Vacuum liquid injection method

The invention provides a vacuum liquid injection method. Firstly, an electrolyte is added into an upper cup body; secondly, the vacuumizing time is set, a first valve between vacuumizing equipment anda lower cup body is controlled through a PLC, when the PLC controls the first valve to be opened, the PLC controls the vacuumizing equipment to be started at the same time, when a set vacuumizing time threshold value is reached, the PLC controls the first valve to be closed and stops operation of the vacuumizing equipment at the same time, and due to the fact that the lower cup body is communicated with a battery shell, the battery shell is also in a vacuum state after the lower cup body is vacuumized; and thirdly, after the vacuumizing operation of the lower cup body is completed, the PLC controls a second valve between the upper cup body and the lower cup body to be opened, and the electrolyte enters the battery shell through the second valve and the lower cup body. Batch liquid injection is completed by means