Conversion-type Anode Materials for Alkali-Ion Batteries: State of the Art and Possible Research Directions

In this study, the potential of conversion-type anode materials for alkali-ion batteries has been examined and analyzed in terms of the parameters of prime importance for practical alkali-ion systems. Issues like voltage hysteresis, discharge profile, rate stabilities, cyclic stabilities, irreversible capacity loss, and Columbic efficiencies have been specifically addressed and analyzed as the key subjects. Relevant studies on achieving a better performance by addressing one or more of the issues have been carefully selected and outlook has been presented on the basis of this literature. Mechanistic insights into the subject of conversion reactions are discussed in light of the use of recent and advanced techniques like in situ transmission electron microscopy, in operando X-ray diffraction, and X-ray absorption spectroscopy. Three-dimensional plots depicting the performance of different materials, morphologies, and compositions with respect to these parameters are also presented to highlight the systematic of multiparameter dependencies. Inferences are drawn from these plots in the form of a short section at the end, which should be helpful to the readers, especially young researchers. We believe that this study differs from others on the subject in being focused toward addressing the practical limitations and providing possible research directions to achieve the best possible results from conversion-type anode materials.