Top side sealing is a key packaging process in the manufacturing of soft pack lithium-ion batteries, which refers to the final sealing of the top injection port area of the battery after the completion of liquid injection and formation. The core purpose is to completely and permanently isolate the interior of the battery cell from the external environment, ensuring that the battery does not leak or swell during its service life, and preventing moisture and oxygen from entering, thereby ensuring the safety and long-term reliability of the battery.

The standard workflow mainly includes the following steps:

Pre treatment and cleaning: Transfer the battery cells that have completed chemical conversion and have undergone exhaust (removal of gases generated by chemical conversion) to the operating position. Carefully clean the injection port and surrounding aluminum-plastic film area to ensure that there are no electrolyte residues, dust, or other pollutants to ensure the quality and sealing strength of subsequent packaging.

Vacuuming and packaging: Place the battery in the fixture of the top side sealing device. When closing the upper and lower molds of the fixture, the packaging area will first be evacuated to remove the air inside the packaging cavity. Subsequently, the PP layer (polypropylene layer) in the inner layer of the aluminum-plastic film is melted and fused together under high temperature (usually 180-220 ℃), specific pressure, and time using a precisely controlled hot head, forming a strong sealing edge.

Cooling shaping and inspection: After heat sealing is completed, the fixture will undergo pressure holding cooling to solidify and shape the melted PP layer, ensuring that the sealing joint is solid and flat. After removing the battery, a 100% inspection of the packaging appearance is required to check whether the sealing edge is uniform, wrinkle free, and free of defects such as burning or melting.

The core control points of this process lie in the precise matching of temperature, pressure, and time, as well as the cleanliness of the packaging area. A perfect and reliable top seal is the last and crucial physical barrier for the long-term safe use of soft pack batteries.