Secondary Battery Separator Thermal Shrinkage Control

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Solution Overview

Problem

In secondary batteries, the exposure of electrode mixture layers due to separator turning or rising can lead to micro-short circuits, especially when using thermocompression bonding with separators having different thermal shrinkage rates, increasing the risk of internal short circuits.

Innovation Solution

A secondary battery design featuring a separator with a first layer having a higher thermal shrinkage rate and a second layer with a smaller thermal shrinkage rate, forming a tubular portion to cover the outermost surfaces of the electrode assembly, where the first layer faces the inner side and the second layer faces the outer side, preventing exposure of the mixture layers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If thermocompression bonding is performed using a separator with multiple layers having different thermal shrinkage rates, then bonding strength is improved, but the end of the separator turns up more, causing exposure of the electrode mixture layer

Engineering Contradiction:

Improvebonding strengthVSAvoidseparator end position

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The separator is divided into multiple layers with different thermal shrinkage rates. The first layer has a larger thermal shrinkage rate and the second layer has a smaller thermal shrinkage rate. This segmentation allows each layer to contribute differently to the overall performance, with the first layer providing bonding strength through greater shrinkage and the second layer preventing end-turning through lesser shrinkage.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the separator structure are assigned different properties. The first layer (inner layer) is designed with high thermal shrinkage for bonding, while the second layer (outer layer) is designed with low thermal shrinkage for end-stability. This local differentiation of properties resolves the contradiction between needing high shrinkage for bonding and low shrinkage for preventing end-turning.

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If the separator end turns up during thermocompression bonding, then bonding process is simplified, but the electrode mixture layer becomes exposed, causing micro-short circuits

Engineering Contradiction:

Improvebonding process simplicityVSAvoidinternal short circuit prevention

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The second layer with smaller thermal shrinkage rate is prepared in advance as a protective layer on the outer side of the separator. This layer acts as a cushion that prevents the separator end from turning up and exposing the electrode mixture layer, thereby preventing micro-short circuits before they can occur during the bonding process.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Device complexity

If a single-layer separator is used, then device complexity is reduced, but it cannot simultaneously achieve high bonding strength and prevent end-turning

Engineering Contradiction:

Improveseparator structureVSAvoidprevention of electrode exposure

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The separator is constructed as a composite structure with two different layers, each having distinct thermal shrinkage characteristics. The first layer (inner) has larger thermal shrinkage for bonding, while the second layer (outer) has smaller thermal shrinkage for preventing end-turning. This composite structure enables the separator to simultaneously achieve both high bonding strength and end-stability, which would be impossible with a single-layer separator.

Inventive Principle:

Principle #40Composite materials

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

This configuration effectively prevents the exposure of electrode mixture layers and subsequent micro-short circuits by controlling thermal shrinkage, maintaining the shape of the separator and ensuring the integrity of the battery.

Implementation Method 1

the separator includes a first layer and a second layer having a thermal shrinkage rate smaller than that of the first layer

Methodology Applied

Scientific EffectThermal shrinkage: Thermal Contraction

Data Source

PatentUS20230036396A1Secondary battery

Publication Date: 2023.02.02 SANYO ELECTRIC CO LTD

AI summary

This secondary battery comprises an electrode body obtained by laminating positive electrodes and negative electrodes with a separator interposed therebetween. The separator includes a first layer and a second layer having lower thermal shrinkage than the first layer, and has a tubular section that is formed into a tube shape and constitutes the outermost surface of the electrode body. The separator is arranged such that, in the tubular section thereof, the first layer faces the inside and the second layer faces the outside.