Theoretical Study of Correlation of Sodium Cluster and NMR Analysis in Sodium-ion Rechargeable Batteries

The lithium ion batteries (LIB) which are a typical secondary batteries, is widely used as an energy storage system. However, due to problems with the resources and costs of lithium in LIB, there is a growing interest in resource-rich sodium-ion batteries (NIB) with equivalent electrode potential. In recent years, a NIB using a Na metal oxide as the positive electrode and hard carbon (HC) as the negative electrode has attracted attention in particular. To develop a NIB with high capacity, high efficiency, long life, and acceptable safety, it is essential to elucidate the state of the sodium ion and the mechanism of charge and discharge on the electrode. The states of sodium electrochemically inserted in HC samples have been experimentally reported using solid ²³Na-NMR ^{[1, 2]}. In this study, in order to study the correlation of NMR shift of Na clusters with pore size in HC and structure and the electron density dependence of the 3s orbital, DFT calculations are performed at the level of B3LYP/6-31G(d) using the Gaussian 16.
As a results, the value of chemical shielding depends on the interaction between Na atoms and the size of clusters from NMR analysis.
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[2] R. Morita, et al., Carbon, 2019, 145, 71