Lithium Iron Phosphate (LiFePO4) Batteries

[davidbrady]

I've long stayed away from Li+ batteries because of the cell balancing issues, the cost, and the risk of thermal runaway and fire. I'm now revisiting the idea and I see that a technology that's been out for a handful of years has incrementally improved Li+ battery performance. Lithium Iron Phospate, LiFePO4, batteries are thermally stable, they don't seem to require complex and dangerous balancing circuitry; however, in lieu of balance circuitry programmable smart chargers may be required. LiFePO4 batteries can safely and reliably handle 5C of current delivery or charge, they don't require charge voltage temperature correction, power densities are around 2X's an AGM, they offer 80% DOD versus AGM's 50%, virtually no Puekert loss (virtually no voltage sag at discharge), and they can be cycled multiple thousand times offering a longer effective lifetime. The list goes on. There's no question that Li+ is an improvement over lead acid.

The problem I have is... They still suck! For instance, the Li+ specific energy measured in Mega Joules per Kilogram of battery weight is in the 0.30 to 0.80 MJ/kg range. The specific energy of a log of firewood is 16 MJ/kg! Yikes!

The energy density, measure in MJ/liter, is around 1 to 2.5. The energy density of diesel fuel is 36 MJ/L! It takes 36 times the volume to deliver the same energy! Double Yikes!

We can applaud Tesla for making huge but incremental (if that makes sense) strides in battery technology, but their latest battery innovations in the Tesla S improved battery specific energy from 0.436 to 0.475 MJ/kg over that in the Tesla Roadster! And, they're making headlines over this improvement. Still a factor of 33 less than a log of wood!

I know they make it work in the cars and they are fabulous, but this slow pace of battery development isn't anything to hoot and holler about, and taking the risk and expense of going from bad (AGM's) to slightly better than bad (LiFePO4) just isn't worth it for me. We need a quantum jump in battery technological development, not incremental evolutionary steps with pain at every junction.