Graphene reinforced carbon nanofiber engineering enhances Li storage performances of germanium oxide

Centrifugally Spun Binder-Free N, S-Doped Ge@PCNF Anodes for Li-Ion and Na-Ion Batteries

Germanium has a high theoretical capacity as an anode material for sodium-ion batteries. However, germanium suffers from large capacity losses during cycling because of the large volume change and loss of electronic conductivity. A facile way to prepare germanium anodes is critically needed for next-generation electrode materials. Herein, centrifugally spun binder-free N, S-doped germanium@ porous carbon nanofiber (N, S-doped Ge@ PCNFs) anodes first were synthesized using a fast, safe, and scalable centrifugal spinning followed by heat treatment and N, S doping. The morphology and structure of the resultant N, S-doped Ge@ PCNFs were investigated by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray mapping, Raman spectroscopy, and X-ray diffraction, while electrochemical performance of N, S-doped Ge@ PCNFs was studied using galvanostatic charge-discharge tests. The results demonstrate that a nanostructured Ge homogeneously distributed on tubular structured porous carbon nanofibers. Moreover, N, S doping via thiourea treatment is beneficial for lithium- and sodium-ion kinetics. While interconnected PCNFs buffered volume change and provided fast diffusion channels for Li ions and Na ions, N, S-doped PCNFs further improved electronic conductivity and thus led to higher reversible capacity with better cycling performance. When investigated as an anode for lithium-ion and sodium-ion batteries, high reversible capacities of 636 and 443 mAhg^-1, respectively, were obtained in 200 cycles with good cycling stability. Centrifugally spun binder-free N, S-doped Ge@ PCNFs delivered a capacity of 300 mAhg^-1 at a high current density of 1 A g^-1, indicating their great potential as an anode material for high-performance sodium-ion batteries.

Tin-based metal-phosphine complexes nanoparticles as long-cycle life electrodes for high-performance hybrid supercapacitors

New tin-based metal-phosphine complexes of [Sn(OH)₄(PPh₃)₂] and [Sn(OH)₂(PPh₃)₂] have been successfully synthesized and used as supercapacitor electrodes for the first time, exhibiting a high specific capacitance, a good rate capability, and an excellent cycling stability. The specific capacitances (highest specific capacitance for tin-based materials) of 1204F g^-1 and 764F g^-1 for two samples at a current density of 1 A g^-1 in 6 M KOH can respectively be achieved, and their capacitance retention remained at 95.1% and 89.2% even after 15,000 cycles at a current density of 10 A g^-1. Furthermore, a flexible quasi-solid-state asymmetric supercapacitor composed of Sn(OH)₂(PPh₃)₂ and activated carbon was assembled and exhibited a specific capacitance of 290.6 mF cm^-2 at a current density of 1 mA cm^-2. More importantly, this device also displayed excellent cyclic stability of ∼100% for 1800 cycles during the galvanostatic charge/discharge process at 5 mF cm^-2.