Necklace-like Si@C nano?bers as robust anode materials for high performance lithium ion batteries

Silicon is believed to be a promising anode material for lithium ion batteries because of its highest theoretical capacity and low discharge potential. However, severe pulverization and capacity fading caused by huge volume change during cycling limits its practical application. In this work, necklace-like N-doped carbon wrapped mesoporous Si nanofibers(NL-Si@C) network has been synthesized via electrospinning method followed by magnesiothermic reduction reaction process to suppress these issues. The mesoporous Si nanospheres are wrapped with N-doped carbon shells network to form yolk-shell structure.Interestingly, the distance of adjacent Si@C nanospheres can be controllably adjusted by different addition amounts of SiO_2 nanospheres. When used as an anode material for lithium ion batteries, the NL-Si@C-0.5 exhibits best cycling stability and rate capability. The excellent electrochemical performances can be ascribed to the necklace-like network structure and N-doped carbon layers, which can ensure fast ions and electrons transportation, facilitate the electrolyte penetration and provide finite voids to allow large volume expansion of inner Si nanoparticles. Moreover, the protective carbon layers are also beneficial to the formation of stable solid electrolyte interface film.

Facile fabrication of interconnected-mesoporous T-Nb_2O_5 nanofibers as anodes for lithium-ion batteries

Niobium pentoxide(Nb2O5) has been extensively studied as anode materials for lithium ion batteries(LIBs) due to its good rate performance and safety advantages.However, the intrinsic low electronic conductivity has largely restricted its practical application. In this work, we report the construction of mesoporous T-Nb2O5 nanofibers by electrospinning followed by heat treatment in air. The interconnected mesoporous structure ensures a high surface area with easy electrolyte penetration. When used as anodes for LIBs, the mesoporous Nb2O5 electrode delivers a high reversible specific capacity of 238 mA h g-1 after 1,000 cycles at a current density of 1 A g-1 within a voltage range of 0.01–3.0 V.Even at a higher discharge cut-off voltage window of 1.0–3.0 V, it still possesses a high reversible capacity of166 mA h g-1 after 200 cycles. Moreover, the porous Nb2O5 electrode also exhibits excellent rate capability. The enhanced electrochemical performances are attributed to the synergistic effects of porous nanofiber structure and unique crystal structure of T-Nb2O5, which has endowed this material a large electrode-electrolyte contact area with improved electronic conductivity.

Bimetallic phosphides embedded in hierarchical Pdoped carbon for sodium ion battery and hydrogen evolution reaction applications

Transition metal phosphides have been explored as promising active materials for sodium-ion batteries(SIBs)and hydrogen evolution reaction(HER) applications owing to their unique physical and chemical characteristics. However,they suffer from the drawbacks such as severe agglomeration,and sluggish reaction kinetics. Herein, bimetallic phosphides(Ni2 P/Zn P4) embedded in P-doped carbon hierarchical microspheres are demonstrated with robust structural integrity,fast charge transfer, and abundant active sites. As expected,the optimally structured Ni2 P/Zn P4 composite exhibits good electrochemical performance as an anode material in SIBs,including high specific capacity, good cycling stability and rate capability. Meanwhile, the Ni2 P/Zn P4 composite also exhibits excellent electrocatalytic performance for HER with a small overpotential of 62 m V, a Tafel slope of 53 m V dec^-1, as well as excellent stability.