The present invention relates to a better passive thermal management process for an
electrochemical system. Particularly, the present invention relates to a process for improving
the thermal management of a battery.
BACKGROUND:
Over the last few decades, advances in electrochemical systems have expanded the capabilities
of these systems in a variety of fields including portable electronic devices, air and spacecraft
technologies, and automotive technologies. Many recent advances in electrochemical systems
are owing to the discovery and integration of new materials for battery components. Lithiumion battery technology has been at the forefront of this advancement. The research in advanced
electrode materials has significantly enhanced the energy capacities, energy densities,
discharge current rates and cycle life provided by these electrochemical cells, positioning
lithium-ion batteries to be the preferred technology for use in hybrid electric vehicles (HEV)
and electric vehicles (EV).
Electrochemical cells have two electrodes; an anode and a cathode, which are electrical
conductors, separated by a purely ionic conductor, the electrolyte. The capacity for positive
and negative ion exchanges at the electrodes with the electrolyte due to chemical reactions and
complementary physical processes results in the generation of electric current. The processes
simultaneously absorb or generate electrons to maintain the electrical neutrality of the whole
system. The potential of each electrode and the reaction rate affect the power density and
energy output of the cell. For rechargeable batteries, the extent of changes at the electrode
surface determine the life of the cell under specific thermodynamic and kinetic conditions like
temperature, voltage limits, current rates, etc.
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Any electrochemical system generates heat broadly due to three reasons, which are the reaction
heat, the polarization heat and the ohmic heat.
The reaction heat is generated due to the electrochemical reaction that takes place that is the
source of the system’s energy. A side product of the reaction is heat. The polarization heat is
generated because of mechanical effects occurring at the interface between electrodes and
electrolyte. Accumulation of gases and development of concentration gradients of reagents at
such interfaces lead to polarization which in turn reduces the efficiency of the cell by
increasingly transforming energy desired for electrochemical potential into heat. Finally, any
electrochemical system has an intrinsic property of an internal resistance, which is the cause
for the ohmic heat generation.
The internal resistance of a battery increases with age primarily due to the formation of a layer
at the anode of the cell. This layer is the solid electrolyte interphase (SEI) layer, the thickness
of which increases as the cell is used, inhibiting further electrolyte decomposition. This
inhibition is the primary cause for the ageing of the cell. The internal resistance of the cell
increases non linearly with the thickness of the SEI. With the increase in SEI thickness, the cell
ages and the internal resistance increases. With the internal resistance, the ohmic heat
generation also increases.
The above processes contribute to the heat generation in an electrochemical system. The
temperature of the electrochemical system should be maintained in the composite cell’s optimal
temperature range for best performance. This is to ensure that the chemical kinetics of the
system are at optimal conditions, and to also prevent any damage to the system.
Electrochemical systems exposed to high temperatures damage quickly due to changes in
reaction kinetics, and could potentially lead to a thermal runaway, at which point a selfpropelling exothermic reaction takes place leading to complete damage and potential fires.
Typically, said optimal temperature range is provided by the manufacturer, and tends to lie
between 15 ℃ to 35 ℃.
A battery is a specific electrochemical system where cells are arranged in a matrix to increase
capacity and output voltage. In such a configuration, the cells in series add to the output voltage
and the cells in parallel increase the capacity. For example, a 13S10P configuration represents
a battery with a matrix of 13 cells in series and 10 in parallel. If cells of voltage 3.6V and
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capacity 2.6 Ah are being used, the output of the battery would be a voltage of 3.6*13 V and a
capacity of 2.6*10 Ah.
In a battery consisting of a matrix of cells, the weakest cell in series becomes the bottleneck in
performance. The supply from the battery is switched off when any cell reaches the voltage
cutoff limit which is pre-decided by the manufacturer. The weakest cell triggers the power
supply cut off function, as it is the first to reach the lower limit owing to its relatively lower
capacity.
The creation of significant differences in the ageing processes of each cell in a battery depends
primarily on the temperature of each cell's surrounding. If the design or manufacturing of the
battery has susceptibilities that lead to an imbalanced temperature profile, the cells in the region
of the battery pack having higher temperatures will age faster compared to other cells.
If the cell has aged or is damaged, the charge and discharge process will generate more heat
and thus the cell's immediate surroundings will be warmer than the other cell's surroundings.
The damaged cell, apart from being a bottleneck, will further incur damage to the neighbouring
cells due to exposure to higher temperatures.
For the above reasons, it is imperative that the cells of a battery are subjected to a uniform
temperature profile. Uniform temperatures would imply uniform ageing of the cells and thus
increase the overall battery life.
The nature of the structure of any battery implies that there exists a region that does not have
proper exposure to the surroundings for heat dissipation. Uneven heat dissipation results in an
uneven temperature profile, and generally speaking, the inner cells get heated more. This
results in battery life reduction as the inner cells become weaker and create the bottleneck for
the battery.
To maintain low temperatures, a battery may have a dedicated battery management system to
monitor the temperature of the battery. The battery management system also has the
capabilities of reducing, limiting and switching off the current being drawn in order to reduce
the temperature or limit the temperature rise of the battery. The battery management system
functions in the ambit of active thermal management of the battery.
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For passive thermal management, generally speaking, batteries use free-flowing air as infill
material, i.e. the material used in between the cells of a battery. The natural convection current
of air between the outside of the battery and the inside helps in temperature regulation to some
extent. But overall, air is a poor choice for infill material. Air is a poor conductor of heat, which
leads to heat assimilation in cells.
The patent prior art document US10516194B2 provides a system, in which a phase change
material is used adjacent to the cells and then at another point the phase change material is
given exposure to a coolant system. The phase change material can absorb large amounts of
heat due to the specific latent heat which is typically higher than the specific heat of any
material. The main drawback of this invention is its use of phase change material, which needs
to be changed back to original phase via a coolant system.
There is a need for better infill materials which is a good conductor of heat, has high specific
heat and is a poor conductor of electricity.
The present invention proposes a silicon-based potting agent as the infill material in batteries
for better passive thermal management.
SUMMARY OF INVENTION:
In accordance with the main embodiment of present invention, a process for improving a
passive thermal management of an electrochemical system is disclosed, comprising the steps
of: using, a battery; and placing, a plurality of sensors at a plurality of strategic locations in the
said battery; preparing, a temperature profile of the said battery on a real time basis by means
of the plurality of temperature sensors placed at the plurality of strategic locations of the said
battery; and discharging, the said battery; and recording, a maximum temperature reached
during discharging of the said battery and minimum temperature reached during discharging
of the said battery. In accordance with the invention, as and when the said battery reaches at a
state of thermal equilibrium, the said battery is filled with a silicon potting agent thereby
reducing the temperature of the said battery and at the same time allowing good thermal
conductivity in the said battery.
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Other objects and advantages of the present invention will become apparent from the following
description taken in connection with the accompanying drawings, wherein, by way of
illustration and example, the aspects of the present invention are disclosed.
BRIEF DESCRIPTION OF DRAWINGS:
The present invention will be better understood after reading the following detailed description
of the presently preferred aspects thereof with reference to the appended drawings, in which
the features, other aspects and advantages of certain exemplary embodiments of the invention
will be more apparent from the accompanying drawings in which:
Figure 1 illustrates temperature profile for the battery where Infill type = Air, internal resistance
= 30 mΩ, ambient temperature = 25℃, current drawn = 1.7 A.
Figures 2a and 2b illustrates temperature profile for the battery where Infill type = potting
agent, internal resistance = 30 mΩ, ambient temperature = 25℃, current drawn = 1.7 A,
Thermal Conductivity = 2 W/(m.K.), Specific Heat at Constt Pressure = 578 J/(Kg.K), density
= 2900 kg/m.
Figures 3a and 3b illustrates temperature profile for the battery where Infill type = potting
agent, internal resistance = 30 mΩ, ambient temperature = 25℃, current drawn = 1.7 A,
Thermal Conductivity = 3 W/(m.K.), Specific Heat at Constt Pressure = 578 J/(Kg.K), density
= 2900 kg/m 3.
Figure 4 illustrates a data table collected from the experiments.

DETAILED DESCRIPTION OF DRAWINGS:
The following description describes various features and functions of the disclosed device and
methods with reference to the accompanying figures. In the figures, similar symbols identify
similar components, unless context dictates otherwise. The illustrative aspects described herein
are not meant to be limiting. It may be readily understood that certain aspects of the disclosed
system, method and apparatus can be arranged and combined in a wide variety of different
configurations, all of which are contemplated herein.
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These and other features and advantages of the present invention may be incorporated into
certain embodiments of the invention and will become more fully apparent from the following
description and claims or may be learned by the practice of the invention as set forth
hereinafter.
Accordingly, those of ordinary skill in the art will recognize that various changes and
modifications of the embodiments described herein can be made without departing from the
scope of the invention. In addition, descriptions of well- known functions and constructions
are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the
bibliographical meanings, but, are merely used to enable a clear and consistent understanding
of the invention. Accordingly, it should be apparent to those skilled in the art that the following
description of exemplary embodiments of the present invention are provided for illustration
purpose only and not for the purpose of limiting the invention.
It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless
the context clearly dictates otherwise.
It should be emphasized that the term “comprises/comprising” when used in this specification
is taken to specify the presence of stated features, integers, steps or components but does not
preclude the presence or addition of one or more other features, integers, steps, components or
groups thereof.
In accordance with the main embodiment of present invention, a process for improving a
passive thermal management of an electrochemical system is disclosed, comprising the steps
of: using, a battery; and placing, a plurality of sensors at a plurality of strategic locations in the
said battery; preparing, a temperature profile of the said battery on a real time basis by means
of the plurality of temperature sensors placed at the plurality of strategic locations of the said
battery; and discharging, the said battery; and recording, a maximum temperature reached
during discharging of the said battery and minimum temperature reached during discharging
of the said battery. In accordance with the invention, as and when the said battery reaches at a
state of thermal equilibrium, the said battery is filled with a silicon potting agent thereby
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reducing the temperature of the said battery and at the same time allowing good thermal
conductivity in the said battery.
As per Figure 1 of the present invention, the Figure 1 has air as an infill type. As is visible in
the figure, the maximum temperature reached is 69.8℃. Additionally, the minimum
temperature of the battery is 28.8℃. At the same instance, there’s a considerable difference in
the temperatures in 2 different regions of the battery. As can be seen from the figure, the inner
cells are subjected to a much higher temperature, and it can be predicted that the inner cells
would age faster, resulting in the shortening of battery life.
As per Figure 2 of the present invention, the Figure 2 has silicon-based potting agent as infill
type, with thermal conductivity set to 2 W/(m.K.). The temperature profile this time shows a
very uniform distribution. The high conductivity and high specific heat play important roles.
The maximum temperature reached is 32.4℃ and the minimum temperature is 29.1℃. It can
be inferred from the considerably small temperature difference that the cells of the battery will
age relatively uniformly. The low temperatures mean that the damage to the cells is minimal
and that there are no temperature shocks that the cells are subjected to.
As per Figure 3 of the present invention, the Figure 3 has silicon-based potting agent as infill
type, with thermal conductivity set to 3 W/(m.K.). The temperature profile this time again
shows a very uniform distribution. The maximum temperature reached is 31.9℃ and the
minimum temperature is 29.1℃. The maximum temperature is 0.5℃ lower than the previous
instance, indicating that a higher thermal conductivity is effective, albeit very slightly.
As per Figure 4 of the present invention, the Figure 4 displays the data collected from the
experiments. To emphasize the effectiveness of the present invention, experiments were carried
out on a battery which is a specific type of electrochemical system. The battery used is a
14S10P configuration. A 14S10P battery represents a matrix of cells with 14 cells in series and
10 cells in parallel, where each cell has a nominal voltage of 3.6V and capacity of 2.6 Ah. This
implies that the total battery voltage is 14*3.6 V and capacity of 10*2.6 Ah, i.e. 50.4 V and 26
Ah.
The intrinsic properties of an electrochemical system imply that heat will be generated and
therefore heat dissipation is an implicit objective for any viable electrochemical system. The
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internal heat generated should be dissipated quickly to inhibit the damage incurred to a cell
subjected to the high temperature that is a result of heat assimilation. The material adjacent to
the cells, which form the infill of a battery, should, therefore, have high thermal conductivity,
in order to quickly absorb heat generated from the cells, and then, transfer any heat it receives
out to the surroundings.
The infill material should, therefore, also have high specific heat so that it doesn’t rise to high
temperatures as it absorbs the cell heat. The capacity for absorbing heat with a high specific
heat implies that the material will not have a sudden rise in temperature, thus preventing a
temperature shock for the cells. These qualities will ensure that the battery life is prolonged.
Additionally, the material should also be a poor conductor of electricity in order to prevent any
short circuits as the defined purpose of the material is to be used as an infill material for an
electrochemical system. This necessitates that the material should insulate the different
components of the system.
The experiments validate the hypothesis presented by the current invention. The proposed
silicon-based potting agent lowers the overall temperature profile and also the variation in the
temperature profile of the battery during the discharge process. The properties of high specific
heat and high thermal conductivity make the proposed potting agent a viable infill material for
electrochemical systems.

We Claim:

1. A process for improving a passive thermal management of an electrochemical system,
comprising the steps of:
a. using, a battery; and placing, a plurality of sensors at a plurality of strategic
locations in the said battery;
b. preparing, a temperature profile of the said battery on a real time basis by means
of the plurality of temperature sensors placed at the plurality of strategic
locations of the said battery;
c. discharging, the said battery; and recording, a maximum temperature reached
during discharging of the said battery and minimum temperature reached during
discharging of the said battery;
wherein as and when the said battery reaches at a state of thermal equilibrium, the
said battery is filled with a silicon potting agent thereby reducing the temperature of the
said battery and at the same time allowing good thermal conductivity in the said battery.
2. The process as claimed in claim 1 wherein, the battery used in the process is a 14S10P
battery.
3. The process as claimed in claim 1 and claim 2 wherein, the said battery represents 14
cells in series and 10 in parallel.
4. The process as claimed in claim 1 wherein, the plurality of sensors used for preparing
a temperature profile on a real time basis are the temperature sensors.
5. The process as claimed in claim 1 wherein, the maximum temperature recorded of the
said battery is 31.9℃ and the minimum temperature recorded is 29.1℃.
6. An electrochemical system with a better passive management system, wherein as and
when a battery reaches at a state of thermal equilibrium, a silicon based potting agent
is filled in the said batter which reduces a temperature of the said battery and at the
same time allows good thermal conductivity in the said battery.
7. The electrochemical system with a better passive management system as claimed in
claim 6 wherein, the battery used in the process is a 14S10P battery.
8. The electrochemical system with a better passive management system as claimed in
claim 6 and 7 wherein, the said battery represents 14 cells in series and 10 in parallel.
9. The electrochemical system with a better passive management system as claimed in
claim 6 wherein, the maximum temperature recorded of the said battery is 31.9℃ and
the minimum temperature recorded is 29.1℃.