Abstract
Recently, interest in aluminium ion batteries with aluminium anodes, graphite cathodes and ionic liquid electrolytes has increased; however, much remains to be done to increase the cathode capacity and to understand details of the anion–graphite intercalation mechanism. Here, an aluminium ion battery cell made using pristine natural graphite flakes achieves a specific capacity of ∼110 mAh g−1 with Coulombic efficiency ∼98%, at a current density of 99 mA g−1 (0.9 C) with clear discharge voltage plateaus (2.25–2.0 V and 1.9–1.5 V). The cell has a capacity of 60 mAh g−1 at 6 C, over 6,000 cycles with Coulombic efficiency ∼ 99%. Raman spectroscopy shows two different intercalation processes involving chloroaluminate anions at the two discharging plateaus, while C–Cl bonding on the surface, or edges of natural graphite, is found using X-ray absorption spectroscopy. Finally, theoretical calculations are employed to investigate the intercalation behaviour of choloraluminate anions in the graphite electrode.
Highlights
Interest in aluminium ion batteries with aluminium anodes, graphite cathodes and ionic liquid electrolytes has increased; much remains to be done to increase the cathode capacity and to understand details of the anion–graphite intercalation mechanism
We recently developed a rechargeable Al-ion batteries (AIBs) with an Al anode that undergoes reversible electrochemical deposition and dissolution at room temperature in an ionic liquid (IL) electrolyte formed by mixing 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl) and aluminium chloride (AlCl3) that produce redox active chloroaluminate anions (AlCl4À and Al2Cl7À )[6,7]
Note that the Al anode was previously paired with a fluorinated graphite as a cathode electrode to afford a capacitor-like device with low discharging voltage of B1 V, which differed from our Algraphite battery with reversible chloroaluminate anion intercalation/de-intercalation redox chemistry[9]
Summary
Interest in aluminium ion batteries with aluminium anodes, graphite cathodes and ionic liquid electrolytes has increased; much remains to be done to increase the cathode capacity and to understand details of the anion–graphite intercalation mechanism. An aluminium ion battery cell made using pristine natural graphite flakes achieves a specific capacity of B110 mAh g À 1 with Coulombic efficiency B98%, at a current density of 99 mA g À 1 (0.9 C) with clear discharge voltage plateaus (2.25–2.0 V and 1.9–1.5 V). A drawback of our previous rechargeable Al battery was the low-specific cathode capacity of o70 mAh g À 1 down to its low C rate, which needed to be improved to match the high capacity of the Al anode side and increase the AIB’s energy density. Our AIB cell exhibits clear discharge voltage plateaus in the ranges 2.25–2.0 V and 1.9–1.5 V, while the graphite cathode exhibits a much improved specific capacity over pyrolytic graphite up to B110 mAh g À 1 with B98% Coulombic efficiency (CE) at a current density of B99 mA g À 1. Density functional theory (DFT) calculations are used to investigate and verify the intercalation behaviour of choloraluminate anions in the NG electrodes
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