Synthesis And Electrochemical Properties Of Titanium Niobium Oxides Anode Materials For Li-ion Batteries

In view of the unique "ReO3 crystallographic shear" structure of titanium niobium oxides,there is negligible change of lattice parameters and cell volume while lithium ion insertion or extraction.The working voltage range of the titanium niobium oxide electrode materials is 1.0-3.0 V.Previous study shows that the SEI film and the dendrite cannot be formed during the charging and discharging processes,which greatly improves the initial coulombic efficiency and cycle life while reducing the security risks.And compared to Li4Ti5O12,titanium niobium oxides show much higher specific capacity.As a result,titanium niobium oxides are identified as very promising anode material.However,the low electrical conductivity and ionic conductivity of titanium niobium oxide severely limit electrochemical performance.Thus,to improve the dynamic properties of titanium niobium oxide is still a serious challenge.We have fully studied the electrochemical performance of Ti2Nb10O29 and the influence of carbon coating on Ti2Nb10O29 electrode material.Porous TiNb2O7 nanospheres have been also synthesized and studied.1.Bulk Ti₂Nb₁₀O₂₉ was synthesized by a simple and efficient solid-state reaction through the commercial niobium pentoxide and titanium dioxide.Without any modification,the prepared Ti2Nb10O29 anode material displays well electrochemical performance.The initial coulombic efficiency of Ti2Nb10O29 electrode is high to 94.2%at 0.1 C.The discharge specific capacity still stays around 144 mAh/g at 10 C（3.96 A/g）after 800 cycles.If the discharging current density consistently fixed at 2 C,there is negligible capacity loss when the charging current increased gradually from 2 C to 20 C.Based on the excellent performance in half-cell,a full cell was assembled by the Ti2Nb10O29 materials coupled with LiFePO4.The reversible capacity of the full cell still maintains stable after 1000 cycles,showing well cycle stability.2.In this work,Ti₂Nb₁₀O₂₉@C materials were synthesized by thermal annealing acetylene with the as-prepared Ti2Nb10O29 materials.The carbon layer is uniformly coated on the surface of the Ti2Nb10O29 material with a thickness about 4 nm.The electrochemical performance of carbon-coated Ti2Nb10O29 electrode is clearly better than that of the bare Ti2Nb10O29.The capacity retention of Ti2Nb10O29@C electrode materials is 90%,while the capacity loss is about 0.38%per cycle for the bare Ti2Nb10O29 at 1 C after 50 cycles.The EIS impedance curve also confirms that carbon coating could improve the conductivity of Ti2Nbi0O29 materials.3.In this paper,we have successfully fabricated porous TiNb2O7 nanospheres with a diameter of around 500 nanometers which are formed by 30-50 nm particles with the presence of Pluronic P123.The reversible capacity of nanoporous TiNb2O7 electrode stays at 160 mAh/g with a capacity retention high to 67%even after 10000 cycles at 5 C.If the discharging current density consistently fixed at 1 C,there is negligible capacity loss when the charging current gradually increased from 1 C to 50 C.In addition,the TiNb2O7 electrode materials still maintain their nano-sized and porous morphology after 10,000 cycles.