Ni-Zn Batteries Based On Bimetallic Compounds And Their Electrochemical Performance

Aqueous zinc-based batteries（AZBs）have attracted widespread attention due to a set of advanctages of Zn,which include improved safety,high theoretical capacity,low redox potential,natural abundance,and low toxicity.Designing and preparing positive electrode materials with outstanding electrochemical performance is the key to obtaining high-performance AZBs.This thesis reports the design and synthesis of two kinds of Ni and Co-based bimetal compounds,which are in-situ grown on a carbon cloth substrate（CC）.The relationship between their structure and electrochemical performance was studied and their structural evotution during the electrochemical reaction was further revealed.Firstly,we crafted bimetallic Ni Co₂S_4-x with tunable sulfur deficiency as effective cathode materials for Zn batteries with large capacity,high rate capability and outstanding cycle stability.Notably,the sulfur vacancies can be judiciously tailored to increase the number of active sites for electrochemical reaction.Moreover,the in-situ growth of sulfur-deficient Ni Co₂S_4-xnanotube arrays on highly conductive CC substrate(denoted sd-Ni Co₂S_4-x@CC)not only shortens the electronic and ionic transport pathways,but also provides a binder-free architecture for flexible devices.The resulting sd-Ni Co₂S_4-x@CC nanocomposites are exploited as cathode for Zn batteries,presenting high capacities of 298.3 and 175.7 m Ah g^-1 at 0.5 and 5 A g^-1,respectively,which outperform the CC-support-free Ni Co₂S_4-x nanotube and Ni Co₂O₄nanowire counterparts.The ex-situ XRD,TEM and XPS studies collectively reveal the redox reaction of sd-Ni Co₂S_4-x@CC with OH^-.More importantly,a flexible solid-state sd-Ni Co₂S_4-x@CC//Zn@CC battery is assembled using sodium polyacrylate hydrogel electrolyte,displaying an unprecedented cyclic durability of 84.7%after 1500 cycles at 5 A g^-1.In order to further explore the nickel-cobalt bimetal compounds,we successfully prepared bamboo structured（Ni,Co）Se₂ which are vertically grown on CC substrate,and further coated the surface of（Ni,Co）Se₂ with polyaniline（denoted PANi@（Ni,Co）Se₂@CC）.PANi coating layer protects and supports the structure of（Ni,Co）Se₂@CC,thereby improving its cycle stability in the electrochemical process.After 1000 cycles,the capacity retention rate of PANi@（Ni,Co）Se₂@CC is as high as 85%.And even after 3000 cycles,the PANi@（Ni,Co）Se₂@CC still has a high capacity retention rate of 70%.This work opens a new avenue for developing high-performance zinc-based battery cathode materials and provides a new approach for the development of flexible energy storage devices.