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124. Direct Observation of the Redistribution of Sulfur and Polysufides in Li–S Batteries During the First Cycle by In Situ X‐Ray Fluorescence Microscopy

Author

Yu, Xiqian, primary, Pan, Huilin, additional, Zhou, Yongning, additional, Northrup, Paul, additional, Xiao, Jie, additional, Bak, Seongmin, additional, Liu, Mingzhao, additional, Nam, Kyung‐Wan, additional, Qu, Deyang, additional, Liu, Jun, additional, Wu, Tianpin, additional, and Yang, Xiao‐Qing, additional

Published
2015
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128. Hydrogen Ion Supercapacitor: A New Hybrid Configuration of Highly Dispersed MnO2 in Porous Carbon Coupled with Nitrogen-Doped Highly Ordered Mesoporous Carbon with Enhanced H-Insertion

Author

Qu, Deyu, primary, Wen, Jianfeng, additional, Liu, Dan, additional, Xie, Zhizhong, additional, Zhang, Xuran, additional, Zheng, Dong, additional, Lei, Jiahen, additional, Zhong, Wei, additional, Tang, Haolin, additional, Xiao, Liang, additional, and Qu, Deyang, additional

Published
2014
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132. Physical and electrochemical basis of induction of reversibility in manganese dioxide reduction and reoxidation

Author

Qu, Deyang.

Subjects
Chemistry, Physical
Abstract

"Chemically Modified" (CM) rechargeable MnO$\sb2$ cathode materials have been prepared, based on patents issued to Ford. The reaction mechanisms of the discharge and recharge of these materials have been extensively studied in the present work and compared with behaviour at Blank MnO$\sb2$ (without Bi) and regular $\gamma$-MnO$\sb2,$ by various experimental techniques including classical electrochemical methods, as well as a newly developed in-situ uv-visible spectro-electrochemical method and a new in-situ X-ray absorption (XAS) electrochemical procedure. The roles of the soluble Mn(+III) species and Bi dopants in the discharge and recharge processes have been investigated in some detail. Firstly, the presence of Bi(III) favours the formation of soluble Mn(OH)$\sb6\sp{3-}$ species in both the processes of discharge and recharge and, secondly, it appears to work as a "catalyst" for the steps involved in further reduction of Mn(OH)$\sb6\sp{3-}$ species to Mn(OH)$\sb2$ in discharge, and re-oxidation of Mn(OH)$\sb2$ to MnO$\sb2$ on recharge. Based on the optical absorbance measurements, an heterogenous mechanism in which the soluble Mn(OH)$\sb6\sp{3-}$ intermediate is involved, is directly indicated as being the preferred pathway at CM MnO$\sb2$ and operates in parallel with the so-called homogenous mechanism in both the processes of reduction of MnO$\sb2$ and re-oxidation of reduced MnO$\sb2$ materials. Thus, from the soluble Mn(OH)$\sb6\sp{3-}$ species, either Mn(OH)$\sb2$ can be deposited, on reduction, or MnO$\sb2$ re-formed on re-oxidation, on the porous electrode matrix at favourable and practically significant current-densities. The CM MnO$\sb2$ is then rechargeable over a practically useable voltage range and, importantly, over the 2-electron charge capacity. On account of the preferred heterogeneous pathway at CM MnO$\sb2,$ high (up to 6C) discharge rates can be realized at a remarkably constant plateau voltage, independent of discharge rate. In the light of the mechanism studies, the electrochemical performance of the CM MnO$\sb2$ has been studied. The CM MnO$\sb2$ cathodes were characterized by (a) good multiple rechargeability, (b) high energy and power densities, (c) achievement of high charging/discharging rates at a surprisingly constant working voltage and (d) low cost. Use of an ion-selective separator enables the CM MnO$\sb2$ to be used in a secondary alkaline MnO$\sb2$ battery system with a Zn anode, and an appreciable cycle-life to be realized which is not possible if ZnO$\sb2\sp{2-}$ ions diffuse to the MnO$\sb2$ cathode. These characteristics make the secondary CM MnO$\sb2$/Zn battery system a promising candidate for electric vehicle applications and also for many other market niches currently occupied by Ni-Cd secondary and MnO$\sb2$/Zn primary cells in the consumer market.

Published
2009
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137. Investigation of the Impact of Stacking Pressure on a Double-Layer Supercapacitor

Author

MASSACHUSETTS UNIV BOSTON, Gourdin, Gerald, Meehan, Alexa, Jiang, Thomas, Smith, Patricia, Qu, Deyang, MASSACHUSETTS UNIV BOSTON, Gourdin, Gerald, Meehan, Alexa, Jiang, Thomas, Smith, Patricia, and Qu, Deyang

Abstract

There are two important steps necessary for the optimization of electrochemical double-layer capacitors (EDLC): maximizing the volumetric capacitance and minimizing the ohmic resistance. The application of force during the assembly of an EDLC cell is one way to achieve this optimization. The effect of the application of force on the performance characteristics of EDLC cells, assembled using porous activated carbon electrodes, was determined. It was shown that applying force to the body of the cell during assembly only provides a significant increase in the performance of the EDLC with the initial application. The results showed that any increase in the applied force beyond that initial stage does not result in a subsequent increase in performance and can result in a substantial decrease in the performance characteristics of the EDLC cell. Furthermore, it was concluded that the substantial decrease shown was attributed to an alteration of the physical structure of the porous material, which produced significant decreases in the accessible surface area and the material resistance of the activated carbon electrodes., Pub. in Journal of Power Source, p1-7, 2010.

Published
2010

141. Investigation of the Li–S Battery Mechanism by Real-Time Monitoring of the Changes of Sulfur and Polysulfide Species during the Discharge and Charge

Author

Zheng, Dong, Liu, Dan, Harris, Joshua B., Ding, Tianyao, Si, Jingyu, Andrew, Sergei, Qu, Deyu, Yang, Xiao-Qing, and Qu, Deyang

Abstract

The mechanism of the sulfur cathode in Li–S batteries has been proposed. It was revealed by the real-time quantitative determination of polysulfide species and elemental sulfur by means of high-performance liquid chromatography in the course of the discharge and recharge of a Li–S battery. A three-step reduction mechanism including two chemical equilibrium reactions was proposed for the sulfur cathode discharge. The typical two-plateau discharge curve for the sulfur cathode can be explained. A two-step oxidation mechanism for Li2S and Li2S2with a single chemical equilibrium among soluble polysulfide ions was proposed. The chemical equilibrium among S52–, S62–, S72–, and S82–throughout the entire oxidation process resulted for a single flat recharge curve in Li–S batteries.

Published
2017
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144. Facile Synthesis of Platelike Hierarchical Li1.2Mn0.54Ni0.13Co0.13O2with Exposed {010} Planes for High-Rate and Long Cycling-Stable Lithium Ion Batteries

Author

Zeng, Jiong, Cui, Yanhui, Qu, Deyang, Zhang, Qian, Wu, Junwei, Zhu, Xiaomeng, Li, Zuohua, and Zhang, Xinhe

Abstract

Lithium-rich layered oxides are promising cathode candidates for the production of high-energy and high-power electronic devices with high specific capacity and high discharge voltage. However, unstable cycling performance, especially at high charge–recharge rate, is the most challenge issue which needs to be solved to foster the diffusion of these materials. In this paper, hierarchical platelike Li1.2Mn0.54Ni0.13Co0.13O2cathode materials were synthesized by a facile solvothermal method followed by calcination. Calcination time was found to be a key parameter to obtain pure layered oxide phase and tailor its hierarchical morphology. The Li-rich material consists of primary nanoparticles with exposed {010} planes assembled to form platelike layers which exhibit low resistance to Li+diffusion. In detail, the product by calcination at 900 °C for 12 h exhibits specific capacity of 228, 218, and 204 mA h g–1at 200, 400, and 1000 mA g–1, respectively, whereas after 100 cycles at 1000 mA g–1rate of charge and recharge the specific capacity was retained by about 91%.

Published
2016
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