| With the rapid development of new energy vehicles and electronic equipment,lithium-ion batteries are gradually increasing.Researching higher performance LIBs is an urgent task we need to accomplish,and electrode materials have been the most important constraints in the development of LIBs.Therefore,researchers have made transition metal oxides?TMOs?with high theoretical specific capacity(700-900 mAh·g-1)and good power performance as the most promising negative electrode materials for LIBs.Among many transition metal oxides,manganese oxides have very distinct advantages,such as high theoretical specific capacity(755mAh·g-1),small voltage hysteresis??0.8 V?and low electromotive force?1.032 V?vs Li/Li+??,High density(5.43 g·cm-3),environment-friendly and resource-rich.However,like many transition metal oxides,manganese oxides also have quite significant drawbacks,including their low intrinsic conductivity and very large volumetric expansion during charging and discharging.These shortcomings can result in very low rate capability of the material and destruction of the integrity of the microstructure leading to very unstable cycling performance.Therefore,the content of this dissertation is to improve the conductivity of materials through the combination of three-dimensional carbon materials;on the other hand,the volume expansion during charging and discharging can be restrained by the binding effect of carbon materials.Specific research work includes the following two aspects:Firstly,graphene was used as the raw material to prepare the graphene oxide supported on manganese dioxide by the microwave treatment method,then the polyaniline was grown on the surface by in situ polymerization and finally the manganese dioxide was reduced to manganese oxide by the heat treatment to prepare the graphene/Manganese oxide/carbon material?IGR/MnO/C?.The composite metal oxide particles prepared by the method are completely covered by the carbon layer,which not only increases the conductivity of the material but also maintains the structural stability.The results show that as the heat treatment temperature increases,the graphitization degree of the material increases,but the metal oxide particles increase,so the stability of the material structure decreases.The IGR/MnO/C exhibits superior electrochemical performances including high specific capacity(1049 mAh·g-1 at 100 mA·g-1),excellent rate capability(547 mAh·g-1 at 2000 mA·g-1)and superior cycling stability(900 mAh·g-1 after 500cycles at 500 mA·g-1).Secondly,the manganese oxide/porous carbon composite material was synthesized by using silicon dioxide as the template and manganese oleate as the raw material through one-step carbonization and reduction at high temperature.The porous structure provided by the template method not only provides a fast channel for transport of ions and electrons,but also provides more active sites by increasing the specific surface area,thereby remarkably improving the specific capacity and stability of the composite material.As a result,the manganese oxide/porous carbon exhibits superior electrochemical performances including high specific capacity(1137 mAh·g-1 at 100 mA·g-1),excellent rate capability(348 mAh·g-1 at 5000mA·g-1)and superior cycling stability(710 mAh·g-1 after 600 cycles at 500 mA·g-1). |
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