Leslie A. Adamczyk

Real Space Mapping of Li-Ion Transport in Amorphous Si Anodes with Nanometer Resolution

The electrical bias driven Li-ion motion in silicon anode materials in thin film battery heterostructures is investigated using electrochemical strain microscopy (ESM), which is a newly developed scanning probe microscopy based characterization method. ESM utilizes the intrinsic link between bias-controlled Li-ion concentration and molar volume of electrode materials, providing the capability for studies on the sub-20 nm scale, and allows the relationship between Li-ion flow and microstructure to be established. The evolution of Li-ion transport during the battery charging is directly observed.

Decoupling electrochemical reaction and diffusion processes in ionically-conductive solids on the nanometer scale.

We have developed a scanning probe microscopy approach to explore voltage-controlled ion dynamics in ionically conductive solids and decouple transport and local electrochemical reactivity on the nanometer scale. Electrochemical strain microscopy allows detection of bias-induced ionic motion through the dynamic (0.1-1 MHz) local strain. Spectroscopic modes based on low-frequency (∼1 Hz) voltage sweeps allow local ion dynamics to be probed locally. The bias dependence of the hysteretic strain response accessed through first-order reversal curve (FORC) measurements demonstrates that the process is activated at a certain critical voltage and is linear above this voltage everywhere on the surface. This suggests that FORC spectroscopic ESM data separates local electrochemical reaction and transport processes. The relevant parameters such as critical voltage and effective mobility can be extracted for each location and correlated with the microstructure. The evolution of these behaviors with the charging of the amorphous Si anode in a thin-film Li-ion battery is explored. A broad applicability of this method to other ionically conductive systems is predicted.

Influence of Periodic Nitrogen Functionality on the Selective Oxidation of Alcohols

An enhancement in catalytic alcohol oxidation activity is attributed to the presence of nitrogen heteroatoms on the external surface of a support material. The same Pd particles (3.1-3.2 nm) were supported on polymeric carbon-nitrogen supports and used as catalysts to selectively oxidize benzyl alcohol. The polymeric carbon-nitrogen materials include covalent triazine frameworks (CTF) and carbon nitride (C(3)N(4)) materials with nitrogen content varying from 9 to 58 atomic percent. With comparable metal exposure, estimated by X-ray photoelectron spectroscopy, the activity of these catalysts correlates with the concentration of nitrogen species on the surface. Because the catalysts showed comparable acidic/basic properties, this enhancement cannot be ascribed to the Lewis basicity but most probably to the nature of N-containing groups that govern the adsorption sites of the Pd nanoparticles.

Direct Visualization of Solid Electrolyte Interphase Formation in Lithium-Ion Batteries with In Situ Electrochemical Transmission Electron Microscopy

Complex, electrochemically driven transport processes form the basis of electrochemical energy storage devices. The direct imaging of electrochemical processes at high spatial resolution and within their native liquid electrolyte would significantly enhance our understanding of device functionality, but has remained elusive. In this work we use a recently developed liquid cell for in situ electrochemical transmission electron microscopy to obtain insight into the electrolyte decomposition mechanisms and kinetics in lithium-ion (Li-ion) batteries by characterizing the dynamics of solid electrolyte interphase (SEI) formation and evolution. Here we are able to visualize the detailed structure of the SEI that forms locally at the electrode/electrolyte interface during lithium intercalation into natural graphite from an organic Li-ion battery electrolyte. We quantify the SEI growth kinetics and observe the dynamic self-healing nature of the SEI with changes in cell potential.

In-situ TEM Characterization of Electrochemical Processes in Energy Storage Systems

The accelerated development of materials for utilization in electrical energy storage systems will hinge critically upon our understanding of how interfaces (particularly electrode-electrolyte solid liquid interfaces) control the physical and electrochemical energy conversion processes in energy storage systems. A prime example is found in Lt ion-based battery systems, where a passive multiphase layer grows at the electrode/electrolyte interface due to the decomposition of the liquid electrolyte [ l]. Once formed, this solid electrolyte interphase (SEI) protects the active electrode materials from degradation and also regulates the transport and intercalation of Lt ions during battery charge/discharge cycling [2]. Due to the dynamically evolving nature of this nm-scaled interface, it has proven difficult to design experiments that will not only elucidate the fundamental mechanisms controlling SEI nucleation and growth, but will enable the SEI microstructural and chemical evolution as a function of charge/discharge cycling to be monitored in real time.