Manipulation of Na_(3)V_(2)(PO_(4))_(2)F_(3) via aluminum doping to alter local electron states toward an advanced cathode for sodiumion batteries

With its unique 3D skeleton structure and exceptional cyclic stability,the Na^(+)superionic conducto(NASICON)-type Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)has been con sidered as a competitive cathode material for advanced Na ion batteries.However,the release of fluorine during th heat treatment leads to the formation of an additional phas Na_(3)V_(2)(PO_(4))_(3)(NVP),which results in a low-voltage plateau and compromises the energy density.Herein,we modulat the local electronic states of the V site by aluminum sub stitution to strengthen the stability of F.The results confirm that the aluminum introduction not only changes the loca electron states of V sites,significantly reducing the for mation of NVP by-product from 6.71 wt%to 1.01 wt%but also effectively reduces the band gap,improving th electronic conductivity of NVPF.The optimized Na_(3)V_(1.9)Al_(0.1)(PO_(4))_(2)F_(3)exhibits higher energy density of 340 Wh·kg^(-1)and excellent rate performance of 106.7 mAh·g^(-1)at 10C compared with the pristine cathode.

Ni_(3)FeN anchored on porous carbon as electrocatalyst for advanced Li-S batteries

Lithium-sulfur(Li-S)battery is one of the newgeneration energy storage systems with great potential.However,the development of Li-S battery now is hampered by the shuttle effect and depressed redox kinetics.Herein,we report a composite of Ni_(3)FeN nanoparticles anchored in grid-like porous carbon(PC)spheres as an effective cathode electrocatalyst with simultaneous polysulfide trapping and rapid polysulfides conversion in Li-S battery.The multi-cavity structure of PC with high-efficiency encapsulation ability can significantly improve sulfur utilization and confinement.Furthermore,Ni_(3)FeN nanoparticles embedded in PC cavities render highly active catalytic sites to promote the redox conversion of solvated poly sulfide,as revealed by the electrochemical results.Moreover,the catalytic mechanism is further analyzed through density functional theory calculations and in-situ Fourier transform infrared analysis.As a result,PC@Ni_(3)FeN@S cathode delivers an outstanding capacity of 1294mAh·g^(-1)at 0.1C and low decay rates of 0.10%per cycle over 500 cycles at 0.5C.