Sodium-ion batteries (NIBs) are gaining traction as a next-generation technology to complement the widely used lithium-ion batteries (LIBs). NIBs offer clear advantages versus LIBs in terms of sustainability and cost, as they rely on sodium—an element that, unlike lithium, is abundant almost everywhere on Earth. However, for NIBs to achieve widespread adoption, they must reach energy densities comparable to LIBs.
State-of-the-art NIB designs use hard carbon (HC), a porous and amorphous type of carbon, as an anode material. Scientists believe that sodium ions aggregate into tiny quasi-metallic clusters within HC nano-pores, and this “pore filling” process remains as the main mechanism contributing to the extended reversible capacity of the HC anode.
Despite some computational studies on this topic, the fundamental processes governing sodium storage and transport in HC remain unclear. Specifically, researchers have struggled to explain how sodium ions can gather to form clusters inside HC pores at operational temperatures, and why the overall movement of sodium ions through the material is sluggish.
