Preparation And Performance Of NASICON-type NaTi₂?PO₄?₃ Nanocrystalline For Sodium-ion Batteries

Sodium-ion batteries have potential for new generation energy storage system because of many advantages,such as similar energy storage mechanism compared with lithium-ion batteries,favorable safety,low cost,environmentally friendliness and so on.However,the practical application of sodium-ion batteries is under restrictions for their badly reversible charge-discharge performance,low specific capacity,poor rate and cycle performance caused by large ionic radius of sodium.So,the research on improving electrochemical performance of anode materials plays a decisive role in the long-term development of sodium-ion batteries.Among the employed anode materials of sodium-ion batteries,NaTi₂?PO₄?₃ with 3D open-framework Na super ion conductor structure?NASICON?has been widely investigated for its high ionic conductivity and good chemical stability.But the poor electronic conductivity of NaTi₂?PO₄?₃ leads to unsatisfactory rate capability and cycling performance.In this paper,we take NaTi₂?PO₄?₃ as the research object and carry out relevant research on the enhancement of Na storage performance using NaTi₂?PO₄?₃ as anode material through modification methods of metal ion doping and carbon-coated.The details are as follows:?1?Different amount of gadolinium ions doped mesoporous NaTi₂?PO₄?₃nanocrystals were prepared by hydrothermal method followed annealing process.The microstructure characterization indicates that the morphology of mesoporous nanoparticles is more uniform after Gd³⁺doping.As anode material for sodium-ion batteries,the NaTi₂?PO₄?₃ nanocrystals with 5%Gd³⁺exhibit discharge capacity of84.5 mA h g^-11 in the first cycle and high capacity of 63.4 mA h g^-11 after 2000 cycles with high coulombic efficiency beyond 99%at 5 C current density.And it shows superior rate capability of 47.5 mA h g^-11 at 50 C current density with coulombic efficiency beyond 97%.Kinetics analysis reveals that Gd³⁺doped mesoporous NaTi₂?PO₄?₃ nanoparticles can effectively enhance intrinsic electron conductivity and ionic mobility.The results show that Gd³⁺doping provides a new technique to improve the electrochemical properties of NASICON materials as anode materials for sodium-ion batteries.?2?Carbon-coated and manganese ions doped mesoporous NaTi₂?PO₄?₃nanocomposites were prepared by hydrothermal method followed annealing process.The microstructure characterization manifests that the manganese elements have uniform distribution in the mesoporous NaTi₂?PO₄?₃ nanocrystals and the thickness of surface carbon coating was about 2 nm.As anode material for sodium-ion batteries,the prepared nanocomposites show good sodium storage performance.It exhibits reversible capacities of 120,118,115,110,106,102,99 and 95 mA h g^-1at a current density of 0.5C,1C,2C,5C,10C,20C,30C and 50C.At a current density of 1C,it exhibit reversible capacity of 111.85 mA h g^-11 after 200 cycles,and the specific capacity still maintains 92 mA h g^-1after 1000 cycles at a current density of 20C.The results show that carbon-coated Mn²⁺doped mesoporous NaTi₂?PO₄?₃nanocomposites possess great application prospect for high-performance sodium ion batteries.