Publications Details
Fabrication and testing capabilities for 18650 Li/(CFx)n cells
Sandia National Laboratories has world-class facilities for building and testing lithium and lithium-ion batteries. In this article we describe the in-house facilities for fabricating electrodes and cells in detail. Our in-house facility includes equipment for: 1) electrode coating, 2) electrode slitting, 3) electrode winding, 4) cell grooving, 5) electrolyte filling, 6) cell crimping and more. We also have a 48-channel Maccor tester and several impedance units for electrochemical characterization. These facilities provide flexibility for cell fabrication techniques which in turn allows us to continually improve cell performance. Under an internally funded program we are developing in-house capability to fabricate and evaluate 18650 Li/(CFx)n cells using "Li-ion" electrode fabrication methodologies to prepare the thin film (CFx)n electrodes. At a C/400 discharge rate cell delivered ~3.6 Ahrs capacity. We also evaluated cathodes of two different lengths for uniformity of loading. The loading along the electrode length was found to be extremely uniform, as the delivered capacity was proportional to cathode length. For example, a 0.91 meters long x 4.2 mil thick electrode gave 3.6 Ahrs capacity while a 0.72 meters long × 4.2 mil thick electrode (19.4% less length) gave 2.9 Ahr of capacity (19.4% less capacity). We also discharged the cells with 0.71 meters long electrodes at different temperatures. The cells delivered practically the same capacity over temperatures from 25 to 72°C. At -20°C the cells delivered 81% of the room temperature capacity at a C/200 rate; however, at -40°C the cells delivered close to 47% of the room temperature capacity under similar test conditions. The performance behavior of 18650 cells will be discussed in more detail in the paper. © 2007 by ESG.