Block Copolymer Separator Coating for Low-Resistance Battery Adhesion
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Solution Overview
Problem
Conventional lithium secondary battery separators face challenges with high-energy density and high-output requirements, as they often experience increased battery resistance and reduced adhesion to electrodes due to the properties of polyolefin-based porous substrates, which can lead to thermal runaway and safety issues.
Innovation Solution
A separator with a porous coating layer containing a block copolymer of polyvinylidene fluoride-hexafluoropropylene, where the block copolymer includes a first block with vinylidene fluoride units and a second block with hexafluoropropylene units, is used, maintaining adequate hexafluoropropylene content for phase separation and solubility, thereby enhancing adhesion and swelling properties while keeping resistance low.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a polyolefin-based porous substrate is used as a separator, then it provides basic separation function, but it shows severe heat shrinking behavior at 100°C or higher causing short-circuit between cathode and anode
Solution Approach 1:
The patent applies composite materials by forming a porous coating layer containing inorganic particles (such as alumina, silica, or boehmite) dispersed in a binder polymer on the polyolefin substrate. This composite structure combines the thermal stability of inorganic particles with the porosity and flexibility of the polymer matrix, preventing heat shrinking while maintaining separation function at elevated temperatures up to 150°C or higher.
Solution Approach 2:
The patent utilizes porous materials by creating a porous coating layer with controlled porosity (30-70%) through the dispersion of inorganic particles and binder polymer. The porous structure allows electrolyte penetration and ion transport while the inorganic particle framework maintains structural integrity during thermal expansion, preventing the heat shrinking that occurs in conventional polyolefin separators.
2Strength
If an adhesive layer is introduced to increase adhesion between separator and electrode, then adhesion is improved, but battery resistance increases
Solution Approach 1:
The porous coating layer serves multiple functions simultaneously: it provides adhesion to electrodes through the binder polymer, maintains thermal stability through inorganic particles, and enables ion transport through its porous structure. This multi-functional layer eliminates the need for separate adhesive layers, preventing additional resistance while achieving strong adhesion (Peel Strength ≥ 20 gf/15mm) through the integrated coating structure.
Solution Approach 2:
The patent applies local quality by creating a porous coating layer with specific local properties on the separator surface: the binder polymer provides local adhesion to the electrode, inorganic particles provide local thermal stability, and the porous structure provides local ion transport pathways. This localized functional distribution achieves strong adhesion without requiring a thick adhesive layer that would increase overall resistance.
3Reliability
If a porous coating layer with inorganic particles and binder polymer is formed, then thermal stability is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-dispersing inorganic particles and binder polymer in a solvent to form a homogeneous slurry before coating. This pre-mixing step ensures uniform distribution of components, simplifying the subsequent coating and drying processes. The slurry can be directly applied to the polyolefin substrate using conventional coating methods, reducing manufacturing complexity while achieving the desired thermal stable porous coating structure.
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 excellent adhesion to electrodes, maintains low resistance, and exhibits high swelling with electrolytes, addressing the limitations of conventional separators and improving safety and performance in lithium secondary batteries.
Implementation Method 1
maintaining adequate hexafluoropropylene content for phase separation and solubility
Implementation Method 2
exhibits high swelling with electrolytes
Data Source
Figure 1~2
Figure 3~4
AI summary
Provided is a separator for an electrochemical device including a first block having repeating units represented by Chemical Formula 1 and a second block having repeating units represented by Chemical Formula 2. A method for manufacturing the same is also provided. The separator shows low resistance, improved adhesion to an electrode and improved swelling property with a solvent.