Low-Temperature Synthesis of Amorphous FePO₄@rGO Composites for Cost-Effective Sodium-Ion Batteries

Abstract

The dramatic growth of the sodium-ion battery market evokes a high demand for high-performance cathodes. In this work, a nanosized amorphous FePO4@rGO composite is developed using coprecipitation combined with low-temperature hydrothermal synthesis, which registered a surface area of 179.43 m2 g–1. The composites maintain three-dimensional mesoporous morphology with a pore size in the range of 3–4 nm. Uniform distribution of amorphous FePO4 allows a reversible capacity of 175.4 mA h g–1 at 50 mA g–1 while maintaining a stable cycle life of 500 cycles at 200 mA g–1. The amorphous FePO4@rGO, obtained by energy-efficient synthesis, significantly improved the rate performance compared to the crystalline material prepared at high temperatures. Cyclic voltammetry tests reveal that the fast reaction kinetics can be attributed to the pseudocapacitive behavior of the electrode. In addition, we demonstrated the promise of FePO4@rGO cathodes for low-temperature sodium-ion batteries.

Iron‐Phosphate‐Based Cathode Materials for Cost‐Effective Sodium‐Ion Batteries: Development, Challenges, and Prospects

“…In contrast, amorphous FePO 4 (a‐FePO 4 ) can withstand uniform volume changes because of more voids and vacancies. [ 35 ] Shiratsuchi et al. first verified the sodium storage properties of amorphous FePO 4 with a reversible capacity of 146 mA h g –1 at a density of 0.1 mA cm –2 .…”

“…via coprecipitation combined with low‐temperature hydrothermal routes designed an amorphous FePO 4 /rGO composite, which delivered 175.4 mA h g –1 at 50 mA g –1 and cycled 500 times at 200 mA g –1 with constant capacity (Figure 7d). [ 35 ]…”

“…In contrast, amorphous FePO 4 (a-FePO 4 ) can withstand uniform volume changes because of more voids and vacancies. [35] Shiratsuchi et al first verified the sodium storage properties of amorphous FePO 4 with a reversible capacity of 146 mA h g -1 at a density of 0.1 mA cm -2 . [36] To understand the reaction mechanism, Kim et al constructed a diagram of the amorphous structure of FePO 4 and its possible diffusion paths through quantum mechanical calculations and the bond valence summation method.…”

“…For example, Zhao et al via coprecipitation combined with lowtemperature hydrothermal routes designed an amorphous FePO 4 /rGO composite, which delivered 175.4 mA h g -1 at 50 mA g -1 and cycled 500 times at 200 mA g -1 with constant capacity (Figure 7d). [35] In this section, we carefully discussed structure, electrochemical performance, and reaction mechanism of NaFePO 4 , Na 3 Fe 2 (PO 4 ) 3 , and FePO 4 . The electrochemical performance of these typical phosphate-type IPBMs has been listed in Table 1.…”

“…d) Long-term cycle performance of the a-FePO 4 @rGO electrode at a current density of 200 mA g −1 . Reproduced with permission [35]. Copyright 2021, American Chemical Society.…”