OPTIMIZING BATTERY SAFETY AND PERFORMANCE IN HARSH CONDITIONS THROUGH ELECTROLYTE ENGINEERING AND CELL DESIGN

Restricted (Penn State Only)
- Author:
- Liao, Jie
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 02, 2024
- Committee Members:
- John Mauro, Program Head/Chair
Chao-Yang Wang, Outside Unit & Field Member
Qing Wang, Major Field Member
Feifei Shi, Chair & Dissertation Advisor
Ralph Colby, Major Field Member - Keywords:
- lithium ion battery
extremely fast charging
high temperature stability
lithium metal battery safety
lithium deposition
lithium plating
electrolyte decomposition - Abstract:
- The development of battery technologies is critical to meeting the fast-growing demands for energy storage. Lithium-ion battery is the most successful solution owing to its high energy density, long cycle life and low self-charge rates. Several cathode and anode materials have been developed for lithium-ion batteries. However, each cathode or anode material has its own advantages and disadvantages, and it’s challenging to achieve a good balance on energy density, cycle life and safety solely from the electrode materials side. Therefore, it is critical to include electrolyte engineering to help optimizing the overall performance of batteries, as the electrolyte is the “blood” of the batteries and can have a huge impact on battery performance and safety, especially under extreme operational conditions. LiNi0.8Co0.1Mn0.1O2 cathode has gained substantial popularity for applications that require high energy density, but it faces critical challenges related to long-term stability and safety, particularly at elevated temperatures. In chapter 3, electrolyte engineering was implemented to enhance the thermal stability and safety of NCM811 batteries. First, Lithium difluoro(oxalato)borate was used to replace LiPF6 and it formed stable electrode/electrolyte interfaces that protect the electrodes. Additionally, high-boil-point propylene carbonate was used to replace the highly flammable and volatile linear carbonates, which decreases the vapor pressure and avoids local electrolyte-dry-out at elevated temperatures. As a result, the risk of battery thermal runaway and further combustion of electrolytes was lowered. Both cycle stability at high temperature and safety during mechanical abuse were improved. LiFePO4 has been increasingly popular owing to its lower cost, high cycle stability and higher safety. However, it faces two major problems: narrow operating temperature range and low charge rates. In chapter 4, we demonstrated that a self-heating cell design and electrolyte engineering (using Lithium bis(fluorosulfonyl)imide can enable a 168.4-Wh/kg LFP/graphite pouch cell to operate in a broad operational temperature range of -50 to +90 °C. With rapid internal preheating, fast charging at a 6C rate was achieved at all ambient temperatures without lithium pleating. The total preheating plus charging time was less than 12 min, and the cell finished 2500 cycles of 6C charging while still retaining 81.3% capacity. Lithium metal batteries have attractive high energy density. However, the deposition and stripping of lithium tend to occur unevenly, which causes formation of lithium dendrites that pose threats to the cycle stability and safety. In chapter 5, we examined the effect of current density and aging on the thermal stability of anode-free cells using two types of electrolytes: baseline carbonate electrolyte and ether-based localized high concentration electrolyte. Electrochemical data demonstrated that cells with localized high concentration electrolyte exhibited much improved cycle stability, which was also supported by materials characterizations that revealed the formation of an inorganic-rich solid-electrolyte interface, which was responsible for the more uniform deposition and stripping of lithium. Differential scanning calorimetry tests indicated that cells with localized high concentration electrolyte had a higher onset temperature compared to baseline cells, which was in accordance with the morphology of the lithium anode and further corroborated by accelerating rate calorimetry data. Overall, in this dissertation, various electrolyte engineering strategies were employed for lithium batteries with different cathode and anode chemistries to improve their cycle life and safety on the intended operating conditions, to meet demands in different environments. Lab-scale coin cell tests and material characterization techniques were utilized, along with pouch cells and industry-focused safety tests, making this dissertation more applicable to practical scenarios.