Battery Separator Film Curling Control via Drying Tension
Solution Overview
Problem
Nonaqueous electrolyte secondary battery separators curl during the drying process due to shrinkage in the functional layer and stress generation in the base material layer, leading to deformation and potential short circuits between the cathode and anode, resulting in a significant decrease in battery production yield.
Innovation Solution
A battery separator film with a curling amount of less than 5 mm is achieved by controlling the drying conditions, such as roller temperature and tension, to balance the shrinkage in the base material layer with the functional layer, reducing interlayer stress and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a functional layer is coated on the base material layer and dried, then heat resistance is improved, but curling deformation occurs due to shrinkage and stress
Solution Approach 1:
The patent applies parameter changes by controlling the drying conditions (temperature, humidity, time) and the composition of the functional layer to manage the shrinkage behavior. By adjusting these parameters, the shrinkage of the functional layer is balanced with the stress in the base material layer, reducing curling while maintaining heat resistance
Solution Approach 2:
The patent uses composite materials by combining the base material layer with a specifically formulated functional layer containing heat-resistant polymers and inorganic fillers. This composite structure provides both the required heat resistance and controlled mechanical properties to minimize curling deformation during drying
2Temperature
If the separator film is produced with a functional layer, then heat resistance is improved, but the film breaks during lamination or winding
Solution Approach 1:
The patent controls the drying parameters (temperature gradient, drying time, humidity) to prevent excessive shrinkage and stress concentration that would cause film breaking. The functional layer composition is also optimized to provide adequate flexibility and strength during handling
Solution Approach 2:
The composite structure of the base material layer and functional layer is designed to provide both heat resistance and mechanical strength. The interfacial bonding between layers is optimized to prevent delamination and breaking during subsequent lamination and winding processes
3Temperature
If the functional layer shrinks during drying, then heat resistance is achieved, but curling toward the functional layer occurs
Solution Approach 1:
The patent adjusts the drying parameters and functional layer composition to control the magnitude and distribution of shrinkage. By balancing the shrinkage with the counteracting stress in the base material layer, the curling is minimized while the heat-resistant function is maintained
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 controlled drying process enhances the handleability and lamination of the battery separator film, reducing the risk of short circuits and improving the yield of battery production by minimizing curling and maintaining the film's structural integrity.
Implementation Method 1
shrinkage in the functional layer during drying of the film after the coating
Implementation Method 2
generation in the base material layer of a stress by which the film is to curl assuming that the functional layer side is an inner side
Data Source
AI summary
A battery separator film that has a small curling amount and is highly handleable is provided. The battery separator film has a curling amount W of not more than 5 mm, the curling amount W being represented by the following equation (1):Curling amount W=W1−W2 (1)where W1 is a width of a film that has been cut out in a longer side direction of the battery separator film, and W2 is a projection width of a part of the film which part is smallest in projection width when seen from a direction perpendicular to a surface of the film while the film, to which a tension of 90 N/m is applied, is stretched between two rollers that are provided in parallel with each other at an interval of 1 m at a temperature of 23 degrees Celsius and a relative humidity of 50%.