Ordered Porous Polyimide Separator for Lithium Dendrite Control
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Solution Overview
Problem
Lithium secondary batteries face issues with dendritic lithium growth due to nonuniform current distribution, leading to short circuits and reduced performance, as conventional separators with random pores fail to control lithium ion diffusion effectively.
Innovation Solution
A lithium secondary battery separator with a porous heat-resistant polyimide film having three-dimensionally ordered pores, specifically a hexagonal close-packed structure, is developed, which controls lithium ion diffusion and current density uniformly, preventing dendritic lithium growth and ensuring high ionic conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a separator with random pores is used, then the separator can be manufactured easily, but lithium ion diffusion is nonuniform causing dendritic lithium growth
Solution Approach 1:
The patent employs a porous polymer film with three-dimensionally ordered pores (3DOM structure) having a hexagonal close-packed arrangement. This ordered porous structure enables uniform lithium ion diffusion throughout the separator, preventing localized current density spikes that cause dendritic lithium growth, while maintaining manufacturing feasibility through colloidal crystal template methods.
Solution Approach 2:
The patent transforms the pore structure from random to three-dimensionally ordered with specific geometric parameters (hexagonal close-packed arrangement, controlled pore size of 50-2500 nm, porosity of 60% or higher). This parameter change in pore organization fundamentally alters lithium ion transport behavior, ensuring uniform diffusion and preventing dendrite formation.
2Strength
If the separator film is made thick, then mechanical strength is improved, but ohmic resistance increases making the battery non-functional
Solution Approach 1:
The three-dimensionally ordered porous structure provides high porosity (60% or higher) which allows the separator to maintain low ohmic resistance even at reduced thickness. The ordered pore network facilitates efficient electrolyte distribution and uniform ion transport, enabling thin films to achieve both mechanical adequacy and low electrical resistance.
Solution Approach 2:
The separator functions as a composite structure combining the polymer matrix with the ordered porous architecture. This composite design allows optimization of both mechanical properties (through the polymer framework) and ionic conductivity (through the ordered pore network), resolving the trade-off between strength and ohmic resistance.
3Reliability
If a porous resin film with high porosity is used, then ionic conductivity is improved, but production cost increases due to film thickness
Solution Approach 1:
The patent optimizes the pore size parameter to 50-2500 nm and porosity to 60% or higher, achieving high ionic conductivity. The three-dimensional ordered structure maximizes electrolyte filling efficiency, allowing high porosity without proportionally increasing film thickness, thus controlling production costs while maintaining superior ionic conductivity.
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 suppresses dendritic lithium growth, preventing short circuits and enhancing cycle characteristics by maintaining uniform ion current density and high ionic conductivity, while being thinner and more cost-effective than previous designs.
Implementation Method 1
the diffusion of lithium ions is controlled, ion current density is made uniform, and lithium deposition reaction is uniformly controlled
Implementation Method 2
a porous heat-resistant polyimide film having three-dimensionally ordered pores... to ensure high ionic conductivity by retaining an electrolyte
Data Source
AI summary
Provided is a lithium secondary battery separator including a laminate of a substrate and a porous heat-resistant polyimide film which covers at least one surface of the substrate. The porous heat-resistant polyimide film has pores which are regularly arrayed three-dimensionally and a film thickness of 5-20 μm. Penetration damage to the separator by growth of dendrite-shaped lithium is avoided, and it is also possible to meet a request which is demanded of the lithium secondary battery separator.