|
Electric Batteries and Cells |
||
Choosing the right batteries can be a very complex problem but when they are finished with be sure to recycle them, dumping them could be lethal, literally. |
|||
|
A Cell is the basic device comprising two electrodes separated
by an electrolyte. The name of the cell usually includes reference to
the materials used in the construction and the voltage of each cell
depends on the chemicals used, eg Alkaline Manganese; nominally 1.5 V, a Lead-acid cell; about 2 V, Nickel Metal Hydride Rechargeable; 1.2 V or Lithium-Ion with a much higher voltage of the order of 3.6 V.
A Battery is a collection of cells eg the PP3 9V (6x1.5 V cells in series) or the Lead-acid car battery (typically 12 V, also 6 cells). Although the voltages are quoted usually as if they were accurate, mostly they are not. Voltages vary according to many factors eg temperature and state of charge. There are 2 fundamental types of cells, Primary and Secondary. Primary cells are meant to be used once only, through to the discharged state and Secondary cells are designed to be recharged over and over (typically several hundreds of times). Some chemistry is conditionally suitable for use either as primary or secondary. The number of different battery types, properties and applications is enormous, quite apart from the fact that each type comes in a variety of sizes, usually dictated by voltage and capacity. Capacity is measured in ampere-hours (Ah) or thousandths of ampere hours (mAh). Even these two basic parameters (V and Ah) are not fully definitive. For example the voltage depends on the load (current drawn and for how long this current is sustained) as well as state of discharge, temperature, internal resistance and normal deterioration due to usage. Similarly the capacity may well vary from the ideal depending on these factors. As an example the ubiquitous Manganese Alkaline AA cells used for portable devices would not achieve the rated capacity if used for demanding work (eg think camera flash) but it might still go on for further application in a non-demanding use such as powering a clock. The following comments give a resumé of certain types, which we hope you may find useful without being too overwhelming with technical detail. If more information is required we give a recommended link near the bottom of this page. |
Primary:Zinc Carbon: nominal 1.5 V, an old type, cheap and voltage varies considerably during use. Suitable for low drain loads only. Despite these being cheap we would always prefer the Alkaline.Alkaline Manganese: nominal 1.5 V, ubiquitous replacement for zinc-carbon, higher energy, more expensive but good buys are there if you search. Mercury: phased out in many applications because mercury is very poisonous, was/is used in small applications such as hearing aids. Lithium: a wide ranging family with voltages varying from 1.5 V to 3.6 V, high energy density, voltage almost constant and very long shelf life. Sounds magic and indeed they are special but the downsides are that they are very expensive and Lithium is a very reactive element which can lead to explosive consequences. The button cells are extremely dangerous if ingested (eg by small children). There are certain restrictions in carrying them on air-transport. They are widely used in Japan but very much less so in Europe. Do not attempt to charge unless explicitly specified and avoid short circuits. Zinc Air: nominal 1.4V, as its name suggests must be exposed to the air (a seal is usually removed when first used), high self-discharge rate. Silver Oxide: nominal 1.55V. Often sold as button cells, for use in calculators, simple cameras, watches etc where its stable discharge characteristics are valuable. Secondary:Lead-acid: nominal 2 V per cell, as used in cars, well known to be rechargeable, large capacities but lead is very poisonous. Can be either wet or dry. Probably the easiest to recycle because the large amount of lead in each battery has a value in the scrap metal industry. Lead-acid and Sealed Lead-acid (SLA) are used where relatively large energy ratings are called for but weight is not a major problem.Nickel-Cadmium (Ni-Cd): 1.2 V per cell. Used extensively in rechargeable situations and because it exhibits a memory effect is either continuously trickle-charged or recharged after complete discharge (ie not partially discharged and then charged). Ni-Cd can be recharged a large number of times (say, more than a thousand), which may be the reason, unfortunately, why they are so popular. Cadmium is very poisonous, it would seem a good idea to avoid Ni-Cd wherever possible but has established a track record and is quite common unfortunately. Nickel Metal Hydride (NiMH): 1.2 V per cell. They are a newer generation which can replace Ni-Cd and have higher energy density and longer life cycle, and don't exhibit memory effect, are usually charged with constant-current source. They do not contain the the most dangerous heavy metals so are more environmentally friendly than Ni-Cd. We feel that NiMH batteries should be used wherever possible to replace Ni-Cd. The disadvantage is that they cannot be recharged so many times as Ni-Cd (maybe less than a thousand), but unless you take care with the charge and recharge discipline needed with Ni-Cd you may well finish up with a battery which doesn't realise its potential and turns out to be inferior to NiMH anyway (we speak from experience). Recently there has emerged a new breed of these batteries called Hybrid Rechargeable. They claim to come precharged; while this is no big deal it may be convenient and we wonder if they might be capable of retaining their charge better than non-hybrids. We don't know but expect them to perform well. Nickel-zinc: 1.65 V per cell: 7 cells for a nominal 12V, it is claimed they provide the lowest impact to the environment of any standard rechargeable battery technology mainly because of the absence of contamination from the dangerous heavy metals. They can have lower cost than NiMH, are lighter and better performers than lead acid, have a high capacity per cycle and high cycle life and they also have low maintenance requirement. They have a low internal resistance and can be recharged quickly. Size may be less than Lead-acid and about the same as Ni-Cd. As far as we can see, they have several advantages and are versatile, however, their availability is quite limited and they have a lower volumetric energy density than eg NiMH. Why they are not more popular we don't know, maybe it's that energy density? Lithium Ion (Li-Ion): typical voltage 3.6 V; comprise a large family of batteries with different applications and some are used, as well as NiMH, in special applications eg laptop computers. They are expensive to produce and hence to buy. They have the advantage that they have about twice the energy density of Ni-Cd and around 50% more than NiMH hence can be much lighter and smaller for the same capacity. They can be recharged for up to 1000 times approximately. They exhibit no memory effect and have a very low self-discharge rate. Currently, Q1 2013, their safety has come under scrutiny following fire incidents on board Boeing’s 787 Dreamliner. Following these incidents the aircraft were grounded worldwide to allow investigation as to the possible dangers of using this battery technology. Lithium Polymer (LI-Polymer): apparently could become the battery of the future. They are reputed to have similar characteristics to Li-Ion but should be much cheaper to produce. |
|
|||||||
General Comments and Recycling:This has been one of the most difficult items to research. There have been significant advances in battery technology over the past few years and it is evident that the consumer culture has led to an increased use. However, unlike the devices they drive (electronic and electro-mechanical) electric cell devices have only developed in a modest evolutionary way. We also note that cells and batteries are not always predictable or precise, nor even safe like the devices they feed. We are tempted to refer to them as organic because of these limitations.Undoubtedly batteries provide us with benefits and conveniences which are valuable. The battery market is a lucrative one and you can see that by surfing the net, indeed the information provided seems to be very protective of the market, with little to say, in the UK, about safe disposal. Choosing the right battery for your purpose is important but due to the large choice, technical specifications and the hype sometimes surrounding them that can be a difficult task. Nevertheless the information is available and you should seek it out. We have found that the most advertised are not always the best buys, also it is usually very costly to buy a manufacturers' proprietary replacement (eg a camera Li-Ion battery). However from our experience it definitely does not pay to buy 'cheap' so beware if you do. Always use batteries from a manufacturer with a reputation to protect and read the specs. Good examples may not seem to be cheap but they may well be good value. That some batteries contain metals which are deadly dangerous to humans and animals is undeniable; such dangers become reality when the items are disposed of in standard waste rather than recycled in some way. All this is compounded by the plethora of battery types (nothing to do with sizes) so that it is difficult to identify the scale of the dangers. Three heavy metals, present in batteries, namely lead, cadmium and mercury pose serious health hazards. The effects of these elements on animals (including humans) are terrible, leading to debilitating pain with fatal consequences [for more detail on the dangers see the WEEE synopsis in the Electrical/Electronic section]. Yet what do we do to prevent haphazard disposal of them? Sadly in the UK, still not enough, although things have improved in recent years. We had expected the British Battery Manufacturers Association (BBMA) to provide us with information that would allow easy recycling. They have been active in setting up REBAT which purports to be interested in recycling and sets targets but we think they could have done more. There is a list of battery recyclers and a location map but a more proactive approach is needed. There are now many more recycling schemes, including council schemes. Many councils have adopted the kerbside approach which is excellent. Also, many supermarkets and electrical goods stores have convenient battery recycling facilities. We have been pleased to note that some specialist recycling takes place, for example some companies who recycle cellular 'phones, recycle the batteries contained therein. Lead-acid car batteries are relatively well catered for because they have an obvious scrap value (a substantial amount of lead) and you could possibly collect money by taking them to the scrap metal dealer. Local councils will usually take them for recycling. Ni-Cd rechargeable batteries contain Cadmium and are still popular. In any piece of equipment they should be easily removable. As long as they're being used they are not dangerous but if they are dumped into landfill they are. Mercury is used in miniature primary cells (hearing aids, some cameras). Certain hospitals and jewellers may take these for safe disposal. You may also like to see our note about Mercury under the Fluorescent Tubes heading in the section on Hazardous Waste. Notes: 1. A good reference to batteries can be found at the Battery University 2. Wikipedia also have reference pages worth consulting. 3. Also see our page on Restriction of Certain Hazardous Substances. |
||||||||
| By Gordon Shaw | ||||||||
© Copyright 2001-2013, Envocare Ltd. ENVOCARE is a registered trade mark of Envocare Ltd. For legal matters see the section "About Us & Contact Us". Originated: Early 2001, Last Amended: 28 October, 2013 |
