PVDF Separator Adhesive Layer Design for Battery Static Control
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Solution Overview
Problem
Non-aqueous secondary battery separators with PVDF layers face issues with static electricity, leading to poor handling properties and potential product defects due to easy charging and difficulty in removing static electricity, and also have insufficient adhesiveness to electrodes, affecting cycle characteristics and production yield.
Innovation Solution
A separator design featuring a porous substrate with an adhesive porous layer containing polyvinylidene-fluoride resin and a filler, where the filler's particle diameter difference is 2 μm or less, and the adhesive layer's thickness ratio to the filler's volume average particle diameter is between 0.5 and 3.0, enhancing adhesiveness and handling properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a PVDF layer is formed on a polyolefin microporous membrane to improve adhesiveness to electrodes, then adhesiveness is improved, but the separator becomes easily charged with static electricity during production, deteriorating handling properties
Solution Approach 1:
The patent applies local quality by creating a multi-layer structure where only specific layers (the porous outer layers) are made from charge-resistant materials, while the inner adhesive layer retains PVDF for bonding functionality. This localized application of charge resistance properties allows the separator to maintain good handling properties in the regions exposed to friction during production, while preserving the necessary adhesiveness at the electrode interface.
Solution Approach 2:
The patent employs composite materials by combining multiple resin types with different properties in a layered structure. The outer porous layers use charge-resistant resins (polyester, polyacrylonitrile, or polyacrylic acid) to prevent static electricity accumulation, while the inner layer uses PVDF resin to provide adhesiveness to electrodes. This composite structure resolves the contradiction by integrating materials with complementary functions.
2Temperature
If a porous layer containing various resins and fillers is provided on a polyolefin microporous membrane to improve heat resistance, then heat resistance is improved, but adhesiveness to electrodes deteriorates
Solution Approach 1:
The patent applies segmentation by dividing the separator into functionally distinct layers: outer porous layers providing heat resistance and charge resistance, and an inner adhesive layer providing bonding to electrodes. This segmentation allows each layer to optimize its specific function without compromising other requirements.
Solution Approach 2:
The patent applies local quality by concentrating heat-resistant and charge-resistant materials in the outer porous layers, while concentrating adhesive materials in the inner layer that contacts electrodes. This spatial differentiation of material properties allows simultaneous achievement of heat resistance and adhesiveness.
3Strength
If a PVDF layer is formed on a polyolefin microporous membrane to improve adhesiveness, then adhesiveness is improved, but static electricity cannot be removed throughout the production process, leading to meandering and wrinkles
Solution Approach 1:
The patent applies preliminary anti-action by incorporating charge-resistant resins in the outer porous layers before the separator enters the production line. This preventive measure counteracts the static electricity generation that would otherwise occur during friction-based conveying processes, eliminating the need for post-formation static removal processes and ensuring consistent handling properties throughout production.
Data Source
AI summary
A separator for a non-aqueous secondary battery includes a porous substrate and an adhesive porous layer provided on one or both sides of the porous substrate, the adhesive porous layer including a polyvinylidene-fluoride resin and a filler whose difference between a particle diameter at 90% cumulative volume and a particle diameter at 10% cumulative volume is 2 μm or less, and the adhesive porous layer satisfying Inequality (1): 0.5≦a/r≦3.0, wherein, in Inequality (1), “a” represents an average thickness (μm) of the adhesive porous layer on one of the sides of the porous substrate; and “r” represents a volume average particle diameter (μm) of the filler contained in the adhesive porous layer.