Lattice-Coupled Si/MXene Confined by Hard Carbon for Fast Sodium-Ion Conduction

Silicon (Si) has been ascertained as one of the most desirable anode candidates for sodium-ion batteries (SIBs), ascribed to its sizeable theoretical capacity and abundant resource. However, the inherent electrochemical inertness of crystalline Si against sodium impedes its practical use. Herein, lattice-coupled Si nanoparticles are uniformly distributed onto delaminated MXene (d-MXene) and further tightly confined by hard carbon (HC), consequently forming a 3D cross-linked (Si/d-MXene)@HC architecture as an anode material for SIBs. Coupling a carbon-coated Si anode with a conductive d-MXene matrix through the local lattice overlapping not only vastly enables the alloying reactivity of Si with Na, but also provides fast-transfer portholes for Na+ and electrons because of the capacitive-like behavior of d-MXene, thus increasing the capacity and achieving fast ion conduction. The Si/d-MXene bonded with HC, constructing a robust architecture, can effectively stabilize the whole electrode structure and accommodate the volume expansion of Si upon cycling and increase capacitive-like contributions, resulting in an enhanced capacity and excellent cycle performance as anodes for SIBs. The developed electrode thus harvests favorable electrochemical performance compared to pure Si and d-MXene electrodes, such as high initial discharge capacity (370 mAh g–1), long cycling stability (a capacity retention above 80% after 500 cycles), and superior rate performance. The protocol to enable the sodium storage performance of Si/MXene anodes by adopting the capacitive-battery dual model would inspire rather far-ranging investigations on other advanced battery systems.