Wet Cell BatteriesBy: Asmir, Jake, & Tyler

What is a wet cell battery?

A wet cell battery is an electrical device that uses electrical currents to provide power. They are called “wet” cell batteries because they use chemical reactions between electrodes and electrolytes in a liquid. What makes a wet cell battery different from other batteries is the electrolyte. There are 2 types of wet cell batteries: primary and secondary. A primary wet cell can be used only until the chemicals deplete and then can no longer function and react with each other. A secondary wet cell can be recharged and used over and over again. (Figure 1) is an example of a wet cell battery. As you can see, there are 2 electrodes (copper and nickel) that are placed into the electrolyte (acid). The battery is all connected using wires and the chemical reaction between the electrodes and the electrolytes is what provides that power.

Figure 1 | http://yongbaoenjanelleace.blogspot.com/2010/01/wet-cell-battery.html
Figure 1 | http://yongbaoenjanelleace.blogspot.com/2010/01/wet-cell-battery.html

History of Wet Cell Batteries:

It is believed by a few archaeologists that the first wet cell battery was created as far back as 2 000 years. In 1938, Baghdad Iraq, Wilhelm Konig and other archaeologists discovered a pot that contained a copper cylinder encasing an iron rod. When lime juice or vinegar is added to the pot, an electric current can be observed; however, there is not enough evidence to show that the pots were used for electricity, and therefore the theory is rejected. So, an Italian physicist, Count Alessandro Volta is credited still with the first ever battery. In the year 1798, Volta built the first ever battery that generated a consistent electric current, the voltaic pile. The voltaic pile was made up of a stack of paired copper zinc disks which are separated from one another by cloth or cardboard disks and moistened with a salt or acid solution (Figure 2). The copper is placed at the bottom of the pile as the positive end, and the zinc at the top as the negative end.

Figure 2 | http://upload.wikimedia.org/wikipedia/commons/0/06/Voltaic_pile.svg

This method, however, produced a few problems. To start with, the cardboard or cloths soaked in an electrolytic solution would leak down the pile and cause short-circuits. The cause of the leak was the weight of the zinc and copper disks on the cardboard or cloth. This problem was solved easily by placing the pile horizontally in a container, rather than vertically (Figure 3). Also, Volta's battery had another problem: the short battery life. Volta's Voltaic Pile, or “battery trough” when placed on it's side, would only last about an hour. This was caused mainly by polarization and local action. Local action is where small short-circuits would form around impurities in the zinc disks, which causes the zinc to degrade. This issue was solved by William Sturgeon, who found that by mixing some mercury into the zinc, the local action would be prevented. Moreover, polarization is caused by the electric current flowing through the circuit which causes the electrolytic solutions to electrolyze and produce a film of hydrogen bubbles. These bubbles form a barrier and increase the internal resistance of the battery. This problem was undertaken by a British chemist: John Frederic Daniell. Daniell's solution to the polarization problem in the Voltaic Pile was adding a second solution. In 1836, Daniell invented his own battery variation based on the Voltaic Pile, the Daniell Cell. The Daniell Cell is made up of a copper pot, filled with a copper sulfate solution, in which an earthenware container filled with sulfuric acid and a zinc electrode (Figure 4). The earthenware provided a barrier between the copper sulfate solution and sulfuric acid solution, but allowed the passage of ions through the barrier. The reactions at each electrode are illustrated as follows:
Zn(s) -> Zn2+(aq) + 2e-
Cu2+(aq) + 2e- -> Cu(s)
Using two solutions eliminates the hydrogen bubble problem as the bubbles produced by one solution are consumed by the second.

Figure 3 | http://upload.wikimedia.org/wikipedia/commons/thumb/9/93/Trough_battery.jpg/222px-Trough_battery.jpg
Figure 4 | http://www.ieeeghn.org/wiki/images/2/22/Daniel_cell.png

How does a wet cell battery work?

A lead acid battery is a secondary wet cell battery that contains lead, lead oxide, plates and an electrolyte solution that contains a mixture of water and acid. The plates in this type of wet cell battery can either be anodes attached to the negative battery terminal or cathodes attached to the positive battery terminal. For the battery to work a load is attached to the terminal and a chemical reaction occurs between the electrolyte solution, the lead, and the lead oxide. The chemical reaction causes electricity to flow through the terminals to the load. When the battery needs to be recharged, the acid is returned to liquid solution to provide more power later.

Rechargeable Lead-Acid Battery:

Moving forward into 1859, lead-acid rechargeable batteries were developed by a French physicist named Gaston Plante (Figure 5: Modern Day Lead-acid batteries). A lead-acid battery is different from most wet cell batteries as it does not rely on the difference in the two metals' potential in an electrolyte. A lead-acid battery, instead, uses the same metal: lead. Because lead does not dissolve in the sulfuric acid, and there is no potential difference between the two metals' as they are the same metal, the cell is stable and there is no reaction. This type of battery uses an initial charge to forcibly remove electrons from the cathode and add these electrons to the anode. This will then split the water molecules into hydrogen and oxygen. The hydrogen bubbles and is drawn off and the oxygen binds to the lead at the cathode, thereby producing lead (II) oxide.

Anode: 2H+(aq) + 2e− → H2(g)
Cathode: Pb(s) + 2H2O(l) → PbO2(s) + 2H+(aq) + 2e−

When discharging, both plates of lead are changed into lead sulfates.

Anode: Pb(s) + HSO4−(aq) → PbSO4(s) + H+(aq) + 2e−
Cathode: PbO2(s) + HSO4−(aq) + 3H+(aq) + 2e− → PbSO4(s) + 2H2O(l)

To recharge these lead-acid batteries, electrons are forcibly removed from the anode and introduced at the cathode. This changes the lead sulfates back into lead and lead (II) oxide, and the battery can be used once more.

Anode: PbSO4(s) + H+(aq) + 2e− → Pb(s) + HSO4−(aq)
Cathode: PbSO4(s) + 2H2O(l) → PbO2(s) + HSO4−(aq) + 3H+(aq) + 2e−

Figure 5 | http://www.kollewin.com/EX/09-16-15/Deep-Cycle-Sealed-Lead-Acid-Battery.jpg

Nickel-Cadmium Battery:

A nickel-cadmium (NiCd) battery is a rechargeable wet cell battery which uses nickel oxide-hydroxide at the cathode, cadmium at the anode, and an alkaline electrolyte, such as potassium hydroxide (Figure 6). The reactions within this battery are as follows:

Anode: Cd(s) + 2OH-(aq) -> Cd(OH)2(aq) + 2e-
Cathode: 2NiO(OH)(aq) + 2H2O(l) + 2e- -> NiO(OH)2 + 2OH-

This nickel-cadmium battery has many pros and cons. To start with, the NiCd battery is more durable than most batteries. It is much tougher to damage as it tolerates deep discharge for long periods. Other batteries are permanently damaged when discharged beyond a minimum voltage. Also, the NiCd battery has lower internal resistance than other batteries, such as the Nickel-metal hydroxide battery. In addition, the NiCd battery has typically over 500 cycles of use and is available in a variety of sizes and capacities. In contrast, NiCd batteries also have a variety of disadvantages. For example, the battery is susceptible to damage through over-charging. This type of battery also has a lower cell voltage when compared to alkaline batteries. The NiCd battery has a typical cell voltage of 1.2V whereas the alkaline battery typically has a cell voltage of 1.5V. These batteries are relatively inexpensive for low power uses, but when used for the same capacity as a lead-acid battery, it can be 3 or 4 times as expensive. Typical applications of the nickel-cadmium battery include power tools, two way radios, electric razors, emergency lighting, and various toys.

Figure 6

Lithium-Ion Battery:

A Lithium-ion battery is a family of rechargeable batteries where the lithium ions are transferred from the negative electrode to the positive electrode. This type of battery is the most commonly used in portable electronics. Lithium-ion batteries are also used in military purposes, electric vehicles and also in aerospace applications.

During discharge, the Li+ carry the current from negative electrodes to positive electrodes. When a lithium based cell is discharging, the lithium is extracted from the anode and inserted into the cathode. Whereas during charging the current moves from positive electrodes to negative electrodes. When the cell is charging, the lithium is extracted from the cathode and inserted into the anode.

Discharge Electrochemistry:
Li(aq)+ + LiCoO2(s) -> Li2O(s) + CoO(s)
Charging Electrochemistry:
LiCoO2(s) -> Li(aq)+ + CoO2(s)

In a lithium battery, the lithium ions are transported to and from the cathode or anode with cobalt which is oxidized from Co3+ to Co4+ during charging and is reduced from Co4+ to Co3+ during discharge.

Lithium ion batteries have many advantages. One advantage of lithium ion batteries is that they are rechargeable and can be used over and over again. Also, they have a very low self-discharge, meaning the life of batteries is longer and they have a higher charge. Another advantage to lithium ion batteries is that they have no memory card effect, meaning that you can recharge them whenever you need to without waiting for them to completely discharge. Lastly, lithium ion batteries are much lighter than other batteries and can come in almost every size.

A lithium ion battery has a few disadvantages. To start with, a lithium ion battery will begin to degrade immediately after production. A standard lithium ion battery will last 2-3 years before becoming ineffective. Also, a lithium ion battery will degrade faster than some other batteries when exposed to higher temperatures. This means that it will degrade faster when being recharged, as heat is produced in a lithium ion battery during recharge. In addition, the lithium ion battery is fairly expensive to produce, therefore, it is more expensive to the consumer.

Dangers and Proper Disposal Methods:

Wet cell batteries typically contain an acid, most commonly sulfuric acid, and lead. To start with, as long as the acid remains within the battery casing, it has no harmful effects to humans or the environment. However, when the acid leaks out of the battery, the acid is a hazard. Sulfuric acid, when in contact with ones skin, can burn human skin. Also, the acid itself as well as the fumes produced can cause serious damage to eyes, such as blindness, if exposed. Furthermore, sulfuric acid can produce a flammable gas which may explode if exposed to sparks or a flame. Another effect upon the human body is lead build up. As these batteries typically contain lead, the lead will accumulate in the body. This is especially negative as lead is a toxic substance and will obstruct bodily functions over time. Lead is especially bad for children as high amounts of lead will obstruct the development of the nervous system and can cause permanent learning and behavioural disorders. In addition to the negative effects to humans through direct interaction, improper disposal of these wet cell batteries can have negative environmental effects. Firstly, the effects of sulfuric acid and lead poisoning also effect animals and plants to an extent. Furthermore, the sulfuric acid and lead can contaminate soil if the soil is exposed to the substances. Also, the sulfuric acid can reach the water table through the soil and contaminate water supplies as well. Similarly, lead can also contaminate water sources. Through these methods, the improper disposal of batteries causes both direct harm to humans, plants, and animals as well as long term effects on soil and water supplies.

To properly dispose of batteries, certain companies and disposal programs have been developed such as Toxco. These companies will take the batteries to a plant specially designed to properly dispose of and handle, and recycle the waste products of batteries and other technologies. Once a battery reaches the end plant, the battery is taken apart in a hammer mill, which simply breaks apart the battery into various pieces. These pieces are placed into containers where they are separated naturally. The heavy metals, such as zinc, sink to the bottom, the lighter objects, such as plastic, will float. The plastics are removed first, followed by the liquids, such as sulfuric acid, which leaves only the heavy metals in the container. The plastics can be recycled by drying them, cleaning them, and placing them into a plastic recycler where they will be melted down and remodeled into pellets used for battery casing once more. The sulfuric acid has two possible fates. In one fate, sulfuric acid can be neutralized into water which is treated, cleaned, and tested to meet clean water standards. The other option is to convert the acid into sodium sulfate, which can be used in laundry detergent, glass, and textile manufacturing. The lead can be recycled similarly to the plastic. The lead is melted down and placed into molds. The impurities in the lead will eventually float to the top of the molten lead. These impurities are removed, and the ingots are left to cool. These lead ingots are then reused in other batteries by battery manufacturers. Batteries other than lead-acid batteries are also recycled in a similar process. All components are shredded and broken apart, separated, cleaned and resold if possible.