Ti₃C₂T_x/Graphene Oxide Free-Standing Membranes as Modified Separators for Lithium–Sulfur Batteries with Enhanced Rate Performance

Abstract

Lithium−sulfur batteries are considered as the most promising candidate for nextgeneration energy storage devices. However, they are subjected to the "shuttle effect" of soluble lithium polysulfides (LiPSs). Herein, a free-standing membrane composed of two-dimensional MXene material (Ti 3 C 2 T x ) and graphene oxide (GO) is synthesized by a simple vacuum-filtration method. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy are carried out to determine structure, morphology, and composition of the Ti 3 C 2 T x /GO composite membrane, respectively. As a functional layer of trapping LiPS species, the Ti 3 C 2 T x /GO composite membrane and commercial polypropylene (PP) are successfully assembled to be a hybrid separator, Ti 3 C 2 T x /GO@ PP, to suppress the shuttle effect of LiPSs. The porous and rough surface of the Ti 3 C 2 T x /GO composite membrane is beneficial to improve the wettability of the commercial separator in an etherbased electrolyte. The cells with the Ti 3 C 2 T x /GO@PP hybrid separator exhibit a low polarization potential of 0.26 V in the conversion from Li 2 S 4 to Li 2 S 2 /Li 2 S and deliver a discharge capacity of 640.0 mA h g −1 for 5 C rate, indicating that the hybrid separator benefits the rate performance. According to the results of electrochemical impedance spectroscopy, increased discharge capacity is attributed to the reduced internal resistance and intensified Li + diffusion. The results of X-ray photoelectron spectroscopy focusing on the surfaces of both sides of the hybrid separator indicate that the shuttle effect of LiPSs is suppressed through a coefficient of the terminated groups' catalytic conversion on long-chain LiPSs and the titanium-reactive centers' Lewis acid−base pairs on short-chain LiPSs. Combining with digital photographs of the H-type electrolytic cell, the results of UV−visible absorption spectroscopy suggest that the concentration of long-chain polysulfides declines instantly under the redox effect of the terminated groups on Ti 3 C 2 T x surfaces and then infiltrate through the hybrid separator by virtue of concentration difference impetus. Generally, a Ti 3 C 2 T x /GO@PP hybrid separator restrains LiPS diffusion and improves the rate performance of Li−S batteries.

Status and Prospects of MXene‐Based Lithium–Sulfur Batteries

“…Moreover, by vacuum-filtrating the mixed solution of Ti 3 C 2 T x MXene and GO, a Ti 3 C 2 T x /GO membrane with good mechanical robustness was obtained. [152] The MXene/GO membrane was freestanding and could be inserted between cathode and separator to physically and chemically block the LiPSs [97] Copyright 2016, American Chemical Society. c) Schematic of the Li + diffusion in the Ti 3 C 2 T x -modified PP separators with different mass loading in Li-S batteries.…”

“…Reproduced with permission. [ 152 ] Copyright 2020, American Chemical Society. h) Schematic of the TiO 2 –Ti 3 C 2 T x heterostructures in trapping LiPSs and conversion process.…”

“…g) Rate properties of the Li-S cells with Ti 3 C 2 T x /GO@PP separator and PP separator. Reproduced with permission [152]. Copyright 2020, American Chemical Society.…”

Restraining Polysulfide with High‐Entropy Metal Nitride towards Long Cycle Life and High Capacity Li−S Batteries

“…The urgent demand on economic and renewable energy storage devices has triggered extensive researches of rechargeable batteries with excellent electrochemical performance and high security as well as low price. [1][2][3] Even though commercial Lithium-ion batteries (LIBs) based on liquid electrolytes have been widely used in the past decades, they still have the defects of low energy density and severe safety hazard. [4][5][6] LiÀ S batteries are expected to replace LIBs in fields with high energy density requirements, as it's able to satisfy the needs of mobile electronic devices with high energy density, or electric vehicles with increased power consumption.…”

“…The urgent demand on economic and renewable energy storage devices has triggered extensive researches of rechargeable batteries with excellent electrochemical performance and high security as well as low price [1–3] . Even though commercial Lithium‐ion batteries (LIBs) based on liquid electrolytes have been widely used in the past decades, they still have the defects of low energy density and severe safety hazard [4–6] .…”