Lithium technology: Specific diagnostic application
When working with the Lithium families of battery chemistries and performing stress testing, rebuilding or testing it is vital that a technician know which Lithium technology that is being used in the vehicle. For example, when working with the Lithium Manganese battery families, the diagnostics and any stress testing would yield data that would look very different from a Lithium Iron Phosphate battery family, due to how the discharge voltage signatures are generated by the battery cells. For example, the Lithium Manganese families have a very linear discharge signature (similar to a Lead Acid battery) vs. the Iron Phosphate families which discharge with an extremely flat discharge signature. This means battery capacity may or may not be easily interpreted for use in diagnosing battery pack module condition through recording battery module voltage data on the scan tool. Therefore, knowing how specific battery chemistries behave is critical in knowing how to interpret scan tool of discharging equipment data. Other battery chemistries have signatures that fall in-between the flat and linear discharge voltage signatures. Whether a vehicle is HEV, PHEV, BEV or FCEV powered, is vital that technicians understand the performance characteristics of the Lithium families (and NiMH) being used by the OEMs and how to interpret whether or not the performance of the battery pack is acceptable (whether a DTC is present or not).
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Other things to consider
Although both NiMH and Lithium technologies suffer from the effects of over temperature, cells drying out, etc., most of the Lithium technologies have one major disadvantage when compared to NiMH. Lithium must be kept within a very specific operating band during charging cell damage and thermal events can occur. This means that expensive electronic circuits and software controls must be used within the battery pack system to maintain cell operation within these bands and for maintaining the optimum top-balancing voltage. This results in a much higher cost to implement Lithium into a vehicle system when compared to a NiMH system. There are some Lithium families that are much more tolerant to overcharging than others (such as Iron Phosphate) when compared to other chemistries that may have narrower operating boundaries. Although most HEVs today continue to utilize NiMH battery technology, all mainstream PHEV and BEV programs use the Lithium technology to take advantage of its significant advantage of energy storage (mass and volume) when compared to NiMH.
In summary, it will vitally important that technicians begin to learn both NiMH and the Lithium family of battery systems. As battery technology continues to evolve, it is inevitable that there will be an overwhelming number of battery families and chemistries used to help the OEMs meet the target of 54.5 mile per gallon fuel economy and lower CO2 emissions that the must achieved by 2025. Lithium battery systems will be an integral technology of how the OEMs reach these mandate targets. The HEV and PHEV vehicles are becoming a higher percentage of OEM product offerings, and the BEV and FCEV have now become more than a mere novelty in the OEM vehicle product lineup.
The time to start embracing the technology is now while there is still time to learn it without the pressure of trying to learn it on the fly. Wouldn’t it be easier to start learning these systems now rather than waiting until the first advanced technology vehicle rolls into your service bay?