Separator Coating with Electrospun Nanofibers for Thermal Stability

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Solution Overview

Problem

Existing separators for electrochemical devices, such as lithium secondary batteries, face challenges with safety due to thermal shrinkage of porous polyolefin substrates, leading to potential short-circuiting and separation of inorganic particles, which compromises the device's safety and performance.

Innovation Solution

A method involving a first porous coating layer with a mixture of inorganic particles and a binder polymer on a porous substrate, followed by a second porous coating layer formed through electroprocessing a polymer solution to create nanofibers, enhancing bindability and preventing particle separation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the content of inorganic particles is increased to improve thermal stability and prevent short-circuiting, then the ability to prevent short-circuiting is improved, but the bindability of the separator to electrodes deteriorates and inorganic particles separate during assembly

Engineering Contradiction:

Improveability to prevent short-circuitingVSAvoidbindability of separator to electrodes

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The coating layer is divided into two distinct layers: a first porous coating layer containing inorganic particles and binder polymer, and a second porous coating layer formed by electroprocessing. This segmentation allows the first layer to provide thermal stability with inorganic particles while the second layer provides bindability through the electroprocessed polymer structure, resolving the contradiction between particle retention and electrode adhesion.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses a composite structure combining inorganic particles with binder polymer in the first coating layer, and overlays it with a second coating layer of electroprocessed polymer. This composite approach allows the inorganic particles to provide thermal stability while the binder polymer and electroprocessed layer ensure proper bindability and prevent particle separation during assembly.

Inventive Principle:

Principle #40Composite materials

2Temperature

If the content of binder polymer is decreased to increase inorganic particle content, then the thermal stability is improved, but the bindability deteriorates causing particle separation under stress

Engineering Contradiction:

Improvethermal stabilityVSAvoidbindability

Core Design Contradiction:

TemperatureVSStrength

Solution Approach 1:

The coating is segmented into two functional layers where the first layer contains the inorganic particles and binder polymer mixture optimized for thermal stability, while the second layer formed by electroprocessing provides the necessary bindability. This segmentation allows each layer to be optimized for its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The binder polymer acts as an intermediary that holds inorganic particles together in the first coating layer, preventing their separation. The second electroprocessed coating layer serves as an intermediary between the first coating layer and the electrodes, ensuring proper adhesion while allowing the first layer to maintain high inorganic particle content for thermal stability.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 suppresses short-circuiting and improves the separator's bindability, ensuring enhanced safety and performance by maintaining porosity and preventing inorganic particle separation during handling and operation.

Implementation Method 1

electroprocessing a polymer solution on the outer surface of the first porous coating layer to form a second porous coating layer consisting of nanofibers having a diameter of 1 to 200 nm, wherein the electroprocessing is electrospinning

Methodology Applied

Scientific EffectElectrospinning: Electrohydrodynamics

Data Source

PatentEP2506339B1Method for preparing separator having porous coating layer, separator formed therefrom and electrochemical device containing same

Publication Date: 2018.01.10 LG CHEM LTD

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Figure 3

AI summary

Disclosed is a method for manufacturing a separator. The method includes (S1) preparing a slurry containing inorganic particles dispersed therein and a solution of a binder polymer in a solvent, and coating the slurry on at least one surface of a porous substrate to form a first porous coating layer, and (S2) electroprocessing a polymer solution on the outer surface of the first porous coating layer to form a second porous coating layer. The first porous coating layer formed on at least one surface of the porous substrate is composed of a highly thermally stable inorganic material to suppress short-circuiting between an anode and a cathode even when an electrochemical device is overheated. The second porous coating layer formed by electroprocessing improves the bindability of the separator to other base materials of the electrodes.