Room-Temperature Ionic Liquid Electrolyte for Lithium-Ion Battery Safety
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Solution Overview
Problem
Lithium-ion secondary batteries face issues with volatility and low flash points when using organic solvents as electrolytes, leading to potential fires and instability due to low reduction resistance in room-temperature ionic liquids, limiting the use of low potential negative electrode materials.
Innovation Solution
The development of room-temperature ionic liquids with cyclic quaternary ammonium cations and specific anions, such as univalent imide, methide, perfluoroalkyl sulfonic acid, tetrafluoroborate, or hexafluorophosphate, which incorporate electron donating substituents to improve reduction resistance and stability, allowing for the use of a wide range of electrode materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If organic solvents with high dielectric constant are used as electrolytes, then ion conductivity is improved, but safety deteriorates due to volatility and low flash point
Solution Approach 1:
The patent changes the physical and chemical parameters of the electrolyte by replacing conventional organic solvents with room-temperature ionic liquids. This substitution fundamentally alters the volatility and flash point parameters while maintaining ion conductivity through the selection of specific ionic liquid compositions with appropriate dielectric constants and ionic mobilities.
Solution Approach 2:
The patent employs composite electrolyte systems combining room-temperature ionic liquids with conventional organic solvents or additives. This composite approach allows the system to inherit the safety benefits of ionic liquids (low volatility, high flash point) while retaining the high ion conductivity characteristics of conventional solvents, thus resolving the contradiction between safety and conductivity.
2Object-affected harmful factors
If room-temperature ionic liquid is used as electrolyte, then safety is improved, but reduction resistance deteriorates limiting use of low potential negative electrode materials
Solution Approach 1:
The patent applies local quality modification by introducing specific functional groups and substituents at particular positions within the ionic liquid molecular structure. By strategically placing electron-donating groups (such as alkyl chains, aryl groups, or heteroatom-containing substituents) on the cation or anion, the local electron density is increased at critical sites, thereby enhancing the overall reduction resistance while maintaining the inherent safety advantages of ionic liquids.
Solution Approach 2:
The patent systematically modifies the chemical structure parameters of the ionic liquid to tune the reduction potential. By changing the molecular weight, branching structure, aromaticity, or introducing electron-donating substituents, the HOMO level of the ionic liquid is raised, making it more resistant to reduction by low potential negative electrode materials while preserving the high flash point and low volatility characteristics.
3Adaptability or versatility
If reduction resistance of room-temperature ionic liquid is improved, then compatibility with low potential negative electrode materials is improved, but oxidation-reduction potential window narrows
Solution Approach 1:
The patent segments the electrolyte system into multiple functional components: a base room-temperature ionic liquid providing safety and structural stability, and specific substituents or additives tailored to enhance reduction resistance. This segmentation allows independent optimization of each component's function - the core ionic liquid structure maintains a wide oxidation-reduction window while the peripheral substituents provide the necessary reduction resistance, thus resolving the contradiction between versatility and energy density.
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 improved reduction resistance and stability of the electrolyte enable the use of low potential negative electrode materials, enhancing the safety and performance of lithium-ion batteries by widening the oxidation-reduction potential window and increasing energy density.
Implementation Method 1
low reduction resistance of a room-temperature ionic liquid
Implementation Method 2
excellent ion conductivity
Data Source
AI summary
One object is to provide a power storage device including an electrolyte using a room-temperature ionic liquid which includes a univalent anion and a cyclic quaternary ammonium cation having excellent reduction resistance. Another object is to provide a high-performance power storage device. A room-temperature ionic liquid which includes a cyclic quaternary ammonium cation represented by a general formula (G1) below is used for an electrolyte of a power storage device. In the general formula (G1), one or two of R1 to R5 are any of an alkyl group having 1 to 20 carbon atoms, a methoxy group, a methoxymethyl group, and a methoxyethyl group. The other three or four of R1 to R5 are hydrogen atoms. A− is a univalent imide anion, a univalent methide anion, a perfluoroalkyl sulfonic acid anion, tetrafluoroborate (BF4−), or hexafluorophosphate (PF6−).