In Situ Visualization of Ion Transport Processes in Aqueous Batteries

Aqueous
rechargeable batteries are regarded as one of the most
reliable solutions for electrochemical energy storage, and ion (e.g.,
H+ or OH–) transport is essential for
their electrochemical performance. However, modeling and numerical
simulations often fall short of depicting the actual ion transport
characteristics due to deviations in model assumptions from reality.
Experimental methods, including laser interferometry, Raman, and nuclear
magnetic resonance imaging, are limited by the complexity of the system
and the restricted detection of ions, making it difficult to detect
specific ions such as H+ and OH–. Herein,
in situ visualization of ion transport is achieved by innovatively
introducing laser scanning confocal microscopy. Taking neutral Zn–air
batteries as an example and using a pH-sensitive probe, real-time
dynamic pH changes associated with ion transport processes are observed
during battery operation. The results show that after immersion in
the zinc sulfate electrolyte, the pH near the Zn electrode changes
significantly and pulsation occurs, which demonstrates the intense
self-corrosion hydrogen evolution reaction and the periodic change
in the reaction intensity. In contrast, the change in the pH of the
galvanized electrode plate is weak, proving its significant corrosion
inhibition effect. For the air electrode, the heterogeneity of ion
transport during the discharging and charging process is presented.
With an increase of the current density, the ion transport characteristics
gradually evolve from diffusion dominance to convection-diffusion
codominance, revealing the importance of convection in the ion transport
process inside batteries. This method opens up a new approach of studying
ion transport inside batteries, guiding the design for performance
enhancement.