Lean‐Water Hydrogel with Multipolar Sites for Flexible and High‐Performance Aqueous Aluminum Ion Batteries

Abstract

Abstract Rechargeable aqueous aluminum ion batteries (AAIBs) offer a promising avenue for achieving safe, high‐energy, and low‐cost large‐scale energy storage applications. However, the practical development of AAIBs is hindered by competitive reduction reactions in the aqueous solution, which lead to insufficient aluminum (Al) deposition and a severe hydrogen evolution reaction (HRE). In this work, an inorganic/organic hybrid hydrogel with a stable silicon‐based network and multiple polar sites is successfully fabricated via an in situ sol‐gel polymerization method. The preferential formation of hydrogen bonds between the polar functional groups and water molecules effectively reduces the thermodynamic reactivity of water. Furthermore, X‐ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF‐SIMS) analyses confirm the formation of a stable, inorganic‐rich solid electrolyte interface (SEI) layer, which kinetically suppresses undesirable side reactions. This hydrogel electrolyte exhibits a high ionic conductivity of 2.9 × 10 −3 S cm −1 at 25 °C, even under lean‐water conditions. As a result, Al|hydrogel|potassium nickel hexacyanoferrate (KNHCF) full cells demonstrate excellent cycling performance, delivering a high initial discharge capacity of 74.9 mAh g −1 at 100 mA g −1 and achieving an outstanding capacity retention of 90.0% after 200 cycles. Additionally, pouch cells exhibit stable open‐circuit voltage under various mechanical abuse conditions.