Batteries

  Novel Electrodes for Batteries and Supercapacitors

Battery Electric Vehicles (BEV) and Plug-in Electric Vehicles (PHEV) are hampered by the amount of stored energy and the cost of the battery pack.  Gasoline has a specific energy density of about 1,000 Wh/kg, while today’s batteries show about 150Wh/kg based on storage to wheel efficiency.  The daunting challenge of “better batteries” inspires many researchers around the globe. One promising approach is silicon (Si) based electrodes that can store up to 4x more energy than today’s lithium (Li-ion) batteries. Four Li-ions instead of the conventional one Li-ion intercalate with the Si matrix. One of the major challenges is the large volume change associated with charge and discharge which requires a tailored electrode design and manufacturing.

Fraunhofer Institute for Laser Technology (ILT) fabricates current collectors using two-beam interference to result in 500nm to 700nm pedestals with well defined pitch. At the University of Michigan, titanium nanotubes are grown on the pedestals and infiltrated with Si.  High energy densities have been demonstrated, and future research will optimize the electrochemical and mechanical design as well as the manufacturing processes.

Supercapacitors store electricity based on charge separation and not based on chemical processes as in batteries. Therefore, supercapacitors can provide high peak power, but they are limited in energy storage, whereas batteries store high energies but are limited in peak power.  A hybrid energy storage system (HES) combines both components delivering power and energy.  CLT will address integration issues of HES over the next few years.

Large surfaces of the active material accessible by the electrolyte and minimum electrical impedance are necessary for high performance supercapacitors.  High porosity metal foams represent a 3 dimensional current collector and thus minimize impedance.  The metal foams are designed and manufactured at the Fraunhofer Institute for Manufacturing Technology and Advanced materials (IFAM) and are infiltrated with Vanadium Nitride, an electroactive material developed at the University of Michigan.  High peak power and good energy storage could be demonstrated and further work will optimize the performance and manufacturing processes.

Cost Effective Manufacturing Processes for Batteries and Solar Cells

  Laser based, cost effective manufacturing of thermal and electrical batteries is developed at CLT.  Laser slitting of coated battery electrodes was developed at CLT and is now installed in volume production for the manufacturing of cylindrical battery cells. With only 50W of laser power, cutting speeds of 30m/min are achieved.  Laser based packaging of these cells using 6 different welding processes was also developed and all processes were introduced into production at one major battery manufacturer.  High weld quality and hermetic sealing are required and the respective processes were developed and qualified.

Remote laser cutting of electrodes was also developed with an industrial customer and fully qualified for production. The laser beam is guided along the contour of the part by a scanner and the electrodes are cut with speeds of 0.5m/s with only 100W of laser power.  An AETT program aims to further increase the productivity of remote cutting by a factor of 5, leading to cutting speeds of 4m/s making it 10x faster than the precision die cut with similar capital cost.