This report is concerned with the testing and evaluation of various battery chemistries for use in PHEVs. Test data are presented for lithium-ion cells and modules utilizing nickel cobalt, iron phosphate, and lithium titanate oxide in the electrodes. Cells with NiCoO2 (nickelate) in the positive electrode have the highest energy density being in the range of 100-170 Wh/kg. Cells using iron phosphate in the positive have energy density between 80-110 Wh/kg and those using lithium titanate oxide in the negative electrode have energy density between 60-70 Wh/kg. The power densities can vary over a wide range even for a given chemistry. In general, it is possible to design high power batteries (500- 1000 W/kg at 90% efficiency) for all the chemistries if one is willing to sacrifice energy density and likely also cycle life. The data indicate that high power iron phosphate cells can be designed without a significant sacrifice in energy density. When power densities greater than 2000 W/kg for lithium-ion batteries are claimed, it is for low efficiency pulses. For example, for an efficiency of 65%, the 15Ah EIG iron phosphate battery has a pulse power of 2330 W/kg rather than the 919 value for a 90% efficient pulse.
Cycle life data were not taken as part of the present study. However, cell cycle life data reported by Altairnano for their cells using lithium titanate oxide in the negative electrode indicate cycle life in excess of 5000 cycles for charge and discharge rates of 2C and greater. It seems likely that the cycle life of both titanate oxide and iron phosphate lithium batteries will be satisfactory for vehicle applications.
The cost of lithium batteries remains high ($500-1000 /kWh) when purchased in relative small quantities, but detailed cost modeling of batteries done at Argonne National Laboratory for the various chemistries indicate that in high production volume (greater than 100,000 packs per year), the costs to the OEMs of all chemistries can be in the range of $250-400/kWh depending on the battery size (kWh energy stored). The lithium titanate chemistry is projected to have the highest cost, but it also will have the longest cycle life.
R&D is continuing to increase the energy density of lithium-ion batteries. Proto-type cells presently being developed have energy densities in the range of 250-300 Wh/kg using layered metal oxides/spinels in the positive electrodes. Higher energy densities appear to be likely combining these electrodes with negative electrodes using composites of silicon oxides and carbon. R&D on electrically rechargeable Zinc-air cells is presently in progress. Energy densities in the range of 300-400 Wh/kg, 700-1000 Wh/L appear to be possible using the Zn-air chemistry. The power capability of the advanced batteries is uncertain at the present time.