Ion-exchange-assisted Li0.27K0.72Ni0.6Co0.2Mn0.2O2 cathode in potassium-ion batteries

A Li0.27K0.72Ni0.6Co0.2Mn0.2O2 (LKNCM) cathode for potassium-ion batteries (PIBs) was obtained from LiNi0.6Co0.2Mn0.2O2 (NCM622) via ion exchange. In-situ X-ray diffraction and high-resolution transmission electron microscopy analyses showed the morphological and structural changes that occur during K+-ion insertion. Particularly, the primary particles became porous, and the (003) interlayer distance expanded from 4.76 to 6.50 Å, providing a potassiation/depotassiation framework. Inductively coupled plasma-optical emission spectroscopy revealed that 0.72 mol of K+ ions were inserted into the Li-extracted NCM622 cathode per formula unit, indicating that the amounts of extracted Li+ and inserted K+ were similar. The developed LKNCM cathode exhibited a theoretical capacity of 160.79 mAh g−1 and an initial discharge capacity of 106.95 mAh g−1 with an average potential of 3.1 V vs. K/K+. These results demonstrate that ion exchange enables layered NCM cathodes for lithium-ion batteries to be applied as cathodes for PIBs.