Laminated Battery Separator for Shutdown Without High-Heat Shrinkage
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Solution Overview
Problem
Current lithium secondary batteries face safety concerns due to thermal runaway and internal short circuits, particularly when the separator's shutdown mechanism is activated, as the separator's material properties do not adequately prevent direct contact between electrodes at high temperatures, leading to potential exothermic reactions and manufacturing issues during electrode winding.
Innovation Solution
An electrochemical device with a separator comprising a first porous layer made of thermoplastic resin and a second porous layer composed of insulating particles with a heat-resistant temperature of 150°C or higher, where the first layer ensures shutdown by melting and filling pores, and the second layer prevents short circuits by maintaining shape stability and preventing direct electrode contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyethylene porous film with low melting point is used as separator to effect shutdown, then safety against short circuit is improved, but the separator shrinks at high temperatures causing internal short circuit
Solution Approach 1:
The separator is constructed as a composite material combining polyethylene microporous film (providing shutdown function) with heat-resistant porous film containing inorganic particles such as alumina or silica (providing dimensional stability). This composite structure allows the separator to both shut down at low temperature and maintain shape at high temperature, resolving the contradiction between safety and stability.
2Strength
If uniaxially- or biaxially-oriented film is used to improve porosity and strength, then mechanical strength is improved, but shutdown temperature approaches thermal runaway temperature reducing safety
Solution Approach 1:
The invention uses a composite separator where the polyethylene layer provides shutdown at low temperature (maintaining safety margin) while the heat-resistant porous layer with inorganic particles provides the necessary mechanical strength and porosity. This avoids the problem of oriented films where shutdown temperature is too close to thermal runaway temperature.
3Strength
If separator is drawn to ensure strength during manufacture, then mechanical strength is improved, but residual stress causes shrinkage at high temperatures
Solution Approach 1:
The heat-resistant porous film layer containing inorganic particles serves as a dimensionally stable substrate that counteracts the shrinkage tendency of the drawn polyethylene layer. The inorganic particles maintain structural integrity at high temperatures, preventing the separator from shrinking even when the polyethylene component undergoes thermal contraction.
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 enhances safety by effectively preventing thermal runaway and internal short circuits at high temperatures, improving the reliability and productivity of the electrochemical device by ensuring reliable shutdown and maintaining structural integrity during manufacturing.
Implementation Method 1
the resin constituting the separator is melted at a temperature not more than the thermal runaway (abnormal heat generation) temperature of the battery and the pores of the separator are closed by melting the resin
Implementation Method 2
a second separator layer composed of a heat-resistant resin, an inorganic oxide, or the like has been proposed
Data Source
AI summary
An electrochemical device of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. The separator includes a first porous layer composed mainly of a thermoplastic resin and a second porous layer composed mainly of insulating particles with a heat-resistant temperature of 150° C. or higher. The first porous layer is disposed to face the negative electrode.