Electric Storage Device Electrolyte Low-Temperature and High-Temperature Reliability
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Solution Overview
Problem
Lithium ion capacitors face reliability issues at high temperatures due to reductive decomposition of γ-butyrolactone and film formation on the negative electrode, which inhibits lithium ion migration and causes internal pressure increases, while existing solutions for high-temperature reliability are inadequate for long-term use.
Innovation Solution
An electric storage device comprising a non-aqueous electrolytic solution with a solvent mix of cyclic ester and cyclic carbonate ester, lithium salt, and a sulfonate ester derivative with a higher reduction potential, which suppresses reductive decomposition and maintains capacitance across temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If γ-butyrolactone is used as the primary solvent to improve low-temperature characteristics, then low-temperature capacitance is improved, but reductive decomposition occurs at high temperature causing reliability issues
Solution Approach 1:
The patent uses a composite solvent system combining γ-butyrolactone (cyclic ester) with cyclic carbonate esters (ethylene carbonate and/or propylene carbonate) in specific ratios. This composite approach allows the electrolyte to exhibit both low-temperature fluidity from γ-butyrolactone and high-temperature stability from the cyclic carbonate esters, resolving the contradiction between low-temperature performance and high-temperature reliability
Solution Approach 2:
The patent optimizes the volume ratio parameters of the solvent components (γ-butyrolactone: cyclic carbonate ester = 1/9 to 7/3, with preferred ranges of 2/8 to 7/3) to achieve the desired balance between low-temperature characteristics and high-temperature stability. By adjusting these compositional parameters, the electrolyte maintains appropriate viscosity and electrochemical stability across a wide temperature range
2Temperature
If vinylene carbonate is added to form a film on the negative electrode to improve low-temperature characteristics, then low-temperature capacitance is improved, but the film inhibits lithium ion migration and causes internal pressure increase at high temperature
Solution Approach 1:
The patent removes vinylene carbonate from the electrolyte composition and replaces it with a sulfonate ester derivative. This extraction of the problematic component eliminates the formation of harmful films that inhibit lithium ion migration and cause internal pressure buildup, while still maintaining low-temperature performance through the optimized solvent composition
Solution Approach 2:
The sulfonate ester derivative acts as an intermediary substance that forms a beneficial interface layer on the negative electrode without the harmful effects of vinylene carbonate. This intermediary layer improves low-temperature characteristics while allowing proper lithium ion migration and preventing excessive internal pressure generation at high temperatures
3Reliability
If methylene bis sulfonate derivative is added to improve high-temperature cycle characteristics, then short-term high-temperature reliability is improved, but long-term high-temperature stability deteriorates due to further film formation and electrolyte decomposition
Solution Approach 1:
The patent employs a sulfonate ester derivative that provides effective protection during short-term high-temperature operation but is designed to be consumed or stabilized over time, preventing the long-term decomposition issues associated with methylene bis sulfonate derivative. This approach achieves adequate short-term reliability without compromising long-term stability
Solution Approach 2:
The patent optimizes the concentration parameter of the sulfonate ester derivative (0.1-5% by weight, preferably 1-5%) to achieve the right balance between short-term protective effects and long-term stability. This parameter optimization ensures sufficient protection during short-term high-temperature cycling while preventing excessive film formation and electrolyte decomposition during long-term operation
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 both good low-temperature characteristics and improved high-temperature reliability by maintaining capacitance and controlling internal resistance, with optimal results achieved within specific ranges of solvent ratios and additive concentrations.
Implementation Method 1
the reductive decomposition of γ-butyrolactone cannot be suppressed in a high-temperature state
Implementation Method 2
combining a positive electrode similar to that of an electric double-layer capacitor or redox capacitor, and a negative electrode using a carbon material capable of occluding lithium ions
Data Source
AI summary
In an embodiment, an electric storage device 1 includes: an electric storage element 50 having a positive electrode and a negative electrode; a non-aqueous electrolytic solution constituted by a non-aqueous solvent primarily containing cyclic ester and cyclic carbonate ester, in which an electrolyte containing lithium salt is dissolved and to which a sulfonate ester derivative whose reduction potential is higher than that of the cyclic ester and cyclic carbonate ester is added; and an outer container 70 that stores the electric storage element 50 and non-aqueous electrolytic solution. The electric storage device can offer both good low-temperature characteristics and good high-temperature reliability.