Graded Filler Coating for Battery Separator Heat Resistance
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Solution Overview
Problem
Existing multilayer porous films used as separators in lithium-ion secondary batteries face issues with insufficient binding force between fillers and inadequate heat resistance, leading to potential short circuits due to thermal contraction and high temperatures.
Innovation Solution
A multilayer porous film with a coating layer containing a specific ratio of filler particle diameters and a resin binder, applied to a porous polyolefin resin film, where the average particle diameter of the filler decreases from the interface to the surface, enhancing binding force and heat resistance while maintaining air permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous film is used as a separator to ensure ion permeability and electrolyte diffusion, then the battery achieves good electrochemical performance, but the separator lacks sufficient heat resistance and filler binding force, leading to potential short circuits at high temperatures
Solution Approach 1:
The patent applies composite materials by combining polyolefin resin with inorganic fillers (such as alumina, silica, or boehmite) to create a separator that integrates both the porous structure for ion permeability and the inorganic components for heat resistance and structural stability. This composite approach allows the separator to maintain porosity while gaining enhanced thermal properties and filler binding force.
Solution Approach 2:
The patent implements local quality by creating a coating layer on the separator surface that contains a specific concentration and distribution of inorganic fillers. This coating layer provides localized heat resistance and structural reinforcement where it is most needed, while the bulk separator maintains its porous structure for ion transport. The fillers are distributed non-uniformly with higher concentration in the coating layer.
2Strength
If the separator structure is simplified to reduce manufacturing complexity, then production becomes easier, but the binding force between fillers decreases, causing filler fall-off and reduced safety
Solution Approach 1:
The patent applies parameter changes by optimizing the particle size distribution of inorganic fillers, controlling the coating layer thickness, and adjusting the resin-to-filler ratio to achieve maximum binding force. By carefully controlling these parameters during manufacturing, the patent enhances filler binding while maintaining a relatively simple production process using conventional coating and drying techniques.
3Temperature
If inorganic fillers are added to enhance heat resistance, then the separator achieves better thermal stability, but the manufacturing process becomes more complex and costly
Solution Approach 1:
The patent utilizes porous materials by maintaining the porous structure of the separator while incorporating inorganic fillers within the pores and on the surface. This approach allows thermal stability to be enhanced without completely filling the pores, thus preserving ion permeability. The porous structure accommodates the fillers naturally, reducing the need for complex manufacturing modifications.
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 provides a multilayer porous film with improved binding force and heat resistance, preventing filler fall-off and maintaining air permeability, thus ensuring the safety and performance of lithium-ion secondary batteries by effectively shutting off ion conduction at high temperatures.
Implementation Method 1
a multilayer porous film with a coating layer containing a specific ratio of filler particle diameters and a resin binder, applied to a porous polyolefin resin film, where the average particle diameter of the filler decreases from the interface to the surface, enhancing binding force and heat resistance
Implementation Method 2
The SD property is the function of preventing the temperature inside the battery from rising owing to closing of micropores when the battery has a high temperature of 100° C. to 150° C., which leads to shut-off of ion conduction inside the battery
Data Source
AI summary
The present invention is capable of providing a multilayer porous film used as a separator for a non-aqueous electrolyte secondary battery. A multilayer porous film which is obtained by laminating a coating layer that contains a filler and a resin binder on at least one surface of a polyolefin resin porous film that serves as a base layer. The ratio of the average particle diameter (Du) of the filler within 25% of the thickness of the coating layer from the surface of the multilayer porous film to the average particle diameter (Db) of the filler within 25% of the thickness of the coating layer from the interface with the base layer, namely, Du/Db is 1.2 to 10; and the average particle diameter (Du) is 0.5 μm or less.