Microporous Film Separator for Lithium-Ion Battery Dendrite Control
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Solution Overview
Problem
Existing polypropylene microporous films and multilayer porous membranes have insufficient lithium ion permeability and non-uniform pore formation, leading to dendrite formation and short circuits in high-power lithium ion batteries, which compromises their long-term safety and discharge capacity.
Innovation Solution
A synthetic resin microporous film with a specific structure, comprising support portions and fibrils that form micropores, is developed, featuring a controlled number of branch structures and optimized molecular weight distribution, which enhances lithium ion permeability and mechanical strength, preventing dendrite formation and maintaining gas permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polypropylene microporous film is manufactured by conventional stretching methods, then the film structure is formed, but the gas permeability and lithium ion permeability are insufficient
Solution Approach 1:
The patent applies parameter changes by controlling the molecular weight distribution (specifically Mw/Mn ratio between 3-10) and using biaxial stretching with specific temperature and strain rate parameters to achieve optimal pore structure and lithium ion permeability
Solution Approach 2:
The patent uses composite material approach by combining polypropylene with specific molecular weight distribution characteristics and controlling the crystalline structure to create a separator with enhanced lithium ion permeability while maintaining mechanical strength
2Reliability
If pores are formed in polypropylene film to improve lithium ion permeability, then permeability increases, but pores become non-uniform causing dendrite formation
Solution Approach 1:
The patent achieves uniform pore distribution by precisely controlling processing parameters including biaxial stretching temperature (below melting point), strain rate (10-100%/min), and molecular weight distribution, resulting in consistent pore size and spacing that prevents dendrite formation
Solution Approach 2:
The patent segments the pore structure into uniform micropores distributed throughout the film by controlling the stretching process to create regularly spaced voids between crystalline regions, ensuring consistent lithium ion flow paths
3Productivity
If the separator has high gas permeability to support high power batteries, then lithium ion transmission improves, but mechanical strength may decrease
Solution Approach 1:
The patent optimizes the balance between permeability and strength by controlling molecular weight distribution (Mw/Mn = 3-10) and crystalline structure through biaxial stretching, achieving high gas permeability (150-500 mL/min) while maintaining adequate mechanical strength for battery application
Solution Approach 2:
The patent creates a controlled porous structure through biaxial stretching that provides high gas and lithium ion permeability for high power output while the pore size and distribution are controlled to maintain structural integrity and mechanical strength
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 synthetic resin microporous film ensures high lithium ion permeability and mechanical strength, reducing the risk of dendrite formation and short circuits, thus enabling high-power and long-lasting power storage devices with improved safety and performance.
Implementation Method 1
a separator is required to favorably transmit lithium ions
Implementation Method 2
it is also important for large-sized lithium ion batteries to reliably have long lifetime and long-term safety
Data Source
AI summary
The present invention provides a synthetic resin microporous film which has excellent permeability of lithium ions, can constitute high performance power storage devices, and is less likely to cause a short circuit between a positive electrode and a negative electrode as well as rapid decrease in discharge capacity due to a dendrite even when used in high power applications. The synthetic resin microporous film of the present invention is a synthetic resin microporous film comprising a synthetic resin, the synthetic resin microporous film being stretched, the synthetic resin microporous film having, in a cross section along a thickness direction and a stretching direction of the synthetic resin microporous film: a plurality of support portions extending in the thickness direction of the synthetic resin microporous film; a plurality of fibrils formed between the support portions; and the support portions having the number of branch structures of 150 or less per 100 μm2; and the synthetic resin microporous film being configured such that micropore portions are formed in areas surrounded by the support portions and the fibrils.