An Ultrastable Na–Zn Solid-State Hybrid Battery Enabled by a Robust Dual-Cross-linked Polymer Electrolyte

This work proposes a dual-cross-linked gel solid electrolyte (SE), here defined as Zn-re-inforced sodium alginate–polyacrylamide SE (Zn-reinforced SA–PAM SE), in which Na+ and Zn2+ coexist. The SE shows a high conductivity of 19.74 mS cm–1. Compared to the pure PAM gel, the tensile strength and compressive strength of Zn-reinforced SA–PAM SE are significantly enhanced to be 674.28 kPa and 16.29 MPa, respectively, because of the strengthening mechanism of Zn2+ cross-linked SA. Based on such a robust electrolyte, a novel hybrid cell is developed by involving Na0.5FeFe(CN)6–carbon nanotube composites (PB@CNT) as the Na+ intercalation-type cathode and metallic Zn as the plating anode. The hybrid cell shows an extremely high stability for 10,000 cycles with a record little capacity loss of 0.0027% per cycle, as Zn-reinforced SA–PAM SE successfully inhibits free water molecules from occupying low-spinning metallic sites (Fe–C) in Na0.5FeFe(CN)6. Ex situ X-ray photoelectron spectroscopy reveals that the dissolution of Na0.5FeFe(CN)6 is highly reduced by 79.5%. It is further noted that the corrosion and dendrites at the Zn2+/Zn plating anode are greatly hindered for the robust electrolyte. This work gives a pathway for the development of new aqueous ion batteries.