Surface-Treated Copper Foil for Lithium-Ion Battery Anodes

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Solution Overview

Problem

Copper foils used in lithium-ion batteries face challenges with adhesion of solvent-based active material layers due to oxidation at high temperatures, leading to potential battery failure during high C-rate charging and discharging.

Innovation Solution

A surface-treated copper foil is developed with a zinc-chromium layer and an organic hydrophobic layer, which improves adhesion to the active material layer and withstands high temperatures without discoloration, featuring a surface tension of 34 to 58 dyne/cm and surface roughness of 0.8 to 2.5 μm.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If a solvent-based slurry is used to achieve good adhesion to the copper foil, then adhesion quality is improved, but the drying temperature must be increased which causes copper foil oxidation and discoloration

Engineering Contradiction:

Improveadhesion between copper foil and active material layerVSAvoidoxidation and discoloration of copper foil

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

A surface treatment layer is applied to the copper foil as an intermediary between the copper substrate and the solvent-based slurry. This treatment layer has controlled surface tension (34-58 dyne/cm) that enables good adhesion to the PVDF binder while preventing direct oxidation of the copper foil during high-temperature drying

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The surface tension of the copper foil is modified through surface treatment to fall within the specific range of 34-58 dyne/cm. This parameter change optimizes the wetting and adhesion properties for solvent-based slurries while maintaining resistance to oxidation at elevated temperatures

Inventive Principle:

Principle #35Parameter changes

2Productivity

If high drying temperature is applied to remove NMP solvent, then solvent evaporation is improved, but copper foil oxidation increases leading to discoloration

Engineering Contradiction:

Improvesolvent removal efficiencyVSAvoidoxidation and discoloration

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The surface treatment layer serves as a protective intermediary that allows high-temperature drying to proceed efficiently for NMP removal while the treatment itself resists oxidation, preventing discoloration of the underlying copper foil

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The high drying temperature, which would normally cause harmful oxidation, is converted into a beneficial process by the surface treatment that enables efficient NMP evaporation while the treatment layer itself remains stable and protects the copper from oxidation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Adaptability or versatility

If the copper foil surface is made hydrophilic through chromium plating, then affinity for water-based slurries is improved, but adhesion to solvent-based slurries deteriorates

Engineering Contradiction:

Improveaffinity for aqueous slurryVSAvoidadhesion to solvent-based slurry

Core Design Contradiction:

Adaptability or versatilityVSStrength

Solution Approach 1:

The surface tension is precisely controlled within the range of 34-58 dyne/cm through the combined plating and organic treatment. This optimized parameter range creates a balance that provides adequate affinity for both aqueous and solvent-based slurries, enabling versatility in slurry type selection

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 treated copper foil ensures durable adhesion of the active material layer, preventing breakdown during high C-rate charging and discharging, and maintains integrity at elevated temperatures, enhancing the performance and lifespan of lithium-ion batteries.

Implementation Method 1

a zinc-chromium layer plated on one or both sides of the copper foil

Methodology Applied

Scientific EffectElectroplating: Electroplating

Implementation Method 2

Subsequent treatment with a silane makes the surface more hydrophobic, which improves adhesion to the active material layer

Methodology Applied

Scientific EffectAdsorption: Adsorption

Implementation Method 3

At higher temperatures, however, copper foil is more susceptible to oxidation, which leads to discoloration

Methodology Applied

Scientific EffectOxidation: Oxidation

Data Source

PatentUS9647272B1Surface-treated copper foil

Publication Date: 2017.05.09 CHANG CHUN PETROCHEMICAL CO LTD

AI summary

The present disclosure relates to a surface-treated copper foil which exhibits excellent affinity for an active material layer that is applied to the copper foil in the manufacture of a negative electrode (anode), for use in secondary lithium-ion batteries. The copper foil is plated with chromium and zinc and subsequently subjected to an organic treatment. The surface-treated copper has a surface tension of 34 to 58 dyne/cm and a surface roughness (Rz) of 0.8 to 2.5 μm, and comprises: (a) copper foil; (b) a zinc-chromium layer plated one or both sides of the copper foil, wherein the zinc content in the zinc-chromium layer is from 10 to 120 μg/dm2 and the chromium content in the zinc-chromium layer is from 10 to 35 μg/dm2; and (c) an organic hydrophobic layer applied to the zinc-chromium layer.