1. An SnO2 Quantum dots CNF anchored electrode, comprising: i. a carbon nanofiber (CNF) mat; and ii. colloidal SnO₂ quantum dots (SnO₂ QDs) anchored on the CNF mat; wherein the SnO₂ QDs have an average particle size in the range of 4.1 to 4.5 nm uniformly and densely distributed on the CNFs, and the optimized electrode.

2. The electrode as claimed in claim 1, wherein the electrode consists of SnO₂ QDs and CNFs in a mass ratio of 0.8:1 corresponding to about 45–50 wt.% SnO₂ and an areal loading of about 1.8–2.4 mg cm⁻².

3. The electrode as claimed in claim 1, wherein the said electrode exhibits an initial reversible capacity of 1235 mAh g⁻¹ at 0.1 A g⁻¹ and a reversible capacity of 1040 mAh g⁻¹ after 200 cycles.

4. The electrode as claimed in claim 1, wherein the average coulombic efficiency greater than 99%.

5. The electrode as claimed in claim 1, wherein the said electrode shows capacity retention of 97% after 500 bending cycles at a bending radius of 3 mm.

6. The electrode as claimed in claim 1, wherein the said electrode consists of capacity in the range of 1230-1250 mAh/g and capacitance in the range of 560-570 F/g.

7. A method for synthesis of SnO₂ QDs for electrode as claimed in claim 1 consists of the following steps: i. dissolving 0.451 g SnCl₂·2H₂O in 25 mL deionized water under magnetic stirring at 600 rpm for 10 minutes at 25 °C to obtain a Sn²⁺ precursor solution, ii. dissolving 0.294 g trisodium citrate in 10 mL deionized water and adding the citrate solution dropwise into the Sn precursor with continued stirring for 15 minutes to act as stabilizing ligand, iii. dissolving 0.190 g thiourea in 10 mL deionized water and adding the thiourea solution slowly to the reaction mixture at 30–40 °C under stirring at 700 rpm for 120 minutes for controlled oxidation of Sn²⁺ to SnO₂ nuclei, iv. adjusting the pH to about 8 using dilute ammonia solution, v. maintaining the solution at 35–40 °C for 2 hours to promote quantum dot formation with slight turbidity and Tyndall effect, and vi. ageing the solution for 12 hours at room temperature to obtain a stable colloidal SnO₂ QD dispersion with average size of 4.3 nm and colloidal stability greater than 30 days due to citrate capping.

8. The method for synthesis of SnO₂ QDs as claimed in claim 6, wherein the synthesized SnO₂ QDs exhibits a typical yield of about 82–86%.

9. A method for preparing a free-standing SnO₂ QD@CNF electrode comprising: i. preparing a CNF mat by dissolving 1 g polyacrylonitrile in 9 g N,N dimethylformamide, electrospinning at 15 kV with 18 cm tip-to-collector distance and 0.6 mL h⁻¹ flow rate onto a rotating drum, ii. stabilizing (step i) at 250 °C in air at 1 °C min⁻¹ for 3 h, and carbonizing at 800 °C in N₂ at 2 °C min⁻¹ for 2 h to obtain a ~30 µm thick CNF mat having surface area 220 m² g⁻¹ and conductivity 460 S m⁻¹, iii. synthesizing SnO₂ QDs to obtain a stable colloidal SnO₂ QD dispersion with average size 4.3 nm, iv. integrating SnO₂ QDs (step iii) onto the CNF mat (step ii) by placing a 2 × 2 cm CNF mat in 20 mL SnO₂ QD dispersion of concentration 1 mg mL⁻¹, subjecting to mild sonication at 100 W for 10 minutes and then immersing under stirring at 25 °C for 30 minutes to achieve decoration of more than 85% CNF surface, v. rinsing the hybrid mat with deionized water and drying at 60 °C for 6 hours, and vi. annealing the dried hybrid mat at 250 °C for 1 hour under N₂ at a heating rate of 2 °C min⁻¹ to remove residual organics and create Sn–O–C interlinkage.

10. The method as claimed in claim 9 resulting SnO₂ QD CNF electrode are assembled into a lithium-ion coin cell to deliver a first-cycle reversible capacity of 1235 mAh g⁻¹ at 0.1 A g⁻¹ and 1150 mAh g⁻¹ at 0.5 A g⁻¹ with 90-95% retention over 500 cycles for a SnO₂ QD areal loading of 2.4 mg cm⁻².

Description:FIELD OF THE INVENTION

[0001] The present invention relates to an SnO2 Quantum dots CNF anchored electrode that is capable of achieving uniform and dense deposition of quantum dots on a flexible nanofiber network while functioning without additional binders for providing strong interfacial bonding, high electrochemical stability, and durable energy storage performance.

BACKGROUND OF THE INVENTION

[0002] Nanostructured materials have high surface area, short ion diffusion pathways, and tunable physicochemical properties. In particular, quantum-scale materials exhibit unique size-dependent electrochemical characteristics that can enhance charge storage capacity and reaction kinetics. Flexible and conductive frameworks have emerged as platforms for accommodating active materials while maintaining structural integrity during repeated charge-discharge cycles. Achieving uniform dispersion, strong interfacial interaction, and structural stability remains central to improving next-generation energy storage performance.

[0003] Traditional electrode materials used in lithium-ion batteries suffer from limited specific capacity and gradual performance degradation during prolonged cycling. Bulk active materials experience significant volume expansion and contraction during lithiation and delithiation processes, leading to pulverization, loss of electrical contact, and rapid capacity fading. In many traditional fabrication approaches, poor dispersion and agglomeration of nanoscale materials reduce effective surface area and hinder ion transport.

[0004] CN106082314A discloses a method for preparing a one-dimensional porous tin dioxide nanotube on a conductive substrate based on an in-situ self-etching template mechanism, and belongs to the field of inorganic chemistry and material synthesis. The method comprises the following steps: cleaning conductive glass, preparing ZnO precursor solution, growing ZnO/conductive glass, preparing SnO2 precursor solution, growing SnO2 nanotubes. The feature of this method is that the two-step template method is based on the self-generated alkaline environment to etch the template in situ without adding strong acid/alkali to prepare SnO2 nanotubes, which simplifies the experimental steps, and the product size is uniform, the cost is low, and it is more energy-saving and environmentally friendly. The method is simple to operate, and provides a new idea for preparing SnO 2 nanotubes in large quantities. At the same time, the prepared tin oxide has a large specific surface area, and has broad application prospects in the fields of photocatalysis and solar cells.

[0005] CN103599797A discloses a preparation method of a SnO 2 PC/CdS photonic crystal structure composite photocatalyst with high stable visible light catalytic activity. The method is to prepare a SnO 2 photonic crystal on an FTO substrate by using a liquid phase deposition method, and then use acoustic wave digestion to assist A new type of SnO 2 PC/CdS photonic crystal structure was prepared by the continuous chemical water bath deposition method and sensitized with CdS quantum dots.

[0006] Conventionally, many systems disclosed in the prior art have been developed to enhance electrochemical energy storage performance, but these systems lack structural stability during repeated charge-discharge cycles, leading to capacity fading and reduced lifespan. They further lack uniform nanoscale dispersion and strong interfacial bonding, resulting in agglomeration and poor conductivity.

[0007] In order to overcome the aforementioned drawbacks, there exists a need in the art to develop a system capable of maintaining structural integrity during repeated electrochemical cycling. Such an approach enhances charge transport, accommodates volume variation, improves cycle life and coulombic efficiency, prevents material agglomeration, and delivers consistent performance under mechanical stress, thereby supporting advanced portable, flexible, and high-energy-density applications.

OBJECTS OF THE INVENTION

[0008] The principal object of the present invention is to overcome the disadvantages of the prior art.

[0009] An object of the present invention is to develop an electrode that is capable of achieving uniform and dense deposition of quantum dots on a flexible nanofiber network for strong interfacial bonding and consistent electrochemical performance.

[0010] Another object of the present invention is to develop an electrode that is capable of functioning without additional binders, providing high electrochemical stability for robust and durable energy storage materials.

[0011] Another object of the present invention is to develop an electrode that is capable of providing strong interaction between the active material and the supporting structure for enhanced structural stability during operation.

[0012] Yet, another object of the present invention is to develop an electrode that is capable of maintaining mechanical flexibility and structural integrity under repeated mechanical stress for durable and flexible energy storage materials.

[0013] The foregoing and other objects, features, and advantages of the present invention will become readily apparent upon further review of the following detailed description of the preferred embodiment as illustrated in the accompanying drawings.

SUMMARY OF THE INVENTION

[0014] The present invention relates to a SnO2 Quantum dots CNF anchored electrode that is capable of providing strong interaction between the active material and the supporting structure while maintaining mechanical flexibility and structural integrity under repeated mechanical stress for durable energy storage performance.

[0015] According to an aspect of the present invention, an SnO2 Quantum dots CNF anchored electrode comprising a carbon nanofiber (CNF) mat and colloidal SnO₂ quantum dots (SnO₂ QDs) anchored on the CNF mat, the SnO₂ QDs have an average particle size in the range of 4.1 to 4.5 nm uniformly and densely distributed on the CNFs, and the optimized electrode, the electrode consists of SnO₂ QDs and CNFs corresponding to about 45–50 wt.% SnO₂, the electrode exhibits an initial reversible capacity and method for synthesis of SnO₂ QDs for electrode consists of the steps of dissolving SnCl₂·2H₂O in deionized water under to obtain a Sn²⁺ precursor solution, dissolving trisodium citrate in deionized water and adding the citrate solution dropwise into the Sn precursor to act as stabilizing ligand, dissolving thiourea in deionized water for controlled oxidation of Sn²⁺ to SnO₂ nuclei, adjusting the pH to about 8 using dilute ammonia solution, maintaining the solution for 2 hours to promote quantum dot formation with slight turbidity and Tyndall effect, and ageing the solution at room temperature to obtain a stable colloidal SnO₂ QD dispersion and colloidal stability greater than 30 days due to citrate capping.

[0016] According to another aspect the present invention, further includes a method for preparing a free-standing SnO₂ QD@CNF electrode with the steps of preparing a CNF mat by polyacrylonitrile in N,N dimethylformamide, electrospinning, stabilizing to obtain a CNF mat ,synthesizing SnO₂ QDs to obtain a stable colloidal SnO₂ QD dispersion, integrating SnO₂ QDs onto the CNF mat, subjecting to mild sonication and then immersing under stirring, rinsing the hybrid mat with deionized water, drying, annealing the dried hybrid mat under N₂ to remove residual organics and create Sn–O–C interlinkage.

[0017] While the invention has been described and shown with particular reference to the preferred embodiment, it will be apparent that variations might be possible that would fall within the scope of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The following description includes the preferred best mode of one embodiment of the present invention. It will be clear from this description of the invention that the invention is not limited to these illustrated embodiments but that the invention also includes a variety of modifications and embodiments thereto. Therefore, the present description should be seen as illustrative and not limiting. While the invention is susceptible to various modifications and alternative constructions, it should be understood, that there is no intention to limit the invention to the specific form disclosed, but, on the contrary, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims.

[0019] In any embodiment described herein, the open-ended terms "comprising," "comprises,” and the like (which are synonymous with "including," "having” and "characterized by") may be replaced by the respective partially closed phrases "consisting essentially of," consists essentially of," and the like or the respective closed phrases "consisting of," "consists of, the like.

[0020] As used herein, the singular forms “a,” “an,” and “the” designate both the singular and the plural, unless expressly stated to designate the singular only.

[0021] The present invention relates to a SnO2 Quantum dots CNF anchored electrode that is capable of functioning without additional binders while providing strong interaction between the active material and the supporting structure for enhanced structural and electrochemical stability.

[0022] According to an embodiment of the present invention, an SnO2 Quantum dots CNF anchored electrode, comprises of i) a carbon nanofiber (CNF) mat, ii) and ii) colloidal SnO₂ quantum dots (SnO₂ QDs) anchored on the CNF mat, a method for synthesis of SnO₂ QDs for electrode comprises of i) dissolving 0.451 g SnCl₂·2H₂O in 25 mL deionized water under magnetic stirring at 600 rpm for 10 minutes at 25 °C to obtain a Sn²⁺ precursor solution, ii) dissolving 0.294 g trisodium citrate in 10 mL deionized water and adding the citrate solution dropwise into the Sn precursor with continued stirring for 15 minutes to act as stabilizing ligand, iii) dissolving 0.190 g thiourea in 10 mL deionized water and adding the thiourea solution slowly to the reaction mixture at 30–40 °C under stirring at 700 rpm for 120 minutes for controlled oxidation of Sn²⁺ to SnO₂ nuclei, iv) adjusting the pH to about 8 using dilute ammonia solution, v) maintaining the solution at 35–40 °C for 2 hours to promote quantum dot formation with slight turbidity and Tyndall effect, and vi) ageing the solution for 12 hours at room temperature to obtain a stable colloidal SnO₂ QD dispersion with average size of 4.3 nm and colloidal stability greater than 30 days due to citrate capping.

[0023] According to another embodiment of the present invention, a method for preparing a free-standing SnO₂ QD@CNF electrode comprises of i) preparing a CNF mat by dissolving 1 g polyacrylonitrile in 9 g N,N dimethylformamide, electrospinning at 15 kV with 18 cm tip-to-collector distance and 0.6 mL h⁻¹ flow rate onto a rotating drum, ii) stabilizing (step i) at 250 °C in air at 1 °C min⁻¹ for 3 h, and carbonizing at 800 °C in N₂ at 2 °C min⁻¹ for 2 h to obtain a ~30 µm thick CNF mat having surface area 220 m² g⁻¹ and conductivity 460 S m⁻¹, iii) synthesizing SnO₂ QDs to obtain a stable colloidal SnO₂ QD dispersion with average size 4.3 nm, iv) integrating SnO₂ QDs (step iii) onto the CNF mat (step ii) by placing a 2 × 2 cm CNF mat in 20 mL SnO₂ QD dispersion of concentration 1 mg mL⁻¹, subjecting to mild sonication at 100 W for 10 minutes and then immersing under stirring at 25 °C for 30 minutes to achieve decoration of more than 85% CNF surface, v) rinsing the hybrid mat with deionized water and drying at 60 °C for 6 hours, and vi) annealing the dried hybrid mat at 250 °C for 1 hour under N₂ at a heating rate of 2 °C min⁻¹ to remove residual organics and create Sn–O–C interlinkage.

EXAMPLE

[0024] The method for synthesizing SnO₂ quantum dots for the electrode as claimed in claim 1 comprises dissolving 0.451 g of SnCl₂·2H₂O in 25 mL of deionized water under magnetic stirring at 600 rpm for 10 minutes at 25 °C to obtain a Sn²⁺ precursor solution. Subsequently, 0.294 g of trisodium citrate is dissolved in 10 mL of deionized water and the resulting citrate solution is added dropwise into the Sn precursor while continuously stirring for 15 minutes to act as a stabilizing ligand.

[0025] Thereafter, 0.190 g of thiourea is dissolved in 10 mL of deionized water and the thiourea solution is slowly added to the reaction mixture at 30–40 °C under stirring at 700 rpm for 120 minutes to enable controlled oxidation of Sn²⁺ to SnO₂ nuclei. The pH of the solution is then adjusted to about 8 using dilute ammonia solution, followed by maintaining the solution at 35–40 °C for 2 hours to promote quantum dot formation, indicated by slight turbidity and a Tyndall effect.

[0026] The solution is then aged for 12 hours at room temperature to obtain a stable colloidal SnO₂ quantum dot dispersion having an average particle size of about 4.3 nm and colloidal stability greater than 30 days due to citrate capping.

[0027] The method for preparing a free-standing SnO₂ QD@CNF electrode comprises preparing a carbon nanofiber (CNF) mat by dissolving 1 g of polyacrylonitrile in 9 g of N,N-dimethylformamide followed by electrospinning at 15 kV with a tip-to-collector distance of 18 cm and a flow rate of 0.6 mL h⁻¹ onto a rotating drum. The obtained mat is then stabilized at 250 °C in air at a heating rate of 1 °C min⁻¹ for 3 hours and subsequently carbonized at 800 °C in a nitrogen atmosphere at a heating rate of 2 °C min⁻¹ for 2 hours to obtain a CNF mat having a thickness of about 30 µm, a surface area of about 220 m² g⁻¹, and a conductivity of about 460 S m⁻¹.

[0028] The synthesized SnO₂ quantum dots are then obtained as a stable colloidal dispersion having an average particle size of about 4.3 nm. The SnO₂ quantum dots are integrated onto the CNF mat by placing a 2 × 2 cm CNF mat in 20 mL of the SnO₂ quantum dot dispersion having a concentration of 1 mg mL⁻¹, subjecting the system to mild sonication at 100 W for 10 minutes and subsequently immersing the mat under stirring at 25 °C for 30 minutes to achieve decoration of more than 85% of the CNF surface.

[0029] The resulting hybrid mat is rinsed with deionized water and dried at 60 °C for 6 hours. Finally, the dried hybrid mat is annealed at 250 °C for 1 hour under a nitrogen atmosphere at a heating rate of 2 °C min⁻¹ to remove residual organic species and to form Sn–O–C interlinkages.

[0030] The electrode consists of SnO₂ quantum dots and carbon nanofibers in a mass ratio of about 0.8:1, corresponding to approximately 45–50 wt.% SnO₂ with an areal loading in the range of about 1.8–2.4 mg cm⁻². The electrode exhibits high electrochemical performance, showing an initial reversible capacity of about 1235 mAh g⁻¹ at a current density of 0.1 A g⁻¹ and maintaining a reversible capacity of about 1040 mAh g⁻¹ after 200 cycles.

[0031] The electrode also demonstrates an average coulombic efficiency greater than 99%, indicating stable charge–discharge behavior. In certain embodiments, the electrode shows a capacity in the range of about 1230–1250 mAh g⁻¹ and a capacitance in the range of about 560–570 F g⁻¹.

[0032] When assembled into a lithium-ion coin cell, the resulting SnO₂ QD–CNF electrode delivers a first-cycle reversible capacity of about 1235 mAh g⁻¹ at 0.1 A g⁻¹ and about 1150 mAh g⁻¹ at 0.5 A g⁻¹, with a capacity retention of approximately 90–95% over 500 cycles for an SnO₂ quantum dot areal loading of about 2.4 mg cm⁻².

[0033] Although the field of the invention has been described herein with limited reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. , Claims:1. An SnO2 Quantum dots CNF anchored electrode, comprising:

i. a carbon nanofiber (CNF) mat; and
ii. colloidal SnO₂ quantum dots (SnO₂ QDs) anchored on the CNF mat;
wherein the SnO₂ QDs have an average particle size in the range of 4.1 to 4.5 nm uniformly and densely distributed on the CNFs, and the optimized electrode.

2. The electrode as claimed in claim 1, wherein the electrode consists of SnO₂ QDs and CNFs in a mass ratio of 0.8:1 corresponding to about 45–50 wt.% SnO₂ and an areal loading of about 1.8–2.4 mg cm⁻².

3. The electrode as claimed in claim 1, wherein the said electrode exhibits an initial reversible capacity of 1235 mAh g⁻¹ at 0.1 A g⁻¹ and a reversible capacity of 1040 mAh g⁻¹ after 200 cycles.

4. The electrode as claimed in claim 1, wherein the average coulombic efficiency greater than 99%.

5. The electrode as claimed in claim 1, wherein the said electrode shows capacity retention of 97% after 500 bending cycles at a bending radius of 3 mm.

6. The electrode as claimed in claim 1, wherein the said electrode consists of capacity in the range of 1230-1250 mAh/g and capacitance in the range of 560-570 F/g.

7. A method for synthesis of SnO₂ QDs for electrode as claimed in claim 1 consists of the following steps:

i. dissolving 0.451 g SnCl₂·2H₂O in 25 mL deionized water under magnetic stirring at 600 rpm for 10 minutes at 25 °C to obtain a Sn²⁺ precursor solution,
ii. dissolving 0.294 g trisodium citrate in 10 mL deionized water and adding the citrate solution dropwise into the Sn precursor with continued stirring for 15 minutes to act as stabilizing ligand,
iii. dissolving 0.190 g thiourea in 10 mL deionized water and adding the thiourea solution slowly to the reaction mixture at 30–40 °C under stirring at 700 rpm for 120 minutes for controlled oxidation of Sn²⁺ to SnO₂ nuclei,
iv. adjusting the pH to about 8 using dilute ammonia solution,
v. maintaining the solution at 35–40 °C for 2 hours to promote quantum dot formation with slight turbidity and Tyndall effect, and
vi. ageing the solution for 12 hours at room temperature to obtain a stable colloidal SnO₂ QD dispersion with average size of 4.3 nm and colloidal stability greater than 30 days due to citrate capping.

8. The method for synthesis of SnO₂ QDs as claimed in claim 6, wherein the synthesized SnO₂ QDs exhibits a typical yield of about 82–86%.

9. A method for preparing a free-standing SnO₂ QD@CNF electrode comprising:

i. preparing a CNF mat by dissolving 1 g polyacrylonitrile in 9 g N,N dimethylformamide, electrospinning at 15 kV with 18 cm tip-to-collector distance and 0.6 mL h⁻¹ flow rate onto a rotating drum,
ii. stabilizing (step i) at 250 °C in air at 1 °C min⁻¹ for 3 h, and carbonizing at 800 °C in N₂ at 2 °C min⁻¹ for 2 h to obtain a ~30 µm thick CNF mat having surface area 220 m² g⁻¹ and conductivity 460 S m⁻¹,
iii. synthesizing SnO₂ QDs to obtain a stable colloidal SnO₂ QD dispersion with average size 4.3 nm,
iv. integrating SnO₂ QDs (step iii) onto the CNF mat (step ii) by placing a 2 × 2 cm CNF mat in 20 mL SnO₂ QD dispersion of concentration 1 mg mL⁻¹, subjecting to mild sonication at 100 W for 10 minutes and then immersing under stirring at 25 °C for 30 minutes to achieve decoration of more than 85% CNF surface,
v. rinsing the hybrid mat with deionized water and drying at 60 °C for 6 hours, and
vi. annealing the dried hybrid mat at 250 °C for 1 hour under N₂ at a heating rate of 2 °C min⁻¹ to remove residual organics and create Sn–O–C interlinkage.

10. The method as claimed in claim 9 resulting SnO₂ QD CNF electrode are assembled into a lithium-ion coin cell to deliver a first-cycle reversible capacity of 1235 mAh g⁻¹ at 0.1 A g⁻¹ and 1150 mAh g⁻¹ at 0.5 A g⁻¹ with 90-95% retention over 500 cycles for a SnO₂ QD areal loading of 2.4 mg cm⁻².