Electrochemical and Structural Study of Layered P2‐Type Na2/3Ni1/3Mn2/3O2 as Cathode Material for Sodium‐Ion Battery

P2-type Na(2/3)Ni(1/3)Mn(2/3)O2 was synthesized by a controlled co-precipitation method followed by a high-temperature solid-state reaction and was used as a cathode material for a sodium-ion battery (SIB). The electrochemical behavior of this layered material was studied and an initial discharge capacity of 151.8 mA h g(-1) was achieved in the voltage range of 1.5-3.75 V versus Na(+)/Na. The retained discharge capacity was found to be 123.5 mA h g(-1) after charging/discharging 50 cycles, approximately 81.4% of the initial discharge capacity. In situ X-ray diffraction analysis was used to investigate the sodium insertion and extraction mechanism and clearly revealed the reversible structural changes of the P2-Na(2/3)Ni(1/3)Mn(2/3)O2 and no emergence of the O2-Ni(1/3)Mn(2/3)O2 phase during the cycling test, which is important for designing stable and high-performance SIB cathode materials.