UC San Diego

The development of high-performing battery materials is critical to meet the ever-increasing demand for portable energy storage for electronics and electric vehicles. Owing to their exceptionally high-rate capabilities, high volumetric capacities and long lifetimes, Wadsley-Roth compounds are promising lithium anode materials for fast-charging and high-powered devices. This study comprises an in-depth structural and initial electrochemical investigation of the Wadsley-Roth phase NaNb13O33 phase. To our knowledge, this is the first alkali-containing Wadsley-Roth compound tested for lithium insertion. Here, we report structural insights obtained from combined neutron and synchrotron diffraction as well as solid-state nuclear magnetic resonance (ss-NMR). We find that a variety of simple, solid-state methods reliably produce a ReO6-like base structure with periodic, ”shear” planes of edge-sharing NbO6 octahedra separating 5 x 3 octahedral blocks with square-planar Na+ occupying block corners. Through ss-NMR, we reveal the presence of sodium cations in block interior sites as well as square-planar block sites. Through combined experimental and computational studies, we demonstrate and rationalize the high-rate performance of this new anode material in lithium-ion half cells. Using X-ray photoelectron spectroscopy (XPS), we show the multi-electron redox of Nb, which enables capacities of 225 mA h g−1 at slow rates and anodic potentials. Without down-sizing or nano-scaling, 100 mA h g−1 of this capacity is retained at 20 C in micrometer-scale particles. By combining bond-valence mapping and DFT, we show that such excellent rate performance results from facile, multi-channel lithium diffusion down octahedral block interiors and from high electronic conductivity within shear planes. Finally, we utilize differential capacity analysis to identify optimal long-term cycling rates and achieve 80% capacity retention over 600 cycles with 30-minute charging and discharging intervals. Without optimization, these results place NaNb13O33 in the ranks of promising new high-rate lithium anode materials and warrant further research.