Mechanochemistry-induced biaxial compressive strain engineering in MXenes for boosting lithium storage kinetics

Strain modulation can endow electrochemical materials with promising mechano-electrochemical coupling owing to its adjustable characteristics, which will unlock great potential for realizing high-performance energy storage. MXenes offer outstanding lithium storage performances due to their exceptional conductivity, excellent mechanical properties, and large interlayer spaces for ion intercalation, however an undesirable issue of sluggish kinetics caused by the restacking of MXene nanosheets in electrodes is not well addressed. Here, we demonstrate an extremely effective strategy to resolve this issue by creating strain in Ti₃C₂T_x MXene via mechanochemistry (MC) method to maximize ion-transfer kinetics for lithium-ion batteries (LIBs). Strain states in Ti₃C₂T_x MXene, namely out-of-plane tension and corresponding in-plane biaxial compression, are comprehensively assessed through X-ray diffraction, Raman spectroscopy, and extended X-ray absorption fine structure spectroscopy. Diverse experimental characterizations and density functional theory calculations both reveal that the mechanochemistry-induced strained Ti₃C₂T_x (MC-Ti₃C₂T_x) MXene exhibits significantly decreased lithium diffusion barrier, which correlates directly to the observed fast ion-transfer kinetics. As expected, MC-Ti₃C₂T_x electrode delivers a high discharge capacity (380.5 mAh g⁻¹ at 0.1 A g⁻¹) and superior rate capability, outperforming most of previously reported Ti₃C₂T_x. More importantly, with the remarkably enhanced ion-transfer kinetics, MC-Ti₃C₂T_x electrode exhibits outstanding lithium storage performances spanning a wide temperature range (40 °C to − 20 °C). This work paves a novel way of strain engineering of MXenes for effectively enhancing diffusion kinetics in LIBs.