Asymmetric Flame-Retardant Separator for Li-Ion Precipitation Risk

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Solution Overview

Problem

Lithium secondary batteries face risks due to lithium ion precipitation in the negative electrode, and existing separators lack effective flame retardant properties and electrochemical stability, particularly when using hydroxide-based inorganic coatings.

Innovation Solution

An electrochemical device with a polyolefin-based separator having a hydroxide inorganic flame retardant coating on the surface facing the positive electrode and a binder and inorganic particle coating on the surface facing the negative electrode, with specific weight ratios and materials to enhance flame retardancy and maintain electrochemical properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a hydroxide-based inorganic flame retardant is coated on the separator surface, then flame retardant performance is improved, but water release may react with Li ions causing safety risks

Engineering Contradiction:

Improveflame retardant performanceVSAvoidwater release reaction with Li ions

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent applies different coating materials to different surfaces of the separator. The hydroxide-based inorganic flame retardant is coated only on the separator surface facing the positive electrode, while the surface facing the negative electrode uses a different coating or no coating. This local differentiation allows flame retardancy where needed while avoiding water release reactions with lithium ions at the negative electrode interface.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent introduces an intermediary layer or alternative coating material between the flame retardant requirement and the lithium ion environment. By using a binder resin layer or other coating materials on the negative electrode side, it mediates the interaction between potential water release and lithium ions, preventing harmful reactions while maintaining flame safety.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If the separator uses a symmetric coating structure, then manufacturing simplicity is improved, but electrochemical performance and safety are compromised

Engineering Contradiction:

Improvecoating structure simplicityVSAvoidelectrochemical performance and safety

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent explicitly adopts an asymmetric coating structure where the separator surfaces facing the positive and negative electrodes have different coating configurations. This asymmetry is designed to match the different electrochemical environments and reaction characteristics at each electrode interface, optimizing both safety and performance.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

Different coating materials and thicknesses are applied to different surfaces of the separator based on the specific requirements of each electrode interface. The positive electrode side receives flame retardant coating while the negative electrode side has different treatment, creating localized optimization for each region's specific needs.

Inventive Principle:

Principle #3Local quality

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 effectively prevents lithium ion precipitation, enhances flame retardant performance, and maintains similar electrochemical characteristics to conventional inorganic coating separators, while ensuring thermal stability and preventing battery damage from external impacts.

Implementation Method 1

The hydroxide-based inorganic flame retardant absorbs heat at a certain temperature and is used in various resins and the like. The hydroxide-based inorganic flame retardant releases water when it absorbs heat.

Methodology Applied

Scientific EffectHeat absorption: Heat Sink

Implementation Method 2

It is necessary for the separator to electrically isolate the positive electrode and the negative electrode from each other and to exhibit high ion permeability

Methodology Applied

Scientific EffectIon permeability: Permeation

Data Source

PatentEP3648197B1Electrochemical device including a flame retardant separator having an asymmetric structure

Publication Date: 2023.09.20 LG ENERGY SOLUTION LTD

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AI summary

Disclosed herein is a flame retardant separator for secondary batteries having an asymmetric structure, and more particularly, a flame retardant separator for secondary batteries having an asymmetric structure in which a hydroxide-based inorganic flame retardant is coated on only a surface facing a positive electrode. The present invention provides a separator, in which is capable of preventing the risk of lithium ions predominantly precipitated from a negative electrode in a lithium secondary battery, enhancing the flame retardant effect, and maintaining electrochemical properties in contrast with a conventional separator coated with inorganic matters, and a lithium secondary battery including the same.