Crosslinked Polyolefin Separator Substrate for Heat-Shrink Resistance
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Solution Overview
Problem
Lithium-ion batteries face safety concerns due to heat shrinking of polyolefin-based separators, leading to potential short-circuits and thermal runaway, and require improvements in thickness uniformity and heat resistance.
Innovation Solution
A separator substrate comprising crosslinked polyolefin resin and chromium, with a gel fraction of 3-80% and a standard deviation in thickness of 0.5 μm or less, formed through radical polymerization initiated by a thermal initiator, enhancing thickness uniformity and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polyolefin-based porous substrate is used as a separator, then ease of manufacture is improved, but heat resistance deteriorates due to severe heat shrinking behavior at 100°C or higher
Solution Approach 1:
The patent applies composite materials by combining polyolefin resin with inorganic particles (such as alumina, silica, or boehmite) to create a separator that maintains the processability of polyolefin while gaining the heat resistance of inorganic materials. The inorganic particles serve as a heat-resistant framework that prevents shrinkage at elevated temperatures.
Solution Approach 2:
The patent changes the physical and chemical parameters of the separator by controlling the gel fraction (3-80%) through crosslinking and by adjusting the content and size of inorganic particles. These parameter changes enable the separator to maintain structural stability at high temperatures while retaining manufacturing feasibility.
2Productivity
If the separator substrate thickness is reduced to improve energy density, then productivity is improved, but manufacturing precision deteriorates due to difficulty in controlling thickness uniformity
Solution Approach 1:
The patent changes the rheological and structural parameters of the separator substrate by controlling gel fraction, crosslinking degree, and inorganic particle distribution. These parameter changes enable better thickness control during manufacturing even at reduced thicknesses, achieving standard deviation of 0.5 μm or less.
Solution Approach 2:
The composite structure with inorganic particles provides a more stable framework that resists deformation during processing, enabling better thickness uniformity control in thin separators. The inorganic particles act as spacers that maintain consistent pore structure throughout the thin substrate.
3Temperature
If crosslinking is increased to improve heat resistance, then temperature stability is improved, but gel fraction becomes too high reducing porosity and ion conductivity
Solution Approach 1:
The patent uses composite materials where inorganic particles provide the heat-resistant framework, allowing moderate crosslinking (3-80% gel fraction) without excessive shrinkage. The inorganic particles maintain porosity by acting as physical spacers that prevent complete collapse of the polymer matrix during crosslinking.
Solution Approach 2:
The patent applies local quality by distributing crosslinking and inorganic particles non-uniformly to optimize performance. The inorganic particles are distributed throughout the matrix to maintain local porosity, while crosslinking is controlled to provide sufficient heat resistance without globally reducing porosity.
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 provides improved safety and stability to electrochemical devices by reducing thickness variations and increasing heat resistance, preventing short-circuits and thermal runaway.
Implementation Method 1
the crosslinked structure including a structure derived from radical polymerization of vinyl groups initiated by a thermal initiator
Implementation Method 2
a polyolefin-based porous substrate used conventionally as a separator for an electrochemical device shows a severe heat shrinking behavior at a temperature of 100° C. or higher due to its material property
Data Source
AI summary
A separator substrate for an electrochemical device, a separator and an electrochemical device including the same are provided. The separator substrate includes a crosslinked polyolefin resin and chromium (Cr), has a gel fraction of 3-80%, has a standard deviation (Δd) of thickness measured at at least 100 optional points of 0.5 μm or less, and has 10 or less spots with a longer side length of 50 μm or more per 1 m2.