Hydrogen-absorbing alloy composition for alkaline battery cycle life
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Solution Overview
Problem
Alkaline storage batteries using hydrogen-absorbing alloys as negative electrodes face challenges in maintaining high hydrogen-absorbing capacity and durability, leading to reduced cycle life due to easy splitting and reaction with the alkaline electrolyte.
Innovation Solution
A hydrogen-absorbing alloy with a specific composition (Ln1-xMgxNiyAz) forming a hexagonal or rhombohedral crystal structure, where 0.15≦x≦0.30 and 2.8≦y+z≦4.0, is developed, along with a fabrication method involving heat-treatment and rapid-cooling to stabilize the crystal structure and prevent subphase growth, ensuring high hydrogen-absorbing capability and enhanced durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a hydrogen-absorbing alloy with high Mg content (≥15% mol ratio) forming hexagonal or rhombohedral structure is used to improve equilibrium pressure and operating voltage, then the operating voltage is improved, but the alloy splits easily during charging/discharging causing oxidation and reduced cycle life
Solution Approach 1:
The invention optimizes the Mg content parameter to a specific range (15-30% mol ratio) and controls the crystal structure to maintain hexagonal or rhombohedral system. This parameter optimization resolves the contradiction by finding the sweet spot where high enough Mg content provides improved operating voltage while the controlled crystal structure prevents excessive splitting during charging/discharging cycles.
Solution Approach 2:
The invention uses a composite alloy system combining rare earth elements (Ln), Mg, Ni, and other elements (A) in specific proportions. This composite material approach allows the alloy to achieve both high equilibrium pressure (for improved operating voltage) and enhanced structural stability (for improved cycle life) by leveraging the synergistic effects of different elements.
2Quantity of substance
If Mg is added to rare earth-nickel hydrogen-absorbing alloy to increase hydrogen-absorbing capability, then the hydrogen-absorbing capability is improved, but the alloy structure becomes unstable and reacts with alkaline electrolyte
Solution Approach 1:
The invention carefully controls the Mg content parameter within the range of 15-30% mol ratio and maintains specific ratios of other elements (where y+z is within 2.8-4.0). This parameter control ensures the alloy achieves high hydrogen-absorbing capacity while maintaining structural stability and preventing reaction with alkaline electrolyte.
Solution Approach 2:
The invention introduces element A (selected from Co, Fe, Mn, V, Cr, Nb, Al, Ga, Zn, Sn, Cu, Si, P, B) in specific proportions to locally enhance the alloy structure. These elements are strategically incorporated to stabilize the crystal structure in regions where Mg is present, preventing the alloy from reacting with the alkaline electrolyte while preserving high hydrogen-absorbing capability.
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 results in an alkaline storage battery with improved cycle life and high hydrogen-absorbing capacity, preventing splitting and reaction with the electrolyte, thus enhancing the battery's performance and longevity.
Implementation Method 1
hydrogen-absorbing alloy having a Ce2Ni7 type or the like crystal structure
Implementation Method 2
hydrogen-absorbing capability of the rare earth-nickel hydrogen-absorbing alloy
Implementation Method 3
fabrication method involving heat-treatment and rapid-cooling to stabilize the crystal structure
Implementation Method 4
rapid-cooling to stabilize the crystal structure and prevent subphase growth
Data Source
AI summary
An alkaline storage battery has a negative electrode using a hydrogen-absorbing alloy represented by a general formula Ln1-xMgxNiyAz wherein Ln is at least one element selected from rare-earth elements including Y, Ca, Zr, and Ti, A is at least one element selected from Co, Fe, Mn, V, Cr, Nb, Al, Ga, Zn, Sn, Cu, Si, P and B, and 0.15≦x≦0.30, 0<z≦1.5, and 2.8≦y+z≦4.0 are satisfied. The hydrogen-absorbing alloy has a hexagonal system crystal structure or a rhombohedral system crystal structure as its main phase and has a subphase of line which average number of not less than 50 nm in thickness existing in the range of 10 μm×10 μm in the cross section of the main phase is 3 or less.