Ionic Liquid Electrolyte Ratio for Stable SEI in Secondary Batteries
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In secondary batteries using electrolytes with ionic liquids, charging and discharging cause cracking in the solid electrolyte interphase (SEI) film, leading to increased reaction resistance and decreased capacity retention due to liquid decomposition and film thickening at the interface between the electrolyte and active material layer.
Innovation Solution
An electrolyte comprising a lithium imide salt and an ionic liquid with a molar ratio of 1.5 or lower, both containing bis(fluorosulfonyl) amide ions, is used to reduce reaction resistance, with the ionic liquid including 1-ethyl-3-methylimidazolium as a cationic species, and is incorporated between the positive and negative electrode layers, including an Si-based active material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an electrolyte containing an ionic liquid is used in a secondary battery including a separator, then the battery can operate with ionic liquid properties, but charging and discharging cause cracking in the SEI film, leading to increased reaction resistance and decreased capacity retention
Solution Approach 1:
The patent changes the chemical composition parameters of the electrolyte by specifying a molar ratio of ionic liquid to lithium imide salt of 1.5 or lower, and requiring both components to contain bis(fluorosulfonyl) amide ions. This parameter optimization prevents excessive SEI film thickening and cracking during charging-discharging cycles, thereby curbing reaction resistance increase while maintaining capacity retention.
2Reliability
If the molar ratio of ionic liquid to lithium imide salt is high, then the electrolyte has good ionic conductivity, but the reaction resistance at the interface increases and capacity retention decreases
Solution Approach 1:
The patent establishes a specific molar ratio parameter (ionic liquid/lithium imide salt ≤ 1.5) that optimizes the balance between ionic conductivity and SEI film stability. This parameter control resolves the contradiction by preventing harmful SEI cracking while maintaining adequate conductivity, without requiring complex multi-component formulations.
3Reliability
If the SEI film becomes thick due to liquid decomposition, then the interface between electrolyte and active material is covered, but the reaction resistance increases and battery performance deteriorates
Solution Approach 1:
The patent modifies the electrolyte composition parameters to achieve a stable SEI film that does not excessively thicken or crack during cycling. By controlling the ionic liquid to lithium imide salt molar ratio and ensuring both contain bis(fluorosulfonyl) amide ions, the SEI film maintains appropriate thickness and integrity, preventing harmful resistance increase while allowing necessary ionic transport.
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 effectively curbs the increase in reaction resistance at the interface between the electrolyte and active material layer, maintaining battery performance and capacity retention by increasing the electrolyte's viscosity and appropriate viscosity level, suitable for batteries with active materials that expand and contract, such as silicon.
Implementation Method 1
charging and discharging cause cracking in the solid electrolyte interphase (SEI) film formed at the interface between the electrolyte and the active material layer
Implementation Method 2
The electrolyte effectively curbs the increase in reaction resistance at the interface between the electrolyte and active material layer, maintaining battery performance and capacity retention by increasing the electrolyte's viscosity
Data Source
AI summary
An electrolyte includes a lithium imide salt and an ionic liquid, and a molar ratio of the ionic liquid to the lithium imide salt (ionic liquid/lithium imide salt) is 1.5 or lower.