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    Battery Chemistry With Money-Saving Tips
    By Enrico Uva | April 1st 2011 05:09 AM | 6 comments | Print | E-mail | Track Comments
    About Enrico

    I majored in chemistry, worked briefly in the food industry and at Fisheries and Oceans. I then obtained a degree in education. Since then I have...

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    When investigating batteries, the chemist is easily reminded that physics is at the heart of all chemistry, and that electrochemistry is not only at work in energized mechanical rabbits, but also in trees, beating hearts and corrosion. This article will explore the inner works of consumer batteries and look at ways of saving you money.

    It takes energy to work against gravity and increase the distance between the center of the earth and an object on its surface. But after being rolled up a hill, a ball can freely roll down and flatten grass in the process. Similarly, it takes energy to create and separate an electron donor from an electron recipient. Instead of gravitational force, we have another another fundamental force at play(coulombic: part of the electromagnetic force), repelling like-charges and attracting opposites. Place a barrier between the donor and recipient, and wrap them up in the same container with a salt-like solution(an electrolyte).  Finally provide a way for electrons to leave and return, and, like the rolling ball, they can do work. You'll have a working battery. When a ball has been pushed to the top of a hill it has acquired gravitational potential energy. When charges have been separated, they have also gained potential, a certain number of Joules per Coulomb of charge; in plain English, voltage.

    1. Duracells, Energizers: Alkaline Batteries

    When zinc ore is mined, it's in no state to lose more electrons. The sulfur that's coulombically bound to it has already snatched as many electrons as zinc can afford to lose. Industry has to first roast the compound and then reduce the subsequent product with either carbon or electricity. Only then does it become the useful donor that can sacrifice itself to protect the steel in your car's body or the membrane-bound powder in an alkaline battery.
    In its casing there's very little oxygen. But being in an electron-deprived state, the manganese ion in MnO2 can easily serve as a recipient. That black powder is what's snatching electrons on the perimeter and below the positive top of the alkaline battery.
    But the battery-recipe is not complete. As zinc loses electrons, Zn2+ ions form, the same kind that appear in its natural sulfur ore.  Positive ions will not repel electrons into that little nail that's supposed to conduct electricity out through the bottom of the battery. This is why potassium hydroxide(KOH) electrolyte is included and why the "alkaline" label is appropriate. OH- ions move towards the positive zinc ions, neutralizing them and keeping the zinc electron-rich. The other end has the opposite problem and aqueous positive ions migrate there to keep the manganese side electron-hungry. When the battery is fresh, the voltage of the standard cell is about 1.5 V. But the number of zinc ions produced gradually overwhelms the electrolyte, lowering the electrolytic potential to about 0.8 V.  Although many toys will not work when the voltage dips to about 1.2 V, a TV or DVD remote control will still function at that potential. Many consumers throw batteries away too soon before trying them elsewhere. What's also not common knowledge is that the C or D varieties(also 1.5 V) can be substituted with AA ones if they are placed inside a plastic stub case of matching size.

    Ironically, the blemishing of zinc's surface is desirable when, for example, we galvanize steel railings. After losing electrons to oxygen in the air, zinc first turns into  zinc oxide (ZnO), and then, with incoming CO2, it becomes zinc carbonate(ZnCO3). Its crystalline structure is such that it clings to the surface of the undercoating, preventing further oxidation. Once upon a time, old hot water tanks were equipped with a connecting zinc rod that would double their life span. The rod would get oxidized, sparing the tank's steel casing.
    Since oxidation is accelerated by higher temperatures, the process could be slowed  down by lowering the thermostat's initial settings . There are usually two sections to the standard 40 or 60 gallon tank, and each control should be set to the same temperature. Simultaneously, you'll save electricity. Thirteen years ago, I added my own zinc plates. We'll see if they make a difference in the near future.

    2. Rechargeable Batteries

    A- NiMH

    If you are still wondering where to get the plastic casing to fit AA batteries, they usually come with rechargeable battery kits. To avoid adding toxic cadmium into the environment, innovators have introduced nickel metal-hydride (NiMH)batteries into the market. They also use KOH as an electrolyte, but instead of zinc, a rare earth metal hydride releases electrons. It's a reaction reminiscent of the way reducing  agents NADH and NADPH give up electrons in fundamental reactions within living cells.  At the other end, the electron-accepting agent is NiOOH, where the Ni3+ ion can revert to its more thermodynamically stable form, Ni2+. What makes the battery rechargeable is that by forcing electricity through it, the products are converted back into their original reactants. The reversal is not 100% efficient, especially with side-reactions to contend with, so eventually the battery cannot be revived.

    NiMH batteries work well with inexpensive digital cameras and some kids' toys. By reusing friends' discarded duracells and after purchasing a kit of NiMH cells, I have not bought batteries in the last three years.

    B- Lithium-Ion

    Rechargeable lithium-ion batteries in laptops or cell phones don't actually use free lithium. The latter is indeed used in those almost flat disposable batteries for watches, where an irreversible reaction takes place. Because lithium is a better electron donor than zinc, there's a larger voltage associated with it. But in rechargeable lithium-ion batteries, a lithium graphite intercalation compound releases an electron. The compound is deceivingly represented by LiC6, but don't try to figure out oxidation states from the formula! The neutral lithium is trapped in between sheets of graphite. Once electrons are released, lithium ions and graphite are left behind. Then each lithium cobalt oxide, LiCoO2, recaptures an electron, converting the unstable Co3+ ion to Co2+. As with NiMH batteries, the two half-reactions are easily reversible. But heat from a running laptop or from the external environment will shorten the lifespan of the battery, and if you've looked into replacing your laptop's portable energy source, you've discovered that they are far from being cheaply priced.

    C- The Lead Storage Battery

    The reason that lead storage batteries have been with us for almost a century(despite their environmental drawback) is that they can produce a large initial current, which is exactly what's needed to start an engine. Elemental lead(Pb) plays a role analogous to that of zinc, LiC6, Li and a metal hydride: it is the electron donor. With the help of acid, solid PbO2 recollects those electrons in a reaction that is reversed by the current delivered by the alternator.

    Twenty months ago, a mechanic from a major car dealer told me our van's battery was going to die soon. I was skeptical. Using a multimeter, I measured 12.0 V, the expected potential difference from six two volt cells connected in series. Fourteen months ago he reiterated his concern. Someone else mentioned that the voltage should also be measured shortly after startup: the spike being the reason that Pb batteries can deliver a high current. I measured it again, and it did rise to 14.0 V, as expected.
    Simple verification diverted the money I would have needlessly spent on a new battery to a different sector of the economy.

    REFERENCES

    Chemistry and Chemical Reactivity . Kotz, Treichel and Harman. Thomson. 2003
    Experiencing Electricity and Electronics  Hazen. Saunders. 1989
    http://www.maximumpc.com/article/features/why_batteries_die
    http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_...
    http://en.wikipedia.org/wiki/Lithium-ion_battery#Electrochemistry

    Comments

    vongehr
    "the voltage should also be measured shortly after startup: the spike being the reason that Pb batteries can deliver a high current. I measured it again, and it did rise to 14.0 V, as expected."

    "Spikes" are due to induction and the 14V is what the engine charges the battery with. Both have nothing to do with whether the battery will be dead soon. You can see whether it is on the way out by putting a load on and see how fast it goes below 12.6V although fully charged, for example. Not sure what you mean by that any of this has something to do with the currents. High voltage comes from "in series", high current from "in parallel" (= how large are the plates' surfaces).
    Anyway, good decision not to give em your money. I have driven with a "dead" battery for two years. All one needs to do is to disconnect it whenever parked, as the non-infinite resistance through the connections will be enough to deplete the "dead" battery (or maybe that was just the main problem with my crappy old car). Also a brilliant anti theft strategy by the way.
    UvaE
    You can see whether it is on the way out by putting a load on and see how fast it goes below 12.6V although fully charged, for example.
    You're probably right about that. What made me sceptical is that we never had problems starting the van, even though it was a bit over 6 yrs old when it was first diagnosed as terminally ill ! Now at age 8 it still give us no problems.
    logicman
    The huge advantage of lead-acid batteries is their robustness.  Quite apart from taking quite a 'wallop' when called upon to start an engine with thick, cold oil in winter: most lead-acid batteries spend their lives being shaken up as a vehicle drives over the local authority's 1,000 per mile pothole and speed bump allocation.  They also get nicely warm under the hood in a traffic jam next to an overheating engine.

    Despite all that abuse, I've known such batteries to last 10 years or more.  Before the rise of nuclear powered submarines, lead-acid batteries powered the world's diesel subs when submerged.

    By way of contrast, modern batteries often have a design life of only 3 or 4 years, tops.  That life would likely be even shorter under a hail of depth charges. ;-)
    Johannes Koelman
    Lead-acid batteries rock. Lead-acid is by far the most advanced type of battery. It's a battery that harvest on advanced quantum-relativistic insights. Each time you start your car, you prove right Einstein and Dirac.
    Aitch
    A money saving tip I like is to 're-charge' standard [non-rechargeable] 1.5v cells in a NiMH/Li-Ion charger....they will sometimes last an extra week or so of occasional use in torches, for example, but care is needed to ensure neither they, nor the charger, overheat

    I'm surprised you didn't mention 'memory effect' as many rechargeable batteries will last longer by being drained fully before charging, and some chargers now have a discharge step for this purpose

    Lead Acid (wet cells) and dry paste cells have different charge requirements, and again, newer 'smart chargers' often advertised as 'battery re-conditioners' charge in several stages, unlike conventional car alternators [though this will surely change] or old transformer style home battery chargers, which only charge by pushing a fixed higher voltage into the batteries

    .....and then there is the new generation of Lithium Ferrite Phosphate LiFePo batteries developed for electric vehicles, plus even newer battery advances with nanowire/stainless, ultracapacitors, and wireless energy sources.....

    Aitch
    UvaE
    I'm surprised you didn't mention 'memory effect' as many rechargeable batteries will last longer by being drained fully before charging, and some chargers now have a discharge step for this purpose
    You're right: definitely a major omission on my part!