Mesoporous MnO2 fibers as an efficient bifunctional absorber for high-performance lithium-sulfur batteries

A novel morphology of mesoporous MnO₂ fibers (MOF) are successfully prepared for the first time as host materials for lithium-sulfur (LiS) batteries. The as-prepared mesoporous MnO₂ fibers can restrain the polysulfides dissolution via chemical bonding and physical trapping at the same time. As a result, the mesoporous MnO₂ fibers sulfur (MOF/S) composites exhibit excellent cycle performance. The MOF/S composite electrodes deliver a high initial capacity of 1015 mAh g^?1 and maintain 815 mAh g^?1 after 200 cycles at 0.1 C.     

Factors impact charging process in lithium/sulfur batteries

为了探究多硫离子在多孔碳材料表面的氧化过程,组装了三电极模拟电池和两电极扣式电池。比较了高硫浓度下和低硫浓度下硫电极的循环伏安曲线和充放电曲线;研究了充放电过程中电解液颜色和极片表面颜色的变化;比较了硫浓度、电解液种类、碳材料比表面积对硫电极在2.6 V处氧化峰电流的影响。结果表明：维持硫的适当过饱和度,对硫电极充电过程的完成是必要的;充电过程中可产生单质硫,同时多硫离子还可通过化学过程生成硫。碳比表面积增大,将使氧化峰电流增大;碳酸酯电解液由于对硫和多硫离子溶解度小,氧化峰电流较小;随着硫浓度的增大,氧化峰电流先线性增大,后快速下降。使用醚类电解液时,合适的总硫浓度为0.125 mol/L。     

Molybdenum carbide nanocrystals modified carbon nanofibers as electrocatalyst for enhancing polysulfides redox reactions in lithium-sulfur batteries

The high performance of lithium sulfur (Li S) batteries is the focus of research in recent years. However, the low sulfur loading, shuttling effect in electrolyte, and poor cycling stability limit their applications. Herein, molybdenum carbide nanocrystals embedded carbon nanofibers (Mo₂C@CFs: MCCFs) hybrid membrane was prepared in situ on CFs membrane based on carbonthermal reduction of ammonium molybdate. The fibrous MCCFs network is used as the current collector with Li₂S₆ catholyte solution for Li S batteries, which inhibits the shuttle effect and accelerates kinetics redox reaction. In addition, Mo₂C, as electrocatalyst, promotes nucleation of Li₂S of the MCCFs substance, which can reduce polarization and increase the specific capacity. As a result, the free-standing MCCFs@Li₂S₆ electrode (sulfur loading: 4.74 mg) shows a capacity of 977 mAh g⁻¹ and maintains at 828 mAh g⁻¹ at 0.2 C over 250 cycles, and indicates excellent reversibility and cycling stability. Even with sulfur loading as high as 7.11 mg, the MCCF@Li₂S₆ electrode exhibits an extremely high capacity of 5.75 mAh. Meanwhile, the Mo₂C modified CFs can be effectively retarding the self-discharge behavior by trapping the polysulfides. Furthermore, the stability improvement of lithium anode state by effectively suppressing the shuttle effect of polysulfide, played an important role in enhancing the electrochemical performance.     

Novel sustainable nitrogen,iodine-dual-doped hierarchical porous activated carbon as a superior host material for high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries exhibit great potential for next-generation high energy density energy storage. However, the insulativity of sulfur and the “shuttle effect” of polysulfides result in low utilization efficiency of active sulfur, fast capacity decay and inferior cycling stability, which pose the key challenge to their practical applications. Herein, a N, I-dual-doped hierarchical porous activated carbon (NIWFC) is successfully prepared for advanced Li-S batteries by the simple one-pot pyrolysis and hydrothermal processes. The obtained NIWFC owns interconnected porous framework with desirable specific surface area (2088.56 m² g^?1) and large volume space (1.106 cm³ g^?1), which can accommodate high content of active sulfur and immobilize polysulfides through physical confinement. Moreover, the existence of N and I heteroatoms could effectively strengthen the chemical adsorption to polysulfides and create more active sites to enhance sulfur utilization. Attributed to these merits, impregnating sulfur into NIWFC (NIWFC/S) as cathode of Li-S batteries achieves a high initial discharge capacity of 1284.1 mAh g^?1 at 0.1 C (remaining at 916.7 mAh g^?1 after 100 cycles) and the outstanding cycling stability with a low capacity fading rate of 0.061% per cycle over 350 cycles at 1.0 C. This work provides a facile and cost-effective strategy to design a novel sustainable N, I-dual-doped porous carbon for high performance Li-S batteries and various energy storage fields.     

Freestanding graphitic carbon nitride-based carbon nanotubes hybrid membrane as electrode for lithium/polysulfides batteries

Lithium sulfur batteries have drawled worldwide attention in recent years, which benefit of its high-density energetic, low cost, and environmental benignity. Nevertheless, the shuttle effect of polysulfides and resulting self-discharge lead to capacity fade loss and poor electrochemical performance. Herein, graphitic-carbon nitride/carbon nanotubes (g-C₃N₄/CNTs) hybrid membrane is fabricated by the flow-direct vacuum filtration process. The as-prepared 3-D freestanding g-C₃N₄/CNTs membrane employed as positive current collector containing Li₂S₆ catholyte solution for lithium/polysulfides batteries. The fabricated g-C₃N₄/CNTs provide a physical barriers and chemisorption resist polysulfide shuttling. Moreover, the conductive network constructed by CNTs can empower sulfur to be evenly distributed in the cathode and accelerates electron transport. Thus, to further prove the cooperative effect of g-C₃N₄ and CNTs, the freestanding g-C₃N₄/CNTs/Li₂S₆ electrode exhibits more stable electrochemical performance than CNTs/Li₂S₆ electrode, deliver the first discharge capacity of 876 mAh g⁻¹ at 0.5 C and maintained at 633 mAh g⁻¹ after 300 cycles. The sulfur mass in electrode was increased to 7.11 mg, and the g-C₃N₄/CNTs/Li₂S₆ electrode also possess a high capacity retention of 75.5%. Meanwhile, g-C₃N₄ modified CNTs can not only trap polysulfides by strong adsorption but also effectively inhibit the self-discharge behavior of lithium/polysulfides batteries. As a consequence, the g-C₃N₄/CNTs composites for lithium/polysulfides batteries are indicating an excellent electrochemical stability with a long-term storage without obvious capacity degradation.     

The host hollow carbon nanospheres as cathode material for nonaqueous room-temperature Al–S batteries

Aluminum-ion batteries have attracted great attention in virtue of their reliable safety performance and cost-effective raw materials. The sulfur element with a high specific capacity gives great development space for aluminum-sulfur (Al–S) battery. However, the dissolution of sulfur in electrolyte hinders the application of Al–S battery. Carbon materials with porous structure has larger specific surface area for adsorption of sulfur, and the porous carbon for sulfur cathode provides a certain barrier for the shuttle effect during the charge-discharge process. In this work, hollow carbon synthesized by template method is applied to Al–S batteries. It is found that the cave-like porous carbon material provides space for storing sulfur and polysulfides, alleviating the sulfur shuttle effect in Al–S batteries. The specific capacity of the hollow carbon materials for Al–S batteries is 1027 mAh g^?1 at the first cycle and the rechargeable specific capacity achieves 378 mAh g^?1 after 28 cycle.     

A thermo-stable poly(propylene carbonate)-based composite separator for lithium-sulfur batteries under elevated temperatures

Lithium-sulfur (Li-S) batteries have a great potential for the future development of energy industry. However, the high-temperature performance of Li-S batteries is still facing great challenge due to the high flammability of the electrolyte, sulfur cathode as well as the separator. The separator modification is an effective method to improve the thermal stability of separator and the electrochemical performance of Li-S batteries under elevated temperatures. However, the reported methods of separator coating are too complicated to be applied in the industrial production. Here, a novel thermo-stable composite separator (M-Celgard-p), in which a layer of silicon dioxide-poly (propylene carbonate) based electrolyte (nano-SiO₂@PPC) with a high ionic-conductivity of 1.03 × 10⁻⁴ S cm⁻¹ is coated on the commercial Celgard-p separator, is prepared by using a simple dipping method. Compared to the Li-S battery assembled with Celgard-p separator, the M-Celgard-p separator combined with a sulfur/polyacrylonitrile (S/PAN) cathode can improve the electrochemical performance of Li-S batteries, especially their high-temperature stability. As a result, the (S/PAN)/M-Celgard-p/Li cell delivers a high specific capacity of 724.7 mAh g⁻¹ at 1.0 A g⁻¹ after 200 cycles and presents a good rate capability of 1408 mAh g⁻¹ at 1.0 A g⁻¹ and 1216 mAh g⁻¹ at 2.0 A g⁻¹. More importantly, the (S/PAN)/M-Celgard-p/Li cell can exhibit a capacity retention ratio of 69.4% after 200 cycles at 60°C. The M-Celgard-p separator with high Li-ion conductivity can not only block the “shuttle-effect” of polysulfides during cycling but also enhance the thermal stability under elevated temperatures. This work presents a simple dipping method to prepare composite separator with excellent thermal stability, which enhance the rate performance and cyclic stability of Li-S batteries under elevated temperatures. We believe this work can provide a new way to develop more reliable Li-S batteries for practical applications.     

A microporous carbon derived from metal-organic frameworks for long-life lithium sulfur batteries

A polyhedral microporous carbon derived from metal-organic frameworks (ZIF-8) could present good property for sulfur loading and trapping. A melting-evaporation route was adopted to synthesize two sulfur/microporous carbon (S/MC) composites, of which sulfur content is controllable, and ether-based or ester-based electrolytes were used to evaluate the synthesized composites for the lithium sulfur batteries. According to electrochemical results, the S/MC composite with 65.2 wt% S in the ether-based electrolyte exhibited optimized performance as compared with the composite with 65.2 wt% S in the ester-based electrolyte, as well as the composite with 58.6 wt% S in the two kinds of electrolytes. For the S/MC composite with 65.2 wt% S in ether-based electrolyte, the initial discharge capacity could reach up to 1505.9 mAh g⁻¹ and the reversible capacity could be 833.3 mAh g⁻¹ after 40 cycles at 0.1 C. Furthermore, while being respectively evaluated at 0.5, 1.0, and 2.0 C, the discharge capacities could still maintain at 544, 493 and 354 mAh g⁻¹ after 300, 500, and 800 cycles, demonstrating appreciable cyclic reversibility and rate capability.     

Fabrication of CoFe/N-doped mesoporous carbon hybrids from Prussian blue analogous as high performance cathodes for lithium-sulfur batteries

CoFe/N-doped mesoporous carbon hybrids are synthesized by a simple pyrolysis of Prussian blue analogue (PBA) and melamine, in which the structure is rationally designed by controlling the weight ratio of PBA/melamine and annealing temperature. By applying the composite as the cathode material for lithium-sulfur batteries, it demonstrates outstanding electrochemical performances including a high reversible capacity (1315 mAh g⁻¹ at 0.2 C), excellent rate capability (724 and 496 mAh g⁻¹ at 2 and 5 C rates, respectively) and superior cycling stability (528 and 367 mAh g⁻¹ at 2 and 5C after 500 cycles, respectively). The synergetic effect of the mesoporous carbon matrix, uniform sized CoFe nanoparticles and N heteroatoms simultaneously contributes to the confinement of sulfur species. The presence of abundant mesopores and micropores can physically confine sulfur species. The formed CoFe-N_x moieties can not only improve the electronic conductivity of the as-prepared composites, but also offer highly effective active sites for chemical absorption and catalytic transformation of polysulfides to suppress any shuttle effect. In addition, the mesoporous structure can effectively alleviate the volume changes resulted from charge–discharge process. The strategy developed in this work proposes an alternative way to obtain N-doped mesoporous carbon matrix modified with CoFe nanoparticles for high performance cathode materials of lithium-sulfur batteries.     

Improving lithium‐sulfur battery performance with lignin reinforced MWCNT protection layer

Multi‐walled carbon nanotube (MWCNT) protection layers have previously been used to trap polysulfides and suppress the shuttle effect in lithium sulfur (Li‐S) batteries, leading to significant performance improvement. While the MWCNT is inherently highly conductive and mechanically strong, the cost can be significant and in turn hampered wider application of MWCNT protection layers. Here, we employed lignin, a byproduct during high‐quality bleached paper manufacturing, to replace a portion of MWCNT in the protection layer to reduce cost and enhance surface properties of pristine MWCNT protection layers. We found that the protection layer with 25 wt% lignin leads to the best overall electrochemical performance of Li‐S batteries during charging/discharging at 0.5°C and 1C rate (1C = 1,675 mA g^?1) among various weight‐ratios of lignin/MWCNT, and a low decay rate (0.20% per cycle) and high initial capacity (1342 mA g^?1 and 1437 mA g^?1 for 1C and 0.5C, respectively) are demonstrated. Besides, Li‐S cells with 25 wt% lignin/MWCNT composite protection layer also exhibited great rate capability, of which the specific capacities at 0.1C, 0.5C, 1C, and 2C were 1150, 913, 824, and 637 mAh g^?1, respectively. The enhanced electrochemical stability and performance of Li‐S batteries can be attributed to strengthened polysulfide trapping and improved lithium ion transport with lignin reinforced MWCNT protection layers. We showcased an economic approach to extend cycle life and improve rate capability of Li‐S batteries.     

A freestanding MoO2‐decorated carbon nanofibers interlayer for rechargeable lithium sulfur battery

Lithium‐sulfur (Li‐S) battery based on sulfur cathodes is of great interest because of high capacity and abundant sulfur source. But the shuttling effect of polysulfides caused by charge‐discharge process results in low sulfur utilization and poor reversibility. Here, we demonstrate a good approach to improve the utility of sulfur and cycle life by synthesizing carbon nanofibers decorated with MoO₂ nanoparticles (MoO₂‐CNFs membrane), which plays a role of multiinterlayer inserting between the separator and the cathode for Li‐S battery. The S/MoO₂‐CNFs/Li battery showed a discharge capacity of 6.93 mAh cm^?2 (1366 mAh g^?1) in the first cycle at a current density of 0.42 mA cm^?2 and 1006 mAh g^?1 over 150 cycles. Moreover, even at the highest current density (8.4 mA cm^?2), the battery achieved 865 mAh g^?1. The stable electrochemical behaviors of the battery has achieved because of the mesoporous and interconnecting structure of MoO₂‐CNFs, proving high effect for ion transfer and electron conductive. Furthermore, this MoO₂‐CNFs interlayer could trap the polysulfides through strong polar surface interaction and increases the utilization of sulfur by confining the redox reaction to the cathode.     

β‐molybdenum carbide/carbon nanofibers as a shuttle inhibitor for lithium‐sulfur battery with high sulfur loading

We report the synthesis of β‐molybdenum carbide/carbon nanofibers (β‐Mo₂C/CNFs) by electrospinning and annealing process, when exploited as an interlayer in Li‐S batteries, demonstrating significantly improved electrochemical behaviors. The synthesized β‐Mo₂C/CNFs with 3D network structure and high surface area are not only conducive to ion transport and electrolyte penetration but also effectively intercept the shuttle of lithium polysulfide by polar surface interaction. Moreover, the reaction kinetics of the batteries enhanced is due to the presence of β‐Mo₂C, promoting the solid‐state polysulfide conversion reaction in the charge‐discharge process. Compared with the batteries with CNF interlayer and without interlayer, the batteries using a β‐Mo₂C/CNFs interlayer with a sulfur loading of 4.2 mg cm^‐2 delivered excellent electrochemical performance because of a facile redox reaction during cycling. The discharge capacity at the first cycle at 0.7 mA cm^?2 was 1360 mAh g^?1, maintaining a specific capacity of 974 mAh g^?1 after 160 cycles. Furthermore, it showed a high‐rate capacity of 700 mAh g^?1 at 14 mA cm^?2. This work demonstrates the β‐Mo₂C/CNFs as a promising interlayer to exploit Li‐S battery commercialization.     

High reversible capacity carbon-lithium negative electrode in polymer electrolyte

Cabonaceous materials from different types are used in polymer electrolyte-based lithium cells in order to evaluate their electrochemical performance during lithium storage in the application as the negative electrode in lithium-ion-type batteries. The formation of a passivating film during the first cathodic polarization may account for the low faradaic yield of the first cycle. It also plays an important role in the stabilization of the carbon/polymer electrolyte interface. Non-graphitized mesocarbon micro beads lead to a higher reversible capacity of 410 mAh/g than the graphitized one. It is suggested that lithium could be reversibly stored as a multilayer ‘deposit’ at the carbon surface. A model of epitaxial lithium electroplating is presented.     

Sulfur/alumina/polypyrrole ternary hybrid material as cathode for lithium-sulfur batteries

Recently, lithium-sulfur batteries (LSBs) have received extensive attention due to its high energy density of 2600 Wh kg^?1. At the same time, sulfur is earth-abundant, economical and non-poisonous. Nevertheless, the poor electrochemical performance restricts its commercial application, including the inferior cycling stability caused by the significant dissolution of lithium polysulfides and the low specific capacity because of the poor electrical conductivity of sulfur. In this work, we adopt a simple and amicable process to prepare sulfur/alumina/polypyrrole (S/Al₂O₃/PPy) ternary hybrid material to overcome these defects. In this strategy, each composition of the ternary hybrid material plays an essential role in cathode: alumina and PPy can provide strong adsorption for the dissolved intermediate polysulfides. Meanwhile, PPy also works as a conductive and flexible additive to expedite electron transport, and is coated on the surface of the as-prepared SAl₂O₃ composite by in situ chemical polymerization. The sulfur is encapsulated uniformly and perfectively by the two components, which is confirmed by field emission scanning electron microscope. The ternary hybrid material manifests good electrochemical performance as expected, and displays high initial discharge capacity of 1088 mA h g^?1 and a discharge capacity of 730 mA h g^?1 after 100 cycles at a current density of 200 mA g^?1. Besides, S/Al₂O₃/PPy also shows good rate capability. The synergy between alumina and PPy is the decisive factor, which gives rise to good electrochemical performance of cathode for high-performance LSBs.     

Guided dendrite-free lithium deposition through titanium nitride additive in Li metal batteries

Metallic lithium (Li) is one of the most potential anode materials in the near future, because of its high theoretical specific capacity (3865 mAh/g), low potential (−3.045 V vs standard hydrogen electrode (SHE)) and low density (0.534 g/cm³). However, fatal dendritic Li growth is the bottleneck of the development of Li anode. In this contribution, we reported a titanium nitride (TiN) nanoparticle additive to guide Li deposition uniformly, hence dead Li and dendritic Li are effectively reduced. There are more nucleation sites on the surface of the electrode due to the stronger adsorption of Li ions on each facet of TiN, and TiN nanoparticles play the role of seeds of Li deposition. The half cells cycling in additive electrolyte exhibit an average Coulombic efficiency (CE) of 97.19% for 270 cycles on plane copper (Cu) electrode and an excellent high average CE of 99.01% for 300 cycles on three-dimensional (3D) carbon paper (CP) electrode at 1 mA/cm² and 1 mAh/cm². Li–S full cells equipped with such TiN nanoparticles additive electrolyte deliver great enhanced cycling and rate performance. This work provides a new insight to suppress Li dendrite and realizing high performance of Li metal batteries.     

All solid state lithium ion rechargeable batteries using NASICON structured electrolyte

Abstract

NASICON (Sodium super ionic conductor) structured Li_1·5Al_0·5Ge_1·5(PO₄)₃ (LAGP) solid electrolyte is synthesized through a solid state reaction. The total conductivity of the LAGP electrolyte is 7×10^?5 S cm^?1 with a potential window larger than 6 V. All solid state lithium batteries are fabricated using LiMn₂O₄ as a cathode, LAGP as an electrolyte and lithium metal as an anode. The LiMn₂O₄/LAGP/Li cell can deliver a capacity of about 80 mAh g^?1 in the first discharge cycle and increases gradually with charge/discharge cycles, indicating that LAGP can be used as a promising electrolyte for lithium rechargeable batteries.     

Electrochemical behavior of an advanced graphite whisker anodic electrode for lithium-ion rechargeable batteries

Graphite whiskers, produced by Nikkiso Co., Ltd., (sample code 2GWH-2A) have been investigated with respect to their electrochemical characteristics in different types of liquid electrolytes: LiClO₄, LiPF₆, LiAsF₆, LiBF₄, LiCF₃SO₃ in ethylene carbonate-diethyl carbonate and in solid electrolytes. A high capacity (363 mAh/g) is obtained when a liquid electrolyte was used and 330 mAh/g at 80 °C in the case of a polymer electrolyte. The coulombic efficiency during the first cycle is lower when polymer electrolyte is used. 2GWH-2A shows very different performances in LiClO₄ and in LiPF₆ electrolytes. The degree of intercalation depends upon of the nature of the binder, composition of the electrode and electrolyte. The color of the carbon electrode also changed from black to gold in the presence of some lithium salt electrolytes, when lithium was fully intercalated into the electrode. The galvanostatic charge/discharge tests show a large plateau near 0 V. On measuring the slow cyclic voltammogram of the 2GWH-2A, five cathodic peaks were observed.     

Graphene oxide coated nanosheet-like γ-MnS@KB-S fabricated by spray drying for high energy density Li-S batteries

In order to prohibit the shuttle influence of lithium polysulfides in lithium sulfur battery, a kind of graphene oxide (GO) coated γ-MnS@KB-S (GO@MKB-S) composite cathode material was successfully fabricated. First of all, the γ-MnS@KB (MKB) composite powders were prepared via a solvothermal reaction, then a spray drying method was used to obtain GO@MKB-S composites, which displays core/shell nanostructure. SEM, TEM, XRD as well as Raman spectrum are implemented to look into the microstructures and the functions of the 2D nanosheet-like γ-MnS in setting in KB on the battery performance were carefully analyzed. It is demonstrated that electrochemical discharge capacity and rate performance are clearly improved by using GO@MKB-S composites compared to the cathode electrode of the GO coated KB-S (GO@KB-S). With a sulfur loading of 5 mg cm⁻², the cathode electrode of GO@MKB-S shows a considerable discharge capacity of 749.9 mAh g⁻¹ at 0.36 C. Additionally, the Li-S battery cycle retention of GO@MKB-S sample maintains 97.36% after 100 cycles and 78.69% after 200 cycles.     

Ionic liquid doped PEO-based solid polymer electrolytes for lithium-ion polymer batteries

The influence of adding the room-temperature ionic liquid 1-ethyl-3-methyllimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) to poly(ethylene oxide) (PEO)–lithium difluoro(oxalato)borate (LiDFOB) solid polymer electrolyte and the use of these electrolytes in solid-state Li/LiFePO₄ batteries has been investigated. Different structural, thermal, electrical and electrochemical studies exhibit promising characteristics of these polymer electrolyte membranes, suitable as electrolytes in rechargeable lithium-ion batteries. The crystallinity decreased significantly due to the incorporation of ionic liquid, investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The ion–polymer interaction, particularly the interaction of cations in LiDFOB and ionic liquid with ether oxygen atom of PEO chains, has been evidenced by FT-IR studies. The polymer electrolyte with ～40 wt% of ionic liquid offers a maximum ionic conductivity of ～1.85 × 10^?4 S/cm at 30 °C with improved electrochemical stabilities. The Li/PEO-LiDFOB-40 wt% EMImTFSI/LiFePO₄ coin-typed cell cycled at 0.1 C shows the 1st discharge capacity about 155 mAh g^?1, and remains 134.2 mAh g^?1 on the 50th cycle. The addition of the ionic liquid to PEO₂₀-LiDFOB polymer electrolyte has resulted in a very promising improvement in performance of the lithium polymer batteries.     

High capacity MgH2 composite electrodes for all-solid-state Li-ion battery operating at ambient temperature

MgH₂ with a theoretical capacity of 2036 mAh/g has been studied using LiBH₄ as solid electrolyte with remarkable results. However, LiBH₄ conductivity is reduced drastically from ~10^?3 to ~10^?8 Scm^?1 when operating at temperatures below ~117 °C, due to the crystal structural transition. This change in the conductivity limits the range of operating temperatures of the battery. In order to have all-solid-state lithium ion batteries operating at room temperature, some alternatives were explored in this work. In this study, different batteries compositions were tested for operating temperatures from 30 °C to 120 °C, using LiBH₄, 3LiBH₄·LiI and 80Li₂S–20P₂S₅ to find a workable configuration for all-solid-state lithium-ion battery with MgH₂ as the active material for the working electrode. The cell MgH₂/3LiBH₄·LiI/Acetylene Black carbon | 80Li₂S–20P₂S₅ | Li, shown the best performance with an initial capacity of 1570 mAh/g operating at 30 °C.