PVDF Separator Adhesive Layer for Battery Electrode Bonding
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Solution Overview
Problem
Conventional separators for non-aqueous secondary batteries face challenges in achieving optimal adhesion to electrodes while maintaining ion permeability and cycle life, particularly when using soft pack outer casings, as they require higher temperature or pressure conditions for bonding, which can damage the porous structure and lead to peeling issues during transport and slitting.
Innovation Solution
A separator with a porous substrate and an adhesive porous layer containing specific polyvinylidene fluoride resins (A and B) with controlled molecular weights and hexafluoropropylene content, ensuring excellent adhesion and ion permeability, and a porosity and pore size that prevent structural damage during bonding and enhance slittability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If higher temperature or pressure conditions are used for bonding the adhesive porous layer to the electrode, then adhesion strength is improved, but the porous structure is damaged and ion permeability deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molecular weight of polyvinylidene fluoride resin (600,000 to 2,500,000) and the content of hexafluoropropylene units (1.5 mol% or less). These parameter optimizations enable the adhesive porous layer to achieve sufficient adhesion strength without requiring excessive temperature or pressure during bonding, thereby preserving the porous structure and maintaining ion permeability.
Solution Approach 2:
The patent uses composite materials by forming an adhesive porous layer that combines polyvinylidene fluoride resin with specific copolymer components containing hexafluoropropylene. This composite structure provides both the necessary adhesive properties and the structural integrity to maintain porosity under bonding conditions, resolving the contradiction between adhesion strength and ion permeability.
2Duration of action of stationary object
If the adhesive porous layer is made more adhesive to ensure better electrode bonding, then cycle life is improved, but the layer becomes more prone to peeling during transport and slitting
Solution Approach 1:
The patent resolves this contradiction through parameter changes by optimizing the molecular weight range (600,000 to 2,500,000) and hexafluoropropylene content (1.5 mol% or less). This precise parameter control creates an adhesive porous layer with balanced properties: sufficient adhesion for long cycle life but controlled stickiness that prevents peeling during handling and slitting operations.
3Weight of moving object
If a soft pack outer casing is used to reduce size and weight, then battery density is improved, but spaces form between electrodes and separators during charging and discharging
Solution Approach 1:
The patent addresses this issue by using composite materials in the adhesive porous layer, combining polyvinylidene fluoride resin with copolymer components. This composite structure provides enhanced adhesive uniformity across the separator surface, ensuring stable bonding between electrodes and separator even when volume changes occur during charging and discharging in soft pack batteries.
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 separator provides enhanced adhesion to electrodes, improved ion permeability, and extended cycle life, while allowing for easier handling and production without compromising battery performance, even with soft pack outer casings.
Implementation Method 1
the adhesive porous layer functions as an adhesive that favorably joins the electrode and the separator together, in a case in which an adhesive porous layer and an electrode are disposed adjacently in layers and subjected to compression bonding or heat pressing
Implementation Method 2
from the viewpoint of achieving both ion permeability and ensuring sufficient adhesive property
Data Source
AI summary
The present invention provides a separator for a non-aqueous secondary battery including a porous substrate and an adhesive porous layer that is formed at at least one side of the porous substrate and contains the following polyvinylidene fluoride-based resin A and the following polyvinylidene fluoride-based resin B. (1) Polyvinylidene fluoride resin A selected from the group consisting of vinylidene fluoride homopolymers having a weight average molecular weight of from 600,000 to 2,500,000, and vinylidene fluoride copolymers having a weight average molecular weight of from 600,000 to 2,500,000 and containing a structural unit derived from vinylidene fluoride and a structural unit derived from hexafluoropropylene, the total content of structural units derived from hexafluoropropylene in each of the vinylidene fluoride copolymers being 1.5 mol % or less of the total content of structural units in each of the vinylidene fluoride copolymer. (2) Polyvinylidene fluoride resin B containing a structural unit derived from vinylidene fluoride and a structural unit derived from hexafluoropropylene, the total content of structural units derived from hexafluoropropylene in the polyvinylidene fluoride resin B being greater than 1.5 mol % of the total content of structural units in the polyvinylidene fluoride resin B.