1. Performance Degradation of Thermal Parameters
During Cycle Ageing of High Energy Density
Ni-Mn-Co based Lithium-Ion Battery Cells ‘ T. Stanciu¹, D.-I. Stroe¹ M. Swierczynski¹, N. Nieto², J. Gastelurrutia², J.-M. Timmermans³, R. Teodorescu¹ ‘ ¹Department of Energy Technology, Aalborg University, Denmark, ²IK4-IKERLAN Technology Research Center, Spain
³MOBI Research Group, Vrije Universiteit Brussel, Belgium
Introduction
NMC-based Li-ion battery
Property
Value
Cathode
Li(NiCoMn)/O2
Anode
Graphite
Nominal capacity
20 Ah
Nominal voltage
3.7 V
Max charging voltage
4.15 V
Min cutoff voltage
3 V
Charge current
Continuous 0.5 C-rate
Discharge current
Continuous 5 C-rate
Operating temp.
-30oC/+50oC
Storage temp.
Electric vehicles (EV) have faced an accelerated market penetration in the last years;
Lithium-ion (Li-ion) batteries (especially the NMC chemistry) are receiving the highest interest from EV manufacturers because of their superior performance parameters (e.g., energy density and specific energy) and increased lifetime in comparison to other battery technologies;
Li-ion batteries still pose thermal management challenges that need to be addressed for maximizing performance and reducing safety concerns;
Thus, the thermal behavior of the battery needs to be assessed under various operating conditions and the evolution during ageing of battery thermal parameters has to be mapped.
Thermal Parameters Assessment
Experimental Set-Up
Cycle Aging – 9 conditions
Stress factor I II
III IV V VI
VII
VIII IX
C-rate (cha/dch)
C/3 – 1C
C/3 – C/3
C/3 – 2C
T (oC) 25 35 45
DOD (%) 80 50 20
Max SOC (%) 90 75 60
Min SOC (%) 10 40
Cell #
G270
G271
G272
G277
G273
G274
G275
G276
G278
Literature Review
Sensitivity Analysis.
Internal Resistance
Entropic Heat Coeff.
Emissivity
Thermal Parameter
Importance
Internal Resistance [mOhm]
HIGH 
Entropic Heat Coeff. [mv/K]
MEDIUM
Heat Capacity [J/gK] X
Thermal Conductivity [W/K]
LOW
Emissivity [-]
At 10°C, 25°C, 40°C
90% SOC … 10% SOC
Results – for cell G277
Capacity
Emissivity
BOL
1500 FEC
Angle [deg.] 30
Distance [m]
0.5
Ambient T [°C]
23.5
26.0
Cell T [°C]
37.2
44.0
Emissivity
0.49
0.45
Internal Resistance
Entropic Heat Coefficient
SOC=80%
T=25°C
SOC=10%
EHC increase
Capacity decrease
EHC decrease
Resistance increase
Resistance increase
No change in EHC
Similar internal resistance increase trend independent on measurement SOC and temperature
The evolution of the EHC with the aging is highly dependent on the measurement SOC
Slight change of the emissivity value during ageing
Conclusions
High increase of the internal resistance (e.g. 150%) – depending on cycling conditions; measurement SOC and temperature do not influence the increase trend;
The EHC changes during cycle ageing – the evolution trend is highly dependent on the measurement SOC;
This work has been part of the NMP Batteries2020 project (Grant agreement GC.NMP /GA nº ). Authors gratefully acknowledge the involved partners for the extended collaboration and the European Union’s Seventh Program for Research for providing financial support.