Porous amorphous FePO₄ nanoparticles connected by single-wall carbon nanotubes for sodium ion battery cathodes

Sodium ion batteries (SIBs) are promising candidates for the applications of large-scale energy storage due to their cost-effective and environmental-friendly characteristics. Nevertheless, it remains a practical challenge to find a cathode material of SIBs showing ideal performance (capacity, reversibility, etc.). We report here a nanocomposite material of amorphous, porous FePO₄ nanoparticles electrically wired by single-wall carbon nanotubes as a potential cathode material for SIBs. The hydrothermally synthesized nanocomposite shows excellent cell performance with unprecedented cycling stability and reversibility. The discharge capacity of as high as 120 mAh/g is delivered at a 0.1 C rate (10 mA/g). The capacity retentions are about 70 mAh/g, 60 mAh/g, and 55 mAh/g at higher currents of 20 mA/g, 40 mA/g, and 60 mA/g, respectively. Even at a 1 C rate (100 mA/g), a capacity of about 50 mAh/g is still retained after 300 cycles. With a simple synthetic procedure, cost-effective chemicals, and desirable cell performance, this method offers a highly promising candidate for commercialized cathode materials of SIBs.