Studies of 18650 cylindrical cells made with doped LiNiO2 positive electrodes for military applications

We studied GP 18650 cylindrical cells made with doped LiNiO2 positive electrode for military application. The studied cells should deliver about 184Wh/kg according to the military specification MIL-PRF-320521 while it delivers about 201 Wh/kg according to the general commercial standard. The difference in the cell specific energy is mainly caused by the difference in the charging voltage. It is 4.1 V in the military specification compared to 4.2 V in the general commercial standard. Clearly, to take full advantage of the commercial lithium-ion cell, either the military increases the voltage limit to 4.2 V from 4.1 V or the cell manufacturers redesign their cells according to the 4.1 V charging voltage limit. The studied cell exceeds all major military requirements including high rate discharging, high current pulse discharging, low temperature discharging, cycle life, high temperature storage, and abuse tolerances such as the overcharging, forced discharging, and external short. Specifically, the capacity of the cell exceeds the requirement by 51 % at a high discharging rate (3.3 A) and by 39% with a high current (6 A) pulse. The cell can discharge not only similar to62% of the expected capacity at similar to30degreesC but also similar to47% at similar to40degreesC and at 0.67 A, which means that the military can extend their specification to -40degreesC. The cell still retained 1.97 Ah (or 92%) after 224 cycles, which exceeds the requirement by similar to9%. The cell retained 1.95 Ah (or 95%) after one-week storage at 50degreesC and at 4.1 V, which exceeds the requirement by 8%. The abuse tolerance is also very high. The maximum cell temperature ranged only from 62 to 70degreesC during overcharging, external short, and forced discharging. Directions for the improvement are also discussed. (C) 2004 Elsevier B.V. All rights reserved.