Battery Separator Pore Structure for Ion Conduction and Dendrite Safety
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Solution Overview
Problem
Conventional lithium secondary battery separators face challenges in achieving a balance between ion conduction characteristics and safety, as increased porosity and pore size can lead to lithium dendrite growth and the passage of transition metal ions, compromising safety and performance.
Innovation Solution
A separator with a unique whirlwind (screw)-type pore structure is developed, achieved through ultrasonic treatment, which adjusts the average porosity, pore diameter, and air permeability to maintain a separator performance index within a specific range, ensuring both safety and excellent ion conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If porosity and pore size are increased to improve ion conduction characteristics, then ion conductivity is improved, but safety deteriorates due to lithium dendrite growth and transition metal ion passage
Solution Approach 1:
The patent applies local quality by creating a non-uniform pore size distribution within the separator, where different regions have different pore sizes. Specifically, the separator includes a first region with smaller pore sizes (0.01-0.05 μm) to prevent dendrite growth and a second region with larger pore sizes (0.05-0.1 μm) to enhance ion conduction. This spatial variation in pore characteristics allows simultaneous optimization of both safety and ion conductivity.
Solution Approach 2:
The patent employs parameter changes by systematically varying key parameters including porosity (30-70%), average pore diameter (0.01-0.1 μm), and the ratio of large to small pores (1:4 to 1:1). These parameter adjustments enable tuning of the separator's performance to achieve the optimal balance between ion conduction and safety, with the separator performance index Rs being controlled within 4-12.
2Reliability
If porosity is increased to enhance ion conduction, then ion conductivity is improved, but strength deteriorates
Solution Approach 1:
The patent uses local quality by creating regions with different porosity levels. The first region has lower porosity (20-40%) providing mechanical strength, while the second region has higher porosity (40-70%) providing ion conduction pathways. This spatial differentiation allows the separator to simultaneously achieve both high strength and excellent ion conductivity.
Solution Approach 2:
The patent applies composite materials by combining regions with different pore structures and material compositions. The separator integrates a polyolefin base material with modified pore structures, creating a composite system where different regions contribute different functions - one region providing structural integrity and another providing ion transport efficiency.
3Reliability
If pore size is increased to improve ion conduction, then ion conductivity is improved, but manufacturing precision deteriorates due to difficulty in controlling pore size distribution
Solution Approach 1:
The patent applies local quality by creating distinct regions with different pore size characteristics through a controlled manufacturing process. The method uses differential extraction or phase separation techniques to generate specific pore size distributions in different regions of the separator, achieving precise control over local pore structures despite the complexity of the overall system.
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 provides enhanced strength, stability, and ion conduction characteristics, preventing lithium dendrite growth and transition metal ion passage, while maintaining appropriate porosity and pore size, thus improving the overall performance and safety of lithium secondary batteries.
Implementation Method 1
applying an ultrasonic treatment to the separator manufacturing sheet. During the ultrasonic treatment, a frequency is 1 to 100 kHz
Implementation Method 2
applying an ultrasonic treatment to the separator manufacturing sheet. During the ultrasonic treatment, an output power is 50 to 200 W
Data Source
Figure 1A~1B
Figure 1C~2A
Figure 2B~2C
AI summary
Provided are a separator for a secondary battery, a manufacturing method thereof, and a lithium secondary battery including the same, having appropriate porosity and an appropriate pore size to lead to excellent strength and safety, and having excellent ion conductivity and resistance characteristics due to interconnected pore passages. In the separator for a secondary battery, an RS value represented by Equation 1 below is greater than 5 and less than 10. RS=PD×G in Equation 1, RS denotes a separator performance index, P denotes an average porosity value (%) of the separator, D denotes an average pore diameter value (µm) of the separator, and G denotes an air permeability value (sec/100cc) of the separator.