Watching a zinc battery while it works

The short version

Most battery testing treats the cell as a black box: put charge in, take charge out, and count how much comes back. That tells you whether a battery is wearing out, not why. I study rechargeable zinc batteries that use a water-based electrolyte, and I watch them while they run by pointing a laser at the electrode and reading the light that scatters back.

Every molecule scatters light with its own fingerprint of colors, so the scattered light tells you what chemistry is happening at the surface, moment to moment.

Why zinc, and why water

Water-based (aqueous) zinc batteries are interesting because water doesn’t burn and zinc is abundant. The catch is that the zinc surface is a busy, messy place: as the battery cycles, zinc dissolves and re-deposits, water and ions rearrange, and side reactions compete with the useful ones. Those surface events decide how long the battery lasts.

My thesis focuses on one of the most important of those events: how zinc plates back onto the electrode. Done badly, it grows in needle-like spikes called dendrites, which waste zinc and can short the battery. Done well, it grows epitaxially, as an orderly layer that follows the crystal pattern of the surface beneath it. I’m investigating what makes that orderly growth reversible, cycle after cycle.

What “operando” means

Operando is Latin for “while working.” Instead of taking a battery apart after the fact, I collect spectra while current is flowing, so each spectrum lines up with a known moment in the charge/discharge cycle. That’s what makes it possible to connect a change in chemistry to a change in behavior.

Technical depth: the measurement

Raman spectroscopy measures inelastic scattering: a small fraction of incident photons exchange energy with molecular vibrations, shifting their wavelength by an amount characteristic of the bond. Pairing a spectrometer with a potentiostat lets each spectrum be time-stamped against the electrochemical program (e.g. cyclic voltammetry or galvanostatic cycling), so spectral changes can be read against potential and state of charge.

TODO(Sidney): instrument details you're comfortable sharing (laser wavelength, spectrometer/potentiostat, objective), the electrochemical techniques you use, and the species or interfacial structure you track.

Questions I’m asking

• What controls whether zinc plates back as an orderly, epitaxial layer or as dendrites?
• What forms at the zinc–electrolyte interface during charging and discharging, and in what order?
• How does the electrolyte’s structure near the surface change as the battery cycles?
• Which of those changes go along with the battery performing well or poorly?

TODO(Sidney): confirm or replace these with the questions your thesis actually asks.

Results

Results from this work aren’t public yet. This section will link to papers and talks as they come out.