Argyrios Karatrantos and Dr. Qiong Cai from the Department of Chemical Engineering, University of Surrey, have recently published a paper on the “Effects of pore size and surface charge on Na ion storage in carbon nanopores” in the Royal Society of Chemistry journal, Physical Chemistry, Chemical Physics.
Sodium (Na) ion batteries are under consideration for grid-scale energy storage, as they may offer a low cost and sustainable alternative to their Li-ion counterparts. The challenge is to achieve similar energy densities and speed of charge/discharge. Porous carbons, currently used in Li ion batteries, make good electrodes, as they are cheap to produce, allow ions to move through them and are conductive. When the mobile ions are Na+, instead of Li+, it is important to understand how these interact with the electrode and particularly to see if changing the structure of the electrode can improve the mobility of Na ions and hence the performance of sodium batteries.
In this paper, the researchers use molecular dynamics simulations to examine how the Na ions behave when confined with carbon nanopores, paying particular attention to the effect of pore size and surface charge density. The operating conditions of sodium ion batteries were simulated and the mobility of the Na ions measured. They found that, through electrostatic interactions, more Na ions enter the pores when the surface charge density is higher, sometimes forming multiple layers. Nanopore width was also found to play a role.
The simulation methodology developed here can be applied more widely to different forms of carbon and different solvents, to help researchers design better anodes and estimate cell performance for sodium ion batteries.