As a new electrochemical power system,safety (especially thermal safety) of Na-ion batteries (NIBs) is the key towards large-scale industrialization and market application.Thus,research on the thermal stability of NIBs is helpful to evaluate the safety properties and to provide effective strategies to prevent the occurrence of battery safety failure.Thermal stability of the high-power 26650 cylindrical NIBs using Cu-based layered oxide cathode and hard carbon anode is studied.The high power NIBs can achieve fast charge and discharge at 5-10 C rate and maintain 80％ capacity after 4729 cycles at 2 C/2 C rate,where the unit C denotes a measure of the rate at which a battery is charge-discharged relative to its maximum capacity.The results of accelerating rate calorimeter and differential scanning calorimetry (ARC-DSC) test results show that NIBs have a higher initial decomposition temperature (≥110 ℃) and a lower maximum thermal runaway temperature (≤350 ℃) than those of Li-ion batteries (LIBs),exhibiting a favorable thermal stability.It should be noted that the heat generation of cathode accounts for a large proportion of the total heat generation while the thermal stability of the anode determines the initial thermal runaway temperature,which is similar to LIBs.Finally,the whole temperature characteristics of the NIBs in the range of-60 ℃-1000 ℃ are summarized,which provide guidance for the safety design and applications of NIBs.