Oval Mandrel Asymmetry Reduces Winding Stress

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Solution Overview

Problem

Conventional mandrels used in manufacturing jelly roll type electrode assemblies experience high wound stress and residual stress due to uneven linear velocity and force distribution, leading to potential breakage of the electrode assembly during the winding process, which compromises battery safety and performance.

Innovation Solution

An oval-shaped mandrel with a length ratio of major to minor axis of 1.5 or more and a continuously changing tilt from minor to major axis is used, minimizing linear velocity change and reducing stress on the sheet type stack, while the edge part is made of a material with lower modulus of elasticity to absorb impact and reduce damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional mandrel with hexagonal or angled oval shape is used, then the winding process can be completed, but high wound stress and residual stress are generated at the folded portion of the sheet type stack, leading to potential breakage

Engineering Contradiction:

Improvesafety of batteryVSAvoidwound stress and residual stress

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The mandrel is designed with an oval cross-section where the major axis is longer than the minor axis, creating an asymmetric geometry that optimizes the winding process. This asymmetric shape reduces the linear velocity change during rotation and minimizes stress concentration at the folded portion of the electrode assembly, thereby reducing wound stress and residual stress while improving battery safety

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The mandrel's geometric parameters are specifically optimized with a major axis to minor axis length ratio of 1.5 or more. This parameter change from conventional shapes fundamentally alters the stress distribution pattern during winding, reducing the linear velocity change and minimizing impact force on the electrode assembly, thus resolving the stress-related reliability issue

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the mandrel rotates at constant speed, then the winding process is efficient, but the linear velocity change at the folded portion is greater than at other regions, increasing impact and residual stress

Engineering Contradiction:

Improvewinding efficiencyVSAvoidresidual stress

Core Design Contradiction:

ProductivityVSStress or pressure

Solution Approach 1:

The oval cross-section with major axis longer than minor axis creates an asymmetric rotation pattern that reduces linear velocity variation during constant speed rotation. This asymmetric geometry ensures more uniform velocity distribution across different positions of the mandrel, minimizing the velocity change at the folded portion while maintaining constant rotation speed for efficient winding

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The oval cross-section provides a curved, continuous surface geometry that smooths the transition of the sheet type stack during winding. This curvature reduces abrupt changes in linear velocity at the folded portion compared to angular shapes, thereby reducing impact force and residual stress while maintaining winding efficiency

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Device complexity

If force is concentrated at the folded portion with maximum radius of gyration, then the mandrel structure is simple, but the acceleration and impact amount increase, causing breakage

Engineering Contradiction:

Improvemandrel structureVSAvoidimpact force

Core Design Contradiction:

Device complexityVSForce

Solution Approach 1:

The oval cross-section with major axis longer than minor axis creates an asymmetric moment of inertia distribution that reduces force concentration at the folded portion. This asymmetric geometry distributes the rotational forces more evenly throughout the structure, minimizing impact force on the electrode assembly while maintaining a relatively simple mandrel design

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The curved oval surface of the mandrel provides a gradual transition zone that distributes contact force along a longer path during winding. This curvature reduces the concentration of force at any single point, particularly at the folded portion, thereby reducing impact force while keeping the mandrel structure simple and manufacturable

Inventive Principle:

Principle #14Spheroidality (Curvature)

Data Source

PatentEP2693553B1Mandrel used in manufacture of jelly roll-type electrode assembly

Publication Date: 2016.04.27 LG CHEM LTD

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AI summary

Disclosed herein is a mandrel configured to be used in a winding process for manufacturing a jelly roll type electrode assembly using a long sheet type stack of a cathode/separator/anode structure, wherein the mandrel is oval in a section perpendicular to a rotational central axis of the mandrel, a length ratio of a major axis to a minor axis of the mandrel being 1.5 or more, and a tilt of an outer side of the mandrel is continuously changed from an end of the minor axis of the mandrel to an end of the major axis of the mandrel in the section perpendicular to the rotational central axis of the mandrel in such a manner that the mandrel is configured to have an oval structure so as to reduce wound stress applied from the end of the major axis of the mandrel to the sheet type stack during constant speed rotation of the mandrel when the sheet type stack is wound on the mandrel in a state in which an end of the sheet type stack is fitted in a central region of the mandrel.