Renewable Energy Global Innovations features: An innovative electronically-conducting matrix

Significance Statement

Energy storage system has been developed to supply electric energy in a stable and efficient way. Sodium sulfur battery as one of energy banks for energy storage system offers high theoretical energy density, high energy efficiency, and long operational lifetime with no self-discharge. They also offer similar advantages in terms of non-toxicity, low cost and ready availability.

In a recent study by Kim et al. (2016) and published in Journal of Power Sources introduced an innovative method of preparing a surface modified carbon felt treated with inorganic nanoparticles for a current collecting matrix of the cathode.

NaS battery consists of sodium for an anode, sulfur for a cathode and β”-alumina solid electrolyte (BASE) for a separator. Carbon felt is known to be a good candidate for commercial NaS battery as a current collector in the cathode because of a high corrosion resistance to corrosive sodium sulfides.

The internal resistance of battery increases due to sulfur precipitation hindering the migration of Na⁺ into the anode section during charge and degrades the charge recovery characteristics due to decrease of electric conduction during charge (Sudworth and  Tilley, The Sodium Sulfur Battery, 1985). Various attempts to suppress formation of sulfur-insulating layer has been reported by simply avoiding unnecessarily fast electron donating-accepting reactions during charge.

Alumina impregnating method is one of the methods used to suppress formation of sulfur insulating layer. However, it has disadvantages such as reduced space for sulfur due to high content of alumina particles, poor adhesion of alumina particles to carbon felt. The method currently adopted is a needle-punching process: a glass fiber mat is placed on a carbon felt and needle-punched to insert a part of the glass fibers into the carbon felt. This process leads to unavoidable mechanical damages and inhomogeneous distribution of glass fibers along thickness direction of the carbon felt.

This has led to Kim et al. (2016) treatment of carbon felt with inorganic nanoparticles on carbon-felt takes a negligible space for sulfur and coating process can be applied to any shape of carbon-felts because the coating is achieved by a sol-gel process using an inorganic-organic hybrid sol.

Kim et al. (2016), prepared an inorganic-organic hybrid sol for surface modification of carbon felt by sol-gel process which provides nanoscale alumina/silica particles upon calcination. The prepared carbon felt was observed by scanning electron microscopy (SEM) and field emission SEM with Energy Dispersive X-ray (EDX). Thickness of coating layer was observed by Scanning Transmission Electron Microscopy (STEM) with EDX. Cell components including stainless steel current collectors, O-rings and alumina gasket were cleaned by sonication in acetone and later dried in order to eliminate impurities and moisture. Sodium and sulfur-impregnated carbon-felt were inserted into anode and cathode compartment, respectively, in an argon-filled glove box. The cell was discharged up to depth-of-discharge (DoD) of 70% and charged up to 2.5 V for 3 cycles at current densities of 60 and 100 mAcm^-2 in order to observe change in charge capacity at various current densities.

Results from STEM-EDX images showed a cross-section of fiber revealing a coating layer of about 6 nm in thickness where aluminum, silicon and oxygen are mapped homogeneously supporting the fact that carbon-felt can be modified with an insulating layer by simple sol-gel process.

Results demonstrating the possibility of surface modified carbon-felt showed cell with coated carbon-felt having a better performance than barely carbon felt in terms of charge capacity and voltage drops as current density increases. The degradation of charge capacity and drastic increase in charge voltage with increased current densities at barely carbon-felt was due to increase of rapid formation of sulfur layer at electrolyte surface while results of coated carbon-felt cell showed sulfur deposition hardly occurs at surface of electrolyte.

Further results show that discharged capacity decreased from 334 mAhg^-1 at first cycle to 330 mAhg^-1 at 70th cycle by 1.2% and columbic efficiency remaining steady throughout number of cycles. This means that effective resistance of the cell is not increased through the cycles.

Kim et al. (2016) fabrication of innovative electronically-conducting cathode matrix showed a columbic efficiency as measures to be more than 99.9% and discharge capacity retained higher than 98% of the discharge of the first to 70th cycle at constant current densities of 100 mAcm^-2 in discharge and 80 mAcm^-2 in charge.

 

About The Author

Seong In Kim received his Master’s degree in the Division of Materials Science and Engineering at Hanyang University in 2016, and now works at the High Temperature Energy Materials Research Center, Korea Institute of Science and Technology.

His main research interest is the development of advanced materials for secondary batteries. 

About The Author

Dr. Chang-Sam Kim is a principal researcher in the Center for Energy Convergence Research at Korea Institute of Science and Technology. He received BS and MS degrees at Hanyang University and Ph.D. degree at Tokyo Institute of Technology in 1992.

His current research interests focus on the surface modification using soft processes for energy storage devices. 

Journal Reference

 

Seong In Kim^1,2, Won Il Park¹, Keeyoung Jung³, Chang-Sam Kim¹. An Innovative Electronically-Conducting Matrix of the Cathode for Sodium Sulfur Battery. Journal of Power Sources, 2016, Volume 320, pp 37-42.

Show Affiliations

1. Center for Energy Convergence Research, Korea Institute of Science and Technology, Seoul 02792, South Korea
2. Division of Materials Science and Engineering, Hanyang University, Seoul 04763, South Korea
3. Energy Storage Materials Research Group, Research Institute of Industrial Science and Technology (RIST), Pohang 37673, South Korea

 

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Renewable Energy Global Innovations features: The effect of diamond-like carbon coating on LiNi0.8Co0.15Al0.05O2 particles for all solid-state lithium-ion batteries based on Li2S–P2S5 glass-ceramics

Significance Statement

Lithium-ion batteries, one of energy storage device for electric vehicles are considered to be the most promising storage device due to their large capacity, excellent rate capability and low cost. They however pose safety concerns due to their rapid temperature rise or even combustion of the batteries.

Researchers from AR-3, Samsung R&D Institute Japan and Energy Lab, SAIT, Samsung Electronics Co. in Republic of Korea proposed a new type of coating, diamond-like carbon to reduce the interface resistivity in sulfide-based all-solid state lithium-ion batteries. Their study published in Journal of Power Sources, investigated the effects of diamond-like carbon coating layer on battery’s electrochemical performance and its positive impact was clarified.

All solid-state lithium-ion batteries have been used widely due to their non-volatile inorganic solids loading to highly conductive materials with lithium-ion conductivities in range of 10^-3-10^-2 Scm^-1. However, high interfacial resistance due to reactions between the sulfide solid electrolyte and active materials affects the performance of all solid-state lithium-ion batteries . In order to curb this, several buffer layers have been proposed to suppress the formation of a high-resistance layer. These buffer layers though, successfully prevents direct contact between solid electrolyte and active materials, they are generally poor in conduction of lithium ions as they hinder the migration of lithium ions at the interface of sulfur-based solid electrolyte and oxide cathode materials.

The proposed diamond-like carbon by Visbal et al. (2016) is known for its uniqueness in physicochemical properties. Diamond-like carbon offers various advantages in terms of hardness, chemical inertness, electrolyte-resistant and compatibility layer with lithium anodes.

For this experiment LiNi_0.8Co_0.15Al_0.05O₂ (NCA) was used as cathode active material. Diamond-like carbon coated NCA was prepared using penning ionization gauge based chemical vapor deposition equipment. Effect of plasma pretreatment during the chemical vapor deposition process was also determined. The crystallinities and impurities of samples were examined by X-ray diffracted patterns using Empyrean X-ray diffraction (XRD) system diffractometer. Morphology and microstructure of the diamond-like carbon layer were characterized using a Transmission Electron Microscopy with Energy Dispersion X-ray analysis while Electron Energy-Loss Spectroscopy (EELS) spectra were taken to characterize the nature of diamond-like carbon coating.

Effect of the diamond-like carbon coating on the performance of sulfide-based all solid-state lithium-ion batteries were investigated using electrochemical cells of amorphous Li₂-P₂S₅ (75:25mol%) electrolyte, cathode composite prepared by mixing Vapor grown Carbon Fiber (VCF) and Li₂-P₂S₅ (75:25mol%) in weight ratio of 60:5:35 respectively. Anode composite was similarly fabricated by mixing artificial graphite with Vapor grown Carbon Fiber (VCF) and Li₂-P₂S₅ (75:25mol%) in weight ratio 60:5:35. Electrochemical behavior of the all solid-state lithium-ion batteries were investigated by galvanostatic charge-discharge cycle and Electrochemical Impedance Spectroscopy (EIS).

Results from the XRD patterns showed that both diamond-like carbon coated and bare NCA samples were single phased and isostructural with LiNiO₂ giving no obvious difference between the two X-ray diffraction spectra. This result indicates that diamond-like carbon coating does not alter crystal structure and lattice constants of NCA.

Mean thickness from Transmission Electron Microscopy image of cross-sectional area of diamond-like carbon coated NCA particle was computed to be 4.3nm. Energy-dispersive X-ray spectroscopy analysis showed the sp² bonding ration of diamond-like carbon coated NCA powder was estimated to be around 55% from C K-edge peak as expected for a diamond-like carbon coating.

Specific capacities of bare, plasma coated and diamond-like carbon coated were 119.9, 114.9 and 120.7mAhg^-1 with initial columbic efficiency of 66.6, 64.9 and 66.5% respectively. Measured impedance of resistance obtained at cell kinetics of both cathode and anode charge transfer for bare, plasma coated NCA and diamond-like coated NCA were 234, 177 and 70Ώ respectively.

Cycle performance of the three cells with different positive electrode materials was compared. The bare and plasma coated NCA cells exhibited the drop to 70% and 75% of their initial capacity after 100cycles while the diamond-like carbon coated NCA cell showed higher capacity retention, retaining 91% after 100 cycles.

Further experiment results showed that diamond-like carbon coating minimizes the formation of fragment species at the surface was the lowest for the sample. These results proved that diamond-like carbon coating prevents S^– and P^– ions of solid electrolyte to react with oxygen of cathode active particles which leads to interfacial resistance and deterioration of electrochemical property.

Based on this analysis, Visbal et al. (2016) fabrication of diamond-like carbon coating of NCA cells prevents slide reaction between the cathode and sulfide electrode and improvement of electrochemical properties of the cell was achieved.

   

 

Journal Reference

 

Heidy Visbal¹,Yuichi Aihara¹ , Seitaro Ito¹, Taku Watanabe¹,Youngsin Park², Seokgwang Doo². The effect of diamond-like carbon coating on LiNi_0.08Co_0.15Al_0.05O₂ particles for all solid-state lithium-ion batteries based on Li₂S-P₂S₅ glass-ceramics. Journal of Power Sources, 2016, Volume 314, pp 85-92.

Show Affiliations

1. AR-3, Samsung R&D Institute Japan, Minoh Semba Center Bldg., 2-1-11 Semba Nishi, Minoh-shi, Osaka 562-0036, Japan
2. Energy Lab, SAIT, Samsung Electronics Co., Ltd., San 14-1, Nongseo-Dong, Giheung-Gu, Yongin-Si, Gyeonggi-Do 446-712, Republic of Korea

 

 

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Renewable Energy Global Innovations features: A small-scale standalone wind energy conversion system featuring SCIG, CSI and a novel storage integration scheme

Significance Statement

Dr. Zuher Alnasir and Professor Mehrdad Kazerani established a focus on developing a Small-scale Standalone wind energy conversion system (WECS) based on current-source inverter.

The study published in Renewable Energy journal made attempts to verify the feasibility of the proposed system by addressing the challenges associated with maximum power tracking, energy storage integration, power management and dc-link inductor design.

As a robust, low-cost and low-maintenance machine, Squirrel-Cage Induction Generator (SCIG) has been employed in the proposed small-scale standalone WECS.

Voltage-Source Inverter (VSI) has been dominantly employed in variable-speed wind turbine systems for converting DC to desired AC output voltage. Current-Source Inverter (CSI) has also been widely used in medium-voltage and high-power applications. To investigate the potential of CSI in low-power off-grid wind turbine applications, the authors conducted a comparison between Pulse-Width Modulated Voltage-Source Inverter (PWM-VSI) and Pulse-Width Modulated Current-Source Inverter (PWM-CSI) in terms of reliability, cost, efficiency, and protection requirements.

Although IGBT-based PWM-VSI offers some advantages in small-scale off-grid wind energy conversion systems in terms of capital cost, overall efficiency and open-circuit fault requirements, IGBT-based PWM-CSI is the winner in the  comparison, in terms of reliability, operation and maintenance costs, short-circuit fault requirements and inherent voltage-boost capability.

The wind energy conversion system proposed by Alnasir and Kazerani (2016) consists of rotor blades, a geared-drive self-excited squirrel-cage induction generator, a three-phase diode bridge rectifier, a dc/dc buck converter , a dc-link inductor, a three phase pulse-width modulated IGBT-based current-source inverter, a capacitor filter, a delta/star transformer, a Y-connected three-phase R-L load, a battery-based energy storage system featuring an H-bridge converter with reduced number of switches, and a dump load controlled by an IGBT switch. The dc-link inductor, shared by three power electronic converters, was systemically designed. The current-source inverter-based wind energy conversion system exchanges power between the battery pack and dc bus through the interfacing H-bridge converter with bipolar-voltage and unidirectional-current capabilities.

Control strategies for controller blocks include: (i) maximum power point tracking (MPPT) control for extraction of maximum power from wind by regulating the generator shaft speed at the optimum value corresponding to present value of wind speed (Vw), (ii) power management in dc-link among battery and dump load, as battery absorbs excess power during high-wind-speed or low-load periods to compensate for shortage of power during low-wind speed or high-load period, and (iii) load-side control to compensate for voltage imbalance at the point of common coupling so that Voltage Unbalance Factor (VUF) does not exceed permissible limit of 1%.

Performance of the system was evaluated under variable wind speed and unbalanced three-phase R-L load. Rated values for unbalanced load in phases a, b and c were 9.3kW/2.7kVar, 4kW/6kVar and 6.7kW/1.3kVar, respectively.

From simulation results, it can be observed that maximum power at various wind speeds was extracted through the MPPT controller, dc-link inductor current was controlled at the desired values through the H-bridge converter, and voltage and frequency were regulated at the desired values through the current-source inverter. Due to unbalanced load, different modulation indexes were produced for three phases. RMS values of line voltages exhibited negligible imbalance with the largest deviation of -2.72% observed in phase voltage magnitude during load changes. The highest value noticed for VUF was 0.7% which is below the permissible limit of 1%.  3.4%, 3.2% and 2.8% were the highest Total Harmonic Distortions (THDs) detected in line voltages V_ab, V_bc and V_ca, respectively, which are lower than the typical limit of 5%. The highest THDs of load currents were 1.1%, 0.82% and 0.98% for i_a, i_b and i_c, respectively, implying close-to-sinusoidal currents.

Generator response, when the proposed system was run under two different wind speed profiles, showed that maximum power point tracking controller under a wind speed profile with lower rate of wind speed change (i.e., lower dV_W/dt) performed better than in the case of higher dV_W/dt. The negative impact of system inertia on MPPT controller was also demonstrated.

Despite achieving high quality voltage and current waveforms at the load bus, Alnasir and Kazerani (2016) emphasized the possibility of incorporating additional features to modulate neutral currents.

About The Author

Zuher Alnasir received the Bachelor of Science (with Honors) in Electrical Engineering from King Fahd University of Petroleum & Minerals, KSA, in 2002.

In 2008, He received the Master of Science (with Distinction) in Electrical Power from the University of Newcastle, England, UK. Recently, he received the Ph.D. degree from University of Waterloo, Ontario, Canada. From 2004 to

2007 and 2009 to 2011, he was a faculty member in the Department of Electrical and Electronic Engineering Technology, Jubail industrial college, KSA. He was involved in teaching, administrative activities, and senior projects supervision. Presently, he is a lecturer with the same Department.

His research interests are in the areas of power electronic applications in renewable energy. 

About The Author

Mehrdad Kazerani received his PhD degree in Electrical Engineering from McGill University in 1995. He is a Full Professor at the University of Waterloo, Department of Electrical and Computer Engineering. Since joining the University of Waterloo in 1997, he has been involved in teaching, administrative activities and experimental research in the general field of power electronics.

Specific research areas include modeling and control of DC/AC voltage-sourced and current-sourced converters, HVDC and FACTS, grid integration of renewable energy, matrix converters, fuel cell/battery electric/hybrid vehicles, renewable energy integration, energy storage systems, battery chargers with V2G capabilities, EV/E-Bike Charging stations and microgrids.

Dr. Kazerani’s research program has been financially supported by various governmental agencies and industry partners. He has actively participated in numerous multidisciplinary projects and has supervised/co-supervised over 40 graduate students and visiting scholars, and over 80 undergraduate students in research projects and 4th-year design projects.

He holds 8 patents and has authored/co-authored over 140 journal and conference papers, technical reports and book chapters. As a senior member of IEEE, he has participated on several IEEE technical sub-committees and Task Forces, organized several special Sessions in IEEE Conferences, and acted as a guest/associate editor of several special sections and issues in IEEE Transactions.

He is also an editor of the IEEE Transactions on Vehicular Technology. Dr. Kazerani has acted as a consultant for the Formula Electric Vehicle team at the University of Waterloo and as an investigator for Association of Professional Engineers Ontario (PEO).

Dr. Mehrdad Kazerani is a registered professional engineer in the province of Ontario, Canada.

 

Journal Reference

Zuher Alnasir, Mehrdad Kazerani, A Small-Scale Standalone Wind Energy Conversion System featuring SCIG, CSI and a Novel Storage Integration Scheme. Renewable Energy, Volume 89, 2016, Pages 360–370.

Electrical and Computer Engineering, University of Waterloo, 200 University Avenue West, N2L 3G1, Ontario, Canada.

 

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Renewable Energy Global Innovations features: Nanostructure anode: A key to low-temperature SOFC

Significance Statement

In a recent article done by Park et al. and published in Journal of Power Sources, investigations showed that electrochemical properties of thin film solid oxide fuel cells (TF-SOFCs) at low temperature is also a function of grain size of nanostructured Ni-yttria-stabilized zirconia (Ni-YSZ) composite anode.

This was achieved by analyzing the output power and impedance spectra at various cells by operating conditions in order to compare electrode reaction mechanism due to amount of grain size of anode in full-cell test.

Despite high efficiency of solid oxide fuel cell (SOFC), its high operating temperature of (≥ 700-800 °C) has been a major setback due to its fast degradation and poor reliability. Lowering the operating temperature of SOFC has been a major case of study because unwanted chemical reactions are prevented and use of less expensive material such as stainless steel are allowed. However at lower operating temperatures, electrode activity of SOFC worsens hence its performance is determined by polarization losses induced by electrode reaction at low temperature.

Although extensive research has been made on nanostructured cathodes due to its polarization loss in low temperature performance of SOFCs, it has also been predicted that loss of anode at temperature (≤ 600 °C) also has significant effect as that of cathode. Since metals are used as catalyst in nanostructured anode, fabrication has been difficult due to agglomeration of metal-phase at SOFC operating temperature leading to reduction in triple-phase boundary (TPB) length, loss of conductivity and cell stability degradation. However, fabrication of a uniform nanostructured Ni-YSZ was successful using PLD. Its layer was designed to suppress Ni agglomeration and effectively support thin-film electrolytes with thickness approximately 1µm or less which has a higher TPB density to that of conventional Ni-YSZ anodes.

Discerning the impact of nanostructured anode functional layer (nano-AFL) has proved difficult experimentally due to the fact that nano-AFL is so thin that catalyst amount in layer is minute in compares to that of whole anode support and it has been extremely difficult to build thin electrolytes directly over supports without nano-AFL due to the surface condition of the supports. Nevertheless, Park et al. has been successful in building TF SOFCs with and without nano-AFL and effect of nano-scale grain-size of AFL has been studied effectively.

In experiment set-up, two different unit cells; one with nano-scale Ni-YSZ AFL was denoted as NS-cell and that without nano-AFL is denoted by MS-cell. Cell operating temperature varied from 650 °C to 500 °C at intervals of 50 °C while electrochemical impedance spectra (EIS) and current-voltage-power (I-V-P) curves were obtained at each temperature. From the results, the peak power density of NS-cell at 650 °C reached 1775 mWcm^-2 which is better than MS-cell with 1650 mWcm^-2.

It was also noticed that performance ratio (P_NS-cell/P_MS-cell) increases with decrease in temperature at 0.7 V as performance of NS-cell was twice higher than MS-cell at 500 °C and I-V drop of MS-cell was faster at lower current density. These two results show that the influence of nano-AFL on the full cell performance increases with decreasing temperature and electrode activation loss is significant in MS- cell.

With each EIS observed over a frequency of 10⁵ Hz to 10^-1 Hz at AC amplitude impedance of 50 mV, impedance in frequency range of 10 Hz ≤ f ≤ 10⁴ Hz was considered to be a major contributor to total impedance of both cells and exhibits a significant temperature dependency, however an overlay in impedance was noticed in two stages; (10² Hz ≤ f ≤ 10³ Hz) and (10³ Hz ≤ f ≤ 10⁴ Hz).

From the Bode plots, first frequency impedance was mainly related to the cathode while at second frequency impedance, temperature was reduced during anode half-cell test and impedance at this stage increased. It was also seen from the Bode plots of NS and MS cells that the resistance of anode reaction is much smaller in the NS-cell than in MS-cell due to small particles size of nano-AFL.

These results prove that performance improvement of NS-cell with respect to MS-cell at lower temperature is due to facilitation of charge transfer at the anode. This shows that anode performance can significantly affect cell performance at low temperature.

Park et al. study proves that anode reaction also affects cell performance at low temperature significantly. Substantial conclusion was also made that it’s important to minimize grain size of Ni-YSZ despite its possible fabrication in order to obtain reasonable cell performance at low temperatures which also aids the lowering of SOFCs operating temperature.

 

About The Author

Dr. Ji-Won Son is a principal researcher at the High-temperature Energy Materials Research Center, Korea Institute of Science and Technology (KIST), and an adjunct professor at Univ. of Science and Technology (UST) and Hanyang Univ., Rep. of Korea. She studied Inorganic Materials Science and Engineering at Seoul National University (SNU) and received BS and MS degrees at SNU. During her master course, she studied the sintering mechanism of transparent conducting oxides used for electronic applications. Afterwards, she entered the graduate school of Stanford University, Dept. of Materials Science and Engineering and received the Ph. D. degree in 2005. Her Ph. D. topic was about oxide thin film materials for optical applications.

Based on her expertise both on oxide bulk materials and thin film materials, she has worked on implementation of thin film and nanostructure materials to high-temperature operating solid oxide fuel cells (SOFCs) in order to lower the operating temperature since she joined the Solid State Ionics Lab at KIST, 2005. By realizing multi-scale-architectured structure at the anode, she successfully achieved both the high performance at lower operating temperatures and the thermomechanical stability of the thin film and nanostructure-base anode-supported SOFCs.

For her achievement, she received the Women of the Year Award in Science and Technology in Korea, 2013, and the Prime Minister Award, 2016.

Journal Reference

Jung Hoon Park^1,2, Seung Min Han², Kyung Joong Yoon^1,3, Hyoungchul Kim^1,3, Jongsup Hong¹, Byung-Kook Kim¹, Jong-Ho Lee^1,3, Ji-Won Son^1,3 . Impact of nanostructured anode on low-temperature performance of thin-film-based anode-supported solid oxide fuel cells. Journal of Power Sources, Volume 315, 31 May 2016, Pages 324–330.

Show Affiliations

1. High-temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 02792, South Korea
2. Graduate School of EEWS, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, South Korea
3. Nanomaterials Science and Engineering, Korea University of Science and Technology, KIST Campus, Seoul 02792, South Korea

 

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Renewable Energy Global Innovations features: Nano “Zylon” Fiber Makes Battery Safer

Significance Statement

Safe and powerful lithium based batteries are important for various technologies, such as electric vehicles, smartphones, and laptops. One of the biggest problems facing this industry is the growth of dendrites sprout from the surfaces of lithium electrodes over the course of several charge/discharge cycles, particularly at a fast rate. The dendrites can spread across the electrolytes and reach the other electrodes, making the batteries short-circuited. The consequent high electric currents may lead the batteries to rapidly overheat and even catch fire.

Researchers in Beijing Institute of Technology, China, and Northwestern University, USA have developed a new type of advanced battery separators to solve this problem. These separators are made of lightweight and ultrastrong materials typically used in Zylon, a commercial microfiber with mechanical properties higher than the well-known Kevlar.

The process for making this advanced battery separators is quite scalable. Zylon microfibers are exfoliated into nanofibers through a special processing step, and then blade-cast into thin and nanoporous membranes. These membranes have a combination of high strength, low ionic resistance, and high heat tolerance, making them exceptionally good separators for preventing dendrite growth in lithium batteries.

The new separators have several advantages in comparison to one of the current state-of-the-art battery separators, Celgard 2400. The electrodes in batteries with the Celgard 2400 show mossy surfaces as a result of dendritic lithium growth, whereas electrode surfaces with the new separator membranes still remain smooth even after 700 hours. The suppression of dendrite formation results in good performance of batteries, including higher long-term stability and higher efficiencies.  As the materials in the separators are highly heat-tolerant, these separators can be used for batteries required in high-temperature environment.

As a comparison, the typical Celgard 2400 separators begin to melt at about 125 °C and make the batteries unusable, while batteries with the new advanced separators can continue to operate up to 185 °C, upon which the electrolytes decompose. In addition, these separators may be applied in other energy storage systems in which dendrite growth is a problem.  

About The Author

Dr. Xiaoming Hao graduated from Beijing Institute of Technology in 2015, and now work at The National Center for Nanoscience and Technology, Chinese Academy of Sciences as a postdoctoral fellow.  

About The Author

Dr. Jian Zhu is currently a postdoctoral fellow at the Northwestern University, USA. He is interested in the assembly of nanomaterials, and their applications in advanced structural and electrical materials.  

About The Author

Dr. Zhenhua Wang worked at Beijing Institute of Technology as an associate professor and vice dean of chemistry and chemical engineering college. His research interests mainly focus on solid oxide fuel cells and various lithium batteries.  

About The Author

Professor Kening Sun is the Cheung Kong Scholar Chair Professor at Beijing Institute of Technology. His research interests mainly focus on fundamental electrochemistry, advanced energy materials, solid oxide fuel cells and various lithium batteries.

Journal Reference

Xiaoming Hao¹ , Jian Zhu^*3, Xiong Jiang¹, Haitao Wu¹, Jinshuo Qiao¹, Wang Sun¹, Zhenhua Wang^*1,2, Kening Sun^*1,2. Ultrastrong Polyoxyzole Nanofiber Membranes for Dendrite-Proof and Heat-Resistant Battery Separators. Nano Lett., 2016, 16 (5), pp 2981–2987.

Show Affiliations

1. Beijing Key Laboratory for Chemical Power Source and Green Catalysis, School of Chemical Engineering and Environment,
2. Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing Institute of Technology, No. 5 Zhongguancun South Avenue, Haidian District, Beijng, 100081, P. R. China
3.  Department of Materials Science and Engineering, Northwestern University, 2200 Campus Drive, Evanston, Illinois 60208, United States

 

 

 

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Renewable Energy Global Innovations features: Oxidized Ni/Au Transparent Electrode in Efficient CH3NH3PbI3 Perovskite/Fullerene Planar Heterojunction Hybrid Solar Cells

Significance Statement

The p-type semiconducting inorganic NiO_x thin film, owing to the high optical transparency, the chemical stability, the good conductivity of hole, the suitable work function, as well as the capability to block the electrons to reach the positive electrode, would be the ideal p-type electrode interlayer for fabricating perovskite solar cells made of a conventional OPV architecture. However, the electric conductivity of NiO_x layer is still insufficient to be solely used as a TCO electrode. The NiO_x needs to function reliably with the highly conductive ITO layer underneath to sustain the electric conduction of the charges.

This work first and successfully demonstrates the application of the well-developed nickel (Ni)/gold (Au) transparent electrode in GaN light-emitting diodes industry for fabricating efficient perovskite-based solar cells. We apply a thermally oxidized, Ni/Au transparent electrode on the glass substrate to prepare methylammonium lead iodide (CH₃NH₃PbI₃) perovskite/fullerene (C₆₀) planar heterojunction hybrid solar cells.

The combination of the oxidized Ni (NiO_x) with the interconnected network Au forms a functionalized Au:NiO_x electrode, capable of transporting holes and blocking electrons from CH₃NH₃PbI₃ perovskite to reach the electrode. Changing Ni/Au compositions and the thermal treatment conditions modulates the optical transparency, electrical conductivity, the work function of Au:NiO_x electrode, as well as the photovoltaic parameters of hybrid cells.

To prepare the electrode and electrode interlayer in one single process simplifies fabricating procedures, and poses to the new design of the functionalized electrode in perovskite-based hybrid devices.

We report both ITO and PEDOT:PSS free devices with the potential for cost-effective, low-weight and stable cell in future application. The merits of the methods and materials we developed in the paper represent a new paradigm for hybrid perovskite-based solar cells of a conventional OPV architecture.  

About The Author

C. Lai received the B.S. degree in electrical engineering from the Feng-Chia University, Taiwan, in 1993, and the M.S. and the Ph.D. degrees in electrical engineering from the National Cheng Kung University (NCKU), Tainan, Taiwan, in 2001. In 2001, he was a Postdoctoral Associate with the Department of Electrical Engineering, NCKU.

He is currently with the Department of Photonics, NCKU, Taiwan, as a professor. His research interest includes the growth and Characterization of III–V nitride semiconductors and devices.

About The Author

Kun-Wei Lin received the B.S. degree in mechanical engineering from the National Taiwan University of Science and Technology, Taipei, Taiwan, in 2001, and the M.S. degree in mechanical engineering from National Cheng Kung University, Tainan, Taiwan, in 2003, where he is currently pursuing the Ph.D. degree with the Department of Photonics.

About The Author

Peter C.-Y Chen. He received Ph. D. from the Photonic Program in EPFL Switzerland at 2009 under the supervision of Prof. Michael Graetzel. Then he moved to Monash University in Australia as a post-doctoral research fellow with Prof. Udo Bach. He joined the Dept. of Photonic in National Cheng Kung University in 2010 and became associate Professor in 2014.

Currently his research interests are in the area of various photovoltaic devices including dye-sensitized solar cells (DSCs), hybrid organic-inorganic perovskite-based solar cells (HOIPs) and semiconductor-sensitization solar cells.

About The Author

Tzung-Fang Guo received the Ph.D. degrees in Materials Science and Engineering from University of California Los Angeles in 2002. He is currently the professor and chairman at Department of Photonics, National Cheng Kung University.

His research focuses on high-performance O/PLEDs, polymer and perovskite-based PVs, n-type pentacene OTFTs, and the magneto conductance responses of organic electronic devices.

 

Journal Reference

Advanced Materials, Volume 28, Issue 17, pages 3290–3297, May 4, 2016. 

Wei-Chih Lai^1,2, Kun-Wei Lin¹, Yuan-Ting Wang¹, Tsung-Yu Chiang¹, Peter Chen^1,3, Tzung-Fang Guo^1,2,3. Oxidized Ni/Au Transparent Electrode in Efficient CH3NH3PbI3 Perovskite/Fullerene Planar Heterojunction Hybrid Solar Cells Show Affiliations

1. Department of Photonics, National Cheng Kung University, Tainan, Taiwan
2. Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan, Taiwan
3. Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan, Taiwan

 

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Renewable Energy Global Innovations features: Reliability-Based Design Optimization Wind Turbine to Reduce Levelized Cost of Energy

Professor K.K. Choi and his team have recently collaborated with Professor Hiroyuki Sugiyama and his student Huaxia Li at the University of Iowa to extend it to reliability-based design optimization of wind turbine drivetrain using multibody gear dynamics simulation considering wind load uncertainty. They have improved the gear fatigue life reliability from 8.3% to 97.725% while increasing the gear weight by 1.4%.

 

 

 

 

About The Author

Weifei Hu received his B.S. (2008) from Zhejiang University, China, M.S. (2010) from Hanyang University, South Korea, and Ph.D. (2015) from University of Iowa, USA, all in mechanical engineering.

Currently, he is a postdoctoral research associate at Cornell University, Ithaca, New York.  Dr. Hu specializes in a wide range of wind energy topics including wind turbine aerodynamics and structure analysis, fatigue analysis of wind turbine composite materials, wind gust detection, wind turbine condition monitoring, and reliability-based design optimization (RBDO) of wind turbine systems.

He is a technical committee member and the secretary (2016-2017) of the Renewable and Advanced Energy Systems committee in the Power Division of ASME. 

About The Author

Hyunkyoo Cho earned his B.S. (2003) and M.S (2005) from Seoul National University, South Korea, in Naval Architecture and Ocean Engineering. He received Ph.D. (2014) from University of Iowa in Mechanical Engineering.

In addition, Dr. Cho has five years of industry experience at the Samsung Heavy Industries, South Korea. Currently, he is working as a Postdoctoral Research Scholar and an Adjunct Assistant Professor at University of Iowa. His research has focused on design optimization under input variability and uncertainty, which includes reliability analysis, reliability-based design optimization (RBDO), RBDO using insufficient input data, and applications of RBDO to engineering projects.

About The Author

Dr. K.K. Choi is Roy J. Carver Professor in the Mechanical and Industrial Engineering Department at the University of Iowa.  He was appointed as a World Class University Professor at the Seoul National University in Korea during 2008-2013.

His research areas are uncertainty quantification, reliability analysis, reliability-based design optimization, design sensitivity analysis, and mathematical theory of optimization and its applications.  He has co-authored 364 papers, including 152 journal papers in leading national and international engineering journals.

He has co-authored several graduate engineering texts (Design Sensitivity Analysis of Structural System, 1986; Methods of Engineering Mathematics, 1993; Design Sensitivity Analysis of Linear and Nonlinear Structural Systems – Two Volume, 2004).

At the University of Iowa, he is a founding member of the Iowa Board of Regents approved Center for Computer Aided Design (CCAD).  He has served as Associate Director (1990-93), Deputy Director (1993-95), and Director (1995-2003) of CCAD.  He is associate editor of five national and international journals including Journal of Mechanics Based Design of Structures and Machines and Journal of Optimization Theory and Applications.

He is Fellow of American Society of Mechanical Engineers (ASME), Fellow of American Institute of Aeronautics and Astronautics (AIAA), Fellow of Society of Automotive Engineering (SAE), and President Elect of the International Society for Structural and Multidisciplinary Optimization (ISSMO, 2007-2011). 

Reliability-based design optimization of wind turbine blades for fatigue life under dynamic wind load uncertainty

Journal Reference

Structural and Multidisciplinary Optimization, October 2016, Volume 54, Issue 4, pp 953–970.

Weifei Hu, K. K. Choi, Hyunkyoo Cho.

Department of Mechanical and Industrial Engineering, The University of Iowa, Iowa City, USA

Abstract

This paper studies reliability-based design optimization (RBDO) of a 5-MW wind turbine blade for designing reliable as well as economical wind turbine blades. A novel dynamic wind load uncertainty model has been developed using 249 groups of wind data to consider wind load variation over a large spatiotemporal range. The probability of fatigue failure during a 20-year service life is estimated using the uncertainty model in the reliability-based design optimization process and is reduced to meet a desired target reliability. Meanwhile, the cost of composite materials used in the blade is minimized by optimizing the composite laminate thicknesses of the blade.

In order to obtain the reliability-based design optimization optimum design efficiently, deterministic design optimization (DDO) of the 5-MW wind turbine blade is carried out first using the mean wind load obtained from the wind load uncertainty model. The reliability-based design optimization is then initiated from the DDO optimum. During the reliability-based design optimization iterations, fatigue hotspots for reliability-based design optimization are identified among the laminate section points.

For an efficient reliability-based design optimization process, surrogate models of 10-min fatigue damages D₁₀ at the hotspots are accurately created using the Kriging method. Using the wind load uncertainty model and surrogate models, probability of fatigue failure during a 20-year lifespan at the hotspots and the design sensitivities are calculated at given design points. Using the probability of fatigue failure and design sensitivity, reliability-based design optimization of the 5-MW wind turbine blade has been successfully carried out, satisfying the target probability of failure of 2.275 %.

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