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September 25 2012 3 25 /09 /September /2012 19:37

The batteries in common use today have a small variety of chemicals that are used to create power. The electricity is created by separating one chemical reaction into two parts and harnessing the flow of electrons between those two parts. Many chemical reactions can be used, but only a few have the properties required by modern batteries.

 

The first primary cells (non rechargeable batteries) used chemical reaction between zinc and manganese dioxide. Ammonium chloride is used as an electrolyte (electrically conductive solution). The zinc is on the outside (often behaving as the case of the battery) while the manganese dioxide is mixed with carbon to improve conductivity and is placed inside the cell. A piece of paper is placed between the two chemicals to prevent a short circuit. A carbon rod in the center is used to collect the current from the manganese dioxide. These batteries are the cheapest batteries sold, as well as the lowest quality. Due to the acidic nature of the electrolyte, the zinc case will wear away and eventually will begin leaking the corrosive electrolyte. These batteries have a shelf life of about 1.5 years at most. The small surface area between the zinc and the manganese dioxide also gives a low capacity as well as a low discharge rate. A typical AA carbon-zinc battery can cost 0.15 USD and provide 500 mAh of current. They are becoming increasingly harder to find as a modified version which costs about the same but has more capacity and shelf life is becoming the new bargain battery.

 

The "heavy duty" or "super heavy duty" batteries contain zinc chloride in their electrolyte in addition to ammonium chloride. Many of the super heavy duty batteries also have an iron case surrounding the zinc can, so the battery does not become soft as it discharges and the zinc dissolves. These batteries cost about USD 0.20 per AA cell but have a capacity of about 900 mAh. There are an abundance of "heavy duty" battery brands, with many manufacturers of cheap devices using them in those devices. These contain much the same chemistry and construction as general purpose Leclanche cells.

 

Alkaline batteries, although they use a very similar chemical reaction, have different properties and a different construction. The electrolyte is an alkaline solution of KOH. This is better because basic solutions do not corrode zinc, prolonging the shelf life. The case is also made of iron instead of zinc; the zinc is stored inside the battery in a powdered form, which enables the battery to produce a higher discharge rate. Alkaline batteries cost about USD 0.50 per AA cell and have a capacity of about 3000 mAh at low current draw (more like 1200 mAh at high current draw). To obtain manganese dioxide or zinc, it is cheaper and better to get heavy duty batteries. Therefore alkaline batteries are not a good source of chemicals.

 

Lithium iron disulfide batteries have much better quality. Lithium is highly energetic and lightweight, making for a high power battery. The electrolyte is an organic solvent because lithium reacts with water. The electrode materials are spiraled within the shell to make a jelly roll construction, which allows high current draw (much higher than alkalines). This is their main advantage. The durable nickel-plated steel case allows for a shelf life of 10-15 years. Lithium batteries cost about USD 1.80 per cell and have a capacity of 3000 mAh at any current draw. They are an excellent source of small quantities of lithium for an element collection. The iron disulfide is full of carbon impurities and does not function as a good source of sulfides. It could probably be thrown into HCl to get hydrogen sulfide gas, but there are cheaper sources of sulfides available.

 

Lithium manganese dioxide batteries are more common in smaller sizes. They can take high loads but they function much better under small loads. With a shelf life of 10 years, they are quite cheap and perfom well in watches and CMOS units. They are also a good source of lithium but small coin cells can be an expensive way to acquire large amounts of the metal. The electrolyte is the same as in the Li - FeS2 batteries. They cost about USD 1.50 and have a capacity of 1500 mAh. They have a nominal voltage of 3 volts, so their capacity is equivalent to 3000 mAh at 1.5 volts. They have a displacement of 7.83 cm3, while AA cells have 8.34 cm3 displacement. This gives them a slightly higher capacity than most other batteries despite their smaller size.

 

Lithium thionyl chloride batteries have the highest capacity of all common batteries in use today, as well as the largest tolerable temperature range. They can only take low loads but some of them have been proven to last over 25 years while still retaining charge. Lithium is the active metal, making these batteries very lightweight. Thionyl chloride is mixed with a lithium salt and carbon powder to form the cathode. These batteries are not a good source of thionyl chloride or lithium because of this. Besides, they are very expensive. They cost about USD 3.00 for a AA cell and have a capacity of 2400 mAh. They have a nominal voltage of 3.6 volts, so their capacity is equivalent to 5760 mAh at 1.5 volts.

 

Zinc air batteries are unique in that they get their cathode from the oxygen in the air. They only contain zinc metal and come in very tiny sizes, so they are only useful for hearing aids and not for chemistry.

 

Silver oxide batteries have some of the highest energy densities outside of lithium batteries. They have a silver oxide cathode (mixed with carbon powder) and a powdered zinc anode. They are very expensive but can be a source of silver. However, they only come in very small sizes.

 

Lead acid batteries, often seen in large packs of 3 or 6, rely on a chemical reaction between lead and lead dioxide in the presence of sulfuric acid to generate large quantities of electricity. A lead acid battery is not the ideal source of lead (fishing sinkers are much cheaper), but lead, its dioxide (which is a powerful oxidizer) and sulfuric acid can be extracted from a fully charged lead acid battery. Discharged ones only contain white lead sulfate crystals, hardly soluble in anything. Lead acid batteries produce 2 volts per cell, a little higher than the 1.5 volts produced by most other batteries. A sealed lead acid battery available on Amazon costs USD 50.00 for a 2300 cm3 battery with a capacity of 18000 mAh at 12 volts, equivalent to 144000 mAh at 1.5 volts. If it were AA size, rough calculations show that it would have a capacity of 520 mAh at 1.5 volts while costing $0.18. This shows that lead acid batteries are quite powerful and economic, which is why they are so prevalent in automobiles. Considering that the technology was invented in 1859 (before any other consumer battery), lead acid batteries are surprisingly good when compared to a modern heavy duty carbon zinc battery which costs just as much but is not rechargeable, has a shorter working life, and has a much lower maximum current draw.

 

Nickel-cadmium batteries were the next rechargeable batteries to become widespread. They use an anode of cadmium, a toxic heavy metal which is difficult to extract from the battery. The cathode is nickel oxide, which also does not come out in a pure form. The electrolyte is potassium hydroxide, which can be economically dissolved out of old batteries. Other than that, these batteries do not offer much in the way of chemistry. They can take large currents and are quite tough but generally have a low capacity and high price. A typical Nicad (as they are called) costs about USD 0.80 for a AA size battery and produces 1000 mAh at 1.2 volts, equivalent to 800 mAh at 1.5 volts.

 

Nickel-metal hydride batteries dispense with the toxic cadmium and use hydrogen stored in a chemical form on metal as the anode. These anodes contain a large mixture of various compounds and are not useful for chemistry. However, due to their high energy capacity, they often catch fire in air and can startle an unsuspecting battery dissection crew. A typical AA cell costs USD 1.80 but produces 2500 mAh at 1.2 volts, equivalent to 2000 mAh at 1.5 volts. Advances in technology means that these batteries can hold current for many months and complete many discharge cycles, definitely justifying their high price.

 

Lithium-ion batteries, instead of using elemental lithium, use a lithium ion - containing material to produce electricity. I have not found any useful chemicals in lithium ion batteries, but they are good for electronics due to their light weight and high power. A typical AA lithium-ion battery costs about USD 3.00 and produces 3.7 V at 900 mAh, equivalent to 1.5 volts at 2220 mAh. Another battery I tried got only 1400 mAh for a AA 1.5 volt equivalent. Oh well, I though lithium ion had the highest capacity of all batteries. It must be their extremely light weight that gets them their high energy density. And they are rechargeable. It is understandable that rechargeable batteries have a lower capacity than non-rechargeable ones, as well as a higher cost.

 

Thus ends my overview of common consumer batteries. I may post pictures in the future.

 

For further learning:

 

  • Battery Energy Density
  • Comparing rechargeable batteries, must keep price in mind
  • A similar battery comparison site, I didn't source anything from here
  • Company selling high-end thionyl chloride batteries
  • Energizer lithium battery technical "data sheet"

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Published by LanthanumK - in Experiments
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