Kevin A. Hays
George Washington University
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Publication
Featured researches published by Kevin A. Hays.
Frontiers in Energy Research | 2015
Jianming Zheng; Pengfei Yan; Meng Gu; Michael J. Wagner; Kevin A. Hays; Junzheng Chen; Xiaohong S. Li; Chong M. Wang; Ji-Guang Zhang; Jun Liu; Jie Xiao
Lithium-sulfur (Li-S) battery is a promising energy storage system due to its high energy density, cost effectiveness and environmental friendliness of sulfur. However, there are still a number of technical challenges, such as low Coulombic efficiency and poor long-term cycle life, impeding the commercialization of Li-S battery. The electrochemical performance of Li-S battery is closely related with the interfacial reactions occurring between hosting substrate and active sulfur species which are poorly conducting at fully oxidized and reduced states. Here, we correlate the relationship between the performance and interfacial reactions in the Li-S battery system, using a hollow carbon nanosphere (HCNS) with highly graphitic character as hosting substrate for sulfur. With an appropriate amount of sulfur loading, HCNS/S composite exhibits excellent electrochemical performance because of the fast interfacial reactions between HCNS and the polysulfides. However, further increase of sulfur loading leads to increased formation of highly resistive insoluble reaction products (Li2S2/Li2S) which limits the reversibility of the interfacial reactions and results in poor electrochemical performances. These findings demonstrate the importance of the interfacial reaction reversibility in the whole electrode system on achieving high capacity and long cycle life of sulfur cathode for Li-S batteries.
ACS Applied Materials & Interfaces | 2018
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.
Journal of The Electrochemical Society | 2013
Jianming Zheng; Meng Gu; Michael J. Wagner; Kevin A. Hays; Xiaohong Li; Pengjian Zuo; Chongmin Wang; Ji-Guang Zhang; Jun Liu; Jie Xiao
JOM | 2017
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
Journal of Magnetism and Magnetic Materials | 2017
G.C. DeFotis; M.J. Van Dongen; A.S. Hampton; C.H. Komatsu; K.T. Trowell; K.C. Havas; C.M. Davis; C.L. DeSanto; Kevin A. Hays; Michael J. Wagner
Journal of Magnetism and Magnetic Materials | 2016
G.C. DeFotis; M.J. Van Dongen; A.S. Hampton; C.H. Komatsu; J.M. Pothen; K.T. Trowell; K.C. Havas; D.G. Chan; Z.D. Reed; Kevin A. Hays; Michael J. Wagner
Journal of Power Sources | 2018
Kevin A. Hays; Rose E. Ruther; Alexander J. Kukay; Peng-Fei Cao; Tomonori Saito; David L. Wood; Jianlin Li
Journal of The Electrochemical Society | 2017
Nathan A. Banek; Kevin A. Hays; Michael J. Wagner
Journal of The Electrochemical Society | 2017
Kevin A. Hays; Nathan A. Banek; Michael J. Wagner
Surface Science | 2016
Nicholas F. Materer; Allen W. Apblett; Evgueni B. Kadossov; Kashif Rashid Khan; Walter Casper; Kevin A. Hays; Eman Freeg Mohamed Freeg Shams