Doctor of Philosophy, The Ohio State University, 2024, Mechanical Engineering

This thesis delves into the investigation of the degradation mechanisms of silicon-based (Si-based) anodes in lithium-ion batteries, a pivotal concern limiting their widespread application despite their high theoretical capacity. Through a bottom-up approach, the fundamental particle level mechano-electrochemical coupling degradation behaviors of the micro-Si anode are first investigated using situ atomic force microscopy (AFM), then the electrochemical degradation of Si-based anodes (Si and SiO anodes) in cell-level was studied using electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) techniques, eventually, the degradation of practical graphite/silicon blended electrode is studied. This research unravels the complex interplay between Si mechanical morphology and anode electrochemical performance. The study initially focuses on the real-time characterization of micro-Si anodes, revealing a Si dynamic evolution sequence of initial pulverization, followed by irreversible volume expansion, Si particle cracking, and the formation of a new solid-electrolyte interphase (SEI). The characterization indicates that the degradation of micro-Si is attributed to the loss of active material (LAM) due to Si isolations and contact impedance increase. Subsequent experiments extend these insights to full-cell configurations employing nano-Si and micro-SiO, comparing their performance and identifying distinct degradation behaviors. Furthermore, the thesis explores the performance of graphite-silicon blended anodes, demonstrating their superior capacity retention and reduced impedance growth, particularly with low Si content. This work not only advances the understanding of Si-based anode degradation mechanisms but also provides concrete strategies for improving the performance and cycle life of lithium-ion batteries. The findings hold broad implications for the development of high-energy-density batteries, crucial for the future of energy storage, (open full item for complete abstract)

Committee: Hanna Cho (Advisor); Gerald Frankel (Other); Marcello Canova (Committee Member); Jung Hyun Kim (Committee Member) Subjects: Energy; Engineering

Master of Science, The Ohio State University, 2022, Mechanical Engineering

The development of next generation electrode materials provides the opportunity to significantly increase the energy density of lithium-ion batteries. These materials form alloy compounds with lithium and have specific capacities that are much higher than of graphite. Of these materials, silicon, which has a theoretical capacity of ~4200 mAh/g, is the closest to commercialization. However, silicon experiences large volume changes during the lithiation and delithiation processes. This ultimately leads to stress generation within the particle causing fracture, loss of active material, and rapid loss of cell capacity. The differences in behavior for silicon-based anodes compared to traditional graphite anodes highlights the need for the development of physics-based models to capture the effects of volume change and stress generation on the solid-state diffusion process. One such model proposed by Christensen and Newman describes the effects of diffusion, volume change, and stress generation in a spherical electrode particle. This mathematical model takes the form of an index-2 set of differential and algebraic equations which require implicit numerical methods to obtain a solution. Due to the mathematical complexity and high computational time and memory requirements, this model is not suited for controls or estimation-based applications. This thesis presents a mathematical reformulation of the Christensen-Newman equations using index-reduction to obtain a semi-explicit index-1 version of the model. Index reduction allows for the differential and algebraic equations to be decoupled enabling the use of explicit time marching methods. This reformulation will enable the integration of this model into larger cell level frameworks as well as estimation and controls-based applications. The reduced index model is verified against a fully implicit benchmark solution for a graphite anode. A local sensitivity analysis is performed to ascertain the effects of the mechanical (open full item for complete abstract)

Committee: Marcello Canova (Advisor); Jung Hyun Kim (Committee Member) Subjects: Mechanical Engineering

Master of Science, University of Akron, 2020, Polymer Science

Silicon (Si) is a promising anode material for the next‐generation high‐energy‐density lithium‐ion batteries. As a host material for lithium at anode, Si provides an ultrahigh capacity of 4200 mAh/g, more than ten times of commercial graphite anode. However, the Si anode suffer from large volumetric changes (>300%) during lithiation/delithiation, as well as unstable interface with liquid electrolyte. The volume change issue of the silicon anode could be reduced by applying small Si nanoparticles. However, the large surface area of nanoparticles will reduce the tap density of the electrode and accelerate the side reactions during the cycles. In this thesis, a silicon secondary particle was prepared through controlled aggregation of silicon nanotubes. With the new secondary particles, the mass loading of the silicon anode was improved up to 5.2mg/cm2 secondary, and the half-cell demonstrated the anode areal capacity of secondary 4.5mAh/cm2. The new secondary particles and related electrochemical energy storage devices are characterized.

Committee: Yu Zhu (Advisor); Steven S.C. Chuang (Committee Member) Subjects: Materials Science

Master of Science, University of Akron, 2017, Polymer Science

ABSTRACT In the recent studies, carbon-silicon based insertion anode material has shown great performance compared with conventional graphite anode of lithium ion batteries (LIB) for the high specific capacity1-3. However, there are still challenges which limits the practical utilization of the carbon-silicon anodes, such as the severe degradation of capacity. In this work, commercial silica gel micron-particles used for chromatography were adopted as starting material and treated with reduction and carbon coating processes, generating micron-sized Si-SiC-C composite anode material. This anode fabricated from cheap precursors and mild synthesis exhibited reasonable capacity and stable electrochemical performance together with graphite. The morphology and composition of the composite were characterized by scanning electron spectroscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Molybdenum disulfide (MoS2), a two dimensional material, has attracted a lot of research interests in these years4. With its large surface area and unique semi-conductor properties, we are inspired to develop MoS2 as a supporting material for the catalyst of selective oxidation reaction. Gold nanoparticles were deposited onto the exfoliated MoS2 flakes by deposition-precipitation method. The morphology of the composite was studied with TEM. Isoproponal was employed as reagent for the photocatalytic reaction catalyzed by the prepared composite catalyst. The reaction process and the final product were characterized by in-stu infrared (IR) spectroscopy and nuclear magnetic resonance (NMR).

Committee: Yu Zhu (Advisor); Steven Chuang (Committee Member) Subjects: Chemistry; Energy; Physical Chemistry

Master of Science in Engineering (MSEgr), Wright State University, 2011, Electrical Engineering

Porous silicon (PS) membranes for lithium-ion batteries (LIBs) anode applications were developed, demonstrated and characterized systematically in this work. Electrochemical measurements were conducted on both Si-wafer supported and free-standing porous Si membranes. It turned out that the specific capacity of LIBs was enhanced remarkably by PS based anode. PS was fabricated by using electrochemical anodization in a mixed solution of Dimethylformamide (DMF) and Hydrofluoric acid (HF wt.49%). By varying the anodization conditions, including HF concentration, anodization etching time and current density, pores were formed in a p-type (1-20Ω cm) boron-doped silicon substrate. Scanning electron microscopy (SEM) was employed to investigate the surface morphology of the pores (pore distribution, diameter and depth). The electrochemical agglomeration was observed on the wall of the pores (WOPs). The surface percentage of WOPs was calculated by Finite Element Analysis (OOF2). It turned out that the 27.5 % of the surface is occupied by the WOPs, and the average diameters of the pores are in the range between 0.85μm to 1.53μm. The Li insertion in the porous silicon was investigated by cyclic voltammetry method (CV) as well as the small constant current discharge/charge analysis. As increase of the depth of the pores, the specific capacity increased due to the enlarged surface area. The PS anode with 89.4μm of depth showed high cycling stability, manifested by the unchanged porous structure after 10 charge-discharge cycles. The specific capacity up to 1150mAh/g was achieved.

Committee: Yan Zhuang PhD (Committee Chair); Kuan-Lun Chu PhD (Advisor); Hong Huang PhD (Advisor) Subjects: Electrical Engineering; Engineering; Materials Science; Nanoscience; Nanotechnology