Black Phosphorus@Ti₃C₂T_x MXene Composites with Engineered Chemical Bonds for Commercial-Level Capacitive Energy Storage

Electrolyte-accessibly porous yet densely packed MXene composite electrodes with high ion-accessible surface and rapid ion transport rate have shown exceptional promise for high-volumetric-performance supercapacitors (SCs), but they are largely limited by the insufficient rate capability and poor electrochemical cyclability, in association with the instability in mechanical robustness of the porous network structures. Taking advantage of chemical bonding design, herein a black phosphorus (BP)@MXene compact film of 3D porous network structure is successfully made by in situ growth of BP nanoparticles on crumbled MXene flakes. The strong interfacial interaction (Ti-O-P bonds) formed at the BP-MXene interfaces not only enhances the atomic charge polarization in the BP-MXene heterostructures, leading to efficient interfacial electron transport, but also stabilizes the 3D porous yet dense architecture with much improved mechanical robustness. Consequently, fully packaged SCs using the BP@MXene composite films with a practical-level of mass loading (∼15 mg cm^-2) deliver a high stack volumetric energy density of 72.6 Wh L^-1, approaching those of lead-acid batteries (50-90 Wh L^-1), together with a long-term stability (90.58% capacitance retention after 50000 cycles). The achievement of such high energy density bridges the gap between traditional batteries and SCs and represents a timely breakthrough in designing compact electrodes toward commercial-level capacitive energy storage.