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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