Electrochemical characterization of P2-type layered Na2/3Ni1/4Mn3/4O2 cathode in aqueous hybrid sodium/lithium ion electrolyte.

P2-type layered Na 2/3 Ni 1/4 Mn 3/4 O 2 has been synthesized by a solid-state method and its electrochemical behavior has been investigated as a potential cathode material in aqueous hybrid sodium/lithium ion electrolyte by adopting activated carbon as the counter electrode. The results indicate that the Na + /Li + ratio in aqueous electrolyte has a strong influence on the capacity and cyclic stability of the Na 2/3 Ni 1/4 Mn 3/4 O 2 electrode. Increase on the Li + content leads to a shift of the redox potential towards a high value, which is favorable for the improvement of the working voltage of the layered material as cathode. It is found that the coexistence of Na + and Li + in aqueous electrolyte can improve the cyclic stability for the Na 2/3 Ni 1/4 Mn 3/4 O 2 electrode. A reversible capacity of 54 mAh g −1 was obtained with a high cyclability as the Na + /Li + ratio was 2:2. Furthermore, an aqueous hybrid ion cell was assembled with the as-proposed Na 2/3 Ni 1/4 Mn 3/4 O 2 as cathode and NaTi 2 (PO 4 ) 3 /graphite synthesized in this work as anode in 1 M Na 2 SO 4 /Li 2 SO 4 (mole ratio as 2:2) mixed electrolyte. The cell shows an average discharge voltage at 1.2 V, delivering an energy density of 36 Wh kg −1 at a power density of 16 W kg −1 based on the total mass of the active materials. [ABSTRACT FROM AUTHOR]