Application Of Layered Manganese Oxides In Cathode Materials For Sodium Ion Batteries

With the advantages of high energy density,long life and no pollution,lithium-ion batteries have been widely used in cell phones,electric vehicles and other industries.However,the small amount and uneven distribution of lithium resources in China seriously restrict its application in the field of mass storage.Since sodium ion batteries and lithium ion batteries have similar working mechanisms,the presence and distribution of sodium elements are wide,so they have broad application prospects in large-scale energy storage systems.p2 layered metal oxide is a cathode material widely used in sodium ion batteries,which has the advantages of high specific capacity,high operating voltage and easy synthesis.However,there is irreversible phase change in the charging and discharging process of this material,which makes it very limited in practical applications.In this paper,Na_0.7MnO_2.05,which has good air stability,high operating voltage and high theoretical specific capacity,is used as the substrate material to investigate the effects of material composition,synthesis method and morphological structure on the electrochemical properties of the material,as follows.（1）In order to explore the influence of process conditions on Na_0.7MnO_2.05 cathode materials,the cathode materials with different solid phase reaction temperatures（400℃,600℃,800℃,1000℃）and different sodium content（5%,10%,15%）were prepared.The results show that the sample prepared by calcination at 800℃with sodium content of 5%has smooth surface,obvious polygonal layered structure,higher purity and crystallinity.At 0.1C current density,the specific capacity of the first cycle is 157.67m Ah g^-1,and the capacity retention rate is 76%after 50 cycles.（2）Na_0.7MnO_2.05 micron particles synthesized by solid phase method were used to fabricate Fe PO₄,Ni₃（PO₄）₂ and Co₃（PO₄）₂ coated Na_0.7MnO_2.05 materials by precipitation method,respectively.Co₃（PO₄）₂ coated Na_0.7MnO_2.05 materials as cathode materials for sodium ion batteries showed better electrochemical performance than pristine Na_0.7MnO_2.05 with Fe PO₄,Ni₃（PO₄）₂-coated Na_0.7MnO_2.05 material with better electrochemical properties.The 5wt%Co₃（PO₄）₂-coated Na_0.7MnO_2.05 provides a high discharge capacity of 237.8m Ah g^-1 at a low current density of 0.1C.In addition,it shows excellent rate capability and cycle performance.It provides a high discharge capacity of 133.23 m Ah g^-1 at a current density of 1C.However,the original Na_0.7MnO_2.05 only showed a discharge capacity of 109.56 m Ah g^-1 under the same conditions.The results show that Co₃（PO₄）₂ coating plays a leading role in enhancing the electrochemical ability of Na_0.7MnO_2.05 of Co₃（PO₄）₂ coating,and the mechanism of enhancing the electrochemical ability of Na_0.7MnO_2.05 of Co₃（PO₄）₂ coating is systematically investigated.