Abstract
Multiple lithium-ion transport pathways and local phase changes upon lithiation in silver hollandite are revealed via in situ microscopy including electron diffraction, imaging and spectroscopy, coupled with density functional theory and phase field calculations. We report unexpected inter-nanorod lithium-ion transport, where the reaction fronts and kinetics are maintained within the neighbouring nanorod. Notably, this is the first time-resolved visualization of lithium-ion transport within and between individual nanorods, where the impact of oxygen deficiencies is delineated. Initially, fast lithium-ion transport is observed along the long axis with small net volume change, resulting in two lithiated silver hollandite phases distinguishable by orthorhombic distortion. Subsequently, a slower reaction front is observed, with formation of polyphase lithiated silver hollandite and face-centred-cubic silver metal with substantial volume expansion. These results indicate lithium-ion transport is not confined within a single nanorod and may provide a paradigm shift for one-dimensional tunnelled materials, particularly towards achieving high-rate capability.
Highlights
Multiple lithium-ion transport pathways and local phase changes upon lithiation in silver hollandite are revealed via in situ microscopy including electron diffraction, imaging and spectroscopy, coupled with density functional theory and phase field calculations
While some hollandite-type materials have been previously studied for battery use[12,13,14], preparation of pure silver hollandite at sufficient scale for electrochemical assessment was elusive until enabled by hydrothermal methods in 2007 and a lowtemperature reflux-based synthesis in 2010
Using an in situ scanning/transmission electron microscopy (S/TEM) approach developed at Brookhaven National ‘Loapbeorraantdoory’,21re, vleitahliinagtionnotoofnAlygL1.i6þMnd8iOffu16sionnanaolornogdsanisinodbisveirdvueadl nanorod, and the first direct experimental observation of lateral (a–b oriented) transfer of Li þ between nanorods
Summary
Multiple lithium-ion transport pathways and local phase changes upon lithiation in silver hollandite are revealed via in situ microscopy including electron diffraction, imaging and spectroscopy, coupled with density functional theory and phase field calculations. A slower reaction front is observed, with formation of polyphase lithiated silver hollandite and face-centred-cubic silver metal with substantial volume expansion. These results indicate lithium-ion transport is not confined within a single nanorod and may provide a paradigm shift for one-dimensional tunnelled materials, towards achieving high-rate capability. The sample with greater quantities of oxygen vacancies exhibited a seven-fold increase in discharge capacity in lithium based batteries[19], where the significant differences in capacity were retained upon extended discharge–charge cycling[17,20] In this prior work, it was hypothesized that the MnO6 octahedral vacancies facilitated lateral (a–b plane) Li distortions and þ diffusion[19]. Coarse-grained thermodynamic simulations capture the formation of polyphase material in the b regime and the evolution of the RF that separates the g regime
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