Alkaline zinc manganese batteries are very popular in the current market. Especially when people’s need for environmental protection is increasing, mercury-free alkaline batteries are the inevitable result of the development of alkaline batteries.
The main measure to achieve mercury-free alkaline batteries is to use additives that can replace mercury in the battery, such as various inorganic or organic additives. However, no matter which additive combination is used, indium is an indispensable component.
Indium is a rare metal element and plays a very important role in achieving mercury-free alkaline batteries. This post will introduce you in detail from three aspects: the characteristics of indium, how to use indium and the role of indium.
Characteristics of indium
Indium is a bright, soft, silvery-white metal. It is not found in high amounts in nature. It has good wear resistance, corrosion resistance, and lubricity. It is mainly used as a coating for metals or alloys such as copper, lead, zinc, tin, and silver to improve the wear resistance, corrosion resistance, and electrical conductivity of metals or alloys.
Indium is very active in acidic environments and exists mainly in the form of indium ions, which can displace hydrogen in acidic solutions. Indium exists mainly in the form of indium oxide in alkaline solutions, and it is very stable in this environment, which is why it is used in alkaline electrolyte batteries.
How to use indium
1. Add indium to zinc powder
Indium is mainly obtained from smoke, slag, and electrolytic anode waste in zinc and lead-zinc smelting. It can be extracted from indium-containing minerals with sulfuric acid or hydrochloric acid. Of course, indium phosphate can also be precipitated from a slightly acidic solution with phosphoric acid, then dissolved and converted into oxides in a strong alkaline solution, and then reduced to metallic indium with hydrogen or carbon. In the manufacturing process of alkaline batteries, zinc-indium alloy can be made by adding indium to zinc powder.
2. Add indium trioxide or indium hydroxide to alkaline solution
The standard electrode potential of indium in alkaline solution is much higher than that of zinc, so indium added to alkaline solution is easily replaced by zinc, forming a zinc-indium alloy or compound coating on the surface of zinc powder. Generally speaking, the effect of adding indium to alkaline solution is better than that of zinc-indium alloy.
3. Indium plating on the current collector copper needle
Compared with tin plating on the negative current collector copper needle of traditional alkaline batteries, indium plating has many advantages.
First, tin is easily oxidized in air, while indium is very stable in air. Indium plating can not only improve the welding performance of metals or alloys, but also improve the oxidation resistance of metals or alloys.
Secondly, the hydrogen evolution overpotential of indium is higher than that of zinc, so indium-plated copper needles can inhibit hydrogen evolution and reduce the self-discharge loss of the negative electrode.
In addition, the contact resistance between zinc-plated copper needles and zinc powder is small. Indium is very soft and easy to deform, which can improve the vibration resistance of batteries, etc.
These advantages of indium make indium-plated copper needles widely used in alkaline batteries.
Role of indium
1. Improve hydrogen evolution overpotential
The main role of mercury in alkaline batteries is to increase the hydrogen evolution overpotential on the surface of zinc powder. The only ones with higher Hydrogen evolution overpotential than zinc are lead, cadmium, mercury, thallium, and indium. Except for indium, the other four metal elements are harmful to the environment. Therefore, indium has become the only metal with a higher hydrogen evolution overpotential than zinc and is safe and environmentally friendly.
Indium easily forms alloys with other metals, which can reduce the hydrogen evolution overpotential on impurity metals in batteries.
2. Improve zinc activity
Indium readily alloys with zinc and, similar to mercury, can provide stability to zinc by increasing its equilibrium electrode potential. More importantly, indium can prevent the passivation of zinc and improve the dissolving activity of zinc.
3. Reduce the contact resistance of the negative electrode and improve the battery’s vibration resistance
Indium has very significant plasticity properties. This enables good electrical contact between zinc powders and between zinc powder and current collector. Especially when the battery is impacted, indium can ensure the electrical contact of the negative electrode because it can deform, so indium can reduce the contact resistance of the negative electrode. , and improve the battery’s vibration resistance.
From the above, we know that indium can replace mercury and plays a very important role in alkaline batteries. However, it must be said that indium cannot fully achieve the role of mercury in alkaline batteries. Therefore, in mercury-free alkaline batteries, in addition to adding indium, other substances need to be added to maximize the potential of alkaline batteries. Release it.
About the Author
Liteway is a professional manufacturer and supplier of alkaline batteries, carbon-zinc batteries, and lithium batteries based in Ningbo, China.
We have more than 20 years of manufacturing and exporting experience in the battery field, providing battery manufacturing and OEM/ODM services to customers all over the world. We are a co-manufacturer for many battery brands and have been unanimously recognized by our partners during the cooperation process.
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