The Battery - Cathodes, Anodes, and Electrodes (Part 2 of 2)!
By Dan Hagopian
In part 1 of “The Battery - Cathodes, Anodes, and Electrodes” we discussed how engineers manufacture disequilibrium to create free negative electrons so that the positive atoms will attract the electrons at the positive electrode, thereby creating an electron flow. We spoke about electrodes and their function in receiving electrons, and we spoke about how a direct current is created in a battery. We also discussed how batteries power mobile devices by the creation of direct electrical current drawn from the flow of electrons, flowing back and forth between the electrodes. Now in part 2 of this report I will look closer at the electrodes and their effect on the flow of electrons. Collectively the anode and the cathode are called the electrodes. The electrodes typically are referenced as a negative electrode and a positive electrode instead of the anode and the cathode in batteries since either electrode can become the anode or the cathode depending on the voltage applied to the cell and the direction of electron flow. The positive electrode can be a lithium cobalite composite (LiCoO2) and the negative electrode can be a carbon-graphite composite. If we can define an anode we would say that the anode is the electrode at which electrons come up from the battery cell and where oxidation occurs. One side bar is that many battery manufacturers regard the anode as the positive electrode, even though that is technically incorrect, however it does help resolve the problem of which electrode is the anode in a rechargeable cell (or secondary cell). The cathode on the other hand could then be defined as the electrode at which electrons enter the cell and reduction occurs. One point that was a challenge for me to grasp was that the each electrode may become either the anode or the cathode depending on the flow of the electrons. In part 1 of this report we learned that positive atoms attract electrons from negative charged atoms to balance the positive atoms. The attraction creates an electron flow, flowing at a speed of 62,000,000,000,000,000,000 electrons per second (62 quintillion electrons per second)! These electrons flow on ions from the anode–to–cathode outside of cell and from cathode–to–anode inside a cell, which results in two types of current [a negative ion (anion) flow and positive ion (cation) flow. The two currents flowing from anode to cathode result in a network of electron flow. As mentioned earlier the positive electrode can be a lithium cobalite composite (LiCoO2) and the negative electrode can be a carbon-graphite composite. But what is key is that in commercial battery cells, the cathode’s active material is a litiated transition-metal oxide such as lithium cobalt oxide. Because lithium is more electropositive then hydrogen, the electrolyte must be nonaqueous and aprotic. A representative formulation is a solution (1:1 by volume) of ethylene carbonate and propylene carbonate containing a suitable lithium salt such as lithium hexaflourophosphate, LiPF6, which raises the conductivity of the electrolyte. A separator of electrolyte, made of polyolefin such as micropourous polypropylene, is placed between the electrodes for safety. If the electrolyte temperature exceeds a certain value the separator melts and current flow ceases. The cells reaction is the formation of lithium cobalt oxide. From part 1 and part 2 of “The Battery - Cathodes, Anodes, and Electrodes” we have learned that at work inside your battery is some really incredible activity - a power source that is really rather marvelous when considered thoughtfully. I hope this review of how batteries power your mobile computing devices was enlightening.
© Dan Hagopian. You have permission to publish this article electronically or in print, free of charge, as long as the bylines are included with link. Dan Hagopian of http://www.batteryship.com is a known electronics author that specializes in portable power gadgets. His work can be found on the BatteryShip blog at http://www.batteryeducation.com He frequently writes about pda batteries, ipod batteries, general battery technology for our mobile world, new fuel cell technology and interesting power related inventions. For further information please visit http://www.batteryship.com where you can also find PDA Battery Replacement Kits, iPod battery, iPAQ battery, Clie battery, Palm Battery, Axim battery, Treos, and Blackberries. #Dan_Hagopian
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