Recently, sodium ion batteries (SIBs) have many attention paid to advantages such as the low price and abundance of sodium raw materials that are appropriable for large-scale energy storage applications. Herein, we report an Mn-based pyrophosphate, Na2MnP2O7, as a new SIB cathode material. Unlike most Mn-based cathode materials, which suffer severely from sluggish kinetics, Na2MnP2O7 exhibits excellent electrochemical activity at                         3.8 V vs Na/Na+ with a reversible capacity of 90 mAh g�1 at room temperature. It also shows a good cycle life and rate performance: 96% capacity retention after 30 cycles and 70% capacity retention at a c-rate (from 0.05C to 1C). These electrochemical activities of the Mn-containing cathode material even at room temperature with relatively large particle sizes are notable considering an almost complete inactivity of the Li counterpart, Li2MnP2O7. Using first-principles calculations, we find that the significantly enhanced kinetics of Na2MnP2O7 is principally due to the locally flexible accommodation of Jahn�Teller distortions aided by the corner-sharing crystal structure in triclinic Na2MnP2O7. By contrast, in monoclinic Li2MnP2O7, the edge-sharing geometry causes multiple bonds to be broken and formed during charging reaction with a large degree of atomic rearrangements. We expect that the similar computational strategy to analyze the atomic rearrangements can be used to predict the kinetics behavior when analyzing new cathode candidates.

Anomalous manganese activation of a pyrophosphate cathode in sodium ion batteries: A combined experimental and theoretical study

246th National Meeting (2013)

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