Multilayer Battery Separator Balancing Ion Transfer and Thermal Shrinkage
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Solution Overview
Problem
Multilayer composite separators in lithium-ion batteries fail to meet the diverse performance requirements of different batteries due to inadequate customization of component contents in the base film, leading to issues such as thermal shrinkage, excessive internal resistance, and hindered lithium ion transfer.
Innovation Solution
A separator design comprising at least two base films with controllable component contents and a functional layer interposed between them, utilizing materials like polyethylene and polypropylene for film layers and inorganic or organic functional materials to enhance properties like thermal stability and wettability, with a thickness of 3 µm to 15 µm and porosity of 30% to 70%, and a preparation method involving electrospinning and pressure-compositing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the base film thickness is reduced to improve ion transfer efficiency, then lithium ion transfer efficiency is improved, but thermal shrinkage resistance deteriorates
Solution Approach 1:
The base film is constructed as a composite material combining polyethylene and polypropylene in specific ratios (polyethylene 20-80 wt%, polypropylene 80-20 wt%). This composite structure allows the separator to achieve both thin thickness (3-15 μm) for good ion transfer and sufficient thermal shrinkage resistance through the complementary properties of the two polymers.
Solution Approach 2:
The invention optimizes specific parameter ranges: thickness (3-15 μm), porosity (30-70%), and component ratios (polyethylene 20-80 wt%, polypropylene 80-20 wt%). By precisely controlling these parameters, the separator achieves the optimal balance between ion transfer efficiency and thermal shrinkage resistance.
2Reliability
If multiple functional layers are added to enhance separator performance, then thermal stability and wettability are improved, but device complexity increases
Solution Approach 1:
The separator is segmented into functionally distinct layers: a base film layer (3-15 μm) providing mechanical strength and thermal shrinkage resistance, and a functional layer (5-20 μm) containing inorganic particles (alumina, silica, titania) and organic binders for enhanced thermal stability, wettability, and chemical resistance. This segmentation allows each layer to specialize in specific functions.
Solution Approach 2:
The functional layer serves multiple purposes simultaneously: inorganic particles provide thermal stability and chemical resistance, while also improving wettability; the organic binder holds the structure together and provides additional chemical stability. This multi-functionality reduces the need for separate specialized layers.
3Ease of operation
If polyethylene content is increased to improve wettability, then wettability is improved, but melting point and stability decrease
Solution Approach 1:
The invention optimizes the polyethylene content within a specific range (20-80 wt%) rather than maximizing it. This controlled parameter change ensures sufficient wettability while maintaining adequate melting point and thermal stability through the balancing effect of polypropylene (80-20 wt%).
Solution Approach 2:
The composite of polyethylene and polypropylene in controlled ratios allows the separator to achieve both good wettability (from polyethylene) and high melting point/stability (from polypropylene), resolving the contradiction between these opposing properties.
4Productivity
If the base film is made thinner to reduce internal resistance, then internal resistance is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The invention defines a specific thickness range (3-15 μm) that balances low internal resistance with manufacturability. This parameter optimization ensures the separator is thin enough for good ion transfer but thick enough to be manufactured with acceptable precision and handling properties.
Solution Approach 2:
The composite structure of polyethylene and polypropylene provides mechanical strength even at thin dimensions (3-15 μm), making the thin separator easier to manufacture and handle while maintaining low internal resistance.
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 allows for precise control of separator performance, reducing thermal shrinkage and internal resistance, enhancing lithium ion transfer efficiency, and providing thermal and chemical stability, thus improving battery performance.
Implementation Method 1
a preparation method involving electrospinning and pressure-compositing
Implementation Method 2
the functional layer may be used for thermal insulation and/or improving the chemical stability of the separator
Implementation Method 3
the functional layer may be used for thermal insulation and/or improving the chemical stability of the separator and/or enhancing the wettability of the separator
Data Source
AI summary
This application discloses a separator and a preparation method thereof, a battery cell, a battery, and an electric device, where the separator includes at least two base films and a functional layer interposed between two adjacent base films, and the base film includes at least two components. A technical solution of this application achieves performance control of the base film and even the separator by incorporating multiple components with controllable contents in film layers of the base film.