Wound Battery Separator Design for Cycle Life
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Solution Overview
Problem
Secondary batteries with wound electrode assemblies face issues due to concentration gradients of the electrolytic solution, leading to decreased output and adverse effects on cycle characteristics, as the existing solutions do not adequately address the degradation of separators during repeated charging and discharging cycles.
Innovation Solution
A secondary battery design featuring a wound electrode assembly with a first separator and a second separator, where the second separator has a larger thickness and porosity than the first, and at least one of them includes a heat-resistant layer, arranged such that the second separator is on the inner side to retain more electrolytic solution and resist collapse, thereby enhancing cycle characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a wound electrode assembly is used to achieve compact battery structure, then energy density is improved, but concentration gradient of electrolytic solution increases leading to decreased output and poor cycle characteristics
Solution Approach 1:
The separator is divided into two distinct parts: a first separator with smaller thickness disposed on the positive electrode side, and a second separator with larger thickness disposed on the negative electrode side. This segmentation allows each separator to be optimized for its specific location, with the thicker second separator compensating for the reduced porosity in the inner region of the wound electrode assembly where concentration gradient is most severe.
Solution Approach 2:
Different regions of the battery are provided with different separator thicknesses to match the local electrolytic solution distribution. The inner region (second separator location) which suffers from higher curvature and reduced porosity is provided with a thicker separator to hold more electrolytic solution, while the outer region (first separator location) uses a thinner separator. This local optimization ensures uniform ion migration throughout the electrode assembly.
2Reliability
If separator thickness is increased to improve solution retention, then cycle characteristics are improved, but battery size and complexity increase
Solution Approach 1:
Instead of uniformly increasing separator thickness throughout the battery, the invention applies different thicknesses locally: the first separator has smaller thickness while the second separator has larger thickness. This localized approach improves solution retention and cycle characteristics in the critical inner region without unnecessarily increasing overall battery size or complexity.
Solution Approach 2:
The separator system is segmented into two functional parts with different thicknesses, allowing each part to perform its specific function optimally. The first separator provides basic separation and ion transport, while the second separator specifically addresses the electrolytic solution retention issue in the inner region, thereby improving cycle characteristics without requiring a complete redesign of the entire separator 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
This configuration effectively reduces the concentration gradient, maintains solution retention ability over long periods, and enhances the durability and cycle characteristics of the battery by suppressing separator degradation and ensuring uniform ion migration.
Implementation Method 1
the second separator includes a second porous film having a porosity P2
Implementation Method 2
at least one of the first separator and the second separator includes a heat resistant layer
Implementation Method 3
If an electrolytic solution has a concentration gradient, ions migrate at nonuniform speeds
Data Source
AI summary
A secondary battery includes an electrode assembly including a positive electrode, a negative electrode, a first separator disposed on one side of the surface of the negative electrode and having a thickness T1, and a second separator disposed on the other side of the surface of the negative electrode and having a thickness T2. The thickness T2 of the second separator is larger than the thickness T1 of the first separator. The first separator includes a first porous film having a porosity P1, and the second separator includes a second porous film having a porosity P2. At least one of the first separator and the second separator includes a heat resistant layer. The positive electrode, the first separator, the negative electrode and the second separator are wound together such that the first separator is arranged on the outer side and the second separator is arranged on the inner side.