Small−Strain Niobium Nitride Anode with Ordered Mesopores for Ultra−Stable Potassium−Ion Batteries
Lithium−ion batteries (LIBs) are considered as fascinating energy storage devices. However, scarcity and high cost of lithium resources lead to increasing research interest in next−generation batteries, such as potassium−ion batteries (KIBs), due to the similar electrochemical characteristic of LIBs and abundant potassium resources. However, significant problems to search for suitable anode materials for KIBs continue to exist due to the hazards of potassium metals and unstable cycle performance of carbonaceous materials and metal oxides due to the large ionic size of potassium. Herein, we report on well−ordered mesoporous niobium nitride/N−doped carbon hybrids (m−NbN/NC), verifying the potential of transition metal nitride as the new K+ insertion host. The electrode delivers reversible capacities of 143 mA h g−1 at 0.01 A g−1 and 49 mA h g−1 at 1 A g−1. More impressively, a capacity retention of 100% at 0.5 A g−1 after 2000 cycles was achieved. In situ X−ray diffraction and ex situ scanning electron microscopy (SEM) analysis indicated that m−NbN/NC electrode retains its structural integrity during potassiation and was accompanied by small strain, which was ascribed to the high proportion of surface−controlled reaction. This work points at a feasible new class of anode materials for ultra−stable KIBs.