challenges in battery pack design for electric vehicles ......challenges in battery pack design for...
TRANSCRIPT
Challenges in battery pack design for electric vehicles with special emphasis on
state-of-charge (SOC) estimation
by Dr. Angelique Janse van Rensburg, North-West University
Overview
• Introduction
• Battery packs
• State-of-charge (SOC)
• Electromotive force (EMF)
• Electrolyte concentration
• Conclusion
https://cleantechnica.com/2017/04/11/panasonic-hints-beyond-lithium-technology-ev-battery-improvements/
http://lygte-info.dk/info/batteryDisassembly5000mAh%20UK.html
Electric vehicle technology
• 2 million EVs on road (2017)
• 0.2% of light-duty passenger vehicles
• Adoption barrier: purchase cost
– Improvements in mass production
– Tax exemptions
• Major adoption barrier for BEV
• ‘Fuel gauging’
• Accurate SOC information for consumer
• Battery management system (BMS) performance + lifetime
• Batteries currently in EVs ≈ 100 GWh
• Managed safely + reliably for performance
Introduction⇛ Battery Pack ⇛ SOC ⇛ EMF ⇛ Concentration ⇛ Conclusion
RANGE
Battery energy storage in electric vehicles
• Battery pack = entire battery energy storage system
http://www.hybridcars.com/chevy-bolt-evs-battery-is-as-big-as-a-teslas/
wiring
Introduction⇛ Battery Pack ⇛ SOC ⇛ EMF ⇛ Concentration ⇛ Conclusion
sensors
switches
ICs
BMS
TMS
holders
tubing
connectors
casings
MSCELLS
Measured voltage of 18650 lithium-ion cell
Introduction⇛ Battery Pack ⇛ SOC⇛ EMF ⇛ Concentration ⇛ Conclusion
100%
0%
100%
intR
Capacity and state-of-charge (SOC)
Introduction⇛ Battery Pack ⇛ SOC⇛ EMF ⇛ Concentration ⇛ Conclusion
• How long can ion transport and electron transfer continue to sustain observed current within voltage range?
= depletion active material / ion concentration, passivation
Observed current from main reaction
Introduction⇛ Battery Pack ⇛ SOC⇛ EMF ⇛ Concentration ⇛ Conclusion
Discharging:
Electrochemical double-layer
REDOX
Maximum work possible by a cell
Introduction ⇛ Battery Pack ⇛ SOC ⇛ EMF⇛ Concentration ⇛ Conclusion
EMF – SOC
The Nernst equation
Introduction ⇛ Battery Pack ⇛ SOC ⇛ EMF⇛ Concentration ⇛ Conclusion
EMF – Concentration
( )Q f m
concentrationm
• Validated model in COMSOL Multiphysics:
Concentration in lead-acid cell during discharge
Introduction ⇛ Battery Pack ⇛ SOC ⇛ EMF ⇛ Concentration⇛ Conclusion
Work, electromotive force and concentration
Introduction ⇛ Battery Pack ⇛ SOC ⇛ EMF ⇛ Concentration⇛ Conclusion
maxw nFE
inttE V I R
ln ( )RT
E E f mnF
, at resttE V E
at restm
during operationw
Measurements/estimates:Equations:
Mapping concentration to work done
Introduction ⇛ Battery Pack ⇛ SOC ⇛ EMF ⇛ Concentration⇛ Conclusion
( )E m
Electrolyte concentration for EMF characterization
• Experimental result for VRLA cell with AGM separator:
Introduction ⇛ Battery Pack ⇛ SOC ⇛ EMF ⇛ Concentration⇛ Conclusion
Final thoughts
Introduction ⇛ Battery Pack ⇛ SOC ⇛ EMF ⇛ Concentration ⇛ Conclusion
Final thoughts
• Understanding of smallest unit
• Meaning behind capacity
• Improve SOC estimation
• Address challenges increase safety, reliability and performance
• Advances in fundamental research
• Accelerate EV adoption
Power of battery energy storage
Enabling EV as disruptive technology
Introduction ⇛ Battery Pack ⇛ SOC ⇛ EMF ⇛ Concentration ⇛ Conclusion
Questions?
Dr. Angelique Janse van RensburgSenior Lecturer in Computer & Electronic Engineering
Unit for Energy and Technology SystemsFaculty of Engineering, North-West University
Potchefstroom, South Africa