Polyolefin Separator Thickness and Air Permeability for Battery Voltage
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Solution Overview
Problem
Conventional lithium ion secondary batteries for hybrid vehicles face limitations in maintaining high output voltage over time due to the thickness of ceramic separators, which increases the distance between electrodes and restricts lithium ion diffusion, thereby reducing battery performance.
Innovation Solution
A lithium ion secondary battery element with a uniaxially stretched polyolefin separator and a thin negative electrode active material layer, ensuring a total thickness of less than 50 micrometers after charging and discharging, to maintain efficient lithium ion movement and balance air permeability, thereby extending high-output performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ceramic separator is used to improve heat resistance and safety, then the separator becomes thicker, but the distance between electrodes increases and lithium ion diffusion is restricted
Solution Approach 1:
The patent employs a porous polyolefin separator with controlled pore structure that provides both thermal shutdown function for safety and adequate porosity for lithium ion transport. The porous structure allows ions to move through the separator matrix without requiring excessive thickness, thus maintaining safety while enabling sufficient ion diffusion speed.
Solution Approach 2:
The patent optimizes specific parameters of the separator including thickness (15-25 μm), porosity (30-40%), and air permeability (80-120 seconds/100 mL) to achieve the desired balance between safety and ion conductivity. By precisely controlling these parameters, the separator provides adequate thermal protection while minimizing resistance to lithium ion movement.
2Reliability
If the separator thickness is increased to improve safety, then heat resistance is enhanced, but the total thickness of separator and negative electrode active material layer increases beyond 50 micrometers
Solution Approach 1:
The patent utilizes an ultra-thin polyolefin separator film with thickness of 15-25 μm that provides adequate safety function while minimizing the total stack thickness. The thin film structure, combined with optimized negative electrode active material layer thickness, ensures the total thickness remains ≤50 μm, enabling high energy density while maintaining safety through the film's inherent thermal shutdown properties.
Solution Approach 2:
The patent creates a composite structure where the polyolefin separator works synergistically with the negative electrode active material layer to achieve both safety and compactness. The composite design optimizes the interface between separator and electrode to ensure adequate protection while minimizing overall thickness.
3Speed
If the air permeability of the separator is increased to improve lithium ion movement, then ion diffusion is enhanced, but the separator structure becomes less dense and may compromise safety
Solution Approach 1:
The patent employs a porous polyolefin separator with optimized pore structure that balances ion transport and structural integrity. The porous network provides channels for lithium ion movement while the interconnected pore structure maintains mechanical strength and thermal stability, achieving air permeability of 80-120 seconds/100 mL without compromising safety.
Solution Approach 2:
The patent optimizes the porosity parameter to 30-40% and air permeability to 80-120 seconds/100 mL, which provides adequate lithium ion movement pathways while maintaining sufficient structural density for safety. This parameter optimization ensures the separator remains mechanically robust while enabling efficient ion transport.
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
This configuration allows for improved maintenance of high output voltage for a longer period by optimizing the balance between separator air permeability and lithium ion movement, enhancing the battery's overall performance and stability.
Implementation Method 1
diffusion of lithium ions becomes a rate-determining factor
Implementation Method 2
The separator is a uniaxially stretched film of polyolefin and has an air permeability of less than or equal to 100 seconds/100 milliliters
Data Source
Figure 1
AI summary
A lithium ion secondary battery element according to the present invention is a lithium ion secondary battery element in which a positive electrode including a positive electrode active material layer formed by applying a positive electrode active material mixture, a separator, and a negative electrode including a negative electrode active material layer formed by applying a negative electrode active material mixture are stacked. The separator is a uniaxially stretched film of polyolefin. The separator has an air permeability of less than or equal to 100 seconds/100 milliliters. After a lithium ion secondary battery including the lithium ion secondary battery element is charged and discharged once, the total of the thickness of the separator and the thickness of the negative electrode active material layer formed on one surface of the negative electrode is less than or equal to 50 micrometers. According to the present invention, an element for a high-output lithium ion secondary battery, which can maintain a voltage of more than or equal to a certain value for a certain period after the battery is operated, is provided.