Electrochemical Charge/Discharge Behavior and Phase Transitions during Cell Cycling of Li(Mg) Alloy Anodes for High Capacity Li Ion Batteries

Abstract

Electrochemical performance of Li(Mg) alloys as potential negative electrodes for Li-ion batteries has been investigated. Two Li(Mg) alloys with nominal compositions, Li-60 wt% Mg (Li7Mg3) and Li-30 wt% Mg (Li8Mg) were synthesized and electrodes were prepared by melting, rolling and annealing. Both the alloys showed a discharge plateau voltage of ∼2 V compared to the ∼2.5 V with pure Li anode with reference to MnO2 as cathode. Detailed ex situ X-ray diffraction analysis revealed that during the discharge of Li(Mg) anodes, a gradual phase transformation, from the BCC Li(Mg) β-phase to the HCP Mg(Li) α-phase, occurred in the electrodes. An intriguing finding is that the Li-depleted Li(Mg) anode was largely intact as solid electrode even after delithiation. The Li(Mg) electrode showed some degree of reversibility (against LiCoO2), possibly by a combination of a small amount of Li alloying and/or deposition at the electrode-electrolyte interface during charging, a promising aspect for further investigation.