Equilibrium isotherms and isosteric heat for CO<Subscript>2</Subscript> adsorption on nanoporous carbons from polymers

Four nanoporous carbons obtained from different polymers: polypyrrole, polyvinylidene fluoride, sulfonated styrene–divinylbenzene resin, and phenol–formaldehyde resin, were investigated as potential adsorbents for carbon dioxide. CO₂ adsorption isotherms measured at eight temperatures between 0 and 60 °C were used to study adsorption properties of these polymer-derived carbons, especially CO₂ uptakes at ambient pressure and different temperatures, working capacity, and isosteric heat of adsorption. The specific surface areas and the volumes of micropores and ultramicropores estimated for these materials by using the density functional theory-based software for pore size analysis ranged from 840 to 1990 m² g^?1, from 0.22 to 1.47 cm³ g^?1, and from 0.18 to 0.64 cm³ g^?1, respectively. The observed differences in the nanoporosity of these carbons had a pronounced effect on the CO₂ adsorption properties. The highest CO₂ uptakes, 6.92 mmol g^?1 (0 °C, 1 atm) and 1.89 mmol g^?1 (60 °C, 1 atm), were obtained for the polypyrrole-derived activated carbon prepared through a single carbonization-KOH activation step. The working capacity for this adsorbent was estimated to be 3.70 mmol g^?1. Depending on the adsorbent, the CO₂ isosteric heats of adsorption varied from 32.9 to 16.3 kJ mol^?1 in 0–2.5 mmol g^?1 range. Overall, the carbons studied showed well-developed microporosity and exceptional CO₂ adsorption, which make them viable candidates for CO₂ capture, and for other adsorption and environmental-related applications.     

Enhanced electrochemical performance of LiFePO<Subscript>4</Subscript>/C nanocomposites due to in situ formation of Fe<Subscript>2</Subscript>P impurities

We have studied LiFePO₄/C nanocomposites prepared by sol-gel method using lauric acid as a surfactant and calcined at different temperatures between 600 and 900 °C. In addition to the major LiFePO₄ phase, all the samples show a varying amount of in situ Fe₂P impurity phase characterized by x-ray diffraction, magnetic measurements, and Mössbauer spectroscopy. The amount of Fe₂P impurity phase increases with increasing calcination temperature. Of all the samples studied, the LiFePO₄/C sample calcined at 700 °C which contains ～15 wt% Fe₂P shows the least charge transfer resistance and a better electrochemical performance with a discharge capacity of 136 mA h g^?1 at a rate of 1 C, 121 mA h g^?1 at 10 C (～70 % of the theoretical capacity of LiFePO₄), and excellent cycleability. Although further increase in the amount of Fe₂P reduces the overall capacity, frequency-dependent Warburg impedance analyses show that all samples calcined at temperatures ≥700 °C have an order of magnitude higher Li⁺ diffusion coefficient (～1.3?×?10^?13 cm² s^?1) compared to the one calcined at 600 °C, as well as the values reported in literature. This work suggests that controlling the reduction environment and the temperature during the synthesis process can be used to optimize the amount of conducting Fe₂P for obtaining the best capacity for the high power batteries.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

Synthesis and thermal decomposition of neodymium(III) peroxotitanate to Nd<Subscript>2</Subscript>TiO<Subscript>5</Subscript>

Neodymium(III) peroxotitanate is used as a precursor for obtaining Nd₂TiO₅. The last one possesses numerous valuable electrophysical properties. TiCl₄, Nd(NO₃)₃·6H₂O and H₂O₂ in mol ratio 1:2:10 were used as starting materials. The reaction ambience was alkalized to pH = 9 with a solution of NH₃. The obtained neodymium(III) peroxotitanate and intermediate compounds of the isothermal heating were proved by the help of quantitative analysis and infrared spectroscopy (IRS). It has Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O composition. The absorption band observed in IRS at 831 cm^?1 relates to a triangular bonding of the peroxo group of Ti, at 1062 cm^?1—terminal groups Ti–OH and at 1491 and 1384 cm^?1—the bridging OH^?-groups Ti–O(H)–Ti. Nd₂TiO₅ was obtained by thermal decomposition of neodymium(III) peroxotitanate. The isothermal conditions for decomposition were determined on the base of differential thermal analysis, thermogravimetric and differential scanning calorimetry results in the temperature range of 20–1000 °C. The mechanism of thermal decomposition of Nd₄[Ti₂(O₂)₄(OH)₁₂]·7H₂O to Nd₂TiO₅ was studied. In the temperature range of 20–208 °C, a simultaneous decomposition of the peroxo groups by the separation of oxygen and hydrate water is conducted and Nd₄[Ti₂O₄(OH)₁₂] is obtained. From 208 to 390 °C, the terminal OH^?-groups are separated and Nd₄[Ti₂O₇(OH)₆] is formed. In the range of 390–824 °C, the bridging OH^?-groups are completely decomposed to Nd₂TiO₅. The optimal conditions for obtaining nanocrystalline Nd₂TiO₅ are 900 °C for 6 h and 20–80 nm.     

Synthesis of Na<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>7</Subscript> nanoparticles by sonochemical method for solid state electrolyte applications

Na₂Ti₃O₇ ceramic materials have been widely used in sodium-ion battery applications with relative good results; however, there are still several studies that might be carried out in the improvement of the Na₂Ti₃O₇ properties and the overall batteries’ performance. In this direction, we used sonochemical method following a thermal treatment in order to synthetized pure phase Na₂Ti₃O₇ nanopowders. X-ray diffraction characterization revealed that Na₂Ti₃O₇ is the primary phase in nanopowders and ceramic sample; although, a high level of amorphization was observed in the sonicated nanopowder without heat treatment process. Nanopowder-prepared ceramic sample showed a crystallite size of 50 nm after sintering at 900 °C for 1 h. The specific surface area, pore volume, and pore size were obtained from the B.E.T. measurements, being 51 m² g^?1, 0.07 cm³ g^?1, and 55 Å, respectively. The capacitance values of the nanopowder-prepared ceramic sample were in the order of microfarad. The total energy of the system was used to determine relaxation time of the sample (τ ₀ = 31 ms).     

Correlation between the structural,electrical and electrochemical performance of layered Li(Ni<Subscript>0.33</Subscript>Co<Subscript>0.33</Subscript>Mn<Subscript>0.33</Subscript>)O<Subscript>2</Subscript> for lithium ion battery

The Li(Ni_0.33Co_0.33Mn_0.33)O₂ (LNCMO) cathode material is prepared by poly(vinyl pyrrolidone) (PVP)-assisted sol-gel/hydrothermal and poly(ethylene glycol)-block-poly(propylene glycol)-block-poly (ethylene glycol) (Pluronic-P123)-assisted hydrothermal methods. The compound prepared by PVP-assisted hydrothermal method shows a comparatively higher electrical conductivity of ~2?×?10^?5 S cm^?1 and exhibits a discharge capacity of 152 mAh g^?1 in the voltage range of 2.5 to 4.4 V, for a C-rate of 0.2 C, whereas the compounds prepared by P123-assisted hydrothermal method and PVP-assisted sol-gel method show a total electrical conductivity in the order of 10^?6 S cm^?1 and result in poor electrochemical performance. The structural and electrical properties of LNCMO (active material) and its electrochemical performance are correlated. The difference in percentage of ionic and electronic conductivity contribution to the total electrical conductivity is compared by transference number studies. The cation disorder is found to be the limiting factor for the lithium ion diffusion as determined from ionic conductivity values.     

BiFeO<Subscript>3</Subscript>-coated spinel LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> with improved electrochemical performance as cathode materials for lithium-ion batteries

Spinel LiNi_0.5Mn_1.5O₄ cathode material is a promising candidate for next-generation rechargeable lithium-ion batteries. In this work, BiFeO₃-coated LiNi_0.5Mn_1.5O₄ materials were prepared via a wet chemical method and the structure, morphology, and electrochemical performance of the materials were studied. The coating of BiFeO₃ has no significant impact on the crystal structure of LiNi_0.5Mn_1.5O₄. All BiFeO₃-coated LiNi_0.5Mn_1.5O₄ materials exhibit cubic spinel structure with space group of Fd3m. Thin BiFeO₃ layers were successfully coated on the surface of LiNi_0.5Mn_1.5O₄ particles. The coating of 1.0 wt% BiFeO₃ on the surface of LiNi_0.5Mn_1.5O₄ exhibits a considerable enhancement in specific capacity, cyclic stability, and rate performance. The initial discharge capacity of 118.5 mAh g^?1 is obtained for 1.0 wt% BiFeO₃-coated LiNi_0.5Mn_1.5O₄ with very high capacity retention of 89.11% at 0.1 C after 100 cycles. Meanwhile, 1.0 wt% BiFeO₃-coated LiNi_0.5Mn_1.5O₄ electrode shows excellent rate performance with discharge capacities of 117.5, 110.2, 85.8, and 74.8 mAh g^?1 at 1, 2, 5, and 10 C, respectively, which is higher than that of LiNi_0.5Mn_1.5O₄ (97.3, 90, 77.5, and 60.9 mAh g^?1, respectively). The surface coating of BiFeO₃ effectively decreases charge transfer resistance and inhibits side reactions between active materials and electrolyte and thus induces the improved electrochemical performance of LiNi_0.5Mn_1.5O₄ materials.     

Effect of molten salt synthesis temperature on TiO<Subscript>2</Subscript> and Li cycling properties

In this project, we synthesized TiO₂ compounds through the molten salt method (MSM) using Ti(IV) oxysulfate, as the Ti source. Molten salts in the ratio of 0.375 M LiNO₃:0.180 M NaNO₃:0.445 M KNO₃ were added and heated at temperatures of 145, 280, 380, and 480 °C for 2 h in air, respectively. A part of the sample prepared at 145 °C was further reheated to 850 °C for 2 h in air. X-ray diffraction studies showed that the amorphous phase was obtained when the sample was prepared at 145 °C, and polycrystalline to crystalline anatase phase was formed when heated from 280 to 850 °C, which is complementary to the results of selected area electron diffraction studies. Electrochemical properties were studied using galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy at a current density of 33 mA g^?1 (0.1 C rate) and a scan rate of 0.058 mV s^?1, in the voltage range 1.0–2.8 V vs. Li. Electrochemical cycling profiles for the amorphous TiO₂ samples prepared at 145 °C showed single-phase reaction with a low reversible capacity of 65 mAh g^?1, whereas compounds prepared at 280 °C and above showed a two-phase reaction of Li-poor and Li-rich regions with a reversible capacity of 200 mAh g^?1. TiO₂ produced at 280 °C showed the lowest capacity fading and the lowest impedance value among the investigated samples.     

Photo-fenton refreshable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@HCS adsorbent for the elimination of tetracycline hydrochloride

A yolk–shell-structured sphere composed of a superparamagnetic Fe₃O₄ core and a carbon shell (Fe₃O₄@HCS) was etched from Fe₃O₄@SiO₂@carbon by NaOH, which was synthesized through the layer-by-layer coating of Fe₃O₄. This yolk–shell composite has a shell thickness of ca. 27 nm and a high specific surface area of 213.2 m² g^?1. Its performance for the magnetic removal of tetracycline hydrochloride from water was systematically examined. A high equilibrium adsorption capacity of ca. 49.0 mg g^?1 was determined. Moreover, the adsorbent can be regenerated within 10 min through a photo-Fenton reaction. A stable adsorption capacity of 44.3 mg g^?1 with a fluctuation <10% is preserved after 5 consecutive adsorption–degradation cycles, demonstrating its promising application potential in the decontamination of sewage water polluted by antibiotics.     

Photocatalytic effect of nano-TiO<Subscript>2</Subscript> loaded cement on dye decolorization and <Emphasis Type="Italic">Escherichia coli</Emphasis> inactivation under UV irradiation

In the present study, titanium dioxide (TiO₂) nano-particles were synthesized by sol–gel technique and then used to provide nano-TiO₂ loaded cement samples at 1, 5, and 10 wt% for investigation of Malachite green pigment decomposition and Escherichia coli inactivation under UV irradiation. Surveys conducted on the synthesized TiO₂ nano-particles showed a 100 % anatase phase with a mean particle size of 66.5 nm, surface area of 64.352 m² g^?1, and a porosity volume of 0.1278 cm³ g^?1. Cement samples containing this catalyst exhibited stronger photocatalytic properties as compared to the same amount of pure catalyst. Considering both photocatalytic performance and cost of catalyst, 5 wt% titanium dioxide was suggested to be added to cement. By addition of 1 wt% polycarboxylic copolymer as super-plasticizer to the cement paste, the photocatalytic sample activities were reinforced so that a similar performance could be obtained at 1 wt% catalyst as compared to 5 wt% catalyst without super-plasticizer.     

Natural graphite enhanced the electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material for lithium ion batteries

Natural graphite treated by mechanical activation can be directly applied to the preparation of Li₃V₂(PO₄)₃. The carbon-coated Li₃V₂(PO₄)₃ with monoclinic structure was successfully synthesized by using natural graphite as carbon source and reducing agent. The amount of activated graphite is optimized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectrum, galvanostatic charge/discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Our results show that Li₃V₂(PO₄)₃ (LVP)-10G exhibits the highest initial discharge capacity of 189 mAh g^?1 at 0.1 C and 162.9 mAh g^?1 at 1 C in the voltage range of 3.0–4.8 V. Therefore, natural graphite is a promising carbon source for LVP cathode material in lithium ion batteries.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/rice husk-based maco-/mesoporous carbon bone nanocomposite as superior high-rate anode for lithium ion battery

Rice husks (RHs), a kind of biowastes, are firstly hydrothermally pretreated by HCl aqueous solution to achieve promising macropores, facilitating subsequently impregnating ferric nitrate and urea aqueous solution, the precursor of Fe₃O₄ nanoparticles. A Fe₃O₄/rice husk-based maco-/mesoporous carbon bone nanocomposite is finally prepared by the high-temperature hydrothermal treatment of the precursor-impregnated pretreated RHs at 600 °C followed by NaOH aqueous solution treatment for dissolving silica and producing mesopores. The macro-/mesopores are able to provide rapid lithium ion-transferring channels and accommodate the volumetric changes of Fe₃O₄ nanoparticles during cycling as well. Besides, the macro-/mesoporous carbon bone can offer rapid electron-transferring channels through directly fluxing electrons between Fe₃O₄ nanoparticles and carbon bone. As a result, this nanocomposite delivers a high initial reversible capacity of 918 mAh g^?1 at 0.2 A g^?1 and a reversible capacity of 681 mAh g^?1 remained after 200 cycles at 1.0 A g^?1. The reversible capacities at high current densities of 5.0 and 10.0 A g^?1 still remain at high values of 463 and 221 mAh g^?1, respectively.     

Layered LiNi<Subscript>0.80</Subscript>Co<Subscript>0.15</Subscript>Al<Subscript>0.05</Subscript>O<Subscript>2</Subscript> as cathode material for hybrid Li<Superscript>+</Superscript>/Na<Superscript>+</Superscript> batteries

LiNi_0.80Co_0.15Al_0.05O₂ (NCA) is explored to be applied in a hybrid Li⁺/Na⁺ battery for the first time. The cell is constructed with NCA as the positive electrode, sodium metal as the negative electrode, and 1 M NaClO₄ solution as the electrolyte. It is found that during electrochemical cycling both Na⁺ and Li⁺ ions are reversibly intercalated into/de-intercalated from NCA crystal lattice. The detailed electrochemical process is systematically investigated by inductively coupled plasma-optical emission spectrometry, ex situ X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The NCA cathode can deliver initially a high capacity up to 174 mAh g^?1 and 95% coulombic efficiency under 0.1 C (1 C?=?120 mA g^?1) current rate between 1.5–4.1 V. It also shows excellent rate capability that reaches 92 mAh g^?1 at 10 C. Furthermore, this hybrid battery displays superior long-term cycle life with a capacity retention of 81% after 300 cycles in the voltage range from 2.0 to 4.0 V, offering a promising application in energy storage.     

A high mass loading electrode based on ultrathin Co<Subscript>3</Subscript>S<Subscript>4</Subscript> nanosheets for high performance supercapacitor

There is a growing need for the electrode with high mass loading of active materials, where both high energy and high power densities are required, in current and near-future applications of supercapacitor. Here, an ultrathin Co₃S₄ nanosheet decorated electrode (denoted as Co₃S₄/NF) with mass loading of 6 mg cm^?2 is successfully fabricated by using highly dispersive Co₃O₄ nanowires on Ni foam (NF) as template. The nanosheets contained lots of about 3～5 nm micropores benefiting for the electrochemical reaction and assembled into a three-dimensional, honeycomb-like network with 0.5～1 μm mesopore structure for promoting specific surface area of electrode. The improved electrochemical performance was achieved, including an excellent cycliability of 10,000 cycles at 10 A g^?1 and large specific capacitances of 2415 and 1152 F g^?1 at 1 and 20 A g^?1, respectively. Impressively, the asymmetric supercapacitor assembled with the activated carbon (AC) and Co₃S₄/NF electrode exhibits a high energy density of 79 Wh kg^?1 at a power density of 151 W kg^?1, a high power density of 3000 W kg^?1 at energy density of 30 Wh kg^?1 and 73 % retention of the initial capacitance after 10,000 charge-discharge cycles at 2 A g^?1. More importantly, the formation process of the ultrathin Co₃S₄ nanosheets upon reaction time is investigated, which is benefited from the gradual infiltration of sulfide ions and the template function of ultrafine Co₃O₄ nanowires in the anion-exchange reaction.

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Graphical abstract The ultrathin 2D Co₃S₄ nanosheets fabricated on 3D Ni foam and the formation process of the ultrathin Co₃S₄ nanosheets upon reaction times has been investigated. At the same time, the Co₃S₄/NF electrode displays an outstanding specific capacitance of 2420 F g^?1 at 1 A g^?1 with high mass loading of 6 mg cm^?2.

     

Facile synthesis of single-crystalline Co<Subscript>3</Subscript>O<Subscript>4</Subscript> cubes as high-performance anode for lithium-ion batteries

Transition metal oxides have great potential as anode for lithium-ion batteries (LIBs), owing to their high theoretical capacity and low cost. However, the poor cycling stability and electron conductivity have limited the widely expected application of transition metal oxides. In this work, highly single-crystalline Co₃O₄ cubes with 400 nm in the average side length are successfully synthesized by a facile hydrothermal method. When used as anode for LIBs, the Co₃O₄ single-crystalline cubes exhibit highly stable and substantial discharge capacities of the amount to 877 mA h g^?1 at 200 mA g^?1 after 110 cycles with remarkable capacity retention of 98%, and 576 mA h g^?1 even at a high rate of 2000 mA g^?1. The scalability of the preparation method and the impressive results achieved here demonstrate the potential for the application to the future development of transition metal oxides anodes. These results suggest that the single-crystalline Co₃O₄ is a promising electrode material for the high-performance energy storage devices.     

Enhanced electrochemical properties of Li<Subscript>2</Subscript>ZnTi<Subscript>3</Subscript>O<Subscript>8</Subscript>/C nanocomposite synthesized with phenolic resin as carbon source

Li₂ZnTi₃O₈/C nanocomposite has been synthesized using phenolic resin as carbon source in this work. The structure, morphology, and electrochemical properties of the as-prepared Li₂ZnTi₃O₈ samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), Raman spectroscopy (RS), galvanostatic charge–discharge, and AC impedance spectroscopy. SEM images show that Li₂ZnTi₃O₈/C was agglomerated with a primary particle size of ca. 40 nm. TEM images reveal that a homogeneous carbon layer (ca. 5 nm) formed on the surface of Li₂ZnTi₃O₈ particles which is favorable to improve the electronic conductivity and inhibit the growth of Li₂ZnTi₃O₈ during annealing process. The as-prepared Li₂ZnTi₃O₈/C composite with 6.0 wt.% carbon exhibited a high initial discharge capacity of 425 and 159 mAh g^?1 at 0.05 and 5 A g^?1, respectively. At a high current density of 1 A g^?1, 95.5 % of its initial value is obtained after 100 cycles.     

Effects of polyvinyl alcohol on the electrochemical performance of LiNi<Subscript>0.8</Subscript>Co<Subscript>0.15</Subscript>Al<Subscript>0.05</Subscript>O<Subscript>2</Subscript> cathode material

In view of the close relationship between the morphology of LiNi_0.8Co_0.15Al_0.05O₂ (NCA) and its electrochemical performance, polyvinyl alcohol (PVA) was added to control the NCA morphology. And thus a new NCA cathode material modified by PVA (NCA-PVA) was prepared. The morphology and structure of the obtained samples were characterized by X-ray diffraction, scanning electron microscopy, and laser diffraction. The electrochemical performance was characterized with electrochemical workstation and cell tester by assembling into CR2032 coin-type half-cell. The results show that the obtained NCA-PVA has a better layer structure and smaller cation mixing degree, smaller particle size, and more uniform particle size distribution than the pristine NCA without adding PVA. The electrochemical performance is also improved: the initial discharge capacity increases from 143.36 to 184.84 mAh g^?1. And the charge-discharge efficiency increases from 78.25 to 86.42%. The specific discharge capacities of NCA-PVA are all higher than that of the NCA (about 50 mAh g^?1) at all testing rates (0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 C).     

Interlayer-expanded MoS<Subscript>2</Subscript>/graphene composites as anode materials for high-performance lithium-ion batteries

A facile strategy was developed to prepare interlayer-expanded MoS₂/graphene composites through a one-step hydrothermal reaction method. MoS₂ nanosheets with several-layer thickness were observed to uniformly grow on the surface of graphene sheets. And the interlayer spacing of MoS₂ in the composites was determined to expand to 0.95 nm by ammonium ions intercalation. The MoS₂/graphene composites show excellent lithium storage performance as anode materials for Li-ion batteries. Through gathering advantages including expanded interlayers, several-layer thickness, and composited graphene, the composites exhibit reversible capacity of 1030.6 mAh g^?1 at the current density of 100 mA g^?1 and still retain a high specific capacity of 725.7 mAh g^?1 at a higher current density of 1000 mA g^?1 after 50 cycles.     

Green fabrication of sandwich-like and dodecahedral C@Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@C as high-performance anode for lithium-ion batteries

Sandwich-structured C@Fe₃O₄@C hybrids with Fe₃O₄ nanoparticles sandwiched between two conductive carbon layers have attracted more and more attention owing to enhanced synergistic effects for lithium-ion storage. In this work, an environment-friendly procedure is developed for the fabrication of sandwich-like C@Fe₃O₄@C dodecahedrons. Zeolitic imidazolate framework (ZIF-8)-derived carbon dodecahedrons (ZIF-C) are used as the carbon matrix, on which iron precursors are homogeneously grown with the assistance of a polyelectrolyte layer. The subsequent polydopamine (PDA) coating and calcination give rise to the formation of sandwiched ZIF-C@Fe₃O₄@C. When being evaluated as the anode material for lithium-ion batteries, the obtained hybrid manifests a high reversible capacity (1194 mAh g^?1 at 0.05 A g^?1), good high-rate behavior (796 mAh g^?1 at 10 A g^?1), and negligible capacity loss after 120 cycles.     

LiMO<Subscript>2</Subscript>@Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript> positive-electrode material for high energy density lithium ion batteries

Li[Ni_1/3Co_1/3Mn_1/3]O₂ (NCM 111) is a promising alternative to LiCoO₂, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g^?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO₂ (R-3m, M?=?Ni, Co) and a shell of Li₂MnO₃ (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li⁺/Ni²⁺ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li_1.15Na_0.5(Ni_1/3Co_1/3)_core(Mn_1/3)_shellO₂ can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g^?1 at 20 mA g^?1, and retains 90 % of its discharge capacity at 100 mA g^?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.

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Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g^?1 for 10 cycles followed by 90 cycles at 100 mA g^?1