Lithium Battery Separator Coating for Thermal Shrinkage Control
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Solution Overview
Problem
Conventional non-aqueous rechargeable lithium batteries face issues with rapid heat generation, internal and external short circuits, and separator degradation due to electrode shrinkage and expansion during charge and discharge cycles, leading to safety concerns and reduced cycle-life.
Innovation Solution
A separator with a porous substrate and a coating layer containing a filler (A) with an average particle diameter of 0.3 µm to 2 µm and a binder (B) comprising an organic polymer and inorganic or organic particles, along with an adhesion layer, is developed to minimize residual moisture and shrinkage at high temperatures, enhancing heat resistance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional porous polyethylene separator is used, then the shutdown characteristic is excellent and cost is low, but the heat resistance is insufficient and the separator shrinks or melts at high temperature
Solution Approach 1:
The separator is constructed as a composite material consisting of a porous polyethylene base layer combined with a coating layer containing inorganic particles (such as alumina, silica, or boehmite) dispersed in a binder resin. This composite structure provides both the shutdown function of the polyethylene and the high-temperature stability of the inorganic coating, preventing shrinkage and melting at elevated temperatures while maintaining the original shutdown characteristic.
2Productivity
If the separator is made thinner to reduce battery size, then the energy density increases, but the mechanical strength decreases and the risk of short circuit increases
Solution Approach 1:
The separator utilizes a porous structure with controlled porosity (30-80%) that maintains mechanical integrity while allowing ion transport. The porous coating layer with inorganic particles provides structural reinforcement that enables thinner designs without compromising strength, as the rigid inorganic framework supports the polymer matrix and prevents collapse under stress.
Solution Approach 2:
The composite structure of polyethylene matrix combined with inorganic particle reinforcement creates a mechanically stronger separator that can be made thinner. The inorganic particles act as structural fillers that enhance tensile strength and dimensional stability, allowing reduced thickness while maintaining adequate mechanical properties to prevent short circuits.
3Temperature
If a coating layer is added to improve heat resistance, then the temperature stability increases, but the residual moisture increases
Solution Approach 1:
The coating process parameters are optimized to control moisture content, including controlling the binder resin composition, drying temperature and time, and inorganic particle surface treatment. By adjusting these parameters, the coating layer achieves high heat resistance while minimizing residual moisture to below 500 ppm, ensuring battery performance and safety.
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 proposed separator design significantly reduces the risk of short circuits and ensures excellent cycle-life and safety characteristics for rechargeable lithium batteries by maintaining porosity and mechanical stability even at elevated temperatures.
Implementation Method 1
a binder (B) including an organic polymer and inorganic or organic particles... maintaining porosity and mechanical stability even at elevated temperatures
Implementation Method 2
a separator made of a porous insulating film and interposed between positive and negative electrodes, and the pores of the film are impregnated by an electrolyte solution
Data Source
Figure 1
AI summary
Disclosed are porous substrate and a coating layer positioned on one side or both sides of the porous substrate, wherein the coating layer includes a filler (A) having an average particle diameter of about 0.3 µm to about 2 µm; and a binder (B) including an organic polymer and an inorganic particle, an organic particle, or a combination thereof, wherein an average particle diameter of each of the inorganic particle and the organic particle is about 5 nm to about 200 nm, and a rechargeable lithium battery including the separator.