Separator Coating Composition Balancing Adhesion and Ion Conductivity
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Solution Overview
Problem
Existing separator coatings for lithium-ion batteries face challenges in achieving a balance between dry adhesion, wet adhesion, ion conductivity, and heat stability, with polyvinylidene fluoride-based coatings needing improvements.
Innovation Solution
A composition comprising polymers P1 and P2, where P1 is a fluoropolymer derived from vinylidene fluoride and P2 is a hydrophilic polymer, with a specific difference between melting point and crystallization temperature greater than 40°C, offering improved adhesion, conductivity, and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polyvinylidene fluoride (PVDF) and derivatives are used as separator coatings, then electrochemical stability and dielectric constant are improved, but adhesion and ion conductivity need improvement
Solution Approach 1:
The patent uses a composite coating system consisting of PVDF binder polymer and hydrophilic pore-forming polymer (such as polyacrylonitrile, polyacrylic acid, or carboxymethyl cellulose). This composite structure combines the electrochemical stability of PVDF with the adhesion and ion conductivity benefits of hydrophilic polymers, resolving the contradiction between reliability and ease of manufacture.
Solution Approach 2:
The coating is designed with differentiated local properties: the PVDF provides electrochemical stability in the binder matrix, while hydrophilic polymer domains provide adhesion and ion conductivity pathways. The pore structure created by the hydrophilic polymer forms localized conductive channels, allowing different regions of the coating to fulfill different functional requirements.
2Quantity of substance
If separator thickness is reduced, then energy density is improved, but mechanical strength and temperature resistance deteriorate
Solution Approach 1:
The patent employs a porous coating structure formed by hydrophilic pore-forming polymers that create interconnected voids. This porous architecture provides mechanical reinforcement through increased surface area and structural complexity, while maintaining thin overall thickness. The pores also facilitate ion transport, compensating for the reduced thickness.
Solution Approach 2:
The composite of PVDF and hydrophilic polymers creates a synergistic structure where the hydrophilic polymer network provides mechanical strength and thermal stability, allowing the use of thinner separators without sacrificing structural integrity or temperature resistance.
3Temperature
If crystallization temperature is increased, then thermal stability is improved, but processing window narrows
Solution Approach 1:
The patent modifies the thermal properties of the coating by adjusting the composition ratio between PVDF and hydrophilic polymers, and by controlling the crystallization process parameters. The hydrophilic polymers act as nucleating agents that promote crystallization at lower temperatures, widening the processing window while maintaining high thermal stability through the formation of stable crystalline structures.
Solution Approach 2:
The patent utilizes controlled phase transitions during coating formation, where the hydrophilic polymers facilitate crystallization at specific temperature ranges. By managing the phase transition behavior of the composite system, the coating achieves high crystallinity and thermal stability while allowing processing within a broader temperature window.
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 composition achieves a good compromise between adhesion, conductivity, and thermal stability, enhancing the performance of lithium-ion battery separators.
Implementation Method 1
Polyvinylidene fluoride (PVDF) and derivatives thereof are advantageous as polyolefin separator coatings because of their electrochemical stability and their high dielectric constant, which promotes ion dissociation and thus conductivity
Implementation Method 2
the difference between the melting point and the crystallization temperature of said composition is greater than or equal to 40° C.
Implementation Method 3
the difference between the melting point and the crystallization temperature of said composition is greater than or equal to 40° C.
Data Source
AI summary
The present invention relates to a composition comprising a polymer P1 comprising monomer units derived from vinylidene fluoride and a polymer P2 comprising monomer units derived from a monomer M2 of formula R1R2C═C(R3)C(O)R wherein the substituents R1, R2 and R3 are, independently from each other, selected from the group consisting of H and C1-C5alkyl; R is selected from the group consisting of —NHC(CH3)2CH2C(O)CH3 or —OR′ with R′ selected from the group consisting of C1-C18 alkyl optionally substituted by one or more —OH group(s) or a five- or six-membered heterocycle comprising at least one nitrogen atom in its cyclic chain, characterised in that the difference between the melting temperature and the crystallisation temperature of the composition is greater than or equal to 40° C.