Polyolefin Separator Crystalline Structure for Thermal Stability
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Solution Overview
Problem
Lithium ion secondary batteries with high energy density or large sizes face increased risk of temperature rise and potential separator melting or fracturing during abnormal currents, necessitating enhanced short-circuit resistance in separators.
Innovation Solution
A polyolefin-based separator with a specific crystal structure, characterized by X-ray diffraction peaks corresponding to (111) and (-131) crystal planes of polypropylene, is developed to enhance short-circuit resistance, featuring a high c-axis directional order that minimizes melting and shrinkage, and optionally includes a ceramic layer for improved heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional porous polyolefin separator is used, then the battery can operate normally under standard conditions, but the separator may melt or fracture when battery temperature greatly rises during abnormal current
Solution Approach 1:
The patent applies parameter changes by controlling the crystallinity and molecular weight of polypropylene within specific ranges (crystallinity: 40-60%, molecular weight: 100,000-500,000). These parameter optimizations enhance the melting point and thermal stability of the separator, preventing melt-through at elevated temperatures while maintaining proper pore structure for ion transport.
Solution Approach 2:
The patent employs composite materials by combining polypropylene with specific additives including inorganic fillers (alumina, silica), antioxidants, and UV stabilizers. This composite formulation improves thermal resistance and mechanical strength, enabling the separator to withstand high temperatures without fracturing while maintaining its shutdown function.
2Temperature
If the separator structure is optimized for high temperature resistance, then thermal stability improves, but the complexity of manufacturing increases
Solution Approach 1:
The patent applies preliminary action by pre-mastering the polymer composition and crystallinity characteristics before separator fabrication. The polypropylene is pre-formulated with specific additives and crystallized to predetermined parameters, simplifying the subsequent membrane formation process while ensuring consistent thermal performance across production batches.
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 provides excellent short-circuit resistance and thermal stability, effectively preventing battery thermal runaway and short-circuiting, even under extreme temperature conditions.
Implementation Method 1
a separator that is constituted by polyolefin having a specific crystal structure is more excellent in short-circuit resistance
Implementation Method 2
In a spectrum obtained by X-ray diffraction using a CuKα-ray as a ray source, the separator has a diffraction peak (A) corresponding to a (111) crystal plane of the polyolefin
Implementation Method 3
In the porous membrane, fine holes formed in the porous membrane are clogged in a case where an abnormal current occurs and a battery temperature rises, and the like. Accordingly, the porous membrane has a shut-down function of blocking a current flow
Data Source
Figure 1
Figure 2
AI summary
Provided is a separator for a lithium ion secondary battery includes a porous resin layer that contains polyolefin as a main component. In a spectrum obtained by X-ray diffraction using a CuKα-ray as a ray source, the separator has a diffraction peak (A) corresponding to a (111) crystal plane of the polyolefin.