Polyolefin Separator Molecular Weight Control for Battery Shutdown
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Solution Overview
Problem
Conventional separators for non-aqueous electrolyte batteries with heat-resistant layers on polyolefin porous films face challenges in achieving rapid shutdown responsiveness and preventing melt-down at high temperatures, leading to potential short circuits and safety issues.
Innovation Solution
A separator design featuring a polyolefin microporous substrate with a heat-resistant porous layer, where the polyolefin content has a molecular weight of 100,000 or less (10-25% by mass), and a heat-resistant polymer layer with specific porosity and pore diameter, ensuring excellent shutdown responsiveness and short circuit resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a heat resistant layer is formed on one or both surfaces of a polyolefin porous film, then the melt-down is inhibited, but the shutdown responsiveness decreases
Solution Approach 1:
The patent applies parameter changes by controlling the molecular weight distribution of polyolefin, specifically setting the content of polyolefin with molecular weight 100,000 or less to 10-25% by mass. This parameter optimization enables the separator to achieve both rapid shutdown responsiveness and adequate heat resistance, resolving the contradiction between shutdown speed and melt-down prevention.
2Reliability
If a heat resistant layer is formed on one or both surfaces of a polyolefin porous film, then the safety at high temperature is improved, but the temperature width from shutdown start to pore closing increases
Solution Approach 1:
The patent optimizes the molecular weight distribution parameter of polyolefin, specifically controlling the content of low molecular weight polyolefin (100,000 or less) to 10-25% by mass. This parameter control narrows the temperature width between shutdown initiation and pore closing while maintaining high-temperature safety, thereby resolving the contradiction between safety and shutdown time efficiency.
3Speed
If polyolefin with lower molecular weight is increased to improve shutdown responsiveness, then the shutdown function is enhanced, but the heat resistance decreases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molecular weight distribution of polyolefin, setting the content of polyolefin with molecular weight 100,000 or less to 10-25% by mass. This optimized parameter range enables the separator to achieve rapid shutdown responsiveness while maintaining sufficient heat resistance, resolving the contradiction between shutdown speed and heat resistance.
Solution Approach 2:
The patent uses composite materials by combining polyolefin with different molecular weights in a specific ratio. The composite structure includes both low molecular weight polyolefin (for rapid shutdown) and higher molecular weight polyolefin (for heat resistance), achieving a balance between shutdown responsiveness and thermal stability.
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 separator exhibits rapid shutdown functionality and high short circuit resistance, ensuring battery safety by effectively blocking ion flow and preventing thermal runaway.
Implementation Method 1
a shutdown function means the function of blocking an ion flow by closing the pores of the porous film as a result of melting polyolefin when abnormal heat generation occurs in the battery
Implementation Method 2
a heat resistant porous layer that is formed on one or both sides of the polyolefin microporous substrate and that includes a heat resistant polymer
Data Source
AI summary
Disclosed is a separator for a non-aqueous electrolyte battery, the separator including a polyolefin microporous substrate in which a content of polyolefin having a molecular weight of 100,000 or less is from 10% by mass to 25% by mass relative to a total amount of polyolefin, and a heat resistant porous layer that is formed on one or both sides of the polyolefin microporous substrate and that includes a heat resistant polymer, wherein a maximum value of S, which is represented by the following formula (1), is 0.8 or more, and a temperature exhibiting the maximum value of S is from 130° C. to 155° C.:S=d(log R)/dT Formula (1):wherein R represents a resistance (ohm·cm2) of a cell, and T represents a temperature (° C.), in a measurement using a battery that includes the cell that is provided with a separator for a non-aqueous electrolyte battery, at a temperature rising rate of 1.6° C./min.