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research-article  
Kyamra Marma, Jayanth Kolli and Kyu Taek Cho
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4040329
In this study, a new type of redox flow battery (RFB) named 'membrane-less hydrogen-iron RFB' was investigated for the first time to resolve the key issues of conventional battery systems such as high cost and safety concerns. Research focus in this study was placed on defining key design parameters to make this new system promising as a RFB. Crossing rate of reactants over carbon porous electrode (CPE) was controlled by modifying its pore structure with Teflon impregnation, and effects of the Teflon on crossover, kinetic, ohmic and mass transfer was investigated by cell-based test and one-dimensional computational model. It was found that cell performance of the membrane-less system was equivalent to that of membrane system. Especially, cell resistance in the membrane-less system was much more stable than in the membrane system, indicating the membrane-less system is more durable than the membrane system. A physics-based one dimensional model was developed additionally to understand the electrochemical behavior of reactants and voltage losses in the cell during operation, and it was found that the reactant crossover, which is the most changeling issue in the conventional membrane-less system, is not the critical issue in the system, and research in the future should be focused on increasing the kinetic losses by using carbon porous electron having least contents of Teflon.
TOPICS: Flow (Dynamics), Hydrogen, Iron, Membranes, Batteries, Carbon, Design, Electrodes, Physics, Mass transfer, Electrons, Safety
research-article  
ShiYou Li, Konglei Zhu, Jinliang Liu, Dongni Zhao and Xiaoling Cui
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4040567
Three types of LiMn2O4 (LMO) microspheres with different pore size are prepared by a facile method, using porous MnCO3-MnO2 and Mn2O3 microspheres as the self-supporting template, for lithium ion batteries cathode material. Briefly, Mn2O3 and MnO2 microspheres are heated in air at 600° C for 10 h to synthesize porous Mn2O3 spheres. Then the mixture of as-prepared spherical Mn2O3 and LiNO3 is calcined to obtain the LMOs. The morphology and structure of LMOs are characterized by SEM, XRD and nitrogen adsorption/desorption analyses. The result shows that the maximum pore diameters of LMOs are 17 nm, 19 nm and 11 nm, respectively. All LMOs microspheres are composed of similar sized nanoparticles, however, the surface of these microspheres are strewed with dense tinier pores or sparse larger pores. Generally, the nanoparticles will reduce the path of Li+ ion diffusion and increases the reaction sites for lithium insertion/extraction. Moreover, the pores can provide buffer spaces for the volume changes during charge-discharge process. The electrochemical performances of LMOs are investigated and LMO2 exhibits extremely good electrochemical behavior, especially the rate capability. The as-prepared LMO2 deliver a discharge capacity of 124.3 mAh g?1 at 0.5 C, retaining 79.6 mAh g?1 even at 5 C. The LMO2 sample also shows good capacity retention of 96.9% after 100 cycles at 0.5 C.
TOPICS: Lithium-ion batteries, Manganese dioxide, Nanoparticles, Desorption, Cycles, Lithium, Nitrogen, Space, Diffusion (Physics), Polishing equipment
research-article  
Kuber Mishra, Wu Xu, Mark H. Engelhard, RG Cao, Jie Xiao, Ji-Guang Zhang and Xiao-Dong Zhou
J. Electrochem. En. Conv. Stor.   doi: 10.1115/1.4039860
A thin and mechanically stable solid electrolyte interphase (SEI) is desirable for a stable cyclic performance in a lithium ion battery. For the electrodes that undergo a large volume expansion such as Si, Ge and Sn, the presence of a robust SEI layer can improve the capacity retention. In this work, the role of solvent choice on the electrochemical performance of Ge electrode is presented by a systematic comparison of the SEI layers in EC-based and FEC-based electrolytes. The results show that the presence of FEC as a co-solvent in a binary or ternary solvent electrolyte results in an excellent capacity retention of ~ 85% after 200 cycles at the current density of 500 mA·g-1; while EC-based electrode suffers a rapid capacity degradation with a capacity retention of just 17% at the end of 200 cycles. Post analysis by an extensive use of x-ray photoelectron spectroscopy was carried out, which showed that the presence of Li2O in FEC-based SEIs was the origin for the improved electrochemical performance.
TOPICS: Anodes, Germanium, Lithium-ion batteries, Electrodes, Cycles, Electrolytes, Solid electrolytes, Tin, Current density, Photoelectron spectroscopy, X-rays

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