BACKGROUND
[0001] Secondary energy storage devices, for example, rechargeable
batteries store energy through reversible electrochemical reactions. These
devices play a central role in a wide range of applications, from portable
5 electronics to electric vehicles (EVs), and are integral to the integration of
renewable energy sources into the grid. The ability to store energy and release
it upon demand makes these devices a cornerstone of modern energy
infrastructure. The development of secondary energy storage devices is
focused on improving energy density, safety, cost-effectiveness, and
10 environmental sustainability. Innovations in electrode materials, electrolytes,
and manufacturing processes are driving the evolution of these devices. Thus,
secondary energy storage devices are a dynamic and rapidly evolving field, with
ongoing research and development aimed at meeting the growing demand for
efficient, reliable, and sustainable energy storage solutions.
15
BRIEF DESCRIPTION OF DRAWINGS
[0002] The detailed description is described with reference to the
accompanying figures. In the figures, the left-most digit(s) of a reference
number identifies the figure in which the reference number first appears. The
20 same numbers are used throughout the drawings to reference like features and
components.
[0003] FIG. 1 illustrates a method for preparing a dry electrode, in
accordance with an embodiment of the present subject matter.
[0004] FIG. 2(A-B) represents the experimental results of fibrillation of
25 binder element before milling process, in accordance with an embodiment of
the present subject matter.
[0005] FIG. 3(A-B) represents the experimental results of fibrillation of
binder element after milling process, in accordance with an embodiment of the
present subject matter.
30 [0006] FIG. 4(A-C) represents experimental results of a comparison
between fibrillation of binder element before and after milling process, in
accordance with an embodiment of the present subject matter.
2
[0007] FIG. 5(A-B) illustrates experimental results of an anode with a
percentage weight of carbon coated binder element and different carbon
additive, in accordance with an embodiment of the present subject matter.
[0008] FIG. 6(A-B) illustrates a graphical representation of particle size
5 distribution prior to milling process, in accordance with an embodiment of the
present subject matter. FIG. 6(C-D) illustrates a graphical representation of
particle size distribution post milling process, in accordance with an
embodiment of the present subject matter.
[0009] FIG. 7(A-C) illustrates a graphical representation of effect of milling
10 process on capacity retention, in accordance with an embodiment of the present
subject matter.
[0010] FIG. 8(A-B) illustrates a graphical representation of electrode
composition with respect to performance cycle and capacity retention, in
accordance with an embodiment of the present subject matter.
15 [0011] It may be noted that throughout the drawings, identical reference
numbers designate similar, but not necessarily identical, elements. The figures
are not necessarily to scale, and the size of some parts may be exaggerated to
more clearly illustrate the example shown. Moreover, the drawings provide
examples and/or implementations consistent with the description; however, the
20 description is not limited to the examples and/or implementations provided in
the drawings.
DETAILED DESCRIPTION
[0012] As may be understood, rapid advances in electric vehicles (EVs)
25 have led to an increased demand for lithium-ion batteries, accompanied by
escalating performance expectations, particularly in areas such as storage
capacity and production costs. However, increased storage capacity has the
potential to address predominantly existing issues related to poor battery life in
EVs. In addition to development of efficient energy storage batteries, the
30 aforementioned resolution may be achieved through optimization and
innovation in the conventional batteries used in EVs.
[0013] One such optimization in the conventional batteries is the usage of
dry electrodes in batteries. Dry electrode preparation is a manufacturing
process for creating electrodes by eliminating or reducing the use of solvents,
3
otherwise used in wet electrode preparation. The electrodes are generally
prepared by directly compacting dry powder electrode materials containing
active substances. Compared to the traditional wet electrode manufacturing
processes using large amounts of volatile organic compounds (VOCs) and
5 other solvents, which are harmful to the environment, dry electrodes are
manufactured by eliminating the use of such toxic solvents, thereby reducing
the environmental footprint of battery production.
[0014] Further, by removing a drying stage that is mandatory in traditional
wet electrode manufacturing processes to evaporate solvent(s), dry electrode
10 manufacturing processes reduces energy consumption and production costs
that is particularly advantageous when scaling up for the high-volume
production of EVs. The dry electrode manufacturing processes may produce
electrodes with higher energy density because of an absence of solvent(s),
allowing for compact and dense structures, which may be desirable for an
15 improved performance of EVs. Often, dry electrode manufacturing aligns with
offering a sustainable and an efficient production method due to the improved
performance characteristics of batteries produced. Thus, it may be inferred that
dry electrode manufacturing processes may play a pivotal role in making EVs
an energy-efficient option for consumers.
20 [0015] Conventionally, dry electrode manufacturing processes begins with
mixing of electrode's constituent materials, including a binder element,
conductive elements, and an active material. The binder is a polymer that holds
the electrode materials together, while the conductive elements ensure
electrical connectivity throughout the electrode. The active material is what
25 stores and releases the electrical charge (for example, lithium in lithium-ion
batteries).
[0016] However, binder plays a pivotal role in dry electrode manufacturing
and is integral to formation of a functional electrode structure by providing
mechanical integrity. It acts as a glue that holds the active material particles and
30 conductive elements together. The binder is fibrillated, generally, using a high
shear milling process. During the milling process, the binder is fibrillated to
create a network of fine fibers that interconnect the particles, thereby enhancing
the structural support of the electrode, thus produced.
4
[0017] Conventional techniques for dry electrode preparation pose
numerous disadvantages. Firstly, the fibrillation of the binder is non-uniform and
dense for the electrodes prepared with bare binder element. Secondly, a
number of particles of the binder element remain non-fibrillated which may
5 cause hindrance in the electro-chemical properties of the dry electrode which
may further reduce the efficiency of the battery. Further, the electrode may be
brittle, mechanically unstable, and may not show desired performance
characteristics. Accordingly, there is a need for preparing an electrode with
uniformly distributed binder element particles throughout the electrode for
10 overcoming the aforementioned disadvantages.
[0018] Approaches for preparing a dry electrode are described. In one
example, a method of preparing a dry electrode comprises pre-mixing a binder
element and a primary conductive element to obtain a first mixture. In one
example, the binder element in the first mixture may have a particle size in a
15 range of about 350 microns to 450 microns. Herein, the pre-mixing of the binder
element and the primary conductive element to obtain the first mixture may be
carried out at a speed in a range of about 600 to 1800 RPM, for a time period
in a range of about 10-30 minutes.
[0019] The first mixture may then be cooled by a milling process to obtain a
20 second mixture. The milling process may be implemented by applying pressure
to the first mixture. By applying pressure to the first mixture, the particle size of
the binder element may be reduced by at least 50-60 percent. For example, the
milling process may help reduce the particle size of the binder element to less
than 100 microns. It may be noted that pre-mixing refers to processing the
25 binder element to reduce the particle size.
[0020] Further, the second mixture may be pre-mixed with an active element
to a first temperature, having range of about 15°C to 25°C to obtain a third
mixture. The second mixture comprises a partially fibrillated binder element. In
one example, the particle size of the binder element in the second mixture may
30 be lying in the range of about 80 to 100 microns.
[0021] Although, the first temperature has been mentioned to be in the range
of 15°C to 25°C, the same should not be construed as a limitation. Other ranges
in which the first temperature lies may also be considered without deviating from
5
the scope of the present subject matter. For example, the first temperature may
be lying within a range of about 17-19°C.
[0022] In another example, the first temperature may be lying within a range
of about 14-17°C.
5 [0023] In yet another example, the first temperature may be lying within a
range of about 10-14°C. It may be noted that other ranges falling within the
above-described ranges may also be applicable as ranges for the first
temperature. Such other ranges or values of the first temperature are only
further examples.
10 [0024] Continuing further, in one example, the pressure applied to the first
mixture may be a feeding pressure and a milling pressure. Herein, feeding
pressure and milling pressure refer to the pressures applied during the milling
process to reduce the particle size of the binder element within the first mixture.
Feeding pressure is a force applied to feed the mixture of binder and conductive
15 element into a milling equipment (for example, a milling chamber). The feeding
pressure may be typically set to ensure a consistent and controlled delivery of
the first mixture to be milled. Further, milling pressure on the other hand refers
to a force applied by the milling equipment to the first mixture to achieve particle
size reduction. This pressure may be exerted by mechanical component(s) of
20 the milling equipment (for example, rollers, balls, hammers) depending on the
type of mill used (such as ball mill, hammer mill, jet mill, and more). The milling
pressure is a determining factor regarding the fibrillation and reduction in
particle size of the binder element in the first mixture.
[0025] In one example, the feeding pressure may be kept slightly higher than
25 the milling pressure, during the milling pressure, to significantly reduce the
particle size of the binder. Further, the feeding pressure may be in a range of
about 1 to 3 kg/cm2
, and the milling pressure may be in a range of about 1 to 2
kg/cm2
. Other ranges of the feeding pressure and the milling pressure may be
present, without deviating from the scope of the present subject matter.
30 [0026] Returning to the present subject matter, the method further comprises
mixing the active element with a secondary conductive carbon and a secondary
binder in the temperature range of about 15°C to 20°C for a time period of about
15 to 30 minutes.
6
[0027] The active element may be mixed with the secondary conductive
element and a secondary binder element in two different steps. The process
comprises mixing the active element with the secondary conductive element in
the temperature range of about 15°C to 20°C at a speed of about 800 to 1200
5 RPM for about 15 to 30 minutes to form the second mixture. The second mixture
may be pre-mixed with the secondary binder element in the temperature range
of about 15°C to 20°C at a speed of about 800 to 1200 RPM for about 15 to 30
minutes to form a third mixture.
[0028] The obtained third mixture may be mixed with the first mixture to
10 obtain a fourth mixture comprising partially fibrillated first mixture. Herein,
mixing the first mixture with the active element comprises passing the fourth
mixture through a high shear mixing process to a second temperature. For
example, mixing the first mixture with the active element may be done until the
second temperature is in a range of about 65°C to 85°C. The fourth mixture is
15 the final electrode mixture prepared by the examples described herein.
[0029] Although, the second temperature has been mentioned to be in the
range of about 65°C to 85°C, the same should not be construed as a limitation.
Other ranges in which the second temperature lies may also be considered
without deviating from the scope of the present subject matter. For example,
20 the second temperature may be lying within a range of about 71-73°C.
[0030] In another example, the second temperature may be lying within a
range of about 68-69°C.
[0031] In yet another example, the second temperature may be lying within
a range of about 70-72°C. It may be noted that other ranges falling within the
25 above-described ranges may also be applicable as ranges for the second
temperature. Such other ranges or values of the second temperature are only
further examples of the claimed subject matter. Continuing further, the highshear mixing process ensures that the active material is evenly distributed
throughout the binder and conductive element. The second temperature
30 attained during the high-shear mixing process is controlled to ensure that the
constituents integrate properly without damaging the structure of the electrode.
In one example, the third mixture may correspond to formation of thin and dense
fibrils of the binder element present in the first mixture due to reduction in the
particle size during the milling process. In one example, the reduction in the
7
particle size of the binder element during the milling process may increase the
extent of fibrillation of the binder element. In one example, the high shear mixing
process of the second mixture may be carried out at a speed in a range of about
3000 to 4000 RPM, for a time period of about 5-60 minutes.
5 [0032] In one example, the third mixture may further be cooled to a third
temperature to obtain a fourth mixture. For example, the third mixture may be
cooled to the third temperature in a range of about 15°C to 25°C. This may
prevent the agglomeration of particles, which may lead to inconsistencies in the
electrode structure. Further, cooling helps stabilize the second mixture and
10 maintain a desired particle size distribution, wherein milling may help fibrillate
the binder element, thereby creating a network of fine fibers. The network of
fine fibers may enhance structural integrity and performance of the electrode.
[0033] Although, the third temperature has been mentioned to be in the
range of about 15°C to 25°C, the same should not be construed as a limitation.
15 Other ranges in which the third temperature lies may also be considered without
deviating from the scope of the present subject matter. For example, the third
temperature may be lying within a range of about 15-17°C. In another example,
the third temperature may be lying within a range of about 17-21°C. In yet
another example, the third temperature may be lying within a range of about 5-
20 10°C. It may be noted that other ranges falling within the above-described
ranges may also be applicable as ranges for the third temperature. Such other
ranges or values of the third temperature are only further examples of the
claimed subject matter.
[0034] In one example, the milling process may be one of a jet milling
25 process, a cryogenic milling process, or combinations thereof. However, other
milling processes for reducing the particle size of the binder element may also
be employed, without deviating from the scope of the present subject matter.
[0035] In one example, the primary binder element may be selected from a
group comprising one of polytetrafluoroethylene (PTFE), Polyether ether ketone
30 (PEEK), poly(tetrafluoroethylene-co-perfluoro propyl vinyl ether) (PFA),
polypropylene, Polyacrylonitrile (PAN), tetrafluoroethylene-cohexafluoropropylene-co-vinylidene (THV), poly(tetrafluoroethylene-cohexafluoropropylene) (FEP), and combinations thereof.
8
[0036] The secondary binder is selected from the group consisting of
polyvinylidene fluoride (PVDF), hydroxypropyl methyl cellulose (HPMC),
hydroxypropyl cellulose (HPC), hydroxyethyl cellulose (HEC), sodium
carboxymethyl cellulose (Na-CMC), carboxymethyl cellulose (CMC), styrene
5 butadiene rubber, polyethylene glycol (PEG), polyacrylic acid (PAA),
polyethylene oxide (PEO) or combinations thereof.
[0037] In one example the primary conductive element is selected form the
group consisting of carbon nanofibers, super-p, vapor grown carbon fibers,
carbon nanotubes or combinations thereof
10 [0038] In one example, the secondary conductive element may be selected
from a group comprising one of carbon black, ketjenblack, acetylene black,
activated carbon, or combinations thereof.
[0039] In one example, the active element may be selected from a group
comprising one of one of natural graphite, synthetic graphite, silicon, Si-Carbon
15 composites, nickel-manganese-cobalt oxide (NMC), lithium-nickel-cobaltaluminium oxides (NCA), lithium iron phosphate (LFP), or lithium-manganeserich (LMR), or combinations thereof.
[0040] In one example the weight percentage of the active element is in the
range of 96 to 97%, the secondary conductive element is in the range of 0 to
20 1%, the secondary binder element is in the range of 0 to 1% and the first mixture
is in the range of 1 to 4%.
[0041] In one example the ratio of the primary binder element to the primary
conductive element is in the range of 95:5 to 99:1.
[0042] In one example, mixing of the binder element and the conductive
25 element may cause coating of the conductive element on the particles of the
binder element, wherein the coating of the conductive element may be at least
5 percent.
[0043] The present approaches provide a number of technical advantages.
For example, fibrillated binder element increases the surface area of the
30 electrode. A higher surface area may allow for more active sites for
electrochemical reactions, which may improve the battery's performance by
enhancing its charge and discharge rates. While the primary conductive
pathway in an electrode comes from the conductive elements, the fibrillated
binder may also contribute to the overall electrical connectivity. The network of
9
fibers helps maintain contact between the active material particles and the
conductive elements, ensuring efficient electron transport throughout the
electrode. Furthermore, the fibrillation process may influence the porosity of the
electrode. A well-fibrillated binder creates a porous structure that facilitates the
5 movement of ions within the electrode that is particularly beneficial for ion
transport during the charge and discharge cycles of the battery. By creating a
network of fibers, the binder enhances the structural integrity, electrical
connectivity, and ion transport within the electrode, all of which are integral to
the efficient functioning of a battery.
10 [0044] The above and other features, aspects, and advantages of the
subject matter will be better explained with regard to the following description
and accompanying figures. It should be noted that the description and figures
merely illustrate the principles of the present subject matter along with examples
described herein and should not be construed as a limitation to the present
15 subject matter. It is thus understood that various arrangements may be devised
that, although not explicitly described or shown herein, embody the principles
of the present disclosure. Moreover, all statements herein reciting principles,
aspects, and examples thereof, are intended to encompass equivalents thereof.
Further, for the sake of simplicity, and without limitation, the same numbers are
20 used throughout the drawings to reference like features and components. While
aspects of the described method of dry electrode preparation may be
implemented in any number of different systems, and/or implementation, the
examples are described in the context of the following example system. It may
be noted that drawings of the present subject matter shown here are for
25 illustrative purposes and are not to be construed as limiting the scope of the
subject matter claimed.
[0045] FIG. 1 illustrates a method 100 for preparing a dry electrode, in
accordance with an embodiment of the present subject matter. The order in
which method 100 is described is not intended to be construed as a limitation,
30 and any number of the described method blocks may be combined in any order
to implement the method 100, or any alternative methods. Furthermore, method
100 may be implemented by apparatus(s) or machine(s) through any suitable
hardware, or combinations thereof. The present method is described in relation
10
to operation of one or more components, elements or stages implemented as
part of an industrial and/or laboratory process for preparing a dry electrode.
[0046] At block 102, a first mixture is obtained by pre-mixing a binder
element and a primary conductive element. The binder element in the first
5 mixture has a particle size in a range of about 350 to 450 microns. In one
example, the pre-mixing of the primary binder element and the conductive
element may be done in a mixing chamber. The mixing of the binder element
and the primary conductive element to obtain the first mixture may be carried
out at a speed in a range of about 600 to 1800 RPM, for about 10-30 minutes.
10 It may be noted that a mixing chamber may be a device or part of a machine
where the binder element and the conductive element may be combined and
homogenized before further processing. Examples of mixing chamber may
include, but not limited to, planetary mixer, rotary drum mixer, V-blender, ribbon
blender, and more. It may be noted that this is one of the many other examples
15 by way of which the binder element and the primary conductive element may
be mixed. Such other examples too fall within the scope of the present subject
matter. Since, milling of bare binder element without pre-mixing exhibits higher
trends towards self-agglomeration due to increased surface energy and heat
generated during the milling process, the pre-mixing of the binder element for
20 passivating fibrillation sites before the milling process may increase milling
efficiency.
[0047] At block 104, a second mixture may be obtained. In one example, the
second mixture may be obtained by cooling the first mixture. The cooling may
be affected through a cold milling processing by passing cold air through the
25 first mixture. In such a case, the cold milling reduces the temperature of the first
mixture comprising the binder element and the primary conductive element.
[0048] In one example, the cold milling process to which the first mixture is
subject to may involve subjecting the first mixture to pressure. The milling
process may be performed in a milling chamber. As may be understood, a
30 milling chamber may be a component of a milling machine where various
mechanical actions comprising grinding, crushing, or pulverizing of materials,
takes place. Different types of milling chambers, such as a jet milling chamber,
ball milling chamber, hammer milling chamber, cryogenic milling chamber, and
11
more, may be used without deviating from the scope of the present subject
matter.
[0049] Returning to the present subject matter, pressure is applied to the
first mixture (e.g., during the milling process in the milling chamber), to achieve
5 particle size reduction of the binder element in the first mixture. By applying
pressure to the first mixture, the particle size of the binder element may be
reduced by at least 50-60 percent, to provide the second mixture. For example,
the milling process may help reduce the particle size of the binder element to
about less than 100 microns. The specific parameters of the pressure applied,
10 such as magnitude, duration, and rate of application, may be accordingly
controlled based on the quantity of the mixture undergoing cold milling. These
parameters may be optimized for particular material(s) and desired end
properties of the electrode, without deviating from the scope of the present
subject matter.
15 [0050] In another example, the pressure applied to the first mixture may be
one of a feeding pressure and a milling pressure. Herein, feeding pressure and
milling pressure refer to the pressures applied during the milling process to
reduce the particle size of the binder element within the first mixture. As may be
understood, feeding pressure is a force applied to feed the mixture of binder
20 and conductive element into a milling equipment (for example, a milling
chamber). The feeding pressure may be typically set to ensure a consistent and
controlled delivery of the first mixture to be milled. Further, milling pressure on
the other hand refers to a force applied by the milling equipment to the first
mixture to achieve particle size reduction. Such pressure may be exerted by
25 mechanical component(s) of the milling equipment (for example, rollers, balls,
hammers) depending on the type of mill used (such as ball mill, hammer mill,
jet mill, and more). The milling pressure is a determining factor regarding the
fibrillation and reduction in particle size of the binder element in the first mixture.
In one example, the feeding pressure may be kept higher than the milling
30 pressure, during the milling pressure, to significantly reduce the particle size of
the binder. Further, the feeding pressure may be in a range of about 1 to 3
kg/cm2
, and the milling pressure may be in a range of about 1 to 2 kg/cm2
. The
method also comprises mixing the active element with a secondary conductive
12
carbon and a secondary binder in the temperature range of about 15°C to 20°C
for a time period of about 15 to 30 minutes.
[0051] In yet another example, the active element may be mixed with the
secondary conductive element and a secondary binder element in two different
5 steps. The process comprises mixing the active element with the secondary
conductive element in the temperature range of about 15°C to 20°C at a speed
of about 800 to 1200 RPM for about 15 to 30 minutes to form the second
mixture. The second mixture may be mixed with the secondary binder element
in the temperature range of about 15°C to 20°C at a speed of about 800 to 1200
10 RPM for about 15 to 30 minutes to form a third mixture. It is again reiterated that
the above approaches and different examples may be used as described or in
different combinations. These examples, and their corresponding variations,
are only other exemplary embodiments and continue to fall within the scope of
the present subject matter.
15 [0052] At block 106, a third mixture may be obtained by mixing the second
mixture with an active element, in a first temperature range of about 15°C to
25°C. In one example, the second mixture comprises a partially fibrillated binder
element. In another example, the particle size of the binder element in the
second mixture may be lying in the range of about 80 to 100 microns. Herein,
20 mixing the second mixture with the active element to obtain the third mixture
may be implemented in a temperature range of about 15°C to 25°C. The mixing
of the second mixture with the active element may be done in a mixing chamber
(as explained previously). It may be noted that a mixing chamber may be a
device or part of a machine where the binder element and the conductive
25 element may be combined and homogenized before further processing.
Examples of mixing chamber may include, but not limited to, planetary mixer,
rotary drum mixer, V-blender, ribbon blender, and more.
[0053] At block 108, the third mixture may be subjected to a high shear
mixing process which is performed at a second temperature which is in a range
30 of about 65°C to 85°C. In an example, for high shear mixing, intense shear force
may be applied to the third mixture to rapidly and thoroughly combine the
constituents into a uniform substance and may be implemented in a high shear
mixing chamber. As may be understood, this may involve a fast rotation or
movement of a component within a mixer, such as a rotor, blade, or impeller,
13
which creates high levels of shear. During the high shear mixing process in the
high shear mixing chamber, the third mixture may be subjected to mechanical
forces for breaking down particles, dispersing aggregates, and homogenizing
the constituents. Herein, the mixing the third mixture with the active element
5 may be done until the second temperature is in a range of about 65°C to 85°C.
The high-shear mixing process ensures that the active material is evenly
distributed throughout the binder and conductive element. The second
temperature attained during the high-shear mixing process is controlled to
ensure that the constituents integrate properly without damaging the structure
10 of the electrode. In one example, the third mixture may correspond to formation
of thin and dense fibrils of the binder element present in the first mixture due to
reduction in the particle size during the milling process. In one example, the
reduction in the particle size of the binder element during the milling process
may increase the extent of fibrillation of the binder element.
15 [0054] At block 110, a fourth mixture may be obtained by cooling the third
mixture after it has been subjected to high shear mixing. In one example, the
obtained third mixture may be mixed with the first mixture to obtain a fourth
mixture comprising partially fibrillated first mixture. In an example, the third
mixture may further be cooled to a third temperature in a cooling chamber. The
20 third mixture may be cooled to the third temperature in a range of about 15°C
to 25°C. This may prevent the agglomeration of particles, which may lead to
inconsistencies in the electrode structure. Further, cooling helps stabilize the
second mixture and maintain a desired particle size distribution, wherein milling
may help fibrillate the binder element, thereby, creating a network of fine fibers.
25 The network of fine fibers may enhance structural integrity and performance of
the electrode. In one example, the binder element and the conductive element
may be mixed at a speed of about 600-1800 RPM, for a predefined time period.
In one example, the predefined time period may be in the range of about 10-30
minutes. Other ranges of speed and predefined may also be present, without
30 deviating from the scope of the present subject matter..
EXPERIMENTAL RESULTS FIGS. (2-8)
[0055] FIGs. (2-8) illustrate experimental result(s) (including SEM images
and graphical representations) in conjunction with the examples of the present
14
subject matter in relation to preparation of the dry electrode. The same as
explained with reference to the first mixture and second mixture disclosed in
FIG. 1 and should not be construed as a limitation in any way.
[0056] FIG. 2(A-B) represents an example fibrillation of binder element
5 before the milling process, in accordance with an embodiment of the present
subject matter. FIG. 2(A-B) depicts a SEM image of a binder element mixed
with a conductive element before the milling process. In an example, to prevent
agglomeration of particles in the binder element during the milling process,
different milling media may be used. For example, the mixing of the binder
10 element with different conductive elements at different weight percentages may
produce varying results. The Table 1 shown below depicts an example of the
material composition comprising the binder element and the conductive element
and their particle size distribution in microns. In an example, the binder element
may be PTFE and the conductive element may be carbon. Other examples may
15 also be used without deviating from the scope of the scope of the present
subject matter.
0058] As explained previously, feeding pressure and milling pressure refer
5 to the pressures applied during the milling process to reduce the particle size of
the binder element within the first mixture. Feeding pressure is a force applied
to feed the mixture of binder and conductive element into a milling equipment
(for example, a milling chamber). The feeding pressure may be typically set to
ensure a consistent and controlled delivery of the first mixture to be milled.
10 Further, milling pressure on the other hand refers to a force applied by the
milling equipment to the first mixture to achieve particle size reduction. This
pressure may be exerted by mechanical component(s) of the milling equipment
(for example, rollers, balls, hammers) depending on the type of mill used (such
as ball mill, hammer mill, jet mill, and more). The milling pressure is a
15 determining factor regarding the fibrillation and reduction in particle size of the
binder element in the first mixture.
[0059] As may be seen from Table 2, the feeding pressure may be kept
slightly higher than the milling pressure, during the milling pressure, to
significantly reduce the particle size of the binder. Further, the feeding pressure
16
may be in a range of about 1 to 3 kg/cm2
, and the milling pressure may be in a
range of about 1 to 2 kg/cm2
. By maintaining a higher feeding pressure, the first
mixture is continuously and forcefully pushed into the milling zone, where the
actual size reduction occurs due to the milling pressure. The differential
5 between the feeding pressure and the milling pressure helps to regulate the
material throughput in the first mixture, ensuring that the milling chamber
receives a steady supply of material without overloading or underfeeding, which
could compromise the quality of the milled product.
[0060] FIG. 3(A-B) represents an example fibrillation of binder element after
10 the milling process, in accordance with an embodiment of the present subject
matter. In an example, FIG. 3(A-B) represents a SEM image of the conductive
element (for example, jet milled carbon coated PTFE powder with 5 percent
weight). As may be understood, after the milling process of the binder element
(for example, PTFE), average particle size is reduced due to uniform distribution
15 of the binder element, which further increases extent of fibrillation and enhanced
particle to particle attachment in the electrode. This improvement in fibrillation
may further lead to a two-fold increase in peel strength for the electrode (anode
or cathode) made with milled binder element.
[0061] FIG. 4(A-C) represents an example comparison between fibrillation
20 of binder element (for example, PTFE) before and after the milling process with
a SEM image of an anode having a percentage weight of carbon coated binder
element, and with different conductive elements (for example, carbon), in
accordance with an embodiment of the present subject matter. In an example,
FIG. 4A represents a SEM image of an anode with bare binder element (without
25 the milling process). In another example, FIG. 4B represent a SEM image of an
anode with for example, jet milled 5 percent weight carbon coated binder
element. As may be seen in FIG. 4B, dense and thin fibrils are uniformly present
across the electrode after the milling process. FIG. 4C represents a SEM image
of an anode with for example, jet milled 5 percent weight carbon coated binder
30 element and a different conductive element for the purposes of establishing the
comparison between the extent of fibrillation due to processing of the binder
element for preparing the electrode for calendaring.
[0062] FIG. 5(A-B) illustrates an example SEM image of a cathode, in
accordance with an embodiment of the present subject matter. As shown in
17
FIG. 5A, the cathode with bare (without the milling process) binder element
shows no dense fibrils present while thick fibrils may be observed at some
areas. FIG. 5B shows a SEM image of a cathode with for example, jet milled 5
percent weight carbon coated binder element wherein uniform, thin and dense
5 fibrils are present across the electrode.
[0063] FIG. 6(A-B) illustrates an example graphical representation of
particle size distribution before the milling process, in accordance with an
embodiment of the present subject matter. FIG. 6(C-D) illustrates a graphical
representation of particle size distribution after the milling process, in
10 accordance with an embodiment of the present subject matter. As depicted in
FIG. 6(A-D), the extent of fibrillation is inversely proportional to the particle size
of the binder element (for example, PTFE) and its distribution into the powdered
mixture.
[0064] FIG. 7(A-C) illustrates an example graphical representation of effect
15 of milling process on capacity retention, in accordance with an embodiment of
the present subject matter. In an example, the milling process of the binder
element (for example, PTFE), shown by reference numerals 702 and 704, in
the treatment process results in the improved discharge capacity and capacity
retention as depicted from the graphical representations in FIG. 7(A-C). The
20 uniform distribution of the binder element may be improved after reduction of
their particle size due to which increases the extent of thin dense fibrillization
and enhanced the electrochemical performance in terms of initial capacity and
capacity retention.
[0065] FIG. 8(A-B) illustrates an example graphical representation of
25 electrode composition, shown by reference numerals 802 and 804, with respect
to performance cycle and capacity retention, in accordance with an embodiment
of the present subject matter. In an example, due to the treatment of the binder
element with the milling process, the performance is improved, and capacity is
retained. In an example, the electrode cells binder elements after the milling
30 process may retain 90% capacity after 28 cycles.
[0066] Although examples for the present disclosure have been described
in language specific to structural features and/or methods, it is to be understood
that the appended claims are not necessarily limited to the specific features or
18
methods described. Rather, the specific features and methods are disclosed
and explained as examples of the present disclosure.
19
I/We Claim:
1. A method of preparing a dry electrode, the method comprising:
pre-mixing of a binder element and a primary conductive element to
5 obtain a first mixture, wherein the binder element in the first mixture has
a particle size in a range of 350 to 450 microns;
cooling the first mixture by passing the first mixture through a cold
milling process, wherein passing the first mixture through the milling
process comprises applying a pressure to the first mixture to obtain a
10 second mixture, for attaining a particle size of the binder element less
than 100 microns;
mixing the second mixture with an active element, in a first
temperature range of about 15°C to 25°C to obtain a third mixture;
subjecting the third mixture through a high shear mixing process to a
15 second temperature, wherein the second temperature is in a range of
about 65°C to 85°C; and
cooling the third mixture to a third temperature, wherein the third
temperature is in a range of 15°C to 25°C, to obtain a fourth mixture.
20 2. The method as claimed in claim 1, wherein the pressure applied to the
first mixture during the cold milling process is a feeding pressure and a
milling pressure, wherein the feeding pressure is greater than the milling
pressure.
25 3. The method as claimed in claim 2, wherein the feeding pressure is in a
range of about 1 to 3kg/cm2
, and the milling pressure is in a range of
about 1 to 2kg/cm2
.
4. The method as claimed in claim 1, wherein the second mixture comprises
30 a partially fibrillated binder element.
5. The method as claimed in claim 1, wherein the particle size of the binder
element in the second mixture is in the range of 80 to 100 microns.
20
6. The method as claimed in claim 1, wherein milling process is one of a jet
milling process, a cryogenic grinder milling process, or combinations
thereof.
5 7. The method as claimed in claim 1, wherein the pre-mixing of the binder
element and the primary conductive element to obtain the first mixture is
carried out at a speed in a range of about 600 to 1800 RPM, for a time
period in a range of about 10-30 minutes.
10 8. The method as claimed in claim 1, wherein the high shear mixing process
of the second mixture is carried out at a speed in a range of about 3000
to 4000 RPM, for a time period of about 5-60 minutes.
9. The method as claimed in claim 1, wherein mixing the second mixture
15 with the active element to obtain the third mixture further comprises premixing the active element with a secondary conductive element and a
secondary binder element.
10. The method as claimed in claim 9, wherein the pre-mixing is carried out
20 in a temperature in the range of 15°C to 25°C at a speed of about 800 to
1200 RPM for a time period of about 10 - 30 min.
11. The method as claimed in claim 1, wherein the primary conductive
element is selected from the group consisting of carbon nanofibers,
25 super-p, vapor grown carbon fibers, carbon nanotubes or combinations
thereof.
12. The method as claimed in claim 1, wherein the primary binder element
is selected from a group comprising one of polytetrafluoroethylene
30 (PTFE), Polyether ether ketone (PEEK), poly(tetrafluoroethylene-coperfluoropropyl vinyl ether) (PFA), polypropylene, Polyacrylonitrile
(PAN), tetrafluoroethylene-co-hexafluoropropylene-co-vinylidene (THV),
poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), or
combinations thereof.
21
13. The method as claimed in claim 9, wherein the secondary conductive
element is selected from a group comprising one of carbon black,
ketjenblack, acetylene black, activated carbon, or combinations thereof.
5
14. The method as claimed in claim 9, wherein the secondary binder element
is selected from polyvinylidene fluoride (PVDF), hydroxypropyl methyl
cellulose (HPMC), hydroxypropyl cellulose (HPC), hydroxyethyl cellulose
(HEC), sodium carboxymethyl cellulose (Na-CMC), carboxymethyl
10 cellulose (CMC), styrene butadiene rubber, polyethylene glycol (PEG),
polyacrylic acid (PAA), polyethylene oxide (PEO) or combinations
thereof.
15. The method as claimed in claim 1, wherein the active element is selected
15 from a group comprising one of natural graphite, synthetic graphite,
silicon, Si-Carbon composites, or combinations thereof.
16. The method as claimed in claim 1 wherein the ratio of the binder to the
conductive carbon is in the range of 95:5 to 99:1.
20
17. The method as claimed in claim 1, wherein the active element is selected
from a group comprising one of one of natural graphite, synthetic
graphite, silicon, Si-Carbon composites, nickel-manganese-cobalt oxide
(NMC), lithium-nickel-cobalt-aluminium oxides (NCA), lithium iron
25 phosphate (LFP), or lithium-manganese-rich (LMR), or combinations
thereof