High-Performance and Scalable Aqueous Na-Ion Batteries Comprising a Co-Prussian Blue Analogue Framework Positive Electrode and Sodium Vanadate Nanorod Negative Electrode for Solar Energy Storage

A unique configuration of aqueous Na-ion batteries is investigated for solar energy storage, where single-wall carbon nanotube (SWCNT)-coated stainless steel (SS304), Co-Prussian blue analogue (Co-PBA/Na₂CoFe(CN)₆), and sodium vanadate (NVO/NaV₃O₈) nanorods are employed as a current collector, positive active material, and negative active material, respectively. The SWCNT coverage on SS radically obstructs the metallic corrosion under anodic polarization and also enhances the electrolyte stability window by preventing direct contact between the metal substrate and electrolyte. Both the positive and negative materials are structurally analyzed by Rietveld refinement of powder X-ray diffraction data. The Co-PBA framework structure demonstrates one-dimensional channels with ∼5.3 and 5.1 Å widths along [100] and [011], respectively, whereas the layered NVO depicts an interlayer spacing of ∼4.2 Å for facile Na-ion transportations. Resultantly, the high diffusion coefficients of Na-ions in Co-PBA and NVO are achieved as 1.6 × 10^-13 and 2.0 × 10^-11 cm² s^-1, respectively. Both Co-PBA and NVO exhibit a diffusion-controlled Faradaic charge storage mechanism, which has been demonstrated by cyclic voltammetry. The Co-PBA provides 122 mAh g^-1 specific capacity at 1C rate, which is the highest reported value in aqueous medium with low-cost current collectors. The electrochemical performance testing of NaV₃O₈ is first described by us, explicitly for the negative electrode, and it delivers 83 mAh g^-1 specific capacity at 1C. The 1.5 V silica gel-based Co-PBA//NVO full cell is fabricated with mass balancing, which shows higher cell voltage by maximizing the water splitting window. The full cell delivers a specific capacity of 141 mAh g^-1 (@ 1C), an energy density of 211 Wh kg^-1 (@ 250 W kg^-1), a power density of 2466 W kg^-1 (@ 94 Wh kg^-1), and good durability (80% capacity retention @ 5C) up to 500 cycles. A 3 V/5 mAh rated prototype device is assembled, and it delivers satisfactory solar energy storage performances under 1 week of continuous operation.