Molecular-Scale Functionality on Graphene To Unlock the Energy Capabilities of Metal Hydrides for High-Capacity Lithium-Ion Batteries.

Metal hydrides have attracted great intentions as anodes for lithium-ion batteries (LIBs) due to their extraordinary theoretical capacity. It is an unsolved challenge, however, to achieve high capacity with stable cyclability, owing to their insulating property and large volume expansion upon lithium storage. Here, we introduce self-initiated polymerization to realize molecular-scale functionality of metal hydrides with conductive polymer, that is, polythiophene (PTh), on graphene, leading to the formation of MgH2@PTh core-shell nanoparticles on graphene. The nanoscale characteristics of MgH2 not only relieve the induced stress upon volume changes but also allow fast diffusivity and high reactivity for Li-ion transport. More importantly, the conformal coating of ultrathin PTh membrane can effectively suppress the detrimental reactions between MgH2 and electrolyte, provide enhanced performance with facile electron and Li+ transport, and preserve its structural integrity, attributed to the strong molecular interaction between PTh and MgH2 as well as its various products during electrochemical reactions. With this structure, a high reversible specific capacity of 1311 mAh g-1 at 100 mA g-1, excellent rate performance of 1025 mAh g-1 at 2000 mA g-1, and a capacity retention of 84.5% at 2000 mA g-1 after 500 cycles are observed for MgH2@PTh nanoparticles as anode for LIBs.