Hyperpolarized 129Xe Nuclear Magnetic Resonance Studies of Si Nanocomposite Electrode Materials

Porosity and interconnectivity of pores play an important role in the performance of composite electrodes in Li ion batteries. Hyperpolarized (HP) Xe-129 nuclear magnetic resonance (NMR) is powerful for probing porosity and interconnectivity of nanopores. This study represents the first time that temperature-dependent HP Xe-129 NMR has been successfully applied to explore the pore structure and interconnectivity in composite electrodes made of nano Si powder, super P carbon, and sodium carboxyl methyl cellulose (CMC) binder. In particular, this work focuses on the influence of the binder content on the porosity and pore interconnectivity in Si composite electrode (Si + C):CMC materials. Our data from HP Xe-129 NMR spectra show that the CMC content has an effect on the porosity and pore interconnectivity of Si nanocomposite electrode materials. We determined parameters, such as pore size, heat of adsorption, and characteristic chemical shift, of (Si + C):CMC samples based on the temperature-dependent HP Xe-129 NMR data. Furthermore, HP Xe-129 NMR data suggest that pore structures are partially collapsed at low temperatures for the electrode materials with a higher CMC content, indicating the potential usefulness of variable-temperature HP Xe-129 MNR for examining the integrity of the electrode. This study demonstrates that HP Xe-129 NMR is a powerful diagnostic tool for probing any changes in porosity and pore connectivity in electrode materials. It provides a better understanding of the mechanical failure as a result of the large volume expansion in Si-based anodes, enabling the design of more robust electrodes in the future.