Laminated Separator Preventing Curling via PVDF Crystal Control
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face issues with separator curling, leading to increased internal resistance and degraded cycle characteristics due to stress between electrodes and the separator, which existing adhesive coatings cannot adequately address.
Innovation Solution
A laminated body is developed using a porous base material with a polyolefin-based resin and a porous layer containing a polyvinylidene fluoride-based resin with controlled crystal forms, ensuring a specific ratio of critical load distances in scratch tests to prevent curling and maintain excellent rate characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a separator is coated with an adhesive material such as polyvinylidene fluoride to increase adhesiveness between the separator and electrodes, then the adhesiveness is improved, but the separator curls visibly
Solution Approach 1:
The invention changes the crystalline form parameters of the polyvinylidene fluoride-based resin from conventional forms to specific crystal forms (α, β, or γ) with defined ratios. This parameter change in the molecular structure prevents curling while maintaining adhesiveness, as the specific crystal forms provide balanced mechanical properties that eliminate the curling tendency caused by adhesive coating.
Solution Approach 2:
The invention uses a composite approach by combining polyvinylidene fluoride-based resin with specific crystalline structures in the adhesive coating layer. The controlled composition and crystal form ratio create a composite material that simultaneously achieves high adhesiveness and curl-free morphology, resolving the contradiction between bonding strength and shape stability.
2Reliability
If the separator is coated to improve adhesion, then the cycle characteristic is improved, but the handling during production becomes difficult
Solution Approach 1:
By changing the crystalline form parameters of the polyvinylidene fluoride-based resin to specific α, β, or γ forms with controlled ratios, the invention achieves both improved cycle characteristic and ease of handling. The specific crystal forms provide optimal mechanical properties that prevent curling, making the separator easy to handle during production while maintaining reliable cyclic performance.
3Reliability
If the separator uses adhesive coating to prevent electrode detachment, then the internal resistance increase is reduced, but the manufacturing complexity increases
Solution Approach 1:
The invention simplifies manufacturing by changing the material parameters to polyvinylidene fluoride-based resin with specific crystalline forms that inherently prevent curling. This eliminates the need for complex post-coating processing steps, reducing manufacturing complexity while maintaining internal resistance stability through improved electrode adhesion.
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 effectively prevents separator curling and maintains a high rate characteristic maintaining ratio after charge and discharge cycles, enhancing the performance and stability of nonaqueous electrolyte secondary batteries.
Implementation Method 1
coating the surface of a separator with an adhesive material such as polyvinylidene fluoride for increased adhesiveness between the separator and electrodes
Implementation Method 2
a porous base material containing a polyolefin-based resin as a main component and a porous layer disposed on the porous base material
Data Source
AI summary
A nonaqueous electrolyte secondary battery separator having a laminated body which is not easily curled is provided. The laminated body includes a porous base material containing a polyolefin-based resin as a main component and a porous layer which is disposed on at least one surface of the porous base material and which contains a polyvinylidene fluoride-based resin. The porous base material has a piercing strength of not less than 26.0 gf/g/m2. The polyvinylidene fluoride-based resin contains 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.