Electrolyte for energy storage composites

Abstract

The present invention provides a novel, preferably fire-resistant, polymer electrolyte that has high ionic conductivity and is mechanically strong by providing a co-continuous nanocomposite consisting of a polymeric matrix having a porous network, the porous network having polymeric particles disposed therein, and wherein the polymeric particles are at least partially coated with an ionic liquid and a lithium salt. Also disclosed are methods of preparing a polymeric electrolyte, an energy storage composite comprising the polymeric electrolyte, and a battery comprising the polymer electrolyte. Preferred polymers are phenolic resins (or phenoplasts), and a preferred ionic liquid is EMIM TFSI, and a preferred lithium salt is LiTFSI.

Description

ELECTROLYTE FOR ENERGY STORAGE COMPOSITES

[0001] This application claims priority from Australian Provisional Patent Application No.2025900290 filed 4 February 2025, the content of which is incorporated herein by reference in its entirety.FIELD OF THE INVENTION

[0002] The present invention relates to the field of electrolytes for energy storage composites. In particular, preferred embodiments of the present invention relates to electrolytes that are flame-retardant. In other preferred embodiments, the electrolytes of the invention are also structural, in that they provide mechanical load-bearing capacity. However, it will be appreciated that the invention is not limited to this particular field of use.BACKGROUND OF THE INVENTION

[0003] The following discussion of the prior art is provided to place the invention in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0004] Structural energy storage composites have attracted much attention over recent years as they are able to provide a light-weight design of composite structures. Such energystorage composite structures hold enormous potential in multiple fields, such as automobiles and aircraft, to achieve lighter and a better energy efficient product design. However, the current state of structural supercapacitors and batteries integrated within these composites suffers from significantly lower energy density and power density compared to standalone energy storage devices. This deficiency stems from the absence of high-performance electrodes and electrolytes essential for developing integrated structural energy storage composites. Additionally, conventional liquid electrolytes provide high ionic conductivity but lack mechanical strength and flame retardancy.

[0005] As an important element of structural energy storage composites, solid polymer electrolytes should simultaneously possess good mechanical strength and excellent ionic conductivity. Achieving this dual functionality presents a significant challenge in advancing structural energy storage composites with high power density. Current methodologies typically involve mixing ionically conductive additives, such as lithium salts and ionic liquids, withpolymers to impart ionic conductivity while retaining mechanical load-carrying capability. However, optimizing the trade-off between ionic conductivity and mechanical properties remains a critical issue in achieving the desired performance. The traditional polymer matrix materials used in carbon fibre-reinforced polymers (CFRPs), such as epoxy, inherently lack conductivity. For instance, a polymer structural electrolyte formulated with 40 wt.% ionic liquid and 60 wt.% epoxy resin can only achieve an ionic conductivity of 0.116 mS / cm, which is merely 2.1% of the ionic conductivity measured for ionic liquid (5.5 mS / cm). This value falls far below the expected conductivity estimated by the rule of mixture. Such limitations may arise due to complex tortuous paths and the boundary layer effect within small ionic channels, hindering efficient ion transport.

[0006] Additionally, commonly used polymer matrices in composites are highly flammable and emit toxic fumes during combustion, posing substantial fire hazards during the operation of structural energy storage composites. Moreover, with the wide application of composite materials in extreme work conditions, the demand for structural energy storage composites capable of withstanding high temperatures has surged alongside their widespread application in extreme work conditions. Potential scenarios include planetary surface activities (e.g., Venus’ surface temperature reaching 480°C) and the powering of electronics in aerospace vehicles close to the engine, etc. However, exposure to high temperatures can degrade the polymer electrolyte, leading to substantial performance losses in the energy storage device. Thus, developing flame-retardant and thermally stable electrolytes for structural energy storage composites is critically important for industries such as oil and gas, military, aerospace, automotive, and electric vehicles. Additionally, in the event of overheating or short-circuiting, thermal runaway can occur, resulting in fire.

[0007] It is an object of the present invention to overcome or ameliorate one or more the disadvantages of the prior art, or at least to provide a useful alternative.

[0008] It is an object of at least one preferred embodiment of the present invention to provide a flame-retardant or thermally stable electrolyte for structural energy storage composites, for industries such as oil and gas, military, aerospace, automotive, and electric vehicles. It is an object of further preferred embodiments of the present invention to provide an electrolyte that provides a high ionic conductivity, preferably in the same or similar order of magnitude as that of the ionic liquid itself. In some preferred embodiments of the present invention the electrolyte conductivity is greater than 2.0, 2.5 or 2.80 mS / cm. It is an object of further preferred embodiments of the present invention to provide an electrolyte that provides mechanical properties comprising tensile strengths of around 20 MPa, and a tensile modulus of over 1.0 GPa.SUMMARY OF THE INVENTION

[0009] The present invention provides a flame-retardant electrolyte formed from a flameretardant polymer, and which is tailored for structural energy storage composites. By incorporating a flame-retardant polymer with ionic liquid and a salt, which is preferably a lithium salt, the resulting polymer electrolyte can achieve a high ionic conductivity of more than 2 mS / cm, and even greater than 2.80 mS / cm, which is of the same order of magnitude as that of the ionic liquid itself. By adjusting the content of each component, it has been surprisingly found that it is possible to develop an electrolyte with balanced electrochemical and mechanical performance. This approach differs from the conventional method of simply mixing an epoxy polymer and ionic liquid to develop a bicontinuous electrolyte, where the ionic liquid and epoxy have limited interaction with each other. The presence of ionic liquid and lithium salt forms unique microstructures with excellent ionic conductivity. This unique combination of phenolic resin, ionic liquid, and lithium salt addresses the challenges of ionic conductivity, mechanical performance, and fire resistance inherent in conventional methods, making the electrolyte of the invention well-suited for structural energy storage composites across various applications, including aerospace, automotive, civil engineering, and wearable electronics.

[0010] In a preferred embodiment of the invention, a novel fire-resistant polymer electrolyte is provided that has high ionic conductivity and is mechanically strong by providing a co-continuous nanocomposite consisting of phenolic resin (or phenoplast), ionic liquid (EMIM TFSI), and lithium salt (LiTFSI). It will be appreciated that, in other embodiments discussed further below, alternative flame-retardant polymers, lithium salts and ionic liquids may be used. Without wishing to be bound by any theory, the present inventors believe that the ionic liquid and lithium salt work synergistically, and may effectively as a hybrid surfactant to facilitate the emulsion polymerization of the phenolic resin, thereby forming unique microstructures where, it is believed (and without wishing to be bound by theory), that the Li+ions complex with hydroxyl groups in the phenoplasts to create ion-conductive pathways in the solid phase, contributing to the enhanced ionic conductivity of the electrolyte. This design yields significantly enhanced ionic conductivities up to 2.87 mS / cm, which is comparable to those of liquid ionic liquids themselves. For structural electrolyte applications, certain formulations achieved an ionic conductivity of approximately 0.15 mS / cm, a tensile strength around 19 MPa, and a tensile modulus of about 1.2 GPa. These properties demonstrate a well-balanced performance between electrochemical and mechanical characteristics, making the electrolytes suitable for advanced structural energy storage applications. The resulting phenoplasts-based electrolyte not only maintains mechanical strength and structural integrity but also achieves the highest flame retardancy rating of V-0. A composite structural supercapacitor fabricated using thiselectrolyte demonstrated excellent electrochemical performance and safety features. This development presents a significant advancement in creating safe, efficient, and multifunctional materials for advanced structural energy storage applications.

[0011] According to a first aspect, the present invention provides a polymeric electrolyte comprising a polymeric matrix having a porous network, the porous network having polymeric particles disposed therein, and wherein the polymeric particles are at least partially coated with an ionic liquid and a lithium salt.

[0012] In preferred embodiments, the polymeric matrix of the polymeric electrolyte is flameretardant and may be selected from a flame-retardant polymer, or a combination of polymers where overall the polymer mixture is flame-retardant, or where the polymer is made to be flameretardant by use of flame-retardant additives.

[0013] Without wishing to be bound by theory, it is believed that the novel morphology disclosed herein (i.e., polymeric particles disposed within a porous network and being at least partially coated with an ionic liquid and a lithium salt) provides a continuous ionically conductive phase provided by the ionic liquid, and advantageously also increases the contact area between the ionic liquid phase and the matrix of the polymeric electrolyte, thus enabling a higher degree of complexation between Li+ and -OH in the electrolyte (Li+ is from the Li salt that dissolved in the ionic liquid). The enhanced ionic conductivity found with the novel polymeric electrolytes of the invention is not merely due to the higher concentration of ionic liquid, as it is believed that the content of the Li salt is also a contributing factor. To explain, a high Li salt content cannot be introduced to, say, an epoxy-based electrolyte because the Li salt can react quickly with the epoxy hardener, releasing a significant quantity of heat, thereby causing the electrolyte to cure rapidly. In contrast, the Li salt does not undergo such a reaction with a phenolic resin or its catalyst. It will be appreciated by the skilled person that there will be other resins / polymers which act similarly to a phenolic resin in this regard.

[0014] Referring to the first aspect, a preferred salt is a lithium salt. However, it will be appreciated by the skilled person that any of the alkali (group 1) metals may be used instead of, or in addition to lithium. The alkali metals consist of the elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). In other embodiments, one or more of the following elements may be used instead of, or in addition to lithium, namely: zinc, magnesium, calcium, and aluminum ions. Purely for convenience, one or more of the aspects of the invention disclosed herein refer to the use of a lithium salt, but it will be appreciated thatthe term "lithium" may be replaced with any of the metals mentioned above, or combinations of metals.

[0015] According to a second aspect, the present invention provides a method of preparing a polymeric electrolyte, the method comprising:providing a first mixture of a polymer, an ionic liquid and a lithium salt; adding a catalyst to the first mixture to obtain a second mixture; and curing the second mixture to obtain the polymeric electrolyte.

[0016] According to a third aspect, the present invention provides a polymeric electrolyte obtained by the method according to the second aspect.

[0017] According to a fourth aspect, the present invention provides an energy storage composite comprising the polymeric electrolyte according to the first or third aspects.

[0018] According to a fifth aspect, the present invention provides a method of producing a polymeric electrolyte for an energy storage composite, the method comprising:providing a first mixture of a polymer, an ionic liquid and a lithium salt; adding a catalyst to the first mixture to obtain a second mixture;infusing the second mixture into an electrode; andcuring the infused electrode.

[0019] According to a sixth aspect, the present invention provides a polymer electrolyte battery comprising:an anode,a cathode;a separator; andthe polymeric electrolyte according to the first or third aspects.

[0020] The polymeric electrolyte of the invention comprises a porous network formed preferably from a flame-retardant polymer. Disposed within the porous network are particlesformed from the flame-retardant polymer, and whereby at least some of the polymeric particles are at least partially coated with an ionic liquid. Preferably the surface of the porous network is also coated with ionic liquid. The presence of polymeric particles within the porous network is a distinction from prior art epoxy systems and appears to be, at least in part, responsible for providing the significant improvements provided by the electrolyte of the present invention.

[0021] The present invention advantageously provides an adjustable electrolyte structure, whereby the electrolyte can be engineered to vary from a composition fully comprising phenolic particles coated with an ionic liquid / lithium salt mixture, to a combination of phenolic blocks and phenolic micro-particles. By controlling the content of each component, the electrolyte can be optimized for different performance goals, i.e. , focusing more on energy storage capability or on mechanical load-bearing capacity, as needed. Specifically, increasing the overall concentration of flame-retardant polymer will tend to increase the mechanical properties and reduce the overall conductivity, and decreasing the overall concentration of flame-retardant polymer will tend to decrease the mechanical properties and increase the overall conductivity. The overall conductivity can be tuned according to requirements depending on the overall content of IL and Li salt which is used in the electrolyte.

[0022] It is believed that prior art electrolytes tend to provide the ionic conductive phase on the surface of the polymer matrix. In contrast, the method of the invention provides the ionic conductive materials to integrate within the polymer matrix, offering a significant distinction in functionality. In particular, the method of the invention provides some ionically conductive phases (ionic liquid or Li salt) embedded within the phenolic microparticles, as these elements can still be detected after washing the surface of the phenolic microparticles (see Fig.3g and relevant discussion below).

[0023] Advantageously, the electrolyte of the invention can be used to fabricate structural energy storage composites and is compatible with all composite manufacturing methods, including hand lay-up, vacuum-assisted resin infusion methods, etc.

[0024] As disclosed herein, the inventors have found that by adjusting the content of the ionic liquid, Li salt, and phenolic resin, it is possible form an electrolyte having microparticles, as shown in Fig. 3e. This electrolyte exhibits very high ionic conductivity compared to the prior art.

[0025] Polymers suitable as the polymeric matrix of the polymeric electrolyte

[0026] Suitable polymers that form the matrix of the polymeric electrolyte are preferably flame-retardant polymers, and may be selected from the group consisting of a phenolic,melamine-formaldehyde, polyimides, bismaleimides, phthalonitriles, benzoxazines, cyanate esters and combinations thereof. Preferably the flame-retardant polymer is a phenolic resin.

[0027] The polymer may alternatively be selected from the group consisting of polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyimide (PI), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoridehexafluoropropylene (PVDF-HFP), styrene-butadiene rubber (SBR), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylenetetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, or any combination thereof.

[0028] In some preferred embodiments, the content of the flame-retardant polymer in the solid electrolyte is 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, or 80 wt%, or is 40 to 42, 42 to 44, 44 to 46, 46 to 48, 48 to 50, 50 to 52, 52 to 54, 54 to 56, 56 to 58, 58 to 60, 60 to 62, 62 to 64, 64 to 66, 66 to 68, 68 to 70, 70 to 72, 72 to 74, 74 to 76, 76 to 78, to 78 to 80 wt%.

[0029] In preferred embodiments the polymer is selected to have excellent flame-retardant properties, including a self-extinguishing behaviour and resistance to high temperatures.

[0030] Preferred embodiments of the present invention utilise thermoset polymers.

[0031] The polymer may also include a flame-retardant additive, which may be selected from one or more of 2-ethoxy-2, 4, 4, 6, 6-pentafluorotriphosphazene (HIE), (trimethylsilyl) phosphite (TMSPi), and tris(trimethylsilyl) borate (TMSB), trimethyl phosphate (TMP) and triphenyl phosphate (TPP). Other flame retardant additives will be known to the skilled person.

[0032] Ionic liquids (IL)

[0033] An ionic liquid is a salt in the liquid state at ambient conditions, and are largely made of ions. These substances are variously referred to in the literature as liquid electrolytes, ionic melts, ionic fluids, fused salts, liquid salts, or ionic glasses. Examples include compounds based on the 1-ethyl-3-methylimidazolium (EMIM) cation and include: EM IM: Cl, EMIMAc (acetate anion), EMIM dicyanamide, and 1-butyl-3,5-dimethylpyridinium bromide.

[0034] Room-temperature ionic liquids (RTILs) are dominated by salts derived from 1-methylimidazole, i.e., 1-alkyl-3-methylimidazolium. Examples include 1-ethyl-3-methyl- (EMIM), 1-butyl-3-methyl- (BMIM), 1-octyl-3 methyl (OMIM), 1-decyl-3-methyl-(DMIM), 1-dodecyl-3-methyl- (dodecylMIM). Other imidazolium cations are 1-butyl-2,3-dimethylimidazolium (BMMIM or DBMIM) and 1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium (DAMI). Other N-heterocyclic cations are derived from pyridine: 4-methyl-N-butyl-pyridinium (MBPy) and N-octylpyridinium (C8Py). Conventional quaternary ammonium cations also form ILs, e.g. tetraethylammonium (TEA) and tetrabutylammonium (TBA). Typical anions in ionic liquids include the following: tetrafluoroborate (BF4), hexafluorophosphate (PFe), bis-trifluoromethanesulfonimide (NTf2), trifluoromethanesulfonate (OTf), dicyanamide (N(CN)2), hydrogensulfate (HSO-4), and ethyl sulfate (EtOSOs). Magnetic ionic liquids can be synthesized by incorporating paramagnetic anions, illustrated by 1-butyl-3-methylimidazolium tetrachloroferrate.

[0035] In some embodiments, the ionic liquid is selected from one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI), 1-ethyl-3-methylimidazolium bis(methanesulfonyl)imide (EMIFSI), tributylmethylammonium bis(trifluoromethanesulfonyl)imide (TBMA-TFSI) and 1 -ethyl- 1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide (Py^TFSI).

[0036] In some embodiments, the ionic liquid is selected from one or more of 1 -vinyl-3-butyl imidazole bis(trifluoromethanesulfonyl) imide, 1-vinyl-3-butyl imidazole hexafluorophosphate, 1-vinyl-3-butyl imidazole tetrafluoroborate, 1 -vinyl-3-butyl imidazole bromide, 1-vinyl-3-ethyl imidazole bis (trifluoromethanesulfonyl) imide, 1 -vinyl-3-ethyl imidazole hexafluorophosphate, 1 -vinyl-3-ethyl imidazole tetrafluoroborate, 1-vinyl-3-ethyl imidazole bromide, 1-vinyl-3-methyl imidazole bis (trifluoromethanesulfonyl) imide, 1-vinyl-3-methyl imidazole iodide, 1-allyl-3-butyl imidazole bis (trifluoromethanesulfonyl) imide, 1 -allyl-3-butyl imidazole hexafluorophosphate, 1-allyl-3-butyl imidazole tetrafluoroborate, 1-allyl-3-butyl imidazole imidazolium bromide, 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-allyl-3-ethylimidazolium hexafluorophosphate, 1-allyl-3-ethylimidazolium tetrafluoroborate, 1-allyl-3-ethylimidazolium bromide, 1-allyl-3-ethylimidazolium chloride, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-allyl-3-methylimidazolium hexafluorophosphate, 1 -allyl-3-methylimidazolium tetrafluoroborate, 1-allyl-3-methylimidazolium bromide, 1-allyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, 1-methyl-3-propylimidazolium bromide, 1-allyl-3-vinylimidazolium bromide, 1-allyl-3-vinylimidazolium chloride, 1-allyl-3-vinylimidazolium tetrafluoroborate or a combination of two or more thereof.

[0037] In some embodiments, the ionic liquid is a sulfonic acid functionalized ionic liquid selected from N-butylpyridinium sulfonate, N-butylpyridinium sulfonate trifluoromethanesulfonate, N-butylpyridinium sulfonate hydrogen sulfate, butylpyridinium sulfonate lactone, N-propylpyridinium sulfonate, N-propylpyridinium sulfonate trifluoromethanesulfonate, N-propylpyridinium sulfonate hydrogen sulfate, propylpyridinium sulfonate lactone, 1-butylsulfonic acid-3-methylimidazole trifluoroacetate, 1-butylsulfonic acid-3-methylimidazole trifluoromethanesulfonate, 1-butylsulfonic acid-3-methylimidazole sulfate The invention can be selected from the group consisting of 1-butyl sulfonic acid-3-methylimidazolium hydrogen salt, 1-butyl sulfonic acid-3-methylimidazolium dihydrogen phosphate, 1-butyl sulfonic acid-3-methylimidazolium chloride, 1-sulfonic acid butyl-3-methylimidazolium inner salt, 1-propyl sulfonic acid-3-methylimidazolium trifluoroacetate, 1-propyl sulfonic acid-3-methylimidazolium trifluoromethanesulfonate, 1-propyl sulfonic acid-3-methylimidazolium hydrogen sulfate, 1-propyl sulfonic acid-3-methylimidazolium dihydrogen phosphate, 1-propyl sulfonic acid-3-methylimidazolium chloride, and 1-propyl sulfonic acid-3-methylimidazolium inner salt, or a combination of two or more thereof.

[0038] One preferred ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI).

[0039] In some embodiments, the mass content of the IL in the solid electrolyte is between 25 to 60 wt%. In particular the mass content of the IL in the solid electrolyte is 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, or 60 wt%, or is between 25 to 26, 26 to 27, 27 to 28, 28 to 29, 29 to 30, 30 to 31, 31 to 32, 32 to 33, 33 to 34, 34 to 35, 35 to 36, 36 to 37, 37 to 38, 38 to 39, 39 to 40, 40 to 41 , 41 to 42, 42 to 43, 43 to 44, 44 to 45, 45 to 46, 46 to 47, 47 to 48, 48 to 49, 49 to 50, 50 to 51, 51 to 52, 52 to 53, 53 to 54, 54 to 55, 55 to 56, 56 to 57, 57 to 58, 58 to 59, or 59 to 60 wt%. Preferably the mass content of the IL in the solid electrolyte is 40 wt%.

[0040] In some embodiments, the mass ratio between the flame-retardant polymer and IL is 3:2, or is 3: 1.333, or is anything in between such as 3: 1.3, 3: 1.35, 3: 1.4, 3: 1.45, 3: 1.5, 3: 1.55, 3: 1.6, 3: 1.65, 3:1.7, 3:1.75, 3:1.8, 3:1.85, 3:1.9, or 3: 1.95. Other ratios are contemplated herein including 3:1, 3:1.05, 3:1.1, 3:1.15, 3:1.2, and 3:1.25. Other ratios are contemplated herein including 3:2.05, 3:2.1, 3:2.15, 3:2.2, 3:2.25, 3:2.3, 3:2.35, 3:2.4, 3:2.45, 3:2.5, 3:2.55, 3:2.6, 3:2.65, 3:2.7, 3:2.75, 3:2.8, 3:2.85, 3:2.9 and 3:2.95.

[0041] To avoid the formation of a layered structure in the solid electrolyte, the mass ratio between the flame-retardant polymer and IL is preferably 3:2.

[0042] Lithium salts

[0043] Any lithium salt typically used in an electrolyte for a lithium battery electrolyte may be used as the lithium salt without limitation, and, specifically, the lithium salt may include Li+ as a cation, and may include at least one selected from the group consisting of BF4-, PFe-, CIO4“, bis(fluorosulfonyl) imide (N(SO2F)2-; FSI), (bis)trifluoromethanesulfonimide (N(SO2CF3)2“, TFSI), bisperfluoroethanesulfonimide (N(SO2C2p5)2-, BETI), and oxalyldifluoroborate (BF2(C2O4)-, ODFB) as an anion. Specifically, the lithium salt may include at least one selected from the group consisting of LiBF4, LiPFe, LiCICU, LiN(SC>2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiBF(C2O4).

[0044] In other embodiments, suitable lithium salts may be selected from the group consisting of: bis(trifluoromethanesulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, bis(nonafluorobutylsulfonyl)imide lithium (fluorosulfonyl)imide, (trifluoromethanesulfonyl)imide lithium, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium trifluoromethanesulfonate, and 4,5-dicyano-2-trifluoromethylimidazole lithium, or a combination of two or more thereof.

[0045] One preferred lithium salt is lithium bis(trifluoromethane)sulfonimide (LiTFSI).

[0046] In some preferred embodiments, the lithium salt is first dissolved in the IL before mixing with the flame-retardant polymer, thereby providing a substantially homogeneous distribution of the lithium salt throughout the electrolyte, and for enhancing the ionic pathways and improving overall conductivity. Preferably the lithium salt is dissolved into the ionic liquid with the assistance of an ultrasonic water bath prior to mixing with the flame-retardant polymer.

[0047] In some preferred embodiments, the lithium salt I IL weight ratio is selected from 0.1 to 0.5, such as 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5, or between 0.1 to 0.15, 0.15 to 0.2, 0.2 to 0.25, 0.25 to 0.3, 0.3 to 0.35, 0.35 to 0.4, 0.4 to 0.45, or 0.45 to 0.5. Preferably higher ratios are selected which provides approved ionic conductivity.

[0048] In some preferred embodiments, the lithium salt is dissolved in the ionic liquid with a weight ratio ranging from 1:0.5 to 1:30.

[0049] In some preferred embodiments, the ratio of polymer to (IL + Li salt) is 3:2, while the IL: Li salt weight ratio ranges from 10:1 to 2:1. In some preferred embodiments the IL: Li salt weight ratio 20:1, 19.5:1, 19:1, 18.5:1, 18:1, 17.5:1, 17:1, 16.5:1, 16:1, 15.5:1, 15:1, 14.5:1, 14:1,13.5:1, 13:1, 12.5:1, 12:1, 11.5:1, 11:1, 10.5:1, 10:1, 9.5:1, 9:1, 8.5:1, 8:1, 7.5:1, 7:1, 6.5:1, 6:1, 5.5:1, 5:1, 4.5:1, 4:1, 3.5:1, 3:1, 2.5:1, 2:1, 1.5:1, 1:1 or 0.5:1.

[0050] Catalysts

[0051] To accelerate the curing of the polymer electrolyte, a catalyst is added preferably with a weight ratio of 6:100 based on the weight of polymer in the mixture.

[0052] The electrolyte composition of the present invention may include a conventional polymerization initiator / catalyst capable of generating radicals by heat and light. An azo-based polymerization initiator or a peroxide-based polymerization initiator may be used as the above polymerization initiator, and representative examples of the polymerization initiator may be at least one peroxide-based compound selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide, or at least one azo-based compound selected from the group consisting of 2,2'-azobis (2-cyanobutane), dimethyl 2,2'-azobis(2-methylpropionate), 2,2'-azo bis(methy Ibutyronitrile), 2,2'-azo bis(iso-butyronitrile) (AIBN), and 2,2'-azobisdimethyl-valeronitrile (AMVN).

[0053] The polymerization initiator may form a radical by being decomposed by heat in the battery, for a non-limiting example, at a temperature of 30° C. to 100° C., for example, 60° C. to 80° C., or by being decomposed at room temperature (5° C. to 30° C.)

[0054] The polymerization initiator may be included in an amount of about 10 parts by weight or less, particularly 0.01 part by weight to 10 parts by weight, and more particularly 5 parts by weight based on total 100 parts by weight.

[0055] Other suitable catalysts may be selected from the group consisting of: diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, 2,2'-azabis (2-imidazoline) dihydrochloride, isooctyl p-dimethylaminobenzoate, 2,2'-azo (2-methyl-N- (2-hydroxyethyl)propionamide), dodecyl peroxide, azobisimidazolinyl propane, tert-butyl perbenzoate, dibenzoyl peroxide, azobisisobutyronitrile and azobisisoheptonitrile. The terms “polymerization initiator” and “catalyst” are used synonymously herein.

[0056] Method of producing the electrolyte and curing conditions

[0057] The present invention provides a method of preparing a flame-retardant electrolyte, the method comprising: providing a first mixture of a flame-retardant polymer, a lithium salt and an ionic liquid; adding a catalyst to the first mixture to obtain a second mixture; and curing thesecond mixture to obtain the flame-retardant electrolyte. The present invention also contemplates embodiment where the lithium salt, ionic liquid and catalyst are combined in any combination. The present invention also provides a method of producing a flame-retardant electrolyte for an energy storage composite, the method comprising: providing a first mixture of a flame-retardant polymer, a lithium salt and an ionic liquid; adding a catalyst to the first mixture to obtain a second mixture; infusing the second mixture into an electrode; and curing the infused electrode. Preferably the lithium salt is dissolved into the ionic liquid with the assistance of an ultrasonic water bath, followed by mixing the lithium salt-dissolved ionic liquid with a flameretardant polymer achieve substantial homogeneity. The method further preferably comprises the step of adding a catalyst to the homogeneous mixture with a weight ratio of about 6:100 based on the weight of phenolic resin, followed by casting the resulting mixture (e.g., into a Teflon mold) and transferring to an oven for curing, wherein the curing cycle preferably comprises two parts: 80°C for 16 hours followed by 135°C for 5 hours. The method may further comprise the step of infusing the homogeneous mixture into structural electrodes for application in structural energy storage composites, followed by subjecting the electrodes to the same curing cycle.

[0058] Electrolyte

[0059] In some preferred embodiments, the electrolyte is substantially solid. In other embodiments the electrolyte may be flexible or rigid.

[0060] The electrolyte of the invention comprises polymeric domains that are interconnected to form a porous matrix. Within that porosity comprises polymeric particles having a coating of IL and Lithium salt. Preferably there is a continuous phase of IL and Li Salt coating the porosity to provide ionically conductive pathways throughout the matrix.

[0061] The electrolyte of the invention may comprise an ionic conductivity between 1.1 x 10'5to 6.0 ms / cm.

[0062] The electrolyte of the invention may comprise a tensile strength of between 1 to 30 MPa, and a tensile modulus of between 0.25 to 8 GPa.

[0063] The electrolyte of the invention has particular utility in a variety of applications, such as un-manned aerial vehicles (UAVs), electric vehicles, in supercapacitors, in solid state batteries, for mobile phones, computers and new energy vehicles, unmanned aerial vehicle (UAV) and electrical vehicles.DEFINITIONS

[0064] In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to be limiting.

[0065] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one having ordinary skill in the art to which the invention pertains.

[0066] Unless the context clearly requires otherwise, throughout the description and the claims, the terms “comprise”, “'comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. For example, a composition, mixture, process or method that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, mixture, process or method.

[0067] The transitional phrase "consisting of” excludes any element, step, or ingredient not specified. If in the claim, such would close the claim to the inclusion of materials other than those recited except for impurities ordinarily associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

[0068] The transitional phrase "consisting essentially of" is used to define a composition, process or method that includes materials, steps, features, components, or elements, in addition to those literally disclosed, provided that these additional materials, steps, features, components, or elements do not materially affect the basic and novel characteristic(s) of the claimed invention. The term "consisting essentially of" occupies a middle ground between "comprising" and "consisting of".

[0069] Where the applicant has defined an invention or a portion thereof with an open-ended term such as "comprising", it should be readily understood that (unless otherwise stated) the description should be interpreted to also describe such an invention using the terms "consisting essentially of" or "consisting of." In other words, with respect to the terms “comprising”, “consisting of”, and “consisting essentially of”, where one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms. Thus, in some embodiments not otherwise explicitly recited, any instanceof “comprising” may be replaced by “consisting of” or, alternatively, by “consisting essentially of”.

[0070] While reference may be made in this disclosure to the invention comprising a combination of a plurality of elements, it is also understood that this invention is regarded to comprise combinations which omit or exclude one or more of such elements, even if this omission or exclusion of an element or elements is not expressly stated herein, unless it is expressly stated herein that an element is essential to the applicant' s combination and cannot be omitted. It is further understood that the related prior art may include elements from which this invention may be distinguished by negative claim limitations, even without any express statement of such negative limitations herein. It is to be understood, between the positive statements of applicant's invention expressly stated herein, and the prior art and knowledge of the prior art by those of ordinary skill which is incorporated herein even if not expressly reproduced here for reasons of economy, that any and all such negative claim limitations supported by the prior art are also considered to be within the scope of this disclosure and its associated claims, even absent any express statement herein about any particular negative claim limitations.

[0071] As used herein, with reference to numbers in a range of numerals, the terms "about," "approximately" and "substantially" are understood to refer to the range of -10% to +10% of the referenced number, preferably -5% to +5% of the referenced number, more preferably -1 % to + 1 % of the referenced number, most preferably -0 .1 % to +0 .1 % of the referenced number. Moreover, with reference to numerical ranges, these terms should be construed as providing support for a claim directed to any number or subset of numbers in that range. For example, a disclosure of from 1 to 10 should be construed as supporting a range of from 1 to 8, from 3 to 7, from 1 to 9, from 3.6 to 4.6, from 3.5 to 9.9, from 8 to 10, and so forth.

[0072] The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

[0073] The complete disclosures of the patents, patent documents and publications cited herein are incorporated by reference in their entirety as if each were individually incorporated.

[0074] Unless expressly stated to the contrary, "or" refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

[0075] The term "and / or" used in the context of "X and / or Y" should be interpreted as "X," or "Y," or "X and Y." Similarly, "at least one of X or Y" should be interpreted as "X," or "Y," or "both X and Y."

[0076] The indefinite articles "a" and "an" preceding an element or component of the invention are intended to be non-restrictive regarding the number of instances (i.e., occurrences) of the element or component. Therefore "a" or "an" should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular.

[0077] As used herein, wt.% refers to the weight of a particular component relative to total weight of the referenced composition.

[0078] It will be understood that use of the term “between” herein when referring to a range of numerical values encompasses the numerical values at each endpoint of the range. For example, a temperature of between 80 °C and 150 °C is inclusive of a temperature of 80 °C and a temperature of 150 °C.

[0079] Various features of the embodiments of the invention disclosed herein are, for brevity, described in the context of a single embodiment, but may also be provided separately or in any suitable sub-combination. All combinations of the embodiments are specifically embraced by the illustrative embodiments disclosed herein just as if each and every combination was individually and explicitly disclosed. In addition, all sub-combinations listed in the embodiments describing such variables are also specifically embraced by the present compositions and are disclosed herein just as if each and every such sub-combination was individually and explicitly disclosed herein.

[0080] In the foregoing paragraphs, where various ratios of components have been disclosed. It will be appreciated that these ratios of components can be combined in any disclosed combination. For example, the ratio of A:B (which may be between about 100:1 and 1:100 or any range therein), may be combined with the ratio of C:D (which may be between about 50:1 and 1:50 or any range therein), and may be combined with the ratio of E:F (which may be between about 10:1 and about 1:10 or any range therein).

[0081] As used herein, the term “polymer” and “resin” are used synonymously.BRIEF DESCRIPTION OF THE DRAWINGS

[0082] The aspects described above, as well as other apparent aspects, advantages, and objectives of the present invention are apparent from the detailed description below in combination with the drawing, in which:

[0083] Figure 1. (a) Ionic conductivity of phenolic resin-based solid electrolytes as a function of ionic liquid (IL) content, with the inset illustrating the formation of a layered structure at higher IL concentrations, (b) Nyquist plot and the corresponding equivalent circuit model used to determine the ionic conductivity of an electrolyte containing 60% phenolic resin and 40% IL. (c) Nyquist plots comparing solid electrolytes with varying LiTFSI content, (d) Ionic conductivity of solid electrolytes with a fixed phenolic resin-to-IL mass ratio of 3:2 and different LiTFSI / IL ratios, (e) Ionic conductivity of solid electrolytes with a fixed phenolic resin-to-(IL+LiTFSI) mass ratio of 3:2 and varying LiTFSI / IL ratios, (f) Ionic conductivity of IL with different LiTFSI contents, (g) Tensile strength and modulus of solid electrolytes with a fixed phenolic resin-to-IL mass ratio of 3:2 and varying LiTFSI / IL ratios, (h) Tensile strength and modulus of solid electrolytes with a fixed phenolic resin-to-(IL+LiTFSI) mass ratio of 3:2 and varying LiTFSI / IL ratios, (i) Plot of ionic conductivity versus tensile strength for all solid electrolytes studied herein.

[0084] Figure 2. (a) TGA and (b) results of phenolic-based electrolytes and epoxy-based electrolyte; (c) TGA results of pure phenolic polymer, epoxy polymer, IL and LiTFSI; (c) UL 94 vertical bunning tests on epoxy-based electrolyte and phenolic-based electrolyte; Comparison of mechanical and electrochemical properties of solid polymer electrolytes: (e) tensile strength / ionic conductivity; (f) tensile young’s modulus I ionic conductivity.

[0085] Figure 3. Microstructural analysis of phenolic resin-based solid electrolytes: (a) pure phenolic polymer, (b) phenolic resin mixed with ionic liquid (mass ratio 3:2); (c) phenolic resin / ionic liquid / lithium salt mixture (3:2:0.2); (d) phenolic resin / ionic liquid / lithium salt mixture (3:2:0.4); (e) phenolic resin / ionic liquid / lithium salt mixture (3:2:1), EDS analysis of (f) original and (g) washed electrolyte sample with a phenolic resin / ionic liquid / lithium salt ratio of 3:2:1.

[0086] Figure 4. Characterizations on phenolic-based electrolyte systems: (a) DSC curves; (b) Exothermic heat generated during the curing process (c) Solid-state nuclear magnetic resonance results on carbon-13 (13C); (d) Fourier-transform Infrared Spectroscopy (FTIR) analysis; Schematic diagram of (e) the emulsion polymerization process and (f) lithium-ion conduction in phenolic-based structural electrolyte.

[0087] Figure 5. Electrochemical performance of the composite energy storage device developed with a phenolic-based electrolyte: (a) CV curves and (b) calculated capacitance of devices under different scan rates; demonstration of the composite structural supercapacitor: (c) lighting up an LED; (d) charged by a battery and then lighting up six LEDs for a long duration; (e) flame retardancy validation.

[0088] Figure 6 shows the fracture surface morphology of an electrolyte with a phenolic resin / ionic liquid / lithium salt, showing the porosity within the phenolic resin (polymer matrix) and containing polymeric microsphere particles within that porosity. Additionally, IL can be seen coating the internal porosity of the porous network of the phenolic resin, and also coating the polymeric particles. Additionally, “closed” porosity can seen within the matrix of the phenolic resin.

[0089] Figure 7 is a schematic of the fracture surface morphology shown in Fig. 6.

[0090] Figure 8 are the EIS measurement results of a flame-retardant polymer electrolyte developed with a specific weight ratio (phenolic resin: ionic liquid: lithum salt =3:2:1).

[0091] Figure 9 are the TGA results comparing the thermal stability of a phenolic resinbased electrolyte to an epoxy resin-based electrolyte.

[0092] Figure 10 shows the surface morphologies of the flame-retardant polymer electrolyte of the invention.DETAILED DESCRIPTION

[0093] The skilled addressee will understand that the invention comprises the embodiments and features disclosed herein as well as all combinations and / or permutations of the disclosed embodiments and features. The present invention will now be described with reference to the following examples which should be considered in all respects as illustrative and non-restrictive.Electrochemical, mechanical, and thermal properties of phenolic resin based solid electrolyte

[0094] In one example, the electrolyte of the invention was prepared by mixing flameretardant phenolic resin / polymer with the ionic liquid (IL). The phenolic resin that was chosen was CELLOBOND J2027 X01 (Hexion Inc., USA), however the skilled person would be aware of equivalent resins / polymers that could be used in addition or instead of the specific one chosen herein. The ionic liquid (IL) that was chosen was 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI, Sigma-Aldrich), however the skilled person wouldbe aware of equivalent ILs that could be used. The mass content of IL in the resulting solid electrolyte was increased from 0% to 50%, and the calculated ionic conductivities of these electrolytes are shown in Fig. 1a. It was observed that no ionic conductivity was measured even when the IL mass content increased to 30%, consistent with previous studies on epoxy resinbased solid electrolytes. The solid electrolyte became ionically conductive when the IL mass content exceeded 30%, with the electrolyte containing 40% IL achieving an ionic conductivity of about 4.2 x 10'3mS / cm. However, further increasing the IL mass content did not result in a constant increase in the ionic conductivity of the solid electrolyte. It was observed that the solid electrolyte containing 50% IL had an ionic conductivity of about 4.9 x 10-4mS / cm. Without wishing to be bound by theory, this is attributed to the density difference between phenolic resin (1.22 g / cm3) and IL (1.52 g / cm3); a high content of IL is more likely to form a layered structure in the solid electrolyte, as shown in the inset of Fig. 1a, leading to a significant decrease in the electrolyte’s ionic conductivity. In this work, the ionic conductivity of the solid electrolyte was calculated based on the Nyquist plots obtained through EIS measurements, and the bulk resistance was determined by fitting the data with an equivalent circuit, as shown in Fig. 1b.

[0095] To avoid the formation of a layered structure in the solid electrolyte, the mass ratio between phenolic resin and IL was controlled to be 3:2. Based on this optimized ratio, further modifications to the solid electrolyte were conducted by introducing different contents of lithium salt, which in this case was chosen as lithium bis(trifluoromethane)sulfonimide (LiTFSI).However the skilled person will be aware that various other lithium salts could be used instead of, or in addition to the one chosen in this study. Since the lithium salt was first dissolved in IL before mixing with phenolic resin, the content of lithium salt was controlled in terms of the LiTFSI / IL ratio. This method ensured a homogeneous distribution of the lithium salt within the electrolyte, enhancing the ionic pathways and improving overall conductivity. The LiTFSI / IL ratio was increased from 0 to 0.5, which reaches the solubility limit of LiTFSI in EMIM TFSI. Fig. 1c shows Nyquist plots of solid electrolytes containing different amounts of LiTFSI. It is observed that the change in bulk resistance does not consistently correlate with the change in LiTFSI content. For the electrolyte sample without LiTFSI, the bulk resistance is roughly about 100 kQ. This resistance increases to over 2000 kQ when the LiTFSI / IL ratio increases to 0.1. However, further increasing the LiTFSI content leads to a decrease in bulk resistance, with values less than 3000 Q and less than 200 Q achieved with LiTFSI / IL ratios of 0.2 and 0.5, respectively, as shown in the inset of Fig. 1c. Therefore, it was found that adding LiTFSI to the electrolyte initially decreases the ionic conductivity, reaching a minimum value of about 1.89 x 10'4mS / cm at a LiTFSI / IL ratio of 0.1. Further increasing the LiTFSI content leads to an increase in ionic conductivity, with the highest value of 2.87 mS / cm achieved at a LiTFSI / IL ratio of 0.5, as shownin Fig.1 d. Although there is a dip in ionic conductivity occurring around the LiTFSI / l L ratio of 0.1 , which looks more pronounced when the y-axis is in logarithmic scale, the overall trend of ionic conductivity appears to increase with the LiTFSI content, as shown in the inset of Fig. 1 d, where the y-axis is in a linear scale.

[0096] Although the mass ratio between phenolic resin and I L was controlled to be constant, adding more lithium salt can lead to a decrease in phenolic content in the electrolyte, which may potentially contribute to the increase in the electrolyte’s ionic conductivity. To validate this, another set of samples was prepared by controlling the mass ratio of phenolic resin to the combined IL and LiTFSI to be 3:2. However, by adjusting the content of lithium salt in electrolyte, a similar trend in ionic conductivity was observed, as shown in Fig. 1e. The ionic conductivity of the solid electrolyte reached its minimum value when the LiTFSI / l L ratio was 0.2, then increased to the highest value at a LiTFSI / l L ratio of 0.5. These results indicate that, besides the decrease in phenolic resin content, there is another mechanism existing when adding LiTFSI that increases the ionic conductivity of the solid electrolyte. Notably, the ionic conductivity of IL decreases with the increase of LiTFSI content, as shown in Fig. 1f. This decrease in the ionic conductivity of IL could explain the initial dip observed in the ionic conductivity curves in Fig. 1d and Fig. 1e when adding LiTFSI to the electrolyte, where the ionic conductivity of the electrolyte is initially dominated by the ionic conductivity of IL.

[0097] To investigate the mechanical properties of the two sets of solid electrolytes mentioned earlier (one with a fixed phenolic resin to IL mass ratio of 3:2, and the other with a fixed phenolic resin to I L+LiTFSI ratio of 3:2) tensile tests were conducted according to ASTM D638, with the results presented in Figs. 1g and 1h.

[0098] For the electrolytes with a fixed phenolic resin to IL mass ratio of 3:2, the tensile strength remained relatively stable, ranging from approximately 16 to 19 MPa, as the LiTFSI / l L ratio increased up to 0.2. However, further increases in the LiTFSI / l L ratio led to a decrease in tensile strength, reaching the lowest value of 1.11 ± 0.4 MPa at a phenolic resin: IL: LiTFSI ratio of 3:2:1. The tensile modulus of this set of electrolytes followed a similar trend, initially around 1.9 GPa, and began to decrease when the LiTFSI / IL ratio exceeded 0.2, eventually dropping to a minimum value of 0.067 GPa with the highest LiTFSI content (Ph:IL=3:2:1). The reduction in strength and modulus for electrolytes with high LiTFSI content is primarily attributed to microstructural changes in the electrolyte, which will be discussed in detail in the following section.

[0099] In contrast, for the electrolytes with a fixed phenolic resin to I L+LiTFSI ratio of 3:2, the tensile strength remained relatively stable even at the highest LiTFSI content. This stability is mainly due to the constant phenolic resin content (60%) in the electrolyte, which helps maintain the mechanical strength. However, the tensile modulus still showed a reduction at higher LiTFSI contents, particularly when the LiTFSI / IL ratio exceeded 0.3, dropping from around 1.9 GPa to about 1.2 GPa. This decrease is also related to the microstructural changes in the electrolyte.[000100] For the application of structural energy storage composites, it is preferable that the electrolyte exhibits both high ionic conductivity and favourable mechanical properties. Fig. 1i presents a plot of ionic conductivity versus tensile strength for all solid electrolytes studied. Two electrolytes are identified as potential candidates for application in structural energy storage composites.(1) The electrolyte with a phenolic resin (Ph): ionic liquid (IL): LiTFSI mass ratio of 3:2:0.4, denoted by a black star in the figure. This electrolyte is part of a set where the mass ratio of phenolic resin to IL is fixed.(2) The electrolyte with a phenolic resin to I L+LiTFSI mass ratio of 3:2, and an LiTFSI / IL ratio of 0.5, indicated by a red sphere in the figure.This electrolyte belongs to a set where the phenolic resin to I L+LiTFSI ratio is fixed. Both of these electrolytes exhibit comparable ionic conductivity and mechanical strength, demonstrating a well-balanced performance that makes them suitable candidates for use in structural energy storage composites.[000101] Thermogravimetric analysis (TGA) in nitrogen environment was conducted on above phenolic-based electrolyte candidates, in comparison to an epoxy-based electrolyte (Epoxy: IL= 3:2), as shown in Fig. 2a. The results demonstrate a significant difference in residual mass between the phenolic and epoxy-based electrolytes at elevated temperatures. At 900 °C, the phenolic-based electrolytes retain approximately 30% of their initial mass, while the epoxybased electrolyte retains only 6.8% under identical testing conditions. This higher residue in the phenolic-based electrolytes indicates a more robust structure that surprisingly resists decomposition. More specifically, electrolyte 1 (Ph: I L: LiTFSI= 3:2:0.4) shows a residual mass of 29.7%, slightly lower than that of electrolyte 2 (Ph:(l L+LiTFSI) = 3:2; I L: LiTFSI= 2:1), which has a residual mass of 31.8%. This variation in residual mass may be attributed to the higher phenolic resin content in electrolyte 2, which enhances thermal stability.[000102] The DTG analysis, as shown in Fig. 2b, further highlights the differences in decomposition profiles between the phenolic and epoxy resin-based electrolytes. The phenolic-based electrolytes exhibit a single, dominant decomposition peak around 500 °C, suggesting a straightforward decomposition process typical of thermally stable materials. In contrast, the epoxy resin-based electrolyte (blue curve) displays a more complex thermal decomposition profile with two distinct peaks in the DTG curve, indicative of a two-step degradation process. The first peak, at around 300 °C, is attributed to the decomposition of the epoxy phase in the electrolyte, while the second peak, around 500 °C, corresponds to the decomposition of the ionic liquid (IL) component. These attributions are supported by the TG curves of pure epoxy and IL, as shown in Fig. 2c. It is notable that, although the second peak occurs at a relatively high temperature of 500 °C, the epoxy-based electrolyte will lose its structural integrity at the first peak (-300 °C), where most of the solid epoxy phase in the electrolyte decomposes, leaving only the liquid IL phase.[000103] Further insights can be drawn from Fig. 2c, where the residual masses of pure phenolic resin and LiTFSI are also presented. Pure phenolic resin retains approximately 53.4% of its initial mass at 900 °C, which is significantly higher than the residual masses of pure epoxy (8.1%), IL (6%), and LiTFSI (6.4%). This high residual mass of pure phenolic resin is a key factor contributing to the excellent thermal stability of the phenolic resin-based electrolytes developed according to the present invention, making them suitable for high-temperature applications where structural integrity is important. The superior thermal resistance of the phenolic resinbased electrolyte, as compared to the epoxy resin-based alternative, demonstrates its potential as a stable material for use in environments requiring sustained thermal endurance.[000104] Flame retardancy is also an important performance factor for polymer structural electrolytes, especially for applications requiring both structural integrity and safety under high-temperature conditions. To assess the flame retardancy of the phenolic resin-based electrolyte, a standard UL94 vertical burning test was conducted, with an epoxy-based electrolyte (Epoxy = 3:2) included as a comparison. The flammability test progression is illustrated in Fig. 2d. The results reveal a stark contrast between the two materials: the epoxy-based electrolyte ignites easily, and the flame spreads rapidly, indicating a complete lack of flame retardancy. Due to its high flammability, the epoxy-based electrolyte was unable to achieve any valid UL94 rating. In contrast, the phenolic resin-based electrolyte developed according to the present invention demonstrates outstanding flame retardancy. It could not be ignited at all during the test, achieving the highest possible flame retardancy rating of V-0. This rating reflects the material’s capability to resist ignition and prevent flame propagation, highlighting its potential as a safe and effective structural electrolyte for high-temperature and flame-resistant applications. Thematerials of the invention provide excellent flame retardancy and are suitable for use in environments that demand both thermal stability and fire safety.[000105] In addition to demonstrating superior thermal stability and flame retardancy, the phenolic-based polymer electrolyte of the invention significantly expands the boundaries of mechanical and electrochemical performance compared to electrolytes based on epoxy. Figs.2e and 2f present a comparative analysis of the mechanical (tensile strength and modulus) and electrochemical (ionic conductivity) properties between the phenolic-based electrolyte developed according to the invention and recently reported epoxy-based electrolytes. For reference, the tensile properties of pure epoxy and phenolic polymers, as well as the ionic conductivity of pure IL, are also indicated in the figures. The data reveal that some phenolic-based electrolytes (marked with red stars) achieve performance levels beyond those of epoxybased electrolytes, particularly in terms of ionic conductivity, which approaches values similar to pure I L. This enhanced ionic conductivity suggests that the phenolic-based electrolytes of the invention may provide more efficient ion transport pathways, potentially due to the optimized composition and structure of the phenolic matrix. Furthermore, the improved mechanical properties of the phenolic-based electrolyte, as shown by increased tensile strength and modulus, demonstrate its suitability as a structurally robust electrolyte material. These advancements in both mechanical and electrochemical performance make the phenolic-based polymer electrolyte according to the invention a promising candidate for applications requiring a balance of mechanical durability, high ionic conductivity, and enhanced thermal and flame resistance.Micro morphology of phenolic resin based solid electrolyte[000106] Investigating the micro morphology of phenolic resin-based solid electrolytes is important for understanding how their internal structure affects ionic conductivity and overall performance. Scanning electron microscopy (SEM) was employed to analyse these microstructural features.[000107] Fig. 3a presents the typical fracture surface morphology of the pure phenolic resin polymer. The SEM image reveals numerous pores within the polymer matrix, which result from the release of water and small gas molecules during the curing process. These pores contribute to the high porosity commonly observed in cured phenolic resin, a characteristic feature of this material.[000108] Upon mixing the phenolic resin with an ionic liquid at a mass ratio of 3:2, slight changes in the microstructure were observed. Fig. 3b shows the fracture surface morphology ofthe cured electrolyte. While the pore size remains similar to that of the pure phenolic resin, the void density is notably reduced, dropping to nearly half of the original value. This decrease in porosity is primarily attributed to the reduced phenolic resin content in the mixture, as the ionic liquid occupies part of the matrix, thereby reducing overall pore formation.[000109] The addition of lithium salt to the electrolyte further alters the fracture surface morphology. In Fig. 3c, which represents a phenolic resin / ionic liquid / lithium salt ratio of 3:2:0.2, the pore size decreases while pore density increases, indicating that lithium salt impacts the microstructure, likely through interactions with the resin and ionic liquid that influence pore formation and distribution.[000110] Significant changes in micro morphology are observed when the lithium salt content is further increased, as shown in Fig. 3d, where the electrolyte has a phenolic resin / ionic liquid / lithium salt ratio of 3:2:0.4. In this sample, a liquid-phase substrate, likely ionic liquid, is clearly visible on the fracture surface. Unlike the surfaces in Figs. 3b and 3c, where the ionic liquid phase is not easily observed and may be isolated by the non-ionic conductive phenolic resin polymer, the higher lithium salt content seems to enable the release of the ionic liquid from isolation. This creates a continuous ionic conductive phase, significantly enhancing the electrolyte’s ionic conductivity. Additionally, some microsphere structures begin to form beneath the ionic liquid phase.[000111] This hypothesis is confirmed with further increases in lithium salt content, as demonstrated in Fig. 3e, showing the fracture surface morphology of an electrolyte with a phenolic resin / ionic liquid / lithium salt ratio of 3:2:1. This composition exhibits a markedly different micro morphology, characterized by numerous polymeric particles (in the form of microsphere structures) closely bonded together, with a liquid-phase substrate adhering to the surface. The enlarged view in Fig. 3e reveals that the liquid-phase substrate, likely the ionic liquid, forms a continuous phase that covers the entire surface. The resulting structure appears as a highly porous skeleton made of phenolic microspheres, with an ionic conductive liquid phase closely adhering to each surface, leading to enhanced ionic conductivity throughout the electrolyte. Fig. 6 shows the fracture surface morphology of an electrolyte with a phenolic resin / ionic liquid / lithium salt, showing the porosity within the phenolic resin (polymer matrix) and containing polymeric microsphere particles within that porosity. Additionally, IL can be seen coating the internal porosity of the porous network of the phenolic resin, and also coating the polymeric particles. Additionally, “closed” porosity can seen within the matrix of the phenolic resin. Fig. 7 is a schematic of the fracture surface morphology shown in Fig. 6. From these figures, the "phenolic block" appears to be formed from 100% phenolic in some regions (andthere are some microbubbles which are visible, too), but in others it is a collection of merged particles of phenolic resin, and there a coating of the ionic liquid on the phenolic block and the merged / coalesced phenolic particles. Also, separately, there seems to be particles of phenolic resin in the void which are also coated with ionic liquid.[000112] Energy Dispersive Spectroscopy (EDS) analysis was conducted on the electrolyte with a phenolic resin / ionic liquid / lithium salt ratio of 3:2:1, as shown in Fig. 3f. Characteristic elements such as sulfur (S), nitrogen (N), and fluorine (F) from TFSI- are clearly identified on the electrolyte’s fracture surface, indicating that the liquid-phase substrate adhering to the microsphere structures is indeed the ionic liquid. Another EDS analysis was performed on the same electrolyte after ultrasonic cleaning with acetone and water for over 4 hours, followed by drying in an oven. The liquid-phase substrate was removed after washing, but the S, N, and F elements remained detectable on the surface, suggesting that some lithium salt (LiTFSI) remains integrated within the microsphere structures even after prolonged ultrasonic cleaning.[000113] It is noted that neither EDS analysis in Figs. 3f and 3g could detect the lithium (Li) element, which is consistent with the understanding that the lithium K X-ray from Li to K shells is not an allowed transition due to the azimuthal quantum number (I) selection rule, where both energy levels have the same orbital angular momentum (l=0). This results in a very low likelihood of X-ray emission. Therefore, the absence of Li in the EDS results does not necessarily indicate its absence in the electrolyte. It is believed that lithium salt resides both in the phenolic resin phase and the ionic liquid phase within the electrolyte.Mechanism analysis on phenolic resin based solid electrolyte[000114] The curing behaviour of phenolic resin-based electrolyte systems were evaluated using Differential Scanning Calorimetry (DSC), as shown in Fig. 4a. Four different samples were examined: (1) pure phenolic resin (Ph), (2) phenolic resin with ionic liquid (Ph:IL= 3:2), (3) phenolic resin with LiTFSI (Ph: Li = 3:1), and (4) phenolic resin with both ionic liquid and LiTFSI (Ph:IL:Li= 3:2:1). All these samples are in uncured liquid state, and the DSC curves provide valuable insights into the curing reactions and interactions between the resin and the added ionic liquid and lithium salt.[000115] The pure phenolic resin (Ph) shows an exothermic peak between 80°C and 110°C, corresponding to the curing process of the resin. This peak reflects the heat release associated with the cross-linking reaction, and the intensity of the peak suggests that the resin undergoes a thorough curing process. Given that this peak serves as a reference for evaluating modifiedsamples, its well-defined location and intensity indicate that, under these conditions, the phenolic resin reaches a high degree of curing with minimal residual reactive sites.[000116] In the sample containing ionic liquid (Ph / IL), the exothermic peak appears in a similar temperature range, starting around 80°C but with a slightly lower intensity compared to the pure phenolic resin. Although the onset temperature of curing does not shift significantly, the lower peak intensity may suggest that the plasticizing effect of ionic liquid results in incomplete curing under the current conditions. This incomplete curing could occur because the enhanced chain mobility might prevent all reactive sites from fully cross-linking, as the flexible matrix does not stabilize as completely as in the pure resin.[000117] For the sample containing LiTFSI (Ph / Li), the exothermic peak starts much earlier, around 50°C, with the peak that extends up to about 100°C. This early onset reflects the catalytic effect of LiTFSI, which lowers the activation energy required for the curing reaction. The Li+ ions can form ion-dipole interactions with the oxygen atoms in the phenolic hydroxyl groups, disrupting the hydrogen bonding network within the resin. This disruption increases the mobility of the polymer chains, allowing the cross-linking to initiate at a lower temperature and proceed more vigorously. However, while the curing is highly accelerated, the decreased peak intensity compared to the pure resin’s peak may imply that the curing process, though faster, is not entirely complete. Rapid initiation of the reaction may lead to premature cross-linking in certain areas, limiting the diffusion of reactants and leaving some reactive sites unreacted.[000118] The Ph / IL / Li sample, which represents the structural electrolyte developed in the present invention, combines both ionic liquid and LiTFSI. It exhibits a broad exothermic peak starting around 50°C and extending to approximately 110°C. Without wishing to be bound by theory, it is believed that the early onset is driven by the catalytic action of LiTFSI , while the ionic liquid enhances chain mobility, creating a more flexible curing environment. However, the lower intensity of the exothermic peak compared to the pure phenolic resin suggests incomplete curing. The broad and lower-intensity peak indicates that, while curing begins early, it proceeds in a different manner, potentially resulting in an incomplete cross-linked network.[000119] Integration of the exothermic peaks to calculate the heat released during curing, shown in Fig. 4b, confirms these observations. The pure phenolic resin sample generated a specific heat of approximately 105 mJ / mg. In comparison, the Ph / IL, Ph / Li, and Ph / IL / Li samples produced lower specific heats of 57.1, 52.3, and 34.2 mJ / mg, respectively. Since the curing process primarily occurs within the phenolic resin, it is more appropriate to normalize the specific heat by the weight fraction of phenolic resin in each sample, as represented by the green barsin Fig. 4b. According to the normalized results, the Ph / IL sample generated a specific heat of 95.2 mJ / mg during curing, indicating a slightly lower curing degree (-91%) compared to the pure phenolic resin. For samples containing LiTFSI, the Ph / Li and Ph / IL / Li samples exhibited normalized specific heats of approximately 69.7 and 68.3 mJ / mg, respectively, representing a curing degree of around 66% relative to the pure phenolic resin sample. These findings suggest that while LiTFSI effectively accelerates curing by lowering the initiation temperature, it also has a more pronounced role in hindering complete cross-linking of the phenolic resin.[000120] Solid-state carbon-13 (13C) nuclear magnetic resonance (NMR) spectroscopy was performed on four groups of samples to further investigate the interaction mechanisms among phenolic resin, IL, and LiTFSI. The curing of phenolic resin follows a typical condensation polymerization mechanism. During curing, the hydroxyl group (-OH) attached to the aromatic ring in the phenolic monomer reacts with methylene groups (-CH2-) from a cross-linking agent, forming methylene bridges between aromatic rings and releasing water as a byproduct. This cross-linking reaction connects the benzene ring structures in the phenolic resin via -CH2-linkages, as shown in Fig. 4c.[000121] It is noteworthy that the -OH groups directly connected to the benzene rings remain unchanged during this cross-linking reaction. Therefore, the carbon atoms in the benzene rings attached to the -OH groups, marked in green, can be used as internal references to evaluate the curing degree of the phenolic resin. In contrast, the carbon atoms from the -CH2- groups, marked in orange in the chemical formula of the phenolic resin, reflect the extent of cross-linking in these samples.[000122] From the NMR results, the peaks located around 150 ppm correspond to the carbon atoms in the benzene rings directly connected to the -OH groups. The intensity of this peak in all samples has been normalized to a value of 1.00. This normalization allows for the determination of the relative intensity of the carbon atoms from the -CH2- groups in each sample. For pure phenolic resin, the intensity of the -CH2- peak is approximately 1.51 , indicating that the number of carbon atoms from -CH2- groups is roughly 1.5 times that of the reference carbon atoms. Similarly calculated, the intensities of the -CH2- peaks in the Ph / IL, Ph / Li, and Ph / IL / Li samples are about 1.71, 1.36, and 1.18, respectively.[000123] The higher intensity observed in the Ph / IL sample may be attributed to the -CH2-groups present in the EMIM+cation of the ionic liquid, as indicated in the figure. Excluding the Ph / IL sample, the intensity values calculated for the Ph / Li and Ph / IL / Li samples are lower thanthat of the pure phenolic resin, suggesting a decreased number of -CH2- groups. This decrease corresponds to a reduced curing degree of the phenolic resin in these two samples.[000124] Without wishing to be bound by theory, it appears that the presence of LiTFSI influences the phenolic resin to form shorter-chain polymer structures rather than fully cured long-chain polymers, particularly in the Ph / IL / Li sample. Even with the additional -CH2- groups from the IL, the total amount of -CH2- is significantly lower than that of the pure phenolic resin. Assuming that the intensity difference (1.71 - 1.51 = 0.20) between the Ph / IL and pure phenolic resin samples is entirely due to the EMIM+from the IL, the actual intensity of the -CH2- groups originating from the phenolic resin in the Ph / IL / Li sample would be 0.98 (1.18- 0.20). Compared to the pure phenolic resin (1.51), this represents about 65% of the -CH2- content, which aligns well with the curing degree (66%) calculated from the DSC results.[000125] Fourier-transform infrared spectroscopy (FTIR) was applied to analyze the four samples. According to the results shown in Figure 4d, the characteristic absorption bands of the cured pure phenolic resin were identified in the FTIR spectrum. These include peaks at around 3500 cm-1, representing the presence of hydroxyl groups (-OH), and at 3005 cm-1, corresponding to the aromatic C-H stretch 29. Peaks at 2918 cm-1and 2849 cm-1are attributed to the stretching vibrations of methylene C-H groups. In addition to these characteristic peaks from the phenolic resin, two more peaks were observed in the FTIR spectra of the Ph / IL and Ph / IL / Li samples, located around 3158-3161 cm-1. These peaks correspond to the C-H stretching vibrations of the imidazolium cation (EMIM+) ring of the ionic liquid. Notably, the characteristic peaks at 2918 cm-1and 2849 cm-1, representing methylene C-H groups from the phenolic resin, were observed in samples Ph, Ph / IL, and Ph / Li but were absent in the Ph / IL / Li sample. This indicates a significantly decreased amount of -CH2- groups in the Ph / IL / Li sample, which aligns well with the observations from the NMR results.[000126] Based on the above characterizations and the observed micro-morphology of the phenolic-based electrolyte, the phenolic-based electrolyte with high loading of LiTFSI of the invention forms a unique microstructure. The microspherical structures (polymeric particles) of the phenolic resin, observed after mixing with the ionic liquid (IL) EMIM TFSI and a high loading of LiTFSI, align with the characteristics of emulsion polymerization. Although EMIM TFSI and LiTFSI are not conventional surfactants typically used to facilitate emulsion polymerization, their combination (especially with a high concentration of LiTFSI) appears to act as a hybrid surfactant to promote the emulsion polymerization of phenolic resin, resulting in microsphere formations as shown in Fig. 4e. Specifically, the ionic liquid EMIM TFSI effectively reduces the interfacial tension and forms a robust ionic layer around the resin droplets. Simultaneously,LiTFSI enhances the ionic strength of the aqueous medium (the phenolic resin used in this study contains about 15% water content, and the curing of phenolic resin also produces water as a byproduct) and interacts synergistically with EM IM TFSI as a co-surfactant, stabilizing the emulsion by promoting electrostatic repulsion between dispersed droplets and preventing their coalescence. The presence of both LiTFSI and EM IM TFSI facilitates the formation of a stable emulsion through their complementary interactions — EMIM TFSI provides steric stabilization via its bulky TFSI-anions, while Li+cations contribute to electrostatic stabilization. Upon initiation with a free radical initiator, which is the catalyst used in this study, polymerization proceeds within the stabilized droplets, resulting in uniformly dispersed phenolic polymer microspheres, eventually forming the microstructure shown in Fig.3e. The catalyst used in this study was RESONANCE MC93-521 (Hexion Inc., USA), however the skilled person would be aware of other equivalent catalysts that could be used instead or in addition to the one used in this study. The innovative use of LiTFSI and EMIM TFSI in this emulsion polymerization system underscores their potential as effective non-traditional surfactants, offering enhanced stability and control over polymerization kinetics compared to conventional surfactant-based methods. Regarding the significantly enhanced ionic conductivity of the phenolic-based electrolyte achieved by forming such a microstructure, this improvement can be attributed to the complexation between Li+ions and the hydroxyl groups in the formed phenolic microspheres. In addition to the ionic liquid that fully covers the phenolic microspheres — providing a continuous and highly ionically conductive medium — the Li+ions can complex with the oxygen atoms of the hydroxyl groups, as illustrated in Fig. 4f. This complexation creates additional ion-conductive pathways, substantially enhancing the ionic conductivity of the electrolyte.Performance of composite structural energy storage device[000127] A composite structural supercapacitor was fabricated using the phenolic-based electrolyte of the invention. The device was constructed with two carbon nanotube mats (dimensions: 2 cm x 2 cm) serving as electrodes and a glass fibre veil (thickness: 40 pm) as a separator. These materials were selected to balance mechanical strength, thermal stability, and electrochemical performance, with the phenolic-based electrolyte providing dual functionality as both an energy storage medium and a structural matrix. The capacitance of the structural supercapacitor was evaluated using the cyclic voltammetry (CV) method, with scan rates ranging from 1 mV / s to 200 mV / s. The CV curves, shown in Fig. 5a, exhibit a quasi-rectangular shape with good symmetry, reflecting efficient charge-discharge behaviour and low resistance at the electrode-electrolyte interface. The absence of significant distortion in the CV profiles across a wide range of scan rates indicates stable electrochemical behaviour and compatibility of the phenolic-based electrolyte with the carbon nanotube electrodes. The calculatedcapacitances under different scan rates are presented in Fig. 5b. At the lowest scan rate of 1 mV / s, the device achieved its highest capacitance of approximately 45.5 mF. This high value is remarkable considering that the electrodes are composed solely of pure carbon materials without additional conductive additives or active materials. The high capacitance is attributed to the efficient interaction between the phenolic-based electrolyte and the carbon nanotube electrodes, which maximizes the utilization of the electrode surface area. As the scan rate increased, the capacitance gradually decreased due to the limited time for ion diffusion within the electrode pores and the electrolyte matrix. Nevertheless, even at the highest scan rate of 200 mV / s, the device retained a capacitance of approximately 0.8 mF. This retention demonstrates the strong ion transport capability and relatively low internal resistance of the phenolic-based electrolyte, highlighting its potential for applications requiring rapid chargedischarge cycles.[000128] To demonstrate the application of the phenolic-based electrolyte of the invention, four composite structural supercapacitors connected in series were first charged to 2 V using an electrochemical (EC) workstation. After charging, they were disconnected from the EC workstation and connected to a circuit to light up an LED. The structural supercapacitors successfully powered an LED for over 30 seconds, as shown in Fig. 5c. The performance of the composite structural supercapacitor was further demonstrated through another experiment. The same structural supercapacitor was charged using a 9 V alkaline battery for approximately 20 seconds and was then able to successfully light up six LEDs for over 5 minutes, as depicted in Fig. 5d. Additionally, the structural supercapacitor demonstrated the ability to store electricity for extended periods after charging. In a test, the supercapacitor was charged for about 20 seconds, then allowed to rest for approximately 1 minute before being connected to LEDs. After powering the LEDs for 1 minute, it was disconnected, rested for another 1 minute, and reconnected to the LEDs. The supercapacitors continued to function well under these conditions, indicating good charge retention capabilities. Moreover, it is worth noting that the second and third charge and discharge demonstrations were performed one month after the first one, and the supercapacitors still functioned effectively. This long-term performance further showcases the excellent stability and efficiency of the phenolic-based electrolytes of the present invention.[000129] Finally, the flame retardancy of the composite structural supercapacitor was evaluated by subjecting it to a direct methane flame for 30 seconds. The device was exposed to the flame to simulate extreme thermal conditions and assess its fire-resistant properties. During the flame exposure, some oxidation and pyrolysis occurred in the components of the composite structural supercapacitor, particularly affecting the surface layers. However, the device maintained a high level of structural integrity after this 30-second flame treatment, asillustrated in Fig. 5e. There were no signs of melting, dripping, or significant deformation, indicating that the core structure remained largely unaffected. Most importantly, the device did not ignite or sustain combustion during and after the flame exposure. This lack of ignition demonstrates the excellent flame retardancy of the phenolic-based structural electrolyte of the invention. The formation of a protective char layer also assisted to inhibit further thermal degradation and prevented the spread of flames. The enhanced safety provided by the phenolic-based structural electrolyte of the invention is crucial for applications where fire resistance is paramount, such as in aerospace, automotive, and construction industries. The ability of the composite structural supercapacitor to withstand direct flame exposure without igniting or losing structural integrity underscores its potential for safe energy storage solutions in environments prone to high temperatures or fire hazards.Methods - Materials[000130] The following chemicals were used to develop the structural solid electrolyte of the invention: phenolic resin (CELLOBOND J2027 X01, Hexion Inc., USA) and a catalyst (RESONANCE MC93-521, Hexion Inc., USA) in a weight ratio of 100:6; an ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EM IM TFSI, Sigma-Aldrich); and a lithium salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, Sigma-Aldrich).[000131] Miralon™ carbon nanotube (CNT) mats (thickness: 30 pm; Nanocomp Technologies, Inc., NH, USA) were used as electrodes in their as-received form for the composite structural supercapacitor developed in this study. A glass fibre veil with a thickness of approximately 50 pm was used as a separator.Preparation of phenolic resin based solid electrolyte and composite structural supercapacitor[000132] The electrolyte of the invention was prepared by mixing phenolic resin and IL in a mass ratio of 3:2 until a homogeneous mixture was obtained. It should be noted that the weight of the phenolic resin includes the catalyst content. To prepare electrolytes containing lithium salt, LiTFSI was first dissolved in the IL with the assistance of an ultrasonic water bath, with LiTFSI / IL mass ratios varying up to 0.5. The resulting mixture was then further mixed with phenolic resin as described above. Once a homogeneous mixture was achieved, the electrolytes were cast into Teflon moulds designed for conductivity measurement samples (cylindrical shape with diameter ~10mm and thickness ~4 mm) and tensile test samples (dog-bone shaped with dimensions 40 mm length, 10 mm width, and ~2mm thickness). The electrolytes were cured in an oven, starting with 16 hours at 80 °C, followed by a 5-hour post-cure at 135 °C.[000133] The composite structural supercapacitor was fabricated using a hand lay-up method. The CNT mat was cut to the size of 2 cm x 2 cm and attached to a small piece of copper foil as a current collector using silver paste. The homogeneous mixed electrolyte was applied evenly to one of the CNT mat electrodes until it was fully impregnated with the electrolyte. Then, the glass fibre veil was placed on top of this electrode, and electrolyte was applied to it in the same manner. The second CNT mat electrode was then stacked on the glass fibre veil separator, followed by the application of electrolyte. The composite structural supercapacitor was cured under the same conditions in an oven.Measurement of Ionic Conductivities[000134] Electrochemical impedance spectroscopy (EIS) was used to analyse the ionic conductivity of the produced solid-state polymer electrolytes. For sample preparation, the moulded cylindrical samples were polished with sandpaper prior to measurement. During EIS measurements, the cylindrical samples were clamped between two stainless steel blocking electrodes, and the complex impedance spectrum was recorded over the frequency range from 100 mHz to 100 kHz at an amplitude of 10 mV using a multi-potentiostat (Bio-Logic VSP-300). The impedance data, comprising real and imaginary components, were plotted in a Nyquist plot. The ionic conductivity was calculated using the equation:where o is the ionic conductivity (mS / cm), t is the thickness (cm), A is the contact area (cm2), and Rb (Q) is the bulk resistance of solid electrolyte sample measured through EIS.Capacitance measurement for composite structural supercapacitor[000135] Electrochemical characterization of the composite structural supercapacitors was conducted using a two-electrode system. Cyclic voltammetry (CV) curves were measured at different scan rates ranging from 1 to 200 mV / s within a potential window from 0 to 2 V. The capacitance under constant voltage scan rate Ck=const (mF) is calculated based on the following equation,where I is the current (mA), A is the surface area of the electrode (cm2), k is the scan rate (V / s), Va and Vc are the lower and upper sweeping voltages (V), respectively. In the present work, Va and Vc were set as 0 V and 2 V, respectively.Mechanical testing[000136] Tensile tests were performed in accordance with ASTM D638 using a universal testing machine (Instron 3369, Illinois Tool Works Inc.) equipped with a 1 kN load cell, at a testing speed of 1 mm / min. The strain of the samples during tensile testing was monitored using a dynamic extensometer (Instron 2620-601).Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC)[000137] Thermogravimetric analysis (TGA) was carried out using a thermo-microbalance (Netzsch TG209) to evaluate the thermal stability of different electrolyte samples. The heating rate was set at 20 °C / min, increasing the temperature from room temperature (~26 °C) to -900 °C under a nitrogen atmosphere. Differential scanning calorimetry (DSC) was performed using a Mettler Toledo DSC 1 to determine the degree of curing of the phenolic-based electrolytes. The samples were heated from 30 °C to 240 °C at a heating rate of 10 °C / min.Flame retardancy test[000138] A standard LIL94 vertical burn test was performed using the GTT0082 LIL94 apparatus (Fire Testing Technology) to evaluate the flame retardancy of the epoxy-based solid electrolyte and the phenolic-based solid electrolyte developed in this study. The sample dimensions were 125 mm * 13 mm x 2 mm, in accordance with the test standard.Electron microscopy and spectroscopic characterizations[000139] The micro morphologies of the phenolic resin-based solid electrolytes were characterized using a scanning electron microscope (FEI Nova NanoSEM 450). Energy-dispersive X-ray spectroscopy (EDS) was conducted on as-prepared and washed electrolytes to identify changes in elemental composition.[000140] Solid-state carbon-13 (13C) nuclear magnetic resonance (NMR) spectroscopy was performed using a Bruker Avance III 300 MHz solid-state NMR spectrometer to investigate the interaction mechanisms among phenolic resin, IL, and LiTFSI. Solid electrolyte samples, including pure phenolic resin polymer, were ground to a fine powder before measurement.[000141] Fourier-transform infrared spectroscopy (FTIR) was conducted using a Shimadzu IRTracer-100 instrument in attenuated total reflection (ATR) mode over the wavenumber range of 500-4000 cm’1.[000142] EMBODIMENTS OF THE INVENTION[000143] Other embodiments of the invention as described herein are defined in the following paragraphs:1. A polymeric electrolyte comprising a polymeric matrix having a porous network, the porous network having polymeric particles disposed therein, and wherein the polymeric particles are at least partially coated with an ionic liquid and a lithium salt.2. A method of preparing a polymeric electrolyte, the method comprising:providing a first mixture of a polymer, an ionic liquid and a lithium salt;adding a catalyst to the first mixture to obtain a second mixture; andcuring the second mixture to obtain the polymeric electrolyte.3. A polymeric electrolyte obtained by the method according to the second embodiment.4. An energy storage composite comprising the polymeric electrolyte according to the first or third embodiments.5. A method of producing a polymeric electrolyte for an energy storage composite, the method comprising:providing a first mixture of a polymer, an ionic liquid and a lithium salt;adding a catalyst to the first mixture to obtain a second mixture;infusing the second mixture into an electrode; andcuring the infused electrode.6. A polymer electrolyte battery comprising:an anode,a cathode;a separator; andthe polymeric electrolyte according to the first or third embodiments.7. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the lithium salt further includes one or more additional alkali metal salts where the alkali metal is selected from sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).8. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the polymeric matrix of the polymeric electrolyte is flame-retardant.9. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the polymeric matrix is selected from the group consisting of a phenolic, melamine-formaldehyde, polyimides, bismaleimides, phthalonitriles, benzoxazines, cyanate esters and combinations thereof.10. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the polymeric matrix is selected from the group consisting of polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyimide (PI), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), styrene-butadiene rubber (SBR), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), tetrafluoroethyleneperfluoroalkyl vinyl ether copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, or combinations thereof.11. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the content of the polymer matrix in the polymeric electrolyte is 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, or 80 wt%, or is 40 to 42, 42 to 44, 44 to 46, 46 to 48, 48 to 50, 50 to 52, 52to 54, 54 to 56, 56 to 58, 58 to 60, 60 to 62, 62 to 64, 64 to 66, 66 to 68, 68 to 70, 70 to 72, 72 to 74, 74 to 76, 76 to 78, to 78 to 80 wt%.12. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the polymeric matrix is selected from thermoset polymers.13. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the polymeric matrix includes a flameretardant additive, selected from one or more of 2-ethoxy-2, 4, 4, 6, 6-pentafluorotriphosphazene (HIE), (trimethylsilyl) phosphite (TMSPi), and tris(trimethylsilyl) borate (TMSB), trimethyl phosphate (TMP) and triphenyl phosphate (TPP).14. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the ionic liquid is selected from one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI), 1-ethyl-3-methylimidazolium bis(methanesulfonyl)imide (EMIFSI), tributylmethylammonium bis(trifluoromethanesulfonyl)imide (TBMA-TFSI) and 1-ethyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide (Py12TFSI).15. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the ionic liquid is selected from one or more of 1-vinyl-3-butyl imidazole bis(trifluoromethanesulfonyl) imide, 1-vinyl-3-butyl imidazole hexafluorophosphate, 1-vinyl-3-butyl imidazole tetrafluoroborate, 1-vinyl-3-butyl imidazole bromide, 1 -vinyl-3-ethyl imidazole bis (trifluoromethanesulfonyl) imide, 1-vinyl-3-ethyl imidazole hexafluorophosphate, 1-vinyl-3-ethyl imidazole tetrafluoroborate, 1-vinyl-3-ethyl imidazole bromide, 1-vinyl-3-methyl imidazole bis (trifluoromethanesulfonyl) imide, 1-vinyl-3-methyl imidazole iodide, 1-allyl-3-butyl imidazole bis (trifluoromethanesulfonyl) imide, 1-allyl-3-butyl imidazole hexafluorophosphate, 1-allyl-3-butyl imidazole tetrafluoroborate, 1-allyl-3-butyl imidazole imidazolium bromide, 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-allyl-3-ethylimidazolium hexafluorophosphate, 1-allyl-3-ethylimidazolium tetrafluoroborate, 1-allyl-3-ethylimidazolium bromide, 1-allyl-3-ethylimidazolium chloride, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-allyl-3-methylimidazolium hexafluorophosphate, 1-allyl-3-methylimidazolium tetrafluoroborate, 1-allyl-3-methylimidazolium bromide, 1-allyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, 1-methyl-3-propylimidazolium bromide, 1-allyl-3-vinylimidazolium bromide, 1-allyl-3-vinylimidazolium chloride, 1-allyl-3-vinylimidazolium tetrafluoroborate ora combination of two or more thereof.16. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the ionic liquid is selected from one or more of N-butylpyridinium sulfonate, N-butylpyridinium sulfonate trifluoromethanesulfonate, N-butylpyridinium sulfonate hydrogen sulfate, butylpyridinium sulfonate lactone, N-propylpyridinium sulfonate, N-propylpyridinium sulfonate trifluoromethanesulfonate, N-propylpyridinium sulfonate hydrogen sulfate, propylpyridinium sulfonate lactone, 1-butylsulfonic acid-3-methylimidazole trifluoroacetate, 1-butylsulfonic acid-3-methylimidazole trifluoromethanesulfonate, 1-butylsulfonic acid-3-methylimidazole sulfate The invention can be selected from the group consisting of 1-butyl sulfonic acid-3-methylimidazolium hydrogen salt, 1-butyl sulfonic acid-3-methylimidazolium dihydrogen phosphate, 1-butyl sulfonic acid-3-methylimidazolium chloride, 1-sulfonic acid butyl-3-methylimidazolium inner salt, 1-propyl sulfonic acid-3-methylimidazolium trifluoroacetate, 1-propyl sulfonic acid-3-methylimidazolium trifluoromethanesulfonate, 1-propyl sulfonic acid-3-methylimidazolium hydrogen sulfate, 1-propyl sulfonic acid-3-methylimidazolium dihydrogen phosphate, 1-propyl sulfonic acid-3-methylimidazolium chloride, and 1-propyl sulfonic acid-3-methylimidazolium inner salt, or a combination of two or more thereof.17. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI).18. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the mass content of the ionic liquid in the solid electrolyte is 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, or 60 wt%, or is between 25 to 26, 26 to 27, 27 to 28, 28 to 29, 29 to 30, 30 to 31 , 31 to 32, 32 to 33, 33 to 34, 34 to 35, 35 to 36, 36 to 37, 37 to 38, 38 to 39, 39 to 40, 40 to 41 , 41 to 42, 42 to 43, 43 to 44, 44 to 45, 45 to 46, 46 to 47, 47 to 48, 48 to 49, 49 to 50, 50 to 51, 51 to 52, 52 to 53, 53 to 54, 54 to 55, 55 to 56, 56 to 57, 57 to 58, 58 to 59, or 59 to 60 wt%.19. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the mass ratio between the (flameretardant) polymer and ionic liquid is 3:2, or is 3: 1.333, or is 3:1.3, 3: 1.35, 3: 1.4, 3: 1.45, 3:1.5, 3:1.55, 3:1.6, 3:1.65, 3:1.7, 3:1.75, 3:1.8, 3:1.85, 3:1.9, 3:1.95, or is 3:1, 3:1.05, 3:1.1, 3:1.15, 3:1.2, 3:1.25, oris 3:2.05, 3:2.1, 3:2.15, 3:2.2, 3:2.25, 3:2.3, 3:2.35, 3:2.4, 3:2.45, 3:2.5, 3:2.55, 3:2.6, 3:2.65, 3:2.7, 3:2.75, 3:2.8, 3:2.85, 3:2.9 or 3:2.95.20. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the lithium salt is selected from the group consisting of: bis(trifluoromethanesulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, bis(nonafluorobutylsulfonyl)imide lithium (fluorosulfonyl)imide, (trifluoromethanesulfonyl)imide lithium, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium trifluoromethanesulfonate, and 4,5-dicyano-2-trifluoromethylimidazole lithium, or a combination of two or more thereof.21. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the lithium salt is lithium bis(trifluoromethane)sulfonimide (LiTFSI).22. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the lithium salt is first dissolved in the IL before mixing with the flame-retardant polymer.23. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the lithium salt : IL weight ratio is selected from 0.1 to 0.5, or is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5, or is between 0.1 to 0.15, 0.15 to 0.2, 0.2 to 0.25, 0.25 to 0.3, 0.3 to 0.35, 0.35 to 0.4, 0.4 to 0.45, or 0.45 to 0.5.24. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the ratio of polymer to (IL + Li salt) is 3:2, or ranges from 10:1 to 2:1, or is 20:1, 19.5:1, 19:1, 18.5:1, 18:1, 17.5:1, 17:1, 16.5:1, 16:1, 15.5:1, 15:1, 14.5:1, 14:1, 13.5:1, 13:1, 12.5:1, 12:1, 11.5:1, 11:1, 10.5:1, 10:1, 9.5:1, 9:1, 8.5:1, 8:1, 7.5:1, 7:1, 6.5:1, 6:1, 5.5:1, 5:1, 4.5:1, 4:1, 3.5:1, 3:1, 2.5:1, 2:1, 1.5:1, 1:1 or 0.5:1.25. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein a catalyst is added with a weight ratio of 6:100 based on the weight of polymer in the mixture.26. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the catalyst is selected from benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2- ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide, or 2,2'-azobis (2- cyanobutane), dimethyl 2,2'-azobis(2-methylpropionate), 2,2'-azo bis(methy Ibutyronitrile), 2,2'-azo bis(iso-butyronitrile) (Al BN), and 2,2'-azobisdimethyl- valeronitrile (AMVN).27. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the electrolyte comprises an ionic conductivity between 1.1 x 10-5to 6.0 ms / cm.28. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the electrolyte comprises a tensile strength of between 1 to 30 MPa, and a tensile modulus of between 0.25 to 8 GPa.29. A polymeric electrolyte, a method, or an energy storage composite according to any one of the previous embodiments, wherein the electrolyte is used in un-manned aerial vehicles (UAVs), electric vehicles, in supercapacitors, in solid state batteries, for mobile phones, computers or for new energy vehicles, in unmanned aerial vehicles (UAV) and electrical vehicles.[000144] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms, and in particular features of any one of the various described examples may be provided in any combination in any of the other described examples. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows.

Claims

CLAIMS1. A polymeric electrolyte comprising a polymeric matrix having a porous network, the porous network having polymeric particles disposed therein, and wherein the polymeric particles are at least partially coated with an ionic liquid and a lithium salt.

2. The polymeric electrolyte according to claim 1 wherein the lithium salt further includes one or more additional alkali metal salts where the alkali metal is selected from sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).

3. The polymeric electrolyte according to claim 1 or claim 2 wherein the polymeric matrix of the polymeric electrolyte is flame-retardant.

4. The polymeric electrolyte according to any one of claims 1 to 3 wherein the polymeric matrix is selected from the group consisting of a phenolic, melamine-formaldehyde, polyimides, bismaleimides, phthalonitriles, benzoxazines, cyanate esters and combinations thereof, or wherein the polymeric matrix is selected from the group consisting of polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyimide (PI), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), styrene-butadiene rubber (SBR), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoridechlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylenetetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinylether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, or combinations thereof.

5. The polymeric electrolyte according to any one of claims 1 to 4 wherein the content of the polymer matrix in the polymeric electrolyte is between 40 to 80 wt%.

6. The polymeric electrolyte according to any one of claims 1 to 3 wherein the polymeric matrix includes a flame-retardant additive, selected from one or more of 2-ethoxy-2, 4, 4, 6, 6-pentafluorotriphosphazene (HIE), (trimethylsilyl) phosphite (TMSPi), and tris(trimethylsilyl) borate (TMSB), trimethyl phosphate (TMP) and triphenyl phosphate (TPP).

7. The polymeric electrolyte according to any one of claims 1 to 7 wherein the ionic liquid is selected from one or more of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI), 1-ethyl-3-methylimidazolium bis(methanesulfonyl)imide (EMIFSI),tributylmethylammonium bis(trifluoromethanesulfonyl)imide (TBMA-TFSI) and 1-ethyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide (Py12TFSI), or wherein the ionic liquid is selected from one or more of 1 -vinyl-3-butyl imidazole bis(trifluoromethanesulfonyl) imide, 1-vinyl-3-butyl imidazole hexafluorophosphate, 1-vinyl-3-butyl imidazole tetrafluoroborate, 1-vinyl-3-butyl imidazole bromide, 1 -vinyl-3-ethyl imidazole bis (trifluoromethanesulfonyl) imide, 1-vinyl-3-ethyl imidazole hexafluorophosphate, 1-vinyl-3-ethyl imidazole tetrafluoroborate, 1-vinyl-3-ethyl imidazole bromide, 1-vinyl-3-methyl imidazole bis (trifluoromethanesulfonyl) imide, 1-vinyl-3-methyl imidazole iodide, 1-allyl-3-butyl imidazole bis (trifluoromethanesulfonyl) imide, 1-allyl-3-butyl imidazole hexafluorophosphate, 1-allyl-3-butyl imidazole tetrafluoroborate, 1-allyl-3-butyl imidazole imidazolium bromide, 1-allyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide, 1-allyl-3-ethylimidazolium hexafluorophosphate, 1-allyl-3-ethylimidazolium tetrafluoroborate, 1-allyl-3-ethylimidazolium bromide, 1-allyl-3-ethylimidazolium chloride, 1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-allyl-3-methylimidazolium hexafluorophosphate, 1-allyl-3-methylimidazolium tetrafluoroborate, 1-allyl-3-methylimidazolium bromide, 1-allyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazolium chloride, 1-methyl-3-propylimidazolium bromide, 1-allyl-3-vinylimidazolium bromide, 1-allyl-3-vinylimidazolium chloride, 1-allyl-3-vinylimidazolium tetrafluoroborate or a combination of two or more thereof, or wherein the ionic liquid is selected from one or more of N-butylpyridinium sulfonate, N-butylpyridinium sulfonate trifluoromethanesulfonate, N-butylpyridinium sulfonate hydrogen sulfate, butylpyridinium sulfonate lactone, N-propylpyridinium sulfonate, N-propylpyridinium sulfonate trifluoromethanesulfonate, N-propylpyridinium sulfonate hydrogen sulfate, propylpyridinium sulfonate lactone, 1 -butylsulfonic acid-3-methylimidazole trifluoroacetate, 1 -butylsulfonic acid-3-methylimidazole trifluoromethanesulfonate, 1-butylsulfonic acid-3-methylimidazole sulfate The invention can be selected from the group consisting of 1-butyl sulfonic acid-3-methylimidazolium hydrogen salt, 1-butyl sulfonic acid-3-methylimidazolium dihydrogen phosphate, 1-butyl sulfonic acid-3-methylimidazolium chloride, 1-sulfonic acid butyl-3-methylimidazolium inner salt, 1-propyl sulfonic acid-3-methylimidazolium trifluoroacetate, 1-propyl sulfonic acid-3-methylimidazolium trifluoromethanesulfonate, 1-propyl sulfonic acid-3-methylimidazolium hydrogen sulfate, 1-propyl sulfonic acid-3-methylimidazolium dihydrogen phosphate, 1-propyl sulfonic acid-3-methylimidazolium chloride, and 1-propyl sulfonic acid-3-methylimidazolium inner salt, or a combination of two or more thereof, preferably the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI).

8. The polymeric electrolyte according to any one of claims 1 to 7 wherein the mass content of the ionic liquid in the solid electrolyte is between 25 to 60 wt%.

9. The polymeric electrolyte according to any one of claims 1 to 8 wherein the mass ratio between the (flame-retardant) polymer and ionic liquid is between 3:1 to 3:3.

10. The polymeric electrolyte according to any one of claims 1 to 9 wherein the lithium salt is selected from the group consisting of: bis(trifluoromethanesulfonyl)imide lithium, bis(fluorosulfonyl)imide lithium, bis(nonafluorobutylsulfonyl)imide lithium (fluorosulfonyl)imide, (trifluoromethanesulfonyl)imide lithium, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium trifluoromethanesulfonate, and 4,5-dicyano-2-trifluoromethylimidazole lithium, or a combination of two or more thereof, preferably the lithium salt is lithium bis(trifluoromethane)sulfonimide (LiTFSI).

11. The polymeric electrolyte according to any one of claims 1 to 10 wherein the lithium salt is first dissolved in the IL before mixing with the flame-retardant polymer.

12. The polymeric electrolyte according to any one of claims 1 to 11 wherein the lithium salt : IL weight ratio is between 0.1 to 0.5.

13. The polymeric electrolyte according to any one of claims 1 to 12 wherein the ratio of polymer to (IL + Li salt) is 3:2.

14. The polymeric electrolyte according to any one of claims 1 to 13 wherein a catalyst is added with a weight ratio of 6:100 based on the weight of polymer in the mixture, preferably the catalyst is selected from benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide, or 2,2'-azobis (2-cyanobutane), dimethyl 2,2'-azobis(2-methylpropionate), 2,2'-azo bis(methy Ibutyronitrile), 2,2'-azo bis(iso-butyronitrile) (Al BN), and 2,2'-azobisdimethyl-valeronitrile (AMVN).

15. The polymeric electrolyte according to any one of claims 1 to 14 wherein the electrolyte comprises an ionic conductivity between 1.1 x 10-5to 6.0 ms / cm, and / or wherein the electrolyte comprises a tensile strength of between 1 to 30 MPa, and a tensile modulus of between 0.25 to 8 GPa, and / or wherein the electrolyte is used in un-manned aerial vehicles (UAVs), electric vehicles, in supercapacitors, in solid state batteries, for mobile phones, computers or for new energy vehicles, in unmanned aerial vehicles (UAV) and electrical vehicles.

16. A method of preparing a polymeric electrolyte, the method comprising:providing a first mixture of a polymer, an ionic liquid and a lithium salt;adding a catalyst to the first mixture to obtain a second mixture; andcuring the second mixture to obtain the polymeric electrolyte.

17. A polymeric electrolyte obtained by the method according to claim 16.

18. An energy storage composite comprising the polymeric electrolyte according to any one of claims 1 to 15 or 17.

19. A method of producing a polymeric electrolyte for an energy storage composite, the method comprising:providing a first mixture of a polymer, an ionic liquid and a lithium salt;adding a catalyst to the first mixture to obtain a second mixture;infusing the second mixture into an electrode; andcuring the infused electrode.

20. A polymer electrolyte battery comprising:an anode,a cathode;a separator; andthe polymeric electrolyte the according to any one of claims 1 to 15 or 17.

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