SU-8 negative photoresist on pyrolysis yields hard carbon that contains very localized arrangement of graphene layers (1). Electrochemical performance of SU-8 derived carbon thin films and 3D structures over silicon wafer were investigated and specific capacity values reported to be smaller than graphite and other hard carbon materials (3, 4). This could be due to higher charge transfer resistance reported for the carbon films over silicon wafer (3). In our recent study we have prepared SU-8 derived carbon thin films over conductive stainless steel (SS) as a current collector. For the SU-8 derived carbon thin film electrode on SS collector, Li ion intercalation capacity value was found to be ~400 mAh/g with good cyclic stability over 100 cycles (5).

In this work we have extended the fabrication of SU-8 derived carbon 3D electrode on SS wafer by using C-MEMS process. C-MEMS process conditions were finely tuned to control the pealing of carbon micro structures during pyrolysis. We have pyrolyzed SU-8 microstructures at 900 ºC. Thus prepared 3D carbon microstructures on SS wafer were characterized by optical profiler for morphology before and after pyrolysis. Prepared carbon microelectrodes were shown enhanced electrochemical performance when compared to carbon thin films over SS wafer and 3D carbon structures over Si wafer. A more detailed comparison of electrochemical performance of thin films and 3D structures will be presented in conference. 

Experimental:

SU-8 2050 was spin coated on single side polished stainless steel wafer after de-hydrated bake for 10 min at 150 °C on hot plate. Thus obtained films were patterned using modified C-MEMS process. Patterned microstructures were then pyrolyzed in tubular furnace at 900 °C in presence of N₂ atmosphere. Prepared carbon microelectrode was used as working electrode, lithium foil as counter electrode in Swagelok half-cell assembly.

Results and discussions:

Optical profiler image of SU-8 3D micropillars is shown in Fig. 1. These 3D SU-8 microarrays were then pyrolyzed to yield 3D carbon microelctrode arrays which were then tested for their electrochemical performance. Galvanostatic (constant current) charge discharge experiments were performed between 0.01 and 3 V at 1C. Galvanostatic charge discharge experiments reveals that improved electrolyte and active electrode contact interface and minimized lithium ion transport distance improves the specific intercalation capacity values and cyclic performance over long cycling. We have also prepared different area fraction (actual surface area/projected surface area) micro patterns and correlated the electrochemical performance with area fraction. Detailed discussion of different area fraction microelectrodes with respect to their electrochemical performance will be presented in conference.

References:

1. A. Mardegan, R. Kamath, S. Sharma, P. Scopece, P. Ugo, M. Madou, J. Electrochem. Soc., 160, B132 (2013).
2. G.T. Fey, C.L. Chen, J. Power Sources, 97-98, 47 (2001).
3. G.T. Teixidor, R.B. Zaouk, B.Y. Park, M. Madou, J. Power Sources, 183, 730 ((2008).
4. T. Zheng, Y. Liu, E.W. Fuller, S. Tseng, U.V. Sacken, J.R. Dahn, J. Electrochem.  Soc., 142, 2581(1995).
5. M. Kakunuri, C.S. Sharma, ECS Trans., 66, 57 (2015).