Conductive Paper and Textile for Rational Designs of Energy Storage Devices

Liangbing Hu, Yi CuiMaterial Science, Stanford

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Renewable Energy Landscape

Production‐Wind‐ Heat ‐ Solar

Usage‐Light

‐Building 

Transmission‐ Electrical grid

Storage‐ Electrochemical‐ Chemical fuels

SupercapacitorsLi-ion Batteries

Transparent Electrode

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Manipulating Electron, Ions, and Photons in Energy Devices

ElectronsPhotonsTransparent Electrodes

IonsElectronsSupercapacitorsLi-ion Batteries

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Specific energy (wh/kg)

Spec

ific

pow

er (w

/kg)

10-2 10-1 1 10 102 1031

10

102

103

104

105

106 Capacitors

Supercapacitors

Batteries Fuel cells

Comparison of Energy Storage Technologies

Important parameters:- Energy density (Energy per weight or volume)- Power density (Power per weight or volume)- Cycle life and safety- Cost

CNT, MnO2 and Si Nano-Nets

Supercapacitor

Li-ion Battery

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Energy Storage Mechanism

+++++

-----

Capacitor

Metal

Dielectrics, thickness: >1000nm.

thicknessC

CVE

1~

21 2=

Supercapacitor (Electrochemical capacitor)+++++

-----Metal

Electrolyte solutionDouble layer thickness, <1nm

-----

+++++

+++++

-----

-----

+++++

+++++

-----

Battery

Electrolyte solution

Capacitors and supercapacitor: surface storage.

Battery: bulk storage.

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Supercapacitor Components

The metal current collectors account for 20 ~ 30%of total weight

ElectrodeCu meshAl mesh

Conductive paperConductive textile

Step out

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The Building Block: SingleThe Building Block: Single--Walled Carbon NanotubeWalled Carbon NanotubeDimensions:

•Diameter ~ 1nm

•Length up to 4 microns

Mechanical/Chemical Properties

•Mechanical flexible

•Chemically inert

Electrical Properties

•Conductivity ~ 3x105 S/cm

•Mobility ~ 105 cm2/V*sec

•Both metallic and semiconducting

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Carbon Nanotube Ink for Conductive Coating

Surfactant

Bad coatingon plastic substrate

Good coatingon plastic substrate

These are critical for obtaining uniform coating• Dispersion of carbon nanotubes in solvent• Ink viscosity• Surface tension match between ink and substrate• Encapsulation for enough mechanical adhesion

Coating on paper ismuch easier!

Carbon nanotube powder Carbon nanotube ink

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Supercapacitor – Double Layer Capacitor

Charges stored in Electrical Double Layer

•Energy Storage by Charge Separation, like regular capacitor

•C=Aε/d

•d is ~ 1 nm, 1000 time smaller than regular capacitor

•A is much bigger than regular capacitor.

•Nanomaterials with high surface area (~ 1000m2 per gram) are with large application potential.

+

+

+

+++++++

+

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Porosity at two different scalesGreatly enhance surface area high A

Microporous carbon nanotube film

X100 μm

Macroporous paper fiber network

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Hu, Choi, Yang, Cui et al. PNAS, 2009

Conductive Paper Fabrication-Scalable Process

2 μmCarbon nanotubes

Silver Nanowires

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CNT/paper

Conductive Paper is highly conductive, mechanical flexible and stable

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Supercapacitor with Conductive Paper

Conductive paperSeparator paper

Conductive paper

• IR voltage drop can be used to calculate resistance

and device power

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Performance of conductive paper for Supercapacitor

High capacitance Stability

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Energy Density and Power Density

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Li ion Battery- An Excellent System to Store Energy

Nature Mater. 2004

Cost breakdown

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Large Scale Energy StorageFor grid applications

Cost

Li-ion Batteries: Opportunities and Challenges

Stanford paper battery

Disposable,Consumer Electronics

Cost

Electrical Vehicle

Energy Density

~ 5000 batteries

Size increases

Power Tools

Power DensityEnergy Density

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•Supercapacitor and Li-ion battery share the similar device structure•The metal current collectors account for ~ 20-30% of total weight

Light-Weight Current Collector Based on ConductivePaper and Textile

Cu meshAl mesh

Conductive paper Conductive Textile

Step out

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Conductive Paper Based Li-ion Batteries for Electrical Vehicles

Use Carbon nanotube/paper To replace Cu and Al current collector

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Performance of conductive paper for Li-ion Battery

Good enough for electrical vehicle applications

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Weight Saving Using Conductive Paper

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New Electrode-Current Collector Design for Li-ion Batateries

Conductive, porous current collector Fill in battery electrode materials

(a)

(b)

Flat metal current collector Coat battery electrode materials on surface

L. Hu et al. Submit to Adv. Mater

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Stretchable, Conductive Textile

- Simple process

Hu, Cui et al. Nano. Lett, 2010

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Conductive Textile: Highly Conductive and Stretchable

Conformal coating carbonnanotubes on textile fibers

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200 μm

(c)

200 μm

Light-weight, Porous Textile Conductor That Allows Loading of Other Materials

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Electrochemical Stability of Conductive Textile

Stability Window: 1 V to 3.8 VValid for Li4Ti5O12 (1.6 V) and LiFePO4 (3.6 V)

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1 μm

Extreme Simple Process for Battery Material Loading

L. Hu et al. Submit to Adv. Mater

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Voltage Profile Comparison

L. Hu et al. Submit to Adv. Mater

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Impedance Comparison between our structure and traditional structure

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Full Cell Cycling Performance

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Advantages of Using New Electrode-Current Collector Design

100 mg/cm2

20 mg/cm2

5Process

separator

1Process

separator

Traditional Ours

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Conclusion• Conductive paper for double layer capacitor

• Conductive textile for psuedocapacitor with high mass loading

• Conductive paper based Li-Ion batteries for electrical vechile applications

• A new design for electrode-current collector design which allows high mass loading for grid applications

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Acknowledgement

Cui Group Funding

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Questions? Questions?