View by Category

The presentation will start after a short

(15 second) video ad from one of our sponsors.

Hot tip: Video ads won’t appear to registered users who are logged in. And it’s free to register and free to log in!

(15 second) video ad from one of our sponsors.

Hot tip: Video ads won’t appear to registered users who are logged in. And it’s free to register and free to log in!

Loading...

PPT – Electrochemical impedance spectroscopy: Applications to LixCoO2 electrodes PowerPoint presentation | free to view - id: 96ed3-ODRkY

The Adobe Flash plugin is needed to view this content

About This Presentation

Write a Comment

User Comments (0)

Transcript and Presenter's Notes

Electrochemical impedance spectroscopy

Applications to LixCoO2 electrodes

- Literature
- Sundeep Kumar
- February 9, 2005

Impedance definition Concept of complex impedance

- Concept of electrical resistance It is the

ability of a circuit element to resist the flow

of electrical current. Ohm's law defines

resistance in terms of the ratio between voltage

E and current I. - R E / I
- it's use is limited to only one circuit element

-- the ideal resistor. - An ideal resistor
- It follows Ohm's Law at all current and voltage

levels. - It's resistance value is independent of

frequency. - AC current and voltage signals though a resistor

are in phase with each other. - Like resistance, impedance is a measure of the

ability of a circuit to resist the flow of

electrical current. Unlike resistance, impedance

is not limited by the simplifying properties

listed above. - Electrochemical impedance is usually measured by

applying an AC potential to an electrochemical

cell and measuring the current through the cell.

Assume that we apply a sinusoidal potential

excitation. The response to this potential is an

AC current signal.

Measurement of impedance

- The excitation signal, expressed as a function of

time, has the form - Et E0 sin(? t)
- Et is the potential at time t, E0 is the

amplitude of the signal, and ? is the radial

frequency. - The response signal, It, is shifted in phase (f)

and has a different amplitude, I0. - It I0 sin (? t f)
- An expression analogous to Ohm's Law allows us to

calculate the impedance of the system as - The impedance is therefore expressed in terms of

a magnitude, Zo, and a phase shift, f.

Data Presentation

- The expression for Z(?) is composed of a real and

an imaginary part. If the real part is plotted on

the Z axis and the imaginary part on the Y axis

of a chart, we get a "Nyquist plot". - The y-axis is negative and that each point on the

Nyquist plot is the impedance at one frequency. - On the Nyquist plot the impedance can be

represented as an vector (arrow) of length Z.

The angle between this vector and the x-axis is

f. - The semicircle is characteristic of a single time

constant corresponding to a physical process in

the system - Impedance spectroscopy is used to extract the

information on these physical processes

Electrical Circuit Elements

- The impedance of a resistor is independent of

frequency and has no imaginary component. Current

stays in phase with the voltage across the

resistor. - A capacitor's impedance decreases as the

frequency is raised. Capacitors also have only an

imaginary impedance component.

Z R

Z 1/j?C

Physical Electrochemistry and Equivalent Circuit

Elements

- Electrolyte resistance and resistance from

current collectors - Double layer capacitance
- A electrical double layer exists on the interface

between an electrode and its surrounding

electrolyte. This double layer is formed as ions

from the solution "stick on" the electrode

surface. Charges in the electrode are separated

from ions charges. - Charge transfer resistance
- Charge transfer resistance corresponds to

interfacial charge transfer of Li ion (related

to ionic motion) and electronic conductivity of

the electrode

Physical Electrochemistry and Equivalent Circuit

Elements

- Diffusion
- Diffusion also can create an impedance called the

Warburg-impedance. At high frequencies the

Warburg impedance is small since diffusing

reactants don't have to move very far. At low

frequencies the reactants have to diffuse

farther, increasing the Warburg-impedance. - Constant Phase Element
- Capacitors in EIS experiments often do not behave

ideally. Instead they act like a constant phase

element as defined below. - The impedance of a capacitor can be expressed

as - where, A 1/C The inverse of the capacitance a

An exponent which equals 1 for a capacitor - For a constant phase element, the exponent a is

less than one. The "double layer capacitor" on

real cells often behaves like a CPE, not a

capacitor.

Example Simulation of impedance data from known

equivalent circuit

- The parameters in this plot were calculated

assuming a 1 cm2 electrode undergoing uniform

corrosion at a rate of 1 mm/year. - RP 250 ?, Cdl 40 µF/cm2 and Rs20 ? were

assumed to simulate the impedance plot - One can simulate the impedance data if one knows

the equivalent circuit before hand - OR
- One can fit the experimental impedance data to an

equivalent circuit

EIS on LiCoO2 electrodes

- Goodenough and co-workers _at_ Oxford University,

England - Aurbach and co-workers _at_Bar-Ilan university,

Isreal - Scrosati and co-workers _at_ Universita di Roma,

Italy

- M.G.S.R. Thomas, P.G. Bruce and J.B. Goodenough,

J. Electrochem. Soc., 132 (1985) 1521 - D. Aurbach et al., J. Electrochem. Soc., 145

(1998) 3024 - M.D. Levi et al., J. Electrochem. Soc., 146

(1999) 1279 - F. Nobil et al., J. Phys. Chem. B., 106 (2002)

3909

Goodenough and co-workers

- AC Impedance Analysis of Polycrystalline

Insertion Electrodes Application to Li1-xCoO2

M.G.S.R. Thomas, P.G. Bruce and J.B. Goodenough,

J. Electrochem. Soc. 132 (1985) 1521 - 1528 - In this paper, an equivalent circuit model is

presented for interpreting the A.C. impedance of

a pressed-powder insertion-compound electrode

(Li1-xCoO2) in contact with a liquid electrolyte

Goodenough and co-workers

- LiLiBF4 (in PC)LiCoO2
- Galavanostatically charged up to Li0.65CoO2
- Impedance measurements at 10mV-rms AC

perturbation sweeping the frequency range 10kHz

to 0.1 mHz. - Assumption The electronic conductivity of the

insertion compound is high and that each particle

is in contact with the aggregate across a

solid-solid interface making an ohmic contact of

low resistance to electron flow

Goodenough and co-workers

Faradic process at electrode

Solution resistance

Non-Faradic process

At least six circuit components 3 resistors,

two capacitors and a Warburg component are

required to produce the basic form of the response

Goodenough and co-workers

- Two processes
- Adsorption of Li ions or PC onto the surface of

the electrode without charge transfer - And formation of an ionically conducting but

electronically insulating surface layer at the

electrode surface

Goodenough and co-workers

Goodenough and co-workers

- Three separate types of experiments
- The time dependence of the AC impedance response
- The influence of premixing of the electrolyte

with the cathode material - The variation of circuit parameters with applied

voltage

Goodenough and co-workers

- Initially a CdlgtCads is found, this is physically

unreasonable situation - And it is most improbable that adsorption should

cause Cdl to decrease with time, rather

increasing electrolyte penetration with time

should increase Cdl - Both the adsorption based model were discarded on

similar basis

Goodenough and co-workers

- According to SL model
- Rsl ?(L/A)
- CSL ?(A/L)
- Hence RSL should increase and CSL should decrease

with time - Therefore, a SL model contains equivalent circuit

parameters that vary in self-consistent manner

with the electrochemical processes they represent

as the cell conditions are varied.

Goodenough and co-workers conclusions

- Evidences of surface layer formation on

electrode surface

Aurbach and co-workers

- Solid-State Electrochemical Kinetics of Li-Ion

Intercalation into Li1-xCoO2 Simultaneous

application of Electroanalytical Techniques SSCV,

PITT and EIS M.D. Levi et al., J. Electrochem.

Soc., 146 (1999) 1279. - Li1M LiAsF6 in ECDMC(13) LiCoO2 (with carbon

and binder) - The analysis of impedance spectra in terms of

equivalent circuit - Impedance measurements were taken during charging

Aurbach and co-workers

- Low solution resistance (25 ohms compared to

60 ohms observed by Goodenough et al. - Semicircles are more resolved than reported by

Goodenough and coworkers - Medium frequency semicircle becomes smaller on

increasing the voltage

Aurbach and co-workers

- High-frequency semicircle surface layer related
- Medium-frequency semicircle Charge transfer

resistance related to slow Li ion interfacial

transfer, coupled with a capacitance at the

surface film/Li1-xCoO2 particle interface - At low frequency, a narrow Warburg region

solid-state diffusion of Li ions into the bulk

cathode material - Steep sloping line at lowest frequencies

accumulation of intercalant (Li) into the bulk

Aurbach and co-workers

- Simulated and experimental impedance data

At E 4.07V Li0.50CoO2

Aurbach and co-workers

- There is some correlation between decrease in Rct

and increase in the LixCoO2 electrical

conductivity with potential in this range. - However, Rct for such an electrode does not

reflect only the electronic conductivity of the

particles, but also interfacial charge transfer

that relates to ionic transport.

Aurbach and co-workers conclusions

Scrosati and co-workers

- An AC Impedance Spectroscopic Study of LixCoO2

at Different Temperatures F. Nobili et al., J.

Phys. Chem. B., 106 (2002) 3909. - The paper presents an EIS of LiCoO2 electrodes at

various temperatures (0-30 C) (Temperature

dependence) - Li1M LiClO4 (ECDMC- 11)LiCoO2 (Composite

cathode with bonder and carbon) - 10mV perturbation and frequency sweep of 100kHz

to 1mHz

Scrosati and co-workers

- At any potential, a not well defined semicircle

is present at high frequency limit - As potential increases, another semicircle

develops at medium frequency - And at lowest frequency limit, Warburg branch

appears

Scrosati and co-workers

- The ill-defined semicircle present at 24C in

both graphs splits progressively into two

distinct semicircles that become fully developed

at the lowest temperature

Scrosati and co-workers

- A high frequency dispersion (gt1kHz) because of

presence of passivating layer - An intermediate frequency dispersion (between

10Hz and 1kHz) because of charge transfer - A low-frequency semicircle associated with the

electronic properties of the material - Very low frequency spike of the ionic diffusion
- The drop of the resistance associated with the

low frequency semicircle occurs over the narrow

x-range that corresponds to the insulator to

metal transition - The growth of the additional semicircle in the

middle frequency range becomes noticeable in

correspondence of potential values at which the

intercalation process takes place at an

appreciable rate.

Scrosati and co-workers

CPE

- Both the circuits give same impedance plots and

they both are equivalent - However, the (b) is more close to the physics of

the processes.

Scrosati and co-workers

- Insulator to metal transition can be seen from

activation - barriers

Scrosati and co-workers Conclusions

Equivalent circuits Conclusions

About PowerShow.com

PowerShow.com is a leading presentation/slideshow sharing website. Whether your application is business, how-to, education, medicine, school, church, sales, marketing, online training or just for fun, PowerShow.com is a great resource. And, best of all, most of its cool features are free and easy to use.

You can use PowerShow.com to find and download example online PowerPoint ppt presentations on just about any topic you can imagine so you can learn how to improve your own slides and presentations for free. Or use it to find and download high-quality how-to PowerPoint ppt presentations with illustrated or animated slides that will teach you how to do something new, also for free. Or use it to upload your own PowerPoint slides so you can share them with your teachers, class, students, bosses, employees, customers, potential investors or the world. Or use it to create really cool photo slideshows - with 2D and 3D transitions, animation, and your choice of music - that you can share with your Facebook friends or Google+ circles. That's all free as well!

For a small fee you can get the industry's best online privacy or publicly promote your presentations and slide shows with top rankings. But aside from that it's free. We'll even convert your presentations and slide shows into the universal Flash format with all their original multimedia glory, including animation, 2D and 3D transition effects, embedded music or other audio, or even video embedded in slides. All for free. Most of the presentations and slideshows on PowerShow.com are free to view, many are even free to download. (You can choose whether to allow people to download your original PowerPoint presentations and photo slideshows for a fee or free or not at all.) Check out PowerShow.com today - for FREE. There is truly something for everyone!

You can use PowerShow.com to find and download example online PowerPoint ppt presentations on just about any topic you can imagine so you can learn how to improve your own slides and presentations for free. Or use it to find and download high-quality how-to PowerPoint ppt presentations with illustrated or animated slides that will teach you how to do something new, also for free. Or use it to upload your own PowerPoint slides so you can share them with your teachers, class, students, bosses, employees, customers, potential investors or the world. Or use it to create really cool photo slideshows - with 2D and 3D transitions, animation, and your choice of music - that you can share with your Facebook friends or Google+ circles. That's all free as well!

For a small fee you can get the industry's best online privacy or publicly promote your presentations and slide shows with top rankings. But aside from that it's free. We'll even convert your presentations and slide shows into the universal Flash format with all their original multimedia glory, including animation, 2D and 3D transition effects, embedded music or other audio, or even video embedded in slides. All for free. Most of the presentations and slideshows on PowerShow.com are free to view, many are even free to download. (You can choose whether to allow people to download your original PowerPoint presentations and photo slideshows for a fee or free or not at all.) Check out PowerShow.com today - for FREE. There is truly something for everyone!

presentations for free. Or use it to find and download high-quality how-to PowerPoint ppt presentations with illustrated or animated slides that will teach you how to do something new, also for free. Or use it to upload your own PowerPoint slides so you can share them with your teachers, class, students, bosses, employees, customers, potential investors or the world. Or use it to create really cool photo slideshows - with 2D and 3D transitions, animation, and your choice of music - that you can share with your Facebook friends or Google+ circles. That's all free as well!

For a small fee you can get the industry's best online privacy or publicly promote your presentations and slide shows with top rankings. But aside from that it's free. We'll even convert your presentations and slide shows into the universal Flash format with all their original multimedia glory, including animation, 2D and 3D transition effects, embedded music or other audio, or even video embedded in slides. All for free. Most of the presentations and slideshows on PowerShow.com are free to view, many are even free to download. (You can choose whether to allow people to download your original PowerPoint presentations and photo slideshows for a fee or free or not at all.) Check out PowerShow.com today - for FREE. There is truly something for everyone!

For a small fee you can get the industry's best online privacy or publicly promote your presentations and slide shows with top rankings. But aside from that it's free. We'll even convert your presentations and slide shows into the universal Flash format with all their original multimedia glory, including animation, 2D and 3D transition effects, embedded music or other audio, or even video embedded in slides. All for free. Most of the presentations and slideshows on PowerShow.com are free to view, many are even free to download. (You can choose whether to allow people to download your original PowerPoint presentations and photo slideshows for a fee or free or not at all.) Check out PowerShow.com today - for FREE. There is truly something for everyone!

Recommended

«

/ »

Page of

«

/ »

Promoted Presentations

Related Presentations

Page of

Page of

CrystalGraphics Sales Tel: (800) 394-0700 x 1 or Send an email

Home About Us Terms and Conditions Privacy Policy Contact Us Send Us Feedback

Copyright 2016 CrystalGraphics, Inc. — All rights Reserved. PowerShow.com is a trademark of CrystalGraphics, Inc.

Copyright 2016 CrystalGraphics, Inc. — All rights Reserved. PowerShow.com is a trademark of CrystalGraphics, Inc.

The PowerPoint PPT presentation: "Electrochemical impedance spectroscopy: Applications to LixCoO2 electrodes" is the property of its rightful owner.

Do you have PowerPoint slides to share? If so, share your PPT presentation slides online with PowerShow.com. It's FREE!

Committed to assisting Mit University and other schools with their online training by sharing educational presentations for free