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.     

The hierarchical porous structure of carbon aerogels as matrix in cathode materials for Li-S batteries

For Li-S batteries, commercial application was hindered by the insulating nature of S and the solubility of polysulfide. Porous carbon materials had proven themselves to be an ideal immobilizer host for S impregnation. Herein, carbon aerogels (CAs) with tunable pore microstructure were synthesized from resorcinol-formaldehyde reaction with increasing catalyst concentration and pyrolysis under high temperature. The results demonstrated that the catalyst concentration played a key role in tuning the porous microstructure of the CAs. In addition, potassium hydroxide (KOH) was introduced to activate the obtained CAs. The activated carbon aerogels (A-CAs) with hierarchical porous structure exhibited the highest specific surface area (1837.4 m² g^?1) and the largest total pore volume (2.276 cm³ g^?1), which combined the advantages of both mesoporous and microporous. The effects of porous microstructure, specific surface area, and pore volume of the CAs and A-CAs on S incorporation were studied. The S/A-CAs exhibited significantly improved reversible capacity (1260 mAh g^?1 at a rate of 0.1 C), enhanced high-rate property, and excellent cycling performance (229 mAh g^?1 after 500 cycles at 1 C) as a cathode for Li-S batteries.     

Surface structure evolution of cathode materials for Li-ion batteries

Lithium ion batteries are important electrochemical energy storage devices for consumer electronics and the most promising candidates for electrical/hybrid vehicles. The surface chemistry influences the performance of the batteries significantly. In this short review, the evolution of the surface structure of the cathode materials at different states of the pristine, storage and electrochemical reactions are summarized. The main methods for the surface modification are also introduced.     

Novel copper redox-based cathode materials for room-temperature sodium-ion batteries

Layered oxides of P2-type Nao.68Cuo.34Mno.6602, P2-type Nao.68Cuo.34Mno.50Tio.1602, and O＇3-type NaCuo.67Sbo.3302 were synthesized and evaluated as cathode materials for room-temperature sodium-ion batteries. The first two materials can deliver a capacity of around 70 mAh/g. The Cu2＋ is oxidized to Cu3＋ during charging, and the Cu3＋ goes back to Cu2＋ upon discharging. This is the first demonstration of the highly reversible change of the redox couple of Cu2＋/Cu3＋ with high storage potential in secondary batteries.     

Ultrathin surface coatings to enhance cycling stability of LiMn2O4 cathode in lithium-ion batteries

Spinel LiMn₂O₄ suffers from severe dissolution when used as a cathode material in rechargeable Li-ion batteries. To enhance the cycling stability of LiMn₂O₄, we use the atomic layer deposition (ALD) method to deposit ultrathin and highly conformal Al₂O₃ coatings (as thin as 0.6–1.2 nm) onto LiMn₂O₄ cathodes with precise thickness control at atomic scale. Both bare and ALD-coated cathodes are cycled at a specific current of 300 mA g^?1 (2.5 C) in a potential range of 3.4–4.5 V (vs. Li/Li⁺). All ALD-coated cathodes exhibit significantly improved cycleability compared to bare cathodes. Particularly, the cathode coated with six Al₂O₃ ALD layers (0.9 nm thick) shows the best cycling performance, delivering an initial capacity of 101.5 mA h?g^?1 and a final capacity of 96.5 mA h?g^?1 after 100 cycles, while bare cathode delivers an initial capacity of 100.6 mA h?g^?1 and a final capacity of only 78.6 mA h?g^?1. Such enhanced electrochemical performances of ALD-coated cathodes are ascribed to the high-quality ALD oxide coatings that are highly conformal, dense, and complete, and thus protect active material from severe dissolution into electrolytes. Besides, cycling performances of coated cathodes can be easily optimized by accurately tuning coating thickness via varying ALD growth cycles.     

Nanoscale zinc-based metal-organic framework with high capacity for lithium-ion batteries

Layered zinc-based metal-organic framework ([Zn(4,4′-bpy)(tfbdc)(H₂O)₂], Zn-LMOF) nanosheets were synthesized by a facile hydrothermal method (4,4′-bpy = 4,4′-bipyridine, H₂tfbdc = tetrafluoroterephthalic acid). The materials were characterized by IR spectrum, elemental analysis, thermogravimetric analysis, powder X-ray diffraction, transmission electron microscope (TEM), scanning electron microscope (SEM), and the Brunauer–Emmett–Teller (BET) surface. When the Zn-LMOF nanosheets with the thickness of about 24 ± 8 nm were used as an anode material of lithium-ion batteries, not only the Zn-LMOF electrode shows a high reversible capacity, retaining 623 mAh g^?1 after 100 cycles at a current density of 50 mA g^?1 but also exhibits an excellent cyclic stability and a higher rate performance.

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Graphical abstract Zinc-based layered metal-organic framework ([Zn(4,4′-bpy)(tfbdc)(H₂O)₂], Zn-LMOF) nanosheets have been synthesized, displaying a high capacity as anode materials for lithium-ion batteries.

     

Synthesis and characterization of mixed vanadium oxide cathode materials for lithium-ion batteries

A family of mixed vanadium oxides LiCo_yNi_(1−y)VO₄ (x=0.2, 0.5 and 0.8) of potential use as high voltage cathode materials in lithium batteries, has been synthesized and characterized. In general the x-ray diffraction analysis showed that these compounds have an inverse spinel structure where about 85 % of the Ni²⁺ and Co²⁺ ions occupies octahedral sites and the rest tetrahedral sites along with the V⁵⁺ ions. Moreover, the annealing temperature plays a key role in determining the particle size, as demonstrated by scanning electron microscope analysis. Cycling voltammetry tests showed that the lithium insertion-extraction process in the LiCo_yNi_(1−y)VO₄ electrode materials occurs reversibly at around 4.3–4.4 V vs. Li and these results are confirmed by cycling tests. The cycling capacity is modest; however the trend of the cycling curves leads to foresee that an increase in capacity may be obtained by extending the charging process beyond 4.6 V vs. Li, once a stable electrolyte will be available. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.     

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.     

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.     

Structure and electrochemical characteristics of LiFePO4 cathode materials for rechargeable Li-Ion batteries

Complex investigations of cathode materials for rechargeable lithium-ion batteries have been carried out using the following techniques: scanning electron microscopy, microanalysis, extended X-ray absorption fine structure (EXAFS) spectroscopy, Mössbauer spectroscopy, and porosimetry. Investigations have been performed on samples prepared according to the original technology at the St. Petersburg State Institute of Technology (Technical University) (SPbSTI (TU)) and on four commercial cathode materials. It has been established that there is a correlation between the nanostructured morphology of the cathode materials, their chemical composition, and electrochemical capacity. It has been found that the internal resistance of the LiFePO₄ cathode material is linearly dependent on the diffusion coefficient of lithium ions. The valence state and local coordination of Fe ions have been studied using the ⁵⁷Fe Mössbauer effect. It has been shown that more than 90% of the iron ions are in the valence state Fe²⁺. Based on the data available in the literature on the methods of synthesizing LiFePO₄ and data on the diagnosis of the studied samples, conclusions have been drawn about a modification of the synthesis for producing high-quality cathode materials for Li-ion batteries.     

Recent advances on Fe- and Mn-based cathode materials for lithium and sodium ion batteries

The ever-growing market of electrochemical energy storage impels the advances on cost-effective and environmentally friendly battery chemistries. Lithium-ion batteries (LIBs) are currently the most critical energy storage devices for a variety of applications, while sodium-ion batteries (SIBs) are expected to complement LIBs in large-scale applications. In respect to their constituent components, the cathode part is the most significant sector regarding weight fraction and cost. Therefore, the development of cathode materials based on Earth’s abundant elements (Fe and Mn) largely determines the prospects of the batteries. Herein, we offer a comprehensive review of the up-to-date advances on Fe- and Mn-based cathode materials for LIBs and SIBs, highlighting some promising candidates, such as Li- and Mn-rich layered oxides, LiNi_0.5Mn_1.5O₄, LiFe_1-xMn_xPO₄, Na_xFe_yMn_1-yO₂, Na₄MnFe₂(PO₄)(P₂O₇), and Prussian blue analogs. Also, challenges and prospects are discussed to direct the possible development of cost-effective and high-performance cathode materials for future rechargeable batteries.     

4-Volt cathode materials for rechargeable lithium batteries wet-chemistry synthesis, structure and electrochemistry

Lithium transition-metal oxides used as intercalation compounds for rechargeable lithium batteries are widely studied in search of structural stability and improved electrochemical performance. Cathode materials belonging to the 4-volt class electrodes were synthesized by wet-chemistry methods, i.e., sol-gel, combustion or co-precipitation techniques. It is shown that synthesis greatly affects the electrochemistry and cycle life characteristics of the cathodes. Extensive damage including local strain variation, nanodomain formation, and changes in cation ordering, has been observed by local probes such as Raman and FTIR spectroscopy. In this work we wish to show the relationship between the local cationic environment and electrochemical characteristics of the 4-volt cathodes. Materials such as LiMn₂O₄, LiCoO₂, LiNi_1−yCo_yO₂, LiNi_1−yCo_yVO₄, and LiMoVO₆ are investigated.     

Excellent long-term electrochemical performance of graphite oxide as cathode materials for lithium-ion batteries

A facile, scalable route has been adopted to synthesize graphite oxides with different degrees of oxidation. Subsequently, graphite oxides with rationally designed functional groups have been utilized as cathode materials for lithium-ion batteries (LIBs). The electrodes deliver the initial and second discharge capacities of 332 and 172 mAh g^?1 at a current density of 0.1 A g^?1, respectively. More importantly, a remarkable long-term cycling performance of 130 mAh g^?1 after 800 cycles has been gathered, with an ultralow capacity fading of 0.03% per cycle from the second cycle. The root cause of excellent cycling stability should be ascribed to the admirable reversibility of epoxy and carbonyl groups in graphite oxides during the Li-cycling. Meanwhile, the deep study has provided a novel way to avoid complex and expensive post-treatment process of graphite oxides, whose synthesis conditions are also optimized. Those striking features make graphite oxides as promising cathode materials for lithium-ion batteries.     

Facile synthesis of phase-pure Sb8O11Cl2 microrods as anode materials for sodium-ion batteries with high capacity

Ionics - Antimony oxychloride (Sb8O11Cl2) microrods with the diameter of about 100 nm are synthesized by a facial solvothermal reaction. And the material of Sb8O11Cl2 is applied as an...     

Sulfur cloaked with different carbonaceous materials for high performance lithium sulfur batteries

Carbon matrices have attracted the attention enthusiastically as the improver materials of sulfur for rechargeable lithium-sulfur battery. In this work, various morphologies (sphere, fiber, tube and layer) based carbon materials have been used for preparing the sulfur-carbon binary composites via melt diffusion method for lithium-sulfur battery application. The prepared binary composites have been characterized for its structural and morphological information using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and, Scanning and Transmission electron microscopy. The electrochemical studies are characterized by cyclic voltammetry, charge-discharge and cycle life after being assembled as lithium-sulfur cell. The S-prGO composite exhibits the initial discharge capacity of 893 mAh g⁻¹ and it sustains over 50 cycles (598 mAh g⁻¹) at 0.1C, with low capacity fading rate when compared to the other composites studied. A remarkable electrochemical performance indicates that the sheet like morphology can accommodate the volume expansion of sulfur and the oxygen groups containing GO minimize the dissolution of lithium polysulfides.     

Nanoflake CoN as a high capacity anode for Li-ion batteries

CoN films with nanoflake morphology are prepared by RF magnetron sputtering on Cu and oxidized Si substrates and characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) techniques. The thickness and composition of the films are determined by the Rutherford back scattering (RBS) technique confirming the stoichiometric composition of CoN with a thickness, 200 (± 10) nm. Li-storage and cycling behavior of nanoflake CoN have been evaluated by galvanostatic discharge–charge cycling and cyclic voltammetry (CV) in cells with Li–metal as counter electrode in the range of 0.005–3.0 V at ambient temperature. Results show that a first-cycle reversible capacity of 760 (± 10) mAhg^? 1 at a current rate 250 mAg^? 1(0.33 C) increases consistently to yield a capacity of 990 (± 10) mAhg^? 1 after 80 cycles. The latter value corresponds to 2.7 mol of cyclable Li/mol of CoN vs. the theoretical, 3.0 mol of Li. Very good rate capability is shown when cycled at 0.59 C (up to 80 cycles) and at 6.6 C (up to 50 cycles). The coloumbic efficiency is found to be 96–98% in the range of 10–80 cycles. The average charge and discharge potentials are 0.7 and 0.2 V, respectively for the decomposition/formation of Li₃N as determined by CV. However, cycling to an upper cut-off voltage of 3.0 V is essential for the completion of the “conversion reaction”. Based on the ex-situ-XRD, -HR-TEM and -SAED data, the plausible Li-cycling mechanism is discussed. The results show that nanoflake CoN film is a prospective anode material for Li-ion batteries.     

Preparation and characteristics of Sb-doped LiNiO2 cathode materials for Li-ion batteries

Compounds LiNi_1−xSb_xO₂ (x=0, 0.1, 0.15, 0.2, 0.25) were synthesized by the two-step calcination method. The structural and morphological properties of the products were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD analysis confirms that the uniform solid solution has been formed in the as-prepared compounds without any impurities. It is shown that the crystal lattice parameters (a, c) of the Sb-doped compounds are bigger than those of pure LiNiO₂ and the Sb-doped compound with x=0.2 consists of spherical-like nanoparticles with a mean grain size of 50 nm. The electrochemical performances of as-prepared samples were studied via galvanostatic charge-discharge cycling tests. The compound with x=0.2 exhibits excellent capacity retention during the charge-discharge processes due to its reinforced structural stability, and a discharge capacity of 102.4 mAh/g is still obtained in the voltage range of 2.5-4.5 V after 20 cycles. Thermal analysis further confirms that the structural stability of LiNi_0.8Sb_0.2O₂ is superior to that of pure LiNiO₂.     

Self-breathing ternary nanocomposite based on nitrogen-doped graphene aerogel/polyaniline/sulfur as a cathode material for lithium-sulfur (Li-S) batteries

Li-S batteries are one of exciting new technologies in high energy density storage devices. But, their widespread commercialization has been limited by several obstacles. Elemental sulfur is not conductive electrically and electrochemical conversion during cycles causes intense change in volume. In this work, a sulfur/polyaniline/nitrogen-doped graphene aerogel (S@PANi-NGA) nanocomposite synthesized through a facile chemical procedure. Nitrogen-doped amino functionalized graphene aerogel (NGA) used as cross-linker for polyaniline to improve the stability of the entire cathode framework. Also, NGA possesses porous structure, high surface area, and enhances electronic conductance due to the nitrogen atoms doped into graphene sheets. As a result, S@PANi-NGA delivered an initial discharge capacity of 1332 mAh g^?1 at a scan rate of 0.2 C and 872 mAh g^?1 of the capacity retained after 100 cycles. The performance was clearly superior to the sulfur/PANi binary composite, in which pure polyaniline used as accommodator.     

Metal oxide-embedded porous carbon nanoparticles as high-performance anode materials for lithium ion batteries

Conjugated microporous polymer (CMP) was used as a precursor to fabricate porous carbon nanoparticles (PCNs) embedded with different metal oxides (NiO_x, CoO_x, and MnO_x). Rate performance tests indicate that 10% MnO_x embedded PCNs (MnO_x10-PCN) show superior rate performance over PCN. MnO_x10-PCN and PCN were further investigated by XRD, XPS, TG, SEM, TEM, FT-IR, BET, cyclic voltammetry, and galvanostatic discharge–charge test. XRD and XPS results reveal that MnO and MnO₂ phase co-exist in the MnO_x10-PCN. SEM results indicate that both MnO_x10-PCN and PCN are spherical particles with a size ranging from 20 to 50 nm. TEM results imply that MnO_x nanoparticles are incorporated inside some porous carbon nanoparticles. FT-IR results indicate some residuary benzene rings remain in the MnO_x10-PCN and PCN. BET analysis reveals that pore properties of MnO_x10-PCN are very near to that of CMP. These unique features ensure MnO_x10-PCN possesses high reversible capacity, excellent rate performance, and long cycling life. MnO_x10-PCN delivers an initial reversible capacity of 986 mAh g^?1 at 0.2 C. In addition, the capacity cycled at 2 C for 700 cycles is even higher than its original capacity.