Composite Separator for Lithium-Ion Battery Thermal Stability
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Solution Overview
Problem
Conventional lithium-ion battery separators made of polyolefin materials suffer from low thermal stability, leading to potential short circuits due to heat shrinking at high temperatures, and lack sufficient mechanical strength and flexibility, making them unsafe for high-power battery applications.
Innovation Solution
A separator with a protective porous layer composed of an organic binder and inorganic filler, such as whisker-type and particulate materials, is applied to both surfaces of a porous base material, ensuring uniform tensile strength in both machine and transverse directions, enhancing thermal stability and mechanical strength while preventing thermal contraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a polyolefin-based separator is used, then the separator provides good mechanical strength and flexibility, but it exhibits low thermal stability and shrinks rapidly at high temperatures causing short circuits
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin base layer combined with an inorganic coating layer containing alumina particles and a polyacrylic acid binder. This composite structure allows the separator to maintain the mechanical strength and flexibility of the polyolefin base while the inorganic coating layer provides thermal stability and prevents heat shrinkage at high temperatures, thus resolving the contradiction between mechanical strength and thermal stability.
2Productivity
If the separator thickness is reduced to improve ion permeability, then the battery energy density increases, but the mechanical strength and safety of the separator deteriorate
Solution Approach 1:
The separator utilizes a porous structure with controlled pore size distribution, where the inorganic coating layer contains pores that allow efficient ion transport. The porous alumina coating layer provides high ion permeability even at thin thicknesses, while the interconnected pore structure and inorganic framework maintain mechanical strength and thermal stability, thus achieving both high ion permeability and safety in a thin separator configuration.
3Reliability
If a shutdown function is added to the separator by using UHMWPE and HDPE, then the separator can stop ion transport at high temperatures, but it still suffers from heat shrinkage and cannot prevent short circuits effectively
Solution Approach 1:
The inorganic coating layer acts as an intermediary between the polyolefin base layer and the external environment. It provides a thermal barrier that prevents the base layer from shrinking at high temperatures, while the shutdown function of the polyolefin base layer remains intact to stop ion transport. The inorganic coating layer mediates the thermal stress, preventing heat shrinkage while preserving the shutdown function, thus resolving the contradiction between shutdown capability and heat shrinkage prevention.
Data Source
AI summary
Provided herein is a separator used for an electrochemical device such as a lithium-ion battery. The separator disclosed herein comprises a porous base material, and a protective porous layer coated on one or both surfaces of the porous base material disclosed herein, wherein the protective porous layer comprises an organic binder and an inorganic filler, and wherein a difference in tensile strength of the separator along the TD direction and MD direction is about 15% or less. Also provided herein is a lithium-ion battery including the separator disclosed herein. The separator disclosed herein is excellent in terms of safety, ion permeability, and cycle characteristics.