Polyolefin PVDF Laminated Separator Prevents Curling
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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 effectively prevent.
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, specifically with a high percentage of crystal form α, to prevent curling and enhance electrolyte retention properties.
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
Solution Approach 1:
The invention uses a composite structure consisting of a polyolefin-based porous base material and a polyvinylidene fluoride-based porous layer. This composite material provides both the necessary adhesiveness through the PVDF layer and maintains flat shape by controlling the crystal form ratio (α/β ≥ 0.3), preventing the curling issue that occurs with conventional adhesive coatings.
2Duration of action of moving object
If the electrodes expand and contract repeatedly during charging and discharging, then the battery operates normally, but stress between electrodes and separator causes electrode active materials to be lost and increases internal resistance
Solution Approach 1:
The invention utilizes the curvature or irregular surface morphology of the porous layer formed by controlling crystal form α content. This curved/irregular surface structure provides better mechanical flexibility and stress distribution during electrode expansion and contraction, preventing material loss and maintaining low internal resistance throughout the battery cycle.
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, improving the discharge rate and cycle characteristics of nonaqueous electrolyte secondary batteries by maintaining electrolyte retention and ion permeability, thus enhancing battery performance.
Implementation Method 1
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
Implementation Method 2
a diminution rate of diethyl carbonate dropped on the porous base material is 15 sec/mg to 21 sec/mg; a spot diameter of the diethyl carbonate 10 seconds after the diethyl carbonate was dropped on the porous base material is not less than 20 mm
Data Source
AI summary
A 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 laminated body being arranged so that: a diminution rate of diethyl carbonate dropped on the porous base material is 15 sec/mg to 21 sec/mg; a spot diameter of the diethyl carbonate 10 seconds after the diethyl carbonate was dropped on the porous base material is not less than 20 mm; and 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. A nonaqueous electrolyte secondary battery separator made of the laminated body is not easily curled.