| With the rapid development of the world economy and the depletion of traditional fossil fuels,it is urgent to develop clean renewable energy and research efficient energy storage materials.As the dominent energy storage equipment,Li-ion batteries(LIB)can find enormous applications ranging from portable electronic devices to electric vehicles.Graphite is common commercial anode material for LIBs because of its abundance and chemical stability.However,the power and energy density of the graphite anodes are limited due to its low theoretical capacity of carbonaceous materials(372 m Ah g-1).Therefore,it is the primary task to search for new anode materials with long cycle stability and high rate capacity for practical applications.Tin oxide(Sn O2)is attractive anode material owing to its high theoretical capacity of 1492 m Ah g-1 and relatively low charge-discharge plateau of 0.6 V.Unfortunately,there is huge volume change(more than 200%)during the alloying and de-alloying process of Sn with Li,leading to the poor cycling stability of Sn O2 anode.Besides,the electrical conductivity of Sn O2 is low,which reduces the electron transport and significantly lowers the electrochemical performances.Miscellaneous kinds of attempts have contributed to buffer the volume changes of Sn O2 and thus improving its cycle stability.First of all,changing the size of the paticles is one of the ways to improve electrochemical properties of negative electrodes based on tin-derived compounds.It related with improving charge transport by shortening the Li-ion diffusion length within the material.The diminutive paticle size offers the existence of more electrochemically active sites which could enhance high rate performance due to curtailment of the diffusion patheway.The other way is to distribute tin oxide grains in a carbonaceous matrix of various origins as a stress-accommodating phase.In this paper,we tried to prepare Sn O2/C composites with soft carbon and hard carbon respectively,and discussed the application of these two kinds of composites in Li-ion battery anode materials.The main content of the paper as follows:(1)Study on Fabrication and Electrochemical Performances of Sn O2@C Com-posite Materials.Gelatin as carbon matrix material which is available and Sn Cl4·5H2O as tin source,respectively.The Sn O2@C composite materials was obtained by using water-bathed(<100?)sol-gel followed calcination(500?).Simultaneously,the electrochemical properties of the Sn O2@C composites were further improved by controlling the amount of carbon in the composites.The first reversible capacity of504.8 m Ah g-1 and the reversible capacity of 353.6 m Ah g-1 was obtained at the current density of 0.1 A g-1 after 100 cycles for the Sn O2@C-40 composite materials.In addition,the reversible capacity of 397 m Ah g-1 was obtained at 0.1 A g-1 after500 cycles for the Sn O2@C-40 composite materials.(2)Study on Fabrication and Electrochemical Performances of Sn O2/WS-P Composite Materials.Water-soluble pitch was obtained which modified of medium temperature coal tar pitch by mixed acid method,followed as carbon source and Sn Cl2·2H2O as tin source,respectively.The Sn O2@C composite materials was obtained by using the method of hydrothermal carbon coating.Meanwhile,the electrochemical properties of the Sn O2/WS-P composites were further improved by adjusting the amount of water-soluble pitch carbon in the composites for hydrothermal process.When added the water-soluble pitch amount of 1.0 g,the first reversible capacity of560 m Ah g-1 and the reversible capacity of 532.5 m Ah g-1 was obtained at the current density of 0.1 A g-1 after 100 cycles for the Sn O2/WS-P-1.0 composite materials.Moreover,the reversible capacity of 532.5 m Ah g-1 was obtained at 1 A g-1 after 30 cycles for the Sn O2/WS-P-1.0 composite materials. |
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