Binder-free silicon-polymer hydrogel composite anode for li-ion batteries with liquid and solid electrolytes

Abstract

The present disclosure relates to a field of lithium-ion batteries Particularly, the present disclosure relates to a silicon polymer hydrogel composite material for electrode. The present disclosure also relates to a process of preparation of a silicon polymer hydrogel composite material using a sol-gel-polymerization. The present disclosure also provides a silicon polymer hydrogel composite anode electrode and its method of preparation. More particularly, the present disclosure provides a lithium-ion battery. A cycle life analysis of a liquid electrolyte system over 500 cycles at a rate of 0.1 Ag-1 was conducted, achieving a specific capacity of 534mAh g-1. Additionally, the specific capacity of a quasi-solid electrolyte system over 100 cycles at the same rate was investigated, which achieved a capacity of 717 mAh g-1.

Description

[0001] BINDER-FREE SILICON-POL YMER HYDROGEL COMPOSITE ANODE FOR LITHIUM-ION BATTERIES WITH LIQUID AND SOLID ELECTROLYTES

[0002] FIELD OF THE INVENTION

[0003] The present disclosure relates to a field of lithium-ion batteries. Particularly, the present disclosure relates to a silicon polymer hydrogel composite material and its process of preparation by using a sol-gel-polymerization. The present disclosure also provides a silicon polymer hydrogel composite electrode and its method of preparation thereof. More particularly, the present disclosure provides a lithium-ion battery.

[0004] BACKGROUND OF THE INVENTION

[0005] The periodic growth of electric vehicles and portable electronics demands a tremendous requirement for high-performance lithium-ion batteries (LIBs). To achieve the demanding performance of lithium-ion batteries for these applications, high-capacity electrochemically active electrode materials are being extensively exploited. Among the electrode materials, the theoretical capacity of conventional graphite material is 372 mAh g’1. Silicon is suggested as the most promising anode material for the lithium-ion battery because of its high theoretical capacity of 4200 mAh g’1. Silicon has emerged as a highly demanding material due to its low operating voltage, high abundance of materials in the earth's crust, and low toxicity. However, the demand for silicon material is hindered by critical challenges: enormous volume expansion (-300—400%) during the lithium insertion leads to internal stress on the silicon, which leads to pulverisation of the silicon, which could result in capacity fading. In addition, the large volume changes cause the repetitive growth of an unstable SEI layer, ultimately resulting in the battery’s capacity fading.

[0006] There are several strategies that have been investigated to overcome the challenges of silicon anode material. The structural modification is one way to improve the cycle life and stability. Structural modification can be achieved by synthesizing nanomaterials, nanoparticles, nanowires, and nanotubes of silicon. The other strategy is the preparation of composites with silicon, such as silicon carbon and silicon polymer composites. In the case of silicon polymer composite materials, the polymer 'acts as a binder and binds the silicon material to the current collector. Wu et al. [Nat. Comm., 2013, 4, 1943] discloses incorporation of a conducting polymer hydrogel into Si -based anodes: the hydrogel is polymerized in-situ, resulting in a well-connected three-dimensional network structure consisting of Si nanoparticles conformally coated by the conducting polymer. A significant limitation is evident in its low electrode loading, which ranges from 0.3 to 0.4 mg / cm2. Such low loading levels are unfeasible for commercial uses, especially in industrial settings where larger loading is sought, even though they might improve cycle stability.

[0007] Chen et al. [ACS Appl. Mater. Interfaces 2014, 6, 5, 3508-3512] discloses to construct a cycle stable Si anode by embedding the nano-Si particles into a Li+ -conductive polymer matrix to prevent the contact of the nanoSi surface with electrolyte, thus suppressing the continual rupturing-reformation of SEI film on the Si surfaces. The composite of SiNP with polyparaphenylene prepared by ball milling, and additionally, they added conducting carbon black and binder (PAA) as in conventional methods. The multistep production procedure outlined in Chen et al. may make the anode more difficult to commercialize due to its increased complexity.

[0008] Li et al. [ACS Appl. Mater. Interfaces 2014, 6, 8, 5996-6002] discloses PANI-grafted SiNP is wrapped in graphene oxide (GO). The study uses in-situ polymerization to create a polymer-silicon composite, which is then wrapped in graphene oxide (GO). After that, binder and conductive carbon black are combined with the finished composite. It is less scalable and more difficult due to the multiple-step process, as explained in the Chen et al. [ACS Appl. Mater. Interfaces 2014, 6, 5, 3508—3512], Furthermore, as mentioned in the Wu et al. [Nat. Comm., 2013, 4, 1943] explanation, the electrode loading is a very low 0.3 mg / cm2.

[0009] Kong et al. [Nanoscale, 2013, 5, 2967-2973] discloses the synthesis process involves multiple steps and based on the electrochemical data provided, they assessed the cyclic stability of the silicon anode over 50 cycles. This article also prepares electrodes by using binder and conducting carbon black.

[0010] In view of above literature known arts and their limitations or problems contained therein, there is a need to develop an effective and better composite material and electrode material thereof for improved effects in electrochemical cell or batteries and overcoming said problems known in the art.

[0011] The present invention provides a solution by providing a silicon polymer hydrogel composites. Specifically, the present invention is related to use of a silicon nanoparticle-poly(N-phenylglycine) (SiNP-PNPG) hydrogel composite material as an anode material for lithium-ion batteries. The SiNP-PNPG anode is prepared without the addition of a binder (PVdF) or conducting material (carbon black), as the PNPG is dual acting material / component as both a conducting material and a binder. The Si-PNPG anode has been developed in a liquid electrolyte system and a quasi-solid-state electrolyte system for a lithium-ion battery.

[0012] OBJECTIVES OF THE INVENTION

[0013] The primary object of the present invention is to provide a silicon polymer hydrogel composite material.

[0014] Another object of the present invention is to provide a method of preparation of a silicon polymer hydrogel composite material using a sol-gel polymerization.

[0015] Still another object of the present invention is to provide a silicon polymer hydrogel composite electrode.

[0016] Another object of the present invention is to provide a method of preparation of a silicon polymer hydrogel composite electrode.

[0017] Yet another object of the present invention is to provide a lithium-ion battery.

[0018] SUMMARY OF THE INVENTION

[0019] In an aspect, the present invention relates to a silicon polymer hydrogel composite material for metal ion battery, comprising: silicon nanoparticles and a conducting polymer, wherein the silicon nanoparticles are encapsulated by the conducting polymer; and wherein the conducting polymer is selected poly(N-phenyl glycine) (PNPG).

[0020] In an embodiment, the conducting polymer acts as a binder and a conductive network within the composite material.

[0021] In an embodiment, the composite material comprises a 3D hydrogel framework. In an embodiment, a size of the silicon nanoparticles is in the range of 50-90 nm.

[0022] In another aspect, the present invention relates to a process of preparation of the silicon polymer hydrogel composite material using a sol-gel polymerization technique, comprising: a) mixing a conducting monomer with an acid in water to obtain a reaction mixture; b) adding silicon nanoparticles to the reaction mixture of step b) followed by sonicating the mixture for a time period ranging from 5 to 20 minutes to obtain a homogeneous dispersion; and c) adding an initiator to the homogeneous dispersion of step b) followed by sonicating the mixture for a time period ranging from 1 to 10 minutes to initiate in-situ polymerization, to obtain the silicon polymer hydrogel composite material.

[0023] In an embodiment, the conducting monomer is N-phenyl glycine.

[0024] In an embodiment, the acid is selected from the group consisting of phytic acid, sulfuric acid, and hydrochloric acid or any of mixture thereof.

[0025] In an embodiment, the process steps a) to c) are done at temperature in the range of 20-35 °C.

[0026] In an embodiment, the initiator is selected from ammonium persulfate, potassium persulfate, ferric chloride, hydrogen peroxide and combinations thereof.

[0027] In another aspect, the present invention provides a silicon polymer hydrogel composite electrode, comprising:

[0028] - the silicon polymer hydrogel composite material; and

[0029] - a current collector; wherein the silicon polymer hydrogel composite material is coated on the current collector to form a composite hydrogel film.

[0030] In an embodiment, the current collector is selected from the group consisting of copper (Cu) foil, nickel (Ni) foil, stainless steel, carbon fiber paper and combinations thereof.

[0031] In an embodiment, the silicon polymer hydrogel composite electrode is a silicon polymer hydrogel composite anode.

[0032] In another aspect, the present invention provides a metal-ion battery comprising: i. the silicon polymer hydrogel composite electrode as claimed in claim 6 (4) as anode; ii. a lithium (Li) metal or sulfur-polyacrylonitrile (SPAN) composite as counter electrode or cathode (6); and iii. a separator and / or electrolyte (5) is positioned between the anode and the counter electrode.

[0033] In an embodiment, the separator comprises a quartz microfiber.

[0034] In an embodiment, the electrolyte is based on LiPFs in a 1:1:1 volume ratio of mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) or a quasi-solid electrolyte.

[0035] In an embodiment, the metal ion battery is selected from lithium ion battery and silicon sulfur battery.

[0036] In an embodiment, the quasi solid electrolyte is selected from QPH gel polymer electrolyte containing at least 10% fluoroethylene carbonate (FEC) as additive, polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) [PVDF-HFP], polyethylene oxide (PEO), poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), and polypropylene carbonate) (PPC).

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 illustrates (a and b) synthesis of Si-PNPG composites, (c) represent coin cell.

[0039] Figure 2 illustrates (a) X-day diffraction patterns of SiNP-PNPG composite, (b) FTIR spectra of Si-PNPG and PNPG

[0040] Figure 3 illustrates UV-Vis spectrum of SiNP-PNPG.

[0041] Figure 4 illustrates (A, B) FESEM of SiNP-PNPG composite (C, D) TEM of SiNP-PNPG composites. Figure 5 illustrates electrochemical performance of the Si-PNPG composite electrode (a)Nyquist plot (b) Cyclic Voltammetry (c)stability of the Si-PNPG electrode at 0.1 Ag-1 for 500 cycles (d)Rate performance.

[0042] Figure 6 illustrates electrospun PVDF-HFP matrix (a) XRD and (b) FESEM.

[0043] Figure 7 illustrates QPH based quasi solid electrolyte (a) ionic conductivity, (b) Linear sweep voltammetry at 10 mVs-1, (c) transference number study and (d) lithium plating stripping study at 0.2 mA cm-2 for 30 minutes.

[0044] Figure 8 illustrates Quasi solid state SiNPPNPG cell, SiNPPNPG|QPH|Li (a) cycling stability at 100 mAg'1without FEC additive, (b) charge discharge at lOOmAg-1 without FEC additive, SiNPPNPG|QPH-FEC|Li (c) cycling stability at 0.1C with FEC additive and (d) charge discharge at 0.1C with FEC additive.

[0045] Figure 9 illustrates Quasi solid state SiNPPNPG cell, SiNPPNPG|QPH|Li with 10% FEC additive (a) cyclic voltammetry at 0.25 mV s-1, (b) galvanostatic charge discharge at 100 mA g-1, (c) cycling stability at 100 mA g-1 and (d) rate performance at various current rates.

[0046] Figure 10 illustrates Quasi solid state Silicon- Sulfur (Lithiated SiPNPG|QPH|SPAN) full cell: (a) Schematic diagram depicting Si-S full cell composition, (b) Cycling stability of Si-S full cell with 5% FEC additive based QPH at 100 mA g-1, (c) Cycling stability of Si-S full cell with 10% FEC additive based QPH at 100 mA g-1 and (d) Cycling stability of shorted Si-S full cell with 5% FEC additive based QPH at 100 mA g-1.

[0047] DETAILED DESCRIPTION OF THE INVENTION

[0048] The following is a detailed description of embodiments of the disclosure. The embodiments are to clearly communicate the disclosure. However, the of detail offered is not intended to limit the anticipated variations of embodiments; to cover all modifications, equivalents, and alternatives fall within the spirit and scope of the present disclosure.

[0049] The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure. It should also be appreciated that the present disclosure can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.

[0050] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0051] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.

[0052] The term QPH in the context of solid-state electrolytes typically refers to "quasi-porous hybrid" or "quasi-solid polymer" electrolytes. These are materials that exhibit characteristics of both solid-state electrolytes and conventional liquid electrolytes, often featuring a porous structure and a blend of polymer and inorganic components.

[0053] The SiNP is silicon nanoparticle disclosed in the present specification.

[0054] The PNPG is one of the examples of the conducting polymer disclosed in the present specification i.e., poly(N-phenyl glycine).

[0055] An aspect of the present disclosure is to provide a silicon polymer hydrogel composite material for Li ion battery. Said composite material comprising of silicon nanoparticle and conducting polymer, wherein the silicon nanoparticles are encapsulated by conducting polymer and combination of silicon nanoparticles and conducting polymer gives a gel composite; and wherein the conducting polymer acts as a binder and as a conductive network within the composite.

[0056] In some embodiments, the conducting polymer is selected from the group consisting of poly(N-phenyl glycine) (PNPG), polypyrrole, polyaniline, polythiophene, poly(3,4-ethylenedioxythiophene) (PEDOT).

[0057] In some embodiments, the composite comprises a 3D hydrogel framework.

[0058] In some embodiments, the composite comprises a core shell structure, wherein the core is based on said silicon nanoparticles, and the shell is based on said conducting polymer.

[0059] In some embodiments, the composite comprises interconnected conductive network between said silicon nanoparticles and conducting polymer.

[0060] In some embodiments, the composite does not comprise of conductive additive or binder as the polymer itself is conductive and acts as binder.

[0061] In some embodiments, the size of the silicon nanoparticles is 50-90 nm.

[0062] The conducting polymer disclosed herein provides superior or improved effects in terms of: i. Superior hydrogen bonding capability: The conducting polymer (e.g. PNPG) exhibits a higher density of hydrogen bonding interactions than polyaniline (PANI), primarily due to the presence of carboxyl groups in its structure. These groups can form strong hydrogen bonds with surface silanol (Si-OH) groups on silicon nanoparticles, enabling more effective encapsulation of silicon within the PNPG hydrogel matrix. ii. Enhanced Biocompatibility and Flexibility: PNPG, PEDOT, or polythiophene hydrogels exhibit superior biocompatibility and flexibility, making them more suitable for dynamic electrode environments. iii. Water Solubility: PNPG is water-soluble, unlike PANI, which facilitates homogeneous dispersion and efficient hydrogel formation around silicon nanoparticles. This improves encapsulation and interfacial contact. iv. Mechanical Adaptability: While polyaniline is rigid and brittle, PNPG, PEDOT or polythiophene demonstrates greater softness and elasticity. This mechanical flexibility allows the PNPG matrix to better accommodate the volume fluctuations of silicon anodes during lithiation and delithiation, mitigating structural degradation and capacity fade.

[0063] Additionally, the improved performance of the composite material results from its morphology and multifunctional structure, which specifically address the fundamental challenges of silicon anodes. The enhancement arises from the synergistic contribution of conformal polymer encapsulation, nanoscale silicon particles, and 3D hydrogel matrix. The encapsulation of silicone nanoparticles by polymer layer (e.g. by poly-N-phenyl glycine polymer), forms a core-shell structure that effectively buffers the -400 % volume expansion of silicon during lithiation, thereby reducing pulverization. Additionally, this encapsulation avoids the direct contact between silicon and the electrolyte, suppressing the formation of an unstable solid electrolyte interphase (SEI). The polymer (PNPG) forms a 3D hydrogel framework that enhances the lithium-ion transport, and its 7i- conjugated backbone facilitates the electron conduction, creating an interconnected conductive network among silicon particles without requiring extra conductive additives. Furthermore, the polymer acts as a binder holding the particles together and eliminating reliance on conventional binders. Nanoscale silicon material provides a high surface area and improved lithiation and delithiation kinetics. The combination of these features ensures uniform dispersion and contact of silicon within the polymer matrix, which enhances interfacial stability and reduces the particle detachment during cycling. Hence the PNPG hydrogel network provides structural durability and efficient ion transport, collectively resulting in increased capacity and lower loading.

[0064] Another aspect of the present disclosure is to provide a process for preparing a silicon polymer hydrogel composite material using a sol-gel polymerization technique. The process comprising:

[0065] - mixing a conducting monomer with an acid in water to obtain a reaction mixture; adding silicon nanoparticles to the reaction mixture of step b) followed by sonicating the mixture for a time period ranging from 5 to 20 minutes to obtain a homogeneous dispersion; and adding an initiator to the homogeneous dispersion of step b) followed by sonicating the mixture for a time period ranging from 1 to 10 minutes to initiate in-situ polymerization, to obtain the silicon polymer hydrogel composite material.

[0066] In an embodiment, the sonication after adding silicon nanoparticles is carried out for a period in the range of 5 to 10 or 10 to 15 or 15 to 20 or 8-12 or 12-16 or 16-20 minutes. In some embodiments, the initiator is selected from ammonium persulfate, Potassium persulfate, Ferric chloride, Hydrogen peroxide or combinations thereof.

[0067] In an embodiment, the initiator is ammonium persulfate.

[0068] In an embodiment, the sonication after adding initiator / ammonium persulphate solution is carried out for a period in the range of 1 to 4 or 4-8 or 8-10 or 3-6 or 6-9 or 10 minutes.

[0069] In some embodiments, the conducting monomer is selected from the group consisting of poly(N-phenyl glycine) (PNPG), N-phenyl glycine, aniline, pyrrole, thiophene, and 3,4-ethylenedioxythiophene or combinations thereof.

[0070] In an embodiment, the conducting monomer is N-phenyl glycine monomer for the synthesis of PNPG polymer.

[0071] In an embodiment, the conducting polymer is a poly(N-phenyl glycine) (PNPG)

[0072] In some embodiments, the acid is selected from the group consisting of phytic acid, sulfuric acid, hydrochloric acid or mixtures thereof; and wherein said process steps a) to c) are done at temperature in the range of 20-35 °C.

[0073] Preferably, the acid is phytic acid, which acts as a dopant as well as a gelator.

[0074] During the synthesis process, the crosslinker, which acts as the dopant and gelator, may be phytic acid. The SiO2 on the surface of Si binds with phytic acid via hydrogen bonding. These bindings aid in the conformal coating of conductive polymer gel on silicon. Additionally, PNPG shows electrostatic interaction with Si, forming a 3D network coating hydrogel. The synthetic composite is coated on top of the current collector. This strategy differs from conventional ones in that it does not use binder or carbon black.

[0075] Another aspect of the present disclosure is to provide a silicon polymer hydrogel composite anode electrode comprising:

[0076] - a silicon polymer hydrogel composite material; and

[0077] - a current collector; wherein the silicon polymer hydrogel composite material is coated on the current collector and dried to form a composite hydrogel film; and drying at a temperature in the range of 20 to 35 °C to obtain the silicon polymer hydrogel composite anode electrode.

[0078] In some embodiments, the current collector is selected from the group consisting of copper (Cu) foil, nickel (Ni) foil, stainless steel, carbon fiber paper and combinations thereof.

[0079] Preferably, the current collector is Cu foil.

[0080] Another aspect of the present disclosure is to provide a method of preparation of a silicon polymer hydrogel composite anode electrode. The process comprising the following steps: coating of a silicon polymer hydrogel composite material on a current collector; drying under condition to obtain a dried composite hydrogel film; pressing the dried composite hydrogel film to remove excess acid; washing with water; and drying at a temperature in the range of 20 to 35 °C to obtain a silicon polymer hydrogel composite anode electrode.

[0081] In an embodiment, the drying is carried out at a temperature in the range of 20 to 35 °C.

[0082] In an embodiment, the excess acid is phytic acid.

[0083] Another aspect of the present disclosure provides a lithium-ion battery comprising:

[0084] - a silicon polymer hydrogel composite anode electrode (4);

[0085] - a lithium (Li) metal counter electrode (6); and

[0086] - a separator (5) positioned between the anode and the counter electrode.

[0087] In some embodiments, the separator comprises quartz microfiber and the electrolyte is selected from 1 M LiPFe in a 1:1:1 volume ratio of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC), or a quasi-solid electrolyte.

[0088] In some embodiments, the quasi solid electrolyte is selected from PVDF-HFP, Polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), poly(methyl methacrylate) (PMMA), polyacrylonitrile (PAN), and polypropylene carbonate) (PPC).

[0089] The present disclosure provides the silicon nanoparticle composite with conductive polymer. Silicon nanoparticle composite will help improve the conductivity, and polymer hydrogel will act as the binder. Hydrogel materials provide more surface area for the volume expansion of silicon anode material. In this study, silicon nanoparticle-polymer composites were synthesized by using poly(n-phenyl glycine) (PNPG) polymer, which is a conductive polymer, as well as being able to bind well with the silicon and current collector. The advantages of the present disclosure include that it is a binder-free method and that it is a one-pot synthesis method. Here the performance of a silicon polymer hydrogel composite as anode material for lithium-ion batteries for liquid electrolyte and solid-state batteries has been discussed.

[0090] EXAMPLES

[0091] The present invention is further explained in the form of following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.

[0092] Example 1: Synthesis

[0093] The conducting SiNP-PNPG hydrogel composite was synthesized using a sol-gel polymerization process. 100 mM of N-phenyl glycine monomer (98% reagent grade, Sigma Aldrich) mixed with 20 mM phytic acid (50 wt% in H2O, Sigma Aldrich) in 0.5 ml deionized water. Later, 60 mg of SiNP (< lOOnm, Sigma Aldrich) was added to the above mixture and sonicated for 10 minutes to obtain a homogeneous mixture, followed by the addition of a 0.1 ml solution containing 100 mM ammonium persulfate and sonicated for 5 minutes to initiate in-situ polymerization (Figure 1). Polymerization was indicated by the colour change from brown to green viscous gel. The SiNP-PNPG anode electrode was prepared by coating the viscous hydrogel on a current collector (Cu foil) and subsequent drying at room temperature. The composite hydrogel film was pressed, excess phytic acid was removed by washing with deionized water, and finally dried in an oven. Cells were assembled in an Argon-filled glove box using the CR2032 button-type half-cell configuration and were used for further electrochemical characterizations. Li metal was used as a counter electrode, quartz microfibre separated the electrodes, and 1 M LiPFe in 1 : 1 : 1 EC:EMC:DMC was used as the electrolyte. Table 1. Half- cell assembly with Liquid electrolyte

[0094] Preparation of PVDF-HFP based Quasi-solid electrolyte

[0095] Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) based solid polymer matrix was prepared by electrospinning method. 16 wt% of PVDF-HFP was dissolved in a mixture of 70:30 (v / v ratio) of N,N dimethylformamide and acetone. Then the solution was stirred overnight at 60 °C and then electrospun with a solution extrusion rate of 0.5 ml / hour and 12 cm distance of needle to drum collector and 14 kV voltage supply. The collected mat was further dried at 60 °C in vaccum oven. The dried mat was cut using 19 mm die. For preparing quasi solid electrolyte IM LiPFe salt was dissolved in EC:EMC:DMC (1 : 1 : 1, v / v / v) plasticiser solvent. The PVDF-HFP polymer matrix was saturated in the Li salt and plasticiser and 5 - 10% FEC was used as additive to stabilize the SEI (with and without FEC cases are given). QPH and QPH-FEC was the named for without and with FEC additive based quasi polymer electrolyte. Table 2. Half- cell assembly with quasi solid state electrolyte

[0096] MATERIALS CHARACTERISATION

[0097] The surface morphology was investigated by scanning electron microscopy (FE-SEM, El, Nova Nano SEM 450 system) and transmission electron microscopy (TEM, FEI, Tecnai F30, FEG instrument). The X-ray photoelectron spectroscopy (XPS, Thermo Scientific K alpha instrument equipped with monochromatic Al Ka X-ray 50 eV source) technique was employed to investigate the chemical composition and valence state of the elements. The chemical structure was examined using FT-IR (instrument name) from 4000-400 cm'1. The crystalline phases were analysed using powder X-ray diffraction (XRD, PanalyticalX’pert Pro) with Cu Ka ( =0.154 nm) radiation. The UV-vis spectroscopy of the samples was characterized using a Varian Cary UV-vis spectrometer.

[0098] Si-polymer composite was synthesized via one-step solution-based polymerization. The polymer synthesis was achieved through an in-situ route at room temperature, which itself is a low-cost method. Prepared a solution (solution 1) of N-phenyl glycine and phytic acid in water. The nitrogen-containing group of N-phenyl glycine forms a hydrogen bond with the phosphoric acid group of phytic acid. Aqueous solution (solution 2) of ammonium persulfate (APS) was prepared, which acts as an oxidizer to initiate oxidative polymerization reaction. Solution 2 was added to solution 1, mixed with 60 mg of SiNP. The formed network of phytic acid and N-ghenyl glycine binds with oxide on the surface of Si via hydrogen bonding. Finally, the mixed solution was sonicated at room temperature to promote crosslinking and polymerization of monomers. The formation of green gel slurry indicates the successful coating of SiNP with PNPG. Structural analysis and crystalline phases of the samples were analyzed using powder X-ray diffraction (XRD, PanalyticalX’pert Pro Diffractometer) technique with Cu Ka (X.=0.154nm) X-ray source. The Si crystal planes (111), (311), (220), (400), and (331) were observed with corresponding 2 theta values of 28.35, 47.25, 56.13, 69.09, and 76.52 degrees, respectively, and the patterns were narrow and sharp (Figure 2a). Observed relatively weak, intense peak at 21.08, representing the (104) plane, and it reveals the successful polymerization of PNPG embedded with Si nanoparticles.

[0099] The functional group and chemical structure analysis were done by fourier transform infrared spectroscopy using ATR mode (FT-IR, Spectrum two, Perkin Elmer) (Figure 2b). The absorption at 1585 cm'1represents the C=C bonds in NPG, peaks at cm'1and 1501 cm'1correspond to C-H vibration and C-C stretching, respectively, which are consistently observed in the spectrum of the Si-PNPG composite. The deformation of the C-H and N-H bond peak at 1068 cm'1reveals the successful polymerization of PNPG hydrogel to trap Si. Figure 3 showed the UV-Vis spectrum of SiNP-PNPG. The wavelength at which maximum absorption occurs for PNPG (kmax = 300 nm) was shifted from 300 to 450 nm in the SiNP-PNPG composite, which suggested the monomer conversion to polymer and the increased PNPG coating occurred over the silicon surface.

[0100] The surface morphologies of the samples were analysed by field emission scanning electron microscopy, and the microstructural analysis was done with the help of transmission electron microscopy. The FESEM of SiNP-PNPG as shown in Figure 4a and b. The PNPG hydrogel produces a seamless coating to encapsulate Si through hydrogen bonding and electrostatic interactions. The pure silicon nanoparticles show a spherical shape with clear edges. In Si-PNPG composites, the silicon nanoclusters are uniformly coated with PNPG.

[0101] Electrochemical characterisation

[0102] Galvanostatic charge-discharge, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were performed to determine the cells' electrochemical properties. Galvanostatic charge-discharge was performed using a voltage window of 0.01 to 2 V in a Neware battery tester, while CV was carried out at a scan rate of 0.25 mV s'1between 0.01 and 2.0 V on a Biologic SP-300 electrochemical workstation. EIS was performed on the same electrochemical workstation over a range of 0.01 Hz to 1 MHz at an alternative (AC) voltage of 5 mV amplitude.

[0103] Electrochemical characterization of quasi- solid state SiNP-PNPG cell

[0104] The following electrochemical measurements were carried out to study quasi solid state Silicon battery. Ionic conductivity measurements were carried out using electrochemical impedance spectroscopy with quasi solid electrolyte placed between stainless steel electrodes. Linear sweep voltammetry was carried out from 2 to 9V. Transference number was calculated using Bruce Vincent equation, where impedance was noted before and after polarization. For polarization lOmV potential applied and current vs time measured for 3 hours. Io was the initial current and Lwas the steady state current after polarization. The stability of polymer electrolyte with lithium metal anode was evaluated in Li / Li symmetric cell format.

[0105] The electrochemical property of solid-state silicon battery was tested using coin cells prepared inside glove box (Oi< 0.1 ppm, H2O < 0.1 ppm). Fig. 1 (c) represents a coin cell consisting of a positive cap (1), spring (2), spacer (3), SiNP / PNPG composite anode (4) prepared previously was used as working electrode, separator (quartz microfibre) electrolyte (IM LiPF6 in 1 : 1 : 1 EC:MC:DMC) (5), lithium metal (6) as counter electrode and a negative cap (7). The charge discharge cycles were done in Neware battery tester between 0.01 V and 2 V.

[0106] The SiNP-PNPG anode electrode was prepared by coating the viscous hydrogel on a current collector (Cu foil) and subsequent drying at room temperature. The composite hydrogel film was pressed, excess phytic acid was removed by washing with deionized water, and finally dried in an oven. Cells were assembled in an Argon-filled glove box using the CR2032 button-type half-cell configuration and were used for further electrochemical characterizations. Li metal was used as a counter electrode, quartz microfibre separated the electrodes, and 1 M LiPFe in 1 : 1 : 1 EC:EMC:DMC was used as the electrolyte. The cyclic voltammetry was carried out at 0.25 mVs'1scan rates with a voltage window ranging between 0.01 V and 2 V (vs. Li+ / Li). Electrochemical impedance spectroscopy was performed on a Biologic SP-300 electrochemical workstation between 0.01 Hz and 1 MHz frequencies and revealed the charge transfer resistance as 75 W (Figure 5a). The charge discharge performance and cycling performance were evaluated using a NEWARE battery testing device with a voltage window ranging from 0.01 V to 2 V. The reduction peaks are associated with the lithiation, and the oxidation peaks are associated with delithiation. Figure 5b shows the cyclic voltammetry of the SiNP-PNPG composite. The reduction peak shown at 0.17 V corresponds to the conversion of Si to LixSi phase, and the oxidation peaks at 0.38 and 0.52 V correspond to the delithiation of amorphous (a) a- LixSi to a-Si. Figure 5d shows the rate capability performance of the Si-PNPG cell at different scan rates of 0.05, Ag'1. The discharge capacity of the cell at different current densities is 1631, 764, 501,463, 429, 270, and 664 mAhg'1for 0.05, 0.1, 0.3, 0.6, 1, 2 and 0.1 Ag'1, respectively. The rate capability performance reveals the superior flexibility and robustness of PNPG as a shell to encapsulate Si for large volume expansion and contraction. The stability performance of the cell was carried out at 0.1 Ag'1for 500 cycles (Figure 5c). The capacity after 500 cycles is 534 mAh g'1and the capacity retention of the cell is 65%. The anode material is stable after the 50thcycle, and the capacity retention from the 50thcycle to the 500thcycle is 95%.

[0107] In the present study, first-time SiNP-PNPG composite material has been reported for a lithium-ion battery. In this study, a capacity of 534 mAh / g with a high loading (0.9-1.2 mg / cm2) has been reported, which is comparatively than the reported materials in the background section. Also, the number of cycles and capacity at said higher cycles is better in case of the present invention.

[0108] SiNP-PNPG anode in quasi solid state electrolyte for Lithium ion battery

[0109] PVdF-HFP is known for its high dielectric constant, high ionic conductivity at room temperature arising from low crystallinity and has some functional groups with strong electron withdrawing effect. The three-dimensional architecture of PVdF-HFP is being studied. Electrospinning PVdF- HFP solution to give polymer nanofibers will give rise to better ionic transport when using it as a solid electrolyte. The electrospun fibres were formed without any beading as shown in figure 6b where thin fibres of 300 — 500 nm diameter are formed as shown in figure (6b). XRD of the PVDF-HFP mat is depicted in figure (6a) which confirms the amorphous nature of PVDF-HFP.

[0110] Ionic conductivity studies are conducted using electrochemical impedance spectroscopy and figure (7a) shows the change in resistance values with QPH quasi solid electrolyte with time and the calculated ionic conductivity is in the range of 10'2mS cm'1. Transference number is calculated from Bruce Vincent equation and is 0.26. Figure (7b) shows where the degree of overpotential with repeated stripping and plating cycles is noted as interfacial stability. The increase in overpotential denotes increase in interface impedance due to the growth of SEI layer.

[0111] The cycling stability of quasi solid-state SiNPPNPG cells are shown in figure 8. Figure (8a) and (8b) shows the cycling stability and charge discharge curves at lOOmAg'1capacity without FEC additive and a discharge capacity of 188 mAh g'1after 100 cycles. Figure (8c) and (8d) shows the cycling stability and charge discharge curves at lOOmAg'1capacity with FEC additive and a discharge capacity of 717 mAh g'1after 100 cycles. The FEC additive serves to provide a stable SEI layer in the quasi-polymer electrolyte which reflects in the contribution of higher capacity retention of QPH-FEC based SiPNPG cell.

[0112] Further electrochemical characterisation of QPH-FEC with 10 % FEC was performed by the inventors. The data for quasi solid state Silicon -Sulfur fuel cell device which included SiPNPG anode (SPAN (sulfurized Polyacrylonitrile) cathode and QPH-FEC as the gel polymer electrolyte is also included.

[0113] SiNP-PNPG anode in quasi solid state electrolyte for silicon sulfur battery The electrochemical performance of the Si-PNPG anode paired with QPH gel polymer electrolyte containing 10% FEC additive was initially assessed using cyclic voltammetry as shown in Figure 9(a). Distinct reduction and oxidation peaks corresponding to the lithiation and delithiation processes are presented in Figure 9(a). The charge-discharge profiles of the quasi-solid-state silicon anode half-cell are shown in Figure 9(b). The Si-PNPG half-cell demonstrated excellent cycling stability, delivering a high specific capacity of 2364 mAh g-1at a current density of 100 mA g-1after 50 cycles, with a capacity retention of 80.4% as shown in Figure 9(c). A rate capability test was further conducted at varying current densities of 0.1, 0.3, 0.6, 1, 2, and returning to 1 A g-1, yielding specific capacities of 2049, 1615, 1307, 1049, 674, and 1799 mAh g-1, respectively as shown in Figure 9(d).

[0114] To evaluate the practical applicability of the silicon anode and QPH-FEC gel polymer electrolyte, full-cell studies were also performed. A full cell was assembled by pairing the Si-PNPG anode with a sulfurized polyacrylonitrile (SPAN)-based sulfur cathode and QPH-FEC gel polymer electrolyte, as illustrated in the schematic in Figure 10(a). Two prelithiation strategies were employed for the Si-PNPG electrode, in the first approach, the electrode was preconditioned by discharging at lO mA g-1to form a stable SEI layer, followed by one charge-discharge cycle at 100 mA g-1. The cell was then disassembled to construct the full cell with the SPAN cathode and QPH-FEC electrolyte. Cycling performance at 100 mA g-1with 5% and 10% FEC additives is shown in Figures 10(b) and 10(c), respectively, with the full cell demonstrating 66% and 58% capacity retention after 100 cycles.

[0115] In the second prelithiation strategy, the Si-PNPG electrode was directly shorted with lithium for 24 hours in the presence of a 20 -50 pl of liquid electrolyte. Figure 10(d) presents the cycling stability of the full cell prepared using this method, showing an impressive capacity retention of 95.2% after 30 cycles. These results underscore the potential for developing high-energy-density practical lithium batteries by harnessing the synergistic theoretical capacities of both silicon and sulfur electrodes.

[0116] In the present invention, electrospun PVDF-HFP membrane has been used as the polymer matrix. Due to the 3 dimensional architecture of electrospun PVDF-HFP matrix it has enhanced porosity and good wettability towards IM LiPFe salt dissolved in EC:EMC:DMC (1 : 1 : 1, v / v / v) plasticizer solvent. Thus, the electrolyte of the present invention is superior to ETPTA in terms of the three-dimensional morphology of electrospun PVDF-HFP and the enhanced porosity it offers. Use of the three-dimensional architecture of PVDF-HFP to accommodate the lithium salt and plasticizer in QPH in silicon battery is the essential feature of the present invention.

[0117] ADVANTAGES OF THE INVENTION

[0118] • The present disclosure successfully developed a conducting polymer hydrogel coat on the surface of silicon that overcomes the problems of volume expansion and low cycle stability.

[0119] • It was found that the SiNP-PNPG hydrogel anode showed enhanced cyclic stability for the quasi-solid electrolyte and liquid electrolyte systems for lithium-ion batteries.

[0120] • In a quasi-solid-state electrolyte system, the specific capacity is 717 mAh g'1for 100 cycles at 0.1 Ag'1, and in a liquid electrolyte system, the specific capacity is 534 mAh g'1for 500 cycles at 0.1 Ag'1.

[0121] • The present approach involves applying a higher loading of 0.9 to 1.2 mg / cm2, demonstrating the potential for scalability and industrial viability.

[0122] • The structure of PNPG is advantageous due to the presence of a carboxylic bond, which facilitates hydrogen bonding with silicon.

[0123] • The present method focuses on the direct coating of the composite onto the surface of the current collector.

[0124] • The present method employs in situ polymerisation that facilitate proper conformal coating on the Si surface, which is likely to yield stronger adhesion compared to the ball milling process.

Claims

WE CLAIM:

1. A silicon polymer hydrogel composite material for metal ion battery, comprising: silicon nanoparticles and a conducting polymer, wherein the silicon nanoparticles are encapsulated by the conducting polymer; and wherein the conducting polymer is poly(N-phenyl glycine) (PNPG).

2. The silicon polymer hydrogel composite material as claimed in claim 1, wherein the conducting polymer acts as a binder and a conductive network within the composite material; the composite material comprises a 3D hydrogel framework; and a size of the silicon nanoparticles is in the range of 50-90 nm.

3. A process of preparation of the silicon polymer hydrogel composite material as claimed in claim 1, using a sol-gel polymerization technique, comprising: a) mixing a conducting monomer with an acid in water to obtain a reaction mixture; b) adding silicon nanoparticles to the reaction mixture of step b) followed by sonicating the mixture for a time period ranging from 5 to 20 minutes to obtain a homogeneous dispersion; and c) adding an initiator to the homogeneous dispersion of step b) followed by sonicating the mixture for a time period ranging from 1 to 10 minutes to initiate in-situ polymerization, to obtain the silicon polymer hydrogel composite material.

4. The process as claimed in claim 3, wherein the conducting monomer is N-phenyl glycine.

5. The process as claimed in claim 3, wherein the acid is selected from the group consisting of phytic acid, sulfuric acid, and hydrochloric acid or any of mixture thereof; and said process steps a) to c) are done at temperature in the range of 20-35 °C; andthe initiator is selected from ammonium persulfate, potassium persulfate, ferric chloride, hydrogen peroxide and combinations thereof.

6. A silicon polymer hydrogel composite electrode, comprising:- the silicon polymer hydrogel composite material as claimed in claim 1; and- a current collector; wherein the silicon polymer hydrogel composite material is coated on the current collector to form a composite hydrogel film.

7. The anode as claimed in claim 6, wherein the current collector is selected from the group consisting of copper (Cu) foil, nickel (Ni) foil, stainless steel, carbon fiber paper and combinations thereof; and wherein the silicon polymer hydrogel composite electrode is a silicon polymer hydrogel composite anode.

8. A metal-ion battery comprising: i. the silicon polymer hydrogel composite electrode as claimed in claim 6 (4) as anode; ii. a lithium (Li) metal or sulfur-polyacrylonitrile (SPAN) composite as counter electrode or cathode (6); and iii. a separator and / or electrolyte (5) is positioned between the anode and the counter electrode.

9. The battery as claimed in claim 8, wherein the separator comprises a quartz microfiber, and the electrolyte is based on LiPFe in a 1:1:1 volume ratio of mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) or a quasi-solid electrolyte; and wherein the metal ion battery is selected from lithium ion battery and silicon sulfur battery.

10. The battery as claimed in claim 9, wherein the quasi solid electrolyte is selected from QPH gel polymer electrolyte containing at least 10% fluoroethylene carbonate (FEC) as additive, polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) [PVDF-HFP], polyethylene oxide (PEO), poly(m ethyl methacrylate) (PMMA), polyacrylonitrile (PAN), and polypropylene carbonate) (PPC).

Images