Composite Separation Membrane for Lithium Battery
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Solution Overview
Problem
Lithium secondary batteries face challenges with adhesive properties between electrodes and separation membranes, leading to reduced battery life and safety concerns due to heat instability and deformation, especially in pouch-type batteries with increased capacity.
Innovation Solution
A composite separation membrane is developed with a porous base layer, a heat-resistant layer of inorganic particles connected by a binder polymer, and a fusion layer of crystalline polymers with a melting temperature of 100°C or higher, where the inorganic particles and crystalline polymer particles satisfy a specific diameter ratio, enhancing adhesive properties and heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a polyvinylidene fluoride resin adhesion layer is added to improve adhesive property, then adhesion with electrode is improved, but heat resistance is insufficient and battery life time is reduced
Solution Approach 1:
The separation membrane is divided into multiple functional layers: a base layer for separation function, an adhesion layer for electrode bonding, and a heat-resistant layer for thermal stability. Each layer performs its specific function independently, resolving the contradiction between adhesion and heat resistance by spatial segmentation of functions.
Solution Approach 2:
The invention uses composite material structure combining polyvinylidene fluoride resin in the adhesion layer with heat-resistant materials (such as polyimide or aramid) in the heat-resistant layer. This composite structure integrates both adhesive properties and heat resistance that cannot be achieved by a single material.
2Strength
If adhesion layer thickness is increased to improve bonding strength, then adhesive property is improved, but battery thickness increases and ion flow is hindered
Solution Approach 1:
The adhesion layer is designed with optimized local thickness (0.5-5 μm) only where needed for electrode bonding, while the overall membrane remains thin. The heat-resistant layer provides additional protection without significantly increasing thickness, achieving local optimization of bonding strength while maintaining overall thinness for ion flow.
3Length of moving object
If separation membrane thickness is reduced to thinning the battery, then battery thickness is reduced, but adhesive property and heat resistance are compromised
Solution Approach 1:
The separation membrane is segmented into multiple thin functional layers (base layer, adhesion layer, heat-resistant layer) where each layer is optimized for its specific function. This allows the overall membrane to remain thin for battery thinning while each sub-layer provides its required performance characteristics.
Solution Approach 2:
Composite material structure with thin adhesion layer (0.5-5 μm) and heat-resistant layer provides both adhesive property and heat resistance in a thin configuration, enabling battery thinning without compromising reliability.
4Reliability
If heat-resistant layer is added to improve safety, then heat resistance is improved, but manufacturing complexity increases
Solution Approach 1:
The adhesion layer and heat-resistant layer are combined into a single integrated composite structure that can be manufactured as one unit using coating and drying processes. This merging reduces the number of separate manufacturing steps and simplifies production while providing both adhesion and heat resistance functions.
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 composite separation membrane improves the battery's life time, heat stability, and safety by ensuring strong adhesion with electrodes and maintaining ion mobility, suitable for large-sized lithium secondary batteries used in electric vehicles.
Implementation Method 1
a heat-resistant layer including inorganic particles connected and fixed by a binder polymer
Implementation Method 2
a fusion layer including crystalline polymers in a form of particles having a melting temperature of 100° C. or higher
Data Source
AI summary
The present invention relates to a composite separation membrane for a lithium secondary battery, having an excellent effect of improving the life time and safety of a battery and a lithium secondary battery including the membrane. The composite separation membrane includes a porous base layer; a heat-resistant layer formed on one side or both sides of the porous base layer; and a fusion layer formed on an outermost layer. The heat-resistant layer includes inorganic particles connected and fixed by binder polymers, and the fusion layer includes crystalline polymers in the form of particles having a melting temperature of 100° C. or higher.