Structural and Dynamical Insights of Cu-Coordinated Cellulose Nanofibers for Li+ Battery by NMR Spectroscopy

Abstract

In the quest of novel sustainable research to meet the global surge of clean energy demand, cellulose nanofibers (CNF) derived from natural wood materials offer exceptional properties for safe, cost-effective, efficient Li+ batteries. A new strategy has been established via introducing Cu2+ into the CNF to achieve a greater mobility of Li+, where Cu2+ opens up one-dimensional nanofibrils and creates molecular channels.1 Various experimental methods and molecular dynamic simulations have been used to characterize these materials. In this context, Nuclear Magnetic Resonance (NMR), a highly sensitive technique plays a significant role in providing new insights into the structure and dynamics of Li-Cu-CNF materials. In collaboration with Prof. Liangbing Hu, University of Maryland, current research focusses on studying highly conductive Li-Cu-CNF materials prepared with different Li-salt via different synthetic approaches in the ARPA-E project. Fast magic angle spinning (MAS) detecting 1H helps in estimating the residual solvent/H2O present in Li-Cu-CNF materials, which is crucial to determine the Li+ transport mechanism. Pulsed Field Gradient (PFG) NMR has been used to measure the diffusivity of Li+ and anion and to estimate the Li+ transference number (t Li+). We found that the estimated t Li+ of studied Li-Cu-CNF materials is much greater as compared to the other polymer-based electrolytes. Additionally, the anisotropic diffusion of Li+ and anion in aligned cellulose wood materials have been well-established through PFG NMR. Lastly, the local structure of cellulose fibers and their spatial interactions with ionic species are probed through multi-dimensional (1D and 2D) solid state NMR detecting 1H, 7Li, 19F, 13C nuclei. Reference. Yang, Q. Wu, W. Xie, X. Zhang, A. Brozena, J. Zheng, M. N. Garaga, B. H. Ko, Y. Mao, S. He, Y. Gao, P. Wang, M. Tyagi, F. Jiao, R. Briber, P. Albertus, C. Wang, S. Greenbaum, Y.-Y. Hu, A. Isogai, M. Winter, K. Xu, Y. Qi, and L. Hu, Copper-coordinated cellulose ion conductors for solid-state batteries. Nature (2021) 598, 590–596.