Heat-Sensitive Battery Separator Coating for Rapid Pore Closure
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Solution Overview
Problem
Existing lithium battery separators have slow pore-closing response times and high pore-closing temperatures, leading to thermal runaway and safety issues due to poor compatibility between materials and vaporization of low-melting point polymers.
Innovation Solution
A separator substrate is prepared using unbranched polyethylene and long-branched polyethylene with a heat-sensitive high molecular material coating to achieve a low pore-closing temperature and rapid response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If low-melting point materials are introduced into polyolefin material to reduce pore-closing temperature, then the pore-closing temperature decreases, but the pore-closing response time becomes slow and heat accumulates causing thermal runaway
Solution Approach 1:
The patent uses a composite structure consisting of a polyolefin base membrane combined with a heat-sensitive polymer coating layer. This composite design allows the base membrane to provide structural stability while the coating layer enables rapid pore closure at lower temperatures, resolving the contradiction between low pore-closing temperature and thermal safety.
Solution Approach 2:
The patent modifies the pore-closing characteristics by changing the material parameters of the coating layer, specifically using heat-sensitive polymers with glass transition temperatures between -50°C to 50°C. This parameter optimization allows the separator to close pores rapidly at temperatures 20-50°C lower than conventional separators without causing thermal runaway.
2Temperature
If low-melting point polymer is coated on polyolefin base membrane to lower pore-closing temperature, then the pore-closing temperature decreases, but the polymer vaporizes at higher temperatures causing bubble breakage and pore re-exposure
Solution Approach 1:
The patent applies local quality by creating a specialized coating layer with distinct properties from the base membrane. The heat-sensitive polymer coating (5-20 μm thick) provides localized heat response functionality, while the underlying polyolefin base membrane maintains structural integrity and stability at higher temperatures, preventing bubble breakage and pore re-exposure.
Solution Approach 2:
The patent optimizes the glass transition temperature parameter of the coating polymer to be between -50°C to 50°C, which is significantly lower than the melting point of the polyolefin base membrane. This parameter differentiation ensures the coating layer responds to moderate temperature increases by closing pores, while the base membrane remains stable and prevents pore re-opening even at higher temperatures.
3Temperature
If composite PP/PE/PP separator is prepared by co-extrusion to achieve low pore-closing temperature, then the pore-closing temperature equals PE melting point, but the compatibility between PP and PE is poor
Solution Approach 1:
The patent segments the separator into two distinct functional layers: a polyolefin base membrane providing mechanical strength and chemical stability, and a heat-sensitive polymer coating layer providing rapid pore closure. This segmentation avoids the material compatibility issues of co-extruding incompatible polymers like PP and PE, while achieving better pore-closing performance.
Solution Approach 2:
The patent creates a composite structure where a heat-sensitive polymer coating is applied onto a polyolefin base membrane. This composite design resolves the compatibility problem by using a coating process rather than co-extrusion, allowing independent optimization of each layer's properties without material incompatibility constraints.
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 effectively closes pores quickly at lower temperatures, reducing thermal runaway risk and enhancing battery safety by shortening the pore-closing response time.
Implementation Method 1
a layer of a heat-sensitive material is coated on the surface of the separator substrate to achieve the effects of lowering the pore-closing temperature and pore-closing response time
Implementation Method 2
When the internal temperature of a battery increases quickly, a separator is rapidly melted to close pores to block lithium ions from passing through
Data Source
AI summary
The present invention provides a separator having a low pore-closing temperature, including a base membrane containing an unbranched polyolefin and a long-branched polyolefin, and a coating formed on at least one surface of the base membrane and containing a heat-sensitive high molecular material. By the aforesaid solution, the present invention can substantially lower the pore-closing response time and pore-closing temperature of the separator, thus improving the safety performance of lithium ion batteries. In addition, the present invention further provides a method for preparing the aforesaid separator having a low pore-closing temperature and a battery containing the aforesaid separator having a low pore-closing temperature.