alloy materials are envisioned to be a suitable candidate for next generation LIBs/NIBs due to their large specific capacities although major drawbacks concern the poor cycling life associated with the volume change and the associated irreversible capacity. To overcome such issues the downsizing of materials from the micro to the nanoscale and the fabrication of composites which incorporate both lithium active and inactive material are viewed as the most promising solutions. Nanostructured transition metal oxides, forming an inactive lithium oxide matrix are appealing candidates.<br/><br/>Through the implementation of a solvent engineered wet chemistry synthesis, various layered SnO microparticles are produced with several morphologies well-suited to energy storage applications whilst also being scalable and cost-effective. While SWCNTs are themselves not suited towards energy storage applications, their incorporation in the electrodes allows them to act as a conductive additive at a lower weight loading than other conventional carbon sources (carbon black/graphite), presenting a more effective strategy to form an effective electrical percolation network while also removing the need for polymer binders.<br/><br/>Four morphologies were selected as promising towards LIB/NIB technology and binder free electrodes were produced via filtration, removing the need for a copper current collector. The four morphologies were “thick squares” (SnO produced in H₂O), “nanoflowers” (ethanol), “platelets” (methanol:water, 70:30) and “perforated thick squares” (1-hexanol). All morphologies of SnO tested produced high capacity anodes in both LIBs/NIBs after mass loading optimization of CNTs. The thinner “platelet” like morphologies formed in ethanol and 70% methanol produced the highest capacities at low C-rates, with initial discharges of 960 and 985 mAh g^-1 recorded respectively in LIBs. The reduced dimensions and significantly increased surface area of the platelet-like structures permit greater contact between electrode and electrolyte resulting in higher Li⁺ ion flux across the interface and thus greater charge capacity. A maximum capacity of 670 mAh g^-1 was recorded for the nanoflower morphology in NIB with testing currently occurring on the remaining morphologies. Furthermore, using the “nanoflower” morphology and a mass loading of 5 mg cm^-2, an areal capacity of 5.41 mAh cm^-2 was recorded which is far in excess of commercial graphite anodes. Issues still remain regarding the cycling performance of the material due to the larger volumetric change associated with the charge/discharge process (360%) and this is where current work is focused.<br/><br/><b>Reference</b><b>s</b><b>:</b><br/><b>[1]</b> S. Jaskaniec, S. R. Kavanagh, S. Ryan, J. Coelho, C. Hobbs, A. Walsh, D. O. Scanlon and V. Nicolosi, <i>npj 2D Mater. Appl.</i>, 2021, <b>5</b>, 27.<br/><b>[2] </b>J. H. Shin and J. Y. Song, <i>Nano Converg.</i>, 2016, <b>3(1)</b>, 9.<br/><b>[3] </b>F. Zhang, J. Zhu, D. Zhang, U. Schwingenschlögl and H. N. Alshareef, <i>Nano Lett.</i>, 2017, <b>17</b>, 1302–1311.