Separator with Dual Tg Polymer Coating for Battery Adhesion
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Solution Overview
Problem
The existing separators for lithium ion batteries face issues with insufficient adhesiveness to electrodes and handling performance, leading to problems with lithium dendrite precipitation and non-uniform charge-discharge current, which affect the cycle life and safety of the batteries.
Innovation Solution
A separator is developed with a thermoplastic polymer coating layer on a polyolefin microporous film, featuring a sea-island configuration and specific glass-transition temperatures to enhance adhesiveness and handling performance, including a high glass-transition temperature on the outermost surface and a low glass-transition temperature at the interface with the film, improving peel strength and adhesiveness to electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the glass-transition temperature of the reactive polymer is decreased to improve adhesiveness between the reactive polymer and the porous film, then adhesiveness is improved, but the outermost surface of the separator becomes sticky and handling performance decreases
Solution Approach 1:
The invention applies local quality by creating a dual-layer coating structure where the inner layer (contacting porous film) uses low Tg polymer for adhesiveness, while the outer layer (contacting electrodes) uses high Tg polymer for non-sticky handling. This spatial differentiation of material properties resolves the contradiction between adhesiveness and handling performance.
Solution Approach 2:
The invention uses composite materials by combining two different polymers with distinct glass-transition temperatures in a layered configuration. The composite structure integrates the advantages of both materials: low Tg polymer provides bonding strength to substrate, while high Tg polymer provides stable surface properties for handling and electrode contact.
2Strength
If a thermoplastic polymer is applied to a polyolefin microporous film to improve adhesiveness to electrodes, then adhesiveness is improved, but handling performance in rolling up electrodes and lithium ion permeability decrease
Solution Approach 1:
The invention maintains porous structure in the thermoplastic polymer coating layer, creating a three-dimensional network with controlled pore size and distribution. This porous configuration allows lithium ions to permeate through the coating layer while the polymer matrix provides adhesiveness to electrodes, thus resolving the contradiction between adhesiveness and ion permeability.
Solution Approach 2:
The coating layer exhibits local quality differentiation where the polymer matrix provides adhesiveness in regions contacting electrodes, while the porous channels throughout the layer facilitate lithium ion transport. This spatial functional differentiation resolves the contradiction between bonding and permeability.
3Duration of action of stationary object
If the separator structure is optimized to improve adhesiveness and handling performance, then cycle life is extended, but device complexity increases
Solution Approach 1:
The invention applies preliminary action by pre-forming the dual-layer thermoplastic polymer coating structure on the separator before battery assembly. The coating is applied in advance with controlled layering, ensuring optimal adhesiveness and handling properties are established beforehand, which simplifies subsequent battery manufacturing processes.
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 solution provides improved adhesiveness to electrodes, enhanced handling performance, and increased cycle life by optimizing the thermoplastic polymer coating layer's structure and properties, leading to better safety and performance in lithium ion batteries.
Implementation Method 1
the thermoplastic polymer coating layer contains the thermoplastic polymer having at least two glass-transition temperatures, at least one of the glass-transition temperatures is in a range of less than 20° C., and at least one of the glass-transition temperatures is in a range of 20° C. or more
Implementation Method 2
The separator functions to prevent direct contact between the positive and negative electrodes and passes ions through an electrolytic solution held in micropores
Data Source
AI summary
An object is to provide a separator excellent in adhesiveness to electrodes and a separator for an electricity storage device also excellent in handling performance. A separator for an electricity storage device having a polyolefin microporous film and a thermoplastic polymer coating layer covering at least a part of at least one of surfaces of the polyolefin microporous film, in which the thermoplastic polymer coating layer, on the polyolefin microporous film, has a portion containing a thermoplastic polymer and a portion not containing the thermoplastic polymer in a sea-island configuration, the thermoplastic polymer coating layer contains the thermoplastic polymer having at least two glass-transition temperatures, at least one of the glass-transition temperatures is in a range of less than 20° C. and at least one of the glass-transition temperatures is in a range of 20° C. or more.