Enabling electron redistribution via electron-deficient boron quantum dots confined in Ti₃C₂ MXene for fast...

Quantum dots have been extensively utilized in diverse components of lithium-ion batteries (LIBs) due to their distinctive electronic structures, extremely high specific surface area, and remarkable interfacial regulation ability. In this work, a facile liquid-phase exfoliation method was employed to break down bulk boron into quantum-sized dots using a probe high-power ultrasonic crusher. The obtained boron quantum dots (BQDs) were confined within highly dispersed Ti₃C₂ MXene, thereby forming BQDs/Ti₃C₂ stacked composite anode materials for lithium-ion batteries. Based on the quantum confinement effect, BQDs exhibit superior electrochemical activity compared to bulk boron, providing abundant active sites for ion insertion and extraction. The well-dispersed BQDs in the Ti₃C₂ MXene form a continuous network, facilitating efficient charge and ion diffusion and transport throughout the entire structure. Electron deficiency induced by BQDs occurs in the interlayers of Ti₃C₂ MXene, thus the local electronic defect is introduced into the originally perfect periodic atomic arrangement and electronic potential field. This would cause ripples in the entire electronic system, leading to a redistribution of electrons. This not only enhances the charge transfer kinetics but also modulates the lithium-ion diffusion pathways through local electric field intensification. The as-prepared BQDs/Ti₃C₂ stacked composite thus delivers an extremely high initial discharge capacity of 2514.5 mAh g^-1 at 0.05 A g^-1, a large reversible capacity of 835.3 mAh g^-1 at 0.1 A g^-1, and outstanding long-term cycle stability, with 958.0 mAh g^-1 retained after 300 cycles. Notably, it also demonstrates exceptional long-term cycling performance at 2.0 A g^-1, with the capacity increasing from 459.5 mAh g^-1 after 163 cycles to 1251.7 mAh g^-1 after 759 cycles. The exploration of BQDs embedded in Ti₃C₂ MXene is anticipated to inspire in-depth investigations into advanced BQD-powered MXene anode materials for LIBs.