Polyolefin Separator with PVDF Porous Layer for High-Rate Battery Capacity
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Solution Overview
Problem
Nonaqueous electrolyte secondary batteries face limitations in charge capacity after high-rate discharge, requiring improved characteristics to enhance their performance.
Innovation Solution
Incorporating a polyolefin porous film separator with a porous layer containing a polyvinylidene fluoride-based resin, specifically with a high percentage of α-form polyvinylidene fluoride, and optimizing the capacitance of the positive and negative electrode plates to facilitate better ion solvation and desolvation, thereby improving charge capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional nonaqueous electrolyte secondary battery is used, then it has basic charge and discharge functionality, but the charge capacity characteristic deteriorates after high-rate discharge
Solution Approach 1:
The patent employs a polyolefin porous film as the battery separator with specifically controlled pore structure. The porous structure allows efficient ion transport during high-rate discharge while maintaining electrolyte retention. The film's porosity and pore size distribution are optimized to balance ion permeability and electrolyte holding capacity, enabling the battery to maintain charge capacity characteristics after high-rate discharge operations.
Solution Approach 2:
The patent implements precise parameter control including: diethyl carbonate diminution rate of 15-21 sec/mg, spot diameter of not less than 20 mm after 10 seconds, and α-form polyvinylidene fluoride content of not less than 35.0 mol %. These parameter optimizations collectively improve the separator's electrolyte retention and ion transport properties, resolving the contradiction between maintaining charge capacity and withstanding high-rate discharge conditions.
2Productivity
If the battery structure is optimized for high-rate discharge, then charge capacity improves, but internal resistance increases
Solution Approach 1:
The patent uses a composite structure combining polyolefin porous film with a porous layer containing polyvinylidene fluoride-based resin (α-form content ≥35.0 mol %). This composite material configuration optimizes both ion transport pathways and electrolyte retention, achieving high charge capacity while minimizing internal resistance through synergistic material properties.
Solution Approach 2:
The porous layer with controlled pore structure facilitates efficient ion transport, reducing resistance to ion flow. The porous structure provides multiple ion conduction pathways, lowering internal resistance while maintaining the battery's charge capacity through enhanced electrolyte distribution and ion accessibility.
3Reliability
If the polyolefin porous film retains more electrolyte, then ion solvation improves, but ion permeability decreases
Solution Approach 1:
The patent applies local quality optimization by creating distinct regions with different functions: the polyolefin porous film provides electrolyte retention and solvation zones, while the porous layer with polyvinylidene fluoride creates ion transport channels. This spatial differentiation allows simultaneous achievement of good ion solvation in the film region and high ion permeability through the porous layer channels.
Solution Approach 2:
The patent controls the diethyl carbonate diminution rate (15-21 sec/mg) and spot diameter (≥20 mm after 10 seconds) to optimize the balance between electrolyte retention and ion permeability. These parameter adjustments ensure that the separator retains sufficient electrolyte for effective ion solvation while maintaining adequate pore connectivity for fast ion transport.
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 enhances the charge capacity and discharge output of nonaqueous electrolyte secondary batteries by promoting efficient ion permeability and reducing internal resistance, especially during high-rate discharge.
Implementation Method 1
diethyl carbonate dropped on the polyolefin porous film diminishes at a rate of 15 sec/mg to 21 sec/mg; the diethyl carbonate has a spot diameter of not less than 20 mm 10 seconds after the diethyl carbonate was dropped on the polyolefin porous film
Implementation Method 2
the porous layer is provided between the nonaqueous electrolyte secondary battery separator and at least one of the positive electrode plate and the negative electrode plate
Data Source
AI summary
A nonaqueous electrolyte secondary battery including: a nonaqueous electrolyte secondary battery separator including a polyolefin porous film; a porous layer containing a polyvinylidene fluoride-based resin; a positive electrode plate having a capacitance falling within a specific range; and a negative electrode plate having a capacitance falling within a specific range, wherein: the polyolefin porous film has a given rate of diminution of diethyl carbonate and a given spot diameter of the diethyl carbonate; the porous layer is provided between the nonaqueous electrolyte secondary battery separator and at least one of the positive electrode plate and the negative electrode plate; and the polyvinylidene fluoride-based resin contained in the porous layer contains an α-form polyvinylidene fluoride-based resin in an amount of not less than 35.0 mol %.