Session 1: Advances in EC Capacitor Materials and Cell Design
To enhance the value proposition of EC Capacitors by boosting cell performance, improvements in electrode capacity, power performance, electrolyte properties, electrode technology, and cell design are desired. In this session, we review the latest advances in materials, including the development of low-cost materials and processes to meet the pricing threshold of most markets, and in cell designs, including development of advanced asymmetric ECs.
Session Chairman: Katsuhiko Naoi, Professor of Chemistry, Institute of Symbiotic Science & Technology, Tokyo University of Agriculture & Technology
Dr. Naoi is a professor of chemistry at the Institute of Symbiotic Science & Technology at Tokyo University of Agriculture & Technology (TAT). He also serves as a CTO of K&W Inc., a TAT venture company dealing with "Energy Solutions for the Future." With a Ph.D. from Waseda University, Tokyo, his research interests are advanced supercapacitors, future nanobatteries, and energy, environmental, and materials science.
SESSION AGENDA
Perspective for Future Supercaps Katsuhiko Naoi, Professor of Chemistry, Institute of Symbiotic Science & Technology, Tokyo University of Agriculture & Technology
Abstract
There has been a major effort, all over the world, to increase an energy density of electrochemical capacitors to meet more demands for electric automotive and regenerative energy storage applications. Hybridizing battery-capacitor electrodes can certainly overcome the energy density limitation of the conventional electrochemical capacitors because they employ both the system of a battery-like (redox) and a capacitor-like (double-layer) electrode, producing a larger working voltage and capacitance. However, the rates for the redox must be substantially increased to the levels of double-layer process in order to balance such asymmetric systems. An in-situ material processing technology called ‘Ultra-Centrifuging (UC) Treatment’ has been developed and applied to prepare a novel ultrafast Li4Ti5O12 (LTO) nanocrystal electrode for capacitive energy storage. This account describes an extremely high supercapacitor performance that utilizes highly optimized ‘nano-nano LTO/carbon composites’ prepared via the UC treatment. The UC- treated LTO nanocrystals are grown as either nanosheets or nanoparticles, both with hyper-links to two types of nanocarbons: carbon nanofiber and super-growth (single-walled) carbon nanotube. The spinel structured LTO has been prepared with two types of hyper dispersed carbons. The UC treatment at 75,000G stoichiometrically accelerates the in situ sol-gel reaction and further forms, anchors and grafts the nanoscale LTO precursors onto the carbon matrices. The instantaneity of the heat-treatment is of utmost importance in achieving high crystallization, inhibiting oxidative decomposition of carbon matrices, and in suppressing agglomeration. Such nanocrystal composites are capable of storing and delivering energy at the highest rate attained to this date. The charge-discharge profiles indicate a very high-sustained capacity of 80 mAh g-1 at an extremely high rate of 1200C. Using such an ultrafast material, we assembled a hybrid device called ‘Nanohybrid capacitor’ that has demonstrated remarkable energy, power, and cycleability performance. New generation ‘Nanohybrid capacitor’ technology produced more than triple the energy density than that of a conventional electrochemical capacitor. Moreover, the synthetic simplicity of the high-performance nanostructures enables scalability for large-volume material production and additional applications in many other electrochemical energy storage devices.
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Asymmetric and Hybrid Carbon/Carbon Ultracapacitors François Béguin, Professor, CNRS University, Orléans
Abstract
This presentation critically discusses about novel asymmetric AC/AC and hybrid AC/graphite ultracapacitors which present several advantages in comparison to the traditional electrical double-layer (EDL) capacitors in organic electrolyte, such as lower cost and safer operation for the former one, and higher energy density for the later.
The asymmetric carbon/carbon ultracapacitor is based on two activated carbon electrodes of different nature or mass in aqueous alkali sulfate solution. Due to the use of these salts, the operating potential window of both electrodes is considerably enhanced in comparison to other systems known to-date in acidic or basic solutions. In optimized conditions, a maximum voltage of 1.8 -2 V could be reached with a good cycle life in lithium sulfate. In view of developing a prototype of this promising system, we have investigated a number of important parameters, in the temperature range -10 to + 50°C, using various concentrations of alkali sulfates, such as:
the self-discharge
the evolution of capacitance and series resistance during floating
gas evolution
the EIS data
The hybrid LiC system combines a positive activated carbon EDL electrode and a negative graphite lithium intercalation electrode, using a lithium-based electrolyte, e.g., 2 mol L-1 lithium bis(trifluoromethane)sulfonimide (LiTFSI) in 1:1 ethylene carbonate/dimethyl carbonate (EC/DMC). The graphite intercalation compound (GIC) at the negative electrode is formed from the electrolyte through few successive charging/self-discharging cycles, without requiring any auxiliary metallic lithium electrode. The various problems to be solved for a proper operation of this system are presented:
the choice of electrode materials
the choice of current collectors compatible with the electrolyte
the optimized parameters for forming the GIC
the performance of the LiC system, which in particular displays 4 times higher energy density compared to a traditional EDL capacitor with the same mass of carbon, while being more environment friendly.
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Today's Research in Aqueous Electrochemical Capacitors: from Oxides to Nitrides Thierry Brousse, Professor of Materials Science, Institut des Matériaux Jean Rouxel (IMN), Université Polytechnique Nantes
Abstract
This presentation is dedicated to aqueous based electrochemical capacitors (ECs), which have been investigated using different electrode materials such as oxides (MnO2, Fe3O4,…)in neutral aqueous electrolytes (Na2SO4, LiNO3, …). The device assembly generally consists of a negative activated carbon electrode which stores charges mainly via capacitive process (double layer capacitance). On the positive side the charge storage mechanism relies upon pseudocapacitive mechanisms which depend upon the choice of the oxide. In the case of manganese dioxide, fast and reversible surface redox reactions rule the charge storage. In such case, the asymmetric device combines two different electrodes with the major benefit of improving the useful electrochemical window of the resulting device, thus enabling to operate cells in mild aqueous electrolytes up to 2.2V.
Recently, transition metal nitrides have also been proposed as possible electrode for ECs in aqueous media (KOH, H2SO4,…). The advantages of nitrides over their oxide counterparts are their excellent electronic conductivity and their good stability in acidic or basic media. This communication will focus on the electrode materials and on the devices using oxides or nitrides.
Carbon/MnO2 asymmetric aqueous device:
Description of the device, recent advances on the cell characterization, optimized voltage, temperature, etc…
Other oxides:
Why other oxides are less studied than MnO2?
Which ones are going to emerge?
Nitrides:
Characterization and performances of different transition metal nitrides
Some example of VN based devices
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Fundamental Design and Practical Considerations En Route to High-Performance Aqueous Asymmetric Electrochemical Capacitors Megan Sassin, Research Chemist, Naval Research Laboratory
Abstract
This presentation highlights both fundamental (charge-storage mechanism) and practical issues (electrode design/fabrication and EC components) that must be addressed to achieve optimal blends of energy and power in size-scalable aqueous asymmetric electrochemical capacitors.
The topics that will be covered include:
Importance of electrode architecture in aqueous asymmetric ECs
Carbon nanofoam electrode platforms
Advantages: Benchtop fabrication
Device-ready electrodes
Tunable pore size (nm to μm)→ pre-select frequency response of device
Size-scalable in x, y (100 cm2) & z (70 μm to 420 μm)
Electroless deposition of nanoscale conformal coatings of metal oxides on carbon nanofoams
Advantages: Self-limits to yield ~10 nm conformal-to-the-carbon surface coatings
Retains the pore structure of the carbon nanofoam→ maintain high power
Short solid-state transport distances for cations involved in pseudocapacitance reaction→ essential for high-rate operation
Geometric capacitances as high as 7.5 F cm-2
Prototype aqueous asymmetric ECs: (+)MnOx//Li2SO4//FeOx(-)
Extended operating voltage (~2 V) in aqueous 2.5 M Li2SO4 electrolyte
Enhanced specific energy compared to ECs with powder-composite electrode architectures
Device time constant of 10 s
Practical issues of EC components
Evaluation of separator materials for aqueous asymmetric ECs
Low-temperature performance of aqueous electrolytes
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Consideration for High Withstand Voltage of SBP-BF4 / AN System Kazumi Chiba, Deputy Manager, New Product Development Office, Japan Carlit Co.
Abstract
This presentation is on how using SBP-BF4, a high-performance electrolyte, will improve EDLC properties.
Specifically, the following items will be covered:
Comparison of electrolytes: SBP, TEMA, and TEA (in solvents: AN, PC, and SL)
The advantages and disadvantages of solvent types: AN, PC, and SL
Discussions on why the electrolyte SBP-BF,4,/AN withstands high voltages
Advantages and disadvantages of each type of electrolyte
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Advanced Electrolytes for Electrochemical Double-Layer Capacitors Andrea Balducci, Scientific Leader Supercapacitors Group, MEET Battery Research, Muenster University
Abstract
The development of advanced electrolytes if essential for the realization of high energy electrochemical double layer capacitors.
Advanced electrolytes need to display the following properties:
High conductivity and low viscosity
Large electrochemical stability window
Low flammability
High safety
In this presentation two types of advance electrolytes will be consider:
Mixtures of ionic liquids and propylene carbonate
Adiponitrile
These advanced electrolytes display all the abovementioned properties and they can be conveniently used for the realization of electrochemical double layer capacitors with cell voltage as high as 3.5 V. These high voltage devices are able to display high performance in term of energy and power. Moreover, they also display remarkable cycling stability.
The presentation concludes with a summary and discussion of next steps necessary for the further optimization of electrochemical double layer capacitors containing these advanced electrolytes.
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Fine-Tuning the Carbon – Electrolyte Interface for Designing High-Energy Density Double-Layer Capacitors Patrice Simon, Professor of Materials Science, Université Paul Sabatier
Abstract
This presentation will focus on different approaches for improving the energy density of carbon-based supercapacitors. In a first step, we will show by electrochemical measurements how the control of the porous structure (pore size) of microporous carbons can greatly enhance their gravimetric capacitance. The basic mechanism of this capacitance enhancement will be explained thanks to recent results obtained by atomistic modeling. The last part of the talk will be dedicated to the characterization of new electrolytes based on ionic liquid mixtures, for widening the operation temperature range and the unit cell voltage.
The talk will detail mainly the following items:
Electrochemical characterization of microporous carbons in organic liquid electrolyte
Electrochemical characterization in ionic liquid electrolytes
Simulation by Molecular Dynamics of the ion adsorption in small micropores
Electrochemical behavior of exohedral carbons in Ionic Liquid mixture
