A novel synthetic route for LiFePO_4/C cathode materials by addition of starch for lithium-ion batteries

LiFePO4/Carbon composite cathode material was prepared using starch as carbon source by spray-pelleting and subsequent pyrolysis in N2. The samples were characterized by XRD, SEM, Raman, and their electrochemical performance was investigated in terms of cycling behavior. There has a special micro-morphology via the process, which is favorable to electrochemical properties. The discharge capacity of the LiFePO4.C composite was 170 mAh g-1, equal to the theoretical specific capacity at 0.1 C rate. At 4 C current density, the specific capacity was about 80 mAh g-1, which can satisfy for transportation applications if having a more flat discharge flat.     

Nanostructured and nanoporous LiFePO4 and LiNi0.5Mn1.5O4-δ as cathode materials for lithium-ion batteries

Recent developments in the synthesis of nanostructured cathode materials are reviewed for the two prominent compounds LiFePO₄ and LiNi_0.5Mn_1.5O₄, and own results on LiFePO₄ and LiNi_0.5Mn_1.5O₄ with different microstructure are presented. The synthesis of LiFePO₄ composites with porous carbons and the scale up of their synthesis is reported, as well as of nanoporous materials. In the case of LiNi_0.5Mn_1.5O₄ the formation of deteriorating cathode surface films is studied with thin film electrodes and ToF-SIMS depth profiling.     

Characterizations of Al–Y thin film composite anode materials for lithium-ion batteries

Al–Y thin films synthesized by the magnetron sputtering technique were evaluated as a possible anode material for lithium-ion batteries. The optimum composition is Al_0.87Y_0.13, which delivers an initial capacity of 625 mAh/g and a capacity loss of 23% during the successive 70 cycles. The improved electrochemical performance, especially the cycling ability, could be attributed to the formation of a hybrid composite where Al nanocrystals are homogenously dispersed in a conductive amorphous Al–Y matrix. This result shows that nanostructural composites could be a way to address the inherent problems with Al-based lithium storage compounds.     

Mössbauer study of LiFeVPO x as a new cathode material for lithium-ion battery

The Mössbauer spectrum of LiFeVPO _x , LiFeV_0.5PO _x and LiFePO _x glasses prepared by conventional melt-quenching method for cathode active material is composed of a doublet due to distorted Fe^IIIO₄ tetrahedra. The Mössbauer spectrum of LiFePO _x glass has an additional doublet due to distorted Fe^IIO₆ octahedra. Heat treatment of LiFeVPO _x and LiFeV_0.5PO _x glasses at a given temperature close to each crystallization temperature causes a marked decrease in the value of Δ, reflecting a decrease in the distortion or an increase in the local symmetry of distorted Fe^IIIO₄ tetrahedra. Heat treatment of LiFeVPO _x glass causes an increase in the electric conductivity from the order of 10^?7 to 10^?3 S·cm^?1, together with an increase in the specific discharge-and charge-capacity of a coin-type Li-ion cell from 50 to 150 mAh·g^?1. These results prove that structural relaxation of the glass network causes an increase in the electric conductivity and an increase in the energy density of the Li-ion cell.     

Cobalt oxide–graphene nanocomposite as anode materials for lithium-ion batteries

Composites of Co₃O₄/graphene nanosheets are prepared and characterized by X-ray diffraction and scanning electron microscopy. Their electrochemical behavior as anode materials of lithium-ion rechargeable batteries is investigated by galvanostatic discharge/charge measurements and cyclic voltammetry. The composite is composed of Co₃O₄ nanorods (around 20??0?nm in diameter) and nanoparticles (around 10?nm in diameter) distributed within the graphene matrix. The specific capacity of the composite is higher than both Co₃O₄ and graphene nanosheets. The cycling stability of Co₃O₄ is obviously enhanced by compositing with graphene. After 100 cycles, the discharge and charge capacity of the composite is 1,005 and 975?mAh g^??, respectively, and the irreversible capacity loss is less than 3%.     

Nano-wire networks of sulfur–polypyrrole composite cathode materials for rechargeable lithium batteries

Polypyrrole (PPy) nanowire was synthesized through a surfactant mediated approach. The sulfur–polypyrrole (S–PPy) composite materials were prepared by heating the mixture of element sulfur and polypyrrole nanowire. The materials were characterized by FTIR, SEM. PPy with special morphology serves as conductive additive, distribution agent and absorbing agents, which effectively enhanced the electrochemical performance of sulfur. The initial discharge capacity of the active materials was 1222 mA h g⁻¹ the remaining capacity is 570 mA h g⁻¹ after 20th cycles.     

Interdispersed silicon–carbon nanocomposites and their application as anode materials for lithium-ion batteries

As an anode material for lithium-ion batteries (LIBs), silicon offers among the highest theoretical storage capacity, but is known to suffer from large structural changes and capacity fading during electrochemical cycling. Nanocomposites of silicon with carbon provide a potential material platform for resolving this problem. We report a spray-pyrolysis approach for synthesizing amorphous silicon–carbon nanocomposites from organic silane precursors. Elemental mapping shows that the amorphous silicon is uniformly dispersed in the carbon matrix. When evaluated as anode materials in LIBs, the materials exhibit highly, stable performance and excellent Coulombic efficiency for more than 150 charge discharge cycles at a charging rate of 1 A/g. Post-mortem analysis indicates that the structure of the Si–C composite is retained after extended electrochemical cycling, confirming the hypothesis that better mechanical buffering is obtained when amorphous Si is embedded in a carbon matrix.     

Effects of oxygen vacancy on the electrochemical properties of γ-V2O5 as cathode material for lithium-ion batteries: a first-principle study

Generating oxygen vacancies is an effective way to improve the lithium-ion storage performance of V₂O₅. However, the mechanism has not been theoretically investigated. In this study, first-principle calculations were performed to study the effect of oxygen vacancy on electrochemical properties of γ-V₂O₅ as cathode material for lithium-ion batteries. γ-V₂O₅ with oxygen vacancy mole fraction of 1.67% shows an open circuit voltage about 0.1 V lower than that of the perfect γ-V₂O₅. Oxygen vacancies generates gap states, which is beneficial to the electronic conductivity of γ-V₂O₅ and γ-LiV₂O₅. In addition, the activation energies for lithium-ion diffusion along [010] in both γ-V₂O₅ and γ-LiV₂O₅ are increased by oxygen vacancy, which might lead to the decrease of diffusion coefficient. Our results will provide guidance for further improving the lithium-ion storage performance of γ-V₂O₅.

     

Improved electrochemical properties of chromium substituted in LiCr1 ? x Ni x O2 cathode materials for rechargeable lithium-ion batteries

Pristine- and chromium-substituted LiNiO₂ nanoparticles were synthesized by sol-gel method using nitrate precursor at 800?°C for 12?h. Physical properties of the synthesized product were analyzed using Fourier transform infrared, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive analysis X-ray. XRD studies revealed a well-defined layer structure and a linear variation of lattice parameters with the addition of chromium and no impurities. Surface morphology and particle size of synthesized materials were changed with chromium addition using SEM and TEM analyses. Assembled lithium-ion cells were evaluated for charge/discharge studies at different rates, cyclic voltammetry, and electrochemical impedance spectra. The initial discharge capacity of LiNiO₂ cathode material was found to be 168?mA hg^?1; however, discharge capacity increased in chromium substitution. Electrochemical impedance spectroscopy revealed that LiCr_0.10Ni_0.90O₂ could enhance charge transfer resistance upon cycling. The substitution of Ni with chromium, LiCr_0.10Ni_0.90O₂, had better cycle life, low irreversible capacity, and excellent electrochemical performance.     

Synthesis and electrochemical performance of TiO2–sulfur composite cathode materials for lithium–sulfur batteries

Titania–sulfur (TiO₂–S) composite cathode materials were synthesized for lithium–sulfur batteries. The composites were characterized and examined by X-ray diffraction, nitrogen adsorption/desorption measurements, scanning electron microscopy, and electrochemical methods, such as cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. It is found that the mesoporous TiO₂ and sulfur particles are uniformly distributed in the composite after a melt-diffusion process. When evaluating the electrochemical properties of as-prepared TiO₂–S composite as cathode materials in lithium–sulfur batteries, it exhibits much improved cyclical stability and high rate performance. The results showed that an initial discharge specific capacity of 1,460 mAh/g at 0.2 C and capacity retention ratio of 46.6 % over 100 cycles of composite cathode, which are higher than that of pristine sulfur. The improvements of electrochemical performances were due to the good dispersion of sulfur in the pores of TiO₂ particles and the excellent adsorbing effect on polysulfides of TiO₂.     

Electrochemical performance of new α-MoO3 nanobelt cathode materials for rechargeable Li-ion batteries

The orthorhombic molybdenum trioxide (α-MoO₃) nanobelts and polyvinyl pyrrolidone (PVP) surfactant MoO₃ nanobelts with high quality were prepared through hydrothermal synthesis. The morphology and microstructure of the samples were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The nanobelts with rectangular cross-section have an orthorhombic phase structure, preferentially grow in [001] direction. The results showed that the H atoms in polyvinyl pyrrolidone are H-bonded with the O atoms in the MoO bonds of MoO₃ nanobelts. When MoO₃ is modified by the intercalation of PVP, it is effectively shielded against electrostatic interaction between the MoO₃ interlayer and Li⁺ ions. The specific capacity of pure MoO₃ nanobelts battery and (PVP)_0.2MoO₃ nanobelts exhibit as 195 mAh g⁻¹ and 237 mAh g⁻¹, respectively after 14 cycles, suggests that the stability of surfactant material is worthy.     

Recent advances in layered LiNi x CoyMn1−x−y O2 cathode materials for lithium ion batteries

Lithium cobalt oxide, LiCoO₂, has been the most widely used cathode material in commercial lithium ion batteries. Nevertheless, cobalt has economic and environmental problems that leave the door open to exploit alternative cathode materials, among which LiNi _x Co_yMn_{1 − x − y} O₂ may have improved performances, such as thermal stability, due to the synergistic effect of the three ions. Recently, intensive effort has been directed towards the development of LiNi _x Co _y Mn_{1 − x − y} O₂ as a possible replacement for LiCoO₂. Recent advances in layered LiNi _x Co_yMn_{1 − x − y} O₂ cathode materials are summarized in this paper. The preparation and the performance are reviewed, and the future promising cathode materials are also prospected.     

Multistep sintering preparation and electrochemical performances of LiFe0.7 V0.2PO4/C cathode material for lithium-ion batteries

Cathode material LiFe_0.7?V_0.2PO₄/C is successfully synthesized by multistep sintering through carbon thermal reaction including 650 °C for 10 h and 750 °C for 6 h. The crystal structure and surface morphology of the synthesized materials are characterized by X-ray diffractometer and scanning electron microscope, respectively. Cycle voltammetry, electrochemical impedance spectroscopy, and charge–discharge test are used to investigate the electrochemical performances of these samples. The results revealed that the synthesized LiFe_0.7?V_0.2PO₄/C material simultaneously contains olivine structure LiFePO₄ and monoclinic structure Li₃V₂(PO₄)₃. It shows improved conductivity, Li-ion diffusion coefficient, excellent charge/discharge performance, and reversibility due to both the incorporation of Li₃V₂(PO₄)₃ fast ion conductor and the employed multistep sintering. The initial discharge specific capacities of LiFe_0.7?V_0.2PO₄/C by multistep sintering are 167.8, 154.7, and 140.8 mAh g^?1 at 0.5, 1, and 2 C, respectively. After a total of 230 cycles at different rates, the sample still shows good performances. After 100 cycles at 2 C, the capacity retention is 99.1 %, and the capacity is 139.6 mAh g^?1. The LiFe_0.7?V_0.2PO₄/C material synthesized by this method can be used as a cathode material for advanced lithium-ion batteries.     

Formation of a vanillic Mannich base — theoretical study

One-pot anti-Mannich reaction of vanillin, aniline and cyclohexanone was successfully catalyzed by ionic liquid triethanolammonium chloroacetate, at room temperature. Yield of the obtained Mannich base was very good and excellent diastereoselectivity was achieved. Mechanism of the reaction was investigated using the density functional theory. The reaction started with a nucleophilic attack of aniline nitrogen at the carbonyl group of vanillin. The intermediate α-amino alcohol formed in this way was further subjected to protonation by the triethanolammonium ion yielding the imminium ion. Theoretically, the obtained imminium ion and the enol form of cyclohexanone can build the protonated Mannich base via the anti and syn pathways. The chloroacetic anion spontaneously abstracts the proton yielding the final product of the reaction anti 2-[1-(N-phenylamino)-1-(4-hydroxy-3-methoxyphenyl)]methylcyclohexanone (MB-H). The syn pathway requires lower activation energy but the anti pathway yields a thermodynamically more stable product, which implies that the examined Mannich reaction is thermodynamically controlled.     

Combined study of vibrational spectra of α-carboline by theoretical and experimental IR methods

This paper reports the application of a scaled ab initio density-functional theory (DFT) at B3LYP/ccpvtz level to calculate the vibrational spectrum of α-carboline (9H-pyrido[2,3-b]indole), αCB, as well as the comparison of theoretical results with the experimental spectra. They have been recorded in Cl₃CD solution and in solid KBr pellets in the 4000-700 cm⁻¹ range. To test the adequacy of the computational method to reproduce the experimental vibrational spectra of αCB, this computational method has also been applied to the related and simpler molecules indole, Ind, and α-azaindole, αAInd. Previously reported assignments for the last compounds have been taken as reference for the subsequent assignments of the αCB vibrational bands. The results show that the hydrogen bonding interactions mainly affect the high frequency region while the skeletal vibration region keeps rather unchanged with the physical state of the sample. Moreover, apart from the vibrations involving the whole carboline nucleus, most of the experimental bands retain their original Ind and/or αAInd frequencies, thus allowing an easy assignment of the computed modes to the αCB vibrational bands.     

Synthesis and electrochemical properties of spinel Li4Ti5O12−x Cl x anode materials for lithium-ion batteries

Li₄Ti₅O_12−x Cl _x (0 ≤ x ≤ 0.3) compounds were synthesized successfully via high temperature solid-state reaction. X-ray diffraction and scanning electron microscopy were used to characterize their structure and morphology. Cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge cycling performance tests were used to characterize their electrochemical properties. The results showed that the Li₄Ti₅O_12−x Cl _x (0 ≤ x ≤ 0.3) compounds were well-crystallized pure spinel phase and that the grain sizes of the samples were about 3–8 μm. The Li₄Ti₅O_11.8Cl_0.2 sample presented the best discharge capacity among all the samples and showed better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂. When the discharge rate was 0.5 C, the Li₄Ti₅O_11.8Cl_0.2 sample presented the superior discharge capacity of 148.7 mAh g⁻¹, while that of the pristine Li₄Ti₅O₁₂ was 129.8 mAh g⁻¹; when the discharge rate was 2 C, the Li₄Ti₅O_11.8Cl_0.2 sample presented the discharge capacity of 120.7 mAh g⁻¹, while that of the pristine Li₄Ti₅O₁₂ was only 89.8 mAh g⁻¹.     

Tin oxide–based anodes for both lithium-ion and sodium-ion batteries

Tin oxide, SnO₂, is a suitable anode for both lithium-ion and sodium-ion batteries (LIBs and SIBs) unlike graphite and silicon, which are only suitable anodes for LIB. SnO₂ has garnered much attention because of its high theoretical capacities (LIB = 1494 mA h g^?1 and SIB = 1378 mA h g^?1). However, the commercialization of SnO₂ anodes is still hugely challenged because these anodes suffer from large volume expansion caused by lithiation/delithiation or sodiation/desodiation during cycling, leading to severe capacity fading. The adopted strategies to solve these problems are nanosizing that greatly improves the structural stability of the material and helps to have fast reaction kinetics. Synthesizing nanocomposite of SnO₂ nanoparticles with nanoporous carbonaceous materials to buffer the volume expansion, enhance cycling stability; create oxygen deficiency to improve intrinsic conductivity. In this review, the recent research trends on SnO₂ as anode for both LIB and SIB systems are presented.