Studies of the energy and power of current commercial prismatic and cylindrical Li-ion cells

We studied the specific energy, energy density, specific power, and power density of current commercial 18650 cylindrical and 103450 prismatic Li-ion cells. It was found that the specific energy, energy density, specific power, and power density have been increased dramatically since 1999. The highest specific energy obtained in this study is 193 Wh/kg, which is 90% more than that reported in 1999 and is only 5% lower than 200 Wh/kg, the long-term DOE goal [The International Energy Agency Implementing Agreement for Electric Vehicle Technologies and Programs, Annex V, Outlook Document, 1996-1997, p. 16.]. The cell energy density has also doubled since 1999 and is as much as about 70% more than 300 Wh/l, the long-term DOE goal. The cells studied here can deliver over 80% of their designed energy at the specific power 200 W/kg while the 18650 cell studied previously could only deliver 10% of their designed energy at the same specific power. Various kinds of the factors in the cell-specific energy and energy density were studied. It seems that the geometric difference can cause as much as a 9% difference in the specific energy and a 12% difference in the energy density between 18650 cylindrical and 103450 prismatic cells. Use of an aluminum can seems to lead to about a 16% improvement in the specific energy of 103450 cells compared with steel can. The decrease in the cell discharge voltage can cause as much as a 9% decrease in the cell energy at the 2 C rate while it has a relatively small effect on the cell energy or specific energy at the 0.2 C rate. Compared with what has been obtained at room temperature, there are 17-35% at -20degreesC, 43-76% at -30degreesC, and 78-100% decreases at -40degreesC, respectively, in the cell discharge energy and specific energy depending on the cell manufacturer. The decrease in the cell average discharge voltage during the cycling test can contribute as much as a 6% decrease in the cell energy at the 1 C rate after 300 cycles, which is 21% of the total energy loss. (C) 2003 Published by Elsevier B.V.