Capacitive Storage Science

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Capacitive Storage Science

• Chairs Bruce Dunn and Yury Gogotsi
• Panelists
• Michel Armand (France) Martin Bazant
• Ralph Brodd Andrew Burke
• Ranjan Dash John Ferraris
• Wesley Henderson Sam Jenekhe
• Katsumi Kaneko (Japan) Prashant Kumta
• Keryn Lian (Canada) Jeff Long
• John Miller Katsuhiko Naoi (Japan)
• Joel Schindall Bruno Scrosati (Italy)
• Patrice Simon (France) Henry White

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Capacitive Storage Science
Supercapacitors bridge between batteries and
conventional capacitors
Supercapacitors are able to attain greater energy
densities while still maintaining the high power
density of conventional capacitors.
Supercapacitors provide versatile solutions to
a variety of emerging energy applications
including harvesting and regenerating energy in
transportation, industrial machinery, and storage
of wind, light and vibrational energy. This is
enabled by their sub-second response time.
Halper, M.S., Ellenbogen, J.C., MITRE
Nanosystems Group, March 2006
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Capacitive Storage Science technology challenges

• Capacitor Systems and Devices
• - Increased energy density
• - Longer life cells
• - Self-balancing
• - Cost
• Electrolytes for Capacitor Storage
• Design electrolytes for EC operation high
  ionic conductivity wide
  electrochemical window, chemical and thermal
  stability non toxic, biodegradable and/or
  renewable
• EDLC and Pseudocapacitive Charge Storage
  Materials
• New strategies are needed to improve power and
  energy density of charge storage materials

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Capacitive Storage Science current status

• Capacitor Systems and Devices
• High specific capacitance (100 F/g) and fast
  response time ( 1 sec),
• but energy storage (2-10 wh/kg) not sufficient
  for many apps
• Long shelf (10 yr) and cycle (gt1M) life
• Electrolytes for Capacitor Storage
• Traditional Electrolytes
• - aqueous (KOH, H2SO4) - corrosive, low
  voltage
• - organic (AN or PC and Et4NBF4 or
  Et3MeNBF4) - low capacitance, toxicity
  and safety concerns
• Ionic Liquid Electrolytes - safer, but
  viscosity too high, conductivity too low for
  capacitor applications improvements in
  properties from mixing with organic solvents
• Theory and Modeling Variety of approaches
  available continuum, atomistic, ab initio
  all have advantages and limitations

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Capacitive Storage Science current status
EDLC Charge Storage Materials Majority of
present day EDLC devices are based on activated
carbon
Multifunctional Materials for Pseudocapacitors Ps
eudocapacitive materials generally exhibit higher
specific capacitance and energy density relative
to high-surface-area carbon
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Capacitive Storage Science basic-science
challenges, opportunities, and needs

• EDLC Charge Storage Materials
• - Materials utilizing only double layer storage
  
• require understanding of pore structure and ion
  size
• influences on charge storage
• - Identify new strategies in which EDLC
  materials
• exploit both multiple charge storage mechanisms
  combine double
• layer charging and pseudocapacitance to enhance
  energy and power densities
• Multifunctional Materials for Pseudocapacitors
• - The underlying charge-storage mechanisms
• for pseudocapacitive materials are not well
  understood.
• - Opportunities for new directions in
• pseudocapacitor materials single phase and
  multi-phase
• nanostructure design of novel 3-D electrode
  architectures
• with tailored ion and electronic transport

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Capacitive Storage Science basic-science
challenges, opportunities, and needs

• Electrolytes for Capacitor Storage
• - Create new electrolyte formulations enabling
• high voltage devices and revolutionary electrode
• combinations for capacitive storage
• - New salts, new solvents, immobilizing
  matrices
• designed for capacitor storage
• Theory and Modeling
• - Structure and dynamics of solvent
• and ions in non-polar nanopores.
• - Electronic characteristics of carbon
• and MOx electrodes.
• - Validation against simple model experiments.

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Capacitive Storage Science basic-science
challenges, opportunities, and needs

• Capacitor Systems and Devices
• Higher volumetric and gravimetric energy
  density with less than one second response time
  Increased voltage, increased specific capacitance
• Improved device safety Non-toxic,
  non-flammable electrolyte

Regenerative Energy Capture using
Capacitors 40 of energy is recovered
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Capacitive Storage Science Materials for
Electrical Double Layer Capacitors

• Ralph Brodd Patrice Simon
• Ranjan Dash John Ferraris
• Subpanel leader

Subpanel members
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Capacitive Storage Science PRD Charge Storage
Materials by Design
Summary of research direction
Scientific challenges
Enhance EDLC materials performance by creating
designed architectures, surface functionality,
tailored porosity, and thin conformal films,
matched synergistically with appropriate
electrolyte systems.
Identify new strategies in which EDLC materials
simultaneously exploit multiple charge storage
mechanisms.
Potential scientific impact
Potential impact on EES
Establish nanodimensional spatial control of the
interface utilizing tethered functionalized
molecular wires. Understand ion transport across
interfaces
EDLC systems will be rationally designed to
revolutionize their utilization throughout the
energy sector Develop new EDLC materials and
architectures to dramatically boost energy and
power densities Anticipate impact in decades
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Capacitive Storage Science Materials for
Electrical Double Layer Capacitors technology
challenges

• New strategies are required to improve both power
  and energy density of EDLC materials
• Materials Synthesis
• Designed Architectures
• Modeling Input/Output

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Capacitive Storage Science PRD Charge Storage
Materials by Design

• Systematic guidelines are currently lacking for
  development of improved charge storage materials
• Materials utilizing only double layer charge
  storage
• Requires fundamental understanding of pore
  structure and effective ion size
• Requires new synthesis methodology

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Capacitive Storage Science PRD Charge Storage
Materials by Design

• Materials utilizing mixed charge storage
• Highly reversible redox-active functionalities on
  high surface area electrodes
• Thin dielectric or conducting coatings on
  ordered high surface area materials
•  
• Surfaces decorated with nanowires having active
  functionality
•   Requires new synthesis methodology

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Capacitive Storage Science PRD Charge Storage
Materials by Design
Materials utilizing synthetic ordered
architectures

• Electrode materials with controlled pore size and
  surface area deposited in ordered geometries with
  intimate contact to current collectors
•   Requires new synthesis methodology

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Capacitive Storage Science PRD Charge Storage
Materials by Design

• Materials Synthesis
• Designed Architectures
• Development of new EDLC materials and
  architectures will dramatically boost
•       Power and Energy!

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Capacitive Storage Science Sub-panel on
Materials for Pseudocapacitors and Hybrid Devices

• Samson Jenekhe, sub-Panel lead
• Prashant Kumta
• Jeffrey Long
• Katsuhiko Naoi
• John Newman

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Capacitive Storage Science PRD
Multifunctional Materials for Pseudocapacitors
and Hybrid Devices
Motivation Pseudocapacitors enable energy
densities significantly higher than for
double-layer capacitors. Challenge
Simultaneously maximize both energy density and
power density, and enhance lifetime.
New Research Directions

• Investigation of new materials?beyond metal
  oxides
• Multifunctional architecture.
• Rational design of materials and structures.
• Understand fundamental charge-storage mechanisms.

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Capacitive Storage Science Multifunctional
Materials for Pseudocapacitors and Hybrid Devices
New Materials Architectures
Vanadium Nitride, VN nanocrystals
New opportunities for fundamental
understanding and scientific advances.
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Capacitive Storage Science Electrolyte subpanel
members
Subpanel lead

• Keryn Lian
• Bruno Scrosati
• Michel Armand
• Wesley Henderson

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Capacitive Storage Science technology challenges
Aqueous and non-aqueous electrolytes with the
following properties immobilized matrix
produced from sustainable sources high ionic
conductivity chemical and thermal stability
large electrochemical stability window (gt5V)
non-toxic, biodegradable and/or recyclable
exceptional performance with long device lifetime
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Capacitive Storage Science PRD Topic Molecular
Understanding of Electrolyte Interactions in
Capacitor Science

• Fundamental lack of understanding solvent-salt
  structure and physical properties.
• Bulk Properties
• Diverse materials (salt, solvent, immobilizing
  matrices, )
• Various conditions (temperature, concentration,
  )
• Experimental measurements (phase diagrams,
  spectroscopy, )
• Modelling and simulations
• Interfacial Effects
• Same approaches to explore interfacial and
  confined pore interactions differ from the bulk
• Performance
• Create a fundamental understanding of link
  between device performance and bulk/interfacial
  molecular interactions.

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Capacitive Storage Science PRD Topic Molecular
Understanding of Electrolyte Interactions in
Capacitor Science
Summary of research direction
Scientific challenges
Explore new salts, new solvents, immobilizing
matrices designed for capacitor storage Examine
bulk properties (solvent-salt interactions),
interfacial effects and behavior in confined
spaces using measurements and modelling Understand
effect of additives and impurities
The ideal electrolyte is an immobilized material
produced from sustainable sources, which has high
ionic conductivity wide electrochemical,
chemical and thermal stability and is non toxic,
biodegradable and/or renewable
Potential scientific impact
Potential impact on EES
Understanding the mechanism of charging and
degradation New electrolyte formulations enabling
revolutionary novel electrochemical capacitor
devices Knowledge will cross-over to battery
systems
Enable high power technologies for load
levelling, improve energy efficiency. Enable
novel energy recovery applications, HEVs and PHEVs
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Capacitive Storage Science Theory Modeling
sub-panel members

• Martin Bazant (MIT), sub-panel lead
• Katsumi Kaneko (Chiba University, Japan)
• Lawrence Pratt (Los Alamos)
• Henry White (University of Utah)

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Capacitive Storage Science current status of
modeling

• Equivalent circuit models (transmission-line
  models)
• Pros Simple formulae, fit to experimental
  impedance spectra
• Cons No nonlinear dynamics, microstructure,
  chemistry
• Continuum models (Poisson-Nernst-Planck
  equations).
• Pros analytical insight, nonlinear,
  microstucture
• Cons point-like ions, mean-field approximation,
  no chemistry
• Atomistic models (Monte Carlo, molecular
  dynamics).
• Pros molecular details, correlations, atomic
  mechanisms.
• Cons lt10,000 atoms, lt 10ns, limited chemical
  reactions.
• Quantum models (ab initio quantum chemistry and
  DFT)
• Pros Mechanisms and chemical reactions from
  first principles.
• Cons lt100 atoms, ltps, periodic boundary
  conditions

VERY FEW MODELS HAVE BEEN APPLIED TO
SUPERCAPACITORS
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Capacitive Storage Science priority research
directions for modeling

• Mathematical theory (beyond equivalent circuits)
• Derivation of nonlinear transmission line models
  for large voltages
• Modified Poisson-Nernst-Planck equations (steric
  effects, correlations)
• Continuum models coupling charging to mechanics,
  energy dissipation,
• Physics chemistry of electrolytes
• Develop accurate models for MD and MC simulations
• Entrance of ions into nanopores -- desolvation
  energy and kinetics.
• Ion transport, wetting, surface activation, and
  chemical modification.
• Physics chemistry of electrode materials
• Electron and ion transport in capacitor
  electrodes.
• Theory of capacitance of metal oxides and
  conducting polymers.
• Validation against simple model experiments
• Ordered arrays of monodisperse pores, single
  carbon nanotubes.
• Spectroscopic and x-ray analysis of ions and
  solvent in confined spaces

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Capacitive Storage Science Theory and Modeling
Summary of research direction
Scientific challenges
Fundamental understanding and modeling tools for
supercapacitors across all length and time scales.
Continuum, atomistic, quantum models
Potential scientific impact
Potential impact on EES

• Discovery of new physical phenomena- nanopore
  behavior, nonlinear dynamics
• New models at system, microstructure, molecular,
  and electronic levels
• New multi-scale simulation methods

• Models for rational design of EES systems
• Prediction of new materials
• Increased power and energy density
• Time scale decades to centuries

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Capacitive Storage Science Sub-panel members
Capacitive Devices and Systems

• Andrew Burke
• John R. Miller
• Pat Moseley
• Joel Schindall

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Capacitive Storage Science Capacitive devices
and systems
Summary of research direction
Scientific challenges
Develop and use efficient, low cost and safe
capacitive products to efficiently harvest and
recover waste energy in applications that include
electrical grid storage, renewable solar and wind
energy, transportation, industrial stop-go
machinery, mining, and microstorage of light,
vibration, and motion energy
New approaches for higher specific capacitance
electrode materials with improved morophology,
uniform micropores, higher cell voltages,
non-toxic, high conductivity, electrolytes, and
low resistance separator materials
Potential scientific impact
Potential impact on EES
Improved understanding of fundamental capacitive
energy storage and optimization of a device as a
system Improved material synthesis and processing
Efficient, fast, distributed capacitive energy
storage for a wide range of applications
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Capacitive Storage Science PRDs Basic science
of Capacitive Devices and Systems

• Increased energy density
• Longer life at high voltages and temperatures
• Self-balancing series strings of cells without
  electronics
• Safe failure modes under extreme conditions
• Technologies to enable reduced device cost