Study Of Preparation And Electrochemical Properties Of Core-shell ZnO@C/Bi Materials For Zinc Anode

Alkaline aqueous battery represented by zinc secondary battery is considered as a green energy storage device with great application prospect owing to its high energy density,high safety and low cost.However,dendrite growth and hydrogen evolution side reactions inevitably occur during the charging and discharging process,which leads to poor cycle performance and rate performance of zinc secondary batteries.It is the key challenge for the commercial application of zinc secondary batteries.In view of the above problems,this paper prepared a unique core-shell structure of ZnO@C/Bi composite for zinc anode by hydrothermal and susequently calcination process,which the shell is porous C/Bi composite inlaid with high hydrogen evolution overpotential metal Bi and the core is ZnO.Furthermore,the forming mechanism of the ZnO@C/Bi materials was analyzed,and the influence of hydrothermal process and heat treatment process on the composition and structure of ZnO@C/Bi material were also studied.On the basis,the effects of composition and structure of ZnO@C/Bi on its electrochemical properties were further studied.The main conclusions are as follows:（1）The formation mechanism of ZnO@C/Bi composite with core-shell structure was revealed:The oxygen atoms in glucose（Glu）complex with Bi atoms in Bi（NO₃）₃ to form a coating layer of glu/Bi（NO₃）₃complex,which coated with ZnO to form ZnO@glu/Bi（NO₃）₃ materials.In a protective atmosphere,glu reduces Bi³⁺to Bi and glu is carbonized at the same time.The coating layer is transformed from glu/Bi（NO₃）₃complex to C/Bi composites embedded with metal Bi,and the core-shell structure ZnO@C/Bi composites are formed.（2）The structure and electrochemical properties of ZnO@C/Bi materials were obtained under different hydrothermal processes and heat treatment conditions,and the preparation process of the materials was optimized.The core-shell structure ZnO@C/Bi composites with uniform coating thickness and uniform Bi distribution can be obtained under the protective atmosphere of hydrothermal temperature of 200℃for 6 h and heat treatment temperature of 600℃for 5 h.When used as the active sustances of zinc anode and built a battery,the discharge specific capacity is 547.4 m Ah g^-1 with a capacity retention rate of 83.06%after 230 cycles at 1 C.And the average discharge specific capacity reaches to 593.6 m Ah g^-1.（3）The influence of the composition of ZnO@C/Bi composite on its electrochemical properties was obtained,and the composition of the materials with good performance was determined as follows:Bi content is5.66%,carbon layer thickness is 14.4 nm,ZnO particle size is 200 nm.When using the composed ZnO@C/Bi materials as the zinc anode active substances and building a battery,the specific discharge capacity reaches527.1 m Ah g^-1 with a capacity retention rate of 79.98%after 480 cycles at1 C.And the average discharge specific capacity of the battery is 589.9m Ah g^-1.