【作者】 王茜；

【导师】 胡俊华；

【作者基本信息】 郑州大学 ， 材料学， 2020， 硕士

【摘要】 锂离子电池作为21世纪最重要的储能器件之一,广受人们的关注。在科技飞速发展的今天,各行各业的发展和进步都跟储能器件的不断革新升级息息相关。目前成熟商业化应用于我们生活中的锂离子电池,所使用的负极材料为理论比容量较低(374 m Ah/g)的碳基材料,虽然碳材料在电池循环中性能稳定,但已不能满足人们对更高能量密度电池的需求,因此科研工作者把目光重新转移到锂金属负极材料上。锂金属负极具有超高的理论比容量(3780 m Ah/g),以及最负的电极电位,被誉为锂离子电池界的“圣杯”。但因其在大电流下易形成枝晶,而影响电池的容量和循环稳定性,且锂枝晶生长到一定程度时会刺破隔膜造成电池内部短路而发生爆炸,因此安全性低。本文致力于解决锂金属作为锂离子电池负极材料时的枝晶问题,通过对锂金属负极表面修饰层结构的构建实现电池循环过程中对锂金属负极保护。探究锡碳复合纤维网络作为修饰层保护锂金属负极的机理,并且测试其对称电池和全电池性能。相比于未经修饰的锂金属负极,被锡碳复合纤维修饰过的锂金属负极的稳定性有所提升。对称电池在1 m A/cm~2的小电流密度下可稳定循环250h,在5 m A/cm~2 5 m Ah/cm~2条件下可稳定循环50 h。且修饰过的锂金属负极与正极材料磷酸铁锂组装的全电池,在0.5 C和1 C倍率下都表现出优异的能量保持率和循环稳定性。在此基础上,本文将锡碳纤维修饰锂金属负极循环失效后的电池进行拆解分析其失效机理。循环失效后的锂负极基体表面被严重的刻蚀,具有较大的粗糙度,不平整的基体表面是导致锂枝晶生长的主要原因,而锂枝晶是电池失效的主要原因。本文通过磁控溅射法对锂金属负极表面进行合金化处理,旨在从根源基体表面保护锂金属负极达到抑制锂枝晶生成的目的。将表面合金化的锂金属与锡碳复合纤维三维网络有机结合,形成对锂金属负极修饰的双层复合结构,并对其保护锂金属负极机理做了相应的研究。双层修饰结构修饰的锂金属负极相比于单层修饰的锂金属负极,在大电流密度和大的容量密度测试的电化学性能表现更为优异。由此证明双层复合修饰结构的协同作用效果比单层修饰结构对锂金属负极的保护更为有效。随后本文还将双层复合修饰结构的实际思路应用于其他材料保护锂金属负极的研究,采用亲锂且具有相对锂较低过电位,同样应用于锂金属负极表面修饰且研究已非常成熟的锂硅合金作为表面合金化修饰层,加上纯碳纤维的三维网络作为用来均匀电场、减小电流密度的修饰层,利用两者的协同作用保护锂金属负极,相比于纯锂金属负极在电化学性能上有了明显提升:在小电流密度下表现出优秀的循环稳定性,在5 m A/cm~25 m Ah/cm~2测试条件下可以稳定循环50 h(25周)。由此证明,双层修饰结构可进一步推广到其他类别材料中,作为锂金属负极保护的修饰结构。更多还原

【Abstract】 As one of the most important energy storage devices in the 21st century,lithium-ion battery has been widely concerned.With the rapid development of science and technology,the development and progress of all walks of life are closely related to the continuous innovation and upgrading of energy storage devices.At present,mature and commercialized lithium-ion batteries are used in our lives.The anode materials used are carbon based materials with low theoretical specific capacity(374 m Ah/g).Although carbon materials have stable performance in the battery cycle,they can no longer meet people’s demand for higher energy density batteries.Therefore,researchers have turned their attention to lithium metal anode materials again.Lithium metal negative electrode has a high theoretical specific capacity(3780 m Ah/g)and the most negative electrode potential,which is known as the"Holy Grail"of lithium-ion battery.However,it is easy to form dendrites under high current,which affects the capacity and cycle stability of the battery.When the lithium dendrite grows to a certain extent,it will break through the diaphragm and cause the internal short circuit of the battery to explode,so the safety is low.This paper aims to solve the problem of dendrite when lithium metal is used as anode material of lithium-ion battery.Through the construction of the surface modification layer structure of lithium metal anode,the protection of lithium metal anode in the process of battery cycle is realized.The mechanism of tin carbon composite fiber network as a modified layer to protect lithium metal negative electrode was explored,and the performance of symmetrical battery and all battery was tested.Compared with the unmodified lithium metal anode,the stability of the modified lithium metal anode is improved.The symmetrical cell can stably cycle for250 h at a small current density of 1 m A/cm~2 and 50 h at 5 m A/cm~2 and 5 m Ah/cm~2.The modified lithium metal negative electrode and the positive material lithium iron phosphate have excellent energy retention and cycle stability at 0.5 C and 1 C.On this basis,this paper analyzes the failure mechanism of the battery after the cyclic failure of tin carbon fiber modified lithium metal anode.After cycling failure,the surface of lithium anode matrix is seriously etched and has a large roughness.The uneven surface of matrix is the main cause of lithium dendrite growth,and lithium dendrite is the main cause of battery failure.In this paper,the surface of lithium metal negative electrode is alloyed by magnetron sputtering,in order to protect the lithium metal negative electrode from the surface of the root matrix and inhibit the formation of lithium dendrites.The surface alloying lithium metal and tin carbon composite fiber three-dimensional network are combined organically to form a double-layer composite structure modified on the lithium metal negative electrode,and the mechanism of protecting the lithium metal negative electrode is studied.Compared with the single-layer modified lithium metal anode,the double-layer modified lithium metal anode has better electrochemical performance in the test of high current density and high capacity density.The results show that the synergistic effect of the double-layer composite modified structure is more effective than that of the single-layer modified structure for the protection of lithium metal anode.Subsequently,this paper also applies the practical idea of double-layer composite modified structure to the study of other materials to protect the lithium metal negative electrode.It uses the lithium-friendly and low overpotential relative to lithium,and also applies to the surface modification of lithium metal negative electrode.The well-developed lithium silicon alloy is used as the surface gold modified layer,plus the three-dimensional network of pure carbon fiber is used to uniform electric field and reduce current density Compared with the pure lithium metal anode,the modified layer can protect the lithium metal anode by the synergistic action of the two.It shows excellent cycle stability at low current density,and stable cycle for 50 h(25 weeks)under the test condition of 5 m A/cm~2 5m Ah/cm~2.Therefore,the double-layer modified structure can be further extended to other kinds of materials as modified structure of lithium metal anode protection.更多还原