LAUSR

Insertion host materials are considered as a candidate to replace metallic Zn anode. However, the high mass loading anode with good electrochemical performances is reported rarely. Herein, a few‐atomic‐layered Co‐doped BiOBr nanosheet (Co‐UTBiOBr) is prepared via one‐step hydrothermal method and a free‐standing flexible electrode consisting of Co‐UTBiOBr and CNTs is designed. Ultrathin nanosheet (3 atomic layers) and CNTs accelerate Zn2+ and electron transfer respectively. The Co‐doping is conducive to the reduced Zn2+ diffusion barrier, the improved volume expansion after Zn2+ intercalation, and the enhanced electronic conductivity of BiOBr, verified by experimental and theoretical studies. An insertion‐conversion mechanism is proposed according to ex situ characterizations. Benefiting from many advantages, Co‐UTBiOBr displays a high capacity of 150 mAh g−1 at 0.1 A g−1 and a long‐term cyclic life with ≈100% capacity attention over 3000 cycles at 1 A g−1. Remarkably, excellent electrochemical performances are maintained even at an ultrahigh mass loading of 15 mg cm−2. Co‐UTBiOBr//MnO2 “rocking chair” zinc‐ion battery exhibits a stable capacity of ≈130 mAh g−1 at 0.2 A g−1 during cyclic test and its flexible quasi‐solid‐state battery shows outstanding stability under various bending states. This work provides a new idea for designing high mass loading anode.