Zinc-air battery overview
A zinc-air battery is a primary battery that uses activated carbon to adsorb oxygen from the air or pure oxygen as the positive electrode active material, zinc as the negative electrode, and ammonium chloride or caustic alkali solution as the electrolyte. It is also known as a zinc-oxygen battery. Zinc-air batteries are divided into neutral and alkaline systems, represented by the letters A and P respectively, followed by numbers to indicate the battery model.
Zinc-air battery structure and principle
A paste-like zinc powder is placed at the anode, while carbon, acting as a catalyst, is located at the cathode. Holes in the battery casing allow oxygen from the air to enter the cavity and adhere to the carbon at the cathode. Simultaneously, the zinc at the anode is oxidized, similar to the chemical reaction in small silver-oxygen or mercury-oxygen batteries.
The cathode is a carbon anode that acts as a catalyst to absorb oxygen from the air.
The anode is a paste-like mixture of zinc powder and electrolyte.
Electrolyte – a highly concentrated aqueous solution of potassium hydroxide.
Isolation layer – used to isolate the movement of solid particles between two stages.
Insulation and sealing gaskets – nylon material.
The battery's outer surface—a nickel-metal casing—is a conductor with excellent corrosion resistance.
Advantages and disadvantages of zinc-air batteries_Which is better, zinc-air batteries or lithium batteries?
Working principle:
Cathode: Zn + 2OH⁻ = ZnO + H₂O + 2e⁻ Anode: O₂ + 2H₂O + 4e⁻ = 4OH⁻
Summary: 2Zn + O2 = 2ZnO
Typically, this reaction produces a voltage of 1.4 volts, but the discharge current and depth of discharge can cause voltage variations. Air must be able to continuously enter the anode; small holes are made in the positive electrode casing to allow a continuous supply of oxygen for the battery to produce a chemical reaction.
Zinc-air battery use
The key to storing zinc-air batteries lies in the seal. The cathode seal should not be removed unless the battery is ready for immediate use. Simulation tests show that at room temperature, the battery capacity drops to 95% after one year, 90% after two years, and still 85% after four years. Removing the seal activates the battery, and when not connected to a load at room temperature, the battery capacity decreases by 50% after 3 to 12 weeks, depending on the battery size, and drops to 0-10% after more than 20 weeks. Therefore, zinc-air batteries are suitable for applications where the battery will be depleted within a few weeks. Once the seal is removed, air enters and activates the electrochemical reaction. Even if the seal is reapplied, the electrochemical reaction will continue until the battery is completely depleted.
Advantages and disadvantages of zinc-air batteries_Which is better, zinc-air batteries or lithium batteries?
Advantages of zinc-air batteries
Compared with other traditional batteries, zinc-air batteries have the following advantages:
1. Large battery capacity
If the air electrode is functioning properly, the theoretical capacity of a zinc-air battery is determined by the amount of negative electrode active material. The negative electrode (zinc electrode) is located inside the battery, while the positive electrode (air electrode) is located immediately inside the battery casing. Since the positive electrode active material comes from oxygen in the air, the air electrode occupies very little space within the battery. Therefore, for the same volume and weight, a zinc-air battery can hold more negative electrode reactive material, resulting in a higher capacity compared to traditional batteries (the manufacturing cost of a zinc-air battery is roughly the same as that of a similar alkaline zinc-manganese battery, but its capacity is more than 2.5 times that of a similar alkaline zinc-manganese battery and 5-7 times that of a regular dry cell battery).
2. High specific energy
The theoretical specific energy of zinc-air batteries is 1320 Wh kg⁻¹, while the actual specific energy has reached 220–300 Wh kg⁻¹.
3. The discharge curve is stable.
During discharge, only oxygen reduction occurs at the positive electrode while the air electrode itself remains unchanged, while zinc is oxidized and lost at the negative electrode. The zinc electrode voltage is stable, so the battery voltage changes little during discharge, with a relatively long discharge plateau around 1.3V.
4. Low self-discharge and long storage life.
During storage, the air inlet of the battery is sealed, and the air electrode is isolated from the outside. As long as air is prevented from entering the zinc-air battery, the electrochemical reaction of the zinc-air battery cannot be carried out, thus the battery capacity loss is small, and the annual capacity loss is less than 2%.
5. Low production cost and low price
The positive electrode active material is oxygen from the air, which is inexhaustible and does not require purchase. The negative electrode active material, zinc, is abundant and inexpensive.
6. Environmentally friendly and pollution-free
Zinc-air batteries eliminate toxic substances such as lead, mercury, and cadmium found in traditional batteries, thus solving the pollution problem of traditional batteries. Moreover, the main reaction product after battery use is zinc oxide, which can be easily recycled.
Advantages and disadvantages of zinc-air batteries_Which is better, zinc-air batteries or lithium batteries?
Problems (disadvantages) that need to be addressed in zinc-air batteries
Although zinc-air batteries have many advantages, their development is limited by the following shortcomings.
1. Battery type
To date, commercially available zinc-air batteries are mainly of two types: square and button. However, cylindrical zinc-air batteries, especially small cylindrical ones, which have huge market demand, have not seen any breakthrough development at home and abroad due to their complex structure and have not yet been mass-produced.
2. Battery sealing issues
One of the main reasons why cylindrical zinc-air batteries have not seen widespread development is the difficulty in sealing them. Zinc-air batteries require a continuous supply of oxygen from the air to discharge, so they are not completely sealed; the battery casing has one or more air pores, allowing the inside of the battery to communicate with the outside. If the air electrode, especially the waterproof and breathable membrane, is poorly made, the battery is prone to alkali seepage and leakage, electrolyte evaporation and drying, or electrolyte thinning due to moisture absorption. External CO2 can also enter the battery, causing electrolyte carbonate formation. All of these factors severely affect the performance and quality of the zinc-air battery.
The catalyst in the air electrode needs improvement.
4. Some problems with zinc electrodes
Zinc electrodes undergo corrosion and self-discharge. Zinc electrodes are thermodynamically unstable in alkaline solutions; zinc dissolves and self-discharges, releasing hydrogen gas. Furthermore, due to impurities in the zinc electrode and its often non-uniform surface, electrochemical activity varies significantly at different points. This creates numerous micro-cells within these cells, causing zinc corrosion.
Advantages and disadvantages of zinc-air batteries_Which is better, zinc-air batteries or lithium batteries?
Which is better, zinc-air batteries or lithium batteries?
Zinc-air batteries have been around for over 100 years, initially used in applications such as railway signal lights. Compared to traditional batteries, the biggest advantage of zinc-air batteries is their environmental friendliness. During operation, the zinc at the negative electrode only reacts with the OH- ions in the electrolyte and oxygen in the air, thus producing no atmospheric pollutants throughout the discharge process.
Furthermore, zinc-air batteries are renowned for their energy density, generating 0.3 kWh per kilogram, double that of lithium-ion batteries. This means that although they weigh only half as much as lithium-ion batteries, zinc-air batteries offer twice the driving range, and the increased energy capacity does not make them more prone to explosion. Moreover, because they use only oxygen from the air and relatively inexpensive zinc, the cost of zinc-air batteries is also reduced; reportedly, their mass-produced price will be only one-third that of lithium-ion batteries.
