O2 Samples Research Articles

Microstructure regulation of WxV1-xO2(B) nanorods with improved electrochemical properties

VO2(B) is regarded as a highly promising cathode material for secondary batteries due to its outstanding theoretical specific capacity and unique expansion tunnel structure, which facilitates reversible insertion and extraction of metal ions. Nonetheless, inherent structural instability, suboptimal ion/electron transport, and constrained capacity resulting from low redox potentials pose challenges to its wider adoption. Hence, in this paper, we proposed a strategy for synthesizing gradient concentration-doped WxV1-xO2(B) nanorods via a one-step hydrothermal method to solve the above problems. The experimental results demonstrated that as the W ion content increased, all fabricated WxV1-xO2(B) nanorods exhibited a monoclinic crystal phase along with noticeable lattice distortion. The positron annihilation lifetime spectra indicated that vacancy clusters were the predominant defect types in WxV1-xO2(B) nanorods. The synergistic effects of grain sizes and vacancy defects contributed to the superior electrochemical performance observed in the W0.01V0.99O2(B) sample. The capacitor retention reached 88.76 % at 0.10 A/g after 1000 charge/discharge cycles. These results had provided experimental foundation for improving electrochemical properties of WxV1-xO2(B) in metal ion secondary batteries.

Sol-gel synthesis, structure and adsorption properties of LiMgxMn(2-x)O4 (0 ≤ x ≤ 0.7) Oxides

Lithium manganese оxides with a spinel structure LiMgxMn(2–x)O4, doped with Mg2+ ions in the range 0 ≤ x ≤ 0.7, were obtained by sol-gel synthesis. Phase composition and morphology of obtained оxides were studied by using X-ray phase analysis and scanning electron microscopy. It is shown, that in the studied range 0 ≤ x ≤ 0.7 Mg-doped lithium manganese оxides saved the structure of the original cubic spinel LiMn2O4, while an increase in parameter a was observed from 8.175 to 8.309 Å and average crystallite size practically unchanged (30–36 nm). Samples of the initial LiMn2O4 and Mg-doped spinels were represented by prismatic particles of submicron (0.1–0.2 µm) and micron (1.0–3.0 µm) sizes, respectively. The effect of the adsorbent dose (0.05–0.3 g/l) and pH (3.0–13.0) of the solution on the adsorption efficiency was studied. The adsorption isotherms of the LiMg0.3Mn1.7O4 samples were described by the Langmuir monomolecular adsorption equation. An increase in the temperature of the model solution from 25 to 45°C was accompanied by an increase in the maximum adsorption of the LiMg0.3Mn1.7O4 samples from 10.50 to 10.98 mmol/g, which indicates the endothermic nature of the adsorption process. The kinetics of adsorption was well described by a pseudo-second order equation, which indicates the occurrence of chemical interaction during the adsorption process.

Visible-light photocatalytic performance of SrTiO3 nanoparticles modified with cobalt

In this article, an experimental study on the photocatalytic performance of SrTi1-yCoyO3 nanoparticles (with y = 0.0, 0.03, 0.06, and 0.09) synthesized by the Pechini-type sol-gel method is presented. The crystalline structure analysis revealed that all the samples exhibited the cubic perovskite phase of SrTiO3. In particular, the SrTi0.91Co0.09O3 sample was found to consist of rough spherical-like particles with an average size of 26 ± 0.5 nm. Cobalt ions with 2+ and 3+ oxidation states are responsible for modifying the electronic band structure of the semiconductor and a narrowing of optical band gap from 3.1 to 1.08 eV. The resulting Co-doped SrTiO3 nanoparticles exhibited photocatalytic activity under visible light due to their enhanced light absorption, effective charge transport and effective surface chemisorption. In particular, the SrTi0.91Co0.09O3 sample exhibited the highest photocatalytic activity with 91 % degradation efficiency of methylene blue dye within 120 min of simulated solar irradiation.

Enhanced Cycling Performance of Spinel LiNi0.5Mn1.5O4 Cathodes through Mg-Mn Hetero-Valent Doping via Microwave Sol-Gel Method.

As a high energy density cathode material, further development of high working voltage spinel LiNi0.5Mn1.5O4 has hindered by its rapid capacity degradation. To address this, a hetero-valent substitution of magnesium for manganese was used to synthesize spinel LiNi0.5MgxMn1.5-xO4 (x = 0, 0.03, 0.05) via a microwave sol-gel method. XRD and refined results indicate that such strategy leads to the modification of the 16c interstitial sites. The electrical performance demonstrates that a modest substitution (x = 0.03) significantly improves both rate performance (113.1 mAh/g, charge and discharge at 5 C) and cycling stability (85% capacity retention after 500 cycles at 1 C). A higher substitution level (x = 0.05) markedly improves high-rate cycling performance, achieving 96% capacity retention after 500 cycles at 5 C. It offers tailored solutions for various application needs, including capacity-focused and high-current-rate applications. Furthermore, the stable LiNi0.5Mg0.05Mn1.45O4 sample could also serve as an effective coating layer for other electrode materials to enhance their cycling stability.

The effect of Bi3+ doping on the structural, magnetic, dielectric, optical, and photocatalytic efficiency of Mg-Ni ferrite nanoparticles

Ferrite nanoparticles with the general formula Mg0.7Ni0.3BixFe2-xO4 (MNB) (0 ≤ x ≤ 0.1, Δx = 0.02) were prepared by the citrate combustion method. X-ray diffraction (XRD) results confirmed the spinel single-phase with crystallite size varied from 30.68 to 43.74 ± 0.01 nm. Scanning electron microscopes with elemental mapping conformed to the nano-nature of the MNB samples with all the constituents present without secondary elements. The sample Mg0.7Ni0.3Bi0.02Fe1.98O4 has the highest saturation magnetization of 31.06 ± 0.01 emu g−1. The sample Mg0.7Ni0.3Bi0.08Fe1.92O4 has the lowest coercivity of 31.06 ± 0.01 G. The high-frequency response of the MNB nanoferrites allows them to be used at frequencies around 6.48± 0.01–6.87± 0.01 GHz. The nanoferrite Mg0.7Ni0.3Bi0.1Fe1.9O4 has notable dielectric parameters at 300 K and 50 Hz: the highest dielectric constant (747.93 with enhancing ratio 371%) and the highest conductivity (26.14 μ(Ω.m)−1 with enhancing ratio 288%). The Mg0.7Ni0.3Bi0.08Fe1.92O4 sample has a loss of 8.65 with an enhancing ratio of 56.79% compared to the loss of the pristine Mg0.7Ni0.3Fe2O4 sample of 15.23. Diffuse reflectance (DR) spectroscopy showed an irregular trend for the band gap values with increasing Bi3+ content, where the nanoferrite Mg0.7Ni0.3Bi0.1Fe1.9O4 had the lowest energy gap of 2 eV. The sample Mg0.7Ni0.3Bi0.1Fe1.9O4 exhibited the maximum photodegradation efficiency (96.16%) for rhodamine B (RhB) dye, with outstanding stability after five cycles (96.16, 95.92, 95.71, 95.56, and 95.23%, respectively). The current work has shown the capability to customize ferrite MNB for soft ferrite applications and to eliminate hazardous RhB from water.

The effect of heating rate on microstructure and electrochemical performance of nickel-rich layered oxides cathode materials

Nickel-rich layered oxides have attracted significant attention as promising cathode materials for lithium-ion batteries due to their high specific capacity, rate capability, and relatively low cost. However, the material still faces challenges such as harsh synthesis conditions, easy cation mixing and large residual alkali on the surface, severely limiting its practical applications. To overcome these drawbacks, this study successfully synthesized a series of LiNi0.8Co0.1Mn0.1O2 (NCM) cathode materials with different heating rates. The results indicate that appropriately reducing the heating rate can improve the cycling performance of the material and reduce cation mixing and surface residual alkalinity. Specifically, among the four samples, the LiNi0.8Co0.1Mn0.1O2 sample (NCM-2 °C min-1) exhibites a lower Li⁺/Ni²⁺ mixed arrangement and fewer surface residual alkalis, demonstrating good cycling performance and rate capability. The NCM-2 °C min-1 sample provides an excellent initial discharge capacity of 210.4 mAh g⁻¹ under 0.1 C conditions, and it achieves the highest capacity retention rate (85.9%) after 100 cycles at 1 C, while the capacity retention rates for NCM-1 °C min-1, NCM-3 °C min-1, and NCM-4 °C min-1 are 75.4%, 75.2%, and 71.2%, respectively. NCM-2 °C min-1 sample also showed excellent rate performance, especially at high rates. The discharge capacity remains at 151.6 mAh g-1 at 10 C, which is much higher than that of other samples (149.3 mAh g-1 for NCM-1 °C min-1, 123.5 mAh g-1 for NCM-3 °C min-1, and 120.6 mAh g-1 for NCM-4 °C min-1). The research of synthesis technology has important guiding significance for the synthesis of high-stability high-nickel layered oxide materials.

Determination of the Activation Energy of Defects in Ferroelectrics by the Method of Temperature Activation–Relaxation of the Dielectric Permittivity

The article proposes a method of temperature activation–relaxation of the permittivity for determining the activation energy of defects in ferroelectrics using lead zirconate–titanate Pb(Zr,Ti)O3 samples as an example. This method is based on the analysis of relaxation of the permittivity after thermal annealing and the analysis of the temperature activation of the permittivity of the Pb(Zr,Ti)O3 ferroelectric. The equality of the activation energy corresponding to the process of migration of oxygen vacancies and the thermal energy of the decay of the domain structure was established, which was confirmed by studying the surface of the samples by scanning electron microscopy. When this temperature was reached, the surface of the domain walls was detached from oxygen vacancies, which are pinning centers. This manifested itself in photographs of the microstructure as a change in the ordering of the domains emerging on the surface of the sample, which led to an irreversible decrease in the permittivity of the sample. For the obtained activation energies, the physical process of domain wall motion activation is established, which is determined by their pinning on structural defects (oxygen vacancies). It is assumed that the irreversible decay of the domain structure occurs when the domain walls are displaced by distances exceeding the elementary lattice parameter of the ferroelectric. The proposed method can be part of a comprehensive study that includes electrophysical, microscopic and X-ray methods.

Scaling up features of photocatalytic degradation and radiation shielding of multicomponent Cr–Co–Zn nanoferrites

Optical, photocatalytic activity, and radiation shielding studies were conducted on CrxCo0.8Zn0.2Fe2-xO4 (0.0 ≤ x ≤ 0.1, Δx = 0.02) nanoferrites for water treatment and radiation shielding applications. The optical absorption analysis revealed that the optical band gap energy values range from 1.864 to 1.803 eV as assessed through Tauc plots. Further analysis of photocatalytic degradation showed that the Cr0.06Co0.8Zn0.2Fe1.94O4 sample exhibited superior methylene blue (MB) dye removal compared to other samples, with an efficiency of 96.74% in 60 min. Additionally, the present nanoferrites exhibited excellent stability in photocatalytic degradation over multiple cycles. The study also investigated the linear attenuation coefficient (LAC) of the current ferrite nanoparticles, demonstrating increased LAC values with higher Cr content, while the half value layer (HVL) diminished with further Cr concentration. The HVL values indicated the potential efficacy of our nanoferrites as radiation shields when compared to standard radiation shielding materials. Overall, this research suggests a new direction for optimizing spinel nanomaterials for applications in water treatment and radiation shielding.

Synthesis of LiCo1-XNiXO2 nanomaterial by hydrothermal method as cathode for lithium ion battery

The compounds of LiCoO2 (LCO) and LiCo1-xNixO2 (LCNO), with (x=0,0.25,0.5,0.75,1) were synthesized as cathode active material for lithium–ion batteries using hydrothermal technique in this study. Structure and morphology characterization were conducted for all prepared samples. The crystalline results indicate that both LCO and LCNO possess a rhombohedral structure, while the morphology results show irregular shapes. Electrochemical tests were carried out for LiCoO2 and LiCo0.25 Ni0.75O2 samples only. From the electrochemical measurements, the LiCo0.25 Ni0.75O2 demonstrate higher charge and discharge capacities compared to the LiCoO2 electrode, findings which are consistent with the electrochemical impedance spectroscopy (EIS) results. The X-ray diffraction (XRD) results of both the prepared Lithium Cobalt Oxide (LCO) and Lithium Cobalt Nickel Oxide (LCNO) samples reveal characteristic peaks at specific angles (2θ) indicating crystallographic planes. For LCO, peaks were observed at 18.96°, 37.40°, 38.35°, 39.07°, 45.29°, 49.45°, and 59.62° corresponding to crystallographic planes (003), (101), (006), (012), (104), (015), and (107) respectively. These peaks confirm the formation of a rhombohedral LiCoO2 nanostructure with space group (R-3m no.166), consistent with standard data (JCPDS 00-016-0427). The EDX spectra of the synthesized Lithium Cobalt Oxide (LCO) and Lithium Cobalt Nickel Oxide (LCNO) were analyzed. The results showed the presence of oxygen (O), cobalt (Co), and nickel (Ni) elements. However, the peak corresponding to lithium (Li) was not visible due to its low activation energy. Finally, the synthesis and characterization of LiCoO2 (LCO) and LiCo1-xNixO2 (LCNO) compounds were conducted, with electrochemical tests indicating superior performance of LiCo0.25 Ni0.75O2 over LiCoO2

Measurement of volatile organic compounds using tethered balloons in a polluted industrial site in Catalonia (Spain).

Understanding the chemical composition of volatile organic compounds (VOCs) near emission sources and in the background atmosphere above the mixing layer height (MLH) provides insight into the fate of VOCs and is essential for developing effective air pollution control strategies. Unfortunately, knowledge of the qualitative and quantitative changes of VOCs and their vertical transport in the atmosphere is limited due to challenging experimental setups. In this study, an innovative method using tethered balloons was tested and implemented to sample 40 VOCs and O3 below and above the MLH at an industrial site in Spain. VOC and O3 samples were collected with different types of sorbent cartridges and analyzed using chromatographic techniques. Overall, a decrease in VOC concentration with altitude was observed along with a homogeneous chemical composition up to 300 m AGL. This decrease with altitude denoted the primary origin of these VOCs, which were strongly influenced by industrial processes and the traffic emissions in the area. Conversely, O3 concentrations were notably higher at balloon level and increased during nighttime temperature inversion episodes in those samples collected above the mixing layer. Ground samples contained freshly emitted pollutants of industrial origin, while balloon samples consisted of aged pollutants from traffic, other combustion sources, or from a secondary origin. This study is the first to assess the vertical composition of VOCs at a site of these characteristics and demonstrates that tethered balloons are a cost-effective method for studying air pollution dynamics from the ground to higher altitudes in the low troposphere.

Exploring the structural and magnetic properties of La-doped nickel ferrite for microwave absorbing application

The intrinsic properties of microwave absorbing materials are influenced by the permeability and permittivity of the material with indicators of changes in reflection loss characteristics. Nickel ferrite is a magnetic material with very high permeability, so the presence of La3+ ion substitution in nickel ferrite can increase the permittivity of this material and is denoted by increased reflection loss. The magnetic material NiLaxFe(2−x)O4 was synthesized effectively through co-precipitation techniques using NiCl2, FeCl3, and LaCl3 powders, with mole ratios varying from x = 0.01 to 0.04, then continued with the sintering process at a temperature of 1200 °C for 5 h.The X-ray diffraction (XRD) analysis indicates that all NiLaxFe(2−x)O4 samples consist of a single phase of NiFe2O4 with a cubic spinel structure. The scanning electron microscope (SEM) image of NiLaxFe(2−x)O4 powders reveals that all samples exhibit a consistent morphology, however, the powder doesn’t look uniform yet, with particle sizes ranging from 100-800 nm. The magnetic properties of the samples were examined using a vibrating sample magnetometer (VSM). The sample shows ferromagnetic behavior, but the Ms value decreases from 35.89 to 21.54 emu/g and the Hc value increases from 249 to 416 Oe as the La3+ ion content in the material increases. Meanwhile, the microwave absorption capacity measured using the vector network analyzer (VNA) shows that reflection loss increases from 11.16 dB to 15.41 dB as the La3+ ion content in the material increases. So, the substitution of La3+ ions in nickel ferrite structure up toa concentration of x = 0.04 can increase microwave absorption up to 97.11 %.

The role of chlorine promoters in mediating particle size effects in silver-catalyzed ethylene epoxidation

Measured chlorine coverages over Ag/α-Al2O3 catalysts with varying Ag weight loadings (1.3–35 wt%) and different Ag particle size distributions when parsed in terms of Cl coverages over particles of varying size constituted in the distribution reveal that Ag particles of size below ∼30 nm are covered in more than 1 monolayer (ML) of chlorine in presence of 3.5 ppm C2H5Cl. These assessments of Cl coverages were made possible by correlating the cumulative Cl coverage to the lognormal surface area distribution of 22 Ag/α-Al2O3 samples using a single exponential decay function. Fully chlorided small Ag particles exhibit low rates of epoxidation and only large Ag particles which exhibit sub-monolayer Cl coverages catalyze ethylene epoxidation with high ethylene oxide (EO) rates and selectivity. The Ag particle size dependence of Cl coverages plausibly explains why ≥ 100 nm Ag particles are typical in promoted Ag/α-Al2O3 ethylene epoxidation catalysts.

Experimental conditions for room temperature ferromagnetism in Fe-doped SnO2 via mechanochemical milling and thermal treatment

Identifying optimal experimental conditions, preferably through a simple and cost-effective method, for the fabrication of oxide-diluted magnetic semiconductors, such as Fe-doped SnO2, holds great significance in the quest for spintronic materials operating at room temperature (RT). While mechanochemical milling is a well-established technique meeting these requirements, its numerous milling variables necessitate careful consideration of restricted experimental conditions. In this study, we present some experimental mechanochemical milling conditions to prepare impurity-free iron-doped tin dioxide nanoparticles exhibiting RT ferromagnetic signal. To achieve this, we investigated the effects of milling time, the choice of the starting Sn reactant, and iron concentration on the purity of Sn1−xFexO2 (x = 0, 0.03, and 0.05) nanopowders obtained through mechanochemical milling followed by thermal treatment. Characterization through XRD, XANES, and EXAFS at the Fe K-edge, RT Raman spectroscopy, 119Sn and 57Fe Mössbauer spectroscopies, and magnetic measurements was conducted. Among the experimental techniques, micro-Raman spectroscopy proved the most effective in detecting the formation of hematite as an impurity phase. Our results indicate that extending the milling time to 12 h, as opposed to 3 h, employing anhydrous SnCl2, instead of SnCl2·2H2O and using the low iron concentration of x = 0.03, results in proper conditions for producing impurity-free samples with a robust RT ferromagnetic signal. The oxidation states for iron and tin ions were determined to be 3+ and 4+, respectively, with both occupying octahedral sites, suggesting iron’s replacement of tin. Our findings propose that both the bound magnetic polaron and RKKY models offer potential explanations for the origin of the ferromagnetic signal observed at room temperature in Sn0.97Fe0.03O2 sample milled for 12 h.

Boosting photoelectrochemical performance through appling magnetic field in manganese-doped cobalt ferrite photoanodes

An efficient photoelectrochemical water-splitting process is of paramount importance as it provides a sustainable and clean method for generating hydrogen fuel, which is crucial for addressing the world’s growing energy needs while mitigating environmental concerns. Herein, the effects of applying a magnetic field on the photoelectrochemical performance of photoanodes composed of Cobalt ferrite (CoFe2O4) and Manganese (Mn)-doped CoFe2O4 are investigated. The CoMnxFe2-xO4 nanoparticles were synthesized using a sol–gel method, with varying values of x (0.0, 0.1, 0.3, and 0.5). X-ray diffraction analysis consistently reveals a singular cubic spinel structure for all four samples. Magnetic analyses demonstrate an enhancement in magnetic characteristics, including saturation magnetization, coercivity, and anisotropy field in the CoMn0.3Fe1.7O4 sample compared to the other three samples. Photoelectrochemical (PEC) measurements indicate that the photocurrent increases in all four samples when a static magnetic field is applied. However, the CoMn0.3Fe1.7O4 sample shows a more pronounced enhancement. Specifically, the dark current density increases by more than 115 % when a magnetic field of 190 ± 20 mT is applied. Additionally, it rises by 387 % under light illumination with the magnetic field. This enhancement in PEC performance is attributed to electron spin polarization adjusted through the external magnetic field.

Mitigating voltage decay of O3‐NaNi1/3Fe1/3Mn1/3O2 layered oxide cathode for sodium‐ion batteries by incorporation of 5d metal tantalum

AbstractThe cycling stability of O3‐type NaNi1/3Fe1/3Mn1/3O2 (NFM) as a commercial cathode material for sodium ion batteries (SIBs) is still a challenge. In this study, the Ni/Fe/Mn elements are replaced successfully with tantalum (Ta) in the NFM lattice, which generated additional delocalized electrons and enhanced the binding ability between the transition metal and oxygen, resulting in suppressed lattice distortion during charging and discharging. This caused significant mitigation of voltage decay and improved cycle stability within the potential range of 2.0–4.2 V. The optimized Na(Ni1/3Fe1/3Mn1/3)0.97Ta0.03O2 sample achieved a reversible capacity of 162.6 mAh g−1 at a current rate of 0.1 C and 73.2 mAh g−1 at a high rate of 10 C. Additionally, the average charge/discharge potential retention reached 98% after 100 cycles, significantly mitigating the voltage decay. This work demonstrates a significant contribution towards the practical utilization of NFM cathodes in the SIBs energy storage field.

Ultrahigh energy storage density and efficiency in A/B-site co-modified silver niobate relaxor antiferroelectric ceramics

AgNbO3-based antiferroelectric ceramics can be used to prepare dielectric ceramic materials with energy storage performance. However, their efficiency is much lower than that of relaxors, which is one of the biggest obstacles for their applications. To overcome this problem, AgNbO3 ceramics co-doped with Eu3+ and Ta5+ at the A- and B-sites were prepared in this work. The Ag0.97Eu0.01Nb0.85Ta0.15O3 sample has a Wr of 6.9 J/cm3 and an η of 74.6%. The ultrahigh energy storage density and efficiency of Ag0.97Eu0.01Nb0.85Ta0.15O3 has been ascribed to the synergistic effect of the increase in the breakdown electric field, the enhancement of antiferroelectric stability, the construction of multiphase coexistence, and the modification of the domain structure morphology. The Ag0.97Eu0.01Nb0.85Ta0.15O3 ceramic is expected to be one of the options for preparing dielectric capacitors.

In situ electric field-dependent structural changes in (Ba,Ca)(Zr,Ti)O3 with varying grain size

The functional properties of piezoelectric ceramic materials, such as barium titanate, are highly dependent on grain size. Lead-free polycrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) samples were prepared with a combination of the hydrothermal method and spark plasma sintering to achieve grain sizes from 100 nm to 10 μm by varying the maximum sintering temperature. In this range, a transition from a nearly linear dielectric to a ferroelectric response can be seen in macroscopic electromechanical measurements, demonstrating the importance of grain size on functional properties in BCZT. Furthermore, in situ electric field-dependent synchrotron x-ray diffraction measurements were performed to quantify the intrinsic and extrinsic strain contributions and their variations with grain size. At lower grain sizes, the data revealed a significant loss of extrinsic contributions in the piezoelectric behavior, limiting the response to intrinsic contribution associated with lattice strain. For BCZT, a critical grain size between approximately 0.08 and 0.18 μm is proposed, below which no piezoelectric response was observed.

Structure, vacancy, and physical properties of non-stoichiometric MnWO4 ceramics

Non-stoichiometric ceramic samples of Mn0.97WO4 and MnW0.97O4 were prepared by a solid-state reaction to study the effects of vacancies at different lattice positions on the structure and properties of MnWO4 materials caused by non-stoichiometric. Positron annihilation technology was introduced to study the vacancy characteristics of the MnWO4, Mn0.97WO4, and MnW0.97O4 ceramics. The results indicated that non-stoichiometric did not affect the monoclinic lattice structure of any of the MnWO4 samples, and had no obvious effect on the lattice parameters of the samples. The analysis of positron annihilation lifetime spectroscopy showed that W vacancies were the main defects in MnW0.97O4 samples, and Mn vacancies were favored in Mn0.97WO4 samples, the vacancies concentration for non-stoichiometric MnWO4 samples was higher than that of stoichiometric MnWO4. It was observed that the magnetization and transition temperatures of the non-stoichiometric MnWO4 system were increased, and the temperature range in which AF2 phase existed was enlarged. This study demonstrated that non-stoichiometric could enhance the magnetic properties of MnWO4, the effect of Mn vacancy on the properties of MnWO4 is higher than that of W vacancy. The intimate correlation between the vacancy defects and magnetic properties provides us strong evidence that the magnetic properties of MnWO4 can be enhanced by regulating vacancy defects.

P2-type layered oxide cathode with honeycomb-ordered superstructure for sodium-ion batteries

Sodium-ion batteries (SIBs) have been proved as one of the most alternative to Lithium-ion batteries (LIBs) by the virtue of the abundant resources of Na. Among the cathodes, layered oxides stand out owing to their high energy density. The Jahn–Teller distortion, structural phase transition and oxygen release are main drawbacks of Mn/Ni based layered oxides. Hence, Li-Ni-Cu co-substituted Na0.67Li0.1(Mn0.7Ni0.2Cu0.1)0.9O2 (NLMNC) sample was prepared. The NLMNC sample exhibits the honeycomb-ordered superstructure at about 22° which is ascribed to cation ordering. By virtue of the Li-Ni-Cu co-substitute, the Jahn–Teller distortion of Mn is suppressed. Attributed to Li+ migrating from the metal oxide layer to the interlayer and the Li+ can play the part of pillar in the interlayer, NLMNC cathode displays the capacity retention rate of 82.5 % at 200 mA g−1 after 100 cycles. The anionic redox reaction of NLMNC is related to the addition of Li ions and O 2p non-bonding which is different from the anionic redox reaction of electrons removing from O 2p in the eg* (Ni–O) states of Na2/3Ni1/3Mn2/3O2. During charge process, peroxo O− emerges with the oxidation of lattice oxygen. During discharge process, the intensity of peroxo O− gradually decreases. DFT calculations were also carried out to reveal the reaction mechanism of NLMNC. The DFT results showed that the anionic redox reaction occurs near Mn ions, while the Ni ions are stable which is corresponding with our results. It is proven that such Li-Ni-Cu co-substituted NLMNC presents a promising cathode material for SIBs.

Preparation and Properties of Spinel LiMn1.90 Ni0.05 Cu0.05 O4

Spinel LiMn2O4 and LiMn1.90Ni0.05 Cu0.05O4 cathode materials were synthesized by a simple solution combustion method. The structure, morphology and properties of the two samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), battery test system and electrochemical workstation. The results show that the two samples are spinel lithium manganate structure, which can be indexed as Fd3m space group. Ni Cu co doping effectively reduces the particle size and agglomeration, improves the crystallinity of the materials, and makes LiMn1.90Ni 0.05 Cu0.05O4 samples show good crystal structure stability and magnification properties. The capacity retention rates of 64.53%,79.52%and 69.47%were obtained after 1000 cycles at current densities of 1 C,5 C and 10 C,respectively, which were higher than 43.75%,55.74%and 44.38%of the corresponding undoped LiMn2O4 samples.