Abstract: Through self-built lithium-ion battery combustion and fire extinguishing platform, taking the ternary lithium nickel cobalt manganese oxide battery as the research object, the fire test of ternary lithium-ion battery by water mist with additive was carried out, the mechanism and effect of solution fire extinguishing were analyzed comprehensively from the aspects of solution surface tension, battery maximum temperature and cooling rate, etc. In the test, the heat abuse method was selected, and a heating furnace was used to heat the ternary lithium-ion battery to cause thermal runaway combustion, and a high-definition camera recorded the whole process. Six kinds of additives including sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, sodium chloride, potassium chloride, ammonium dihydrogen phosphate and carbonamide were selected for single and compound solution water mist fire extinguishing test. The surface tension of each solution was measured, and its change with the concentration of the solution and its influence on the fire extinguishing performance were analyzed. It was found that the surface active agent could reduce the surface tension of the solution, thereby improving the atomization effect of water mist.When the surfactant tends to be saturated, the surface tension of the solution remains basically stable. A K-type thermocouple was used to measure the temperature during the thermal runaway of the ternary lithium-ion battery and the water mist fire extinguishing process, and the measured characteristic parameters such as the highest temperature and cooling rate of the battery were compared and analyzed. The result shows that, compared with pure water mist, the fire extinguishing performance of the additive-containing water mist is improved greatly in atomization effect, diluted oxygen concentration, and blocking the combustion reaction chain, and the battery does not reignite.The best mass fraction of single additive water mist with sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, sodium chloride, potassium chloride, ammonium dihydrogen phosphate, and carbamide to suppress the fire of ternary lithium-ion battery is 1.5%, 1%, 8%, 10%, 10%, 0.3% respectively. Compounding on this basis, it was found that the single extinguishing effect of potassium chloride and ammonium dihydrogen phosphate was better than the combined solution, the fire extinguishing effects canceled each other out. Coordination of surfactants, alkali metal salts and three additives that are easily decomposed by heat can improve the fire extinguishing efficiency effectively, the mixed solution of sodium dodecyl benzene sulfonate (1.5%), potassium chloride (10%) and ammonium dihydrogen phosphate (10%) had the best fire-extinguishing effect. The compound solution works synergistically through various mechanisms such as reducing the surface tension of the solution, reducing the particle size of fine water mist droplets, and combining ionized metal ions with free radicals in the combustion chain, absorbing a large amount of heat, thereby obtaining better fire extinguishing effect.The article carried out relevant experiments on the suppression of thermal runaway fires in ternary lithium-ion batteries with fine water mist containing different additives. In future research, more additives of different types and concentrations can be selected for compounding experiments considering fully from the perspective of high efficiency and environmental protection, and the advantages and disadvantages of various fire extinguishing agents, to provide support for lithium-ion battery fire protection technology.

Key words: ternary lithium-ion battery; additive; water mist; fire extinguishing performance