CNT Undercoat Electrode for High-Density Lithium-Ion Batteries

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Solution Overview

Problem

Lithium-ion secondary batteries face issues with increased battery resistance and reduced volumetric capacity density when conductive additives are not used in the active material layer, leading to inadequate charging and discharging performance.

Innovation Solution

A conductive additive-free active material layer is formed on a current-collecting substrate with a carbon nanotube (CNT)-containing undercoat layer, which enhances electrical conductivity and adhesion, thereby increasing the volumetric capacity density of the battery.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of stationary object

If no conductive additive is added to the active material layer, then the density of the active material layer increases, but the active material layer has low conductivity and sufficient charging and discharging do not take place

Engineering Contradiction:

Improvedensity of active material layerVSAvoidconductivity of active material layer

Core Design Contradiction:

Volume of stationary objectVSReliability

Solution Approach 1:

A conductive undercoat layer containing carbon nanotubes is introduced as an intermediary between the current collector and the active material layer. This undercoat layer has high electrical conductivity and provides efficient electron transport pathways, compensating for the low conductivity of the conductive additive-free active material layer. The undercoat layer acts as a mediator that enables sufficient charging and discharging while allowing the active material layer to maintain high density.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If carbon black is used as conductive additive, then the electrical conductivity of the active material layer increases, but the density of the active material layer decreases due to low bulk density of carbon black

Engineering Contradiction:

Improveelectrical conductivity of active material layerVSAvoiddensity of active material layer

Core Design Contradiction:

ReliabilityVSVolume of stationary object

Solution Approach 1:

The conductive additive (carbon black) is extracted from the active material layer and relocated to the undercoat layer. The active material layer is formulated without conductive additives to achieve high density, while the undercoat layer contains the carbon nanotube-based conductive material to provide the necessary electrical conductivity. This separation allows each layer to optimize its function without compromising the other.

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If carbon black is used as conductive additive, then the electrical conductivity increases, but adhesion at the current collector/active material layer interface is lowered due to binder uptake in carbon black pores

Engineering Contradiction:

Improveelectrical conductivityVSAvoidadhesion at current collector/active material layer interface

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The conductive undercoat layer serves as an intermediary that provides both electrical conductivity and strong adhesion. The undercoat layer is applied directly to the current collector and forms a robust interface, preventing binder uptake issues that would occur if carbon black were present in the active material layer. This intermediary layer ensures good interfacial adhesion while maintaining high electrical conductivity through the carbon nanotube network.

Inventive Principle:

Principle #24Intermediary (Mediator)

4Reliability

If carbon black is used as conductive additive, then the electrical conductivity increases, but internal shorting may occur due to shedding of small carbon black particles

Engineering Contradiction:

Improveelectrical conductivityVSAvoidinternal shorting of battery

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The particle size parameter of the conductive material is changed from fine carbon black particles to larger carbon nanotube structures. Carbon nanotubes have significantly larger dimensions compared to carbon black particles, preventing them from shedding through the electrode structure. This parameter change eliminates the internal shorting hazard while maintaining electrical conductivity through the nanotube network.

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 use of a CNT-containing undercoat layer allows for effective charging and discharging with higher volumetric capacity density, preventing issues like internal shorting and adhesion problems associated with conductive additives, while maintaining low battery resistance.

Implementation Method 1

the undercoat layer which contains carbon nanotubes (CNTs)... increasing the electrical conductivity... decreasing the contact resistance

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

increasing adhesion between the current collector and the active material layer... structural network (including nanotubes and a binder)

Methodology Applied

Scientific EffectAdhesion: Adhesive

Data Source

PatentEP3401981B1Electrode for energy storage devices

Publication Date: 2021.03.17 NISSAN CHEM CORP

AI summary

Provided is an electrode for energy storage devices, which is provided with a collector substrate, an undercoat layer that is formed on at least one surface of the collector substrate and contains carbon nanotubes, and an active material layer that is formed on the surface of the undercoat layer, and wherein the active material layer does not contain a conductive assistant.