High Wettability and Fast Ion Conduction of Polyimide-Based Separator for High-Rate Capability in Aqueous Zn-Ion Battery

Aqueous Zn ion batteries (AZIBs) are increasing in interest as next-generation rechargeable batteries due to the nonflammability of the aqueous electrolyte, the high theoretical capacity (820 mA h g⁻¹) of the Zn anode, and their high price competitiveness. However, the capacity and cycle life characteristics are significantly lower than those of current lithium-ion batteries (LIBs) due to the low cycle life caused by dendrite formation on the Zn anode and the decreased capacity problem caused by structure collapse from the cathode. In this work, we utilized the high internal phase emulsion (HIPE) and KOH-derived ring cleavage reaction techniques to construct a hydrophilic polyimide-based separator (HPI) with enhanced wettability and ion transfer properties. Comparing this HPI separator to the glass fiber (GF) separator, which is widely used in AZIBs, the cycle life of the Zn anode was increased from 150 h to 350 h at 1 mA cm⁻² of current density. Additionally, a full cell using a NaV₃O₈ cathode achieved a specific capacity of 162.2 mA h g⁻¹ after 1,000 cycles at a current density of 0.5 A g⁻¹. This is significantly higher than the 89.8 mA h g⁻¹ obtained when using a GF separator, and at a high current density of 2 A g⁻¹, the capacity was 194.8 mA h g⁻¹, which is much greater than the 103.4 mA h g⁻¹ obtained when using the GF separator. The polyimide-based separator with high ion transfer characteristics developed in this study will probably have a crucial role in developing next-generation AZIBs.