Use of Carbon Additives towards Rechargeable Zinc Slurry Air Flow Batteries

Nak Heon Choi,Peter Fischer,Karsten Pinkwart,Jens Tübke,Nadia El Kissi,Diego Del Olmo,Diego Milian

doi:10.3390/en13174482

Abstract

The performance of redox flow batteries is notably influenced by the electrolyte, especially in slurry-based flow batteries, as it serves as both an ionic conductive electrolyte and a flowing electrode. In this study, carbon additives were introduced to achieve a rechargeable zinc slurry flow battery by minimizing the zinc plating on the bipolar plate that occurs during charging. When no carbon additive was present in the zinc slurry, the discharge current density was 24 mA∙cm−2 at 0.6 V, while the use of carbon additives increased it to up to 38 mA∙cm−2. The maximum power density was also increased from 16 mW∙cm−2 to 23 mW∙cm−2. Moreover, the amount of zinc plated on the bipolar plate during charging decreased with increasing carbon content in the slurry. Rheological investigation revealed that the elastic modulus and yield stress are directly proportional to the carbon content in the slurry, which is beneficial for redox flow battery applications, but comes at the expense of an increase in viscosity (two-fold increase at 100 s−1). These results show how the use of conductive additives can enhance the energy density of slurry-based flow batteries.

Highlights

The use of energy storage systems (ESS) to support renewable energies, like solar energy and wind energy, has attracted remarkable attention [1]
Initial testing of the cycling behavior of our prototype zinc slurry air flow battery revealed that, during charging, part of the regenerated zinc was plated on the bipolar plate
The plating of metal on the bipolar plate is the working principle of flow-assisted batteries, such as zinc-nickel [42]. It is an undesired process for zinc slurry air flow batteries, as it limits the capacity of the plated the zincmaximum can growamount to formofdendrites blockwould the slurry flowbyand, system

Summary

Introduction

The use of energy storage systems (ESS) to support renewable energies, like solar energy and wind energy, has attracted remarkable attention [1]. To achieve high energy densities for renewable energy, redox flow batteries (RFBs) are a promising candidate owing to their ability to decouple the control of energy capacity and power [2,3]. The energy densities of RFBs can be tuned by the capacity of electrolyte and the concentration of active species. Using zinc as an active metal is very attractive, due to its abundance and low cost, including the electrolyte component, such as potassium hydroxide and zinc oxide [7,8]. Zinc itself has a relatively high theoretical energy density (1350 Wh kg−1 ) compared to other active materials [3]. Conventional zinc-air batteries consist of a positive compartment where air can flow in and out and a static porous zinc electrode in Energies 2020, 13, 4482; doi:10.3390/en13174482 www.mdpi.com/journal/energies

Methods

Results

Conclusion