Porous Battery Separator Coating for Adhesion Without Ion-Channel Loss
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Solution Overview
Problem
Existing separators for electrochemical devices face challenges in achieving both improved adhesion to electrodes and porous substrates while maintaining low resistance and air permeability, due to issues with binder distribution and pore formation during the phase separation process.
Innovation Solution
A separator for electrochemical devices is designed with a porous coating layer comprising a combination of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and poly(vinylidene fluoride-co-tetrafluoroethylene) (PVdF-TFE) binder polymers, which have specific electrolyte uptake ranges and viscosities, to enhance adhesion and maintain low resistance and air permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a binder is coated on the surface of a porous polymer substrate to bind the separator with an electrode, then adhesion between the separator and electrode is improved, but the function of the separator as an ion channel is degraded
Solution Approach 1:
The coating layer is designed with a porous structure containing pores with an average diameter of 0.01 μm to 1 μm, allowing ion transport through the coating layer while maintaining adhesion. The porous structure ensures that the separator continues to function as an ion channel even with the presence of the binding coating layer.
Solution Approach 2:
The coating layer is applied selectively on the separator surface with controlled thickness (1 μm to 10 μm) and porosity, creating different functional zones: the porous coating layer provides adhesion while maintaining ion permeability, whereas the bulk separator maintains its structural integrity and ion channel function.
2Productivity
If phase separation kinetics are excessively high during binder coating, then pore formation occurs rapidly, but most binder forms large pores on the coating layer surface resulting in low adhesion between substrate and coating layer
Solution Approach 1:
The phase separation kinetics are controlled by adjusting parameters such as non-solvent concentration, temperature, and coating layer composition. By optimizing these parameters, the phase separation rate is moderated to form a balanced pore structure that maintains both porosity for ion transport and sufficient adhesion strength.
3Stability of the object's composition
If phase separation kinetics are excessively low during binder coating, then most binder is formed at the bottom surface of the coating layer with small pores or with no porous structure, but no adhesive layer with the electrode is formed
Solution Approach 1:
The coating process is designed to establish proper binder distribution and pore formation characteristics before final adhesion to the electrode. By pre-controlling the phase separation conditions and coating parameters, the coating layer is prepared with optimal adhesive properties that enable effective bonding to the electrode surface.
4Reliability
If a porous coating layer is formed to maintain ion channel function, then air permeability is improved, but resistance increases
Solution Approach 1:
The coating layer is designed with optimized porosity (30% to 70%) and pore size (0.01 μm to 1 μm) to balance ion transport capability and electrical resistance. The porous structure allows efficient ion passage while minimizing resistance, achieving both low resistance and high air permeability required for separator function.
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 combination of PVdF-HFP and PVdF-TFE binder polymers improves adhesion to electrodes and substrates, reduces resistance, and maintains high air permeability, resulting in enhanced battery performance.
Implementation Method 1
a process for forming pores in the coated binder through phase separation is used
Implementation Method 2
the binder not only is coated on the surface of a porous polymer substrate but also infiltrates into the pores of the porous polymer substrate
Data Source
AI summary
A separator for an electrochemical device is provided. The separator comprises: a porous substrate having a plurality of pores, and a porous coating layer positioned on at least one surface of the porous substrate, the porous coating layer including a plurality of inorganic particles and a binder polymer positioned on a whole or a part of the surface of the inorganic particles to connect the inorganic particles with one another and fix the inorganic particles, wherein the binder polymer comprises a first binder polymer and a second binder polymer. The first binder polymer is poly(vinylidene fluoride-co-hexafluoroproyplene) (PVdF-HFP), and the second binder polymer is poly(vinylidene fluoride-co-tetrafluoroethylene) (PVdF-TFE). The first binder polymer has an electrolyte uptake of 80-165%, and the second binder polymer has an electrolyte uptake of 20-40%. An electrochemical device including the separator is also disclosed.