Spray Drying Synthesis And Electrochemical Characterization Of Tin And Tin Oxide-graphene Based Composites

Sn and SnO2have a high theoretical lithium storage capacity of990mAh·g-1and782mAh·g-1respectively, therefore, they are selected as a kind of promising anode material for lithium ion battery. However, they suffer from large volume changes with the charging and discharging process, which brings about failure of the battery and restrictsits commercial application final. In order to address the problems, we will do some modification about the materials and some related performance tests in this paper.Graphene is widely used to be a electrode material carrior because of its excellent electronic conductivity and high surface area. A composite with SnO2-anchored grapheme can be sythesized by spray-drying method. The results show that, SnO2@Graphene compositeswith mass ration5:1have superior electrochemical performance. After100cycles, the reversible discharge capacity is maintained at much more than760mAh·g-1at the current density200mA·g-1and its still remains730mAh·g-1reversible capacity at the current density1000mA·g-1. But, the capacity of SnO2@Graphene materials occurs fluctuations after70cycles, indicating the structual instability of composites need tobe further improved. In order to improve the cycle stability of the composite, the binding force between SnO2and graphene can be enhanced by adding a binder PVP or further relieving the stress which is generated by SnO2particles via coated with pyrolytic carbon. Electrochemical performance results of composite with adding0.3g PVP show that, its has a cycle stability performance after20cycles and the capacity shows a slow upword trend after40cycles. What’s more, after100cycles, the reversible discharge capacity is maintained at much more than685mAh·g-1at the current density200mA·g-1. The reason why its has excellent performance is that composites have a dense graphene framework after adding binder PVP, which experience a sight loosening with repeated charging and discharging, leading to an increase of active SnO2accessible by electrolytes and allowing the materials to maintain a excellent revesible capacity during subsequent cycles. There has two ways to make the hybrids coated with pyrolytic carbon, one is spray drying mode, the other is spray drying-hydrothermal way. Two composites prepared by the two ways have a better cycle stability than original composite material. However, SnO2@C/Graphene composites synthesized by spray drying-hydrothermal method exhibits superior performance. SnO2@C/Graphene composites have800mAh·g-1reversible capacity at the current density200mA·g-1within100-300cycles, exhibiting extremely excellent cycle stability. Even at high current density of800mA·g-1and1000mA·g-1, its still has the reversible discharge capacity of850mAh·g-1and815mAh·g-1respectively. Such excellent electrochemical properties of SnO2@C/Graphene composites are attributed to hierarchical structure, which is SnO2-anchored graphene hybrids coated with a layer of pyrolytic carbon layer. Based on excellent electrochemical properties of SnO2based composites by spray drying, we can synthesize Sn based materials by high tempreture H2atmospherereduction or NaBH4reduction, achieving a high initial coulombic efficiency and battery voltage. After high tempreture H2atmosphere reduction or NaBH4reduction combined with H2, Sn particles emerge from the graphene surface and melte into μm classball, and nitial coulombic efficiency of the materials has been raised only a few percentage points with almost no capacity after20cycles. Only after coated with a carbon layter, the size of Sn particles becomes nm class and its possesses350mAh·g-1reversible capacity after100cycles. But the cycling stability of the material is still very poor, the capacity has been in the process of decay state.The results indicate that the spray drying method is not feasible for Sn based materials.