Ultrathin MXene Nanosheets Decorated with TiO₂ Quantum Dots as an Efficient Sulfur Host toward Fast and Stable Li–S Batteries

Abstract

Being conductive and flexible, 2D transition metal nitrides and carbides (MXenes) can serve in Li-S batteries as sulfur hosts to increase the conductivity and alleviate the volume expansion. However, the surface functional groups, such as OH and F, weaken the ability of bare MXenes in the chemisorption of polysulfides. Besides, they create numerous hydrogen bonds which make MXenes liable to restack, resulting in substantial loss of active area and, thus, inaccessibility of ions and electrolyte. Herein, a facile, one-step strategy is developed for the growth of TiO quantum dots (QDs) on ultrathin MXene (Ti C T ) nanosheets by cetyltrimethylammonium bromide-assisted solvothermal synthesis. These QDs act as spacers to isolate the MXene nanosheets from restacking, and preserve their 2D geometry which guarantees larger electrode-electrolyte contact area and higher sulfur loading. The stronger adsorption energy of polysulfides with TiO (than with Ti C T ), as proven by density functional theory calculations, is essential for better on-site polysulfide retention. The ultrathin nature and protected conductivity ensure rapid ion and electron diffusion, and the excellent flexibility maintains high mechanical integrity. In result, the TiO QDs@MXene/S cathode exhibits significantly improved long-term cyclability and rate capability, disclosing a new opportunity toward fast and stable Li-S batteries.

A Robust, Freestanding MXene‐Sulfur Conductive Paper for Long‐Lifetime Li–S Batteries

“…As the most widely studied MXene, Ti 3 C 2 T x boasts excellent electronic conductivity, as high as 9880 S cm −1 , and impressive mechanical strength in few‐layered nanosheets . Consequently, MXene showcases promising electrochemical performance in supercapacitors, metal‐ion batteries (including Lithium, sodium, potassium, aluminum ion batteries), Li–S batteries, conductive binders, current collectors, etc. Gogotsi et al reported the selective extraction of Ti from the Ti 2 SC “MAX phase” to form carbon/sulfur electrodes for Li–S batteries .…”

“…Nazar et al employed Ti 2 CT x and Ti 3 C 2 T x MXene powders as sulfur hosts for the first time, and revealed that the polar MXene surface coupled with the metallic conductivity effectively immobilizes the LiPSs shuttle . Following up on the work of Nazar et al, several other studies investigated MXene and corresponding composites as a sulfur host, separator coating material, respectively or simultaneously . However, the immobilization mechanism of LiPSs on the pristine MXene (that is, without apparent oxidation) were not fully understood.…”

Vortex Fluidic Mediated Synthesis of TiO2 Nanoparticle/MXene Composites

“…[70][71] Post VFD processing (after oxidation and fabrication of MXene composites), the XRD of the collected and retained material had peaks corresponding to MXene, [28] with additional peaks for anatase at 2θ 29.6°(101), 44.3°(004), 63.7°(105), 64.9°(211), 74.1 (204) and 83.8°( 215). [20,[72][73] The peak at 29.6°overlaps with a peak for MXene. 30 The Scherrer equation was used to determine the average size of the anatase TiO 2 NPs retained in the VFD tube, at 18.5 nm.…”

“…[69,74,75] Ti 2p had peaks corresponding to Ti + 2 (2p 3/2 ), Ti + 3 (2p 3/2 ) for TiÀ C (sp 3 ) at 456 eV and 457.2 eV respectively, and Ti + 2 (2p 1/2 ) and Ti + 3 (2p 1/2 ) for TiÀ C (sp 1 ) at 461 eV and 463.2 eV respectively. [14,20,30,58,60] The peaks at 459.1 eV and 465.1 eV for TiÀ O (sp 3 ) and TiÀ O (sp 1 ) for TiO 2 . [74]…”

A Novel Strategy for the Selection of Polysulfide Adsorbents Toward High‐Performance Lithium‐Sulfur Batteries

“…And the preparation processes of the carbon materials used are usually complex and time‐consuming. 2) Metal oxides have been widely studied as electrode materials and strong chemical interaction of the metal oxides with polysulfides has been utilized to limit the shuttle effect during cycles . It was found that the metal oxides can form strong chemical adsorption affinity with polysulfides, which significantly inhibits the shuttle effect and improves the cycle performance of LSBs.…”