High Nickel Content Research Articles

Structural analysis and electrochemical investigation of dual-doped NMC622 cathode material: Effect of sodium and neodymium on the performance in Li-ion batteries

Ni-rich layered oxides are the most promising cathode materials for high-energy-density Li-ion batteries. Full utilization of their potential resulting from high nickel content, mainly high capacity, is impaired due to the rapid performance degradation. Mitigating the main limitations of Ni-rich materials is possible through element doping. In this work, a series of LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode materials doped with sodium and/or neodymium was synthesized and systematically studied (XRD, SEM, TEM, STEM-EDX, XPS, galvanostatic charge/discharge tests, cyclic voltammetry). The strategies of single-element and dual-element doping were applied to study the effect of Na and Nd doping on the electrochemical performance of the modified NMC622 materials. The Na-doped NMC622 material exhibited improved capacity retention of 80.5% after 100 cycles, which is superior to the undoped one (62.7%), possibly owing to enlarged Li layer spacing and decreased Li ion migration activation energy. For the Nd-doped NMC622 cathode material, both the initial discharge capacity and capacity retention were much improved compared to the undoped NMC622. This can be related to the enhanced structural stability brought by the formation of strong bonds between neodymium and oxygen atoms. In contrast, the dual-doping of Na and Nd in NMC622 material resulted in much poorer electrochemical and cycling performance, but the reason for this is unclear. The experimental data suggest that the combination of Na and Nd dopants caused the deterioration of crystal structure, possibly due to the introduced impurities. This consequently affected the structural stability of the dual-doped material, leading to the lowest discharge capacity and capacity retention among the studied NMC622 materials.

The dangerous link between coal dust exposure and DNA damage: unraveling the role of some of the chemical agents and oxidative stress

Exposure to coal mining dust poses a substantial health hazard to individuals due to the complex mixture of components released during the extraction process. This study aimed to assess the oxidative potential of residual coal mining dust on human lymphocyte DNA and telomeres and to perform a chemical characterization of coal dust and urine samples. The study included 150 individuals exposed to coal dust for over ten years, along with 120 control individuals. The results revealed significantly higher levels of DNA damage in the exposed group, as indicated by the standard comet assay, and oxidative damage, as determined by the FPG-modified comet assay. Moreover, the exposed individuals exhibited significantly shorter telomeres compared to the control group, and a significant correlation was found between telomere length and oxidative DNA damage. Using the PIXE method on urine samples, significantly higher concentrations of sodium (Na), phosphorus (P), sulfur (S), chlorine (Cl), potassium (K), iron (Fe), zinc (Zn), and bromine (Br) were observed in the exposed group compared to the control group. Furthermore, men showed shorter telomeres, greater DNA damage, and higher concentrations of nickel (Ni), calcium (Ca), and chromium (Cr) compared to exposed women. Additionally, the study characterized the particles released into the environment through GC–MS analysis, identifying several compounds, including polycyclic aromatic hydrocarbons (PAHs) such as fluoranthene, naphthalene, anthracene, 7H-benzo[c]fluorene, phenanthrene, pyrene, benz[a]anthracene, chrysene, and some alkyl derivatives. These findings underscore the significant health risks associated with exposure to coal mining dust, emphasizing the importance of further research and the implementation of regulatory measures to safeguard the health of individuals in affected populations.Graphic abstract

Water Pollution in Cobalt and Nickel by the Effect of Adding Urban Waste in Al-Diwaniyah River / Iraq

This study was conducted in Al-Diwaniyah Governorate, Iraq, across four seasons with the intention of determining the impact of introducing liquid urban waste (including sewage, waste water, factory, and sewer water) on the content of cobalt and nickel in river water. At each location and during each of the following four seasons: summer in July, 2021; autumn in October, 2021; winter in January, 2022; and spring in April, 2022; for the following three locations: The first site was positioned at the entrance to Diwaniyah (Saniaa), which represents the control treatment as it is located before to the pollution outputs. The numerous sources of pollution that are discharged into the river, as well as the second location in the city center (the neighborhood of Refaat), and the third location in the Al-Sidair region, which is the final location in the city of Diwaniyah following the cessation of all pollution discharges into the river. The third, where the highest significant concentration of cobalt was 0.2400 μg l-1 in the summer, the third site, where it exceeded the limits recommended by the World Health Organization (WHO), and the lowest concentration was 0.0033 μg l-1 In the winter, the first site, while the highest concentration of Nickel was 0.382 μg l-1 in the summer, the third site, thus exceeding the critical limits of the World Health Organization (WHO), and its lowest concentration was 0.022 μg l-1 in the winter, the first site.

Assessment of the Hydrophysical and Hydrochemical Characteristics of Lake Burabay (Akmola Region, North Kazakhstan)

This paper shows the results of a study on the morphometric, hydrophysical, and hydrochemical indicators of Lake Burabay, North Kazakhstan. The Burabay Protected Area, also known as Burabay National Park or Kokshetau National Park, is a protected natural area located in the north of Kazakhstan. It encompasses a diverse landscape characterized by lakes, forests, and unique rock formations. This analysis includes an eco-toxicological assessment of the hydrochemical composition of waters and benthal deposits by studying the content of metals. The degree of mineralization, ionic composition of water, hydrogen index, pollution index, and water quality class were also determined. Reductions in the area and depth of the lake were identified. The pollution index is 1.5–1.7, which belongs to class 3—moderately polluted. Relatively high concentrations of cadmium, nickel, copper, and arsenic were found in the lake sediments. Therefore, Lake Burabay and its surrounding ecosystem face certain environmental risks and potential water pollution. Although the increase in the number of tourists did not have a significant impact on the water pollution index in Lake Burabay, some of the common threats that impact the area are induced by touristic development, agricultural practices and industrial pollution. Significant efforts should be made to reduce these risks using the environmental indicators as a reference for control environmental quality.

Influence of edge-deposited layers on mechanical and corrosion properties of laser beam welds of 15 mm thick AISI 2205 duplex stainless steel

AISI 2205 duplex stainless steel is used in a variety of industries, including the chemical and petrochemical industries. This is due to its high tensile strength combined with good ductility and corrosion resistance. However, in laser beam welding, these properties are negatively affected by the high cooling rates typical of the welding process. The resulting higher ferrite content in the weld metal than in the base material leads to a reduction in the ductility and corrosion resistance of the welded joint. To overcome this problem, in this study, thick plates were coated by direct energy deposition (DED) prior to laser beam welding, whereas a duplex powder mixture containing a higher nickel concentration was used as a coating material. To improve the weld quality for the proposed two-step process, a method of additional material deposition instead of conventional tack weld was investigated. The resulting welded joints showed a well-balanced austenite to ferrite ratio and their properties and microstructure were verified by metallographic analysis, electron backscatter diffraction and Charpy impact testing. Using the standard ASTM G48 test method, it was found that the corrosion resistance of the welds was improved by a factor of four in average compared to the conventionally welded joints. The resulting properties, such as good ductility and corrosion resistance, of the welds with pre-coated edges showed good agreement with those of the base metal and confirmed the proposed two-step process as a promising alternative to the conventional approaches for welding thick duplex stainless steel plates.

Application of rare earth elements as modifiers for Ni-rich cathode materials for Li-ion batteries: a mini review

This mini review article summarizes the recent progress in the modification of Ni-rich cathode materials for Li-ion batteries using rare earth elements. Although layered materials with high nickel content are the most promising cathodes due to their high capacity, the significant chemical, structural and thermal instability considerably hinders their practical application. Overcoming these limitations is possible through morphological or structural modifications based on doping and coating. Numerous reports regarding the use of various elements of the periodic table for this type of modification can be found in the literature. Surprisingly, rare earth elements are the least applied and described in the literature so far, even though they possess all the necessary features qualifying them as effective modifiers of layered cathode materials. This work summarizes the up-to-date publications regarding the application of rare earth elements as a highly prospective group of modifiers for layered Ni-rich cathode materials. These reports provide a better understanding of mechanisms of modification by rare earth elements and their beneficial effects on the electrochemical performance of the studied materials. New prospective strategies for layered cathode materials improvement have also been indicated.

Application of vacuum membrane distillation process for lithium recovery in spent lithium ion batteries (LIBs) recycling process

The feasibility of using vacuum membrane distillation (VMD) for lithium recovery by concentrating the discharged leachate from spent lithium ion batteries (LIBs) recycling process was evaluated. The performance of VMD was compared with that of direct contact membrane distillation (DCMD) in terms of water flux, concentration rate, membrane wetting, and economic feasibility. VMD achieved a higher volume concentration factor (VCF) of 45 compared to the VCF of 25 achieved by DCMD in the LiCl feed solution. In the Li2SO4 feed solution, VMD and DCMD were concentrated to VCF15 and VCF 17, respectively, before wetting occurred. The stability of the MD process was verified using feed solutions containing nickel and manganese, which are cathode materials that can cause scaling even at low concentrations. Low concentrations of nickel and manganese did not significantly affect the maximum VCF or wetting; however, high concentrations of nickel and manganese affected the stability of the MD process. VMD exhibited a higher flux and 32 % lower thermal energy consumption than DCMD. Furthermore, the expected cost of Li2CO3 production with VMD for leachate concentration was $8.31–10.65/kg. The VMD concentration process is a feasible option for recovering lithium from the discharged leachate from spent LIBs recycling process.

Nb-doped NCM622 shows improved capacity under high-temperature cycling—An experimental and theoretical study

Ni-rich layered lithiated transition metal oxide LiNi0.6Co0.2Mn0.2O2 (NCM622) is a promising candidate for Li-ion batteries. However, the high nickel content in NCM622 leads to significant capacity degradation during battery cycling. In this study, we investigated the effectiveness of niobium (Nb) doping in enhancing the performance of NCM622. Our findings demonstrate that Nb-doping reduces cation mixing and preserves the solid solution state of NCM622, as confirmed by calculated formation energy. Furthermore, the introduction of Nb imparts remarkable electrochemical properties to the material. Even under high-temperature and high-voltage conditions, the Nb-doped sample exhibits significantly improved cycling performance compared to the undoped sample, starting from the fifth cycle onwards. Through a combination of atomic-level mechanisms and experimental techniques, this research establishes that Nb-doping can enhance the structural stability and electrochemical properties of NCM622, providing a viable pathway for the industrial advancement of Ni-rich materials.

Regeneration of Spent Nickel Catalyst via Hydrometallurgical Method

<p><strong>Abstract.</strong> Nickel Catalyst is one of the common catalysts found in chemical industries. However, this catalyst has a limited lifetime indicated by having performance or activity drop so it is potentially become dangerous waste if the handling is not proper. The spent nickel catalyst needs to be processed to recover and avoid pollution towards the environment. The Hydrometallurgy method is a proper method to process nickel catalyst waste. The purpose of this research is to investigate the characteristic of a regenerated nickel catalyst when it is treated with HCl and H<sub>2</sub>SO<sub>4</sub> as the lixiviant. In this research, the spent nickel catalyst was treated with HCl and H<sub>2</sub>SO<sub>4</sub> in the presence of 2% H<sub>2</sub>O<sub>2</sub> reductant under room conditions and mixing rate at 200 rpm for 30 minutes of reaction. The leaching filtrate was precipitated using NaOH solution while the formed precipitate was heated at 800 °C for 3 hours. The regenerated catalyst was characterized using FTIR and SEM-EDX. The SEM images showed regenerated catalyst prepared using the HCl solution has a different morphology compared to the one using the H<sub>2</sub>SO<sub>4</sub> solution. Based on FTIR analysis, both samples exhibit Ni-O and C-O groups. Based on elemental analysis, the highest nickel concentration was obtained by using HCl with a Ni content of 25.98%w/w, compare to sulfuric acid (H<sub>2</sub>SO<sub>4</sub>) with a Ni content of 10.94%w/w. The Ni content can be improved by the addition of a washing step after the sintering process.</p><p><strong>Keywords:</strong></p><p align="left">Hydrometallurgy Nickel Catalyst, Waste, Leaching, Sintering</p><p><strong><br /></strong></p>

Reflectance spectroscopy as a promising tool for ‘sensing’ metals in hyperaccumulator plants

Main conclusionThe VNIR reflectance spectra of nickel hyperaccumulator plant leaves have spectral variations due to high nickel concentrations and this property could potentially be used for discovery of these plants. Hyperaccumulator plants accumulate high concentrations of certain metals, including manganese, cobalt, or nickel. Of these metals, the divalent ions of nickel have three absorption bands in the visible to near-infrared region which may cause variations in the spectral reflectance of nickel hyperaccumulator plant leaves, but this has not been investigated previously. In this shortproof-of-concept study, the spectral reflectance of eight different nickel hyperaccumulator plant species leaves were subjected to visible and near-infrared and shortwave infrared (VNIR-SWIR) reflectance spectrum measurements in dehydrated state, and for one species, it was also assessed in hydrated state. Nickel concentrations in the plant leaves were determined with other methods and then correlated to the spectral reflectance data. Spectral variations centred at 1000 ± 150 nm were observed and had R-values varying from 0.46 to 0.96 with nickel concentrations. The extremely high nickel concentrations in nickel hyperaccumulator leaves reshape their spectral reflectance features, and the electronic transition of nickel-ions directly contributes to absorption at ~ 1000 nm. Given that spectral variations are correlated with nickel concentrations it make VNIR-SWIR reflectance spectrometry a potential promising technique for discovery of hyperaccumulator plants, not only in the laboratory or herbarium, but also in the field using drone-based platforms. This is a preliminary study which we hope will instigate further detailed research on this topic to validate the findings and to explore possible applications.

Multi-Year Monitoring of the Toxicological Risk of Heavy Metals Related to Fish Consumption by the Population of the Kendari Region (Southeast Sulawesi, Indonesia).

This study measured the concentrations of Hg, As, Ni, Cd, and Pb in six fish species commonly consumed in Kendari. Samples were bought within local markets from 2012 to 2017 at the end of the dry season. Results showed that mercury concentrations fluctuated between years and within species, except in the Caranx sexfasciatus, which showed no significant differences (Kruskall-Wallis, p-value > 0.05, df = 5) and an average concentration of 0.371 ± 0.162 µg g-1 DW. Arsenic was found in high concentrations across species and years and varied widely in C. sexfasciatus, the lowest value being 0.32 ± 0.01 µg g-1 DW in 2012 and the highest was 5.63 ± 1.89 µg g-1 DW in 2017. The highest nickel concentrations were found in 2016 across four of the six species. The fish samples displayed very low cadmium and lead concentrations throughout the study. In addition, the potential human health risk due to fish consumption was assessed. This showed that mercury is the only one of the five metals present in concentrations high enough to individually pose a potential hazard, the only metal likely to be accumulated beyond a safe concentration in Kendari. Chanos chanos never posed a toxicological risk based on the results of this research.

Water Pollution in Cobalt and Nickel by the Effect of Adding Urban Waste in Al-Diwaniyah River / Iraq

This study was conducted in Al-Diwaniyah Governorate, Iraq, across four seasons with the intention of determining the impact of introducing liquid urban waste (including sewage, waste water, factory, and sewer water) on the content of cobalt and nickel in river water. At each location and during each of the following four seasons: summer in July, 2021; autumn in October, 2021; winter in January, 2022; and spring in April, 2022; for the following three locations: The first site was positioned at the entrance to Diwaniyah (Saniaa), which represents the control treatment as it is located before to the pollution outputs. The numerous sources of pollution that are discharged into the river, as well as the second location in the city center (the neighborhood of Refaat), and the third location in the Al-Sidair region, which is the final location in the city of Diwaniyah following the cessation of all pollution discharges into the river. The third, where the highest significant concentration of cobalt was 0.2400 μg l-1 in the summer, the third site, where it exceeded the limits recommended by the World Health Organization (WHO), and the lowest concentration was 0.0033 μg l-1 In the winter, the first site, while the highest concentration of Nickel was 0.382 μg l-1 in the summer, the third site, thus exceeding the critical limits of the World Health Organization (WHO), and its lowest concentration was 0.022 μg l-1 in the winter, the first site.

Metal microspherules in breccias of the Onaping Formation, Sudbury impact structure, Ontario, Canada

AbstractMetallic microspheres have been found in rocks from the Onaping Formation of the Sudbury impact structure, Canada. Microspherules are common in contact breccias, the lowest part of the Dowling Member, and rare microspherules have been found in the upper sequences of the Dowling Member. Separate microspherules are dispersed in the breccia matrix and do not form clusters. The sizes of the microspheres range from 5 to 30 μm; most commonly, they are 8–15 μm in size. The microspherules have a regular spherical shape, and in some cases show concentric zonal structures. The microspherules consist mostly of the refractory elements Cr, Co, Fe, Mo, W, and Ti, with a predominant Ni content of 40–75 wt%. The formation of the Sudbury metal microspherules by condensation in a high‐temperature plume is suggested by their spherical shape, concentric‐zoned structure, uniform composition, and distribution in fallback breccias of the crater‐fill Onaping Formation. The content of the most refractory W in the composition of the microspheres indicates early condensation. A decrease in the content of W and an increase in the content of Ni in the microspheres of the upper layers relative to the content of these elements in the earliest microspheres of the contact layers indicate that they could have formed by fractional condensation during the expansion and cooling of the impact vapor plume. As source material, a combination of target rocks with high nickel content with a chondritic impactor is suggested.

The role of nickel in forming a structure providing increased service properties of reactor structural materials

Nickel is an essential alloying element in steels used as structural materials in the most common nuclear power reactors of the VVER type. The paper considers reviews the results of structural studies of traditional and advanced materials of the vessels and internals of VVER-type reactors with high nickel contents in their compositions. It is shown that an increased nickel content (up to 5 wt.%) in the steels of VVER pressure vessels contributes to the formation of a more dispersed structure with a smaller size of substructural elements and an increased density of dislocations, as well as a higher volume density of carbide phases. The revealed features of the structure of the reactor pressure vessel steel with high nickel content have the prerequisites for improving the strength and viscoplastic properties due to the increased number of barriers both for the dislocation motion and brittle crack propagation. Using the example of materials for VVER internals, it is shown that the nickel content increased in them up to 25 wt.% contributes to an increase in the volume density of radiation defects (dislocation loops of various types) and radiation-induced phase precipitates (G-phase). As nickel increases from 10 to 25 wt.%, there is a tendency to reduce swelling, which contributes to less shape change of the components of the reactor vessel internals. At the same time, in the steel with the highest nickel content, the highest nickel content was found in the near-boundary regions of the matrix, which contributes to greater austenite stability and a lower probability of the formation of an embrittling α-phase. The data obtained in the work on the effect of nickel alloying on the steel structural phase state and service characteristics were used in the development of new materials for the vessels and internals of advanced reactors.

Utilizing waste carbon residue from spent lithium-ion batteries as an adsorbent for CO2 capture: A recycling perspective

Recycling and reusing the carbon-residues (i.e., graphite), as well as recovering valuable metals by leaching from spent lithium-ion batteries, is environmentally and economically significant. In particular, since a large amount of spent lithium-ion batteries (LIBs) will be generated along with the rapid growth of electric vehicles (EVs), research on recycling carbon-residues from LIB anodes is urgently needed. Herein, the battery powder (BP) was obtained from spent lithium-ion batteries (LIBs) through physical-pyrolysis and sieving. Chemical composition analysis confirmed that the battery used in this work was composed of NCM cathode with high-nickel content and graphite anode material. The average particle size of the obtained BP was 87 μm. In order to obtain the residue having high concentration of carbon, the metal extraction was applied using an HCl solution. As a result, metals (Li, Ni, Co, Mn, Al, Cu, and Fe) in the final remnant were found to be less than 2%, and carbon was found to have a purity of 97% or more. The obtained BP was tested as both the adsorbent and support for indoor CO2 capture. Various activation treatments were examined to enhance the textural properties of BP. BP-K (K2CO2 impregnated BP) adsorbents were prepared, and their CO2 adsorption performances were evaluated with CO2 adsorption isotherms, thermogravimetric analysis (TGA), and 0.1m3 chamber (CO2 IR analyzer) at low CO2 level (1000–2000 ppm). Through XRD and FT-IR analyses, the adsorption mechanism between K2CO3 and CO2 under moisture-containing indoor air conditions was confirmed to depend on chemisorption in the following reaction pathway: R1–R3(K2CO3(s) + H2O (g) + CO2 (g) ⇋ 2KHCO3(s) (R1), K2CO3(s) + 1·.5H2O(g) ⇋ K2CO3·1·.5H2O(s) (R2), K2CO3·1·.5H2O(s) + CO2(g) ⇋ 2KHCO3(s) + 0·.5H2O(g)(R3)). The adsorption working capacities of the recycled BP-K adsorbents were remained relatively constant during four consecutive cycles.

Enhancing the Electrochemical Properties of Nickel-Rich Cathode by Surface Coating with Defect-Rich Strontium Titanate.

Ni-rich layered ternary cathodes (i.e., LiNixCoyMzO2, M = Mn or Al, x + y + z = 1 and x ≥ 0.8) are promising candidates for the power supply of portable electronic devices and electric vehicles. However, the relatively high content of Ni4+ in the charged state shortens their lifespan due to inevitable capacity and voltage deteriorations during cycling. Therefore, the dilemma between high output energy and long cycle life needs to be addressed to facilitate more widespread commercialization of Ni-rich cathodes in modern lithium-ion batteries (LIBs). This work presents a facile surface modification approach with defect-rich strontium titanate (SrTiO3-x) coating on a typical Ni-rich cathode: LiNi0.8Co0.15Al0.05O2 (NCA). The defect-rich SrTiO3-x-modified NCA exhibits enhanced electrochemical performance compared to its pristine counterpart. In particular, the optimized sample delivers a high discharge capacity of ∼170 mA h/g after 200 cycles under 1C with capacity retention over 81.1%. The postmortem analysis provides new insight into the improved electrochemical properties which are ascribed to the SrTiO3-x coating layer. This layer appears to not only alleviate the internal resistance growth, from uncontrollable cathode-electrolyte interface evolution, but also acts as a lithium diffusion channel during prolonged cycling. Therefore, this work offers a feasible strategy to improve the electrochemical performance of layered cathodes with high nickel content for next-generation LIBs.

Delicately Designed Cyano‐Siloxane as Multifunctional Additive Enabling High Voltage LiNi0.9Co0.05Mn0.05O2/Graphite Full Cell with Long Cycle Life at 50 °C

AbstractLithium‐ion batteries (LIBs) adopting layered oxide cathodes with high nickel content (Ni ≥ 0.9) always suffer from extremely poor cycle life, especially at elevated temperatures and higher charging cut‐off voltages. Adding small amounts of functional additives is considered to be one of the most economic and efficacious strategies to resolve this issue. Herein, cyano‐groups are introduced innovatively into a siloxane to delicately synthesize a novel cyano‐siloxane additive, namely 2,2,7,7‐tetramethyl‐3,6‐dioxa‐2,7‐disilaoctane‐4,4,5,5‐tetracarbonitrile (TDSTCN). Encouragingly, 0.5 wt.% TDSTCN additive enables ultrahigh nickel LiNi0.9Co0.05Mn0.05O2/graphite (NCM90/Gr) full cells with dramatically increased cycle life, especially at an elevated temperature of 50 °C and a high charging cut‐off voltage of 4.5 V. The characterizations reveal that the TDSTCN additive can scavenge HF and promote the formation of robust stable interface layers on NCM90 cathode and Gr anode due to the synergistic effects of cyano‐groups and Si−O bonds. These results reveal the great significance of designing one single additive with several functional groups in enhancing the comprehensive electrochemical performances of high Ni LIBs.

Chemical weathering intensity controls the accumulation of nickel in rice (Oryza sativa L.) cultivated in basalt-derived paddy fields

Globally, a high concentration of nickel (Ni) in agricultural soil is closely related to basalt weathering. Rice grains readily accumulate Ni, however, the evolution of Ni distribution and mobility in paddy fields with basalt weathering remain unclear. This study investigated the distribution, geochemical fraction, and mobilization of Ni in basalt bedrock-paddy soil-rice plant continuums under contrasting climates through a combination of field surveys, chemical extractions, X-ray diffraction, and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analyses. Results show that the soils developed in tropical climates were more enriched in Ni than those in temperate climates. The concentration of Ni in rice grains from the studied temperate regions (3.71 ± 2.01 mg/kg) was higher than that in the tropical regions (0.57 ± 0.37 mg/kg). The concentration of Ni bound to Fe (hydro)oxides in paddy soils from temperate regions was five times higher than that in tropical regions. In contrast, the concentration of Ni found in phyllosilicate clays (mainly smectite/illite) in paddy soils from the temperate regions was only ∼1/4 of that of clay (mainly kaolinite) in the tropical paddy soils, and the ratio of Ni concentration in phyllosilicate clays to highly reactive Fe (hydro)oxides in paddy topsoil in temperate regions was one order of magnitude less than that in tropical regions, which contributes to the low bioavailability of Ni in tropical paddy soils. Furthermore, the accumulation of Ni in rice grains was insensitive to soil pH in tropical regions but showed significant negative correlations with the degree of chemical weathering (chemical index of alteration and index of laterisation) in temperate and tropical regions. These observations support the hypothesis that chemical weathering and the dissolution–recrystallization of Fe (hydro)oxides induced by frequent redox fluctuations in paddy soils cause Ni repartition between Fe (hydro)oxides and phyllosilicate minerals, which influence Ni geochemical cycling and bioavailability, and fundamentally regulate Ni accumulation in rice. This study elucidates the mechanism and controlling factors underlying Ni partition in the basalt-paddy soil-rice plant continuum under distinct climates, providing new insights into the understanding of geochemical behavior and environmental fate of Ni.

Mechanical Alloying Behavior and Thermal Stability of CoCrCuFeMnNix High-Entropy Alloy Powders Prepared via MA.

CoCrCuFeMnNix (x = 0, 0.5, 1.0, 1.5, 2.0 mol, named as Ni0, Ni0.5, Ni1.0, Ni1.5, and Ni2.0, respectively) high-entropy alloy powders (HEAPs) were prepared via mechanical alloying (MA), and XRD, SEM, EDS, and vacuum annealing were used to study the alloying behavior, phase transition, and thermal stability. The results indicated that the Ni0, Ni0.5, and Ni1.0 HEAPs were alloyed at the initial stage (5-15 h), the metastable BCC + FCC two-phase solid solution structure was formed, and the BCC phase disappeared gradually with the prolonging of ball milling time. Finally, a single FCC structure was formed. Both Ni1.5 and Ni2.0 alloys with high nickel content formed a single FCC structure during the whole mechanical alloying process. The five kinds of HEAPs showed equiaxed particles in dry milling, and the particle size increased with an increase in milling time. After wet milling, they changed into lamellar morphology with thickness less than 1 μm and maximum size less than 20 μm. The composition of each component was close to its nominal composition, and the alloying sequence during ball milling was Cu→Mn→Co→Ni→Fe→Cr. After vacuum annealing at 700~900 °C, the FCC phase in the HEAPs with low Ni content transformed into FCC2 secondary phase, FCC1 primary phase, and a minor σ phase. The thermal stability of HEAPs can be improved by increasing Ni content.

Cobalt-Free Layered LiNi0.8Mn0.15Al0.05O2/Graphene Aerogel Composite Electrode for Next-Generation Li-Ion Batteries.

In this work, we introduce LiNi0.8Mn0.15Al0.05O2 (NMA), which is cobalt-free and has a high nickel content, and a conductive composite material to NMA by supporting it with a three-dimensional (3D) graphene aerogel (GA). With an easy freeze-drying approach, NMA nanoparticles are properly dispersed on graphene sheets, and GA creates a strong and conductive framework, significantly improving the structure and conductivity. The structure of the pure NMA and NMA/graphene aerogel (NMA/GA) composite was investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). XRD and FE-SEM analyses clearly indicated that ultrapure NMA structures are homogeneously dispersed among the GAs. In addition, the composite structure was examined using transmission electron microscopy (TEM) to determine the dispersion mechanisms. The electrochemical cycling performance of the pure NMA and NMA/GA composite was evaluated by rate capacitance, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The synthesized NMA/GA was able to provide 89.81% specific capacity retention after the 500th cycle at C/2. The average charge/discharge rates of the obtained cathode show good electrochemical results and exhibit capacities of 190.2,186.3, 185.2, 176.2, 161.2,142.6, and 188.5 mAh g-1 at C/20, C/10, C/5, C, 3C, 5C, and C/20, respectively. EIS data showed an improvement in the impedance of the composite containing GA. According to the results of the electrochemical tests, NMA nanoparticles formed a conductive network with its porous structure thanks to GA, formed a protective layer on the surface, prevented the side reactions between the cathode and the electrolyte, decreased the impedance of the cathode, and increased the redox kinetics. In addition, the changes in the structure were investigated in the NMA/GA composite cathode by XRD, FE-SEM, and Raman analyses at the end of the 50th, 250th, and 500th cycles. In summary, the NMA/GA cathode is expected to play an important role in lithium-ion batteries (LIBs) by taking advantage of its easy synthesis and excellent cycle stability.