A synergistic modification of polypropylene separator toward stable lithium–sulfur battery

Advancements in Research and Applications of PP-Based Materials Utilizing Melt-Blown Nonwoven Technology

Melt-blown nonwoven materials have demonstrated significant advancements in a multitude of industrial sectors, mainly due to their high production efficiency, extensive specific surface area, and narrow aperture. The demand for melt-blown nonwoven materials has increased further in recent time, particularly in the wake of the novel coronavirus (COVID-19) pandemic. Polypropylene (PP) is extensively used in production and research due to its low cost, low weight, and easy processing, and the melt-blown materials made from it share similar characteristics. We systematically summarize the research advancements of melt-blown nonwoven technology and applications of PP-based melt-blown materials over the last few years. First, the principles and processes of melt-blown nonwoven that govern the production of micro/nano fibers are described. Then the raw materials and process technology of melt-blown are reviewed. After these, we highlight the use of PP-based melt-blown materials in key fields, including media filtration, oil-water separation, heavy metal ions removal, organic pollutants removal and battery separator. Finally, we summary and suggest some potential future research directions of melt-blown nonwoven technology and PP-based melt-blown materials.

A NiCo oxide/NiCo sulfate hollow nanowire-coated separator: a versatile strategy for polysulfide trapping and catalytic conversion in high-performance lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are highly anticipated due to their remarkable theoretical specific energy and energy density. Nevertheless, the polysulfide shuttle effect severely curtails their cycle life, posing a significant obstacle to commercialization. Herein, we introduce nickel-cobalt oxide/nickel-cobalt sulfate hollow nanowires (NCO/NCSO-HNWs) as a separator modification material. The ingeniously designed hollow nanostructure of NCO/NCSO-HNWs endows it with a profusion of adsorption and catalytic active sites. This unique feature enables it to not only physically adsorb lithium polysulfides (LiPSs) but also catalytically convert them, thereby remarkably enhancing the anchoring and conversion efficiency of LiPSs. The LSBs equipped with NCO/NCSO-HNWs-modified separators exhibit an outstanding initial capacity of 1260 mA h g-1 at 0.2C. Even after 100 cycles, a high capacity of 956 mA h g-1 is retained, corresponding to an impressive retention rate of 75.9%. Notably, at 1C, after enduring 500 cycles, the discharge capacity still stabilizes at 695 mA h g-1. The utilization of such hollow nanowire-based separator modification materials represents a novel and effective strategy for elevating the performance of LSBs, holding substantial promise for surmounting the challenges associated with the shuttle effect and expediting the commercialization journey of LSBs.

Recycling and Reuse of Spent LIBs: Technological Advances and Future Directions

Recovering valuable metals from spent lithium-ion batteries (LIBs), a kind of solid waste with high pollution and high-value potential, is very important. In recent years, the extraction of valuable metals from the cathodes of spent LIBs and cathode regeneration technology are still rapidly developing (such as flash Joule heating technology to regenerate cathodes). This review summarized the studies published in the recent ten years to catch the rapid pace of development in this field. The development, structure, and working principle of LIBs were firstly introduced. Subsequently, the recent developments in mechanisms and processes of pyrometallurgy and hydrometallurgy for extracting valuable metals and cathode regeneration were summarized. The commonly used processes, products, and efficiencies for the recycling of nickel-cobalt-manganese cathodes (NCM/LCO/LMO/NCA) and lithium iron phosphate (LFP) cathodes were analyzed and compared. Compared with pyrometallurgy and hydrometallurgy, the regeneration method was a method with a higher resource utilization rate, which has more industrial application prospects. Finally, this paper pointed out the shortcomings of the current research and put forward some suggestions for the recovery and reuse of spent lithium-ion battery cathodes in the future.

Rational Design of TiO2@g-C3N4/CNT Composite Separator for High Performance Lithium-Sulfur Batteries to Promote the Redox Kinetics of Polysulfide

Lithium-sulfur batteries (LSB) show excellent potential as future energy storage devices with high energy density, but their slow redox kinetics and the shuttle effect seriously hinder their commercial application. Herein, a 0D@2D composite was obtained by anchoring polar nano-TiO2 onto a 2D layered g-C3N4 surface in situ, and a functional separator was prepared using multi-walled carbon nanotubes as a conductive substrate. Due to their long-range conductivity, multi-walled carbon nanotubes make up for the low conductivity of TiO2@g-C3N4 to some extent. A lithium-sulfur battery prepared with a modified separator exhibited excellent long-term cycle performance, a good lithium ion diffusion rate, and rapid redox kinetics. The initial specific discharge capacity of the composite was 1316 mAh g-1 at 1 C, and a high specific discharge capacity of 569.9 mAh g-1 was maintained after 800 cycles (the capacity decay rate per cycle was only 0.07%). Even at the high current density of 5 C, a specific capacity of 784 mAh g-1 was achieved. After 60 cycles at 0.5 C, the modified separator retained the discharge capacity of 718 mAh g-1 under a sulfur load of 2.58 mg cm-2. In summary, the construction of a heterojunction significantly improved the overall cycle stability of the battery and the utilization rate of active substances. Therefore, this study provides a simple and effective strategy for further improving the overall performance and commercial application of lithium-sulfur batteries.

Bifunctional K3PW12O40/Graphene Oxide-Modified Separator for Inhibiting Polysulfide Diffusion and Stabilizing Lithium Anode

Lithium-sulfur (Li-S) batteries are considered as promising candidates for next-generation batteries due to their high theoretical energy density. However, the practical application of Li-S batteries is still hindered by several challenges, such as the polysulfide shuttle and the growth of lithium dendrites. Herein, we introduce a bifunctional K3PW12O40/graphene oxide-modified polypropylene separator (KPW/GO/PP) as a highly effective solution for mitigating polysulfide diffusion and protecting the lithium anode in Li-S batteries. By incorporating KPW into a densely stacked nanostructured graphene oxide (GO) barrier membrane, we synergistically capture and rapidly convert lithium polysulfides (LiPSs) electrochemically, thus effectively suppressing the shuttling effect. Moreover, the KPW/GO/PP separator can stabilize the lithium metal anode during cycling, suppress dendrite formation, and ensure a smooth and dense lithium metal surface, owing to regulated Li+ flux and uniform Li nucleation. Consequently, the constructed KPW/GO/PP separator delivered a favorable initial specific capacity (1006 mAh g-1) and remarkable cycling performance at 1.0 C (626 mAh g-1 for up to 500 cycles with a decay rate of 0.075% per cycle).

Novel hydrothermal synthesis of Mn-TaS3@rGO nanocomposite as a superior multifunctional mediator for advanced Li-S batteries

Because of its high theoretical capacity and energy density, the lithium-sulfur (Li-S) battery is a desirable next-generation energy storage technology. However, the shuttle effect of lithium polysulfide and the slow sulfur reaction kinetics remain significant barriers to Li-S battery application. In this work, tantalum trisulfide (TaS₃) and selective manganese-doped tantalum trisulfide (Mn-TaS₃) nanocomposites on reduced graphene oxide surface were developed via a one-step hydrothermal method for the first time and introduced as a novel multifunctional mediator in the Li-S battery. The surface engineering of Mn-TaS₃@rGO with abundant defects not only exhibits the strong adsorption performance on lithium polysulfides (LiPSs) but also demonstrates the remarkable electrocatalytic effect on both the LiPSs conversion reaction in symmetric cell and the Li₂S nucleation/dissolution processes in potentiostatic experiments, which would substantially promote the electrochemical performance of LSB. The cell assembled with Mn-TaS₃@rGO/PP modified separator could significantly improve the cell conductivity and effectively accelerate the redox conversion of active sulfur during the charging/discharging process, which delivers exceptional long-term cycling with 683 mA h g^-1 retention capacity after the 1000th cycle at 0.3C under the sulfur loading of 2.7 mg cm^-2. Even at the E/S ratio as low as 5.0 µL mg^-1, the reversible specific capacity of 692 mA h g^-1 can be offered at 0.2C over 300 cycles. This research indicates that the novel Mn-TaS₃@rGO multifunctional mediator is successfully fabricated and applied in Li-S batteries with extraordinary electrochemical performances and gives a strategy to explore the construction of a modified functional separator.

A Ni-MOF derived graphene oxide combined Ni3S2-Ni/C composite and its use in the separator coating for lithium sulfur batteries

Lithium-sulfur batteries (LSBs) are widely regarded as reliable novel secondary batteries due to their low price and high capacity. Nevertheless, the notorious "shuttle effect" limits the commercialization of LSBs. In order to solve this problem, we fabricated a Ni₃S₂-Ni/C composite through carbonization, vulcanization and hydrothermal reactions by using a Ni-MOF precursor and applied it as a separator modification layer to enhance the electrochemical properties of LSBs. To further increase the conductivity of the material, a small amount of GO was added during the experiment. The prepared material was also used as separator modified coating material to optimize the electrochemical performance of LSBs. The as prepared Ni₃S₂-Ni/C(GO) composite shows good conductivity and has a superior porous structure and abundant active sites. Lithium polysulfides (LPs) can be physically confined and chemically adsorbed, what is more, the Ni and Ni₃S₂ active sites enable fast conversion of LPs which further optimizes the rate performance. From the cycle performance measurement, the initial discharge specific capacity of the Ni₃S₂-Ni/C(GO) modified separator battery is found to be 1263.4, 1181.5, 1090.6, and 840.3 mA h g^-1 at 0.05, 0.1, 0.3 and 0.5C, respectively. After 400 charge/discharge cycles at 0.5C, the capacity remains at 483.6mA h g^-1 with a capacity retention ratio of 57.56%.

Effect of Cross-Linking and Surface Treatment on the Functional Properties of Electrospun Polybenzimidazole Separators for Lithium Metal Batteries

In this work, electrospun PBI separators with a highly porous structure and nanofiber diameter of about 90-150 nm are prepared using a multi-nozzle under controlled conditions for lithium metal batteries. Cross-linking with α, α-dibromo-p-xylene and surface treatment using 4-(chloromethyl) benzoic acid successfully improve the electrochemical as well as mechanical properties of the separators. The resulting separator is endowed with high thermal stability and excellent wettability (1080 to 1150%) with commercial liquid electrolyte than PE and PP (Celgard 2400) separators. Besides, attractive cycling stability and rate capability in LiFePO₄/Li cells are attained with the modified separators. Prominently, CROSSLINK PBI exhibits a stable Coulombic efficiency of more than 99% over 100 charge-discharge cycles at 0.5 C, which is superior to the value of cells using commercial PE and PP (Celgard 2400) separators. The half cells assembled using the CROSSLINK PBI separator can deliver a discharge capacity of 150.3 mAh g^-1 at 0.2 C after 50 cycles corresponding to 88.4% of the theoretical value of LiFePO₄ (170 mAh g^-1). This work offers a worthwhile method to produce thermally stable separators with noteworthy electrochemical performances which opens new possibilities to improve the safe operation of batteries.

Ultrathin Two-Dimensional Fe-Co Bimetallic Oxide Nanosheets for Separator Modification of Lithium-Sulfur Batteries

The shuttle effect is understood to be the most significant issue that needs to be solved to improve the performance of lithium-sulfur batteries. In this study, ultrathin two-dimensional Fe-Co bimetallic oxide nanosheets were prepared using graphene as a template, which could rapidly catalyze the conversion of polysulfides and inhibit the shuttle effect. Additionally, such ultrathin nanostructures based on graphene provided sufficient active sites and fast diffusion pathways for lithium ions. Taking into account the aforementioned benefits, the ultrathin two-dimensional Fe-Co bimetallic oxide nanosheets modified separator assembled lithium-sulfur batteries delivered an incredible capacity of 1044.2 mAh g^-1 at 1 C and retained an excellent reversible capacity of 859.4 mAh g^-1 after 100 cycles. Even under high loading, it still achieved high area capacity and good cycle stability (92.6% capacity retention).

An interwoven carbon nanotubes/cerium dioxide electrocatalyst accelerating the conversion kinetics of lithium sulfide toward high-performance lithium-sulfur batteries

Rechargeable lithium-sulfur (Li-S) batteries with environmental friendliness, low price, high specific capacity and energy density could be promising alternatives to a larger scope of energy storage in the near future. However, the practical application is impeded by the intrinsic insulation of sulfur and the fatal shuttle effect during the (dis)charging process. Herein, we report a strategy to address the drawbacks of Li-S batteries by inserting an interwoven carbon nanotubes/cerium dioxide electrocatalyst interlayer material (CNTs@CeO₂) between the sulfur cathode and the separator. In the CNTs@CeO₂ composite, the conductive network interwoven by CNTs facilitates electron transportation, and the abundant active sites in CeO₂ cavities ensuring the adsorption-catalytic conversion of lithium polysulfides as well as the hollow structure of CeO₂ is conducive to rapid electrolyte penetration and lithium ion migration. Benefiting from such multifunction, the battery with a CNTs@CeO₂ interlayer exhibits superior rate performance, delivering a high discharge specific capacity of 1040.6 mAh g^-1 at 0.2C and 652.5 mAh g^-1 at 4C, respectively. Moreover, the battery shows excellent cycling stability with a capacity decay rate of 0.064% per cycle at 1C over 1000 cycles. These promising results demonstrate the potential application of CeO₂-based electrocatalysts for high energy density Li-S batteries.

Dual-role Magnesium Aluminate Ceramic Film as an Advanced Separator and Polysulfide Trapper in Li-S battery: Experimental and DFT investigations

Developing an advanced separator that could stop the polysulfide shuttling remains a work-in-progress in the Li-S battery domain. Most of the work reported so far concentrates on functionalizing the commercial...

Enormous-sulfur-content cathode and excellent electrochemical performance of Li-S battery accouched by surface engineering of Ni-doped WS2@rGO nanohybrid as a modified separator

The poor conductivity of sulfur, the lithium polysulfide's shuttle effect, and the lithium dendrite problem still impede the practical application of lithium-sulfur (Li-S) batteries. In this work, the ultrathin nickel-doped tungsten sulfide anchored on reduced graphene oxide (Ni-WS₂@rGO) is developed as a new modified separator in the Li-S battery. The surface engineering of Ni-WS₂@rGO could enhance the cell conductivity and afford abundant chemical anchoring sites for lithium polysulfides (LiPSs) adsorption, which is convinced by the high adsorption energy and the elongate SS bond given using density-functional theory (DFT) calculation. Concurrently, the Ni-WS₂@rGO as a modified separator could effectively catalyze the conversion of LiPSs during the charging/discharging process. The Li-S cell with Ni-WS₂@rGO modified separator achieves a high initial capacity of 1160.8 mA h g^-1 at the current density of 0.2C with a high-sulfur-content cathode up to 80 wt%, and a retained capacity of 450.7 mA h g^-1 over 500 cycles at 1C, showing an efficient preventing polysulfides shuttle to the anode while having no influence on Li⁺ ion transference across the decorating separator. The strategy adopted in this work would afford an effective pathway to construct an advanced functional separator for practical high-energy-density Li-S batteries.

A novel battery separator coated by a europium oxide/carbon nanocomposite enhances the performance of lithium sulfur batteries

Lithium sulfur (Li-S) batteries represent one of the most promising future power batteries due to their remarkable advantages of low cost and ultrahigh theoretical energy density. However, the commercial applications of Li-S batteries have long been plagued by the shuttling effect of polysulfides and sluggish redox kinetics of these species. Herein, we designed a novel battery separator coated by a europium oxide-doped porous Ketjen Black (Eu₂O₃/KB) and tested its performance for the Li-S batteries for the first time. Experimental results and theoretical calculations reveal that the improved electrochemical performance can be attributed to the presence of Eu₂O₃. The strong binding effect between Eu₂O₃ and polysulfides is demonstrated in two aspects: (1) there exist strong interactions between Eu₂O₃ as a Lewis acid and polysulfides of strong Lewis basicity; (2) Eu₂O₃ with oxygen-vacancy defects provides active sites for catalyzing polysulfide conversion and polysulfide trapping. Thus, a Li-S battery with the Eu₂O₃/KB modified separator delivers highly stable cycling performance and excellent rate capability, with the capacity decay ratio of merely 0.05% per cycle under 1 C rate during 500 cycles, and high specific capacity of 563 mAh g^-1 at 3 C rate. This work offers a meaningful exploration of the application of rare earth oxides for the modification of the separator towards high performance Li-S batteries.

Multifunctional Polypropylene Separator via Cooperative Modification and Its Application in the Lithium-Sulfur Battery

The continuous shuttling of dissolved polysulfides between the electrodes is the primary cause for the rapid decay of lithium-sulfur batteries. Modulation of the separator-electrolyte interface through separator modification is a promising strategy to inhibit polysulfide shuttling. In this work, we develop a graphene oxide and ferrocene comodified polypropylene separator with multifunctionality at the separator-electrolyte interface. The graphene oxide on the functionalized separator could physically adsorb the polysulfide while the ferrocene component could effectively facilitate the conversion of the adsorbed polysulfide. Due to the combination of these beneficial functionalities, the separator exhibits an excellent battery performance, with a high reversible capacity of 409 mAh g^-1 after 500 cycles at 0.2 C. We anticipate that the combinatorial separator functionalization proposed herein is an effective approach for improving the performance of lithium-sulfur batteries.