In order for a battery to discharge with complete use of all the active material, electrons and ions must be able to access every particle effectively. Typical transition metal oxides and in particular phosphate materials are poorly electrically conducting. Thus, practical deployment of these active material classes within a battery electrode demands distribution of the active material with a conductive additive, such as carbon, and a polymeric binder providing attachment to a current collector. The distribution of the multiple components of an electrode are typically random where localized resistances can result in isolation or non-uniform active material utilization. A different approach to material and the accompanying electrode design is the use of multi-functional active materials where the materials are both electrochemically active and electrically conductive. We have been successful at identifying, synthesizing and studying several bimetallic families of compounds incorporating a silver metal cation in the parent structure. Upon initiation of reduction, the silver cation, Ag+, is reduced to silver metal, Ag0. The silver metal forms nanoparticles on the surface of each particle through the electrochemical reduction-displacement reaction enveloping each particle in a highly conductive shell and generating a conductive network throughout the electrode structure. We have demonstrated the breadth of this approach through investigation of several classes of compounds. Examples include silver ferrite, a layered delafossite with the formula AgFeO2, silver vanadium oxide Ag2V4O11, as well as silver hollandite AgxMn8O16, a tunnel structured material. The most dramatic increase in conductivity was observed for the silver vanadium phosphorous oxides, AgwVxPyOz, with an increase in conductivity of ~10,000X on initiation of the reduction-displacement reaction. The formation of silver metal on reduction has provided us a mechanistic probe to follow the in-situ formation and evolution of electrical conduction pathways within functioning battery electrodes. Synchrotron based X-ray diffraction was effectively used due to detect high atomic number silver yielding unprecedented insights into rate dependent behavior measured in 3-dimensional electrodes during cell operation. Understanding the operation of energy storage systems under application relevant conditions is key to realizing the goals of full utilization of every electroactive particle.

Electrochemical reduction-displacement: Multifunctional material paradigm for mechanistic inquiry and effective material utilization

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.