Description:“A PROCESS FOR PREPARATION OF FLEXIBLE GEL POLYMER ELECTROLYTE CUM SEPARATOR COMPOSITION”
FIELD OF INVENTION
[0001] The present disclosure relates to a gel polymer electrolyte cum separator for lithium-ion batteries. In particular, the present invention discloses a composition and a method of fabrication of conductive flexible solid polymer sheet at ambient and sub-ambient temperatures using solution casting method.
BACKGROUND OF THE INVENTION
[0002] Flexible ion conducting polymer sheets having high ionic conductivity at sub-ambient and ambient temperatures coupled with adequate thermal, mechanical and voltage stability are considered important for dual function as separator cum electrolyte for storage cell applications unlike the conventional practice of using separator and electrolyte as the two separate components in the commercial storage cells. The significance of the present invention lies in its inventive steps comprising choice of a suitable combination of precursors, stoichiometry and process conditions yielding a free-standing solid gel polymer electrolyte sheet with adequate flexibility and dual function of electrolyte cum separator unlike the conventional electrolyte that requires separator as an additional component for device application. The gel polymer electrolyte stoichiometry comprises a host polymer (PVDF-HFP), a strongly polar solvent (-butyrolactone) with dielectric permittivity ~42, an aprotic Li+ salt (LiTFSI), an ionic liquid (EMIMTFSI) and secondary solvent acetone having room temperature (RT) volatility and adequate miscibility with -butyrolactone.
[0003] The formation of unstable solid-electrolyte interphase (SEI) resulted from the consumption of electrolyte and lithium metal anode, leading to the increase of interfacial resistance and safety risks (i.e., internal short-circuits and explosion). So, the focus is to suppress the growth of Li dendrites and stabilize the SEI.
[0004] To control the growth of Li dendrites and stabilize the SEI film, multiple techniques have been proposed, including the use of electrolyte additives, solid or quasi-solid electrolytes, modifications to separators, and lithium metal hosts. Solid or gel electrolytes have become increasingly popular due to their ability to create strong interfacial contact with the Li electrode and effectively inhibit the growth and spread of Li dendrites.
[0005] In comparison with solid-state inorganic electrolytes, solid polymer gel electrolytes exhibit superior flexibility and easier processability.
[0006] The addition of ionic liquid (IL) into conventional organic solution (liquid) electrolyte can stabilize lithium anode against Li dendrite growth. Theoretical studies also confirmed that tethered anions in ILs can improve the plating stability of lithium metal anode. Moreover, the anion-tethered ILs can offer a localized reservoir of anions to mitigate the unstable electric field in the space-charge region near Li anode.
[0007] Therefore, it is quite evident that all of the above disclosures face the challenges such as the high reactivity of lithium metal, unstable SEI film formation, and limited scalability in manufacturing. Additionally, there are concerns about cost-effectiveness for commercial use, compatibility with specific applications, and ensuring consistent performance across varied operational conditions.
[0008] Thus, there is a pressing need to achieve the same.
OBJECTS OF THE INVENTION
[0009] Some of the objects of the present subject matter, which at least one embodiment herein satisfy, are listed herein below.
[0010] It is an object of the present subject matter to overcome the aforementioned and other drawbacks existing in the prior art apparatus and methods.
[0011] It is a principal object of the present invention to provide a composition and a method of preparation of gel polymer electrolyte cum separator using a blend of Gamma-butyrolactone (GBL), 1-ethyl-3-methylimidazolium bis (trifluoromethane sulfonyl) imide (EMIMTFSI), Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and poly (vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP).
[0012] It is another object of the present invention is to provide a composition and a method of preparation of gel polymer electrolyte cum separator with enhanced mechanical, thermal, voltage stability and ionic conductivity at ambient and sub-ambient temperatures.
[0013] It is another object of the present invention is to provide a composition and a method of preparation of gel polymer electrolyte cum separator with an electrochemical potential window of ~5V, making the GPE suitable for various energy storage applications.
[0014] These and other objects and advantages of the present subject matter will be apparent to a person skilled in the art after consideration of the following detailed description taking into consideration with accompanied drawings in which preferred embodiments of the present subject matter are illustrated.
SUMMARY OF THE INVENTION
[0015] This summary is provided to introduce the concept of a gel polymer electrolyte cum separator composition and a method of preparation of gel polymer electrolyte cum separator. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0016] The invention relates to a gel polymer electrolyte cum separator composition and a method of preparation of a gel polymer electrolyte cum separator composition comprising a lithium salt, an aprotic polar solvent, an ionic liquid, a semi-crystalline polymer and a common solvent.
[0017] The method comprises dissolving a pre-determined quantity of a semi-crystalline polymer in acetone and mechanical agitation for 24 hours in an inert medium to form a low viscous solution. Dissolving, a mixture of a lithium salt and an ionic liquid in an aprotic polar solvent followed by mechanical agitation for 24 hours in an inert medium to form a high viscous solution. Both the above solutions were added together and proceeded with mechanical agitation for 24 hours in the inert medium to form a homogeneous solution. Then followed by solution casting of the homogeneous solution under inert medium. Wherein the film is solidified to form a freestanding and flexible gel polymer electrolyte cum separator.
[0018] In one aspect of the present invention, the lithium salt is at least one selected from a group consisting of Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).
[0019] In another aspect of the present invention, the polar solvent is at least one selected from a group consisting of gamma-Butyrolactone (GBL).
[0020] In another aspect of the present invention, the ionic liquid is at least one selected from a group consisting of 1-Ethyl-3-methylimidazolium bis (trifluoro-methanesulfonyl) imide (EMIMTFSI).
[0021] In another aspect of the present invention, the semi-crystalline polymer is at least one selected from a group consisting of Poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP).
[0022] In one aspect of the present invention, the common solvent is at least one selected from a group of volatile organic solvents consisting of acetone.
[0023] In another aspect of the present invention, the room temperature conductivity is 9.2× 10^-4 S cm^-1 (~10^-3 S cm^-1).
[0024] In one aspect of the present invention, the Gamma-butyrolactone (GBL) dissolve and dissociate the electrolyte salt.
[0025] In another aspect of the present invention, the ionic liquid EMIMTFSI stabilize lithium anode against Li dendrite growth.
[0026] In one aspect of the present invention, the gel polymer electrolyte cum separator exhibits a thermal stability up to a temperature of 300°C.
[0027] In another aspect of the present invention, the gel polymer electrolyte cum separator exhibits an electrochemical potential window of approximately 5V, making it suitable for various electrochemical applications.
[0028] In one aspect of the present invention, the gel polymer electrolyte cum separator is used in lithium-ion batteries, including but not limited to, consumer electronics, electric vehicles, and renewable energy storage systems.
[0029] To further understand the characteristics and technical contents of the present subject matter, a description relating thereto will be made with reference to the accompanying drawings. However, the drawings are illustrative only but not used to limit the scope of the present subject matter.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0030] It is to be noted, however, that the appended drawings illustrate only typical embodiments of the present subject matter and are therefore not to be considered for limiting of its scope, for the invention may admit to other equally effective embodiments. The detailed description is presented with reference to the accompanying figures. In the figures, a reference number identifies the figure in which the reference number first appears some embodiments of apparatus or methods or structure are described, by way of example, and with reference to the accompanying figures, in which
[0031] Fig. 1 illustrates a schematic block diagram of the method of preparation of the gel polymer electrolyte cum separator in accordance with an embodiment of the present disclosure;
[0032] Fig. 2 (I) depicts a mechanical property analysis of prepared GPE films using a universal testing machine (UTM) in accordance with an embodiment of the present disclosure;
[0033] Fig. 2 (II) illustrates a graphical representation depicting a thermo-gravimetric analysis of prepared GPE in accordance with an embodiment of the present disclosure;
[0034] Fig. 2(III) illustrates a graphical representation depicting an electrochemical stability window measurements of PGE and PGES in accordance with an embodiment of the present disclosure;
[0035] Fig. 3 illustrates a graphical representation depicting a room temperature impedance spectra of PG, PGS, PGE and PGES GPE films with ionic conductivity in accordance with an embodiment of the present disclosure;
[0036] Fig. 4 illustrates graphical representation depicting a sub ambient conductivity analysis of PGS, PGE and PGES in accordance with an embodiment of the present disclosure;
[0037] Fig. 5 illustrates graphical representation depicting an ionic transport number measurement of PGS and PGES in accordance with an embodiment of the present disclosure;
[0038] Fig. 6 illustrates a graphical representation depicting a (I) X-ray diffraction pattern of the prepared gel polymer electrolyte films & (II) Field emission scanning electron microscopy analysis of (a) PVDF-HFP + GBL (b) PVDF-HFP + GBL+ LiTFSI (c) PVDF-HFP + GBL+ EMIMTFSI (d) PVDF-HFP + GBL+ EMIMTFSI + LiTFSI in accordance with an embodiment of the present disclosure;
[0039] Fig. 7(a) illustrates a graphical representation depicting a vibrational spectrum pattern of FTIR spectra for prepared gel polymer electrolyte films in accordance with an embodiment of the present disclosure;
[0040] Fig. 7(b) illustrates a graphical representation depicting a vibrational spectrum pattern of Raman spectra for prepared gel polymer electrolyte films in accordance with an embodiment of the present disclosure;
[0041] Fig 8 illustrates a graphical representation depicting a cyclic voltammetry (CV) curve of Li ǁ PGES ǁ NMC in accordance with an embodiment of the present disclosure; and
[0042] Fig 9 illustrates a graphical representation depicting a Li-Po cell performance results with charge discharge and room temperature electrochemical impedance spectroscopy (EIS) results in accordance with an embodiment of the present disclosure.
[0043] The figures depict embodiments of the present subject matter for the purpose of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
[0044] The salient features of the invention are presented in the drawings that illustrate the disclosed contents, not to limit its scope, which is defined by the claims. Those of ordinary skill in the art will recognize a number of equivalent variations of the various features provided in the description that follows.
[0045] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0046] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the “invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0047] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.
[0048] Various embodiments are further described herein with reference to the accompanying figures. It should be noted that the description and figures relate to exemplary embodiments and should not be construed as a limitation to the subject matter of the present subject matter. It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the subject matter of the present subject matter. Moreover, all statements herein reciting principles, aspects, and embodiments of the subject matter of the present subject matter, as well as specific examples, are intended to encompass equivalents thereof. Yet further, for the sake of brevity, operation or working principles pertaining to the technical material that is known in the technical field of the present subject matter have not been described in detail so as not to unnecessarily obscure the present subject matter.
[0049] The invention relates to a gel polymer electrolyte cum separator composition and a method of preparation of gel polymer electrolyte cum separator. Ion conducting gel polymer electrolytes (GPEs) are a class of electrolytes that have gained attention in recent years due to dimensional flexibility, easier processing, high ionic conductivity ~10-3 Scm-1 at room and low temperatures, with improved stability pertaining to tensile, thermal, voltage and transport properties unlike conventional gel electrolytes.
[0050] The gel polymer electrolyte cum separator composition comprises of a lithium salt, an aprotic polar solvent, an ionic liquid, a semi-crystalline polymer and a common solvent.
[0051] The lithium salt is at least one selected from a group consisting of Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). LiTFSI is a hydrophilic salt with the chemical formula LiC2F6NO4S2.
[0052] The polar solvent is at least one selected from a group consisting of gamma-Butyrolactone (GBL). GBL has a strong ability to dissolve and dissociate lithium salts. Ionic liquids are organic salts with melting points below or equal to room temperature. They are also known as green solvents. EMIM-TFSI can serve as a good choice of ILs because of their high ionic strength, high electrochemical stability and non-flammability.
[0053] The ionic liquid is at least one selected from a group consisting of 1-Ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl)imide (EMIMTFSI). The ionic liquid EMIMTFSI stabilize lithium anode against Li dendrite growth.
[0054] The semi-crystalline polymer is at least one selected from a group consisting of Poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)). It is a semi-crystalline copolymer with crystalline VDF units that provide good mechanical and chemical stability and amorphous HFP units supporting better ionic conductivity.
[0055] The common solvent is at least one selected from a group consisting of acetone. The gel polymer electrolyte cum separator is used in lithium-ion batteries, including but not limited to, consumer electronics, electric vehicles, and renewable energy storage systems. The combination of flexible gel polymer electrolytes (GPEs), composed of a blend of Gamma-butyrolactone (GBL) as the solvent and an ionic liquid 1-ethyl-3-methylimidazolium – bis(trifluoromethanesulfonyl) imide (EMIMTFSI) incorporated within the host polymer PVDF-HFP (poly (vinylidene fluoride-co-hexafluoropropylene)), with a pre-determined salt ratio. The freestanding solid gel polymer electrolyte film is observed to be mechanically stable and dimensionally flexible. The structural, spectroscopic, thermal and mechanical analyses have indicated predominantly amorphous texture with attributes of crystallinity and acceptable thermal and mechanical stability. Room temperature conductivity measurements of the prepared GPE samples suggest jump of several orders in magnitude reaching σdc ~10-3 Scm-1 when compared with pristine host polymer (~10-8 S cm-1). Temperature-dependent conductivity analysis over a temperature range -50 °C to +20 °C indicated a predominant Vogel–Tammann– Fulcher (VTF) type conduction mechanism. Transport number measurement results confirmed purely ionic transport mechanism with tion~ 99.5%, tensile stress ~1.52 MPa for optimal composition of GPE as evaluated using stress-strain profile, thermo-gravimetric results suggested thermal stability up to ~305oC. Linear sweep voltammetry measurements confirmed operational voltage stability window in the limit ~3.96 – 5 V. The results so obtained indicated suitability of the optimal GPE composition, under investigation, for electrochemical redox action as a separator-cum-electrolyte component in lithium polymer cell.
[0056] The present invention also relates to a lithium ion cell comprising, in particular materials;
[0057] An anode comprising of an alkali metal is made up of lithium;
[0058] An anode comprising of MCMB (mesocarbon microbeads), conducting carbon Super-P and polymer in (resin /PVDF) binder in weight ratio (85:10:5) in N-methyl-2-pyrrolidinone (NMP) is casted on Cu foil;
[0059] A cathode comprising of Lithium nickel manganese cobalt oxide (NMC333); conducting carbon Super-P and polymer in (resin /PVDF) binder in weight ratio (85:10:5) in N-methyl-2-pyrrolidinone (NMP) is casted on Al foil;
[0060] A polymer electrolyte cum separator comprises {Poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), gamma-Butyrolactone (GBL), 1M Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 1-ethyl-3-methylimidazolium bis (trifluoromethane sulfonyl) imide (EMIMTFSI).
EXAMPLE 1:
[0061] The polymer electrolyte cum separator comprises {Poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), gamma-Butyrolactone (GBL), 1M Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)} named as Example 1 is cell comprising PGS. In yet another aspect, the present invention discloses a lithium polymer electrochemical cell comprising NMC cathode. The lithium polymer electrochemical cell CR2032 was fabricated inside the argon glove box (H2O and O2 level ≤ 0.1 ppm). The cell comprising, a working cathode NMC, Lithium foil as counter and prepared polymer electrolyte cum separator PGS. The system can be represented as Li ‖ PGS ‖ NMC.
EXAMPLE 2:
[0062] The polymer electrolyte cum separator comprises; {Poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), gamma-Butyrolactone (GBL), 1-Ethyl-3-methylimidazolium bis (trifluoromethane sulfonyl) imide (EMIMTFSI)} named as Example 2 as cell comprising PGE.
[0063] In yet another aspect, the present invention discloses a lithium polymer electrochemical cell comprising NMC cathode. A lithium ion cell comprising a NMC electrode, the counter electrode of lithium foil, and prepared polymer electrolyte cum separator PGE which was fabricated inside the argon atmosphere in the glove box (H2O and O2 level ≤ 0.1 ppm). The system can be represented as Li ‖ PGE ‖ NMC.
EXAMPLE 3:
[0064] The polymer electrolyte cum separator comprises; {Poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), gamma-Butyrolactone (GBL), 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIMTFSI), 1M Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI} named as Example 3 as cell comprising PGES.
[0065] In yet another aspect, the present invention discloses a lithium polymer cell comprising NMC cathode. A lithium ion cell comprising a NMC working electrode, the counter electrode of lithium foil, and prepared polymer electrolyte cum separator PGES which was fabricated inside the argon atmosphere in the glove box (H2O and O2 level ≤ 0.1 ppm). The system can be represented as Li ‖ PGES ‖ NMC.
EXAMPLE 4:
[0066] The polymer electrolyte cum separator comprises; {Poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), gamma-Butyrolactone (GBL), 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIMTFSI), 1M Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI} named as Example 4 as cell comprising PGES with anode MCMB with respect to Lithium counterpart.
[0067] In yet another aspect, the present invention discloses a process for preparing lithium polymer cell using anode MCMB with respect to Lithium counterpart. The cell was assembled in an argon-filled glovebox (H2O and O2 level ≤ 0.1 ppm), in coin-type half cells CR2032. The calendared MCMB coated Cu-foil as the working electrode, Lithium foil as the counter electrode, and prepared polymer electrolyte cum separator PGES. The system can be represented as Li ‖ PGES ‖ MCMB.
[0068] Fig. 1 illustrates a schematic block diagram of the method of preparation of the gel polymer electrolyte cum separator in accordance with an embodiment of the present disclosure. The method (100) comprises (102), dissolving a pre-determined stoichiometric ratio of a semi- crystalline polymer in acetone and mechanical agitation for pre-determined duration in an inert medium (argon/mixture gases) to form a low viscous solution; (104), dissolving a mixture of a lithium salt and an ionic liquid in an aprotic polar solvent followed by mechanical agitation for pre-determined duration in an inert medium (argon/mixture gases) to form a high viscous solution. Further in (106), Adding a pre-determined quantity of a semi- crystalline polymer solution in the mixture of the lithium salt and ionic liquid solution, wherein the semi- crystalline polymer solution and the mixture of the lithium salt and ionic liquid solution is mixed homogeneously for 24h in an inert medium to form a homogeneous solution.
[0069] Then followed by solution casting (108) of the homogeneous solution under inert medium. Wherein the film is solidified to form a freestanding and flexible gel polymer electrolyte cum separator.
[0070] At step 102 of the method (100) for preparing the gel polymer electrolyte cum separator, semi-crystalline polymer in acetone is introduced into an inert medium, initiating the dissolution process. Under the influence of mechanical agitation for 24 hours, the acetone gradually dissolves, forming a low viscous solution characterized by its fluidity and uniformity.
[0071] At step 104, a meticulously prepared mixture comprising lithium salt and ionic liquid is dissolved in an aprotic polar solvent. This solvent system, chosen for its efficacy in solubilizing both the lithium salt and ionic liquid components, undergoes mechanical agitation for 24 hours. This extended agitation period yields a high viscous solution, a consequence of the ionic liquid's inherent viscosity in the solvent.
[0072] At step 106, the low viscous solution from step 102 is carefully introduced into the mixture obtained in step 104. This addition serves the crucial purpose of incorporating the semi-crystalline polymer into the solution, initiating the formation of the gel polymer electrolyte cum separator.
[0073] At step 106, the components undergo further processing to ensure homogeneity. Subjected to mechanical agitation for an additional 24 hours within an inert medium, this step facilitates thorough mixing, resulting in a homogeneous solution with consistent composition throughout.
[0074] Then followed by solution casting (108) of the homogeneous solution under inert medium. This casting process involves the careful spreading of the solution to form a film. The controlled environment ensures that the film retains its integrity and prevents any undesirable reactions or contaminations. The cast film undergoes a critical solidification process, marking the conclusion of the method. This solidification step is essential for transforming the film into a freestanding and flexible gel polymer electrolyte cum separator, primed for various applications requiring efficient electrolyte and separator functionalities.
TEST RESULTS:
[0075] The stress versus strain graphs of each sample is provided in Fig. 2 (I) (a-d). The calculated values of mechanical properties via stress strain plot of prepared gel polymer electrolyte films are provided in Table 1. The Maximum tensile stress decreased to 2.44 MPa with addition of LiTFSI salt. Further maximum tensile stress decreased to 2.16 on addition of ionic liquid. This is due to the plasticization effect of the ionic liquid. It is further reduced in the case of PGES to 1.52 MPa.
S. No GPE Composition Stress at 100% Elongation
(MPa) Elongation at break
(%) Tensile strength
(MPa) Thermal stability
(℃) Voltage stability
(V)
1. PVDF-HFP 11 61 13.34 430 -
2. PVDF-HFP+GBL+LiTFSI 1.57 442 2.44 288 -
3. PVDF-HFP+GBL+EMIMTFSI 0.969 607 2.16 308 3.96
4. PVDF-HFP+GBL+EMIMTFSI+LiTFSI 0.97 460 1.52 305 5.00

Table 1. Stability properties of Gel Polymer Electrolytes (GPEs)
[0076] Fig. 2 (II) illustrates thermo-gravimetric analysis of the prepared GPE in accordance with an embodiment of the present disclosure. An initial mass loss was observed in all the samples around ~50℃. This 1% mass loss may be due to loss of the traces of water or volatile elements. Another slope change region is observed in Pristine and PG samples around ~242℃ to ~275℃. The thermal degradation temperature for PVDF-HFP and PG is around ~430℃ in this case. The thermal decomposition temperature for PGE, PGS and PGES is noted to be ~308℃, 288℃ and 305℃, respectively.
[0077] Fig. 2(III) illustrates a graphical representation of an electrochemical stability window measurements of PGE and PGES in accordance with an embodiment of the present disclosure. The I-V characteristic curves so obtained [Fig. 2(III) (a & b)] has a typical feature of very slow rise in current up to a limiting applied voltage beyond this threshold limit, current rises abruptly as if the applied voltage has no control over the flow of current. This represents sample breakdown. It gives a true picture of the voltage stability of the samples under study observed in terms of the breakdown voltage. The resulting I-V characteristics give an estimate of the “optimum working voltage” limit estimated in terms of the point of intercept of the suddenly rising current on the voltage axis. Linear sweep voltammetry measurements confirmed operational voltage stability window in the limit ~ 3.96-5V.
[0078] Fig. 3. illustrates room temperature impedance spectra of PG, PGS, PGE and PGES GPE films with ionic conductivity in accordance with an embodiment of the present disclosure. It is observed that the typical Nyquist plot consists of a semicircle at higher frequency side followed by a slanted line (spike) at lower frequency. The bulk resistance (Rb) of each sample was obtained from the intercept of the semicircle on the real axis.
[0079] The semi-log plot of σdc with reciprocal of temperature for different GPE is shown in Fig. 4. Temperature-dependent conductivity analysis indicated a predominant VTF type conduction mechanism. The calculated conductivity of prepared gel polymer electrolyte films is summarised in Table 2.
S.N. Temperature →
Samples ↓ Electrical conductivity/Ionic conductivity (σdc) Scm-1
-50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 +5 +10 +15 +20
1. PVDF-HFP 2.4× 10-10 3.2 × 10-10 5.0 × 10-10 5.6 × 10-10 6.5 × 10-10 1.5 × 10-10 8.9 × 10-11 1.2 × 10-10 2.7 × 10-10 3.0 × 10-10 2.2 × 10-10 1.1 × 10-10 9.3 × 10-10 3.6 × 10-10 1.9 × 10-10
2. PVDF-HFP + GBL 1.96 × 10-9 1.9 × 10-9 9.4 × 10-9 2.8 × 10-9 2.2 × 10-9 2.1 × 10-9 1.6 × 10-9 3.4 × 10-9 2.6 × 10-10 5.9 × 10-9 3.0 × 10-9 1.1 × 10-9 5.2 × 10-9 1.3 × 10-9 3.3 × 10-9
3. PVDF-HFP + GBL + LiTFSI 8.5 × 10-8 9.2 × 10-8 2.1 × 10-7 5.0 × 10-7 1.1 × 10-6 2.1 × 10-6 3.8 × 10-6 7.2 × 10-6 1.3 × 10-5 1.9 × 10-5 3.0 × 10-5 4.4 × 10-5 6.1 × 10-5 8.3 × 10-5 1.1 × 10-4
4. PVDF-HFP + GBL + EMIMTFSI 6.1 × 10-6 2.7 × 10-6 5.4 × 10-6 1.7 × 10-5 5.1 × 10-5 9.2 × 10-5 1.6 × 10-4 2.2 × 10-4 3.0 × 10-4 4.1 × 10-4 5.2 × 10-4 6.6 × 10-4 8.3 × 10-4 1.0 × 10-3 1.2 × 10-3
5. PVDF-HFP + GBL + EMIMTFSI+ LiTFSI 2.9 × 10-7 6.8 × 10-7 2.9 × 10-7 3.8 × 10-7 7.6 × 10-6 1.3 × 10-5 2.3 × 10-5 3.6 × 10-5 3.6 × 10-5 8.9 × 10-5 1.2 × 10-4 1.7 × 10-4 2.2 × 10-4 2.2 × 10-4 9.2 × 10-4

Table 2. Gel Polymer Electrolytes (GPEs) Sample Examples: Ambient and Sub-ambient conductivities.
[0080] Fig. 5 shows an ionic transport number measurement of PGS and PGES in accordance with an embodiment of the present disclosure. A high total ionic transport number ~99.5% was observed in the prepared GPE films.
[0081] Fig. 6 (I) illustrates X-ray diffraction pattern of the prepared gel polymer electrolyte films in accordance with an embodiment of the present disclosure. It can be observed from the XRD pattern of pristine PVDF-HFP that it is semi-crystalline in nature with major peak positions at 2θ = ~18.2°, ~20°, ~26.6°, ~39°. The first two peaks 18.2° and 20° are superimposed over a broad halo from 14° - 25°. The peak around ~ 18.2° corresponds to [(100) + (020)] reflection, peak around ~ 20° corresponds to (110) reflection, peak around ~ 26.6° corresponds to (021) reflection and peak around ~ 39° corresponds to (002/211) reflection. Peak profile is observed to change considerably indicated by change in the intensity, peak shape and position with addition of GBL and EMIMTFSI.
[0082] The SEM micrographs of the prepared GPE films are shown in Fig 6(II) (a-d). The pure PVDF-HFP micrographs shows large crystalline grains with lamellar structure. On addition of LiTFSI salt, it is observed that some white crystallites were observed and it may due to the undissolved LITFSI salt present in the polymer. Some pores were also present in the micrograph Fig. 6(II) (b). When we add the ionic liquid EMIMTFSI the polymer membrane became more flexible. The number of pores and pore size has got increased after the addition of IL.
[0083] Fig. 7(a) illustrates vibrational FTIR spectra of the prepared gel polymer electrolyte films in accordance with an embodiment of the present disclosure. The peak profile confirmed strong interaction between precursor components and phase purity of the GPE sheet. Raman spectrum illustrated in Fig. 7(b) for prepared gel polymer electrolyte films in accordance with an embodiment of the present disclosure shows predominant peak around 743-737 cm-1 observed in PGS, PGE and PGES. This may be assigned to overlapping of symmetric bending mode of CF3 and combination of S-N stretching of LiTFSI. Another peak around 794 cm-1 and 808 cm-1 is observed in the case of PVDF-HFP and PG. Peak around 835 and 834 cm-1 observed in the pristine PVDF-HFP and PG. Broad halo is observed in the case of PGS, PGE and PGES. This can be assigned to mixed mode of CH2 rocking. Combined CF2 and CC symmetric stretching vibrations observed at 879 cm-1 in all the composition except PGE. Peak around 1024 cm-1 is observed in the PGE and PGES compositions corresponding to the stretching vibrations of the sulfonyl groups (SO2) in the TFSI anion. Bending modes of the CF3 groups in the TFSI anion observed around 1133-1137 cm-1 for PGS, PGE and PGES compositions. Another peak around 1236 cm-1 is observed in PGS, PGE and PGES composition and assigned to C-F stretching.
[0084] Fig. 8 Illustrates a graphical representation of cyclic voltammetry curve of Li ǁ PGES ǁ NMC in accordance with an embodiment of the present disclosure. The presence of redox peak confirmed presence of DE lithiation and lithiation in the prepared PGES.
[0085] Fig 9 illustrates a graphical representation depicting a Li-Po cell performance results with charge discharge and room temperature electrochemical impedance spectrum (EIS) in accordance with an embodiment of the present disclosure.
Electrochemical response of Example 1 with NMC (Li ‖ PGS ‖ NMC)
[0086] For a half cell testing, PGS was employed as an electrolyte cum separator. The cell was constructed with Li ‖ PGS ‖ NMC as coin cells with NMC cathode and lithium counterpart while maintain the area of the NMC cathode and lithium anode. The charge discharge measurements were carried out at C/10 current rate and results are summarized in Table 3. The first discharge capacity of the Li ‖ PGS ‖ NMC cell at room temperature was found to be 70 mAhg-1. As the cell is run up to 5th cycles, the discharge capacity moves down to 65 mAhg-1. In general, cell comprising liquid electrolyte and separator show the high capacity with respect to NMC cathode in half cell configurations. In our preferred solid electrolyte cum separator we obtained such type of charge discharge behavior. The low value of solid electrode electrolyte interface resistance (Rs = 323 Ω) and charge transfer resistance (Rct = 795 Ω) obtained in electrochemical impedance spectroscopy results. After 5th charge discharge cycles, there is change in (Rs = 659 Ω) and (Rct = 1938 Ω) show the good stability of the fabricated cell.

Electrochemical response of Example 2 with NMC (Li ‖ PGE ‖ NMC)
[0087] In the present embodiment, when the prepared PGE film are employed as an electrolyte cum separator, the cathode may be NMC. The cell was constructed with Li ‖ PGE ‖ NMC as coin cells with NMC cathode and lithium counterpart. The lithium cell according to the present invention has been measured using charge discharge measurement and results are incorporated in the Table 3. The Li ‖ PGE ‖ NMC cell has showed first reversible capacity of 82 mAhg-1 and after 5th cycle it was found to be 70 mAhg-1. Small change in EIS results of the assembled cell Li ‖ PGE ‖ NMC are found as shown in table 3. The overall cycling stability of the Li ‖ PGE ‖ NMC cell after 5th cycles show relatively satisfactory results.
Example Coin cell configuration Cell performance
Voltage range (V) Initial
Voltage (V) Discharge Capacity mAh/g @ C/10 rate EIS before cycle test EIS after 5 cycles
R (Ω) RCT(Ω) R (Ω) RCT(Ω)
1 Li // PGS // NMC 3.0 - 4.2 3.35 70 323 795 659 1938
2 Li // PGE // NMC 3.0 - 4.2 2.8 82 10 390 35 1315
3 Li // PGES // NMC 3.0 - 4.2 3.34 126 23 326 34 395
4 Li //PGES// MCMB 0.01 – 2.0 2.61 200 65 263 130 207

Table 3. Electrochemical performance of Gel Polymer Electrolytes in coin cell configurations
Electrochemical response of Example 3 with NMC (Li ‖ PGES ‖ NMC)
[0088] In the present embodiment, the prepared PGES film is employed as an electrolyte cum separator, the cathode may be NMC and Lithium as counterpart. The cell characteristic according to the present invention has been measured using charge discharge measurement at room temperature at constant C/10 current rate. Fig. 9 (a) shows a graphical representation of capacity vs. voltage plot. Referring to Fig. 9 (a), voltage plateau behavior can be seen in case of PGES polymer electrolyte cum separator device of Li ‖ PGES ‖ NMC, similar to reported half-cell behavior of NMC cathode with liquid electrolyte. The discharge capacity for Li ‖ PGES ‖ NMC cell is found to be 126 mAh g−1 with 90.48% columbic efficiency. The improvement of the capacity in comparison to other fabricated cells with PGS and PGE can be ascribed to the improved electrical conductivity at ambient and sub ambient conditions with good electrochemical activity and low potential polarization as shown in Fig. 8. Obviously, the Li ‖ PGES ‖ NMC cell presents superior cycle stability at C/10 rate. Referring to Fig. 9 (b), EIS results having nominal change in the value of Rs and Rct before and after 5 charge discharge cycles also confirm the utility of PGES for the application point of view in ambient and sub ambient conditions for lithium ion cells.
Electrochemical response of Example 4 with MCMB (Li ‖ PGES ‖ MCMB)
[0089] The electrochemical characteristic of PGES polymer electrolyte cum separator according to the present invention has been measured with respect to MCMB anode material using charge discharge measurement at room temperature. Fig. 9 (c) represents a graphical representation of capacity vs. voltage plot. Fig. 9 (c) shows the three charge/discharge profiles at C/10 rate in the potential range of 0.01−1.0 V. The symmetrical charge discharge profile indiactes the reversible electrochemical features with easy diffusion of Li+ ion in PGES material with low polarization. The Li ‖ PGES ‖ MCMB cell exhibits the discharge capacity of 200 mAh g−1 with smooth charge–discharge features. However, an increase in capacity after 3rd cycle is observed for the MCMB anode with PGES polymer electrolyte cum separator indicated good electrochemical response for anode material. Moreover, EIS results (Fig. 9 d) of the Li ‖ PGES ‖ MCMB, Lithium ion cell described herein have achieved low value of Rs and Rct. As a result of the improvements in the lithium cell performance, the particular interest of herein, anode show remarkable electrochemical performance of prepared example PGES polymer electrolyte cum separator for assembly of lithium cells utilizing the ambient and sub ambient features of prepared polymer in electrolyte cum separator for commercial applications.
ADVANTAGES OF THE INVENTION

[0090] The critical advantages that are impacted from the novel composition and method of preparation of Gel Polymer Electrolyte (GPE) cum separator are briefly outlined below:
• Mechanical Resilience: The resulting GPE film exhibits remarkable mechanical stability and dimensional flexibility, enhancing its versatility for diverse applications.
• Enhanced Strain Tolerance: A substantial 10-15 times improvement in strain-bearing capacity over pure PVDF-HFP showcases improved mechanical performance.
• Uncommon Elasticity: The stress-strain diagram reveals a rare metal-like elastic behavior in the GPE film, distinct within the realm of polymer electrolytes.
• High Thermal Stability: Thermal analysis demonstrates stability up to temperatures ≥ 300℃, making it suitable for elevated-temperature applications.
• Wide Voltage Window: The GPE demonstrates a stable electrochemical potential window of approximately 5V, ideal for applications requiring consistent voltage operation.
• Superior Electrical Conductivity: The GPE exhibits electrical conductivity akin to liquid transport properties while maintaining exceptional stability across various domains.
[0091] The above description does not provide specific details of the manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
[0092] Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other apparatus or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present subject matter as encompassed by the following claims.
[0093] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0094] It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different apparatus or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
, Claims:We Claim
1. A method (100) for preparing a gel polymer electrolyte cum separator, the method (100) comprising:
dissolving (102), a pre-determined quantity of a semi- crystalline polymer in acetone by performing a mechanical agitation for pre-determined duration in an inert medium (argon/mixture gases) to form a low viscous solution;
dissolving (104), a mixture of a lithium salt and an ionic liquid in an aprotic polar solvent by performing the mechanical agitation for pre-determined duration (24h) in an inert medium to form a high viscous solution;
adding (106), a pre-determined quantity of a semi- crystalline polymer solution in the mixture of the lithium salt and ionic liquid solution, wherein the semi- crystalline polymer solution and the mixture of the lithium salt and ionic liquid solution is mixed homogeneously in an inert medium to form a homogeneous solution; and
casting (108), the homogeneous solution to form a film under inert medium, wherein the film is solidified to form a freestanding and flexible gel polymer electrolyte cum separator.
2. The method (100) as claimed in the claim 1, wherein the lithium salt is at least one salt selected from a group consisting of Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).
3. The method (100) as claimed in the claim 1, wherein the aprotic polar solvent is at least one solvent selected from a group consisting of gamma-Butyrolactone (GBL).
4. The method (100) as claimed in the claim 1, wherein the ionic liquid is at least one liquid selected from a group consisting of 1-Ethyl-3-methylimidazolium bis (trifluoromethanesulfonyl)imide (EMIMTFSI).
5. The method (100) as claimed in the claim 1, wherein the semi-crystalline polar polymer is at least one polymer selected from a group consisting of Poly (vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)).
6. The method (100) as claimed in the claim 1, wherein the common solvent is at least one solvent selected from a group consisting of acetone.
7. The method (100) as claimed in the claim 1, wherein the gel polymer electrolyte cum separator comprises of the polymer PVDF-HFP, Li salt LiTFSI, GBL and ionic liquid EMIMTFSI.
8. The method (100) as claimed in the claim 1, wherein the room temperature conductivity is in the order of ~10^-3 S cm^-1.
9. The method (100) as claimed in the claim 1, wherein the aprotic polar solvent dissolve and dissociate the electrolyte salt.
10. The method (100) as claimed in the claim 1, wherein the ionic liquid (EMIMTFSI) stabilizes lithium anode against an Li dendrite growth.
11. The method (100) as claimed in the claim 1, wherein the gel polymer electrolyte cum separator exhibits a thermal stability up to a temperature of ~300°C.
12. The method (100) as claimed in the claim 1, wherein the gel polymer electrolyte cum separator exhibits an electrochemical potential window of approximately 5V.
13. The method (100) as claimed in the claim 1, wherein the gel polymer electrolyte cum separator is used in lithium-ion batteries for consumer electronics, electric vehicles, and renewable energy storage systems.