Laminated Battery Separator Prevents Curling via PVDF Crystal Control
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Solution Overview
Problem
Nonaqueous electrolyte secondary battery separators curl due to stress from electrode expansion and contraction, leading to increased internal resistance and degraded cycle characteristics, which existing adhesive coatings cannot adequately address without causing production handling issues.
Innovation Solution
A laminated body with a porous base material containing polyolefin resin and a porous layer with polyvinylidene fluoride-based resin, having controlled crystal forms and low anisotropy in viscoelasticity, is used as a separator to prevent curling and reduce internal resistance increases during charge and discharge cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a separator is coated with an adhesive material to increase adhesiveness between the separator and electrodes, then the adhesion is improved, but the separator curls visibly causing handling difficulties
Solution Approach 1:
The invention changes the physical and chemical parameters of the porous layer by controlling the crystal form content (α form ≥36 mol%) and using specific binders to achieve the right balance between adhesion and flatness. This parameter optimization prevents curling while maintaining sufficient adhesiveness.
Solution Approach 2:
The invention uses a composite structure with a polyolefin base material and a porous layer containing PVDF-based resin with specific crystal forms. This composite material design provides both the required adhesion properties and dimensional stability to prevent curling.
2Ease of operation
If the separator structure is modified to prevent curling, then handling ease is improved, but the adhesion between separator and electrodes may be reduced
Solution Approach 1:
The invention optimizes parameters including porosity (30-80%), thickness (1-20 μm), and crystal form content to achieve a balance where the separator remains flat and handleable while maintaining adequate adhesion through controlled pore structure and binder selection.
3Reliability
If the porous base material has high anisotropy in viscoelasticity, then the internal resistance increases rapidly during charge and discharge cycles, but reducing anisotropy may affect other mechanical properties
Solution Approach 1:
The invention reduces the anisotropy of tan δ to 20% or less by controlling the porous structure and material composition, which directly reduces the rate of internal resistance increase during cycling while maintaining necessary mechanical properties through optimized porosity and crystal form distribution.
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 laminated body effectively prevents curling and reduces the rate of internal resistance increase in nonaqueous electrolyte secondary batteries, improving their cycle characteristics and handling during production.
Implementation Method 1
the porous base material having a parameter X of not more than 20, the parameter X being calculated in accordance with a formula below, where MD tan δ represents a tan δ measured in a machine direction through a viscoelasticity measurement performed at a frequency of 10 Hz and a temperature of 90° C.
Implementation Method 2
the polyvinylidene fluoride-based resin containing crystal form α in an amount of not less than 36 mol % with respect to 100 mol % of the total amount of the crystal form α and crystal form β contained in the polyvinylidene fluoride-based resin
Implementation Method 3
a porous base material containing a polyolefin-based resin as a main component; and a porous layer on at least one surface of the porous base material
Data Source
AI summary
To afford a laminated body that is usable as a nonaqueous electrolyte secondary battery separator and that is not easily curled, a laminated body includes: a porous base material containing a polyolefin-based resin as a main component; and a porous layer containing a polyvinylidene fluoride-based resin, the porous base material having a parameter X of not more than 20, the parameter X being calculated in accordance with a particular formula, the polyvinylidene fluoride-based resin containing crystal form α in an amount of not less than 36 mol % with respect to 100 mol % of a total amount of the crystal form α and crystal form β contained in the polyvinylidene fluoride-based resin.