ENVIRONMENTAL ASPECTS OF BATTERIES

In this article, we will cover the environmental aspects of collection and recycling of batteries. It is not a secret that batteries represent one of the most ecologically problematic types of waste that can be found in everyday life. This is due to the operation principle of any battery as its characteristics depend on the type of electrochemical system and additives aimed at improving the quality and reliability of the battery. Let's take a look at the operation principle.

Operational principle

Using a watch battery as an example, we will demonstrate the construction of the battery. The principle is the same for AA batteries while taking into consideration differences in the form of the casing.

As we can see, in the casing consisting of two element divided by an isolator, electrochemical system is located, where reactions generating EMF are going. Let’s consider the composition of materials which all battery elements are made of:

Now let’s check what substances have changed due to the reaction while discharge:

As we can observe, zinc has turned into zinc oxide and manganese dioxide into manganese oxide. As zinc oxide occupies larger space than zinc that formed it, the excess pressure occurs in the casing, which often results in casing deformation and, sometimes, in its destruction. Because of overpressure the leakage of electrolyte through the gaps formed in sealed insulator between the casing components may happen.

So, where do voltage and energy come from? To understand this process let’s examine chemical reactions going on inside the battery:

As we see, oxidation of zinc and reduction of the oxide of manganese happen. In result of the reaction, zinc oxidizes on the cathode giving two electrons into external circuit and oxide of manganese restores on the anode by taking from external circuit two electrons for each molecule. Since the areas of the reactions divided by isolator, the electrons have nothing else to do but move through conductors from one electrode to another. The red lines show the motion of electrons. This is an electric current. So what does the voltage at the battery contacts depend on? In fact, the energy released during the reaction on the cathode is substantially greater than the energy spent on the anode reaction. Exactly this difference of energies drives the electrons. Assume, if energy released while reaction on the cathode is equal to 4 eV on each zinc atom, and energy absorbed while anode reaction is 1 eV per molecule of manganese dioxide, so two electrons will gain energy equal to residual of energies of two reactions, i.e. 3 eV. As there are two electrons, each of them will get energy equal to 1.5 eV, that is to say theoretical voltage on the not connected battery will be equal to 1.5 V. When battery is not connected electrical field created by battery prevents movement of ions through the electrolyte and reactions, that is why battery gives energy only when it is connected.

The use of harmful materials in the construction

Parameters of batteries such as operating voltage, power consumption, characteristic of the discharge, etc., depend on the type of the electrochemical system. That’s why the manufacturers are forced to use the heavy metals and harmful substances to build the battery with high-capacity, reliability and durability, to reduce self-discharge, etc. Besides the main heavy metal in batteries - zinc, there also may be added salts of mercury and cadmium, which prevent deterioration of components during storage and the flow of parasitic reactions, also compounds reducing the internal resistance and improving the quality of the electrolyte are added. The casing itself contains nickel and when it hits in a moist environment it corrodes and all metals pass into soluble compounds and are carried away by rainwater into the ground. Finally, the EMF of the battery, though depleted, contributes to rapid corrosion of one of the casing electrodes in the future leading to leakage of hazardous components of electrochemical systems. At the moment, the complete replacement of the connections by more secure ones is not possible because of its considerable influence on the characteristics of the battery, although studies in this field are carried out.

Promising solutions to the environmental problems of batteries

Despite the fact of an increased level of awareness and environmental responsibility of citizens of all countries of the world, it doesn't seem to be possible to solve the problem of proper recycling of batteries by collection methods. A certain percentage of the batteries is inevitably lost getting into environment. Therefore, the main solution for reducing heavy metals emission is the transition to the brand new operational principles of batteries. Hydrogen and its compounds have broad prospects since the result of its oxidation is simple water. Besides pure hydrogen, certain organic compounds have shown their ability to be used as power source components with different parameters and applications. Fuel cells based on methanol and ethanol are designed, whose work results in a formation of water and carbon dioxide. The industry of alternative power sources is experiencing intensive growth. Solar batteries are now embedded in certain cell phone models, calculators, watches and other portable electronic devices. This allows completely or partly get rid of batteries and significantly increase service life.

In conclusion, we can say that environmental friendliness of batteries has increased considerably these last years, as did requirements made by ecologists and governments of the countries. But still, the handling of such type of waste as batteries and accumulators should not be taken light-mindedly as each recycled battery saves the nature from negative impact of human. And pure nature, as we know, is a pledge of beauty and health of mankind.