Electrochemical performance of ionic liquid-molybdenum disulfide Li-ion batteries

In this work, molybdenum disulfide (MoS₂) nanostructures with three different morphologies are synthesized and tested with respect to their applicability as anode material in lithium ion batteries with ionic liquid-based electrolytes. The nanostructured samples are compared with thin-film samples to evaluate the influence of the morphologies on the electrochemical performance. Characterization methods include X-ray diffraction, cyclic voltammetry, galvanostatic cycling, and thin-film calorimetry. The thin-film samples show a reversible capacity of 525 mAh g^?1, whereas for the nanostructured samples a maximum capacity 225 mAh g^?1 is found.     

SmPO4-coated Li1.2Mn0.54Ni0.13Co0.13O2 as a cathode material with enhanced cycling stability for lithium ion batteries

SmPO₄ coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials were prepared by the precipitation method and calcined at 450 °C. The crystal structures and electrochemical properties of the pristine and coated samples are studied by X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, electron diffraction spectroscopy, galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). It has been found that the electrochemical performances of the Li-rich cathode material have been substantially improved by SmPO₄ surface coating. Especially, the 2 wt% SmPO₄-coated sample demonstrates the best cycling performance, with capacity retention of 88.4% at 1 C rate after 100 cycles, which is much better than that of 72.3% in the pristine sample. The improved electrochemical properties have been ascribed to the SmPO₄ coating layer, which not only stabilizes the cathode structure by decreasing the loss of oxygen, but also protects the Li-rich cathode material from side reaction with the electrolyte and increases the Li⁺ migration rate at the cathode interface.     

Wet-Chemical Synthesis and Electrochemical Properties of Ce-Doped FeVO4 for Use as New Anode Material in Li-ion Batteries

Ce-doped FeVO₄ nanocomposites were successfully synthesized using reverse micro-emulsion route. Thermal and microstructural characteristics were comprehensively investigated by simultaneous thermal analysis, X-ray diffraction (XRD), scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and laser particle size analyzer. Moreover, as the anode material of lithium-ion batteries, the electrochemical properties were studied by galvanostatic charge and discharge tests and electrochemical impedance spectroscopy. The thermal analysis illustrated that the triclinic crystal structure of FeVO₄ nanoparticles is formed at about 520 °C, which is confirmed by XRD and FT-IR results. Furthermore, the microstructural analyses revealed more regular particles and high specific surface area for wet-chemical derived FeVO₄:Ce, which decreases the diffusion pathway of the lithium ions during the insertion/extraction process. The electrochemical measurements indicated that the electrode cycling performance and rate retention ability of Ce-doped FeVO₄ are better than those of pure FeVO₄ due to the expansion of the crystal lattice, which provided more lattice space for lithium intercalation and de-intercalation. Consequently, the as-prepared Ce-doped FeVO₄ with relatively high specific and reversible capacity, thermal stability and satisfactory cycling performance is a promising candidate for use as a lithium batteries anode material.     

Carbon-tolerance effects of Sm0.2Ce0.8O2−δ modified Ni/YSZ anode for solid oxide fuel cells under methane fuel conditions

Samarium-doped ceria (SDC) is coated onto a Ni/yttria-stabilized zirconia (Ni/YSZ) anode for the direct use of methane in solid-oxide fuel cells. Porous SDC thin layer is applied to the anode using the sol–gel coating method. The experiment was performed in H₂ and CH₄ conditions at 800 °C. The cell performance was improved by approximately 20 % in H₂ conditions by the SDC coating, due to the high ionic conductivity, the mixed ionic and electronic conductive property of the SDC, and the increased triple phase boundary area by the SDC coating in the anode. Carbon was hardly deposited in the SDC-coated Ni/YSZ anode. The cell performance of the SDC-coated Ni/YSZ anode did not show any significant degradation for up to 90 h under 0.1 A cm^?2 at 800 °C. The porous thin SDC coating on the Ni/YSZ anode provided the electrochemical oxidation of CH₄ over the whole anode, and minimized the carbon deposition by electrochemical carbon oxidation.     

Electrochemical characterization of zirconium-doped LiNi0.8Co0.2O2 cathode materials and investigations on deterioration mechanism

The electrochemical performance and the degradation mode of the zirconium doped cathode material, LiNi_0.8Co_0.18Zr_0.02O₂ were investigated and compared with the pristine cathode, LiNi_0.8Co_0.2O₂. The cyclic performance of the doped cathode was superior to the pristine cathode, especially under the high voltage cutoff, although its rate capability remained unimproved. The trend in the graphs of the differential capacity showed that the impedance growth of the cell made of the pristine cathode was much faster than the doped. From the results of the XRD pattern changes between before and after the galvanostatic cycling, less cation mixing and more ordered hexagonal structure were observed for the doped cathode. The impedance spectra showed that the charge transfer resistance for the pristine cathode grew significantly with cycling, while that for the doped cathode increased just moderately. Considerable decrease in the impedance was observed when the new lithium was substituted with the cycled anode, which implied that the interfacial impedance growth on the anode accounted for about 20% of the total impedance measured. It is concluded that the fading mode for LiNi_0.8Co_0.2O₂ is mainly due to the cation mixing, partially contributed by the impedance growth on the anode and by doping the pristine cathode with Zr, cation mixing can be efficiently suppressed.     

Synthesis of LiNi1/3Mn1/3Co1/3O2@graphene for lithium-ion batteries via self-assembled polyelectrolyte layers

LiNi_1/3Co_1/3Mn_1/3O₂ cathode coated with a thin layer of graphene (~8 nm) is successfully synthesized by self-assembly and pyrolysis of polyelectrolyte layers on the surface of NMC particles. The graphene coated NMCs still possess a layered structure with good crystallinity and demonstrate a superior electrochemical performance (e.g., rate capability and cycling stability). The best graphene coated NMC cathode is prepared at a calcination temperature of 800 °C, exhibiting a capacity retention of ~90% vs. 78% for pristine NMC @ cycle 100 and 1 C rate. The improvement in cycling performance is further enlarged after 500 cycles (74% vs. 51%). This can be attributed to the dual functions of graphene coating in enhancing electronic conductivity and protecting NMC surface from the contact with electrolyte during the electrochemical reaction.     

Improvement of structural and electrochemical properties of commercial LiCoO2 by coating with LaF3

Commercial LiCoO₂ has been modified with LaF₃ as a new coating material. The surface modified materials were characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM), field emission scanning electron microscopy (FE-SEM), auger electron spectroscopy (AES) and galvanostatic charge–discharge cycling. The LaF₃-coated LiCoO₂ had an initial discharge specific capacity of 177.4 mAh g⁻¹ within the potential ranges 2.75–4.5 V (vs. Li/Li⁺), and showed a good capacity retention of 90.9% after 50 cycles. It was found that the overcharge tolerance of the coated cathode was significantly better than that of the pristine LiCoO₂ under the same conditions – the capacity retention of the pristine LiCoO₂ was 62.3% after 50 cycles. The improvement could be attributed to the LaF₃ coating layer that hinders interaction between LiCoO₂ and electrolyte and stabilizes the structure of LiCoO₂. Moreover, DSC showed that the coated LiCoO₂ had a higher thermal stability than the pristine LiCoO₂.     

The effect of Co-Co3O4 coating on the electrochemical properties of Si as an anode material for Li ion battery

In order to improve the electrochemical performance of Si as an anode material for Li ion secondary batteries, a biphasic layer composed of Co and Co₃O₄ was coated on Si particles by sol-gel method. Compared to Si, Co-Co₃O₄ coated Si showed the drastic improvement in several electrochemical properties, such as initial coulombic efficiency (55% → 88%), cyclic efficiency and cycle life. The comparison between Co-Co₃O₄ coated Si and heat-treated Si without the coating let us know that the improvement of electrochemical properties only results from Co-Co₃O₄ coating layer. Little changed cyclic properties (cyclic efficiency and cycle life) of Co-Co₃O₄ coated Si even at a higher charge-discharge rate insinuated that Co-Co₃O₄ coating layer plays a crucial role in maintaining the electronic contacts between particles and conducting parts. When trying to measure a thickness variation of the electrodes each containing Si and Co-Co₃O₄ coated Si as active materials, it was notified that Co-Co₃O₄ coating layer can accommodate the volume expansion of Si during Li⁺ insertion, which has its original thickness almost recovered after Li⁺ extraction.     

The influence of carbon content on the lithium diffusion and electrochemical properties of lithium vanadium phosphate

The influence of carbon content and porosity of lithium vanadium phosphate, Li₃V₂(PO₄)₃, on its diffusion properties and electrochemical performance was examined by GITT and galvanostatic charge/discharge experiments. The diffusion coefficient of Li₃V₂(PO₄)₃, as determined by GITT measurements, appears relatively high, thus making this material interesting also for high power application. Moreover, the results of this study clearly show that the porosity and the carbon content of the electrode materials is an important factor affecting the diffusion as well as the electrochemical performance of Li₃V₂(PO₄)₃. It was demonstrated that excessive carbon coating may lead to kinetic hindrances but may also contribute specific capacity in anode materials in voltage regions below 1.0 V versus Li/Li⁺.     

微米级P-Si@a-TiO2负极材料的制备及电化学性能

以微米级Al-Si合金粉为原料，采用去合金法和溶胶-凝胶法工艺制备了无定形TiO2包覆珊瑚状多孔Si结构的P-Si@a-TiO2材料，通过XRD、XPS、SEM和TEM测试对材料的结构和形貌进行了表征，分析并揭示了TiO2层的制备机理及包覆层厚度对复合材料电化学性能的影响规律。结果表明，珊瑚状多孔Si结构和适当厚度的包覆层可以有效缓冲材料的体积膨胀，提高电极的循环稳定性。当TiO2包覆层为10 nm时，对材料的改性效果最佳。此时的P-Si@a-TiO2材料的电极电势差仅为0.321 V，在1.0 A/g下循环50次后具有1357.4 mA·h/g的放电比容量，展现出优越的电化学性能。     

Coaxial MnO/C nanotubes as anodes for lithium-ion batteries

Coaxial MnO/C nanotubes with an average diameter of about 450 nm, a wall thickness of about 150 nm, a length of 1–5 μm and a 10 nm thick carbon layer have been prepared using β-MnO₂ nanotubes as self-templates in acetylene at 600 °C. The microstructure of the product has been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The electrochemical performance of the product has been evaluated by galvanostatic charge/discharge cycling. It is found that the product exhibits a reversible capacity of nearly 500 mAh g⁻¹ at a current density of 188.9 mA g⁻¹, and 83.9% of capacity retention, higher than bare MnO nanotubes (58.2%) and MnO nanoparticles (25.8%). The results reveal that coaxial MnO/C nanotubes would be a promising anode material for next-generation lithium-ion batteries.     

ZrO2-coated Li3V2(PO4)3/C nanocomposite: A high-voltage cathode for rechargeable lithium-ion batteries with remarkable cycling performance

In this study, we show that the poor cycling performance which seriously hinders the application of Li₃V₂(PO₄)₃/C for rechargeable lithium-ion batteries is overcome by amorphous ZrO₂ nano-coating. The ZrO₂-coated Li₃V₂(PO₄)₃/C was synthesized via a conventional solid-state method followed by the application of wet coating. The crystalline structure, morphology and electrochemical performance of the as-synthesized samples were investigated by XRD, SEM, TEM, EDS, galvanostatic charge/discharge and EIS measurements. Compared with the pristine Li₃V₂(PO₄)₃/C, the structure of ZrO₂-coated Li₃V₂(PO₄)₃/C sample had no change, and the existence of ZrO₂ nano-coating effectively enhanced the cycling performance. From the above results, it is believed that the improved cycling performance is attributed to the ability of ZrO₂ layer in preventing direct contact of the active material with the electrolyte resulting in a decrease of electrolyte decomposition reactions.     

Evaluation of the corrosion protection performance of epoxy coatings containing Mg nanoparticle on carbon steel in 0.1 M NaCl solution by SECM and EIS techniques

The effect of corrosion protection performance of epoxy coatings containing magnesium (Mg) nanoparticles on carbon steel was analyzed using scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS). Localized measurements such as oxygen consumption and iron dissolution were observed using SECM in 0.1 M NaCl in the epoxy-coated sample. Line profile and topographic image analysis were measured by applying ?0.70 and +0.60 V vs the Ag/AgCl/saturated KCl reference electrode as the tip potential for the cathodic and anodic reactions, respectively. The tip current at ?0.70 V for the epoxy-coated sample with Mg nanoparticles decreased rapidly, which is due to cathodic reduction in dissolved oxygen. The EIS measurements were conducted in 0.1 M NaCl after wet and dry cyclic corrosion test. The increase in the film resistance (R _f) and charge transfer resistance (R _ct) values was confirmed by the addition of Mg nanoparticles in the epoxy coating. Scanning electron microscope/energy-dispersive X-ray spectroscope analysis showed that Mg was enriched in corrosion products at a scratched area of the coated steel after corrosion testing. Focused ion beam–transmission electron microscope analysis confirmed the presence of the nanoscale oxide layer of Mg in the rust of the steel, which had a beneficial effect on the corrosion resistance of coated steel by forming protective corrosion products in the wet/dry cyclic test.     

Modification of LiNi0.5Co0.2Mn0.3O2 with a NaAlO2 coating produces a cathode with increased long-term cycling performance at a high voltage cutoff

A long-lived cycling property is an important factor for the extensive use of the lithium-ion batteries. In this study, a NaAlO₂ layer was initially coated on the LiNi_0.5Co_0.2Mn_0.3O₂ surface. Electrochemical tests indicate that the coated surface achieves better cycling stability and a higher capacity at 25 °C. In addition, the 1 wt % NaAlO₂-coated sample exhibits the best performance, and it also exhibits a discharge specific capacity of 189.6 mAh∙g⁻¹ at 0.1C in the first cycle. After 800 cycles at 1C, the capacity retention of the 1 wt % NaAlO₂-coated sample is approximately 73.31%, a value that is 21.26% higher than the pristine sample. The electrochemical impedance spectroscopy (EIS) analysis reveals a decrease in the LiNi_0.5Co_0.2Mn_0.3O₂ charge transfer impedance and a significant increase in lithium ion diffusion after the application of the NaAlO₂ coating. The high ion diffusion coefficient and low charge transfer impedance are conducive to the better rate performance of NaAlO₂-coated LiNi_0.5Co_0.2Mn_0.3O₂.     

Highly enhanced electrochemical performances of LiNi0.815Co0.15Al0.035O2 by coating via conductively LiTiO2 for lithium-ion batteries

LiTiO₂ film-coated layered LiNi_0.815Co_0.15Al_0.035O₂ (NCA) material was successfully synthesised through in situ hydrolysis–lithiation to improve electrochemical properties. Herein, NCA was synthesised using solid state reaction, coated by hydrolysis of tetrabutyl titanate and subjected to lithiation process. The optimal molar ratio (LiTiO₂: NCA) was found to be 1.0 mol%, and the thickness of LiTiO₂ film coated on the surface of NCA of 18 nm was observed through HRTEM images. Compared with pristine NCA, 1.0 mol% LiTiO₂-coated NCA demonstrated better electrochemical performance with larger capacity of 20 mAh g⁻¹ under 1 C after 100 cycles. Its related capacity retention was 90.8%. The 1.0 mol% LiTiO₂-coated sample exhibited high discharge capacity of 157.6 mAh g⁻¹ at a current rate of 10 C, whereas the pristine sample only presented 145.3 mAh g⁻¹. The considerably improvement of the rate and cycling properties of the NCA cathode material is achieved using LiTiO₂ as a Li⁺-conductive coating layer. These new findings contribute towards the design of a stable-structured Ni-rich material for lithium-ion batteries.     

An amorphous Si thin film anode with high capacity and long cycling life for lithium ion batteries

A Si thin film of thickness 275 nm was deposited on rough Cu foil by magnetron sputtering for use as lithium ion battery anode material. X-ray diffraction (XRD) and TEM analysis revealed that the Si thin film was completely of amorphous structure. The electrochemical performance of the Si thin film was investigated by cyclic voltammetry and constant current charge/discharge test. The film exhibited a high capacity of 3,134 mAh g⁻¹ at 0.025 C rate. The capacity retention was 61.3% at 0.5 C rate for 500 cycles. An island structure formed on the Cu foil substrate after cycling adhered to the substrate firmly and provided electrical connection. This is the possible reason for the long cycling life of Si thin film anode. Moreover, the cycling performance was further improved by annealing at 300 °C. The Li⁺ diffusion coefficients (D ₀) of Si thin film, measured by cyclic voltammetry, are 1.47 × 10⁻⁹ cm² s⁻¹ and 2.16 × 10⁻⁹ cm² s⁻¹ for different reduced peaks.     

Enhanced electrochemical performance and thermal stability of La2O3-coated LiCoO2

An enhanced electrochemical performance LiCoO₂ cathode was synthesized by coating with various wt.% of La₂O₃ to the LiCoO₂ particle surfaces by a polymeric method, followed by calcination at 923 K for 4 h in air. The surface-coated materials were characterized by XRD, TGA, SEM, TEM, BET and XPS/ESCA techniques. XRD patterns of La₂O₃-coated LiCoO₂ revealed that the coating did not affect the crystal structure, α-NaFeO₂, of the cathode material compared to pristine LiCoO₂. TEM images showed a compact coating layer on the surface of the core material that had an average thickness of about ∼15 nm. XPS data illustrated that the presence of two different environmental O 1s ions corresponds to the surface-coated La₂O₃ and core material. The electrochemical performance of the coated materials by galvanostatic cycling studies suggest that 2.0 wt.% coated La₂O₃ on LiCoO₂ improved cycle stability (284 cycles) by a factor of ∼7 times over the pristine LiCoO₂ cathode material and also demonstrated excellent cell cycle stability when charged at high voltages (4.4, 4.5 and 4.6 V). Impedance spectroscopy demonstrated that the enhanced performance of the coated materials is attributed to slower impedance growth during the charge-discharge processes. The DSC curve revealed that the exothermic peak corresponding to the release of oxygen at ∼464 K was significantly smaller for the La₂O₃-coated cathode material and recognized its high thermal stability.     

Electrochemical impedance characterization of FeSn2 electrodes for Li-ion batteries

This work reports the electrochemical characterization of a micro-scale FeSn₂ electrode in a lithium battery. The electrode is proposed as anode material for advanced lithium ion batteries due to its characteristics of high capacity (500 mAh g⁻¹) and low working voltage (0.6 V vs. Li). The electrochemical alloying process is studied by cyclic voltammetry and galvanostatic cycling while the interfacial properties are investigated by electrochemical impedance spectroscopy. The impedance measurements in combination with the galvanostatic cycling tests reveal relatively low overall impedance values and good electrochemical performance for the electrode, both in terms of delivered capacity and cycling stability, even at the higher C-rate regimes.     

Nano-CaCO3 templated mesoporous carbon as anode material for Li-ion batteries

Mesoporous hard carbon is obtained by pyrolyzing a mixture of sucrose and nanoscaled calcium carbonate (CaCO₃) particles. The microstructure of the carbon is characterized by N₂ adsorption/desorption, Hg porosimetry, field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Raman spectroscopy. The electrochemical performances of the carbon as an anode material for lithium ion batteries are evaluated by galvanostatic charge/discharge and cyclic voltammetry tests. It is shown that this mesoporous carbon possesses high capacity, good cycling performance and rate capability, indicating the promising application of nano-CaCO₃ particle as template in massive fabrication of mesoporous carbon anode materials for lithium ion batteries.     

Properties of Li4Ti5O12 as an anode material in non-flammable electrolytes

Two non-flammable electrolytes 1 M LiPF₆ in sulfolane (TMS) + 5 wt% VC and 0.7 M lithium bis(trifluoromethanesulphonyl)imide (LiNTf₂) in N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulphonyl)imide (MePrPyrNTf₂) + 10 wt% gamma-butyrolactone (GBL) were tested with Li₄Ti₅O₁₂ (LTO) as highly promising anode material for application in lithium-ion batteries. The results were compared for the titanium anode in the classic electrolyte: 1 M LiPF₆ in propylene carbonate + dimethyl carbonate (PC + DMC, 1:1). The performances of LTO/electrolyte/Li cell were tested using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge and scanning electron microscopy (SEM). SEM images of electrodes and those taken after electrochemical cycling showed changes which may be interpreted as a result of solid-state interface formation. Good charge/discharge capacities and low capacity loss at medium C rates preliminary cycling was obtained for the Li₄Ti₅O₁₂ anode. For LTO/1 M LiPF₆ in PC + DMC/Li system, the best capacity was obtained at C/10 and C/3 (145 and 154 mAh g^?1, respectively). In the case of a system working on the basis of a TMS solution (1 M LiPF₆ in TMS + 5 wt% VC) the best value was obtained at a C/5 current and an average of more than 150 mAh g^?1 (86 % of theoretical capacity). For the 0.7 M LiNTf₂ in MePrPyrNTf₂ + 10 wt% GBL electrolyte, the highest capacitance value (at C/20 current) of about 150 mAh g^?1 was observed. The 1 M LiPF₆ in TMS + 5 wt% VC and 0.7 M LiNTf₂ in MePrPyrNTf₂ + 10 wt% GBL electrolytes had a relatively broad thermal stability range and no decomposition peak was observed below 150 °C.