Abstract: AC impedance of Li(Ni_1/3Co_1/3Mn_1/3)O₂/graphite power battery was tested under simulated UPS. The effect of different storage time and SOC on ohmic resistance R_s, charge transfer impedance R_ct and diffusion impedance CPE_W was analyze by the equivalent circuit. The variation trend of capacity and impedance of Li(Ni_1/3Co_1/3Mn_1/3)O₂/graphite power battery under UPS was studied. The results show that the capacity of the cell decrease about 1.7%, the ohmic resistance R_s at different SOC has the same tendency to change and the charge transfer impedance increase significantly with increasing storage days. The charge transfer impedance generated by the electric double layer is increases significantly as SOC decreases. The diffusion resistance (SOC=0%) increases and the diffusion impedances at SOC=100% and 50% slightly increase as storage day increases. Capacity degradation and impedance results show that the Li(Ni_1/3Co_1/3Mn_1/3)O₂/graphite power battery can be used well in UPS.

Key words: lithium-ion cell, AC impedance, UPS