A Permselective Graphene Oxide/Polyvinyl Alcohol Composite Membrane for Rechargeable Alkaline Zinc Manganese Dioxide Batteries

Abstract

Rechargeable alkaline Zn/MnO2 batteries are currently attractive candidates for grid-scale energy storage due to its low cost, safety characteristics, and high gravimetric capacity of MnO2 (308 mAh/g per electron). However, commercialization of this battery has not achieved big success due to its limited cycle life and restricted depth of discharge (DOD). Accessing higher DOD results in higher energy densities, but leads to detrimental characteristics like phase transformation of MnO2 and the zinc redistribution. Recently, a class of Bi-birnessite (a layered MnO2 structure with bismuth oxide) material intercalated with Cu2+ has been reported as being able to stabilize the MnO2 structure and deliver near-full two-electron capacity for more than 6,000 cycles in the absence of zinc [1]. However, when a zinc anode is used, the most detrimental effect arises from zincate ions ([Zn(OH)4]2-) that traverse to the cathode side and react to form a spinel phase ZnMn2O4, a highly resistive and electrochemically inactive compound, leading to rapid energy density loss and battery failure [2]. Therefore, inhibiting ZnMn2O4 formation remains a major challenge for the long-term cycling of an energy dense secondary Zn/MnO2 battery. Previously, we reported the use of a zincate-absorbing interlayer fabricated of calcium hydroxide, which successfully prevents ZnMn2O4 formation [3]. In this presentation, we report the strategy of developing a separator featuring selective transport of OH- and [Zn(OH)4]2- ions. We fabricate a graphene oxide-poly(vinyl alcohol) (GO-PVA) composite membrane with a layered structure. The GO membrane, which is composed of stacked and overlapped GO monolayers with a narrow interlayer spacing (~13.5Å for GO laminates swelled in water), has been demonstrated to be excellent filters for gases and liquids. The nanocapillaries formed within the membranes as well as the oxygen functional groups which repel the bulky [Zn(OH)4]2- anions are responsible for its ion sieving properties. PVA is impregnated to provide a conductive pathway for OH- ions and to improve the mechanical stability. We successfully demonstrate the superiority of the GO/PVA composite membrane in suppressing zincate ion crossover (Fig.1(a)), while minimally impairing OH- conduction. Its application in primary batteries significantly increases the energy density by obtaining capacity of more than 1.5 e- per Mn atom above 0.9V (Fig.1(b)). In rechargeable batteries, it slows down the capacity fade of a conventional zinc/electrolytic γ-MnO2 (Zn/EMD) battery during deep cycling within the 1st electron capacity (Fig.1(c)), while it helps to achieve more than 200 cycles with full 2-electron capacity retained in a zinc/birnessite battery (Fig.1(d)).