WO2025224744A1

WO2025224744A1 - Polymer electrolyte composition for tailoring cathode/ electrolyte interface in quasi-solid state metal batteries

Info

Publication number: WO2025224744A1
Application number: PCT/IN2025/050625
Authority: WO
Inventors: Priyanka Pandinhare PUTHIYAVEETIL; Sreekumar Kurungot
Original assignee: Council of Scientific and Industrial Research
Current assignee: Council of Scientific and Industrial Research
Priority date: 2024-04-26
Filing date: 2025-04-21
Publication date: 2025-10-30
Anticipated expiration: 2026-10-26

Abstract

The present disclosure relates to a hydrogel polymer electrolyte composition. Further, the present disclosure also relates to a method of preparation of a hydrogel polymer electrolyte composition. Furthermore, the present disclosure also provides hydrogel polymer electrolyte integrated cathode. The present disclosure provides a Quasi-solid state metal battery, where the battery e.g. QSS-Zn | PHPZ-30 | i-Zn-MnO cell delivers a specific capacity of 229 mAhg^-1 at the current density of 0.10 A g^-1 and a capacity retention of 85 % over 1000 stability cycles at 1.0 A g^-1, which is better than its bare Zn-MnO cell, i.e., QSS-Zn|PHPZ-30|Zn-MnO, which delivers a specific capacity of 164.6 mAh g^-1 at the current density of 0.10 A g^-1 and 75% capacity retention over 100 stability cycles at 1.0 A g^-1.

Description

POLYMER ELECTROLYTE COMPOSITION FOR TAILORING CATHODE/ ELECTROLYTE INTERFACE IN QUASI-SOLID STATE METAL BATTERIES

FIELD OF THE INVENTION

The present disclosure relates to a hydrogel polymer electrolyte composition. Further, the present disclosure also relates to a method of preparation of a hydrogel polymer electrolyte composition. Furthermore, the present disclosure also provides hydrogel polymer electrolyte integrated cathode. The present disclosure provides a Quasi-solid state metal battery.

BACKGROUND OF THE INVENTION

Aqueous rechargeable zinc metal batteries (ARZMBs) are gaining a lot of research interest because of their high reliability, environmental friendliness and safety. In literature, there are many problems discussed related to aqueous electrolytes in the rechargeable metal batteries which is the aqueous electrolytes in the battery cause O2 evolution (OER) at 1.98 V vs Zn|Zn²⁺ which restricts the operating voltage of the cell also, corrosion, random zinc deposition over time, sluggishness, dendrite piercing of separator, etc. limiting the usage of cell for longer duration. However, to get beyond these challenges electrolyte engineering is found to be an effective strategy to stabilize the electrode|electrolyte interface. In this context quasi-solid state gel polymer electrolyte has been considered recently owing to their interfacial stability, good ionic conductivity (IO^-4 to 10’³ S cm ¹ at room temperature), and adequate mechanical strength. The hydrogel polymer electrolyte (HGPE) generally consists of a polymer 3D network with trapped liquid which reduces the corrosion over the zinc anode and extend the cycle life. However, even with these obvious benefits challenges at the cathode|electrolyte interfaces are often overlooked in these quasi-solid state rechargeable zinc metal batteries (QSS-RZMBs). The conventional way of keeping the electrolyte membrane/film in between an anode and cathode (ex-situ process) results in the inferior cathode|electrolyte interface formation.

Hence, to address such problems, and obtain efficient quasi-solid state rechargeable zinc metal batteries, there is need to provide tuning the cathode-electrolyte interface to improve the performance of quasi-solid state zinc metal batteries.

OBJECTIVES OF THE INVENTION The primary object of the present invention is to provide a hydrogel polymer electrolyte composition.

Another object of the present invention is to provide a method of preparation of a hydrogel polymer electrolyte composition.

Still another object of the present invention is to provide a hydrogel polymer electrolyte integrated cathode.

Yet another object of the present invention is to provide a Quasi- solid state rechargeable metal battery.

SUMMARY OF THE INVENTION

An aspect of the present disclosure is to provide a hydrogel polymer electrolyte composition for a quasi-solid state metal battery, comprising: a. polyethylene glycol (PEG) as a plasticizer, b. a monomer, c. a crosslinker, d. UV-initiator, e. a zinc salt as additive, and f. water; wherein the monomer is present with a concentration in the range of 20.8 to 25.6 %w/w of the total composition.

In an embodiment, the plasticizer is present with a concentration in the range of 5.2 to 6.4 %w/w of the total composition.

In an embodiment, the crosslinker is present with a concentration in the range of 1.3 to 1.6 %w/w of the total composition.

In an embodiment, the UV-initiator is present with a concentration in the range of 0.1 to 0.2 %w/w of the total composition.

In an embodiment, the additive is present with a concentration in the range of 20 to 35 %w/w of the total composition.

In an embodiment, the water is present with concentration in the range of 39 to 48 %w/w of the total composition.

In an embodiment, the monomer is selected from hydroxyethyl methacrylate (HEMA) and 2 -hydroxypropyl methacrylate (HPMA).

In an embodiment, the crosslinker is selected from poly(ethylene glycol) diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), and polyethylene glycol diacrylamide (PEGDAA).

In an embodiment, the UV-initiator is selected from 2-hydroxy-2-methylpropiophenone (HMPP) and 2,2-dimethoxy-2-phenylacetophenone (DMPA).

In an embodiment, the zinc salt is selected from a group consisting of zinc trifluromethane sulfonate (ZniCFvSOsh), zinc sulfate heptahydrate (ZnSO4.7H2O), zinc nitrate tetrahydrate [Zn(NO3)2.4H2O], and zinc chloride (ZnCh), or any of combination thereof.

In another aspect, the present disclosure provides a process of preparation of the hydrogel polymer electrolyte composition as claimed in claim 1, comprising steps of: i) mixing 5.2 to 6.4 %w/w of plasticizer with 20.8 to 25.6 %w/w of monomer to obtain a first mixture; ii) blending and mixing the first mixture of step i) with 1.3 to 1.6 %w/w of crosslinker to form a second mixture; iii) adding and mixing the second mixture of step ii) with 39 to 48 %w/w of water to form a third mixture; iv) adding and mixing the third mixture of step iii) with 20 to 35 %w/w of zinc salt to form a fourth mixture; and v) adding and mixing the fourth mixture of step iv) with 0.1 to 0.2 %w/w of UV initiator to initiate polymerization and to obtain the hydrogel polymer electrolyte composition.

In an embodiment, the steps i) to iv) are done under stirring temperature in the range of 20-35 C in a vertex stirrer for time period in the range of 10-20 minutes.

In an embodiment, the step v) is carried out under UV light for time period in the range of 10 min to 30 min, wherein UV wavelength of the UV light is in the range of 315-400 nm.

In another aspect, the present disclosure provides a quasi-solid state metal battery, comprising: i. the hydrogel polymer electrolyte composition; ii. a hydrogel polymer electrolyte integrated cathode; and iii. a battery assembly components.

In an embodiment, the battery assembly components comprises a top case, a spring, a spacer, zinc foil as anode, and a bottom case.

In an embodiment, the quasi-solid state metal battery is selected from sodium ion battery, lithium ion battery, zinc-air battery, and quasi-solid-state reversible zinc metal battery.

In an embodiment, the hydrogel polymer electrolyte integrated cathode comprises coating of the hydrogel polymer electrolyte composition onto Zn-MnO cathode.

In an embodiment, the hydrogel polymer electrolyte integrated cathode is prepared by a process comprising in situ cross-linking of the hydrogel polymer electrolyte composition over the Zn-MnO cathode surface, wherein the in situ cross-linking is done by drop casting the hydrogel polymer electrolyte composition onto the Zn-MnO cathode for time period in the range of 0.5 to 2 minutes for the complete infiltration followed by exposing to UV light for 20-45 minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates method of preparation of a hydrogel polymer electrolyte composition, and its integration with the cathode.

Figure 2 illustrates FESEM Images of MnO and Zn-MnO.

Figure 3 illustrates (a-c) HRTEM images of MnO, (d-f) Zn-MnO recorded at different magnifications respectively; (g) and (h) the corresponding enlarged portion from (c) and (f) respectively, (i) twin boundary region from (f) ;(j) HAADF STEM image (k-m) the corresponding STEM-EDS elemental mapping images of Mn, 0, and Zn in Zn-MnO sample respectively.

Figure 4 illustrates (a) The XRD Profiles, (b) the corresponding enlarged portion from XRD (c) the raman spectra; (d) the BET isotherms (e) the pore-size distribution profile (f,g) water contact angle study of MnO and Zn-MnO sample respectively.

Figure 5 illustrates deconvoluted (a) Mn 2p spectra and (b) O Is spectra of MnO and Zn-MnO sample respectively.

Figure 6 shows EIS plot of the PHPZ-x polymer gel electrolyte.

Figure 7 shows stress versus strain plots associated with the PHPZ-x samples showing the mechanical properties under compression mode

Figure 8 illustrates (a) ESV analysis at O.lmV s’¹ scan rate from 1 to 2.5 V and (b) CV analysis at 0.1 mV s’¹ scan rate from -0.25 to 0.25 V in an asymmetric cell SS|PHPZ-x|Zn showing oxidation and reduction stability respectively.

Figure 9 illustrates (a) Galvanostatic plating/stripping profiles of the PHPZ-30 membranes in symmetric Zn||Zn cell (b) the corresponding voltage vs time plot.

Figure 10 illustrates (a) Galvanostatic plating/stripping profiles of the 0.5M Zn/CFsSChh aqueous electrolyte in symmetric Zn||Zn cell (b) the corresponding voltage vs time plot.

Figure 11 illustrates (a) the XPS survey spectra comparison of Zn-MnO and i-Zn-MnO electrode, (b) FESEM image of Zn-MnO electrode (c) i-Zn-MnO electrode and (d) the EDS elemental mapping of i-Zn-MnO respectively.

Figure 12 illustrates (a) the 3D computed tomography image of Zn-MnO, (b) The 3D computed tomography image of PHPZ-30 electrolyte (c) The 3D computed tomography image of percolation pathway and Zn-MnO metal oxide (d) Confocal 3D images obtained by z stacking and 3D construction of the i-Zn-MnO cathode demonstrating the homogeneous polymer coating over the cathode, as evident from the uniform distribution of the fluorescent particles (tracers) throughout the surface (green).

Figure 13 illustrates (a) the CV profile at 1 mV s’¹, (b) the GCD profile at 0.1 A g’¹ current rate (c) the impedance spectra (d) rate capability plot of QSS-Zn|PHPZ-30|i-Zn-MnO and QSS-Zn|PHPZ-30|Zn-MnO cell respectively.

Figure 14 illustrates a) the CV profiles acquired at the scan rates of 1.0, 0.50, 0.30, and 0.10 mV s’¹, (b) the log (i, current) vs. log (v, scan rate) plot of QSS-Zn|PHPZ-30| i-Zn-MnO cell.

Figure 15 illustrates a) the cycling stability plot of QSS-Zn|PHPZ-30|i-Zn-MnO cell.

Figure 16 illustrates a quasi-solid state metal battery.

Figure 17 shows digital photographs of the PHPZ-x electrolyte film: PHPZ-20 (a, b), PHPZ-25 (c, d), and PHPZ-35 (e, f).

Figure 18 shows the comparison of the ionic conductivity of the PHPZ-x series of the membranes.

Figure 19 shows the Nyquist plots of the SS|Electrolyte|SS cell.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure provides an efficient quasi-solid state zinc metal battery; the present disclosure provides stunning the cathode-electrolyte interface to improve the performance of quasi-solid state zinc metal batteries. The combination of gel polymer electrolyte and modified cathode using the gel polymer electrolyte offers improved interface stability, increased ion transport, Zn dendrite not forming, extended cycle life, and corrosion mitigation etc.

The 2 -hydroxyethyl methacrylate (HEMA) as a monomer in the disclosed composition, is a hydrophilic monomer having hydroxyl and carbonyl functional groups which enhances the salt solubility and the cationic transport property.

The PEGDMA (polyethylene glycol dimethacrylate) has almost identical to PEGDA but with methacrylate groups instead of acrylates (slower polymerization).

The DMPA (2, 2-dimethoxy-2-phenylacetophenone), also known as an alpha-hydroxy ketone type; highly efficient under 365 nm wavelength.

An embodiment of the present disclosure provides a hydrogel polymer electrolyte composition comprising: 5.6 to 6.4 %w/w of polyethylene glycol (PEG), 22.4 to 25.6 %w/w of hydroxyethyl methacrylate (HEMA), 1.4 to 1.6 %w/w of poly(ethylene glycol) diacrylate (PEGDA), 0.1 to 0.2 %w/w of 2-Hydroxy-2-methylpropiophenone (HMPP), 20 to 30 %w/w of Zinc salt and 42 to 48 %w/w of water.

In an embodiment, the zinc salt can be selected from a group consisting of zinc trifluromethane sulfonate (ZnfGFsSCh ), ZnSC .VHiO, Zn(NO3)2.4H2O, ZnCh and combination thereof.

In a preferred embodiment, the polyethylene glycol is present in the range of 5.6 to 6.2 %w/w. More preferably, the polyethylene glycol is present in the range of 5.6 to 6.0 %w/w.

In a preferred embodiment, the hydroxyethyl methacrylate is present in the range of 22.4 to 24.0 %w/w. More preferably, the hydroxyethyl methacrylate is present in the range of 22.4 to 23.0 %w/w.

In a preferred embodiment, the poly(ethylene glycol) diacrylate is present in the range of 1.4 to 1.5 %w/w. More preferably, the poly(ethylene glycol) diacrylate is present in the range of 1.4 to 1.45

In a preferred embodiment, the 2-hydroxy-2-methylpropiophenone is present in the range of 0.1 to 0.18 %w/w. More preferably, the 2-hydroxy-2-methylpropiophenone is present in the range of 0.1 to 0.16 %w/w.

In a preferred embodiment, the zinc salt is present in the range of 22 to 30 %w/w. More preferably, the zinc salt is present in the range of 24 to 30 %w/w.

In a preferred embodiment, water is present in the range of 42 to 46 %w/w. More preferably, water is present in the range of 42 to 44%w/w.

Another embodiment of the present disclosure provides a process of preparation of a hydrogel polymer electrolyte composition comprising: i) mixing 5.6 to 6.4 %w/w of polyethylene glycol (PEG) with 22.4 to 25.6 %w/w of hydroxyethyl methacrylate (HEMA) to form a first mixture; ii) blending the first mixture with 1.4 to 1.6 %w/w of poly (ethylene glycol) diacrylate (PEGDA) with stirring to form a second mixture; iii) adding 42 to 48 %w/w of water to the second mixture with stirring to form a third mixture; iv) adding 20 to 30 %w/w of zinc salt to the third mixture to form a fourth mixture; v) adding 0.1 to 0.2 %w/w of 2-Hydroxy-2-methylpropiophenone (HMPP) to the fourth mixture to initiate the UV polymerization under condition to form a hydrogel polymer electrolyte composition. In each step, the stirring of the electrolyte precursor done at room temperature (about 20-35 °C) in a vertex stirrer for 10-20 minutes.

In an embodiment, the polymerization in step v) is carried out under UV light in the range of 10 min to 30 min in an UV chamber (OSRAM LBL UVA 15w/78) having UV wavelength in the range of 315-400 nm.

Still another embodiment of the present disclosure provides a hydrogel polymer electrolyte integrated cathode comprising: Zn-MnO cathode and hydrogel polymer electrolyte composition.

In an embodiment, firstly, Zn-MnO cathode material is prepared. Initially, potassium permanganate (KMnO4) in the reaction mixture ionizes in the slightly acidic medium to form manganese oxoanion (MnC ). The manganese oxoanion is quickly reduced by H3O⁺ species. In the second step an additional solution containing Mn²⁺ ions were added. These MnO⁴7Mn²⁺ species in the reaction mixture eventually get oxidized into manganese oxide in the course of the reaction. The synthesis of Zn-MnO follows the same as the above except in the last step a trivial amount of dopant (Zn) was introduced. The substitutional doping of Zn in the MnO lattice was achieved in the course of the reaction.

In an embodiment, cathode slurry was prepared by mixing 80 wt. % of active material, 15 wt. % conductive carbon, 5 wt.% PVDF binder in 250 pl NMP solution followed by ultra- sonication for a period in the range of 2 h to 4 h. In the second step, the homogeneous slurry was coated over the foil current collector of 1 cm² area to get a loading of 1 mg via the drop-casting method. The coated electrode dried in an oven at a temperature in the range of 50 to 70 °C for a period of 8 to 12 h, preferably, at temperature of 60 °C for a period of 10 h.

In an embodiment, the gel polymer electrolyte integrated cathode (i-Zn-MnO) was prepared by in situ cross-linking of the electrolyte precursor over the cathode surface. 5 pl of PHPZ electrolyte precursor was drop casted over the Zn-MnO cathode allowed to rest for 30 second to 5 minutes, preferably for 1 minute for the complete infiltration and then exposed to UV light for a period in the range of 10 to 60 minutes, preferably for 30 minutes.

Still another embodiment of the present disclosure provides a Quasi-solid state metal battery comprising: a top case; a spring; spacer; zinc foil; a hydrogel polymer electrolyte composition; a hydrogel polymer electrolyte integrated cathode; and a bottom case. In an embodiment, the metal batteries can be selected from sodium ion batteries, lithum ion batteries, zinc-air batteries and like.

In a nutshell, the present disclosure provides a novel 2-hydroxyethyl methacrylate (HEMA) based Zn²⁺ ion conductive hydrogel polymer electrolyte membrane with high transference number, ionic conductivity, and mechanical strength was developed by the UV light-assisted polymerization process for the quasi- solid state rechargeable zinc metal battery (QSS-RZMB) applications. The electrolyte composition membrane developed here is flexible and freestanding, with the ability to withstand a stable voltage window of up to 2.1 V vs. Zn|Zn²⁺. With the electrolyte composition Zn ion conducting membrane, an epitaxial deposition of zinc was obtained over the Zn anode by the 3D diffusion kinetics of the Zn²⁺ ions, which significantly irradiated the zinc dendrites development. This resulted in increased interfacial stability for the Zn anode in comparison to its liquid counterpart. Benefiting the hydrogel polymer electrolyte membrane, the lifespan of the symmetric Zn|PHPZ-30|Zn cells extends to 962 h at the current density of 0.10 mA cm^-2 and the capacity of 0.1.0 mAh cm^-2. Additionally, a compactable 3D cathode skeleton, i.e., zinc-doped manganese oxide (Zn-MnO), for the hydrogel polymer electrolyte was synthesized by a reflux reaction, where the Zn doping was found to be generating the twin boundary defects and oxygen defects in the MnO lattice with a concomitant enhancement in the specific surface area, porosity, and hydrophilicity. Further, as a concerted effort to minimize the contact problem between the Zn-MnO cathode and hydrogel polymer electrolyte composition in the QSS-RZMB cell, the electrolyte integration to the Zn-MnO cathode (i-Zn-MnO) was done by a UV-assisted “in situ polymerization”. This technique has created a Zn²⁺ ion conductive hydrogel polymer electrolyte network directly within the porous cathode structure by polymerizing the hydrogel polymer electrolyte into the pores dispersed across the cathode’s submicron regions, creating a better cathode | electrolyte interface with improved adhesion characteristics and compatibility. The coexistence of nanowires for direct electron routes and the enhanced electrolyte ion infiltration and diffusion by the 3D porous flower structure with a wide open surface of the Zn-MnO complemented the interface formation during the in situ polymerization process. The better-designed QSS-Zn | PHPZ-30 | i-Zn-MnO cell delivers a specific capacity of 229 mAh g^-1 at the current density of 0.10 A g^-1 and a capacity retention of 85% over 1000 stability cycles at 1.0 A g^-1. In contrast, the device based on bare Zn-MnO, i.e., QSS-Zn|PHPZ-30|Zn-MnO, delivers a specific capacity of 164.6 mAh g^-1 at the current density of 0.10 A g^-1 and 75% capacity retention over 100 stability cycles at 1.0 A g^-1. Furthermore, the demonstration of a pouch cell based on 2 series connected Zn|PHPZ-30|i-Zn-MnO cells was able to illuminate a blue light-emitting diode (LED) for 12 h.

EXAMPLES

Example 1

(i) Hydrogel polymer electrolyte composition:

Composition of monomer/oligomer used in the preparation of gel polymer electrolyte is given in Table 1.

Table 1: PHPZ-x hydrogel polymer electrolyte composition.

*2-hydroxy-2-methylpropiophenone (HMPP) is added with a concentration in the range of 0.1 to 0.2 %w/w in said formulations/compositions

(ii) Hydrogel polymer electrolyte preparation process

A series of PHP-based hydrogel polymer electrolytes were prepared by UV curing process and designated as PHPZ-x, where x indicates the weight percentage of ZniCFvS 6)3)2 in the hydrogel polymer electrolyte (HPE). In the typical synthesis process, 20, 25, and 30 % w/w of Zn(CF3SO3)2 mixed with PHP of particular weight percentage and a particular amount of UV initiator 2-hydroxy-2-methylpropiophenone (HMPP) were added and subjected to UV polymerization for about 30 minutes. The order of addition of hydrogel polymer electrolyte precursor is as follows, for example, in the case of PHPZ-30 5.6%w/w of PEG-400 was mixed with 22.4 %w/w of HEMA which was subjected to vigorous stirring for uniform blending to the above solution 1.4 %w/w of PEGDA-700 was added as the cross-linker. The above monomer/oligomer mixture (29.4 %w/w) was added to 42 %w/w of water and subjected to stirring. To the above solution, 30 %w/w of Zn(CF3SO3)2 salt was added as a final additive. To initiate the UV polymerization 0.1 %w/w of HMPP was added as UV initiator and precursor solution was cast in between the mylar films and subjected to UV polymerization for 30 minutes. The PHPZ-20, PHPZ-25, PHPZ-30 and PHPZ-35 differ in the weight percentage of electrolyte components given in the Table 1.

(iii) Preparation of Zn-MnO material

Zinc doped manganese oxide (Zn-MnO), the three-dimensional cathode skelton for the gel polymer electrolyte was synthesized by a reflux reaction in an oil bath at 160 °C for 6h (Figure 1). Initially, potassium permanganate (KMnC ) in the reaction mixture ionizes in the slightly acidic medium to form manganese oxoanion (MnOF). The manganese oxoanion is quickly reduced by H3O⁺ species. In the second step an additional solution containing Mn²⁺ ions were added. These reduced Mn²⁺ species in the reaction mixture eventually get oxidized by the dissolved oxygen into manganese oxide at a higher temperature (about 160 °C). The synthesis of Zn-MnO follows the same as the above except in the last step a trivial amount of dopant (Zn) was introduced. The substitutional doping of Zn in the MnOi lattice was achieved in the course of the reaction.

(iv) Cathode Preparation

Cathode slurry was prepared by mixing 80 wt. % of active material (Zn-MnO), 15 wt. % conductive carbon, 5 wt.% PVDF binder in 250 pl NMP solution followed by ultra- sonication for 3 h. In the second step, the homogeneous slurry was coated over the foil current collector of 1 cm² area to get a loading of Img via the drop-casting method. The coated electrode dried in an oven at 60 °C overnight.

(v) Preparation of gel polymer electrolyte integrated cathode

The gel polymer electrolyte integrated cathode (i-Zn-MnO) was prepared by in situ cross-linking of the electrolyte precursor over the cathode surface. 5 pl of PHPZ-30 electrolyte precursor (composition given in the Table 1) was drop casted over the Zn-MnO cathode allowed to rest for 1 minute for the complete infiltration and then exposed to UV light for 30 minutes.

(vi) Characterization of Zn-MnO cathode material

The morphology of MnO was analyzed by the Field Emission Scanning Electron Microscopy method (FESEM) (Figures 2 a, b, c). The corresponding images show a three-dimensional (3D) porous flower structure, formed by the ordered crosslinking of two-dimensional (2D) MnO sheets to minimize the surface energy. These individual sheets with an average thickness of around 22 nm make up the large open surface. As in the case of Zn-MnO (Figures 2 d, e, f), the FESEM images show the coexistence of long nanowires with a 3D flower structure. Although a long wire structure was created by elemental Zn doping in the MnOi lattice, the 3D flower structure accounts for the majority of Zn-MnO morphology (Figure 2f). The average diameter of the nanowire and individual sheet’s thickness was observed to be 17.7 nm and 16.7nm respectively. The Zn doping causes the thickness of 2D MnCh sheets to decrease, which results in a high surface area to volume ratio, exposing more active sites for electrochemical reactions.

The High-Resolution Transmission Electron Microscopy (HRTEM) images of MnO were recorded, and the corresponding images (Figure 3A-a-c) display the 2D sheets. However, the long nanowires and 2D thin sheets are seen in the HRTEM images of Zn-MnO (Figure 3A-d to f).The lattice fringes for MnO were detected at an inter planar spacing of 0.24 nm, corresponding to the (110) plane (Figure 3A-g) which is lower than that of the interplanar distance observed for Zn-MnO (110) plane, d= 0.246 nm (Figure 3h). This results from Zn ions (ionic radius: 0.074 nm) replacing Mn⁴⁺ (ionic radius: 0.053 nm) in the O-MnOi lattice. Additionally, twin boundary regions were observed (Figure 3A-i) in Zn-MnO sample.

Figure 3A-j depicts the High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF-STEM) image and the STEM-EDS elemental mapping images (Figure 3A - k to m) of the Zn-MnO sample show a uniform distribution of Mn, O, Zn elements however the intensity of Zn is found to be less due to doping. The compositional analysis by EDS shows that the Zn is present in 0.4 At% (Table 2).

Table 2: The composition analysis by EDS.

The FESEM images of the Zn-MnO cathode surface (Figure 3B- a to c) show an undulating surface with more voids due to its 3D structural characteristics. Such 3D pockets can act as “electrolyte reservoirs” and provide more active material electrolyte contact areas. In comparison to the Zn-MnO cathode, the i-Zn-MnO (after polymerization) cathode has negligible cracks over the surface with intact 3D structure after the in situ polymerization process (Figure 3B-d). The PHPZ-30 wrapping layer over Zn-MnO cathode material was analyzed through TEM (Figure 3B - g to i). As shown in Figure 3B-i, the TEM images of the i- Zn-MnO cathode display the PHPZ-30 hydrogel polymer electrolyte coating (indicated by arrow) over the Zn-MnO surface (indicated by arrow). This ensures intimate contact between the active material and the PHPZ-30 hydrogel polymer electrolyte. In addition to this morphological analysis, the presence of the PHPZ-30 layer over the Zn-MnO cathode was confirmed through FESEM-EDAX elemental mapping. There is a uniform distribution of the elements Zn, S, F, C, O, and Mn over the surface of the Zn-MnO cathode. The elemental composition of the surface of the i-Zn-MnO and Zn-MnO cathodes was also analysed through XPS analysis. This confirms the presence of the elements Zn, S, F, C, O, and Mn over the i-Zn-MnO cathode, assuring the successful polymerization. The results suggest that the cathode | electrolyte interface contains the Zn(CF3SO3)2 salt and the polymer matrix. The water contact angle measurement of i-Zn-MnO which demonstrate the super hydrophilicity of the electrode surface. This also proves the successfulness of the in situ polymerization process, indicating that the hydrophilic ionomer layer creates an increased affinity of the cathode surface toward the water. Thus, i-Zn-MnO cathode holds the ion conduction channels in the electrode matrix and allows more efficient movement of the ions with enhanced utilization of the active material than the Zn-MnO cathode in a quasi-solid-state zinc metal battery.

The major diffraction peaks of MnO appear at 26 = 12.3, 24.8, 37, 66.4 corresponding to the (001), (002), (110), and (020) planes respectively. All the XRD peaks can be indexed to the bimessite MnOi (5-MnO2, JCPDS 42-1317). The XRD peak of the Zn-MnO sample appears at 26 = 12.1, 24.6, 36.4, 65.4 for the (001), (002), (110), and (020) planes respectively. It is worth noting that all the peaks of Zn-MnO have a 26 shift towards the left indicating the lattice expansion (Figure 4a, b). The Raman spectra were recorded for the MnO and Zn-MnO samples, and the Raman bands for symmetric stretching of symmetric Mn-0 stretching vibrations of [MnOe] octahedra were observed at 639 cm'¹ for both samples however the much broader in case of Zn-MnO sample implying the presence of amorphous regions, and defects in the material (Figure 4c). The impact of Zn doping on the specific surface area and porosity of the material was assessed through Brunauer-Emmett-Teller (BET) measurements. Both MnO and Zn-MnO samples exhibit Type IV nitrogen adsorption-desorption isotherm, the existence of hysteresis loop in both isotherms suggest that materials are mesoporous in nature (Figure 4d). According to pore size distribution profile (Figure 4e), MnO, and Zn-MnO materials exhibit prominent pores across 3-4 nm. In comparison to MnO, the Zn-MnO sample exhibits a highly porous architecture due to the creation of abundant pores. The MnO porosity is altered by Zn doping, resulting in enhanced electrolyte infiltration thus enabling adequate contact between the electrode active material and electrolyte. Also the highly porous design of Zn-MnO cathode helps to evenly distribute the electrolyte throughout the material, ensuring consistent electrochemical performance. Additionally, the BET specific surface of MnO and Zn-MnO samples are compared, whose values are 83.5 and 84.3 m² g^-1 respectively.

Wettability of the electrodes plays a vital role in determining the performance of the battery cell. The wettability of MnO and Zn-MnO cathodes were determined by measuring contact angles; the lack of a contact angle for MnO cathode indicates super hydrophilicity (Figure 4f); on the other hand, the Zn-MnO sample created a water contact angle of 53.3°, demonstrating the hydrophilic characteristics (Figure 4g).

The Mn2p XPS spectra of MnO exhibits two characteristics spin-orbit peaks at 642 and 653.6 eV corresponds to the Mn 2p3/2 and Mn 2p 1/2 respectively. The deconvoluted Mn 2p3/2 exhibits peaks at 641.6 and 642.7 eV corresponds to Mn³⁺ and Mn⁴⁺ oxidation state respectively. Likewise the deconvoluted Mn 2p XPS spectra for Zn-MnO sample exhibits two peaks at binding energy 641.7 and 642.6eVconfirming the coexistence of Mn³⁺ and Mn⁴⁺ respectively (Figure 5a). The deconvoluted O ls spectra of MnO sample (Figure 5b) show three peaks at 529.3, 530.9 and 532.8 eV respectively, designated as Oi (lattice oxygen) and O2 (oxygen defects). The O Is spectra of Zn-MnO exhibits only two peaks corresponds to the lattice oxygen (Oi) and oxygen defects (O2) at 529.4 and 530.7 eV respectively. The peaks for oxygen defects are more intense and broad indicates more defects are created in the MnO lattice by Zn²⁺ doping. By adding tiny gaps to the crystal lattice, oxygen defects can improve materials porosity and also the electron transit can be enhanced (Figure 5b).

(vii) Impedance spectra for conductivity measurement Through-plane conductivity of the electrolyte film were measured by electrochemical impedance spectroscopy (EIS).The CR2032 cells were fabricated by keeping the desired electrolyte film having a radius of 0.65 cm and thickness around 0.055 cm in between two stainless steel plates of 1 mm thickness. The conductivity measurements were carried out between 25° to 70 °C at every 10 °C interval. The temperature was controlled by using an environmental test chamber. The impedance analysis shows that PHPZ-30 has highest ionic conductivity of 2.1*10^-2 S cm ¹. Whereas, PHPZ-20 and PHPZ-25 exhibit an ionic conductivity of 1.5* 10’² and 1.8* 10’² respectively as shown in Table 3 and Figure 6.

Table 3: Results of conductivity measurements

(viii) Characterization and Mechanical strength study of PHPZ-x membrane

All the PHPZ-x membranes synthesized were self-standing, transparent, and highly flexible [refer, figure 17 - PHPZ-20(a, b), PHPZ-25(c, d), and PHPZ-35(e, f)], having a thickness in the range 500-600 pm (specifically around 550 pm).

The polymer gel electrolyte formulation was optimized by considering key factors like the ionic conductivity at room temperature and its mechanical properties. Electrochemical impedance spectroscopy (EIS) was utilized to measure the ionic conductivity of the PHPZ-x electrolytes in the SS | PHPZ-x | SS cell configuration. For PHPZ-20, PHPZ-25, PHPZ-30, and PHPZ- 35, the ionic conductivity values obtained are 1.5, 1.8, 2.1, and 2.2 x 10^-2 S cm^-1 (Figure 18). The ionic conductivity gently improved with the increased content of the Zn(CF3SOs)2 salt due to the increase in the concentration of the mobile ions. The ionic conductivity of PHPZ-30 synthesized without PEG (sample is denoted as PHPZ-30/WO-PEG) was also evaluated and the conductivity value obtained is 9.9 x 10^-3 S cm^-1, significantly lower than that of PHPZ-30 sample, which further supports the importance of PEG as a component in the hydrogel polymer electrolyte synthesis. The EIS plots for all samples are given in Figure 19. The ionic conductivity of the PHPZ-x gel electrolyte series outperforms many of the reported gel electrolytes, as summarized in Table 4, and is sufficient for ion migration.

To evaluate the mechanical properties, compressive strength tests for every PHPZ-x membrane were conducted. The capacity of the polymer electrolyte to hold the stress and strain has increased with a gradual increase in the ZniCFsSOsJi salt content for PHPZ-20, PHPZ-25, and PHPZ-30, as shown by the stress versus strain plot in Figure 7. Among the series, PHPZ- 30 has exciting compressive stress and strain values of approximately 219 kPa and 75%, respectively.

Electrochemical Analysis was done to determine the oxidation and reduction stability of PHPZ-x membranes in an asymmetric (SS|PHPZ-x|Zn) cell. SS indicates stain less steel, Zn indicates Zn foil. The Figure 8a showed the linear sweep voltammetric curves of PHPZ-x done at a scan rate of 0.1 mV s ¹ from 1 to 2.5 V. The LS V profile shows an increase in the current only after 2.1V vs. Zn|Zn²⁺ indicates water decomposition. Reduction stability analysis is done by cyclic voltammetric scanning technique (Figure 8b). The CV profile clearly shows well defined peaks for plating and stripping of zinc ions.

The zinc plating- stripping experiment for PHPZ-30 were carried out in a Zn||Zn symmetric cell at 0.1 mA cm^-2 current rate. The cell was able run more than 962 h with stable voltage (Figure 9). The over potential for charge-discharge were measured and found to be 228 mV.

The zinc plating-stripping experiment for Zn||Zn symmetric cell configured with 0.5M Zn(CF3SO3)2 liquid electrolyte were carried out at 0.1 mA cm^-2 current rate. The cell was able run upto 325 h (Figure 10). There were voltage fluctuations in the charge-discharge profile indicating non-uniform deposition of zinc. The over potential for charge-discharge were measured and found to be 70 mV, lower as compared to PHPZ-30 based cell due to higher ionic conductivity of the liquid electrolyte.

(ix) Physical characterization of cathode|electrolyte interface

The physical characterization of cathode|electrolyte interface has been done through various techniques. The XPS survey spectra comparison of i-Zn-MnO and Zn-MnO given in the Figure Ila. The intense peaks for the elements Zn, F, O, C, S are observed in i-Zn-MnO cathode as compared to Zn-MnO cathode confirming the successful polymerization. The FESEM images of Zn-MnO and i-Zn-MnO having more or less similar texture implies polymer electrolyte precursor are infiltrated well across the pores of the cathode material (Figure 11 b,c). The energy dispersive spectroscopy (EDS) mapping confirms the presence of elements Mn, O, Zn, S, F, and C over the cathode surface (Figure 11 d).

The mapping of electrode microstructural constituents in 3D by X-ray tomography was performed and three phases were identified. Figure 12a shows an overlay of all three phases in i-Zn-MnO cathode vzz; 1) the Active material domain dark grey), 2) the network of the electrolyte-filled domain (white), and 3) the Carbon-binder domain (light grey). It is evident from Figure 6a that the surface of the Zn-MnO cathode is not planar due to the 3D structure of the material and there is a higher fraction of electrolyte domain present. The electrolyte percolation pathway in the segmented 3D dataset was stimulated in the Y direction using PoroDict® module of GeoDict® software (Version 2018). A long-range electron percolation pathway towards the current collector is visible from Figure 6b, with an average path length of 44 microns. The electrolyte phase with the electrolyte percolation path stimulated in the y direction is given in Figure 6b. The percolation path through the metal oxide phase is given in the Figure 6c. The volume- specific surface area calculated through PoroDict® module for the metal oxide, electrolyte, and carbon-binder phases is 2.5, 3.4, and 5.9 x 10⁵ m²/m³ respectively. It can be concluded from the surface area measurements that the domains of metal oxide and electrolytes coexist significantly all over the electrode volume.

The formation of polymer gel electrolyte layer over the cathode was further confirmed by the Confocal 3D imaging of the electrode by using a florescent tracer particle in the electrolyte precursor solution. The presence of green dot over the cathode surface implies the uniform electrolyte coating (Figure 12d).

Example 2: Quasi-solid-state reversible zinc metal battery Analysis (refer, Figure 16):

To investigate the potential application of QSS-RZMB with PHPZ-30 as the electrolyte and separator based on the proposed strategy, the QSS-Zn|PHPZ-30|i-Zn-MnO and QSS-Zn|PHPZ-30|Zn-MnO coin cells were assembled and tested. For comparison, a similar assembly based on 0.5 M Zn(CF3SO3)2 liquid electrolyte and Zn-MnO cathode along with activated Nation as the separator was also fabricated and tested. The CV profile comparison of QSS-Zn|PHPZ-30|i-Zn-MnO and QSS-Zn|PHPZ-30|Zn-MnO cell given in Figure 13a. The cyclic voltammetric (CV) profile for QSS-Zn|PHPZ-30|i-Zn- MnO cell was recorded at a scan rate of 1.0 mV s^-1 within the potential window of 0.60 to 2.0 V versus Zn|Zn²⁺, which displays (Figure 13a) a well-resolved redox peak for the Mn⁴⁺/Mn³⁺ redox pair at 1.3 and 1.6 V, respectively. Conversely, the CV profile of the QSS-Zn|PHPZ-30|Zn-MnO cell, which was made by replacing i-Zn-MnO cathode with the normal Zn-MnO cathode, shows a very weak redox peak, suggesting a poorly designed cathode|electrolyte interface (Figure 13a). These findings validate that a better-designed interface in the QSS-RZMB can greatly aid in controlling the mass transfer issues while nearly replicating the charge- storage characteristic of its liquid equivalent. The well resolved redox peaks are appeared for i-Zn-MnO cathode rather than the Zn-MnO cathode.

The GCD profile at 0.1 A g ¹ current rate in Figure 13b shows higher capacity output for the QSS-Zn|PHPZ-30|i-Zn-MnO cell. QSS-Zn|PHPZ-30|i-Zn-MnO exhibits a specific capacity of 229.2 mAh g^-1 which is distinctively superior to that of the conventional QSS-Zn|PHPZ-30|Zn-MnO cell (165 mAh g^-1). The better charge storage ability of i-Zn-MnO cathode as compared to Zn-MnO can correlate with the better cathode | electrolyte interface formation as in case of i-Zn-MnO due to in situ-polymerization approach. As previously stated, unlike Zn-MnO, i-Zn-MnO possesses an enhanced electrode-electrolyte interface, which enables the QSS-Zn| PHPZ-30|i-Zn-MnO cell to exhibit a charge- storage capacity nearly comparable to its liquid-state counterpart (210.1 mAh g^-1 at 0.10 A g^-1).

The rate capability analysis of both cells further reveal the better rate performance as in case of QSS-Zn | PHPZ-30 | i-Zn-MnO cell due to better interface formation (Figure 13c). This in turn reflected in the impedance spectra of the cells, in the lower solution resistance (R_s) and charge-transfer resistance (R_ct) for the QSS-Zn | PHPZ-30 | i-Zn-MnO cell is observed as compared to QSS-Zn-MnO | PHPZ-30 | Zn cell (Figure 13c).

Further, the Zn|0.5 M Zn(CF₃SO₃)₂|Zn-MnO, Zn|PHPZ-30|i- Zn-MnO, and Zn|PHPZ-30|Zn-MnO cells were subjected to the EIS measurements and the corresponding Nyquist plots obtained after the first discharge (refer, figure 13d). The liquid cell, i.e., Zn|0.5 M Zn(CF₃SO₃)2|Zn-MnO, exhibits a charge transfer resistance (R_ct) of 234 Q, compared to 427 Q displayed by QSS-Zn|PHPZ-30|i-Zn-MnO and a significantly high value of 800 Q shown by QSS-Zn|PHPZ-30|Zn-MnO. This stands out as valid evidence of the reduced interfacial resistance conceived at the cathode | electrolyte interface by adopting the in situ polymerization strategy.

Furthermore, by recording the CV profiles at various scan rates of 1.0, 0.50, 0.30, and 0.10 mV s’¹, the kinetic modulation on the Zn²⁺ storage behavior of the i-Zn-MnO electrode was assessed (Figure 14a and 14b), by using the equation 1: z = av^b (1). where, z indicates the peak current, v stands for the scan rate, and a and b are the adjustable parameters. The analysis was extended by plotting log i versus log v, from the equation 2: log i = b log v + log a (2). From the plot, the deduced slope of the line, i.e., the b value, was utilized to predict the charge storage mechanism followed by the electrode. For the system based on the i-Zn-MnO cathode, the b value calculated for the respective anodic and cathodic peaks as marked in Figure 14a are 0.80 and 0.86 (Figure 14b), respectively, implying that the redox reactions at the anodic and cathodic region are mainly dominated by the surface controlled process within the above scan rates.

To assess the sustainability of the QSS-Zn|PHPZ-30|i-Zn-MnO, QSS-Zn|PHPZ-30|Zn-MnO and Zn|0.5 M Zn(CF3SO3)2|Zn-MnO cells, the cycling stability tests were conducted at the current density of 1.0 A g^-1. With capacity retention and coulombic efficiency of 85% and 99%, respectively, QSS-Zn|PHPZ-30|i-Zn-MnO cell displayed the best cycling life among the cells, lasting over 1000 charge-discharge cycles (Figure 15).

Example 3: QSS-Zn|PHPZ-30|i-Zn-MnO Pouch Cells:

Finally, the study was also extended to the demonstration of a pouch cell based on 2 QSS-Zn|PHPZ-30|i-Zn-MnO cells connected in series. For this purpose, two 2 x 2 cm² Zn|PHPZ-30|i-Zn-MnO pouch cells were made and connected in series (the cathode loading was maintained as 1.0 mg cm^-2), which displays an open circuit voltage (OCV) of 2.5 V when connected to the multimeter. The cells were able to illuminate a blue light-emitting diode (LED) for 12 h and could be recharged to continue the lighting process while preserving the same performance characteristics as in the first cycle. This indicates the assembly’s excellent structural durability and potential for use in practical real-world applications.

Example 4 (Comparative analysis)

(A) Comparison of hydrogel polymer electrolyte composition of the present disclosure with the reported electrolyte.

A comparison of hydrogel polymer electrolyte composition of the present disclosure with the reported electrolyte is given in Table-4 below. Table 4: Table of comparison of gel polymer electrolyte.

Performance comparison of i-Zn-MnO | PHPZ-30 | cell with Zn based other cathodes employed with aqueous electrolyte are shown in Table-5. Table 5: Performance comparison of Zn|PHPZ-30|i-Zn-MnO cell with other cathodes.

ADVANTAGES OF THE INVENTION i. The present disclosure provides a hydrogel polymer electrolyte composition integrated cathode. ii. The present disclosure provides a Quasi-solid state rechargeable metal battery. iii. The present disclosure provides a gel polymer electrolyte and modified cathode using the gel polymer electrolyte which offers improved interface stability, increased ion transport and non-formation of Zn dendrite. iv. The present disclosure provides a battery with extended cycle life, and corrosion mitigation. v. The present disclosure provides a battery with improved electrochemical performance. vi. It demonstrates that when an interfacial structure that closely resembles that of the liquid-state equivalents is created (QSS-Zn|PHPZ-30|i-Zn-MnO, and Zn|0.5 M Zn(CF3SO3)2|Zn-MnO cells), an improved electrode | electrolyte interface substantially enhances the electrochemical performance of QSS-RZMBs.

Claims

WE CLAIM:

1. A hydrogel polymer electrolyte composition for a quasi-solid state metal battery, comprising: a. polyethylene glycol (PEG) as a plasticizer, b. a monomer, c. a crosslinker, d. UV-initiator, e. a zinc salt as an additive, and f. water; wherein the monomer is present with a concentration in the range of 20.8 to 25.6 %w/w of the total composition.

2. The hydrogel polymer electrolyte composition as claimed in claim 1, wherein the plasticizer is present with a concentration in the range of 5.2 to 6.4 %w/w of the total composition; the crosslinker is present with a concentration in the range of 1.3 to 1.6 %w/w of the total composition; the UV-initiator is present with a concentration in the range of 0.1 to 0.2 %w/w of the total composition; the additive is present with a concentration in the range of 20 to 35 %w/w of the total composition; and the water is present with concentration in the range of 39 to 48 %w/w of the total composition.

3. The hydrogel polymer electrolyte composition as claimed in claim 1, wherein the monomer is selected from hydroxyethyl methacrylate (HEMA) and 2-Hydroxypropyl Methacrylate (HPMA); the crosslinker is selected from poly(ethylene glycol) diacrylate (PEGDA), polyethylene glycol dimethacrylate (PEGDMA), and polyethylene glycol diacrylamide (PEGDAA); the UV-initiator is selected from 2-hydroxy-2-methylpropiophenone (HMPP) and 2,2-Dimethoxy-2-phenylacetophenone (DMPA); and the zinc salt is selected from a group consisting of zinc trifluromethane sulfonate (ZniCFvSOsh), zinc sulfate heptahydrate (ZnSO4.7H2O), zinc nitrate tetrahydrate [Zn(NO3)2.4H2O], and zinc chloride (ZnCh), or any of combination thereof.

4. A process of preparation of the hydrogel polymer electrolyte composition as claimed in claim 1, comprising steps of: i) mixing 5.2 to 6.4 %w/w of the plasticizer with 20.8 to 25.6 %w/w of the monomer to obtain a first mixture; ii) blending and mixing the first mixture of step i) with 1.3 to 1.6 %w/w of the crosslinker to form a second mixture; iii) adding and mixing the second mixture of step ii) with 39 to 48 %w/w of the water to form a third mixture; iv) adding and mixing the third mixture of step iii) with 20 to 35 %w/w of the zinc salt to form a fourth mixture; and v) adding and mixing the fourth mixture of step iv) with 0.1 to 0.2 %w/w of the UV initiator to initiate polymerization and to obtain the hydrogel polymer electrolyte composition.

5. The process as claimed in claim 4, wherein the steps i) to iv) are done under stirring temperature in the range of 20-35 °C in a vertex stirrer for time period in the range of 10-20 minutes.

6. The process as claimed in claim 4, wherein the step v) is carried out under UV light for time period in the range of 10 min to 30 min, wherein UV wavelength of the UV light is in the range of 315-400 nm.

7. A quasi-solid state metal battery, comprising: i. the hydrogel polymer electrolyte composition as claimed in claim 1; ii. a hydrogel polymer electrolyte integrated cathode; and iii. a battery assembly components.

8. The quasi-solid state metal battery as claimed in claim 7, wherein the battery assembly components comprises a top case, a spring, spacer, zinc foil as anode, and a bottom case; and wherein the quasi-solid state metal battery is selected from sodium ion battery, lithium ion battery, zinc-air battery, and quasi-solid-state reversible zinc metal battery.

9. The quasi-solid state metal battery as claimed in claim 7, wherein the hydrogel polymer electrolyte integrated cathode comprises coating of the hydrogel polymer electrolyte composition onto Zn-MnO cathode.

10. The quasi- solid state metal battery as claimed in claim 7, wherein the hydrogel polymer electrolyte integrated cathode is prepared by a process comprising in situ cross-linking of the hydrogel polymer electrolyte composition over the Zn-MnO cathode surface, wherein the in situ cross-linking is done by drop casting the hydrogel polymer electrolyte composition onto the Zn-MnO cathode for time period in the range of 0.5 to 2 minutes for the complete infiltration followed by exposing to UV light for 20-45 minutes.