CAS OpenIR
锂金属电池固态电解质构筑及表界面微观机制研究
汶凯华
Subtype硕士
Thesis Advisor陈仕谋
2018-07
Degree Grantor中国科学院研究生院
Degree Name硕士
Degree Discipline化学工程
Keyword固态电解质,电极-电解质界面,锂负极,枝晶,锂金属电池
Abstract

金属锂(Li)以其极高的理论比容量(3860 mA h g-1)、最低的还原电势(-3.04 V,vs. 标准氢电极)以及低密度(0.534 g cm-3)等优点,成为下一代高比能二次电池负极材料的最佳选择之一。然而,锂离子在负极表面的不规则沉积引发的不可控锂枝晶的生长,造成了锂金属电池使用过程中的安全问题,进而制约了锂金属电池的广泛应用。本论文通过新型固体电解质的开发和电极-电解质界面的构筑,调节均匀锂沉积,以抑制锂枝晶不均匀生长。研究了锂离子在固体电解质中的输运机理和改性界面对锂沉积的作用机理,结合大量的实验、计算等手段,表明通过新型固体电解质的开发和电极-电解质界面的构筑都能极大程度上改善锂金属负极的稳定性。主要研究内容和结果如下:1.通过界面接枝聚乙二醇修饰具有有序纳米孔的多孔Al2O3陶瓷膜,进而与液态电解液复合制备得到一种复合型类固态电解质。SLEs具有较高的室温离子电导率、低界面阻抗、高机械模量和与锂负极在室温和高温下均具有稳定性。将该电解质组装在Li/Li4Ti5O12半电池体系中研究其长期循环性能,测试结果显示电池充放电循环超过1000圈也无因锂枝晶引起的短路发生。2.通过分子动力学模拟,对聚合物/氧化铝复合电解质特殊的两相结构中锂离子的传输机制进行了研究。研究结果表明,该两相结构一方面使锂沉积均匀化,另一方面加快锂离子在电极-电解质界面处的传输。这种复合电解质结构有利于锂金属电池的负极稳定性和循环性,可满足下一代能源存储系统尤其是先进金属电池技术。3.采用一步磁控溅射技术在聚丙烯隔膜表面制备Pt纳米层进而得到一种改性聚丙烯隔膜。Pt纳米层具有良好的电子传导能力,可以为锂负极在反复充电/放电过程中提供可靠的锂沉积位点。此外,Pt纳米层结构可以提高商业化聚丙烯隔膜的力学性能和改善其微观结构。该系统能实现枝晶的双向生长,在反复循环过程中,受限生长的锂枝晶和死锂有效地填补了Pt层和锂负极之间的间隙,最终形成了光滑致密的新的锂负极。对称电池Li|PP@Pt|Li具有较低的过电位,得到的锂负极平整光滑且对大电流密度有很好的相容性。同时,Li/LiFePO4半电池表现出良好的电化学性能,1 C下平均比容量为131 mA h g-1。该改性聚丙烯隔膜不仅保证电池使用中的循环稳定性和实用性能,而且具有易于制作的优点,这使得它很可能被应用于先进的金属电池体系。;Lithium (Li) metal has been pursued as one of the most promising anodes for high energy density electrochemical systems, and these high specific energies derive from the high theoretical specific capacity (3860 mA h g-1), low density (0.59 g cm-3) and the lowest negative electrochemical potential (-3.04 V vs. the standard hydrogen electrode) of the Li metal. However, the issue of uncontrollable Li dendrite growth, causing by irregular lithium deposition, restricts the wide applications of Li metal based high energy batteries.In this thesis, we intend to modulate uniform Li deposition by novel solid electrolyte and modified electrode-electrolyte interface to suppress uneven Li dendrite growth. The mechanisms of Li-ion transportation in solid electrolyte and the Li deposition on the modified interface were fully investigated. The electrochemical performances in these systems show that both the methods can greatly improve the stability of Li metal anodes. The main research contents and results are summarized as following:1. Solid-liquid electrolytes with well-aligned nanopores were fabricated via absorbing polyethylene glycol engineered nanoporous Al2O3 ceramic membranes with liquid electrolytes. The SLEs show high ionic conductivity, low Rint, high mechanical modulus and good stability against Li anode at both room and elevated temperatures. The materials were assembled as Li/Li4Ti5O12 half cells to investigate their longtime cycling performance. These measurements show more than 1000 charge/discharge cycles can be achieved with no evidence of dendritic deposition.2. The transport mechanism of Li+ in the two phases were analyzed by using molecular dynamics simulations. The results indicated that the SLEs can make homogeneous Li+ distribution and rapid transportation in its two special nanophases. This configuration facilitates the application of LMBs with stable Li deposition and long lifetime performance and can be used in next-generation energy storage systems for advanced stable battery technologies.3. A platinum modified polypropylene separator were prepared by a one-step sputter technology. Pt nanolayers with good electronic conduction provide Li deposition sites during repeated charging/discharging. Moreover, Pt nanolayers can enhance the mechanical properties and micro-structures of commercial polypropylene separators. This system achieved the bidirectional growth of Li dendrites, which efficiently filled gaps between Pt layers and Li anodes by integrating dead Li and Li dendrites into smooth and dense Li layer. The symmetric Li|PP@Pt|Li cells exhibit low overpotentials, dense Li anode and strong tolerance under high current densities. Meanwhile, Li/LiFePO4 cells present excellent electrochemical performance with an average specific capacity of 131 mA h g-1 at 1 C. The Pt modified PP separator not only ensures stable cycling performance and practical application, but also possesses ease to be fabricated, which makes it possible to be used in advanced metallic batteries. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26856
Collection中国科学院过程工程研究所
研究所(批量导入)
Recommended Citation
GB/T 7714
汶凯华. 锂金属电池固态电解质构筑及表界面微观机制研究[D]. 中国科学院研究生院,2018.
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