Mesoporous carbon prepared by etching halloysite nanotubes (HNTs) with pyrrole as a precursor for a sulfur carrier of superior lithium–sulfur batteries

Using pyrrole as a carbon precursor and halloysite nanotubes (HNT) as a templating agent, mesoporous carbon (MC) was prepared by template etching and combined with sulfur as a composite cathode for lithium–sulfur batteries. The mesoporous carbon/sulfur (MC/S) composite cathode exhibits a first cycle discharge specific capacity of 1355 mA h g⁻¹ at 0.2C, and the utilization rate of active sulfur can reach 80.9%. Even after 500 cycles, the discharge specific capacity still remains at 496.9 mA h g⁻¹ when tested at 0.5C. Furthermore, the hollow groove structure present in the MC/S electrode provides a large number of active sites for electrochemical reactions. The prepared MC/S composite cathode not only has a high discharge specific capacity and good cycle stability, but also increases the energy density of the lithium–sulfur battery. Therefore, this preparation process of MC is more conducive to practical application.

Using pyrrole as a carbon precursor and halloysite nanotubes (HNT) as a templating agent, mesoporous carbon (MC) was prepared by template etching and combined with sulfur as a composite cathode for lithium–sulfur batteries.     

A N-doped graphene–cobalt nickel sulfide aerogel as a sulfur host for lithium–sulfur batteries

Herein, three-dimensional (3D) N-doped reduced graphene oxide (N-rGO) nanosheets were decorated with a uniform distribution of Co–Ni–S (CNS) nanoparticles to form the CNS/N-rGO composite as a sulfur host material for lithium–sulfur batteries. The CNS nanoparticles and N in CNS/N-rGO strongly interact with polysulfides, whereas graphene, as a conductive network, can improve its electrical conductivity. A CNS/N-rGO/sulfur composite cathode was prepared via the sulfur melting diffusion method. The electrochemical study showed that the CNS/N-rGO/sulfur cathode delivered an initial discharge capacity of 1430 mA h g⁻¹ at a current density of 0.1C. Moreover, it retained a specific capacity of 685 mA h g⁻¹ after 300 cycles at 0.5C with a coulombic efficiency of 98%, which was better than that of commercial rGO. This composite was used as a sulfur cathode for a lithium–sulfur battery, exhibiting excellent rate capability and remarkable performance in terms of long cycling stability.

Herein, three-dimensional (3D) N-doped reduced graphene oxide (N-rGO) nanosheets were decorated with a uniform distribution of Co–Ni–S (CNS) nanoparticles to form the CNS/N-rGO composite as a sulfur host material for lithium–sulfur batteries.     

Enhanced performance of lithium–sulfur batteries based on single-sided chemical tailoring,and organosiloxane grafted PP separator

Even after a decade of research and rapid development of lithium–sulfur (Li–S) batteries, the infamous shuttle effect of lithium polysulfide is still the major challenge hindering the commercialization of Li–S batteries. In order to further address this issue, a functionalized PP separator is obtained through selective single-sided chemical tailoring, and then organosiloxane fumigation grafting. During the charge–discharge process, the grafted functional groups can effectively block the transportation of the dissolved polysulfides through strong chemical anchoring, inhibit the shuttle effect and greatly enhance the cycle stability of the Li–S battery. Interestingly, the specially designed single-sided enlarged channel structure formed by chemical tailoring can well accommodate the deposition with intermediate polysulfides on the separator surface toward the cathode chamber, resulting in enhanced initial discharge capacity and rate performance. Compared to the battery assembled with PP, the Li–S battery employing the separator grafted with a 3-ureidopropyltrimethoxysilane (PP–O^x−–U) displays better electrochemical performance. Even at 2C, it can still deliver a high capacity of 786 mA h g⁻¹, and retain a capacity of 410 mA h g⁻¹ with a low capacity fading of 0.095% per cycle over 500 cycles. This work provides a very promising and feasible strategy for the development of a special functionalization PP separator for Li–S batteries with high electrochemical performance.

Even after a decade of research and rapid development of lithium–sulfur (Li–S) batteries, the infamous shuttle effect of lithium polysulfide is still the major challenge hindering the commercialization of Li–S batteries.     

Bagasse as a carbon structure with high sulfur content for lithium–sulfur batteries

A bagasse-based 3D carbon matrix (BC) with high specific surface area and high conductivity was obtained by carbonization and pore-forming processes with bagasse as the carbon precursor and K₂FeO₄ as the pore-former. The microporous structure and nitrogenous functional groups were determined in the prepared carbon matrix, which could allow high sulfur loading and improve the polysulfide absorption capacity during cycling. After sulfur infusion, the S/BC composite with 68.8% sulfur content was obtained. The lithium–sulfur (Li–S) battery with the S/BC cathode shows high specific capacity and good cycling performance. It delivers a specific capacity of 1360 mA h g⁻¹ at 0.2C and remains at 790 mA h g⁻¹ after 200 cycles. At 1C, the Li–S with this composite cathode exhibits 601 mA h g⁻¹ after 150 cycles. This work offers a new kind of green material and a new method for Li–S batteries.

Bagasse-based carbon matrix with microporous structure and nitrogenous functional groups could have high sulfur loading and excellent polysulfide absorption capacity.     

Fast conversion of lithium (poly)sulfides in lithium–sulfur batteries using three-dimensional porous carbon

The slow redox kinetics of polysulfide hinders the rapid and complete conversion between soluble polysulfides and Li₂S₂/Li₂S, resulting in unsatisfactory rate and cycle performance in lithium-sulfur batteries. Electrochemical catalysis, one effective method, promotes the reaction kinetics and inhibits the “shuttle effect”. Here, we present a three-dimensional ordered macro-porous carbon with abundant cobalt–nitrogen–carbon active sites as a matrix catalyst, leading to accelerated polysulfide redox kinetics. In addition, the interconnected conductive frameworks with ordered macro-porous carbon afford fast ion/electron transport and provide sufficient space to adapt to the volume expansion of the sulfur electrode. Owing to the aforementioned advantages, a lithium–sulfur battery with the matrix catalyst delivers a high specific capacity (1140 mA h g⁻¹ at 0.1C) and a low capacity decay rate (0.0937% per cycle over 500 cycles). Moreover, there is a high rate capacity (349.1 mA h g⁻¹) even at the high current density of 2C and sulfur loading of 3.8 mg cm⁻² due to the improved polysulfide redox kinetics by a catalytic effect.

A three-dimensional porous carbon was prepared as a sulfur host. It effectively restrains dissolution of polysulfides by improving the conversion kinetics between polysulfides, thereby enhancing the electrochemical cycling stability.     

Polyvinylchloride-derived N,S co-doped carbon as an efficient sulfur host for high-performance Li–S batteries

The intrinsic polysulfide shuttle in lithium–sulfur (Li–S) batteries have significantly limited their practical applications. Conductive carbon materials with heteroatom doping and rich porosity is the most common strategy for the effective prevention of polysulfide shuttle, but are usually obtained with high costs and tedious procedures. Herein, we managed to obtain highly porous N, S-codoped carbon materials (NS-C) through treating waste plastic of polyvinylchloride (PVC) with KOH. The resulting NS-C was revealed to be highly efficient hosts for sulfur cathode, achieving large reversible capacities of 1205 mA h g⁻¹ and 836 mA h g⁻¹ at 0.1C and 1.0C, respectively, and remaining at 550 mA h g⁻¹ after 500 cycles at 1C rate, showing an outstanding cycling stability. The significantly enhanced cycling performance was mainly ascribed to both the hierarchically porous structure and heavy N, S co-dopants, which respectively provided physical blocks and chemical affinity for the efficient immobilization of intermediate lithium polysulfides. The results provide an effective paradigm in the surface chemistry and sulfur cathode materials design for high-performance Li–S batteries and a new application for recycled plastic waste.

The intrinsic polysulfide shuttle in lithium–sulfur (Li–S) batteries have significantly limited their practical applications.     

Self-assembled layer-by-layer partially reduced graphene oxide–sulfur composites as lithium–sulfur battery cathodes

Constructing a reliable conductive carbon matrix is essential for the sulfur-containing cathode materials of lithium–sulfur batteries. A ready-made conductive matrix infiltrated with sulfur as the cathode is the usual solution. Here, a partially reduced graphene oxide–sulfur composite (prGO/S) with an ordered self-assembled layer-by-layer structure is introduced as a Li–S battery cathode. The prGO/S composites are synthesized through a facile one-step self-assembly liquid route. An appropriate amount of sulfur is in situ deposited on the surface of the prGO nanosheets by adjusting the reduction degree of the GO nanosheets. The combined effect of the electrostatic repulsions and surface energy makes the sulfur wrapped prGO nanosheets self-assemble to form an ordered layer-by-layer structure, which not only ensures the uniform distribution of sulfur but also accommodates the volume change of the sulfur species during cycling. Moreover, the conductivity of the prGO/S composites improves when the reduction time increases. XPS spectra confirm that sulfur is still chemically bonded to the prGO. After applying the prGO coating of the prGO/S composite particle and as an interlayer in a lithium–sulfur battery configuration, a high initial discharge capacity of 1275.8 mA h g⁻¹ is achieved and the discharge capacity of the 100th cycle is 1013.8 mA h g⁻¹ at 0.1C rate.

The general procedures for the synthesis of the self-assembled layer-by-layer prGO/S composites.     

Fabrication of NiO–carbon nanotube/sulfur composites for lithium-sulfur battery application

The practical applications of lithium–sulfur batteries are still a great challenge due to the polysulfide shuttle and capacity decay. Herein, we report a NiO–carbon nanotube/sulfur (NiO–CNT/S) composite by hydrothermal and thermal treatments. This hybrid combines the high conductivity of CNTs and double adsorption of CNTs and NiO (physical and chemical adsorption) to improve the electrochemical performance for the sulfur electrodes. Compared with CNT/S and NiO/S, the developed NiO–CNT/S composites present a preferable initial reversible discharge capacity (1072 mA h g⁻¹) and is maintained at 609 mA h g⁻¹ after 160 cycles at 0.1C.

The NiO–CNT/S composites combine the high conductivity of CNT and double adsorption of CNT and NiO (physical adsorption and chemical adsorption) to enhance electrochemical performance for sulfur electrode materials.     

Cationic polymer-grafted graphene oxide/CNT cathode-coating material for lithium–sulfur batteries

A cathode-coating material composed of cationic polymer-grafted graphene oxide (CPGO) and carbon nanotube (CNT) was prepared, where the CPGO was synthesized by grafting quaternized 2-(dimethylamino)ethyl methacrylate (QDMAEMA) onto graphene oxide (GO) via atom transfer radical polymerization (ATRP). GO has good compatibility with carbon black, the main component of the cathode in lithium–sulfur (Li–S) batteries. Here, the cationic polymer having the QDMAEMA unit was intentionally grafted onto GO to decrease the shuttle effect by increasing the chemical adsorption of polysulfide (PS). In addition, when CNT was mixed with CPGO, the compatibility with carbon black was found to be further increased. The lithium–sulfur (Li–S) battery with a sulfur-deposited Super P® carbon black (S/C) cathode coated with a mixture of CPGO and CNT was found to have much improved cell performance compared to those coated without any coating material, with only CPGO, with the mixture of GO and CNT, and with the mixture of PQDMAEMA and CNT. For example, the Li–S battery with the cathode coated using the mixture of CPGO and CNT retained a discharge capacity of 744 mA h g⁻¹ after 50 cycles at 0.2C-rate, while those of the Li–S batteries with bare S/C and CPGO-S/C cathodes were found to be much smaller, i.e., 488 mA h g⁻¹ and 641 mA h g⁻¹, respectively, under the same conditions. Therefore, the mixture of CPGO with CNT as the cathode-coating material showed a synergetic effect to enhance the cell performance of the Li–S battery system.

A cathode-coating material composed of cationic polymer-grafted graphene oxide (CPGO) and carbon nanotube (CNT) was prepared and used as a cathode-coating material for lithium sulfur batteries.     

Ultradispersed titanium dioxide nanoparticles embedded in a three-dimensional graphene aerogel for high performance sulfur cathodes

Lithium–sulfur (Li–S) batteries are regarded as one of the most promising energy storage technologies, however, their practical application is greatly limited by a series of sulfur cathode challenges such as the notorious “shuttle effect”, low conductivity and large volume change. Here, we develop a facile hydrothermal method for the large scale synthesis of sulfur hosts consisting of three-dimensional graphene aerogel with tiny TiO₂ nanoparticles (5–10 nm) uniformly dispersed on the graphene sheet (GA–TiO₂). The obtained GA–TiO₂ composites have a high surface area of ∼360 m² g⁻¹ and a hierarchical porous structure, which facilitates the encapsulation of sulfur in the carbon matrix. The resultant GA–TiO₂/S composites exhibit a high initial discharge capacity of 810 mA h g⁻¹ with an ultralow capacity fading of 0.054% per cycle over 700 cycles at 2C, and a high rate (5C) performance (396 mA h g⁻¹). Such architecture design paves a new way to synthesize well-defined sulfur hosts to tackle the challenges for high performance Li–S batteries.

GA–TiO₂ composites as a cathode material realize an excellent electrochemical performance in Li–S batteries.     

Lychee-like TiO2@TiN dual-function composite material for lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are promising candidates for next generation rechargeable batteries because of their high energy density of 2600 W h kg⁻¹. However, the insulating nature of sulfur and Li₂S, the “shuttle effect” of lithium polysulfides (LiPSs), and the volumetric change of sulfur electrodes limit the practical application of Li–S batteries. Here, lychee-like TiO₂@TiN hollow spheres (LTTHS) have been developed that combine the advantages of high adsorption TiO₂ and high conductivity TiN to achieve smooth adsorption/spread/conversion of LiPSs and use them as a sulfur host material in Li–S batteries for the first time. The cathode exhibits an initial specific capacity of 1254 mA h g⁻¹ and a reversible capacity of 533 mA h g⁻¹ after 500 cycles at 0.2C, which corresponds to an average coulombic efficiency up to 99%. The cell with the LTTHS@S cathode achieved an extended lifespan of over 1000 cycles. Such good performance can be assigned to the good adsorption and catalysis of the dual-function TiO₂@TiN composite. This work proved that the TiO₂@TiN composite can be an attractive matrix for sulfur cathodes.

Lithium–sulfur (Li–S) batteries are promising candidates for next generation rechargeable batteries because of their high energy density of 2600 W h kg⁻¹.     

Enhanced storage behavior of quasi-solid-state aluminum–selenium battery

The current aluminum batteries with selenium positive electrodes have been suffering from dramatic capacity loss owing to the dissolution of Se₂Cl₂ products on the Se positive electrodes in the ionic liquid electrolyte. For addressing this critical issue and achieving better electrochemical performances of rechargeable aluminum–selenium batteries, here a gel-polymer electrolyte which has a stable and strongly integrated electrode/electrolyte interface was adopted. Quite intriguingly, such a gel-polymer electrolyte enables the solid-state aluminum–selenium battery to present a lower self-discharge and obvious discharging platforms. Meanwhile, the discharge capacity of the aluminum–selenium battery with a gel-polymer electrolyte is initially 386 mA h g⁻¹ (267 mA h g⁻¹ in ionic liquid electrolyte), which attenuates to 79 mA h g⁻¹ (32 mA h g⁻¹ in ionic liquid electrolyte) after 100 cycles at a current density of 200 mA g⁻¹. The results suggest that the employment of a gel-polymer electrolyte can provide an effective route to improve the performance of aluminum–selenium batteries in the first few cycles.

A quasi-solid-state aluminum–selenium battery has been established using gel-polymer electrolyte between the Se positive electrode and Al negative electrode which increasing the utilization of the active materials.     

ZnO quantum dot-modified rGO with enhanced electrochemical performance for lithium–sulfur batteries

Lithium–sulfur batteries are considered the most promising next-generation energy storage devices. However, problems like sluggish reaction kinetics and severe shuttle effect need to be solved before the commercialization of Li–S batteries. Here, we successfully prepared ZnO quantum dot-modified reduced graphene oxide (rGO@ZnO QDs), and first introduced it into Li–S cathodes (rGO@ZnO QDs/S). Due to its merits of a catalysis effect and enhancing the reaction kinetics, low surface impedance, and efficient adsorption of polysulfide, rGO@ZnO QDs/S presented excellent rate capacity with clear discharge plateaus even at a high rate of 4C, and superb cycle performance. An initial discharge capacity of 998.8 mA h g⁻¹ was delivered, of which 73.3% was retained after 400 cycles at a high rate of 1C. This work provides a new concept to introduce quantum dots into lithium–sulfur cathodes to realize better electrochemical performance.

ZnO quantum dot-modified rGO was first introduced into lithium–sulfur cathodes, realizing better reaction kinetics and enhanced electrochemical performance.     

Flexible quasi-solid-state zinc ion batteries enabled by highly conductive carrageenan bio-polymer electrolyte

Flexible Zn–MnO₂ batteries as wearable electronic power source have attracted much attention in recent years due to their low cost and high safety. To promote the practical application of flexible Zn–MnO₂ batteries, it is imperative to develop flexible, mechanically robust and high performance solid state electrolyte. Herein, we construct a rechargeable quasi-solid-state zinc ion battery using kappa-carrageenan bio-polymer electrolyte. The kappa-carrageenan electrolyte is eco-friendly, low cost, and highly conductive (3.32 × 10⁻² S cm⁻¹ at room temperature). The mechanical robustness of kappa-carrageenan electrolyte is further reinforced by using a rice paper as scaffold. Benefiting from high ionic conductivity of the bio-polymer electrolyte, our zinc ion battery delivers a significant high energy density and power density (400 W h kg⁻¹ and 7.9 kW kg⁻¹, respectively), high specific capacity (291.5 mA h g⁻¹ at 0.15 A g⁻¹), fast charging and discharging capability (120.0 mA h g⁻¹ at 6.0 A g⁻¹). The zinc ion battery with bio-polymer electrolyte also shows excellent cycling stability and high bending durability. This work brings new research opportunities in developing low-cost flexible solid-state zinc ion batteries using green natural polymer.

The zinc ion batteries with KCR electrolyte show a high specific capacity and fast charging and discharging capability.     

Tetramethylpyrazine: an electrolyte additive for high capacity and energy efficiency lithium–oxygen batteries

Lithium–oxygen batteries have attracted great attention in recent years owing to their extremely high theoretical energy density, however, factors such as low actual capacity and poor rate performance hinder the practical application of lithium–oxygen batteries. In this work, a novel electrolyte additive, tetramethylpyrazine (TMP), is introduced into an electrolyte system to enhance the electrochemical performance of the lithium–oxygen batteries. TMP does not undergo its own redox reaction within the charge–discharge voltage range, which will not affect the electrochemical stability of the electrolyte. The results show that the addition of TMP can increase the reduction current of oxygen, which will promote the ORR process, and with an optimal TMP content (50 mM), the cell shows a high discharge capacity of 5712.3 mA h g⁻¹ at 0.1 mA cm⁻². And its rate capability is almost doubled compared with the system without TMP additive at a large current density of 1 mA cm⁻². Further analysis by SEM and XRD reveals that the addition of TMP can reduce the formation of by-products and promote the solution growth of large-size Li₂O₂ particles to achieve a large discharge capacity. This approach could provide a new idea for improving the electrochemical performance of lithium–oxygen batteries.

TMP has a strong interaction with Li⁺, which promotes the solution mechanism of Li₂O₂, thereby increasing the discharge capacity.     

Self-supporting S@GO–FWCNTs composite films as positive electrodes for high-performance lithium–sulfur batteries

Although lithium–sulfur (Li–S) batteries are a promising secondary power source, it still faces many technical challenges, such as rapid capacity decay and low sulfur utilization. The loading of sulfur and the weight percentage of sulfur in the cathode usually have a significant influence on the energy density. Herein, we report an easy synthesis of a self-supporting sulfur@graphene oxide-few-wall carbon nanotube (S@GO–FWCNT) composite cathode film, wherein an aluminum foil current collector is replaced by FWCNTs and sulfur particles are uniformly wrapped by graphene oxide along with FWCNTs. The 10 wt% FWCNT matrix through ultrasonication not only provided self-supporting properties without the aid of metallic foil, but also increased the electrical conductivity. The resulting S@GO–FWCNT composite electrode showed high rate performance and cycle stability up to ∼385.7 mA h g_electrode⁻¹ after 500 cycles and close to ∼0.04% specific capacity degradation per cycle, which was better than a S@GO composite electrode (353.1 mA h g_electrode⁻¹). This S@GO–FWCNT composite self-supporting film is a promising cathode material for high energy density rechargeable Li–S batteries.

We report a synthesis of a self-supporting composite cathode film, wherein aluminum foil current collector is replaced by FWCNTs and sulfur particles are uniformly wrapped by graphene oxide along with FWCNTs.     

A defective MOF architecture threaded by interlaced carbon nanotubes for high-cycling lithium–sulfur batteries

Metal organic frameworks (MOFs) have been deemed among the most promising sulfur hosts for lithium–sulfur (Li–S) batteries owing to their high specific surface areas, novel pore structures and open metal sites. However, their highly coordinated, electronically insulating and structurally unstable nature overshadows the merits of MOFs to a great extent. In this work, a novel UiO-66/carbon nanotube (UC) composite was initially synthesized via a facile one-pot synthesis strategy, in which abundant linker-missing defects were caused by introduced competitive coordination. Meanwhile, flexible and interlaced carbon nanotubes (CNTs) throughout mechanically stable UiO-66 nanoparticles constructed a reliable conductive network. Because of its superior structural stability, high electronic conductivity and strong polysulfide chemisorption, the UC architecture as the sulfur cathode in Li–S batteries shows stable cycling, delivering an initial capacity of 925 mA h g⁻¹ at 0.5 A g⁻¹ and a very low fading rate over 800 cycles of 0.071% per cycle at 1 A g⁻¹. A strong chemical affinity between coordination defects and LiPSs was revealed by first principles calculations and apparent absorption, which indicates significant entrapment of soluble polysulfides by the UC composite, thus leading to the outstanding cycling performance of S@UC electrodes.

Abundant artificial linker-missing defects as active sites display superior chemisorption of LiPSs, which contribute to outstanding cycling performance in Li–S cells.     

Conducting polymer-coated MIL-101/S composite with scale-like shell structure for improving Li–S batteries

Lithium–sulfur batteries are regarded as a promising energy storage system. However, they are plagued by rapid capacity decay, low coulombic efficiency, a severe shuttle effect and low sulfur loading in cathodes. To address these problems, effective carriers are highly demanded to encapsulate sulfur in order to extend the cycle life. Herein, we introduced a doped-PEDOT:PSS-coated MIL-101/S multi-core–shell structured composite. The unique structure of MIL-101, large specific area and conductive shell ensure high dispersion of sulfur in the composite and minimize the loss of polysulfides to the electrolyte. The doped-PEDOT:PSS-coated sulfur electrodes exhibited an increase in initial capacity and an improvement in rate characteristics. After 192 cycles at the current density of 0.1C, a doped-PEDOT:PSS-coated MIL-101/S electrode maintained a capacity of 606.62 mA h g⁻¹, while the MIL-101/S@PEDOT:PSS electrode delivered a capacity of 456.69 mA h g⁻¹. The EIS measurement revealed that the surface modification with the conducting polymer provided a lower resistance to the sulfur electrode, which resulted in better electrochemical behaviors in Li–S battery applications. Test results indicate that the MIL-101/S@doped-PEDOT:PSS is a promising host material for the sulfur cathode in the lithium–sulfur battery applications.

Lithium–sulfur batteries are regarded as a promising energy storage system.     

In situ template synthesis of hierarchical porous carbon used for high performance lithium–sulfur batteries

Hierarchical porous carbon (HPC) consists of micropores, mesopores and macrospores which are synthesized by in situ formation of template followed by acid etching. The obtained pores are three-dimensional and interconnected, and evenly distributed in the carbon matrix. By adjusting the ratio of the raw materials, the high specific surface area and large pore volume is afforded. The obtained HPC-3 samples possess graphite flakes and locally graphited-carbon walls, which provide good electrical conductivity. These unique characteristics make these materials suitable cathode scaffolds for Li–S batteries. After encapsulating 61% sulfur into HPC-3 host, the S/HPC-3 composite exhibits excellent cycling stability, high columbic efficiency, and superior rate cycling as a cathode material. The S/HPC-3 composite cathode displays an initial discharge capacity of 1059 mA h g⁻¹, and a reversible capacity of 797 mA h g⁻¹ after 200 cycles at 0.2C. The discharge capacities of the S/HPC-3 composite cathode after every 10 cycles at 0.1, 0.2, 0.5, 1, and 2C are 1119, 1056, 982, 921, and 829 mA h g⁻¹, respectively.

In situ template synthesis of HPCs used for lithium–sulfur batteries, which exhibits excellent cycling stability and superior rate cycling.     

MoO2 nanoparticles embedded in N-doped hydrangea-like carbon as a sulfur host for high-performance lithium–sulfur batteries

Lithium–sulfur batteries are considered to be promising energy storage devices owing to their high energy density, relatively low price and abundant resources. However, the low utilization of insulated active materials and shuttle effect have severely hindered the further development of lithium–sulfur batteries. Herein, MoO₂ nanoparticles embedded in N-doped hydrangea-like carbon have been synthesized by liquid-phase reaction followed by an annealing process and used as a sulfur host. The nitrogen-doped carbon matrix improves electrical conductivity and provides pathways for smooth electron and Li ion transfer to uniformly dispersed sulfur. Meanwhile, MoO₂ nanoparticles can absorb polysulfide ions by forming strong chemical bonds, which can effectively alleviate the polysulfide shuttling effect. These results showed a good rate performance: 1361, 1071, 925, 815 and 782 mA h g⁻¹ at the current densities of 0.1, 0.2, 0.5, 1 and 2 A g⁻¹, and capacity retention of 85% after 300 cycles at 1 A g⁻¹. The excellent performance was due to the synergistic effects of the polar MoO₂ and nitrogen-doped carbon matrix, which can effectively restrain and reutilize active materials by absorbing polysulfides and catalyzing the transformation of polysulfides.

Lithium–sulfur batteries are considered to be promising energy storage devices owing to their high energy density, relatively low price and abundant resources.