(5g) Key Parameters for Electrothermal Dynamics and Control of 15-Ah Prismatic Li-Ion Batteries

Four dimensionless
key parameters that describe the electrical and thermal response of prismatic
lithium-ion batteries are presented. Understanding of the thermal response of
lithium-ion cells is essential because it would allow the batteries to be
operated more efficiently in extreme environments. Two important issues about
the thermal response are "cold start" and "thermal runaway." Thermal instability
can be leveraged for the fast cold start of military vehicles and robotic
platforms. Thermal instability can be suppressed to prevent thermal runaway,
making operation in very warm environments safer.¹

To introduce the
minimum number of essential parameters of the battery responses, the simplest
models are carefully chosen. At least two physical models are necessary for
describing an electrochemical system: an electrochemical model and a local
energy balance. For the electrochemical model, we select Newman and Tobias
model, which provides an analytic solution with an assumption that the ion concentration
gradient is negligible.²The
analytic solution describes how the reaction current is distributed in the
porous electrodes.

For the energy
balance^3,4, three different
heat sources are necessary to match our experimental data: (1) Joule heating of
electrode matrix and electrolyte (simple IR
heating), (2) another Joule heating generated by the interfacial resistance between
electrode and electrolyte, and (3) the reaction heating from reversible entropy
change. The Joule heating is always exothermic; however, the reversible heat
can be endothermic or exothermic depending on the electrochemical reaction.

Even though the
physics are minimalized for simplicity, the number of physicochemical parameters
in our models was more than ten; however, the number could be decreased to four
after rigorous dimensional analysis. The analytic solutions in 1D geometry
allow demonstration of how these four essential properties affect the system
responses (see Fig. 1). Therefore, not only do these parameters suggest what are
important factors for the battery response, but they also help to control the
battery in efficient ways, since this test shows that many parameters have the same
effect in the electrical/thermal response.

[1] T. M. Bandhauer, S. Garimella, and T.
F. Fuller, Journal of The Electrochemical Society 158, R1 (2011).

[2] J. S. Newman and
C. W. Tobias, 109(12), 1183 (1962).

[3]
D. Bernardi, E. Pawlikowski,
and J. Newman, J. Electrochem. Soc.
132, 5 (1985).

[4] J. Newman and K.
E. Thomas-Alyea, Electrochemical Systems, 3rd
ed. Wiley, 2004.