Space Confinement and Rotation Stress Induced Self-Organization of Double-Helix Nanostructure: A Nanotube Twist with a Moving Catalyst Head

Inorganic materials with double-helix structure have attracted intensive attention due to not only their elegant morphology but also their amazing morphology-related potential applications. The investigation on the formation mechanism of the inorganic double-helix nanostructure is the first step for the fundamental studies of their materials or physical properties. Herein, we demonstrated the space confinement and rotation stress induced self-organization mechanism of the carbon nanotube (CNT)-array double helices under scanning electron microscopy by directly observing their formation process from individual layered double hydroxide flakes, which is a kind of hydrotalcite-like material composed of positively charged layers and charge-balancing interlayer anions. Space confinement is considered to be the most important extrinsic factor for the formation of CNT-array double helices. Synchronous growth of the CNT arrays oppositely from LDH flakes with space confinement on both sides at the same time is essential for the growth of CNT-array double helices. Coiling of the as-grown CNT arrays into double helices will proceed by self-organization, tending to the most stable morphology in order to release their internal rotation stress. Based on the demonstrated mechanism, effective routes were carried out to improve the selectivity for CNT-array double helices. The work provides a promising method for the fabrication of double-helix nanostructures with their two helices connected at the end by self-assembly

Permselective Graphene Oxide Membrane for Highly Stable and Anti-Self-Discharge Lithium–Sulfur Batteries

Lithium–sulfur batteries hold great promise for serving as next generation high energy density batteries. However, the shuttle of polysulfide induces rapid capacity degradation and poor cycling stability of lithium–sulfur cells. Herein, we proposed a unique lithium–sulfur battery configuration with an ultrathin graphene oxide (GO) membrane for high stability. The oxygen electronegative atoms modified GO into a polar plane, and the carboxyl groups acted as ion-hopping sites of positively charged species (Li⁺) and rejected the transportation of negatively charged species (S_<i>n</i>^2–) due to the electrostatic interactions. Such electrostatic repulsion and physical inhibition largely decreased the transference of polysulfides across the GO membrane in the lithium–sulfur system. Consequently, the GO membrane with highly tunable functionalization properties, high mechanical strength, low electric conductivity, and facile fabrication procedure is an effective permselective separator system in lithium–sulfur batteries. By the incorporation of a permselective GO membrane, the cyclic capacity decay rate is also reduced from 0.49 to 0.23%/cycle. As the GO membrane blocks the diffusion of polysulfides through the membrane, it is also with advantages of anti-self-discharge properties

Dual-Phase Lithium Metal Anode Containing a Polysulfide-Induced Solid Electrolyte Interphase and Nanostructured Graphene Framework for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries, with a theoretical energy density of 2600 Wh kg^–1, are a promising platform for high-energy and cost-effective electrochemical energy storage. However, great challenges such as fast capacity degradation and safety concerns prevent it from widespread application. With the adoption of Li metal as the anode, dendritic and mossy metal depositing on the negative electrode during repeated cycles leads to serious safety concerns and low Coulombic efficiency. Herein, we report a distinctive graphene framework structure coated by an <i>in situ</i> formed solid electrolyte interphase (SEI) with Li depositing in the pores as the anode of Li–S batteries. The graphene-based metal anode demonstated a superior dendrite-inhibition behavior in 70 h of lithiation, while the cell with a Cu foil based metal anode was short-circuited after only 4 h of lithiation at 0.5 mA cm^–2. The graphene-modified Li anode with SEI induced by the polysulfide-containing electrolyte improved the Coulombic efficiency to ∼97% for more than 100 cycles, while the control sample with Cu foil as the current collector exhibited huge fluctuations in Coulombic efficiency. The unblocked ion pathways and high electron conductivities of frameworks in the modified metal anode led to the rapid transfer of Li ions through the SEI and endowed the anode framework with an ion conductivity of 7.81 × 10^–2 mS cm^–1, nearly quintuple that of the Cu foil based Li metal anode. Besides, the polarization in the charge–discharge process was halved to 30 mV. The stable and efficient Li deposition was maintained after 2000 cycles. Our results indicated that nanoscale interfacial electrode engineering could be a promising strategy to tackle the intrinsic problems of lithium metal anodes, thus improving the safety of Li–S cells

An Analogous Periodic Law for Strong Anchoring of Polysulfides on Polar Hosts in Lithium Sulfur Batteries: S- or Li-Binding on First-Row Transition-Metal Sulfides?

Lithium–sulfur (Li–S) batteries are strongly considered for next-generation energy storage devices. However, severe issues such as the shuttle of polysulfides restrict their practical applications. Exploring the design principle of anchoring polysulfides physically and chemically through the polar substrate is therefore highly necessary. In this Letter, first-row transition-metal sulfides (TMSs) are selected as the model system to obtain a general principle for the rational design of a sulfur cathode. The strong S-binding that is induced by charge transfer between transition-metal atoms in TMS slabs and S atoms in Li₂S is confirmed to be of great significance in TMS composite cathodes. An analogous periodic law is proposed, which is also extended to first-row TM oxides. VS has the strongest anchoring effects on Li₂S immobilization and a relatively low lithium ion diffusion barrier. The binding energies and Li diffusion properties are considered as the key descriptors for the rational design of sulfur cathodes

An Analogous Periodic Law for Strong Anchoring of Polysulfides on Polar Hosts in Lithium Sulfur Batteries: S- or Li-Binding on First-Row Transition-Metal Sulfides?

Lithium–sulfur (Li–S) batteries are strongly considered for next-generation energy storage devices. However, severe issues such as the shuttle of polysulfides restrict their practical applications. Exploring the design principle of anchoring polysulfides physically and chemically through the polar substrate is therefore highly necessary. In this Letter, first-row transition-metal sulfides (TMSs) are selected as the model system to obtain a general principle for the rational design of a sulfur cathode. The strong S-binding that is induced by charge transfer between transition-metal atoms in TMS slabs and S atoms in Li₂S is confirmed to be of great significance in TMS composite cathodes. An analogous periodic law is proposed, which is also extended to first-row TM oxides. VS has the strongest anchoring effects on Li₂S immobilization and a relatively low lithium ion diffusion barrier. The binding energies and Li diffusion properties are considered as the key descriptors for the rational design of sulfur cathodes

Graphene/Single-Walled Carbon Nanotube Hybrids: One-Step Catalytic Growth and Applications for High-Rate Li–S Batteries

The theoretically proposed graphene/single-walled carbon nanotube (G/SWCNT) hybrids by placing SWCNTs among graphene planes through covalent C–C bonding are expected to have extraordinary physical properties and promising engineering applications. However, the G/CNT hybrids that have been fabricated differ greatly from the proposed G/SWCNT hybrids because either the covalent C–C bonding is not well constructed or only multiwalled CNTs/carbon nanofibers rather than SWCNTs are available in the hybrids. Herein, a novel G/SWCNT hybrid was successfully fabricated by a facile catalytic growth on layered double hydroxide (LDH) at a high temperature over 950 °C. The thermally stable Fe nanoparticles and the uniform structure of the calcined LDH flakes are essential for the simultaneously catalytic deposition of SWCNTs and graphene. The SWCNTs and the CVD-grown graphene, as well as the robust connection between the SWCNTs and graphene, facilitated the construction of a high electrical conductive pathway. The internal spaces between the two stacked graphene layers and among SWCNTs offer room for sulfur storage. Therefore, the as obtained G/SWCNT-S cathode exhibited excellent performance in Li–S batteries with a capacity as high as 650 mAh g^–1 after 100 cycles even at a high current rate of 5 C. Such a novel G/SWCNT hybrid can serve not only as a prototype to shed light on the chemical principle of G/CNT synthesis but also as a platform for their further applications in the area of nanocomposites, heterogeneous catalysis, drug delivery, electrochemical energy storage, and so on

Healing High-Loading Sulfur Electrodes with Unprecedented Long Cycling Life: Spatial Heterogeneity Control

Self-healing capability helps biological systems to maintain their survivability and extend their lifespan. Similarly, self-healing is also beneficial to next-generation secondary batteries because high-capacity electrode materials, especially the cathodes such as oxygen or sulfur, suffer from shortened cycle lives resulting from irreversible and unstable phase transfer. Herein, by mimicking a biological self-healing process, <i>fibrinolysis</i>, we introduced an extrinsic healing agent, polysulfide, to enable the stable operation of sulfur microparticle (SMiP) cathodes. An optimized capacity (∼3.7 mAh cm^–2) with almost no decay after 2000 cycles at a high sulfur loading of 5.6 mg_(S) cm^–2 was attained. The inert SMiP is activated by the solubilization effect of polysulfides whereas the unstable phase transfer is mediated by mitigated spatial heterogeneity of polysulfides, which induces uniform nucleation and growth of solid compounds. The comprehensive understanding of the healing process, as well as of the spatial heterogeneity, could further guide the design of novel healing agents (e.g., lithium iodine) toward high-performance rechargeable batteries

Catalytic Self-Limited Assembly at Hard Templates: A Mesoscale Approach to Graphene Nanoshells for Lithium–Sulfur Batteries

Hollow nanostructures afford intriguing structural features ranging from large surface area and fully exposed active sites to kinetically favorable mass transportation and tunable surface permeability. The unique properties and potential applications of graphene nanoshells with well-defined small cavities and delicately designed graphene shells are strongly considered. Herein, a mesoscale approach to fabricate graphene nanoshells with a single or few graphene layers and quite small diameters through a catalytic self-limited assembly of nanographene on <i>in situ</i> formed nanoparticles was proposed. The graphene nanoshells with a diameter of ca. 10–30 nm and a pore volume of 1.98 cm³ g^–1 were employed as hosts to accommodate the sulfur for high-rate lithium–sulfur batteries. A very high initial discharge capacity of 1520 mAh g^–1, corresponding to 91% sulfur utilization rate at 0.1 C, was achieved on a graphene nanoshell/sulfur composite with 62 wt % loading. A very high retention of 70% was maintained when the current density increased from 0.1 C to 2.0 C, and an ultraslow decay rate of 0.06% per cycle during 1000 cycles was detected

Healing High-Loading Sulfur Electrodes with Unprecedented Long Cycling Life: Spatial Heterogeneity Control

Self-healing capability helps biological systems to maintain their survivability and extend their lifespan. Similarly, self-healing is also beneficial to next-generation secondary batteries because high-capacity electrode materials, especially the cathodes such as oxygen or sulfur, suffer from shortened cycle lives resulting from irreversible and unstable phase transfer. Herein, by mimicking a biological self-healing process, <i>fibrinolysis</i>, we introduced an extrinsic healing agent, polysulfide, to enable the stable operation of sulfur microparticle (SMiP) cathodes. An optimized capacity (∼3.7 mAh cm^–2) with almost no decay after 2000 cycles at a high sulfur loading of 5.6 mg_(S) cm^–2 was attained. The inert SMiP is activated by the solubilization effect of polysulfides whereas the unstable phase transfer is mediated by mitigated spatial heterogeneity of polysulfides, which induces uniform nucleation and growth of solid compounds. The comprehensive understanding of the healing process, as well as of the spatial heterogeneity, could further guide the design of novel healing agents (e.g., lithium iodine) toward high-performance rechargeable batteries

Powering Lithium–Sulfur Battery Performance by Propelling Polysulfide Redox at Sulfiphilic Hosts

Lithium–sulfur (Li–S) battery system is endowed with tremendous energy density, resulting from the complex sulfur electrochemistry involving multielectron redox reactions and phase transformations. Originated from the slow redox kinetics of polysulfide intermediates, the flood of polysulfides in the batteries during cycling induced low sulfur utilization, severe polarization, low energy efficiency, deteriorated polysulfide shuttle, and short cycling life. Herein, sulfiphilic cobalt disulfide (CoS₂) was incorporated into carbon/sulfur cathodes, introducing strong interaction between lithium polysulfides and CoS₂ under working conditions. The interfaces between CoS₂ and electrolyte served as strong adsorption and activation sites for polar polysulfides and therefore accelerated redox reactions of polysulfides. The high polysulfide reactivity not only guaranteed effective polarization mitigation and promoted energy efficiency by 10% but also promised high discharge capacity and stable cycling performance during 2000 cycles. A slow capacity decay rate of 0.034%/cycle at 2.0 C and a high initial capacity of 1368 mAh g^–1 at 0.5 C were achieved. Since the propelling redox reaction is not limited to Li–S system, we foresee the reported strategy herein can be applied in other high-power devices through the systems with controllable redox reactions