The state of the art of conversion reactions of
metal hydrides (MH) with
lithium is presented and discussed in this review with regard to the use of these hydrides as
anode materials for
lithium-ion batteries. A focus on the gravimetric and volumetric storage capacities for different examples from binary, ternary and complex hydrides is presented, with a comparison between thermodynamic prediction and experimental results. MgH2 constitutes one of the most attractive
metal hydrides with a reversible capacity of 1480 mA·h·g(-1) at a suitable potential (0.5 V vs Li(+)/Li(0)) and the lowest
electrode polarization (<0.2 V) for conversion materials. Conversion process reaction mechanisms with
lithium are subsequently detailed for MgH2, TiH2, complex hydrides Mg2MH x and other Mg-based hydrides. The reversible
conversion reaction mechanism of MgH2, which is
lithium-controlled, can be extended to others hydrides as: MH x + xLi(+) + xe(-) in equilibrium with M + xLiH. Other reaction paths-involving solid solutions, metastable distorted phases, and phases with low
hydrogen content-were recently reported for TiH2 and Mg2FeH6, Mg2CoH5 and Mg2NiH4. The importance of fundamental aspects to overcome technological difficulties is discussed with a focus on
conversion reaction limitations in the case of MgH2. The influence of MgH2 particle size, mechanical grinding,
hydrogen sorption cycles, grinding with
carbon, reactive milling under
hydrogen, and
metal and catalyst addition to the MgH2/
carbon composite on kinetics improvement and reversibility is presented. Drastic technological improvement in order to the enhance conversion process efficiencies is needed for practical applications. The main goals are minimizing the impact of
electrode volume variation during
lithium extraction and overcoming the poor electronic conductivity of LiH. To use
polymer binders to improve the cycle life of the hydride-based
electrode and to synthesize nanoscale composite hydride can be helpful to address these drawbacks. The development of high-capacity hydride
anodes should be inspired by the emergent nano-research prospects which share the knowledge of both
hydrogen-storage and
lithium-
anode communities.