Polyimide Binder Pillar Negative Electrode Silicon Expansion

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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 existing structural limitations of the negative electrode.

Innovation Solution

A negative electrode with a current collector and a mixture layer containing a binder and lithium alloy active material particles, where the binder is a polyimide resin with an average molecular weight of 60000 or more, forming a base portion and pillar-shaped structures that absorb expansion and maintain conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If a material containing silicon is used as a negative electrode active material to increase energy density, then the volumetric energy density is improved, but volume expansion and shrinkage during lithium occlusion and release cause cell swelling, stress on current collector, and degradation of cycle characteristics

Engineering Contradiction:

Improvevolumetric energy densityVSAvoidcycle characteristics

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The negative electrode active material layer is divided into multiple pillar-shaped protruding portions with hollow interiors. This segmentation allows each pillar to independently expand and shrink during lithium occlusion and release, preventing stress accumulation and maintaining structural integrity over multiple charge-discharge cycles, thereby improving cycle characteristics while maintaining high energy density

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The pillar-shaped protruding portions have hollow interiors that provide buffer space for volume expansion during lithium insertion. This porous structure absorbs the expansion stress without causing cell swelling or detachment from the current collector, enabling the use of high-capacity silicon-based materials while maintaining reliable cycle performance

Inventive Principle:

Principle #31Porous materials

2Manufacturing precision

If a sputtering method is used to form a silicon thin film and pillar-shaped protruding portions, then the negative electrode structure is improved, but a large-scale vacuum apparatus is required and the manufacturing process becomes complex

Engineering Contradiction:

Improvenegative electrode structureVSAvoidvacuum apparatus and etching equipment

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The invention replaces the complex sputtering and etching process with a casting method that forms pillar-shaped protruding portions directly. This mechanical substitution eliminates the need for large-scale vacuum apparatus and chemical etching equipment, simplifying the manufacturing process while achieving the same functional structure

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention changes the manufacturing approach from physical vapor deposition (sputtering) to a casting process. By altering the fabrication parameters and method, the same pillar-shaped structure is achieved through a simpler, more accessible process that does not require vacuum equipment

Inventive Principle:

Principle #35Parameter changes

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 polyimide resin binder enhances moldability and electron conductivity, reducing stress on the current collector and maintaining capacity retention, while the pillar structure effectively absorbs expansion, resulting in improved cycle characteristics and high energy density.

Implementation Method 1

the binder contains a polyimide resin... the bonds between the negative electrode active material particles and between the negative electrode active material particle and the current collector are maintained by the binder

Methodology Applied

Scientific EffectAdhesion: Adhesive

Implementation Method 2

the plurality of pillar-shaped protruding portions are made of silicon and have a larger thickness than portions around the protruding portions... the negative electrode has cavities that absorb the volume expansion of the negative electrode active material during charging

Methodology Applied

Scientific EffectMechanical deformation: Deformation

Data Source

PatentUS9705135B2Negative electrode for nonaqueous electrolyte secondary battery and nonaqueous electrolyte secondary battery

Publication Date: 2017.07.11 PANASONIC ENERGY CO LTD

AI summary

There are provided a negative electrode for a nonaqueous electrolyte secondary battery having excellent initial efficiency and good moldability of pillar portions included in a negative electrode mixture layer, and a nonaqueous electrolyte secondary battery. A negative electrode (20) for a nonaqueous electrolyte secondary battery according to one aspect of the present invention includes a negative electrode current collector (21) and a negative electrode mixture layer (22) formed on the negative electrode current collector (21) and containing a binder and a negative electrode active material particle that forms an alloy with lithium. The negative electrode mixture layer (22) includes a base portion (22a) near the negative electrode current collector (21) and pillar portions (22b) formed on the base portion (21a). The binder contains a polyimide resin. The polyimide resin has an average molecular weight of 60000 or more.