Bulk-Type All-Solid-State Lithium-Ion Batteries: Remarkable Performances of a Carbon Nanofiber-Supported MgH₂ Composite Electrode

Magnesium hydride, MgH₂, a recently developed compound for lithium-ion batteries, is considered to be a promising conversion-type negative electrode material due to its high theoretical lithium storage capacity of over 2000 mA h g^-1, suitable working potential, and relatively small volume expansion. Nevertheless, it suffers from unsatisfactory cyclability, poor reversibility, and slow kinetics in conventional nonaqueous electrolyte systems, which greatly limit the practical application of MgH₂. In this work, a vapor-grown carbon nanofiber was used to enhance the electrical conductivity of MgH₂ using LiBH₄ as the solid-state electrolyte. It shows that a reversible capacity of over 1200 mA h g^-1 with an average voltage of 0.5 V (vs Li/Li⁺) can be obtained after 50 cycles at a current density of 1000 mA g^-1. In addition, the capacity of MgH₂ retains over 1100 mA h g^-1 at a high current density of 8000 mA g^-1, which indicates the possibility of using MgH₂ as a negative electrode material for high power and high capacity lithium-ion batteries in future practical applications. Moreover, the widely studied sulfide-based solid electrolyte was also used to assemble battery cells with MgH₂ electrode in the same system, and the electrochemical performance was as good as that using LiBH₄ electrolyte.