Design, Optimization and Study on Multiple Electrochemical Systems in Energy Dense Rechargeable Lithium Batteries

Abstract

Lithium-ion batteries (LIBs) are commonly and widely applied in current numerous devices such as smart phones, laptops, electric vehicles and medical devices. The LIBs are considered as a mature technology in todays commercial market bene ted from their uncomplicated lithium intercalation and de-intercalation reactions, stable cycling performance and good working life as energy storage devices and power resources. However, the conventional LIBs with technical limits such as high weight, low lithium utilization and low speci c energy density hit the bottlenecks of further improvements and optimizations for meeting the growing power supply requirements. It is urgent to develop the second generations of rechargeable lithium batteries, which have the bene ts of low cost, high speci c capacity and high energy density with light weight. In this context, lithium-sulfur batteries (LSBs) and lithium-selenium (Li-Se) batteries attract much attention due to the high possibility to meet the requirements of high speci c capacity and high energy density. However, the technical challenges they are facing put some barriers before they can be successfully commercialized. By a brief summary, the challenges to be solved are current low energy density because of requiring large amount of liquid electrolyte, the highly ammability and unsafety of lithium metal, low active material content due to the necessary requirement of carbon and binder, and severe so-called shuttle effect resulting in low Coulombic effciency. Before solving these challenges, Li-S batteries or Li-Se batteries are unlikely to be successfully commercialized in our market. Therefore, numerous research is aimed at solving the challenges and further developing more advanced Li-S and Li-Se battery systems. In the present dissertation, the contributions are mainly focused on sulfur-based and selenium-based materials, which aim to solve the current existing challenges and improve the battery performance, herein obtain a higher potential for application. Four chapters are included in this dissertation, which aim to present the four studied projects. The rst research conducted in this dissertation is developing organo S/Se hybrid materials which require low E/S ratios of liquid electrolyte and show light shuttle effect, therefore indicate promising high energy density and cycling life. Secondly, the tin foil is used as lithium sources instead of metallic lithium anode, then incorporated with sulfur cathode as a full cell. The full cell design provides the potential using a metallic anode other than pure lithium and increase the safety factor of a battery system. In addition, nano-scale selenium/carbon nanotubes composite electrode is synthesized via a chemical reduction method. With the optimization on thickness of the composite electrodes, the Se cathode has an active material content of ~60% and shows stable long cycling life with maximizing the utilization of selenium. The nal research conducted in this dissertation is applying a macro molecule named cyanostar, which has the ability to chemically bind with polysul de species, thereupon to alleviate the shuttle effect in Li-S batteries. With the evidence from chemistry analysis and electrochemical comparison results presented in this dissertation, cyanostar is proven to have the potential for further applications in Li-S batteries.