Study of Capacity Retention of Mcmb Anode Using Various Nanostructured Conductive Additives

Abstract

The global lithium-ion battery industry is growing at an impressive rate and is expected to grow even further in the near future. The main reasons for this are the high energy density and excellent cycling performance that these batteries exhibit. Researchers are experimenting with a handful of ideas that could make batteries vastly better than they are today, which could lead to more affordable electric cars and cheaper ways to store the intermittent energy1. The use of lithium-ion batteries (LIBs) in the automotive sector has been receiving quite significant attention. However, limitation of low electronic conductivity of electrodes has prohibited rapid commercialization of LIBs for automotive applications (such as EVs, HEVs, PHEVs, etc.) where high power density is required2. In addition, the lower electronic conductivity of active materials makes it difficult to achieve their theoretical capacities at implementation. A number of methods, such as surface coating with conductive material3, lattice doping4, addition of metallic particles (copper and nickel)5 were adopted to improve the conductivity of active materials with reasonable success. In this work, we examine the capacity retention characteristics of mesocarbon microbeads (MCMB) by the use of various nanostructure conductive additives such as carbon black (CB), multiwalled carbon nanotubes (MWCNTs) and graphene in a CR2016 type coin. Figure 1(a) shows the plot of electrical conductivity of MCMB anode with various proportion of CB and CNT. For the purpose of meaningful comparison, the weight percent of conducting agent in MCMB with CB, MCMB with CB and CNT, and MCMB with CNT composite anode remains the same. When some content of CB is replaced by CNT, electrical conductivity improves because of formation of hybrid conductive that meets both the long-range and short-range conduction requirement. In Figure 1(b) the experimental cycling behaviour for discharge capacity of MCMB-4 wt.% CB and MCMB-(3 wt.% CB+1 wt.% CNT) anode at 1C and 4C rate for first 50 cycles are compared and the effect of composite anodes with hybrid conductive network at 1C rate show 348 mAhg-1 capacity for initial cycle whereas electrodes with CB as additive exhibit about 337 mAhg-1. The MCMB-(CB+CNT) anode exhibits almost 99% capacity retention while MCMB-CB display the capacity retention of 92.6% after 50 cycles at 1C rate. Similarly, at 4C rate the initial capacity and capacity retention for mix conductive additives are superior as shown in Figure 1(b). The improvement of capacity retention performance is mainly because of improved electrical conductivity on addition of CNT due to their higher conductivity and high aspect ratio in comparison to CB. The cycling performance of MCMB anode with graphene as conductive additive will also be presented. 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 characterization at fresh and cycled stages. Reference [1] H. Y. Tran, G. Greco, C. Täubert, M. W. Mehrens, W. Haselrieder, A. Kwade, “Influence of electrode preparation on the electrochemical performance of LiNi0.8Co0.15Al0.05O2 composite electrodes for lithium-ion batteries” J. Power Sources 210 (2012) 276. [2] S. E. Cheon, C. W. Kwon, D. B. Kim, S. J. Hong, H. T. Kim, S. W. Kim, “Effect of binary conductive agents in LiCoO2 cathode on performances of lithium ion polymer battery” Electrochim. Acta 46 (2000) 599. [3] H. Momose, H. Honbo, S. Takeuchi, K. Nishimura, T. Horiba, Y. Muranaka, Y. Kozono, H. Miyadera, “X-ray photoelectron spectroscopy analyses of lithium intercalation and alloying reactions on graphite electrodes” J. Power Sources 68 (1997) 208. [4] Y. P. Wu, E. Rahm, R. Holze, “Effects of heteroatoms on electrochemical performance of electrode materials for lithium ion batteries” Electrochim. Acta 47 (2002) 3491. [5] F. Joho, B. Rykart, R. Imhof, P. Novak, M. E. Spahr, A. Monnier, “Key factors for the cycling stability of graphite intercalation electrodes for lithium-ion batteries”. J. Power Sources 81 (1999) 243. Figure 1