Polyacrylonitrile-Nanofiber-Based Gel Polymer Electrolyte for Novel Aqueous Sodium-Ion Battery Based on a Na₄Mn₉O18 Cathode and Zn Metal Anode.

A gel polymer electrolyte was formed by trapping an optimized Na⁺/Zn2+ mixed-ion aqueous electrolyte in a polyacrylonitrile nanofiber polymer matrix. This electrolyte was used in a novel aqueous sodium-ion battery (ASIB) system, which was assembled by using a zinc anode and Na₄Mn₉O18 cathode. The nanorod-like Na₄Mn₉O18 was synthesized by a hydrothermal soft chemical reaction. The structural and morphological measurement confirmed that the highly crystalline Na₄Mn₉O18 nanorods are uniformly distributed. Electrochemical tests of Na₄Mn₉O18//Zn gel polymer battery demonstrated its high cycle stability along with a good rate of performance. The battery delivers an initial discharge capacity of 96 mAh g-1, and 64 mAh g-1 after 200 cycles at a high cycling rate of 1 C. Our results demonstrate that the Na₄Mn₉O18//Zn gel polymer battery is a promising and safe high-performance battery.