Nickel Hydroxide Electrode Oxidation for Cobalt Migration Control

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Solution Overview

Problem

Conventional nickel-zinc batteries face issues with cobalt migration from the positive electrode to the negative electrode, leading to increased impedance, self-discharge, and premature failure due to the solubility of cobalt species in alkaline electrolytes, which affects the conductivity and cycle life of the battery.

Innovation Solution

Treating nickel hydroxide or cobalt-coated nickel hydroxide particles with a strongly oxidizing agent like alkali metal persulfate to increase the oxidation state of cobalt to 3 or higher, reducing its solubility and migration, and incorporating these treated particles into the positive electrode to form a paste that is then used in the nickel electrode, thereby enhancing the battery's high-rate charge and discharge capabilities and shelf-life.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If cobalt compound is included to increase conductivity, then electrical conductivity is improved, but cobalt migration to negative electrode occurs causing self-discharge and premature failure

Engineering Contradiction:

Improvebattery conductivityVSAvoidcobalt migration

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the oxidation state parameter of cobalt from +2 to +3 by treating with strong oxidizing agents (persulfate, ozone, or permanganate). This parameter change transforms soluble Co2+ into insoluble Co3+, preventing cobalt migration while maintaining conductivity enhancement benefits

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs strong oxidizing agents (alkali metal persulfate, ozone, or permanganate) to accelerate the oxidation of cobalt from +2 to +3 state. This accelerated oxidation ensures complete conversion and stable formation of the insoluble cobalt oxide coating on nickel hydroxide particles

Inventive Principle:

Principle #38Strong oxidants (Accelerated oxidation)

2Reliability

If cobalt is added to enhance conductivity, then electrical performance is improved, but shelf-life decreases due to cobalt solubility in alkaline electrolyte

Engineering Contradiction:

Improveelectrical conductivityVSAvoidshelf-life

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent changes the solubility parameter of cobalt by oxidizing it from soluble Co2+ to insoluble Co3+ state. This parameter change eliminates cobalt dissolution in alkaline electrolyte, thereby extending battery shelf-life while preserving conductivity benefits

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful soluble cobalt species into beneficial insoluble cobalt oxide coating. The oxidation process transforms the problematic soluble cobalt that causes self-discharge into a stable, insoluble form that enhances conductivity without migration

Inventive Principle:

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

3Reliability

If standard oxidizing treatment is used, then cobalt oxidation is achieved, but manufacturing time window is limited to less than one hour

Engineering Contradiction:

Improvecobalt oxidation stateVSAvoidelectrolyte soak time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent performs preliminary oxidation treatment of nickel hydroxide particles with strong oxidizing agents before cell assembly and electrolyte filling. This preliminary action ensures cobalt is already in the stable +3 state, allowing extended electrolyte soak time (up to 24 hours) without fear of cobalt migration or performance degradation

Inventive Principle:

Principle #10Preliminary action

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 treatment results in improved battery performance with higher conductivity, lower impedance, extended shelf-life, and reduced probability of premature failure by locking cobalt in the positive electrode, allowing for a longer electrolyte soak time without detrimental effects, thus enhancing the manufacturing process and cell uniformity.

Implementation Method 1

nickel hydroxide particles or cobalt-coated nickel hydroxide particles treated with strongly oxidizing reagents such as alkali metal persulfate in alkaline solution

Methodology Applied

Scientific EffectOxidation: Oxidation

Data Source

PatentUS8043748B2Pasted nickel hydroxide electrode for rechargeable nickel-zinc batteries

Publication Date: 2011.10.25 ZINCFIVE INC

AI summary

Active material for a positive electrode of a rechargeable alkaline electrochemical cell is made with nickel hydroxide particles or cobalt-coated nickel hydroxide particles treated with strongly oxidizing reagents such as alkali metal persulfate in alkaline solution. The active material also may be made with cobalt-coated nickel hydroxide particles having a high percentage of cobalt(III) on a surface or an average cobalt oxidation state of about 3 measured across the particles. The treated nickel hydroxide or cobalt-coated nickel hydroxide decreases the cobalt solubility in the alkaline electrolyte and increases the high-rate charge and discharge capability. The lower cobalt solubility decreases cobalt migration that can increase self discharge and lead to premature failure.