MATERIALS DEVELOPMENT TO ENABLE HIGH-ENERGY DENSITY AND LONG-CYCLING LI METAL BATTERIES
Restricted (Penn State Only)
- Author:
- Le, Linh
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 02, 2024
- Committee Members:
- John Mauro, Program Head/Chair
Donghai Wang, Chair & Dissertation Advisor
Hojong Kim, Major Field Member
Adri van Duin, Major Field Member
Feifei Shi, Outside Unit & Field Member - Keywords:
- Electrolytes
Li Protection
Lithium Batteries
Fast-charging - Abstract:
- Rechargeable Li-metal batteries using high-voltage cathodes can deliver the highest possible energy densities among all electro-chemistries. However, the notorious reactivity of metallic lithium as well as the catalytic nature of high-voltage cathode materials largely prevents their practical application. The stability of lithium metal anodes in rechargeable batteries heavily depends on the formation of a solid-electrolyte interphase (SEI). However, this SEI undergoes continuous reforming and consumes electrolyte during cycling, posing challenges in designing a stable SEI due to the difficulty in controlling its structure and stability. This work reports a significant advance in the development of materials with improved SEI and cycling stability. Firstly, a carbonate-based saturated fluorinated electrolyte was developed that supports the most aggressive and high-voltage cathodes to realize a high stable Li metal full-cell. Secondly, a novel molecular-level approach to SEI design using a triple layer (TL) coating was introduced. This TL coating consists of three layers: a nucleation-driven bottom layer based on Mg(TFSI)2, a middle layer using a reactive inorganic polymer composite that effectively reduces electrolyte consumption during SEI formation and maintenance, and a top layer based on a cross-linked polymer that prevents solvent penetration from the electrolyte and confines the inside layers. Finally, a unique formulated electrolyte was made to stabilize the SEI as well as modulate polysulfide shuttle effect which is the most important issue in Lithium metal- sulfur batteries. The SEI layer comprises polymeric lithium salt, lithium fluoride, as confirmed by cryo-transmission electron microscopy, atomic force microscopy, and surface-sensitive spectroscopies, which further mitigate side reactions between Li and electrolyte. Utilizing these advantages, the full Li metal cells exhibit remarkable cycling stability at a high current density under extremely lean electrolyte and limited excess lithium. These findings enhance our understanding of lithium nucleation and pave the way for high-energy, fast-charging Li-metal batteries.