Inorganic-Coated Battery Separator for Thin-Film Breakdown Resistance
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Solution Overview
Problem
The thinning of separator thickness in electrochemical devices leads to a decrease in breakdown voltage, compromising battery stability and increasing defect rates, while maintaining high capacity and output characteristics is essential.
Innovation Solution
A separator with an inorganic particle layer on a porous substrate, featuring a specific breakdown voltage to thickness ratio, FT-IR peak ranges, and controlled heat shrinkage and permeability, enhances withstand voltage, adhesion, and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If separator thickness is reduced to achieve high capacity and output characteristics, then energy density and power density improve, but breakdown voltage decreases leading to deteriorated withstand voltage characteristics and increased defect rates
Solution Approach 1:
The patent applies composite materials by forming an inorganic particle layer on the porous substrate. This composite structure combines the flexibility and ion permeability of the polymer substrate with the high breakdown voltage and thermal stability of inorganic particles (such as alumina, silica, or boehmite), thereby achieving both high capacity and excellent withstand voltage characteristics even at reduced thickness
Solution Approach 2:
The patent utilizes porous materials by employing a porous substrate with controlled porosity and pore size distribution. The porous structure allows efficient ion transport for high capacity while the inorganic particle layer coating maintains structural integrity and enhances breakdown voltage, resolving the contradiction between thinness and reliability
2Volume of moving object
If separator thickness is reduced to improve energy density, then battery volume efficiency increases, but breakdown voltage decreases causing flame discharge and loss of insulation characteristics
Solution Approach 1:
The inorganic particle layer forms a composite structure that provides high breakdown voltage strength. The inorganic particles (alumina, silica, boehmite) have inherently high dielectric strength and thermal stability, which compensates for the reduced thickness and prevents flame discharge, maintaining insulation characteristics at lower volumes
Solution Approach 2:
The inorganic particle layer acts as an intermediary protective layer between the porous substrate and the electrolyte. This intermediate structure enhances the overall breakdown voltage of the separator system, preventing direct electrical breakdown even when the total separator thickness is reduced for higher energy density
3Productivity
If separator is thinned to achieve high capacity characteristics, then ion migration path efficiency improves, but heat shrinkage resistance and stability deteriorate
Solution Approach 1:
The composite structure of porous substrate with inorganic particle layer coating provides both efficient ion migration pathways through the porous structure and superior heat shrinkage resistance from the thermally stable inorganic particles. The inorganic layer acts as a thermal barrier and structural stabilizer at high temperatures
Solution Approach 2:
The inorganic particle layer is applied locally on the porous substrate surface, providing targeted enhancement of heat shrinkage resistance and breakdown voltage specifically where needed for stability, while maintaining the overall thin profile and ion migration efficiency of the separator
Data Source
AI summary
Provided are a separator having significantly improved withstand voltage characteristics and a lithium secondary battery including the same. The separator includes a porous substrate and an inorganic particle layer including a binder and inorganic particles formed on at least one surface of the porous substrate, wherein the separator has a ratio of a breakdown voltage (kV) of the separator to an overall average thickness (μm) of the separator of 0.15 kV/μm or more, has a peak in a range of 1070 cm−1 to 1082 cm−1 in a spectrum by Fourier transform infrared spectroscopy (FT-IR), has heat shrinkage rates in the machine direction and in the transverse direction of 5% or less as measured after being allowed to stand at 150° C. for 60 minutes, and has ΔGurley permeability of 100 sec/100 cc or less.