Hierarchically porous carbon encapsulating sulfur as a superior cathode material for high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are deemed to be a promising energy storage device for next-generation high energy power system. However, insulation of S and dissolution of lithium polysulfides in the electrolyte lead to low utilization of sulfur and poor cycling performance, which seriously hamper the rapid development of Li-S batteries. Herein, we reported that encapsulating sulfur into hierarchically porous carbon (HPC) derived from the soluble starch with a template of needle-like nanosized Mg(OH)2. HPC has a relatively high specific surface area of 902.5 m(2) g(-1) and large total pore volume of 2.60 cm(3) g(-1), resulting that a weight percent of sulfur in S/HPC is up to 84 wt %. When evaluated as cathodes for Li-S batteries, the S/HPC composite has a high discharge capacity of 1249 mAh g(-1) in the first cycle and a Coulombic efficiency as high as 94% with stable cycling over prolonged 100 charge/discharge cycles at a high current density of 1675 mA g(-1). The superior electrochemical performance of S/HPC is closely related to its unique structure, exhibiting the graphitic structure with a high developed porosity framework of macropores in combination with mesopores and micropores. Such nanostructure could shorten the transport pathway for both ions and electrons during prolonged cycling.

Sulfur gradient-distributed CNF composite: a self-inhibiting cathode for binder-free lithium–sulfur batteries

A novel sulfur gradient cathode was developed with a high specific capacity and improved cycling stability for Li–S batteries.

One-pot low-temperature synthesis of a MnFe2O4–graphene composite for lithium ion battery applications

A MnFe₂O₄–reduced graphene oxide (rGO) nanocomposite was successfully synthesized by a one-pot low-temperature process by coprecipitation of Mn ions produced in the modified Hummer's method and in situ reduction of GO at 90 °C.

One-pot synthesis of thin Co(OH)2 nanosheets on graphene and their high activity as a capacitor electrode

We synthesized Co(OH)₂/graphene composites from graphite without a graphene oxide (GO) step. The Co(OH)₂/graphene composite exhibited a specific capacitance of 960 F g⁻¹ at a current density of 10 A g⁻¹.

Reduction mechanisms of additives on Si anodes of Li-ion batteries

Lithiated Si anodes facilitate reduction of carbonate additives through multiple electron transfers.

Improvement of desolvation and resilience of alginate binders for Si-based anodes in a lithium ion battery by calcium-mediated cross-linking

Calcium-mediated cross-linking of alginate improves toughness, resilience and electrolyte desolvation of the alginate binder. These improved properties contribute to enhance the capacity and lifetime of Si anode in LIB.

Facile hydrothermal synthesis of SnO2/C microspheres and double layered core–shell SnO2 microspheres as anode materials for Li-ion secondary batteries

SnO₂/C microspheres and double layered core–shell SnO₂ microspheres can be synthesized in large scale by a facile hydrothermal method followed by heat-treatment.

Inhibiting the shuttle effect in lithium–sulfur batteries using a layer-by-layer assembled ion-permselective separator

A novel strategy for introducing ion-permselective properties in a conventional polyethylene (PE) separator to inhibit the shuttle effect of polysulfides in high-performance lithium–sulfur batteries is reported.

CoxP compounds: electrochemical conversion/partial recombination reaction and partially disproportionated nanocomposite for Li-ion battery anodes

In this report, Co_xP binary compounds and their nanocomposites were synthesized using simple solid-state synthetic routes, and their potential as anode materials for Li-ion batteries was investigated.

Si-Based Anode Materials for Li-Ion Batteries: A Mini Review

Si has been considered as one of the most attractive anode materials for Li-ion batteries (LIBs) because of its high gravimetric and volumetric capacity. Importantly, it is also abundant, cheap, and environmentally benign. In this review, we summarized the recent progress in developments of Si anode materials. First, the electrochemical reaction and failure are outlined, and then, we summarized various methods for improving the battery performance, including those of nanostructuring, alloying, forming hierarchic structures, and using suitable binders. We hope that this review can be of benefit to more intensive investigation of Si-based anode materials.

Design of a high performance thin all-solid-state supercapacitor mimicking the active interface of its liquid-state counterpart

Here we report an all-solid-state supercapacitor (ASSP) which closely mimics the electrode-electrolyte interface of its liquid-state counterpart by impregnating polyaniline (PANI)-coated carbon paper with polyvinyl alcohol-H2SO4 (PVA-H2SO4) gel/plasticized polymer electrolyte. The well penetrated PVA-H2SO4 network along the porous carbon matrix essentially enhanced the electrode-electrolyte interface of the resulting device with a very low equivalent series resistance (ESR) of 1 Ω/cm(2) and established an interfacial structure very similar to a liquid electrolyte. The designed interface of the device was confirmed by cross-sectional elemental mapping and scanning electron microscopy (SEM) images. The PANI in the device displayed a specific capacitance of 647 F/g with an areal capacitance of 1 F/cm(2) at 0.5 A/g and a capacitance retention of 62% at 20 A/g. The above values are the highest among those reported for any solid-state-supercapacitor. The whole device, including the electrolyte, shows a capacitance of 12 F/g with a significantly low leakage current of 16 μA(2). Apart from this, the device showed excellent stability for 10000 cycles with a coulombic efficiency of 100%. Energy density of the PANI in the device is 14.3 Wh/kg.

Reduction mechanisms of ethylene carbonate on si anodes of lithium-ion batteries: effects of degree of lithiation and nature of exposed surface

Ab initio molecular dynamics simulations are used to identify mechanisms of reduction of ethylene carbonate on Si surfaces at various degrees of lithiation, where the low-coordinated surface Si atoms are saturated with O, OH, or H functional groups. The lowest Si content surfaces are represented by quasi-amorphous LiSi4 and LiSi2; intermediate lithiation is given by LiSi crystalline facets, and the highest Li content is studied through Li13Si4 surfaces. It is found that ethylene carbonate (EC) reduction mechanisms depend significantly on the degree of lithiation of the surface. On LiSi surfaces EC is reduced according to two different two-electron mechanisms (one simultaneous and one sequential), which are independent of specific surface functionalization or nature of exposed facets. On the less lithiated surfaces, the simultaneous two-electron reduction is found more frequently. In that mechanism, the EC reduction is initiated by the formation of a C-Si bond that allows adsorption of the intact molecule to the surface and is followed by electron transfer and ring-opening. Strongly lithiated Li13Si4 surfaces are found to be highly reactive. Reduction of adsorbed EC molecules occurs via a four-electron mechanism yielding as reduction products CO(2-) and O(C2H4)O(2-). Direct transfer of two electrons to EC molecules in liquid phase is also possible, resulting in the presence of O(C2H4)OCO(2-) anions in the liquid phase.

Tailoring porosity in carbon nanospheres for lithium-sulfur battery cathodes

Porous hollow carbon spheres with different tailored pore structures have been designed as conducting frameworks for lithium-sulfur battery cathode materials that exhibit stable cycling capacity. By deliberately creating shell porosity and utilizing the interior void volume of the carbon spheres, sufficient space for sulfur storage as well as electrolyte pathways is guaranteed. The effect of different approaches to develop shell porosity is examined and compared in this study. The most highly optimized sulfur-porous carbon nanosphere composite, created using pore-formers to tailor shell porosity, exhibits excellent cycling performance and rate capability. Sulfur is primarily confined in 4-5 nm mesopores in the carbon shell and inner lining of the shells, which is beneficial for enhancing charge transfer and accommodating volume expansion of sulfur during redox cycling. Little capacity degradation (∼0.1% /cycle) is observed over 100 cycles for the optimized material.

Multifunctional CNT-polymer composites for ultra-tough structural supercapacitors and desalination devices

Pulsed electrodeposition of polyaniline (PANI) allows the fabrication of flexible, electrically conductive, nonwoven PANI-carbon nanotube (PANI-CNT) composite fabrics. They possess specific tensile strength and a modulus of toughness higher than that of aluminum matrix composites, titanium and aluminum alloys, steels, and many other structural materials. Electrochemical tests show that these nanocomposites additionally offer excellent cycle stability and ion electro-sorption and storage properties.

Nonaqueous lithium-ion capacitors with high energy densities using trigol-reduced graphene oxide nanosheets as cathode-active material

One HEC of a material: The use of trigol-reduced graphene oxide nanosheets as cathode material in hybrid lithium-ion electrochemical capacitors (Li-HECs) results in an energy density of 45 Wh kg(-1) ; much enhanced when compared to similar devices. The mass loading of the active materials is optimized, and the devices show good cycling performance. Li-HECs employing these materials outperform other supercapacitors, making them attractive for use in power sources.

Synthesis of nanostructured materials by using metal-cyanide coordination polymers and their lithium storage properties

Herein, we demonstrate a novel and simple two-step process for preparing LiCoO2 nanocrystals by using a Prussian blue analogue Co3[Co(CN)6]2 as a precursor. The resultant LiCoO2 nanoparticles possess single crystalline nature and good uniformity with an average size of ca. 360 nm. The unique nanostructure of LiCoO2 provides relatively shorter Li(+) diffusion pathways, thus facilitating the fast kinetics of electrochemical reactions. As a consequence, high reversible capacity, excellent cycling stability and rate capability are achieved with these nanocrystals as cathodes for lithium storage. The LiCoO2 nanocrystals deliver specific capacities of 154.5, 135.8, 119, and 100.3 mA h g(-1) at 0.2, 0.4, 1, and 2 C rates, respectively. Even at a high current density of 4 C, a reversible capacity of 87 mA h g(-1) could be maintained. Importantly, a capacity retention of 83.4% after 100 cycles is achieved at a constant discharge rate of 1 C. Furthermore, owing to facile control of the morphology and size of Prussian blue analogues by varying process parameters, as well as the tailored design of multi-component metal-cyanide hybrid coordination polymers, with which we have successfully prepared porous Fe2O3@NixCo3-xO4 nanocubes, one of the potential anode materials for lithium-ion batteries, such a simple and scalable approach could also be applied to the synthesis of other nanomaterials for energy storage devices.

Hierarchical hollow spheres of Fe2O3 @polyaniline for lithium ion battery anodes

Hierarchical hollow spheres of Fe2 O3 @polyaniline are fabricated by template-free synthesis of iron oxides followed by a post in- and exterior construction. A combination of large surface area with porous structure, fast ion/electron transport, and mechanical integrity renders this material attractive as a lithium-ion anode, showing superior rate capability and cycling performance.

Covalent bond glued sulfur nanosheet-based cathode integration for long-cycle-life Li-S batteries

High-capacity electrochemical active material-based electrodes for lithium ion batteries (LIBs), such as sulfur (S), always face the collapse of the electrode due to the big volume change during insertion of the lithium (Li) ion and therefore shorten the cycle life of the cells. Herein, a series of design from the viewpoint of both individual components and the entire cathode in lithium-sulfur (Li-S) cell was introduced aiming at addressing the issues of poor conductivity, leakage of intermediate polysulphides, and large volumetric expansion upon insertion of the Li ion. In the designed electrode, polydopamine (PD)-coated S nanosheets (NSs) were used as active materials, carboxylic acid functionalized multiwall carbon nanotube (MWCNT-COOH) as conductive additives, and poly(acrylic acid) (PAA) as binders. Far different from the traditional hydrogen bond and/or van der Waals force linked electrodes, stronger covalent bonds formed by cross-linking of PD/MWCNT-COOH and PD/PAA into amide bonds, respectively, were built throughout the whole electrode to firmly integrate all of the individual components in the electrode together. As a result, the cathode demonstrated excellent cyclic performance with a charge capacity of 640 mAh/g after 500 cycles at a current density of 1 A/g. Besides, the charge capacity decay after 500 cycles is as small as 0.021% per cycle, which represents the best capacity retention so far.

Cheap glass fiber mats as a matrix of gel polymer electrolytes for lithium ion batteries

Lithium ion batteries (LIBs) are going to play more important roles in electric vehicles and smart grids. The safety of the current LIBs of large capacity has been remaining a challenge due to the existence of large amounts of organic liquid electrolytes. Gel polymer electrolytes (GPEs) have been tried to replace the organic electrolyte to improve their safety. However, the application of GPEs is handicapped by their poor mechanical strength and high cost. Here, we report an economic gel-type composite membrane with high safety and good mechanical strength based on glass fiber mats, which are separator for lead-acid batteries. The gelled membrane exhibits high ionic conductivity (1.13 mS cm⁻¹), high Li⁺ ion transference number (0.56) and wide electrochemical window. Its electrochemical performance is evaluated by LiFePO₄ cathode with good cycling. The results show this gel-type composite membrane has great attraction to the large-capacity LIBs requiring high safety with low cost.

A novel strategy to construct high performance lithium-ion cells using one dimensional electrospun nanofibers, electrodes and separators

We successfully demonstrated the performance of novel, one-dimensional electrospun nanofibers as cathode, anode and separator-cum-electrolyte in full-cell Li-ion configuration. The cathode, LiMn2O4 delivered excellent cycle life over 800 cycles at current density of 150 mA g(-1) with capacity retention of ~93% in half-cell assembly (Li/LiMn2O4). Under the same current rate, the anode, anatase phase TiO2, rendered ~77% initial reversible capacity after 500 cycles in half-cell configuration (Li/TiO2). Gelled electrospun PVdF-HFP exhibits liquid-like conductivity of ~3.2 mS cm(-1) at ambient temperature conditions (30 °C). For the first time, a full-cell is fabricated with enitrely electrospun one-dimensional materials by adjusting the mass loading of cathode with respect to anode in the presence of gelled PVdF-HFP membrane as a separator-cum-electrolyte. Full-cell LiMn2O4|gelled PVdF-HFP|TiO2 delivered good capacity characteristics and excellent cyclability with an operating potential of ∼2.2 V at a current density of 150 mA g(-1). Under harsh conditions (16 C rate), the full-cell showed a very stable capacity behavior with good calendar life. This clearly showed that electrospinning is an efficient technique for producing high performance electro-active materials to fabricate a high performance Li-ion assembly for commercialization without compromising the eco-friendliness and raw material cost.

A stable cathode for the aprotic Li-O2 battery

Rechargeable lithium-air (O2) batteries are receiving intense interest because their high theoretical specific energy exceeds that of lithium-ion batteries. If the Li-O2 battery is ever to succeed, highly reversible formation/decomposition of Li2O2 must take place at the cathode on cycling. However, carbon, used ubiquitously as the basis of the cathode, decomposes during Li2O2 oxidation on charge and actively promotes electrolyte decomposition on cycling. Replacing carbon with a nanoporous gold cathode, when in contact with a dimethyl sulphoxide-based electrolyte, does seem to demonstrate better stability. However, nanoporous gold is not a suitable cathode; its high mass destroys the key advantage of Li-O2 over Li ion (specific energy), it is too expensive and too difficult to fabricate. Identifying a suitable cathode material for the Li-O2 cell is one of the greatest challenges at present. Here we show that a TiC-based cathode reduces greatly side reactions (arising from the electrolyte and electrode degradation) compared with carbon and exhibits better reversible formation/decomposition of Li2O2 even than nanoporous gold (>98% capacity retention after 100 cycles, compared with 95% for nanoporous gold); it is also four times lighter, of lower cost and easier to fabricate. The stability may originate from the presence of TiO2 (along with some TiOC) on the surface of TiC. In contrast to carbon or nanoporous gold, TiC seems to represent a more viable, stable, cathode for aprotic Li-O2 cells.

Synthesis of highly stable sub-8 nm TiO2 nanoparticles and their multilayer electrodes of TiO2/MWNT for electrochemical applications

Next-generation electrochemical energy storage for integrated microsystems and consumer electronic devices requires novel electrode materials with engineered architectures to meet the requirements of high performance, low cost, and robustness. However, conventional electrode fabrication processes such as doctor blading afford limited control over the electrode thickness and structure at the nanoscale and require the incorporation of insulating binder and other additives, which can promote agglomeration and reduce active surface area, limiting the inherent advantages attainable from nanoscale materials. We have engineered a route for the synthesis of highly stable, sub-8 nm TiO2 nanoparticles and their subsequent incorporation with acid-functionalized multiwalled carbon nanotubes (MWNTs) into nanostructured electrodes using aqueous-based layer-by-layer electrostatic self-assembly. Using this approach, binder-free thin film electrodes with highly controllable thicknesses up to the micrometer scale were developed with well-dispersed, nonagglomerated TiO2 nanoparticles on MWNTs. Upon testing in an Li electrochemical half-cell, these electrodes demonstrate high capacity (>150 mAh/gel(ectrode) at 0.1 A/gel(ectrode)), good rate capability (>100 mAh/gel(ectrode) up to 1 A/g(electrode)) and nearly no capacity loss up to 200 cycles for electrodes with thicknesses up to 1480 nm, indicating their promise as thin-film negative electrodes for future Li storage applications.

Recent progress in supercapacitors: from materials design to system construction

Supercapacitors are currently attracting intensive attention because they can provide energy density by orders of magnitude higher than dielectric capacitors, greater power density, and longer cycling ability than batteries. The main challenge for supercapacitors is to develop them with high energy density that is close to that of a current rechargeable battery, while maintaining their inherent characteristics of high power and long cycling life. Consequently, much research has been devoted to enhance the performance of supercapacitors by either maximizing the specific capacitance and/or increasing the cell voltage. The latest advances in the exploration and development of new supercapacitor systems and related electrode materials are highlighted. Also, the prospects and challenges in practical application are analyzed, aiming to give deep insights into the material science and electrochemical fields.

Bottom-up catalytic approach towards nitrogen-enriched mesoporous carbons/sulfur composites for superior Li-S cathodes

We demonstrate a sustainable and efficient approach to produce high performance sulfur/carbon composite cathodes via a bottom-up catalytic approach. The selective oxidation of H₂S by a nitrogen-enriched mesoporous carbon catalyst can produce elemental sulfur as a by-product which in-situ deposit onto the carbon framework. Due to the metal-free catalytic characteristic and high catalytic selectivity, the resulting sulfur/carbon composites have almost no impurities that thus can be used as cathode materials with compromising battery performance. The layer-by-layer sulfur deposition allows atomic sulfur binding strongly with carbon framework, providing efficient immobilization of sulfur. The nitrogen atoms doped on the carbon framework can increase the surface interactions with polysulfides, leading to the improvement in the trapping of polysulfides. Thus, the composites exhibit a reversible capacity of 939 mAh g⁻¹ after 100 cycles at 0.2 C and an excellent rate capability of 527 mAh g⁻¹ at 5 C after 70 cycles.

Electrochemically Active Polymers for Electrochemical Energy Storage: Opportunities and Challenges

Polymers have a particularly important place in electrochemical energy storage (EES), not just as the electrolyte, as has been a large focus for solid-state batteries, but also as the electrode. This Viewpoint will introduce how electrochemically active polymers (EAPs) are utilized in electrochemical energy storage with an emphasis on battery cathodes. Recent advances in high capacity EAPs and selected challenges (high voltage stability and ion transport) are presented. Should these needs be met, the resulting electrode would bear a high capacity, energy, power, and cycle life. The low cost, potential application in flexible EES, and synthetic versatility of EAPs offer many unique aspects relative to conventional metal oxides. In composites with metal oxides, EAPs can be used as a means to boost ionic and electronic conductivity. Promising examples regarding high capacity polymeric sulfur electrodes, electrochemically stable polyaniline/polyacid complexes, porous polyaniline/V₂O₅ electrodes, and hydrogel-based electrodes are highlighted.

Self-assembled Fe3O4 nanoparticle clusters as high-performance anodes for lithium ion batteries via geometric confinement

Although different kinds of metal oxide nanoparticles continue to be proposed as anode materials for lithium ion batteries (LIBs), their cycle life and power density are still not suitable for commercial applications. Metal oxide nanoparticles have a large storage capacity, but they suffer from the excessive generation of solid-electrolyte interphase (SEI) on the surface, low electrical conductivity, and mechanical degradation and pulverization resulted from severe volume expansion during cycling. Herein we present the preparation of mesoporous iron oxide nanoparticle clusters (MIONCs) by a bottom-up self-assembly approach and demonstrate that they exhibit excellent cyclic stability and rate capability derived from their three-dimensional mesoporous nanostructure. By controlling the geometric configuration, we can achieve stable interfaces between the electrolyte and active materials, resulting in SEI formation confined on the outer surface of the MIONCs.

Sulfur-infiltrated micro- and mesoporous silicon carbide-derived carbon cathode for high-performance lithium sulfur batteries

Novel nanostructured sulfur (S)-carbide derived carbon (CDC) composites with ordered mesopores and high S content are successfully prepared for lithium sulfur batteries. The tunable pore-size distribution and high pore volume of CDC allow for an excellent electrochemical performance of the composites at high current densities. A higher electrolyte molarity is found to enhance the capacity utilization dramatically and reduce S dissolution in S-CDC composite cathodes during cycling.

Critical thickness of SiO2 coating layer on core@shell bulk@nanowire Si anode materials for Li-ion batteries

Amorphous SiO2 coating layers with thicknesses of ca. 2, 7, 10, and 15 nm are introduced into bulk@nanowire core@shell Si particles via direct thermal oxidation at 650-850 °C. Of the coated samples, Si with a coating thickness of ca. 7 nm has the best electrochemical performance. This sample shows an initial discharge capacity of 2279 mA h g(-1) with a Coulombic efficiency of 92% and displays 83% capacity retention after 50 cycles at 0.2C rate.

Assembly of tin oxide/graphene nanosheets into 3D hierarchical frameworks for high-performance lithium storage

3D hierarchical tin oxide/graphene frameworks (SnO2 /GFs) were built up by the in situ synthesis of 2D SnO2 /graphene nanosheets followed by hydrothermal assembly. These SnO2 /GFs exhibited a 3D hierarchical porous architecture with mesopores (≈3 nm), macropores (3-6 μm), and a large surface area (244 m(2) g(-1) ), which not only effectively prevented the agglomeration of SnO2 nanoparticles, but also facilitated fast ion and electron transport in 3D pathways. As a consequence, the SnO2 /GFs exhibited a high capacity of 830 mAh g(-1) for up to 70 charge-discharge cycles at 100 mA g(-1) . Even at a high current density of 500 mA g(-1) , a reversible capacity of 621 mAh g(-1) could be maintained for SnO2 /GFs with excellent cycling stability. Such performance is superior to that of previously reported SnO2 /graphene and other SnO2 /carbon composites with similar weight contents of SnO2 .