Supercapacitor Electrolyte Voltage Window Extension
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Solution Overview
Problem
Current supercapacitors face limitations in energy density due to restricted voltage windows, which are sensitive to electrolyte composition, electrode materials, and temperature, leading to rapid degradation and reduced capacitance over time.
Innovation Solution
A supercapacitor design utilizing a sodium hexafluorophosphate electrolyte composition with ethylene glycol dimethyl ether or similar solvents, which extends the electrochemical voltage window to 3.5 V, preventing sodium intercalation and minimizing aluminum corrosion, thereby enhancing energy density and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional electrolyte compositions (TEABF4 in acetonitrile or propylene carbonate) are used, then high specific conductivity and high power operation are achieved, but the voltage window is limited to 2.5-3.0 V and capacitor lifetime is significantly reduced beyond this range
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by using sodium hexafluorophosphate instead of tetraethylammonium tetrafluoroborate, combined with specific carbonate solvents. This parameter change enables the electrolyte to maintain high ionic conductivity while expanding the electrochemical stability window to 3.5 V or higher, thereby extending capacitor lifetime without sacrificing power operation capability
Solution Approach 2:
The patent creates a composite electrolyte system by combining sodium hexafluorophosphate salt with specific carbonate solvents (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate). This composite material approach leverages the beneficial properties of each component: the sodium salt provides high ionic conductivity while the carbonate solvents provide electrochemical stability at high voltages, resolving the contradiction between power and duration
2Use of energy by moving object
If the voltage window is extended beyond 4.5 V vs. Na/Na+, then energy density is improved, but aluminum current collector corrosion and carbon oxidation occur
Solution Approach 1:
The patent changes the electrolyte composition parameters to use sodium hexafluorophosphate in carbonate solvents, which creates a more stable electrochemical environment. This parameter change allows the system to operate at higher voltages (3.5 V or higher in practical cells) without causing aluminum current collector corrosion or carbon oxidation, thereby improving energy density while maintaining reliability
Solution Approach 2:
The patent introduces a specifically formulated electrolyte composition as an intermediary between the electrodes and the external circuit. This electrolyte acts as a protective medium that enables high voltage operation without direct harmful interactions between the electrodes and the aluminum current collector, preventing corrosion and oxidation while allowing energy density improvement
3Reliability
If solvents like carbonates and ACN are used, then electrode passivation occurs below 1.2 V vs. Na/Na+, but this is detrimental for double-layer capacitors as insulating films reduce capacitance and block pores
Solution Approach 1:
The patent changes the solvent parameters by selecting specific carbonate solvents with appropriate dielectric constants and viscosity characteristics. These parameter changes allow the electrolyte to maintain stability without forming thick insulating passivation films on the electrode surfaces, preserving both electrode reliability and high double-layer capacitance for optimal supercapacitor performance
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 solution provides a stable voltage window of up to 3.5 V, significantly increasing energy density and reducing degradation, while maintaining high conductivity and preventing electrode passivation, thus improving the long-term performance of supercapacitors.
Implementation Method 1
Supercapacitors store ionic charge electrostatically at the interface of high surface area electrodes, such as carbon electrodes, in a liquid electrolyte composition
Implementation Method 2
Ionic liquids have generated the most interest due to their high stability, but remain limited by high cost, low purity, and low conductivity
Data Source
AI summary
A supercapacitor according to the present invention includes a negative carbon-comprising electrode which does not intercalate sodium, and a positive carbon-comprising electrode. An electrolyte composition comprises sodium hexafluorophosphate and a non-aqueous solvent comprising at least one selected from the group consisting of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The supercapacitor has an electrochemical voltage window of from +0.0 V to 3.5 V (full cell voltage). The electrolyte has an electrochemical voltage window of from +0.05 V to 3.9 V vs. Na/Na+. A method of making and a method of operating a supercapacitor is also disclosed.