John Bachman

Inorganic Solid-State Electrolytes for Lithium Batteries: Mechanisms and Properties Governing Ion Conduction

This Review is focused on ion-transport mechanisms and fundamental properties of solid-state electrolytes to be used in electrochemical energy-storage systems. Properties of the migrating species significantly affecting diffusion, including the valency and ionic radius, are discussed. The natures of the ligand and metal composing the skeleton of the host framework are analyzed and shown to have large impacts on the performance of solid-state electrolytes. A comprehensive identification of the candidate migrating species and structures is carried out. Not only the bulk properties of the conductors are explored, but the concept of tuning the conductivity through interfacial effects-specifically controlling grain boundaries and strain at the interfaces-is introduced. High-frequency dielectric constants and frequencies of low-energy optical phonons are shown as examples of properties that correlate with activation energy across many classes of ionic conductors. Experimental studies and theoretical results are discussed in parallel to give a pathway for further improvement of solid-state electrolytes. Through this discussion, the present Review aims to provide insight into the physical parameters affecting the diffusion process, to allow for more efficient and target-oriented research on improving solid-state ion conductors.

Electrochemical polymerization of pyrene derivatives on functionalized carbon nanotubes for pseudocapacitive electrodes

Electrochemical energy-storage devices have the potential to be clean and efficient, but their current cost and performance limit their use in numerous transportation and stationary applications. Many organic molecules are abundant, economical and electrochemically active; if selected correctly and rationally designed, these organic molecules offer a promising route to expand the applications of these energy-storage devices. In this study, polycyclic aromatic hydrocarbons are introduced within a functionalized few-walled carbon nanotube matrix to develop high-energy, high-power positive electrodes for pseudocapacitor applications. The reduction potential and capacity of various polycyclic aromatic hydrocarbons are correlated with their interaction with the functionalized few-walled carbon nanotube matrix, chemical configuration and electronic structure. These findings provide rational design criteria for nanostructured organic electrodes. When combined with lithium negative electrodes, these nanostructured organic electrodes exhibit energy densities of ∼350 Wh kg−1electrode at power densities of ∼10 kW kg−1electrode for over 10,000 cycles.

Tuning mobility and stability of lithium ion conductors based on lattice dynamics

Lithium ion conductivity in many structural families can be tuned by many orders of magnitude, with some rivaling that of liquid electrolytes at room temperature. Unfortunately, fast lithium conductors exhibit poor stability against lithium battery electrodes. In this article, we report a fundamentally new approach to alter ion mobility and stability against oxidation of lithium ion conductors using lattice dynamics. By combining inelastic neutron scattering measurements with density functional theory, fast lithium conductors were shown to have low lithium vibration frequency or low center of lithium phonon density of states. On the other hand, lowering anion phonon densities of states reduces the stability against electrochemical oxidation. Olivines with low lithium band centers but high anion band centers are promising lithium ion conductors with high ion conductivity and stability. Such findings highlight new strategies in controlling lattice dynamics to discover new lithium ion conductors with enhanced conductivity and stability.