Interface modifications for improving performance and reversibility of aqueous secondary batteries

Abstract

As the demand and need for renewable energy sources have been amplified, the grid-scale energy storage system (ESS) market has been showing explosive growth prospects. However, with the recent successive fire accidents of grid-scale ESS in South Korea, there is a growing interest in developing safe and reliable batteries. The hazards of fire accidents for the conventional ESS are originated from the flammability of organic electrolytes in the typical lithium-based batteries. Therefore, aqueous batteries using nonflammable aqueous electrolytes are considered a promising candidate for grid-scale ESS due to their freedom from fire hazards. For further commercialization of aqueous batteries, however, system cost reduction is still needed to overcome the present lithium-based battery systems by increasing the battery performance and substituting high-priced battery component materials to cheaper ones. In this work, we suggests several interface modification strategies to improve the performance and reversibility of aqueous batteries. The battery is basically comprises various components (i.e. anode, electrolyte, membrane or separator, and cathode), and thus the battery is considered to be an assembly of interfaces. Therefore, we tried to engineer the characteristics of various interfaces in the aqueous battery to propose a blueprint for the advanced battery system. Specifically, this work deals with vanadium redox flow battery (VRFB) and zinc metal battery (ZMB) systems with the aqueous electrolytes. Chapter 2 includes the three-dimensional interlocking interfacial layer between two different polymer membranes to achieve the adhesion without losing proton conductivity. By combining highly cheap and efficient hydrocarbon-based polymer membrane with chemically stable perfluorinated polymer, the composite membrane shows enhanced durable and cost-effective in VRFBs. Chapter 3 deals with highly ion-selective interfacial layer to increase the performance and reversibility of VRFBs. The key idea was to control the effective pore size of interfacial layer to selectively separate the hydrated diameter of vanadium ions (> 6.0 Å) and that of protons (< 2.5 Å), and thus a pore-size-tuned graphene oxide framework (GOF) membranes is introduced showing a proper pore size for the VRFB application. Due to the high ion-selectivity of GOF, the GOF introduced membrane shows improved efficiencies and reversibility for VRFBs. Chapter 4 introduces an electrokinetic effect-inducing polymeric structure to improve the reversibility of zinc metal anodes in ZMBs. We design a negatively charge porous layer (NPL) to accelerate electrokinetic zinc-ion transport, and demonstrate the surface conduction inducing properties of the NPL by multi-physics simulation. By overcoming the diffusion limitation of zinc-ion, zinc metal electrodes exhibit homogeneous deposition morphologies, and significantly improved reversibility even for the ultra-high current density. Based on the great reversibility of NPL introduced zinc metal anode, the high capacity-ZMB full cell shows considerably improved cycling life.