Insights into the Ti^(4+) doping in P2-type Na_(0.67)Ni_(0.33)Mn_(0.52)Ti_(0.15)O_(2) for enhanced performance of sodium-ion batteries

Due to the sodium abundance and availability,sodium-ion batteries(SIBs)have the potential to meet the worldwide growing demand of electrical energy storage.P2-type sodium transition-metal layer oxides with a high energy density are considered as the most promising cathode materials for SIBs.We present here a detailed study of the enhanced rate capability and cyclic stability of the Ti-doped Na_(0.67)Ni_(0.33)Mn_(0.67)O_(2)cathode material.The combined analysis of ex-situ X-ray absorption fine structure(XAFS)spectroscopy,aberration-corrected high resolution transmission electron microscopy(AB-HRTEM)and X-ray diffraction(XRD)show that the strong Ti–O bond in the transition metal layers stabilizes the local structure,destroy the Na+-vacancy ordering and arrest the irreversible multiphase transformation that occurs during the intercalation/deintercalation process.Actually,Na_(0.67)Ni_(0.33)Mn_(0.52)Ti_(0.15)O_(2)exhibits a reversible capacity of 89.6 mA h g^(-1)even at 5 C,an excellent cyclability with 88.78%capacity retention after 200 cycles at 0.5 C.This study provides a better understanding in optimization of the design of high-energy cathode materials based on titanium doped layered oxides for SIBs.

Metal-organic framework-derived Ni2P/nitrogendoped carbon porous spheres for enhanced lithium storage

Transition metal phosphides(TMPs)/carbonaceous matrices have gradually attracted attention in the field of energy storage.In this study,we presented nickel phosphide(Ni2P)nanoparticles anchored to nitrogen-doped carbon porous spheres(Ni2P/NC)by using metal-organic framework-Ni as the template.The comprehensive encapsulation architecture provides closer contact among the Ni2P nanoparticles and greatly improves the structural integrity as well as the electronic conductivity,resulting in excellent lithium storage performance.The reversible specific capacity of 286.4 mA hg^-1 has been obtained even at a high current density of 3.0 Ag^-1 and 450.4 mA hg^-1 is obtained after 800 cycles at 0.5 Ag^-1.Furthermore,full batteries based on LiNi1/3Co1/3Mn1/3O2||Ni2P/NC exhibit both good rate capability and cycling life.This study provides a powerful and indepth insight on new advanced electrodes in high-performance energy storage devices.