Sodium storage behavior of Na0.66Ni0.33-xZnxMn0.67O2 (x=0, 0.07 and 0.14) positive materials in diglyme-based electrolytes

The promising application of Na-ion batteries in large-scale energy storage such as smart grid has encouraged intensive research on Na-based insertion compounds and their implementation in full Na-ion cells. Herein, the electrochemical performance of half cells using Na0.66Ni0.33-xZnxMn0.67O2 (x = 0, 0.07 and 0.14) cathodes in diglyme-based electrolyte are first studied. For x = 0.07, high discharge capacities of 120 and 80 mA h g(-1) at 15 and 150 mA g(-1), respectively are measured, with stable operation voltage exceeding 4.0 V vs. Na+/Na and cycling life over 200 cycles. Moreover, DSC results of the charged positive electrodes confirmed that the thermal stability was improved distinctively by zinc modification. Also, graphitized petroleum coke exhibits good performance in diglyme-based electrolyte in terms of stable capacity (100 mA h g(-1)) over 200 cycles in a stable plateau within 0.5-1.0 V vs. Na+ /Na. Thereafter, a full Na-ion battery using Na0.66Ni0.26Zn0.07Mn0.67O2 cathode, diglyme electrolyte, and petroleum coke anode is proposed here that shows impressive performances, i.e. shows high discharge capacity of 86 mA h g(-1) and 85% retention after 155 cycles. It is believed that diglyme-based electrolytes should be readily extended to other layered sodium oxide electrodes and their full cells.