Effect of 1D diffusion channel size and ionic content on Li+ ion and Na+ ion diffusion in tunnel manganese oxides

Abstract

The conduction of both electrons and cations is important for battery electrode materials to deliver high capacities at higher current rates. Here, we investigate the ion diffusion and electronic conductivities of three tunnel manganese oxide phases with different size structural tunnels and templating cations for use as Li-ion and Na-ion battery (LIB and SIB) electrodes. The galvanostatic intermittent titration technique is used to measure the apparent diffusion coefficients of Li+ ions and Na+ ions in each material, and a four-point probe technique is used to measure the electronic conductivity of each phase. It is found that in LIBs, the material with the largest tunnels and greatest volume available for Li+ ion intercalation demonstrated the highest DLi+ value, correlating with the highest performance at the highest current rate used in this work. In SIBs, however, it is not the material with the largest tunnels that demonstrates the highest rate performance. Rather, it is the material templated by Na+ ions, the same ions as the electrochemically cycled charge carriers. These results highlight the importance of the relationship between the structural tunnel size, nature of templating ions and charge-carrying ion size and provide insights into the design of electrode material for improved energy storage systems.