Zinc-silver oxide batteries, also known as zinc-silver-oxide batteries, may experience a series of side reactions when overcharged. These reactions not only affect battery performance but may also shorten their lifespan. During overcharge, the elemental silver at the anode should normally be oxidized to silver oxide. However, if the charging process is uncontrolled, hydroxide ions at the anode may be over-oxidized to generate oxygen. Although this reaction is not part of the standard charging process for zinc-silver oxide batteries, it can occur under overcharge conditions, leading to increased internal battery pressure and posing a safety hazard. Simultaneously, if the zinc hydroxide at the cathode is excessively reduced, metallic zinc may precipitate. Uneven zinc deposition can easily form dendrites, which may puncture the separator, causing an internal short circuit.
The silver oxide cathode may also undergo structural changes during overcharge. During normal charging, silver oxide, as the active material, is reduced to silver. However, overcharge may cause silver oxide to react further, generating silver compounds with higher valence states, such as silver peroxide. This structural change alters the electrochemical properties of the cathode, reduces the battery's charge and discharge efficiency, and may accelerate the battery's aging process. Furthermore, overcharging exacerbates internal side reactions in the battery, such as electrolyte decomposition. In alkaline electrolytes, overcharging can cause water molecules in the electrolyte to be electrolyzed, generating hydrogen and oxygen, further increasing internal battery pressure and consuming electrolyte, thus affecting the battery's ion conductivity.
To suppress side reactions during overcharging of zinc silver oxide batteries, several approaches can be taken. Regarding electrolyte modification, specific additives can be added to inhibit side reactions. For example, the addition of certain organic solvents or inorganic salts can alter the electrochemical stability window of the electrolyte, reducing electrolyte decomposition during overcharging. These additives form a protective layer by adsorbing onto the electrode surface or reacting with active materials in the electrolyte, preventing further side reactions.
Optimization of electrode materials is also crucial for suppressing side reactions. For silver oxide cathodes, their overcharge resistance can be improved by doping with other metal elements or altering their crystal structure. Doping elements can stabilize the crystal structure of silver oxide, preventing structural changes during overcharging. Meanwhile, optimizing the zinc anode fabrication process, such as employing porous structures or surface coating technologies, can improve the uniformity of zinc deposition and reduce dendrite formation. Porous structures provide more deposition sites, allowing zinc ions to be deposited more uniformly on the anode surface; while surface coatings form a physical barrier, preventing the direct growth of zinc dendrites.
The introduction of a battery management system (BMS) is also an effective means of suppressing overcharge side reactions. By precisely controlling the charging current and voltage, the battery is prevented from being in an overcharged state for extended periods. The BMS can monitor battery parameters such as voltage, current, and temperature in real time. Once an overcharge signal is detected, the charging strategy is immediately adjusted, such as reducing the charging current or stopping charging, to protect the battery from damage.
The selection and improvement of the separator are equally important. High-performance separators can effectively prevent zinc dendrite penetration, preventing internal short circuits in the battery. Novel separator materials, such as polymer separators with high porosity and good mechanical strength, can provide better ion conduction performance and physical isolation effects. Simultaneously, surface treatment technologies for the separator, such as coating with inorganic nanoparticles or organic polymer materials, can further improve its resistance to dendrite penetration.
