Cathode For Lithium-sulfur Batteries Research Articles

Sulfur-rich polymer/Ketjen Black composites as lithium-sulfur battery cathode with high cycling stability

Lithium-sulfur (Li-S) battery is considered as one of the most promising energy storage devices due to its exceptional energy density. However, its development is largely hampered by the shuttle effect of lithium polysulfide and the sluggish electrochemical kinetics of sulfur cathode. In this study, a novel sulfur-rich polymer is synthesized through the inverse vulcanization of sulfur with 2,4,6,8-tetravinyl-2,4,6,8-tetramethylcyclotetrasiloxane (TVTCSi) and used as cathode material for Li-S batteries, which can effectively immobilize the lithium polysulfides through covalent bonds to impede its shuttling, leading to marked improvement in the cycling performance of the batteries. Furtherly, with the addition of Ketjen Black, the resulting composite cathode exhibited faster electrochemical reaction kinetics and higher cycling stability, which could deliver a reversible discharge capacity of 652 mAh g−1 after 500 cycles at a high current density of 0.5 C,0.5C with quite a low capacity decay rate of only 0.037% per cycle, which indicates broad perspectives of sulfur-rich polymer/Ketjen Black composite as cathode material in lithium-sulfur battery.

Uncovering the solid-phase conversion mechanism via a new range of organosulfur polymer composite cathodes for lithium-sulfur batteries

The sulfur cathodes operating via solid phase conversion of sulfur have natural advantages in suppressing polysulfide dissolution and lowering the electrolyte dosage, and thus realizing significant improvements in both cycle life and energy density. To realize an ideal solid-phase conversion of sulfur, a deep understanding of the regulation path of reaction mechanism and a corresponding intentional material and/or cathode design are highly essential. Herein, via covalently fixing of sulfur onto the triallyl isocyanurate, a series of S-triallyl isocyanurate organosulfur polymer composites (STIs) are developed. Relationship between the structure and the electrochemical conversion behavior of STIs is systematically investigated. It is found that the structure of STIs varies with the synthetic temperature, and correspondingly the electrochemical redox of sulfur can be controlled from conventional “solid–liquid–solid” conversion to the “solid–solid” one. Among the STI series, the STI-5 composite realizes an ideal solid-phase conversion and demonstrates great potential for building a Li–S battery with high-energy density and long-cycle-life: it realizes stable cycling over 1000 cycles in carbonate electrolyte, with a degradation rate of 0.053% per cycle; the corresponding pouch cell shows almost no capacity decay for 125 cycles under the conditions of high sulfur loading (4.5 mg cm−2) and lean electrolyte (8 μL mgs−1). In addition, the tailoring strategy of STI can also apply to other precursors with allyl functional groups to develop new organosulfur polymers for “solid–solid” sulfur cathodes. The vulcanized triallyl phosphate (STP) and triallylamine (STA) both show great lithium storage potential. This strategy successfully develops a new family of organosulfur polymers as cathodes for Li–S batteries via solid-phase conversion of sulfur, and brings insights to the mechanism study in Li–S batteries.

Establishing Transition Metal Phosphides as Effective Sulfur Hosts in Lithium-Sulfur Batteries through the Triple Effect of "Confinement-Adsorption-Catalysis".

Structurally optimized transition metal phosphides are identified as a promising avenue for the commercialization of lithium-sulfur (Li-S) batteries. In this study, a CoP nanoparticle-doped hollow ordered mesoporous carbon sphere (CoP-OMCS) is developed as a S host with a "Confinement-Adsorption-Catalysis" triple effect for Li-S batteries. The Li-S batteries with CoP-OMCS/S cathode demonstrate excellent performance, delivering a discharge capacity of 1148 mAh g-1 at 0.5 C and good cycling stability with a low long-cycle capacity decay rate of 0.059% per cycle. Even at a high current density of 2 C after 200 cycles, a high specific discharge capacity of 524 mAh g-1 is maintained. Moreover, a reversible areal capacity of 6.56 mAh cm-2 is achieved after 100 cycles at 0.2 C, despite a high S loading of 6.8 mg cm-2 . Density functional theory (DFT) calculations show that CoP exhibits enhanced adsorption capacity for sulfur-containing substances. Additionally, the optimized electronic structure of CoP significantly reduces the energy barrier during the conversion of Li2 S4 (L) to Li2 S2 (S). In summary, this work provides a promising approach to optimize transition metal phosphide materials structurally and design cathodes for Li-S batteries.

Structural Design of Electrocatalyst-Decorated MXenes on Sulfur Spheres for Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) are known to be potential next-generation energy storage devices. Recently, our group reported an LSB cathode made using sulfur spheres that has been spherically templated by MXene nanosheets decorated with CoSe2 nanoparticles, forming a "loose-templating" configuration. It was postulated that the minimal restacking of the outer nanoparticle-decorated MXene layer helps to enable facile ionic transport. However, as the nanosheets do not adhere conformally to the internal sphere's surface, such a configuration can be controversial, thus requiring a more systematic understanding. In this work, we report and quantify for the first time the independent and dependent variables involved in this morphology, allowing us to identify that having smaller nanoparticles resulted in better Li+ ion transport and enhanced electrochemical performances. The optimized cathode structure exhibited an initial specific capacity of 1274 mAh/g and a 0.06% decay rate per cycle at 0.5 C over 1000 cycles in LSBs.

Solvation Structure of Conjugated Organosulfur Polymers for Lithium–Sulfur Battery Cathodes

Solvation Structure of Conjugated Organosulfur Polymers for Lithium–Sulfur Battery Cathodes

Synergistic Effect of Zn–Co Bimetallic Selenide Composites for Lithium–Sulfur Battery

Compared with monometallic selenides, heterogeneous bimetallic selenides have rich phase boundaries and superior electrical conductivity. ZnSe/CoSe2 composites were prepared by introducing Zn metal and using ZIF-8/67 as the precursor through the synergistic effect between Zn and Co after selenification. The electrocatalytic conversion of polysulfide is accelerated by ZnSe through chemical adsorption and the catalytic effect. The conductive CoSe2 surface provides a rapid diffusion path for lithium ions, accelerating the conversion of the polysulfide. On the basis of their individual strengths, ZnSe and CoSe2 can jointly promote the smooth adsorptive–diffuse–catalytic conversion process of polysulfide and induce the growth of lithium sulfide around its heterogeneous interface, thus enhancing the electrochemical performance of the lithium–sulfur battery cathode materials. The ZnSe/CoSe2–S electrode, at the optimal Zn-to-Co ratio of 1:1, has a 790.06 mAh g−1 initial specific capacity at 0.2 C and excellent cycling stability at 1 C. After 300 cycles, the final capacity is 300.85 mAh g−1, and the capacity retention rate reaches 82.71%.

Enhanced performance of lithium-sulfur battery cathode via composition optimization using modified MWCNTs as a conductive material and poly (acrylic acid) as a binder

Lithium–sulfur (Li–S) batteries are promising candidates for the next-generation energy storage devices for portable electronics and electric vehicles owing to their low-cost, high-energy density, and minimal environmental impact. However, low sulfur utilization and short life-cycle limit their performance and commercialization. Herein, Li–S battery cathodes were prepared by blending different proportions of active material sulfur (S) with modified multiwall carbon nanotubes (MWCNTs) as a conductive material, and poly (acrylic acid) (PAA) as a binder to optimize the electrode composition. Specially, we found that the oxidation of MWCNT improves not only their dispersion in water-based slurry during the electrode preparation but also improves the adsorption of lithium polysulfides during the electrochemical reaction. Cathode prepared with a 5:4:1 wt ratio of S: oxidized MWCNT: PAA shows the uniform dispersion of cathode slurry and exhibits the highest discharge capacity of ∼480 mA h g−1 when compared to other mixing ratios. This work demonstrates the feasibility of redox mediation to reinforce the electron accessibility with appropriately loaded sulfur on MWCNT.

WO2 nanoparticle anchored hollow carbon spheres enhanced performance of lithium-sulfur battery

Lithium–sulfur battery has drawn considerable attention because of its high theoretical capacity and density, but poor electrical conductivity, volume expansion, and slow redox reactions in lithium–sulfur batteries limit their commercial applications. Hollow carbon nanospheres (HCN) loaded with tungsten dioxide (WO2) nanoparticles were prepared using polystyrene spheres as templates via in situ polymerization, heat treatment, soaking, and high-temperature decomposition reduction. The composites possessed a hollow spherical structure, which can alleviate the volume change of sulfur and anchored the polysulfides. The anchored WO2 nanoparticles with abundant oxygen vacancies can generate many active sites and accelerate the electrochemical reaction kinetics. Therefore, the WO2/HCN/S cathode exhibited 593.5 mAh g−1 over 300 cycles at 1.0 A g−1 with a capacity decay rate of 0.15 % per cycle. This study provides a feasible solution for fabricating high performance cathode for lithium-sulfur battery.

High Areal Capacity and Sustainable High Energy in Ferroelectric Doped Holey Graphene/Sulfur Composite Cathode for Lithium-Sulfur Batteries

In this study, we are reporting the impact of the incorporation of ferroelectric nanoparticles (FNPs), such as BaTiO3 (BTO), BiFeO3 (BFO), Bi4NdTi3Fe0.7Ni0.3O15 (BNTFN), and Bi4NdTi3Fe0.5Co0.5O15 (BNTFC), as well as the mass loading of sulfur to fabricated solvent-free sulfur/holey graphene-carbon black/polyvinylidene fluoride (S/FNPs/CBhG/PVDF) composite electrodes to achieve high areal capacity for lithium-sulfur (Li-S) batteries. The dry-press method was adopted to fabricate composite cathodes. The hG, a conductive and lightweight scaffold derived from graphene, served as a matrix to host sulfur and FNPs for the fabrication of solvent-free composites. Raman spectra confirmed the dominant hG framework for all the composites, with strong D, G, and 2D bands. The surface morphology of the fabricated cathode system showed a homogeneous distribution of FNPs throughout the composites, confirmed by the EDAX spectra. The observed Li+ ion diffusion coefficient for the composite cathode started at 2.17 × 10−16 cm2/s (S25(CBhG)65PVDF10) and reached up to the highest value (4.15 × 10−15 cm2/s) for S25BNTFC5(CBhG)60PVDF10. The best discharge capacity values for the S25(CBhG)65PVDF10 and S25BNTFC5(CBhG)60PVDF10 composites started at 1123 mAh/gs and 1509 mAh/gs and dropped to 612 mAh/gs and 572 mAh/gs, respectively, after 100 cycles; similar behavior was exhibited by the other composites that were among the best. These are better values than those previously reported in the literature. The incorporation of ferroelectric nanoparticles in the cathodes of Li-S batteries reduced the rapid formation of polysulfides due to their internal electric fields. The areal capacity for the S25(CBhG)65PVDF10 composites was 4.84 mAh/cm2 with a mass loading of 4.31 mgs/cm2, while that for the S25BNTFC5(CBhG)60PVDF10 composites was 6.74 mAh/cm2 with a mass loading of 4.46 mgs/cm2. It was confirmed that effective FNP incorporation within the S cathode improves the cycling response and stability of cathodes, enabling the high performance of Li-S batteries.

Freestanding cathode design for lithium-sulfur batteries: CoP/Co-PCNF sandwich structure to enhance adsorption and catalysis for polysulfides

Lithium-sulfur (Li-S) batteries are exceedingly restrained in practical application originating from the shuttling of soluble lithium polysulfides (LiPSs), despite their superelevated theoretical specific capacity as well as energy density. Herein, a flexible carbon nanofiber membrane in situ embedded with Co, CoP nanoparticles (Co-PCNF, CoP/Co-PCNF) was designed to fabricate a unique sandwich structure, as a free-standing cathode for Li-S batteries. These innovative Li-S batteries deliver an initial capacity of 993.5 mAh g−1 at 1 C, along with a substantial capacity of 814.18 mAh g−1 even over 300 cycles, which corresponds to a low capacity decay of only 0.06% per cycle. Besides, with a sulfur content of 4.5 mg cm−2, an initial discharge capacity of 700.1 mAh g−1 was realized at 0.2 C with an excellent capacity retention rate of 91% over 200 cycles, prominent in long-cycle Li-S batteries. In this aspect, rosy cycling stability was achieved because of the impeded shuttle effect by the synergistic effect of Co and CoP compared with Co-PCNF sandwich structure as well as traditional aluminum foil. Moreover, underlying the DFT calculation, the enhanced overlap of electronic state ascribed to the conversion of fraction Co nanoparticles to CoP, triggering the adsorption capacity of CoP/Co-PCNF crucially higher than that of Co-PCNF. This observation paves ways into implementing the CoP/Co-PCNF sandwich structure as a free-standing cathode for the high-performance Li-S batteries.

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.

Design of Size-Controlled Sulfur Nanoparticle Cathodes for Lithium-Sulfur Aviation Batteries.

Lithium-sulfur (Li-S) battery has been considered as a strong contender for commercial aerospace battery, but the commercialization requires Ah-level pouch cells with both efficient discharge at high rates and ultra-high energy density. In this paper, the application of lithium-sulfur batteries for powering drones by using the cathode of highly dispersed sulfur nanoparticles with well-controlled particle sizes have been realized. The sulfur nanoparticles are prepared by a precipitation method in an eco-friendly and efficient way, and loaded on graphene oxide-cetyltrimethylammonium bromide by molecular grafting to realize a large-scale fabrication of sulfur-based cathodes with superior electrochemical performance. A button cell based on the cathode exhibits an excellent discharge capacity of 62.8 mAh cm-2 at a high sulfur loading of 60mg cm-2 (i.e., 1046.7 mAh g-1 ). The assembled miniature pouch cell (PCmini) shows a discharge capacity of 130 mAh g-1 , while the formed Ah-level pouch cell (PCAh) achieves energy density of 307Wh kg-1 at 0.3C and 92Wh kg-1 at 4C. Especially, a four-axis propeller drone powered by the PC has successfully completed a long flight (>3 min) at high altitudes, demonstrating the practical applicability as aviation batteries.

Application of Strontium-Doped Bismuth Ferrate in Lithium-Sulfur Battery Cathode

The modification of high-performance lithium-sulfur battery cathode have been extensively studied. Suppressing the shuttle effect of polysulfide, solving the volume expansion of sulfur and the poor electrical conductivity of sulfur are the main directions for scientists to modify the cathode. Here we prepared bismuth ferrate powder doped with different molecular percentages of strontium by sol-gel method. Compared with the unmodified cell, the capacity and cycle stability were improved by adding as-prepared material to the cathode, which indicates that bismuth ferrate doped with certain amount of strontium plays a positive role in the cathode material modification.

Highly monodispersed Li2SO4 crystals towards Li2S-based lithium-sulfur battery cathodes

Li2S as a cathode of lithium sulfur batteries (LSB) and a precursor of advanced solid electrolytes have been widely investigated. However, suffered from the high cost and the low ionic/electronic conductivity, the controllable fabrication of Li2S crystals from the carbothermal conversion of Li2SO4 need to be improved urgently. Herein, polyacrylic acid (PAA) as a blocking agent is introduced to fabricate the monodispersed Li2SO4 (m-Li2SO4) crystals and the m-Li2S/carbon nanotube (CNT) cathode via subsequent carbothermal reaction. Our constructed Li2S/CNT||Li cells deliver a high initial discharge capacity of ∼900 mAh/g and a reversible specific capacity of 500 mAh/g at 2C. These results suggest the importance of regulating size and morphology of Li2SO4 crystals towards high-performance Li2S crystals.

A review of cathode for lithium-sulfur batteries: progress and prospects

A review of cathode for lithium-sulfur batteries: progress and prospects

Structural Transformation in a Sulfurized Polymer Cathode to Enable Long-Life Rechargeable Lithium–Sulfur Batteries

Sulfurized polyacrylonitrile (SPAN) represents a class of sulfur-bonded polymers, which have shown thousands of stable cycles as a cathode in lithium-sulfur batteries. However, the exact molecular structure and its electrochemical reaction mechanism remain unclear. Most significantly, SPAN shows an over 25% 1st cycle irreversible capacity loss before exhibiting perfect reversibility for subsequent cycles. Here, with a SPAN thin-film platform and an array of analytical tools, we show that the SPAN capacity loss is associated with intramolecular dehydrogenation along with the loss of sulfur. This results in an increase in the aromaticity of the structure, which is corroborated by a >100× increase in electronic conductivity. We also discovered that the conductive carbon additive in the cathode is instrumental in driving the reaction to completion. Based on the proposed mechanism, we have developed a synthesis procedure to eliminate more than 50% of the irreversible capacity loss. Our insights into the reaction mechanism provide a blueprint for the design of high-performance sulfurized polymer cathode materials.

Enhancement of Organic Oxygen Atoms on Metal Cobalt for Sulfur Adsorption and Catalytic Polysulfide Conversion

Metals and their compounds effectively suppress the polysulfide shuttle effect on the cathodes of a lithium-sulfur (Li-S) battery by chemisorbing polysulfides and catalyzing their conversion. However, S fixation on currently available cathode materials is below the requirements of large-scale practical application of this battery type. In this study, perylenequinone was utilized to improve polysulfide chemisorption and conversion on cobalt (Co)-containing Li-S battery cathodes. According to IGMH analysis, the binding energies of DPD and carbon materials as well as polysulfide adsorption were significantly enhanced in the presence of Co. According to in situ Fourier transform infrared spectroscopy, the hydroxyl and carbonyl groups in perylenequinone are able to form O-Li bonds with Li2Sn, facilitating chemisorption and catalytic conversion of polysulfides on metallic Co. The newly prepared cathode material demonstrated superior rate and cycling performances in the Li-S battery. It exhibited an initial discharge capacity of 780 mAh g-1 at 1 C and a minimum capacity decay rate of only 0.041% over 800 cycles. Even with a high S loading, the cathode material maintained an impressive capacity retention rate of 73% after 120 cycles at 0.2 C.

Multiscale Structural Engineering of Sulfur/Carbon Cathodes Enables High Performance All-Solid-State LiS Batteries.

Constructing all-solid-state lithium-sulfur batteries (ASSLSBs) cathodes with efficient charge transport and mechanical flexibility is challenging but critical for the practical applications of ASSLSBs. Herein, a multiscale structural engineering of sulfur/carbon composites is reported, where ultrasmall sulfur nanocrystals are homogeneously anchored on the two sides of graphene layers with strong SC bonds (denoted as S@EG) in chunky expanded graphite particles via vapor deposition method. After mixing with Li9.54 Si1.74 P1.44 S11.7 Cl0.3 (LSPSCL) solid electrolytes (SEs), the fabricated S@EG-LSPSCL cathode with interconnected "Bacon and cheese sandwich" feature can simultaneously enhance electrochemical reactivity, charge transport, and chemomechanical stability due to the synergistic atomic, nanoscopic and microscopic structural engineering. The assembled InLi/LSPSCL/S@EG-LSPSCL ASSLSBs demonstrate ultralong cycling stability over 2400 cycles with 100% capacity retention at 1 C, and a record-high areal capacity of 14.0mAhcm-2 at a record-breaking sulfur loading of 8.9mgcm-2 at room temperature as well as high capacities with capacity retentions of ≈100% after 600 cycles at 0 and 60°C. Multiscale structural engineered sulfur/carbon cathode has great potential to enable high-performance ASSLSBs for energy storage applications.

Lithium Iron Phosphate Enhances the Performance of High-Areal-Capacity Sulfur Composite Cathodes.

Lithium iron phosphate (LiFePO4, "LFP") was investigated as an additive in the cathode of lithium-sulfur (Li-S) batteries. LFP addition boosted the sulfur utilization during Li-S cycling, achieving an initial capacity of 1465 mAh/gS and a long cycle life (>300 cycles). Polysulfide adsorption experiments showed that LFP attracted polysulfides, and thus, the presence of LFP should alleviate the shuttle effect, a common failure mode. Postmortem characterization found iron phosphides, iron phosphates, and LiF in the electrode, indicating that LFP underwent dynamic reconstruction during Li-S cycling. We suspect that the formation of these species played a role in the observed performance. From the processing standpoint, adding LFP improved slurry rheology, making the preparation of a high-loading electrode more consistent. Benefiting from the high sulfur utilization and the ability to prepare electrodes with high mass loading, the S-LFP hybrid cell showed an excellent areal capacity of 2.65 mAh/cm2 and could be stably cycled at 2 mAh/cm2 for 250 cycles. Our results demonstrated the LFP addition as a promising strategy for realizing Li-S batteries with high sulfur loading and areal capacity.

Recent Advances of Metal Groups and Their Heterostructures as Catalytic Materials for Lithium-Sulfur Battery Cathodes

Recent Advances of Metal Groups and Their Heterostructures as Catalytic Materials for Lithium-Sulfur Battery Cathodes