Energy storage: EDLC & Pseudo Capacitors

Energy storage: EDLC & Pseudo –

Capacitors

Doron Aurbach Department of chemistry, Bar Ilan University

Ramat-Gan 52900 Israel Email: [email protected]

Energy is found everywhere

we just need to harvest and store it

We lack good storage technologies

We want to move ASAP to sustainable energy

Supercapacitors can be used for load leveling applications

overview Material design Aqueous SC High voltage SC PsC Summery

Spe

cifi

c Po

wer

(W

kg-1

)

Specific energy (Whkg-1)

Comm. Li-ion 5V. Li-ion

Primary Li

Ni/MH 1h

1 min 1 s

105

104

103

10

102

1 10 10-1 10-2 102 103 1

Ni/Cd

Lead acid

capacitor

Suprecapacitors (EDLC) fill the Energy Vs. Power gap between batteries and capacitors

Batteries are evaluated in terms of energy

and power densities

A typical Ragone plot, of common Faradaic electrochemical energy storage

cells (time constants in red)

Spe

cifi

c Po

wer

(W

kg-1

)

Comm. Li-ion 5V. Li-ion

Primary Li

Ni/MH 1h

1 min 1 s

105

104

103

10

102

1 10 10-1 10-2 102 103 1

Ni/Cd

ECs (2008)

Lead acid


What is Capacitor?

• A capacitor (originally known as condenser) is a passive two-

terminal electrical component used to store energy in an

electric field.

• When there is a potential difference across the conductors, a

static electric field develops across the dielectric, causing

positive charge to collect on one plate and negative charge to

accumulate on the other plate. Energy is formed in terms of

electrostatic field.


What is Supercapacitor? Supercapacitor (SC) also known as electric double-layer capacitor (EDLC)

or Ultracapacitor, is electrochemical capacitor. The capacitance value of an

electrochemical capacitor is determined by two storage principles, which both

contribute indivisibly to the total capacitance:

• Double layer capacitor – Electrostatic storage achieved by separation of charge in

a Helmholtz double layer at the interface between the surface of a

conductive electrode and an electrolyte. The separation of charge is of the order of

a few angstrom (0.3–0.8 nm), much smaller than in a conventional capacitor

than in a conventional capacitor.

• Pseudocapacitor - Faradaic electrochemical storage with electron charge

transfer, achieved by redox interaction, intercalation or electrosorption.


Up to 109 V/m potential fall exist

on charged interfaces Electrical Double Layer (EDL)

+

+

+

-

+

-

-

+

-

OHP

-

-

-

-

-

-

-

-

Counter ion

Co-ions

+

-

Water molecule

+

Outer Helmholtz

plane


The difference between

More power is required for short time interval in 200m race

Constant but less power required for long time in 20km race


A = Surface area (very high in Activated

carbon).

d = Dielectric thickness, single solvent

molecule.

εr = limited by the solvent properties.

Possible electrolytes:

1. Aqueous electrolyte, high rates small ions high

ionic conductivity, limited voltage.

2. Organic electrolyte, moderate conductivity and

capacity up to 3V.

3. Ionic liquids- Low conductivity, lower capacity,

high voltage, safe.

dC

rA

0

www.youtube.com/watch?v=FJZKm5khaAA

Charged species can be stored

electrostaticly by the EDL


M. Biswal, A. Banerjee, M. Deo, S. Ogale, Energy & Environmental Science 2013, 6, 1249-1259.

From dead

leaves till

energy storage

devices


High capacitance graphene SC

P. A. Basnayaka, M. K. Ram, E. K. Stefanakos, A. Kumar, Electrochimica Acta 2013, 92, 376-382


Increasing the

electrochemical window using

neutral electrolyte solutions

Q. Gao, L. Demarconnay, E. Raymundo-Pinero, F. Beguin, Energy & Environmental Science 2012, 5, 9611-9617.


Electrodeposition

of Mn-Mo oxide

film on CNT/ITO

M. Nakayama, K. Okamura, L. Athouël, O. Crosnier, T. Brousse, ECS Transactions 2012, 41, 53-64.


General features:

• Highly disordered

• Electrically conductive

• High surface area (up

to ~3000m2/g)

Activated carbon (AC)

Activated carbons possess unique

physicochemical properties:

M M M

M M M M

M

M M M

M M M M

M

Carbon

precursor

Carbon

material

Carbonization

under inert

atmosphere

Oxidizing

agent

Activated

carbon Carbon

precursor

Polymerization


-100

-50

0

50

100

E (volts) vs S.C.E

C (

F/g

r)

0

50

100

150

200

250

300

350

400

0 0.2 0.4 0.6 0.8 1 1.2

Relative pressure (p/p0)

vo

lum

e a

dso

rb

ed

(m

l/g

r)

cc/g

Relative Pressure

0

50

100

150

200

250

300

0 0.2 0.4 0.6 0.8 1 1.2

Relative pressure (p/p0)

vo

lum

e a

dso

rb

ed

(m

l/g

r)

Relative Pressure

cc/g

-200

-150

-100

-50

0

50

100

150

-0.6 -0.4 -0.2 0 0.2 0.4 0.6

E (volts) Vs S.C.E C

(F

/gr)

CO 2+

C C

CO2

O

CO+

C

Activation

M. Noked, E. Avraham, A. Soffer, D. Aurbach, The Journal of Physical Chemistry C 2009, 113, 21319-21327.


Using CNTs as a conductive additive and as a

reinforcing agent in novel electrodes

Rolling up a graphene sheet to form a tube. Properties: • Very strong and flexible molecular material due to the C-C covalent bonding and seamless hexagonal network architecture. •Thermal conductivity ~ 3000 W/m.K in the axial direction •Electric conductivity six orders of magnitude higher than copper

CNTs grow methods: a) Arc-discharge b) Laser ablation c) Catalytic chemical vapor deposition (CCVD)

b a


Carbon

precursor

Stirring

CNT dispersion

Carbon

material

Oxidizing

agent

Activated

carbon

5µm

5µm

CNT

Carbonization

under inert

atmosphere


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Energy storage: EDLC & Pseudo Capacitors