PSOC cycle testing method for lithium-ion secondary batteries

A cycle testing procedure is proposed which carries out charge and discharge in a partial state of charge (PSOC) with some testing levels such as an averaged state of charge, temperature, etc. The PSOC cycle test with this procedure was carried out for a commercial lithium-ion cell for about 20,000 cycles, and the testing procedure and test results are discussed. The features of the degradation due to PSOC cycle test in the tested lithium-ion cell were clarified as follows. The degradation during the PSOC cycle test was greater at higher environmental temperature. The degradation was greatest at a high average SOC, and smallest at SOC=50%. The degradation increased again at a low average SOC. In the test results for 2 years with 20,000 PSOC cycles, which converted to 2200 cycles of full-capacity charge and discharge, capacity degradation was 32% even at the greatest degradation at 318 K and 8% or less at 278 K. The proposed testing procedure is useful for evaluating a cell used on partial charge and discharge cycles.