Carbon nanofibers (CNFs) have drawn a great attention for being used as anode materials for lithium ion battery due to short lithium ion transport distances, high resilience to volume expansion during cycling even at high current densities and enhanced electronic conductivity (1). Electrospinning is a promising and scalable method for preparing continuous nanofibers. Among wide range of electrospun polymer fibbers high carbon yield polyacrylonitrile (PAN) derived carbon nanofibers were well studied for Li-ion battery application (2, 3).

In this work, we have synthesized SU-8/CNT composite carbon nanofibers web over stainless steel current collector. Thus prepared composite carbon nanofiber web was tested for lithium ion intercalation. Electrochemical performance of composite fibers was compared with SU-8 derived carbon fiber web and SU-8 derived carbon thin film (4).

Experimental

0.5% multi walled carbon nanotubes (MWCNTs) were dispersed into SU-8 (2015) photoresist solution using probe  sonication for 30 min. Electrospun composite nanofiber web was prepared by modified C-MEMS process to keep morphology intact during the baking and pyrolysis. Galvanostatic charge discharge experiments were performed at different C-rates using Li metal as reference electrode.

Results and discussions:

SU-8/CNT composite carbon nanofibers morphology was investigated by scanning electron microscopy. FESEM images of nanofibers before and after pyrolysis were shown in Fig. 1a and 1b. Electrochemical performance of these carbon fibers was studied at different current densities form 0.1 to 1 C as shown in Figure 1c. Initial reversible specific capacity found to be 1317 mAh/g for SU-8/CNT composite carbon fiber web at 0.1 C. This specific capacity value is far better than reversible capacity values of SU-8 derived carbon films (~385 mAh/g) and other electrospun carbon nanofibers. Furthermore these CNFs web shown very good cyclic performance at higher C-rates. Specific reversible capacity at 1C rate (372 mA/g) was found to be 516 mAh/g.  This performance can be ascribed to tolerance of expansion and shrinkage during lithium insertion and de-insertion and enhanced electronic conductivity due to CNTs presence during the pyrolysis. Detailed comparison of electrochemical performance of composite fibers with photoresist derived carbon thin films and other carbon nanofibers will be presented during the conference.

References:

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2. X. Mao, T. A. Hatton, G. C.  Rutledge, Curr. Org. Chem., 17, 1390 (2013).
3. J. K.  Lee, K. Wan, J. B. Ju, B. W. Cho, W. II. Cho, D. Park, K. S. Yun, Carbon, 39, 1299 (2001).
4. M. Kakunuri, C. S. Sharma, ECS Trans., 61, 37(2014).