Polyolefin Separator with Heat-Resistant Layer for Battery Safety
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Solution Overview
Problem
Lithium secondary batteries face challenges in increasing energy density while maintaining ion permeability and preventing leak defects, particularly due to the damage caused by cathode and anode bumps to the separator and the resulting insulation issues.
Innovation Solution
A nonaqueous electrolyte secondary battery separator with a porous film made of polyolefin, having a thickness of 3 μm to 16 μm and a Gurley value of 50 sec/100 cc to 200 sec/100 cc, which satisfies the formula 0.85≤((SMD/Sm)+(STD/Sm))/2≤0.91, optimizing melting behavior under tension and no tension to reduce leak defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the separator thickness is reduced to increase energy density, then the energy density is improved, but the insulation function deteriorates due to damage from cathode and anode bumps
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin base layer providing mechanical strength and a heat-resistant resin layer providing insulation protection. This composite structure allows the separator to maintain thin dimensions for high energy density while the heat-resistant layer compensates for insulation loss due to bump damage.
Solution Approach 2:
The invention changes the thermal parameter of the separator by incorporating heat-resistant resin with a higher melting point than the polyolefin base layer. This parameter change enables the separator to withstand mechanical stress from bumps without compromising insulation, even at reduced thickness.
2Reliability
If the porosity of the separator is decreased to prevent leak defects, then the reliability is improved, but the ion permeability deteriorates
Solution Approach 1:
The separator employs local quality differentiation where the polyolefin base layer provides porosity for ion permeability while the heat-resistant resin layer provides structural integrity to prevent leaks. Each layer has optimized properties for its specific function, resolving the contradiction between porosity and leak prevention.
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 achieves excellent ion permeability and reduces the occurrence of leak defects, enabling a higher energy density without compromising safety.
Implementation Method 1
a porous film made of a material that is meltable in the event of abnormal heat generation... the porous film to be melted and made non-porous in the event of abnormal heat generation to block the ion passage
Implementation Method 2
a shutdown function, which is a function of a separator blocking passage of ions between the anode and the cathode in the event of abnormal heat generation
Data Source
AI summary
Provided is a nonaqueous electrolyte secondary battery separator that has (i) an excellent ion permeability and (ii) reduced occurrence of a leak defect despite a small thickness. The nonaqueous electrolyte secondary battery separator includes a porous film containing polyolefin as a main component, the nonaqueous electrolyte secondary battery separator having a Gurley value within a range of 50 sec/100 cc to 200 sec/100 cc, the nonaqueous electrolyte secondary battery separator having a thickness within a range of 3 μm to 16 μm, the nonaqueous electrolyte secondary battery separator satisfying 0.85≤((SMD/Sm)+(STD/Sm))/2≤0.91.