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 Na_0.5FeFe(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 Na_0.5FeFe(CN)₆. Ex situ X-ray photoelectron spectroscopy reveals that the dissolution of Na_0.5FeFe(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.