Deconvolution of composition and crystallite size of silver hollandite nanorods: Influence on electrochemistry

Silver hollandite (Ag_1.4Mn₈O₁₆) has been synthesized by an aqueous, low-temperature co-precipitation technique to afford silver hollandite with distinct crystallite sizes (10 and 15 nm, identified as S-Ag_1.4Mn₈O₁₆ and L-Ag_1.4Mn₈O₁₆, respectively) and equivalent silver content (x), allowing for the deconvolution of electrochemical effects related to crystallite size and silver content. The as-prepared silver hollandite materials were confirmed to be structurally analogous. Notably, TEM imaging reveals a high degree of bundling of S-Ag_1.4Mn₈O₁₆ nanorods compared to L-Ag_1.4Mn₈O₁₆ which facilitates more intimate connection of the S-Ag_1.4Mn₈O₁₆ material with enhanced interparticle contact. The electrochemical behavior and lithium diffusion properties were investigated by galvanostatic cycling, CV, electrochemical impedance, pulsed-discharge experiments, and ex-situ XAS analysis of cycled cathodes. Lithium based electrochemical cells containing S-Ag_1.4Mn₈O₁₆ delivered a capacity 15X higher than L-Ag_1.4Mn₈O₁₆ on cycle 1. Ex-situ XAS demonstrated structural change for S-Ag_1.4Mn₈O₁₆ and formation of Ag⁰ on insertion of 3.8 Li⁺ intercalation. However, the samples of L-Ag_1.4Mn₈O₁₆ were lithiated by a more limited 0.25 molar equivalents, where no significant structural changes were observed. The findings affirm crystallite size significantly impacts electrochemistry independent of cation occupancy of the α-MnO₂ type structure.