Design Stable Solid Electrolyte Interphase For Anodes In Rechargeable Lithium Batteries PDF Download

Solid-electrolyte interphase (SEI) is a nanoscale composite layer of organic and inorganic lithium (Li) salts formed on the electrode surface by electrolyte decomposition. It is ionically conductive and electrically insulating, thus allowing facile Li-ion transport and preventing further electrolyte decomposition. Owing to these features, SEI stability is crucial to the performance of rechargeable Li batteries. Unfortunately, SEI layer are unstable for most advanced battery materials, including high-capacity anodes materials (e.g., silicon (Si) and Li) in liquid electrolyte and Li anodes in solid electrolytes (e.g., Li10GeP2S12 (LGPS)). An unstable SEI layer may cause poor battery performance including consumption of active materials and electrolyte, capacity fading, resistance increase., etc. The structure and property of SEI have generally eluded rational control since its formation and growth processes involve a series of complex and competitive electrochemical reactions. The main efforts to addressing this issue have been made on the development of new electrolyte systems to form alternative SEI layers and preformed artificial SEI layers on the electrode surface to replace the electrolyte-derived SEI.This dissertation focuses on intrinsically regulating the chemical composition and nanostructure of SEI for advanced battery materials in conventional electrolyte systems, which enables not only optimized chemical and physical properties of SEI but improved battery performance. This is realized by developing chemical and electrochemical reactive materials and allowing them to participate in the SEI formation. These materials can contribute functional components in the SEI layer and therefore alter the structure and property of the SEI deliberately. The design of functional material is based on the requirement of SEI layers for different anodes. In Chapters 2 and 3, I presented approaches to manipulating the formation process, chemical composition, and morphology of SEI for nano-sized and micro-sized Si anodes, respectively. The SEI layers were fabricated through a covalent anchoring of multiple functional components onto the Si surface, followed by electrochemical decomposition of the functional components and conventional electrolyte. We showed that to covalently bond organic oligomeric species at the surface of nano-sized Si anodes can effectively increase its SEI flexibility and realized an intimate contact between SEI and Si surface (Chapter 2). In the case of micro-sized Si anodes, we reported that to covalently bond a functional salt, N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI), at the surface of micro-sized Si anodes can effectively stabilize the interface and SEI (Chapter 3). In Chapters 4 and 5, we designed chemically and electrochemically active organic polymer, namely poly((N-2,2-dimethyl-1,3-dioxolane-4-methyl)-5-norbornene-exo-2,3-dicarboximide), and polymeric composite containing poly(vinylsulfonyl fluoride-ran-2-vinyl-1,3-dioxolane) and graphene oxide (GO) nanosheets to alter SEI formation process and regulate the composition and nanostructure of SEI for Li metal anodes. The reactive organic polymer and polymeric composite can generate stable SEI layers in situ by reacting with Li to occupy surface sites and then electrochemically decomposing to form nanoscale SEI components. The formed SEI layers presented excellent surface passivation, homogeneity, and mechanical strength. Using the polymer, we can implant polymeric ether species in the electrolyte-derived SEI, enabling improved SEI flexibility and homogeneity. In the case of polymeric composite, the SEI is mainly generated by the composite instead of electrolyte. In this way, we realized an intrinsic control of SEI structure and property. The formed SEI presented excellent homogeneity, mechanical strength, ionic conductivity, and surface passivation.In Chapter 6, we reported a novel approach based on the use of a nanocomposite consisting of organic elastomeric salts (LiO-(CH2O)n-Li) and inorganic nanoparticle salts (LiF, -NSO2-Li, Li2O), which serve as an interphase to protect Li10GeP2S12 (LGPS), a highly conductive but reducible SSE. The nanocomposite is formed in situ on Li via the electrochemical decomposition of a liquid electrolyte, therefore possessing excellent chemical and electrochemical stability, affinity for Li and LGPS, and limited interfacial resistance. We concluded this dissertation work in Chapter 7 and briefly discussed the possible future work.