University of Cambridge > > Mineral Sciences Seminars > Energy Storage and Conversion: Using Local Structural Probes to Understand and Optimise Function of Battery and Fuel Cell Materials

Energy Storage and Conversion: Using Local Structural Probes to Understand and Optimise Function of Battery and Fuel Cell Materials

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The application of new Nuclear Magnetic Resonance (NMR) approaches to correlate structure and dynamics with function in materials lithium-ion batteries and solid oxide fuel cells will be described. A particular focus is the development of methodology to allow these systems to be investigated in-situ, i.e., under realistic operating conditions. This allows processes to be captured, which are very difficult to detect directly by ex-situ methods. For example, we can detect side reactions involving the electrolyte and the electrode materials, and processes that occur during extremely fast charging and discharging. The approach will be demonstrated for the anode material silicon. Lithium-ion batteries (LIBs) containing silicon have been the subject of much recent investigation, because of the extremely large gravimetric and volumetric capacity of this anode material. This material undergoes a crystalline-to-amorphous phase transition on electrochemical Li insertion into crystalline Si, during the first discharge, hindering attempts to link structure in these systems with electrochemical performance. We apply a combination of static, in-situ and magic angle sample spinning, ex-situ 7Li and 29Si nuclear magnetic resonance and pair distribution function analysis studies to investigate the changes in local structure that occur in the actual working LIB . The first discharge occurs via the formation of isolated Si ions and smaller Si-Si clusters embedded in a Li-ion matrix; the latter are broken apart at the end of the discharge forming isolated Si ions. In a second example, we illustrate the use of NMR to investigate the nature of the defects in materials that have been proposed for use as electrolytes that operate via either oxygen-ion or protonic conduction in solid oxide fuel cells. For example, BaZrO3 or BaSnO3 can be doped with Y3+ to create oxygen vacancies. These vacancies can be filled with H2O , the water molecules dissociating to form mobile ions that contribute to the long-range ionic transport in these systems. NMR experiments are used to examine the local structure, the locations of the vacancies and how this affects protonic/oxygen ion motion in these systems.

This talk is part of the Mineral Sciences Seminars series.

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