Propylene Resin Microporous Film Separator for Li-Ion Batteries
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Solution Overview
Problem
Current lithium ion battery separators, such as polypropylene and multilayered porous membranes, suffer from low air permeability and insufficient lithium ion permeability, which limits their ability to support high output power batteries and leads to dendrite short circuits and rapid discharge capacity degradation.
Innovation Solution
A propylene resin microporous film with uniaxially stretched micropores, characterized by air permeability of 100 to 400 s/100 mL, a surface aperture rate of 30 to 55%, and a pore density of 15 pores/µm² or more, is produced using a method involving extrusion, aging, uniaxial stretching, and annealing, ensuring high lithium ion permeability and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyethylene porous film is used for separator to ensure safety through shutdown function, then safety is improved, but heat resistance deteriorates because polyethylene melts at about 130°C
Solution Approach 1:
The patent changes the material parameter from polyethylene to polypropylene, which has a higher melting point (about 160°C), thereby improving heat resistance while maintaining the shutdown safety function
Solution Approach 2:
The patent uses a composite structure combining polypropylene microporous film with specific molecular weight distribution (Mw/Mn = 7.5 to 12.0) to achieve both heat resistance and shutdown functionality
2Temperature
If polypropylene microporous film is used to improve heat resistance, then heat resistance is improved, but air permeability and lithium ion permeability deteriorate
Solution Approach 1:
The patent optimizes the molecular weight distribution parameter (Mw/Mn = 7.5 to 12.0) and pore size parameters (0.03 to 0.5 μm) of polypropylene to achieve both high heat resistance and high lithium ion permeability
Solution Approach 2:
The patent creates micropores with specific size distribution (0.03 to 0.5 μm) throughout the polypropylene film to locally enhance lithium ion transport pathways while maintaining overall heat resistance
3Productivity
If micropore size is increased to improve lithium ion permeability, then lithium ion permeability is improved, but dendrite short circuit risk increases
Solution Approach 1:
The patent optimizes the micropore size parameter to a specific range (0.03 to 0.5 μm) that allows efficient lithium ion passage while being small enough to block dendrite penetration
Solution Approach 2:
The patent creates a uniform micropore structure that replicates optimal pore dimensions throughout the separator film, ensuring consistent lithium ion transport and dendrite blocking performance
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 propylene resin microporous film enables efficient lithium ion migration, preventing dendrite short circuits and maintaining stable battery performance even in high output power applications, thereby extending the battery's lifespan and preventing rapid discharge capacity decline.
Implementation Method 1
having micropores formed by uniaxially stretching a propylene resin film
Implementation Method 2
lithium ions migrate from the positive electrode to the negative electrode
Implementation Method 3
polyethylene forming the porous film melts at a temperature region of about 130°C and a porous structure thereof is blocked
Data Source
AI summary
Provided is a propylene resin microporous film which has excellent lithium ion permeability, and can be used to fabricate a high-performance lithium ion battery and prevent short circuits between positive and negative electrodes by dendrites. The propylene resin microporous film has micropores formed by uniaxially stretching a propylene resin film, a degree of air permeability of 100 to 400 s/100 mL, and a rate of surface aperture of 30 to 55%.