Transition metal oxalates as energy storage materials. A review

Recently, there has been growing interest in the application of transition metal oxalates as energy storage materials. In addition to energy storage applications, these materials also offer the potential to act as a carbon sink, thereby offering an opportunity for more sustainable/greener energy storage materials. Over the past decade, the electrochemical performance of transition metal oxalates has been explored in the context of various energy storage devices such as lithium ion batteries, sodium ion batteries, supercapacitor electrodes and redox flow batteries. This review presents recent work and advances relating to the application of transition metal oxalates as potential energy storage materials. Transition metal oxalates are a versatile material, with a variety of roles depending on the energy storage method (e.g. conversion-type negative electrode material in lithium ion batteries or stabiliser additive in redox flow batteries). Mn, Fe, Cu, Ni, Co and Zn based oxalates have been investigated predominantly in the context of lithium ion batteries and supercapacitors, with electrochemical performances comparable to and at times better than their equivalent oxides. Although their performances can be improved via elemental substitution and mixing with carbon-based materials, details of the electrochemical reactions are still not fully understood.