Preparation Of MNb₃O₉ Type Niobates And Study Of Their Lithium Storage Propertie

With the development of society and technology,the excessive consumption of energy has also brought about resource and environmental problems.In recent years,the development momentum of the electric vehicle industry has been vigorous,which has also promoted the rapid development of electrochemical energy storage technology.Lithium-ion battery has better electrochemical performance than other secondary batteries,so it is considered to be an ideal power source for pure electric vehicles.As one of the core components of lithium battery,anode can not meet the high-performance requirements of pure electric vehicle at present.Li₄Ti₅O₁₂is the most famous anode material with fast-and stable-charging capability,but its electron conductivity and theoretical capacity is low,Ti⁴⁺will catalyze electrolyte decomposition,especially at high operation temperature,which restricts the development of Li₄Ti₅O₁₂.In recent years,niobate has been explored as a high performance anode material,but its the shear ReO₃structures are still insufficiently open,and the tungsten bronze structures are insufficiently stable after deep lithiation,which restricts its further development.Therefore,it is very necessary to develop a kind of electrode material with excellent crystal structure suitable for the anode electrode of lithium-ion battery.Here,we explore a MNb₃O₉anode material for lithium-ion batteries,which has an open and stable A-site-cation-deficient perovskite structure,which is beneficial to its magnification and cycling properties.Therefore,the MNb₃O₉anode material is designed rationally in this paper,and its electrochemical properties and mechanism are studied deeply.（1）LaCeNb₆O₁₈（LCNO）micrometer-sized particles are prepared through solid-state reaction.The results show that LCNO owns a very open A-site-cation-deficient perovskite structure,in which（vacancy/La/Ce）O₁₂layers with electrochemical inactivity and superior volume-buffering capability locate between active NbO₆layers,leading to not only fast Li⁺diffusivity but also low-and negative-strain behavior at different temperatures.LCNO not only owns higher rate capability and cyclability than other Nb-based anode materials at 25℃,but also shows more excellent rate capability and excellent cyclability at 60℃.（2）LaNb₃O₉（LNO）is selected as the raw material model to prepare high-entropy oxide(La_0.25Ce_0.25Pr_0.25Nd_0.25)Nb₃O₉（LCPNNO）with configuration entropy of 1.56R by substituting different elements.LCPNNO as an example,we systematically studied the effect of four core effects of high-entropy on electrochemical energy-storage materials for the first time.Firstly,pure LCPNNO（1200℃）is obtained at lower temperatures than that of LNO can attributed to the high-entropy effects.Secondly,based on the occurrence of lattice distortion in LCPNNO,its maximum V-value change（-1.36%）is limited,resulting in its better cyclability（95.1%capacity retention after 2000 cycles at 20C）.Thirdly,the Li⁺diffusivity of LCPNNO is limited by the sluggish diffusion effect at 25℃,leading to the decay of the rate capability（50C vs.0.1C capacity ratio of 55.2%）.However,the lattice distortion of LCPNNO at 60℃is alleviated lead to its faster Li⁺diffusivity compared with LNO,further contributing to its higher rate capability（50C vs.0.1C capacity ratio of 69.3%）.Finally,the multi-ion interaction of LCPNNO（cocktail effects）allows its significantly larger electronic conductivity(3.6×10^-7S cm^-1),better electrochemical activity,more intensive Nb⁵⁺（?）Nb³⁺redox reaction,and larger reversible capacity(136 mAh g^-1at 0.1C).