Solvent Co-intercalation into Few-layered Ti3C2Tx MXenes in Lithium Ion Batteries Induced by Acidic or Basic Post-treatment

MXenes, as an emerging class of 2D materials, display distinctive physical and chemical properties, which are highly suitable for high-power battery applications, such as lithium ion batteries (LIBs). Ti₃C₂T_x (T_x = O, OH, F, Cl) is one of the most investigated MXenes to this day; however, most scientific research studies only focus on the design of multilayered or monolayer MXenes. Here, we present a comprehensive study on the synthesis of few-layered Ti₃C₂T_x materials and their use in LIB cells, in particular for high-rate applications. The synthesized Ti₃C₂T_x MXenes are characterized via complementary XRD, Raman spectroscopy, XPS, EDX, SEM, TGA, and nitrogen adsorption techniques to clarify the structural and chemical changes, especially regarding the surface groups and intercalated cations/water molecules. The structural changes are correlated with respect to the acidic and basic post-treatment of Ti₃C₂T_x. Furthermore, the detected alterations are put into an electrochemical perspective via galvanostatic and potentiostatic investigations to study the pseudocapacitive behavior of few-layered Ti₃C₂T_x, exhibiting a stable capacity of 155 mAh g^-1 for 1000 cycles at 5 A g^-1. The acidic treatment of Ti₃C₂T_x synthesized via the in situ formation of HF through LiF/HCl is able to increase the initial capacity in comparison to the pristine or basic treatment. To gain further insights into the structural changes occurring during (de)lithiation, in situ XRD is applied for LIB cells in a voltage range from 0.01 to 3 V to give fundamental mechanistic insights into the structural changes occurring during the first cycles. Thereby, the increased initial capacity observed for acidic-treated MXenes can be explained by the reduced co-intercalation of solvent molecules.