Voltage Hysteresis in Transition Metal Oxide Cathodes for Li/Na-Ion Batteries

The pursuit of rechargeable batteries with high energy density has triggered enormous efforts in developing cathode materials for lithium/sodium (Li/Na)-ion batteries considering their extremely high specific capacity. Many materials are being researched for battery applications, and transition metal oxide materials with remarkable electrochemical performance stand out among numerous cathode candidates for next-generation battery. Notwithstanding the merits, daunting challenges persist in the quest for further battery developments targeting lower cost, longer lifespan, improved energy density and enhanced safety. This is, in part, because the voltage hysteresis between the charge and discharge cycles, is historically avoided in intercalation electrodes because of its association with structural disorder and electrochemical irreversibility. Given the great potential of these materials for next-generation batteries, a review of the recent understanding of voltage hysteresis is timely. This review presents the origin of their undesirable behaviors and materials design criteria to mitigate them by integrating various schools of thought. A large amount of progressive characterization techniques related to voltage hysteresis are summarized from the literature, along with the corresponding measurable range used in their determination. Finally, promising design trends with eliminated voltage hysteresis are tentatively proposed to revive these important cathode materials toward practical applications.