Ion-Trapping Separator Coating for Battery Cycle Stability
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Solution Overview
Problem
Secondary batteries experience performance degradation due to the dissolution of transition metal ions from positive electrode materials, which disrupt structural stability, migrate to the negative electrode, and catalyze electrolyte decomposition, leading to reduced cycling performance.
Innovation Solution
A separator with a coating containing an ion-trapping agent having a reduction potential of 0 V to 2 V relative to lithium metal is used, capable of reducing dissolved transition metal ions into low-valence ions or elemental metal, and also reduces H+ to enhance mechanical strength and reduce direct contact with electrode materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional separator is used, then the battery structure is simple, but transition metal ions dissolve and migrate to the negative electrode, causing electrolyte decomposition and performance degradation
Solution Approach 1:
The ion-trapping agent is pre-loaded into the separator coating layer before battery assembly. This preliminary action enables the separator to proactively reduce transition metal ions as soon as they dissolve from the positive electrode, preventing their migration to the negative electrode and subsequent electrolyte decomposition, thereby improving cycling performance without requiring complex external systems
Solution Approach 2:
The ion-trapping agent in the separator coating acts as an intermediary substance between the positive and negative electrodes. It mediates the interaction by reducing transition metal ions that dissolve from the positive electrode, converting them into insoluble forms that precipitate near the separator, thus preventing direct contact between harmful ions and the negative electrode while avoiding the need for complex protective systems
2Strength
If the separator has high mechanical strength, then the battery structure is stable, but the separator cannot effectively reduce transition metal ions and remove acidic substances
Solution Approach 1:
The separator is constructed as a composite structure combining base film materials (such as polyolefin or ceramic) that provide high mechanical strength with a coating layer containing ion-trapping agents (such as lithium-containing compounds or transition metal compounds). This composite design enables the separator to simultaneously achieve robust mechanical properties for structural stability and effective ion-trapping capability for reducing transition metal ions and removing acidic substances like HF
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 ion-trapping agent mitigates electrolyte decomposition and improves cycling performance by stabilizing the electrode interface, while enhancing mechanical strength and removing acidic substances, thus improving the overall performance of the secondary battery.
Implementation Method 1
a reduction potential of the ion-trapping agent relative to lithium metal is 0 V to 2 V... the ion-trapping agent is capable of reducing the dissolved transition metal ions in the secondary battery into low-valence ions that are less prone to dissolution or into elemental metal
Implementation Method 2
since a reduction potential of H+ relative to lithium metal is higher than that of transition metal ions relative to lithium metal, the ion-trapping agent is also capable of reducing H+ in a battery cell, thereby serving to remove acidic substances (such as HF, organic acid RH+, or H radicals) from the electrolyte
Data Source
AI summary
Embodiments of the present application provide a separator, a preparation method thereof, a secondary battery, and an electric apparatus. The separator includes a first base film, a coating, and a second base film, where the coating is disposed between the first base film and the second base film, the coating includes an ion-trapping agent, and a reduction potential of the ion-trapping agent relative to lithium metal is 0 V to 2 V. A secondary battery containing the separator exhibits improved cycling performance.