Abstract
1. Introduction Rechargeable lithium ion batteries become a solution to the world’s ever-increasing demand for energy storage and created excellent opportunities for communication via portable electric devices. However, LIBs are limited to the portable electronic devices and are still too expensive to be used in large-scale applications such as renewable energies. Transition metal hexacyanoferrates (MHCFs) are promising cathode materials because of easy production, low cost and promising electrochemical performance. MHCF were investigated as hosts for alkali ions in 1999 [1]. In 2012, Prof. J. Goodenough’s group showed promising Na ion battery using MHCF as a cathode [2]. In this work, NiHCF is synthesized via a simple co-precipitation method. This cathode showed very promising performance in LIBs with stable cycle life and flat charge/discharge plateaus. 2. Experiments NiHCF was synthesized via a simple co-precipitation method. Typically, 0.01 mol Ni(NO3)2 and 0.005 mol K3Fe2(CN)6were dissolved in 250 mL DI water, respectively. These two solutions were added dropwise into DI water in a round bottom flask under magnetic stirring at 70 °C [3]. The yellow precipitates were filtered, washed and dried in a vacuum oven at 35 °C for 72 h. The NiHCF was characterized by XRD (X’Pert PRO, PANalytical) and TEM (Libra 120, Carl Zeiss). NiHCF was homogeneously mixed with Acetylene Black (MTI Co.), polyvinylidene difluoride (Kynar) in 8:1:1 ratio and coated on a carbon current collector (Alfa Aesar), and dried in 35 °C for 24 h. The mass loading of NiHCF was around 4-5 mg/cm2. CR2032 coin cells were assembled to investigate NiHCF electrochemical behavior. Lithium chips was used as reference/counter electrode, Celgard 2400 was used as a separator and 1 M LiPF6 in EC:DEC:DMC (1:1:1 vol.) was used as electrolyte. The electrochemical investigations were carried out using galvanostat/potentiostat tester (VMP3, Biologic). 3. Results and discussion The pure NiHCF phase was confirmed from the XRD result, and sharp characteristic peaks indicated good crystallinity of NiHCF as presented in Fig. 1a. Transmission electron microscopy (Fig. 1b)showed that NiHCF consisted of agglomerated nanoparticles around 20–50 nm in size. Fig. 2 is the cyclic voltammetry of NiHCF at 0.1 mV s-1 between 2 - 4.2 V vs. Li/Li+. NiHCF has a well distinguished pair of symmetric peak around 3.3 V, which corresponds to the lithiation/delithiation of NiHCF during discharge and charge process. The charge/discharge profiles are shown in Fig. 3. The excellent flat plateaus around 3.3 V are well-matched with the CV results in Fig. 2. NiHCF showed a capacity of 52 mAh g-1at a current density of 0.2 C, which is about 87% of its theoretical capacity. Further information and results on this research will be presented at the Meeting. Acknowledgments This research was supported by the Institute of Batteries LLC, a research grant from the Ministry of Education and Science of Kazakhstan, and a Research Project from Nazarbayev University. References 1. N. Imanishi, T. Morikawa, J. Kondo, Y. Takeda, O. Yamamoto, N. Kinugasa, T. Yamagishi, J. Power Sources, 79 (1999) 215–219. 2. L. Wang, Y.H. Lu, J. Liu, M.W. Xu, J.G. Cheng, D.W. Zhang, J.B. Goodenough, Angew. Chem. Int. Ed.52 (2013) 1964 –1967. 3. C.D. Wessells, S.V. Peddada, R.A. Huggins, Yi Cui, Nano Lett. 11 (2011) 5421–5425. Figure 1