DESC:FIELD OF THE INVENTION:
The present invention relates to the development of a rubber formulation for compression pad tailored as cell separators in Li-ion battery packs. This present invention focuses on creating a compressible, fire-retardant, lightweight and thermally/electrically insulative rubber foam pad with the purpose to enhance the overall performance, safety, and efficiency of Li-ion batteries by introducing a specialized separator that addresses key considerations such as weight compressibility, fire resistance, and effective thermal and electrical insulation. The present advancement aims to contribute significantly to the evolution of battery technology, particularly in applications demanding lightweight and secure energy storage solutions.
BACKGROUND ART:
The evolution of battery technology necessitates innovations that overcome challenges in achieving uniform compression and ensuring compatibility with diverse cell configurations. Traditional designs faced issues of uneven pressure distribution, hampering performance and safety. Variations in cell sizes and shapes posed additional complications, demanding adaptable solutions. Moreover, for advanced battery designs additional properties such as high thermal & electric insulation with UL94 V0 fire retardancy is desirable.
Modern age battery makers mostly prefer prismatic cells in their battery packs, due its specific rectangular cuboid shape, which makes it more efficient in terms of cell packing, energy storage and heat management. However, such type of battery cells also exhibits swelling property during charging and discharging cycles. This swelling results from thermal cycling, causing gas formation, electrolyte degradation, and electrode expansion. Such bulging effect start pushing the adjacent cells and develops stress within the module pack over time, thereby increasing the risk of burst or thermal runaway events, potentially leading to fire or explosion. To reduce such possibilities, it is recommended to insert a compressible cell separator in between the cells which can withstand such compressive stress over time. Critical compressibility requirement is shown in Table 1.
Critical Situation Compressive load (KN) Compression %
Start of life (Battery Assembly) 3-5 25-35
After 1000 cycles 10-12 45-55
End of life 20-22 60-75

Table 1: Critical compressive force deflection requirement.
References in relation to the above and prior art knowledge are drawn as per the following prior arts:
JP6116787B1 teaches rubber composition for vulcanization molding, which is excellent in dimensional stability, has good surface properties, and can effectively produce a lightweight rubber product, and a production method and use thereof. The hollow particles are composed of an outer shell made of a thermoplastic resin and foaming agent encapsulated therein and vaporized by heating, and have a specific expansion capacity. If the rubber composition for vulcanization molding has a Mooney viscosity ML (1 + 4) at 100 ° C. measured in accordance with JIS K6300 of 5 to 90, the above problem can be solved. The rubber composition for vulcanization molding according is stated to comprise, as necessary, conventionally known reinforcing agents, fillers, vulcanization/ crosslinking agents, vulcanization accelerators, vulcanization accelerators, softeners, processing assistants, dispersing agents including silica, and also includes silicone rubber.
US8247465B2 is directed to heat-expandable microspheres include a shell of thermoplastic resin and core material encapsulated in the shell. The core material include a blowing agent having a boiling point not higher than the softening point of the thermoplastic resin and a gas migration inhibitor having a boiling point higher than the softening point of the thermoplastic resin. The ratio of the gas migration inhibitor to the core material is at least 1 weight percent and below 30 weight percent. The average particle size of the heat-expandable microspheres ranges from 1 to 100 micrometers. The base component of such microspheres except diene rubbers are taught is not specifically restricted and includes, for example, polymerized resins such as unsaturated polymerized resins and ring-opened polymerized resins; condensation resins such as addition-condensation resins, condensation-polymerization resins, and addition-polymerization resins; semi-synthesized polymers such as cellulose resins and protein resins; and inorganic materials such as cements and ceramics. Silicone resins are also taught as base components. Thermoplastic resin constituting the shell of microspheres, a more preferable peroxydicarbonate is at least one selected from the group consisting of diisopropyl peroxydicarbonate, bis(4-t-butylcyclohexyl)peroxydicarbonate, di-sec-butyl peroxydicarbonate, and di(2-ethylhexyl) peroxydicarbonate, and a further more preferable peroxydicarbonate is at least one selected from the group consisting of di-sec-butyl peroxydicarbonate and di(2-ethylhexyl)peroxydicarbonate. The dispersion stabilizer includes, for example, colloidal silica.
JP04349301A teaches conductive elastomer comprises dispersion of insulating elastic fibers with =10 denier, elastomer particles with grain diameter 10-300 µm, conductive particles with grain diameter 1-40 µm, hollow elastic microspheres with grain diameter 10-150 µm in a non-conductive elastomer. Preferably, the non-conductive elastomer may be a silicone rubber, a liquid silicone rubber, or a silicone varnish as an essential component, and a silicone tacking agent; the insulating elastic fibers may be polyethylene, polyamide, aramide, polyester, polyurethane fibers, or composite fibers thereof; the conductive particles may be spherical C particles; the insulating particles may be Ca particles; and the hollow elastic microspheres may be vinylidene chloride-acrylonitrile copolymer.
Patent No CN105261420 relates to an aging-resistant power cable, including a conductor, an insulating layer, a shielding layer and a sheath layer. The insulating layer is set outside the conductor, the shielding layer is set outside the insulating layer, and the sheath layer is outside the shielding layer. The insulating layer is prepared of silicone rubber, and the raw materials of silicone rubber include: vinyl-terminated Me vinyl silicone crude rubber, low-Ph silicone rubber, butenedioic acid propylene glycol polyester, dicumyl peroxide, activated magnesium oxide, styrene, Bu oleate, vinyl-terminated silicone oil, oxidized polyethylene wax, white carbon black, konilite, silicon carbide, silica powder, extra-fine activated clay, modified hollow glass microbeads, silane coupling agent KH-902, calcium-zinc stabilizer, HPG antioxidant and 4010NA antioxidant. The aging-resistant power cable of the present invention has excellent mechanical and aging-resistant properties.
This patent No CN108059832 discloses a method for preparing high-temperature decomposition- resistant silicone rubber. The method comprises the steps of: compounding Methyl-vinyl raw rubber, heavy calcium carbonate and vinyl triethoxysilane to obtain a rubber compound, adding sepiolite powder complex, expanded graphite, glass microbeads, calcined kaolin and aminopropyl triethoxysilane, continuing compounding, heating, vacuumizing, keeping the temperature and pressure, cooling, adding lanthanum oxide, stirring to obtain preform, adding vulcanizing agent to the preform, and vulcanizing to obtain the high-temperature decomposition-resistant silicone rubber. The silicone rubber of the invention has extremely excellent elongation at break and tensile strength, high heat resistance, ultrahigh resistance to high-temperature decomposition, no obvious drop in performance at high temperature and excellent flame retardancy.
Patent No DE202006018227 teaches a protective device for cables, cable trees, hydraulic, fuel, pneumatic or further lines showing a high shear and scrub resistance, a high electric penetration resistance at good long-term behavior and at permanent high temperatures as well as a good mountablity comprises a first inner protective layer (A) of a knitted, braided, or woven hose of glass silk threads or fibers, optionally, mixed with plastic fibers and a second layer (B) of a plastic material filled with fine-particulated metal (oxide), graphite or mineral particles, or with glass microspheres or hollow plastic beads. The inner layer is impregnated with a material selected from the group consisting of PTFE, silicone (resin) and/or polyurethane, whereby the impregnating material may contain metal (oxide) particles, graphite, mineral fillers, glass microspheres, and/or PEEK beads. The second layer (thickness =1.0 mm) is made of silicone (rubber), polyurethane and/or a further rubber-like material and is applied on the first layer by coating, coextrusion or wrapping a plastic film. Preferably, at least a further third and a forth protective layer cover the first two layers and consist of a material used in layer A or B, optionally containing other fillers.
Patent No US20060013793 relates to a solid water-in-oil emulsion comprising an aqueous phase emulsified in a fatty phase comprising at least one ester oil and at least one wax, and at least one silicone surfactant comprising at least one polyhydroxylated chain or at least one alkyl dimethicone copolyol chosen from C8-C22 alkyl dimethicone copolyols, as well as a process for making up or caring for skin, comprising applying to the skin the emulsion. For example, a solid foundation contained candelilla wax, ozokerite, isotridecyl isononanoate, cyclopentasiloxane, iron oxide coated with disodium stearoyl glutamate and alumina, Aerosil R972, silica microbead, polymethyl methacrylate, Elfacos ST 9, polyglyceryl-4 isostearate, KF6104, and butylene glycol glycerol, magnesium sulfate, DC25225 in water phase.
Patent No JP04349301A involves conductive elastomer comprises dispersion of insulating elastic fibers with =10 denier, elastomer particles with grain diameter 10-300 µm, conductive particles with grain diameter 1-40 µm, hollow elastic microspheres with grain diameter 10- 150 µm in a non-conductive elastomer. Preferably, the non-conductive elastomer may be a silicone rubber, a liquid silicone rubber, or a silicone varnish as an essential component, and a silicone tacking agent; the insulating elastic fibers may be polyethylene, polyamide, aramide, polyester, polyurethane fibers, or composite fibers thereof; the conductive particles may be spherical C particles; the insulating particles may be Ca particles; and the hollow elastic microspheres may be vinylidene chloride-acrylonitrile copolymer.
Patent No CN108943932A disclosed layer is formed from the raw materials including (a) first random copolymer polypropylene having a m.p. of 135-145 °C, a first block copolymer polypropylene having a m.p. of 155-165 °C and formed by alternating polymerization of propylene and ethylene segments, and (c) a polyolefin elastomer, wherein the first random copolymer polypropylene is a random copolymer of propylene and ethylene. Thus, a heat seal layer prepared from 70 parts of first random polypropylene copolymer, 10 parts of propylene-based elastomer (polyolefin elastomer), 20 parts a first block copolymer polypropylene, core layer prepared from 70 parts of the second block copolymerized polypropylene, 20 parts of the polyethylene copolymer and 10 parts of random polypropylene and a composite layer prepared from 80 parts of the second random copolymer polypropylene and 20 parts of the third block copolymerized polypropylene were respectively blended and extruded to obtain the title CPP film.
US6967221B2 discloses a silicone rubber that is produced by curing a silicone rubber composition which includes (A) a curable organopolysiloxane composition, and (B) at least one hollow organic resin filler, whereby the filler forms cells in an open-cell state. The open-cell state gives the silicone rubber good cushioning property and a low compression set. Background art admissions states that heat-curable liquid silicone rubber compositions are used in many different applications since they are effectively moldable and once molded, they provide cured products (silicone rubbers) having excellent qualities, including heat resistance, weather resistance and electrical insulating properties. One distinctive type of silicone rubber having a broad range of potential applications is sponge-like silicone rubber. In addition to possessing the above outstanding performance features of silicone rubbers (heat resistance, weather resistance, electric insulating properties, etc.), silicone rubber sponges can be made lightweight. Moreover, the inclusion of a gas in the molded material provides volumetric shrinkage qualities that enable the silicone rubber sponge to be used as an shock-absorbing, or cushioning, material. The low heat conductivity resulting from the incorporation of a gas also allows silicone rubber sponges to be used as heat-insulating or heat-storing materials.
In spite of the above state of the art knowledge there is thus a longfelt need in the art to provide for compressible, fire-retardant, lightweight and thermally/electrically insulative rubber foam pad that would be adapted as a specialized separator to enhance the overall performance, safety, and efficiency of batteries including Li-ion batteries by addressing the key considerations such as weight compressibility, fire resistance, and effective thermal and electrical insulation.
OBJECTS OF THE INVENTION:
The basic objective of the present invention is directed to provide for compressible rubber based formulation suitable for compression rubber pads that would be adapted as battery cell separators to enhance overall battery safety and thereby reduce the evolving chances of thermal runaway around the globe.
Another objective of the present invention is to provide for said compressible rubber based formulation as compression rubber pad and a process of manufacture thereof which can deliver uniform and consistent compression between battery cells, ensure compatibility with diverse cell configurations and satisfy all modern age compression force deflection requirements.
Yet another objective of the present invention is to provide for said compression rubber pad with high thermal and electrical insulation, so that it could prevent cell-to-cell heat transfer and internal short-circuit.
Still another objective of the present invention is to provide for said compression rubber pad that would be adapted as a fire-retardant compression pad to ensure its fire safety and reduce the chances of thermal runaway.
Yet another object of the present invention is to provide for said compression rubber pad that would contribute significantly to the evolution of battery technology, particularly in applications demanding lightweight and secure energy storage solutions.
BRIEF DESCRIPTION OF FIGURES
Fig 1: illustrates CFD curve of compression pads, Experiment (1-3)
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a compressible rubber based formulation comprising synergistic co-acting blend of silicone rubber with 6-10 phr of foaming agent incorporated silicone rubber and functional fillers, wherein said foaming agent includes expandable thermoplastic microspheres favouring improved mechanical strength and compressive strength attributes of the rubber.
Preferably said compressible rubber based formulation is provided wherein said silicone rubber is heat cured silicone rubber based on peroxides preferably organic peroxide including 2, 5-Dimethyl-2, 5-di (tert-butylperoxy) hexane in the range of 0.5-3 phr, dicumyl peroxide, or based on sulphur in the range of 0.5-5 phr.
More preferably said compressible rubber based formulation is provided wherein said functional fillers include 30-40 phr more preferably 33-37 phr fire retardant fillers including aluminium hydroxide, ammonium polyphosphate, antimony trioxide, tri (2,3-dibromopropyl) isocyanurate and combinations thereof and insulator based fillers including fumed silica in the range of 1-5 phr more preferably 10-15 phr.
According to another preferred aspect of the present invention there is provided said compressible rubber based formulation wherein said formulation includes titanium dioxide in the range of 5-20 phr to introduce white colour and enhance mechanical stability of the product.

More preferably said compressible rubber based formulation is provided wherein the co-acting blend of select levels of foaming agent includes in Parts per hundred (100) of Silicone Rubber, Ammonium polyphosphate 5-20 parts, tri(2,3-dibromopropyl) isocyanurate 5-20 parts, Aluminium hydroxide 5-20 parts, Antimony trioxide 5-20 parts, Fume Silica 1-6 parts, 10-20 parts Titanium dioxide, 2,5-Dimethyl-2,5-di (tert-butylperoxy) hexane 1-4 parts.
According to another preferred aspect of the present invention there is provided said compressible rubber based formulation suitable as specialized cell separators in Li-ion battery packs and is adapted as compressible, fire-retardant, lightweight and thermally/electrically insulative rubber foam pad for enhancement of overall performance, safety, and efficiency of Li-ion batteries having tensile strength in the range of 0.2-1 MPa as per IS 3400:2021 Hardness in range of 10-30 Shore A as per ASTM D2240, Compression of 5-25% at 50 °C as per ASTM D1056, Dielectric strength in the range of 2-10 KV/mm as per ASTM D149-20, Volume resistivity in the range of 2x1014 -4x1016as per ASTM D 257, Thermal conductivity in the range of 0.01-0.10 at 50 °C as per ASTM D 7984 and UL94 V0 category in terms of fire retardancy.
According to another aspect of the present invention there is provided a process for manufacturing said compressible rubber based formulation as rubber foam pad including the steps of
Pre-mixing silicone rubber with functional fillers in a shear kneader till uniform dispersion of fillers in rubber matrix is achieved followed by uniformly dispersing foaming agent in said rubber matrix, per-forming and thereafter curing to attain rubber formulation therefrom as rubber foam pad.
Preferably in said process for manufacturing said compressible rubber based formulation is carried out by including the following sub-steps
Said pre-mixing silicone rubber with functional fillers in two stages with the first stage involving mixing with fire-retardant, thermal insulation and colouring agents in a shear kneader grinder till uniform dispersion of fillers into silicone rubber matrix is achieved, and the second stage involving uniformly dispersing foaming agent and curing agent with silicone rubber matrix at ambient temperatures of 20 to 40?C till uniform dispersion is achieved;
Converting said functional filler and foaming agent dispersed silicone rubber matrix into performs including sheets by maintaining desired thickness upon employing two-roll mill machine followed by cutting into desired shape to develop pre-forms for molding;
Molding the pre-forms by curing by maintaining 30-60% mould cavity, 160-190 °C temperature and 50-300 bar pressure.

DETAILED DESCRIPTION OF THE INVENTION:
As described hereinbefore, the present invention provides for compressible rubber based formulation to favour rubber compression pads and a process of manufacture thereof suitable for battery cell separators by addressing the challenges of overall battery safety by reducing the evolving chances of thermal runaway.
According to the basic aspect of the present invention there is provided said compressible rubber based formulation suitable for rubber compression pad crafted from flexible elastomeric materials, with the pad conforming precisely to the contours of battery cells and separators suiting diverse cell configurations. The present make and configuration of compression pad ensures uniform compression, optimal contact, fire retardant, high thermal & electrical insulation and consistent pressure distribution, contributing to enhanced energy transfer, thermal management, and overall safety.
A compressible, thermal insulative, fire retardant, light weight rubber foam pad formulation is thus provided wherein said formulation includes heat-cured silicone rubber as base material with functional fillers and foaming agent. Said formulation enabling a matrix comprises heat-cured silicone rubber, cured by organic peroxide such as 2,5-Dimethyl-2,5-di(tert-butylperoxy) hexane within the range of 0.5-3 phr.
Another aspect of the present invention provides a compressible, thermal & electrical insulative, fire retardant, light weight rubber foam pad comprising synergistic co-acting blend of silicone rubber with 2-10 phr of foaming agent incorporated silicone rubber and functional fillers, wherein said foaming agent includes expandable thermoplastic microspheres for improved mechanical strength and compressive strength properties.
A further aspect of the present invention provides a compressible, thermal & electrical insulative, fire retardant, light weight rubber foam pad wherein in said formulation includes a set of fire-retardant fillers such as aluminium hydroxide and/or, ammonium polyphosphate and/or, antimony trioxide and/or, tri(2,3-dibromopropyl)isocyanurate and/or, combination thereof adapted in the range of 30-40phr, to introduce fire retardant property. In addition to that fumed silica has been introduced in the range of 1-5 phr to introduce thermal insulation property.
Yet another aspect of the present invention provides a compressible, thermal & electrical insulative, fire retardant, light weight rubber foam pad wherein in said formulation includes a titanium dioxide in the range of 5-20 phr, to introduce white colour and enhance mechanical stability of the product.
A further aspect of the present invention provides a compressible, thermal & electrical insulative, fire retardant, light weight rubber foam pad wherein its physical properties include tensile strength in the range of 0.2-1 MPa as per IS 3400:2021 Hardness in range of 10-30 Shore A as per ASTM D2240, Compression set in the range of 5-25% at 50 °C as per ASTM D1056, Dielectric strength in the range of 2-10 KV/mm as per ASTM D149-20, Volume resistivity in the range of 2x1014 -4x1016as per ASTM D 257, Thermal conductivity in the range of 0.01-0.10 at 50 °C as per ASTM D 7984 and receivedUL94 V0 category in terms of fire retardancy.
A further aspect of the present invention provides a selective process of manufacturing a compressible, thermal& electrical insulative, fire retardant, light weight rubber foam pad, which includes steps of:
1. Pre-mixing of silicone rubber with all abovementioned functional fillers. This mixing process comprises of two steps. In first step silicone rubber mixed well withfire-retardant, thermal insulation and colouring agents in a shear kneader grinder till uniform dispersion of fillers into matrix achieved. In second step, foaming agent and curing agent were mixed with the rubber-compound at ambient temperature till uniform dispersion achieved.
2. In further step, the rubber compound gets converted into sheet form, maintaining desired thickness by using two-roll mill machine. Then cut into desired shape to develop pre-forms for molding.
3. In molding stage, compression pads get produced by curing such pre-forms, maintaining 30-60% mould cavity, 160-190 °C temperature and 50-300 bar pressure.
As mentioned earlier the prime focus of the present invention relates to development of compressible, thermal& electrical insulative, fire retardant, light weight rubber foam pad, comprising heat-cured silicone rubber with functional fillers and foaming agents, wherein the functional fillers are categorised into three categories such as fire retardant, thermal insulative and colouring agents.
According to one embodiment organic curing agent is used as curing agent of heat-cured silicone rubber, preferably 2,5-Dimethyl-2,5-di(tert-butylperoxy) hexane is used within the range of 0.5-3 phr, more preferably 1-2 phr.
According to one embodiment fire-retardant fillers comprise of a combination of select chemicals such as ammonium polyphosphate, ammonium hydroxide, antimony trioxide and tri(2,3-dibromopropyl) isocyanurate preferably in the range of 30-40 phr, more preferably 33-37 phr. Whereas fumed silica is used as thermal insulative filler preferably within range of 1-5 phr, more preferably 1-3 phr. As coloring agent titanium dioxide is used preferable within range of 5-20 phr, more preferably 10-15 phr.
Another embodiment of the present invention refers heat expandable thermoplastic microsphere is used as foaming agent preferably within range of 2-6 phr, more preferably within 3-5 phr.
Another embodiment relates to the method of production, which comprises of three steps which includes mixing of fillers into rubber matrix, pre-form formation and final curing within mould cavity at high temperature and pressure.
Mixing process comprises of two steps. In first step functional fillers get introduced into the rubber matrix. Preferably high shear kneader is used for this process. Filled rubber compound then subjected to shear mixing under ram pressure, preferably for 20-50 minutes, more preferably for 30-40 minutes. In next step foaming and curing agents get introduced into the same compound at ambient temperature and mixed under same condition for another 10-30 minutes, more preferably for 15-20 minutes to get uniform mixing of all additives into the rubber matrix.
In further steps, the mixed rubber compound gets converted into preform preferably using two-roll mill machine. Which in next process get cured within mould cavity, maintaining 30-60% mould cavity, more preferably 40-50% mould cavity, preferably at 160-190 °C temperature and 50-300 bar pressure, more preferably at 165-175 °C temperature and 150-200 bar pressure.
The following examples are illustrative of some compositions of compressible, thermal insulative, fire retardant, light weight rubber foam pad. These examples are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.

EXAMPLES
Following examples (1-3) were carried out in order to identify the ideal composition of compression pad which can satisfy all safety requirements of electronic vehicle battery packs as cell separator, especially for prismatic cell-based modules.
Basic formulations for the example (1-3) are mentioned in Table 2 below.
The levels of the other ingredients of the present formulation of the table below excluding the expandable thermoplastic microsphere are also as important to reach to the desired CFD curve shown under Figure 1.
Material Example 1 Example 2 Example 3
Silicone Rubber 100 100 100
Ammonium polyphosphate 5~20 5~20 5~20
Tri (2,3-dibromopropyl) isocyanurate 5~20 5~20 5~20
Aluminium hydroxide 5~20 5~20 5~20
Antimony trioxide 5~20 5~20 5~20
Fume Silica 1~6 1~6 1~6
Expandable thermoplastic microsphere, foaming agent 10~14 8~10 4~6
Titanium dioxide 10~20 10~20 10~20
2,5-Dimethyl-2,5-di (tert-butylperoxy) hexane 1~4 1~4 1~4

Table 2 above illustrates formulations of Examples (1-3)
As per the given formulations the functional fillers get introduced into the rubber matrix and mixed well in a kneader for 30-40 minutes. Then foaming and curing agents added into the same compound at ambient temperature and mixed under same condition for another 15-20 minutes to get uniform mixing of all additives into the rubber matrix. Preform sheets were prepared from these compounds using two-roll mill machine. Finally get cured within mould maintaining 40-50% volume cavity, under 165-175 °C temperature and 150-200 bar pressure.
All necessary testings were carried out with the developed samples and results are tabulated in Table 3 below.
Table 3:
Property Unit Standard Experiment 1 Experiment 2 Experiment 3
Hardness Shore AO ASTM D 2240 30± 5 25± 5 20± 5
Specific Gravity g/cm3 - 0.7±0.1 0.6±0.1 0.5±0.1
Tensile Strength MPa IS 3400:2021 0.55 0.53 0.51
Dielectric Strength KV/mm ASTM D 149 20 5.37 5.37 5.37
Volume Resistivity Ohm.cm ASTM D 257 257.31 x 1012 257.31 x 1012 257.31 x 1012
Compression Set at 50 °C % ASTM D 1056 19.54 19.54 19.54
Flame Retardancy - UL 94 V0 V0 V0
Thermal Conductivity at 50 °C W/mK ASTM D 7984 0.16 0.16 0.16

Table 3 above illustrates compression pad test results, Experiment (1-3)
Fig 1: illustrates CFD curve of compression pads, Experiment (1-3) in relation to compression load deflection results.
Table 4

Code
Critical Region Requirement Experiment 2 value Experiment 1 value Experiment 3 value
Compressive load (KN) Compression % Compressive load (KN) Compression % Compressive load (KN) Compression % Compressive load (KN) Compression %
C1 Start of life (Battery Assembly) 3-5 25-35 4.35 30 6.97 30 2.02 30
C2 After 1000 cycles 10-12 45-55 10.68 50 17.09 50 6.43 50
C3 End of life 21-23 60-70 22.04 61 22.09 55 22.04 72
Table 4 above gives critical compression load requirement Vs. Compression load data from Experiment 2.
Form the test results mentioned in Table 3, Fig 1 and Table 4, it is very clear that all the experimented combinations satisfied all safety data requirements, whereas in case of compressibility requirement, Experiment 2 shows selectively favourable result, which highly fits all the modern battery thermal management criteria as cell separator.
Thus a compressible, thermal & electrical insulative, fire retardant, light weight heat cured silicone rubber foam pad is provided comprising synergistic co-blend of functional fillers and foaming agent. Wherein the curing agent includes organic peroxide such as 2, 5-Dimethyl-2, 5-di (tert-butylperoxy) hexane or, dicumyl peroxide within range of 0.5-3 phr or, conventional sulphur curing system within range of 0.5-5 phr.
Said compressible, thermal & electrical insulative, fire retardant, light weight heat cured silicone rubber foam pad is provided wherein said product includes tensile strength in the range of 0.2-1 MPa as per IS 3400:2021 Hardness in range of 10-30 Shore A as per ASTM D2240, Compression set in the range of 5-25% at 50 °C as per ASTM D1056, Dielectric strength in the range of 2-10 KV/mm as per ASTM D149-20, Volume resistivity in the range of 2x1014 -4x1016 as per ASTM D 257, Thermal conductivity in the range of 0.01-0.10 at 50 °C as per ASTM D 7984 and received UL94 V0 category in terms of fire retardancy.
Preferably said compressible, thermal & electrical insulative, fire retardant, light weight heat cured silicone rubber foam pad formulation is provided wherein said formulation includes expandable thermoplastic microspheres as foaming agent within range of 2-10 phr.
In said compressible, thermal & electrical insulative, fire retardant, light weight heat cured silicone rubber foam pad said formulation includes a set of fire-retardant fillers such as aluminium hydroxide and/or, ammonium polyphosphate and/or, antimony trioxide and/or, tri(2,3-dibromopropyl)isocyanurate and/or, combination thereof adapted in the range of 30-40 phr, to introduce fire retardant property. In addition to that fumed silica has been introduced in the range of 1-5 phr to introduce thermal insulation property and titanium dioxide in the range of 5-20 phr to get white colour and added mechanical strength in the pad.
It is also possible to provide for a process of manufacturing of compressible, thermal & electrical insulative, fire retardant, light weight heat cured silicone rubber foam pad comprising of the following sub steps:
a. Pre-mixing of silicone rubber with all abovementioned functional fillers. This mixing process comprises of two steps. In first step silicone rubber mixed well with fire-retardant, thermal insulation and colouring agents in a shear kneader grinder till uniform dispersion of fillers into matrix achieved. In second step, foaming agent and curing agent were mixed with the rubber-compound at ambient temperature till uniform dispersion achieved.
b. In further step, the rubber compound gets converted into sheet form, maintaining desired thickness by using two-roll mill machine. Then cut into desired shape to develop pre-forms for molding.
c. In molding stage, compression pads get produced by curing such pre-forms, maintaining 30-60% mould cavity, 160-190 °C temperature and 50-300 bar pressure.

,CLAIMS:We Claim:
1. Compressible rubber based formulation comprising synergistic co-acting blend of silicone rubber with 6-10 phr of foaming agent incorporated silicone rubber and functional fillers, wherein said foaming agent includes expandable thermoplastic microspheres favouring improved mechanical strength and compressive strength attributes of the rubber.

2. The compressible rubber based formulation as claimed in claim 1 wherein said silicone rubber is heat cured silicone rubber based on peroxides preferably organic peroxide including 2, 5-Dimethyl-2, 5-di (tert-butylperoxy) hexane in the range of 0.5-3 phr, dicumyl peroxide, or based on sulphur in the range of 0.5-5 phr.

3. The compressible rubber based formulation as claimed in claims 1 or 2 wherein said functional fillers include 30-40 phr more preferably 33-37 phr fire retardant fillers including aluminium hydroxide, ammonium polyphosphate, antimony trioxide, tri (2,3-dibromopropyl) isocyanurate and combinations thereof and insulator based fillers including fumed silica in the range of 1-5 phr more preferably 10-15 phr.

4. The compressible rubber based formulation as claimed in claims 1-3 wherein said formulation includes titanium dioxide in the range of 5-20 phr to introduce white colour and enhance mechanical stability of the product.

5. The compressible rubber based formulation as claimed in claims 1-4 wherein the co-acting blend of select levels of foaming agent includes in Parts per hundred (100) of Silicone Rubber, Ammonium polyphosphate 5-20 parts, tri(2,3-dibromopropyl)isocyanurate 5-20 parts, Aluminium hydroxide 5-20 parts, Antimony trioxide 5-20 parts, Fume Silica 1-6 parts, 10-20 parts Titanium dioxide, 2,5-Dimethyl-2,5-di (tert-butylperoxy) hexane 1-4 parts.

6. The compressible rubber based formulation as claimed in claims 1-5 suitable as specialized cell separators in Li-ion battery packs and is adapted as compressible, fire-retardant, lightweight and thermally/electrically insulative rubber foam pad for enhancement of overall performance, safety, and efficiency of Li-ion batteries having tensile strength in the range of 0.2-1 MPa as per IS 3400:2021 Hardness in range of 10-30 Shore A as per ASTM D2240, Compression of 5-25% at 50 °C as per ASTM D1056, Dielectric strength in the range of 2-10 KV/mm as per ASTM D149-20, Volume resistivity in the range of 2x1014 -4x1016as per ASTM D 257, Thermal conductivity in the range of 0.01-0.10 at 50 °C as per ASTM D 7984 and UL94 V0 category in terms of fire retardancy.

7. A process for manufacturing said compressible rubber based formulation as claimed in claims 1-6 as rubber foam pad including the steps of
Pre-mixing silicone rubber with functional fillers in a shear kneader till uniform dispersion of fillers in rubber matrix is achieved followed by uniformly dispersing foaming agent in said rubber matrix, per-forming and thereafter curing to attain rubber formulation therefrom as rubber foam pad.

8. The process for manufacturing said compressible rubber based formulation as claimed in claim 7 carried out by including the following sub-steps
Said pre-mixing silicone rubber with functional fillers in two stages with the first stage involving mixing with fire-retardant, thermal insulation and colouring agents in a shear kneader grinder till uniform dispersion of fillers into silicone rubber matrix is achieved, and the second stage involving uniformly dispersing foaming agent and curing agent with silicone rubber matrix at ambient temperatures of 20 to 40?C till uniform dispersion is achieved;
Converting said functional filler and foaming agent dispersed silicone rubber matrix into performs including sheets by maintaining desired thickness upon employing two-roll mill machine followed by cutting into desired shape to develop pre-forms for molding;
Molding the pre-forms by curing by maintaining 30-60% mould cavity, 160-190 °C temperature and 50-300 bar pressure.

Dated this the 19th day of April, 2025 Anjan Sen
Of Anjan Sen and Associates
Applicants Agent
IN/PA-199