Alkaline Batteries

INTRODUCTION

Alkaline batteries are primary batteries that derive electrical energy from the chemical reaction between manganese oxides and zinc metal. Alkaline batteries were first invented by scholar Waldemar Jungner and Thomas Edison way back in the early 1900s. The science of making batteries that utilizes alkaline electrolyte instead of acids got momentum in the application in the early 1990s from point of their invention as many opt for the use of dry alkaline batteries due to the improved potential difference compared to the then wet cell batteries. In the early 1950s, a Canadian scientist by name Lewis Urry applied the alkaline batteries concept of scholar Edison and Jungner and fused it with the Zinc/Manganese chemistry to develop the modern portable dry cell alkaline batteries while working for Eveready Battery Company.

The development of alkaline batteries has improved with time as currently there are sizable alkaline batteries in the market with high EMF and reduced environmental risks. Ranging from simple to highly sophisticated forms, alkaline batteries exist in a plethora of varieties. Generally, alkaline cells are electrochemical cells that generate electric current through a series of chemical reactions. Alkaline batteries basically consist of two electrodes; that is cathode terminal where all reduction reactions take place and anode where all oxidation reactions take place. The flow of dislodged electrons is from the positive terminal (anode) to the negative terminal (cathode).

Construction of the alkaline battery

The construction of an alkaline battery consists of a hollow stainless steel metal drum that hosts all other battery elements and at the same time serves as the cathode terminal. The anode of alkaline batteries is projected on the top of the stainless steel drum enclosing the battery. The hollow cylindrical drum is filled with a fine-grained manganese oxide powder (MnO2) properly mixed with coal dust or graphite. For insulation and avoidance of short-circuiting, the inner surface of the moulded cathode is separated by a layer of a paper separator. The moulded inner portion of the battery made from coal dust and manganese oxide forms the cathode of the alkaline battery.

The innermost and central space provided by paper separator is filled with potassium hydroxide and zinc powder. The zinc powder forms the positive terminal of the battery and its powder form is to increase the contact surface. The paper separator in the middle of the hollow drum is soaked in potassium hydroxide that holds the electrolyte in between the positive terminal (anode, Zn) and the negative terminal (cathode, MnO2). A brass metallic pin is laterally inserted along the central axis to concentrate the negative charges and this pin is often referred to as the collector pin as it is connected to the end sealed end anode cap. Within the ends of the metallic seal, caps lays a plastic cover that electrically separates the negative end cap from a positive end cap of an alkaline battery.

Generation of electricity through REDOX reaction in alkaline batteries

Alkaline batteries source power to many of the devices that we use in daily operations such as mobile phones, calculators, wall clocks, wristwatches and some other devices. The electric current generation in alkaline cells involves moving electrons carrying electric charges through a wire from battery to the electric device. This is facilitated by chemical reactions within the cells of the battery that ensure the transfer of an electron carrying charge. Therefore the transfer of electron and chemical reactions result in the generation of electric energy.

Alkaline batteries despite being referred to as the dry cells, they are typically ‘wet cells’ since their electrolyte is a paste of an acid or acidic water-based paste having either NH4Cl, ZnCl2, MnO2 starch or graphite.

The process of the electric current generation in alkaline batteries occurs through two reactions; that is through oxidation reaction at the anode and reduction reaction at the cathode.

The first half-reactions at the anode (oxidation reaction) and at the cathode (reduction reaction) are as follows. Generally, the “redox” reaction entails one atom losing electrons and another atom gaining these electrons in a chemical reaction.

Oxidation at anode

Zn_(s)  → Zn²⁺⁽_aq)+2e

Zn(s)+2OH−(aq)→ZnO(s)+H2O(l)+2e−

Reduction reaction at cathode

MnO_2(s) + 2NH₄⁺_(aq) + 2e⁻ → Mn2O3_{(s) +} 2NH_3(aq) + H₂O_(l)

2MnO2(s)+H2O(l)+2e−→Mn2O3(s)+2OH−(aq)

The oxidation of zinc metal Zn(s) results to the formation of zinc ions Zn²⁺ and reduction reaction at the cathode results to the release of NH3 and Cl- in the solution. There4fore the Overall reaction becomes

 2MnO₂(s) + 2NH₄Cl(aq)  + Zn(s) → Mn2O3(s) + Zn(NH₃)2Cl2(s) + H₂O(l)

Zn(s)+ 2MnO₂(s ) → ZnO(s )+ Mn₂O₃(s)

Durability of Alkaline Batteries

Alkaline batteries are generally non-rechargeable non-rechargeable batteries and the lasting period depends on the specifications of manufactures therefore it is quite difficult to quantify a specific time period of the cells. However, research has established that they can last for about five to ten years when kept at room temperature and other preferable conditions. On run time while in operations also depends on the rate of the voltage of EMF dispensation by the device.

Advantages and disadvantages of alkaline batteries

Alkaline batteries since their invention back in the 1900s have maintained market preference due to more advantages over other types of batteries. Some of the advantages and disadvantages are as follows

Advantages

• Alkaline batteries have a prolonged shelf life compared to other paste-based electrolyte batteries
• Alkaline batteries have higher energy density than other batteries. through this, they produce the almost same energy as others but last much longer than then.
• They are rechargeable batteries, therefore, when properly charged they can last for hundreds of times
• They are considerably cheaper compared to other sophisticated batteries such as cadmium or nickel.
• The disposal procedure is quite simple therefore can be disposed of just like any other waste hence does not require any complicated disposal techniques.
• They are capable to operate effectively even in low temperatures
• When properly stored at room temperature conditions, they can last for more than 4 years and still retain over 90% of the charge.

Disadvantages

• The internal resistance of alkaline batteries are quite high compared to lithium batteries that give much energy
• When not properly charged might results in explosion thus posing danger
• Alkaline batteries are left unused in devices for long might leak thus completely destroying the circuit systems of the device.
• In terms of size, alkaline batteries are quite bulkier than other dry cell batteries.

Disposal method/recycling of the used alkaline cells

One of the advantages of alkaline batteries is on the environment safety since they can be safely disposed of just like other regular wastes in most locations, however, it is not encouraged to dispose these batteries on landfills since there are some elements of heavy metals like mercury that might cause complications and hazards. The warning is that they should never be exposed to fire or higher temperatures since they might explode causing fire hazards. In most developed countries with dispensable waste management has embraced alkaline battery recycling by companies responsible for their production thus reducing the chances of hazards they would pose when disposed of in landfills.

Environmental impact of disposal

Proper disposal of these batteries has a positive impact on the environment as this prevents the release of heavy metals such as potassium, zinc or manganese into the environment thus helps in conserving the environment. Recycling alkaline batteries proved to be the most environment cognisant method of disposing of batteries that have received 100% support by environmentalists

Conclusion

Alkaline batteries are the true proliferation for portable or hand-held electronics such as watches, calculators, remotes, etc.. since their discovery in the 1900s by Urry, they have been detrimental in the power supply for essential hand-held devices. They utilize REDOX chemical reactions to dispense electrons through manganese ions and zinc ions to generate electricity. They are the preferred choice among other dry cell batteries due to their numerous advantages such as portability, high EMF and most importantly environmental safety in their disposal mechanisms.

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