The Research Of Lithium-Ion Storage Properties Based On Ferric Oxide,Iron Selenide And Graphene Composites

Previous researches indicate that transition metal oxides exhibit excellent electrochemical performance and most of them have a theoretical capacity more than 600 mAh/g.Therefore,they are believed to be good candidates for lithium-ion batteries.As one of the transition metal oxides,ferric oxide has intrigued much attention due to its excellent properties,such as high theoretical capacity(1007 mAh/g),abundant resources,and environmental friendliness.People also found that transition metal oxides have some fatal drawbacks,such as poor electrical conductivity,which are easily to be pulverized after many cycles of charge and discharge and lead to the quick decline of the performance for lithium-ion batteries.Many researches suggest that graphene can not only be used to increase the conductivity of metal oxides and reduce the random stack of metal oxide particles,but also can be transformed into three-dimensional conductive network structure,which can obviously improve the conductivity and specific surface area of the electrode through self-assembled reaction.And it can also be used as flexible electronic devices.Integrated nanoscale porous metal oxides into three-dimensional graphene with encapsulated structure is a promising route but remains challenging to develop high-performance and flexible lithium-ion battery.Herein,we have finished these works below:(1)We have successfully designed 3DG/metal organic framework composite by an excessive metal-ion-induced combination and spatially confined Ostwald ripening strategy,which can be transformed into 3DG/Fe2O3 aerogel with porous Fe2O3 nanoframeworks well encapsulated within graphene.There are many advantages for this structure.Firstly,micropores and mesopores interpenetrate total Fe2O3 particles,which can effectively relieve the volume expansion effect.Secondly,three-dimensional graphene provides an excellent conductive network,which ensures the effective charge transport,and avoids Fe2O3 particles suffering the stress of electrolyte directly to reach the function of buffering.At last,the electrode exhibits robust structural stability ensuring the process of electrochemical characterization successfully.The prepared 3DG/Fe2O3 composites not only exhibit a good mechanical performance,but also an excellent electrochemical performance for Lithium ion batteries(LIBs).The discharge specific capacity is 1129 mAh/g at a current density of 0.2 A/g after 130 cycles,and the discharge specific capacity was 523.5 mAh/g at a current density of 5 A/g after 1200 cycles,and the cycle retention rate was 98%,which is the best results that have been reported so far.(2)We obtain carbon-coated iron selenide encapsulated within three-dimensional graphene composites by annealing the Se powders and the three-dimensional graphene-wrapped Prussian blue composites.The carbon layer can effectively avoid the direct contact between the electrolyte and the active material(iron selenide)and relieve the volume expansion effect.The prepared composites exhibit excellent rate performance and cycle performance:for LIBs,the discharge specific capacity is 884.1 mAh/g at a current density of 0.2 A/g after 120 cycles,and the discharge specific capacity was 815.2 mAh/g at a current density of 1 A/g after 250 cycles.Our works provide an effective route that could be extended to the synthesis of other 3DG-based composites with this special structure and excellent performance for various electrochemical applications as well as the next generation of high-performance flexible electronic devices.