Molecular-level heterostructures assembled from layered black phosphorene and Ti3C2 MXene as superior anodes for high-performance sodium ion batteries

Phosphorus, as one of the most promising anodes for sodium-ion batteries, its electrochemical performance improvement seriously suffers from insulated characteristics and poorly structural stability. Herein, we report an elaborately designed strategy to rationally synthesize molecular-level PDDA-BP/Ti3C2 nanosheet heterostructures taking advantages of high theoretical capacity of black phosphorene (BP) and high electronic conductivity, abundant functional groups of Ti3C2. Due to the face-to-face contact of both components, the parallel 2D interlayer spacing provides effective charge transfer and diffusion channels. DFT calculations show that strong interactions between BP and Ti3C2 could efficiently lower binding energy to facilitate the sodiation process. More importantly, surface functional groups of –F, –O and –OH in Ti3C2 play important roles to immobilize BP and act as more synergistic adsorption sites to accelerate sodiation. The PDDA-BP/Ti3C2 electrode displays extremely structure-stability confining monodispersed BP nanoparticle within Ti3C2 to buffer volume expansion and prevent aggregation of BP, exhibiting an ultrahigh reversible capacity of 1112 mA h g-1 at 500th-cycle at 0.1 A g-1 and ultralong cycling stability of 658 mA h g-1 with only 0.05% degradation per cycle within 2000 cycles at 1.0 A g-1. The related soidation mechanism and effects of functional groups of Ti3C2 on sodiation/desodiation redox reaction are deeply investigated.