Preparation And Electrochemical Performance Of Tin-based Oxide

Energy is the essential material basis of the human survival and development,and it's also an important pillar industry for human well-beings at present as well as in the future.Lithium battery becomes the subject of current research focus due to its excellent properties such as high energy density,big output power,good cycle performance etc.However,the theoretical capacity of traditional carbon anode material is low,which is difficult to meet the requirement of LIBs with high energy density.As lithium anode material,SnO₂ has numerous attractive properties,including high theoretical capacity,natural abundance,low potential lithium-ion intercalation etc.But,its large volume expansion?about 300%?and the agglomeration of tin dioxide particles during alloying reaction seriously affected the cycle stability of the battery,which remains to be the urgent problem.Aimed to solve the problem,three solutions were put forward,which is making materials nanocrystallization,introducing specialization structures and preparing SnO₂/C composite materials.In this paper,nano mesoporous SnO₂ coated acid-treated MWCNTs were prepared combining the three ways to improve the electrochemical property of tin based oxide,which is quite important for the development of lithium battery.The idiographic work is as follows:1.Nano mesoporous SnO₂ was synthesized using a block polyether F127?EO106-PO70-EO106?and polyethylene glycol PEG-20000 as a template,respectively,via a hydrothermal process and direct precipitation method.The influence of different templates on the structure and the electrochemical property of the materials was detected.X-ray diffraction,transmission electron microscope and nitrogen adsorption/disoportion were used to test the mico-morphology and pore structures of the composites.Galvanostatic charge-discharge tests,cyclic voltammetry?CV?and electrochemical impedance spectroscopy were used to discuss the electrochemical properties.The study results show as follows:?1?Nano mesoporous SnO₂ can be synthesized both by a hydrothermal process and direct precipitation method.The samples prepared by a hydrothermal process disper more uniformly and the particle size is smaller;the specific surface area increases,which is amost 128 m2/g;and the pore size distribution becomes relatively broader,that is about 2-9 nm;the electrochemical property is better than that prepared by direct precipitation method.The first reversible capacity of 6F-SnO₂ samples can reach up to 609 mAh/g,and it remains at 434 mAh/g after 30 th cycles.?2?Because of that mesopores can buffer the huge volume expansion of SnO₂ during deinsertion and insertion of Li+,the negative material SnO₂ with special mesoporous structure shows perfect charge/discharge cycle stability.What's more,the existence of mesopores can also buffer the huge volume expansion of tin dioxide,and thus the electrochemical performances of mesoporous SnO₂ as an anode material has been improved consequently.Material with small sizes can enhance its surface energy,shorten the path for deinsertion and insertion of Li+,thus the rate capability can be improved.2.Nano mesoporous SnO₂ coated acid-treated MWCNTs were prepared by dispersing acid-treated multi-walled carbon nanotubes?MWCNTs?into as-prepared Tin metal precursor solution,using MWCNTs treated at different tempreture as carbon matrix.?1?The content of oxygen-containing functional groups on the surface of the MWCNTs are influenced by acid temperature,thus the load capacity of mesoporous oxide on carbon nanotubes is influenced.The higher the acid tempreture is,the more the oxygen-containing functional groups there are,thus the charge-discharge capacity increases on account of SnO₂.When the temperature is 120 °C,the as-prepared SnO₂ coated acid treated MWCNTs displays the optimal cycle performance and rate performance,which the reversible capacity of the 40%-120°C maintains to be 400 mAh/g at 60 mA/g after 50 cycles.While the cycle performance of 40%-160°C fares the worst,that may because the structure of MWCNTs is destroyed.?2?The adding of MWCNTs helps to buffer the huge volume expansion of tin dioxide,and thus the electrochemical cycle performances of mesoporous SnO₂ coated on MWCNTs as an anode material has been improved consequently.When the amount of MWCNTs is 40%,mesoporous SnO₂ can be dispersed well on the surface of MWCNTs,showing perfect electrochemical performance.The reversible capacity of the 40%-120°C maintains to be 400mAh/g after 50 cycles and the capacity retention remains 87%.