Self-assembled Ti3C2 MXene and N-rich porous carbon hybrids as superior anodes for high-performance potassium-ion batteries

Potassium-ion batteries (PIBs) are attracting increased attention because of their low cost and similar energy storage mechanism to lithium-ion batteries. Considering the low structural stability and poor electrochemical redox reaction kinetics resulting from the large size of K+ (1.38 A), we elaborately designed novel PDDA-NPCN/Ti3C2 hybrids as PIBs anodes via an electrostatic attraction self-assembly approach, while N-rich porous carbon nanosheets (NPCNs) are derived from metal–hexamine frameworks. The coupled PDDA-NPCN/Ti3C2 hybrids with stacked structure and large specific surface area could ensure intimate contact between Ti3C2 and the NPCNs to efficiently take advantage of both components and more accessible active sites. The hybrids afford enlarged interlayer spacing and unique 3D interconnected conductive networks to accelerate the ionic/electronic transport rates. Meanwhile, the robust hybrids contribute high chemical stabilities due to favorable tolerance to volume change caused by phase transformations during the fast charge/discharge process. DFT calculations further indicate that the PDDA-NPCN/Ti3C2 hybrids efficiently reduce the adsorption energy of K+ and accelerate the reaction kinetics. The hybrids possess a remarkable synergetic effect, leading to a high reversible capacity of 358.4 mA h g−1 after 300 cycles at 0.1 A g−1 and long cycling stability of 252.2 mA h g−1 with only 0.03% degradation per cycle within 2000 cycles at 1.0 A g−1. This work paves the way for further self-assembled coupled hybrids in energy storage devices.