Ion-exchange-assisted Li_0.27K_0.72Ni_0.6Co_0.2Mn_0.2O₂ cathode in potassium-ion batteries

Highlights: • A Li_0.27K_0.72Ni_0.6Co_0.2Mn_0.2O₂ (LKNCM) cathode was developed for K-ion batteries. • The LKNCM cathode was fabricated using NCM622 via an ion-exchange method. • The (003) interlayer distance provides a framework for potassiation/depotassiation. • The LKNCM cathode exhibits an initial discharge capacity of 106.95 mAh g⁻¹. • An average potential of 3.1 V vs K/K⁺ was exhibited by the LKNCM cathode. -- Abstract: A Li_0.27K_0.72Ni_0.6Co_0.2Mn_0.2O₂ (LKNCM) cathode for potassium-ion batteries (PIBs) was obtained from LiNi_0.6Co_0.2Mn_0.2O₂ (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.