Synergistic Improvement in Capacitive Deionization Performance Using a Novel Phase-Integrated Na0.55Mn2O4@Na0.7MnO2

Capacitive deionization (CDI) is currently restricted by inferior desalination performance. To overcome this limitation, exploring novel pseudocapacitive materials is ongoing. Herein, we made the first attempt to construct a phase-integrated sodium manganese oxide (NMO) by the intergrowth of Na0.55Mn2O4 with Na0.7MnO2 via a feasible method of one-step high-temperature calcination at various temperatures. The optimal NMO sample sintered at 800 °C (NMO-800), with a formula of 0.71Na0.55Mn2O4@0.29Na0.7MnO2, delivered an ultrahigh desalination capacity of 173.5 mg/g in 500 mM NaCl solution with a voltage of 1.0 V along with remarkable cycling stability, energy consumption, and charge efficiency. Electrochemical and material measurements manifested that the dominant ion removal principle of the phase-integrated NMO samples was the Faradic intercalation/deintercalation reactions and that the core mechanism responsible for the superior desalination capacity of the NMO-800 was associated with its higher levels of intercalation/deintercalation reactions owing to the boosted synergistic effect of biphases as compared with the NMO samples sintered at other temperatures. The presented phase-integration engineering strategy could provide a new perspective on the optimal design of pseudocapacitive materials for high-performance desalination.