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

Abstract

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 Ti 3 C 2 T x MXene via mechanochemistry (MC) method to maximize ion-transfer kinetics for lithium-ion batteries (LIBs). Strain states in Ti 3 C 2 T 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 Ti 3 C 2 T x (MC-Ti 3 C 2 T x ) MXene exhibits significantly decreased lithium diffusion barrier, which correlates directly to the observed fast ion-transfer kinetics. As expected, MC-Ti 3 C 2 T 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 Ti 3 C 2 T x . More importantly, with the remarkably enhanced ion-transfer kinetics, MC-Ti 3 C 2 T 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. Guided by the exponential relationship between ion diffusivity and strain, we designed strained Ti 3 C 2 T x via a facile mechanochemistry strategy that features enhanced ion-transfer kinetics in Li-ion batteries. Benefitting from its out-of-plane tension and corresponding in-plane biaxial compression, the strained Ti 3 C 2 T x anode demonstrates a capacity enhancement of ~100%, significantly increased pseudocapacitive storage, and excellent temperature tolerance, as compared to the unstrained counterpart. • We designed strained Ti 3 C 2 T x MXene via an effective mechanochemistry strategy. • The strained Ti 3 C 2 T x exhibits significantly improved ion-transfer kinetics. • The fast ion-transfer kinetics promotes intercalation pseudocapacitive behavior. • The strained Ti 3 C 2 T x shows excellent lithium storage in wide temperature range.