IEEE Electrification - September 2020 - 66

Many researchers
have tried to
manipulate the
current during
charging and create
a dynamic charging
profile to attenuate
the negative
effects of the high
charging rate.

4.35
4.25
4.15
4.05

60
90
Cycles
(a)

120

150

35 °C

To validate the effectiveness of the
PCC-based passive thermal management system, the cycling tests were
repeated with the presence of PCC.
The temperature curves during the
2-C charge of the first cycle have
been plotted in Figure 6. The peak
surface temperature of the cell
dropped from 57 °C (air, no PCC) to
50 °C (with PCC). To study the thermal
balance at 2-C fast charge rates at the
pack level, a thermal simulation
study was done with a battery pack
consisting of nine cells. The results
(Figure 7) showed that after 15 min of
charging at a 2-C rate, the temperature gradient of the pack was controlled within 1 °C.
Furthermore, cylindrical cells
within PCC are fully in contact with the cooling medium, maximizing the heat transfer in a way that is
practical for high power applications. If one cell goes
into thermal runaway, PCC can absorb the heat and
prevent propagation to other cells.
A nail penetration test was performed to evaluate the
thermal runaway propagation effects in a 10S-4P battery
pack with PCC-based thermal management. The test
setup is shown in Figure 8(a). The battery pack was
penetrated with a nail at the trigger cell located in the
corner of the pack (cell 1) to initiate a thermal runaway. The pack was equipped with 10 thermocouples
to monitor the temperature. The locations and the
temperature profile during the test are shown in Figure 8(b). After the thermal runaway was initiated at 0 s,
the -trigger cell temperature reached around 300 °C.
There was also a substantial increase in the temperature in the neighboring cells (cells 2, 3, and 4). However, the peak temperature of the neighboring cells

Maximum Temperature (°C)

Maximum Voltage (V)

aging kinetics. This issue can be
addressed by integrating an effective thermal management solution
into the design of high-energy Li-ion
battery packs. Optimization of the
system is required to achieve ideal
Li kinetics and diffusion as well as
reduce pack temperature gradients
and risk of battery temperatures
reaching thermal runaway threshold temperatures.
Phase change composite (PCC) is
a patented wax-graphite material
that has been used as a standalone
thermal management system for a
variety of Li-ion batteries. The material is composed of a phase-change
component, typically a wax, and a
graphite matrix as a host. PCC can be
used to encase battery cells, as shown in Figure 4(a).
When in use, the solid wax inside the PCC material
absorbs the heat generated by Li-ion battery cells and
undergoes phase change into the liquid state, which limits the temperature rise of the battery. The graphite
matrix provides high thermal conductivity, aiding rapid
and uniform heat distribution; thus eliminating hot
spots within the battery, as shown in Figure 4(b).
The status of the PCC thermal management system
can be monitored by determining the thermal state of
charge (TSoC) to ensure the safe operation of the system.
The TSoC estimation is based on temperature measurements and the identified heat capacity of PCC, as shown
in Figure 5.
PCC stands out to be a practical, passive, inexpensive
thermal management solution. The lightweight, maintenance-free design and absence of moving parts give PCC
an edge over air and liquid active cooling methods, which
require additional power and control.

40
0

60
90
Cycles
(b)

120

150

45 °C

Figure 3. (a) The maximum voltage versus cycle numbers at different ambient temperatures. (b) The maximum temperature versus cycle numbers at different ambient temperatures.

I E E E E l e c t r i f i cati o n M agaz ine / SEPTEMBER 2020

IEEE Electrification - September 2020

Table of Contents for the Digital Edition of IEEE Electrification - September 2020