Effects of nitrogen and sulfur atom regulation on electrochemical properties of Na3V2(PO4)2F3 cathode material for Na-ion batteries

The cathode material Na₃V₂(PO₄)₂F₃ of sodium-ion battery is well-known for its large number of ion migration channels and high working voltage. However, the electrochemical performance of Na₃V₂(PO₄)₂F₃ is not very outstanding. Thus, in the present study, Na₃V₂(PO₄)₂F₃ cathode materials were successfully synthesized by using the sol-gel method and mechanical milling method to enhance the electrochemical performance. The physicochemical properties of synthesized Na₃V₂(PO₄)₂F₃ were investigated by using X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transition electron microscopy. X-ray diffraction spectroscopy indicates that the doping of nitrogen and sulfur did not alter the crystal form of Na₃V₂(PO₄)₂F₃. Transition electron microscopy image shows that Na₃V₂(PO₄)₂F₃ has a thin carbon layer, and x-ray photoelectron spectroscopy illustrates the successful doping of nitrogen and sulfur into the carbon layer. The cyclic voltammetry curves show that the nitrogen and sulfur co-doped Na₃V₂(PO₄)₂F₃ samples have good reversibility and low polarization. Materials with 15% thiourea has a high discharge specific capacity (126.9 mA h g^?1 at 0.2 C) at the first cycle and excellent cycle stability (126.3 mA h g^?1 after 100 cycles, a capacity retention of 99.5%) among the synthesized cathode materials. In the present study, the electrochemical performance of the Na₃V₂(PO₄)₂F₃ cathode material was enhanced by regulation of co-doping of nitrogen and sulfur atoms.     

Temperature-controlled synthesis of spinel lithium nickel manganese oxide cathode materials for lithium-ion batteries

In this work, we successfully synthesized series of LiNi_0.5Mn_1.5O₄ (LNMO) cathode materials with spinel structure by using a facile sol-gel method and then calcined at various temperature ranging from 600 to 1000 °C. The application of different calcination temperatures significantly influenced the surface morphology, stoichiometry and crystalline nature of the as-synthesized LNMO material. According to the results of physical characterizations, the LNMO materials calcined at various temperatures mainly revealed the stoichiometric disordered Fd-3m structure with a small amount of well-ordered P4₃32 phase. The structural analysis also exhibited that the control of the calcination temperature contributed to the higher crystalline nature. Moreover, the morphological investigations indicated that the increasing calcination temperatures caused the formation of large micron-sized LNMO material. In turn, the electrochemical evaluations revealed the impact of the calcination temperatures on enhancing the electrochemical performances of the LNMO electrode materials up to 900 °C. The LNMO electrode calcined at 900 °C exhibited an impressive initial discharge specific capacity of ca. 142 mAh g⁻¹ between 3.5 and 4.9 V vs. Li/Li⁺, and remarkably improved capacity retention of 97% over 50 cycles. Those excellent electrochemical properties were associated with the presence of the dominant Fd-3m phase over the P4₃32 phase. Additionally, the results of the corrosion and dissolution tests which were performed for all calcined LNMO materials in order to estimate the amount of manganese and nickel ions leached from them, proved that the micro-sized LNMO calcined at 900 °C was the most stable.     

Electrospinning synthesis of Na2MnPO4F/C nanofibers as a high voltage cathode material for Na-ion batteries

Three-dimensional carbon nanofibers embedded with Na₂MnPO₄F nanoparticles are fabricated via electrospinning method and investigated as cathode material for sodium ion batteries. The Na₂MnPO₄F nanoparticles with a size of about 10–30?nm are well-crystallized and the diameter of the carbon nanofibers are about 100?nm. Due to the ultrafine particle size of Na₂MnPO₄F together with high conductivity of the three-dimensional electron/ion hybrid network of carbon nanofibers, the material synthesized at 650?°C exhibit good electrochemical performance at room temperature. It is found that an obvious potential platform as high as 3.6?V during charge/discharge processes occurs and there is an initial specific capacity of 122.4?mAh?g^?1 at 0.05C rate, which is close to the theoretic capacity (one Na⁺ extracted) of Na₂MnPO₄F. This work suggests a new design strategy for high-performance Na₂MnPO₄F cathodes of sodium-ion batteries.     

Synthesis of copper hexacyanoferrate nanoflake as a cathode for sodium-ion batteries

Prussian blue analogues are considered as the promising cathodes for sodium-ion batteries. Since the electrochemical properties are closely related to the morphology, the monodisperse copper hexacyanoferrate nanoflakes with highly crystalline are synthesized by a glycol-assisted coprecipitation method and a tentative synthetic mechanism is proposed to explain the formation of nanostructures. The structure and electrochemical properties are characterized by X-ray photoelectron spectroscopy, FTIR spectra and galvanostatic cycle tests, respectively. Due to the novel architecture of copper hexacyanoferrate, a high electrochemical activity is obtained, resulting a high initial coulombic efficiency of 93%, a capacity retention of 73% at 1?C after 300 cycles and 51?mAh?g^?1 is maintained at high rate of 15?C at 25?°C.     

Synthesis and characterization of sulfur-doped carbon decorated LiFePO4 nanocomposite as high performance cathode material for lithium-ion batteries

This is the first report where crystalline sulfur-doped carbon decorated LiFePO₄ nanocomposite are employed as cathode material for lithium-ion batteries. The electrode has been synthesized via a sol–gel route, in which benzyl disulfide and oxalic acid are used as the sulfur and carbon source, respectively. Meanwhile, the as-synthesized sample is characterized by XRD, SEM, EDS mapping, TEM, Raman spectra, XPS and electrochemical techniques. The results reveal that the sulfur-doped carbon is uniformly coated on the surface of LiFePO₄ without destroying the crystal structure of the bulk material. Moreover, both the electronic conductivity and defect level of the carbon clearly increase, as a consequence, the electron and Li-ion diffusion of the electrode is further improved. As a cathode material for lithium-ion batteries, it exhibits a more outstanding electrochemical performance, especially the rate capability and long cyclic performance. Thus, it can be drawn a conclusion that the sulfur-doped carbon coating approach is an effective method to improve the electrochemical performance of LiFePO₄ and could be extended to modify other electrode materials for lithium-ion batteries.     

Optimized synthesis of Na2/3Ni1/3Mn2/3O2 as cathode for sodium-ion batteries by rapid microwave calcination

Microwave calcination is proposed as an alternative route to conventional heating to prepare layered P2–Na_2/3Ni_1/3Mn_2/3O₂ as a positive electrode for sodium-ion batteries. The sample obtained by the fastest conditions, with a heating ramp of 20 °C min⁻¹ for only 2 h, showed well-crystallized rounded particles. Cyclic voltammetry and impedance spectroscopy evidenced a low internal cell resistance, and high diffusion coefficients, which justify its capability to sustain the highest capacity at 1 C and retain the discharge capacity for at least two hundred cycles.     

Optimal synthesis and new understanding of P2-type Na2/3Mn1/2Fe1/4Co1/4O2 as an advanced cathode material in sodium-ion batteries with improved cycle stability

A sol-gel method with ethylene diamine tetraacetic acid and citric acid as co-chelates is employed for the synthesis of P2-type Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ as cathode material for sodium-ion batteries. Among the various calcination temperatures, the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ with a pure P2-type phase calcined at 900 °C demonstrates the best cycle capacity, with a first discharge capacity of 157 mA h g^?1 and a capacity retention of 91 mA h g^?1 after 100 cycles. For comparison, the classic P2-type Na_2/3Mn_1/2Fe_1/2O₂ cathode prepared under the same conditions shows a comparable first discharge capacity of 150 mA h g^?1 but poorer cycling stability, with a capacity retention of only 42 mA h g^?1 after 100 cycles. Based on X-ray photoelectron spectroscopy, the introduction of cobalt together with sol-gel synthesis solves the severe capacity decay problem of P2-type Na_2/3Mn_1/2Fe_1/2O₂ by reducing the content of Mn and slowing down the loss of Mn on the surface of the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, as well as by improving the activity of Fe³⁺ and the stability of Fe⁴⁺ in the electrode. This research is the first to demonstrate the origin of the excellent cycle stability of Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, which may provide a new strategy for the development of electrode materials for use in sodium-ion batteries.     

Study on the performance characteristics of Li–V–O nanocomposite as cathode material for Li-ion batteries

The Li–V–O composite (n_Li:n_V = 1:3.5) was synthesized by a hydrothermal method and post-treated at 300 °C. XRD analysis confirms that the composite is a binary LiV₃O₈–V₂O₅ composite system with the formula of 0.8LiV₃O₈·0.2V₂O₅. The composite consists of small laminar nanocrystallites with numerous cavities between the stacked laminar nanocrystallites, which can provide good channels for Li⁺ transfer during charge–discharge cycling. The initial discharge capacities of LiV₃O₈ and 0.8LiV₃O₈·0.2V₂O₅ samples were 276 and 365 mAh/g after 20 cycles, the discharge capacities of the two samples were 197.6 and 304 mAh/g, respectively. Smaller capacity loss indicates that the capacity retention of the composite is superior to that of bare LiV₃O₈ cathode.     

Synthesis and properties of novel organic thiolane polymer as cathode material for rechargeable lithium batteries

A novel thiolane polymer, poly[1,2,4,5-tetrakis(propylthio)benzene] (PTPB), was synthesized by facile oxidative-coupling polymerization, characterized by FT-IR, XPS, XRD, TGA and EA, and tested as cathode active material in rechargeable lithium batteries. The FT-IR, XPS and elemental analysis confirm the occurrence of polymerization and show the existence of C–S–C bonds. The results show that the thiolane polymer has electrochemical activity as cathode material in lithium batteries and thioether bonds may be the centers of the electrode reaction. A maximum specific capacity of 200 mAh g⁻¹ was obtained and this agrees roughly with the theoretical prediction. In addition, high voltage efficiency was obtained first time from sulfide polymer.     

Scalable synthesis of novel V2O3/carbon composite as advanced cathode material for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are now receiving incremental attention because of their inherent security and reduced cost of metal zinc. As one type of promising cathode candidates for AZIBs, V₂O₃-based materials have been widely investigated due to the special tunnel structure and high energy density. Nevertheless, the wide application of V₂O₃-based materials is still limited by the weak reaction kinetics, inferior cycling stability as well as unsatisfying strategies for large-scale synthesis. Herein, we designed and synthesized V₂O₃/carbon composite with V₂O₃ coated with a thin carbon layer (denoted as B–V₂O₃@C) via a facile ball-milling route as cathode material for AZIBs. Benefiting from the desirable structural and process features, the bottlenecks above can be effectively addressed. As a result, the as-synthesized B–V₂O₃@C delivers a considerable reversible capacity (as high as 430 mAh g^?1 at 1000 mA g^?1) and enhanced cycling stability (84 mAh g^?1 after 2000 cycles at 5000 mA g^?1), which are much superior than the those of the commercial V₂O₃ (C–V₂O₃). Besides, the Zn-storage mechanism and application in full battery based on B–V₂O₃@C were successively investigated. This work might contribute to the possible large scale application of high-performance V₂O₃-based cathode materials for AZIBs.     

CeF3-modified LiNi1/3Co1/3Mn1/3O2 cathode material for high-voltage Li-ion batteries

A facile chemical deposition method has been adopted to prepare cerium fluoride (CeF₃) surface modified LiNi_1/3Co_1/3Mn_1/3O₂ as cathode material for lithium-ion batteries. Structure analyses reveal that the surface of LiNi_1/3Co_1/3Mn_1/3O₂ particles is uniformly coated by CeF₃. Electrochemical tests indicate that the optimal CeF₃ content is 1 wt%. The 1 wt% CeF₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ can deliver a discharge capacity of 107.1 mA h g⁻¹ even at 5 C rate, while the pristine does only 57.3 mA h g⁻¹. Compared to the pristine, the 1 wt% CeF₃-coated LiNi_1/3Co_1/3Mn_1/3O₂ exhibits the greatly enhanced capacity and cycling stability in the voltage range of 3.0–4.5 V, which suggests that the CeF₃ coating has the positive effect on the high-voltage application of LiNi_1/3Co_1/3Mn_1/3O₂. According to the analyses from electrochemical impedance spectra, enhanced electrochemical performance is mainly because the stable CeF₃ coating layer can prevent the HF-containing electrolyte from continuously attacking the LiNi_1/3Co_1/3Mn_1/3O₂ cathode and retard the passivating layer growth on the cathode.     

Mg2+-doped Na3V2(PO4)3/C decorated with graphene sheets: An ultrafast Na-storage cathode for advanced energy storage

NASICON-type Na₃V₂(PO₄)₃ is one of the most promising cathode materials for sodium-ion batteries, delivering about two Na⁺-ions extraction/insertion from/into the unit structure. However, the low electronic conductivity which leads to bad rate capability and poor cycle performance, limits its practical application for sodium-ion batteries. To overcome the kinetic problem, we attempt to prepare the carbon-coated Na₃V₂(PO₄)₃ nanocrystals further decorated by graphene sheets and doped with Mg²⁺ ion via the two steps of sol-gel process and solid-state treatment for the first time. Such architecture synergistically combines the advantages of two-dimensional graphene sheets and 0-dimensional Mg²⁺-doped Na₃V₂(PO₄)₃/C nanoparticles. It greatly increases the electron/Na⁺-ion transport kinetics and assures the electrode structure integrity, leading to attractive electrochemical performance. When used as sodium-ion batteries cathode, the hybrid composite delivers an initial discharge capacity of 115.2 mAh g⁻¹ at 0.2 C rate, and retains stable discharge capacities of 113.1, 109.0, 102.4, 94.0 and 85.2 mAh g⁻¹ at high current rates of 1, 2, 5, 10 and 20 C rate, respectively. Thus, this nanostructure design provides a promising pathway for developing high-performance Na₃V₂(PO₄)₃ material for sodium-ion batteries.     

Solvent-free, oxidatively prepared polythiophene: High specific capacity as a cathode active material for lithium batteries

Polythiophene (PTH) was prepared by the chemical polymerization of thiophene under ambient, solvent-free conditions in the presence of FeCl₃. This PTH was characterized by FTIR, UV–vis, NMR, and XRD. The NMR spectrum showed a PTH oligomer consisting of both aromatic thiophene and hydrogen-saturated tetrahydrothiophene moieties. The insoluble PTH was studied as a cathode active material for rechargeable lithium batteries with LiN(CF₃SO₂)₂ (LiTFSI), 1,2-dimethoxyethane (DME), and 1,3-dioxolane (DOL) as electrolytes. Charge–discharge tests were conducted at room temperature. The discharge specific capacity, for levels above 400 mA h g⁻¹, was obtained. The detected stable specific capacity and isolated, conjugated structure indicate that the charge–discharge mechanism was different from a classical ‘doping–dedoping’ process. We tentatively propose that the high specific capacity of PTH results from multi-electron electrode reactions on S atoms.     

Enhanced electrochemical performance of ZrO2 modified LiNi0.6Co0.2Mn0.2O2 cathode material for lithium ion batteries

LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cathode has been modified by incorporating ZrO₂ nanoparticles to improve its electrochemical performance. Compared to the pristine electrode, the cycling stability and rate capability of 0.5 wt% ZrO₂ modified-NCM622 have been improved significantly. The 0.5 wt% ZrO₂ modified-NCM622 cathode shows a capacity retention of 83.8% after 100 cycles at 0.1 C between 2.8 and 4.3 V, while that of the pristine NCM622 electrode is only 75.6%. When the current rate is set as 5C, the capacity retention of the 0.5 wt% ZrO₂-modified NCM622 is 10% higher than that of the pristine NCM622. Also, the rate capability of 0.5 wt% ZrO₂-modified NCM622 is better than that of the pristine NCM622 at various C-rates in a voltage range of 2.8–4.3 V. The enhanced electrochemical performances of the ZrO₂-modified NCM622 cathodes can be attributed to their high Li-ion conductivity and structural stability.     

The NaxMnO2 materials prepared by a glycine-nitrate method as advanced cathode materials for aqueous sodium-ion rechargeable batteries

Cathodic material for sodium-ion rechargeable batteries based on Na_xMnO₂ were synthesized by glycine nitrate method and subsequent annealing at high temperatures. Different crystal structures with different morphologies were obtained depending on the annealing temperature: hexagonal layeredα-Na_0.7MnO_2.05 nanoplates were obtained at 850 °C, while 3-D tunnel structured Na_0·4MnO₂ and Na_0·44MnO₂, both with rod-like morphology, were obtained at 800 °C and 900 °C, respectively. The investigations of the electrochemical behavior of obtained cathodic materials in aqueous NaNO₃ solution have shown that Na_0·44MnO₂ obtained at 900 °C has shown the best battery performance. Its initial discharge capacities are 123.5 mA h/g, 113.2 mA h/g, and 102.0 mA h/g at the high current densities of 1000, 2000 and 5000 mA/g, respectively.     

Structural and electrochemical studies of PPy/PEG-LiFePO4 cathode material for Li-ion batteries

A simple chemical oxidative polymerization of pyrrole (Py) directly onto the surface of LiFePO₄ particles was applied to the synthesis of polypyrrole-LiFePO₄ (PPy-LiFePO₄) powder. The LiFePO₄ sample without carbon coating was synthesized by a solvothermal method. The polyethylene glycol (PEG) was used as additive during Py polymerization for increasing the PPy-LiFePO₄ conductivity. Properties of resulting LiFePO₄, PPy-LiFePO₄ and PPy/PEG-LiFePO₄ samples were characterized by XRD, SEM, TGA and galvanostatic charge-discharge measurements. These methods confirmed the presence of polypyrrole on LiFePO₄ particles and its homogeneous distribution in the resulting powder material. The PPy/PEG-LiFePO₄ composites show higher discharge capacity than pure LiFePO₄, as PPy/PEG network improves the electron conductivity. It presents specific discharge capacity of 153 mAh/g at C/5 rate.     

锂离子电池正极材料LiNi_(0.8)Al_(0.2)O_(2-x)F_x的制备及其性能的研究

通过掺杂合成锂离子电池正极材料LiNi0.8Al0.2O2-xFx,研究了掺杂离子氟对材料性能的影响。XRD分析表明,该种材料具有层状结构,从结构上保证了该材料具有较好的嵌锂性能。SEM观察显示,材料的颗粒比较均匀。     

锂离子电池正极材料铌掺杂LiNiO2 的制备与电化学性能

为了提高LiNiO₂的电化学性能,用固相反应法制备了铌掺杂LiNiO₂材料,并用X射线衍射（XRD）分析、恒电流滴定技术（GITT）、电化学阻抗谱（EIS）等方法研究铌掺杂量对LiNiO₂的结构和性能的影响。结果表明适量的铌（Nb）掺杂可以提高LiNiO₂层状结构的有序程度,降低Li⁺/Ni²⁺混合程度,降低电荷转移阻抗,提高活性材料中锂离子的扩散系数。其中LiNi_0.99Nb_0.01O₂在0.5C循环100次的容量保持率为91.4%,5C时放电比容量为143 mA·h/g。而未掺杂铌的LiNiO₂在相同条件下的容量保持率和比容量仅为69.2%和127 mA·h/g。结果说明铌掺杂能够有效提高LiNiO₂的电化学性能。     

Nano-sized over-lithiated oxide by a mechano-chemical activation-assisted microwave technique as cathode material for lithium ion batteries and its electrochemical performance

Over-lithiated oxide has been attracting enormous attention due to its high work voltage and high specific capacity. However, the bottlenecks of low initial coulombic efficiency and voltage decay block its industrial application. In this paper, nano-sized Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ was successfully synthesized by a mechano-chemical activation-assisted microwave technique, in which Mn-Co-Ni-based micro spherical precursor by conventional co-precipitation method was ball milled with Li₂CO₃ as lithium source and alcohol as dispersant into nano size and then sintered by microwave to obtain the final product. The as-prepared sample sintered for 30 min exhibited a superior electrochemical performance: almost no capacity fading after 100 cycles at 0.1 C. The rate performance was also improved significantly and the one sintered for 30 min delivered a discharge capacity of 239, 228, 215, 193 mA h g^?1 at 0.1 C, 0.2 C, 0.5 C and 1 C respectively. The distinctive electrochemical performance benefits from the uniform nano-sized particle distribution and good electrode kinetics. It is concluded that such mechano-chemical activation-assisted microwave technique featuring high time and energy efficiency can be considered as one of the dominant routes to realize the industrialization of over-lithiated oxide.     

Reduced graphene oxide coated Fe-soc as a cathode material for high-performance lithium-sulfur batteries

To solve the problem of the rapid decrease in capacity caused by poor conductivity, polysulfide shuttling, and the volume expansion associated with the reaction process, we attempt to use metal-organic framework (MOF) Fe-soc coated with reduced graphene oxide through electrostatic adsorption as a sulfur carrier material for lithium sulfur batteries. The research results show that S/Fe-soc@rGO has a high initial discharge specific capacity of 1634.3 mA h g⁻¹ with a stable specific capacity retention rate of 865.3 mA h g⁻¹ after 80 cycles and displays enhanced rate performance with high discharge specific capacities of 638.8 and 334.3 mA h g⁻¹ after 200 cycles at 0.5 and 1 C, respectively. Fe-soc has unsaturated metal sites can adsorb sulfur and polysulfide, effectively bind polysulfide, symmetrical stable structure is conducive to speed up the electron and ion transmission efficiency while buffering the volume expansion during charge and discharge. In addition, reduced graphene oxide as a coating layer can better assist Fe-soc to increase the utilization rate of sulfur, and improve the conductivity of the cathode material, thereby improving the cycle performance and rate performance of lithium-sulfur batteries. This article is also expected to stimulate the application of MOF derivatives in energy storage materials.