Dissertation Defence: Separator Structure and Stack Pressure Effects on Zinc Metal Anode Stability in Aqueous Zinc-ion Batteries

Evan J. Hansen, supervised by Dr. Jian Liu, will defend their dissertation titled “Separator Structure and Stack Pressure Effects on Zinc Metal Anode Stability in Aqueous Zinc-ion Batteries” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mechanical Engineering.

An abstract for Evan J. Hansen’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. This examination will be offered in hybrid format.  Registration is not required to attend in person, but please email jian.liu@ubc.ca to receive the Zoom link for this exam.

Abstract

Global adoption of renewable energy sources, such as wind and solar generation, has rapidly accelerated to reduce CO2 emissions and support reliable energy access. However, the intermittent nature of these sources has forced significant growth of supplemental electrochemical energy storage systems, increasing the demand on Li-ion batteries (LIBs) and motivating the development of safe, affordable, and durable alternative battery chemistries. Among emerging chemistries, aqueous Zn-ion batteries (AZIBs) are promising candidates for stationary energy storage due to their low-cost, the high volumetric capacity and low volatility of Zn metal, and the non-flammable nature of aqueous electrolytes. However, several challenges limit deployment of practical AZIBs, including unstable Zn plating/stripping at the Zn metal anode that can form deposits within the porous structure of the separator that can lead to an internal short-circuit and insufficient cycling life. Across AZIB research, commercial glass fibre (GF) membranes are widely applied as the separator due to their high porosity and hydrophilicity, yet they are available with varying properties (i.e., pore size and thickness) that are often treated as interchangeable. In addition, the effects of stack pressure and pressure distribution in proof-of-concept coin cells are not well understood despite the dependence on overall thickness of the active component stack.

This dissertation investigates how the GF separator structure, asymmetric GF separator modification, and stack pressure influence Zn deposition behaviour and cycling stability in Zn|Zn cells. First, a systematic comparison of GF membranes demonstrates that reduced pore size and increased thickness are critical properties that extend cycling life but with varying magnitudes of sacrifice to cell-to-cell stability. Next, the application of a chitin/poly(vinyl alcohol) film coating onto GF extended Zn|Zn cycling life to 2450 cycles (vs. 51 cycles of GF), improved Zn plating/stripping reversibility, and suppressed pore-filling deposits. Finally, stack pressure modulated by varying the current-collector thickness, yielded non-uniform pressure maps with edge-localized and central high-pressure regions of the Zn electrode, and increased stack pressure improved the mean cycling life from 145 to 951 cycles, but also increased cell-to-cell variability. Across all three studies, the application of X-ray computed tomography to characterize intact cell stacks provides visualization of the resulting Zn morphologies and failure-inducing deposits while avoiding disassembly that can cause the removal of separator-restrained deposits.