Morphology And Size Control Of Nanostructured Zn-containing Hybrid Metal Oxides And Their Lithium Storage Performance

Zn-containing hybrid metal oxides are promising anode materials for next-generation Li-ion batteries.They are advantageous because they possess high theoretical capacities and can be flexibly designed and optimized by a wide variety of methods.However,the low electronic conductivity and poor cycling stability of Zn-containing hybrid metal oxides have greatly hindered their practical application.Besides,the interaction between oxides will bring a lot of variables into the electrode system.The variables such as size,shape,composition,interfacial adhesion,dispersity,valence states and crystal structure will significantly influence the electrochemical performance of the hybrid oxides.Currently,there still lack an accurate model or theory to predict the influence of these variables on the performance of hybrid metal oxides,which has made it difficult to efficiently design Zn-containing hybrid metal oxides anodes.In this work,we have optimized the lithium storage performance of Zn-containing hybrid metal oxides by rational control of their morphology,size and composition.The obtained results are analyzed and summarized,which might be useful for the controlled synthesis of Zn-containing hybrid metal oxides.The following are the main conclusions:?1?Potassium sodium tartrate is firstly used as the complexing agent to synthesize mesoporous nanoring-like ZnO/ZnCo₂O₄/Co₃O₄ hybrid oxides.The influence of the added amount of potassium sodium tartrate on the morphology of the hybrid oxides is investigated.It is found that the formation of the nanoring structure is strictly controlled by the amount of potassium sodium tartrate.Only when its added amount is controlled at 2 mmol,can the unique structure be obtained.The unique morphology and small size can greatly improve the lithium storage performance of ZnO/ZnCo₂O₄/Co₃O₄.The hybrid metal oxides can retain a high capacity of 1102 mAh g^-1 at a current density of 500 mA g^-1 after 200 cycles.The synthesis method is easy and scalable.It is also highly possible that the potassium sodium tartrate,with its special complexing ability,can be applied to optimize the morphology and structure of other metal oxides anodes.?2?The effects of the particle size of ZnMoO₄ and NiMoO₄ on the lithium storage performance of ZnMo O₄-NiMoO₄ hybrid metal oxides are investigated.A electrode optimization route based on the rational control of Zn/Ni ratio is proposed.It is found that the ZnMoO₄ and NiMo O₄ particles contribute differently to the cell performance.The submicro-sized ZnMoO₄ particles can remain stable during charge-discharge processes,which is helpful in improving the long-term cycling stability.The nano-sized NiMoO₄particles can shorten the diffusion pathway of ions and enhance the rate capability.The amount of these two particles is controlled by the Zn/Ni ratio.When the Zn/Ni ratio is controlled at 3,the hybrid oxides possess the highest performance.A reversible capacity of621 mAh g^-1 can be retained at 500 mA g^-1 after 200 cycles.?3?ZnO-NiO-Co₃O₄ hybrid nanoflakes are designed and synthesized via a simple hydrothermal method.The effects of the morphology,size and composition on the electrochemical performance are studied.The obtained hybrid materials possess a novel 2D nanoflake structure which is mainly constructed by firmly interconnected ZnO and NiO nanoparticles.The unique nanoflake structure can guarantee the immersion of electrolyte and provide large surface area for reactions.Hybridization between ZnO and NiO has mutually optimized their morphologies.For Zn O,connecting with small NiO nanoparticles will help to accommodate its severe volume expansion during cycling,while for NiO,interconnection with ZnO can alleviate its aggregation problem.The lithium storage performance of the hybrid nanoflakes with different Zn/Ni ratio is investigated.The ZnO-NiO-Co₃O₄ hybrid nanoflakes with the Zn/Ni ratio of 3 show the highest electrochemical performance.Despite the insignificant amount,Co₃O₄ also plays an indispensible role in the hybrid electrode as it can help to further reduce the charge transfer resistance.Owing to the synergistic effects between the morphology,size and composition,the ZnO-NiO-Co₃O₄ hybrid nanoflakes show excellent lithium storage performance.?4?ZnS nanoparticles are in situ grown on reduced graphene oxides?rGO?via a simplified one-step hydrothermal method.It is found that the introduction of rGO can greatly improve the dispersity of ZnS nanoparticles and increase the specific surface area of the composites.Sodium carboxymethyl cellulose?CMC?is firstly applied as the binder for ZnS based anodes and shows a more advantageous binding effect than PVDF.As advantageous binder,CMC can offer a homogeneous 3D networking around the active materials and modify the Li diffusion coefficient and accelerate the ion transport,thus enhancing the cycling stability and rate capability of the composite materials.The study of Zn-containing sulfides can be regarded as an extension from the Zn-containing hybrid metal oxides.If the matured optimization techniques for Zn-containing hybrid metal oxides is successfully applied in the Zn-containing sulfides,it is highly possible that more high-performance anode materials can be obtained.