Synthesis and electrochemical characterization of phosphorus / carbon composites for sodium ion battery applications

Renewable energy sources, such as wind and sun, have attracted ever-growing attention due to exhaustion of fossil fuels and environmental concerns. In some applications, lithium ion batteries are not suitable candidates because of the low abundance of lithium resources and their high cost. In comparison, sodium is abundant and cheap, and also has similar physical and chemical properties to lithium. Thus, more and more investigations on sodium ion batteries have been emerging in recent years. In this thesis work, promising red phosphorus was chosen as the objects of study, although their cycling performance is not yet satisfactory. Through reducing the particle size and forming composites with conductive carbon, P/carbonnanotube (CNT) and P/graphene nanoplate composites were synthesized. Therefore P samples amorphization different times. Moreover, the influences of the morphology and the sodium storage mechanism of these electrode materials were investigated through various characterization techniques, including field emission scanning electron microscopy, X-ray powder diffraction. P/CNT composite was prepared just by simply mixing microsized red phosphorus with CNTs by ball milling. The thus-prepared P/CNT composite unexpectedly exhibited highly reversible sodium storage. It is concluded that the poor electronic conductivity and huge volume expansion of red P is the main obstacles which inhibit the reversibility and cycling stability of red P. Consequently, we propose some strategies to dissolve these problems in chapter 2. One of them is combination with graphene nanoplate to prepare (P/GnP) composite by the ball-milling method. The particle size was reduced and incorporated in graphene nanoplates, in addition, the phosphoruscarbon bonds were formed in the P/GnPs composite. This chemical bond improves the electrical connectivity between the P particles and the graphene nanoplates, consequently stabilizing the structure of the composite to achieve high cycling performance and rate capability. As a result, the red phosphorus and graphene nanoplate composite delivered high reversible capacity of 1146 mAh g-1 at the current density of 100 mA g-1 and excellent cycling stability for 200 cycles with 92.5% capacity retention.