Highly Stable Lithium–Sulfur Batteries Based on Laponite Nanosheet‐Coated Celgard Separators

Lithium–sulfur (Li–S) batteries are of great interest due to their high theoretical energy density. However, one of the key issues hindering their real world applications is polysulfide shuttle, which results in severe capacity decay and self‐discharge. Here, a laponite nanosheets/carbon black coated Celgard (LNS/CB‐Celgard) separator to inhibit polysulfide shuttle and to enhance the Li⁺ conductivity simultaneously is reported. The polysulfide shuttle is efficiently inhibited through strong interactions between the O active sites of the LNS and polysulfides by forming the Li···O and O? S bonds. Moreover, the separator features high Li⁺ conductivity, fast Li⁺ diffusion, excellent electrolyte wettability, and high thermal stability. Consequently, the Li–S batteries with the LNS/CB‐Celgard separator and the pure S cathode show a high initial reversible capacity of 1387 mA h g^?1 at 0.1 C, high rate performance, superior cycling stability (with a capacity decay rate of 0.06% cycle^?1 at 0.2 C and 0.028% cycle^?1 at 1.0 C over 500 cycles), and ultralow self‐discharge. The separator could also enhance the performance of other batteries such as the LiFePO₄/separator/Li battery. This work sheds a new light on the design and preparation of novel separators for highly stable Li–S batteries via a “green” and cost‐effective approach.     

Separator Modified by Cobalt‐Embedded Carbon Nanosheets Enabling Chemisorption and Catalytic Effects of Polysulfides for High‐Energy‐Density Lithium‐Sulfur Batteries

Lithium‐sulfur (Li‐S) batteries are considered to be one of the promising next‐generation energy storage systems. Considerable progress has been achieved in sulfur composite cathodes, but high cycling stability and discharging capacity at the expense of volumetric capacity have offset their advantages. Herein, a functional separator is presented by coating cobalt‐embedded nitrogen‐doped porous carbon nanosheets and graphene on one surface of a commercial polypropylene separator. The coating layer not only suppresses the polysulfide shuttle effect through chemical affinity, but also functions as an electrocatalyst to propel catalytic conversion of intercepted polysulfides. The slurry‐bladed carbon nanotubes/sulfur cathode with 90 wt% sulfur deliver high reversible capacity of 1103 mA h g^?1 and volumetric capacity of 1062 mA h cm^?3 at 0.2 C, and the freestanding carbon nanofibers/sulfur cathode provides a high discharging capacity of 1190 mA h g^?1 and volumetric capacity of 1136 mA h cm^?3 at high sulfur content of 78 wt% and sulfur loading of 10.5 mg cm^?2. The electrochemical performance is comparable with or even superior to those in the state‐of‐the‐art carbon‐based sulfur cathodes. The separator reported in this work holds great promise for the development of high‐energy‐density Li‐S batteries.     

Tailoring the Pore Size of a Polypropylene Separator with a Polymer Having Intrinsic Nanoporosity for Suppressing the Polysulfide Shuttle in Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are being considered as one of the most promising candidates for the development of next‐generation energy storage technologies. Although much progress has been made over the past decade, the development of Li–S batteries is still held back by a crucial polysulfide‐shuttle problem. To address this critical issue, an approach to reduce the pore size of the separator is presented here, to prevent the penetration of soluble polysulfide species. A polymer with intrinsic nanoporosity (PIN) is developed within the micrometer‐scale pores of a polypropylene separator. The framework of polypropylene acts as a skeleton to sustain reliable mechanical properties with the thin membrane. Upon the formation of PIN in the pores, the polypropylene separator maintains its thickness. With the thin PIN–polypropylene membrane, the Li–S cells can be operated with a relatively high sulfur loading. The PIN allows the transport of Li⁺ ions, but suppresses the penetration of the polysulfide species. The Li–S batteries with the PIN‐modified polypropylene separator exhibit enhanced cycling performance.     

Polysulfide‐Shuttle Control in Lithium‐Sulfur Batteries with a Chemically/Electrochemically Compatible NaSICON‐Type Solid Electrolyte

A NaSICON‐type Li⁺‐ion conductive membrane with a formula of Li_{1+ x} Y _x Zr_{2? x} (PO₄)₃ (LYZP) (x = 0–0.15) has been explored as a solid‐electrolyte/separator to suppress polysulfide‐crossover in lithium‐sulfur (Li‐S) batteries. The LYZP membrane with a reasonable Li⁺‐ion conductivity shows both favorable chemical compatibility with the lithium polysulfide species and exhibits good electrochemical stability under the operating conditions of the Li‐S batteries. Through an integration of the LYZP solid electrolyte with the liquid electrolyte, the hybrid Li‐S batteries show greatly enhanced cyclability in contrast to the conventional Li‐S batteries with the porous polymer (e.g., Celgard) separator. At a rate of C/5, the hybrid Li ||LYZP|| Li₂S₆ batteries developed in this study (with a Li‐metal anode, a liquid/LYZP hybrid electrolyte, and a dissolved lithium polysulfide cathode) delivers an initial discharge capacity of ≈1000 mA h g^?1 (based on the active sulfur material) and retains ≈90% of the initial capacity after 150 cycles with a low capacity fade‐rate of <0.07% per cycle.     

Sulfur‐Embedded Activated Multichannel Carbon Nanofiber Composites for Long‐Life,High‐Rate Lithium–Sulfur Batteries

Despite the 3–5 fold higher energy density than the conventional Li‐ion cells at a lower cost, commercialization of Li–S batteries is hindered by the insulating nature of sulfur and the dissolution of intermediate polysulfides (Li₂S _X , 4 < X ≤ 8) into the electrolyte. The authors demonstrate here multichannel carbon nanofibers that are composed of parallel mesoporous channels connected with micropores as sulfur containment. In addition, hydroxyl functional groups are formed on the carbon surface through a chemical activation to enhance the interaction between sulfur and carbon. In the sulfur embedded composite, the mesoporous multichannel enhances the active material utilization and sulfur loading, while the micropores act as a reaction chamber for sulfur component and trap site for polysulfide with the assistance of the functional groups. This sulfur–carbon composite electrode with 2.2 mg cm^?2 sulfur displays excellent performance with high rate capability (initial capacity of 1351 mA h g^?1 at C/5 rate and 847 mA h g^?1 at 5C rate), maintaining 920 mA h g^?1 even after 300 cycles (a decay of 0.07% per cycle). Furthermore, a stable reversible capacity of as high as ≈1100 mA h g^?1 is realized with a higher sulfur loading of 4.6 mg cm^?2.     

Synergetic Protective Effect of the Ultralight MWCNTs/NCQDs Modified Separator for Highly Stable Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries are highly attractive due to their high energy density, potentially low cost, and environmental compatibility. However, their commercialization has been greatly hindered by their poor cycle life and severe self‐discharge, which can be attributed to the polysulfides dissolution. To overcome these issues, much effort has been devoted to engineering the electrode structure and composition to improve the performance which is often expensive and laborious. In this study, an ultralight multiwall carbon nanotube/N‐doped carbon quantum dot (MWCNT/NCQD)‐coated separator is first designed, which is cost effective and facile. The MWCNTs/NCQDs‐coated separator is then applied in Li–S batteries. The MWCNTs/NCQDs coating provides a physical shield against polysulfide shuttling and chemical adsorption of polysulfides by MWCNTs and NCQDs. The synergetic effect of MWCNTs and NCQDs enables the production of Li–S cell with a relative high initial discharge capacity of 1330.8 mA h g^?1 and excellent cyclic performance with a corresponding capacity fade rate of as low as 0.05% per cycle at 0.5 C over 1000 cycles. Excellent rate capability and anti‐self‐discharge behavior are also displayed. The design of MWCNTs/NCQDs‐coated separator is a viable approach for successfully developing practical Li–S batteries.     

Autonomic Shutdown of Lithium‐Ion Batteries Using Thermoresponsive Microspheres

Autonomic, thermally‐induced shutdown of Lithium‐ion (Li‐ion) batteries is demonstrated by incorporating thermoresponsive polymer microspheres (ca. 4 μm) onto battery anodes or separators. When the internal battery environment reaches a critical temperature, the microspheres melt and coat the anode/separator with a nonconductive barrier, halting Li‐ion transport and shutting down the cell permanently. Three functionalization schemes are shown to perform cell shutdown: 1) poly(ethylene) (PE) microspheres coated on the anode, 2) paraffin wax microspheres coated on the anode, and 3) PE microspheres coated on the separator. Charge and discharge capacity is measured for Li‐ion coin cells containing microsphere‐coated anodes or separators as a function of capsule coverage. For PE coated on the anode, the initial capacity of the battery is unaffected by the presence of the PE microspheres up to a coverage of 12 mg cm^?2 (when cycled at 1C), and full shutdown (>98% loss of initial capacity) is achieved in cells containing greater than 3.5 mg cm^?2. For paraffin microspheres coated on the anode and PE microspheres coated on the separator, shutdown is achieved in cells containing coverages greater than 2.9 and 13.7 mg cm^?2, respectively. Scanning electron microscopy images of electrode surfaces from cells that have undergone autonomic shutdown provides evidence of melting, wetting, and resolidification of PE into the anode and polymer film formation at the anode/separator interface.     

Minimizing the Electrolyte Volume in Li–S Batteries: A Step Forward to High Gravimetric Energy Density

Sulfur electrodes confined in an inert carbon matrix show practical limitations and concerns related to low cathode density. As a result, these electrodes require a large amount of electrolyte, normally three times more than the volume used in commercial Li‐ion batteries. Herein, a high‐energy and high‐performance lithium–sulfur battery concept, designed to achieve high practical capacity with minimum volume of electrolyte is proposed. It is based on deposition of polysulfide species on a self‐standing and highly conductive carbon nanofiber network, thus eliminating the need for a binder and current collector, resulting in high active material loading. The fiber network has a functionalized surface with the presence of polar oxygen groups, with the aim to prevent polysulfide migration to the lithium anode during the electrochemical process, by the formation of S–O species. Owing to the high sulfur loading (6 mg cm^?2) and a reduced free volume of the sulfide/fiber electrode, the Li–S cell is designed to work with as little as 10 µL cm^?2 of electrolyte. With this design the cell has a high energy density of 450 Wh kg^?1, a lifetime of more than 400 cycles, and the possibility of low cost, by use of abundant and eco‐friendly materials.     

Updated Metal Compounds (MOFs, ?S, ?OH, ?N, ?C) Used as Cathode Materials for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have the potential to be as efficient and as widespread as lithium‐ion (Li‐ion) batteries, since sulfur electrode has high theoretical capacity (1672 mA h g_sul^?1) and this element is affordable. However, unlike their ubiquitous lithium ion (Li‐ion) counterparts, it is difficult to realize the commercialization of Li‐S battery. Because the shuttle effect of polysulfide inevitably results in the serious capacity degradation. Tremendous progress is devoted to approach this problem from the aspect of physical confinement and chemisorption of polysulfide. Owing to weak intermolecular interactions, physical confinement strategy, however is not effective when the battery is cycled long‐term. Chemisorption of polysulfide that derived from polar–polar interaction, Lewis acid–base interaction, and sulfur‐chain catenation, are proven to significantly suppress the shuttle effect of polysulfide. It is also discovered that the metal compounds have strong chemical interactions with polysulfide. Therefore, this review focuses on latest metal–organic frameworks metal sulfides, metal hydroxides, metal nitrides, metal carbides, and discusses how the chemical interactions couple with the unique properties of these metal compounds to tackle the problem of polysulfide shuttle effect.     

Updated Metal Compounds (MOFs, S, OH, N, C) Used as Cathode Materials for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have the potential to be as efficient and as widespread as lithium‐ion (Li‐ion) batteries, since sulfur electrode has high theoretical capacity (1672 mA h g_sul^?1) and this element is affordable. However, unlike their ubiquitous lithium ion (Li‐ion) counterparts, it is difficult to realize the commercialization of Li‐S battery. Because the shuttle effect of polysulfide inevitably results in the serious capacity degradation. Tremendous progress is devoted to approach this problem from the aspect of physical confinement and chemisorption of polysulfide. Owing to weak intermolecular interactions, physical confinement strategy, however is not effective when the battery is cycled long‐term. Chemisorption of polysulfide that derived from polar–polar interaction, Lewis acid–base interaction, and sulfur‐chain catenation, are proven to significantly suppress the shuttle effect of polysulfide. It is also discovered that the metal compounds have strong chemical interactions with polysulfide. Therefore, this review focuses on latest metal–organic frameworks metal sulfides, metal hydroxides, metal nitrides, metal carbides, and discusses how the chemical interactions couple with the unique properties of these metal compounds to tackle the problem of polysulfide shuttle effect.     

Rationalizing Electrocatalysis of Li–S Chemistry by Mediator Design: Progress and Prospects

The lithium–sulfur (Li–S) battery is regarded as a next‐generation energy storage system due to its conspicuous merits in high theoretical capacity (1672 mAh g^?1), overwhelming energy density (2600 Wh kg^?1), and the cost‐effectiveness of sulfur. However, the practical application of Li–S batteries is still handicapped by a multitude of key challenges, mainly pertaining to fatal lithium polysulfide (LiPS) shuttling and sluggish sulfur redox kinetics. In this respect, rationalizing electrocatalytic processes in Li–S chemistry to synergize the entrapment and conversion of LiPSs is of paramount significance. This review summarizes recent progress and well‐developed strategies of the mediator design toward promoted Li–S chemistry. The current advances, existing challenges, and future directions are accordingly highlighted, aiming at providing in‐depth understanding of the sulfur reaction mechanism and guiding the rational mediator design to realize high‐energy and long‐life Li–S batteries.     

A Metal Organic Framework Derived Solid Electrolyte for Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are currently considered as promising candidates for next‐generation energy storage technologies. However, their practical application is hindered by the critical issue of the polysulfide‐shuttle. Herein, a metal organic framework (MOF)‐derived solid electrolyte is presented to address it. The MOF solid electrolyte is developed based on a Universitetet i Oslo (UIO) structure. By grafting a lithium sulfonate (‐SO₃Li) group to the UIO ligand, both the ionic conductivity and the polysulfide‐suppression capability of the resulting ‐SO₃Li grafted UIO (UIOSLi) solid electrolyte are greatly improved. After integrating a Li‐based ionic liquid (Li‐IL), lithium bis(trifluoromethanesulfonyl)imide in 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide, the resulting Li‐IL/UIOSLi solid electrolyte exhibits an ionic conductivity of 3.3 × 10^?4 S cm^?1 at room temperature. Based on its unique structure, the Li‐IL/UIOSLi solid electrolyte effectively restrains the polysulfide shuttle and suppresses lithium dendritic growth. Lithium–sulfur cells with the Li‐IL/UIOSLi solid electrolyte and a Li₂S₆ catholyte show stable cycling performance that preserves 84% of the initial capacity after 250 cycles with a capacity‐fade rate of 0.06% per cycle.     

Long‐Life,High‐Rate Lithium–Sulfur Cells with a Carbon‐Free VN Host as an Efficient Polysulfide Adsorbent and Lithium Dendrite Inhibitor

Lithium–sulfur (Li‐S) batteries are a promising next‐generation energy‐storage system, but the polysulfide shuttle and dendritic Li growth seriously hinder their commercial viability. Most of the previous studies have focused on only one of these two issues at a time. To address both the issues simultaneously, presented here is a highly conductive, noncarbon, 3D vanadium nitride (VN) nanowire array as an efficient host for both sulfur cathodes and lithium‐metal anodes. With fast electron and ion transport and high porosity and surface area, VN traps the soluble polysulfides, promotes the redox kinetics of sulfur cathodes, facilitates uniform nucleation/growth of lithium metal, and inhibits lithium dendrite growth at an unprecedented high current density of 10 mA cm^?2 over 200 h of repeated plating/stripping. As a result, VN‐Li||VN‐S full cells constructed with VN as both an anode and cathode host with a negative to positive electrode capacity ratio of only ≈2 deliver remarkable electrochemical performance with a high Coulombic efficiency of ≈99.6% over 850 cycles at a high 4 C rate and a high areal capacity of 4.6 mA h cm^?2. The strategy presented here offers a viable approach to realize high‐energy‐density, safe Li‐metal‐based batteries.     

A Multifunctional Separator Enables Safe and Durable Lithium/Magnesium–Sulfur Batteries under Elevated Temperature

Rechargeable metal–sulfur batteries encounter severe safety hazards and fast capacity decay, caused by the flammable and shrinkable separator and unwanted polysulfide dissolution under elevated temperatures. Herein, a multifunctional Janus separator is designed by integrating temperature endurable electrospinning polyimide nonwovens with a copper nanowire‐graphene nanosheet functional layer and a rigid lithium lanthanum zirconium oxide‐polyethylene oxide matrix. Such architecture offers multifold advantages: i) intrinsically high dimensional stability and flame‐retardant capability, ii) excellent electrolyte wettability and effective metal dendritic growth inhibition, and iii) powerful physical blockage/chemical anchoring capability for the shuttled polysulfides. As a consequence, the as constructed lithium–sulfur battery using a pure sulfur cathode displays an outstandingly high discharge capacity of 1402.1 mAh g^?1 and a record high cycling stability (approximately average 0.24% capacity decay per cycle within 300 cycles) at 80 °C, outperforming the state‐of‐the‐art results in the literature. Promisingly, a high sulfur mass loading of ≈3.0 mg cm^?2 and a record low electrolyte/sulfur ratio of 6.0 are achieved. This functional separator also performs well for a high temperature magnesium–sulfur battery. This work demonstrates a new concept for high performance metal–sulfur battery design and promises safe and durable operation of the next generation energy storage systems.     

Highly Solvating Electrolytes for Lithium–Sulfur Batteries

There is a critical need to evaluate lithium–sulfur (Li–S) batteries with practically relevant high sulfur loadings and minimal electrolyte. Under such conditions, the concentration of soluble polysulfide intermediates in the electrolyte drastically increases, which can alter the fundamental nature of the solution‐mediated discharge and thereby the total sulfur utilization. In this work, an investigation into various high donor number (DN) electrolytes that allow for increased polysulfide dissolution is presented, and the way in which this property may in fact be necessary for increasing sulfur utilization at low electrolyte and high loading conditions is demonstrated. The solvents dimethylacetamide, dimethyl sulfoxide, and 1‐methylimidazole are holistically evaluated against dimethoxyethane as electrolyte co‐solvents in Li–S cells, and they are used to investigate chemical and electrochemical properties of polysulfide species at both dilute and practically relevant conditions. The nature of speciation exhibited by lithium polysulfides is found to vary significantly between these concentrations, particularly with regard to the S₃^?? species. Furthermore, the extent of the instability in conventional electrolyte solvents and high DN solvents with both lithium metal and polysulfides is thoroughly investigated. These studies establish a basis for future efforts into rationally designing an optimal electrolyte for a lean electrolyte, high energy density Li–S battery.     

Stable Li–Organic Batteries with Nafion‐Based Sandwich‐Type Separators

Similar to Li–S batteries, Li–organic batteries have also been plagued by the dissolution of active materials and the resulting shuttle effect for many years. An effective strategy to eliminate the shuttle effect is adopting solid electrolytes or Li–ion permselective separators to prohibit the dissolved electroactive species from migrating to the Li anode. A polypropylene/Nafion/polypropylene (PNP) sandwich‐type separator is reported with many advantages in comparison with previously reported LISICON, polymer electrolyte, and other Nafion utilization forms. The physical and chemical properties of PNP separators are studied in detail by cross‐section scanning electron microscopy (SEM), infrared spectroscopy (IR), and electrochemical impedance spectroscopy. 1,1′‐Iminodianthraquinone (IDAQ), a novel organic cathode, is taken as an example to quantitatively investigate the function of PNP separators. In the presence of PNP5 with the most appropriate Nafion loading of 0.5 mg cm^–2, IDAQ is able to achieve dramatically improved cycling stability with capacity retention of 76% after 400 cycles and Coulombic efficiency above 99.6%, which reaches the highest level for reported soluble organic electrode materials. Besides Li–organic batteries, such kind of Nafion‐based sandwich‐type separators are also promising for Li–S batteries and other new battery designs involving dissolved electroactive species.     

1T′‐ReS2 Nanosheets In Situ Grown on Carbon Nanotubes as a Highly Efficient Polysulfide Electrocatalyst for Stable Li–S Batteries

The practical viability of Li–S cells depends on achieving high electrochemical utilization of sulfur under realistic conditions, such as high sulfur loading and low electrolyte/sulfur (E/S) ratio. Here, metallic 2D 1T′‐ReS₂ nanosheets in situ grown on 1D carbon nanotubes (ReS₂@CNT) via a facile hydrothermal reaction are presented to efficiently suppress the “polysulfide shuttle” and promote lithium polysulfide (LiPS) redox reactions. The designed ReS₂@CNT nanoarchitecture with high conductivity and rich nanoporosity not only facilitates electron transfer and ion diffusion, but also possesses abundant active sites providing high catalytic activity for efficient LiPS conversion. Li–S cells fabricated with ReS₂@CNT exhibit high capacity with superior long‐term cyclability with a capacity retention of 71.7% over 1000 cycles even at a high current density of 1C (1675 mA g^?1). Also, pouch cells fabricated with the ReS₂@CNT/S cathode maintain a low capacity fade rate of 0.22% per cycle. Furthermore, the electrocatalysis mechanism is revealed based on electrochemical studies, theoretical calculations, and in situ Raman spectroscopy.     

Hybrid Lithium‐Sulfur Batteries with an Advanced Gel Cathode and Stabilized Lithium‐Metal Anode

The insulating nature of sulfur, polysulfide shuttle effect, and lithium‐metal deterioration cause a decrease in practical energy density and fast capacity fade in lithium‐sulfur (Li‐S) batteries. This study presents an integrated strategy for the development of hybrid Li‐S batteries based on a gel sulfur cathode, a solid electrolyte, and a protective anolyte composed of a highly concentrated salt electrolyte containing mixed additives. The dense solid electrolyte completely blocks polysulfide diffusion, and also makes it possible to investigate the cathode and anode independently. This gel cathode effectively traps the polysulfide active material while maintaining a low electrolyte to sulfur ratio of 5.2 mL g^?1. The anolyte effectively protects the Li metal and suppresses the consumption of liquid electrolyte, enabling stable long‐term cycling for over 700 h in Li symmetric cells. This advanced design can simultaneously suppress the polysulfide shuttle, protect Li metal, and reduce the liquid electrolyte usage. The assembled hybrid batteries exhibit remarkably stable cycling performance over 300 cycles with high capacity. Finally, surface‐sensitive techniques are carried out to directly visualize and probe the interphase formed on the surface of the Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) pellet, which may help stabilize the solid–liquid interface.     

High‐Performance All‐Solid‐State Lithium–Sulfur Batteries Enabled by Amorphous Sulfur‐Coated Reduced Graphene Oxide Cathodes

Safety and the polysulfide shuttle reaction are two major challenges for liquid electrolyte lithium–sulfur (Li–S) batteries. Although use of solid‐state electrolytes can overcome these two challenges, it also brings new challenges by increasing the interface resistance and stress/strain. In this work, the interface resistance and stress/strain of sulfur cathodes are significantly reduced by conformal coating ≈2 nm sulfur (S) onto reduced graphene oxide (rGO). An Li–S full cell consisting of an rGO@S‐Li₁₀GeP₂S₁₂‐acetylene black (AB) composite cathode is evaluated. At 60 °C, the all‐solid‐state Li–S cell demonstrates a similar electrochemical performance as in liquid organic electrolyte, with high rate capacities of 1525.6, 1384.5, 1336.3, 903.2, 502.6, and 204.7 mA h g^?1 at 0.05, 0.1, 0.5, 1.0, 2.0, and 5.0 C, respectively. It can maintain a high and reversible capacity of 830 mA h g^?1 at 1.0 C for 750 cycles. The uniform distribution of the rGO@S nanocomposite in the Li₁₀GeP₂S₁₂‐AB matrix generates uniform volume changes during lithiation/delithiation, significantly reducing the stress/strain, thus extending the cycle life. Minimization of the stress/strain of solid cells is the key for a long cycle life of all‐solid‐state Li–S batteries.     

Interface Engineering of MXene Composite Separator for High‐Performance Li–Se and Na–Se Batteries

Selenium (Se), due to its high electronic conductivity and high energy density, has recently attracted considerable interest as a cathode material for rechargeable Li/Na batteries. However, the poor cycling stability originating from the severe shuttle effect of polyselenides hinders their practical applications. Herein, highly stable Li/Na–Se batteries are developed using ultrathin (≈270 nm, loading of 0.09 mg cm^?2) cetrimonium bromide (CTAB)/carbon nanotube (CNT)/Ti₃C₂T_x MXene hybrid modified polypropylene (PP) (CCNT/MXene/PP) separators. The hybrid separator can immobilize the polyselenides via enhanced Lewis acid–base interactions between CTAB/MXene and polyselenides, which is demonstrated by theoretical calculations and X‐ray photoelectron spectroscopy. The incorporation of CNT helps to improve the electrolyte infiltration and facilitate the ionic transport. In situ permeation experiments are conducted for the first time to visually study the behavior of polyselenides, revealing the prohibited shuttle effect and protected Li anode from corrosion with CCNT/MXene/PP separators. As a result, the Li–Se batteries with CCNT/MXene/PP separators deliver an outstanding cycling performance over 500 cycles at 1C with an extremely low capacity decay of 0.05% per cycle. Moreover, the hybrid separators also perform well in Na–Se batteries. This study develops a preferable separator–electrolyte interface and the concept can be applied in other conversion‐type battery systems.