Study On Preparation And Electrochemical Performance Of Manganese Oxide Anode Materials

Lithium ion batteries have been considered as a new generation of power equipment,due to the high energy,environment-friendly,low cost and no memory effect.Graphite-based carbon has stable structure and long cycling life,which is the current conventional anode material,however its low theoretical capacity cannot meet the demands for large energy and power density,so searching for new anode materials with high capacity has become a hot topic.Recently,transition metal oxides have been studied to reach excellent performance in terms of high theoretical specific capacity and simple preparation.Particularly,there are still challenges in the application to practical LIBs: the slow kinetics of Li ion and electron transport in electrodes and at the interface of electrode/electrolyte,low electronic conductivity,large volume expansion and severe collapse of the electrode may occur upon cycling.These problems can be partly solved by constructing micro/nanostructured or metal oxide-based composite materials.Nanostructured materials have high surface area,short the route of Li ion transport.Addition of carbon could effectively relieve large volume expansion,enhance the reaction kinetics during the electrochemical reaction.Mixing metal oxide with inorganic compounds to form complex effect and structure effect,enhancing the electrochemical performance.This work mainly focuses on the synthesis of manganese oxides/carbon,manganese oxides/inorganic compounds and calcium manganate material and their structure and application in lithium ion storage,the following are the specific works:1.MnO/C composites were prepared by simple liquid phase precipitation method and calcination treatment,using manganese acetate as manganese source,polyvinyl alcohol and oxalic acid as chelating agents and precipitating agents,and tested its electrochemical performance as lithium anode materials for the first time.By adjusting the concentration of polyvinyl alcohol,selecting the best experimental condition.When the concentration of polyvinyl alcohol and manganese acetate are 1.0% and 0.9 mol/L,sintering temperature is 600 oC,the composite exhibits an initial discharge capacity of 1410 mAhg-1,and a reversible capacity of 1084 mAhg-1 could still be obtained even after 250 cycles,also displays a better rate capacity.2.MnO/Na₂CO₃ composites were prepared by simple mixting manganese carbonate precursor and with sodium carbonate followed by heat treatment and tested its electrochemical performance as lithium anode materials for the first time.The precursor of manganese carbonate was obtained by liquid phase precipitation,using sodium carbonate and manganese sulfate as the initial reaction reagent.Then mixing appropriate amount precursor and sodium carbonate to obtain the composites.By adjusting the adding amount of sodium carbonate to acquire the products with electrochemical performances,the results displays that the content of sodium carbonate is 4%,sintering temperature is 750 oC,the material has a best electrochemical performance.A first discharge capacity is 1478.5 mAhg-1 and the reversible capacity is 1419.9 mAhg-1 after 180 cycles.Meanwhile,it also exhibits better rate capacity and the coulombic efficiency is almost 99%.3.For the first time,Calcium manganate materials were used as lithium anode materials.It was obtained through hydrothermal and subsequent calcinations,using calcium alginate fiber and manganese acetate as reactant.By optimizing the concentration of manganese acetate and mix proportion,achieving the porous material with high electrochemical capacity.The results indicate that when the mass rate of manganese acetate and alginate fiber is 1.5:1,sintering temperature is 750 oC,the material represents a first discharge capacity of 1341.8 mAhg-1,and after 400 cycles the reversible capacity is 1246.7 mAhg-1.