Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Batteries with liquid metal electrodes are attractive candidates for sustainable
energy storage applications due to low manufacturing cost as well as high recyclability. For
broad applications, these batteries should be developed for lower operating temperature,
higher cell voltage, and membrane-free cell configuration. Here, we demonstrate a new type
of membrane-free electrochemical energy storage system relying on liquid alkali metals and
iodide. As a proof-of-concept study, membrane-free alkali metal-iodide (A-AI) batteries were
constructed by a facile cell assembly introducing current collectors, LiI-LiCl-KI-CsI salt mixture,
and an insulator without relying on solid-state mediums for separating electrolytes. For the
initial assembly, no active electrode materials were required since they can be naturally
formed during battery operation. Despite the unoptimized cell construction, the membrane-
free A-AI batteries showed promising electrochemical performance such as voltage efficiency
of ca. 40 % at 500 mA/cm2, maximum specific energy of 34.2 Wh/kg with an energy efficiency
of 59 % for a charging/discharging period of 5.8 h and reliable stability for 250 cycles. Even
without ion-selective membranes, we observed a relatively low self-discharge rate of
3.56 mA/cm2, which implies the possibility of an iodine-concentrated layer at the bottom of
the cell. This was further supported by post-mortem analyses using neutron radiography.
Additionally, X-ray photoemission spectroscopy was performed to identify the changes in the
iodine concentration in the cell.