Effect of Different Conductive Additives on Electrochemical Performance of Li-Ion Coin Cells

Enormous increase in energy demand and depletion of fossil fuel resources have been drawing researchers towards alternative energy sources. In this connection, lithium-ion batteries (LIBs) are being used as power sources in automobile sector to drive electric vehicles (EVs) and hybrid-electric vehicles (HEVs). For these power applications, LIBs should be capable of high discharge capacity with longer cycle life at high discharge rate. Application of LIBs at high current increase the rate of capacity loss by rapid increase in rate-associated side reactions such as electrolyte decomposition, active material dissolution, SEI film formation and gas generation^1,2. As a solution to these difficulties, various groups have put efforts to find out new materials for electrodes and electrolytes. Some work has also been directed in the area of modern additives for cathode, anode, and electrolyte which can enhance battery capacity for longer life at high discharge rate especially in case of EVs and HEVs. A review of the current academic and industry practices has revealed a lack of standard on the exact amount of conductive additives that should be added to the active material³. The amount of the active material should be highest for higher energy density and better discharge capacity and at the same time sufficient amount of conductive additive should be added to provide proper conduction network for electronic movement. In addition, the effect of addition of nanostructured additives requires significant attention and needs to be studied as well. These nanostructured additives have better electronic conductivity and higher surface area than conventional additives which may result in improved electrochemical performance of the cell⁴. However, nanomaterials are much costlier than simple additives, limiting their application as conduction agent. A carefully controlled mixture amount of these advanced with traditional additives is required for better capacity retention and higher discharge capacity while keeping a close control on the cost of fabrication.

In this work, we examine the effect of various conductive additives and their combinations to fabricate 2032 coin cells to achieve higher discharge capacity with improved cycle life at low cost. In this connection, electrodes will be prepared by using carbon black (CB), single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and combinations of CB & SWCNTs, CB & MWCNTs, SWCNTs & MWCNTs and CB & CWCNTs & MWCNTs with LiMn₂O₄as the active material. Schematic representation of the electrodes using these conductive additives is shown in Figure 1. The cell fabricated by using these electrodes will be analyzed for capacity retention, discharge capacity and cycling performance. Electrochemical impedance spectroscopy (EIS) will be employed to analyze the aging effects and rate of capacity degradation of cells by quantifying the growth of internal resistances with cycling. The morphological and structural changes of electrodes due to cycling will be examined by using SEM and XRD techniques respectively at fresh and cycled stage. The results obtained from this study will be expected to frame a standard on the amount of conductive additives to be added during electrode fabrication to result in improved cycling performance of these cells.

References:

1. M. Rashid and A. Gupta, “Mathematical model for combined effect of SEI formation and gas evolution in li-ion batteries”, ECS Electrochem. Lett., 3, A95 (2014).
2. M. Rashid, A. Gupta, “Effect of relaxation periods over cycling performance of a li-ion battery”, J. Electrochem. Soc., 162, A3145 (2015).
3. T. Marks, S. Trussler, A. J. Smith, D. Xiong, and J. R. Dahn, “A Guide to Li-Ion Coin-Cell Electrode Making for Academic Researchers,” J. Electrochem. Soc., 158, A51 (2011).
4. X.M. Liu, Z.D. Huang, S. Oh, P.C. Ma, P. C. H. Chan, G. K. Vedam, K. Kang, and J.-K. Kim, “Sol–gel synthesis of multiwalled carbon nanotube-LiMn₂O₄ nanocomposites as cathode materials for Li-ion batteries,” J. Power Sources, 195, 4290 (2010).