Morphology and performance optimization for laser side welded prismatic lithium-ion battery cell by parameter-geometry synergistic control

Prismatic lithium-ion cells dominate the majority of the electric vehicle market. Laser side welding represents a relatively novel and more reliable method for welding cell lids of power battery cells, though its weld reinforcement constrains cell stacking dimensional precision. This study employed annular spot laser to side weld the cell lids and cell cans, systematically investigating the effects of laser power (3600 W to 4000 W), core-to-ring ratio (25%-75% to 45%-55%), and joint geometric dimensions. Through comprehensive analysis of weld macrostructure, microstructure characteristics, and mechanical properties, a laser parameter process window was established for achieving sound welds. It is demonstrated that the welds with relatively small reinforcement height and excellent mechanical properties can be obtained within the parameter range of 3700W at core-to-ring ratio 30%-70% to 3900W at core-to-ring ratio 40%-60%. In order to further control the weld reinforcement high, this study evaluated the role of cell lid geometry in controlling the weld reinforcement and its impact on mechanical performance by changing the length of the lid overlap edge (0.3mm - 0.6mm), which is a critical feature in sealing cell lids to cell cans. The results of this study indicate that the lid geometry significantly reduces the weld reinforcement height. When the heat input is at a low level, the weld performance mainly depends on lid overlap length, while at high heat input, the weld performance maintains a consistently favorable level. Microstructural analysis corroborates that the variations in the grain size of the melt pool fundamentally drive the changes in performance. These findings provide effective solutions for both controlling the weld reinforcement and sound quality in laser side welding of battery cell.