Research On The Tin Dioxide/carbonized Cotton Covered By Graphene For Flexible Lithium-ion Batteries Anode

Lithium-ion batteries(LIBs)due to its advantages of high energy,high voltage,low self discharge efficiency and environment friendly,has been applied in the field of consumer electronic,communication and electric vehicle.In recent years,the flexible and wearble electronic equiptments rapid development,however,the current LIBs electrode preparation method unable meet the bendable,high capacity,and simple process for flexible power demand.In this paper,a novel technology for preparing flexible lithium-ion batteries anode,the free-standing composite materials has been obtained by a facile “immersing and calcination” method using carbonized cotton as self-supporting and high capacity SnO2 as actives.We studied the effect of the carbon sources,graphene oxide(GO)concentrations,Sn2+ concentrations,and calcination temperatures influence on morphologies,components,structures and electrochemical properties,and analysis the mechanism of different modified methods.Based on cotton covered by graphene/SnO2(CGN/SnO2),for improving the cycling performance,using the carbon coating and Fe-doping on SnO2.The main results obtained in this paper were summarized below:Fabrication the self-supporting of carbonized cotton covered by graphene(CGN)material has been obtained by a facile “immersing and calcination” method using cotton and graphene oxide(GO).The graphene not only cover on carbonized cotton fibers but also interconnect with neighbor.As electrode,without using polymer binders,conductive addtives and current collectors.The conductivity and electrochemical performance of CGN was better than that of carbonized cotton.With increasing the GO concentration,the specific capacity of materials was increased.With increasing the calcination temperatures,the oxygen groups and resitivity was decreased and cycling performance was increased.However,when the temperature was too high,more disorder defects of materials to the disadvantage of lithium ions storage.Using cotton covered by graphene oxide and SnCl2,we insitu growth SnO2 nanoparticles on cotton covered by graphene,by “immersing and calcination” route.The results show that the ultrafine SnO2 nanoparticles uniformly anchored on thee graphene sheets and cotton fibers,and avoid avoid large particles aggregation,throught the graphene added.With increasing the GO concentrations,the size of SnO2 decreased,the SnO2 content first increased and then decreased with the maximun value was reached at 7 mg/m L.With increasing the Sn2+ concentrations,the size of SnO2 increased,appear aggregation when the concentrations at 22.0 mmol/L.With increasing the calcination temperatures,the oxygen groups decreased,the disorder structure increased,the size of SnO2 increased.When the temperature was higher than 600 ?,there have some impurities of Sn,and some big SnO2 bulks appear.The CGN/SnO2 could be directly applied as electrode materials for assembling batteries.We studied the effect of the carbon sources,GO concentrations,Sn2+ concentrations,and calcination temperatures for the properties.The results show that the cycling performance has been greatly improved,especially for 7 mg/m L of GO concentration,13.2 mmol/L of Sn2+ concentration,and 500 ? of calcination temperature,at a current density of 50 m A/g,delivering a highly reversible capacity of 488.2 m Ah/g after 60 cycles.The super cycling performance caused by the space between graphene and cotton fibers was benefit for electrolyte and lithium ions transport,provide space for electrode changes during cycling.The Sn O 2 nanoparticles could offer much reaction points,decrease the lithium ions transport pathway,and accelerate reactions.Even after bending 1000 times,the capacity of CGN/SnO2 was 92% of orgional,reflecting good flexible property.Base on above method,expand other oxide metal compose with the matrix of cotton covered by graphene,a flexible carbonized cotton covered by graphene/Mo O2(CGN/Mo O2)material was fabricated similar with prepare of CGN/SnO2 method,at a current density of 100 m A/g,the retained capacity was 385.6 m Ah/g after 100 cycles.Hydrothermal synthesis of carbon coating on SnO2 particles,which effectively decrease the size of SnO2 particles,increase conductive and protect cotton covered by graphen.During cycling process the coating prevents the direct contact between the SnO2 nanoparticles and the electrolyte,which can format a stable solid electroly interphase(SEI),decrease irreversible reaction,and grealy increase the lithium storage performance,at a current density of 100 m A/g,the reversible specific capacity of 496.3 m Ah/g after 200 cycles.Based on the CGN/SnO2 materials,the impacts of Fe doping in the SnO2 was researched,at a current density of 100 m A/g,the reversible specific capacity of 453.4 m Ah/g after 200 cycles.The improved cycling performance was caused by the SnO2 grains are decreased,the structure stability was increased,the conductivities were improved after doping with Fe,which was improved the reaction points,accelerate ions and electron transport speed,increase the lithium ions sotre ability.Furthermore,there were some defects in SnO2 crystalline after Fe doping,the defects and heterogeneous Fe elements would release stress,a nd increase cycling stability.Base on Fe doped CGN/SnO2 work,free-standing Codoped cotton covered by graphene/Mo O2 materials were fabricated,at a current density of 100 m A/g,the reversible specific capacity of 549.6 m Ah/g after 100 cycles.Using the similarity principle,preparing the Co-doped CGN/SnO2 materials,the electrochemical properties of Co-doped CGN/SnO2 is enhanced than that of CGN/SnO2.