Lithium-ion batteries are easily overheated during discharge/charge operations with large current output/input. Traditional battery tests are difficult to pinpoint the internal thermal mechanism for an overheated battery. In this study, it is proposed a model to investigate the thermal behavior of the charge and discharge processes of lithium-ion battery with very high C-rate. The model combines an electrochemical-thermal (ECT) coupled module and a thermal abuse module. The whole successive process of the cell operation including charge/discharge, battery material exothermic reactions, and even thermal runaway within a cell, is fully described, by a single model. Predictions of individual LiNixCoyMnzO2 (NCM) lithium-ion cell high C-rate (up to 8C) discharge/charge processes compare well with experimental data. A detailed analysis is conducted to evaluate the influence of external heat release condition and charge/discharge C-rate on the thermal behavior of batteries during and after very high C-rate (>8C) charge/discharge operations. Results indicate: (1) the very large output/input current leads to the early-coming of cut-off voltage, terminating the discharge/charge operation; (2) compared with the very high C-rate charge operation, the discharge operation of the same C-rate is easier to cause battery overheat, leading to the occurrence of battery thermal runaway; (3) the high C-rate charge operation with cut-off voltage control fault is very dangerous as it can cause very fast heat generation and eventually possible thermal runaway; (4) favorable heat release condition or effective and active thermal control may be the key to the thermal control and restraining thermal runaway of lithium-ion batteries. (C) 2017 Elsevier Ltd. All rights reserved.