Composite Separator for Non-Aqueous Electrolyte Battery
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Solution Overview
Problem
Non-aqueous electrolyte secondary batteries face reduced cycle performance due to the compression and deformation of separators, which affects the migration of lithium ions and increases battery resistance, despite existing improvements in impedance and air permeability.
Innovation Solution
A separator with a dynamic hardness of 1000 or more, comprising a porous layer with polyolefin and a heat-resistant resin layer, maintaining porosity between 35% and 65% and thermal deformation temperature of 160°C or more, to prevent compression and ensure lithium ion migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the separator is made porous to facilitate lithium ion migration, then the battery resistance is reduced, but the separator becomes easily compressed or deformed under internal pressure
Solution Approach 1:
The separator is constructed as a composite material consisting of a polyolefin base layer combined with a heat-resistant resin layer. This composite structure provides both the porosity needed for lithium ion migration and the mechanical strength to resist compression under internal pressure, resolving the contradiction between permeability and structural integrity.
Solution Approach 2:
The invention changes the physical parameters of the separator by controlling the porosity within a specific range (30-70%) and specifying the dynamic hardness (1000 or more). These parameter optimizations ensure the separator maintains adequate pore volume for ion transport while possessing sufficient rigidity to withstand battery internal pressure without excessive deformation.
2Productivity
If the separator porosity is increased to improve lithium ion migration, then the battery resistance is reduced, but the separator becomes more susceptible to compression and deformation
Solution Approach 1:
The invention optimizes the porosity parameter within a specific range (30-70%) rather than maximizing it. This controlled parameter change ensures adequate pore volume for lithium ion migration while maintaining sufficient structural stability to prevent excessive compression and deformation under battery operating conditions.
Solution Approach 2:
The composite structure combining polyolefin and heat-resistant resin creates a synergistic effect where the heat-resistant resin provides structural stability and compression resistance while the polyolefin matrix maintains the necessary porosity for ion transport, resolving the contradiction between productivity and stability.
3Reliability
If the separator is compressed to increase contact between electrodes, then the electrical connection is improved, but the voids in the separator are decreased, inhibiting lithium ion migration
Solution Approach 1:
The invention specifies that the pore shape should be substantially spherical rather than flattened. Spherical pores maintain their volume more effectively under compression forces compared to flattened pores, allowing the separator to maintain both good electrical contact and adequate pore volume for lithium ion migration during battery operation.
Solution Approach 2:
The heat-resistant resin component in the composite separator provides enhanced mechanical support that prevents excessive compression of the porous structure. This maintains the pore volume necessary for ion migration while still allowing sufficient electrode contact for reliable electrical connection.
4Ease of manufacture
If a single-layer polyolefin separator is used to simplify structure, then the manufacturing is easier, but the separator cannot maintain dynamic hardness of 1000 or more while preserving porosity
Solution Approach 1:
The invention uses a composite structure of polyolefin and heat-resistant resin to achieve the required dynamic hardness of 1000 or more while maintaining adequate porosity (30-70%). Although more complex than a single-layer structure, this composite approach enables both high cycle performance and the necessary mechanical properties that a single polyolefin layer cannot achieve alone.
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 separator effectively maintains cycle performance by preventing compression and deformation, ensuring lithium ion migration and reducing battery resistance, even under elevated internal pressure, and provides safety at high temperatures.
Implementation Method 1
the amount of electrolyte impregnated into the voids of the separator is decreased, inhibiting the migration of lithium ions
Implementation Method 2
the separator effectively maintains cycle performance by preventing compression and deformation
Data Source
AI summary
In a non-aqueous electrolyte secondary battery, a separator in which its dynamic hardness DH obtained when the load to an indenter reaches 12 kgf/cm2 is 1000 or more is used. This separator includes at least one porous layer X including a polyolefin, and at least one porous layer Y including a heat resistant resin. The porosity of the porous layer X is 35% or more and 65% or less. In a pore size distribution of the porous layer X measured with a mercury porosimeter, a ratio of pores having a pore size of 0.02 μm or more and 0.2 μm or less is 40 vol % or more relative to a total pore volume. The thermal deformation temperature of the heat resistant resin is 160° C. or more.