High-capacity potassium ion storage mechanisms in a soft carbon revealed by solid-state NMR spectroscopy

Carbon materials are crucially important for the realization of potassium-ion batteries. However, the potassium storage mechanisms in various carbon materials are incompletely understood. Herein, solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy coupled with Raman and X-ray diffraction (XRD) techniques are employed to study the reaction mechanism in a soft carbon quantitatively. It is revealed that the insertion of potassium ions into the soft carbon firstly induces a transformation of the disordered region to short-range ordered stacking, involving both the pristine local unorganized and organized carbon layers. Subsequently, potassium ions intercalate into the rearranged carbon structure, finally producing the nano-sized KC 8 . Moreover, a remarkable capacity of 322 mAh·g −1 with a low mid potassiation voltage of < 0.3 V is present for the prepared soft carbon, which is on account of the underlying potassium storage sites, including the disordered stacking carbon as a main component of the soft carbon. These results suggest that regulating the disordered stacking region in the turbostratic structure of soft carbon is a critical issue for further improving the potassium storage performance. Graphical Abstract