Search

Summary 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 Mg 2+ 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 Mg 2+ into a metastable one-dimensional polymorph of V 2 O 5 up to a capacity of 0.33 Mg 2+ per formula unit. An electrochemical capacity of 90 mA hr g −1 was retained after 100 cycles with an average operating potential of 1.65 V versus Mg 2+ /Mg 0 . Not only does ζ-V 2 O 5 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.