Lithium-ion Battery Separator with Molecular Weight Gradient
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional lithium-ion secondary battery separators using polyethylene and polypropylene face challenges in achieving sufficient strength at high temperatures and safety, particularly in large-capacity batteries, leading to internal short circuits and compromised safety due to inadequate heat resistance and adhesion with electrodes.
Innovation Solution
A lithium-ion secondary battery separator with a laminated structure comprising a high-melting-point first polymer layer and a low-melting-point second polymer layer, where the second layer has higher and lower molecular parts with a specific weight-average molecular weight ratio, enhancing heat resistance and shutdown properties while maintaining low impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a material having a high heat resistance is used in a separator, then heat resistance is improved, but shutdown property deteriorates and impedance increases
Solution Approach 1:
The separator is divided into multiple functional layers: a heat-resistant polymer layer (first polymer layer) that maintains structural integrity at high temperatures, and shutdown polymer layers (second polymer layers) with lower melting points that provide the shutdown function. This segmentation allows each layer to perform its specific function without compromising the other, resolving the contradiction between heat resistance and shutdown property.
Solution Approach 2:
The invention uses a composite structure combining different polymer materials with distinct properties. The heat-resistant polymer layer (e.g., polyacrylonitrile, polyimide) provides thermal stability, while the shutdown polymer layers (e.g., polyethylene, polypropylene) provide the shutdown function at lower temperatures. This composite approach enables the separator to simultaneously achieve both heat resistance and shutdown property.
2Temperature
If a material having a high heat resistance is used in a separator, then heat resistance is improved, but adhesion between electrodes and separators deteriorates, increasing impedance
Solution Approach 1:
The separator exhibits different properties at different locations: the heat-resistant polymer layer provides thermal stability, while the shutdown polymer layers in contact with electrodes provide both shutdown function and good adhesion. The lower molecular weight components in the shutdown layers specifically enhance adhesion to electrodes, resolving the contradiction between heat resistance and adhesion.
Solution Approach 2:
The invention controls the molecular weight distribution of the shutdown polymer layers, specifically maintaining a weight-average molecular weight of 10,000 or less. This parameter change enables the shutdown layers to provide both the shutdown function and sufficient adhesion to electrodes, while the heat-resistant layer maintains thermal stability.
3Reliability
If conventional PE and PP separators are used, then shutdown property is achieved, but heat resistance and strength at high temperatures are insufficient
Solution Approach 1:
The separator is segmented into distinct functional layers: the heat-resistant polymer layer (first polymer layer) that provides high-temperature strength and structural support, and the shutdown polymer layers (second polymer layers) that provide the shutdown function. This segmentation allows PE and PP to maintain their shutdown property while the heat-resistant layer compensates for their insufficient high-temperature strength.
Solution Approach 2:
The invention creates a composite separator structure where conventional shutdown polymers (PE, PP) are combined with heat-resistant polymers (polyacrylonitrile, polyimide, etc.). The shutdown polymers retain their low melting points for shutdown function, while the heat-resistant polymers provide the necessary strength at high temperatures, resolving the contradiction between shutdown property and heat resistance.
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 raises the shutdown temperature, improves battery safety by preventing thermorunaway, and maintains favorable interface formation between electrodes and separators, thereby reducing impedance and enhancing overall battery performance.
Implementation Method 1
the second polymer layer has a melting point lower than that of the first polymer layer; wherein the second polymer layer has a higher molecular part formed on a side in contact with the first polymer layer and a lower molecular part formed on a side farther from the first polymer layer than is the higher molecular part
Data Source
AI summary
A lithium-ion secondary battery separator has a porous structure formed by laminating a second polymer layer, a first polymer layer, and a second polymer layer in sequence. The second polymer layer has a melting point lower than that of the first polymer layer. The second polymer layer has a higher molecular part formed on a side in contact with the first polymer layer and a lower molecular part formed on a side farther from the first polymer layer than is the higher molecular part. The higher and lower molecular parts have a weight-average molecular weight ratio (higher molecular part/lower molecular part) of 4 to 19 therebetween.