Li-Ion Separator Coating Balancing Adhesion and Ionic Conductivity
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Solution Overview
Problem
Existing separator coatings for Li-ion batteries face challenges in achieving a balance between dry adhesion, adhesion in the wet state, ionic conductivity, and heat stability, particularly due to issues like swelling or dissolution in electrolyte solvents, which affect their performance and durability.
Innovation Solution
A monolayer coating comprising a hybrid fluoro-acrylic polymer resin with inorganic particles, where the fluoro-acrylic polymer is synthesized via an aqueous route, providing a compromise between adhesion properties and ionic conductivity while resisting electrolyte solvents, and is applied as a monolayer on a separator for Li-ion batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a coating is applied to improve adhesion, then dry adhesion increases, but ionic conductivity decreases due to pore closure
Solution Approach 1:
The coating is designed with a porous structure containing voids and channels that allow Li ion transport. The porosity is maintained through controlled formulation and processing, ensuring that the coating provides adhesion while preserving ionic conductivity pathways for battery operation.
2Strength
If pressing pressure is increased to improve adhesion, then dry adhesion increases, but pore closure occurs reducing ionic conductivity
Solution Approach 1:
The coating formulation includes porosity agents or void-forming components that create and maintain open pore structures even under pressing conditions. This allows the coating to adhere to the separator while preserving continuous pathways for ion transport.
3Reliability
If polymer coating is applied to improve affinity with electrolyte, then ionic conductivity increases, but adhesion decreases due to swelling and dissolution
Solution Approach 1:
The coating combines polymer matrices with inorganic particles or crosslinking agents to create a composite structure. This composite formulation provides both electrolyte wettability for ionic conductivity and structural integrity for adhesion, preventing swelling-induced detachment.
Solution Approach 2:
The coating uses polymers with adjusted glass transition temperatures and crosslinking densities to control swelling behavior. By optimizing these parameters, the coating maintains adhesion while allowing controlled swelling that enhances electrolyte penetration and ionic conductivity.
4Strength
If polyolefin separator is used to provide mechanical strength, then mechanical strength increases, but heat stability decreases due to temperature shrinkage
Solution Approach 1:
The separator combines polyolefin base material with a coating layer containing inorganic particles or heat-resistant polymers. This composite structure provides the mechanical strength of polyolefin while the coating layer maintains dimensional stability at elevated temperatures, preventing shrinkage.
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 hybrid fluoro-acrylic polymer resin with inorganic particles offers improved dry adhesion, resistance to electrolyte solvents, and maintained ionic conductivity, ensuring the integrity and performance of the separator coating, even under exposure to electrolytes, thereby enhancing the battery's overall efficiency and longevity.
Implementation Method 1
a very good compromise between, on the one hand, dry adhesion and adhesion in the wet state
Implementation Method 2
The ionic conductivity represents the migration of the Li ions through the separator and its coating by virtue of the porosity
Implementation Method 3
The adhesion of the coating on the separator in the wet state is measured after impregnation with the electrolyte. This adhesion decreases when the coating is softened by electrolyte solvents, leading to the swelling of the polymer present in the coating
Data Source
AI summary
The invention relates to a coating based on a fluoro acrylate polymer latex comprising inorganic particles, said coating exhibiting a very good compromise between, on the one hand, dry adhesion and adhesion in the wet state, and, on the other hand, between adhesion and ionic conductivity. This coating is intended for a separator application, in particular for Li-ion batteries. The invention also relates to a Li-ion battery comprising a separator covered with such a coating.