Few-Atomic-Layered Co-Doped BiOBr Nanosheet: Free-Standing Anode with Ultrahigh Mass Loading for "Rocking Chair" Zinc-Ion Battery.

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 Zn 2+ and electron transfer respectively. The Co-doping is conducive to the reduced Zn 2+ diffusion barrier, the improved volume expansion after Zn 2+ 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//MnO 2 "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.