Characterization of phase and structural evolution in battery materials using advanced electron imaging and diffraction methods

Pidaparthy, Saran

Permalink

https://hdl.handle.net/2142/117531 Copy

Description

Title

Characterization of phase and structural evolution in battery materials using advanced electron imaging and diffraction methods

Author(s)

Pidaparthy, Saran

Issue Date

2022-09-16

Director of Research (if dissertation) or Advisor (if thesis)

Zuo, Jian-Min

Doctoral Committee Chair(s)

Zuo, Jian-Min

Committee Member(s)

• Braun, Paul V
• Abraham, Daniel P
• Huang, Pinshane
• Chen, Qian

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Transmission electron microscopy (TEM)
• Scanning electron nanodiffraction (SEND)
• Liquid cell electron microscopy (LCEM)
• Four-dimensional scanning transmission electron microscopy (4D-STEM)
• Cepstrum
• Batteries
• Graphite
• Silicon

Abstract

Despite the widespread adoption of lithium-ion batteries (LIBs) in consumer electronics, electric vehicles, and potentially for grid storage as well, there is an increasing societal demand for energy capability beyond what state-of-the-art battery technology can deliver. To meet this demand, research efforts are needed to develop novel batteries capable of greater delivered capacity, faster recharging times, and longer lasting reliability. These performance metrics are linked to how battery materials evolve and, consequently, how they degrade through their use. Redox reactions within batteries alter the structure, phase, and chemical composition of the constituent materials in a way that spans the atomic scale to the macroscopic level. This thesis investigates the working mechanisms involved in battery electrode evolution using a multi-length scale characterization approach. Specifically, we focus fundamental materials issues behind the limited system-level performance. We also emphasize the need for novel electron imaging and diffraction techniques, such as liquid cell electron microscopy (LCEM) and scanning electron nanodiffraction (SEND), in uncovering the nano- to atomic-scale physicochemical properties that comprise the macroscopic observations. In this thesis, we report on the following research topics: (1) cathode reaction kinetics in the lithium-oxygen battery (LOB), (2) anode degradation in fast-charged LIBs, and (3) origin of capacity fade in LIBs with silicon anodes. On LOBs, understanding the nature of the discharge products is critical to improve their practical performance, which is limited by the large charging overpotential beyond 4.0 V vs. Li/Li+ and the resulting electrochemical instabilities. Here we show that a mixture of nanocrystalline Li2O2 and LiOH phases are formed upon discharge under an intermediate rate in a dimethyl sulfoxide (DMSO)-based electrolyte. This nanocrystalline phase is formed by a fractal growth process according to real-time LCEM. Compared to the crystalline toroidal Li2O2, and flower-like LiOH phases, which also form on the cathode, the nanocrystalline fractal mixture decomposes at a significantly lower overpotentials below 3.7 V vs. Li/Li+ upon charging. Thus, this work suggests the promotion of fractal nanocrystalline discharge products is key to realizing a rechargeable LOB. On anode degradation in fast-charged LIBs, fast-charging (e.g., 6C rate) of LIBs creates conditions favorable for Li-metal deposition on the graphite anode results from structural, morphological, and chemical modifications to the active graphite material. In this work, we use a multi-length scale characterization approach to understand the aforementioned damage. At the micron-scale, the fast-charged anode thickness increases and its surface and internal pores roughen. At the nano-scale, strain and rotation analysis of SEND data reveals permanent turbostratic disorder in the graphite manifests near particle edges with greater damage penetration where electrolyte reduction products are formed. Regarding silicon anodes, the severe capacity fade of LIBs with these anodes has hindered their widescale commercialization. Here, we link cell capacity fade to the heterogeneous physicochemical evolution of silicon anodes through a multi-length scale characterization approach. In particular, we highlight a new SEND analysis method developed in this work, called fluctuation cepstral STEM (FC-STEM), based on fluctuation analysis of the cepstral transform of diffraction patterns to decouple and visualize distinct ordered and disordered chemistries via diffractive image reconstruction. To this end, we find highly nanocrystalline wispy silicon encased in a highly fluorinated matrix of electrolyte-reduction products occurring near the anode surface. In contrast, closer to the current collector, the silicon retains more of its initial morphology and structure, suggesting the presence of isolated active particles. The results show that accessibility of active silicon to Li+ varies across the anode matrix.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Saran Pidaparthy

Owning Collections