A comparative study of the effect of synthesis method on the formation of P2- and P3-Na0.67Mn0.9Mg0.1O2 cathodes

Na-ion batteries offer a way to develop large-scale energy storage necessary for the increased adoption of renewable energy sources. Layered transition metal oxide materials for electrodes can be synthesised using abundant and non-toxic materials, decreasing costs and risks compared to lithium-ion batteries. Solid state processing is commonly used for synthesis, using long calcinations at high temperatures (>800 °C). Other synthetic routes, such as biotemplating, offer the opportunity to reduce reaction temperatures and times, and can enable access to different polymorphs. Here, we compare the properties of Na0.67Mn0.9Mg0.1O2 synthesised by both solid state and biotemplating, producing both P2 and P3 polymorphs to understand the differences which arise as a result of synthesis and temperature choice. We show that biotemplated P3-Na0.67Mn0.9Mg0.1O2 offers increased discharge capacity over the more commonly reported P2 phase for 50 cycles at C/5, 103 mAh g−1 for biotemplated P3-NMMO. Furthermore, the biotemplating samples demonstrate improved capacity after 50 cycles at C/5, and higher capacity delivered at 5C in both P2 and P3 phases over conventional solid state synthesis.