KTH ROYAL INSTITUTEOF TECHNOLOGY

Electrochemical Characterization of Li-ion Batteries for Hybrid Application

Ageing Study

Abdilbari Shifa Mussa, Rakel Wreland Lindström, Mårten Behm, Göran Lindbergh

Li-ion Battery

Works by shuttling lithium ions between the two electrodes

Lithiated metal oxides: LCO, LFP, LMO, NMC etc...

Shuttling doesn’t continue indefinitely without loosing performance

Lithium ion battery during charging operation

Adapted from http://www.sigmaaldrich.com/technical-documents/articles/material-matters/u-s-department-of0.html

- Graphite

+ Lithiated metal oxides

Electrolyte

Ageing

Capacity and power fade with time and use.

Temperature, C-rate, DOD, SOC are the main factors of ageing

Life time is a challenge for batteries in vehicles!!

( Klett et. al, Journal of power sources 257 (2014) 126-137)

c)

Hybrid Electric Vehicle Cycle

Constant Current Cycle

How the battery age?

Jens Groot, Main ageing mechanisms in Li-ion battery, 2012

Complex set of ageing mechanisms due to multiple interactions Complementary charcterization techniques and models needed

Electrochemical Characterization

Using electrochemical techniques to observe changes in parametres affecting the performance with ageing

Charge/Discharge cycling

- Discharge capacity vs cycle number

- Coulombic efficiency (CE)

- Differential voltage (dV/dQ vs Q

plot)

etc...

Potentiostatic test

Charge/Discharge Cycling

Coulombic effciency

CE=

For precise measurement of CE:

the voltage limits, the current,

time and temperature should be

precise

Cost of instrumentation and time are in perspective

High precision battery cyclers custom set up in our lab

High precission battery cycler experimental set up

Charge/Discharge Cycling

dV/dQ vs Q

State analysis

Quantitative determination of active electrode mass and lithium loss

=

K.Honkura, ECS Transactions, 13 (19) 61-73 (2008)

Vcell Cell voltageVc Cathode half cell voltageVa Anode half cell voltageQc Cathode half cell capacityQa Anode half cell capacity

𝜹𝒄 Cathode Slippage𝜹a Anode SlippageS= a - c𝜹 𝜹ma anode active mass (cell)mc cathode active mass (cell)

Potentiostatic test

• The cathodic current is an indication of a continuous reduction at the graphite probably due to SEI layer development.

• Generally, lower state of charge gives lower side reaction rate.

• The growth of SEI deviates from a parabolic rate law for higher % SOC.

How side reaction rate depends on state of charge (SOC)?

Summary and Future works

• Ageing of lithium ion battery is a challenge being very complex.

• Need for complementary models and characterization techniques to determine aging rates and mechanisms.

Future additional works:• Physics based models for performance prediction and

ageing.• Electrochemical Impedance Spectroscopy (Model and

Experiment).

Tack för uppmärksamheten!