Date of Award

March 2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Junjie Niu

Committee Members

Pradeep Rohatgi, Benjamin Church, Deyang Qu, Yi Hu

Keywords

concentration gradient, lithium-ion batteries, mass production, MOF, Ni-rich cathode, Silicon

Abstract

Lithium-ion batteries (LIBs) have been widely used in various devices such as portable devices, communication systems, and electric vehicles (EVs). In this dissertation, towards building LIBs with enhanced energy density and improved performance, Ni-rich cathode and Si-based anode are selected as the electrodes. The performance of LIBs is improved through optimization on both cathode and anode material. Ni-rich layered transition metal oxide with dual gradient on both primary and secondary particles was successfully designed and synthesized through introducing Ni-based metal-organic framework (Ni-MOF) to the coprecipitation of the precursor. During the calcination process, the presence of organic components of Ni-MOFs promotes the formation of reduced Ni oxidation state, leading to the formation of self-induced cation mixing layer with stable rock salt phase on the surface of primary particles. It can successfully increase the structural stability through inhibiting the generation of internal cracks caused by the internal strain and phase transition within primary particles during cycling process. The metallic components from Ni-MOFs in the core lead to the formation of Ni concentration gradient within secondary particles. As results, a greatly improved electro-chemo-mechanical stability was achieved, which contributed to the enhanced battery capacity retention upon long cycling. At the same time, to overcome the disadvantages of Si-based anode material, including huge volume change, poor cycling stability, and low conductivity, micro-sized AlSi alloy was used to form the Si skeleton with an ultra-thin (<5 nm) mesoporous polypyrrole (PPy) skin (μ-Si cage) through a facile wet-chemical method. Under this configuration, the hollow skeleton provides sufficient space to accommodate the large volume change upon lithiation/delithiation process. The conductive PPy layer serves as a protective layer and fast channel for Li+/e- transport. In addition, the application of micro-sized Si ensures high active mass loading and areal capacity. The battery with the obtained μ-Si cage as anode displayed excellent capacity retention upon long cycling at high charge/discharge rates and high active mass loadings. Additionally, the development of other Si-based materials was also explored in this dissertation. SiGe@MXene composite was obtained through a low-temperature reduction from the corresponding oxide. Through alloying with Ge, SiGe alloy showed improved rate performance and cycling stability compared with pure Si anode. Herein, the combination of SiGe alloy and MXene can further increase the performance of SiGe-based anode material. The autoadjustable layer space of MXene can provide sufficient space to accommodate the volume expansion/shrinkage upon Li+ insertion/extraction process. At the same time, it can provide superior conductivity, which can promote fast transportation of Li+/e-. With the incorporation of MXene, the SiGe@MXene composite exhibited improved cycling stability and rate capability, which shows great potential as anode material for high-performance LIBs

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