Electrochemical performances of MgH2 and MgH2-C films for lithium ion battery anode

As a high-capacity hydrogen storage material, MgH2 also shows specific advantages for LIB anode. In this work, MgH2 and MgH2-C films were prepared by magnetron sputtering and hydrogenation treatment, and their microstructural and electrochemical properties were investigated. Through the conversion reaction of MgH2 with lithium (MgH2 + 2Li+ → Mg + 2LiH), the reversible lithium storage was achieved in the MgH2 and MgH2-C films. The MgH2 film delivers the initial discharge capacity of 313.9 μAh cm−2 (∼2956 mAh g−1), the discharge and charge capacities related to the conversion process are respectively 150.0 μAh cm−2 (∼1412 mAh g−1) and 55.0 μAh cm−2 (∼518 mAh g-1), with the inefficiency of 63.3%. The GITT measurement determined the equilibrium potential of this conversion reaction to be 0.55 V vs. Li/Li+, and the voltage hysteresis between discharge and charge is only 10 mV vs. Li/Li+. In comparison with the MgH2 film, the MgH2-C film has smaller crystallite size, lower polarization effect and structural stability, but exhibiting lower capacity and equally poor cyclic performance. The poor cycle life of MgH2-C film electrode is due to the large irreversibility of conversion reaction of MgH2, instead of structural damage of film electrode during cycling.