Porous FeF3 Microspheres/Reduced Graphene Oxide Composites as a High Performance Cathode Material for Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have high energy density, high operating voltage, environmental friendliness and long cycle lifetime. They are applied to the energy storage system such as the mobile phones, laptop computers, and electric-vehicles (EVs). However, modern energy storage device requires the development of LIBs with enhanced reversible specific capacities, which are mainly limited by electrode materials, especially cathode materials. Therefore, it is needed to develop the cathode materials with higher theoretical capacity. FeF₃ is of great interest as a potential alternative cathode material for LIBs because of its low cost, abundance, environmental friendliness, and high theoretical capacity of about 237 mAhg⁻¹ in the voltage range of 2.0−4.5 V and 712 mAhg⁻¹ in the 1.5−4.5 V, respectively.^{[1, 2]} However, FeF₃ has drawbacks of poor capacity retention and rate performance because of its low intrinsic electrical conductivity and slow diffusion of lithium ions.

In this study, porous FeF₃ microspheres/reduced graphene oxide (r-GO) composites were synthesized by a simple hydrothermal route with aqueous HF solution. The size of the microspheres was controllable simply by adjusting the amount of the graphene oxide from about 1 to 10 wt% in the precursor solution. The oxygen functional groups of the graphene oxide played a role as an anchoring site for the FeF₃ precursor and its crystallization to primary FeF₃ nanoparticles, which were structured as a building block to porous FeF₃ microspheres. The FeF₃ microspheres/r-GO composites showed the improved discharge capacity and cycling stability in the voltage ranges of 1.5-4.5 V and 2.0-4.5 V at room temperature compared to those of bulk FeF₃. For example, they delivered an initial discharge capacity of about 195 mAhg^-1 at 0.1 C rate with 0.27% fading per cycle during 50 cycles in the 2.0-4.5 V. The composites also showed the significantly enhanced rate capabilities in the range of 0.1-20 C (e.g., about 170 mAhg^-1 at 1 C rate). The detailed electrochemical data in the range of 1.5-4.5 V will be presented as well.

References

 [1]       N. Yamakawa, M. Jiang, B. Key, C. P. Grey, J. Am. Chem. Soc. 2009, 131, 10525.

 [2]       F. Badway, F. Cosandey, N. Pereira, G. G. Amatucci, J. Electrochem. Soc. 2003, 150, A1318.