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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

30 MJ CAPACITOR STORAGE SYSTEM30 MJ CAPACITOR STORAGE SYSTEM

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Capacitive Storage Science: current status

Capacitor Systems and DevicesHigh specific capacitance (100 F/g) and fast response time (~ 1 sec), but energy storage (2-10 wh/kg) not sufficient for many appsLong shelf (10 yr) and cycle (>1M) life

Electrolytes for Capacitor StorageTraditional Electrolytes:

- aqueous (KOH, H2SO4) - corrosive, low voltage

- organic (AN or PC and [Et4N][BF4] or [Et3MeN][BF4]) - 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

0

200

400

600

800

1000

1200

1400

AC

CNT

MPC CAGC60 NRC

PANI/AC

PEDT/AC

PIThi

PFDT

PPy/AC

MPFPT

DAAQ

PAn/CNT

P3MTPEDT

PAn

RuO2/PAPPA

RuO2(sol-gel)

RuO2(ED)

RuO2(sol-gel)RuO2/ACRuO2/AC

RuO2(ESD)RuO2/CB

RuO2/CNTRuO2/ACRuO2/CXG

RuO2/MPCRuO2/ACNiO SnO2 / Fe3O4

MnOx

NiO/RuO2

MnO2

NiO

MnO2

Ir0.3Mn0.7O2

MnO2

Spe

cific

Cap

acita

nce

/ F

g-1

Carbons Polymers Metal Oxides RuO20

200

400

600

800

1000

1200

1400

0

200

400

600

800

1000

1200

1400

AC

CNT

MPC CAGC60 NRC

PANI/AC

PEDT/AC

PIThi

PFDT

PPy/AC

MPFPT

DAAQ

PAn/CNT

P3MTPEDT

PAn

RuO2/PAPPA

RuO2(sol-gel)

RuO2(ED)

RuO2(sol-gel)RuO2/ACRuO2/AC

RuO2(ESD)RuO2/CB

RuO2/CNTRuO2/ACRuO2/CXG

RuO2/MPCRuO2/ACNiO SnO2 / Fe3O4

MnOx

NiO/RuO2

MnO2

NiO

MnO2

Ir0.3Mn0.7O2

MnO2

Spe

cific

Cap

acita

nce

/ F

g-1

Carbons Polymers Metal Oxides RuO2

EDLC Charge Storage Materials: Majority of present day EDLC devices are based on activated carbon

Multifunctional Materials for Pseudocapacitors:Pseudocapacitive 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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Potential scientific impact

Potential impact on EES

Summary of research directionScientific challenges

Capacitive Storage Science: PRD: Charge Storage Materials by Design

Identify new strategies in which EDLC materials simultaneously exploit multiple charge storage mechanisms.

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

Enhance EDLC materials performance by creating designed architectures, surface functionality, tailored porosity, and thin conformal films, matched synergistically with appropriate electrolyte systems.

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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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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

Capacitive Storage Science: PRD Charge Storage Materials by Design

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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

Capacitive Storage Science: PRD Charge Storage Materials by Design

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Capacitive Storage Science: PRD Charge Storage Materials by Design

Electrode materials with controlled pore size and surface area deposited in ordered geometries with intimate contact to current collectors

  Requires new synthesis methodology

Materials utilizing synthetic ordered architectures

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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

New Research Directions

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

Motivation: Pseudocapacitors enable energy densities significantly higher than for double-layer capacitors.

Challenge: Simultaneously maximize both energy density and power density, and enhance lifetime.

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Capacitive Storage Science: Multifunctional Materials for Pseudocapacitors and Hybrid Devices

= New opportunities for fundamental understanding and scientific advances.

New Materials + Architectures

Vanadium Nitride, VN nanocrystals

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Capacitive Storage Science: Electrolyte subpanel members

Keryn Lian*

Bruno Scrosati

Michel Armand

Wesley Henderson

* Subpanel lead

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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 (>5V)■ non-toxic, biodegradable and/or recyclable■ exceptional performance with long device lifetime

Bulk

Interfacial Device Performance

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Capacitive Storage Science: PRD Topic: Molecular Understanding of Electrolyte Interactions in Capacitor ScienceFundamental 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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Potential scientific impact Potential impact on EES

Summary of research directionScientific challenges

Capacitive Storage Science: PRD Topic: Molecular Understanding of Electrolyte Interactions in Capacitor Science

Understanding the mechanism of charging and degradation

New electrolyte formulations enabling revolutionary novel electrochemical capacitor devices

Knowledge will cross-over to battery systems

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

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

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: <10,000 atoms, < 10ns, limited chemical reactions.

Quantum models (ab initio quantum chemistry and DFT) Pros: Mechanisms and chemical reactions from first principles. Cons: <100 atoms, <ps, periodic boundary conditions

VERY FEW MODELS HAVE BEEN APPLIED TO SUPERCAPACITORS

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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

Capacitive Storage Science: priority research directions for modeling

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Potential scientific impact Potential impact on EES

Summary of research directionScientific challenges

Capacitive Storage Science: Theory and Modeling

Continuum, atomistic, & quantum models

Fundamental understanding and modeling tools for supercapacitors across all length and time scales.

•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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Potential scientific impact Potential impact on EES

Summary of research directionScientific challenges

Capacitive Storage Science: Capacitive devices and systems

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

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

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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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

Capacitive Storage Science: PRDs: Basic science of Capacitive Devices and Systems