Separator Coating Composition for Heat Resistance and Ion Permeability
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Solution Overview
Problem
Conventional separators for lithium secondary batteries face challenges in achieving a balance between heat resistance, adhesiveness, air permeability, and conductivity due to the use of ceramic particles in heat-resistant layers, which block pores and reduce ion migration paths, leading to degraded performance and safety issues.
Innovation Solution
A coating composition for separators is developed, comprising a water-soluble polymer and a water-insoluble polymer with solid and annular hollow particles, which provides a core-shell structure and specific particle size distributions to maintain air permeability and conductivity while enhancing adhesiveness and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a heat-resistant layer containing ceramic particles is formed on the separator surface, then heat resistance is improved, but air permeability is reduced due to pore blocking
Solution Approach 1:
The invention uses a porous polymer coating layer with controlled porosity (30-80%) that maintains ion migration paths while providing heat resistance. The porous structure prevents complete pore blocking, allowing air permeability to be maintained at acceptable levels (100-500 mL/min) while the coating provides thermal stability up to 150°C.
Solution Approach 2:
The invention creates a composite coating layer combining polymer matrix (for adhesiveness and flexibility) with ceramic particles (for heat resistance). This composite structure achieves synergistic effects where the polymer provides binding and porosity while ceramic particles provide thermal stability, resolving the contradiction between heat resistance and air permeability.
2Temperature
If a heat-resistant layer containing ceramic particles is formed on the separator surface, then heat resistance is improved, but ion migration paths are reduced
Solution Approach 1:
The porous structure of the coating layer (with 30-80% porosity) creates continuous ion migration channels that prevent the blocking effect. The pores allow lithium ions to pass through the coating layer while the polymer matrix and ceramic particles provide heat resistance, thus maintaining conductivity (≤100 mΩ) while achieving heat resistance.
Solution Approach 2:
The coating layer is designed with heterogeneous local properties: the polymer matrix provides adhesiveness and flexibility in contact with electrodes, while ceramic particles concentrated in certain regions provide heat resistance. The porous regions maintain ion conductivity, creating local quality variations that resolve the contradiction between heat resistance and conductivity.
3Strength
If PVDF-based binder is used to improve adhesive strength, then adhesiveness is improved, but air permeability is reduced due to pore blocking by polymer particles
Solution Approach 1:
The invention changes the physical state parameter of the binder from particulate (PVDF particles) to molecular dissolved state (polyvinyl alcohol). This parameter change eliminates pore blocking while maintaining adhesiveness, as the dissolved polymer forms a continuous adhesive matrix that bonds to both the separator and electrodes without blocking ion migration paths, maintaining air permeability above 100 mL/min.
4Ease of manufacture
If polyethylene separator is used, then ease of manufacture is improved, but heat resistance is reduced leading to shrinkage at high temperature
Solution Approach 1:
The invention applies a heat-resistant coating layer containing ceramic particles and porous polymer as a preliminary protective action before the separator encounters high temperature conditions. This pre-applied coating prevents thermal shrinkage and transformation of the polyethylene substrate at temperatures above 135°C, maintaining separator dimensions and preventing short circuits while preserving the ease of manufacturing polyethylene-based separators.
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 coating composition achieves a balance of heat resistance, adhesiveness, air permeability, and conductivity, reducing thermal shrinkage and maintaining ion migration paths, thereby improving the performance and safety of lithium secondary batteries.
Implementation Method 1
a coating composition for a separator, which includes a water-soluble polymer and a water-insoluble polymer
Implementation Method 2
facilitate the migration of lithium ions
Implementation Method 3
a microporous separator using a polyolefin such as polyethylene, which is advantageous for forming pores by thermally-induced phase separation
Data Source
AI summary
One aspect of the present invention provides a coating composition for a separator including a water-soluble polymer and a water-insoluble polymer, wherein the water-insoluble polymer includes solid particles and annular hollow particles, and an electrode-adhesive separator, which includes an adhesive layer made of the coating composition.