Development of High Capacity Cathode Material for Sodium Ion Batteries Na_0.95Li_0.15(Ni_0.15Mn_0.55Co_0.1)O₂

A high-capacity layered metal oxide material, Na 0.95 Li 0.15 (Mn 0.55 Co 0.10 Ni 0.15 )O 2 , was obtained by the electrochemical Li-Na ion-exchange of Li 1.2 Mn 0.55 Co 0.10 Ni 0.15 O 2 . The electrochemical reaction of the Na 0.95 Li 0.15 (MnCoNi) 0.8 O 2 was divided into three redox reactions, i.e., Mn, Ni and Co. The Na 0.95 Li 0.15 (MnCoNi) 0.8 O 2 electrode showed good electrochemical properties in a sodium ion cell, such as a high capacity of over 200 mAhg −1 and its 40 th discharge capacity was 170 mAhg −1 which is about 85% of the 2 nd discharge capacity. An ex-situ synchrotron X-ray diffraction analysis revealed that the Na 0.95 Li 0.15 (Mn 0.55 Co 0.10 Ni 0.15 )O 2 maintains the O3-type layered structure with a large volume change of 20% during the charge-discharge cycles along with the formation of a secondary phase which has the same crystal structure as that of the Na 0.95 Li 0.15 (Mn 0.55 Co 0.10 Ni 0.15 )O 2 in the high voltage range. When the open circuit voltage of the Na 0.95 Li 0.15 (Mn 0.55 Co 0.10 Ni 0.15 )O 2 reached 4.2 V, the secondary phase was present as a single phase.