Operando investigation of SEI formation during Na insertion in hard carbon

We are becoming increasingly reliant on energy storage technologies as a vital part of the solution to the energy crisis we currently face. Therefore, the diversification of battery technology is of increasing importance and one such alternative to the dominant Li-ion technology is Na ion batteries (NIBs) as sodium is significantly more abundant and well distributed in the Earth’s crust compared to lithium. The current anode of choice for NIBs is hard carbon (HC) - a class of disordered, porous and non-graphitic carbonaceous material. There are still key questions about the structure, Na-insertion mechanism, and solid-electrolyte interface (SEI) formation in HC that are unanswered. An operando experiment on NIMROD using our custom cell can shed light on these areas simultaneously, as we will focus on SEI formation. We will use contrast matching through deuterated electrolytes to extract chemical information on the SEI formation during cycling. The large Q-range we can access on NIMROD will allow us to identify changes occurring at all the relevant length scales in this system – at the surface of the particles, in the closed pores, as well as in the graphite layers. We can therefore not only observe SEI formation in the pores, but also on the surface, as well as tracking changes in the graphite as Na intercalation occurs. This will contribute to fundamental understanding of this system needed to optimise the electrochemical properties of the hard carbon anode.