Preparation And Electrochemical Performance Of Na_0.9Ni_0.45Ti_0.55O₂ And Na_0.68Ni_0.34Ti_0.66O₂ As Electrode Material For Sodium Ion Batteries

With the increasing of population,the demand for energy is increasing.However,the excessive exploitation of fossil energy has led to the high levels CO₂ emissions and brought a series of worsening environmental issues such as the greenhouse effect and desertification.Secondary ion batteries has been widely studied as a carrier to store electrical energy.The sodium ion batteries?SIBs?have attracted great attention as the alternatives to lithium ion batteries due to its low cost,high resource availability of sodium.There have been extensive studies on and long life of electrode materials for SIBs to meet the demands of applied in large-scale energy storage.However,there still exist the issues such as low rate,poor cycle performance for SIBs owing to the ion diffusion process with electrode material volume expansion.And a symmetric sodium ion battery with different anode and cathode materials may bring some challenges,such as the complex of battery assembly process of the complex,the high cost and hidden danger.In order to solve these problems,it is necessary to develop the electrode materials that can be used as both positive electrode and negative electrodes.In this work,O3-type Na_0.9Ni_0.45Ti_0.55O₂ and P2-type Na_0.68Ni_0.34Ti_0.66O₂ was synthesized by convention solid-state as bipolar material for SIBs.The X-ray powder diffraction,Raman spectrum,field emission scanning electron microscope,X-ray photoelectron spectroscopy analysis and inductively coupled plasma mass spectrometer were used to characterize the physical properties of the samples such as the structure,surface composition and other information.The electrochemical performance of Na_0.9Ni_0.45Ti_0.55O₂ and Na_0.68Ni_0.34Ti_0.66O₂ as bipolar material for SIBs was performed on the LANHE battery test system and the electrochemical workstation.The transition metal oxides are bipolar materials owing to two different redox active substances with Ni⁺⁴/Ni⁺22 redox electricity for the high voltage,Ti⁴⁺/Ti³⁺redox for low voltage.It is found that,Na_0.9Ni_0.45Ti_0.55O₂ as cathode material for SIBs,the initial reversible capacity can be achieved of¹10 mAh g^-11 at0.05 C rate and the capacity retention is 54%after 100 cycles.When severing as anode material at the same condition,it displays a reversible but lower capacity(45 mAh g^-1),and capacity of 55%from first cycle to the 100 th cycle.The electrochemical performance investigation shows that the capacity of Na_0.68Ni_0.34Ti_0.66O₂ cathode material for SIBs up to 57 mAh g^-1,and the capacity remains at a rate of 52%after100 cycles.The capacity of Na_0.68Ni_0.34Ti_0.66O₂ as anode material is poor.In addition,it is the first time that Na_0.9Ni_0.45Ti_0.55O₂ and Na_0.68Ni_0.34Ti_0.66O₂ were studied as bipolar materials for SIBs.