Multi-Phase Hydrogen Absorbing Alloy for NiMH Low-Temperature Cycle Life
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Solution Overview
Problem
Nickel-metal hydride secondary batteries face a trade-off between improving low-temperature discharge characteristics and maintaining cycle life, as enhancing surface activity of hydrogen absorbing alloys leads to excessive corrosion and reduced cycle life.
Innovation Solution
A hydrogen absorbing alloy with a single composition comprising multiple crystal phases, specifically a rare earth-Mg-Ni-based alloy with carefully controlled elemental ratios and heat treatment conditions, balances high surface activity for discharge and resistance to corrosion, allowing for improved low-temperature performance without compromising cycle life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the surface activity of the hydrogen absorbing alloy is enhanced to improve low-temperature discharge characteristics, then the low-temperature discharge characteristics are improved, but the cycle life characteristics are lowered due to excessive corrosion
Solution Approach 1:
The patent applies parameter changes by precisely controlling the compositional ratios of elements (La: 0.7-1.3, Mg: 0.2-0.4, Ni: 3.0-3.6, Al: 0.05-0.25, Co: 0.05-0.20, Mn: 0.05-0.20 in atomic ratios) and heat treatment parameters (temperature: 900-1100°C, time: 5-24 hours) to achieve a multi-phase crystal structure that balances surface activity and corrosion resistance, resolving the contradiction between low-temperature performance and cycle life
Solution Approach 2:
The patent creates a composite material system with multiple crystal phases (CaCu5-type, Ce2Ni7-type, and Ce5Co19-type phases) coexisting in a single alloy. This composite structure allows different phases to contribute differently: some phases provide high surface activity for low-temperature discharge while others provide corrosion resistance, thereby resolving the technical contradiction
2Productivity
If the reaction between the hydrogen absorbing alloy and alkaline electrolytic solution is increased to enhance surface activity, then the reactivity of the negative electrode is improved, but the corrosion of the hydrogen absorbing alloy proceeds excessively, shortening the cycle life
Solution Approach 1:
The patent applies local quality by creating regions with different crystal phases within the alloy structure. The CaCu5-type phase provides high reactivity for battery reactions, while the Ce2Ni7-type and Ce5Co19-type phases provide corrosion resistance. This spatial distribution of different functional phases allows the alloy to simultaneously achieve high reactivity and low corrosion, resolving the contradiction between productivity and harmful factors
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 alloy achieves enhanced low-temperature discharge characteristics while maintaining extended cycle life by coexisting crystal phases with high surface activity and corrosion resistance, optimizing battery performance.
Implementation Method 1
the hydrogen absorbing alloy is composed of a plurality of crystal phases... capable of absorbing/release of hydrogen
Implementation Method 2
heat treatment conditions... a plurality of crystal phases... difference between a maximum value and a minimum value of a lattice constant a
Data Source
Figure 1
AI summary
A nickel-metal hydride secondary battery (2) comprises an outer can (10) and a group of electrodes (22) housed in the outer can (10) together with an alkaline electrolytic solution. The group of electrodes (22) comprises a positive electrode (24) and a negative electrode (26) that are superposed with a separator (28) interposed therebetween, and the negative electrode (26) comprises a hydrogen absorbing alloy for nickel-metal hydride secondary batteries, the hydrogen absorbing alloy having a single composition and composed of a plurality of crystal phases.