Polymer electrolytes

Abstract

The present invention relates to a polymer electrolyte comprising a co-polymer and alkali metal ions, the co-polymer comprising a first, a second and optionally a third constitutional unit, wherein, the first constitutional unit is formed from a first monomer selected from the group consisting of a 5 to 8 membered cyclic carbonate and a 5 to 8 membered cyclic ether, wherein said cyclic carbonate or cyclic ether comprises an unsaturated carbon-carbon bond or is substituted by a methylidene, vinyl or allyl group, and is unsubstituted or substituted by one or two C1-6alkyl or phenyl groups; the second constitutional unit is formed from a second monomer selected from the group consisting of a C1-6alkyl acrylate and a C1-6alkyl methacrylate, said C1-6alkyl of the C1-6alkyl acrylate or C1-6alkyl methacrylate substituted by one or more halogen atoms; and the third constitutional unit is formed from a third monomer selected from the group consisting of a poly(ethylene glycol) acrylate and poly(ethylene glycol) methacrylate Also disclosed herein is a method of preparing the polymer electrolyte of the present invention and a battery comprising the polymer electrolyte of the present invention.

Description

[0001] POLYMER ELECTROLYTES

[0002] FIELD OF INVENTION

[0003] The present invention relates to a polymer electrolyte comprising a co-polymer and alkali metal ions as defined herein. Also provided herein is a battery comprising the polymer electrolyte of the present invention, and a method of preparing the polymer electrolyte of the present invention.

[0004] BACKGROUND

[0005] The listing or discussion of a prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.

[0006] The advancement of high-energy density and safe lithium metal batteries (LMBs) necessitates innovations in electrolytes. Traditional liquid electrolytes, prone to continuous reactions with Li anode, not only compromise cyclable capacity but also pose significant safety hazards (Jagger and Pasta, Joule, 2023, 7, 2228-2244). In response, solid ceramic and polymer electrolytes have emerged as leading alternatives, offering enhanced safety and energy density. While ceramic electrolytes are distinguished by their superior ionic conductivity ( δLi+) and mechanical strength, their inherent rigidity poses challenges for conformal interfacial contact and large-scale manufacturing (Kim et al., Adv. Energy Mater., 2021 , 11 , 2002689). In comparison, solid polymer electrolytes (SPEs) offer better compatibility with existing manufacturing processes and superior interfacial wettability, positioning them as frontrunners for the mass production of semi or all-solid-state batteries (Han et al., Adv. Mater., 2023, 35, 2205194; Qi et al., Adv. Mater., 2023, 35, 2304951 , 2304951 ). Nevertheless, the insufficient ion dissociation and slow segmental relaxation time (10-7-106s) in common polymer matrices usually lead to low room temperature δLi+ (106~104S cm1). The δLi+ of SPEs can be enhanced by increasing the concentration and diffusion coefficient of the ionic species (Lopez et al., Nat. Rev. Mater., 2019, 4, 312-330; Zhao et al., Nat. Rev. Mater., 2020, 5, 229-252; Sangoro et al., Soft Matter, 201 1 , 7, 1678-1681 ; Bocharova and Sokolov, Macromolecules, 2020, 53, 4141—4157). Therefore, methods such as raising operational temperatures and adding liquid plasticizers are widely applied. However, these strategies consume excessive energy and inherit the drawbacks of liquid electrolytes, including flammability and electrochemical instability (Butzelaar et al., ACS Appl. Polym. Mater., 2021 , 3, 1573-1582). More importantly, the interfacial issues such as Li dendrite growth and cathodic degradation cannot be properly addressed. Recently, the manipulation of molecular structures in polymers has demonstrated huge potential in optimizing the properties of SPEs. In this aspect, compared with the limited main chain tailoring (e.g., the -C-O-C- bonds in PEO electrolytes), the manipulation of polymer side chain structures offers greater advantages in terms of functional integration and controllability. For instance, copolymer electrolytes with fixed anionic groups and ion-conducting ethylene oxide (EO) side chains have been constructed, resulting in high lithium transference number ( tLi+ )a nd fast site-to-site ion transport, thereby enhancing the ambient electrochemical performance and stabilizing lithium (Li) / electrolyte interfacial contact (Han et al., Nat. Mater., 2023, 1-8).

[0007] While there is recognized importance of side chains in shaping polymer properties, a demand- driven design strategy of SPEs based on the structure and functionality of side chains remains elusive. This gap in understanding hinders the development of novel polymer electrolytes and practical solid state batteries.

[0008] Thus, there remains a need for improved or alternative electrolytes for use in alkali metal batteries, in particular, improved or alternative polymer electrolytes for solid-state alkali metal batteries, such as solid state lithium-metal batteries.

[0009] SUMMARY OF INVENTION

[0010] The present invention provides a polymer electrolyte comprising a co-polymer and alkali metal ions, the co-polymer comprising a first, a second and optionally a third constitutional unit, wherein, the first constitutional unit is formed from a first monomer selected from the group consisting of a 5 to 8 membered cyclic carbonate and a 5 to 8 membered cyclic ether, wherein said cyclic carbonate or cyclic ether comprises an unsaturated carbon- carbon bond or is substituted by a methylidene, vinyl or allyl group, and is unsubstituted or substituted by one or two C1-6alkyl or phenyl groups; the second constitutional unit is formed from a second monomer selected from the group consisting of a C1-6alkyl acrylate and a C1-6alkyl methacrylate, said C1-6alkyl of the C1-6alkyl acrylate or C1-6alkyl methacrylate substituted by one or more halogen atoms; and the third constitutional unit is formed from a third monomer selected from the group consisting of a poly( ethylene glycol) acrylate and poly( ethylene glycol) methacrylate.

[0011] The present invention also provides a battery comprising the polymer electrolyte of the present invention, in certain preferred embodiments, the battery of the present invention is an alkali metal battery, for example, a lithium-metal battery. The present invention also provides a method of preparing the polymer electrolyte of the present invention for use in an alkali metal battery, said method comprising forming the polymer electrolyte of the present invention by a polymerisation reaction between the first monomer, second monomer, and optionally the third monomer as defined herein, on a surface of a substrate.

[0012] Preferred but optional features are set out in the dependent claims. Additional aspects and embodiments of the polymer electrolyte, battery, methods and kits of the present invention will be apparent from the following description, drawings and claims. As can be appreciated from the foregoing and following description, each and every feature described herein, and each and every combination of two or more such features, is included within the scope of the present disclosure provided that the features included in such a combination are not mutually inconsistent. In addition, any feature or combination of features may be specifically excluded from any embodiment.

[0013] BRIEF DESCRIPTION OF DRAWINGS

[0014] FIG. 1 depicts the materials used in this invention.

[0015] FIG. 2 depicts the reaction equation and photographs showing the copolymerization process of copolymer electrolyte (CPE) (65 °C with 0.5 wt.% azobisisobutyronitrile (AIBN)).

[0016] FIG. 3 depicts tensile stress-strain curves of copolymer (CP) with varying ratios.

[0017] FIG. 4 depicts the (a) side chain design strategy of polymer electrolyte matrix (left) and the selected side chains (right); (b) the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbitals (HOMO) energy levels of P(HFBA-VC), P(TFPA-VC), and P(TFEA-VC); (c) linear sweep voltammetry (LSV) of selected polymer electrolytes (Li| |polymer electrolyte|| Al, 0.1 mV s1); (d) structures and binding energies of P(TFEA-VC), P(TFPA-VC), and P(HFBA-VC) calculated by density functional theory (DFT); (e) ionic conductivity- temperature relationship of CPE, P(TFEA-VC), P(TFPAVC), and P(HFBA-VC); and (f) glass transition temperatures (Tg) of the studied samples. (HFBA: 2,2,3,4,4,4-hexafluorobutyl acrylate; TFPA: 2,2,3,3-tetrafluoropropyl acrylate; TFEA: 2,2,2-trifluoroethyl acrylate; VC: vinylene carbonate)

[0018] FIG. 5 depicts (a) structures TFEA, PTFEA, TFPA, PTFPA, HFBA and PHFBA; (b) the LUMO and HOMO geometry structures of PTFEA, PTFPA, and PHFBA; (c) LSV test of three fluorinated homopolymers with 1 .3 M LiTFSI and 0.2 M LiDFOB, scant rate: 0.1 mV s1, using polished aluminum foil as the working electrode and Li foil as the counter and reference electrodes. (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide; LiDFOB: lithium difluorooxalatoborate)

[0019] FIG. 6 depicts the electrochemical impedance spectroscopy (EIS) of PTFEA and PTFPA- based electrolytes (1.3 M LiTFSI and 0.2 M LiDFOB). stainless steel||polymer electrolyte! | stainless steel.

[0020] FIG. 7 depicts the regulation of CPEs. (a) Ionic conductivity-temperature relationship of P(TFEA-VC), P(TFPA-VC), and P(HFBA-VC) with 1.3M LiTFSI and 0.2M LiDFOB. (b) LSV curve of three copolymers with 1.3M LiTFSI and 0.2M LiDFOB. (c) Symmetric Li cell cycling performances of P(TFEA-VC), P(TFPA-VC), and P(HFBA-VC). (d) Coulombic efficiency test of Li||Cu cells. (0.1 mA cm-2with a capacity of 0.1 mAh cm-2).

[0021] FIG. 8 depicts (a) the LUMO and HOMO energy levels of vinylene carbonate (VC) monomer and poly (vinylene carbonate) (PVC) homopolymer, the molecular structures and corresponding visual LUMO and HOMO geometry structures are shown as insets; and (b) LSV curves of vinylene carbonate (VC) and poly (vinylene carbonate) (PVC) (1.3 M LiTFSI and 0.2 M LiDFOB), scant rate: 0.1 mV s1, using aluminum foil as the working electrode and Li foil as the counter and reference electrodes.

[0022] FIG. 9 depicts (a) in-situ fourier transform infrared spectroscopy (FT-IR) of CP during copolymerization and (b) corresponding conversion rate of TFEA. (C-F bond was set as reference); and (c) in-situ Raman of CP during copolymerization and (d) corresponding conversion rate of VC.

[0023] FIG. 10 depicts the DSC of selected samples with the scanning rate of 10 °C min1.

[0024] FIG. 1 1 depicts (a) the photograph of the crosslinked copolymer electrolyte P(TFEA-VC- PEGDA) and CPE; and (b) ionic conductivity-temperature relationship of P(TFEA-VC-PEGDA) and CPEs. (PEGDA: polyethylene glycol diacrylate)

[0025] FIG. 12 depicts the Dynamic Mechanical Analyzer (DMA) traces of (a) P(TFEA05-VC05) and (b) CPE.

[0026] FIG. 13 depicts the (a) EIS and (b) corresponding histogram showing the ionic conductivities of CPE with different Li salt content; and (c) LSV curves and (d) corresponding histogram showing the oxidation resistance of CPE with different Li salt content. FIG. 14 depicts the molecule structures of the studied monomers.

[0027] FIG. 15 depicts (a) EIS and (b) LSV of CPE with varying monomer volume ratios.

[0028] FIG. 16 depicts (a) FT-IR spectra of monomers and polymer matrices; (b) differentiated thermogravimetry (DTG) and thermogravimetric analysis (TGA) (insert) of PTFEA, PVC, CP, and CPE; (c) small angle X-ray scattering (SAXS) of PTFEA, CP, and CPE (insert is the two- dimensional SAXS ring); (d) tensile stress-strain curves of CPE, CP, PTFEA and PVC; (e) elastic fatigue testing of CPE; and (f) flame resistance test of CPE and commercial liquid electrolyte.

[0029] FIG. 17 depicts the Raman spectra of selected samples. The calculated vibration modes of VC and TFEA monomers are shown near their corresponding peaks.

[0030] FIG. 18 depicts the in-situ Raman spectra, which show the vanishing of unsaturated bond vibrates of VC and TFEA monomers in the copolymerization of CPE.

[0031] FIG. 19 depicts the FT-IR of VC, PVC, TFEA, and PTFEA.

[0032] FIG. 20 depicts the Raman spectra of VC, PVC, TFEA, and PTFEA.

[0033] FIG. 21 depicts (a) polymerization equation and photographs of VC and PTFEA monomers; (b) the yield rates of PTFEA, PVC, and CPE, the yield rates were the ratio of actual yield / initial weight x 100%. (65°C, 12h)

[0034] FIG. 22 depicts the1H nuclear magnetic resonance (NMR) spectrum of selected samples. The standard spectra are available from the Spectral Database for Organic Compounds SDBS (https: / / sdbs.db.aist.go.jp / sdbs / cgi-bin / direct_frame_top.cgi}.

[0035] FIG. 23 depicts the photographs showing the solubility of CPE in 9 solvents under ultrasound and heating. CPE cannot completely dissolve in any of these solvents due to the high chemical stability and low surface energy of fluorinated groups. It swells in dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), acetone, and dimethylsulfoxide (DMSO).

[0036] FIG. 24 depicts (a) single ion curves of VC and oligomers during simultaneous TGA for CP; (b-d) stacked plot diagram of evolved gases during simultaneous TGA for CP; and (e) matrix- assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS) profile of oligomers of the CP extracted by tetrahydrofuran (THF).

[0037] FIG. 25 depicts SAXS of PTFEA, CP, and CPE.

[0038] FIG. 26 depicts atomic force microscope (AFM) height image (left) and phase image (right) of CPE.

[0039] FIG. 27 depicts FT-IR spectra of selected samples.

[0040] FIG. 28 depicts scanning electron microscopy (SEM) images of (a) PTFEA, (b) PVC, and (c) CP.

[0041] FIG. 29 depicts photographs showing the elasticity of CPE with different TFEA / VC ratios.

[0042] FIG. 30 depicts photographs showing the elasticity of CPE at different temperatures.

[0043] FIG. 31 depicts the optimized Li+coordination and transpiration environment enabled by PVC and PTFEA side chains - glass transition temperature (Tg) of selected samples.

[0044] FIG. 32 depicts (a) the comparison of dielectric constant among the selected polymers and solvents; (b) ionic conductivities (30 °C) of CPE and other gel electrolytes comprising PTFEA skeletons (50 vol%) and liquid plasticizers (50 vol%) with varying e; raman spectra of (c1) PTFEA electrolyte and (c2) CPE; radial distribution function (RDF) and coordination number (CN) of (d1) PTFEA electrolyte and (d2) CPE; molecular dynamics (MD) snapshots of (e1) PTFEA electrolyte and (e2) CPE; migration trajectories of five randomly selected Li+within 2 ns in (fi) P(TFEAVC) electrolyte and (f2) CPE; (g) mean square displacement (MSD) of Li+in PTFEA, P(TFEA-VC), and CPE.

[0045] FIG. 33 depicts the Nyquist plot of CP and the fitted curve using Zfit-Biologic.

[0046] FIG. 34 depicts the EIS of CP(TFEA0.9-PEGMEA0.1) and CP(TFEA0.45-PEGMEA0.1)+VC0.45. (30 °C) for the calculation of dielectric constants.

[0047] FIG. 35 depicts the EIS of CP(TFEA0.9-PEGMEA0.1) and CP(TFEA0.45-PEGMEA0.1)+VC0.45. (30 °C) for calculation of ionic conductivities. FIG. 36 depicts the chain unit structures and polymer cells of (a) CPE, (b) PTFEA, and (c) P(TFEA-VC) for MD simulation cell.

[0048] FIG. 37 depicts the electrochemical performances of symmetric Li cells, (a) Critical current density (CCD) and (b) Rate tests of CPE-based symmetric Li cells, (c) Cycling performance at 0.8 mA cm2for CPE, P(TFEA-VC), and PVC-based symmetric cells, (d) Long-term cycling performance at 0.2 mA cm2. All tests were performed at 25±3 °C.

[0049] FIG. 38 depicts the cycling performances of symmetric Li cells using different buffer materials to avoid short-circuit. The current density is 0.2 mA cm2.

[0050] FIG. 39 depicts the EIS spectrum of CPE-based symmetric Li cell tested during long-term cycling.

[0051] FIG. 40 depicts the CE tests of Li plating-stripping with a cut-off capacity of 0.1 mAh cm-2in Li ||Cu cells.

[0052] FIG. 41 depicts the characterizations of Li surface, (a) XPS spectra of C 1 s, O 1 s, F 1s and corresponding solid electrolyte interphase (SEI) atomic ratios in (b) CPE and (c) P(VC- PEGMEA). (d) Schematics of the surface configuration in CPE and P(VC-PEGMEA). (e) SEM images of deposited Li (1 .5 mAh cm2) in CPE and P(VC-PEGMEA). Scale bar of 10 μm.

[0053] FIG. 42 depicts the X-ray photoelectron spectroscopy (XPS) spectra at different etching times of the SEI in CPE and PVC. (a) S2p, (b) N1 s, (c) B1s.

[0054] FIG. 43 depicts the SEM images of deposited Li in (a) CPE and (b) P(VC-PEGMEA) at different magnifications.

[0055] FIG. 44 depicts photographs showing the surface morphology in CPE and P(VC-PEGMEA) with a cut-off capacity of 1 mAh cm-2in Li| |Cu cells.

[0056] FIG. 45 depicts (a) optical observation showing the growth of Li in CPE and liquid electrolyte (LE); and (b) SEM image of the plated Li on Cu (1 mAh cm2). Scale bar of 10 μm.

[0057] FIG. 46 depicts Nyquist plots and steady-state current measurement of the symmetric Li cells under 10 mV polarization for 3 hours in (a) CPE and (b) PVC. FIG. 47 depicts (a) structures and binding energies of P(TFEA-VC) (left) and PEG Tri coordination complex (right) calculated by DFT; and (b) schematics showing the steric effect of polymer structures.

[0058] FIG. 48 depicts the electrochemical performances of CPE-based full cells - LSV curves of CPE (1.3M LiTFSI and 0.2M LiDFOB), CPE with single salt (1.5M LITFSI), and P(VC- PEGMEA) (1 .3M LiTFSI and 0.2M LiDFOB). Scan rate of 0.1 mV s1. Charging / discharging curves of CPE.

[0059] FIG. 49 depicts the LSV curves of CPE. Li foils act as the counter and reference electrodes and polished Al, porous Al, and porous carbon (Freudenberg H23C6)) act as the working electrodes. (Scan rate of 0.1 mV s1). The reduced oxidation resistance voltage on the porous electrode can be ascribed to the larger active surface area.

[0060] FIG. 50 depicts the charging / discharging curves of NCM81 1 full cell using (a) CPE (b) CPE with single LiTFSI salt (1 .5 M) and (c) P(VC-PEGMEA). The cell cycles at 0.1 C for 3 cycles and then at 0.2 C.

[0061] FIG. 51 depicts the electrochemical performances of CPE-based full cells, (a) Rate performance of CPE-based NCM81 1 full cell, (b) Cycling performance of CPE and liquid electrolyte (LE)-based NCM811 full cells, (c) Cycling performance of CPE-based NCM81 1 pouch cell, (d) TEM images of the cycled NCM811 cathodes, (e) Cycling performance of high- loading LFP full cell using CPE. (f) Photographs showing the CPE-based flexible battery.

[0062] FIG. 52 depicts the cycling performances of CPE-based NCM811 full cells at different discharge rates.

[0063] FIG. 53 depicts the electrochemical performance of CPE-based high-loading NCM81 1 cathode.

[0064] FIG. 54 depicts the optimised elastic ternary copolymer electrolyte (CPE), developed through deciphering and integrating functionalized side chains, exhibits a superior ionic conductivity of 2.19 x 103S cm1(30 °C), oxidation-resistance up to 4.97 V, 2700% elongation and fire resistance. Its dual physical-chemical protection endows Li||Li cells a high CCD of 2.55 mA cm2and over 1000 hours of stable cycling at 0.8 mA cm2. DESCRIPTION

[0065] As discussed in more detail below, the present inventors have developed a class of polymer electrolytes suitable for use as solid electrolytes in alkali metal batteries. The polymer electrolytes comprise a co-polymer and alkali metal ions. The co-polymer of the polymer electrolytes of the present invention comprise halogenated acrylates or halogenated methacrylates as a soft and elastic constituent and cyclic carbonates or cyclic ethers as a hard and ion-conducting constituent. In addition, the present inventors have found that the incorporation of poly( ethylene glycol) acrylate or poly( ethylene glycol) methacrylate into the co-polymer can decrease the glass transition point of the co-polymer and promote segmental movement.

[0066] Thus, the polymer electrolyte of the present invention comprises a co-polymer and alkali metal ions, and the co-polymer comprises a first, a second and optionally a third constitutional unit, wherein, the first constitutional unit is formed from a first monomer selected from the group consisting of a 5 to 8 membered cyclic carbonate and a 5 to 8 membered cyclic ether, wherein said cyclic carbonate or cyclic ether comprises an unsaturated carbon- carbon bond or is substituted by a methylidene, vinyl or allyl group, and is unsubstituted or substituted by one or two C1-6alky I or phenyl groups; the second constitutional unit is formed from a second monomer selected from the group consisting of a C1-6alkyl acrylate and a C1-6alkyl methacrylate, said C1-6alkyl of the C1-6alkyl acrylate or C1-6alkyl methacrylate substituted by one or more halogen atoms; and the third constitutional unit is formed from a third monomer selected from the group consisting of a poly( ethylene glycol) acrylate and poly( ethylene glycol) methacrylate.

[0067] The term “co-polymer” as used herein refers to a polymer containing two or more different constitutional units, formed, for example, by co-polymerizing two or more different monomers and / or chemically modifying one or more constitutional units of a precursor polymer. Typically, the polymer electrolyte of the present invention comprises a co-polymer that is a random co- polymer in which the two or more different constitutional units are arranged in a random sequence. The term “constitutional unit’ as used herein refers to a species of atom or group of atoms present in a chain of a polymer. The polymer electrolyte of the present invention may be referred to herein as a copolymer electrolyte or “CPE”. The polymer electrolyte of the invention is a solid at the typical operation temperatures of an alkali metal battery (e.g. from about -30 °C to about 150 °C, such as about 0 °C to about 50 °C. The term “comprising” as used herein may be interpreted as requiring the features mentioned, but not limiting the presence of other features. Alternatively, the term “comprising” may also relate to the situation where only the components / features listed are intended to be present (e.g. the word “comprising” may be replaced by the phrases “consists of or “consists essentially of”). It is explicitly contemplated that both the broader and narrower interpretations can be applied to all aspects and embodiments of the present invention. In other words, the word “comprising” and synonyms thereof may be replaced by the phrase “consisting of” or the phrase “consists essentially of’ or synonyms thereof and vice versa.

[0068] As used herein, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. The term “plurality” as used herein means two or more.

[0069] The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, within 1%, within 0.5%, within 0.1%, within 0.05%, within 0.01 %, within 0.005%, or within 0.001% of a stated value or of a stated limit of a range, and includes the exact stated value or range.

[0070] The first constitutional unit of the co-polymer is formed from a first monomer selected from the group consisting of a 5 to 8 membered cyclic carbonate and a 5 to 8 membered cyclic ether, wherein said cyclic carbonate or cyclic ether comprises an unsaturated carbon-carbon bond or is substituted by a methylidene, vinyl or allyl group, and is unsubstituted or substituted by one or two C1-6alkyl or phenyl groups.

[0071] For the avoidance of doubt, the term “methylidene group” as used herein refers to a group that has the structure , the term “vinyl group” as used herein refers to a group that has the structure :and the term “allyl group” as used herein refers to a group that has the structure , wherein indicates the point of attachment of the methylidene, vinyl or allyl group to the 5 to 8 membered cyclic carbonate or the 5 to 8 membered cyclic ether.

[0072] In certain embodiments, the first monomer is selected from the group consisting of a 5 to 8 membered cyclic carbonate and a 5 to 8 membered cyclic ether, wherein said cyclic carbonate or cyclic ether comprises an unsaturated carbon-carbon bond or is substituted by a methylidene or vinyl group. For example, the first monomer may be selected from the group consisting of vinylene carbonate, vinylethylene carbonate, and 2-methylene-1 ,3-dioxepane. Without wishing to be bound by theory, it is believed that the first constitutional unit of the co- polymer provide rigidity to the co-polymer structure and, by way of its polar nature, enable efficient ion separation and short-range ion-hopping. In certain embodiments, the first monomer is vinylene carbonate.

[0073] The second constitutional unit of the co-polymer is formed from a second monomer selected from the group consisting of a C1-6alkyl acrylate and a C1^alkyl methacrylate, said C1-6alkyl of the C1-6alkyl acrylate or C1-6alkyl methacrylate substituted by one or more halogen atoms. Typically, the C1-6alkyl group of the C1-6alkyl acrylate or C1-6alkyl methacrylate is substituted by one or more Cl or F atoms, for example, one or more F atoms. For example, the second monomer may be selected from the group consisting of a C1-6alkyl acrylate or a C1-6alkyl methacrylate, said C1-6alkyl group of the C1-6alkyl acrylate or C1-6alkyl methacrylate substituted by three or more F atoms. Without wishing to be bound by theory, it is believed that the second constitutional unit of the co-polymer imparts elasticity to the co-polymer. The halogenated pendent group of the second constitutional unit also believed to stabilise the polymer backbone and enhance its antioxidant ability. This can result in an increase in the oxidation resistance voltage of a battery comprising the polymer electrolyte compared to when liquid electrolytes are used. It also allows the polymer electrolyte to be paired with high-voltage cathode materials, which can increase the energy density of the battery and its cycle stability. In certain embodiments, the second monomer is selected from the group consisting of 2,2,2 - Trifluoroethyl acrylate (TFEA), 2,2,3,3-Tetrafluoropropyl acrylate (TFPA), 2, 2, 3, 4, 4,4,4- hexafluorobutyl acrylate (HFBA), 2-perfluorohexylethyl acrylate, 2-(perfluorobutyl)ethyl acrylate, 1 ,1 ,2,2-tetrafluoroethyl acrylate, 2-(perfluorooctyl)ethyl methacrylate, and 3,3,4,4,5,5,6,6,6-nonafluorohexyl acrylate, for example, the second monomer is 2,2,2- trifluoroethyl acrylate (TFEA).

[0074] As used herein, the term “alkyl” means both linear and branched chain saturated hydrocarbon groups. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, isobutyl, sec-butyl, pentyl and hexyl groups. Examples of linear alkyl groups include methyl, ethyl, n-propyl, isopropyl and n-butyl groups. Examples of branched alkyl groups include tert- butyl, sec-butyl, isobutyl, 1 -ethylpropyl and 1 -ethylbutyl groups. As used herein, the term "halogen" refers to fluorine, chlorine, bromine or iodine.

[0075] The third constitutional unit of the co-polymer is formed from a third monomer selected from the group consisting of a poly( ethylene glycol) acrylate and poly( ethylene glycol) methacrylate. For example, the third monomer may be poly( ethylene glycol) monomethyl ether acrylate. Without wishing to be bound by theory, it is believed that the third constitutional unit of the co- polymer promotes segmental motion and interchain ion migration within the co-polymer, which imparts toughness whilst also contributing to ion conductivity of the co-polymer. Typically, the poly( ethylene glycol) acrylate or poly(ethylene glycol) methacrylate has a number average molecular weight (Mn) of from about 200 g / mol to about 3000 g / mol, for example from about 400 g / mol to about 1500 g / mol (e.g. about 900 g / mol).

[0076] The term “number average molecular weight” or “Mn” as used herein refers to the arithmetic mean of the molecular weights of the individual molecules of a given polymer sample. It may be calculated using equation (1 ): where x, is the number fraction of molecules with molecular weight Mi Methods for determining the “number average molecular weight” of a poly( ethylene glycol) acrylate or polyethylene glycol) methacrylate are known in the art. For example, the number average molecular weight of the poly( ethylene glycol) acrylate or poly( ethylene glycol) methacrylate, may be determined by Gel Permeation Chromatography (GPC), for example by GPC at room temperature (e.g. 20-25 °C, e.g. about 25 °C), or about 30-40 °C (e.g. about 30 °C or about 40 °C).

[0077] As demonstrated by the Examples section herein, the present inventors have exemplified a polymer electrolyte of the present invention that incorporates three functionalized side chains of copolymerizing 2,2,2-trifluoroethyl acrylate (TFEA), vinylene carbonate (VC), polyethylene glycol monomethyl ether acrylate (PEGMEA), and Li salts (LiTFSI and LiDFOB). The fluorine- rich TFEA side chain contributes to improved stability and interfacial compatibility, the highly polar VC side chain facilitates efficient Li salt dissociation and ion migration, and the PEGMEA side chain with high spatial freedom promotes segmental motion and interchain ion exchanges. The resulting polymer electrolyte was shown to demonstrate high ionic conductivity of 2.19x10-3S cm1at 30 °C ( (δLi+), a high lithium transference number of 0.59, exceptional antioxidant capacity of up to 4.97 V, remarkable elasticity (2700%), and non-flammability. The fluorine-rich organic-inorganic hybrid solid electrolyte interphase (SEI) and elastic polymer electrolyte was found to enable a dual physical-chemical protection for an Li anode, and symmetric Li cells was found to achieve a critical current density (CCD) of 2.55 mA cm2and maintain cyclability of over 1000 hours at 0.8 mA cm2. A LiNi08Co0 1Mn0.1O2(NCM81 1 ) full cell comprising the polymer electrolyte of the present invention was also demonstrated to exhibit high capacity retention (-90%, 0.5C) after 200 cycles. Amongst other beneficial effects, the high ionic conductivity and oxidation stability of the polymer electrolyte makes it particularly suitable for use in high-loading high voltage cathodes (e.g. Lithium Cobalt Oxide (LiCoO2) or Lithium Nickel Manganese Oxide (LiNi0.5Mn1.5O4)), and the elastic and non-flammable nature of the polymer electrolyte enables it to accommodate lithium volume changes during continuous plating / striping and hinder battery thermal runaway, thus improving safety of lithium-metal batteries.

[0078] Thus, in certain preferred embodiments, the polymer electrolyte of the invention comprises a co-polymer comprising a first, a second and optionally a third constitutional unit, wherein the first constitutional unit is formed from vinylene carbonate, the second constitutional unit is formed from a C1 -6alkyl acrylate or C1-6alkyl methacrylate, said C1-6al kyl of the C1-6alkyl acrylate or C1-6alkyl methacrylate substituted by two or more fluorine atoms, and the third constitutional unit is formed from a poly( ethylene glycol) acrylate or poly( ethylene glycol) methacrylate. For example, the polymer electrolyte of the present invention may comprise a co-polymer comprising a structure according to formula (I): wherein, each m , n and p are integers independently selected from 1 to 10; each s is an integer selected from 1 to 20 (e.g. 1 to 15 or 10 to 15, for example 13);

[0079] R1and R2are each independently H or methyl;

[0080] X is C1-10alkylene optionally substituted by one or more fluorine atoms; and

[0081] Y is H or a fluorine atom.

[0082] For example, in formula (I), R1and R2may each be H or methyl, X may be C1-8alkylene substituted by one or more fluorine atoms, and Y may be H or a fluorine atom. For example, R1and R2are each H or methyl, X is C1-salkylene (e.g. C1alkylene) optionally substituted by one or more fluorine atoms, and Y may be H or a fluorine atom.

[0083] In certain embodiments, R1and R2are each H, X is C1alkylene optionally substituted by one or two fluorine atoms, and Y is H or a fluorine atom. For example, R1and R2are each H, X is C1alkylene (i.e. X is -CH2-), and Y is a fluorine atom. Or, for example, R1and R2are each H, X is C1alkylene substituted by one or two fluorine atoms, and Y is a fluorine atom. Or, for example, R1and R2are each H, X is C1alkylene substituted by one or two fluorine atoms, and Y is H. In certain other embodiments, R1and R2are each H, X is C2alkylene substituted by two fluorine atoms (e.g. X is -CH2CF2-), and Y is H or a fluorine atom. In certain other embodiments, R1and R2are each H, X is C3alkylene substituted by three or more fluorine atoms (e.g. X is -CH2CF2CHF-), and Y is H or a fluorine atom.

[0084] In certain exemplary embodiments, R1and R2are each H, X is C1alkylene (i.e. X is -CH2-), and Y is a fluorine atom. For example, the polymer electrolyte of the invention may comprise a co-polymer comprising a first, second and third constitutional unit, wherein the first constitutional unit is formed from vinylene carbonate, the second constitutional unit is formed from 2,2,2-trifluoroethyl acrylate (TFEA), and the third constitutional unit is formed from poly( ethylene glycol) monomethyl ether acrylate.

[0085] In certain embodiments, the polymer electrolyte of the present invention is formed by a polymerisation reaction between the first, second, and third monomers, wherein the first, second, and third monomers react in a reaction mixture comprising equal to or less than 70 mol% of the second monomer relative to the total number of moles of the first, second, third monomer in the reaction mixture. The present inventors have found that including the second monomer at an amount equal to or less than 70 mol% relative to the total number of moles of the first, second, third monomer in the reaction mixture provides a co-polymer with especially suitable properties for use in an alkali metal battery.

[0086] Typically, the reaction mixture comprises about 25 mol% to about 40 mol% (e.g. about 30 mol% to about 40 mol%) of the second monomer relative to the total number of moles of the first, second, third monomer in the reaction mixture.

[0087] In certain embodiments, the co-polymer of the polymer electrolyte of the present invention comprises the first and second constitutional units at a molar ratio of first to second constitutional unit of from about 8:1 to about 1 :8, for example from about 7:1 to about 1 :7, about 6:1 to about 1 :6, about 5:1 to about 1 :5, about 4:1 to about 1 :4, about 3:1 to about 1 :3, for example 2:1 .

[0088] In certain embodiments wherein the co-polymer of the polymer electrolyte of the present invention comprises the third constitutional unit, the co-polymer may comprise the first and third constitutional units at a molar ratio of first to third constitutional unit of from about 600:1 to about 1 :1 , for example from about 600:1 to about 20:1 , for example about 600:1 , about 60:1 , or about 30:1. For example, in certain embodiments wherein the co-polymer of the polymer electrolyte of the present invention comprises the third constitutional unit, the first, second and third constitutional unit are present in the co-polymer at a molar ratio of first, second to third constitutional unit of from about 1 :1 :1 to 600:600:1 , for example, 1 :1 :1 to 600:300:1 , such as about 600:300:1 , about 60:30:1 , or about 30:15:1 (e.g. about 585:290:1 , about 59:29:1 , or about 29:15:1)

[0089] As disclosed here, the polymer electrolyte of the present invention also comprises alkali metal ions. Typically, the alkali metal ions are selected from the group consisting of lithium ions, sodium ions, potassium ions, and a combination of two or more thereof. In certain exemplary embodiments, the alkali metal ions are lithium ions. The alkali metal ions may be derived from any suitable alkali metal salt. As described in the Examples section herein, the alkali metal ions are added into the polymer electrolyte during manufacture in the form of an alkali metal salt. Thus, the polymer electrolyte may comprise both the alkali metal ions and the counter ion of the alkali metal salt. Thus, in certain embodiments, the polymer electrolyte may be considered to comprise an alkali metal salt. In certain embodiments, when the alkali metal ions present in the polymer electrolyte of the present invention are lithium ions, the alkali metal salt is selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFS I), lithium difluorooxalatoborate (LiDFOB), and a combination of two or more thereof. For example the one or more alkali metal salts present in the polymer electrolyte of the present invention may be a combination of LiTFSI and LiDFOB. In embodiments wherein the one or more alkali metal salts may be a combination of LiTFSI and LiDFOB, the combination may comprise LiTFSI and LiDFOB at a molar ratio of LiTFSI to LiDFOB of from about 1 :20 to about 20:1 , for example about 1 :15 to about 15:1 , about 1 :13 to about 13:1 (e.g. about 13:2).

[0090] In certain embodiments, when the alkali metal ions present in the polymer electrolyte of the present invention are sodium ions, the alkali metal salt may be selected from the group consisting of sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, sodium tetrafluoroborate, sodium trifluoroacetate, sodium trifluoromethanesulfonate, sodium fluorosulfonyl imide), and a combination of two or more thereof.

[0091] In certain embodiments, when the alkali metal ions present in the polymer electrolyte of the present invention are potassium ions, the alkali metal salt may be selected from the group consisting of potassium hexafluorophosphate, potassium bis(trifluoromethanesulfonyl)imide, potassium tetrafluoroborate, potassium trifluoromethanesulfonate, potassium trifluoroacetate, and a combination of two or more thereof.

[0092] In one exemplary embodiment, the polymer electrolyte of the present invention comprises a structure according to formula (la):

[0093] wherein, n, m and p each represent integers corresponding to the number of each constitutional unit present in the co-polymer. The lithium ions present in the polymer electrolyte of the present invention comprising a structure according to formula (la) may be derived from one or more alkali metal salts selected from the group consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalatoborate (LiDFOB), and a combination of two or more thereof. In certain exemplary embodiments, the lithium ions present in the polymer electrolyte of the present invention comprising a structure according to formula (la) are derived from a combination of LiTFSI and LiDFOB, and more specifically, a combination of LiTFSI and LiTFSI with a molar ratio of LiTFSI to LiDFOB of from 1 :20 to about 20:1 , for example about 1 :15 to about 15:1 , about 1 :13 to about 13:1 (e.g. about 13:2).

[0094] Typically, the polymer electrolyte of the present invention has an elasticity of greater than about 100%, for example greater than about 500%, greater than about 1000%, greater than about 1500%, greater than about 2000%, greater than about 2500%, or greater than about 3000% (e.g. about 2700%). The % elasticity of the polymer electrolyte corresponds to the increase in size of the polymer electrolyte when stretched relative to the polymer electrolyte when in a relaxed form. In particular, the % elasticity of the polymer electrolyte of the present invention was determined using a cyclic elasticity test with constant strain rate of 100 mm min-1for both stretching and relaxing with various predetermined maximum strains under ambient conditions (i.e. room temperature and atmospheric pressure). In certain embodiments, the polymer electrolyte of the present invention displays an ionic conductivity of at least about 1 x104S cm1at 30 °C (e.g. about 1 x103S cm1at 30 °C). For example, the polymer electrolyte may have an ionic conductivity of at least about 1 X103S cm- 1 at 30 °C, such as about 1 .5x103S cm1to about 2.5x10-3S cm1at 30 °C (e.g. 2.19x103S cm1at 30 °C). The ionic conductivity of the polymer electrolyte may be determined using electrochemical impedance spectroscopy, and a specific method for determining the ionic conductivity of the polymer electrolyte is provided in the Examples section herein.

[0095] In certain embodiments, when the alkali metal ions in the polymer electrolyte are lithium ions, the polymer electrolyte of the present invention displays a lithium transference (tu+) number when used in a lithium-metal battery of at least about 0.1 , for example about 0.1 to about 1 (e.g. 0.6, or about 0.59). The lithium transference (ki+) of the polymer electrolyte of the present invention may be calculated using equation (2): wherein, l0and lsare the initial and steady-state currents, AV is the potential applied across the cell, and R0and Rsare the initial and steady-state interfacial resistances of the passivation layers on the metallic Li electrode. The lithium transference number is the ratio of the electric current derived from the cation to the total electric current. If the lithium transference number is close to 1 , it implies that the ion conducting performance of the polymer electrolyte is mainly accomplished by the cation.

[0096] In certain embodiments, the polymer electrolyte of the present invention, when used as an electrolyte for a lithium-metal battery, displays an antioxidant capacity of greater than about 2 V, for example about 4.97 V. The oxidation capacity of the polymer electrolyte refers to the highest oxidation potential at which the polymer electrolyte remains stable. Beyond the oxidation capacity, the polymer electrolyte may begin to undergo oxidation reactions, leading to degradation and possibly the formation of byproducts that could interfere with the performance of the polymer electrolyte.

[0097] The present invention also provides a battery comprising the polymer electrolyte of the present invention. For example, the battery may be an alkali metal battery, such as a lithium-metal battery, a sodium-metal battery, a potassium-metal battery, a lithium-ion battery, a sodium-ion battery, or a potassium-ion battery. In certain preferred embodiments, the battery of the present invention is a lithium-metal battery. A battery of the present invention will typically comprise an anode, a cathode, a separator that separates the anode and the cathode, and the polymer electrolyte of the present invention. The selection of suitable materials and components for a battery is well understood by the person skilled in the art. The cathode of the batteries disclosed herein comprise any suitable positive active material, and the anode may be composed of any suitable negative active material.

[0098] In a lithium-metal battery, the anode is made of metallic lithium. Similarly, in a sodium-metal battery, the anode is made of metallic sodium, and in a potassium-metal battery the anode is made of metallic potassium. In lithium-ion, sodium-ion, and potassium-ion batteries, the anode typically comprises an anode active material. Suitable anode active materials include, but are not limited to, a carban-based material, a silicon-based material, a tin-based material, an antimony-based material, a lead-based material, a metal oxide (e.g. a lithium, sodium or potassium metal oxide). The carbon-based material may be, for example, soft carbon or hard carbon or a graphite-based material such as artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, or the like. Carbon nano-tube materials may be used. The silicon-based material may be, for example, silicon, a silicon oxide, a silicon-containing alloy, a mixture of the graphite-based material with the foregoing materials, or the like. The silicon oxide may be represented by SiOx (0< x<2). The silicon containing alloy may be an alloy including silicon in the largest amount of the total metal elements (e.g., silicon being the metal element that is present in the largest amount of all the metal elements) based on the total amount of the alloy, for example, a Si-AI-Fe alloy. The tin-based material may be, for example, tin, a tin oxide, a tin-containing alloy, a mixture of the graphite-based material with the foregoing materials, or the like. Likewise for antimony and lead-based materials.

[0099] Typically, the cathode comprises a current collector with a layer of a cathode active material thereon, which layer typically also comprising at least one of a binder and a conductive material in addition to the cathode active material. The current collector may be any suitable conductor for a cathode, for example, aluminium (Al), stainless steel, nickel-plated steel, and / or the like.

[0100] When the anode is made of metallic lithium or an anode active material, the cathode active material is typically a lithium-containing material. Example of suitable a lithium-containing material for use as a cathode active material include lithium-containing complex phosphate having the general formula LiMPCU, wherein M is one or more of Fe(ll), Mn(ll), Co(ll), and Ni(ll))). Examples of lithium-containing complex phosphate include, but are not limited to, LiFePO4, LiNiPC4, LiCoPO4, LiMnPC4, LiFeaNibPO4, LiFeaCobPO4, LiFeaMnbPO4, LiNiaCobPO4, LiNiaMnbPO4(a+b≤1 , 0<a<1 , and 0<b<1 ), LiFecNidCoePO4, LiFecNidMnePO4, LiNicC0dMnePO4(c+d+e≤1 , 0<c<1 , 0<d<1 , and 0<e<1 ), and LIFe1NigCOhMniPO4(f+g+h+i≤1 , 0<f<1 , 0<g<1 , 0<h<1 , and 0<i<1 ). Further examples of cathode active material that may be used include LixNi08Co0 1Mn0 1O2(e.g. LINi0 8Co0 1Mn0 1O2), LixCoO2(e.g. LICoC2), LixNiO0 33Co0 33AI0 33O2, LixMn2O4, and LixNi0 5Mn1.5O4(0<x<1) (e.g. LiNi0.5Mn1 5O4). In certain exemplary embodiments, the cathode active material is LiNi0.8Co0.1Mn0.1O2(NCM81 1 ).

[0101] When the anode is made of metallic sodium or an anode active material, the cathode active material is typically a sodium-containing material. Examples of sodium-containing active material include, but are not limited to, NaFePO4and NaCoO2When the anode is made of metallic potassium or an anode active material, the cathode active material is typically a potassium-containing material. Examples of potassium-containing active material include, but are not limited to, KCo02, KMnO2KNIO2, KFePO4, and potassium Prussian Blue (KFe[FeCN]6)), and analogues thereof.

[0102] The separator may comprise any suitable separator substrate utilized for an alkali metal battery. For example, the separator may comprise a porous layer or a nonwoven fabric showing a suitable rate discharge performance and / or may be utilized alone or as a mixture (e.g., in a laminated structure). Further examples of materials suitable for use as a separator include, for example, a glass fiber, a cellulose, a non-woven fabric, a polyolefin-based resin, a polyester-based resin, polyvinylidene difluoride (PVDF), a vinylidene difluoride- hexafluoropropylene copolymer, a vinylidene difluoride-perfluorovinylether copolymer, a vinylidene difluoride-tetrafluoroethylene copolymer, a vinylidene difluoride-trifluoroethylene copolymer, a vinylidene difluoride-fluoroethylene copolymer, a vinylidene difluoride- hexafluoroacetone copolymer, a vinylidene difluoride-ethylene copolymer, a vinylidene difluoride-propylene copolymer, a vinylidene difluoride-trifluoropropylene copolymer, a vinylidene difluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and a vinylidene difluoride-ethylene-tetrafluoroethylene copolymer. The polyolefin-based resin may be polyethylene or polypropylene; and the polyester-based resin may be polyethylene terephthalate or polybutylene terephthalate. In certain embodiments, the separator is formed from polypropylene and / or polyethylene, for example the separator may be a polypropylene and / or polyethylene porous film (e.g. a Celgard® 3501 separator).

[0103] The polymer electrolyte of the present invention may be disposed within the battery in a suitable arrangement that separates the anode and cathode. For example, the polymer electrolyte may be disposed on a surface of a substrate, for example on a surface of a separator. The present invention also provides a method of preparing the polymer electrolyte of the present invention, the method comprising forming the polymer electrolyte by polymerisation reaction between the first monomer, the second monomer, and optionally the third monomer, on a surface of a substrate. In certain embodiments, the substrate is a separator for an alkali metal battery. For example, the substrate may be a polypropylene film. In certain embodiments, the separator may be present in an alkali metal battery when the polymer electrolyte is formed on a surface of the separator Thus, in such embodiment, the polymer electrolyte may be considered to be formed by an in situ polymerisation reaction in the alkali metal battery. The polymerisation reaction may be initiated using any suitable radical initiator, such as an azo compound, an organic and inorganic peroxide, or an alkyl halide. Typically, the polymerisation reaction is initiated using azobisisobutyronitrile (AIBN). The alkali metal salt may be added to polymerisation reaction such that the alkali metal salt is disposed throughout the resulting polymer electrolyte. The one-pot, in-situ, polymerization reaction for preparing the polymer electrolyte of the present invention provides a time-saving and easy to scale up approach for providing the polymer electrolyte of the present invention in form suitable for use in an alkali metal battery. For the avoidance of doubt, the first, second, and third monomer used in the method of the invention are according to the first, second and third monomer described above with respect to the polymer electrolyte of the present invention. In an exemplary embodiment, the first monomer is vinylene carbonate, the second monomer is 2 ,2,2-trifluoroethyl acrylate (TFEA), and the third monomer is poly( ethylene glycol) monomethyl ether acrylate.

[0104] Also provided herein is a kit of parts comprising a first, second, and third monomer as defined herein for the polymer electrolyte of the present invention. For example, the kit may comprise vinylene carbonate, 2,2,2-trifluoroethyl acrylate (TFEA), and a polyethylene glycol) monomethyl ether acrylate. The kit may also comprises a radical initiator such as azobisisobutyronitrile (AIBN), and a separator suitable for an alkali metal battery (e.g. a polypropylene and / or polyethylene porous film, such as a Celgard® 3501 separator). In certain embodiments, the kit may also comprise materials suitable for use as an anode and cathode of an alkali metal battery. For example, the kit may comprise an alkali metal anode (e.g. metallic lithium anode) and a suitable cathode (e.g. a cathode comprising LiNi0.8Co0.1Mn0.1O2(NCM81 1 ). The kit may also comprises an alkali metal salt suitable for incorporation into the polymer electrolyte formed from the first, second and third monomers. For example, the kit may comprise LiTFSI and / or LiDFOB. Further suitable anode and cathode material, and alkali metal salts, are described above with respect to the polymer electrolyte and battery of the present invention.

[0105] Typically, the kit comprises instructions, for example instructions that instruct a user to admix a stated amount of the first, second and third monomer together with an initiator and alkali metal salt. The instructions may also instruct a user on how to form the polymer electrolyte of the present invention on the surface a separator suitable for use in an alkali metal battery.

[0106] The contents of the articles, patents, and patent applications, and all other documents and electronically available information mentioned or cited herein, are hereby incorporated by reference in their entirety to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. The applicant reserves the right physically to incorporate into this application any and all materials and information from any such articles, patents, patent applications, or other physical and electronic documents.

[0107] Further aspects and embodiments of the invention will now be discussed by reference to the following non-limiting examples.

[0108] EXAMPLES

[0109] Materials

[0110] 2,2,2-Trifluoroethyl acrylate (TFEA), acrylic acid 2,2,3,3-tetrafluoropropyl ester (TFPA), 2,2,3,4,4,4,4-hexafluorobutyl acrylate (HFBA), polyethylene glycol monomethyl ether acrylate (PEGMEA, average Mn = 900), Polyethylene Glycol Diacrylate (PEGDA, average Mn = 1000), 2,2'-azobis(2-methylpropionitrile) (AIBN) were purchased from Sigma-Aldrich, Adamas or TCI. Vinylene carbonate (VC) and Li salts were purchased from Duoduochem. All materials used in this patent are listed in the following illustration (FIG. 1 ).

[0111] Experimental Section

[0112] Example 1 - Preparation of copolymer electrolyte (CPE)

[0113] The copolymerization process of CPE is shown in FIG. 2. The liquid precursor containing monomers and Li salts transformed into a transparent gel after 2 hours (catalyzed by AIBN at 65 °C) and eventually became a milky translucent elastomer after 12 hours. This synthesis process can be in-situ conducted within batteries, thereby ensuring an ultra-conformal electrolyte-electrode interfacial contact.

[0114] Preparation of the CPE (copolymer electrolyte):

[0115] CPE was synthesized via a solvent-free, single-step and thermal-triggered free radical polymerization: Initially, 0.45 ml of TFEA, 0.45 ml of VC, and 0.1 ml of polyethylene glycol monomethyl ether acrylate (PEGMEA) were added into a glass vial. Subsequently, 1 .3 M of LiTFSI and 0.2 M of LiDFOB were introduced and stirred for 2 hours to form the liquid precursor. To initiate the polymerization, 0.5 wt% (the mass vs. monomer mass) of AIBN initiator was added to the above solution. The sealed vial was then placed in a heating device inside the glove box and heated at 65 °C for 12 hours to complete the polymerization. The synthesis of CPE containing other fluorinated acrylate monomers was similar to the above method, except TFEA was replaced with acrylic TFPA or HFBA. For the crosslinked CPE, the entire synthesis process was similar to the above method, except PTGMEA was replaced with PEGDA. The PTFEA, PVCA polymers, and their salt-containing polymers were synthesised by following the above steps.

[0116] In-situ synthesis of CPE in a cell

[0117] CPE was fabricated by one-pot polymerization on a selected matrix (separator). In a typical fabrication, vinylene carbonate (VC), fluorine-containing monomer (2,2,2-trifluoroethyl acrylate, or 2,2,3,4,4,4-hexafluorobutyl acrylate, or methacrylic acid 2,2,3,3-tetrafluoropropyl ester), PEGMA were added in a glass in appropriate proportions (optimized proportion is by volume ratio of 1 :2:0.2.The density of TFEA, VC and PEGMEA are around 1.216 g / mL, 1 .355 g / mL, and 1.1 g / mL, respectively. The temperature was 25 °C.

[0118] Then LiTFSI and LiDFOB were added to form a 1.3 M LiTFSI-0.2M LiDFOB double salt electrolyte. After continuous stirring for 2 hours, 30-50 pL electrolyte precursor was dropped on the selected matrix (organic separators such as polyethylene and polypropylene separators, cellulose-type separators, etc). Then the soaked matrix was placed between the cathode and anode to form an intimate interfacial contact and heated at 65 °C for 6-24 hours (optimized time is 12h). The cell was then assembled as per normal procedures.

[0119] Example 2 - Side-chain design strategy for copolymer electrolytes

[0120] For liquid electrolytes (LEs), a classic strategy involves pairing cyclic carbonates with linear carbonates. The former usually have high dielectric constant (ε) and ionic separation capabilities and the latter can facilitate rapid ionic transport due to their low viscosity and high fluidity. Analogous to the LEs solvent match principle, the side-chain engineering in polymers integrates individual units with distinct functions into one polymer electrolyte to achieve a harmonious equilibrium among ionic conductivity, stability, mechanical strength, and safety.

[0121] Dielectric constant measurement:

[0122] The dielectric constant was measured according to reported impedance method and described in FIG. 3 (Membranes (Basel) 2011 , 1, 132).

[0123] Molecular dynamics (MD) simulations and density functional theory (DFT) calculation: The MD simulations were performed using Materials Studio 2018 with the COMPASS 11 force field. Copolymers and homopolymers were constructed containing 20 polymer chains and 70 LiTFSI molecules (experimental density of 1.51 g cm3for CPE and 1.56 for PTFEA). Annealing and relaxation ensemble were achieved by conducting 10 cycles of temperature variation in the range of 303 K to 600 K. The annealing was followed by NPT and NVT runs at 1 atm and 333 K for 4000 ps in total. The Nose-Hoover thermostat and Berendsen barostat were used.

[0124] Quantum chemical calculations were conducted using the density functional theory (DFT) method with Becke’s three parameters (B3) exchange functional in Lee-Yang-Parr (LYP) nonlocal correlation functional (B3LYP) (J. Chem. Phys. 1993, 98,5648-5652; J. Chem. Phys. 1980, 72, 650-654). All the geometry optimizations proceeded with B3LYP / 6-31+G(d,p) level. All DFT calculations were performed by using the Gaussian 16 program package. Models were analyzed using Multiwfn (J. Comput. Chem. 2012, 33, 580).

[0125] Electrochemical measurements:

[0126] The ionic conductivity was evaluated by measuring the corresponding electrochemical impedance spectroscopy (EIS), which was conducted with Bio-logic SP-150e electrochemical workstation or with CHI 760E electrochemical workstation (Chenhua, Shanghai). The glass fiber separators (Whatman® glass microfiber filters, Grade GF / A) are used to avoid short circuit during the ionic conductivity test. 40 pL of the precursor solution is dropped onto the separator and polymerizes after heating treatment. The thickness of the glass fiber with CPE is measured after disassembling it from the pressed cells and an average value is used (0.22 mm). Frequency ranges from 100 kHz to 1 Hz with an alternating current amplitude of 5 mV. Linear sweep voltammetry (LSV) method was used to evaluate the oxidation resistance and the stability of the phase change electrolyte. In this test, Li foils act as both counter and reference electrodes and an aluminum blocking plate is the working electrode. Voltage ranges from Open Circuit Voltage (OCV) of 1 V to 7 V at a scan rate of 0.1 mV s1. While the set voltage range is from 1 V to 7 V, electrolytes would decompose at certain voltages and thus the currents that were out of range were omitted in the related figures. Conventionally, the voltage range applied during the LSV test exceeds the oxidation voltage of the studied electrolyte. Once the applied voltage reaches the onset of the oxidation reaction of the electrolyte, the response current increases sharply. This may cause the relevant axis of the figure to extend largely, making it difficult to compare the take-off voltage values.

[0127] Cell preparation: LiFeP04(LFP) or LiNi0.8Co0.1Mn0.1O2(NMC81 1 ), Ketjenblack or Super P, and Polyvinylidene fluoride (PVDF) were mixed at 80:10:10 wt% ratios in a mortar to form a uniform slurry. Then Al foil was coated with cathode slurry and dried at 80 °C overnight. The loading of active materials was 2 - 5 mg cm2. During the assembly of the cells, after adding AIBN to the precursor solution mentioned above, 40 pl of the solution was dropped onto a Celgard 3501 separator. The separator was then laminated with the cathodes or anodes. After sealing, the assembly was heated at 65°C in a conventional oven for 12 hours to complete the in-situ polymerization. The Celgard 3501 separator could also be replaced with other barrier materials, such as glass fiber or non-woven fabric mentioned in the manuscript. In the assembly of batteries without a separator, a polytetrafluoroethylene (PTFE) O-ring was used. The electrolyte precursor was dropped into the O-ring, and the battery was sealed to prevent short-circuiting before the in-situ polymerization occurred. Single-layer Li | |NCM81 1 pouch cell was assembled in a glove box. Ni and Al tabs were anchored on anodes and cathodes, respectively. The pouch cells were degassed after polymerization process and sealed again before cycling. Flexible batteries were prepared using a casting method. The electrodes were cut into strips measuring 6 cm in length and 1 .5 cm in width, with the separator being slightly larger than the electrode materials. The precursor electrolyte was dropped onto the separator to ensure thorough saturation, followed by the lamination of the positive and negative electrode sheets. Glass was attached to both sides of the battery and sealed, then heated at 65°C for 12 hours. Subsequently, the polymerized bare battery was placed into a PTFE mold. PDMS (polydimethylsiloxane) or a precursor liquid without lithium salt was cast over it. After sealing, the assembly was heated at 65°C for 12 hours to complete the battery assembly.

[0128] TGA characterization:

[0129] TGA characterizations were performed from ambient temperature to 800°C at the heating rate of 10°C / min using the TA Instruments Q50 TGA.

[0130] Mechanical property measurements:

[0131] Tensile tests of the samples were carried out on a universal testing machine (Instron 5900, USA) using 100 N load cell and pneumatic grips, at a R.H. = 50 % and 25 °C. The samples were cut into rectangular specimens of 60 x 5.0 x 0.70 mm by a scalpel knife with gauge length L«10 mm. They were loaded onto the tester at ~1.5 bar pressure, and monotonically stretched to failure at a strain rate of 5 min"1. The Young’s moduli in Table 4 were measured from the slope at 0.2% strain. Dynamic Mechanical Analyzer (DMA 850) was used on polymer samples (30x8x1 mm3) in tension mode at a frequency of 1 Hz, an oscillatory amplitude of 15 μm, and a static force of 0.01 N. Samples were cooled to -100°C and held for 3 min before being subsequently heated to 100°C at a rate of 3°C / min. Glass transition temperatures were determined from the peak values of tanδ. For the cyclic elasticity test (DMA Q800), stretching- releasing tests were performed at the same constant strain rate of 100 mm min1for both stretching and relaxing with various predetermined maximum strains under ambient conditions.

[0132] Results and Discussions

[0133] As illustrated in FIG. 4a, three factors are considered when screening the composing side chains: 1) Molecular orbitals, especially the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbital (LUMO), serve as important indicators for assessing the ease of electron gain or loss within the polymer matrix and impact the constitution of SEI / CEI; 2) Polarity, which reflects the dissociation ability for lithium salts, dictates the concentration of free carriers within the polymer electrolyte. 3) Spatial freedom, such as molecular rotation, vibration, and segmental motion, directly impacts the free volume of polymers and the efficiency of ion migration through segmental relaxation.

[0134] As a demonstration, a ternary copolymer electrolyte composition featuring fluorinated, highly polar, and flexible dangling moieties is introduced based on the outlined criteria (FIG. 4a). Firstly, the fluorinated carboxylate monomer was chosen due to its stable C-F bonds, freely entangled features, and polar ester group, which can bolster the electrochemical-thermal stability of polymer matrix and benefit ionic dissociation, thereby establish a stable and elastic framework of CPE (Advanced Materials 2023, 35, 2209581 ; Advanced Materials 2021 , 33, 2105306). Concurrently, the incorporation of the vinylene carbonate (VC) monomer, with its notably high dielectric constant (E -126), ensures efficient ionic dissociation and short-range hopping. Additionally, a minor fraction of long-chain ester branches was copolymerized to promote segmental motion and facilitate long-range interchain ion transfer.

[0135] Stability is the premise of constructing polymer electrolytes. Three fluorinated acrylate derivatives - TFEA, TFPA (2,2,3,3-Tetrafluoropropyl Acrylate), and HFBA (2, 2, 3, 4,4,4- Hexafluorobutyl acrylate) - differing in fluorine atom count and chain length were selected as candidates (FIG. 5a). According to the density functional theory (DFT) calculation (FIG. 5b), three fluorinated homopolymers exhibit comparable highest occupied molecular orbitals (HOMO) (PTFEA: -7.59 eV; PTFPA: -7.54 eV; PHFBA: -7.82 eV), all lower than the conventional PEO matrix (-7.0 eV) (Advanced Functional Materials 2023, 33, 2303718). Their electrochemical stability windows, assessed via linear sweeping voltammetry (LSV) (FIG. 5c), indicated stabilities with no current rise up to 7 V. These results indicate that fluorinated side chains with strong electron-withdrawing effects can stabilize the polymer skeleton and enable the electrolyte with a high antioxidant ability. However, the weak dipole-ion interactions with Li salts and limited segmental movement of these homopolymers result in low ionic conductivities (10-7-108S cm1at 30 °C, FIG. 6), limiting their direct applications.

[0136] FIG. 7a-f displays the influence of the fluorine-containing monomers (TFEA, TFPA, and HFBA) and the long-chain esters (PEGMEA and PEGDA) on the ionic conductivity, oxidation resistance and mechanical properties. Among the fluorine-containing monomers, TFEA-based CPE exhibited the best overall performance. The cross-linking points in crosslink CPE will limit the movement of the chain segments, increasing the rigidity of the material while reducing its flexibility and ductility. In contrast, PEGMEA remains flexible and linear ether segments (-C- O-C-) while avoiding high-density crosslink. These ether bonds allow the side chains to rotate freely inside the molecule, thereby increasing overall flexibility. In addition, under external forces, these flexible segments can adjust their conformation easily, thereby absorbing and releasing energy, increasing the elasticity of the CPE. The basic electrochemical performances are summarized in Table 1. The optimized CPE contains TFEA, VC, and PEGMEA monomers (1 :1 :0.2 volume ratio) with 1 .3 M LiTFSI and 0.2 M LiDFOB.

[0137] Table 1. The regulation of CPEs with different components and corresponding properties.

[0138] The improvement of ionic conductivity ( δLi+) can be realized by elevating the concentration of dissociated ions, which largely hinges on the efficient dissociation of Li salt, and promoting the efficiency of ion conduction. In this context, the PVC side chain is incorporated due to its high polar carbonyl group. The inherent polarity of the PVC side chain can break the ion-ion electrostatic interaction with a stronger ion-dipole effect, thus decreasing the ion aggregation and releasing more free Li ions (J. Electrochem. Soc. 2016, 163, A851). In addition, the copolymerization between PVC and fluorinated carboxylates also compensated for the electrochemical vulnerability of PVC (FIG. 8a, b). VC monomers with high HOMO will easily lose electrons during charging, which can be confirmed by the escalated oxidation current at 4.2V. While PVC is hard to lose electrons theoretically, the incomplete polymerization and residual VC (FIG. 9) lead to a narrow voltage window. As FIG. 7a shows, after grafting PVC side chains, the ionic conductivities of P(TFEA-VC), P(TFPA-VC), and P(HFBA-VC) increase significantly. Notably, P(TFEA-VC) has the highest δLi+ of 2.08x10-3S cm-1at 30 °C, coupled with the lowest ionic activation energy of 0.232 eV. According to the DFT calculation (FIG. 4b), the HOMO energy levels of P(TFEA-VC), P(TFPA-VC), and P(HFBA-VC) decrease marginally with an increasing number of fluorine atoms. Their actual oxidation resistances were further investigated by LSV. As shown in FIG. 4c, due to the coordination between polymer and ions and the reactions at the electrode surface, the three copolymer electrolytes show slightly different oxidative resistance compared to the computational prediction (P(TFEA-VC): 4.92 V, P(TFPAVC): 4.65 V, P(HFBA-VC): 5.1 V). These values exceed that of PVC (4.4 V), further validating the stabilizing effect enabled by the fluorine-rich side chains. Additionally, P(TFEA- VC) demonstrates enhanced compatibility with Li metal, evidenced by its stable and lower polarization voltage and higher Coulombic efficiency (GE), as detailed in FIG. 7c, d. Consequently, TFEA and VC were selected as the principal monomers. It should be noted that the poor oxidation resistance of VC and PVC can also be improved by copolymerization with TFEA. The P(TFEA-VC) exhibits an oxidation voltage of 4.92 V, excelling that of the VC monomer (4.2 V) and PVC (4.4 V) (as discussed in FIG. 8).

[0139] The binding energies (Ending) between Li+and the three binary copolymer matrices are calculated (FIG. 4d), among which P(TFEA-VC) possesses the smallest Ebindingof 1.80 eV, indicating a more efficient Li+transportation. As further confirmed by the temperature- dependent ionic conductivity test (FIG. 4e), P(TFEA-VC) has the highest δLl+ of 2.08x103S cm1at 30 °C, and the lowest ionic activation energy of 0.232 eV among the three binary copolymer electrolytes. Moreover, P(TFEA-VC) demonstrates better compatibility with Li metal, as evidenced by the lower polarization and higher Coulombic efficiency (CE) (FIG. 7c, d). Consequently, PTFEA and PVC are integrated as the principal side chains of the polymer matrix. While the high polar PVC moieties enhance the Li salt dissociation ability of P(TFEA-VC), it also increases polymer intermolecular forces, reflected in the increased glass transition temperature (Tg). As shown in FIG. 4f and FIG. 10, the Tgof P(TFEA-VC) rises with the increased content of the PVC moieties. Polymers with high Tgusually have low segmental motions and high Li+migration energy barriers at room temperature. In the case of CPE, PEGMEA side chains are grafted onto the polymer. This modification aims to expand the polymer's free volume, reduce the Tg, and enhance chain mobility. As shown in FIG. 31 , the Tgof PTFEA is approximately 4 °C. This value incrementally rises with the addition of the VC monomer, illustrating the correlation between the dielectric constant and Tg. After copolymerizing with PEGMEA, the Tgdrops back to 3.2 °C. To break the trade-off, long PEGMEA side chains are integrated to form the ternary copolymer P(TFEA-VC-PEGMEA) matrix (abbreviated as CP). The PEGMEA side chain (n=13) is introduced, resulting in a comb-like copolymer (CP). This integration of a long side chain increases the free volume within the polymer matrix, which in turn lowers the glass transition temperature (Tg) and enhances segmental relaxation. Furthermore, the ether groups present in PEGMEA facilitate accelerated interchain ionic conduction. Consequently, this structural modification leads to a reduction in ionic activation energy, decreasing from 0.232 eV in P(TFEA-VC) to 0.194 eV in the comb-like CP (FIG. 1 1b). With a similar structure, the copolymerization with polyethylene glycol diacrylate (PEGDA, n=14) was also synthesized and compared (FIG. 1 1 ). As a horizontal comparison, the telechelic bifunctional polyethylene glycol diacrylate (PEGDA, n=14) is compared with PEGMEA (n=13). Although PEGDA can increase free volume of polymer and facilitate interchain ionic exchanges, the formed crosslinked network restricts segmental oscillation, rendering the P(TFEA-VC-PEGDA) rigid and fragile, susceptible to pulverization under external forces (FIG. 1 1 a). In contrast, the linear ether bonds of PEGMEA enhance spatial freedom and avoid high-density crosslinks. Furthermore, under external forces, the unrestricted flexible PEGMEA branches can adjust their conformation easily, thereby absorbing and releasing energy, and increasing the resilience of CPE. More importantly, the higher spin degree of freedom enabled by PEGMEA increases the free volume within CPE, resulting in enhanced ionic conductivity (FIG. 1 1 b). The resulting crosslinked structure compromises both the elasticity and ionic conductivity of the electrolyte, demonstrating the importance of rotational freedom in backbones. Also due to the high spin degree of ether bonds and the flexible linear structure of PEGMEA, the Tgof CP is 3.2 °C, which is only half that of P(TFEA0.5-VC0.5). After adding Li salts into CP (abbreviated as CPE), the Tgof CPE further drops to ~1 °C. Dynamic mechanical analysis (DMA) also corroborates these variations (FIG. 12). The reduced Tg and enhanced spatial freedom in CPE reflect an improved ionic transportation efficiency. As exhibited in FIG. 4e, the prepared CPE has the highest ionic conductivity of 2.19x103S cm1at 30 °C and the lowest activation energy of 0.194 eV, outperforming the other binary polymer electrolytes. The oxidation voltage of CPE is 4.97 V, very close to the binary polymer P(TFEA-VC) (as shown in FIG. 4c).

[0140] Therefore, the optimized composition of CPE comprises PTFEA, PVC, and PEGMEA side chains and Li salts (1.3M LiTFSI+0.2 M LiDFOB, discussed in FIG. 1 1 and FIG. 13-15, and Table 1 and 2). Here, LiTFSI is selected as a representative Li salt. According to the results (FIG. 13), 1 .5 M Li salt remains both high ionic conductivity and antioxidation ability as, thereby the total Li salt concentration of 1 .5 M is used in the following studies. As shown in FIG. 2, the liquid precursor containing three monomers and Li salts transformed into a transparent gel after 2 hours of heating (catalyzed by AIBN at 65°C), eventually becoming a milk-white elastomer after 12 hours. The resulting CPE is highly stretchable, and its synthesis can be integrated within batteries, ensuring conformal interfacial contact.

[0141] Table 2. Performance comparison of copolymer electrolytes with varying monomer ratios.

[0142] *the values shown as subscript for each polymer sample are volume ratios.

[0143] Example 3: Characterisation of copolymer electrolytes

[0144] Multiple analytical techniques were employed to characterize the copolymerization process.

[0145] Characterization:

[0146] XPS spectra were collected using an Omicron EA125 system with Al Ka (1486.7 eV) X-ray source. A home-built vacuum transfer chamber was implemented for transferring the samples from the glovebox into the XPS chamber to avoid degradation toward air. The sputtering was conducted using an Argon ion sputtering gun with an operation energy of 1 .Ok eV at an Argon pressure of 5.0x10-5 mbar.

[0147] SEM images were obtained by a JEOL JSM-6701 F FESEM. Raman spectroscopy was recorded at room temperature using a confocal WiTec Alpha 300R with laser excitation at 532 nm.

[0148] Matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS) measurements were conducted on MALDI-TOF-MS (JEOL JMS-S3000). Atomic force microscope (AFM) measurements were conducted on the Bruker FastScan / lcon® equipment (Dimension FastScan) in tapping mode.

[0149] Fourier transform infrared spectroscopy (FT-IR) The vibrational spectra for all samples were obtained using a Broker TENSOR 27 FTIR spectrometer, equipped with an infrared source and attenuated total reflection (ATR) FTIR.

[0150] Due to the insensitivity of the symmetric -C=C- vibration in VC (FIG. 9a), the conversion rate of TFEA can be estimated from the integrated area ratio of -C=C- (1620-1640 cm1) in the polymerized gel / solution to that in the pristine precursor solution (C-F bond was set as reference). Although the -C=C- in VC and TFEA can be detected in Raman spectra, they partially overlap (FIG. 9b). Therefore, the skeletal stretch near -C=C- (1085 cm1) is used to identify the conversion rate of VC monomer during copolymerization

[0151] Results and Discussions

[0152] As FIG. 2 shows, the optimized CPE was synthesized via a solvent-free, single-step and thermal-triggered free radical polymerization. Photographs of the fabricated CPEs are also presented in FIG. 2. The liquid precursor containing three monomers (TFEA, VC, and PEGMEA) and Li salts transformed into a transparent gel after 2 hours of heating (catalyzed by AIBN at 65°C), eventually becoming a milk-white elastomer after 12 hours.

[0153] The copolymerization was confirmed using Fourier transform infrared spectroscopy (FT-IR) analysis. As shown in FIG. 16a, Fourier transform infrared spectroscopy (FT-IR) analysis demonstrates that the characteristic signals of unsaturated C=C bonds at 3165 cm1(VC) and 1632 cm1(TFEA) vanish after reaction, suggesting the successful copolymerization, which is further supported by Raman spectroscopy (FIG. 17) (Journal of Power Sources 2019, 427, 77; Polym. Sci. Ser. A 2011 , 53, 85; Chem. Mater. 2020, 32, 9167; Nat Commun 2022, 13, 4181 ). These peaks are associated with the unsaturated C=C bonds in VC and TFEA monomers, respectively (Journal of Power Sources 2019, 427, 77; Polym. Sci. Ser. A 2011 , 53, 85; Chem. Mater. 2020, 32, 9167; Nat Commun 2022, 13, 4181 ).

[0154] In-situ FT-IR measurements (FIG. 18) show that the C=C bond of TFEA completely disappears after 6 hours while the C=C bond of VC exists until 15 hours, indicating a faster polymerization rate compared to that of VC. The reaction rate of monomers in CPE is investigated using in-situ FTIR and Raman (FIG. 9 and FIG. 18-20), demonstrating different degrees of monomer polymerization. This difference in polymerization kinetics is further evidenced by the different curing speeds (FIG. 21 a). This disparity in polymerization kinetics is further evidenced by the differential conversion and yield rates in their homopolymers and corroborated by1H NMR spectra (ACS Appl. Mater. Interfaces 2019, 11, 43056), where CPE manifests an approximate yield rate of 83% (FIG. 9 and FIGs. 19-21 ). The disparity is attributed to the electron-withdrawing effect of the adjacent oxygen atom in VC, reducing electron cloud density around the unsaturated bond. Conversely, the higher electron cloud density present in TFEA renders its π electrons more prone to engagements with free radicals, enhancing the reactivity and consequently leading to a more rapid polymerization process. According to the weight loss test, yield rates of PTFEA, PVC, and CP are 99%, 82%, and 83.3%, respectively (FIG. 21 b). The difference in conversion rate is also corroborated by1H NMR spectra (FIG. 22 and FIG. 23), manifesting an incomplete polymerization of VC monomer (ACS Appl. Mater. Interfaces 2019, 11, 43056).

[0155] CPE was collected after copolymerizing for 1 h. Prolonged polymerization results in incomplete dissolution of CPE. The solubility of CPE (after 12 h polymerization) is shown in FIG. 21.

[0156] The copolymerization is then analyzed via differentiated thermogravimetry (DTG). As shown in FIG. 16b, CP and CPE exhibit two weight-loss rate peaks at 350 °C and 445 °C, a notable deviation from the single weight-loss rate peak observed in PVC (335 °C) and PTFEA (410 °C) homopolymers. This feature distinguishes CPE from physical mixture and signifies an enhancement in thermal stability (Polymer Degradation and Stability 2008, 93, 1753). As observed in the insert (thermogravimetric analysis, TGA), even postpolymerization, 14-16 wt% of VC monomer / oligomer persists in CPE, consistent with the measured yield rate of PVC. The detailed evaporation and decomposition products were analysed using the coupled Thermogravimetric Analysis-Mass Spectrometry-Fourier Transform Infrared Spectroscopy (TGA / MS / FT-IR) technique and matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDITOF-MS) (FIG. 24). The detected C=O stretch (1867 cm-1) begins to increase at 150 °C and decreases at 250 °C. Due to the overlap of the C=O group in VC and TFEA, it is challenging to separate them. However, it is deduced that the initial increase (150 °C-200 °C) of the C=O signal should be attributed to VC monomers / oligomers since the PTFEA homopolymer does not show significant weight loss until 200 °C. The highest weight- loss rate peak at 335°C is attributed to the evaporation of CO2, as demonstrated in FIG. 24d. The MALDI-TOF-MS result demonstrate the presence of low molecular weight VC oligomers (FIG. 24e). The residual small molecule VC exists in the form of coordination with ions, forming a vehicle transportation mechanism within the polymer matrix. This mechanism facilitates high-speed Li+migration, resulting in CPE exhibiting one of the highest ionic conductivities among the recently reported high ion-conductive polymer electrolytes (Table 3).

[0157] Thermogravimetric analysis (TGA) confirms that about 14% of VC monomers remain unreacted in the CPE, yet it still exhibits one of the highest ionic conductivities among quasi- solid-state polymer electrolytes even with less liquid content (Table 3). Small Angle X-ray Scattering (SAXS) analysis of PTFEA, CP, and CPE samples (FIG. 16c) reveals no discernible peaks, suggesting a random microscale distribution and the absence of specific microstructures or phase separation (Mat. Mater. 2023, 1 ; Nat. Mater. 2022, 21, 1057; Advanced Energy Materials 2022, 12, 2103187). Small angle x-ray scattering (SAXS) analysis of PTFEA, CP, and CPE samples (FIG. 16c) reveals a microphase separation within CP and CPE. In CPE, the addition of Li salts notably fosters phase separation, which is attributed to the selective affinity between anions / cations and fluorinated / non-fluorinated side chains (FIG. 25 and FIG. 26). As shown in FIG. 25, after an ordinate transformation of the original SAXS data, a broad peak around q=0.01 A-1shows in the scattering of CPE, suggesting a microphase-separation scale of d=2π7q=62.8 nm. This result was further confirmed by atom force microscopy (AFM) (FIG. 26). In tapping mode AFM, height and phase images can provide additional evidence of microphase separation. Height images show the physical topography, while phase images can indicate differences in material properties such as

[0158]

[0159] stiffness or adhesion. Consistent patterns in both height and phase images, corresponding to different phases, strongly support microphase separation. To be specific, the fluorinated and non-fluorinated form the bi-continuous structure, where Li+ and organic fluorinated anions (TFSI-) of LiTFSI are selectively enriched in the non-fluorinated and fluorinated side chains of the CPE, respectively. Li+ions are enriched in the non-fluorinated PVC and PEGMEA side chains due to the coordination between the Li+ions and oxygen atoms, thus forming a continuous ion migration channel among these coordination sites; the TFSI- ions are concentrated in the fluorinated microphase due to the “fluorous effect” between the TFSI- and fluorinated side chains (J. Am. Chem. Soc. 2020, 142, 7393).

[0160] This conclusion is further supported by the disentanglement of FT-IR spectra (FIG. 27) (Advanced Materials 2023, 35, 2209581 ). Due to the electronegative nature of adjacent oxygen atoms, the force constant of the carbonyl bond (C=O) increases, resulting in a slight difference in the characteristic peak positions of the C=O bond in VC (1800-1830 cm ') and TFEA (1750 cm1) monomers. This character can be utilized to decouple the coordination states with Li+ions. In addition, the single Tg(FIG. 10) and isotropic 2D SAXS (FIG. 16c, insert) ring suggest that CPE is a random ternary copolymer (Nat. Mater. 2023, 1 ; Nat. Mater. 2022, 21, 1057; Advanced Energy Materials 2022, 12, 2103187).

[0161] The micro morphologies are detected using scanning electron microscopy (SEM). From the scanning electron microscopy (SEM) (FIG. 28), it was observed that the surface of the PTFEA homopolymer is very smooth while the PVC surface exhibits noticeable cracking. Differently, the copolymer surface presents a distinct undulating and wrinkled state. This morphological disparity is reflective of the inherent rigidity and elasticity properties associated with PVC and PTFEA, respectively.

[0162] The mechanical properties of CPE, PTFFA, PVC and copolymers (CPs) across different monomer ratios were assessed via tensile testing, (FIG. 3, FIG. 16d, FIG. 29-30, and Table 4). The PVC (FIG. 16d, insert) homopolymer exhibits a non-deformable and rigid nature with a high tensile strength of 3.7 MPa. The PTFEA possesses good elasticity with a fracture strain of 1035%.

[0163] Table 4. A summary of the mechanical properties of the studied polymers.

[0164] As shown in FIG. 3, a sudden decrease in stress can be found in less elastic polymers such as P(TFEA0.68-VC0.23-PEGMEA0 1). The PVC side chains function as rigid segments within the polymer matrix. As the PVC content increases, there is a corresponding increase in the polymer's strength and a decrease in its elongation. Additionally, the formation of interpenetrating micro-voids leads to yield and crazing during tensile testing, which is characterized by an abrupt stress drop.

[0165] With the addition of PEGMEA, the ternary copolymer CP achieves a well-balanced mechanical profile with a maximum tensile strength of 1.01 MPa and a fracture strain of 2640%. Maintaining a constant PEGMEA content, an increased proportion of VC monomer correlates with heightened maximum tensile stress and diminished fracture elongation in CPs, manifesting the rigidity contribution from PVC moieties. Without the addition of PEGMEA, CP(TFEA0.5-VC0.5) shows reduced tensile stress compared to CP(TFEA0.45-VC0.45- PEGMEA0 1), underscoring the role of long-chain PEGMEA in enhancing the flexibility and ruggedness of polymer matrix. Subsequent elastic fatigue testing of CPE shows no loss of elasticity even after 1000 stretching cycles within a 100% strain range (FIG. 16e), affirming its exceptional durability.

[0166] After the addition of lithium salts to form an electrolyte, the maximum tensile stress drops to 0.46 MPa, with fracture strain increasing to 2745%. Subsequent elastic fatigue testing of the CPE samples underscores their durability, revealing no significant loss of elasticity after 1000 stretching cycles within a 100% strain range (FIG. 16e).

[0167] In the ternary copolymer, the PTFEA, PVC and PEGMEA segments contribute to elasticity, rigidity and toughness, respectively. In CPE, PVC side chains are the “hard segment” and PTFEA side chains are the “soft segment”. With the increase of TFEA side chains, the elasticity improves while the rigidity decreases. Meanwhile, the flexible long PEGMEA side chain not only enhances the pliability but also acts as a pathway for stress dissipation, allowing the CPE to withstand deformation under external forces without fracturing.

[0168] With a suitably chosen ratio, the synthesized CPE exhibits superior elasticity and resilience, enabling it to endure repeated deformation without any fracture. In addition to the mechanical durability, owing to the strong C-F bonds and the high thermal stability of PTFEA side chains, CPE exhibits flame retardancy. As shown in FIG. 16f, the CPE cannot be ignited when exposed to flame, which is in sharp contrast to combustible commercial liquid electrolytes (LE: 1.0 M LiPF6in EC (ethylene carbonate): DMC (dimethyl carbonate) = 1 :1 in volume).

[0169] Example 4: Kinetics of ionic dissociation and transportation

[0170] Within CPE, high polar PVC side chains can effectively shield the ion-ion interaction and increase the concentration of free carriers. Furthermore, it has been demonstrated that Li+ions are capable of migrating along adjacent PVC segments through a rapid hopping mechanism (J. Electrochem. Soc. 2016, 163, A851 ).

[0171] Potentiostatic EIS (PEIS)

[0172] The measurements are carried out with potentiostatic EIS (PEIS) techniques at open circuit voltage Eoc in the 100 kHz - 100 mHz frequency range and with an amplitude of 10 mV. The dielectric constant is calculated using the following equation (Eq(1 )): Eq(1 ) where: C is capacitance (Farads), E0is the relative electrical permittivity of free space (8.854 x 10-12F.m-1), εris the relative dialectic constant of the membrane, A is the area of overlap of the two plates (m2) and d is the distance between the two plates of the capacitor (m).

[0173] Results and Discussions

[0174] As shown in FIG. 32a and FIG. 33-35, the CP exhibits a high ε of 27, not only surpassing polymer matrices such as PEG (Polyethylene oxide)) (ε ~5), PMMA (poly(acrylonitrile)) (s —3.5), and PAN (poly(acrylonitrile)) (ε ~4), but also exceeding that of many liquid solvents. The high s of CP derives from the carbonate group of PVC monomer whose ε value is 126: the electronegativity difference between the C=O and C-0 bonds, combined with the presence of lone pair electrons on oxygen atoms, imparting a strong dipole moment across the entire side chains (J. Electrochem. Soc. 2016, 163, A851). Without the polar PVC side chains, CP(TFEA- PEGMEA) (ε -4.2) exhibits a poor δLi+of 1 .0x106S cm1(30 °C) (Table 5 and Table 6).

[0175] Table 5. A summary of dielectric constants of the studied samples.

[0176] Table 6. A summary of ionic conductivities (right) of the studied samples. The integration with high polar VC significantly improves the ionic conductivity of polymer electrolytes. Among the polymer electrolytes investigated, CP(TFEA0 9-PEGMEA0 1)+VC (in gel state) demonstrates the highest dielectric constant (79) and ionic conductivity of 5.2 x 103S cm1. However, its compromised mechanical properties and inadequate oxidation resistance render it unsuitable for practical use. The copolymerization approach with TFEA and PEGMEA side chains effectively mitigates these shortcomings, rendering CPE a well- balanced performer in terms of performance characteristics.

[0177] To further elucidate the direct relationship between E and δLi+, the δLi+ of CPE is compared with other selected gel electrolytes comprising PTFEA skeletons and liquid plasticizers with varying E (FIG. 32b). Despite the relatively low VC monomer / oligomer content within CPE, in contrast to other control samples comprising 50 wt% of liquid solvents, the high E of CP and residual VC confers upon CPE the highest δLi+ among all the samples (FIG. 32b). Notably, the δLi+ of other gel electrolytes decreases monotonically with the reduction of their plasticizers’ E. This trend is in alignment with the findings of Barteau et al., where δLi+ is significantly influenced by the E of the polymer matrix (Barteau, K. P. Poly (Glycidyl Ether)- Based Battery Electrolytes: Correlating Polymer Properties to Ion Transport. Ph.D. thesis, University of California, Santa Barbara, 2015).

[0178] The efficient ionic dissociation enabled by PVC side chains is demonstrated using Raman spectroscopy. As shown in FIG. 32 C1, C2, the aggregated ion clusters (AGGs) in CPE account for 3.5% of the total coordination states, a value ten times lower than that observed in PTFEA (34.2%). Additionally, the percentage of free anions in CPE is high, indicating a sufficient dissociation of Li salt in the presence of PVC side chains. The Raman results are supported by Molecular dynamics (MD) simulation (FIG. 36). According to the calculated radial distribution function (RDF) and coordination number (CN) (FIG. 32 d1, d2), Li+primarily binds to the carbonyl oxygen (O=C) and ether oxygen (O-C) of the polymer matrix, with only a small fraction associating with the oxygen atoms in the TFSI anions. In contrast, in the PTFEA electrolyte, Li+tends to coordinate with the anions, with a coordination number of 2.7, indicating the overly tight interaction of Li salt molecule. Moreover, from the snapshot of MD simulation (FIG. 32 e1, e2), Li+and cations are uniformly dispersed in CPE while distinct aggregation or clusters appear in PTFEA, characterized by cation-anion contact pairs and anion triplets. In addition to the concentration of dissociated ions, the δLi+ of polymer electrolyte is influenced by the efficiency of ion conduction. The PEGMEA side chains present in CPE, characterized by their high spatial freedom, play a facilitative role in segmental motion and interchain ion exchanges. During MD simulation, the migration trajectories of five randomly selected Li+ions is depicted in FIG. 32 f1, f2. In comparison with the Li+ions observed in P(TFEA-VC), those within CPE demonstrate notably heightened dynamic activity, as evidenced by their wider migration ranges. In addition, according to the mean square displacement (MSD) (FIG. 32g), the Li+ diffusion coefficient (DLi+) in CPE is 2.3 x 10-8cm2s1, significantly higher than that of PTFEA (5.5 x 10-9cm2S-1) and P(TFEA-VC) (7.9 x 10-9cm2S-1) electrolytes. In summary, the high ionic conductivity of CPE can be attributed to three factors: 1) PVC facilitates the efficient dissociation of Li salts, increasing the concentration of free carriers and fostering rapid short-range ion hopping between adjacent PVC side chains. 2) PEGMEA promotes polymer segment mobility and promotes long-range interchain ion transfer. 3) A small amount of residual VC coordinates with lithium ions, further accelerating ion conduction through vehicle transport mechanisms.

[0179] Example 5: Electrochemical performance of CPE symmetric Li cell

[0180] To investigate the compatibility and stability between CPE and Li anode, the liquid precursor of CPE is dropped on separators (polypropylene, PP) or other buffer materials and in-situ copolymerized in the symmetric Li||Li cells.

[0181] When buffer material is O-ring : The O-ring was first placed on the Li surface. Then heat the liquid precursor until it becomes viscous. Dropping viscous CPE inside the O-ring and encapsulating cells.

[0182] Results and Discussions

[0183] The crucial current density (CCD) test was conducted to measure the maximum short-term current density tolerance. As shown in FIG. 37a, the CPE-based Li||Li cells exhibit a high crucial current density (CCD) value of 2.55 mA cm2and maintain a steady increment of overpotential during the following rate test (FIG. 37b). Upon long-term cycling (current density of 0.8 mA cm-2), the CPE-based Li||Li cell runs stably over 1000 hours whereas the P(VC- PEGMEA)-based cell fails at the 180th cycle (FIG. 37c). These results highlight the superiority of CPE among the contemporary quasi-solid polymer electrolytes (FIG. 37d). As summarized in FIG. 37d and Table 7, the CPE-based Li||Li cells stand out in terms of CCD and cycling tests among the contemporary quasi-solid polymer electrolytes (Angewandte Chemie International Edition 2023, 135, e202304339; Advanced Materials 2020, 32, 2000575; ACS Appl. Mater. Interfaces 2023, 15, 26047; Energy Storage Materials 2021 , 36, 171 ; Advanced Functional Materials 2023, 33, 2303739; Journal of Colloid and Interface Science 2022, 615, 627; Advanced Energy Materials 2023, 13, 2204218; Nano Energy 2024, 119, 109075; EcoMat 2023, 5, e12325; Small 2023, 19, 2303422; Advanced Functional Materials 2023, 33, 2307263; Advanced Energy Materials 2022, 12, 2103720; Advanced Energy Materials 2023, 13, 2301470; Advanced Materials 2023, 35, 2304686; Angewandte Chemie 2023, 135, e202308309; Science Advances 2023, 9, eadh9020; Angewandte Chemie International Edition 2023, 62, e202307255; Nat. Nanotechnol. 2023, 1 ; Nat Commun 2023, 14, 2301 ; Advanced Functional Materials 2023, 33, 2213702). At a current density of 0.2 mA cm-2, the CPE Li||Li cell exhibits superior stability over 3500 h (FIG. 37e). Besides PP, other materials can also serve as separators (FIG. 38). In addition, the electrochemical impedance spectroscopy (EIS) measurements show that the overall resistance remains low during the extended long-term cycling (FIG. 39). Li||Cu cells were then assembled, and the average Coulombic efficiency (ACE) within CPE was 96.2%, exceeding that of the liquid VC monomer and binary P(VC-PEGMEA) electrolytes (FIG. 40).

[0184]

[0185] Example 6: Stabilizing Li anode via chemical and physical protection of CPE

[0186] The compatibility of CPE with Li metal arises from two key factors. Microscopically, the organic (F-rich high molecular weight, i.e., F-HMW)-inorganic hybrid solid electrolyte interphase (SEI) mitigates side reactions and Li-dendrite growth. Macroscopically, the high elasticity of CPE effectively accommodates the volume fluctuations of Li metal, ensuring consistent contact between Li and CPE. In-depth X-ray photoelectron spectroscopy (XPS) was employed to reveal the surface constituents of Li deposited in CPE and P(VC-PEGMEA) (1 mAh cm2).

[0187] Results and Discussions

[0188] X-ray photoelectron spectroscopy (XPS) analysis of Li (1 mAh cm2Li deposited on Cu foil) reveales the significant role of PTFEA side chains.

[0189] As shown in FIG. 41a, before etching, the top surface of Li deposited in CPE is covered by a layer of residual copolymers due to the adhesive and insoluble nature of F-containing CPE. More direct evidence is displayed in the atomic composition ratios (FIG. 41 b-c) where almost no Li signals are detected from the pristine surface of Li in CPE. This can be deduced from the signals of -CF3(292.6 eV in C1 s, 688.2 eV in F1 s) and C-OC (533.2 eV in O1s), as well as the 1% atomic ratio of Li (FIG. 41 b), assigning to PTFEA, PVC / PEGMEA side groups, respectively (Electrochimica Acta 2020, 337, 135843). Without PTFEA, the top surface of Li deposited in P(VC-PEGMEA) is covered by alkyl carbonate and Li2CO3, evident from the C 1 s and O 1s signals (0 min), along with the presence of an 8% atomic ratio of Li (FIG. 41c). As the etching goes deeper into the SEI layer (5 min), there is a synchronous decrease of the C signal observed in both CPE and P(VC-PEGMEA) while the Li signals elevate to 32%. At this stage, the intensity and proportion of the C-C signal (C 1 s) in P(VC-PEGMEA) diminish significantly, accompanied by an increase in the C-0 signal (O 1 s). This trend continues with further etching (15 min). This discrepancy demonstrates that the organic components of SEI in PVC are low molecule weight (LMW) with low modulus and fragility, which cannot protect Li from electrochemical corrosion (Nano Energy 2022, 95, 106983; Energy Storage Materials 2020, 27, 69). In contrast, the proportion of C-C and C-0 signals remains relatively stable in CPE, yet the C-F (688.6 eV) and Li-F (685.0 eV) signals constitute a significant portion.

[0190] According to the XPS results, in P(VC-PEGMEA), the SEI primarily comprises oligomers and low molecular weight (LMW) polymers of organic origin, while in CPE, fluorine-rich high molecular weight (F-HMW) polymers dominate. The LMW polymers, due to their inherent low modulus and fragility, prove ineffectual in shielding the anode from electrochemical corrosion (Nano Energy 2022, 95, 106983; Energy Storage Materials 2020, 27, 69). Conversely, F-rich HMW polymers exhibit high thermodynamic stability and flexibility, enabling them to accommodate the micro-volume changes of Li (Advanced Science 2021 , 8, 2003240; Journal of Materials Chemistry A 2019, 7, 17782; Advanced Energy Materials 2022, 12, 2103972). For the inorganic components, the SEI in CPE has discernible quantities of Li F, Li2CO3, Li3N, and Li2S (FIG. 42), encapsulated within the F-rich HMW polymers. These inorganic constituents act as reinforcing agents, suppressing Li dendrite growth (FIG. 41 d). Conversely, Li2CO3prevails as the predominant inorganic species in the SEI of P(VC-PEGMEA). Upon reaction with Li, Li2CO3forms electrically conductive LiCx, compromising the SEI's stability (J. Am. Chem. Soc. 2017, 139, 14992; Nano Lett. 2020, 20, 418; Electrochimica Acta 2016, 222, 221 ; Journal of Materials Chemistry A 2023, 11, 5636). Consequently, Li deposits horizontally and densely within CPE, in stark contrast to the disordered, dendritic growth observed in P(VC- PEGMEA) (FIG. 41 e and FIG. 43). The differences are further highlighted when examining the surface morphologies of the electrodes (FIG. 44). In P(VC-PEGMEA), the Li and Cu surfaces display noticeable rhagades, whereas in CPE, the surfaces are quite smooth.

[0191] According to the electrochemical and XPS results, it is the PTFEA side chains of CPE that play a special role in stabilizing Li anode. Microscopically, the formed F-rich organic-inorganic hybrid SEI with rigidity and flexibility suppresses side reactions and Li dendrite growth. Macroscopically, highly elastic CPE enabled by PTFEA accommodates intense volume fluctuations upon cycling, ensuring consistent conformal contact between Li and CPE. This process can be observed under an optical microscope. Moreover, the elastic CPE covers above the SEI, serving as an ideal buffer layer to accommodate the volume changes of Li. This process can be observed under the optical microscope. As shown in FIG. 45a, the Li dendrites appear during plating in LE while the interface remains flat in CPE. Cross-sectional SEM images reveal dense and columnar Li within CPE (FIG. 45b), confirming the physical buffer effect and chemical (unique SEI) dual protection.

[0192] At last, due to the preferential concentration of TFSI-cations in the fluorinated microphase and the small binding energy between non-fluorinated side chains and Li+in CPE, the Li-ion transference number (tLi+) reaches 0.59 (FIG. 46 and FIG. 47), higher than the conventional PEO-based electrolyte (~0.3). The microphase-separated structure of PCE greatly improves the lithium-ion transference number (tLi+). The TFSI- ions are concentrated in the hydrophobic fluorinated microphase due to the “fluorous effect” between the TFSI- and fluorinated segments, restricting the movement of anions and increasing (J. Am. Chem. Soc. 2020, 142, 7393). In addition, the interaction between carbonate groups and Li+in CPE is much weaker than that between ether groups and Li+in PEG. According to DFT calculated (FIG. 47a), the binding energy (Ebinding) of PEG is -4.05 eV. Such a strong coordination of EO-t Li+results in low room-temperature ionic conductivity and a slower Li+migration efficiency than that in P(TFEA-VC) side chains. Furthermore, compared with the linear structure in PEO, the long side chains in comb-like or crosslinked polymer matrix will create abundant steric hindrance (FIG. 47b). Consequently, large bis(trifluoromethane) sulfonamide anions are entrapped within the polymer network but small Li+ions are almost unaffected (Polymer International 2019, 68, 684). The high tu+ of CPE can reduce the concentration polarization and space charge layer effect, facilitating uniform Li deposition.

[0193] Example 7: Electrochemical performances of CPE-based full cells

[0194] The high oxidation resistance stability of CPE is attributed to the F-rich PTFEA side chains, which bolsters the electron-withdrawing capability of the polymer matrix, and the addition of LiDFOB (0.2 M), a salt widely recognized for high-voltage film-forming ability (Journal of Power Sources 2017, 357, 97; J Appt Electrochem 2012, 42, 291 ).

[0195] Results and Discussions

[0196] As FIG. 48 shows, the oxidation window of CPE extends up to 4.97 V (with a current < 5pA cm2), surpassing that of CPE with a single salt (1.5 M LiTFSI) at 4.82 V, and significantly higher than P(VC-PEGMEA) at 4.38 V.

[0197] The LSV test of CPE is conducted using different working electrodes (FIG. 49), demonstrating high oxidation-resistant voltage. The cathodic compatibility of CPE is further examined by comparing the charge / discharge profile (3.0-4.3 V) of Li||NCM81 1 full cells. As shown in FIG. 50a-c, CPE-based full cell exhibits overlapped charge / discharge curves (0.1 C— > 0.2 C, 20 cycles), indicative of high interfacial and structural stability. When paired with LiNi08Co0.1Mn0.1O2 (NCM81 1 ) cathode and Li anode, CPE-based full cell exhibits overlapped charging / discharging curves (FIG. 50a). The cells operating without LiDFOB show an inferior capacity retention. In sharp contrast, the P(VC-PEGMEA)-based cell fails abruptly by the 7th cycle, and the continuous charging process suggests severe decomposition of the polymer matrix.

[0198] As FIG. 51 a shows, the CPE-based Li| NCM81 1 cell maintains a high discharge capacity of 110 mAh g-1at 0.8C and a capacity recovery of 97% when the rate gets back to 0.3 C. During long-term cycling (FIG. 51 b), the CPE-based Li |NCM811 cell exhibits a high discharge capacity of -190 mAh g-1during initial formation cycles and capacity retention of 90% after 200 cycles (0.5C), excelling cell that cycled in the commercial liquid electrolyte-based (LE) (45% capacity retention after 76 cycles). The cycling performances with varying mass-loading and rate are shown in FIG. 52. Furthermore, single-layer pouch cells with 200 μm Li foils as anodes and cathodes comprising 4 mg cm-2NCM81 1 were assembled and tested (FIG. 51c). The discharge capacity of the CPE-based pouch cell exhibits a 92% capacity retention after 86 cycles at 0.3C under a low stack pressure of 0.1 MPa. At a high mass loading of 10mg cnr2and a charge / discharge voltage range between 3-4.3 V, the solid polymer full battery exhibits 197 mAh g1initial capacity at 0.1 C and remains 176 mAh g1(642.4 Wh / kg based on cathode materials) at 40thcycles (FIG. 53). LiFePO4(LFP) cathode (19.8 mg cm2) and a Li anode, the full cell maintains 97% of capacity retention (133 mAh g1, 425 Wh / kg on cathode materials) after 80 cycles.

[0199] To investigate the structural evolution of cathode, the cycled NCM81 1 (20 cycles, 0.1 C) was examined under a transmission electron microscope (TEM). As shown in FIG. 51 d, the cathode particles cycled in CPE exhibit a thin layer of CEI. However, thick inactive phases (disordered and rock-salt) are evident on the surface of the cycled cathode in LE. The destruction of the original layered structure of NCM811 and the thick CEI blocks normal Li ion- exchange, causing increased polarization (S. Hwang, S. M. Kim, S.-M. Bak, K. Y. Chung, W. Chang, Chem. Mater. 2015, 27, 6044; Chem. Mater. 2018, 30, 692; ACS Appt. Mater. Interfaces 2020, 12, 32698). When the CPE is paired with the high-loading LiFePO4(LFP) cathode (19.8 mg erm2), the full cell maintains 97% of capacity retention after 80 cycles (FIG. 51 e). Furthermore, the mechanical durability of CPE enables the assembly of a flexible naked battery (without metal casing). As FIG. 51 f show, the flexible battery operates normally under repeating bending, stretching, and needling tests, demonstrating its huge potential for application in flexible electronic devices.

Claims

CLAIMS:

1. A polymer electrolyte comprising a co-polymer and alkali metal ions, the co-polymer comprising a first, a second and optionally a third constitutional unit, wherein, the first constitutional unit is formed from a first monomer selected from the group consisting of a 5 to 8 membered cyclic carbonate and a 5 to 8 membered cyclic ether, wherein said cyclic carbonate or cyclic ether comprises an unsaturated carbon- carbon bond or is substituted by a methylidene, vinyl or allyl group, and is unsubstituted or substituted by one or two C1 -6alkyl or phenyl groups; the second constitutional unit is formed from a second monomer selected from the group consisting of a C1-6alkyl acrylate and a C1-6alkyl methacrylate, said C16alkyl of the C1-6alkyl acrylate or C1-6alkyl methacrylate substituted by one or more halogen atoms; and the third constitutional unit is formed from a third monomer selected from the group consisting of a polyethylene glycol) acrylate and polyethylene glycol) methacrylate.

2. The polymer electrolyte of claim 1 , wherein the first constitutional unit is formed from a first monomer selected from the group consisting of vinylene carbonate, vinylethylene carbonate, and 2-methylene-1 ,3-dioxepane.

3. The polymer electrolyte of claim 1 or 2, wherein the C1 -6alkyl group of the C1-6alkyl acrylate or the C1-6alkyl methacrylate is substituted by three or more halogen atoms, for example three or more fluorine atoms.

4. The polymer electrolyte of claim 3, wherein the second constitutional unit is formed from a second monomer selected from the group consisting of 2,2,2-trifluoroethyl acrylate (TFEA), 2,2,3,3-tetrafluoropropyl acrylate (TFPA), 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA), 2-perfluorohexylethyl acrylate, 2-(perfluorobutyl)ethyl acrylate, 1 , 1 ,2,2- tetrafluoroethyl acrylate, 2-(perfluorooctyl)ethyl methacrylate, and 3, 3, 4, 4, 5, 5, 6,6,6- Nonafluorohexyl acrylate, for example, the second monomer is 2,2,2-trifluoroethyl acrylate (TFEA).

5. The polymer electrolyte of any one of the preceding claims, wherein the first and second constitutional units are present in the co-polymer at a molar ratio of first to second constitutional unit of from about 8:1 to about 1 :8 (e.g. 1 :1 ).. The polymer electrolyte of any one of one of the preceding claims, wherein the co- polymer comprises the first, second and third constitutional units.

7. The polymer electrolyte of claim 6, wherein the third monomer is a poly( ethylene glycol) acrylate or poly( ethylene glycol) methacrylate with a number average molecular weight of from about 200 g / mol to about 3000 g / mol, for example from about 400 g / mol to about 1500 g / mol (e.g. about 900 g / mol).

8. The polymer electrolyte of any one of one of the preceding claims, wherein the polymer electrolyte is formed by a polymerisation reaction between the first, second, and third monomers, wherein the first, second, and third monomers react in a reaction mixture comprising equal to or less than 70 mol% of the second monomer relative to the total number of moles of the first, second, third monomer in the reaction mixture.

9. The polymer electrolyte of claim 8, wherein the first, second, and third monomers react at a molar ratio of first, second, to third monomer of from about 1 :1 :1 to 600:600:1 (e.g. about 600:300:1 , about 60:30:1 , or about 30:15:1 ).

10. The polymer electrolyte according of any one of one of the preceding claims, wherein the co-polymer comprises a structure according to formula (I):each m , n and p are integers independently selected from 1 to 10; each s is an integer selected from 1 to 20 (e.g. 1 to 15 or 10 to 15, for example 13);R1and R2are each independently H or methyl;X is C1 10alkylene optionally substituted by one or more fluorine atoms; andY is H or a fluorine atom.11 . The polymer electrolyte of claim 10, wherein R1and R2are each H or methyl, X is C1-8alkylene substituted by one or more fluorine atoms, and Y is H or a fluorine atom.

12. The polymer electrolyte of claim 10, wherein R1and R2are each H, X is C1alkylene, and Y is a fluorine atom.

13. The polymer electrolyte of any one of the preceding claims, wherein the alkali metal ions are lithium ions, sodium ions or potassium ions.

14. The polymer electrolyte according of claim 1 , wherein the polymer electrolyte comprises a structure according to formula (la):wherein, n, m and p each represent integers corresponding to the number of each constitutional unit present in the co-polymer.

15. The polymer electrolyte of claim 13 or 14, wherein the alkali metal ions are derived from one or more alkali metal salts selected from the group consisting of lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalatoborate (LiDFOB), and a combination of two or more thereof.

16. The polymer electrolyte of claim 15, wherein the alkali metal ions are derived from a combination of LiTFSI and LiDFOB.

17. The polymer electrolyte of claim 16, wherein the molar ratio of LiTFSI to LiDFOB is 1 :20 to 20:1 , for example 13:2 (i.e. 13:2).

18. The polymer electrolyte of claim 13, wherein the alkali metal ions are derived from one or more alkali metal salts selected from the group consisting of sodium hexafluorophosphate, sodium bis(trifluoromethanesulfonyl)imide, sodium tetrafluoroborate, sodium trifluoroacetate, sodium trifluoromethanesulfonate, sodium fluorosulfonyl imide), and a combination of two or more thereof.

19. The polymer electrolyte of claim 13, wherein the alkali metal ions are derived from one or more alkali metal salts selected from the group consisting of potassium hexafluorophosphate, potassium bis(trifluoromethanesulfonyl)imide, potassium tetrafluoroborate, potassium trifluoromethanesulfonate, potassium trifluoroacetate, and a combination of two or more thereof.

20. A method of preparing the polymer electrolyte of one of claims 1 to 19 for use in an alkali metal battery, said method comprising forming the polymer electrolyte by a polymerisation reaction between the first monomer, the second monomer, and optionally the third monomer, on a surface of a substrate.21 . The method of claim 20, wherein the substrate is a separator for an alkali metal battery, for example a polypropylene separator film.

22. A battery comprising the polymer electrolyte of any one of claims 1 to 19.

23. The battery of any one of claims 21 to 22, wherein the alkali metal battery is a lithium- metal battery.

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