Date of Award

December 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Junjie Niu

Committee Members

Benjamin C Church, Pradeep K Rohatgi, Nathan P Salowitz, Yi Hu

Keywords

dendrite, in-situ TEM, lithium ion batteries, lithium metal anode, solid electrolyte interphase

Abstract

Lithium-ion battery technology has wide impact on our daily life. However, most of the commercial batteries with limited energy density are unable to meet the growing demand of electrical vehicles, portable electronic devices and other energy storage systems. Therefore, the development of new electrode materials with high energy density and reliable performance has become a critical mission for researchers. Particularly replacing graphite anode with Li metal is one of most viable approaches to break the limitation of energy density in batteries. Metallic lithium is one of the most promising anode materials, which has a high theoretical specific capacity of 3860 mAhg-1 and a low electrochemical potential of -3.04V versus the standard hydrogen electrode. however, the growth of mossy/dendritic Li that can induce internal short circuiting, is considered as the main safety concern. Another challenge is the uncontrollable solid electrolyte interphase (SEI) that leads to a low columbic efficiency and thus a poor cycling performance.In this dissertation, the history and motivation of Li metal are discussed, and challenges in Li metal are stated. The characterizations of Li metal including the root cause of Li metal nucleation and dendrite growth are discussed. The current state of art of Li metal efforts including electrolyte engineering, interfacial engineering and 3D Li host configuration are reviewed. In main body of this dissertation, several Li pretreatment methods are explored to suppress the Li dendrite growing from the most primitive Li metal nucleation state. This dissertation also aims to explore the methods for stabilizing SEI of lithium metal anode in liquid electrolyte-based Li-ion batteries. Also, the interfacial evolution of metallic lithium between one typical solid-state electrolyte-LiPON was investigated. The following projects for developing highly reversible Li metal anode are introduced: (1) A mass controllable Li carbon fiber fabric (LiCFF) composites is developed, which displayed excellent Li dendrite suppression by reducing effective current density in 3D carbon fiber fabric configuration. This novel all-in-one LiCFF composite has low electrical resistivity of 1.1 × 10−3 Ω cm. The large surface area of porous carbon fiber combined with good electrical conductivity can reduce effective current density in 3D conductive host for mossy/dendritic Li suppression. The excellent interfacial Li+/e- transport provides low Li metal nucleation/growth energy barrier. (2) An inter-layer-calated thin Li metal MXene hybrid electrode was developed, which has significant improvement in battery capacity retention and dendrite suppression. The high surface area 2D lamination structure of MXene as a hybrid interlayer and intercalation Li storage host, which provides enough space for reliable Li plating/stripping by regulating the Li ion flux. The excellent electrical conductivity also reduces the effective local current density, thus leading to a homogenous Li deposition/dissolution and thin inorganic part of SEI conformation. (3) Electro-chemo-mechanical stable artificial pre-SEI on Li metal anode with enhanced cycling performance was developed via a facile drop coating method. The artificial pre SEI has high uniformity nanoscale organic components, inorganic lithium compounds and local high concentration Li salt, thus leading to homogenous Li ion transport and enhanced mechanical stability to deal with the fracture caused by Li cycling volume expansion. (4) Thin film solid state electrolyte LiPON showed excellent stability and compatibility with Li metal. We revealed the interfacial evolution between Li metal anode and LiPON by using in-situ transmission electron microscope configuration. A thin 60 nm interfacial passivation layer was found to be stable under 5 V voltage, which exhibited high conductivity and excellent mechanical strength to suppress Li dendrite growth.

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