PVdF Adhesive Porous Layer Crystal Size Control for Battery Separator
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Solution Overview
Problem
Nonaqueous secondary batteries face challenges in achieving both strong adhesion to electrodes and sufficient ion permeability, particularly when using polyvinylidene-fluoride-based resins, as high temperatures and pressures required for adhesion can damage the porous structure, and styrene-butadiene rubber complicates achieving good battery characteristics.
Innovation Solution
A separator with a porous substrate and an adhesive porous layer containing polyvinylidene-fluoride-based resin, where the adhesive porous layer has a crystal size of 1 nm to 13 nm and a weight of 0.5 g/m2 to 1.5 g/m2, formed on both sides of the substrate, ensuring better adhesion and ion permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If heat pressing is performed under high temperature and pressure to ensure adhesion, then adhesion strength is improved, but the porous structure of the adhesive porous layer is destroyed, reducing ion permeability
Solution Approach 1:
The invention controls the crystal size of the polyvinylidene-fluoride-based resin in the adhesive porous layer within a specific range (1 nm to 13 nm). This parameter control allows the material to maintain both adhesion strength and ion permeability, as the controlled crystal structure provides adequate bonding while preserving the porous architecture for ion transport.
Solution Approach 2:
The separator comprises a composite structure with a polyolefin microporous membrane substrate and an adhesive porous layer made of polyvinylidene-fluoride-based resin. This composite design combines the shutdown function and baseline porosity of the polyolefin substrate with the adhesive properties of the PVdF layer, achieving both adhesion and ion permeability without requiring extreme heat pressing conditions.
2Strength
If the binder resin content in the electrode is increased to improve adhesion, then adhesion is improved, but the active material content decreases, reducing energy density
Solution Approach 1:
The invention changes the parameter of crystal size of the adhesive porous layer to 1 nm to 13 nm, which optimizes the adhesion mechanism. This allows effective adhesion with minimal binder resin content in the electrode, as the controlled crystal structure enhances the adhesive function of the porous layer itself, reducing the need for large amounts of binder resin and thereby preserving active material content for higher energy density.
3Weight of moving object
If a soft pack outer casing is used to reduce size and weight, then portability is improved, but a space forms between electrode and separator during charging and discharging, reducing cycle life
Solution Approach 1:
The invention uses an adhesive porous layer that conformally adheres to the electrode surface, creating a flexible bonding interface that accommodates the volume changes of electrodes during charging and discharging. This flexible adhesion mechanism, enabled by the controlled crystal structure, maintains contact between separator and electrode even in soft pack batteries, preventing space formation and extending cycle life.
Solution Approach 2:
The composite separator structure with adhesive porous layer provides flexible adhesion that accommodates electrode expansion and contraction in soft pack batteries. The controlled crystal size (1-13 nm) in the adhesive layer creates a compliant bonding interface that maintains electrical and physical contact during cycling, solving the delamination problem in lightweight soft pack designs.
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 adhesion to electrodes and maintains ion permeability, enabling the production of high-energy-density, high-performance nonaqueous secondary batteries with an aluminum laminate pack outer casing.
Implementation Method 1
When such an adhesive porous layer with an electrolyte contained therein is stacked on an electrode and heat-pressed, the electrode and the separator can be well joined together
Implementation Method 2
in order to ensure sufficient adhesion and ion permeability
Data Source
AI summary
An object of the invention is to provide a separator for a nonaqueous secondary battery, which has good adhesion to electrodes and is also capable of ensuring sufficient ion permeability even after attachment to electrodes. The separator for a nonaqueous secondary battery of the invention includes a porous substrate and an adhesive porous layer that is formed on at least one side of the porous substrate and contains a polyvinylidene-fluoride-based resin. The separator for a nonaqueous secondary battery is characterized in that the adhesive porous layer has a crystal size of 1 to 13 nm.