Identification and design of new inorganic Li+/Na+ conductors for all-solid-state batteries

Lin, Yuying Steven

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https://hdl.handle.net/2142/121298 Copy

Description

Title

Identification and design of new inorganic Li+/Na+ conductors for all-solid-state batteries

Author(s)

Lin, Yuying Steven

Issue Date

2023-06-02

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

Perry, Nicola H

Doctoral Committee Chair(s)

Krogstad, Jessica A

Committee Member(s)

• Braun, Paul V
• Shoemaker, Daniel P
• Ertekin, Elif

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)

• Batteries
• Solid Electrolyte, Ceramics

Abstract

All-solid-state batteries (ASSB) have attracted significant attention recently because of their promise for higher energy density and improved safety/longevity. To realize ASSB technology, the liquid electrolyte in a conventional Li+/Na+ battery is replaced with a solid electrolyte (SE). An ideal SE should have sufficient Li+/Na+ conductivity, low electronic conductivity, and electrochemical stability over a wide voltage range. In this dissertation, I aim to identify new inorganic Li+/Na+ conductors as SE by using design rules and high-throughput descriptors. To identify new inorganic SE materials, I start by reviewing conduction mechanisms in many known superionic conductors (SIC), as well as strategies for superior electrochemical performance, with an emphasis on Li+/Na+ conductivity. By understanding key features governing ionic conduction, the design of new Li+/Na+ conductors can be more efficient, reducing time-consuming trial-and-error experimental attempts. Two main aspects were explored in this dissertation: (1) designing and demonstrating a new perovskite Na+ conductor by chemically stretching an existing perovskite Li+ SIC; (2) designing high-throughput descriptors to mine a material database to discover and demonstrate new promising Li+ conductors. In CHAPTER 2, I explore using chemo-mechanical and defect engineering to convert a perovskite SIC Li3xLa2/3-xTiO3 (LLTO) into Na+ conducting perovskites NaxLa2/3-1/3xZrO3 (NLZ) and NaxLa1/3-1/3xBa0.5ZrO3 (NLBZ). By substituting the host B-site/A-site cations with larger cations, the lattice can be effectively expanded, which led to significant improvements in conductivity for the larger Na+ ion (vs. Li+). Defect chemistries in NLZ and NLBZ were also explored extensively; however, only a limited amount of the desired cation vacancy defects could be introduced in equilibrium conditions. Densification challenges were overcome using field- and pressure- assisted sintering, which boosted conductivity. Overall, I demonstrated lattice enlargement as a very effective approach for increasing ionic conductivity. In CHAPTER 3, I explore using novel descriptors to select potential Li+ conductors from the Materials Project (MP). I hypothesized that coordination flexibility can be correlated with Li+ sublattice disorder, an important feature for high ionic conductivity found in many SICs. To that end, I designed a “proximal stoichiometry” descriptor to identify materials with coordination flexibility — this is the first descriptor focusing on Li-defect properties to my knowledge. In my search process, I found that many SICs exhibited the “proximal stoichiometry” feature. Motivated by this result, I selected Li7BiO6 and Li2B4O7 as new materials systems with similar features, and the team explored their defect chemistries and phase stabilities extensively through both experimental and computational methods. Although limited improvements in conductivity can be achieved in Li7BiO6, and Li2B4O7, both systems support facile Li vacancy/interstitial formation. In summary, based on the literature survey on SICs and my investigation in Li7BiO6, and Li2B4O7, our results support a correlation between coordination flexibility and Li+ sublattice disorder. In CHAPTER 4, I used more conventional descriptors to select potential Li+ conductors from MP. Many candidates with low electronic conductivity, suitable conduction channels, wide electrochemical stability windows, etc. were identified. Promisingly, I also rediscovered LiTaSiO5 as a high-voltage stable SE. To improve its conductivity, I inserted Li interstitials into the system to make Li1+xTixTa1-xSiO5. With the careful separation of grain and grain boundary/intergranular transport processes, I successfully showed that concerted ion transport can be triggered in bulk transport through Li interstitial stuffing, leading to a significant increase in conductivity and a decrease in activation energy. Additionally, Li1+xTixTa1-xSiO5 consisted of mostly crystalline grains, with a Si-rich amorphous phase forming in between. Interestingly, both the effective and specific grain boundary conductivity increased significantly as the Ti dopant concentration increased, when more of the intergranular phase formed. In addition, a wide electrochemical window could be retained at high dopant concentrations. In this work, I identified many candidate SE materials and demonstrated that Li1+xTixTa1-xSiO5 is a promising high-voltage stable SE. At the end of each chapter and CHAPTER 5, this dissertation concluded on key findings in each investigation, followed by proposing a few future directions for research toward achieving better SE materials. For example, strategies for improving densities, designing new descriptors, microstructural engineering, etc., were proposed as future directions. With the use of solid-state electrolytes, all-solid-state batteries have great potential for achieving higher energy density and better longevity/safety features. This dissertation demonstrated multiple approaches to effectively design and identify new Li+/Na+ conductors. Several strategies (ex. chemo-mechanical engineering, defect engineering) for improving conductivities were proposed and tested on new material systems, broadening the pool of candidates with potential as solid electrolyte materials.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Yuying Lin

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