Melt-diffusion Method Research Articles

Exploration of Optimization Strategies for Locking Sulfur in 2D Layered/Polymer-Enveloped Cathode Composite for High Power Li-S Batteries.

In Lithium sulfur (Li-S) batteries the sulfur host material is a significant area of research that could impart enhanced conductivity and alleviate the shuttling of polysulfides. In the present study, graphene oxide- sulfur, GO-S was synthesized in melt diffusion method by exploring the two different strategies: Ambient (G2-M) and Inert (G2-T) conditions. Within the cathode, efficient storage of S with sufficient space in GO interlayers was outperformed by G2-T method. Further with PEDOT nanostructures enveloped by oxidative polymerisation proves to be a robust conductive layer and an adsorbing agent. It is evidenced physicochemically by XRD, FTIR, TGA, HR-SEM. Moreover, in addition to the supporting studies, high binding energies of 168.3 and 169.5 eV confirms the superior performance of PEDOT/GO-S (G3-T) as most suitable cathode within the system. The electrochemical behaviour of G3-T possess very low cell impedance with an excellent cyclic reversibility in CV during (de)lithiation process. At 0.1 C, an initial discharge capacity of 868 mAh g-1 has been achieved confirming a high catalytic activity with a low polarisation potential of (ΔE=0.25) inducing fast reaction kinetics. Thus potential locking of sulfur under inert condition is explored with a proven OCV of 2.3 V with red LED glow.

High performance all-solid-state Li–Se battery based on selenium loaded on Ti3C2 MXene cathode

Selenium has high theoretical volumetric capacity of 3253 mAh cm−3 and acceptable electronic conductivity of 1 × 10−5 S m−1, which is considered as a potential alternative to sulfur cathode for all-solid-state rechargeable batteries with high energy density. However, the development of all-solid-state Li–Se batteries (ASSLSBs) are hindered by sluggish kinetics and poor cycling life. In this work, trigonal Se nanocrystallines are homogenously distributed in the interspace and on the surface of MXene layers (denoted as Se@MXene composite) by a novel melt-diffusion method. ASSLSBs based on this Se@MXene composite cathode exhibit large specific capacity of 632 mAh g−1 at 0.05 A g−1, high-rate capability over 4 A g−1, and excellent cycling stability over 300 cycles at 1 A g−1. The ex-situ analytical techniques demonstrate that the excellent electrochemical performance of Se@MXene cathode largely arises from structural stability with the assistance of conductive MXene and reversible redox behavior between Li2Se and Se during the repeating charge/discharge process. Our study points out the potential of material design of Se cathode based on conducting 2D materials with good electrochemical behavior, which may accelerate the practicability of ASSLSBs.

Valorisation of argan seeds: Production of cathode material for high-performance lithium-sulphur batteries

Porous carbon is considered a key factor in mitigating the shuttle effect, which remains one of the biggest challenges to developing lithium-sulphur (Li-S) batteries. Reusing agricultural waste as a raw material is a sustainable and eco-friendly source for producing carbon. Here we propose fabricating carbonaceous material from argan shells by simple pyrolysis. The synthesis of argan shell carbon (ASC) involved a straightforward approach with non-activating pyrolysis. Carbonisation at three different temperatures was employed to obtain ASC. A high sulphur loading of 70 % was incorporated into the ASC using the melt diffusion method, resulting in the formation of three different sulphur‑carbon composites (ASC@S). All of the prepared materials were characterised and evaluated as cathodes for Li-S batteries. The electrochemical performance of composites was compared, and ASC-800@S was identified as the best-performing composite. Thanks to its excellent properties this material combines (surface area, pore volume, conductivity), it delivers a capacity of 674 mAh g−1 and 513 mAh g−1 after 500 cycles at C/10 and 1C rate, respectively. This work provides a simple, economical, and effective strategy for preparing advanced carbonaceous sulphur host materials and significant improvement of Li-S cell performance.

Orange peel derived hierarchical porous carbon/sulfur composite cathode material for Li–S battery

A hierarchical porous carbon (HPC) structure was developed from the waste orange peel using KOH as an activating agent. In HPC, the carbon has interconnected hierarchical pores size of which lies between 2 nm and 5 μm. HPC/S composite was prepared by melt-diffusion method and analysed for electrochemical performance. HPC/S exhibits a high initial discharge capacity of 870 mAhg−1 at 0.2C and 734 mAhg−1 at 0.4C. The Carbon-black (CB)/Sulfur (S) composite was also prepared and characterized. A comparative study was done with the CB/S composite, which shows poor cyclability and a discharge capacity of 332 mAhg−1 at 0.2C rate considering 1C = 1672 mAhg−1. Sulfur confinement in the HPC structure leads to superior electrochemical performance of the HPC/S composite ensuring a promising cathode material.

Alleviating the Polysulfide Shuttle Effect by Optimization of 3D Flower-Shaped Vanadium Dioxide for Lithium-Sulfur Batteries

With the rapid development of portable devices and Energy Storage Systems (ESS), secondary batteries with high energy density and high capacity are in great demand. Among various candidates, Lithium-sulfur (Li-S) batteries have been considered for next-generation energy devices given their high theoretical capacity (1675 mAh g<sup>-1</sup>) and energy density (2500 Wh kg<sup>-1</sup>). However, the commercialization of Li-S batteries faces challenges due to sulfur’s low electrical conductivity and the shuttle effect, caused by the dissolution of lithium polysulfide intermediates in the electrolyte during the charge-discharge process. Herein, to resolve these problems, we report the fabrication of a vanadium dioxide (VO<sub>2</sub>) composite via a simple hydrothermal method and optimize the structure of VO<sub>2</sub> for constructing an effective Multi-Walled Carbon Nano Tube (MWCNT) and 3D flower-shaped VO<sub>2</sub> (MWCNT@VO<sub>2</sub>) binary sulfur host by a simple melt diffusion method. In particular, the polar VO<sub>2</sub> composite not only physically absorbs the soluble lithium polysulfides but also has strong chemical bonds with a higher affinity for lithium polysulfides, which act as a catalyst, enhancing electrochemical reversibility. Additionally, MWCNT improves sulfur’s poor electrical conductivity and buffers volume expansion during cycling. The designed S-MWCNT@VO<sub>2</sub> electrode also exhibits better capacity retention and cycling performance than a bare S-MWCNT electrode as a lithium polysulfide reservoir.

3D Electrode architecture of high surface area carbon-sulfur composite as high energy density cathode for lithium-sulfur battery

High-performance lithium-sulfur (Li-S) battery is a potential candidate for next-generation energy storage systems to mitigate the ever-rising energy demand. The low cost of sulfur, eco-friendliness, and high energy density compared to the emerging LIBs (450 Wh kg−1 for Li-S batteries vs. 150–250 Wh kg−1 for LIBs) inspires the research on Li–S technology. In this work, carbon fiber-based free-standing electrodes are fabricated using a high surface area carbon-sulfur (HSAC-S) composite synthesized by the melt-diffusion method. The porous carbon host facilitates high sulfur loading in the void spaces and benefits the electrolyte infiltration and Li-ion diffusivity. Electrochemistry reveals that HSAC-S@CF exhibits an enhanced discharge capacity of 1000 mAh g−1 (750 mAh g−1 for HSAC-S@Al) in the 2nd cycle and maintains 620 mAh g−1 capacity till the 100th cycle. In comparison, HSAC-S@Al delivers 350 mAh g−1 capacity at the 80th cycle at a current density of 100 mA g−1. Besides, at 200 mA g−1, the free-standing electrode HSAC-S@CF delivers an initial capacity of 600 mAh g−1 (498 mAh g−1 HSAC-S@Al) and retains 497 mAh g−1 till the 100th cycle with 83 % capacity retention (60 % HSAC-S@Al). HSAC-S@CF displays good C-rate performance at a higher current density of 1 A g−1 (408 mAh g−1) and 1.5 A g−1 (346 mAh g−1). The conductive CF backbone provides mechanical stability, accommodates volume changes, and reduces particle agglomeration. The internal void spaces of the CF matrix act as a reservoir for polysulfides and minimize the shuttling effect. This work represents an effective cathode modification approach to understand the impact of high surface area carbon additives on free-standing 3D electrode architecture and its interaction with sulfur for improving the capacity and cycling stability in Li-S batteries.

Impact of composite preparation method on the electrochemical performance of lithium–sulfur batteries

Due to their lower prices, higher energy density, and more environmentally friendly active components, Lithium–Sulfur batteries will soon compete with the current Lithium-ion batteries. However, issues persist that hinder this implementation, such as the poor conductivity of S and sluggish kinetics due to the polysulfide shuttle, among others. The most common strategy to solve these problems is the use of carbon@sulfur (C@S) composites as the cathode of the battery. Composite preparation is a key step for the performance of the electrochemical cell, and yet few studies are focused on this stage. Herein, C@S composites have been prepared following the four most common synthesis methods (melt diffusion; ball milling; dissolution–crystallization; chemical deposition), and in-depth physical-chemical characterization studies and electrochemical analysis have been carried out with these composites in Li–S cells. Properties such as sulfur size, the structural arrangement of the carbon and the type of S infiltration in the matrix have been found to be key parameters in the performance of the composite as a positive electrode in the battery. The comparative analysis shows that the melt diffusion method gives the composite the ideal properties for superior electrochemical performance in tests under different current densities.

Turning yerba mate waste into high-performance lithium–sulfur battery cathodes

In this study, a non-activated carbon (YMCC) derived from waste yerba mate was examined as a matrix for the development of a carbon‑sulfur composite cathode (YMC-C@S). The carbonaceous material is produced through a simple process of pyrolyzing extracted cellulose from residual yerba mate, avoiding costly and complex stages of chemical activation or additional purification. Due to its high carbon content and mesoporous structure, YMC-C can serve as an effective host for sulfur. After adding 70 % sulfur via the melt diffusion method, the YMC-C@S composite shown a remarkable initial capacity of 1678 mAh gS−1 as a cathode material, along with high reversible capacity at a low charge/discharge rate. Additionally, even when subjected to an increased C-rate during long cycling, discharge capacities at 1C of 777 mAh gS−1 and 674 mAh gS−1 after 165 cycles demonstrate good rate capability. When the cycling protocol is optimized, the YMC-C@S composite exhibits very low loss of capacity per cycle, even when using fast charge stages. The efficacy of YMC-C as an efficient cathode material in LSB is confirmed by the positive results of a self-discharge test conducted over a period of 7.5 months.

A high-performance tellurium-sulfur cathode in carbonate-based electrolytes

The current technology of lithium-sulfur (Li-S) batteries is hindered by the sluggish kinetics and low utilization of sulfur (S) due to its electronic insulating nature. Herein, tellurium (Te) is introduced into S by forming TexSy solid solutions to reshape Li-S chemistry and facilitate the solid-state conversion of the cathode in carbonate-based electrolytes. Numerical calculations suggest a more delocalized charge-density difference around the Te atoms in Li16Te1S7 compared to site-equivalent S atoms in Li2S, thus enabling lower energy barriers throughout the Li migration pathway. Mesoporous carbon Ketjenblack (KB) is employed to confine TexSy materials via a melt diffusion method. By tuning the molar ratio of Te/S, it is found that the Te1S7/KB cathode delivers the highest reversible capacity of 1306.7 mAh g−1 at 0.1 A g−1 and maintains a capacity of 959.8 mAh g−1 after 400 cycles at 1 A g−1. Kinetics analysis reveals that the introduction of Te accelerates Li-ion diffusion and decreases reaction resistance during the charge/discharge process, thus enabling fast and reversible redox conversion. Moreover, the Te-containing solid electrolyte layer on the electrode surface is generated to prevent the loss of Te1S7 active materials. These encouraging findings suggest that the heteroatomic Te1S7/KB is a promising cathode to achieve long cycle life and high energy density for Li-S batteries.

Water Kefir Grains-Microbial Biomass Source for Carbonaceous Materials Used as Sulfur-Host Cathode in Li-S Batteries.

Nowadays, the use of biomass to produce cathode materials for lithium-sulfur (Li-S) batteries is an excellent alternative due to its numerous advantages. Generally, biomass-derived materials are abundant, and their production processes are environmentally friendly, inexpensive, safe, and easily scalable. Herein, a novel biomass-derived material was used as the cathode material in Li-S batteries. The synthesis of the new carbonaceous materials by simple carbonization and washing of water kefir grains, i.e., a mixed culture of micro-organisms, is reported. The carbonaceous materials were characterized morphologically, texturally and chemically by using scanning electron microscopy, N2 adsorption-desorption, thermogravimetric analysis, X-ray diffraction, and both Raman and X-ray photoelectron spectroscopy. After sulfur infiltration using the melt diffusion method, a high sulfur content of ~70% was achieved. Results demonstrated that the cell fitted with a cathode prepared following a washing step with distilled water after carbonization of the water kefir grains only, i.e., not subjected to any chemical activation, achieved good electrochemical performance at 0.1 C. The cell reached capacity values of 1019 and 500 mAh g-1 sulfur for the first cycle and after 200 cycles, respectively, at a high mass loading of 2.5 mgS cm-2. Finally, a mass loading study was carried out.

N/S co-doped biomass-based porous carbon surface-embedded small-molecule selenium as cathode for high-performance K-Se batteries

Potassium-selenium (K-Se) batteries, as an emerging energy storage system, have attracted extensive attention due to their high energy density and abundance of potassium in the earth's crust. However, similar to chalcogenide batteries, K-Se batteries also face problems such as severe pulverization of Se during the insertion/extraction of K+ ions, and the shuttle effect generated by polyselenides. In this work, small-molecule selenium was encapsulated in the natural nanoscale pores of N/S co-doped walnut shell-derived biomass carbon by a two-step carbonization method and a melt-diffusion method. The encapsulated small-molecule selenium can effectively cope with the volume change during cycling, and the abundant heteroatom doping greatly inhibits the generation of the shuttle effect. The assembled battery has a stable capacity of 581.8 mAh g−1 after 200 cycles at a current density of 0.2C and a capacity of 211.7 mAh g−1 after 3500 cycles at a current density of 10C. This study provides a rational design for K-Se battery cathode for energy storage with high energy density and long cycle life.

Novel One-Dimensional Nanofiber MnSe/CMK-3 High-Performance Cathode Material for Aluminum Batteries.

Transition metal selenides have shown outstanding performance as cathode materials for aluminum-ion batteries and have thus become a popular choice for cathode materials. Herein, Mn-based carbon fibers (Mn/CNFs) were first synthesized by electrospinning as a precursor, and then MnSe composites were prepared by a melt-diffusion method. However, due to polyselenides and selenides being generated during electrochemical reactions, the cycling stability of MnSe cathode materials is poor. After 200 cycles, the discharge specific capacity is only 176 mA h/g. To suppress the shuttle effect of selenides and polyselenides, a CMK-3-modified separator was used instead of a glass fiber separator. Compared with MnSe-800, the replaced MnSe-800/CMK-3 has a great capacity improvement; the initial discharge specific capacity is 1029.85 mA h/g, which after 3000 cycles, still remains at 297.84 mA h/g. The soft pack battery can still light up the LED normally under different degrees of folding, which proves the application of this material in wearable devices. This work provides a new way to improve the performance of transition metal selenides.

Microalgae Derived Nano Carbon-Sulfur Composite Cathodes for Sulfur Batteries

Nano porous carbon and sulfur composites were prepared using microalgae as carbon precorsors by the melt diffusion method. Initially, nano porous carbon materials were synthesized by the hydrothermal method, followed by the chemical activation method with and without ferrocene as catalyst. Therefore, we have two types of porous carbon samples, the first sample was denoted as NPC (preparation with ferrocene) and the other one is PC (preparation without ferrocene) Brunauer–Emmett–Teller analysis indicated that the surface area and total pore volume (at P/P o) of NPC samples were lower than those of the PC samples. The NPC and PC samples were then mixed with sulfur to obtain NPC-S and PC-S composites. Those composites were then utilized as cathode materials for Lithium Sulfur Battery. The NPC-S samples with a sulfur content of 76.7 wt.% exhibited a higher initial specific capacity and better cycle retention than those of the PC-S. Optimized sulfur content for NPC-S was investigated to handle the shuttle effect problem. improved electrochemical performance is attributed to the increased conductivity of the NPC-S samples and optimized sulfur loading content, which effectively confined lithium polysulfide intermediates.

S-sphere/C/MoS2 composite for high-performance Lithium–Sulfur batteries

With the development of energy storage systems, Lithium–Sulfur (Li–S) batteries represent an ideal choice due to extremely high theoretical specific capacity (1675 mAh/g−1) and energy density (2500 Wh/kg−1) of Sulfur cathode. However, it is a challenge to solve the electroconductibility of Sulfur, shuttle effect of polysulfide and volume expansion. Although tremendous works have been carried out to improve the capacity, the practical application of Li–S batteries is still hindered by low electroconductibility of Sulfur, poor cycle life and low rate performances. Herein, S-sphere/C/MoS2 composite was prepared by the melt diffusion method for the nano-sulfur host. In comparison with the large particles sublimate Sulfur, nano-sulfur particles can shorten the diffusion path of ions and facilitate the smooth diffusion of Li+ into the interior of Sulfur at high discharging current densities. Therefore, the formation of insulating Li2S2 and Li2S is delayed. Moreover, the Few-layered MoS2 can be used to achieve chemical adsorption with Lithium polysulfide (LiPS) and Carbon spheres has good electronic conductivity, thus the rate performance and the cyclic capability of Li–S batteries have been improved. The S-sphere/C/MoS2 composite exhibits an initial discharging capacity of 1016.3 mAh/g−1 at 0.1 C, and a high capacity of 753 mAh/g−1 at 1 C with a low fade rate of 0.211%. These indicate that the S-sphere/C/MoS2 composite has good electrochemical performance and is expected to be a candidate electrode for Li–S batteries industrialization in the future.

Electrochemical Performance of Carbon-Rich Silicon Carbonitride Ceramic as Support for Sulfur Cathode in Lithium Sulfur Battery

As a promising matrix material for anchoring sulfur in the cathode for lithium-sulfur (Li-S) batteries, porous conducting supports have gained much attention. In this work, sulfur-containing C-rich SiCN composites are processed from silicon carbonitride (SiCN) ceramics, synthesized at temperatures from 800 to 1100 °C. To embed sulfur in the porous SiCN matrix, an easy and scalable procedure, denoted as melting-diffusion method, is applied. Accordingly, sulfur is infiltrated under solvothermal conditions at 155 °C into pores of carbon-rich silicon carbonitride (C-rich SiCN). The impact of the initial porosity and microstructure of the SiCN ceramics on the electrochemical performance of the synthesized SiCN-sulfur (SiCN-S) composites is analysed and discussed. A combination of the mesoporous character of SiCN and presence of a disordered free carbon phase makes the electrochemical performance of the SiCN matrix obtained at 900 °C superior to that of SiCN synthesized at lower and higher temperatures. A capacity value of more than 195 mAh/g over 50 cycles at a high sulfur content of 66 wt.% is achieved.

Covalent encapsulation of sulfur in a graphene/N-doped carbon host for enhanced sodium-sulfur batteries

Application of emerging room temperature sodium-sulfur (RT Na-S) battery is restrained by the poor conductivity, volume expansion of sulfur cathode and the shuttle effect of soluble polysulfides in electrolytes. Herein, an N-doped two-dimensional (2D) carbon host was derived from the polydopamine coated graphene for sulfur storage. Different from the conventional used melt-diffusion method to integrate sulfur on graphene layer physically, we employed a vapor-infiltration method to realize the homogenous incorporation of sulfur in the graphene-based host via C-Sx-C bond. A polydopamine-derived N-doped carbon layer was further coated on graphene to confine the high-temperature-induced gas-phase sulfur, which effectively increase the covalently bonded sulfur content in the host. Moreover, based on Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) measurement, the C-S bonds are mainly formed beside N-doped carbon, being well explained by the stronger interaction between N-doped carbon and S4 (sulfur vapor) than that of pure carbon from density functional theory (DFT) calculation results. When tested as a cathode for RT Na-S battery, the obtained N-doped graphene/sulfur cathode shows superior cycle stability.

3D Interconnected N-doped Carbon/Sulfur Derived from Organic-inorganic Hybrid ZnS Superlattice Nanorods for High-performance Lithium-sulfur Batteries

Abstract S/C composites in lithium-sulfur (Li-S) batteries are conventionally prepared by melt-diffusion method, by which S is difficult to uniformly distribute into matrix. Herein, a novel 3D N-doped carbon/sulfur (S/CNx) composite is fabricated by a simple in situ oxidizing reaction, which delivers a specific capacity of 830 mA h g−1 at 1 C after 100 cycles with 98.8% of capacity retention. The unique synthetic strategy in this work could provide a new thought for designing high performance Li-S batteries.

Vacuum-assisted sulfur crystallization process to improve the electrochemical performance of S@PC composite cathode materials for Li–S batteries

The melt-diffusion method and vapor-phase infusion method are high-frequency approach to composite sulfur to porous materials, but in these methods the crystallization process of sulfur occurs naturally and cannot be controlled. In this work, we prepared the S@PC composites via a facile dissolution-crystallization method and vacuum was used to assist the sulfur crystallization process. Comparing the composites prepared under vacuum and atmosphere, the results show that crystallized sulfur obtains a finer particle size under vacuum condition, which leads to an obviously increase in the initial discharge capacity, rate performance and cycle stability of the battery. The improvement of electrochemical performance is attributed to the fact that the finer sulfur provides quantities interface contact with conductor matrix and sufficient reaction sites between the electrode and electrolyte, accelerating charge transfer and the electrolyte diffusion. This research provides a technical support for the simplified and controllable preparation of cathode materials for lithium-sulfur batteries.

PPy-constructed core–shell structures from MOFs for confining lithium polysulfides

Core–shell structured MIL-96-Al composites are prepared through a melt-diffusion method followed by a water-phase polymerization process. The composites can strongly confine lithium polysulfides in a cathode.

Encapsulation of selenium in MOF-derived N,O-codoped porous flower-like carbon host for Na-Se batteries

Na-Se batteries have their drawbacks such as large volumetric expansion and shuttle effect related to generation of soluble sodium polyselenides. To address these issues, a nitrogen and oxygen codoped flower-like porous carbon host is derived from a Ni-based metal–organic framework (MOF) for Se storage. The use of 4,4′-oxybisbenzoic acid and 4,4′-dimethyl-2,2′-bipyridyl ligands ensure the in-situ doping of the carbon host with oxygen and nitrogen upon carbonization of MOF, which increases its polarity and restricts the diffusion of selenium. Highly porous microflower-like carbon morphology provides sufficient space for Se storage. To avoid undesirable aggregation of Se particles which happens when using conventional melt-diffusion method, we employed a vapor-infiltration method for Se loading, which ensures the homogeneous dispersion of selenium and high utilization of pores in the carbon host. Density functional theory calculations confirmed that the increased polarity of the carbon host due to N,O codoping promotes the adsorption of polyselenides. When tested as a cathode for sodium-selenium battery, the optimized carbon/selenium composite shows an excellent electrochemical performance.