Cathode materials with high capacity and cyclic durability are urgently needed for capacitive deionization . Na 3 V 2 (PO 4 ) 3 is an emerging pseudocapacitive candidate for this process on account of its high capacity and Na + reversible insertion, while it suffers from the intrinsic low electrical conductivity and small electrolyte-accessible surface area. Herein, a sea urchin-like Na 3 V 2 (PO 4 ) 3 @carbon (NVP@C) compound material was synthesized from MXene-V 2 C via hydrothermal method followed by annealing treatment, and then assembled as capacitive deionization (CDI) electrode material . Benefiting from three-dimensional sea urchin-like structure, where the nanoneedles of NVP@C serve as fast transport channel for Na + , NVP@C performed high specific capacity (437 F g −1 at 5 mV s −1 ) and fast ionic diffusion kinetics. Moreover, the NVP@C showed attractive desalination performance as cathode material for CDI, achieving a remarkable adsorption capacity of 74.0 mg g −1 in a NaCl salt solution (1000 mg L −1 ) and long life cycle stability. The present work provides a novel perspective to construct practical redox-active and stable CDI electrode with 3D structure from MXene for highly capacitive and durable desalination application .
O3 phase layered oxides are highly attractive cathode materials for sodium-ion batteries because of their high capacity and decent initial Coulombic efficiency. However, their rate capability and long cycling life are unsatisfactory due to the narrow Na + transfer channel and irreversible phase transitions of O3 phase during sodiation/desodiation process. Constructing O3/P2 multiphase structures has been proven to be an effective strategy to overcome these challenges. In this study, we synthesized bi-phasic structured O3/P2 Na(Ni 2/9 Fe 1/3 Cu 1/9 Mn 1/3 ) 1- x Mn x O 2 ( x = 0.01, 0.02, 0.03, 0.04, 0.05) materials through Mn doping during sodiation process. Benefiting from surface P2 phase layer with the enhanced Na + transfer dynamics and high structural stability , the Na(Ni 2/9 Fe 1/3 Cu 1/9 Mn 1/3 ) 0.98 Mn 0.02 O 2 (NFCM-M2) cathode delivers a reversible capacity of 139.1 mA h g −1 at 0.1 C, and retains 71.4 % of its original capacity after 300 cycles at 1 C. Our work provides useful guidance for designing multiphase cathodes and offers new insights into the structure-performance correlation for sodium-ion cathode materials.
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