Nitrogen-Fluorine Doped Graphene for High-Density Supercapacitors
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Solution Overview
Problem
Existing supercapacitors have low volumetric energy densities and power densities due to the low density of carbon-based electrodes, which limits their competitiveness with batteries, and previous methods of nitrogen and fluorine doping have not achieved densities necessary to significantly improve these properties.
Innovation Solution
A method involving the preparation of nitrogen-doped graphene through the use of fluorinated graphite, sonication, mechanical treatment, thermal treatment, and reaction with an azide reagent to achieve high nitrogen doping and residual fluorine content, resulting in a density above 1.2 g/cm³ and volumetric energy densities exceeding 170 Wh/L at 5.2 kW/L.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If high surface area porous carbons are used to improve ion adsorption, then energy storage capability is improved, but volumetric energy density deteriorates due to low material density
Solution Approach 1:
The invention changes the density parameter of the electrode material from conventional low-density porous carbons (0.3-0.5 g/cm³) to high-density nitrogen-doped graphene (above 1.2 g/cm³). This parameter change allows the material to maintain high surface area for ion adsorption while achieving much higher volumetric energy density, resolving the contradiction between energy storage capability and volumetric energy density.
Solution Approach 2:
The invention uses nitrogen-doped graphene as a composite material that combines the high surface area characteristics of porous carbons with the high density of graphene. The nitrogen doping (1-30 at.%) modifies the electronic structure and enhances both the energy storage capability through pseudocapacitance and the material density, simultaneously addressing both requirements.
2Use of energy by moving object
If nitrogen doping is increased to improve electronic conductivity and pseudocapacitance, then energy storage performance is improved, but material density deteriorates
Solution Approach 1:
The invention optimizes the nitrogen doping level parameter to achieve a balance between energy storage performance and material density. By controlling nitrogen content at moderate levels (1-30 at.%) rather than extreme high doping, the material maintains good electronic conductivity and pseudocapacitance while preserving the high density characteristic of graphene, thus resolving the contradiction between energy storage performance and material density.
3Quantity of substance
If fluorination is used to create vacancies for higher nitrogen doping, then nitrogen loading is improved, but residual fluorine content may affect material stability
Solution Approach 1:
The invention uses partial fluorination as an intermediate step to create vacancies for nitrogen doping, but does not proceed to complete defluorination. By maintaining controlled residual fluorine content rather than completely removing it, the material achieves high nitrogen loading (1-30 at.%) while the residual fluorine helps maintain structural stability and prevents excessive nitrogen aggregation, thus resolving the contradiction between nitrogen loading and material stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method achieves unprecedented high densities and performance in supercapacitors, enabling ultrahigh volumetric energy and power densities, surpassing previous materials and making supercapacitors a more competitive energy storage option.
Implementation Method 1
subjecting the dispersion of fluorinated graphite to sonication and/or mechanical treatment
Implementation Method 2
subjecting the dispersion of fluorinated graphite to sonication and/or mechanical treatment and/or thermal treatment
Implementation Method 3
contacting the product from step b) with an azide reagent at a temperature of 40 to 200° C.
Implementation Method 4
dialysis of the product against water
Data Source
AI summary
A method is disclosed for preparation of nitrogen-doped graphene having these steps: a) providing a dispersion of fluorinated graphite; b) subjecting the dispersion of fluorinated graphite to sonication and/or mechanical treatment and/or thermal treatment; c) contacting the product from step b) with an azide reagent at a temperature within the range of 40 to 200° C.; d) separating the solid product formed in step c) from the mixture; e) dialyzing the product obtained in step d) against water. A nitrogen-doped graphene containing at least 8.9 at. % of nitrogen and up to 16.6 at. % of fluorine is yielded, wherein the at. % are relative to the total atoms present in the sample and determined by X-ray photoelectron spectroscopy (XPS) using an Al-Kα source; and having a density above 1.2 g/cm3 when pressed at 80 kN for 1 min. This nitrogen-doped graphene is particularly useful as a supercapacitor material.