Design of Ion Channel Confined Binary Metal Cu‐Fe Selenides for All‐Climate, High‐Capacity Sodium Ion Batteries

Abstract Exploring special anode materials with high capacity, stable structure, and extreme temperature feasibility remains a great challenge in secondary sodium based energy systems. Here, a bimetallic Cu‐Fe selenide nanosheet with refined nanostructure providing confined internal ion transport channels are reported, in which the structure improves the pseudocapacitance and reduces the charge transfer resistance for making a significant contribution to accelerating the reaction dynamics. The CuFeSe 2 nanosheets have a high initial specific capacity of 480.4 mAh g −1 at 0.25 A g −1 , showing impressively excellent rate performance and ultralong cycling life over 1000 cycles with 261.1 mAh g −1 at 2.5 A g −1 . Meanwhile, it exhibits a good sodium storage performance at extreme temperatures from −20 °C to 50 °C, supporting at least 500 cycles. Besides, the CuFeSe 2 ||Na 3 V 2 (PO 4 ) 3 /C full cell delivers a high specific capacity of 168.5 mAh g −1 at 0.5 A g −1 and excellent feasibility for over 600 cycles long cycling. Additionally, the Na + storage mechanisms are further revealed by ex situ X‐ray diffraction (XRD) and in situ transmission electron microscopy (TEM) techniques. A feasible channelized structural design strategy is provided that inspires new instruction into the development of novel materials with high structural stability and low volume expansion rate toward the application of other secondary batteries.