Sodium-Based Supercapacitor Electrolyte Voltage Window
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Solution Overview
Problem
Current supercapacitor electrolyte compositions have a limited operating voltage window of about 2.7 volts, which restricts the energy density of supercapacitors, as energy stored increases quadratically with voltage.
Innovation Solution
A non-aqueous electrolyte composition comprising sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) and dimethoxyethane (DME) at a molar ratio of 1:1 to 1:3, forming a solvated ionic liquid, which extends the electrochemical potential window to at least 3.25 volts with high coulombic efficiency, and optionally includes corrosion inhibitors like tetrabutylammonium perchlorate or tetrabutylammonium hexafluorophosphate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional electrolyte compositions (TEABF4 in acetonitrile or propylene carbonate) are used, then high specific conductivity is achieved minimizing resistive losses, but the operating voltage window is limited to around 2.7 volts
Solution Approach 1:
The patent changes the chemical parameters of the electrolyte by replacing conventional TEABF4 salts with sodium salts (NaPF6, NaBF4, NaTFSI) and using glyme solvents (DMG, DME, TEGDME) in specific molar ratios. This parameter change enables the electrolyte to maintain high conductivity while extending the operating voltage window from 2.7V to above 3.0V, resolving the contradiction between minimizing resistive losses and expanding voltage window.
Solution Approach 2:
The patent creates a composite electrolyte system by combining specific ratios of sodium salts with glyme solvents to form solvated ionic liquids. This composite approach leverages the complementary properties of the components: sodium salts provide high ionic conductivity while glyme solvents provide electrochemical stability at higher voltages, achieving both low resistive losses and extended voltage window simultaneously.
2Quantity of substance
If the operating voltage window is extended beyond 2.7 volts, then energy density increases quadratically, but capacitor lifetime is significantly reduced
Solution Approach 1:
The patent modifies the electrolyte composition parameters by using sodium salts with glyme solvents in controlled molar ratios (1:1 to 1:3). This parameter optimization allows the system to operate at voltages above 3.0V with maintained capacitor lifetime, enabling quadratic increase in energy density without sacrificing reliability.
Solution Approach 2:
The patent employs corrosion inhibitor additives (TBAClO4, TBAPF6) that can decompose or be consumed to protect the main electrolyte system. These sacrificial additives prevent degradation of the primary electrolyte components, allowing extended voltage operation while maintaining capacitor lifetime through controlled decomposition of the inhibitor rather than the main electrolyte.
3Duration of action of moving object
If sodium salts with glyme solvents are used to extend voltage window, then electrochemical potential window increases to at least 3.25 volts, but corrosion of aluminum current collectors may occur
Solution Approach 1:
The patent introduces corrosion inhibitor additives (TBAClO4, TBAPF6) as intermediary substances that mediate between the sodium salt/glyme electrolyte system and the aluminum current collector. These inhibitors form protective films or react preferentially with corrosive species, preventing direct contact and corrosion of the aluminum while allowing the high-voltage electrolyte composition to function.
Solution Approach 2:
The patent converts the potentially harmful corrosive action of sodium salts on aluminum into a beneficial protective mechanism by using sacrificial corrosion inhibitors. These inhibitors are designed to undergo controlled decomposition or reaction that consumes the corrosive agents, transforming what would be harmful corrosion into a protective barrier formation that extends capacitor lifetime while maintaining the extended voltage window.
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 electrolyte composition significantly increases the energy density of supercapacitors by extending the voltage window and improving coulombic efficiency, reducing corrosion, and maintaining charge retention, while suppressing unwanted intercalation reactions with carbon electrodes.
Implementation Method 1
The non-aqueous solvent component and the conductive sodium salt component can be combined to form a solvated ionic liquid in the space between the negative and positive electrodes
Implementation Method 2
Supercapacitors store ionic charge electrostatically at the interface of high surface area electrodes, such as carbon electrodes, in a liquid electrolyte composition
Implementation Method 3
Energy density of supercapacitors can also be increased through faradaic mechanisms commonly known as pseudocapacitance, which arises from the introduction of redox active groups through functionalization of the carbon electrode surface or the incorporation of metal oxides
Data Source
AI summary
A supercapacitor and a related electrolyte composition suitable for use in a supercapacitor are provided. An electrolyte composition can include a conductive sodium salt component comprising NaTFSI and a non-aqueous solvent component comprising dimethoxy ethane (DME). The conductive sodium salt component and the non-aqueous solvent component can be present at a molar ratio of NaTFSI:DME of 1:1 to 1:3, inclusive.