Lithium Ion Capacitor Electrolyte Mixture for High-Temperature Stability
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Solution Overview
Problem
Lithium ion capacitors face challenges in maintaining high capacitance and low internal resistance when exposed to high-temperature, high-voltage environments due to issues like electrolyte decomposition and increased internal resistance caused by ion dissociation and corrosion of current collector foils.
Innovation Solution
A lithium ion capacitor with an electrolytic solution composed of a mixture of LiFSI and LiBF4 in a specific mol ratio, combined with a cyclic or chained carbonate solvent and a film-forming agent, which maintains initial performance and minimizes changes under high-temperature, high-voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LiPF6 is used as the electrolyte to achieve high electrical conductivity, then the internal resistance is reduced, but the reliability deteriorates at high temperatures due to thermal decomposition
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by replacing LiPF6 with LiBF4 and adding LiBETI in specific proportions. This parameter change eliminates thermal decomposition at high temperatures while maintaining electrical conductivity, directly resolving the contradiction between reliability and harmful decomposition factors.
Solution Approach 2:
The patent creates a composite electrolyte system combining LiBF4 and LiBETI in a specific ratio (0.3:0.7 to 0.7:0.3). This composite approach leverages the high voltage resistance of LiBF4 and the high conductivity of LiBETI to simultaneously achieve both reliability and low internal resistance, resolving the contradiction between these two properties.
2Reliability
If LiBETI is used to improve high-temperature stability, then the electrolyte stability increases, but the current collector foils corrode at positive electrode potential around 4V
Solution Approach 1:
The patent optimizes the concentration ratio of LiBETI relative to LiBF4 (maintaining LiBETI at 70-93% of total electrolyte concentration). This precise parameter control ensures sufficient high-temperature stability while limiting the amount of LiBETI that could cause corrosion, thereby resolving the contradiction between stability and corrosion resistance.
3Reliability
If LiBF4 is used as the primary electrolyte to improve high-temperature resistance, then the thermal stability increases, but the internal resistance rises due to low ion dissociation
Solution Approach 1:
The patent creates a composite electrolyte combining LiBF4 (providing high-temperature resistance) and LiBETI (providing high conductivity through superior ion dissociation). The synergistic effect of this composite system maintains thermal stability while achieving low internal resistance, resolving the contradiction between these two properties.
Solution Approach 2:
The patent optimizes the concentration ratio of LiBF4 to LiBETI (maintaining LiBF4 at 7-30% of total electrolyte concentration). This parameter optimization ensures sufficient thermal stability from LiBF4 while maintaining low internal resistance through the high dissociation of LiBETI, resolving the contradiction between thermal resistance and internal resistance.
4Duration of action of moving object
If the discharge depth of the negative electrode is reduced to extend battery life, then the duration of action increases, but the capacitance per unit volume decreases
Solution Approach 1:
The patent changes the electrolyte composition parameters to enable operation at higher discharge depths (up to 80% or more) without compromising cell life. The improved electrolyte stability and ion conductivity allow deeper discharge cycles while maintaining acceptable lifespan, thereby increasing the usable capacitance per unit volume while preserving duration of action.
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 effectively maintains initial high capacitance and low internal resistance, with minimal characteristic changes after exposure to high-temperature, high-voltage environments, improving the reliability and stability of the lithium ion capacitor.
Implementation Method 1
the electrolyte is a mixture of LiFSI and LiBF4... reduced electrolyte dissociation in the electrolytic solution
Implementation Method 2
electrical conductivity... a large number of ions migrate during charge and discharge
Implementation Method 3
Electrical double-layer capacitors using non-aqueous electrolytic solution... achieve high voltage resistance
Data Source
AI summary
A lithium ion capacitor has an electrolytic solution that contains: an electrolyte which is a mixture of LiFSI and LiBF4, where the mol ratio of LiFSI to LiBF4 is in a range of 90/10 to 30/70; a solvent that contains at least one type of cyclic or chained carbonate compound; and a film-forming agent; wherein the concentration of electrolyte in the electrolytic solution is in a range of 1.2 to 1.8 mol/L. The lithium ion capacitor can maintain its initial high capacitance and low internal resistance, while also undergoing minimal characteristics changes after exposure to a high-temperature, high-voltage environment.