Polyaniline-Assisted Synthesis of Si@C/RGO as Anode Material for Rechargeable Lithium-Ion Batteries

A novel approach to fabricate Si@carbon/reduced graphene oxides composite (Si@C/RGO) assisted by polyaniline (PANI) is developed. Here, PANI not only serves as “glue” to combine Si nanoparticles with graphene oxides through electrostatic attraction but also can be pyrolyzed as carbon layer coated on Si particles during subsequent annealing treatment. The assembled composite delivers high reversible capacity of 1121 mAh g^–1 at a current density of 0.9 A g^–1 over 230 cycles with improved initial Coulombic efficiency of 81.1%, while the bare Si and Si@carbon only retain specific capacity of 50 and 495 mAh g^–1 at 0.3 A g^–1 after 50 cycles, respectively. The enhanced electrochemical performance of Si@C/RGO can be attributed to the dual protection of carbon layer and graphene sheets, which are synergistically capable of overcoming the drawbacks of inner Si particles such as huge volume change and low conductivity and providing protective and conductive matrix to buffer the volume variation, prevent the Si particles from aggregating, enhance the conductivity, and stabilize the solid–electrolyte interface membrane during cycling. Importantly, this method opens a novel, universal graphene coating strategy, which can be extended to other fascinating anode and cathode materials

A Deep Reduction and Partial Oxidation Strategy for Fabrication of Mesoporous Si Anode for Lithium Ion Batteries

A deep reduction and partial oxidation strategy to convert low-cost SiO₂ into mesoporous Si anode with the yield higher than 90% is provided. This strategy has advantage in efficient mesoporous silicon production and <i>in situ</i> formation of several nanometers SiO₂ layer on the surface of silicon particles. Thus, the resulted silicon anode provides extremely high reversible capacity of 1772 mAh g^–1, superior cycling stability with more than 873 mAh g^–1 at 1.8 A g^–1 after 1400 cycles (corresponding to the capacity decay rate of 0.035% per cycle), and good rate capability (∼710 mAh g^–1 at 18A g^–1). These promising results suggest that such strategy for mesoporous Si anode can be potentially commercialized for high energy Li-ion batteries

Ultramicroporous Carbon through an Activation-Free Approach for Li–S and Na–S Batteries in Carbonate-Based Electrolyte

We report an activation-free approach for fabricating ultramicroporous carbon as an accommodation of sulfur molecules for Li–S and Na–S batteries applications in carbonate-based electrolyte. Because of the high specific surface area of 967 m² g^–1, as well as 51.8% of the pore volume is contributed by ultramicropore with pore size less than 0.7 nm, sulfur cathode exhibits superior electrochemical behavior in carbonate-based electrolyte with a capacity of 507.9 mA h g^–1 after 500 cycles at 2 <i>C</i> in Li–S batteries and 392 mA h g^–1 after 200 cycles at 1 <i>C</i> in Na–S batteries, respectively

Honeycomb-like Macro-Germanium as High-Capacity Anodes for Lithium-Ion Batteries with Good Cycling and Rate Performance

Macro-Ge powder has been synthesized with a novel hydrothermal reduction of commercial GeO₂ at 200 °C in an autoclave. The obtained macro-Ge product demonstrates a honeycomb-like macroscopic network structure with a high tap density of 2.19 g cm^–3. As for the anode material of lithium ion batteries, the macro-Ge electrode exhibits 1350 mAh g^–1 at the current rate of 0.2 C and with 64% capacity retention over 3500 total cycles at 1 C. The macro-Ge contains a honeycomb porous structure, which allows for a high volumetric capacity (∼3000 mAh cm^–3). Moreover, the symmetrical and asymmetric rate behaviors also provide its excellent electrochemical property. For example, the macro-Ge electrode can be rapidly charged to 1130 mAh g^–1 in 3 min (20 C) and 890 mAh g^–1 in 90 s (40 C) using the constant discharge mode of 1 C. Furthermore, the Ge electrode still maintains over 1020 mAh g^–1 at 1 C for 300 cycles at the high temperature (55 °C) environment. When coupled with a commercial LiCoO₂ cathode, a 3.5 V lithium-ion battery with capacity retention of 91% (∼364 Wh kg^–1) over 100 cycles is achieved. These outstanding properties may be attributed to the honeycomb structure, for which the porous architectures supply the high efficient ionic transport and buffers the volume change during the lithiation/delithiation processes. Moreover, with bulk frameworks it ensures the high tap density and further improves the energy density. It is supported that the macro-Ge acts as attractive anode materials for further application in rechargeable lithium ion batteries

Vacuum Topotactic Conversion Route to Mesoporous Orthorhombic MoO₃ Nanowire Bundles with Enhanced Electrochemical Performance

The growth of mesoporous bundles composed of orthorhombic MoO₃ nanowires with diameters ranging from 10 to 30 nm and lengths of up to 2 μm by topotactic chemical transformation from triclinic α-MoO₃·H₂O nanorods under vacuum condition at 260 °C is achieved. During the process of vacuum topotactic transformation, the nanorod frameworks of the precursor α-MoO₃·H₂O can be preserved. The crystal structures, molecular structures, morphologies, and growth behavior of the precursory, intermediate and final products are characterized using powder X-ray diffraction (PXRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED). Detailed studies of the mechanism of the mesoporous MoO₃ nanowire bundles formation indicate topotactic nucleation and oriented growth of the well-organized orthorhombic MoO₃ nanowires inside the nanorod frameworks. MoO₃ nanocrystals prefer [001] epitaxial growth direction of triclinic α-MoO₃·H₂O nanorods due to the structural matching of [001] α-MoO₃·H₂O//[100] MoO₃. The electrochemical measurement of the mesoporous MoO₃ nanowire bundles indicates that their galvanostatic Li storage performance can be significantly improved. The high reversible capacities of 954.8 mA h g^–1 can be retained over 150 cycles. The topotactic growth under vacuum based on the crystal structural relationship of hydrated metal oxide and related metal oxide will provide an effective and all-purpose route to controlled preparation of novel micro/nanostructured oxides (such as V₂O₅ and WO₃ nanowires, etc.) with enhanced properties (energy storage/conversion, organic electronics, catalysis, gas-sensor, and so on)

SnS₂- Compared to SnO₂‑Stabilized S/C Composites toward High-Performance Lithium Sulfur Batteries

The common sulfur/carbon (S/C) composite cathodes in lithium sulfur batteries suffer gradual capacity fading over long-term cycling incurred by the poor physical confinement of sulfur in a nonpolar carbon host. In this work, these issues are significantly relieved by introducing polar SnO₂ or SnS₂ species into the S/C composite. SnO₂- or SnS₂-stabilized sulfur in porous carbon composites (SnO₂/S/C and SnS₂/S/C) have been obtained through a baked-in-salt or sealed-in-vessel approach at 245 °C, starting from metallic tin (mp 231.89 °C), excess sulfur, and porous carbon. Both of the in situ-formed SnO₂ and SnS₂ in the two composites could ensure chemical interaction with lithium polysulfide (LiPS) intermediates proven by theoretical calculation. Compared to SnO₂/S/C, the SnS₂/S/C sample affords a more appropriate binding effect and shows lower charge transfer resistance, which is important for the efficient redox reaction of the adsorbed LiPS intermediates during cycling. When used as cathodes for Li–S batteries, the SnS₂/S/C composite with sulfur loading of 78 wt % exhibits superior electrochemical performance. It delivers reversible capacities of 780 mAh g^–1 after 300 cycles at 0.5 C. When further coupled with a Ge/C anode, the full cell also shows good cycling stability and efficiency

B,N-Co-doped Graphene Supported Sulfur for Superior Stable Li–S Half Cell and Ge–S Full Battery

B,N-Co-doped graphene supported sulfur (S@BNG) composite is synthesized by using melamine diborate as precursor. XPS spectra illustrates that BNG with a high percentage and dispersive B, N (B = 13.47%, N = 9.17%) and abundant pyridinic-N and N–B/NB bond, show strong interaction with Li₂S_<i>x</i> proved by adsorption simulation experiments. As cathode for Li–S half cell, S@BNG with a sulfur content of 75% displays a reversible capacity of 765 mA h g^–1 at 1 C even after 500 cycles (a low fading rate of 0.027% per cycle). Even at a high sulfur loading of 4.73 mg cm^–2, S@BNG still shows a high and stable areal capacity of 3.5 mA h cm^–2 after 48 cycles. When S@BNG composite as cathode combines with high performance lithiated Ge anode (discharge capacity of 1138 mA h g^–1 over 1000 cycles at 1 C in half cell), the assembled Ge–S full battery exhibits a superior capacity of 530 mA h g^–1 over 500 cycles at the rate of 1 C

Manipulating the Redox Kinetics of Li–S Chemistry by Tellurium Doping for Improved Li–S Batteries

Fundamentally altering the essential properties of a material itself is always of great interest but challenging as well. Herein, we demonstrate a simple tellurium doping method to intrinsically reshape the electronic properties of the sulfur and manipulate the kinetics of Li–S chemistry for improving the performance of Li–S batteries. DFT calculation indicates that Te doping can effectively facilitate the lithiation/delithiation reactions and lower the lithium ion diffusion energy barrier in Li₂S. Additionally, electrochemical studies prove that the reaction kinetics of Li–S chemistry and cycling performance of Li–S batteries have been significantly improved with Te dopants. An exceptional specific capacity of ∼656 mA h g^–1 and a high Coulombic efficiency of ∼99% have been achieved at 5 A g^–1 even after 1000 cycles. More importantly, the capability to manipulate the intrinsic properties of materials and explore the synergistic effects between conventional strategies and element doping provides new avenues for Li–S batteries and beyond