A Hierarchical Hybrid MXenes Interlayer with Triple Function for Room‐Temperature Sodium‐Sulfur Batteries

Room temperature sodium sulfur (RT Na‐S) batteries with high theoretical energy density and low cost have recently gained extensive attention for potential large‐scale energy storage applications. However, the shuttle effect of sodium polysulfides is still the main challenge that leads to poor cycling stability, which hinders the practical application of RT Na‐S batteries. Herein, a multifunctional hybrid MXene interlayer is designed to stabilize the cycling performance of RT Na‐S batteries. The hybrid MXene interlayer comprises a large‐sized Ti3C2Tx nanosheets inner layer followed by a small‐sized Mo2Ti2C3Tx nanoflake outer layer on the surface of the glass fiber (GF) separator. The large‐sized Ti3C2Tx nanosheet inner layer provides an effective physical block and chemical confinement for the soluble polysulfides. The small‐sized Mo2Ti2C3Tx outer layer offers an excellent polysulfide trapping capability and accelerates the reaction kinetics of polysulfide conversion, due to its superior electronic conductivity, large specific surface area, and Mo‐rich catalytic surfaces. As a result, RT Na‐S batteries with this hybrid MXene interlayer modified glass fiber separator deliver a stable cycling performance over 200 cycles at 1 C with an enhanced capacity retention of 71%. This unique structure design provides a novel strategy to develop 2D material‐based functional interlayer for high‐performance metal‐sulfur batteries.


Introduction
RT Na-S batteries have attracted increasing interest due to their high theoretical energy density (1672 mAh g −1 ), [1] high energy efficiency of charge-discharge, excellent life cycle, and low cost of the electrode materials, which exhibit the potential to become promising alternatives to replace the state-of-the-art lithium-ion (Li-ion) batteries for future grid energy storage. However, the shuttle effect of soluble sodium polysulfides (Na 2 S 8 , Na 2 S 6 , and Na 2 S 4 ) generated during dischargecharge leads to a loss of active material and unstable cycling performance, which is still challenging to the practical application of RT Na-S batteries. [2][3][4] Different strategies have been reported to alleviate the shuttling of soluble polysulfides in the RT Na-S battery system, including improving the cathode host design to form suitable porous structures for physically trapping the polysulfides, [5][6][7][8][9][10] optimizing liquid electrolytes by using novel additives, applying (quasi-)solid-state electrolytes to reduce the solubility of polysulfides, [11][12][13][14][15][16] and modifying the separator to immobilize polysulfides at the cathode side. [17][18][19][20][21][22][23][24][25] Among these methods, www.advancedsciencenews.com www.advmattechnol.de introducing a functional interlayer between the separator and the sulfur cathode (also known as modified separators) is a facile and efficient strategy to suppress the shuttle effect, as it avoids a complicated fabrication process and maintains the energy density of sulfur cathodes. For example, sodiated-Nafion coated polypropylene (PP) separators have been employed to realize improved ion selectivity, which could permit Na + transfer but restrict polysulfide permeation. [17][18][19] Later, a number of inorganic materials with strong chemical adsorption and high catalytic effects, such as Pt, Co, Ni, FeS 2 , MoS 2 , and MoSe 2 , have been investigated as functional interlayers to address the polysulfides shuttling concerns and improve the cycling performance. [24,[26][27][28][29][30][31][32][33] Recently, 2D materials such as MXenes and thin layers of MOF particles have been used as the functional interlayer to modify separators, due to their large aspect ratio, excellent flexibility, and tunable interlayer spacing (allowing selective ion transport). In particular, MXenes, as a new class of 2D transition metal carbides and/or nitrides, have shown promising potential for alkali metal-chalcogenides batteries. Beyond the common advantages of 2D materials mentioned above, MXenes also show excellent metallic conductivity, strong chemical adsorption and catalytic conversion toward the polysulfides, thereby boosting the reaction kinetics and elevating the electrochemical performance of sulfurbased batteries. [10,25,[34][35][36][37][38][39][40][41][42][43][44][45] Currently, the MXene family is already very large, with various members containing redox-active transition metals such as V, Ta, Cr, Nb, and Mo. [46] Among these elements, Mo bonds with C and N to form MoC or MoN dictated on the surface of MXenes have demonstrated catalytic roles to promote the conversion reactions from soluble long-chain polysulfides to short-chain solid discharge products, which fundamentally inhibit the shuttle effects of RT Na-S batteries. [22][23]47] However, these still lacked a rationally designed interlayer that could maximize the functionalities of MXenes and enhance the electrochemical performance of RT Na-S batteries.
Herein, we designed a hierarchical hybrid MXene-based interlayer by integrating one layer of large-sized Ti 3 C 2 T x nanosheets with another layer of small-sized Mo 2 Ti 2 C 3 T x nanoflakes to simultaneously exploit the physical and chemical functions of hybrid MXenes (Figure 1). The large-sized Ti 3 C 2 T x nanosheets layer directly coated onto the glass fiber separator offers much smaller channels that can effectively block the permeation of polysulfide molecules and prevent the puncture of small pieces of Mo 2 Ti 2 C 3 T x to the macroporous glass fiber (GF) separator (which easily leads to a short circuit). The outer layer of small-sized Mo 2 Ti 2 C 3 T x nanoflakes has more exposed active sites that can efficiently adsorb and accelerate the conversion of soluble longchain Na polysulfides into solid short-chain Na polysulfides, and thus keeps the active materials on the cathode side of the system and contributes to a high reversible capacity and stable cycling performance. This work provides a new strategy to improve the functioning of separators in RT Na-S batteries by optimizing the interlayer structure and adding catalytic components.

Results and Discussion
The hybrid MXene interlayer consists of two different layers of MXenes, which were prepared through wet-etching methods. [46,[48][49][50] The large-sized Ti 3 C 2 T x nanosheets were selected to construct the inner layer directly attached to the GF sep- arator, and the small-sized Mo 2 Ti 2 C 3 T x nanoflakes were used to fabricate the outer layer that faces the sulfur cathodes, as shown in Figure 1. To prepare the large-sized Ti 3 C 2 T x nanosheets, a mild etchant of LiF and HCl rather than the concentrated HF was employed to treat the Ti 3 AlC 2 MAX precursor (see details in Supporting Information). The reacted sediment was washed with de-ionized water and sonicated to obtain the delaminated Ti 3 C 2 T x nanosheets. The vanishing of the characteristic peaks of Ti 3 AlC 2 and the shift of the (002) peak to a lower angle in the XRD result of the derived sample demonstrates the successful exfoliation and delamination of the Ti 3 C 2 T x ( Figure S1, Supporting Information). After that, the suspension was centrifuged at 6000 rpm to select the large-sized Ti 3 C 2 T x nanosheets in the sediment. The topography of the Ti 3 C 2 T x MXene is measured by AFM and exhibits typical nanosheet morphology with a lateral size ranging from 2.5 to 3.8 μm ( Figure S2, Supporting Information).
Subsequently, the small-sized Mo 2 Ti 2 C 3 T x nanoflakes were prepared by etching the Mo 2 Ti 2 AlC 3 MAX with a concentrated HF solution (48%) at 55°C for 120 h. The resultant mixture was thoroughly washed with deaerated water until the pH value reached 6. The obtained sediment was then treated with TBAOH to achieve TBA + intercalated MXene, which was further delaminated under ultrasonication. Finally, the suspension was centrifuged at 3500 rpm for 25 min to separate few-layer Mo 2 Ti 2 C 3 T x nanoflakes (supernatant) from the unreacted MAX and multilayer MXene (sediment). The comparison of the XRD patterns presents an obvious (002) peak shift from 14.9°in the raw Mo 2 Ti 2 AlC 3 material to 5.6°in the as-prepared Mo 2 Ti 2 C 3 T x (Figure 2a), indicating the remarkable increase of interlayer spacing from MAX phase to 2D MXene. Besides this effect, the crystalline peaks of Mo 2 Ti 2 AlC 3 completely disappeared in the derived Mo 2 Ti 2 C 3 T x , demonstrating the success of the exfoliation and delamination processes.
The morphology and microstructure of the Mo 2 Ti 2 C 3 T x nanoflakes were characterized by SEM and TEM techniques. The SEM image of the etched sample shows an accordion-like morphology, which implies the extraction of Al layer from the MAX precursor ( Figure 2b). The delaminated Mo 2 Ti 2 C 3 T x presents a typical 2D nanosheet morphology with the average size of around   Figure 2e shows a monolayer Mo 2 Ti 2 C 3 T x consisting of four metal atomic layers with a thickness of 2.3 nm. Compared with its piece size shown in Figure 2c,d, the delaminated Mo 2 Ti 2 C 3 T x nanoflakes provide a very large aspect ratio of approximately 500:2, which is beneficial to adsorb and accelerate the conversion of polysulfides. The topography profile of Mo 2 Ti 2 C 3 T x also indicates its lateral size is around 0.5 μm on average ( Figure 2f). The much smaller size of Mo 2 Ti 2 C 3 T x flakes can be attributed to the harsh etching environment, long etching time, and extensive mechanical shearing during the preparation process.
XPS was used to understand the surface chemistries of the as-prepared Mo 2 Ti 2 C 3 T x nanoflakes ( Figure S3, Supporting Information). The predominant peaks at 228.9 and 232.1 eV in the Mo 3d XPS spectrum can be assigned to C−Mo−T x bonds, which is in accordance with the atomic structure in the theoretical study. [51] The small peaks at the binding energy of 230.3 (233.5) and 232.6 (235.6) eV (numbers in parenthesis represent the peak of Mo 3d3/2) can be assigned to the Mo +5 3d 5/2(3/2) and Mo +6 3d 5/2(3/2) , respectively, originating from the inevitable surface oxidation of the Mo 2 Ti 2 C 3 T x . [52] The C−Ti and C−Mo/Ti−Tx bonds located at 282.1 and 282.6 eV in the C 1s region further confirm the local environment of Ti and Mo metal elements. [51,53,54] All these measurements comprehensively confirm that few-layer Mo 2 Ti 2 C 3 T x nanoflakes with a smaller lateral size have been prepared successfully.
Small-sized Mo 2 Ti 2 C 3 T x nanoflakes were selected to prepare the outer layer of the hybrid MXene interlayer because of the ideally exposed catalytic Mo atom layer (Figures 3a,b) and its rela- tively good stability. To the best of our knowledge, it is the first time Mo 2 Ti 2 C 3 T x was applied in RT Na-S batteries. Density functional theory (DFT) calculation was further applied to investigate the electronic structure of Mo 2 Ti 2 C 3 MXene. The band structure and density of states (DOS) in Figure 3c indicate that the Mo 2 Ti 2 C 3 monolayer is metallic, which is similar to the Ti 3 C 2 MXene. [55][56][57] The high electronic conductivity of this coating layer could reduce the internal impedance and benefit fast reaction kinetics for polysulfide conversion in RT Na-S batteries.
To prepare the hybrid MXene interlayer, the as-prepared Ti 3 C 2 T x and Mo 2 Ti 2 C 3 T x colloidal solutions were mixed with PTFE in a mass ratio of 95: 5 and then dispersed in isopropanol by ultrasonication, respectively. Here the PTFE works as a binder to bridge the MXenes and GF separator. The large-sized Ti 3 C 2 T x nanosheet inner layer was deposited on the surface of the GF separator by directly dropping the suspension on the separator. Then, the small-sized Mo 2 Ti 2 C 3 T x outer layer was deposited on top of the Ti 3 C 2 T x layer via the same method to form a complete hybrid MXene interlayer coated GF (GF@Hybrid MXene) separator. Meanwhile, a solely Ti 3 C 2 T x coated separator (GF@Ti 3 C 2 T x ) with the same total loading amount of MXenes was also prepared for comparison. For the hybrid MXene interlayer, large-sized Ti 3 C 2 T x nanosheets can directly provide a physical block to the sodium polysulfides, and in the meantime, they can improve the kinetics of the transition of polysulfides. [20,39] Meanwhile, the small-sized Mo 2 Ti 2 C 3 T x nanoflakes coated on the large-sized Ti 3 C 2 T x layers have the excellent binding capability with the sodium polysulfides, which are blocked by the Ti 3 C 2 T x nanosheets and thus confine and accelerate the transformation of soluble polysulfides on the cathode side. [58] To learn the possible interaction between the Ti 3 C 2 T x layer and Mo 2 Ti 2 C 3 T x layer, the zeta potential testing was used to study the surface charge of both Ti 3 C 2 T x and Mo 2 Ti 2 C 3 T x in an aqueous solution with the centration of 0.01 mg mL −1 . According to the zeta potential measurement results ( Figure S4, Supporting Information), both Ti 3 C 2 T x and Mo 2 Ti 2 C 3 T x flakes have negative surface charges and no interaction appeared. Furthermore, Raman spectra measurements were applied to further confirm the interaction between these two MXenes. The comparison among the intersection layer of hybrid MXene, Ti 3 C 2 T x layer, and Mo 2 Ti 2 C 3 T x layer Raman spectra results ( Figure S5, Supporting Information) shows that the peaks in the intersection layer of hybrid MXene are only coming from the superposition of the Ti 3 C 2 T x layer peaks (199, 280, 375, 622, and 720 cm −1 ) [59][60][61] and the Mo 2 Ti 2 C 3 T x layer peaks (219, 383, 429, 645, and 732 cm −1 ), [62] indicating the excellent phase stability of the hybrid MXene. Figure 4a shows the SEM image and digital photo of the GF@Hybrid MXene separator. The macropores in GF ( Figure  S6 (Figure 4b, insets) indicate the successful fabrication of the designed hierarchical layered structure. The impedance of the as-prepared separators was evaluated in full Na-S cells by EIS. Figure 4c displays the Nyquist plots of the cells with different separators, in which the GF@Hybrid MXenes separator exhibits the lowest charge transfer resistance (206 Ω) in comparison with the GF@Ti 3 C 2 T x (313 Ω) and bare-GF (326 Ω). The improved charge transfer kinetics can be ascribed to the balance of the electronic conductivity and ionic conductivity of GF@Hybrid MXenes deriving from the unique hierarchical structural design.
By contrast, the GF@Ti 3 C 2 T x with stacked large flakes only shows sacrificed considerable electrolyte permeation capability.
The chemical adsorption and catalytic potential of the selected MXenes were measured before any battery testing. As shown in Figure 4d, the color of Na 2 S 6 solution with hybrid MXenes (Ti 3 C 2 T x and Mo 2 Ti 2 C 3 T x ) changes from deep yellow to almost transparent after 24 h, while the solution with Ti 3 C 2 T x has a color change from deep yellow to light green during the same time span, indicating the stronger adsorption capability of the hybrid MXene compared to the Ti 3 C 2 T x . The results were further verified by the UV-Vis testing of the hybrid MXene and Ti 3 C 2 T x soaked solution after 24 h (Figure 4e). The signals of Na 2 S 6 weakened after treating with Ti 3 C 2 T x , but almost vanished after mixing with hybrid MXenes in the same period. The excellent adsorption ability of hybrid MXenes can be ascribed to the more exposed active sites of the small-sized Mo 2 Ti 2 C 3 T x nanoflakes.
To investigate the catalytic function of hybrid MXenes for sodium polysulfide conversion, cyclic voltammetry (CV) curves of symmetric cells were gathered in a solution of 0.1 m Na 2 S 6 in DEGDME at a scan rate of 0.1 mV s −1 (Figure 4f). The symmetric cells with carbon black loaded carbon cloth as cathodes show low current responses and no significant voltage peaks. In contrast, the symmetric cells with hybrid MXene loaded carbon cloth cathodes offer significantly higher current responses and two pairs of well-defined peaks (at −0.21/0.21 and −0.48/0.48 V, respectively). Because Na 2 S 6 is the only active reactant in the symmetric cells, the peaks at −0.21 V almost certainly originated from the conversion of Na 2 S 6 to Na 2 S 2 , and the peak at −0.48 V is ascribed to the reduction from Na 2 S 2 to Na 2 S. The redox peaks are still distinct, and a higher current response was observed when the scan rate increases to 0.5 mV s −1 ( Figure S8, Supporting Information), which implies the efficacy of hybrid MXenes' catalytic effects under different charging-discharging rates. These results validate that the hybrid MXenes can accelerate the conversion of sodium polysulfides.
The merits of GF@Hybrid MXene separator were examined in RT Na-S batteries by using porous carbon/sulfur composite (pC@S) as the cathode, 1 m NaClO 4 in EC/PC (1: 1 in vol) with 5% FEC as the electrolyte, and sodium metal disc as the anode. The porous carbon (pC) host was obtained by sintering the activated Sterculia lychnophora in Ar atmosphere in accordance with our precious work ( Figures S9 and S10, Supporting Information). The sulfur loading in the pC@S was confirmed by XRD characterization, and the thermal gravimetric analysis result indicates the S content in the pC@S composite is around 53.5 wt% ( Figure S11, Supporting Information). CV profiles of the RT Na-S battery with GF@Hybrid MXene separator were collected to understand the electrochemical behavior of the sulfur cathode during the charge-discharge processes. As shown in Figure 5a, two cathodic peaks at around 2.0 and 0.8 V appear in the first cycle. The peak at 2.0 V corresponds to the conversion from S 8 to longchain Na 2 S x (4 < x ≤ 8) and irreversible side reactions between the carbonate-based electrolyte and the polysulfides. [63] The peak at 0.8 V can be ascribed to the long-chain sodium polysulfides to short-chain solid-state Na 2 S/Na 2 S 2 conversion and the solid state interphase (SEI) formation. [64] The broad anodic peak at around 1.9 V can be ascribed to the conversion reaction from insoluble Na 2 S/Na 2 S 2 to long-chain sodium polysulfides. In the second cathodic scan, the two prominent peaks convert to three new peaks at 1.6, 1.2, and 0.84 V, corresponding to the conversion to Na 2 S x (4 < x ≤ 8), Na 2 S 2 and Na 2 S. The CV curves nearly overlap from the second cycle onwards, indicating the highly reversible electrochemical conversion reaction when using GF@Hybrid MXene separators. It is worth noting that the peak representing the formation of soluble long-chain Na 2 S x (4 < x ≤ 8) dramatically fades after the second cycle, which implies that S is quickly converted to insoluble short-chain sodium polysulfides with a very short existence of soluble long-chain sodium polysulfides due to the excellent catalytic effects of hybrid MXene interlayer. [5,65] Figure 5b shows the first and the second discharge-charge curves of an RT Na-S battery with GF@Hybrid MXene separator. The initial reversible capacity is 1016 mAh g −1 with a Coulombic efficiency of 62%. The capacity fade in the first cycle could be assigned to the SEI layer formation and irreversible side reactions. In contrast, the RT Na-S battery with bare-GF separator provided a charge capacity of 697 mAh g −1 with a low Coulombic efficiency of 43.3% ( Figure S12, Supporting Information). The cycling performances of the RT Na-S cells at 0.1 C (1672 mA g −1 = 1 C) with various separators (bare-GF, GF@Ti 3 C 2 T x , and GF@Hybrid MXenes) are shown in Figure 5c. The GF@Hybrid MXene offered the highest capacity of 992 mAh g −1 in discharge from the second cycle and retained a capacity of 620 mAh g −1 after 100 cycles with the smallest capacity degradation of 0.36% per cycle. By contrast, the batteries with bare-GF and GF@Ti 3 C 2 T x separators can only provide a respective capacity of 240 and 387 mAh g −1 after 100 cycles. Figure 5d exhibits the rate performance of the RT Na-S batteries with various separators. The cell with GF@Hybrid MXene separator achieved a reversible capacity of 316 mAh g −1 at a high current of 2 C, and the capacity recovered to 860 mAh g −1 when the current density was decreased to 0.5 C. In contrast, the cells with bare-GF and GF@Ti 3 C 2 T x separators only exhibited low capacities of 52 and 112 mAh g −1 at 2C, respectively. The enhanced cycling stability and rate performance of the batteries with the GF@Hybrid MXene separators can be attributed to the improved Na + transport kinetics, good wettability in the carbonate-based electrolyte, and efficient interlayer structural design that can effectively trap the soluble polysulfides and accelerate the conversion kinetics. Consequently, the battery with GF@Hybrid MXene separator delivered a stable long-term cycling performance at a high current density (Figure 5e). After five activation cycles at 0.1 C, the cells achieved a reversible capacity of 562 mAh g −1 at 1 C and remained around 357 mAh g −1 after 500 cycles with a high average Coulombic efficiency of ≈99.5%. Notably, the Coulombic efficiencies in some cycles are slightly higher than 100% due to the oxidation of Na 2 S to polysulfides in hybrid MXene interlayer and the recapture of those polysulfides by the cathode, which results in an extra charge capacity. [14] Additionally, the RT Na-S batteries with GF@hybrid MXene separator also achieve a decent capacity of 531 mAh g −1 at 1 C and a capacity retention of 302 mAh g −1 after 100 cycles at a high sulfur loading of ≈2.2 mg cm −2 ( Figure S13, Supporting Information). Compared with previous works by applying MXene architectures in the RT Na-S battery system, this work indicates a new effective structural design and explores the function of Mo 2 Ti 2 C 3 T x applied in the RT Na-S batteries. Moreover, the hybrid MXene prepared in this work used a cheap and scalable method and achieved competitive electrochemical performance (Table S1, supporting information). Figure 5. a) Selected CV profiles of the room temperature sodium sulfur (RT Na-S) battery with GF@Hybrid MXene separator at a scan rate of 0.1 mV s −1 . b) First and second discharge-charge curves of an RT Na-S battery with GF@Hybrid MXene separator. c) Cycling performance and d) rate performance of an RT Na-S battery with bare-GF, GF@Ti 3 C 2 T x , and GF@Hybrid MXene separators. e) Long-term cycling performance of the RT Na-S battery with GF@Hybrid MXene separator at 1 C rate.
To better verify and understand the mechanism and functions of the hybrid MXene interlayer, we performed in situ synchrotron XRD testing for the RT Na-S battery with GF@Hybrid MXene separator, as well as the postmortem characterizations on the separators and Na metal anodes from cycled RT Na-S batteries. As illustrated in Figure 6a, the S 8 (JCPDS no. 00-001-0478) and long-chain polysulfides (Na 2 S x , 6 ≤ x ≤ 8) are both existing during the initial discharging from 2.4 to 1.5 V, and the S 8 transferred to long-chain polysulfides and Na 2 S 4 (JCPDS no.00-071-0516) after discharging to 1.5 V. [19] During the continuing discharge to 1.2 V, the Na 2 S 4 further splits into short-chain sodium polysulfide Na 2 S (JCPDS no. 04-003-6920). [66,67] Subsequently, as shown in the following charge, the Na 2 S 4 peak becomes weaker, which indicates the acceleration of the conversion from Na 2 S transferring back to Na 2 S x (6 ≤ x ≤ 8) due to the MXene interlayer and thus reduces the shuttle effect and maintains a high reversible transition between short-chain polysulfides to long-chain polysulfides ( Figure   S14, Supporting Information). In addition, there is no peak of Na 2 S 2 detected during the discharge or charge, which might be due to the fast kinetically transition from Na 2 S 4 to Na 2 S. [68] For the postmortem characterizations, Figure S15 (Supporting Information) shows optical images of the GF@Hybrid MXene and bare-GF separators after 100 cycles. It can be seen that the hybrid MXene interlayers still maintain their integrity after cycling, and the anode side of the GF@Hybrid MXene separators displays a much lighter yellow color than those of the bare-GF separators. The yellow color can be assigned to the accumulation of insoluble sodium sulfides on the anode surface, from the reaction between the shuttled soluble long-chain sodium polysulfides and Na metal anode, leading to the active material loss in the battery. Moreover, some dark areas were observed on the anode side of bare-GF separator, which could be the consequence of the formation of sodium dendrites and continuous side reactions with shuttled polysulfides. [69][70][71][72] Fewer dark spots were visualized in the modified separator, indicating that the GF@hybrid MXene can suppress the dendrite formation to some extent. To further verify the function of GF@Hybrid MXene separator to the cycling performance of Na metal anode, the Na|GF@Hybrid MXene|Na and Na|GF|Na symmetric cells were assembled and tested at the current of 1 mA cm −2 with the capacity limitation of 1 mAh cm −2 ( Figure S16, Supporting Information). The Na|GF|Na cell occurred short circuit after around 257 h of cycling, while the Na|GF@Hybrid MXene|Na cells can keep stable cycling after 300 h, which indicates the hybrid MXene interlayer can regulate sodium plating/stripping and suppress Na dendrite formation.
Moreover, the sodium metal anodes of the cells with GF@Hybrid MXene separator and bare-GF separator were investigated by using the SEM and EDS mapping techniques. As exhibited in Figures 6b,c, the cycled Na metal anode from a cell with a GF@Hybrid MXene separator displays a much smoother surface than that from the bare-GF separator anode, which indicates that the hybrid MXene interlayer could deliver effective protection to the Na metal anode by providing a more homogenous Na plating/stripping during cycling due to its active interaction with Na + flux. Moreover, the content of sulfur on the surface of Na metal anode from the cell with GF@Hybrid MXene separator is 0.43 wt%, which is significantly lower than that from