Study on poor welding of anode tab and battery case of 21700 lithium ion battery

The 21700 battery is a standard battery used by Tesla vehicles in the United States. It has the advantages of high energy density ratio, high output, low cost and high safety factor. The demand for 21700 battery is gradually increasing on the market. In order to meet the needs of new energy vehicles, the 21700 battery uses copper tab as the anode, which can minimize the internal resistance and improve the charge and discharge efficiency. However, the material of the battery case is steel, and the melting point of the steel is 452°C higher than that of copper. It is difficult to solder firmly using the traditional resistance welding process. In this paper, using TRIZ theory, through the causal analysis, technical conflict, material-field, physical conflicts and other tools, the 21700 battery anode resistance welding problem is analyzed in detail, and based on the analysis results to propose solutions: punching out the pitting on the tab forming a projection welding; inserting metal tungsten in the copper welding head; changing the welding pin head from the platform to the curved surface; introducing nitrogen gas. Under the premise of constant material and no increase in cost, the problem of poor welding of the anode and the battery case can be effectively solved. © 2020 Trans Tech Publications Ltd, Switzerland.