Lew Urry developed the alkaline-manganese cell, at the Eveready Battery Company Laboratory in Parma, Ohio in 1949 (Aifantis, Hackney & Kumar 2010, p. 36). The development of the alkaline cells stemmed from the idea that it was able to supply more total energy at elevated currents compared to the Leclanch? cells that were majorly used at that time. Over the years, increased technological discoveries and advancements have led to further improvements by increasing the energy storage within a particular size package. A year later, an independent inventor called Samuel Ruben developed the zinc-mercuric oxide alkaline cell that later became Duracell. Duracell was licensed to the P.R. Mallory Co. Since that time; mercury compounds have been eliminated from the cells to minimize environmental pollution and risks. The alkaline cell is ideal for applications that require high voltages and high current continuous discharge, such as high power remote control, camera, electric toy, electric shaver, flashlight, and CD player.
Chemical reaction responsible for electricity production
In the alkaline cell, zinc is the negative electrode while manganese dioxide is and the positive electrode (Hummel 2011, p. 107). The potassium hydroxide alkaline electrolyte is, however, not part of the reaction since only the manganese dioxide and zinc are consumed during the discharge (Abdullah 2012, p. 229). The potassium hydroxide as an electrolyte does not undergo consumption. The reason is that there are equal amounts of ions of OH? produced and consumed. The equations for the reaction are as shown below.
Zn + 2 OH- ?Zn (OH)2 + 2e- (oxidation)
2 MnO2 + H2O + 2e-? Mn2O3 + 2 OH- (reduction)Basic set up of the alkaline cell
The basic set up of the alkaline cell is as illustrated in the diagram below. The major components of the cell include the cathode, separator, cathode cap, anode, insulator, anode cap, and anode collector.
The generation of electricity in the alkaline cells is by the redox reaction. In the alkaline cells, power is generated by the reduction-oxidation reaction that takes place at the anode (Zinc) and cathode (Manganese Oxide) through an electrolyte (potassium hydroxide). The redox reaction results in the flow of electrons from the anode (oxidation reaction) to the cathode (reduction reaction) to create a reduction potential of the half-reactions (Linden and Reddy 2002, p. 10.4).
The equations for the reactions and the EMF of the alkaline cellThe half-equation for the reaction
The half-equation for the reaction at the cell is given as
Zn(s) + 2OH?(aq) ? ZnO(s) + H2O(l) + 2e? [e° = 1.28 Volts] (Abdullah 2012, p. 229)
2MnO2(s) + H2O(l) + 2e? ? Mn2O3(s) + 2OH?(aq) [e° = +0.15 Volts]
The complete equation for the reaction
The complete equation for the reaction of the cells is expressed as
Zn(s) + 2MnO2(s) + ZnO(s) + Mn2O3(s) [e° = 1.43 Volts] (Linden and Reddy 2002, p. 10.4)
The EMF of the cell
The EMF of the cell is calculated by adding the half-equations
Anode: Zn(s) + 2 OH-(aq) ?ZnO(s) + H2O(l) + 2e-; [e° = 1.28 Volts]
Cathode: 2 MnO2(s) + H2O(l) + 2e- ? Mn2O3(s) + 2 OH-(aq); [e° = +0.15 Volts]
Overall reaction: Zn(s) + 2 MnO2(s) ?ZnO(s) + Mn2O3(s) [e° = 1.43 Volts]
Therefore, the EMF of the cell = 1.28 + 0.15 = 1.43 V
Alkaline cells last for a long period and have a comparatively long shelf life of at least 2 years during which they can retain about 90% of their original charge capacities. As a result, they have better performance at both high and low temperatures. In addition, there are two types of alkaline batteries available namely premium alkaline and standard alkaline.
Advantages and disadvantages of Alkaline CellAdvantages
One of the benefits of alkaline cells is reduced costs. Instead of discarding the standard alkaline cells, they can be recharged to save money. In addition, there is less environmental pollution from disposed electrolyte cells due to the reduced mercury content. Secondly, alkaline cells are significantly reliable compared to the nickel–cadmium battery since they do not suffer from loss of capacity due to shallow discharges or cell failure due to trickle charging. Thirdly, alkaline cells discharge slowly and consequently have a longer shelf life of characteristically between 2 to 4 years compared to nickel–cadmium battery whose shelf life is between 2 to 3 months (Aifantis, Hackney & Kumar 2010, p. 37). Therefore, they are appropriate for applications where the appliance requires standby power. Fourthly, alkaline cells have a superior power capacity per cell compared to most standard batteries such as nickel–cadmium battery and zinc-carbon battery. Fifthly, the alkaline cell has a higher voltage output (1.5 V) compared to nickel–cadmium battery (1.2 V) and this further increases its reliability.Disadvantages
On the other hand, alkaline cells have a high internal resistance that impairs their run time and leads to an early low battery warning in most appliances (Doble & Schoch, 2008, p 86). Consequently, alkaline cells will not last long in applications that have high start up current demands or even require much power while in use. In addition, rechargeable alkaline cells offer a much lower performance compared to standard alkaline cells although that variance has narrowed these days owing to superior technology and using perfect raw materials for the manufacturing. Secondly, recharging cells can sometimes be irritating and abrupt. However, keeping track of their usage and recharging at standard intervals when not yet fully discharged may greatly help in overcoming this problem. Thirdly, the high cost of the battery charger can be a drawback and a source of convenience. Furthermore, a defective battery charger may lead to the explosion of the alkaline cells. Fourthly, alkaline cells are bulkier compared to the other lithium cells that are capable of giving much higher energy.
Disposal method/recycling of the used Alkaline Cells
Alkaline cells can be disposed of as ordinary wastes in the landfills today owing to the 1996 reduction of the mercury content. Nevertheless, alkaline cells with high amounts of heavy metals such as lead and cadmium, corrosive chemicals, and mercury pose a significant challenge of disposal, particularly in the landfills. The biggest problem is the threat of environmental pollution and the danger imposed on human life, particularly those living or working near the landfills (Bernardes, Espinosa & Ten?rio 2004, p. 292). The authors argue further that the other methods of disposal of alkaline cells other than landfills are stabilization and incineration. The waste alkaline cells are not regarded as valuable materials. One of the common ways of recycling the alkaline cells is by shredding and separating the zinc and manganese case metals from the other components. Alternatively, the cells can be used as a furnace feedstock in the manufacture of products such as rebar and other low-grade steel metals. During this process, zinc metal is separated from the furnace components in the form of fumes.
Environmental impact of the disposal of Alkaline Cells
The extensive use of alkaline cells has resulted in many environmental concerns across the globe. To start with, the disposal of the used alkaline cells as electronic waste leads to pollution by the toxic chemicals and metals such as lead, cadmium, and mercury (Kang, Chen & Ogunseitan 2013, p. 5495). Secondly, the manufacturers of the alkaline cells consume the resources such as the metal ores as the primary raw materials, and this leads to environmental degradation due to the resulting landfills and the depletion of the natural resources. For instance in the United States, approximately 3 billion alkaline cells are purchased annually, and an estimated 179,000 tons of the waste alkaline cells end up in landfills throughout the country.
The alkaline cell is durable, produces much current, have long shelf life, and have a shell that is resistant to corrosion compared to carbon battery. In addition, the alkaline cell uses opposite electrode structure, and this leads to an increased relative volume between the anode and the cathode. Moreover, conductive potassium hydroxide solution replaces both the zinc chloride and ammonium chloride solution to improve the electric properties of the cell. Furthermore, the capacity and discharge time is between 3 to 7 times longer than that of an ordinary battery of the same model. Besides, during the discharge process, the reaction does not produce gas or bubbles, and this leads to a constant voltage.
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Kang, D, Chen, M & Ogunseitan, O 2013, Potential Environmental and Human Health Impacts of Rechargeable Lithium Batteries in Electronic Waste, Environmental Science & Technology, 47(10), pp. 5495-5503.
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