K-Doped P2-Type P2-Na0.67-Xkxni0.22mn0.67cu0.11o2 Cathode Electrode Material with Enhanced Cycle Performance for Sodium-Ion Batteries

P2-Na0.67Ni0.33Mn0.67O2 as one of typical composition for P2-type Ni/Mn based layered transition metal oxides has received wide attention on account of its high capacity and wide voltage, but its electrochemical performance still needs to be further promoted in order to be used as cathode electrode material of sodium-ion batteries (SIBs) for practical application. According to a convenient sol-gel method, we have successfully synthesized a series of K-doped P2-Na0.67-xKxNi0.22Mn0.67Cu0.11O2 (x = 0, 0.01, 0.06, 0.10) cathode electrode materials. During the initial discharge, P2-Na0.61K0.06Ni0.22Mn0.67Cu0.11O2 cathode electrode delivers a high capacity of 120.3 mAh g-1 at 100 mA g-1 when charged and discharged from 1.5 to 4.2 V. And the cathode electrode still remains a specific capacity of 101.6 mAh g-1 with a good capacity retention rate of 84.5% after 100 cycles. Moreover, it shows a better rate performance compared to the undoped sample. The enhanced cycle performance can be explained that the appropriate amount of K+ take up the prismatic Na+ sites and play a supporting role between the transition metal layer, which can stabilize the crystal structure to improve cycle stability. And K+ with larger size take up the prismatic Na+ sites, resulting in the expansion of Na+ diffusion channel to facilitate Na+ diffusion. Thus, this work may provide an effective strategy in order to enhance cycle performance of cathode electrode for SIBs and make a step further to practical application.