Abstract
Understanding the sodium (Na) storage mechanism in hard carbon (HC) is critical for the development of high-performance Na-ion batteries, which are a promising alternative to lithium-ion batteries owing to the abundance and low cost of Na. In this study, we investigate the Na storage mechanism in commercial HC using operando small- and wide-angle neutron scattering (SANS and WANS). The experiments cover a wide range of scattering vectors, enabling the simultaneous observation of the structural evolution of nanoporous regions and graphene layers during electrochemical charging. Both SANS and WANS analyses reveal that Na storage proceeds sequentially via initial surface adsorption, subsequent insertion into graphene layers, and final filling of nanopores. These results demonstrate the effectiveness of simultaneous operando SANS and WANS measurements for elucidating the complex, multiscale mechanisms of Na storage in HC.