Sulfur/mesoporous carbon composites combined with γ-MnS as cathode materials for lithium/sulfur batteries

With the aim to develop high-performance sulfur electrode, manganese sulfide (MnS) was combined with sulfur/porous carbon composite electrode by a simple precipitation method. Both X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results show that as-prepared MnS corresponds to Rambergite phase with a hexagonal structure (γ-MnS). MnS could be uniformly dispersed in the carbon matrix when the content was less than 20 wt%. When the content of MnS increased, γ-MnS particles aggregated on both outside of the mesoporous carbon channels and the surface of carbon particles. The CV curves of MnS/MC in the first cycle were similar to elemental sulfur, indicating partially decomposed MnS at the surface of mesoporous carbon. Charge/discharge tests indicated that the initial discharge-specific capacity of S/MnS/MC was 1412.5 mAh g^?1 and remained a reversible capacity of 727.4 mAh g^?1 after 50 cycles at a current of 100 mA g^?1, which is superior to that of sulfur composite electrode without MnS.     

Synthesis of selenium/EDTA-derived porous carbon composite as a Li–Se battery cathode

The carbon substrate with unique 3D macroporous structure has been prepared through the immediate carbonization of ethylenediaminetetraacetic acid (EDTA) and KOH mixture. The porous carbon composed of micro- and small mesoporous (2–5 nm) structure has a BET specific surface area of 1824.8 m² g^?1. The amorphous and nanosized Se is uniformly encapsulated into the porous structure of porous carbon using melting diffusion route, and the weight content of Se in target Se/C composite can be as high as ~50 %. As an Li–Se battery cathode, the Se/C composite delivers a reversible (2nd) discharge capacity of 597.4 mAh g^?1 at 0.24C and retains a discharge capacity of 538.4 mAh g^?1 at 0.24C after 100 cycles. Furthermore, the composite also has a stable capacity of 291.0 mAh g^?1 at a high current of 4.8C. The high specific area and good porous size of EDTA-derived carbon substrate may a be responsibility for the excellent electrochemical performances of Se/C composite.     

Facile synthesis of a sulfur/multiwalled carbon nanotube nanocomposite cathode with core–shell structure for lithium rechargeable batteries

A novel sulfur/multiwalled carbon nanotube nanocomposite (S/MWCNT) was prepared by a facile quasi-emulsion template method in an O/W system. Transmission and scanning electronic microscopy show the formation of a highly developed core–shell tubular structure consisting of S/MWCNT composite with uniform sulfur coating on its surface. The homogenous dispersion and integration of MWCNT in the S/MWCNT composite create a highly conductive and mechanically flexible framework, enhancing the electronic conductivity and consequently the rate capability of the material. The S/MWCNT composite cathode could deliver a stable discharge (the fifth cycle) capacity of about 903 mAh g^?1 at 0.1 C, 751 mAh g^?1 at 0.5 C, and 631 mAh g^?1 at 1 C.     

Strong lithium-polysulfide anchoring effect of amorphous carbon for lithium–sulfur batteries

Solving the shuttle effect caused by lithium polysulfide (LPS) dissolution is important in lithium−sulfur batteries. The anchoring of LPSs to carbon combined with sulfur is a method of suppressing the shuttle effect. This first-principles study is the first to report that amorphous carbon offers the best ability to anchor LPSs. The adsorption energies of LPSs on amorphous carbon are at least six times higher than those on graphene and at least two times higher than those on pyridinic-N doped graphene. The LPSs adsorbed on amorphous carbon undergo significant molecular distortion and/or partial dissociation due to the S-to-C electron transfer of 1.2–1.8 e per molecule, as well as the formation of strong bonds between both the Li and S atoms and the sp- and sp²-site C atoms. We propose an amorphous carbon−graphite hybrid anchoring material, because amorphous carbon can strongly capture LPSs and graphite can act as an electron channel.     

TiN synergetic with micro-/mesoporous carbon for enhanced performance lithium–sulfur batteries

Porous carbon has high specific area and total pore volume but weak interaction with dissolved polysulfides. Conductive polar metal compound has strong chemical adsorption of polysulfides but difficult to attain high porosity to encapsulate sulfur series. Instead of efforts on the cathode, we prepared a composite made up of titanium nitride and three-dimensional micro-/mesoporous carbon by a facile and economic way. This composite was coated on the commercial Celgard separator as a polysulfide interceptor to enhance the performances of lithium–sulfur battery. The strategy exerts the synergetic merits of porosity, chemical adsorption, physical interception, and benign conductivity. The hierarchical carbon possesses a high specific surface area of 1571 m²/g and total pore volume of 1.56 cm³/g with the pore size centered at 1.27 and 5.30 nm. TiN can immobilize sulfur intermediates by strong chemical interaction. In addition, excellent electrical conductivity of TiN facilitates redox kinetics. The pure sulfur cathode with the modified separator delivers high initial capacity of 1130 mAh/g at 1 C (1 C?=?1675 mAh/g) and retains 500 mAh/g after 400 cycles, demonstrating superior cycling stability, rate capabilities. Discharge-charge profiles, electrochemical impedance spectrum, and cyclic voltammetry curves of batteries were investigated to support the prominent electrochemistry of the material. Further analysis and observation on the modified separator disassembled from the coin cells after cycling were conducted to probe the evolution and reaction mechanism of the coating.     

First principles study on Mn-doped LiFePO4 as cathode material for rechargeable lithium batteries

The electronic structure and diffusion energy barriers of Li ions in pure and Mn-doped LiFePO4 have been studied using density functional theory （DFT）. The results demonstrate clearly that Fe - O covalent bond is weaker than P- O covalent bond. Pure LiFePO4 has band gap of 0.56 eV and diffusion energy barrier of 2.57 eV for Li ions, while the dopant has small band gap of 0.25 eV and low diffusion energy barrier of 2.31 eV, which indicates that the electronic and ionic conductivity of LiFePO4 have been improved owing to doping.     

First principles study on Mn-doped LiFePO4 as cathode material for rechargeable lithium batteries

The electronic structure and diffusion energy barriers of Li ions in pure and Mn-doped LiFePO4 have been studied using density functional theory(DFT).The results demonstrate clearly that Fe-O covalent bond is weaker than P-O covalent bond.Pure LiFePO4 has band gap of 0.56 eV and diffusion energy barrier of 2.57 eV for Li ions,while the dopant has small band gap of 0.25 eV and low diffusion energy barrier of 2.31 eV,which indicates that the electronic and ionic conductivity of LiFePO4 have been improved owing to doping.     

Synthesis and characterization of multi–wall carbon nanotubes supported-hydrated iron phosphate cathode material for lithium–ion cells by a novel homogeneous precipitation method

Iron phosphate (FePO₄) is a promising candidate for the cathode material in lithium-ion cells due to its easy synthesis and low cost. However, the intrinsic drawbacks of FePO₄ material (i.e., the low electronic conductivity and the low lithium-ion diffusion coefficient) result in poor capacity. To overcome the shortcomings, multi-wall carbon nanotubes (MWNTs) supported hydrated iron phosphate nanocomposites (FePO₄·2H₂O/MWNTs) are prepared using a novel homogeneous precipitation method. Meanwhile, the formation mechanism of highly dispersed and ultrafine FePO₄·2H₂O nanoparticles is discussed in detail. Electrochemical measurements show that FePO₄·2H₂O/MWNTs nanocomposites have a superior discharge capacity and stability. For example, FePO₄·2H₂O/MWNTs nanocomposites exhibit a high initial discharge capacity (129.9?mAhg^?1) and a stable capacity retention (114.3?mAhg^?1 after 20 cycles). The excellent electrochemical performance is attributed to the small particle size of FePO₄·2H₂O nanoparticles, the good electronic conductivity of MWNTs, and the three-dimensional conductive network structure of FePO₄·2H₂O/MWNTs nanocomposites.     

Effect of LiBOB as additive on electrochemical properties of lithium–sulfur batteries

The effect of varying amounts (in the range 1–10 wt.%) of LiBOB (lithium bis(oxalato) borate) as additive in mixed liquid electrolyte on the electrochemical performance of lithium–sulfur batteries is investigated at room temperature. The electrochemical impedance spectroscopy (EIS) of lithium anode with LiBOB has two semicircles, corresponding to charge transfer impedance and ion migration impedance, respectively. The lithium anode with LiBOB shows a higher ion migration impedance, which could reduce the ionic diffusion rate in the anode. Scanning electron microscopy (SEM) observations shows that lithium anode with LiBOB has a smoother and denser surface morphology than the anode without LiBOB. The lithium–sulfur batteries with LiBOB shows the improvement of both the discharge capacity and cycle performance, a maximum discharge capacity of 1,191 mA h g⁻¹ is obtained with 4 wt.% LiBOB. The lithium–sulfur batteries with 4 wt.% LiBOB can maintain a reversible capacity of 756 mA h g⁻¹ after 50 cycles.     

Cellulose-based carbon—A potential anode material for lithium-ion battery

A series of hard carbons was produced by the carbonization of microcrystalline cellulose powder in the temperature range of 950–1100 °C. The properties of the carbons were characterized using elemental analysis, X-ray diffraction and N₂ and CO₂ adsorption. The effect of heat-treatment temperature (HTT), pyrolytic carbon (PC) coating and discharging mode on the lithium insertion/deinsertion behavior of the carbons was assessed in a coin-type half-cell with metal lithium cathode. Increasing cellulose HTT modifies mostly carbon porosity, the surface area (S_DFT) decreases from about 500 to 167 m² g⁻¹. It is associated with lowering the reversible C_rev and irreversible C_irr capacities, but without improving relatively low (0.72) 1st cycle coulombic efficiency. Applying constant current (CC)+constant voltage (CV) discharging mode instead of conventional CC enhances the reversible capacity by 15–18%. PC coating is effective in reducing C_irr by ∼20% with a little change of C_rev. The best capacity parameters, C_rev of 458 mA h g⁻¹ and C_irr of 139 mA h g⁻¹, were measured for PC coated 1000 °C carbon. The prolonged cycling of full-cell assembled with anode of the carbon and commercial cathode revealed that after initial 20 cycles the capacity decay (0.029 mA h/cycle) is comparable to that of commercial cell with graphite-based anode.     

A facile method to prepare monodispersed ZnO–Ag core-shell microspheres

Monodispersed and core-shell structured ZnO–Ag microspheres were realized by coating the Ag nanoparticles onto the surface of ZnO microspheres via a novel solution method. The obtained materials were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible (UV–Vis) absorption measurement. It was shown that face-center-cubic Ag nanoparticles with the mean size of 20 nm were successfully grown on the surface of ZnO microspheres. The absorption band of ZnO–Ag core-shell microspheres showed a large redshift comparing to pure Ag nanoparticles, indicating the strong interfacial interaction between ZnO and Ag. The effects of Ag coating thickness on the structure, morphology and optical absorption of ZnO–Ag core-shell microspheres were investigated. The discussion on the growth process of ZnO–Ag core-shell microspheres revealed the important role of Sn²⁺. This approach was simple, mild and readily scaled up, affording a simple method for the synthesis of size-tunable inorganic-metal core-shell nanostructures.     

Free-standing,curled and partially reduced graphene oxide network as sulfur host for high-performance lithium–sulfur batteries

Lithium–sulfur(Li–S) batteries have received more and more attention because of higher specific capacity and energy density of sulfur than current lithium–ion batteries. However, the low electrical conductivity of sulfur and its discharge product, and also the high dissolution of polysulfides restrict the Li–S battery practical applications. To improve their performances, in this work, we fabricate a novel free-standing, curled and partially reduced graphene oxide(CPrGO for short) network and combine it with sulfur to form a CPrGO–S composite as a cathode for Li–S battery. With sulfur content of 60 wt%, the free-standing CPrGO–S composite network delievers an initial capacity of 988.9 m Ah·g~(-1). After 200 cycles,it shows a stable capacity of 841.4 m Ah·g~(-1) at 0.2 C, retaining about 85% of the initial value. The high electrochemical performance demonstrates that the CPrGO–S network has great potential applications in energy storage system. Such improved properties can be ascribed to the unique free-standing and continous CPrGO–S network which has high specific surface area and good electrical conductivity. In addition, oxygen-containing groups on the partially reduced graphene oxide are beneficial to preventing the polysulfides from dissolving into electrolyte and can mitigate the "shuttle effect".     

A carbon–LiFePO<Subscript>4</Subscript> nanocomposite as high-performance cathode material for lithium-ion batteries

A cathode material of an electrically conducting carbon–LiFePO₄ nanocomposite is synthesized by wet ball milling and spray drying of precursor powders prior to a solid-state reaction. The structural characterization shows that the composite is composed of LiFePO₄ crystals and 4.8 wt.% amorphous carbon. Galvanostatic charge/discharge measurements indicate that the composite exhibits a superior high energy and high cycling stability. This composite delivers a discharge capacity of 159.1 mAh g⁻¹ at 0.1 C, 150.8 mAh g⁻¹ at 1 C, and 140.1 mAh g⁻¹ at 2 C rate. The capacity retention of 99% is achieved after 200 cycles at 2 C. The 18,650 cylindrical batteries are assembled using the composite as cathode materials and demonstrate the capacity of 1,400 mAh and the capacity retention of 97% after 100 cycles at 1 C. These results reveal that the as-prepared LiFePO₄–carbon composite is one of the promising cathode materials for high-performance, advanced lithium-ion batteries directed to the hybrid electric vehicle and pure electric vehicle markets.     

Preparation and performance of sulfur–carbon composite based on hollow carbon nanofiber for lithium-sulfur batteries

A unique structured hollow carbon nanofiber–sulfur composite material (HCF–S) was fabricated and characterized in lithium-sulfur batteries. It is found that a part of spherical sulfur particles are located in the voids formed by the intertwined fibers and the others are confined in hollow channel of the HCF. The high conductive and porous HCF favors the construction of stable three-dimensional conducting network and convenient infiltration of the electrolytes into the cathode. The HCF–S cathode exhibits excellent electrochemical performance in the electrolyte with LiNO₃. By contrast, the ionic liquid electrolyte provides insufficient shuttle suppression and weakens ion transport, which leads to poor cycle and rate capability.     

Effect of Ni/Mn ratio on the performance of LiNi x Mn2 − x O4 cathode material for lithium-ion battery

Lithium nickel manganate is recognized as a type of promising cathode material for lithium-ion battery, due to its advantages such as high voltage, high power density, and relative lower cost. In this paper, a series of LiNi _x Mn_2???x O₄ cathode materials with various molar ratio of Ni/Mn have been prepared with a co-precipitation method, followed by a solid state reaction, and the effect of the molar ratio of Ni/Mn on the structure and properties of materials are intensively investigated by means of X-ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), scanning electron microscopy (SEM), and performance measurements, etc. It is revealed that all the samples with x from 0 to 0.5 have well-defined spinel structure and fit well to Fd-3 m space group. With the increase of the molar ratio of Ni/Mn, the diffraction peaks shift to higher angle slightly and the lattice parameter decreases gradually by the XRD results. Furthermore, it is found that the capacity at the 4.0 V plateau decreases while the capacity at 4.7 V plateau increases with the increase of the ratio of Ni/Mn, and the total discharge capacity shows growth trend with the increase of Ni content. It is important that all the samples with various molar ratio of Ni/Mn exhibit good cyclic stability. Based on the experimental results, we suggest that the Ni may incorporate into the lattice of LiMn₂O₄ substituting of Mn. The plateau at 4.7 V is related to the Ni ions and the plateau at 4.0 V is related to the Mn ions in the materials.     

Revisiting lithium K and iron M₂,₃ edge superimposition: the case of lithium battery material LiFePO₄

Experimental electron energy-loss spectra are presented for FePO₄, LiFePO₄ and NaFePO₄ from 0 to 80 eV. With the help of the NaFePO₄ spectrum in the 50-80 eV range, the double peak observed in LiFePO₄ could be ascribed to the presence of Fe^II and not to the Li K edge, contrary to what was thought previously. Crystal field multiplet calculations confirm this attribution. Using VASP programme based on density functional theory, dielectric response calculations including local field effects in the Hartree approximation are then proven to properly simulate the fine structures due to the lithium K edge. By comparing absolute spectrum intensities, it is shown that the lithium K edge cannot be used to quantify lithium in such compounds. This detailed comparison between theoretical calculations and experimental spectra helps defining the relevant parameters governing intensities in the 50-80 energy range.     

Unique combination of zero–one–two dimensional carbon–titania hybrid for cold cathode application

A unique multi-dimensional hybrid system has been developed by incorporating titania nanoparticle into chemically synthesized amorphous carbon nanotubes (a-CNTs)-amorphous graphene composites. The as-synthesized samples were characterized by x-ray diffraction, scanning and transmission electron microscopy; Raman spectroscopy and photoluminescence spectroscopy. The microscopic studies confirm the attachment of the TiO₂ nanoparticles on carbon structures. The performance of the both the pure and hybrid samples as cold cathode emitter has been investigated and it has been found that cold emission performance of the pure carbon system improves considerably after TiO₂ nanoparticles being added to it giving a turn on field as low as 2.1 V/μm and enhancement factor 2746. The enhancement of field emission characteristic after TiO₂ addition was justified from the ‘ANSYS- Maxwell’ software based simulation study.     

Scientific and technological challenges toward application of lithium–sulfur batteries

Recent progress in improving Li–S batteries' cathodes, anodes, and electrolytes via different approaches is summarized. The poor conductivity of sulfur cathodes, the dissolution of polysulfide intermediates, and the high reactivity of metal Li anodes currently motivate a great deal of research. Urgent challenges concerning Li anodes are also emphasized.