Renewable Energy Global Innovations features: Facile Fabrication of Porous Ti2Nb10O29 Microspheres for High-Rate Lithium Storage Applications

Significance 

Most microelectronic devices use lithium-ion batteries as their main power source. This is due to their high power density and long life. However, current trends in microelectronic evolution demand higher energy output and therefore there is need to develop new electrode materials with improved cycling stability, high power density and higher safety. For a long time, graphite has been the main anode material despite the fact that it poses safety issues related to lithium dendrites formation. Dendrite formation is attributed to the relatively low lithium ion intercalation potential, overcharge and high current. Recently, titanium based oxides have drawn much attention. Specifically, Titanium-Niobium-Oxide (TNO) has received a higher concern due to its high theoretical capacity and a higher discharge platform. Unfortunately, fabricating TNO is quite challenging as it requires high temperatures for processing and a long reaction time. More so, the particle size and morphology, which display a significant influence on the electrochemical performance, cannot be effectively controlled.

A team of researchers led by Professor Bo Jin from the Key Laboratory of Automobile Materials, at Jilin University in China developed a facile preparation technique for fabricating TNO materials with a meticulous morphology that would ensure improved electrochemical performance. They aimed at fabricating the TNO microspheres by combining a solvothermal method with a subsequent heat-treatment. Their work is now published in International Journal of Hydrogen Energy.

The researchers commenced the proposed investigation by preparing TNO microspheres. They then characterized the structural and morphological properties of the prepared samples by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption/desorption. Eventually, they evaluated the electrochemical performance by performing cyclic voltammograms and galvanostatic discharge/charge tests.

From the electrochemical tests undertaken, the authors of this paper were able to demonstrate that the as-prepared TNO microspheres exhibited high yet stable electrochemical properties. To be precise, they noted that TNO microspheres exhibited a discharge capacity of 185 mAh g^-1 after 200 cycles at 10 C. The team therefore argued that the good electrochemical properties of TNO microspheres were ascribed to its convenient structure with porosity and small particle size, which favors the infiltration of the electrolyte, accelerates Li-ion diffusion, and improves the cycling lifetime by an efficient accommodation of the volume change upon charging/discharging.

In their study, Bo Jin and colleagues have presented a new facile technique for fabricating TNO materials of improved electrochemical performance. From the electrochemical characterization undertaken, it has been demonstrated that the as-prepared TNO microspheres exhibit a good electrochemical performance with an excellent discharge capacity and an outstanding capacity retention. This is a clear indication that the proposed TNO microspheres are prospective high power anode materials application which may react with lithium at voltages above 1.0 V vs. Li⁺/Li.

Ti₂Nb₁₀O₂₉ – Titanium-Niobium-Oxide (TNO)

About the author

Associate Professor Bo Jin is currently serving in College of Materials Science and Engineering at Jilin University, China. He joined Jilin University in 2003, having received M.S. and Ph.D. degrees in 2003 and 2008, respectively, at Chonnam National University, Korea, both in Department of Electrical Engineering. He then continued his career as a postdoctoral fellow at Key Laboratory of Automobile Materials, Ministry of Education, Jilin University for two years.

Asso. Prof. Jin’s research is focused on energy storage & conversion, and seeks to prepare electrode materials in micro- and/or nanostructures for the purpose of improving electrochemical performance of lithium batteries.

Reference

Guangyin Liu, Bo Jin*, Keyan Bao, Ying Liu, Haiquan Xie, Min Hu, Ruixue Zhang, Qing Jiang. Facile fabrication of porous Ti₂Nb₁₀O₂₉ microspheres for high-rate lithium storage applications. International Journal of Hydrogen Energy volume 42 (2017) pages 22965-22972.

 

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Renewable Energy Global Innovations features: Thermodynamic Analytical Solution and Exergy Analysis for Supercritical Compressed Air Energy Storage System

Significance Statement

Globally, research and development of electrical energy storage is rapidly gaining popularity amongst scholars. These can be attributed to the fact that it plays a crucial role in the areas of: renewable energy power generation, smart grid, off-peak electricity utilization, distributed energy system, micro-grid and energy internet. At present, several power storage techniques exist. Amongst these techniques, compressed air energy storage system is the most promising technique given its highly desired advantages that include: low initial, operational and maintenance costs, environmental friendliness, deployable at large scale, high efficiency and long lifetime. Conversely, conventional compressed air energy storage systems are subject to limitations such as: dependency on fossil fuels and large chambers, reduced efficiency and minimal energy density, thereby, their development and large scale application is limited. To counteract these issues, researchers have sought to introduce the supercritical compressed air energy storage system.

In a recent paper published in the journal, Applied Energy, Haisheng Chen and colleagues from Institute of Engineering Thermophysics at Chinese Academy of Sciences set out to present an analytical solution for a novel compressed air energy storage system – supercritical compressed air energy storage system. Their goal was to explore the influence of key parameters on system efficiency since it is known that the coupling relationships of system processes and parameters cannot be explored thoroughly with numerical approaches.

The research team commenced their empirical work by obtaining and calculating the exergy destruction for each part of the model. A method of sectional treatment of the system and Taylor expansion ignoring higher order terms was also carried out so as to obtain the variation of system efficiency with key parameters through the analytical solution as well as the reasons for such variation.  Eventually, a sensitivity analysis and an exergy analysis were undertaken for supercritical compressed air energy storage system.

The authors mainly observed that the system efficiency varies linearly with isentropic efficiencies of compressor and expander, temperature difference of intercooler and reheater, pressure loss of intercooler and reheater. More so, they noted that the analytical solution was universal for compressed air energy storage system systems with similar layout to the supercritical compressed air energy storage system due to the deduced method of sectional treatment.

Concise analytical model of the supercritical compressed air energy storage system has been established in their study. A comparison of the existing compressed air energy storage system with our novel supercritical compressed air energy storage system has also been presented. It has been mainly noted that our novel system possesses great development potential with important advantages such as: eliminating reliance on fossil fuel and large chambers, increased energy storage density and high system efficiency. The outcomes of this study are impressive and can be used as reference for designing and optimizing of the supercritical compressed air energy storage system and other similar compressed air energy storage systems.

Currently, the world’s first 10MW advanced CAES plant has been built in Bijie, China by the research team, and the plant is shown in Fig.1.The test data of the plant will provide support to verify the analytical solution of this work.

About the author

Professor Haisheng Chen, BEng, PhD, is currently the deputy director of Institute of Engineering Thermophysics (IET), Chinese Academy of Sciences (CAS). He joined IET-CAS in 2009 as a “100-Talents” professor after previous employments at University of Leeds, IET-CAS, Vrije University of Brussels and Beihang University. He is also the director of China National Research Centre of Physical Energy Storage.

He has been working on fluid dynamics, heat transfer and system analysis related to energy storage and power engineering. More specifically, his research includes compressed air energy storage, thermal energy storage, internal flow of turbomachinery. He has been involved with 50+ research projects with 30+ of which being the principal investigator.

His research has led to 300+ papers, 9 book chapters and 140+ patents. The publications have received 4000+ citations according to the Thomson ISI Web of Science Database (SCI). He also acts as committee member/session chair of 8 international conferences and editorial board member for 7 peer reviewed journals. He is currently the deputy editor-in-chief of 3 peer reviewed Journals and deputy director of China Energy Storage Alliance.
chen_hs@mail.etp.ac.cn

About the author

Dr. Huan Guo is an assistant professor at Institute of Engineering Thermophysics, Chinese Academy of Sciences (CAS). He studied in Graduate University of Chinese Academy of Sciences majoring in Engineering Thermophysics, and obtained his PhD degree in 2016.

His research interest includes thermodynamic analysis and optimization methods of energy system, novel compressed air energy storage technology as well as the utilization of renewable energy. He participated in more than 10 research projects including CAS projects, sub-project of 863 project, 973 project of China.
guohuan@iet.cn

About the author

Dr. Cong Guo is an assistant professor in the Institute of Engineering Thermophysics (IET) of the Chinese Academy of Science (CAS). He has been engaged in research on Energy Storage, Organic Rankine Cycle (ORC), CHP / CCHP and solar-thermal power system. He received his Ph.D. (2015) and B.S. (2009) in Energy & Power Engineering from North China Electric Power University, P. R. China. He is the person in charge of the project of the National Natural Science Foundation of People’s Republic of China.
congguo@iet.cn

Reference

Huan Guo, Yujie Xu, Haisheng Chen, Cong Guo, Wei Qin. Thermodynamic analytical solution and exergy analysis for supercritical compressed air energy storage system. Applied Energy volume 199 (2017) pages 96–106.

 

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Renewable Energy Global Innovations features: Molecularly Imprinted Polymer Enables High-Efficiency Recognition and Trapping Lithium Polysulfides for Stable Lithium Sulfur Battery

Significance Statement

Molecularly imprinted polymers have in recent times been attracting widespread interest especially arising from their application in the development of tools for organic synthesis as a result of their high specificity, easy availability, stability and low cost. These synthetic polymers are fabricated by polymerizing polymerizable reagents in the presence of a template. More so, these molecularly imprinted polymers have the capability to selectively reorganize and bind target molecules with tailor made molecular recognition binding sites. With such binding capabilities, molecularly imprinted polymers have been widely applied in catalysis, analytical chemistry, water treatment, sensors and biochemistry field.

However, their potential can still be tapped by constructing different binding sites which would in turn yield new applications. Consequently, the mutual demand for clean energy from modern industries inclusive of military power supplies, civil transportation and stationary storage have placed urgent demands on the energy density of the battery. Lithium-sulfur batteries have been considered promising for powering portable electronics because they have an overwhelming advantage in energy density.

Prof. Chenglin Yan and colleagues from Soochow University in China proposed a breakthrough study on the adaptability of molecularly imprinted polymers to enable high efficiency recognition and trapping of lithium polysulfides for the development of stable lithium-sulfur battery. The researchers aimed at exploiting the ability of the molecularly imprinted polymers to recognize and target specific molecules. Their research work is now published in Nano Letters.

The researchers commenced their empirical procedure by preparing molecularly imprinted polymers with Lithium-Sulphur recognition characteristics by polymerization of acrylamide monomer molecular with tetraglyme catholyte as the target template. Polymerization by initiation at 70⁰C with azodiisobutyronitrile as the initiator was then effected. Eventually, the removal of template molecule by anhydrous dimethylformamide washing and cyclic voltammetry scans, that left featured binding sites in the polymer matrix was done.

The research team observed that the approached they used, permitted them achieve a high capacity retention of over 82% after just 400 cycles at one coulomb. They also noted that the UV/vis spectroscopy revealed low concentrations of tetraglyme catholyte in the electrolyte indicating that the molecularly imprinted polymers matrix has excellent ionic sieving ability to tetraglyme catholyte during electrochemical cycle. More so, the visual characterization gave direct evidence on the affinity and absorbability of molecularly imprinted polymers to tetraglyme catholyte, which was theoretically confirmed by density functional theory calculations.

Herein, a new strategy of using molecularly imprinted polymers as recognition sites for polysulfides in Lithium-Sulphur battery system so as to trap long chain polysulfides, has been brought forward. Acrylamide and tetraglyme catholyte molecule have been employed as functional monomer and template, respectively, for the construction of molecularly imprinted polymers material, which can constraint tetraglyme catholyte in the molecularly imprinted polymers matrix by rebinding the target molecules. Undoubtedly, the original design demonstrated here opens a new direction of the electrochemical application of molecularly imprinted polymers materials in Lithium−Sulphur batteries.

About The Author

Chenglin Yan is a full professor at Soochow University and executive director of key laboratory of advanced carbon materials and wearable energy technology in Suzhou, China. He received his PhD from Dalian University of Technology in 2008. In 2011, he became a staff scientist and a group leader at the Institute for Integrative Nanoscience at the Leibniz Institute in Dresden. In 2013, the IFW-Dresden awarded Dr Chenglin Yan the IIN Research Prize 2013 for his group’s research work. He received the Thousand Young Talents Award from the Chinese Thousand Talents Program in 2014.

Reference

Jie Liu, Tao Qian, Mengfan Wang, Xuejun Liu, Na Xu, Yizhou You, and Chenglin Yan. Molecularly Imprinted Polymer Enables High-Efficiency Recognition and Trapping Lithium Polysulfides for Stable Lithium Sulfur Battery. Nano letters 2017, volume 17, pages 5064−5070.

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Renewable Energy Global Innovations features: Titanium Oxide Nanofibers Decorated Nickel-Rich Cathodes as High Performance Electrodes in Lithium Ion Batteries

Significance Statement

Layered cathode active materials partially-substituted cobalt with transition metals and spinel active materials have been received more attention due to their cost effectiveness as compared to lithium cobaltate. Scholars have realized with time that the spinel cathode active materials are safe with limited specific capacities while layered cathode active materials possess high specific capacity with safety issues. Presently, layered cathode active materials are more preferred as cathode materials for lithium ion batteries, where nickel-rich layered cathode active materials are front runners except for safety issues, due to their high capacity. To overcome the safety issue challenge, measures, such as the substitution of the transition metal ions with other metal counter ions and the modification of the surface by means of coating with metal oxides, have been put in place.

Nanoparticle coatings on layered cathode active materials have been known to suppress the thermal reaction between the electrode and electrolyte. It has thus been seen necessary to coat or decorate the surface of the cathode since probable exothermic reaction starts from the cathode surface when the electrolyte is decomposed. Extensive studies have been performed on coating materials that inhibit this reaction but little exists about nanofibers-based metal oxides decorated on lithium nickel cobalt aluminum oxide cathode active materials.

Professor Chang Woo Lee and colleagues from the Department of Chemical Engineering, College of Engineering, Kyung Hee University, Yongin, Gyeonggi, South Korea, proposed a study to modify the surface of lithium nickel cobalt aluminum oxide particles by decorating them with titania nanofibers. They aimed at comparatively studying, with the novel lithium nickel cobalt aluminum oxide, the various quantities of titania nanofibers decorated over lithium nickel cobalt aluminum oxide (LNCA). Their research work is now published in the peer-reviewed journal, Journal of Industrial and Engineering Chemistry.

The researchers commenced their empirical procedure by obtaining titania nanofibers precursor through electrospinning a sol-gel polymeric solution. They then obtained the LNCA precursor. The titania nanofibers precursors were split at 0.5 wt%, 1 wt% and 1.5 wt% before addition of the LNCA precursor powders. The precursor powder mixture was then sintered at 465^oC for three hours and then calcined at 850^oC for five hours in air. The team then conducted an X-ray photoelectron spectroscopic analysis to investigate the chemical composition of the cycled electrode surface. The team eventually obtained cathode samples and used them to conduct differential scanning calorimetry scans.

The authors also observed that the increase of titania nanofibers decoration over 1wt% ratio showed negative effect during the electrochemical process, as observed using electrochemical impedance spectra for the 1.5wt% titania nanofibers-decorated LNCA. Hence usage of titania nanofibers more than 1wt% was excluded from detailed investigation. The surface modification of LNCA electrodes by 1wt% titania nanofibers decoration greatly increased the cycleability, capacity, and thermal stability of lithium ion batteries at room temperature as well as at elevated temperature. Among titania nanofibers decorated LNCAs, the 1wt% titania nanofibers -decorated LNCA cathode had shown better capacity retention of 89.2% and 81.9% at room and elevated temperature, respectively.

The results of their study second the suggestion of the applicability of titania nanofibers as surface modifiers in order to enhance the electrochemical and thermal properties of lithium ion batteries. Moreover, it has been seen that the capability of the titania nanofibers-decorated LNCA was enhanced compared to that of the pristine LNCA. The onset temperature of thermal decomposition is also shifted towards higher temperature for titania nanofibers-decorated LNCA electrodes than pristine LNCA electrodes.

About The Author

Professor Chang Woo Lee is currently serving in the Department of Chemical Engineering and also Director of Center for the SMART Energy Platform at Kyung Hee University, S. Korea. He joined Kyung Hee University in 2006, having received B.S. and M.S. degrees in 1994 and 1996, respectively, at Kyung Hee University, S. Korea and a Ph.D. at the Illinois Institute of Technology, USA in 2003, both in the field of Chemical Engineering. Prof. Lee has also worked as a Senior Researcher at Korea Electrotechnology Research Institute (KERI) since he obtained Ph.D. degree. He was appointed as a Visiting Scholar in the Materials Department, College of Engineering and Applied Science, at the University of Wisconsin-Milwaukee, for the 2012-2015 academic year.

Prof. Lee’s research is focused on electrochemical energy storage & conversion and seek to synthesize energy materials in metallic micro- and/or nanostructures for the purpose of improving electrochemical properties in the area of batteries, supercapacitors, and fuel cells.

About The Author

Mr. Kijae Kim is currently a Ph.D. candidate at the Department of Chemical System Engineering in The University of Tokyo, Japan. He received his B.S. and M.S. degrees in the Department of Chemical Engineering at Kyung Hee University, S. Korea. He has studied synthesis and analysis of electrode materials for energy storage devices for the M.S. under the supervision of Prof. Chang Woo Lee. He has published several scientific papers and received the Best Poster Award from Korean Battery Society and bachelor graduation with honors.

About The Author

Dr. K. Prasanna obtained his B.S. and M.S. degrees from Bharathidasan University and Anna University in India, respectively. He then joined as assistant professor in the Department of Biotechnology at Vinayaka Missions University, Salem. He joined as a Ph.D. student under Professor Chang Woo Lee in the Department of Chemical Engineering at Kyung Hee University, S. Korea in September, 2011 and received his Ph.D. degree in Aug, 2015. He then continued his career as a postdoctoral fellow at Electrochemical Energy Storage and Conversion Laboratory, Kyung Hee University for two years. Currently he is working as a postdoctoral fellow in Technical University of Denmark, under the H.C. Ørsted Postdoc programme, co-funded by Marie Skłodowska-Curie Actions. His recent research interests include supercapacitors, Li-ion batteries, Mg-ion batteries, and Metal-air batteries.

About The Author

Dr. T. Subburaj received his Ph.D. at Kyung Hee University, South Korea in 2015 under the supervision of Prof. Chang Woo Lee in the Department of Chemical Engineering and he received his M.S. degree from the Department of Chemical Engineering, Anna University, Chennai, India in 2010. Currently, he works with Prof. Chung-Hsin Lu as a MoST Postdoctoral Scholar at National Taiwan University, Taiwan. His research interests focus on synthesis and applications of nanostructured and hybrid materials for electrochemical energy storage and conversion, including rechargeable batteries, electrochemical capacitors, and solar cells.

About The Author

Dr. Yong Nam Jo received his M.S. and Ph.D. degrees in Department of Chemical Engineering from Kyung Hee University, S. Korea in 2013 and 2017, respectively, under the supervision of Prof. Chang Woo Lee. He received Best Thesis Award for the Ph.D. from the President of Kyung Hee University and also several Best Poster and Outstanding Paper Awards from domestic and international conferences. He is currently working as a postdoctoral fellow at the Center for SMART Energy Platform at Kyung Hee University. His current research is focused on enhancement of materials for energy storage and conversion with Li-ion batteries and metal-air batteries.

Reference

Subburaj, Yong Nam Jo, K. Prasanna, Ki Jae Kim, Chang Woo Lee. Titanium oxide nanofibers decorated nickel-rich cathodes as high performance electrodes in lithium ion batteries. Journal of Industrial and Engineering Chemistry, volume 51 (2017) pages 223–228.

 

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Renewable Energy Global Innovations features: Ultralong cycling stability of carbon-nanotube/LiFePO4 nanocomposites as electrode materials for lithium-ion batteries

Significance Statement

The long cycle stability of electrode materials is required for lithium-ion batteries used in electric vehicles.  The effective conductivity and the stable structure of these electrode materials are critical to the cycle stability. The olivine-type lithium iron phosphate is one such electrode material, that is able maintain its crystal structure stability, which in turn minimizes volumetric changes in the charge-discharge process. Advances geared towards improving the effective conductivity have been made by increasing the electrical conductivity of lithium iron phosphate electrode materials through applying carbon nanotubes in these materials. However, the preparation of uniformly distributed carbon nanotubes in the lithium iron phosphate faces many obstacles that some synthetic techniques have tried to address.

In a recent paper published in Electrochimica Acta and led by Professor Tong De Shen and Professor Yu Qing Qiao at Yanshan University developed an innovative technique of coating carbon nanotubes with polyvinylpyrrolidone, which effectively combines the carbon nanotubes and lithium iron phosphate to produce a nanocomposite that exhibits an excellent ultralong cycling stability and high-rate capacity.

The research team made polyvinylpyrrolidone-carbon nanotube-water dispersions which were subjected to repeated freezing and thawing to produce modified carbon nanotubes. They then prepared lithium iron phosphate particles which were then combined with the modified carbon nanotubes to produce lithium iron phosphate-carbon nanotube electrode material. The polyvinylpyrrolidone acts as a dispersant, surfactant and binder. The nanocomposite was heated at 600 ^OC in the presence of nitrogen to eliminate the polyvinylpyrrolidone, after which the carbon nanotubes were manipulated to form uniform three-dimensional conductive networks in lithium iron phosphate electrode.

The authors deduced that the polyvinylpyrrolidone coating process reduces the amount of disordered and defected carbon atoms. It was observed that the synthesized lithium iron phosphate exhibits a single phase of orthorhombic olivine-type structure. The observed average crystallite size of the lithium iron phosphate was about 30 nm.

The research team observed that the discharge capacity of the lithium iron phosphate electrode material with 3% carbon nanotubes, is about 9.4% greater than the lithium iron phosphate without any carbon nanotubes.

From the impedance spectra, it was deduced that there was a lower charge-transfer resistance in the electrode with 3% carbon nanotubes, which was about a third of the charge transfer resistance of the electrode without any carbon nanotubes. This shows that about 3% carbon nanotubes can develop a conductive network that is highly efficient, and therefore the lithium iron phosphate electron conduction is significantly improved.

The authors noted that the lithium iron phosphate electrode material with 3% carbon nanotubes had a lithium ion diffusion coefficient that was 25 times faster as compared with that without any carbon nanotubes, which shows that the carbon nanotubes effectively improve the diffusion of lithium ions. Also, the conductivity of the former is about 7.5 times higher as compared with the latter.

Further analysis showed excellent cycle stability of the lithium iron phosphate electrode containing about 3% carbon nanotubes, such that after about 1000 charge/discharge cycles at a discharge rate of 10C, there was only 1.6% loss in capacity, and a discharge capacity that was as high as about 123.0 mAhg^-1. Additionally, the nanocomposite was observed to have a cycling lifetime of 3400 cycles as compared with 750 cycles for the commercially available lithium iron phosphate electrode materials.

Loss in capacity of various LiFePO4/carbon nanocomposites with 1D to 3D carbon as conducive agents after 1,000 cycles at a discharge rate of 10C. PVP: polyvinylpyrrolidone; CNSs: carbon nanosheets; CFs: carbon fibers; RGO: reduced graphene oxide; GN: graphene; N-GN: nitrogen-doped graphene; GNO: graphene oxide.

About The Author

Prof. Qiao is a professor with the College of Environmental and Chemical Engineering at Yanshan University. She received her Ph.D. degree in 2006 from Yanshan University. Her current research interests are on the processing and performance of nanostructured electrode materials for energy storage and conversion. She has authored/coauthored more than 50 papers.

About The Author

T.D. Shen is a professor with the Coellege of Materails Science and Engineering at Yanshan University. He obtained the National 1000 Talents award in 2010. He received his B. S. degree in Materials Science from the Zhejiang University in 1986 and his Ph.D. degree in Material Sciences from the Institute of Metal Research, Chinese Academy of Sciences in 1995. He was a postdoctoral associate from 1995 to 1998 and a Staff Member from 1998 to 2008, both with the U.S. Department of Energy’s (DOE) Los Alamos National Laboratory (LANL) in Los Alamos, New Mexico.

His current research interests are on the processing, characterization, and physical/mechanical/electrochemical properties of nanocrystalline, nanostructured, and amorphous materials. He has authored/coauthored more than 100 papers.

Reference

Yu Qing Qiao, Wei Liang Feng, Jing Li, Tong De Shen. Ultralong cycling stability of carbon-nanotube/LiFePO₄ nanocomposites as electrode materials for lithium-ion batteries. Electrochimica Acta 232 (2017) 323-331.

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Renewable Energy Global Innovations features: Improvement of Cyclability of Li-Ion Batteries Using C-Coated Si Nanopowder Electrode Fabricated from Si Swarf with Limitation of Delithiation Capacity

Significance Statement

Silicon is among the most promising building blocks for negative electrode active materials used in the fabrication of lithium ion batteries. It has been identified that silicon has a theoretical capacity of approximately 3578 mAh/g and this is much more than 372 mAh/g for graphite currently applied in standard lithium ion batteries. Silicon powder prepared by expensive approaches including laser ablation as well as plasma-enhanced chemical vapor deposition has been evaluated to mitigate the stress of silicon caused by the change in size in the course of delithiation and lithiation.

Despite the outstanding attributes of silicon, silicon nanopowder still suffers several problems to use as lithium ion battery electrode active materials. Silicon nanopowder experiences volume expansion of about four times during lithiation, and considerable shrinkage during delithiation. This results in the formation of cracks in the nanopowder. Electrical isolation of the silicon nanopowder is another problem, which leads to an increase in internal resistance, low columbic efficiency and poor cyclability.

In a bid to suppress the volume change of the silicon powder, the lithiation capacity has been limited at 1500 mAh/g and 1200 mAh/g after considerable delithiation. Nevertheless, the impact of limitation of the delithiation capacity after deep lithiation on cyclability has not been studied.

Researchers led by Professor Taketoshi Matsumoto from Osaka University fabricated lithium ion battery half cells using silicon nanopowder generated from silicon swarf and investigated the impact of delithiation and lithiation capacity after deep lithiation at 0.01V on the performance of the cell. They found that the limitation of the delithiation capacity at 1500mAh/g improved the cyclability. Their work is published in Journal of The Electrochemical Society.

Silicon swarf was annealed in hydrogen atmosphere at 1000°C and later at 1000°C in ethylene environment to coat the silicon nanopowder with a 10nm carbon layer. The carbon coated silicon nanopowder was then mixed with polymer binders. The authors coated copper foil with the resulting slurry and the sample was dried where it was then packed as working electrode in a coin cell with a lithium foil counter electrode. The coin cell was also equipped with a polyethylene separator and an electrolyte.

The authors then cycled the cells in the cell voltage range of 0.01-1.5V in the course of 300 cycles using a battery charge-discharge unit. They set delithiation and lithiation current densities at 180mA/g for the first 5 cycles and 1800mA/g for the next 295 subsequent cycles.

The authors observed that limitation of delithiation capacity at 1500mAh/g resulted in the best cyclability. This capacity remained constant at 1500mAh/g until the 290^th cycle, where it reduced slightly to 1480mAh/g at the 300^th cycle. The overvoltage for delithiation-limited case was observed to be lower than that for lithiation-limited case. The low overvoltage as well as excellent cyclability was referenced to suppression of electrical isolation of silicon nanopowder owing to limited shrinkage of the silicon powder in the high lithium concentration zone.

Limitation of lithiation capacity at 1500mAh/g caused the delithiation capacity to remain at 1470mAh/g until the 137^th cycle and then decreased to 860mAh/g at the 300^th cycle. Electrical isolation, high overvoltage, and peeling-off of the silicon nanopowder resulted from low inter-particle contact reference to large size change of the silicon powder.

About The Author

Dr. Taketoshi Matsumoto is an Associate Professor in The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan.  His research is focused on energy related nano-materials and devices.  He has been engaged in research on Li ion batteries, luminous materials, solar cells, ultra-low power thin film transistors and MOS transistors, permanent memories, fuel cells, hydrogen storages and catalysts.

He received his Ph.D. (2001) and M.S. (1998) in Electronic Chemistry from Tokyo Institute of Technology, Japan, and B.S. (1996) in Chemistry from Keio University, Japan.  He was a research fellow of the Japan Society for the Promotion of Science, a Postdoctoral Research Associate in University of Southern California, US, a Lecturer in University of Tsukuba, Japan, a Research Associate in Institute for Molecular Science, Japan, and an Assistant Professor in Osaka University, Japan.

Reference

Katsuya Kimura, Taketoshi Matsumoto, Hirotomo Nishihara, Takatoshi Kasukabe, Takashi Kyotani, and Hikaru Kobayashi. Improvement of Cyclability of Li-Ion Batteries Using C-Coated Si Nanopowder Electrode Fabricated from Si Swarf with Limitation of Delithiation Capacity. Journal of the Electrochemical Society, 164 (6) A995-A1001 (2017).

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Renewable Energy Global Innovations features: Mesoporous single-crystal-like TiO2 mesocages threaded with carbon nanotubes for high-performance electrochemical energy storage

Significance Statement

The commercial lithium ion batteries based on graphite anode is known for its low rate performance.  Titanium oxide appears to be a promising building block for electrodes used in lithium-ion storage owing to its superior charge storage capability, environmental benignity and low cost. Unfortunately, titanium oxide has poor ionic and electronic conductivity as well as substantially low lithium-storage capacity. This poses numerous challenges towards achieving high performance devices.

Several researchers have devoted their efforts explore various polymorphs, including titanium oxide-bronze, rutile and anatase phases. Titanium oxide-bronze exhibit faster lithiation/delithiation kinematics and higher capacity as compared to rutile and anatese. However, it preparation requires harsh and complex conditions making it less attractive for large-scale preparation.

Another promising approach is through structure and morphology control.  Including composite architectures based on low-dimensional titanium oxide;  Core-shell morphologies such as carbon coated titanium oxide nanoparticles and cable like titanium oxide carbon nanotubes. The low-dimensional titanium oxide offers shortened ion diffusion length and the conductive inclusions enable effective electron transport granting these composites high electrochemical storage performance. However, the titanium oxide nanocrystals are assembled around the conductive moieties that may disassemble easily from the conductive networks and lead to rapid capacity fading. More importantly, previous works with low dimensional crystals often demonstrate very low tapping density (<0.2 g cm³) which would not be feasible in real applications.

Researchers led by professors Yunfeng Lu and Hexing Li at university of California Los Angeles and in collaboration with scientists at Shanghai University of Electric Power and Shanghai Normal University, developed a nanocomposite architecture prepared by in-situ growth mesoporous single-crystal-like titanium oxide particles threaded through by carbon nanotubes. Their work is now published in Nano Energy.

Assembled from sub-10 nm anatase nanocrystals, single-crystal secondary particles in micrometer scale with mesoporous features and threaded by carbon nanotubes (CNTs) was synthesized by one step sovolthermal method. No further high temperature heating required.

The electrochemical performance of the composite was characterized by using coin-type cells with loading of 2-3 mg/cm². From the galvanostatic charge/discharge curves, the composite achieved 260 mAh g^-1 at 0.5C which is among the highest capacities of the reported TiO₂ anode. A relatively short voltage plateau (phase charge) with a long slopping “tail” (200 mAh g^-1) indicated a high surface charge contribution. Even at an extremely high rate of 30C, it still delivered 120 mAh g^-1.  The researchers also investigated the composite performance at extended voltage window from 0.005-2.7V. Such lower voltage was often avoided due to formation of solid electrolyte interface (SEI) and further lithium insertion would challenge the robustness of the active materials. With sub-10nm building nanocrystals, the composite achieved 440 mAh g^-1 at 50mA g^-1. As seen from the cyclic voltammetry diagram, such “extra” capacity below 1V main came from surface contribution. Above 1V to 2.7V, the composite still maintained the reversible anatase phase confirmed by the in-situ X-Ray Diffraction. Overall, high rate charge discharge at 2000 mA g^-1  for 1000 cycles was demonstrated with negligible capacity fading. The scanning electron microscopy after cycling confirmed the structure was maintained

By threading single crystal -like  titanium oxide mesocrystals with carbon nanotubes, the research team was able to realize high rate anode composite for lithium ion batteries. The composites with iso-orientated primary nanocrystals has successfully enhanced the rate and cycling performance. Importantly, the tapping density (1.12 g cm³) is much closer to the real applications which was often ignored in nano-scale engineering. This method might bring some guidelines for the functional materials and device towards highly efficient energy storage systems.

Tapping-Density-Comparison

Synthesis-Scheme

Design-Stratagies

About The Author

Yiting Peng obtained her Ph.D. degree under the co-supervision of Professor Hongbin Geng in Harbin institute of technology and Professor Yunfeng Lu in University of California, Los Angeles at 2013. She is now a Lecturer at Shanghai University of Electric power.

Her research mainly focused on composition and architecture design towards supercapacitors, lithium-ion batteries, advanced Lead-acid batteries.

About The Author

Zaiyuan Le received his BASc degree in Materials Science and Engineering from University of Toronto (Canada) in 2012. He is currently a Ph.D. candidate under supervision of Prof. Yunfeng Lu in Chemical and Biomolecular Engineering at University of California, Los Angeles.

His research interests lie in titanium oxide based lithium and sodium based energy storage, including rechargeable batteries and hybrid capacitors.

About The Author

Meicheng Wen received his M.S. degree in physical chemistry from Shanghai Normal University under supervision of Professor Hexing Li and Associate Professor Dieqing Zhang in 2013 and his Ph.D. degree in engineering from Osaka University under the supervision of Professor Hiromi Yamashita in 2016. He is currently a specially appointed Assistant Professor in the Division of Materials and Manufacturing Science at Osaka University.

About The Author

Dieqing Zhang received her PhD (2010) in environmental chemistry from The Chinese University of Hong Kong under Prof. Jimmy C. Yu. Currently is an Associate Professor in Department of Chemistry at Shanghai Normal University. She is now engaged in the design and fabrication of novel and efficient photocatalysts for nitric oxide oxidation/reduction, hydrogen production and CO₂ reduction, etc.

About The Author

Zheng Chen received his Ph.D. at UCLA in 2012 under the supervision of Prof. Yunfeng Lu in the Department of Chemical and Biomolecular Engineering. From 2013-2016, he was a postdoctoral associate working with Prof. Zhenan Bao in Chemical Engineering and Prof. Yi Cui in Materials Science and Engineering at Stanford University.

Currently as Assistant Professor at Department of NanoEngineering at UCSD, his research focuses on functional polymers, nanostructured materials and hybrids for applications in electrochemical energy, flexible devices and sustainable environment.

About The Author

Hao Bin Wu received his BS degree in chemistry from Fudan University (China) in 2010. He obtained his Ph.D. degree in materials science from Nanyang Technological University (Singapore) under the supervision of Professor Xiong Wen (David) Lou in 2015.

Currently he works with Professor Yunfeng Lu as a Postdoctoral Scholar at University of California, Los Angeles. His research interests focus on synthesis and applications of nanostructured and hybrid materials for electrochemical energy storage and conversion, including rechargeable batteries, electrochemical capacitors and electrocatalysis.

About The Author

Prof. Hexing Li received his doctor degree from Fudan University. Now, he is working as the president of Shanghai University of Electric Power and the director of Chinese Education Ministry Key Laboratory and International Joint Laboratory on Resource Chemistry, as well as an Associated Editor of Appl. Catal. B Environ.

His research interest is photocatalysis for environmental cleaning and thermocatalysis for green chemistry. Up to now, more than 395 papers and 3 monographs have been published. His H-index is 59.

About The Author

Yunfeng Lu obtained his Ph.D. degree under the supervision of Professor C. Jeffrey Brinker in University of New Mexico at 1998. He became a Brown Chair Professor at Tulane University in 2005 and now he is a Professor at University of California, Los Angeles.

His research interest focused on composition and architecture design towards energy storage and conversion, including supercapacitors, lithium and sodium-ion batteries, lithium metal batteries, flow batteries, intermediate-temperature fuel cells, and effective methane conversion.

Reference

Yiting Peng, Zaiyuan Le, Meicheng Wen, Dieqing Zhang, Zheng Chen, Hao Bin Wu, Hexing Li, Yunfeng Lu. Mesoporous single-crystal-like TiO2 mesocages threaded with carbon nanotubes for high-performance electrochemical energy storage. Nano Energy, volume 35 (2017), pages 44–51.

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Renewable Energy Global Innovations features: Potential threshold of anode materials for foldable lithium-ion batteries featuring carbon nanotube current collectors

Significance Statement

Energy storage devices present a noteworthy challenge in creating a robust deformable system because they must be flawlessly integrated with intelligent wearable devices such as stretchable circuits, epidermal health electronics and flexible displays. The lithium ion batteries are the preferred source of power for such deformable functional devices if they can be compressed, rolled, stretched, buckled and folded. However, selecting an active material for convectional lithium ion batteries poses a major challenge since it easily delaminates or fractures upon being deformed. Moreover, the high-density attribute of the metal restricts the energy density of the lithium ion batteries. Therefore, replacing the metallic foils with light weight, flexible and highly conductive current collector can impart flexibility to the devices and may also rise the energy density of lithium ion batteries.

In a recent paper published in Journal of Power Sources, researchers led by professor Zi Ping Wu at Jiangxi University of Science and Technology in China proposed a study on Potential threshold of anode materials for foldable lithium-ion batteries featuring carbon nanotube current collectors. They aimed at providing a principle for the selection of an active material based on flexible current collectors for foldable lithium ion batteries.

First the research team prepared flexible carbon nanotube macro-film composed of carbon nanotube bundles by chemical vapor deposition. They then fabricated the electrodes by using slurry-based preparation technique. Next, they assembled coin-type half-cells in an argon filled glove box with bare flexible carbon nanotube macro-film disks as working electrodes, lithium titanium oxide and GPE that use copper foil as current collector for loading, lithium cobalt oxide that uses aluminum foil as current collector and lithium metal as reference electrode. These cells were then assembled in a de-humidified room with moisture content less than 2%. Eventually, cyclic voltammetry measurements were carried out using standard electrochemical instrumentation.

From the set up described it was observed that the electrochemical behavior characteristic for the two electrodes, lithium cobalt oxide -aluminum and lithium cobalt oxide – Flexible carbon nanotube macro-film was similar except for the current of oxidation peak. No notable difference was observed in their CV curves and galvano-static discharge/charge profiles. It was noted that when the anode material had a potential higher than 0.9V, good performance of the flexible carbon nanotube macro-film based foldable lithium ion batteries is obtained since the lithium ion passed the potential threshold and the flexible carbon nanotube macro-film retained its electrochemical inactivity. However, if the potential anode is lower than 0.9V several free lithium ions will be constrained. In return the capacity of the flexible carbon nanotube macro-film based electrode will be lowered and the cycling performance will be poor.

The flexible carbon nanotube macro-film based foldable lithium ion batteries generally performed well experimentally. Therefore, it is expected that the mechanism of potential threshold of anode materials will provide new impetus to both industry and academia to explore the development of lithium ion batteries in flexible and foldable energy storage devices.

About The Author

Dr. Wu is an associate professor at Jiangxi University of Science and Technology. He currently specializes on carbon nanotube macro-films for flexible batteries and electromagnetic shielding applications. Under his guidance, a folding insensitive and high energy density lithium-ion battery has been reported in 2015.

Reference

Qing Hui Wang, Sheng Wen Zhong, Jing Wei Hu, Ting Liu, Xian Yan Zhu, Jing Chen, Yin Yan Hong, Zi Ping Wu. Potential threshold of anode materials for foldable lithium-ion batteries featuring carbon nanotube current collectors. Journal of Power Sources volume 310 (2016) pages 70-78.

Show Affiliations

1. School of Materials Science and Engineering, Jiangxi University of Science and Technology, 86 Hong Qi Road, Ganzhou 341000, PR China
2. School of Materials Science and Engineering, Guilin University of Technology, 12 Jiangan Road, Guilin 541004, PR China

 

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Renewable Energy Global Innovations features: Coupled electrochemical thermal modelling of a novel Lithium-ion battery pack thermal management system

Significance Statement

Thermal management systems are crucial for a lithium ion battery pack. High performance, safe operation and longer battery life can be achieved when the battery is operated within a small temperature variation around the room temperature. This demands the application of a thermal management system so as to maintain a safe temperature operation range. Air cooling is among the simplest cooling systems but drawbacks such as low thermal conductivity and low heat capacity discourages its use. This has therefore motivated the development of new liquid coolant thermal management systems for the lithium ion battery pack used mainly for vehicular propulsion.

In a recent paper published in Applied Energy, Suman Basu and colleagues presented a new coupled electrochemical thermal modelling of Lithium-ion battery pack thermal management system. Their aim was to develop an economically feasible, safe, compact and high performance thermal management system for the lithium ion battery pack mainly used in the electric vehicles.

First, the research team designed the novel liquid cooling based thermal management system for the lithium ion pack which comprised of commercially available cells in 6S5P formation (Fig. 1). The design ensured safety and compactness by thermally connecting the cells with conduction elements made of aluminum which are used to conduct the heat away. They then developed a coupled electrochemical thermal model for the battery pack and simulated it. A three-dimensional computational fluid dynamics was then developed and validated based on numerical model for the electrochemical thermal modeling of the battery pack at high accuracies. The performance of the battery pack under various arrangements and operating conditions was then investigated and reported.

Fig1: Geometry of the Li-ion battery pack and thermal management system.

They observed that the heat generation from the cells is the function of local temperature and reaction rate which had to be resolved so as to predict the thermal performance correctly. The three-dimensional electrochemical model was used to obtain a complete description of the heat generation from the battery pack system. The system also helped in validation against experimental results used to evaluate the performance of the thermal management system under various operating conditions. Thermal contact resistances at the conduction element-channel and cell-conduction element interfaces were observed to be the main hindrance to the operation of this thermal management system (Fig. 2).

Excellent agreement has been achieved between the experimental measurements and simulation predictions from the tests conducted. Application of the thermal interface material at the interfaces is seen to reduce the contact resistances and improve the heat transfer. The thermal management system is seen to cool the pack effectively even at minimal coolant flow rates. At high discharge rate and low coolant flow rate, the maximum temperature rise is kept at a small range. Therefore, this novel and compact thermal management system can work effectively under stringent conditions and is a suitable candidate for electric vehicle battery pack.

Fig 2: Temperature contours of the first set of parallel cells in the pack as a function of contact resistance at the solid-solid interfaces at 0.9 C discharge rate and 0.2 ms-1 flow velocity.

About the author

Suman Basu received his PhD from the Pennsylvania State University working in Electrochemical Engine Center with Prof. C. Y. Wang. He is working in Li-ion battery modelling and simulation project in Samsung R&D India – Bangalore. His main interests are in electrochemical energy storage system, Li-ion battery management system including thermal management and capacity fade, two-phase flow modeling and heat transfer in PEMFC. He received his bachelors and masters degree in Mechanical Engineering from Jadavpur University, Kolkata and Indian Institute of Technology, Kanpur respectively.

Reference

Suman Basu¹, Krishnan S. Hariharan¹, Subramanya Mayya Kolake¹, Taewon Song², Dong Kee Sohn², Taejung Yeo². Coupled electrochemical thermal modelling of a novel Li-ion battery pack thermal management system. Applied Energy volume 181 (2016) pages 1–13

Show Affiliations

1. Next Generation Research (SAIT-India), Samsung R&D Institute India-Bangalore, #2870 Phoenix Building, Bagmane Constellation Business Park, Outer Ring Road, Doddanekundi Circle, Marathahalli Post, Bangalore 560 037, India
2. Energy Material Lab, SAIT, Samsung Electronics, Republic of Korea

 

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Renewable Energy Global Innovations features: On-board capacity estimation of lithium iron phosphate batteries by means of half-cell curves

Significance Statement

Battery management systems face usually different challenging tasks. One of the most important concerns the on-board evaluation of the total battery capacity in electric and hybrid electric vehicles. This is due to the fact that the battery capacity has to be computed without necessarily discharging the battery entirely starting from a fully charged state. In fact, during the vehicle operations, the discharge process is mainly carried out in a dynamic condition under variable current rates and temperature. Selecting a method to be used in this process has poised a challenge mainly for lithium iron phosphate cells.

In a recent paper published in Journal of Power Sources, Andrea Marongiu and colleagues estimated lithium iron phosphate batteries capacity by means of half-cell curves. Their research mainly focused on developing a new approach that is based on the detection of the actual degradation mechanisms by collecting plateau information.

First, a model was developed and introduced which described the characteristics of the electrode voltage curves of the lithium iron phosphate cells and the impact of aging on the full cell voltage. A description of the main degradation mechanisms that can occur during the lifetime of the lithium iron phosphate cell and a model capable of describing the effects of degradation on the electrode and on the full cell voltage curves were presented. The research team then introduced a new battery management system structure with an implemented algorithm for on-board capacity estimation.

The results reported in the work show that not all the information from the voltage plateaus has to be collected at the same time although the collection phases have to be over short duration intervals. The new introduced algorithm is simple to parametrize, since only the characteristics of the cell in a fresh state are needed, in terms of stoichiometry and half-cell voltage curves. Eventually, both during charge and discharge the algorithm is able to correctly track the actual battery capacity with an error of approximately 1%. Also, the new proposed BMS structure is designed in a way that part of the novel methodology can run offline (not-real time). This means that the approach can be implemented in cheap microcontrollers, as it does not need to be executed in real time.

The method presented in this paper is valid for lithium iron phosphate /G cells, primarily due to the need of collecting data of plateaus, which is one of the main features of this type of cells. Nevertheless, the proposed model and the approach shown in the literature have a general formulation, which demonstrate the benefit of the tracked aging information for different lithium-ion technologies and additional application scopes.

About The Author

Andrea Marongiu received his master degree in Electrical Engineering from the Cagliari University, Italy, in 2010. In March 2011 he joined the Institute for Power Electronics and Electrical Drives (ISEA) at the RWTH Aachen University, Germany, as a research associate and PhD student.

His areas of interest were lithium-ion batteries with special focus on lithium iron phosphate-based cells, EV batteries and the related on board Battery Management System. From August 2016 to February 2017 he worked as Lead Engineer Battery Algorithm at National Electric Vehicle Sweden AB in Sweden. Since March 2017 he works as battery expert at IK4-CIDETEC in Spain, in the field of hybrid system for automotive applications.

About The Author

Dirk Uwe Sauer currently holds the title of professor for electrochemical energy conversion and storage systems at the Institute for Power Electronics and Electrical Drives (ISEA) & Institute for Power Generation and Storage Systems (PGS) at E.ON ERC RWTH Aachen University as well as Principle Investigator at Helmholtz Institute Münster Ionics in Energy Storage.

Originally, professor Sauer studied physics at University of Darmstadt, Germany, and upon graduating in 1994 became a scientist, project coordinator and head of group at Fraunhofer Institute for Solar Energy Systems ISE in Freiburg until 2003. While at the Fraunhofer Institute for Solar Energy Systems ISE, Professor Sauer headed the groups for storage systems, the interdisciplinary team for off-grid and remote power supply-systems, and was the managing director of the club for rural electrification. In 2003, he was appointed as junior professor at RWTH Aachen University, in 2009 he was appointed as professor, and in 2012 he was appointed as full professor for electrochemical energy conversion and storage systems at RWTH Aachen University. In 2010, he became a founding partner of P3 Energy & Storage, and in 2015 he became a founding partner of both BatterieIngenieure GmbH as well as eBusplan GmbH. Together with Prof. Martin Winter he is chairman of the conference “Kraftwerk Batterie / Advanced Battery Power”.

About The Author

Nsombo Nlandi has studied computer science at the RWTH Aachen University in Germany and received his master degree in 2009. In 2013 he got his second master degree in electrical engineering at the University of Hagen, Germany. From 2009 to 2016 he worked as researcher associate at the Institute for Power Electronics and Electrical Drives (ISEA), where he pursued his PhD. His research interests were mainly focused on software for battery diagnostic, namely the development of intelligent Battery Management Systems (BMS). Since August 2016 he has joined National Electric Vehicle Sweden AB (Sweden) as Lead Engineer for Embedded Systems.

About The Author

Yao RONG was born in Nanjing, China. He received his bachelor degree in Electrical Power Engineering and Automation from the Shanghai Jiao Tong University in 2007. Afterwards he studied at the RWTH Aachen University the master course of Electrical Power Engineering. During this period he wrote his master thesis at the Institute for Power Electronics and Electrical Drives (ISEA), working meanwhile a student assistant. He obtained his master degree in 2014. In 2015 he joined Jiangsu Marathon Investment Management Co., Ltd In China, where he works currently as chief research officer.

References

Andrea Marongiu^1,3, Nsombo Nlandi^1,3, Yao Rong^1,3, Dirk Uwe Sauer^1,2,3. On-board capacity estimation of lithium iron phosphate batteries by means of half-cell curves.  Journal of Power Sources volume 324 (2016) pages 158-169.

Show Affiliations

1. Electrochemical Energy Conversion and Storage Systems Group, Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen University, Jägerstrasse 17/19, D-52066 Aachen, Germany
2. Institute for Power Generation and Storage Systems (PGS), E.ON ERC, RWTH Aachen University, Mathieustrasse, D-52074 Aachen, Germany
3. Jülich Aachen Research Alliance, JARA-Energy, Germany

 

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Renewable Energy Global Innovations features: Fe-Based Metal-Organic Framework and Its Derivatives for Reversible Lithium Storage

Significance Statement

Researchers led by Professor Cai Shen from Ningbo Institute of Materials Technology and Engineering in China used iron-based metal organic framework as an anode for the first time in lithium ion battery applications. The research work is now published in Journal of Materials Science & Technology.

They synthesized MIL-88B_(Fe) as the iron-based metal organic framework followed by production of Fe₂O₃ and Fe₃O₄/C  composites via thermal treatment. In current density of 200mAg^-1, the columbic efficiency increases up to 100% of the 100th cycle with an increase in discharge and charge capacity. After 200 cycles, the cyclic performance of the metal organic framework was up to 700mA hg^-1 and reduced to an approximate value of 680mA hg^-1 after 500 cycles, showing a high cyclic stability. An increase in current density up to 2.0Ag^-1 maintained a capacity as high as 475mA hg^-1, indicating a high cyclic performance despite reduction in discharge capacity of the metal organic framework.

Following the successful preparation of Fe₂O₃ and Fe₃O₄/C composites, They found that the metal oxide of Fe₂O₃ had a discharge capacity of 460mA hg^-1 at a current density of 0.5C which remained after 100th cycle with a columbic efficiency of 100%. The discharge capacity was 180mA hg^-1 at a current density of 5C, but attained a discharge capacity of 700mA hg^-1 when current density was reversed to 0.2C, indicating high cycling stability.

For composites of Fe₃O₄/C, discharge capacity was approximately 800mA hg^-1 in the 100th cycle and attained a value of 928mA hg^-1 when the number of cycles was 200. As current density increases to 5C, a steady discharge capacity was attained, showing high cycling stability.

The iron-based metal organic framework MIL-88B(Fe) coupled with metal oxides of Fe₂O₃  and Fe₃O₄/C  composites both demonstrated high capacity and excellent cycling stability.

About The Author

Dr. Cai Shen received his Ph. D. in Chemistry from the University of St Andrews at UK in 2008. Before joining Ningbo institute of Materials Technology and Engineering, Chinese Academy of Science as an Associate Professor, he worked as a postdoc fellow in the University of Maryland (USA) and Aarhus University (Denmark).

His current research area involves lithium-ion batteries and the application of scanning probe microscopy techniques (in-situ electrochemical STM, AFM) to investigate the surface chemistry of nano materials.

Journal Reference

Jin, Y., Zhao, C., Lin, Y., Wang, D., Chen, L., Shen, C. Fe-Based Metal-Organic Framework and Its Derivatives for Reversible Lithium Storage, Journal of Materials Science & Technology (2016), doi: 10.1016/j.jmst.2016.11.021.

Chinese Academy of Sciences, Ningbo Institute of Materials Technology & Engineering, Ningbo 315201, China.

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Renewable Energy Global Innovations features: Hydrothermal Synthesis of Manganese Oxide Encapsulated Multiporous Carbon Nanofibers for Supercapacitors

Significance Statement

Hydrothermal carbonization is a newly developed technique used in generating carbon nanofibers. Despite its many advantages have certain challenges due to its undesired surface morphology and singly resultant production of microporous carbon. A better use of the hydrothermal carbonization technique in fabricating multiporous carbon nanofibers with the encapsulation of certain metal oxides is of relevance to areas where supercapacitors, in view of energy storage application is needed. Hence, various methods need to be implemented in improving the hydrothermal carbonization technique in order to achieve this feat.

Researchers led by Professor Yong Wang from Zhejiang University in China developed a new dopamine-assisted hydrothermal carbonization technique to fabricate manganese oxide encapsulated multiporous carbon nanofibers M-MCNFs from glucose. The research work is now published in peer-reviewed journal, Nano Research.

With the addition of cryptomelane nanowires, the authors were able to verify the importance of dopamine addition, as it supported the formation of carbon nanofibers. The manganese oxide encapsulated multiporous carbon nanofibers structures contained hierarchical pore structures such as macropores, mesopores and micropores.

The presence of dopamine, which was responsible for the quick formation of carbon nanofibers also aided the cryptomelane hard-templates of manganese oxide nanowires and glucose reaction. The presence of F127 aided the discovery of mesoporous structures with higher specific surface area and volume for manganese oxide encapsulated multiporous carbon nanofibers compared with the manganese oxide carbon nanofibers.

Further results also highlighted the reduction of the cryptomelane hard-template of manganese oxide to nanowires of Mn₃O₄ nanoparticles after high-temperature  annealing. The presence of Mn₃O₄ favored the capacitive performance of the manganese oxide encapsulated multiporous carbon nanofibers as the active redox sites were enhanced by the multipores which prevents the introduction of post disposition procedure.

The structural properties with large surface areas and hierarchical pores (macropores, mesopores and micropores) made the manganese oxide encapsulated multipores carbon nanofibers a far better choice for applications of supercapacitors.

From electrochemical measurements, the authors were able to show that manganese oxide encapsulated carbon nanofibers possess a favorable charge-discharge properties as well as high cycle stability and high capacity retention when tested under different electrolytes.

The method used in fabricating the manganese oxide encapsulated multiporous carbon nanofibers by the way of the authors creates an avenue for improved energy storage applications with the use of renewable source such as biomass. The strategy also pave a way to synthesize porous carbon nanofibers from biomass.

About The Author

Yong Wang studied chemical engineering at Xiang-tan University from 1998 to 2002. He received his Ph.D. degree from Zhejiang University in 2007. After a postdoctoral stay at the Department of Chemistry, Zhejiang University, he joined the Max Planck Institute for Colloids and Interfaces in Potsdam/Germany in 2009. He rejoined Zhejiang University and became a Professor for Chemistry in 2011. His research focuses on design and synthesis of novel materials for energy conversion and storage, heterogeneous catalysis and biomass conversion.

About The Author

Haiyan Wang is a Ph.D. candidate in the Advanced Materials and Catalysis Group at Zhejiang University under the direction of Prof. Yong Wang. She received her Bachelor’s degree from Henan Normal University in 2013. Her research interests are synthesis of carbon-based nanomaterials and their applications in electrochemical energy storage and conversion devices.

Journal Reference

Wang, H., Deng, J., Chen, Y., Xu, F., Wei, Z., Wang, Y. Hydrothermal Synthesis of Manganese Oxide Encapsulated Multiporous Carbon Nanofibers for Supercapacitors, Nano Research 9 (2016) 2672-2680.

Advanced Materials and Catalysis Group, ZJU-NHU United R&D Center, Center for Chemistry of High-Performance and Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, China.

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