Fluorinated Graphene-Based High Performance Electrodes for Primary Lithium Batteries

Though rechargeable Li ion battery has become the dominant power source for portable electronics applications, primary batteries are used in applications like military and defense tools, medical implants, long time spatial exploratory missions, cameras etc.¹ By virtue of the low molecular weight and high redox potential of the constituting elements, Li/CF_x primary battery has clear dominance over any other competing primary battery technologies like Li/MnO₂ or Li/SOCl₂ in terms of its energy density, exceptionally long shelf life and a wide operating temperature window.^{2, 3} However, with its poor rate capability, owing to low electrical conductivity and diffusion limited kinetics, Li/CF_x battery system is less preferred compared to other battery chemistry like MnO₂ based systems.² Different strategies have been developed specifically for improving energy density, power density and faradic yield of Li/CF_x batteries.¹ However, a single step strategy capable of improving all the electrochemical parameters still remains to be challenge. Here, we demonstrate the use of fluorinated graphene (FG) as high performance cathode for Li primary battery. FG, obtained through chemical exfoliation of fluorinated graphite polymer (CF_0.25)_n using improved method,⁴ exhibited enhancements in energy density and power capability along with exceptional faradaic yield, all in a single step. The obtained specific capacity for FG derived from (CF_0.25)_n in the present work, is comparable to the theoretical capacity of (CF_0.75)_n. Further improvements in electrochemical performance could be achieved by optimizing the fluorine content in the starting material. The excellent electrochemical performance achieved here using fluorinated graphene with a very low fluorine content (x= 0.22) could lead to the development of highly efficient primary battery systems with low cost and minimum environmental impact.

Figure 1. Comparison of specific capacities of (CF_0.25)_nand FG electrodes when galvanostatically discharged against lithium at different current rates.

References

1       K. Guérin, M. Dubois, A. Houdayer and A. Hamwi, J. Fluorine Chem., 134 (2012), 11

2       P. Lam and R. Yazami, J. Power Sources, 153 (2006), 354

3      Z. Sheng , D. Foster and J. Read, J. Power Sources,      188 (2009), 601

4      A. Mathkar, T. N. Narayanan, L. B. Alemany, P. Cox, P. Nguyen, G. Gao, P. Chang, R. Romero-Aburto, S. A. Mani and P. M. Ajayan, Part. Part. Syst. Charact., 30 (2013), 266