Preparation And Properties Of Na_0.67MnO₂ Based Sodium Ion Battery Cathode Materials

Among the variety new energy sources,lithium-ion batteries?LIBs?are playing a critical role in the transition from fossil fuel to renewable energy.With the advantages of high power density and high energy density,green environment protection,LIBs have been widely used in mobile devices,electric vehicles and power gird storage.However,the rising cost of LIBs due to a shortage of lithium resources has raised awareness of the need to develop a new generation of energy storage devices.In recent years,there has been a lot of interest in developing sodium ion batteries?SIBs?.SIBs work in the same?rocking chair mechanism?as LIBs,and Na⁺is abundant in nature,which greatly reduces development costs,making them one of the most promising alternative energy storage devices.The cathode material plays an important role in the energy density,power density and safety of SIBs.Until now,SIBs technology has been driven by the properties of the cathode material.Therefore,it has been the focus of research to find and develop cathode material with high specific capacity,superior cycle stability and high energy density.In this paper,preliminary synthesis and modification of P2-type layered cathode material Na_0.67Mn O₂ were carried out,and its electrochemical properties were studied.The main contents are as follows:1. The P2-type layered Na_0.67MnO₂ cathode material was prepared by simple coprecipitation and solid phase method,manganese sulfate and sodium carbonate as raw materials.The material has a stable P2 layered structure,and sodium ions can be transported directly from one layer to another,and the manganese oxide layer,plays a role in stabilizing the layered structure.Na_0.67Mn O₂ exhibits a discharge specific capacity of 147 m Ah g^-1 at the current density of 50 m A g^-1.After 100 cycles,the discharge specific capacity is 58 m Ah g^-1,the capacity retention rate is about 39%.2. Ni-MOF material with thin lamellar morphology was prepared by hydrothermal method and doped into Na₍0.₆₇Mn O₂ to synthesized Na_0.67Mn O₂@Ni-MOF?NMO@Ni?,which greatly increased the capacity of the Na_0.67Mn O₂.NMO@3%Ni,NMO@6%Ni and NMO@9%Ni were prepared through regulating doping amount of N i-MOF?3%,6%,9%?with different nickel contents.By replacing some manganese ions with nickel ions,the structure damage caused by the dissolution of Mn²⁺was reduced and the layered structure was stabilized.Among them,NMO@6%Ni has the best electrochemical performance.At the current density of 50 m A g^-1,the first cycle discharge capacity is 188 m Ah g^-1,under 100 cycles,it still has 74 m Ah g^-1.3. By adding cobalt nitrate and regulating its doping amount,cobalt ions were successfully introduced into the P2-type layered Na_0.67Mn O₂ cathode material,and Na0.67Mn0.75Co0.25O2,Na0.67Mn0.65Co0.35O2 and Na0.67Mn0.85Co0.15O2 were synthesized.The incorporation of cobalt ions replaces some of the manganese ions,and suppresses the ginger-taylor effect of Mn³⁺,reduces the distortion of the material,and improves the stability and electrochemical performance of the material.Among them,Na_0.67Mn_0.75Co_0.25O₂ has the best performance.At a current density of 50 m A g^-1,it has an initial discharge specific capacity of up to 198 m Ah g^-1.After 100 cycles,the discharge specific capacity remains at 119 m Ah g^-1.4. Through the double doping of Ni-MOF and cobalt nitrate,Na_0.67Mn_0.75Co_0.25O₂@Ni-MOF?NCMO@Ni?cathode material was successfully synthesized.The introduction of nickel and cobalt makes the material have a mixed metal oxide layer of nickel,cobalt and manganese,which stabilizes the layered structure and improves the structure stability under high voltage.NMCO@3%Ni,NMCO@6%Ni and NMCO@9%Ni were synthesized by adjusting the doping amount of N i-MOF?3%,6%,9%?,respectively.Among them,NMCO@6%Ni has an initial discharge specific capacity of 177 m Ah g^-1 at a current density of 50 m A g^-1,and maintains a discharge specific capacity of 120 m Ah g^-1 after 100 cycles.The cycle performance has improved greatly.