PVDF Porous Separator Prevents Curling in Nonaqueous Batteries
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face issues with separator curling due to adhesive material coatings, leading to production defects and degraded cycle characteristics, and struggle with maintaining rate capacity at high electric currents.
Innovation Solution
A laminated body comprising a porous base material with polyolefin resin and a porous layer containing polyvinylidene fluoride-based resin, with controlled crystal forms and optical parameters, is developed to prevent curling and enhance ion permeability, ensuring a higher rate capacity maintaining property.
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 adhesiveness is improved, but the separator curls visibly causing handling difficulties and production defects
Solution Approach 1:
The invention uses a composite porous layer comprising PVDF-based resin and porogen particles. This composite structure provides both the necessary adhesiveness to electrodes and maintains planarity by controlling the physical and chemical properties of the coating material, thereby preventing curling while achieving strong bonding.
Solution Approach 2:
The porous layer is designed with controlled porosity through the use of porogen particles that create void spaces. This porous structure allows the adhesive material to bond effectively with electrodes while maintaining flexibility and preventing stress-induced curling, thus resolving the contradiction between adhesiveness and shape stability.
2Shape
If the separator structure is modified to prevent curling, then the shape stability is improved, but the ion permeability may be compromised affecting rate capacity
Solution Approach 1:
The porous layer incorporates porogen particles that create a controlled porous network. This structure ensures high ion permeability by providing channels for ion transport while the overall layer configuration maintains shape stability and prevents curling, thus achieving both objectives simultaneously.
Solution Approach 2:
The porous layer is designed with spatially varying properties: the PVDF-based resin provides structural integrity and shape stability, while the porogen particles create localized porous regions that facilitate ion permeability. This local differentiation allows the separator to maintain shape while enabling efficient ion transport.
3Illumination intensity
If the porous base material has high lightness and white index to improve optical parameters, then the aesthetic quality is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The invention specifies precise ranges for lightness (L* value) and white index (WI) parameters of the porous base material. By controlling these optical parameters within defined ranges, the invention achieves consistent aesthetic quality while providing clear manufacturing guidelines that balance precision requirements with production feasibility.
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 improves the battery's rate capacity maintaining property, enabling better performance under high electric currents and reducing production defects.
Implementation Method 1
a porous layer on at least one surface of the porous base material, the porous layer containing a polyvinylidene fluoride-based resin
Implementation Method 2
a porous base material containing a polyolefin-based resin as a main component
Data Source
AI summary
To afford a nonaqueous electrolyte secondary battery separator that is not easily curled, a laminated body of the present invention includes: 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, the porous layer containing a polyvinylidene fluoride-based resin, the porous film having a lightness (L*) of not less than 83 and not more than 95 and a white index (WI) of not less than 85 and not more than 98, the polyvinylidene fluoride-based resin containing crystal form α in an amount of not less than 34 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.