Confining Conversion Chemistry in Intercalation Host for Aqueous Batteries

Abstract Conversion‐type anode materials with high theoretical capacities play a pivotal role in developing future aqueous rechargeable batteries (ARBs). However, their sustainable applications have long been impeded by the poor cycling stability and sluggish redox kinetics. Here we show that confining conversion chemistry in intercalation host could overcome the above challenges. Using sodium titanates as a model intercalation host, an integrated layered anode material of iron oxide hydroxide‐pillared titanate (FeNTO) is demonstrated. The conversion reaction is spatially and kinetically confined within sub‐nano interlayer, enabling superlow redox polarization (ca. 4–6 times reduced), ultralong lifespan (up to 8700 cycles) and excellent rate performance. Notably, the charge compensation of interlayer via universal cation intercalation into host endows FeNTO with the capability of operating well in a broad range of aqueous electrolytes (Li + , Na + , K + , Mg 2+ , Ca 2+ , etc.). We further demonstrate the large‐scale synthesis of FeNTO thin film and powder, and rational design of quasi‐solid‐state high‐voltage ARB pouch cells powering wearable electronics against extreme mechanical abuse. This work demonstrates a powerful confinement means to access disruptive electrode materials for next‐generation energy devices.