Porous Battery Separator Coating for Adhesion Without Pore Blocking
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Solution Overview
Problem
Existing separators for electrochemical devices, particularly lithium secondary batteries, face issues with adhesion to electrodes and porous substrates, leading to degraded ion channel function due to binder infiltration and poor phase separation kinetics, which affect adhesion and air permeability.
Innovation Solution
A separator for electrochemical devices comprising a porous substrate with a porous coating layer containing a mixture of two binder polymers with specific electrolyte uptake ranges and melting points, forming a unique porous structure with improved adhesion and air permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a binder is used to bind the separator with the electrode, then adhesion between the separator and electrode is improved, but the binder infiltrates into the pores of the porous polymer substrate and degrades the function of the separator as an ion channel
Solution Approach 1:
The coating layer is designed with a porous structure containing pores with a diameter of 0.01 μm to 1 μm, matching the pore size of the porous polymer substrate. This porous structure allows ion transport while preventing binder infiltration into the substrate pores, thus maintaining the separator's ion channel function while providing adequate adhesion.
Solution Approach 2:
The coating layer is formed as a composite material consisting of inorganic particles (such as Al2O3, SiO2, TiO2, or ZnO) and binder polymer. This composite structure provides both adhesion to the electrode and maintains pore structure for ion transport, preventing binder infiltration while ensuring mechanical bonding.
2Productivity
If phase separation kinetics are excessively high during coating, then pore formation is accelerated, but most of the binder forms large pores on the coating layer and adhesion between the substrate and coating layer is low
Solution Approach 1:
The phase separation kinetics are controlled by adjusting parameters such as the glass transition temperature (Tg) of the binder polymer and the concentration of non-solvent in the solidifying solution. By optimizing these parameters, the phase separation rate is moderated to form pores of appropriate size (0.01 μm to 1 μm) while ensuring strong adhesion between the substrate and coating layer.
3Manufacturing precision
If phase separation kinetics are excessively low during coating, then pore formation is slowed, but most of the binder is formed at the bottom surface of the coating layer with small pores or with no porous structure, and no adhesive layer with the electrode is formed
Solution Approach 1:
The phase separation process is optimized by controlling the glass transition temperature of the binder polymer and the non-solvent concentration. These parameter adjustments ensure that phase separation occurs at an appropriate rate, forming a porous structure throughout the coating layer with pores of 0.01 μm to 1 μm diameter, while also forming an adhesive layer that bonds effectively with the electrode.
4Strength
If the coating layer is made denser to improve adhesion, then adhesion strength increases, but air permeability and ion transport capability decrease
Solution Approach 1:
The coating layer is designed with a controlled porous structure containing pores with a diameter of 0.01 μm to 1 μm. This porous structure maintains air permeability and ion transport capability while the inorganic particles and binder polymer provide sufficient adhesion strength. The porosity is optimized to balance adhesion and ion transport requirements.
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 separator achieves enhanced adhesion to electrodes and substrates, maintaining low resistance and high air permeability, thereby improving the performance and stability of electrochemical devices.
Implementation Method 1
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
Implementation Method 2
a process for forming pores in the coated binder through phase separation is used
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 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.