Silicon Negative Electrode Pillar Structure for Battery Volume Expansion

Solution Overview

Problem

Nonaqueous electrolyte secondary batteries using silicon as a negative electrode active material face issues with volume expansion and shrinkage, leading to cell swelling, stress on the current collector, and degradation of cycle characteristics due to the formation of fine powder and detachment of the active material from the current collector.

Innovation Solution

A negative electrode with a current collector and a mixture layer containing a binder and lithium alloy active material particles, featuring pillar-shaped portions formed near the current collector, where the particle diameter of the active material is 20% or less of the maximum diameter of the pillar-shaped portions, allowing for absorption of expansion and maintaining electron conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a material containing silicon is used as a negative electrode active material to increase energy density, then the energy density and output are improved, but volume expansion and shrinkage occur during lithium occlusion and release, causing cell swelling, formation of fine powder, and detachment from the current collector

Engineering Contradiction:

Improveenergy densityVSAvoidcycle characteristics

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The negative electrode active material is divided into granular particles with a diameter of 1 μm or less, which are then filled into a porous coating layer. This segmentation allows the material to accommodate volume changes during lithium occlusion and release without causing cell swelling or detachment, while maintaining high energy density.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention creates a specific local structure where granular silicon particles are embedded within a porous coating layer that is itself coated on the current collector. This local quality differentiation allows the granular particles to expand and contract independently while the porous coating layer provides a buffer and maintains structural integrity, preventing detachment and fine powder formation.

Inventive Principle:

Principle #3Local quality

2Volume of moving object

If a thin film negative electrode active material is deposited on the current collector to achieve high volumetric energy density, then the volumetric energy density is improved, but stress during charging and discharging causes wrinkling and swelling of the cell

Engineering Contradiction:

Improvevolumetric energy densityVSAvoidstress on current collector

Core Design Contradiction:

Volume of moving objectVSStress or pressure

Solution Approach 1:

The invention creates a specific local structure where granular silicon particles are embedded within a porous coating layer that is itself coated on the current collector. This local quality differentiation allows the granular particles to expand and contract independently while the porous coating layer provides a buffer and maintains structural integrity, preventing detachment and fine powder formation.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

A porous coating layer is formed on the current collector, and granular negative electrode active material particles are filled into the pores. This porous structure provides void space that absorbs volume expansion during charging, reducing stress on the current collector and preventing cell swelling while maintaining high volumetric energy density.

Inventive Principle:

Principle #31Porous materials

3Stability of the object's composition

If pillar-shaped protruding portions are formed on a thin film negative electrode to suppress wrinkling and cell swelling, then the structural stability is improved, but the cycle characteristics and electrode structure require further improvement

Engineering Contradiction:

Improvestructural stabilityVSAvoidcycle characteristics

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The negative electrode active material is divided into granular particles with a diameter of 1 μm or less, which are then filled into a porous coating layer. This segmentation allows the material to accommodate volume changes during lithium occlusion and release without causing cell swelling or detachment, while maintaining high energy density.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A porous coating layer is formed on the current collector, and granular negative electrode active material particles are filled into the pores. This porous structure provides void space that absorbs volume expansion during charging, reducing stress on the current collector and preventing cell swelling while maintaining high volumetric energy density.

Inventive Principle:

Principle #31Porous 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 design enhances capacity retention, reduces stress on the current collector, and improves initial cycle characteristics by maintaining particle and collector bonds, while ensuring good moldability and density of the pillar-shaped structure.

Implementation Method 1

a negative electrode active material particle that forms an alloy with lithium

Methodology Applied

Scientific EffectAlloy formation:

Implementation Method 2

the bonds between the negative electrode active material particles and between the negative electrode active material and the current collector are maintained by the binder

Methodology Applied

Scientific EffectAdhesion: Adhesive

Implementation Method 3

The negative electrode has cavities that absorb the volume expansion of the negative electrode active material during charging and discharging around the pillar-shaped protruding portions

Methodology Applied

Scientific EffectVolume expansion absorption:

Data Source

PatentUS9711783B2Negative electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery

Publication Date: 2017.07.18 PANASONIC ENERGY CO LTD

AI summary

A negative electrode for a nonaqueous electrolyte secondary battery according to one aspect of the present invention includes a negative electrode mixture layer that contains a binder and a negative electrode active material particle that forms an alloy with lithium and is formed on a current collector. The negative electrode mixture layer includes a base portion near the current collector and pillar-shaped portions formed on the base portion. A negative electrode for a nonaqueous electrolyte secondary battery according to another aspect of the present invention includes a negative electrode mixture layer that contains a binder and a negative electrode active material particle that forms an alloy with lithium and is formed on a current collector. The negative electrode mixture layer includes pillar-shaped portions and the particle diameter of the negative electrode active material particle is 20% or less of the maximum diameter of the pillar-shaped portions.