Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 150275

150275 - Enhancing the Longevity of Silicon Electrode Lithium-Ion Batteries With Fluoroethylene Carbonate 

The capacity of the Lithium-ion batteries used in most electric vehicles limits their driving range. Lithium-ion batteries that use Silicon as the anode material have a capacity approximately 10 times higher than the ones with traditional standard graphite anode and have gained popularity as a potential alternative.  However, due to its large volume change (300% increase during charging) Silicon has poor cycling stability. With this significant volume change, the solid electrolyte interphase (SEI) breaks down, exposing the electrode to the electrolyte, forming a more resistive SEI and lowering the coulombic efficiency. Using Fluoroethylene Carbonate (FEC) as an additive to the organic electrolyte solution appears to help stabilize Silicon electrodes in a lithium-ion battery during long-term cycling. In practical applications, batteries may rest for long periods of time. It is imperative to investigate how the use of FEC as an additive affects a battery during long-term aging. This study explores how FEC affects the calendar aging of silicon electrodes by comparing coin cell batteries with and without FEC. To investigate this, full cells are assembled using lithium ferro phosphate (LFP, 92%) as cathode and Silicon as anode. One set of cells is cycled with baseline electrolyte, which comprises 1.2M LiPF6 in EC: EMC (3:7, w/w), and another set of cells is cycled by adding 10wt% FEC to the baseline electrolyte. The cycling protocol includes formation cycles of 10x charge and discharge @C/10, followed by aging for 180 hours by applying open circuit voltage. To investigate the effect of aging on electrochemical performance, the cells are further cycled at C/3 rate and C/10 rate. Following these cycles, the cells are aged for another 180 hours by applying open circuit voltage. During the formation cycles, the FEC cell showed a better capacity retention than the FEC free cell (74.67% versus 48.8%), and a higher Coulombic efficiency. Following the aging period at the C/3 rate, the FEC cell continued to show better capacity retention than the FEC-free cell (79.9% vs 24.9%). Furthermore, the average Coulombic efficiency for the FEC cell was 98.8%, while the FEC free cell had a Coulombic efficiency of 88.2%. Before and after cycling and aging, electrochemical impedance spectroscopy (EIS) measurements were performed in a potentiostat with a frequency ranging from 10 mHz to 100000 Hz. A theoretical circuit was constructed and curve-fitted to the EIS impedance data. The circuit analysis shows that the charge transfer resistance for the FEC free cycled cell is larger than the one of the FEC cycled cell; the charge transfer resistance is highest after the first cycle and then decreases after 11 cycles. As cycling and aging continues, the charge transfer resistance of the FEC-free cell increases and remains higher than that of the FEC cell. These results indicate that FEC cells last longer and perform better after aging. Finding longer-lasting batteries is a step towards a cleaner and more renewable future.

Presenting Author: Andrei Proca Texas A&M University

Presenting Author Biography: I am an undergraduate chemical engineer with a minor in biomedical engineering from Texas A&M University. In the summer of 2024, I researched at the University of Delaware for the NSF REU Site in Sustainable Resilient Transportation Systems. I worked in Dr. Koffi Pierre Yao's lab and was mentored by Sattajit Barua.

Authors:

Andrei Proca Texas A&M University
Koffi Pierre Yao University of Delaware