Connecting electronic structure to phenomenological descriptions of dynamic processes in electrodes

Anton van der Ven
University of California, Santa Barbara (UC Santa Barbara)

Kinetic processes within the electrodes of energy storage devices remain poorly understood and characterized. Lithium insertion and removal from electrode materials, for example, requires solid-state diffusion at non-dilute concentrations and is often also accompanied by a sequence of diffusional and structural phase transitions. Since these phase transformations happen rapidly at room temperature, they are difficult to characterize experimentally. First-principles statistical mechanical approaches are now capable of predicting key electronic, thermodynamic and kinetic properties of electrode and electrolyte materials. They have been especially useful in elucidating the role of chemistry and crystal structure on ionic mobility as a function of concentration in intercalation compounds. By relying on effective Hamiltonians and kinetic Monte Carlo simulations to evaluate Kubo-Green expressions, it is possible to predict diffusion coefficients in arbitrarily complex crystal structures and at non-dilute concentrations. Electrode materials used in energy storage devices are also affected by a strong coupling between chemistry and mechanics. Charging and discharging of electrode materials can produce local stress intensities due to concentration gradients and misfit strain across migrating interfaces. First-principles electronic structure calculations have demonstrated that fracture properties can depend strongly on the local chemistry, making the susceptibility of electrode materials to fracture very sensitive to the state of charge.

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