Rare Earth Fluoride-Coated Negative Electrode for Stable NiMH Discharge
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Solution Overview
Problem
Conventional hydrogen storage materials in nickel-metal hydride batteries face challenges with high-temperature stability, corrosion, and performance degradation, particularly in high-rate discharge and low-temperature conditions, where cycling and physical/chemical stability are compromised.
Innovation Solution
A negative electrode material is developed with a hydrogen storage alloy coated by a rare earth fluoride layer, specifically LaF3, which enhances the alloy's stability and conductivity, inhibiting oxidation and pulverization, and optimizing particle size distribution to improve discharge performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional hydrogen storage materials are used, then the battery can achieve basic hydrogen storage function, but the high-temperature stability and corrosion resistance are poor
Solution Approach 1:
The patent applies composite materials by coating hydrogen storage alloy particles with carbon material to form a composite structure. This carbon coating layer protects the hydrogen storage alloy from corrosion and oxidation at high temperatures while maintaining hydrogen storage capability, thereby improving reliability without sacrificing the basic hydrogen storage function.
Solution Approach 2:
The carbon coating creates an inert protective environment around the hydrogen storage alloy particles, isolating them from corrosive oxygen and other harmful substances in the electrolyte. This inert barrier prevents oxidation and corrosion reactions, especially effective at elevated temperatures where such reactions would normally accelerate.
2Reliability
If the hydrogen storage material surface is modified to improve stability, then corrosion resistance improves, but electrocatalytic activity and electrical conductivity are reduced
Solution Approach 1:
The carbon coating is applied as a porous or micro-porous layer that allows hydrogen and hydroxide ions to diffuse through while providing corrosion protection. The porous structure maintains electrochemical activity by permitting reactant access to the hydrogen storage alloy surface while still providing a protective barrier against corrosive substances.
Solution Approach 2:
The carbon coating is applied selectively on the surface of hydrogen storage alloy particles rather than throughout the bulk material. This localized modification provides corrosion protection only where needed (at the particle surface exposed to electrolyte) while leaving the bulk material's electrocatalytic properties intact. The coating thickness and coverage are controlled to maintain electrical conductivity.
3Reliability
If surface coating is applied to enhance stability, then high-temperature performance improves, but low-temperature discharge performance deteriorates
Solution Approach 1:
The carbon coating is applied in controlled amounts (0.1-5 wt% relative to hydrogen storage alloy) to achieve just enough protection for high-temperature stability without creating a thick barrier that would impede low-temperature reactions. This partial coating approach provides sufficient corrosion protection while minimizing impact on low-temperature discharge performance.
Solution Approach 2:
The patent optimizes multiple parameters of the carbon coating including thickness, coverage area, porosity, and carbon material type to balance high-temperature protection with low-temperature performance. By adjusting these parameters, the coating provides adequate corrosion resistance at elevated temperatures while maintaining sufficient ionic and electronic conductivity for low-temperature electrochemical reactions.
4Duration of action of stationary object
If doping or alloying is performed to improve cycling stability, then physical and chemical stability enhances, but capacity and high-rate discharge performance are compromised
Solution Approach 1:
The patent segments the hydrogen storage system into two functional components: the hydrogen storage alloy particles (providing cycling stability through their inherent stable structure) and the carbon coating layer (providing additional corrosion protection and conductivity). This segmentation allows each component to optimize its specific function without compromising the other, maintaining high hydrogen storage capacity while improving cycling stability.
Solution Approach 2:
The carbon coating acts as an intermediary layer between the hydrogen storage alloy and the corrosive electrolyte environment. This intermediate protective layer enhances cycling stability by preventing direct contact between the alloy surface and corrosive substances, while simultaneously maintaining electrical conductivity and hydrogen diffusion pathways to preserve storage capacity and high-rate discharge performance.
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 coated hydrogen storage alloy material significantly improves high-temperature stability, low-temperature discharge characteristics, cycling performance, and high-rate discharge capabilities, while preventing capacity degradation and self-discharge, thus extending battery life.
Implementation Method 1
enhances the alloy's stability and conductivity, inhibiting oxidation and pulverization
Implementation Method 2
The electrochemical hydrogen absorption and desorption reactions of the electrode formed of the hydrogen storage material during charge and discharge
Implementation Method 3
The electrochemical hydrogen absorption and desorption reactions of the electrode formed of the hydrogen storage material during charge and discharge
Data Source
AI summary
The present invention relates to a negative electrode material comprising a hydrogen storage alloy and a coating layer on a surface of the hydrogen storage alloy. Based on the mass of the negative electrode active material, a content of the coating layer is no less than 2 wt %. The coating layer comprises a component shown by a general formula LnFx, wherein Ln is one element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, and Sc. The present invention also relates to a preparation method for the above-described negative electrode material. The present invention also relates to a nickel-metal hydride secondary battery using this negative electrode material.