Jay Keist

Jay Keist, PhD 2012
Advisor: Paul Wright
Email: jkeist@berkeley.edu

Zinc Based Energy Storage Utilizing Ionic Liquid Electrolytes: In-situ Analysis of the Electrode/Electrolyte Interface

Zinc based batteries offer the highest power density of rechargeable batteries that are available commercially with power densities approaching 600 mW/g. This research centers on analysis of zinc based micro-batteries utilizing ionic liquid electrolytes. Ionic liquids are salts that remain liquid at low temperatures. The ionic liquid remains liquid at low temperatures since the coordination between the cations and anions within the ionic liquid are very weak. The unique properties of ionic liquids make them an attractive electrolyte for battery systems. These properties include high ionic conductivity, high electrochemical stability, and a wide temperature ranges. In addition, ionic liquids are chemically inert and non-volatile. As with conventional electrolyte systems, however, detrimental morphologies can still form within the ionic liquid electrolyte resulting in a reduced cycling lifetime for the rechargeable battery system. To understand how detrimental morphologies form and grow during cycling, in-situ analysis is being conducted at the electrode/electrolyte interface during charging and discharging (deposition and dissolution). The in-situ analysis includes both atomic force microscopy (AFM) and in-situ optical microscopy. The in-situ AFM allows for excellent spatial resolution to investigate nucleation and the initial growth behavior of zinc. The in-situ optical microscopy will allow for a wide field of view and high image rates to investigate the kinetics behind the morphological evolution of zinc. Our goal is to develop an understanding on how the charging parameters and electrolyte chemistries control the nucleation and growth of zinc. With this understanding, we can optimize the charging parameters to prevent the formation of detrimental morphologies such as dendrites. Since the last BWRC meeting, research has initiated on both the optical and AFM in-situ analysis of the zinc electrode during deposition and dissolution. The optical analysis allowed for direct measurement of zinc deposition growth rate and density. Subsequent SEM analysis showed that the growth rate directly influenced the resulting morphology of the zinc. In addition, AFM analysis has been conducted to understand the formation of detrimental morphologies from surface instabilities that develop during charging. For the next year, subsequent analysis will concentrate on how the charging behavior and electrolyte chemistry can be optimized to reduce the formation of detrimental morphologies.

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