Insights into the reversibility of aluminum graphite batteries

Abstract

Herein we report a novel study on the reaction mechanism of non-aqueous aluminum/graphite cell chemistry employing 1-ethyl-3-methylimidazolium chloride:aluminum trichloride (EMIMCl:AlCl 3 ) as the electrolyte. This work highlights new insights into the reversibility of the anion intercalation chemistry besides confirming its outstanding cycle life exceeding 2000 cycles, corresponding to more than 5 months of cycling test. The reaction mechanism, involving the intercalation of AlCl 4 À in graphite, has been fully characterized by means of ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure spectroscopy (XANES) and small-angle X-ray scattering (SAXS), evidencing the accumulation of anionic species into the cathode as the main factor responsible for the slight initial irreversibility of the electrochemical process. Fig. 7 Ex situ SEM images of PG and aluminum electrodes subjected to different numbers of cycles (pristine, and 50 th and 500 th cycles). The electrodes (in the fully discharged state) were taken from Al/EMIMCl:AlCl 3 /PG cells cycled at 25 mA g À1 for the first 5 cycles and 75 mA g À1 for the following cycles (25 C).This journal is

Perspective—State of the Art of Rechargeable Aluminum Batteries in Non-Aqueous Systems

“…Gifford et al described this novel battery system in 1988 with aluminum and graphite as the negative and positive electrodes respectively, in a Lewis acidic chloroaluminate ionic liquid at room temperature. Chloroaluminate anions intercalated into the graphite electrode reaching 64 Wh kg −1 specific energy at 1.7 V discharge voltage over 150 cycles and 80-90% coulombic efficiency.2 The same idea was taken up several years later by various research groups 1,[3][4][5] …”

“…24 In non-aqueous electrolytes the passive oxide layer found on the aluminum electrodes, is not formed 1,15,17 while the electrochemical stability window enables the deposition of aluminum and the realization of higher cell voltages. 21 In contrast to high temperature molten salts, ionic liquids are liquid at room temperature.…”

“…Dendrite growth was only observed at high current densities over 100 mA cm −2 . 1,5,15,21,32,33 The electrodeposition of aluminum on glassy carbon, tungsten and platinum electrodes follows an instantaneous mechanism with diffusion controlled growth, in contrast, the deposition on aluminum electrodes has kinetic limitations. 32 The deposition (charge reaction) and dissolution (discharge reaction) of aluminum (Equation 1) at the negative electrode is only possible in a Lewis acidic chloroaluminate ionic liquid, containing…”

“…Chloroaluminate anions intercalated into the graphite electrode reaching 64 Wh kg −1 specific energy at 1.7 V discharge voltage over 150 cycles and 80-90% coulombic efficiency. 2 The same idea was taken up several years later by various research groups 1,[3][4][5] using different oxides, sulfides and zeolites materials as intercalation electrodes. [6][7][8][9][10][11][12][13] More recently the introduction of conductive polymers (CP) as intercalation electrode sets a further development with great potential for a rechargeable aluminum hybrid battery-capacitor energy storage system.…”

“…Furthermore, its specific capacity of 2980 mAh g −1 and volumetric capacity of 8040 mAh cm −3 , respectively, are higher than lithium. 1 The number of studies on rechargeable aluminum-based batteries in non-aqueous systems has increased 10-fold in the last decade ( Figure 1). Therefore, it seems appropriate and timely to review the state of the art and the implementation of novel ideas and approaches made for rechargeable high performance aluminum-based batteries and reflect on the perspectives, challenges and limitations that these relatively new systems face.…”