Wadsley-Roth (W-R) crystallographic shear structures exhibit multi-electron redox (beyond 1.0 Li+/transition metal) and extraordinarily fast Li-ion diffusion coefficients (DLi+) that are two orders of magnitude greater than commercialized LTO. Shear structures are highly tunable and distinguished by their chemistry, stoichiometry, block size, and characteristic block joining.&lt;font size="1"&gt; &lt;/font&gt;W-R shear structures consist of n×m blocks of corner-sharing octahedra connected to neighboring blocks via edge-sharing octahedra. The blocks extend indefinitely in the direction perpendicular to the n×m block plane. Here we test a literature hypothesis that DLi+ increases with block size. We synthesized three compounds in the Nb2O5-WO3 system: (3×4) Nb12WO33, (4×4) Nb14W3O44, and (4×5) Nb16W5O55. These compounds share the same block connectivity (i.e., joined by tetragonal site at the block corners). Keeping this structural motif consistent is important because the blocks connected by tetragonal sites have different Li-ion binding sites than those that do not. We discuss electrochemical properties and performance trends in coulombic efficiency, capacity, and Li-ion diffusivity as a function of block size and available Li-ion binding sites.

Lithium-ion diffusivity increases with block size in niobium tungsten oxide shear structures

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ACS Fall 2022

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