Nickel Electrode Lithium Solid Solution Cycle Stability
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Solution Overview
Problem
Conventional nickel electrodes for alkaline secondary batteries face challenges in achieving high charge/discharge capacity, low irreversible capacity, superior cycle characteristics, and high-rate discharging, while also requiring improved charge efficiency and productivity.
Innovation Solution
A nickel electrode with a solid solution of lithium (Li) in the active material particle, specifically containing 0.01 to 0.5 wt % Li, is developed, where Li is retained even after rinsing with water, and is combined with rare earth elements and natural polysaccharides to enhance discharge capacity and cycle stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cobalt hydroxide layer is formed on the nickel hydroxide surface and oxidized to high-order cobalt compound to improve electrical conductivity, then current collection function is improved, but discharge capacity decreases due to increased discharge reserve production
Solution Approach 1:
The invention changes the oxidation state parameter of cobalt from +2 to higher than +2 (forming high-order cobalt compound), which improves electrical conductivity and current collection function while reducing discharge reserve production, thereby resolving the contradiction between reliability and quantity of substance
Solution Approach 2:
The invention creates a composite structure with a nickel hydroxide core layer and a high-order cobalt compound surface layer, combining the high capacity of nickel hydroxide with the high conductivity of cobalt compound to simultaneously achieve both discharge capacity and current collection function
2Loss of energy
If oxidant is used to increase the oxidation number of Ni higher than +2 to decrease discharge reserve, then irreversible capacity is reduced, but charge efficiency and capacity of nickel electrode remain difficult to improve
Solution Approach 1:
The invention changes the oxidation number parameter of nickel to higher than +2 through controlled oxidation, which decreases discharge reserve and irreversible capacity while maintaining charge efficiency by preventing excessive oxygen evolution
Solution Approach 2:
The invention applies different oxidation levels to different parts of the active material - the core remains as nickel hydroxide while the surface forms a high-order nickel compound layer, creating local quality differences that optimize both irreversible capacity reduction and charge efficiency
3Reliability
If Li is added to active material containing Zn solid solution by heating with alkaline solution to inhibit capacity decay during overdischarge, then cycle characteristic is improved, but capacity density of Ni(OH)2 is not increased
Solution Approach 1:
The invention changes the chemical composition parameter by incorporating Li into the active material structure, which improves cycle characteristic by stabilizing the crystal structure during charge/discharge cycles while maintaining capacity density
Solution Approach 2:
The invention uses Li as an intermediary element that mediates between the nickel hydroxide and zinc solid solution, stabilizing the overall structure and improving cycle characteristic without significantly affecting capacity density
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 nickel electrode achieves a large discharge capacity, low irreversible capacity, and excellent charge/discharge cycle characteristics, with improved high-rate discharge performance and charge efficiency, while maintaining productivity and stability.
Implementation Method 1
lithium (Li) is contained to be a solid solution in the active material particle
Implementation Method 2
generating a high-conductive and high-order cobalt compound with an oxidation of aforementioned cobalt compound whose oxidation number of cobalt is +2 by charging
Implementation Method 3
nickel electrode for alkaline secondary battery and alkaline secondary battery whose discharge capacity is larger compared to the conventional products, with excellent cycle characteristic
Data Source
AI summary
A nickel electrode for an alkaline secondary battery includes an electrically conductive base plate, and an active material particle supported on the conductive base plate and including a complex particle with a surface layer that mainly formed of a high-order cobalt compound whose oxidation number of cobalt is higher than +2 on a surface of a core layer particle that forms a high-order nickel hydroxide whose oxidation number of nickel is higher than +2. Lithium (Li) is contained to be a solid solution in the active material particle from 0.01 to 0.5 wt % of a converted amount as a lithium metal by weight of lithium metal divided by a total weight of the high-order nickel hydroxide, the high-order cobalt compound and the lithium metal.