A Scalable Method for Improving Zn Crystallinity for Low-Gassing Alkaline Batteries

Abstract

The corrosion of zinc particles in alkaline environments is an energetically parasitic process that produces hydrogen gas as a byproduct. This “gassing” phenomenon is thermodynamically favorable in standard zinc-alkaline battery chemistries. Building hydrogen pressure within these primary cells can eventually lead to cell rupture, leaking the high-pH electrolyte and slurry from the cell, often destroying the electronic device that the cell was meant to power. One of the particle-level variables that can control the gassing and corrosion rate is the particle crystallinity. As the crystallinity of the zinc particles is enhanced (larger grains and fewer grains per particle), a reduction in the rate of this undesirable gassing phenomenon is expected.In this study, we demonstrate a systematic method for enhancing zinc particle crystallinity by thermally growing zinc grains. Since thermally growing zinc grains requires temperature exposure above the melting point of metallic zinc, an oxide layer is first grown around the outside of the particle surface. Oxides tend to have significantly higher melting temperatures than their metallic counterparts and this is true in the zinc/zinc oxide case where the melting temperature of metallic zinc is 420 oC and the melting temperature of zinc oxide is 1975 oC. Forming a thin oxide layer around the particle allows the metallic zinc core to be recrystallized whilst simultaneously retaining the particle shape. Following the grain growth step, the oxide layer is easily washed away with a quick acetic acid treatment. Outlined in this work is a detailed study on the scalable three-step process for growing zinc grains and enhancing bulk zinc powder crystallinity by the following: 1) oxide layer formation, 2) grain growth, and 3) oxide layer removal. Following the treatment, both achievable capacity and the corrosion rate were tested. It will be shown that the higher crystallinity particles have superior performance and lower gassing than traditional Zn powders without the treatment.