Hydrogen Storage Alloy Electrode Nickel Gradient Control
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Solution Overview
Problem
Alkaline storage batteries using hydrogen storage alloy electrodes with AB5-type structures suffer from inadequate high-output performance due to nickel content gradients caused by dissolution of rare earth elements and Al/Mn into the electrolyte, leading to altered crystalline structures and inhibited hydrogen diffusion.
Innovation Solution
A hydrogen storage alloy electrode with a mixed phase of A2B7 and A5B19 structures is used, where the nickel content ratio in the surface layer is greater than in the bulk, reducing the nickel gradient and maintaining the crystalline structure, thereby enhancing hydrogen diffusion and output characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If AB5-type rare earth hydrogen storage alloy is used with partial replacement of Al or Mn, then hydrogen storage capacity is improved, but nickel content gradient increases due to dissolution of rare earth elements and Al/Mn into electrolyte
Solution Approach 1:
The patent applies local quality by creating a controlled nickel-rich surface layer on the hydrogen storage alloy particles. This surface layer has a different composition (higher nickel content) than the bulk material, which prevents the formation of harmful concentration gradients during battery operation. The surface layer acts as a protective barrier that maintains compositional stability while allowing the bulk material to provide high hydrogen storage capacity through Al/Mn replacement.
2Power
If surface activity is increased by providing nickel-rich regions, then high output performance is enhanced, but crystalline structure alteration occurs due to dissolution of surface components
Solution Approach 1:
The patent applies preliminary action by pre-forming a nickel-rich surface layer on the hydrogen storage alloy particles before they are assembled into the battery. This surface layer is created in advance to prevent the dissolution of rare earth elements and Al/Mn from the bulk material. By preparing this protective layer beforehand, the patent ensures that the crystalline structure remains stable during battery operation while maintaining the nickel-rich surface conditions necessary for high output performance.
3Productivity
If hydrogen diffusion is enhanced through surface modification, then output characteristics improve, but hydrogen diffusion resistance increases due to crystalline structure alteration
Solution Approach 1:
The patent applies local quality by creating a nickel-rich surface layer that has different properties from the bulk material. This surface layer maintains a stable crystalline structure that facilitates hydrogen diffusion, while the bulk material provides the necessary hydrogen storage capacity. The local nickel enrichment at the surface prevents structure alteration that would otherwise increase diffusion resistance, thereby maintaining high output characteristics without sacrificing hydrogen diffusion rate.
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 A2B7 and A5B19 mixed phase hydrogen storage alloy electrode achieves high output characteristics by reducing hydrogen diffusion resistance and maintaining the crystalline structure, resulting in batteries with superior assist output performance compared to existing technologies.
Implementation Method 1
the crystal lattice's a-axis and c-axis are shorter than in AB5 type structure. As a result, the lattice volume is small and it is possible to increase the content ratio of nickel per unit crystal lattice. By causing such A5B19 type structure, whose nickel content ratio can be increased, to be present in the bulk of the hydrogen storage alloy particles, the gradient between the content ratio of the nickel in the surface layer of the hydrogen storage alloy particles and the content ratio of the nickel in the bulk is alleviated, unlike with the AB5 type structure hydrogen storage alloy particles of the related art. Thereby, alteration (such as decrystallization) of the crystalline structure in the surface layer of hydrogen storage alloy particles is curbed, and hydrogen diffusion resistance is reduced.
Data Source
Figure 1
AI summary
A hydrogen storage alloy used in a hydrogen storage alloy electrode 11 has a crystalline structure having a mixed phase made up of at least an A2B7 type structure and an A5B19 type structure, and a surface layer of hydrogen storage alloy particles is so formed as to have a nickel content ratio greater than that of a bulk. The ratio (X/Y) of the nickel content ratio X (% by mass) of the surface layer to the nickel content ratio Y (% by mass) of the bulk is greater than 1.0 but no more than 1.2 (1.0 < X/Y ≤ 1.2). The gradient between the content ratio of the nickel in the surface layer of the hydrogen storage alloy particles and the content ratio of the nickel in the bulk is alleviated and a hydrogen storage alloy electrode with high output characteristics is obtained.