The maximum power output and minimum charging time of a lithium-ion battery – key parameters for use in e.g. transportation applications – depend on mixed ionic–electronic transport. While the rate and capacity can be tuned by varying the composite electrode structure, ionic transport within the active particles represents a fundamental limitation. Thus, to achieve high rates, particles are frequently reduced to nanosize dimensions despite disadvantages in volumetric packing density as well as cost, stability, and sustainability. As an alternative to nanoscaling, we show that complex niobium tungsten oxides with topologically frustrated polyhedral arrangements and dense μm-scale particle morphologies can rapidly and reversibly intercalate large quantities of lithium. Multielectron redox, buffered volume expansion, and Li transport approaching that of a liquid lead to extremely high volumetric capacities and rate performance in both crystallographic shear and bronze-like oxides. The active materials Nb16W5O55 and Nb18W16O93 offer new strategies toward designing electrodes with advantages in energy density, scalability, electrode architecture, and cost as alternatives to state-of-the-art high-rate anodes (Figure 1). The direct measurement of solid-state lithium diffusion coefficients (DLi) with PFG NMR demonstrates DLi values of 10–12–10–13 m2 × s–1, which is orders-of-magnitude faster than typical electrode materials and corresponds to a characteristic diffusion length of ~10 μm in 1 minute. Structural and chemical analysis of high-rate and multi-electron energy storage will be discussed with insights from operando X-ray diffraction and multi-edge X-ray absorption spectroscopy. Materials and mechanisms that enable lithiation of μm particles in minutes have implications for high power applications, fast charging devices, all-solid-state batteries, and general approaches to electrode design and material discovery.

Niobium tungsten oxides for high-rate lithium-ion energy storage

2019 Spring National Meeting

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