Seong Jin An

Seong Jin An; Jianlin Li; Claus Daniel; Harry M. Meyer; Stephen E. Trask; Bryant J. Polzin; David L. Wood

This study aims to explore the correlations between electrolyte volume, electrochemical performance, and properties of the solid electrolyte interphase in pouch cells with Si-graphite composite anodes. The electrolyte is 1.2 M LiPF6 in ethylene carbonate:ethylmethyl carbonate with 10 wt % fluoroethylene carbonate. Single layer pouch cells (100 mA h) were constructed with 15 wt % Si-graphite/LiNi0.5Mn0.3CO0.2O2 electrodes. It is found that a minimum electrolyte volume factor of 3.1 times to the total pore volume of cell components (cathode, anode, and separator) is needed for better cycling stability. Less electrolyte causes increases in ohmic and charge transfer resistances. Lithium dendrites are observed when the electrolyte volume factor is low. The resistances from the anodes become significant as the cells are discharged. Solid electrolyte interphase thickness grows as the electrolyte volume factor increases and is nonuniform after cycling.

Seong Jin An; Jianlin Li; Yangping Sheng; Claus Daniel; David L. Wood

Effects of ultraviolet (UV) light on dried graphite anodes were investigated in terms of the cycle life of lithium ion batteries. The time variations for the UV treatment were 0 (no treatment), 20, 40, and 60 minutes. UV-light-treated graphite anodes were assembled for cycle life tests in pouch cells with pristine Li1.02Ni0.50Mn0.29Co0.19O2 (NMC 532) cathodes. UV treatment for 40 minutes resulted in the highest capacity retention and the lowest resistance after the cycle life testing. X-ray photoelectron spectroscopy (XPS) and contact angle measurements on the graphite anodes showed changes in surface chemistry and wetting after the UV treatment. XPS also showed increases in solvent products and decreases in salt products on the SEI surface when UV-treated anodes were used. In conclusion, the thickness of the surface films and their compositions on the anodes and cathodes were also estimated using survey scans and snapshots from XPS depth profiles.

Rose E. Ruther; Kevin A. Hays; Seong Jin An; Jianlin Li; David L. Wood; Jagjit Nanda

Silicon-graphite composites are under development for the next generation of high-capacity lithium-ion anodes, and vibrational spectroscopy is a powerful tool to identify the different mechanisms that contribute to performance loss. With alloy anodes, the underlying causes of cell failure are significantly different in half-cells with lithium metal counter electrodes compared to full cells with standard cathodes. However, most studies which take advantage of vibrational spectroscopy have only examined half-cells. In this work, a combination of FTIR and Raman spectroscopy describes several factors that lead to degradation in full pouch cells with LiNi0.5Mn0.3Co0.2O2 (NMC532) cathodes. The spectroscopic signatures evolve after longer term cycling compared to the initial formation cycles. Several side-reactions that consume lithium ions have clear FTIR signatures, and comparison to a library of reference compounds facilitates identification. Raman microspectroscopy combined with mapping shows that the composite anodes are not homogeneous but segregate into graphite-rich and silicon-rich phases. Lithiation does not proceed uniformly either. A basis analysis of Raman maps identifies electrochemically inactive regions of the anodes. The spectroscopic results presented here emphasize the importance of improving electrode processing and SEI stability to enable practical composite anodes with high silicon loadings.

Seong Jin An; Jianlin Li; Claus Daniel; Debasish Mohanty; Shrikant C. Nagpure; David L. Wood

Jianlin Li; Claus Daniel; Seong Jin An; David L. Wood

Jianlin Li; Zhijia Du; Rose E. Ruther; Seong Jin An; Lamuel David; Kevin A. Hays; Marissa Wood; Nathan D. Phillip; Yangping Sheng; Chengyu Mao; Sergiy Kalnaus; Claus Daniel; David L. Wood

Seong Jin An; Jianlin Li; Zhijia Du; Claus Daniel; David L. Wood

Seong Jin An; Jianlin Li; Debasish Mohanty; Claus Daniel; Bryant J. Polzin; Jason R. Croy; Stephen E. Trask; David L. Wood

Zhijia Du; K.M. Rollag; Jianlin Li; Seong Jin An; Marissa Wood; Yangping Sheng; Partha P. Mukherjee; Claus Daniel; David L. Wood

Seong Jin An; Jianlin Li; Claus Daniel; Sergiy Kalnaus; David L. Wood