The fire hazard of lithium-ion batteries (LIBs) poses a serious threat to their transportation and use. The purpose of this study is to investigate the efficiency of low-pressure twin-fluid water mist (TFWM) on suppressing lithium-ion battery fires. Experiments were executed to research the effect of working pressures and release stages on extinguishing the fire. Aqueous vermiculite dispersion (AVD), a commercial agent that was specifically designed to extinguish battery fires, was chosen to compare with the fire suppression performance of TFWM under the same conditions. The results indicate that the type 21,700 LIB fires could be controlled by applying the water mist within 10 s. The cooling ability at various working pressures (0.4, 0.8, 1.0, and 1.2 MPa) demonstrated an increase in inhibitory effects as the working pressure increased, and the optimal pressure was 1.2 MPa. The results further show that the extinguishing ability of the TFWM was better than the AVD agent. When the water mist was applied at the optimal working pressure, the surface temperature, flame temperature and concentration of CO reduced more significantly, compared with the AVD agent. Therefore, the TFWM shows considerable merit as a candidate to fight LIB fires.