Reversible Mg-Ion Insertion in a Metastable One-Dimensional Polymorph of V2O5
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2017 Elsevier Inc. The Li-ion paradigm of battery technology is constrained by the monovalency of the Li ion. A straightforward solution is to transition to multivalent-ion chemistries, where Mg2+ is the most obvious candidate because of its size and mass. The realization of Mg batteries has faced myriad obstacles, including a sparse selection of cathode materials demonstrating the ability to reversibly insert divalent ions. Here, we provide evidence of reversible topochemical and electrochemical insertion of Mg2+ into a metastable one-dimensional polymorph of V2O5 up to a capacity of 0.33 Mg2+ per formula unit. An electrochemical capacity of 90 mA hr g1 was retained after 100 cycles with an average operating potential of 1.65 V versus Mg2+/Mg0. Not only does -V2O5 represent a rare addition to the pantheon of functional Mg battery cathode materials, but it is also distinctive in exhibiting a combination of high stability, high specific capacity, and moderately high operating voltage. The worldwide push to advance renewable energy is limited by the availability of energy storage vectors. Currently, Li-ion technology dominates; however, the safety and long-term criticality of Li remain serious concerns. Mg is much more abundant than Li, has a higher melting point, and does not form dendrites, making it a safer and more environmentally sustainable choice for intercalation batteries. The improved safety further allows for the use of Mg anodes, leading to a 6-fold increase in specific energy density at the anode. The development of Mg-ion intercalation batteries has been plagued by a dearth of suitable cathode chemistries. Here, we describe a metastable cathode material that is one of the few materials capable of reversibly inserting Mg2+ and elucidate the chemical mechanisms of insertion with an eye toward developing high-energy-density and high-cycle-performance cathode materials for the realization of Mg-ion batteries. Compared with Li-ion batteries, Mg-ion batteries would represent a transformative advance in terms of safety, cost, and performance. Achieving the reversible storage of divalent Mg ions within solid-state frameworks has been exceedingly difficult. Here, Banerjee and colleagues have designed a cathode material that combines high voltage, high capacity, and excellent cycle stability for Mg-ion batteries. They provide definitive evidence of reversible Mg-ion insertion within a metastable V2O5 cathode material, illustrating the use of metastable phase space for realizing novel function.
