CNT Undercoat Layer for Low-Resistance Lithium-Ion Electrodes

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Solution Overview

Problem

Lithium-ion secondary batteries using titanium-containing oxides as negative electrode active materials face high internal resistance and impedance due to low electrical conductivity, limiting rapid charging and discharging at large currents without significantly reducing electrode capacity.

Innovation Solution

Incorporating carbon nanotubes (CNTs) in an undercoat layer on a current-collecting substrate reduces the resistance of the electrode, allowing for rapid charging and discharging without diminishing the electrode capacity, even with a small coating weight of the undercoat layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If titanium-containing oxide is used as negative electrode active material, then battery safety is improved, but electrical conductivity decreases and internal resistance increases

Engineering Contradiction:

Improvebattery safetyVSAvoidinternal resistance

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

A conductive coating layer comprising carbon material is introduced as an intermediary between the titanium-containing oxide active material and the current collector. This coating layer mediates the electrical contact, providing a conductive pathway that reduces contact resistance while allowing the titanium-containing oxide to maintain its safety benefits.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The negative electrode is constructed as a composite structure combining titanium-containing oxide particles with a carbon-based conductive coating layer. This composite approach integrates the high safety of titanium-containing oxide with the high electrical conductivity of carbon materials, resolving the contradiction between safety and conductivity.

Inventive Principle:

Principle #40Composite materials

2Loss of energy

If conductive additive is added to negative electrode active material layer, then electrical conductivity is improved, but electrode capacity decreases

Engineering Contradiction:

Improveelectrical conductivityVSAvoidelectrode capacity

Core Design Contradiction:

Loss of energyVSQuantity of substance

Solution Approach 1:

The conductive coating layer acts as a dedicated intermediary for electrical conduction, separating the conductivity function from the capacity-providing active material. This allows the active material layer to maintain high capacity while the coating layer handles the conductivity requirement, eliminating the need to add conductive additives that would reduce capacity.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

Conductivity enhancement is applied locally only at the critical interfaces (between active material particles and at the current collector contact point) through the coating layer, rather than uniformly throughout the entire electrode. This localized approach improves conductivity without unnecessarily reducing the overall electrode capacity.

Inventive Principle:

Principle #3Local quality

3Loss of energy

If undercoat layer with conventional conductive material is used, then contact resistance is reduced, but coating weight increases and electrode capacity is reduced

Engineering Contradiction:

Improvecontact resistanceVSAvoidelectrode capacity

Core Design Contradiction:

Loss of energyVSQuantity of substance

Solution Approach 1:

The invention changes the material parameter of the undercoat layer from conventional conductive materials to carbon nanotubes, which have exceptionally high electrical conductivity per unit mass. This parameter change allows achieving the same contact resistance reduction with a much smaller coating weight, thereby preserving electrode capacity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The undercoat layer is designed as an ultrathin film structure comprising carbon nanotubes. This thin film approach provides effective electrical contact with minimal material usage, reducing the coating weight to less than 1 mg/cm² while still achieving low contact resistance.

Inventive Principle:

Principle #30Flexible shells and thin films

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 CNTs in the undercoat layer enables lithium-ion secondary batteries to maintain high discharge capacity and facilitate rapid charging and discharging at large currents, overcoming the limitations of titanium-containing oxide electrodes.

Implementation Method 1

Incorporating carbon nanotubes (CNTs) in an undercoat layer on a current-collecting substrate reduces the resistance of the electrode

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

a positive electrode and a negative electrode capable of intercalating and deintercalating lithium

Methodology Applied

Scientific EffectIntercalation: Absorption (physical)

Data Source

PatentEP3401982B1Electrode for energy storage devices

Publication Date: 2021.09.22 NISSAN CHEM CORP

Figure 1~2

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 contains an active material which contains a titanium-containing oxide.