In this study， the aging mechanism of commercial LiNi0.8Co0.15Al0.05O2/Graphite lithium-ion batteries at fixed nodes was studied experimentally， and the degradation modes in the whole life cycle were identified by differential voltage analysis method and electrochemical impedance spectroscopy analysis method， and verified by microscopic morphology observation. The results show that the capacity degradation of these lithium-ion batteries has two stages. In the first stage， the capacity degradation is slow， and the degradation modes in this stage are mainly composed of loss of anode active material and loss of lithium ions. In the second stage， the capacity degradation is sharp due to the lithium plating on the surface of the anode， which consumes a large number of recycled lithium ions directly， so the loss of lithium ions increases. The metallic lithium then reacts with the electrolyte and forms a dense covering layer， which increases the mechanical stress of the electrode in the process during the Li+ intercalation/deintercalation processes， and makes the loss of electrode active material increase. Generally speaking， the lithium plating causes the capacity plunge phenomenon， the formation of the passivation layer aggravates the loss of active material， and the continuous lithium plating causes drastic capacity decay in the second stage of aging.