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!