Design Of Novel Bismuth Oxyhalide Anode And Study On Zn²⁺ Storage Mechanism

At present,the green and clean new battery system has high application value and special development prospect in the field of electrochemical energy storage.Aqueous zinc ion battery has attracted worldwide attention due to its inherent safety,low environmental impact,simple manufacturing process and high energy density.However,when zinc is used as the negative electrode of zinc ion battery,it will inevitably produce a series of problems such as zinc dendrite,corrosion passivation and hydrogen evolution reaction,which will affect the electrochemical performance of the battery.The development of high capacity intercalated anode materials is an effective way to solve the above problems.Layered materials have been gradually applied to zinc ion batteries due to their advantages of large layer spacing,fast charge transfer and storage,and stable structure.The interlayer spacing between BiOBr and Bi OI is as high as 0.81 nm and 0.91 nm,both of which are larger than common layered materials and have excellent zinc storage potential.However,there are no reports about Bi OX（X=Br,I）applied in zinc ion batteries.Therefore,it is highly innovative to use Bi OX as a new interlayer negative electrode for zinc ion batteries.This study focuses on Bi OI and BiOBr,two bismuth halide oxide materials,as the interlayer negative electrode of zinc ion battery.The main research contents are as follows:（1）According to density functional theory calculation,layered Bi OI has a large interlayer distance（0.91 nm）and a low Zn²⁺diffusion barrier（0.57 e V）,which may have excellent Zn²⁺storage capacity,and a Bi OI self-supported electrode nanosheet was designed.The insertion process and storage mechanism of Zn（H₂O）_n²⁺in Bi OI were confirmed by ex-situ X-ray diffraction,Raman spectroscopy and X-ray photoelectron spectroscopy.Bi OI nanosheets have suitable potential(0.6 V vs.Zn/Zn²⁺),high reversible capacity(253 m Ah g^-1),good magnification performance(171 m Ah g^-1 at 10 A g^-1),and long cycle life(113 m Ah g^-1after 5000 cycles at 5 A g^-1)and dendrite-free,demonstrating its potential as a super intercalated anode electrode of zinc ion batteries.When coupled to the Zn-free Mn₃O₄ cathode electrode,the quasi-solid-state full battery has an initial capacity of up to 149 m Ah g^-1（based on the anode electrode）and a capacity retention rate of up to 70 m Ah g^-1 after 400 cycles.In addition,the self-assembled flexible full battery also showed stable charging and discharging process in flexible electrochemical test.（2）In order to improve the cycling stability of BiOBr,Co-doped ultra-thin BiOBr was prepared by ionic liquid-assisted hydrothermal method.The ultrathin structure of BiOBr is conducive to the full contact between material and electrolyte,providing more reactive sites and shortening the Diffusion path of Zn²⁺.At the same time,the Zn²⁺intercalation kinetics was enhanced by the chemically inserted cobalt ions,which greatly enhanced the reversibility and cyclic stability.Meanwhile,the mechanism of BiOBr embedded energy storage was proved by ex-situ XRD.Therefore,the Co-UTBiOBr self-supported electrode exhibits excellent electro-chemical performance,with a capacity of up to 187 m Ah g^-1,and still provides a stable capacity of 74 m Ah g^-1 after 3000 cycles at 1 A g^-1 current density.More importantly,the zinc-ion battery was successfully assembled based on Co-UTBIOBr negative electrode and Zinc-free Mn₃O₄ positive electrode.The full cell showed a high reversible capacity(168 m Ah g^-1),with a discharge capacity of 126 m Ah g^-1even after 100 cycles at a current density of 0.2 A g^-1,and the capacity retention rate of 75%.（3）In order to improve the conductivity of BiOBr,a new type of nitrogen-doped carbon intercalated ultra-thin BiOBr material was designed in this work.UTBiOBr@NC self-supporting electrode was prepared by inserting aniline guest between the ultra-thin BiOBr layers and carbonizing at high temperature.The prepared UTBiOBr@NC has nano-structure size and shortens the diffusion path of Zn²⁺.As the buffer layer of the main material,the conductive carbon layer can not only provide a fast charge transfer channel,but also greatly enhance the structural stability of the main material.Due to the unique design of this work,UTBiOBr@NC self-supported electrode shows excellent cycle stability and good rate performance.The excellent electrochemical stability was proved by ex-situ X-ray diffraction from reversible intercalation mechanism and super-stable structure.At a current density of0.2 A g^-1,UTBiOBr@NC self-supported electrode can stably provide a high specific capacity of 166 m Ah g^-1,coulomb efficiency is close to 100%,and a high reversible capacity of 156 m Ah g^-1 can be maintained at a current density of 0.5 A g^-1 for nearly5000 cycles.More importantly,the zinc-ion full battery based on UTBiOBr@NC//Mn O₂ has an energy density of up to 48.6 Wh kg^-1.