Polyamic Acid Separator Coating for Battery Thermal Stability
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Solution Overview
Problem
Existing separator coatings for electrochemical batteries face challenges with thermal resistance and drying processability, particularly with polyolefin-based films, which can melt at low temperatures and result in reduced air permeability and compatibility issues due to the use of high thermal resistance organic binders that do not dissolve in low boiling point solvents.
Innovation Solution
A coating composition using polyamic acid as the binder, which is soluble in low boiling point solvents, applied to a polyolefin-based substrate film to form a coating layer with minimal solvent residual, enhancing thermal resistance and air permeability, and including inorganic particles for improved heat dissipation and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If polyolefin-based substrate film is used for separator, then weight reduction and miniaturization are achieved, but thermal resistance deteriorates as the film melts at relatively low temperature
Solution Approach 1:
The patent applies composite materials by combining polyolefin-based substrate film with a coating layer containing inorganic particles (such as metal oxides or hydroxides) and organic binder. This composite structure allows the separator to maintain the light weight advantage of polyolefin while the inorganic coating layer provides enhanced thermal resistance, preventing film melting at elevated temperatures.
2Temperature
If organic binder with high thermal resistance (e.g., polyimide) is used as coating agent, then thermal resistance is improved, but solubility in low boiling point solvent deteriorates making drying process difficult
Solution Approach 1:
The patent changes the chemical parameter of the organic binder by selecting compounds with specific functional groups (carboxyl, hydroxyl, amine, or isocyanate groups) that provide both high thermal resistance and good solubility in low boiling point solvents. This parameter change allows the coating to be applied and dried effectively while maintaining thermal performance.
Solution Approach 2:
The patent applies local quality by using different materials with specific properties in different layers: the polyolefin substrate provides light weight and basic separation function, while the coating layer contains inorganic particles for thermal stability and specifically selected organic binders for both thermal resistance and solubility. Each layer has optimized local properties to address specific requirements.
3Temperature
If coating layer is formed to improve thermal resistance, then thermal stability is enhanced, but air permeability deteriorates
Solution Approach 1:
The patent applies porous materials by forming a coating layer with controlled porosity that allows ion and air permeability. The inorganic particles are distributed within a porous matrix of the organic binder, creating a structure that provides thermal resistance while maintaining sufficient permeability for battery operation.
Solution Approach 2:
The patent uses a thin film coating layer applied on the polyolefin substrate that provides thermal protection without significantly blocking permeability. The flexible and porous nature of the thin coating allows ions and air to pass through while the layer remains intact to provide thermal resistance.
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 polyamic acid coating composition achieves excellent thermal stability, reduced solvent residual, and maintained air permeability, preventing thermal shrinkage and electrode short-circuits, thus improving the safety and longevity of electrochemical batteries.
Implementation Method 1
polyamic acid having excellent solubility in a low boiling point solvent
Implementation Method 2
drying process of the solvent after coating a separator
Data Source
AI summary
Disclosed herein is a coating composition having excellent thermal resistance and drying processability, utilizing polyamic acid having high thermal resistance and excellent solubility in a low boiling point solvent. Specifically, the coating composition includes polyamic acid and a low boiling point solvent having a boiling point less than 150° C. Also, disclosed herein a separator having improved thermal resistance by coating the coating composition on one or both surfaces of a polyolefin-based substrate film, and an electrochemical battery having improved thermal stability by using the separator.