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finally to the poor performance of Li-S batteries. [1][2][3][4][5][6][7][8][9][10] The state-of-the-art separators used in Li-S batteries are commonly porous polypropylene (PP) films, but their pores are too large to restrict polysulfide shuttling (Figure 1a). Lots of efforts have been made to mitigate this shuttle effect by physical repulsion or chemical adsorption routes such as filling or covering the pores with polymers, [11][12][13][14] metal-organic frameworks (MOFs), [15] metal oxides, [16,17] graphene, [18][19][20] modified carbon nanotubes, [21,22] etc. (Figure 1b). Unfortunately, the filled or covered pores also restrict the transportation of Li + ions, increase the inner resistance, and finally deteriorate the performance of Li-S batteries.In this report, we propose a new strategy to selectively coordinate high-order polysulfides with "tertiary amine layer (TAL)" by which to simultaneously keep the pores of the separator still open to lithium ion's transportation. The construction of the polysulfide tongs is based on the classic "soft and hard acid-base (SHAB) theory." Different from the literature chemical interaction strategies, the anchoring groups to trap polysulfide are chemically grafted onto the PP separator, which is tough and stable. Also, the dissolved high-order Li 2 S x (x = 4, 6, and 8) can be more efficiently grasped when they try to diffuse across the narrowed but opening complex pores (Figure 1c). Li 2 S x species are relatively "soft" acids as the positive charges are mainly dispersed on the surface of the agglomerated polysulfide mole cules. Moreover, after the lithium ions are coordinated by sulfur, there are still "electron cloud holes" in Li 2 S x molecules to accept electrons from other molecules ( Figure S2, Supporting Information). In this regard, if we construct a "soft" base on the separator, the high-order Li 2 S x (x = 4, 6, and 8) soft acid can be grasped when they are further reduced and released in the cathode. On the contrary, lithium ion, which is commonly recognized as "hard" acid because of its small size and concentrated charge density, will be repulsed away by the "soft" base on the separator according to the SHAB theory. The chosen "soft" base for grasping polysulfide tong is tertiary amine (TA) group, which has a dispersed electron cloud and large head volume. TA group do not possess N-hydrogen atom, so we do not need to worry about the potential side reactions between active hydrogen and lithium-related compounds. Also, because the largest binding energy (E b ) between Li 2 S x Rechargeable lithium-sulfur batteries, which use sulfur as the cathode material, promise great potentials to be the next-generation high-energy system. However, higher-order lithium polysulfides, Li 2 S x (x = 4, 6, and 8), regardless of in charge or in discharge, always form first, dissolve subsequently in the electrolyte, and shuttle to the cathode and the anode, which is called "shuttle effect." The polysulfides shuttle effect leads to heavy loss of the active-sulfur materials. Literatu...

The Ti3C2@CF–S cathode features high sulfur loading capacity, strong polysulfide attachment, superior pulverization inhibiting properties, and demonstrates remarkable cycling stability.

High theoretical specific capacity and rich resources in nature make sulfur an ideal cathode material for lithium–metal batteries. However, the shuttle effect and sluggish reduction reaction kinetics of lithium polysulfides (LiPSs) seriously affect the performance of the batteries. Here, we report GO-d-Ti3C2T x MXene aerogels with a novel three-dimensional (3D) reticular structure that served as sulfur host cathode materials for lithium–sulfur batteries (LiSBs), which benefits adsorption/catalytic conversion of LiPSs simultaneously. The dissolved LiPSs can be rapidly captured through chemisorption and then catalyzed into insoluble Li2S by low-coordinated-state Ti on the d-Ti3C2T x MXene surface. The combination of adsorption and catalysis enormously improves the capacity and cycling performance of LiSBs. At an S mass loading of 1.5 mg cm–2, the cell with the S@GM0.4 composite electrode achieves excellent cycling performance. The discharge specific capacity of 1039 mA h g–1 (1.56 mA h cm–2) decays to 542.9 mA h g–1 after 1000 cycles with a capacity fading rate of 0.048% per cycle at 0.5 C. Even at an S mass loading of 4.88 mg cm–2, an areal capacity of 4.3 mA h cm–2 can be achieved at 0.2 C.

Li metal anodes, which possess ultrahigh theoretical capacity, are considered the ultimate solution for high energy density batteries. However, issues regarding safety and rapid electrode degradation due to Li dendrite...

Lithium–sulfur (Li–S) batteries are promising next-generation high-density energy storage systems due to their advantages of high theoretical specific capacity, environmental compatibility, and low cost. However, high-order polysulfides dissolve in the electrolyte and subsequently lead to the undesired polysulfide shuttle effect, which hinders the commercialization of Li–S batteries. To tackle this issue, morpholine molecules were successfully grafted onto a commercial polypropylene separator. Density functional theory (DFT) calculations were performed and revealed that morpholine side chains could equally and reversibly grasp all the high-order polysulfides. This diatomic chemisorption adjusted the transformation process among the sulfur-related compounds. The modified separator battery possessed a discharge capacity as high as 827.8 mAh·g–1 after 500 cycles at 0.5 C. The low capacity fading rate, symmetrical cyclic voltammogram, and retention of the electrode morphology all suggest that the diatomic equal adsorption approach can successfully suppress the polysulfide shuttle effect while maintaining excellent battery performance.

graphite anodes) and the lowest electrochemical potential (-3.04 V versus the standard hydrogen electrode). [5] However, the application of Li-metal anodes in batteries still faces many challenges due to its low coulombic efficiency (CE), rapid capacity decay, poor cycle life, [6] and safety concerns [7] resulting from the uncontrollable growth of dendritic Li during cycling. [8] On the one hand, Li dendrites may pierce the fragile solid electrolyte interface (SEI) and even separators, resulting in internal short circuits, thermal runway, and even the explosion of the battery. [9] On the other hand, Li dendrites can easily fall off from the bulk Li, reducing the utilization of active Li and the CE. [10] Therefore, preventing the formation of Li dendrites is the crucial step to realize the practical application of Li-metal batteries (LMBs) with high energy density. [11] To alleviate the abovementioned problems related to the growth of Li dendrites, enormous efforts have been devoted to finding solutions. These solutions can be roughly divided into five categories: the modification of the SEI layer by the addition of additives, [12] introduction of various ex-situ artificial SEI protective layers, [13] construction of 3D structured Li anodes, [14] utilization of solid-state electrolytes, [15] and design of functional separators. [16] Among these strategies, coatings or interlayers of the separator, such as MOFs, [16a] Al 2 O 3 , [16b] MnCO 3 , [16c] VS 2 flakes, [16d] carbon materials, [2b] and nonporous gel electrolytes, [17] are facile and convenient ways to suppress the growth of Li dendrites. All these works have achieved good results. Herein, we introduced the positively charged layer (PCL) to polypropylene (PP) separator. PCL is composed of polymer sidechains with freely moving multication groups, can regulate the lithium-ion deposition behavior in sub-nano scales.During the deposition process of a commercial PP separator cell, Li ions will deposit to regions with higher current density and then inevitably form protuberant Li metal tips (LMTs) due to the inherent heterogeneity of Li metal. [18] Then, the electric field strength around the formed LMTs will be significantly enhanced based on Gauss's flux theorem. Consequently, more Li ions will preferentially deposit around the LMTs to form Li dendrites. [19] However, unlike the reported strategies in the literature, this study is based on the "dynamic tip-occupying electrostatic shield" (DTOES) effect for achieving uniform Lithium-metal batteries (LMBs) have long been considered the "holy grail" of next-generation energy storage systems due to the unique advantages of Li metal, such as having a high specific capacity and the lowest potential. Unfortunately, the practical application of LMBs is seriously hindered by the uncontrollable growth of dendritic Li. To address this issue, a positively charged layer (PCL) with freely moving multication sidechains is successfully polymerized on a commercial polypropylene (PP) separator. The cationic groups on the ...

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