Composite Nanofiber Separator for Lithium Ion Battery Shutdown
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional separators for lithium ion batteries face issues with high impedance due to the melting of low-melting-point nanofiber layers during the heat press process, which can lead to inadequate shutdown function and compromised battery performance.
Innovation Solution
A separator formed by crossing nanosize fibers with two or more kinds of aqueous resins having different melting points, where the second aqueous resin with a lower melting point is used to fill voids and enhance electrolyte retention and impedance, while the first aqueous resin maintains structural integrity at elevated temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low-melting-point nanofiber layer is used to achieve shutdown function, then the shutdown function is improved, but the nanofiber layer melts during heat press process causing porus stopping up and high impedance
Solution Approach 1:
The separator is divided into multiple functional layers: a base material layer, a heat-resistance nanofiber layer (melting point ≥180°C), and a low-melting-point nanofiber layer (melting point 80-120°C). This segmentation allows each layer to perform its specific function independently - the heat-resistance layer maintains structural integrity during heat press while the low-melting-point layer provides shutdown function at lower temperatures.
Solution Approach 2:
Different regions of the separator have different melting points tailored to their functional requirements. The heat-resistance layer has high melting point for structural stability during manufacturing and normal operation, while the low-melting-point layer is strategically positioned to melt at shutdown temperature to close pores and stop ion transport.
2Speed
If nanofiber fibers with narrow diameter are used to improve ion mobility, then the void rate becomes small and electrolyte liquid retention becomes insufficient
Solution Approach 1:
The separator uses a composite structure combining nanofiber materials with appropriate void rates. The nanofiber layer has a void rate of 30-70% which balances ion mobility and electrolyte retention. The composite nature of the nanofiber material allows it to maintain narrow fiber diameters for good ion mobility while the optimized void rate ensures sufficient electrolyte liquid is retained in the pores.
3Reliability
If polyethylene separator is used to achieve shutdown function, then the shutdown function operates at melting point, but the shutdown temperature is fixed at approximately 140°C which may not be optimal
Solution Approach 1:
The separator uses nanofiber materials with adjustable melting points rather than fixed polyethylene. By selecting nanofiber materials with melting points in the range of 80-120°C for the low-melting-point layer, the shutdown temperature can be optimized for specific battery applications. This parameter adjustment allows the shutdown function to operate at more appropriate temperatures for different battery chemistries and safety requirements.
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 proposed solution achieves a shutdown function, improved heat-resistance, electrolyte-liquid retention, and reduced impedance, ensuring safety and performance in lithium ion batteries by maintaining structural integrity and controlling the melting behavior of the resins.
Implementation Method 1
the second aqueous resin with a lower melting point is used to fill voids and enhance electrolyte retention and impedance
Implementation Method 2
by allowing the electric resistance of the separator to increase, the battery reaction is blocked, and a remarkable rise of the battery temperature is prevented
Data Source
AI summary
The separator of a nonaqueous electrolyte secondary battery is characterized by having a composite nanofiber fiber which is a nanosize fiber that contains two or more kinds of aqueous resins whose melting points are different.