Structural and Electrochemical Studies of High Voltage Na(Ni 2/3Sb1/3)O2 Cathodes for Secondary Na-ion Batteries.

摘要

Lithium ion batteries have been dominating the energy field in energy storage with its efficiency and performance unmatched. However, the over-exhaustion of the limited amounts of lithium has been causing rising prices. In order to alleviate the use of lithium batteries, scientists have turned some focus to other energy storage alternatives, like sodium batteries. Sodium is abundant, affordable, and environmentally friendly. Sodium batteries have gravimetric energy density comparable to lithium batteries, and are promising for large scale energy grid storage.;In this work, Na(Ni2/3Sb1/3)O2 have been synthesized and identified as a sodium battery cathode candidate. An ordered and disordered phase of this layered material has been identified, depending on the temperature used for synthesis. Both phases have been studied structurally using synchrotron radiation and laboratory x-rays. The disordered Na(Ni2/3Sb1/3)O2 belongs to the R3¯m space group with the lattice parameters a = 3.0619(6) A and c = 16.0549(5) A. The ordered Na(Ni2/3Sb1/3)O2 belongs to the C2/m space group with the lattice parameters a= 5.3048(5) A, b= 9.1847(7) A , c= 5.6285(4) A. Ex situ studies were also performed to study the structural morphology during Na(Ni2/3Sb1/3)O2's electrochemical cycling. The cycling of the material shows a transformation from an initial O3 layered phase to a P3 layered phase during charge, which is reversed during discharge. The electrochemical performance of Na(Ni 2/3Sb1/3)O2 shows promising results, with the ordered phase being able to yield 133mAh/g capacity.