Insights into the Electrochemical Degradation of Aluminum Dual-Ion Batteries: Influence of Internal Cell Resistance & Applied Current Density
Authors: Eckert Martin , Jach Franziska , Wassner Maximilian , Wunderwald Ulrike 
Published: February 2024

To face the upcoming demand on high-power energy storage systems, e.g, for high-dynamic grid-stabilization , stationary devices as used in photovoltaics, and mobile applications led to invention of various battery technologies like sodium-ion batteries (SIB), zinc-ion batteries (ZIB) and high-power lithium-ion batteries (LIBs). Especially the several lithium-ion battery technologies have in common that currently used raw materials like lithium-salts and heavy metals (Ni, Co, Mn) are becoming increasingly scarce and therefore expensive. Without substitution by less-critical materials the ongoing energy system transformation cannot be successfully achieved.

One promising system that gained attention in the last few years is the so-called aluminum graphite dual-ion battery (AGDIB). The active electrodes are made of cheap and abundant materials like graphite as cathode material and an aluminum-foil as anode1. During operation chloroaluminate anions from the electrolyte, which is currently based on ionic liquids like 1-ethyl-3-methylimidazoliumchloride ([EMIm]Cl) and AlCl3 in stoichiometric ratios as well as deep-eutectic solvents based on mixtures of urea and AlCl3, are (de)intercalated in the graphitic host-structure while on the anode metallic aluminum is electrochemically deposited and dissolved see equation (1) and (2), respectively2, 3. The overall mechanism is quite comparable with Li-metal batteries, where metallic Li is reversibly dissolved and deposited.

The big advantages of AGDIBs are cheap electrode materials (graphite & aluminum), electrolytes based on urea and an extraordinary high-power cell-chemistry. Recent publications showed charging rates up to 20 A g-1
Graphite equal to 9 kW kg-1
Graphite in laboratory-scaled cells. Also, the lifetime of those batteries seems to be non-competitive, cycles up to half a million were reported with negligible capacity fading or degradation effects.4

To develop scalable and more representative battery cells, we established the AGDIB cell chemistry in a new corrosion-stable pouch bag design. Due to the significant increased electrode surface area and overall capacity, hitherto unknown effects were observed which limited the end of lifetime (EOL) of those batteries to less than 8,000 cycles. Herein, we report on a detailed analysis of the cell failure, including several electrochemical in-situ techniques like galvanostatic intermittent titration techniques (GITT), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV).5 The obtained data will allow a fundamental understanding of the cell operation under low (≤ 1 C-rates) and very high C-rates ≥ 15 C, which is important for establishing a durable AGDIB with high cycling stability.

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Figure 1