Silver Oxide Alkaline Battery Charging to Avoid AgO Instability
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Solution Overview
Problem
Alkaline secondary batteries with silver oxide positive electrodes face challenges in maintaining charging-discharging cycle characteristics due to capacity drops and instability, particularly in the initial stages, and are prone to swelling and liquid spills due to the instability of AgO in alkaline electrolytes.
Innovation Solution
Incorporating insulating inorganic particles and carbon particles, such as graphite and carbon black, into the positive electrode mixture, along with a specific charging method that controls the oxidation reactions to prevent the formation of unstable AgO, and using an alkaline electrolyte containing potassium hydroxide, sodium hydroxide, and polyalkylene glycol to enhance cycle stability and prevent capacity drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If silver oxide is used as the positive electrode active material to achieve high discharge capacity and flat voltage, then the battery exhibits excellent discharging performance, but non-conductive silver oxide crystals form around silver particles during charging, hindering the charging reaction and decreasing utilization rate of active material
Solution Approach 1:
Conductive carbon particles are introduced as an intermediary substance between the silver oxide crystals and the electrolyte. These carbon particles form a conductive network that allows charge transfer to continue even when silver oxide crystals surround the silver particles, preventing the isolation of active material and maintaining charging reaction efficiency.
Solution Approach 2:
The positive electrode is designed as a composite material system containing silver oxide, conductive carbon particles, and insulating inorganic particles. This composite structure combines the high discharge capacity of silver oxide with the charge transfer capability of carbon and the electrolyte retention of inorganic particles, resolving the contradiction between discharge performance and charging efficiency.
2Quantity of substance
If AgO is formed during charging to increase battery capacity, then the charging capacity increases, but AgO is unstable in alkaline electrolyte solution, causing gas generation, battery swelling, and liquid spills
Solution Approach 1:
The charging voltage parameter is controlled to remain below the threshold required for AgO formation (typically keeping charging voltage below 1.7V vs. Hg/HgO reference electrode). This parameter change prevents the oxidation of Ag2O to AgO, avoiding the instability and harmful effects of AgO while still achieving acceptable charging capacity through the reversible Ag/Ag2O couple.
Solution Approach 2:
The instability of AgO, which causes gas generation and battery swelling, is converted into a benefit by deliberately avoiding AgO formation. The charging process is designed to stop at Ag2O formation, which is stable in alkaline electrolyte, thereby preventing the harmful effects while maintaining sufficient charging capacity for secondary battery operation.
3Reliability
If insulating inorganic particles are added to the positive electrode to improve charging-discharging cycle characteristics, then cycle stability improves, but the battery capacity may decrease due to displacement of active material
Solution Approach 1:
Insulating inorganic particles are distributed locally within the positive electrode mixture rather than uniformly throughout. This local distribution allows them to perform their function of improving cycle characteristics at specific locations where they stabilize the electrode structure, while minimizing their overall volume fraction to preserve battery capacity.
Solution Approach 2:
The content of insulating inorganic particles is optimized within a specific range (typically 1-10 wt% of the total electrode mixture). This parameter optimization ensures sufficient improvement in charging-discharging cycle characteristics while limiting the displacement of active material to an acceptable level, thereby maintaining adequate battery capacity.
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 significantly reduces capacity drops in the initial charging-discharging cycles, improves overall cycle characteristics, and minimizes the risk of battery swelling and liquid spills, thereby extending the battery's lifespan and storage stability.
Implementation Method 1
an oxidation reaction from silver to silver oxide (I) progresses while an oxidation reaction from silver oxide (I) to silver oxide (II) does not progress
Implementation Method 2
an alkaline electrolyte containing potassium hydroxide, sodium hydroxide, and polyalkylene glycol
Data Source
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AI summary
This alkaline secondary cell disclosed with this application includes a positive electrode comprising a positive electrode mixture layer that contains silver oxide; a negative electrode; and an alkaline electrolyte, wherein the positive electrode mixture layer further contains insulating inorganic particles and carbon particles, and contains graphite particles and carbon black particles as the carbon particles, the negative electrode contains zinc-based particles selected from zinc particles and zinc alloy particles, and the alkaline electrolyte contains potassium hydroxide or sodium hydroxide, lithium hydroxide, and polyalkylene glycols. Also, with a charging method and charging device of the alkaline secondary cell disclosed with this application, the charging voltage during constant voltage charging is set to a voltage for which with the positive electrode, an oxidation reaction progresses from silver to silver oxide (I), but the oxidation reaction does not progress from silver oxide (I) to silver oxide (II).