Enhanced Li‐Ion Accessibility in MXene Titanium Carbide by Steric Chloride Termination

Abstract

high power and high energy. Although state-of-the-art Li-ion batteries efficiently store energy by Li-ion (de)intercalation into the host electrode materials, their power is limited in part by slow ion transfer. [1,2] Furthermore, carbonaceous compounds, which are the most used negative electrode materials in Li-ion batteries, exhibit Li-ion (de)intercalation near the Li metal plating potential, hindering the charging of batteries at a high rate. [3,4] Accordingly, the development of negative electrode materials that are capable of more charge at a faster rate remains a major challenge.Electrode materials for electrochemical capacitors store the charge by surface ion adsorption, which intrinsically achieves a high power density. [5][6][7] The modest energy density of conventional double-layer capacitors owing to their insufficient capacitance can be enhanced by accumulating pseudocapacitance by surface ion adsorption accompanied with surface redox reactions. [8][9][10][11][12] However, the use of electrochemical cells composed of pseudocapacitive electrodes do not avoid the compromise between the high power and high energy densities, and a practical technical solution has been Li-ion hybrid capacitor, in which intercalation-type compounds are employed either in the cathode or anode. [13,14] One option is a Li-ion hybrid capacitor with a pseudocapacitive porous carbon cathode and an intercalation-type anode (e.g., Li 4 Ti 5 O 12 ). [15][16][17] Another example is a combination of an intercalation-type cathode (e.g., LiMn 2 O 4 ) and a pseudocapacitive anode such as a MnO 2 /carbon nanotube composite. [18,19] However, the energy and power densities of the Li-ion hybrid capacitors are not yet satisfactory for commercialization. Hence, tremendous efforts have been devoted to the development of superior pseudocapacitive electrode materials, such as nitrogendoped carbon, [20] RuO 2 ⋅nH 2 O, [21] or T-Nb 2 O 5 . [22] In particular, nanosheet compounds are of potential interest because (1) the stacked nanosheets enable a high packing density for the high volumetric capacitance;(2) open interlayer space between the nanosheets offers fast ion accessibility to the redox center, what we call "intercalation pseudocapacitance"; [22] and (3) electrically conductive nanosheets permit high power operation. [23][24][25] Among various nanosheet compounds, MXene (M n+1 X n T x ; M: Ti, V, Cr, Nb, etc.; X: C, N; n = 1-3; T: surface termination groups) is an important emerging class of electrode materials for both supercapacitors and batteries. [26][27][28][29][30][31][32] One of the advantages of MXene is its very high electronic conductivity which Pseudocapacitance is a key charge storage mechanism to advanced electrochemical energy storage devices distinguished by the simultaneous achievement of high capacitance and a high charge/discharge rate by using surface redox chemistries. MXene, a family of layered compounds, is a pseudocapacitor-like electrode material which exhibits charge storage through exceptionally fast ion accessibil...

Preparation and electrochemical performance of modified Ti3C2Tx/polypyrrole composites

“…It implies the presence of ‐O, ‐OH, and ‐F terminals on the surface of Ti 3 C 2 T x . This corresponds to the result reported recently . Therefore, the successful preparation of Ti 3 C 2 T x sample has created favorable conditions for the pyrrole monomer to intercalate and polymerize in the interlayer space of Ti 3 C 2 T x , or to grow on the surface of the layers by an in situ polymerization method, and further to form a good spatial structure for good electrical performance.…”

Electrophoretic Deposition of Two-Dimensional Titanium Carbide (MXene) Thick Films

“…It should be noted that Cl is probably present as one of the possible surface terminations that can result when LiF-HCl etching is used to make MXenes. 48 Kinetics of deposition.-Considering the diverse benefits shown by EPD of MXene, understanding the deposition kinetics in terms of deposition rate (and subsequently thickness) is fundamentally and technologically crucial. In this work, the kinetics of constant-voltage deposition at 5 V were studied for both aqueous and PC suspensions by measuring the mass of dried films as a function of deposition time and suspension concentration.…”

Surface Modified MXene‐Based Nanocomposites for Electrochemical Energy Conversion and Storage

“…Interestingly, except the extraction of A atoms and the generation of the surface functioned M n X n− 1 T m layers, the modified method also allows the intercalation of metal ions into the interlayered space and thus weakens the interlayered interaction. A recent work has also demonstrated that through the modified acid etching method, Cl groups can be introduced as the surface terminal groups . Following, ammonium bifluoride (NH 4 HF 2 ) was demonstrated as another available etchant as well .…”