Battery Separator Coating With Metastable Aluminum Hydroxide
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Solution Overview
Problem
The flame retardant properties of lithium secondary battery separators are non-uniform even when represented by the same chemical formula, leading to inconsistent performance and safety issues.
Innovation Solution
A separator for secondary batteries is developed using a flame retardant inorganic material that exists in both stable and metastable forms, with at least 2 wt% of the metastable form, specifically aluminum hydroxide in the form of gibbsite and polymorphs like bayerite, doyleite, and nordstrandite, ensuring consistent flame retardant properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flame retardant inorganic material is used in a separator, then flame retardant properties are improved, but the properties become non-uniform due to polymorph variations
Solution Approach 1:
The patent applies parameter changes by controlling the crystal structure parameters of aluminum hydroxide, specifically maintaining the metastable polymorph form (bayerite, doyleite, or nordstrandite) with specific lattice parameters and interlayer distances that differ from the stable gibbsite form. This parameter control ensures uniform flame retardant properties by preventing transformation to the stable but less effective polymorph form during storage and processing.
Solution Approach 2:
The patent utilizes phase transition principles by deliberately maintaining the flame retardant inorganic material in a metastable phase rather than allowing it to transform to the stable phase. The metastable polymorph form exhibits superior flame retardant performance, and the patent employs processing conditions and additives that kinetically stabilize this metastable phase, preventing unwanted phase transitions that would compromise performance uniformity.
2Object-affected harmful factors
If heat-absorbing inorganic particles are added to enhance flame retardancy, then safety at high temperature is improved, but the complexity of separator composition increases
Solution Approach 1:
The patent applies universality by selecting aluminum hydroxide as a multi-functional material that simultaneously provides flame retardancy through its decomposition reaction, heat absorption through endothermic decomposition, and physical barrier formation. This single material performs multiple safety functions, reducing the need for additional separate additives and simplifying the overall separator composition despite the enhanced safety requirements.
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 ensures that the flame retardant properties are consistently exhibited, enhancing the safety and performance of lithium secondary batteries by maintaining stability and effectiveness even at elevated temperatures.
Implementation Method 1
A flame retardant separator for secondary batteries... comprising a metal hydroxide... which absorbs heat at a certain temperature
Implementation Method 2
the flame retardant inorganic material which can exist in a stable form and a metastable form... the separator always comprises the flame retardant inorganic material in the metastable form
Data Source
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AI summary
Disclosed herein is a flame retardant separator for secondary batteries, and more particularly, a flame retardant separator for secondary batteries comprising or coated with a metal hydroxide having a low Gibbs free energy among polymorphs of a metal hydroxide used as an inorganic flame retardant.