Nanostructured electrodes for 3D microbatteries

Sammanfattning

This master thesis can be considered a preliminary study. It examines the effect of current densities varying from 0.5-4.0 mA/cm2, when electro-depositing antimony on two different copper substrates that are to be tested as lithium battery anodes. One substrate type is flat, the other is covered in copper nano-pillars. The nano-structure causes roughly a 35 times area gain regarding contact with an electrolyte, as the samples are constructed into lithium-ion half-cells. The samples work as anodes during two series of cycling tests at different speeds (constant current). 10 cycles of each C/10, C/5, C/2, C and C/10, followed by similar 2C, 5C, 10C, 20C and C/10, where C=100% capacity, and C/10 means full capacity in 10 hours. After 100 cycles, the nano-structured samples retain a capacity of 79-89%, while the flat samples retain 68-76%. The variations of current density while depositing antimony does not seem to effect the results. The nano-structured samples better utilize their capacity at C/10, but not at the higher cycling speeds. This is counter intuitive as an increase in contact area with the electrolyte is expected to allow for faster and higher ion transport. The result is speculated to be due to an artefact caused by the cycling programs safety precautions in combination with either interference from the SEI-layer or depletion of lithium-ions along the pillar length.