Asymmetric Composite Separator for Thermal Stability
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Solution Overview
Problem
Lithium secondary batteries face safety issues due to thermal shrinkage of porous polyolefin substrates, leading to potential short circuits and capacity deterioration, and existing composite separators do not adequately address these problems.
Innovation Solution
A lithium secondary battery design featuring a composite separator with a thicker first porous coating layer facing the anode and a thinner second porous coating layer facing the cathode, both composed of inorganic particles and a binder polymer, to inhibit thermal shrinkage and improve cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous polyolefin substrate is used as separator, then it provides good electrochemical performance, but it undergoes thermal shrinkage at high temperature causing short circuits
Solution Approach 1:
The patent applies composite materials by coating a porous layer containing inorganic particles (such as alumina, silica, or titania) and binder polymer on the porous polyolefin substrate. This composite structure combines the electrochemical benefits of the polyolefin substrate with the thermal stability of inorganic particles, preventing thermal shrinkage while maintaining good electrochemical performance.
Solution Approach 2:
The patent uses porous materials by forming a porous coating layer with controlled porosity (30-70%) on the separator substrate. The porous structure allows ion transport while the inorganic particles within the porous matrix provide thermal stability and prevent shrinkage at elevated temperatures.
2Reliability
If coating layers are added to prevent thermal shrinkage, then safety is improved, but ion transport resistance increases
Solution Approach 1:
The patent resolves this contradiction by creating a porous coating layer with optimized porosity (30-70%) that allows efficient ion transport while the inorganic particles provide thermal stability. The porous structure ensures that safety is improved through thermal resistance while ion transport resistance is minimized through adequate porosity.
Solution Approach 2:
The patent applies parameter changes by optimizing the porosity, thickness, and composition of the coating layer to balance safety and ion transport. By controlling these parameters, the coating provides thermal stability without creating excessive resistance to ion flow, thus resolving the contradiction between safety improvement and ion transport resistance.
3Ease of manufacture
If uniform thickness coating is applied, then manufacturing is simplified, but cycle characteristics deteriorate
Solution Approach 1:
The patent applies asymmetry by using different coating thicknesses on opposite sides of the separator substrate. The first coating layer has a thickness of 1-20 μm while the second coating layer has a thickness of 0.1-10 μm. This asymmetric design optimizes cycle characteristics by providing enhanced protection on the side that benefits most, while still maintaining reasonable manufacturing complexity.
Solution Approach 2:
The patent uses local quality by applying different coating thicknesses to different sides of the separator based on their specific functional requirements. The thicker first coating layer provides enhanced thermal and mechanical stability where needed, while the thinner second coating layer maintains good ion transport properties, optimizing overall battery performance.
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 design prevents short circuits and enhances cycle characteristics by reducing ion transport rates at the anode, thereby maintaining battery capacity and safety.
Implementation Method 1
the inorganic particles present in the porous coating layer coated on the porous substrate serve as spacers that can maintain a physical shape of the porous coating layer to inhibit the porous substrate from thermal shrinkage when an electrochemical device overheats
Implementation Method 2
The design prevents short circuits and enhances cycle characteristics by reducing ion transport rates at the anode
Data Source
Figure 1
AI summary
Disclosed is an electrochemical device. The electrochemical device includes: (a) a composite separator including a porous substrate, a first porous coating layer coated on one surface of the porous substrate, and a second porous coating layer coated on the other surface of the porous substrate; (b) an anode disposed to face the first porous coating layer; and (c) a cathode disposed to face the second porous coating layer. The first and second porous coating layers are each independently composed of a mixture including inorganic particles and a binder polymer. The first porous coating layer is thicker than the second porous coating layer. The electrochemical device has good thermal stability and improved cycle characteristics.