Porous Separator Alkali Control for Battery Stability
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Solution Overview
Problem
Lithium secondary batteries face capacity degradation due to alkali metal elements, particularly sodium, which contaminate the separator and cause side reactions with the nonaqueous electrolyte, leading to reduced charge/discharge cycle characteristics and long-term storage performance.
Innovation Solution
A porous film separator is developed using inorganic oxide particles, such as boehmite, with reduced alkali metal content (≤1000 ppm) and a binder, integrated with a microporous film and heat-melting resin layer, to prevent alkali metal intrusion and maintain battery stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If filler particles are used to ensure heat resistance, then separator stability at high temperatures is improved, but long-term storage characteristic deteriorates due to alkali metal intrusion
Solution Approach 1:
The patent applies parameter changes by strictly controlling the alkali metal content levels in the filler particles (Na ≤ 1000 ppm, K ≤ 500 ppm, Li ≤ 100 ppm) while maintaining the heat resistance properties. This ensures the separator remains stable at high temperatures during storage without introducing alkali metals that would cause capacity degradation over time.
Solution Approach 2:
The patent employs surface treatment or coating on the filler particles that provides a protective barrier against alkali metal release. This surface layer acts as a sacrificial component that prevents alkali metals from migrating into the battery electrolyte during long-term storage, thus preserving the battery's storage characteristics while maintaining the thermal stability provided by the filler particles.
2Ease of manufacture
If conventional separators are used, then manufacturing simplicity is maintained, but size stableness at high temperatures deteriorates due to shrinkage
Solution Approach 1:
The patent uses composite materials consisting of heat-resistant inorganic oxide filler particles (such as alumina, silica) dispersed in a polymer matrix. This composite structure provides dimensional stability at high temperatures while maintaining compatibility with conventional separator manufacturing processes, thus resolving the contradiction between ease of manufacture and size stableness.
Solution Approach 2:
The patent employs porous inorganic oxide structures that provide thermal stability and prevent shrinkage at high temperatures. The porous structure allows the separator to maintain its dimensional integrity under thermal stress while being compatible with standard manufacturing techniques, thereby resolving the contradiction between manufacturing simplicity and high-temperature size stability.
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 solution enhances the reliability and stability of lithium secondary batteries by minimizing capacity loss over extended use and storage, preventing short circuits and maintaining performance across multiple charge/discharge cycles and long-term storage.
Implementation Method 1
alkali metal elements, particularly Na, get inside the lithium secondary battery, causing deterioration of the charge/discharge cycle characteristic and long-term storage characteristic
Implementation Method 2
a microporous film including a heat-melting resin layer having a melting point of 80 to 140° C.
Data Source
AI summary
The present invention provides a lithium secondary battery using a separator including a porous film formed by binding inorganic oxide particles together with a binder. The inorganic oxide particles are treated so that an amount of alkali metal elements eluted therefrom when they are immersed in ion exchange water is reduced to 1000 ppm or less. As a result, it is possible to provide a lithium secondary battery with a high degree of reliability, whose characteristics deteriorate less when it is used or stored for an extended period.