Nb2CT MXene: High capacity and ultra-long cycle capability for lithium-ion battery by regulation of functional groups

Strategies for Fabricating High‐Performance Electrochemical Energy‐Storage Devices by MXenes

“…[90] As À F groups were unstable in alkaline solution and were easily to be replaced by À OH groups, [176] À OH content increased from 6.5 % to 12.4 % while À F content decreased from 10.6 % to 3.2 % after Li + intercalation by LiOH treatment, as shown in Figure 15 (i). [90] In addition, the À O content increased to 28.5 % and the À OH content decreased to 2.6 % after annealing the sample at 400°C, which was possibly due to the conversion of À OH into À O groups after annealing. [177] As a result, the specific capacity of the pristine Nb 2 CT x electrode was considerably improved from 159 to 448 mAh g À 1 at 50 mA g À 1 by regulating the surface chemistry with this two-step procedure.…”

“…MXenes with unique properties have been experimentally synthesised or theoretically predicted. These properties include tuneable band gap (the band gap of Ti 3 C 2 changes from 0.1 to 0.9 eV after Nb doping), [88] superconductivity (α-Mo 2 C and η-Mo 3 C 2 ), [89] high capacity (the specific capacity of Nb 2 CT x after the intercalation of Li + is~450 mAh g À 1 at 50 mA g À 1 ), [90] excellent tensile strength (670 MPa for Ti 3 C 2 sheets) [91] and so on. Therefore, it is necessary to understand the most important property of the material (i. e., the electrical conductivity) related to the fabrication of high-performance energy storage devices.…”

“…[90] (i) The content of various functional groups of Nb 2 CT x MXenes (estimated by XPS measurements) before and after the post treatment. [90] Reproduced with permission from Ref. [90].…”

“…[175] For example, a two-step procedure was proposed by Zhao et al to regulate the surface terminations of Nb 2 CT x MXenes. [90] In detail, pristine Nb 2 CT x MXenes prepared by HF etching were treated by LiOH aqueous solution, which was then followed by an annealing process in Ar/H 2 at different temperature levels, as shown in Figure 15 (h). [90] As À F groups were unstable in alkaline solution and were easily to be replaced by À OH groups, [176] À OH content increased from 6.5 % to 12.4 % while À F content decreased from 10.6 % to 3.2 % after Li + intercalation by LiOH treatment, as shown in Figure 15 (i).…”

“…[90] In detail, pristine Nb 2 CT x MXenes prepared by HF etching were treated by LiOH aqueous solution, which was then followed by an annealing process in Ar/H 2 at different temperature levels, as shown in Figure 15 (h). [90] As À F groups were unstable in alkaline solution and were easily to be replaced by À OH groups, [176] À OH content increased from 6.5 % to 12.4 % while À F content decreased from 10.6 % to 3.2 % after Li + intercalation by LiOH treatment, as shown in Figure 15 (i). [90] In addition, the À O content increased to 28.5 % and the À OH content decreased to 2.6 % after annealing the sample at 400°C, which was possibly due to the conversion of À OH into À O groups after annealing.…”