Laser-welded multi-battery cells solve energy supply challenge

28 Apr 2015

Fraunhofer ILT-developed “oscillation laser welding” delivers precise energy burst to join batteries.

The Fraunhofer Institute for Laser Technology (ILT) has developed a new laser welding technology for temperature-sensitive cylindrical battery cells that is now ready for series production. The ILT’s scientists have been working on joining batteries into more powerful, longer lasting multi-packs since 2009. They are currently working with other Fraunhofer Institutes to integrate a complete battery pack.

The new battery-joining process is performed using fiber lasers with a maximum power output of 1kW. The method is called oscillation laser welding, a technology that applies a precise energy input to the batteries. It does so by superimposing a circular or swinging oscillation of the laser beam onto the feed movement. This local modulation allows the control of the welding process very precisely. Significantly, it enables the scientists to perform circular welding on the battery tops.

Linking 4,800 cells

As the metals are melted during the laser-welding process, a small spot (0.1 to 0.25 mm across) is briefly heated to a super-high temperature, only to rapidly cool again once the welding is finished. Benjamin Mehlmann, expert in metallic materials micro-joining at the Fraunhofer ILT, commented, “Take notebook cells, for instance. Here, we weld very thin steel plates to copper alloys directly over temperature-sensitive plastic. What makes this possible is that the method is incredibly fast and has a low energy input.”

Typical applications for these cylindrical batteries include portable computers, power tools and non-standard electric cars, such as the Tesla Roadster. Oscillation laser welding is currently being used to join 4,800 standard cells, each with a diameter of 18mm and a length of 65mm, into a multi-battery pack suitable for use in an electric vehicle. The Aachen-based scientists weld the cells in their charged state, which makes safety of paramount importance as the cells contain electrolytes that must not be allowed to leak.

Oscillation laser welding

Fraunhofer ILT is currently in the “validation phase” of the battery-welding project, in which Mehlmann and his team are working to improve the process and making it safe to use. “This is s an interesting option for SMEs wanting to use the method to develop their own solutions for portable and stationary applications,” he said.

Integrating the process into a conventional ribbon bonder is also part of the brief (ribbon bonding is an assembly and joining technology process for bonding metallic ribbon, usually with ultrasound, to electrically connect components). Central to this application is the electrical contact between battery and electronics. This development came about in a publicly funded project that saw Fraunhofer ILT collaborating with F & K Delvotec, a company based in Ottobrunn, Germany.

Now on tour

• Fraunhofer ILT is presenting this joint project on April 27-29 at the Battery Power conference at the Eurogress in Aachen, Germany. Both parties will be showcasing the prototype at F & K Delvotec’s booth at the SMT Hybrid Packaging trade fair in Nuremberg, Germany, May 5 – 7, 2015.