Polyolefin Separator Uniformity via Pre-Stretch and Composite Coating
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge lies in providing a polyolefin microporous membrane with a uniform porous layer thickness for wider applications, such as lithium-ion rechargeable batteries, where conventional coating technologies struggle to maintain uniformity, leading to defects and reduced battery capacity and productivity.
Innovation Solution
A polyolefin microporous membrane with a controlled F25 value, produced through a method involving longitudinal and transverse stretching, followed by coating with a water-soluble or water-dispersible resin and heat-resistant particles, ensures a uniform porous layer thickness, enhancing the battery separator's performance and capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional coating technologies are used to coat porous layers on polyolefin microporous membranes, then coating process is simple, but uniformity of porous layer thickness cannot be maintained for wider applications
Solution Approach 1:
The polyolefin microporous membrane is pre-stretched in the width direction by 5-20% before coating to create a tension state that compensates for subsequent shrinkage during drying, ensuring uniform porous layer thickness is maintained throughout the coating and drying process
Solution Approach 2:
The membrane tension state is controlled by adjusting the stretching rate (5-20%) and maintaining specific temperature conditions during coating and drying, where the tension parameter dynamically compensates for thickness non-uniformity that would otherwise occur during the process
2Reliability
If the polyethylene microporous membrane shrinks at high temperature, then pore blocking effect is achieved to prevent excessive temperature increase, but the membrane may be punctured due to shrinkage
Solution Approach 1:
A multi-layer composite structure is created by coating heat-resistant resin particles (such as polyacrylonitrile, polyvinylidene fluoride, or carboxymethyl cellulose) onto the polyolefin microporous membrane, forming a porous layer that combines the low-temperature pore blocking capability of polyethylene with high-temperature structural stability of heat-resistant resins
Solution Approach 2:
The heat-resistant porous layer acts as a protective cushion that prevents membrane puncture at high temperatures while allowing the underlying polyethylene membrane to perform pore blocking, effectively decoupling the pore blocking function from the structural integrity function
3Area of stationary object
If wider polyolefin microporous membranes are produced for larger battery applications, then battery capacity increases, but uniformity of porous layer thickness deteriorates
Solution Approach 1:
The membrane is stretched to create a uniform tension state across the entire width (100mm or more), ensuring that each local region experiences consistent mechanical conditions during coating, which maintains uniform porous layer thickness distribution across the large-area membrane surface
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 achieves a uniform porous layer thickness, improving the battery separator's quality, reducing defects, and increasing battery capacity while maintaining mechanical strength and air permeation resistance.
Implementation Method 1
a method of production thereof, involving longitudinal and transverse stretching
Implementation Method 2
coating with a water-soluble or water-dispersible resin and heat-resistant particles
Implementation Method 3
exhibits ion permeability due to electrolytic solution impregnation
Data Source
AI summary
A polyolefin microporous membrane is disclosed. The membrane has a width of not less than 100 mm, and a variation range of an F25 value in a width direction is not greater than 1 MPa. The F25 value is a value obtained by dividing a load at 25% elongation of a sample of the laminated polyolefin microporous membrane as measured with a tensile testing machine by a cross-sectional area of the sample.