【作者】 李鑫；

【导师】 蔡舒； 孙晓红；

【作者基本信息】 天津大学 ， 材料学， 2020， 博士

【摘要】 钠离子电池作为潜在的新一代大规模储能器件,受到了科学研究者的广泛关注。而目前用于锂离子电池的商业化负极材料石墨却几乎不具备储钠性能。因此探索新型的具有优异性能的负极材料用于钠离子电池具有十分重要的意义。在各种各样的负极材料中,锡基材料因为具有理论比容量高,成本低,储量丰富和平均反应电势低等优点成为了最有潜力的负极材料之一。在各种锡基材料中,氧化锡和硫化锡因毒性相对较低,制备条件相对容易,得到了研究人员的广泛关注。但是在储钠过程中氧化锡和硫化锡负极材料会发生较大的体积膨胀,而且其自身导电性也较差,这些都限制了氧化锡/硫化锡负极材料在钠离子电池中的实际应用。为了解决上述问题,制备出具有长循环稳定性、高倍率性能、低成本的氧化锡/硫化锡钠离子电池负极材料具有重要意义。因此,本文在设计材料微观结构,探究新型储能机理和改善材料制备工艺等方面展开研究,具体研究内容如下:1.为了改善二氧化锡作为钠离子电池负极材料的循环稳定性,使用水热法和高温处理法相结合成功制备了具有多级结构的二氧化锡纳米颗粒/碳复合材料,即多孔碳球@二氧化锡纳米颗粒@纳米碳层复合材料（PCS@Sn O₂@C）。该复合材料表现出了优异的循环稳定性,即在50 m A g^-1电流密度条件下,循环80周后,其可逆比容量仍可保持在326 m Ah g^-1。在1600 m A g^-1的大电流密度条件下,循环550周,其容量保持率可以保持在99.1%。通过研究PCS@Sn O₂@C复合材料微观结构在充放电前后的变化并分析该复合材料的储钠机理,阐明了这种独特的微观结构设计对电极材料电化学性能的影响,即多孔碳球和纳米碳层的协同作用有效地抑制了二氧化锡活性物质的体积膨胀,从而实现了电极材料的结构稳定性,有效地改善了二氧化锡作为钠离子电池负极材料的循环性能。2.为了改善二氧化锡作为钠离子电池负极材料的倍率性质,探索改善电极材料电荷传输的新机理,通过一步水热法制备出具有异质结结构和较大比表面积的二氧化锡/四氧化三钴/石墨烯复合材料（GSC）。该复合材料展现出了优异的电化学性能,即在0.1 A g^-1电流密度条件下,循环80周后,其可逆比容量仍可保持在461 m Ah g^-1。在1 A g^-1的大电流密度条件下,循环500周,其可逆比容量仍可保持在241 m Ah g^-1。通过对多种表征手段结果和多种电化学计算结果的分析,得出了异质结结构和赝电容效应的协同作用促进GSC复合材料电化学性能,特别是倍率性能提升的机理。3.为了简化二硫化锡/石墨烯复合材料的制备工艺,降低材料制备成本,设计了低温省时节能高效的一步水浴法制备二硫化锡/石墨烯复合材料的工艺。通过调控石墨烯的添加量来调整二硫化锡/石墨烯复合材料的结构,并系统地分析不同石墨烯含量对于复合材料的结构和电化学性能的影响,最终确定了具有最优电化学性能的石墨烯添加量。结果显示,利用这种低制备成本的一步水浴法制备出来的二硫化锡/石墨烯复合材料展现出了非常优异的储钠性能,即在0.1 A g^-1的电流密度条件下,循环50周后,其可逆比容量仍可保持在702 m Ah g^-1。复合材料在1 A g^-1的大电流密度条件下,循环600周后,其可逆比容量仍可保持在330 m Ah g^-1。更多还原

【Abstract】 Sodium-ion batteries（SIBs）have attracted lots of interest as potential applications in large scale stationary energy storage.However,commercial graphite,which is mostly used as anode materials in lithium-ion batteries,has little ability of sodium storage.So,it is vital to explore new anode materials with high electrochemical performance in order to realize the successful application of SIBs.Among various anode materials,tin-based materials are considered as one of the most promising candidates due to their high theoretical capacity,low cost,large abundant,and low average reaction voltage.Specifically,tin dioxides and tin sulfides are widely explored because of their lower toxicity and easier preparation process.However,for tin dioxides and tin sulfides anode materials,large volume expansion and intrinsic poor conductivity limit their practical application in SIBs.To fabricate tin dioxides/tin sulfides anode materials with long-term stability,high rate capability and low cost for SIBs,we conduct some researches by rational microstructure design,novel energy storage mechanism exploration and materials fabrication process modification,which are listed in detail as followed:1.In order to improve the cycling performance of tin dioxides as anode materials for SIBs,we successfully prepared tin dioxides/carbon composites with hierarchical microstructures by combing hydrothermal method and annealing process,which can be descried as porous carbon sphere@Sn O₂@nano-scale carbon layer（PCS@Sn O₂@C）.The PCS@Sn O₂@C composite exhibits superior cycling stability.At a current density of 50 m A g^-1,the PCS@Sn O₂@C electrode can deliver a capacity of 326 m Ah g^-1 after80 cycles.At a high current density of 1600 m Ah g^-1,the capacity retention can reach to as high as 99.1%after 550 cycles.By comparing the microstructure changes of the PCS@Sn O₂@C before and after sodium storage and analyzing the sodium storage mechanism,we conclude that it is this unique microstructure that facilitates the electrochemical performance,which means that the synergistic effect of porous carbon sphere and nano-scale carbon layer helps to accommodate the volume expansion and maintain the stability of the electrode.2.In order to improve the rate capability of tin dioxides as anode materials for SIBs,we try to explore novel mechanism to improve the charge transfer in electrode materials.We prepared Sn O₂/Co₃O₄/graphene oxide（GSC）composite with heterostructures through one-step hydrothermal.The GSC composite exhibits excellent electrochemical performance.Specifically,at a current density of 0.1 A g^-1,the GSC electrode can deliver a reversible capacity of 461 m Ah g^-1 after 80 cycles.At a high current density of 1 A g^-1,the GSC electrode can still deliver a reversible capacity of241 m Ah g^-1after 500 cycles.By using various characterization methods and electrochemical calculations,we conclude that it is the synergistic effect of heterostructures and pseudocapacitance that facilitates the rate capability.3.In order to simplify the preparation process of Sn S₂/graphene composite and lower the cost of production,we design a one-pot synthesis approach with features of low-temperature,short-time,low-energy consumption to successfully prepare Sn S₂/graphene composite.By modulating the amount of added graphene,we analyze the effect of graphene amount on the microstructure of the composite and the electrochemical performance.And we get to know the most suitable amount of added graphene.Therefore,this Sn S₂/graphene composite prepared by this simple one-pot method exhibits great sodium storage performance.Specifically,at a current density of0.1 A g^-1,the Sn S₂/graphene composite can deliver a capacity of 702 m Ah g^-1 after 50cycles.At a high current density of 1 A g^-1,the Sn S₂/graphene composite can still deliver a reversible capacity of 330 m Ah g^-1after 600 cycles.更多还原