喷雾干燥法制备锡及与锡氧化物—石墨烯复合材料及其电化学性能研究

发布时间：2018-03-19 21:50

  本文选题：锂离子电池　切入点：复合材料　出处：《哈尔滨工业大学》2014年硕士论文　论文类型：学位论文

【摘要】：Sn、SnO2材料分别具有990mAh·g-1、782mAh·g-1的高容量，因此在锂离子电池电极材料快速发展的今天受到人们的关注。但是，材料在充放电过程中巨大的体积变化，导致电池性能迅速下降，限制材料商业化应用。针对材料的劣势，本文将对材料进行一定的改性研究及相关性能测试。 石墨烯因为具有比表面积大、导电性好的优点被广泛用于电极材料的载体，本文采用喷雾干燥的实验方法将SnO2颗粒负载到石墨烯片层上。实验结果表明，5:1比例的SnO2@Graphene复合材料表现出优异的电化学性能，200mA·g-1的电流密度、100次循环之后，材料依然具有760mAh·g-1以上的容量；1000mA·g-1的电流密度时，材料的可逆容量仍保持在730mAh·g-1左右。但是，70次循环之后SnO2@Graphene复合材料的容量出现波动，表明材料的结构不稳定。为了改善复合材料的循环稳定性，通过添加粘结剂PVP增强SnO2与石墨烯之间的结合力、包覆热解碳达到进一步缓解SnO2所产生的应力的作用。添加0.3g PVP的复合材料电化学性能测试结果表明，20个循环之后材料的循环性能开始稳定，40个循环之后容量呈缓慢增加的趋势，100个循环之后材料的可逆容量维持在685mAh·g-1。复合材料优异的性能是因为，PVP添加后使复合材料的结构更加紧凑，充放电过程开始时，电解液未完全浸润，随着循环的进行结构有所松动，，电解液开始慢慢渗透使材料呈现出如此优异的电化学性能。热解碳的包覆有两种方式，一是直接喷雾干燥的方式；二是喷雾干燥-水热的方式。两种方式制备的复合材料均具有比原复合材料更加优异的循环稳定性，但是通过喷雾干燥-水热的方式制备的SnO2@C/Graphene表现出更加优异的性能。SnO2@C/Graphene在200mA·g-1电流密度下，100-300次循环内可逆容量始终维持在800mAh·g-1左右，表现出极其优异的循环稳定性；即使在800mA·g-1和1000mA·g-1的高电流密度下，材料的可逆容量仍可达到850mAh·g-1、815mAh·g-1。如此优异的电化学性能来源于复合材料的层级结构，即负载有SnO2颗粒的石墨烯片层外包覆有一层热解碳层。 基于喷雾干燥制备的电化学性能优异的SnO2基复合材料，通过高温H2还原或NaBH4还原，制备Sn基复合材料以此提高材料的首次库伦效率，提高电池电压。经H2高温或NaBH4与H2结合所还原出的复合材料，因为锡颗粒从石墨烯表面脱出并熔化团聚成微米级锡球之后，材料的首次库仑效率只提升了几个百分点，但材料在20个循环之后已无容量可言。只有经包碳处理之后，材料中的锡球颗粒呈纳米级且100次循环之后具有350mAh·g-1的可逆容量，但是材料的循环稳定性依然较差，整个充放电循环过程中材料的容量一直处于衰减状态。这说明喷雾干燥法由SnO2基材料还原制备Sn基材料是不可行的。
[Abstract]:The SnO _ 2 materials have a high capacity of 990mAh 路g-1C 782mAh 路g ~ (-1), so they have attracted much attention in the rapid development of electrode materials for lithium ion batteries. However, the huge volume change of the materials during the charging and discharging process leads to the rapid decline of the battery performance. In view of the disadvantages of the materials, this paper will study the modification of the materials and test the properties of the materials. Graphene is widely used as a carrier of electrode materials because of its large specific surface area and good conductivity. In this paper, SnO2 particles were loaded on graphene sheets by spray drying method. The experimental results showed that the SnO2@Graphene composites with 5: 1 ratio exhibited excellent electrochemical properties after 100 cycles of current density of 200mA 路g-1. When the material still has the current density of 1000mA 路g-1 or more than 760mAh 路g-1, the reversible capacity of the material remains around 730mAh 路g-1, but the capacity of SnO2@Graphene composites fluctuates after 70 cycles. In order to improve the cyclic stability of composites, the adhesion between SnO2 and graphene was enhanced by adding binder PVP. The results of electrochemical performance test of composites added 0.3 g PVP show that the cyclic properties of the composites begin to stabilize after 20 cycles, and the capacity of 40 cycles is slow. After 100 cycles, the reversible capacity of the composite was maintained at 685 mAh 路g-1.The excellent properties of the composite were due to the compactness of the structure of the composite with the addition of PVP. At the beginning of the charge-discharge process, the electrolyte was not completely infiltrated. As the structure of the cycle was loosened, the electrolyte began to permeate slowly so that the material showed such excellent electrochemical performance. There were two ways to cover the pyrolytic carbon. One is direct spray drying; the other is spray drying-hydrothermal. The composites prepared by both methods have better cycling stability than the original composite. But the SnO2@C/Graphene prepared by spray drying and hydrothermal method showed better performance. Sno _ 2 @ C _ (r) G _ (ene) kept the reversible capacity of 100mAh 路g ~ (-1) at 200mA 路g ~ (-1) current density, showing excellent cycle stability. Even at the high current density of 800mA 路g-1 and 1000mA 路g-1, the reversible capacity of the composites can reach 850mAh 路g-1N 815mAh 路g-1.The excellent electrochemical properties are derived from the hierarchical structure of the composite, that is, the graphene lamellar coated with SnO2 particles is covered with a layer of pyrolytic carbon layer. Based on the excellent electrochemical properties of SnO2 matrix composites prepared by spray drying, Sn matrix composites were prepared by H _ 2 reduction or NaBH4 reduction at high temperature to improve the first Coulomb efficiency of the composites. Increase battery voltage. Composites reduced by H _ 2 at high temperatures or by NaBH4 combined with H _ 2, because the first Coulomb efficiency of the material increased by only a few percentage points after tin particles were removed from the surface of graphene and melted and agglomerated into micron tin balls, However, after 20 cycles, the material has no capacity. Only after carbon treatment, the tin ball particles in the material are nano-sized and have a reversible capacity of 350 mAh 路g-1 after 100 cycles, but the cyclic stability of the material is still poor. During the whole cycle of charge and discharge, the capacity of the material has been in the state of decay, which shows that it is not feasible to reduce and prepare Sn based material from SnO2 base material by spray drying method.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912.9


本文编号：1636155