Unravelling Twin Topotactic/Nontopotactic Reactive TiSe 2 Cathodes for Aqueous Batteries.

Titanium selenide (TiSe 2 ), a model transition metal chalcogenide material, typically relies on topotactic ion intercalation/deintercalation to achieve stable ion storage with minimal disruption of the transport pathways but has restricted capacity (<130 mAh g -1 ). Developing novel energy storage mechanisms beyond conventional intercalation to break capacity limits in TiSe 2 cathodes is essential yet challenging. Herein, we revisited the ion storage properties of TiSe 2 and unraveled an unusual thermodynamically stable twin topotactic/nontopotactic Cu 2+ accommodation mechanism for aqueous batteries. In-situ synchrotron X-ray diffraction and ex-situ microscopy jointly demonstrated that topotactic intercalation sustained the ion transport framework, nontopotactic conversion involved localized multielectron reactions, and these two parallel reactions were miraculously intertwined in nanoscale space. Comprehensive experimental and theoretical results suggested that the twin-reaction mechanism significantly improved the electron transfer ability, and the reserved intercalated TiSe 2 structure anchored the reduced titanium monomers with high-affinity and promoted efficient charge transfer to synergistically enhance the capacity and reversibility. Consequently, TiSe 2 nanoflake cathodes delivered a never-before-achieved capacity of 275.9 mAh g -1 at 0.1 A g -1 , 93.5% capacity retention over 1000 cycles, and endow hybrid batteries (TiSe 2 -Cu||Zn) with a stable energy supply of 181.34 Wh kg -1 at 2339.81 W kg -1 , offering a promising model for aqueous ion storage. This article is protected by copyright. All rights reserved.