Sodium insertion cathode material Na0.67[Ni0.4Co0.2Mn0.4]O2 with excellent electrochemical properties

• Different cooling procedures lead to different phase compositions.
• Mixed P2-O3 Na0.67[Ni0.4Co0.2Mn0.4]O2 shows excellent electrochemical properties.
• Initial coulombic efficiency is below 100% despite of its Na-deficient composition.

Layered-structured ternary oxide Na0.67[Ni0.4Co0.2Mn0.4]O2 is synthesized as cathode material for sodium-ion batteries. Using a liquid nitrogen quenching process during the synthesis procedure, a Na0.67[Ni0.4Co0.2Mn0.4]O2 powder with a mixed P2-O3 structure is obtained, and then characterized. The Na//Na0.67[Ni0.4Co0.2Mn0.4]O2 cell delivers a reversible capacity of 167 mA h g−1 and exhibits excellent cycling and rate performances without abnormal initial coulombic efficiency.