Polyolefin Microporous Separator Membrane for Heat-Stable Shutdown
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Solution Overview
Problem
Existing polyolefin microporous membranes for secondary batteries lack sufficient heat resistance, mechanical strength, and gas permeability, particularly at high temperatures, leading to safety risks such as internal short circuits and ignition due to rapid temperature rises.
Innovation Solution
A polyolefin microporous membrane composed of 60-80 wt% polypropylene with a viscosity average molecular weight of 1×10^6 to 3×10^6 g/mol and 20-40 wt% polyethylene with a weight average molecular weight of 1×10^5 to 10×10^5 g/mol, manufactured through a wet biaxial stretching process, achieving puncture strength of 0.25 N/um or more, gas permeability of 1.0×10^-5 Darcy or more, porosity of 30-70%, average pore size of 20-40 nm, and shutdown temperature of 150°C or lower.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the film thickness of the separator is reduced to improve battery energy density, then the capacity increases, but the mechanical strength and heat resistance deteriorate
Solution Approach 1:
The patent uses a composite structure consisting of a polyolefin microporous membrane layer and a heat-resistant coating layer. The heat-resistant coating layer contains inorganic particles (such as alumina, silica, or boehmite) dispersed in a binder polymer, creating a composite material that provides both mechanical reinforcement and high-temperature stability to the thin separator film.
Solution Approach 2:
The patent employs a microporous membrane structure with controlled pore size distribution (average pore size of 0.01-10 μm) and porosity (30-80%). The porous structure provides ion permeability for battery operation while the pore walls provide mechanical strength. The heat-resistant coating is applied on the porous surface, filling some pores while maintaining ion transport pathways.
2Quantity of substance
If the film thickness is reduced to improve battery energy density, then the capacity increases, but the heat resistance deteriorates
Solution Approach 1:
The heat-resistant coating layer contains inorganic particles (alumina, silica, boehmite, magnesia, or titania) with high melting points dispersed in a binder polymer. This composite structure raises the overall heat resistance of the thin separator, enabling it to maintain structural integrity at temperatures up to 200°C or higher, preventing thermal runaway even when the base film is very thin.
Solution Approach 2:
The heat-resistant coating is applied in advance to the polyolefin microporous membrane before the separator is installed in the battery. This preliminary protective layer ensures that when the battery operates or experiences thermal abuse, the thin separator is already protected against heat-induced degradation, allowing immediate high-capacity operation without compromising safety.
3Power
If the gas permeability is increased to improve power output, then the power increases, but the mechanical strength deteriorates
Solution Approach 1:
The patent utilizes a microporous membrane with optimized pore structure (average pore size 0.01-10 μm, porosity 30-80%) that balances gas permeability and mechanical strength. The porous polyolefin base layer provides ion and gas permeability for high power output, while the heat-resistant coating layer with inorganic particles reinforces the pore walls, preventing mechanical failure even with high porosity.
Solution Approach 2:
The composite structure combines the permeable polyolefin microporous membrane with a heat-resistant coating containing inorganic particles and binder polymer. This composite allows the separator to achieve high gas permeability (10-10000 mL/min/cm²) for improved power while the coating provides mechanical reinforcement to maintain adequate strength despite the highly porous structure.
4Reliability
If the puncture strength is increased to improve safety, then the safety improves, but the gas permeability deteriorates
Solution Approach 1:
The heat-resistant coating layer containing inorganic particles and binder polymer is applied on the polyolefin microporous membrane to provide mechanical reinforcement. This composite structure increases puncture strength (to 0.1-10 N or more) for improved safety while the coating is designed with controlled thickness (1-100 μm) and porosity to maintain adequate gas permeability (10-10000 mL/min/cm²) for battery power.
Solution Approach 2:
The microporous structure of both the base membrane and the coating layer allows gas permeability to be maintained. The porous coating with interconnected pores provides both mechanical strength (through the rigid inorganic particle network) and gas transport pathways, resolving the contradiction between puncture strength and gas permeability.
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 membrane provides enhanced mechanical strength, gas permeability, and heat resistance, maintaining a separator form at high temperatures, thereby improving battery safety and performance, especially in high-capacity and high-power applications.
Implementation Method 1
a polyolefin microporous membrane composed of 60-80 wt% polypropylene with a viscosity average molecular weight of 1×10^6 to 3×10^6 g/mol and 20-40 wt% polyethylene with a weight average molecular weight of 1×10^5 to 10×10^5 g/mol, manufactured through a wet biaxial stretching process
Implementation Method 2
the polyethylene may have a melting temperature of 133°C or higher... A shutdown function is a function of significantly increasing resistance of a separator by melting a polyolefin to close holes
Implementation Method 3
the polypropylene may have a melting temperature of 160°C or higher... development of a polyolefin microporous membrane having excellent heat resistance so that it may withstand a rapid temperature rise of a battery
Data Source
AI summary
Provided are a polyolefin microporous membrane, a method for manufacturing the same, and a separator including the microporous membrane. According to an exemplary embodiment, a polyolefin microporous membrane including: 60 wt% to 80 wt% of a polypropylene having a viscosity average molecular weight of 1×106 g/mol to 3×106 g/mol and 20 wt% to 40 wt% of a polyethylene having a weight average molecular weight of 1×105 g/mol to 10×105 g/mol is provided, wherein the polyolefin microporous membrane has a puncture strength of 0.25 N/um or more, a gas permeability of 1.0×10-5 Darcy or more, a porosity of 30% to 70%, an average pore size of 20 nm to 40 nm, and a shutdown temperature of 150°C or lower.