Vanadium-Substituted Tunnel Structured Silver Hollandite (Ag_1.2VMn_8-O₁₆): Impact on Morphology and Electrochemistry

A series of tunnel structured V-substituted silver hollandite (Ag_1.2VMn_8-O₁₆, x = 0-1.4) samples is prepared and characterized through a combination of synchrotron X-ray diffraction (XRD), synchrotron X-ray absorption spectroscopy (XAS), laboratory Raman spectroscopy, and electron microscopy measurements. The oxidation states of the individual transition metals are characterized using V and Mn K-edge XAS data indicating the vanadium centers exist as V⁵⁺, and the Mn oxidation state decreases with increased V substitution to balance the charge. Scanning transmission electron microscopy of reduced materials shows reduction-displacement of silver metal at high levels of lithiation. In lithium batteries, the V-substituted tunneled manganese oxide materials reveal previously unseen reversible nonaqueous Ag electrochemistry and exhibit up to 2.5× higher Li storage capacity relative to their unsubstituted counterparts. The highest capacity was observed for the Ag_1.2(V_0.8Mn_7.2)O₁₆·0.8H₂O material with an intermediate level of V substitution, likely due to a combination of the atomic composition, the morphology of the particle, and the homogeneous distribution of the active material within the electrode structure where factors over multiple length scales contribute to the electrochemistry.