Negative Electrode with Lumpy Projections for Battery Cycle Life

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Solution Overview

Problem

Lithium ion secondary cells face challenges in enhancing first-time discharge capacity and charge-discharge cycle characteristics due to the expansion and contraction of negative electrode active materials, which can lead to pulverization and detachment from the current collector, resulting in reduced cycle characteristics.

Innovation Solution

A negative electrode with a conductive foil featuring lumpy projections aligned in a specific direction is used, allowing for controlled expansion and contraction, reducing stress on the current collector and enhancing adhesion between the active material and collector, while a region for accommodating expansion is provided within the cell.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If silicon or tin is used as negative electrode active material to enhance capacity, then first-time discharge capacity is improved, but the negative electrode active material layer expands and contracts severely during charging and discharging, causing pulverization and detachment from the current collector, which deteriorates cycle characteristics

Engineering Contradiction:

Improvedischarge capacityVSAvoidcycle characteristics

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The negative electrode active material layer is divided into a first layer containing silicon or tin and a second layer containing a material different from the first layer. This segmentation reduces the overall expansion and contraction of the active material layer during charging and discharging, preventing pulverization and detachment while maintaining high discharge capacity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The negative electrode active material layer is formed as a composite structure with a first layer (silicon or tin) and a second layer (different material). This composite structure combines the high capacity benefits of silicon/tin with the structural stability of the second layer material, resolving the contradiction between capacity enhancement and cycle characteristic deterioration.

Inventive Principle:

Principle #40Composite materials

2Strength

If the negative electrode active material layer is laminated on the current collector to improve adhesion, then the active material is restrained from disintegration, but severe expansion and contraction still exert stresses on the current collector, causing electrode deformation or collapse

Engineering Contradiction:

Improveadhesion between active material and current collectorVSAvoidelectrode structure stability

Core Design Contradiction:

StrengthVSShape

Solution Approach 1:

Dividing the active material layer into multiple layers with different materials reduces the overall expansion and contraction magnitude. This segmentation maintains strong adhesion to the current collector while minimizing the stresses that cause electrode deformation or collapse during cycling.

Inventive Principle:

Principle #1Segmentation

3Shape

If a region for accommodating expansion is provided in the cell, then electrode deformation is reduced, but the cell structure becomes more complex

Engineering Contradiction:

Improveelectrode structure stabilityVSAvoidcell structure complexity

Core Design Contradiction:

ShapeVSDevice complexity

Solution Approach 1:

The segmentation of the active material layer into multiple layers with different materials addresses electrode stability through material composition rather than structural modifications. This approach maintains simple cell structure while achieving the same effect as providing expansion accommodation regions.

Inventive Principle:

Principle #1Segmentation

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 enhances first-time discharge capacity and charge-discharge cycle characteristics by minimizing deformation and breakage of the electrode structure, leading to improved capacity retention and reduced thickness increase during charging.

Implementation Method 1

expansion and contraction of the negative electrode active material layer attendant on the charging and discharging

Methodology Applied

Scientific EffectExpansion and contraction: Thermal Expansion

Implementation Method 2

allowing for controlled expansion and contraction, reducing stress on the current collector

Methodology Applied

Scientific EffectStress distribution:

Data Source

PatentUS7476464B2Negative electrode and secondary cell

Publication Date: 2009.01.13 MURATA MFG CO LTD

AI summary

A negative electrode wherein a negative electrode current collector has a conductive foil including a conductive substrate and a multiplicity of conductive lumpy projections provided at a surface of the substrate is provided. The multiplicity of lumpy projections are so disposed that a plurality of the lumpy projections are aligned substantially in one direction to form a lumpy projection row and that a plurality of the lumpy projection rows are arrayed side by side at a predetermined interval in a direction substantially orthogonal to the one direction.