Preparation Of Niobium-based Oxides With Different Structures And Their Lithium Storage Properties

Lithium-ion batteries（LIBs）as typical representative of secondary batteries have dominated power sources for consumable electronics.To satisfy the booming development need for electric vehicles,the exploration of high-performance electrode materials with high reversible capacities,safe operation,superior rate capabilities,excellent cyclic stability and high first-cycle is highly desirable.Therefore,most intercalation-type niobium oxides niobates have drawn researchers’attention due to their large practical/theoretical capacities and high safety performance.The niobium oxides display the unique crystal structures,which enable ultra-fast Li⁺diffusivity,leading to high rate performance,such as open and stable Wadsley–Roth shear crystal structure and tetragonal tungsten bronze crystal structure.Therefore,we explore that niobium oxide anode materials with different structures have the influence on the structural robustness and good electrochemical properties.BiNb_5.4O₁₅ with a tetragonal tungsten bronze crystal structure（Cmmm space group）is synthesized by a solid-state reaction.Abundant large-sized tunnels and a large interlayer spacing of～3.97?are found in this open structure,enabling fast Li⁺diffusivity(3.25×10^–11/1.68×10^–10 cm² s^–1 during lithiation/delithiation).Additionally,this structure is very stable after the first lithiation process,resulting in excellent cyclability（95.4%/～100%capacity retention after 100/1000 cycles at 1C/10C）.BiNb_5.4O₁₅ further exhibits a safe Li⁺-storage potential（～1.55 V）and large reversible capacity(309.7 m Ah g^–1@0.1C).Porous Nb₄W₇O₃₁ microspheres constructed by nanorods are synthesized based on a facile solvothermal method.This new material contains different tungsten bronze structures and 4×4 ReO₃-type blocks confined by tungsten bronze matrices,generating plenty of pentagonal and quadrangular tunnels for Li⁺storage,as confirmed by spherical-aberration-corrected scanning transmission electron microscopy.Such structural mixing enables three-dimensionally uniform and small lattice expansion/shrinkage during lithiation/delithiation,leading to good structural and cyclic stability（95.2%capacity retention over 1500 cycles at 10C）.The large interlayer spacing（～3.95?）coupled with the abundant pentagonal/quadrangular tunnels results in ultra-high Li⁺diffusion coefficients(2.9×10^–10 cm² s^–1 during lithiation and 1.2×10^–9 cm² s^–1 during delithiation)and a high rate capability（10C vs.0.1C capacity retention percentage of 47.6%）.Nb₄W₇O₃₁ further exhibits a large reversible capacity(252 m Ah g^–1 at 0.1C),high first-cycle Coulombic efficiency（88.4%at 0.1C）and safe working potential（～1.66 V vs.Li/Li⁺）.This comprehensive study demonstrates that the porous Nb₄W₇O₃₁ microspheres are a very promising anode material for future use in high-performance Li⁺storage.