Aqueous zinc batteries have been regarded as a promising energy storage technology due to their high energy, high material abundance, low toxicity, and intrinsic safety. NASICON-type materials have been proposed as efficient cathodes for rechargeable batteries, yet they suffer from fast degradation and low Coulombic efficiency in aqueous batteries. Here we demonstrate that a rationally designed aqueous electrolyte containing a supporting Na salt and polymer additive can efficiently suppress the water activity through hydrogen bonding and facilitate the anion involvement in interfacial reactions, thus enabling the stable operation of sodium superionic conductor (NASICON) cathodes in aqueous zinc batteries. As exemplified by a Na 3 V 2 (PO 4 ) 3 cathode, the cell with zinc metal anode exhibits high cycling Coulombic efficiencies (around 99.9 % in average) with a steady output voltage and capacity retention for 300 cycles. This work addresses the potential issues with NASICON-type cathodes in aqueous zinc batteries and proposes an effective solution via fundamental interphasial chemistry to design efficient and sustainable aqueous electrolytes. Graphical Engineering electrode-electrolyte interphase : A rationally designed aqueous electrolyte with bi-cation and polymer additive is reported for aqueous zinc batteries with NASICON cathodes. As exemplified by a Na 3 V 2 (PO 4 ) 3 cathode, the full cells exhibited remarkable cycling stability and efficiency, benefiting from the well-suppressed material dissolution by electrolyte-induced interfacial engineering.
Sodium-ion batteries (SIBs), as an emerging energy storage technology, have been recognized as one of the most promising alternatives to lithium-ion batteries (LIBs). Among various cathode materials, the NASICON-type Na 4 VMn(PO 4 ) 3 (NVMP) composite material has garnered considerable attention owing to its distinctive 3D framework structure, high redox potential, stable crystal structure, and rapid Na + diffusion rate. Nevertheless, the practical application of NVMP cathodes is constrained by several inherent limitations, including inherently low electronic conductivity, Mn 3+ Jahn–Teller distortion, and structural degradation mechanisms, which collectively contribute to compromised rate capability and limited cycling durability. To tackle this challenge, an N-doped dual nano-carbon coating was applied to the NVMP material to enhance the conductivity of the composite. Building upon this foundation, a series of Na 4 VMn 1- x Cr x (PO 4 ) 3 /NC@CNTs cathode materials (where x = 0, 0.25, 0.5, 0.75, and 1) were successfully prepared using the sol–gel method, enabling targeted regulation of Mn/Cr ratios for enhanced electrochemical performance. The N-doped dual nano-carbon coating is capable of forming carbon layer defects and active sites, as well as constructing a 3D conductive network structure, which can enhance the diffusion rate of Na + ions and shorten their transport path. The results indicate that the Na 4 VMn 0.5 Cr 0.5 (PO 4 ) 3 /NC@CNTs cathode material demonstrates the highest discharge capacity, achieving 132.1 mAh·g −1 when x = 0.5. Notably, the capacity decreases rapidly at high rates, potentially attributed to the collapse of the crystal structure and excessive polarization, resulting in a deterioration of the material’s electrochemical performance. The optimized Na 4 VCr(PO 4 ) 3 /NC@CNTs (when x = 1) demonstrates exceptional rate performance with 91.2% capacity retention at 1C, accompanied by significantly reduced charge transfer resistance (Rct = 331.9 Ω). This study establishes a design paradigm for NASICON-type cathode materials through dual-transition metal synergistic doping and demonstrates the efficacy of Cr/Mn co-substitution in balancing ionic/electronic conductivity for next-generation high-power sodium-ion batteries.
NASICON-type cathodes as promising candidates have attracted more and more attention, and Na 3 V 2 (PO 4 ) 3 is one of the outstanding representatives. In particular, it can tolerate complex interface reaction processes during the Zn 2+ insertion/desertion in the aqueous environment. However, existing three-dimensional channels in the intrinsic Na 3 V 2 (PO 4 ) 3 always hardly play to their advantages as narrow pathways and some other defects. This work has considered both the conductivity and capacity of this vanadium-based NASICON cathode at the same time, where a sodium-rich cathode material Na 3.2 V 1.8 Mn 0.15 Mg 0.05 (PO 4 ) 3 (NVMMP) with Mn 2+ and Mg 2+ dual-substituents has been designed considering the low cost and environmentally friendly characteristics. The synergistic effects introduced by Mn 2+ and Mg 2+ substitution led to a significant increase in the capacity and cycle life of the optimized NVMMP cathode material (with a capacity retention rate of 90.6 % after 2500 cycles at 2 A g −1 ). Furthermore, the reversible storage mechanism of Zn 2+ in NVMMP cathode materials and the theoretical study of such synergistic substitution on intrinsic electronic conductivity have been revealed by different in/ex-situ characterization techniques and theoretical calculations, where redox processes generated by Mn 3+ /Mn 4+ , enhanced ionic/electron pathway, and the pinning effect caused by injecting inert MgO 6 octahedra into the NASICON framework are key points to high capacity and long-life span.
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