The leading cause for safety vent rupture in alkaline cells is the intrinsic instability of zinc in the highly alkaline reacting environment. Zinc and aqueous KOH react in a parasitic process to generate hydrogen gas, which can rupture the seal and vent the hydrogen along with small amounts of electrolyte. The expelled electrolyte is known to cause damage to consumer electronics equipment, and also leads to brand damage. Under most circumstances, cells are engineered to slow the hydrogen evolution process, and its effects are never apparent to the end user. However, abusive conditions (i.e. over discharge) can accelerate the rate of gassing. Industry leaders have been cognizant of this for years, and improved techniques to understand and mitigate zinc corrosion have long been desired.

In order to understand the fundamental drivers and mechanisms for such gassing behavior, our team has developed a new research platform that enables a cross-sectional view of the cell during charge and discharge (Figure 1). There also exists version of the cell that can actively measure pressure as well as the potential distribution across the cell. In this study, several parameters were investigated and it was confirmed that the formation of high surface area (or so-called “black”) zinc during cell discharge was the root cause for accelerated gassing. Steep concentration gradients caused by the cell balance and chemistry are responsible for black zinc formation and subsequent hydrogen evolution. Also, it was confirmed that in deeply discharged cells, significant hydrogen evolution does not occur during discharge because of unfavorable electrochemical conditions; gassing occurs when the cell is off load. In this talk, the fundamental mechanisms and operational parameters controlling black zinc formation will be discussed. Also, possible pathways forward for action and further research will be proposed.