Study On Improving Cycling Stability And Coulombic Efficiency Of Anode Materials For Lithium/Sodium Ion Batteries

With the rapid development of economy,China's energy industry,especially the new energy industry,has also developed rapidly.Industries like smart phones,electric vehicle and smart grid are thriving,which makes the new energy storage technology(especially lithium/sodium ion batteries technology)become the hot spot of scientific and technological development.In order that researching and developing lithium/sodium ion batteries(LIBs/SIBs)is the key for current new energy devices and new materials.In this paper,the typical conversion-alloyinganode materials for LIBs/SIBs are chosen as the research object.Aiming at overcoming the prominent problems like poor performance stability and low initial Coulombic efficiency(ICE)in experimental research and practical production of anode materials,some unique structures are designed.Sb2S3 composites with amorphous tin sulfide and graphene(Sn@Sb2S3-rGO)are prepared as ternary anode material for SIBs;commercial Sn02 composites with ZIF-67,then the mixture was treated again by heating to get commercial SrnO2-Co-C(N-c-SCC)ternary anode material for LIBs;ultrafine Sn02 was also used to composite with ZIF-67 for better ternary anode material-ultrafine SnO2-Co-C(N-u-SCC).All of the three anode materials demonstrate much improved electrochemical stability and ICE when tested as LIBs/SIBs.The works in this paper provide new design ideas,theoretical and experimental support for the practical application of the new anode materials for LIBs/SIBs.The specific results are as follows:(1)Graphene oxide served as carbon compositing template can be combined with metal ions by electrostatic adsorption.Sn2+ ions were introduced the precursor solution before the hydrothermal synthesis step,so that the synergistic inhibition effect between Sb3+ ions and Sn2+ ions made the synthesized particles of metal sulfides smaller,which is beneficial for the transportation of sodium ions and shared less stress during the de/intercalation of sodium.Due to the excellent electrical conductivity and mechanical properties of graphene,the volume change of Sb2S3 electrode can be alleviated during the de/intercalation process.Sb2S3 can get complete crystal shape under argon atmosphere at 300 'C,while tin sulfide which serves as good barrier in the process of charging and discharging keeps amorphous.The amorphous tin sulfide not only prevents the Sb3S3 particles aggregation,but reduces the volume variations effectively.All of the above are the features of the Sn@Sb2S3-rGO ternary anode material When tested as anode for SIBs,the Sn@Sb2S3-rG0 electrode keeps a specific capacity of?600 mAh g-1 after 60 cycles at a current density of 200 raA g-1,the capacity retention is 82.3%compared with the second cycle,the specific capacity can reach 360 mAh g'1 at an extreme current of 5000 mA g'1.The ICE improved significantly to 69.8%.(2)The huge surface area,porous feature,easy absorption and easy synthesis of ZIF-67 make it good sacrificial template.Commercial nano SnO2 was adopted to composite with ZIF-67 under liquid phase,after which the mixture was annealed elaborately under argon atmosphere.The cobalt metal and N-doped carbon framework formed in situ durnng the calcination process.Thus the commercial SnO2-Co-C(N-c-SCC)ternary anode material for LIBs obtained.The main role of Cosimilar with the amorphous tin sulfide is to inhibit the volume change and serve as strong barrier preventing particles agglomeration,which increases contact area of Sn and Li2O,increase the conductivity.The N-doped carbon framework is to improve the conductivity and provide space for volume variations.The Co metal and carbon framework extend the cycling life of the electrodes cooperatively.The N-c-SCC electrodes demonstrated improved performance stability and ICE,confirming the feasibility of ZIF-67 as a sacrificial template.(3)On the basis of N-c-SCC anode material,the self-made ultrafine SnO2 was designed to replace the commercial SnO2.The ultrafine S1nO2-Co-C(N-u-SCC)ternary anode material for LIBs was obtained and behaved excellently.The ICE of one typical N-u-SCC-2 is as high as 82.3%,which is much higher than that of 61.4%for pure ultrafine SnO2 electrode and 75.0for N-c-SCC electrode.Due to the unique structure,the N-u-SCC-2 electrodes present excellent electrochemical properties.Including extremely high ICE-82.3%,large specific capacity and cycling performance-a capacity of?975 mAh g-1 after 100 cycles at the current density of 200 mA g-1,prolonged cycling life-a capacity of?760 mAh g-1 after 450 cycles at a current density of 500 mA g-l and excellent rate performance.In this paper,Sb2S3 an anode material for SIBs,and SnO2,an anode materials for LIBs,were selected to be studied for their similar reaction mechanism.The results prove that integrating carbon coating,bimetallic composite and nanosizing is an effective solution for improving electrochemical property of conversion-alloying type LIBs and SIBs materials.The experiments also provide a new idea for researching conversion-alloying type LIBs and SIBs materials.