Battery Separator Coating for Thin-Film Hi-Pot Withstand Voltage
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Solution Overview
Problem
Lithium-ion secondary batteries face challenges in achieving high capacity and energy density due to reduced separator thickness, leading to potential defects in high-potential tests and increased risk of low-voltage phenomena, as thinner separators may fail to maintain adequate withstand voltage characteristics.
Innovation Solution
A separator with a porous polymer material and an inorganic coating layer, where the ratio of average to maximum pore size is controlled between 0.5 to 0.99, and surface roughness is maintained at 2.5 μm or less, enhancing insulation breakdown voltage and air permeability, thereby improving withstand voltage characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the separator thickness is reduced to increase energy density, then the spacing distance between anode and cathode decreases, but the withstand voltage characteristics deteriorate and the separator may fail Hi-pot tests
Solution Approach 1:
The patent applies composite materials by combining a polyolefin porous substrate with an inorganic coating layer (such as Al2O3, SiO2, or TiO2) to create a separator that maintains both thinness for high energy density and sufficient withstand voltage characteristics through the composite structure. The inorganic coating layer provides enhanced electrical insulation properties while the porous substrate maintains ion conductivity.
Solution Approach 2:
The patent utilizes porous materials by controlling the pore size distribution of the polyolefin porous substrate to have a larger average pore size than the inorganic coating layer pore size. This porous structure ensures adequate ion conductivity for battery performance while the coating layer provides the necessary electrical insulation for withstand voltage characteristics.
2Length of moving object
If the separator thickness is reduced, then the spacing distance between anode and cathode decreases, but leakage current increases in damaged portions
Solution Approach 1:
The patent converts the potential harm of thin separator design by applying an inorganic coating layer that transforms the structure into a composite material system. The coating layer acts as an additional insulation barrier that compensates for the reduced thickness, preventing leakage current while maintaining the benefits of close electrode spacing for high energy density.
3Stability of the object's composition
If the pore size of the inorganic coating layer is smaller than the porous substrate, then the separator structure is stabilized, but the withstand voltage characteristics may be insufficient in thin-film separators
Solution Approach 1:
The patent applies parameter changes by optimizing the pore size distribution parameters, specifically ensuring the average pore size of the porous substrate is larger than the inorganic coating layer pore size within specific ranges (substrate: 0.01-1 μm, coating layer: 0.1-0.5 μm). This parameter optimization maintains structural stability while the coating layer provides sufficient electrical insulation for withstand voltage characteristics in thin-film 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 controlled pore structure and surface flatness of the separator ensure it passes high-potential tests, prevents low-voltage defects, and supports high capacity and energy density battery performance by maintaining excellent withstand voltage characteristics and overcharge performance.
Implementation Method 1
the separator may act as a dielectric barrier
Implementation Method 2
a ratio of average pore size of the separator to a maximum pore size, measured by a bubble point method, is 0.5 to 0.99
Data Source
AI summary
A separator for a secondary battery includes a porous polymer material; and a coating layer including an inorganic material and a binder on one or both surfaces of the porous polymer material, wherein a ratio of average pore size of the separator to a maximum pore size, measured by a bubble point method, is 0.5 to 0.99, and surface roughness Rz is 2.5 or less, and the separator may have excellent withstand voltage characteristics as a thin film and may exhibit suitable evaluation characteristics in a Hi-pot test performed during a battery assembly process.