High-Valent Cobalt Conductive Layer for Alkaline Battery
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Solution Overview
Problem
Alkaline secondary batteries with non-sintered nickel positive electrodes suffer from low conductivity and high self-discharge rates, leading to reduced utilization of active materials and decreased battery capacity over time.
Innovation Solution
A positive electrode for alkaline secondary batteries is developed, incorporating a nickel hydroxide powder with a conductive layer formed by a high-valent cobalt compound containing sodium, which enhances conductivity and suppresses self-discharge by maintaining a suitable ratio of the cobalt compound to nickel hydroxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cobalt hydroxide is added as a conductive material to enhance the rate of utilization of positive electrode active material, then the conductivity is improved, but self-discharge increases
Solution Approach 1:
The patent changes the chemical parameters of the conductive material from cobalt hydroxide (Co(OH)2) to a high-valent cobalt compound containing sodium (such as sodium cobalt oxyhydroxide NaCoO2 or sodium cobalt oxide NaCoO3). This parameter change in oxidation state and chemical composition provides both high conductivity and suppression of self-discharge, resolving the contradiction between improving active material utilization and reducing harmful self-discharge effects.
Solution Approach 2:
The patent uses a composite conductive material that combines high-valent cobalt compound with sodium content. This composite structure provides dual functionality: the high-valent cobalt compound ensures high conductivity for improved rate of utilization, while the specific sodium-containing composition suppresses self-discharge, thereby resolving the technical contradiction between these two opposing requirements.
2Quantity of substance
If nickel hydroxide is used as positive electrode active material to achieve high capacity, then the battery capacity increases, but conductivity is low leading to reduced rate of utilization
Solution Approach 1:
The patent introduces a high-valent cobalt compound containing sodium as an intermediary conductive material between the nickel hydroxide particles and the foam nickel core. This intermediary substance forms a conductive network that facilitates electron transport throughout the positive electrode, enabling high capacity nickel hydroxide to be effectively utilized without suffering from its inherent low conductivity.
3Productivity
If non-sintered nickel positive electrode is used to pack large amount of nickel hydroxide, then charge/discharge capacity per unit volume increases, but self-discharge occurs easily
Solution Approach 1:
The patent changes the chemical composition parameter of the conductive additive from conventional cobalt hydroxide to high-valent sodium-containing cobalt compound. This parameter change maintains the non-sintered structure's high packing density and capacity while fundamentally altering the electrochemical properties to suppress self-discharge, thus resolving the contradiction between high productivity and harmful self-discharge.
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 solution achieves a higher rate of utilization of positive electrode active materials while significantly reducing self-discharge, thereby improving the battery's overall performance and user-friendliness.
Implementation Method 1
the conductive material is a high-valent cobalt compound provided with a high valence and having a valence of more than three, the high-valent cobalt compound containing sodium
Implementation Method 2
Nickel hydroxide is oxidized and converted into nickel oxyhydroxide (NiOOH) according to progression of charge. After the completion of charge and the start of discharge, nickel oxyhydroxide is reduced and changed to nickel hydroxide (Ni(OH) 2 ) according to progression of discharge.
Data Source
Figure 1
AI summary
A battery (2) includes an outer can (10), and an electrode group (22) that is accommodated in the outer can (10) together with an alkaline electrolyte solution, in which the electrode group (22) includes a positive electrode (24) and a negative electrode (26) superposed with a separator (28) being interposed therebetween, the positive electrode (24) includes a positive electrode core and a positive electrode mixture packed in the positive electrode core, the positive electrode mixture includes a nickel hydroxide powder that is an aggregate of a particle of nickel hydroxide as a positive electrode active material, and a conductive material, the conductive material is a high-valent cobalt compound provided with a high valence and having a valence of higher than three, the high-valent cobalt compound containing sodium, and the conductive material is in an amount of 0.5 parts by mass or more and 5.0 parts by mass or less based on 100 parts by mass of the positive electrode active material.