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In-Pb anodes for use with Mg-ion batteries

​A team from the CEA-Iramis has developed a new negative electrode material for Mg-ion batteries, based on the compound In-Pb. The synergistic action of indium and lead favors a high electrical capacity, to the detriment of the material's reversibility, which needs to be further investigated.
Published on 14 December 2020

Magnesium-ion batteries are emerging as a potential alternative to lithium-ion batteries with two advantages: their volumetric storage capacity could be almost twice as high (Mg2+ carrying a double charge and Li+ a single charge); and magnesium is much more abundant on earth than lithium.

Like Li+ in a lithium-ion accumulator, the Mg2+ ion is exchanged between a cathode and an anode, ideally magnesium metal, via an electrolyte. The electrolytes used form a passivation layer upon contact with the Mg metal, which limits the number of recharging cycles.

Iramis researchers have proposed replacing the magnesium in the electrode with an alloy that is inert with regard to the electrolyte and capable of accepting Mg2+ ions thanks to alloying effects. After having studied the In-Sb compound, they chose to evaluate the advantages of In-Pb.

First, they found that the synthesis of the In-Pb electrode material strongly influences its reactivity. Manufactured by mechano-synthesis, In-Pb does not react with Mg2+ ions. In contrast, when carbon is added during grinding, the size of the In-Pb particles decreases by a factor of 20 to 40 (reaching ~ 10 µm), making them electrochemically active.

Electrochemical and structural analyses by X-ray diffraction show the formation of the compound Mg2Pb. The electrical capacitance obtained by the insertion of Mg (calculated from the electrochemical curve) thus surpasses what can be stored in this single crystalline Mg2Pb phase, implicating the existence of a MgIn phase in amorphous form.

The electrochemical study shows that the coupling between In and Pb provides a real advantage in the first charge cycle, where a capacity of 488 mAhg-1 could be reached – much higher than those obtained for In and Pb alone – thanks to the partially reversible formation of Mg2Pb. But after a few cycles, the capacity stabilizes at about 300 mAh/g, on the same order as that obtained for InSb.

A finer understanding of the chemical reactions is now needed, especially to determine whether better control of the presence of MgIn in amorphous form would improve the number of charge-discharge cycles while maintaining the initial high electrical capacity.

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