KTH ROYAL INSTITUTE OF 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 - + Graphite Lithiated metal oxides Lithiated metal oxides: LCO, LFP, LMO, NMC etc... Shuttling doesn’t continue indefinitely without loosing performance Electrolyte Lithium ion battery during charging operation Adapted from http://www.sigmaaldrich.com/technical-documents/articles/material-matters/u-sdepartment-of0.html Ageing Capacity and power fade with time and use. Hybrid Electric Vehicle Cycle Temperature, C-rate, DOD, SOC are the main factors of ageing Constant Current Cycle Life time is a challenge for batteries in vehicles!! c) ( Klett et. al, Journal of power sources 257 (2014) 126-137) 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= ℎ ℎ 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 (+ ) (/) = − Vcell Cell voltage Vc Cathode half cell voltage Va Anode half cell voltage Qc Cathode half cell capacity Qa Anode half cell capacity Cathode Slippage a Anode Slippage S= a - c ma anode active mass (cell) mc cathode active mass (cell) ((−)/) K.Honkura, ECS Transactions, 13 (19) 61-73 (2008) Potentiostatic test How side reaction rate depends on state of charge (SOC)? • 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. 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!