| As a promising energy storage device,lithium-ion batteries（LIBs）have been widely used in daily life due to their high energy density and rechargeable property.However,with the rapid development of electric vehicle,the low storage capacity and high production cost bring in new challenges to improve LIBs.It is well known that the energy density of LIBs mainly depends on the lithium storage capacity of electrode materials.At present,the main commercial anode materials are graphite materials.Their theoretical capacity is only 372mAh/g,which cannot meet the future high energy density requirements of devices.In recent years,considerable studies have found that the theoretical specific capacity of tin dioxide（SnO2）can reach 1494 mAh/g with medium work voltage.In addition,SnO2 is resource abundant and cost effective.Thus,it has a broad application prospect as anode material for the next-generation of LIBs.However,during the discharge/charge process,the volume change of SnO2 materials is large,leading to the particle agglomeration,slow reaction kinetics and poor reversibility.These problems result in the rapid decline of lithium storage capability,which greatly limits the wide application of SnO2-based anode materials in the field of LIBs.Therefore,it is very important to improve the reaction kinetics and structural stability of SnO2 based materials.To overcome these problems,we improve the electrochemical properties of tin dioxide by adding and compounding with graphene and other materials.Experimental results show that this method can not only effectively buffer the volume change of SnO2,but also greatly improve the coulomb efficiency,specific capacity,ion and electron transfer efficiency and cycle life of SnO2material.Specific researches are as follows:（1）The SnO2/graphene（SnO2/G）composites doped with Fe and Co（Fe&Co-SnO2/G）were prepared by hydrothermal and annealing method.The experimental results show that the electrochemical performance of Fe&Co-SnO2/G is the best when the molar ratio of Sn,Fe and Co is 15:4:1.At the current density of 0.1 A/g,the initial coulomb efficiency is 65.32%and the initial discharge specific capacity was 1691.9 mAh/g.After four cycles,the specific discharge capacity of the Fe&Co-SnO2/G electrode is stable at around1100 mAh/g.By contrast,the specific discharge capacity of the SnO2/G electrode is stable at 650 mAh/g after the 22nd cycles.After 100 cycles,the specific discharge capacities of Fe&Co-SnO2/G and SnO2/G electrode were1100 mAh/g and 480 mAh/g,respectively.This is mainly due to the incorporation of Fe and Co into the SnO2/G composite,which reduces the grain size of SnO2 and effectively prevents the agglomeration of SnO2.At the same time,the incorporation of Fe and Co can improve the conductivity of the material,accelerating the electron/ion transportation.The synergistic effect of Fe,Co and graphene can effectively improve electrochemical stability,rate and cycling capability.（2）SnO2/graphene materials with the addition of ferrocene were prepared by oil bath and mixing,and the electrochemical properties of ferrocene-added SnO2/G with different mass ratios were compared.Experimental tests showed that when the mass ratio of ferrocene was 10%,ferrocene-added SnO2/G exihibits the best electrochemical performance.Testing at the current density of0.1 A/g,the discharge capacity of ferrocene-added SnO2/G was 1084.5 mAh/g after 150 cycles.At current densities of 0.1,0.2,0.5 and 1 A/g,ferrocene-added SnO2/G electrode has high reversible discharge capacities of 1033.8,969.1,861.4 and 752 mAh/g,respectively.The synergistic effect of ferrocene and graphene can significantly enhanced the electron migration and lithium ion diffusion in electrode materials.In addition,the metallic Fe forms in the discharge process,and acts a catalyst to promote the decomposition of Li2O and the conversion reaction from Sn/Li2O to SnO2,thus significantly improving the lithium storage performance of SnO2/graphene material.（3）The SnO2/G composite with the addition of maleic acid was prepared by oil bath and mixing.As an organic acid,maleic acid also has the lithium storage capacity.Therefore,an electrode using maleic acid as the active material was made.According to electrochemical test,it is found that discharge specific capacity of maleic acid is only 300 mAh/g at the current density of 0.1 A/g,but its cycling stability is quite excellent.Therefore,10%Ma-SnO2/G electrode was prepared by simply mixing and grinding 10 wt.%maleic acid with SnO2/G composite.When testing at 0.5 A/g current density,the discharge specific capacity of 10%Ma-SnO2/G electrode can be maintained at 800 mAh/g.Even at1.0 A/g,the discharge specific capacity of 10%Ma-SnO2/G electrode can be stabilized at 400 mAh/g.These results show that adding maleic acid into SnO2/G composite material can significantly enhance the electrochemical cycling stability of the SnO2/G material under high current density. |
