Enhanced electrochemical performance of sulfur/polyacrylonitrile composite by carbon coating for lithium/sulfur batteries

A carbon-coated sulfur/polyacrylonitrile (C@S/PAN) core-shell structured composite is successfully prepared via a novel solution processing method. The sulfur/polyacrylonitrile (S/PAN) core particle has a diameter of ~ 100 nm, whereas the carbon shell is about 2 nm thick. The as-prepared C@S/PAN composite shows outstanding electrochemical performance in lithium/sulfur (Li/S) batteries delivering a high initial discharge capacity of 1416 mAh g^?1. Furthermore, it exhibits ~ 89% retention of the initial reversible capacity over 200 cycles at a constant current rate of 0.1 C. The improved performance contributed by the unique composition and the core-shell structure, wherein carbon matrix can also withstand the volume change of sulfur during the process of charging and discharging as well as provide channels for electron transport. In addition, polyacrylonitrile (PAN) matrix suppresses the shuttle effect by the covalent bonding between sulfur (S) and carbon (C) in the PAN matrix.

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Graphical abstract Cycling performance of the S/PAN and C@S/PAN electrodes and TEM image of the C@S/PAN composite.

     

A simple approach to synthesize nanosized sulfur/graphene oxide materials for high-performance lithium/sulfur batteries

We report on a simple and facile synthesis route for the sulfur/graphene oxide composite via ultrasonic mixing of the nano-sulfur and graphene oxide aqueous suspensions followed by a low-temperature heat treatment. High-resolution transmission and scanning electronic microscopy observations revealed the formation of a highly porous structure consisting of sulfur with uniform graphene oxide coating on its surface. The resulting sulfur/graphene oxide (S/GO) composite exhibited high and stable specific discharge capacities of 591 mAh g^?1 after 100 cycles at 0.1 C and good rate capability. This enhanced electrochemical performance could be attributed to the effective confining the polysulfides dissolution and accommodation of the volume changes during the Li-S electrochemical reaction by the functional groups on the graphene oxide coating layer. Furthermore, the highly developed porous structure of S/GO composite favors the enhanced ion transport and electrolyte diffusion.     

A simple approach to synthesize novel sulfur/graphene oxide/multiwalled carbon nanotube composite cathode for high performance lithium/sulfur batteries

A sulfur/graphene oxide/multiwalled carbon nanotube (S/GO/MWNT) composite was synthesized via a simple ultrasonic mixing method followed by heat treatment. By taking advantage of this solution-based self-assembly synthesis route, poisonous and noxious reagents and complicated fabrication processes are rendered unnecessary, thereby simplifying its manufacturing and decreasing the cost of the final product. Transmission and scanning electronic microscopy observations indicated the formation of the three-dimensional interconnected S/GO/MWNT composite through the environmentally friendly process. The GO layers and long MWNTs synergistically constructed hierarchical electron/ion pathways, favoring the ion transport and electrolyte diffusion. The interlaced network can serve as sponges to physically absorb polysulfides to their wrinkled surface and porous structure. In addition, GO could confine the polysulfides’ dissolution through chemical absorption by the functional groups on GO layers. Therefore, the resulting S/GO/MWNT composite exhibits good rate capability and highly stable specific discharge capacity of 773 mA h g^?1 after 100 cycles at 0.1 C.     

Layered lithium chromium manganese oxide compounds for high capacity electrode materials in rechargeable lithium batteries

A series of Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ cathode materials were prepared by the sol-gel process. The structural characterization was carried out by fitting the XRD data by the Rietveld method. The results of X-ray diffraction show that the crystal structure is similar to that of thelayered lithium transition metal oxides (R3-m space group). The particle morphology and size were observed by SEM, and the elemental content was determined by ICP. The electrochemical performance of the cathode was evaluated in the voltage range of 2.0 ∼ 4.9 V with a current density of 7.947 mA/g. The Li_1.27Cr_0.2Mn_0.53O₂ electrode delivered a high reversible capacity of around 280 mAh/g in cycling. Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ was found to be a promising cathode material. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

Nanostructured BaTi1-xSnxO3 ferroelectric materials for electrocaloric applications and energy performance

Nanostructured BaTi_1-xSn_xO₃ (x = 0, 0.05 & 0.075) were successfully synthesized using the modified Pechini processing method. The phase purity and symmetry were examined by X-ray diffraction and Raman spectroscopy. Tetragonal symmetry was obtained for BaTiO₃ (BT) while orthorhombic symmetry for Sn doped BT. BT exhibits an up-shift of the Curie temperature towards high temperatures (T_C = 139 °C). In contrast, a down-shift was recorded for Sn doped BT. Then, indirect electrocaloric (EC) adiabatic temperature change ΔT and the energy storage performances were determined based on ferroelectric hysteresis loops. Interestingly, large EC responsivity of ΔT/ΔE = 0.81 × 10⁻⁶ K m/V was obtained for the BT accompanied with a moderate stored energy of 23 mJ/cm³ but with a high energy efficiency of 67%. The incorporation of Sn in BT was found to broaden the EC responsivity and to improve the energy efficiency up to 90%, recorded for the 5% Sn doped BT.     

Applications of carbon nanotubes in high performance lithium ion batteries

The development of lit;triton ion batteries （LIBs） relies on the improvement in the performance of electrode materials with higher capacity, higher rate capability, and longer cycle lift;. In this review article, the recent advances in carbon nanotube （CNT） anodes, CNT-based composite electrodes, and CNT current collectors for high performance LIBs are concerned. CNT has received considerable attentions as a candidate material for the LIB applications. In addition to a possible choice for anode, CNT has been recognized as a solution in improving the performance of the state-of-the-art electrode materials. The CNT-based composite electrodes can be fabricated by mechanical or chem- ical approaches. Owing to the large aspect ratio and the high electrical conductivity, CNTs at very low loading can lead to an efficient conductive network. The excellent mechanical strength suggests the great potential in forming a structure scaffold to accommodate nano-sized electrode materials. Accordingly, the incorporation of CNTs will enhance the conductivity of the composite electrodes, mitigatc the agglomeration problem, decrease the dependence on inactive binders, and improve the clcctrochenfical properties of both anode and cathode materials remarkably. Freestanding CNT network can be used as lightweight current collectors to increase the overall energy density of LIBs. Finally, research perspectives for exploiting CNTs in high-performance LIBs are discussed.     

Synthesis and elevated temperature performance of a polypyrrole-sulfur-multi-walled carbon nanotube composite cathode for lithium sulfur batteries

A sulfur-multi-walled carbon nanotube composite (S/MWCNT) was prepared using a two-step procedure of liquid-phase infiltration and melt diffusion. Polypyrrole (PPy) conductive polymer was coated on the surface of the as-prepared S/MWCNT composite by in situ polymerization of pyrrole monomer to obtain PPy/S/MWCNT composite. The composite materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The electrochemical performance of the as-prepared cathode material was investigated at 25, 40, and 70 °C at various rates. It was found that temperature has dual effects on the performance of Li/S cells. Increasing the temperature, on one hand, facilitates the lithium ion transport through the cathode and, on the other hand, leads to faster dissolution of active material into the electrolyte. The PPy coating can effectively trap polysulfides in its porous structure, even at elevated temperatures, leading to the improvement of the discharge capacity, the cycle stability, and the coulombic efficiency. The electrochemical impedance spectroscopy (EIS) results reveal that the PPy coating reduces the formation of passive layer on the cathode surface, even at high temperatures, resulting in a better elevated temperature performance. A high reversible capacity of 945 mAh g^?1 was maintained after 50 cycles for the PPy/S/MWCNT composite at 70 °C at a rate of 0.5 C.     

锂离子电池电极材料的第一性原理研究进展

文章综述了第一性原理计算在锂离子电池电极材料模拟与设计方面的研究进展.电极材料的研究包括电极材料的电子结构和电子导电性的研究,嵌锂电位、锂离子输运特性、嵌锂过程中局部结构弛豫与相变以及材料表面特性研究等方面,第一性原理计算在上述诸方面的研究都取得了一定的进展.这些理论上的研究成果,可以帮助人们加深对材料性能与机理的理解,同时对材料的设计也具有指导意义.     

锂离子电池硅基负极材料嵌锂行为的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势方法,计算不同数量的锂离子引起的硅材料晶体结构的变化以及在嵌锂过程中形成Li_xSi(x=1、2、2.4、4.4)合金相的形成能与电子结构.采用LST/QST方法计算过渡态,模拟合金体相中的锂离子迁移过程.计算结果表明,随着嵌锂数量的增加,硅晶胞的体积在不断增大;Li_xSi合金相的形成能为负值,表明在嵌锂过程中锂离子和硅原子可以自发形成这些合金相,其中Li₇Si₃合金最容易形成;随着嵌锂量的增加,锂离子在费米能级处s轨道提供的电子数逐渐增加,锂硅合金在费米能级处的电子数量呈增大趋势,表明锂硅合金的导电性越来越优;常温下Li₂Si体相中很难直接形成锂离子空位,但锂离子空位的迁移过程很容易发生.     

Template-free synthesis of hierarchical NiO microtubes as high performance anode materials for Li-ion batteries

Hierarchical nanostructured NiO (h-NiO) microtubes were prepared by a simple wet-chemical synthesis without the use of template or surfactant, followed by the calcination of α-Ni(OH)₂ precursor. The structural characterization of the h-NiO microtubes were performed by scanning microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), the results of which indicated that the obtained h-NiO microtubes are covered by the nanosheet grown perpendicularly on the tube surface. The unique hierarchical nanostructure of h-NiO microtubes with high surface area and many voids facilitates the electrochemical reaction as well as the short ion and electron transport pathway. Therefore, as anode electrode of Li-ion batteries, the h-NiO microtubes deliver largely enhanced cycle capacity of 770 mAh·g⁻¹ at a current density of 0.5 C after 200 cycles with high columbic efficiency, compared to the NiO rods. These results suggest that the h-NiO microtubes can be a promising anode material for Li-ion batteries.     

Charge/discharge characteristics of sulfur composite electrode at different temperature and current density in rechargeable lithium batteries

The charge/discharge characteristics of the sulfur composite cathodes were investigated at different temperatures and different current densities. The composite presented the discharge capacities of 854 and 632 mAh g⁻¹ at 60 and −20 °C, respectively, while it had the discharge capacities of 792 mAh g⁻¹ at 25 °C. The composite presented the discharge capacities of 792 and 604 mAh g⁻¹ at 55.6 and 667 mA g⁻¹, respectively, at room temperature. The results showed that the sulfur composite cathodes presented good charge/discharge characteristics between 60 and −20 °C and at a high c-rate up to 667 mA g⁻¹.     

Pyrolytic carbon derived from coffee shells as anode materials for lithium batteries

Disordered carbonaceous materials have been obtained by pyrolysis of coffee shells at 800 and 900 °C with pore-forming substances such as KOH and ZnCl₂. X-ray diffraction studies revealed a carbon structure with a large number of disorganized single layer carbon sheets. The structure and morphology of the materials have been greatly varied upon the addition of porogens. The prepared carbon materials have been subjected to cycling studies. The KOH-treated products offered higher capacity with improved stability than those with untreated and ZnCl₂-treated one.     

Electrochromic & magnetic properties of electrode materials for lithium ion batteries

Progress in electrochromic lithium ion batteries(LIBs) is reviewed, highlighting advances and possible research directions. Methods for using the LIB electrode materials' magnetic properties are also described, using several examples.Li_4Ti_5O_(12)(LTO) film is discussed as an electrochromic material and insertion compound. The opto-electrical properties of the LTO film have been characterized by electrical measurements and UV–Vis spectra. A prototype bi-functional electrochromic LIB, incorporating LTO as both electrochromic layer and anode, has also been characterized by charge–discharge measurements and UV–Vis transmittance. The results show that the bi-functional electrochromic LIB prototype works well. Magnetic measurement has proven to be a powerful tool to evaluate the quality of electrode materials. We introduce briefly the magnetism of solids in general, and then discuss the magnetic characteristics of layered oxides, spinel oxides, olivine phosphate Li Fe PO_4, and Nasicon-type Li_3Fe_2(PO_4)_3. We also discuss what kind of impurities can be detected, which will guide us to fabricate high quality films and high performance devices.     

Co-precipitation synthesis and performance of multi-doped LiCrxNixMn2-2xO4-zFz cathode materials for lithium ion batteries

Multiple ion-doped lithium manganese oxides LiCr_xNi_xMn_2-2xO_4-zF_z (0 < x ≤ 0.25, z =  0.05, 0.1) with a spinel structure and space group Fd m were prepared by using the co-precipitation procedure carried out in water–alcohol solvent using adipic acid as the chelating agent. The electrochemical measurements indicated that the charge/discharge capacities of the samples prepared at 600 °C are higher than that of the treatment at 800 °C or microwave heating. The capacitance-voltage (CV) curves of LiCr_xNi_xMn_2-2xO_4-zF_z (0 < x ≤ 0.25, z = 0.05, 0.1) showed that when x ≤ 0.1, the samples had two reduction–oxidation peaks at 4.0 to 4.2-V region, whereas when x > 0.1, the samples had only one reduction–oxidation peak at 4.0- to 4.2-V region in CV measurements and could offer more stable voltage plateau in a 4-V region and also had stable electrical conductivity after 20 cycles. Another reduction–oxidation peak appeared in 4.6-4.8-V region (Ni²⁺–Ni⁴⁺ reduction–oxidation peaks); this suggests that the LiCr_xNi_xMn_2-2xO_4-zF_z (0.1 < x≤ 0.25, z = 0.05, 0.1) cathode material could offer 4.6 to 4.8-V charge/discharge plateaus, and its specific capacity increases with increasing Ni²⁺. The impedance measurements of the cell proved that the F⁻ anion doped can not only prevent Mn³⁺ from disproportion but also can prevent the passivation film from forming and can help keep stable the cell’s electrical properties. The LiCr_0.05Ni_0.05Mn_1.9O_3.9F_0.1 sintered at 600 °C shows the best cycle performance and the largest capacity in all prepared samples; its first discharge capacity is 120 mAh/g, and the discharge capacity loses only 1.78% after 20 cycles. After 100 cycles, it still remains in the spinel structure.     

Positive electrode materials for lithium batteries based on VOPO4

A detailed electrochemical study of Li insertion in the -form of VOPO₄ and the optimization of the cycling performance are presented. The redox process occurs in one step close to 3.76 V, along with a phase transition. In order to improve the intercalation kinetics, the electronic conductivity was optimized by introducing a mixed valency, and the ionic conductivity was favored by introducing ‘pillaring’ molecules or ions in the interlayer space. In this way, the electrochemical behaviors of -VOPO₄·2H₂O, -Na_xVOPO₄, -K_xVOPO₄ and -Mg_xVOPO₄ (0≤x≤1) have been studied: the hydrate compound shows a good specific capacity (100 mA h/g at a C/5 regime), but a poor cyclability was mainly because of water oxidation. The inserted large alkaline ions improved the cyclability up to 80 cycles (Na⁺) or over 100 cycles (K⁺). Enhancements of the VOPO₄ specific capacity have been obtained as well by mechanical ball-millings.     

Electrochemical and structural characteristics of tungstic acids as cathode materials for lithium batteries

The electrochemical characteristics and structural changes associated with discharge and charge of several tungstic acids such as H₂WO₄ and H₂WO₄ · H₂O have been investigated. The suitability of these substances as new cathode materials for nonaqueous lithium batteries has been assessed. H₂WO₄, having only coordinated water molecules, showed a discharge capacity of about 410 Ah kg^–1 of acid weight and a discharge potential around 2 V vs. Li/Li⁺. This capacity was much higher than the 40 180 Ah kg^–1 of anhydrous WO₃. H₂WO₄ showed a good charge-discharge cycling behavior at a capacity below 1e ^–/W. However, the formation of a stable phase such as Li₂WO₄ during the cyclings limited the cycling number. In addition, the crystal structure of H₂WO₄ changed from orthorhombic to tetragonal during discharge, but the original layered lattice was kept on discharge to 1.5e ^–/W. On the other hand, a significant decrease in the layer spacing of H₂WO₄ · H₂O took place with discharge, due to the direct interaction between the interlayer water molecule and the lithium inserted between the layers. In this paper, in particular, the effect of the coordinated and hydrated water molecules in the acid structure on the electrochemical behavior is discussed.     

Preparation and characterization of sulfur-polypyrrole composites with controlled morphology as high capacity cathode for lithium batteries

Sulfur was highly combined with two types of polypyrrole (PPy) in granular (G-PPy) and tubular(T-PPy) morphology by in-situ oxidation and co-heating methods. The morphology of polypyrrole shows a significant effect on the dispersion status and electrochemical behaviors of the sulfur. A stable capacity close to 500 mAh/g was maintained over 60 cycles for the S/T-PPy composite. Electrochemical measurement results suggest that the S/T-PPy composite is obviously superior to the S/G-PPy composite. It is suggested that the as-proposed tubular PPy could be a promising electric matrix for sulfur active host for a high energy density lithium-sulfur battery.     

Challenges regarding thin film deposition of garnet electrolytes for all-solid-state lithium batteries with high energy density

In this work, we studied the deposition of garnet electrolyte thin films in order to realize an all-solid-state battery with high energy density. Therefore, in a first step we investigated the stability of the garnet Li₅La₃Ta₂O₁₂ with the spinel LiCoMnO₄ in order to determine the temperature window for a successful thin film deposition on high-voltage spinels. A mixture of both materials showed a thermal stability up to 600 °C, so that all-solid-state batteries could be realized when the electrolyte is applied at a low deposition temperature. The second part of the work was the thin film deposition of Li₅La₃Ta₂O₁₂ by a sputter deposition process. When a stoichiometric Li₅La₃Ta₂O₁₂ sputter target was used, the surface of the target showed a depletion of lithium after several depositions, which leads to decreasing Li content in the thin films. In order to compensate the lithium loss we enriched the target with LiOH?H₂O. Depositions carried out with the lithium rich target showed the garnet structure on glass substrates after deposition at 500 °C. The garnet structure was observed on Au-coated EN 1.4767 substrates already at a substrate temperature of 400 °C, which is 300 K lower than comparable depositions of Li₇La₃Zr₂O₁₂. These results show that the combination of thin garnet-structured electrolytes and high-voltage spinels is possible.