PVDF Battery Separator Coating for Low-Shrinkage Electrode Bonding
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Solution Overview
Problem
Non-aqueous secondary batteries face challenges with adhesion between electrodes and separators, particularly at high temperatures, leading to thermal shrinkage and reduced capacity retention due to decomposition of electrolytes during hot pressing treatments.
Innovation Solution
A separator with a porous substrate and an adhesive porous layer containing polyvinylidene fluoride type resin and inorganic fillers, where the inorganic filler's average primary particle size is between 0.01 μm and 0.50 μm, and the polyvinylidene fluoride resin exhibits specific thermal properties as determined by differential scanning calorimetry, ensuring excellent adhesion by both dry and wet heat press methods while minimizing thermal shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If wet heat press is performed at a relatively high temperature to ensure good adhesion between electrode and separator, then adhesion is improved, but electrolytic solution or electrolyte decomposes to generate gas causing deterioration of cycle characteristics and dimensional stability
Solution Approach 1:
The invention changes the chemical composition parameters of the polyvinylidene fluoride type resin by incorporating specific copolymer structures (vinylidene fluoride-hexafluoropropylene copolymer with 7-15 mol% hexafluoropropylene units, and vinylidene fluoride-trifluoroethylene copolymer with 7-15 mol% trifluoroethylene units). This compositional modification enables the resin to achieve adequate adhesion at lower hot-pressing temperatures, preventing electrolyte decomposition while maintaining bonding strength.
Solution Approach 2:
The invention uses a composite resin system combining multiple polyvinylidene fluoride type resins with different copolymer structures and properties. This composite approach synergistically improves both adhesion characteristics and thermal stability, allowing the separator to bond effectively to electrodes without causing electrolyte decomposition at high temperatures.
2Reliability
If dry heat press is performed to bond electrode and separator without electrolytic solution impregnation, then decomposition of electrolyte is suppressed, but adhesion between electrode and separator may be insufficient
Solution Approach 1:
The modified polyvinylidene fluoride type resin with specific copolymer compositions changes the thermal and adhesive parameters of the separator material. This enables effective bonding at lower temperatures where electrolyte decomposition is minimized, achieving both good adhesion and prevention of electrolyte degradation.
3Temperature
If the separator is exposed to high temperature during battery operation, then the porous structure or dimension of separator changes, but capacity retention ratio deteriorates
Solution Approach 1:
The invention modifies the thermal parameters of the separator by incorporating copolymer structures with higher thermal stability. The vinylidene fluoride-hexafluoropropylene and vinylidene fluoride-trifluoroethylene copolymers maintain the porous structure and dimensional integrity at elevated temperatures, preventing capacity deterioration during high-temperature battery operation.
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 separator that maintains high capacity retention and adhesion to electrodes under high temperatures, reducing thermal shrinkage and electrolyte decomposition, thereby enhancing the performance and stability of non-aqueous secondary batteries.
Implementation Method 1
a thermal shrinkage is less likely to be occur under high temperature
Implementation Method 2
adhesion between the electrode and the separator is good, and favorable battery characteristics are easily obtained
Implementation Method 3
when differential scanning calorimetry is performed with all of the polyvinylidene fluoride type resin contained in the adhesive porous layer as a sample, two or more endothermic peaks and/or two or more exothermic peaks are observed
Implementation Method 4
decomposition of an electrolytic solution and an electrolyte does not occur
Data Source
AI summary
Provided is a separator for a non-aqueous secondary battery, the separator contains a porous substrate and an adhesive porous layer that is provided on one side or on both sides of the porous substrate, and that contains a polyvinylidene fluoride type resin and an inorganic filler, in which an average primary particle size of all of the inorganic filler contained in the adhesive porous layer is from 0.01 μm to less than 0.50 μm, and when differential scanning calorimetry is performed with all of the polyvinylidene fluoride type resin contained in the adhesive porous layer as a sample, two or more endothermic peaks and/or two or more exothermic peaks are observed.