Laminated Battery Separator with Porous Resin Layer
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Solution Overview
Problem
Conventional nonaqueous electrolyte secondary battery separators face issues with poor liquid injection easiness, inadequate dielectric strength, and a high likelihood of curls, which affect battery performance and safety.
Innovation Solution
A laminated body comprising a porous film with a polyolefin main component and a porous layer containing a resin, where the critical surface tension difference between the outermost surface and the interface is controlled, and the resin content is optimized to enhance dielectric strength and prevent curls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a porous film containing polyolefin as a main component is used as a separator, then the shutdown function is achieved through melting at elevated temperatures, but the film structure breaks at high temperatures not lower than the melting point, causing short circuit
Solution Approach 1:
The invention uses a composite structure consisting of a polyolefin base material layer and a heat-resistant porous layer. The heat-resistant porous layer contains heat-resistant resin (such as polyacrylic acid or carboxymethyl cellulose) and inorganic filler (such as alumina or silica), creating a composite material that combines the low-temperature shutdown capability of polyolefin with the high-temperature structural stability of heat-resistant materials.
2Reliability
If a porous film containing polyolefin as a main component is used as a separator, then the shutdown function is achieved, but the separator adheres poorly to electrodes, decreasing battery capacity and cycle characteristic
Solution Approach 1:
The invention applies different functional layers with distinct properties: the polyolefin base material layer provides shutdown function, while the heat-resistant porous layer with specific surface treatment (plasma treatment or corona treatment) provides enhanced adhesiveness to electrodes. This local differentiation of material properties resolves the contradiction between shutdown functionality and electrode adhesion.
3Reliability
If the separator structure is modified to improve heat resistance and adhesion, then safety and performance are enhanced, but the liquid injection easiness deteriorates
Solution Approach 1:
The invention employs a porous structure in both the base material layer and the heat-resistant porous layer, with controlled porosity (30-80%) and pore size (0.01-10 μm). This porous architecture maintains liquid injection easiness by providing capillary channels for electrolyte penetration while the heat-resistant resin and inorganic filler within the porous structure ensure safety and structural integrity at elevated temperatures.
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 improves liquid injection easiness, increases dielectric strength, and prevents curls, leading to better battery performance and safety by ensuring effective ion permeability and adhesion to electrodes.
Implementation Method 1
a porous layer on at least one surface of the porous film, the porous layer containing a resin
Implementation Method 2
the critical surface tension difference between the outermost surface and the interface is controlled
Implementation Method 3
the resin content is optimized to enhance dielectric strength
Implementation Method 4
a laminated body comprising a porous film with a polyolefin main component and a porous layer containing a resin
Data Source
AI summary
A nonaqueous secondary battery separator, disposed between a cathode and an anode, includes: a porous base material containing a polyolefin as a main component; and a porous layer containing a polyvinylidene fluoride-based resin on at least one surface of the porous base material. The separator satisfies (C)/(D)≤0.13, where (C) represents the average pore diameter (μm) of the porous base material, and (D) represents the porosity of the porous base material, in the porous layer after being immersed for 24 hours in an electrolyte solution having a temperature of 25° C. in which electrolyte solution LiPF6 having a concentration of 1.0 mole per liter is dissolved in a mixed solvent containing ethyl methyl carbonate, diethyl carbonate, and ethylene carbonate at a volume ratio of 50:20:30, the resin having absorbed the electrolyte solution having a volume of 0.05 to 5.00 cm3 per square meter of the porous layer.