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Understanding The Factors In The Lithium-Battery Equation

Designing a power system for a new portable design starts with an understanding of the functionality of the powered device. From there, it moves to an understanding of the latest in battery technology and of the ICs that control the way the battery charges and discharges. Here is an update on lithium-based battery technology from a chemical standpoint and a look at a design approach that aims at getting the most out of whatever battery type is selected.
Table Of Contents
Anodes, Cathodes, And Electrolytes
EVs In The Driver’s Seat
Current And Power Output
Safety
Lithium-Polymer/Li-ion Differences
System Design For Portable Battery Packs
Cell Balancing
Diagnostics
Supercaps For Rapid Response
Smart Loads
Authentication
Wireless Charging
Final Considerations
References

Anodes, Cathodes, And Electrolytes
In any battery, the materials used for the anode and the cathode determine the voltage and its capacity. The electrolyte determines the boundaries or operating window for these materials. Today, the usual anode material is graphite or coke—carbon, if you will. That may be changing. Interest in silicon-based anodes is growing, but carbon anodes prevail for now.
In the meantime, innovation is focused on cathodes. Differentiation arises from the choice of cathode material. From the early 1970s until recently, almost all lithium cells were based on lithium cobalt oxide (LiCoO2). It’s relatively easy to process, and it exhibits good cycle life. Cobalt’s rarity presents a problem in terms of cost, though.
Some 64% of the world’s known cobalt deposits are in the Congo and the Caribbean, and the Chinese have been stockpiling these resources. The cobalt market is volatile, and there are large and frequent price fluctuations. Also, LiCoO2 is more volatile than newer potential cathode materials.
To find a workable compromise between energy density, operational safety, and good current delivery, manufacturers of lithium-ion (Li-ion) batteries are turning to mixtures of cobalt, nickel, manganese, and sometimes aluminum (Fig. 1). The benefits of the new chemistries include increased safety, fewer raw metal price fluctuations, and improved charge-rate and discharge-rate capabilities.
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