Lithium Ion Cell Comparison, Data, and Discharge Curves

[William Lynch]

I have developed some spreadsheets for cell modeling and cell comparison. High specific energy cells provide a weight reduction benefit to a solar car however high round trip efficiency is vital to doing well in a solar car competition. Using a cell with a significantly better C rate than required can provide exceptional round trip efficiency thereby providing more net energy to the drive system. Low energy dissipation in the battery pack provides the added benefit of lower battery operating temperature which can help keep the temperature of the cells below the manufacturer's rated maximum when the ambient temperature is high. Detailed datasheets with discharge curves are needed to accurately estimate cell performance. Doing your own in house testing can validate the manufacturer's data and is also useful for cell matching. 

The Lithium_Cells comparison spreadsheets use a target efficiency to project discharge capability. This is the red cell near the top that is 90 in the posted versions of the spreadsheets. It is a variable so can be changed in a modified version of the spreadsheet. The second tab Sheet2 includes cell models and links to manufacturer or vendor data. 

I also have spreadsheet model and data spreadsheets for a model of a specific lithium iron phosphate cell. This is complicated but some teams may be interested. It also estimates cell temperature. It includes many variables that can be modified. Results are described in the attached paper. I could model another cell type if a team is interested. I would like to make a version with another tool such as PSpice.

The following link includes discharge curves of a wide variety of lithium ion cells.

http://lygte-info.dk/review/batteries2012/Common18650IndividualTest%20UK.html

Teams may want to consider using Saft lithium ion cells. These appear to be premium cells designed for military applications.

http://www.houseofbatteries.com/documents/LithiumIonAdvantage.pdf

Bill