Additives for Suppressing Zinc Dendrites in Rechargeable Zinc Metal Batteries

Rechargeable zinc-based battery systems hold great promise for future energy storage devices due to their low cost and high theoretical energy density.¹ However, the development of portable or stationary rechargeable zinc batteries has been hindered by several critical issues. The key issue has been the evolution of dendritic zinc electrodeposit morphology during battery charging,^2,3leading to battery capacity fade and cell shorting.

In this work, we focus on the use of organic electrolyte additives to suppress zinc dendrite growth. We examine both acidic and alkaline electrolytes, which are relevant to acidic zinc-halogen flow batteries and alkaline zinc-metal batteries, respectively. To study zinc dendrite propagation, we employ in-situ microscopy during growth of the electrodeposit.⁴ To study the mechanism by which organic additives modulate the dendrite propagation rate, we utilize classical polarization measurements on a rotating disc electrode. For acidic zinc electrolytes, we studied numerous additives (Figure 1) and their dendrite suppression efficacy. We observed that strongly polarizing additives suppress zinc dendrites more than weak polarizers. For zinc electrodeposition from an alkaline electrolyte, we identified that polyethylenimine (PEI) enables near-complete dendrite suppression,⁵even at low concentrations (~50 ppm, see Figure 2). Figure 2 also shows electrochemical polarization measurements on a rotating disk electrode, which confirm the polarizing effect of the PEI.

The aforementioned characterization techniques, together with electrochemical quartz crystal microgravimetry, ex-situscanning electron microscopy, and various ‘additive-injection’ tests, provide insights into the mechanism by which additives suppress dendritic growth of zinc. Additives are believed to adsorb onto the zinc surface and suppress zinc electrodeposition kinetics locally, thereby inhibiting activation-controlled dendrite propagation. In the talk, we will develop the mechanistic understanding further and provide guidelines for judicious selection of the additive chemistry for dendrite-free zinc electrodeposition in acidic and alkaline systems. 

References:

[1]: Y. Li and H. Dai, Chem. Soc. Rev., 43, 5143 (2014).

[2]: K. Wang, P. Pei, Z. Ma, H. Xu, P. Li, X. Wang, J. Power Sources, 271, 65 (2014).

[3]: C. P. de Leon, A. Frias-Ferrer, J. Gonzalez-Garcia, D. A. Szanto, and F. C. Walsh, J. Power Sources, 160, 716 (2006).

[4]: S. J. Banik and R. Akolkar, J. Electrochem. Soc., 160, D519 (2013).

[5]: S. J. Banik and R. Akolkar, Manuscript submitted to Electrochimica Acta, October 2014.