Multilayer Battery Anode Structure for Si Expansion Control

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Solution Overview

Problem

The compound containing Si undergoes significant volumetric changes during charge and discharge, leading to deterioration of charge-discharge cycle characteristics in batteries, and existing solutions do not adequately inhibit these changes, resulting in suboptimal cycle characteristics.

Innovation Solution

A negative electrode with a multilayer structure comprising a first layer containing Si or other metal elements, multiwall or single-wall carbon nanotubes, and a binder, and a second layer of graphite with specific fracture strength, which controls porosity and expansion, improving cycle characteristics.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If a compound containing Si is used as negative electrode active material to increase battery capacity, then the battery capacity increases, but the charge-discharge cycle characteristics deteriorate due to large volumetric change

Engineering Contradiction:

Improvebattery capacityVSAvoidcharge-discharge cycle characteristics

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The negative electrode mixture layer is divided into two distinct layers: a first layer containing the Si compound and carbon nanotubes, and a second layer containing graphite particles. This segmentation allows each layer to perform its specific function - the first layer provides high capacity while the second layer provides structural stability, thereby resolving the contradiction between high capacity and good cycle characteristics

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention uses composite materials in both layers. The first layer combines Si compound with carbon nanotubes to form a composite that accommodates volumetric changes. The second layer uses graphite particles with specific fracture strength properties. These composite materials enable the electrode to maintain both high capacity and structural integrity during cycling

Inventive Principle:

Principle #40Composite materials

2Reliability

If existing multilayer structures are used to improve cycle characteristics, then cycle characteristics improve slightly, but the volumetric expansion rate is not sufficiently inhibited

Engineering Contradiction:

Improvecycle characteristicsVSAvoidvolumetric expansion rate

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The invention specifies precise parameter ranges for optimal performance: carbon nanotube content of 0.2-10 mass%, binder content of 6-18 mass%, and graphite particle fracture strength of 10-35 MPa. By controlling these parameters within specific ranges, the electrode achieves both low volumetric expansion and good cycle characteristics

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The first layer containing carbon nanotubes and binder creates a porous structure that can accommodate the volumetric expansion of Si compounds during lithiation. This porous architecture allows the electrode to absorb expansion stresses without significant overall volume increase, thereby reducing the volumetric expansion rate while maintaining cycle stability

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

The proposed solution enhances charge-discharge cycle characteristics by reducing expansion rates while maintaining high capacity, and when combined with graphite B, it improves storage characteristics at high temperatures and charge characteristics.

Implementation Method 1

Since the compound containing the metal such as Si undergoes a large volumetric change with charge and discharge

Methodology Applied

Scientific EffectVolumetric expansion: Thermal Expansion

Implementation Method 2

a second layer including a graphite A having a particle fracture strength of greater than or equal to 10 MPa and less than or equal to 35 MPa

Methodology Applied

Scientific EffectFracture strength: Fracture Mechanics

Implementation Method 3

greater than or equal to 3 mass % and less than or equal to 10 mass % of a multiwall carbon nanotube; and greater than or equal to 0.2 mass % and less than or equal to 0.7 mass % of a single-wall carbon nanotube

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS20240055583A1Negative electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

Publication Date: 2024.02.15 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

A negative electrode for a nonaqueous electrolyte secondary battery, according to one embodiment of the present invention, is provided with a negative electrode core and a negative electrode mixture layer provided on the surface of the negative electrode core. The negative electrode mixture layer has a first layer that includes: at least one of at least one kind of metal element selected from Si, Sn, Sb, Mg, and Ge, and a compound containing said metal element; at least one of multi-walled carbon nanotubes and single-walled carbon nanotubes; and a binding agent. The negative electrode mixture layer also has a second layer that includes graphite A with a particle fracture strength of 10-35 MPa. The porosity of the first layer is preferably 50-65%.