MOF-Derived Hollow Carbon Supported Nickel-Cobalt Alloy Catalysts Driving Fast Polysulfide Conversion for Lithium-Sulfur Batteries

Co0.7Fe0.3/Co alloy nanoparticles encapsulated in N-doped carbon polyhedrons as efficient catalysts for advanced lithium-sulfur batteries

The widespread adoption of lithium-sulfur (Li-S) batteries is hindered by several critical challenges, including the inherently poor electrical conductivity of sulfur, the sluggish reaction kinetics arising from the complex multi-step conversion process, and the abominable shuttle effect of lithium polysulfides (LiPSs). Herein, Co0.7Fe0.3/Co alloy nanoparticles were in-situ constructed and confined within CNTs-grafted N-doped carbon polyhedrons (Co0.7Fe0.3/Co@NC-CNT), and utilized as efficient catalysts for Li-S batteries. Impressively, the electronic modulation of the Co0.7Fe0.3/Co alloy nanoparticles not only effectively accelerates the sulfur redox reaction, but also acts as a strong adsorbent to effectively inhibit the shuttling of polysulfides. Additionally, the hierarchical porous carbon structure facilitates the electron transfer and ion transport, while the derived carbon shell protects binary active sites of Co0.7Fe0.3/Co core from electrolyte corrosion. Benefiting from the abundant bimetallic active sites and the meticulously engineered structure, the Co0.7Fe0.3/Co@NC-CNT/S cathode yields a promising specific capacity of 1355.2 mAh g-1 at 0.1C, and outstanding capacity retention of 552.3 mAh g-1 over 500 cycles at 2C (∼67.6 % of initial capacity).

Synthesis of Vacancy-Rich NiTex-NC Catalyst under Mild Conditions for High-Performance Lithium Sulfur Batteries

Due to the slow conversion kinetics of polysulfides, the practical application of lithium-sulfur batteries faces significant challenges. Transition metal tellurides exhibit good catalytic activity and are expected to help mitigate the shuttle effect in lithium-sulfur batteries. Vacancies, as a form of defect, can further enhance the conductivity and catalytic activity of the catalysts. However, most vacancy creation is achieved by the action of strong reducing agents (such as H2, NaBH4, hydrazine, etc.). Here, we utilized the similarity in lattice parameters between NiTe and NiTe2 to adjust the extent of lattice contraction in NiTe2 by controlling the Te powder content, ultimately obtaining a Te-vacancy-rich NiTex-NC catalyst under mild conditions. The unsaturated coordination between Ni and Te provides abundant active sites for the chemical adsorption and catalytic conversion of polysulfides, thus allowing NiTex-NC to significantly lower the reaction energy barrier of polysulfides and effectively inhibit the shuttle effect. The results show that NiTex-NC can achieve a specific capacity of 589.4 mAh g-1 at a rate of 7 C, and after 1000 cycles at 2 C, the capacity decay per cycle is only 0.0278%. Even under complex conditions (with a sulfur loading of 7.5 mg cm-2 and a liquid sulfur ratio of 10 μL mg-1), it still maintains good cycling stability.

Bimetallic Metal-Organic Framework Catalyst to Accelerate Sulfur Conversion Kinetics for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are highly attractive due to their exceptional theoretical energy density (2600 Wh kg-1) and low cost. However, their practical deployment is limited by critical issues, including pronounced polysulfide shuttling and slow reaction kinetics. In this study, we report the development of a novel Mo-Zn bimetallic ZIF-8 catalyst designed to address these issues. Compared with pristine ZIF-8, the Mo-ZIF-8 catalyst exhibited an effectively tuned surface area and pore structure, significantly enhancing its ability to trap polysulfides. Moreover, the optimized pore architecture increased the exposure of active sites, strengthening the chemical interactions between Mo-ZIF-8 and sulfur species and thereby accelerating sulfur reaction kinetics. The incorporation of Mo also induced a redistribution of the electronic structure around the Zn active sites, boosting the intrinsic conductivity of the catalyst and reducing the electrochemical diffusion resistance during the redox processes. The synergistic design of Mo-Zn active sites further enhanced the chemical adsorption of lithium polysulfides and catalytic conversion of sulfur species. As a result, Li-S batteries with Mo-ZIF-8-modified separators exhibit minimal capacity decay (0.04% per cycle) over 1000 cycles at 1C. Under a high sulfur loading of 5.8 mg cm-2, they achieve an areal capacity of 5.8 mAh cm-2, retaining 5.0 mAh cm-2 after 100 cycles. These findings highlight the potential of bimetallic metal-organic framework (MOF) catalysts in advancing the Li-S battery performance.

N-doped carbon nanotubes and CoS@NC composites as a multifunctional separator modifier for advanced lithium-sulfur batteries

Lithium-sulfur batteries (LSBs), with their high theoretical energy density and specific capacity, are considered optimal candidates for next-generation energy storage systems. However, significant challenges remain in their cycle life and efficiency for practical applications, primarily due to the shuttle effect of lithium polysulfides (LiPSs) and the poor electrical conductivity of sulfur materials. The key to addressing these challenges lies in designing materials with excellent dispersion, good electrical conductivity, and high catalytic activity. In this work, we have designed and successfully synthesized a unique structural material consisting of in-situ grown cobalt sulfide nanoparticles embedded in zeolite imidazolate frameworks (ZIFs), which are derived from N-doped carbon wrapped around polypyrrole-derived N-doped carbon nanotubes (CoS@NC/NCNT). This design effectively mitigates the shuttle effect of lithium polysulfides (LiPSs) and enhances the conductivity of the material. As a result, batteries with CoS@NC/NCNT-modified separators achieved a high specific discharge capacity of 1518 mAh g-1 at 0.1 C. This work provides a reliable design strategy for synthesizing N-doped carbon nanotube/high-activity transition metal sulfide composite materials and opens new avenues for enhancing the modification and separation of high-performance lithium-sulfur batteries (LSBs).

Versatile Separators Toward Advanced Lithium-Sulfur Batteries: Status, Recent Progress, Challenges and Perspective

Lithium-sulfur batteries (LSBs) have recently gained extensive attention due to their high energy density, low cost, and environmental friendliness. However, serious shuttle effect and uncontrolled growth of lithium dendrites restrict them from further commercial applications. As "the third electrode", functional separators are of equal significance as both anodes and cathodes in LSBs. The challenges mentioned above are effectively addressed with rational design and optimization in separators, thereby enhancing their reversible capacities and cycle stability. The review discusses the status/operation mechanism of functional separators, then primarily focuses on recent research progress in versatile separators with purposeful modifications for LSBs, and summarizes the methods and characteristics of separator modification, including heterojunction engineering, single atoms, quantum dots, and defect engineering. From the perspective of the anodes, distinct methods to inhibit the growth of lithium dendrites by modifying the separator are discussed. Modifying the separators with flame retardant materials or choosing a solid electrolyte is expected to improve the safety of LSBs. Besides, in-situ techniques and theoretical simulation calculations are proposed to advance LSBs. Finally, future challenges and prospects of separator modifications for next-generation LSBs are highlighted. We believe that the review will be enormously essential to the practical development of advanced LSBs.

Preparation of a lithium-sulfur battery diaphragm catalyst and its battery performance

Lithium-sulfur batteries (LSBs) with metal lithium as the anode and elemental sulfur as the cathode active materials have attracted extensive attention due to their high theoretical specific capacity (1675 mA h g-1), high theoretical energy density (2600 W h kg-1), low cost, and environmental friendliness. However, the discharge intermediate lithium polysulfide undergoes a shuttle side reaction between the two electrodes, resulting in low utilization of the active substances. This limits the capacity and cycle life of LSBs and further delays their commercial development. However, the number of active sites and electron transport capacity of such catalysts still do not meet the practical development needs of lithium-sulfur batteries. In view of these issues, this paper focuses on a zinc-cobalt compound catalyst, modifying it through heteroatom doping, bimetallic synergistic effect and heterogeneous structure design to enhance the performance of LSBs as a separator modification material. A carbon shell-supported boron-doped ZnS/CoS2 heterojunction catalytic material (B-ZnS/CoS2@CS) was prepared, and its performance in lithium-sulfur batteries was evaluated. A carbon substrate (CS) was prepared by pyrolysis of sodium citrate, and the boron-doped ZnS/CoS2 heterojunction catalyst was formed on the CS using a one-step solvothermal method. The unique heterogeneous interface provides numerous active sites for the adsorption and catalysis of polysulfides. The uniformly doped, electron-deficient boron further enhances the Lewis acidity of the ZnS/CoS2 heterojunction, while also regulating electron transport. The B-ZnS/CoS2@CS catalyst effectively inhibits the diffusion of LiPS anions by utilizing additional lone-pair electrons. The lithium-sulfur battery using the catalyst-modified separator achieves a high specific capacity of 1241 mA h g-1 at a current density of 0.2C and retains a specific capacity of 384.2 mA h g-1 at 6.0C. In summary, B-ZnS/CoS2@CS heterojunction catalysts were prepared through boron doping modification. They can promote the conversion of polysulfides and effectively inhibit the shuttle effect. The findings provide valuable insights for the future modification and preparation of lithium-sulfur battery catalysts.

Juice Vesicles Bioreactors Technology for Constructing Advanced Carbon-Based Energy Storage

The construction of high-quality carbon-based energy materials through biotechnology has always been an eager goal of the scientific community. Herein, juice vesicles bioreactors (JVBs) bio-technology based on hesperidium (e.g., pomelo, waxberry, oranges) is first reported for preparation of carbon-based composites with controllable components, adjustable morphologies, and sizes. JVBs serve as miniature reaction vessels that enable sophisticated confined chemical reactions to take place, ultimately resulting in the formations of complex carbon composites. The newly developed approach is highly versatile and can be compatible with a wide range of materials including metals, alloys, and metal compounds. The growth and self-assembly mechanisms of carbon composites via JVBs are explained. For illustration, NiCo alloy nanoparticles are successfully in situ implanted into pomelo vesicles crosslinked carbon (PCC) by JVBs, and their applications as sulfur/carbon cathodes for lithium-sulfur batteries are explored. The well-designed PCC/NiCo-S electrode exhibits superior high-rate properties and enhanced long-term stability. Synergistic reinforcement mechanisms on transportation of ions/electrons of interface reactions and catalytic conversion of lithium polysulfides arising from metal alloy and carbon architecture are proposed with the aid of DFT calculations. The research provides a novel biosynthetic route to rational design and fabrication of carbon composites for advanced energy storage.

Boosting Polysulfide Redox Kinetics by Temperature-Induced Metal-Insulator Transition Effect of Tungsten-Doped Vanadium Dioxide for High-Temperature Lithium-Sulfur Batteries

The practical application of Li-S batteries is still severely restricted by poor cyclic performance caused by the intrinsic polysulfides shuttle effect, which is even more severe under the high-temperature condition owing to the inevitable increase of polysulfides' solubility and diffusion rate. Herein, tungsten-doped vanadium dioxide (W-VO2 ) micro-flowers are employed with first-order metal-insulator phase transition (MIT) property as a robust and multifunctional modification layer to hamper the shuttle effect and simultaneously improve the thermotolerance of the common separator. Tungsten doping significantly reduces the transition temperature from 68 to 35 °C of vanadium dioxide, which renders the W-VO2 easier to turn from the insulating monoclinic phase into the metallic rutile phase. The systematic experiments and theoretical analysis demonstrate that the temperature-induced in-suit MIT property endows the W-VO2 catalyst with strong chemisorption against polysulfides, low energy barrier for liquid-to-solid conversion, and outstanding diffusion kinetics of Li-ion under high temperatures. Benefiting from these advantages, the Li-S batteries with W-VO2 modified separator exhibit significantly improved rate and long-term cyclic performance under 50 °C. Remarkably, even at an elevated temperature (80 °C), they still exhibit superior electrochemical performance. This work opens a rewarding avenue to use phase-changing materials for high-temperature Li-S batteries.

Vanadium-doped graphitic carbon nitride for high performance lithium-sulfur batteries

To promote polysulfide conversion in lithium sulfur batteries (LSB) and alleviate the shuttle effect, we designed and fabricated a novel catalyst of vanadium-doped graphite phase carbon nitride with nitrogen defects (V@gC3N4-ND) and high vanadium loading (3.46 at%) by defect engineering and two-step pyrolysis. Employing a V@gC3N4-ND modified separator, the LSB yielded capacities of 934 mA h g-1 at 1C and 404 mA h g-1 at 4C; the former was retained by 61% and 45% after 500 and 1000 cycles, respectively. In particular, the initial capacity of the battery reached 969 mA h g-1 at a sulfur loading of 10.0 mg cm-2. This work provides a facile route to the preparation of high-loading vanadium active site catalysts with nitrogen defects in the support, which are promising for high performance LSB applications.