Ni Fraction Research Articles

Development and Upscaling of a Waterborne Formulation for High‐Energy Density NMC811 Cathodes

AbstractThe pursuit of high‐energy lithium‐ion cells has led to an increase in the fraction of nickel in the LiNixMnyCozO2 (NMC, with x+y+z=1) layered oxide, a state‐of‐the‐art cathode material in electric vehicles. NMC is usually processed using organic solvents that are non‐sustainable. Nevertheless, increasing the Ni fraction entails a decrease in the electrode stability and the processability of this material in water. In this work, high‐nickel NMC materials have been subjected to water processing. In an initial stage, water sensitivity of the materials has been studied. Then, the formulation has been adapted to enhance the NMC fraction without penalizations in the electrochemical performance and compared to an organic solvent‐based formulation. The recipe developed, consisting of 93 % of NMC, has been successfully upscaled to a semi‐industrial coating line. The pH buffering has been observed as a critical step to mitigate lithium leaching and implement this process in an industrial environment. The obtained electrodes have been tested in single‐layer pouch cells using silicon‐based negative electrodes, also processable in water‐based slurries. The resulting cells provide limited cycling life due to the low cyclability of the negative electrode but evidence that it is industrially viable to manufacture high‐energy cells consisting only of water‐processed electrodes.

Formation Characteristics of Pt-Ni Alloy Nanoparticles Fabricated by Nanolamination of Atomic Layer Deposition in Hydrogen.

Forced-flow atomic layer deposition nanolamination is employed to fabricate Pt-Ni nanoparticles on XC-72, with the compositions ranging from Pt94Ni6 to Pt67Ni33. Hydrogen is used as a co-reactant for depositing Pt and Ni. The growth rate of Pt is slower than that using oxygen reactant, and the growth exhibits preferred orientation along the (111) plane. Ni shows much slower growth rate than Pt, and it is only selectively deposited on Pt, not on the substrate. Higher ratios of Ni would hinder subsequent stacking of Pt atoms, resulting in lower overall growth rate and smaller particles (1.3-2.1nm). Alloying of Pt with Ni causes shifted lattice that leads to larger lattice parameter and d-spacing as Ni fraction increases. From the electronic state analysis, Pt 4f peaks are shifted to lower binding energies with increasing the Ni content, suggesting charge transfer from Ni to Pt. Schematic of the growth behavior is proposed. Most of the alloy nanoparticles exhibit higher electrochemical surface area and oxygen reduction reaction activity than those of commercial Pt. Especially, Pt83Ni17 and Pt87Ni13 show excellent mass activities of 0.76 and 0.59AmgPt -1, respectively, higher than the DOE target of 2025, 0.44AmgPt -1.

Sedimentation and transformation of heavy metals during the transport from the Yellow River estuary to the sea: Evidence from surface sediments of the Yellow River subaqueous delta

Estuarine and coastal areas are one of the ultimate sinks for terrestrial heavy metals which play a vital role on the aquatic ecosystem. This study examined heavy metals contents and speciations in Yellow River subaqueous delta surface sediment, to characterize their sedimentation and transformation during transport from estuary to the sea. The results showed that higher concentrations were found in the seaward and the shear front affected areas. The surface sediments were generally not contaminated by heavy metals, except for Cd was highly enriched, while the post-standardization spatial distribution reflected the effect of estuarine processes as a “filter” that effectively intercepting heavy metals. The dominated phase was residual fraction for Cr, Cu, Zn, Cd, while reducible fraction for Ni and carbonate fraction for Pb. The transformation of heavy metal species was mainly influenced by the changes in the sediment components such as carbonate minerals, organic matter and FeMn oxides.

Impact of nickel and alkaline earth metals interaction on sustainable carbon nanotubes generation from plastic face masks via catalytic pyrolysis

The one-pot synthesis of carbon nanotubes (CNTs) emerges as a promising approach for plastic valorization, owing to its simplicity and scalability. However, limited attention has been given to catalyst design for this method, particularly regarding the influence of Group 2 alkaline earth metal elements (X) on the Ni-based catalyst activity. This study investigates the impact of X on the catalytic activity of Ni towards sustainable CNTs synthesis using plastic face masks. The findings revealed that X influenced the carbon yield of NiMo-X catalysts and the morphology of the resultant carbon nanomaterials. Notably, NiMo-Ca demonstrated the highest carbon yield, whereas NiMo-Mg and NiMo-Ba exhibited the lowest. Furthermore, NiMo-Mg tends to produce clean and thin CNTs, while NiMo-Ba tends to yield carbon flakes with numerous irregular cokes. In addition to the effect of Ni crystallite size, which influences the transition from tubular to flake-like carbon structures, environmental factors are also considered. Specifically, NiMo-Mg generated a high CO2/CH4 environment, while NiMo-Ba exhibited slower catalytic cracking of polymeric chains from face masks, both of which were unfavorable for CNTs growth. Conversely, NiMo-Ca facilitated higher carbon recovery, likely due to its creation of a low CO2/CH4 environment via CO2 methanation. Optimization studies indicated that increasing pyrolysis temperatures and durations lead to reduced carbon yield, while cyclic pyrolysis of face masks up to five iterations enhances the reusability of NiMo-X catalysts with improved carbon recovery. Overall, this study provides valuable insights into the early pyrolytic gas formation and carbon nucleation phase, which are influenced by the surface Ni fraction and Ni polarization, as well as the later CNTs growth phase, which is related to the Ni crystallite size.

Capacity Fading Mechanism of Ni-Rich Cathode Materials Focusing on Particle Interior

With the prevalence of electric vehicles, Ni-rich layered cathodes have been extensively developed to increase the energy density of Li-ion batteries (LIBs). However, cathodes with a high Ni content suffer from inherent structural and chemical instabilities, which lead to rapid capacity fading and thermal instability.1 The degradation of Ni-rich cathode materials is largely caused by the high proportion of reactive Ni4+ combined with the mechanical instability originated from microcracks. This unstable Ni4+ can be readily reduced to Ni2+ by parasitic reactions with the electrolyte concurrently with oxygen release, forming a NiO-like rocksalt impurity phase.2 This phase increases the charge-transfer resistance and thus deteriorates the electrochemical performance of Ni-rich cathodes. As the degradation mainly occurs at the surface of cathode by deleterious electrolyte attack, the rate of degradation is significantly determined by the area exposed to the electrolyte. For cathodes with low Ni contents of ≤60%, the cathode−electrolyte interphase is only limited to the exterior surface of cathode particles in which microcracks are not severe; thus, the decrease in the cycling stability of cathodes is directly proportional only to their Ni4+ fraction. However, as the Ni content in the cathode increases above 60%, the extent of microcracks rapidly increases owing to the buildup of anisotropic strain induced by abrupt lattice volume changes during the H2−H3 phase transition.2 The resultant microcracks in Ni-rich cathode particles can create channels through which the electrolyte infiltrates into the particle interior, thereby increasing the surface area exposed to the electrolyte attack. Janek et al. reported that the specific surface area of 0.2 m2 g−1 for pristine LixNi0.8Co0.1Mn0.1O2 cathode increased to ∼1.4 m2 g−1 when charged to 4.2 V (vs Li/Li+) owing to crack formation.3 This increased surface area further accelerated the rate of capacity fading for Ni-rich cathodes (especially Ni fraction ≥90%), as not only the particle exteriors but also the interiors were exposed to deleterious electrolyte attack and were thus also passivated by NiO-like impurity phases caused by surface degradation.In this study, we performed comparative post-mortem analyses of Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) and Li[Ni0.90Co0.05Mn0.05]O2 (NCM90) cathodes after long-term cycling to elucidate the degradation mechanism of Ni-rich cathodes, focusing on the particle interior. Furthermore, we demonstrated correlations between the degradation of cathodes and the resultant changes in electrochemical properties (e.g., ionic and electrical conductivities). This systematic approach enables us to identify the mechanism by which cathode degradation deteriorates the electrochemical performance, which we expect to lead to breakthroughs in developing Ni-rich cathodes appropriate for EV applications. Reference s : [1] H.-J. Noh, S. Youn, C. S. Yoon, Y.-K. Sun, J. Power Sources, 2013, 233, 121.[2] H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater. 2018, 30, 1155.[3] E. Trevisanello, R. Ruess, G. Conforto, F. H. Richter, J. Janek, Adv. Energy Mater. 2021, 11, 2003400.

Multifunctional Doping Strategy to Develop High‐Performance Ni‐Rich Cathode Material

AbstractA high fraction of reactive Ni4+ ions at the cathode–electrolyte interfaces lead to capacity fading of Ni‐rich cathodes. Therefore, a core–shell (CS) design encapsulating the Ni‐rich region by a Ni‐less shell is an effective approach for improving the cycling stability of the cathodes. However, with increasing average Ni content to increase the capacity, the thickness of the shell should be reduced or the Ni fraction of the shell will be inevitably higher, making it susceptible to interdiffusion, which flattens the concentration gradient during the lithiation process. Herein, the limit of the average Ni composition in the CS‐type cathode is pushed to 94% via Ta doping, which suppresses interdiffusion by segregating the Ta‐rich phases at the particle boundaries. Ta doping allows the maintenance of the highly aligned microstructure and the ordered intermixing structure of Li and transition metal ions, as well as the concentration gradient, over a wide lithiation temperature range. The Ta‐doped CS‐type cathode retains 92.6% of its initial capacity after 1000 cycles and exhibits resistance to damage from fast charging. Multifunctional Ta doping in the CS‐type cathode provides a simple and all‐around solution to maximize the electrochemical performance of Ni‐rich cathodes, providing flexibility in the lithiation process.

Promoting effect of magnesium introduced in Li/Ni sites of LiNiO2 for lithium-ion batteries

The high cost of Co strongly drives the increase of Ni fraction and the decline of Co ingredient in commercial Ni-rich cathodes, generating convergence towards LiNiO2 (LNO). However, pure LNO suffers from poor cycling and rate performance due to severe Li+/Ni2+ cation mixing and structural degradation. Herein, a series of Mg-doped LNO are synthesized to elucidate the effect of the Mg dopant. It is demonstrated that around 2.21% and 2.79% of Mg2+ ions occupy the Li and Ni sites, respectively. The presence of Mg in the Li sites reduces Li+/Ni2+ cation mixing, enlarges the c-axis lattice, and acts as pillar ions, which facilitates Li+ diffusion and significantly improves the rate performance of Mg-doped LNO. Additionally, the introduction of Mg in the Li/Ni sites disturbs Li/vacancy ordering in the Li layers and electronic rearrangements in the Ni layers, which inhibits the two-phase separation transition at the end of charge. Furthermore, the pillaring effect of Mg2+ ions in Li sites and the stabilizing effect of Mg2+ ions in Ni sites at the end of delithiation alleviate the drastic c-axis shrinkage. Therefore, the optimized Mg-doped LNO exhibits reversible structure evolution, less microcracks, stable impedance growth, and excellent electrochemical performance during long-term cycling.

Effect of Low-Molecular Organic Acids on the Migration Characteristics of Nickel in Reclaimed Soil from The Panyi Mine Area in China.

This study investigated the effects of low molecular weight organic acids (citric acid and malic acid) on the migration properties of nickel in soil. A reclaimed soil sample was obtained from the Panyi Mine in Huainan City, China. The effects of adding different concentrations of Ni, citric acid (CA) and malic acid (MA) were assessed on the migration and transformation of soil Ni forms. The results showed: (1) An increase in soil Ni activity with increasing Ni concentrations. (2) An increased proportion of exchangeable forms of Ni in soil with increased malic acid and citric acid concentrations, effectively promoting Ni mobility. In addition, the active Ni fraction in reclaimed soil increased significantly with increasing concentrations of citric and malic acid. The nickel activation effect of citric acid was found to be higher than that of malic acid. (3) The activation effect of organic acids on Ni weakened with aging, exhibiting a gradual transformation from the loosely bound form of Ni, to the strongly bound form. The results of this study provide a theoretical basis for improving the effectiveness and efficiency of the phytoremediation techniques used for the treatment of Ni-polluted soils.

A Comparative Analysis of the Capacity Fading Mechanisms in Ni-Rich Single-Crystal and Polycrystalline Cathodes

Layered [Ni1–x–yCox(Mn or Al)y]O2 (NCM or NCA) oxides are the main cathode materials for powering current electric vehicles. Increasing the Ni fraction is the primary approach to increase the energy density of NCM and NCA cathodes, and thus enhancing the driving range of associated electric vehicles. However, high–Ni NCM and NCA cathodes with Ni contents near 90% suffer from inherent structural instability, especially in the deeply charged state, resulting in rapid capacity fading and high thermal instability. One method to address this inherent structural instability involves removing the interparticle boundaries by growing a single-crystal cathode. Single-crystal cathodes, free from interparticle microcracking, are regarded to improve cycling and thermal stability by minimizing parasitic surface degradation. Despite mechanical stability, the single-crystal cathode has some problems. In this presentation, we report a comprehensive evaluation of the fundamental properties of single-crystal and polycrystalline cathodes with a wide range of Ni-rich compositions. The electrochemical performances of single-crystal and polycrystalline cathodes are correlated with their structural changes to elucidate the dominant capacity fading mechanism of single-crystal cathodes.

Single-Crystalline Ni-Rich layered cathodes with Super-Stable cycling

Robust single-crystalline Ni-rich cathodes with increasing Ni proportion, LiNi 0.83 Co 0.11 Mn 0.06 O 2 (SC83), LiNi 0.88 Co 0.06 Mn 0.06 O 2 (SC88), and LiNi 0.95 Co 0.03 Mn 0.02 O 2 (SC95) were successfully designed with molten salt-assisted method, and the correlation between the Li + storage properties, particle microcracking, surface phase transitions, and Ni fraction in the single-crystalline Ni-rich cathodes have been profoundly investigated. • -crystalline Ni-rich cathodes with increasing Ni proportion were designed with molten salt-assisted method. • The single-crystalline LiNi 0.83 Co 0.11 Mn 0.06 O 2 cathode presents superior structural stability and cycling durability. • Performance degradations were attributed to the aggravated Li/Ni mixing and H2 ↔ H3 phase transition. • It provides approach for designing high-energy density and stable single-crystalline Ni-rich cathodes. Further commercial development of polycrystalline Ni-rich layered cathode is severely hindered by the deep-rooted particle microcracking, mainly initiated among the randomly orientated grain boundaries of the primary particles. Herein, robust single-crystalline Ni-rich LiNi 0.83 Co 0.11 Mn 0.06 O 2 (SC83) prepared by molten salt-assisted method shows the enhanced structure stability and cycling durability. It’s found that the particle microcracking is effectively removed for SC83 cathode during prolonged cycling helped with its eliminated grain boundaries and slight crystal shrinkage, leading to superior capacity retention of 92.8% after 100 cycles. Notably, the discharge capacity and energy density are effectively boosted with increasing Ni fraction majorly based on the more available Ni 2+ /Ni 3+ redox, giving rise to high capacities of 211.2 and 219.4 mAh g −1 for LiNi 0.88 Co 0.06 Mn 0.06 O 2 (SC88) and LiNi 0.95 Co 0.03 Mn 0.02 O 2 (SC95) cathodes, respectively. However, the particle microcracking is progressively exacerbated owing to the aggravated Li/Ni mixing and H2 ↔ H3 phase transition with Ni proportion higher than or equal to 88% in SC cathodes, resulting in severe structure collapse and capacity fading during high-rate cycling, in which a poor capacity retention of 51.8% after 250 cycles at 5C is observed for single-crystalline SC95cathode. This work sheds light on the rational design of single-crystalline Ni-rich cathodes, and highlighted the trade-off between the energy density and cycling durability, facilitating the extensive applications of single-crystalline Ni-rich cathodes in high-performance electric vehicles (EVs).

The effect of the Ni/Cu ratio on H-induced ductility loss and its mechanism in Cu–Ni binary alloy system

The effect of the Ni/Cu ratio on hydrogen embrittlement (HE) behavior is studied in the context of the Cu–Ni binary alloy system. When classifying HE sensitivity as a function of the Ni fraction, two regimes are obtained: Regime 1 (wherein Ni fraction is less than 80 wt%) with moderate HE and Regime 2 (where Ni fraction exceeds 80 wt%) with more severe HE, although hydrogen- (H-)induced intergranular (IG) cracking is noted to be the common primary cause of H-induced degradation. Necessities of H-transportation towards grain boundaries (GBs) via H–dislocation interaction and/or dynamic H-diffusion are discussed via the slow strain rate tensile tests at −196 °C. Specifically, in Regime 1, H-transportation is necessary for the triggering of IG cracking. Conversely, in Regime 2, such H-transportation plays a minor role and the initially concentrated hydrogen along GBs can sorely cause IG cracking.

Biochar application alters soil Ni fractions and phytotoxicity of Ni to pakchoi (Brassica rapa L. ssp. chinensis L.) plants

Soil contamination with nickel (Ni) from anthropogenic activities can have serious environmental impacts. The consequences of Ni contamination on the Ni fractional distribution in the soil, their potential phytotoxicity, and the possible use of biochar are least deliberated. A greenhouse experiment was conducted to determine the effect of selected Ni contamination levels and kunai grass biochar on soil Ni fractions and crop growth response. A bulk soil in polythene bags was spiked with NiCl 2 solution at 0, 56, 100, and 180 mg Ni kg −1 soil. Another set of bags received kunai grass ( Imperata cylindrica ) biochar at 0.75% on a dry weight basis. The treatments were replicated 3 times and planted with pakchoi seeds. Results indicated dose-dependent variations in the distribution of Ni fractions namely, exchangeable and acid-soluble, oxidizable, and residual Ni upon fractionation of soil samples drawn on days 30 and 60. As the level of Ni contamination increased, a significant enhancement of soil exchangeable and acid-soluble portion of Ni and oxidizable Ni with concomitant failure of pakchoi seedling growth. The biochar application significantly (p < 0.05) decreased exchangeable and acid-soluble Ni (58%) and enhanced residual Ni pools in low Ni contaminated soils (56 mg) thereby relieving pakchoi plants from toxic effects of Ni. Biochar incorporation to the soil decreased the Ni uptake by pakchoi plants and decreased bioaccumulation factor from 1.81 to 1.20 in low Ni contaminated soil only. Chemical transformation of Ni fractions due to biochar application can effectively reduce toxicity to crop plants, and Ni uptake thus a safe option to manage soil contaminant Ni. • Biochar application investigated in spike Ni contaminated soils under pakchoi plants. • Biochar @ 0.75% transformed exchangeable Ni to more stable residual Ni fraction. • Reduced phytotoxicity , and Ni uptake coupled with decreased Ni bioaccumulation. • Soil incorporation of biochar is potentially safe approach in Ni contaminated soils.

Ni-Rich Li[Ni0.9Co0.045Mn0.045Al0.01]O2 (NCMA) Cathode with Optimized Microstructure for Microstrain Control

Layered Ni-rich cathode materials Li[Ni x Co y M 1-x-y ]O2 (M = Mn and Al are denoted as NCM and NCA, respectively) has been common cathodes for the batteries of electric vehicles (EVs). Recently, Li[Ni x Co y Mn z Al1-x-y-z ]O2 (NCMA), a hybrid of NCM and NCA cathodes, has received significant attention owing to the announcement by General Motors of its intention to deploy NCMA cathodes for Li-ion batteries (LIBs) in its next EVs.1 The NCMA cathode can provide high discharge capacity with stable cycle life owing to strong Al-O bonding which strengthens the host layered structure. However, an introduction of the high concentration of Al dopant for stabilization of Ni-rich cathodes is restricted as an electrochemically inactive Al lowers the capacity of cathode.For Ni-rich cathodes, it is well acknowledged that increasing the Ni composition in the cathodes for higher capacity leads to the deterioration in both cycling performance and thermal stability.2 The fast capacity fading of Ni-rich cathode is mostly attributed to the H2–H3 phase transition at the charged state, and the extent of H2–H3 phase transition increases with increasing Ni fraction in the cathodes. As the phase transition induces a lattice volume change generating microcracks in the particles, the alleviation of internal microstrain is required to suppress the microcrack formation in the cathode particles and to improve the cycling stability of Ni-rich cathodes.To reinforce the mechanical stability of Ni-rich NCMA cathodes, we proposed a hybrid structure cathode in which Li[Ni0.92Co0.04Mn0.03Al0.01]O2 in the interior of the particle is encapsulated by Li[Ni0.845Co0.067Mn0.078Al0.01]O2 that acts as a buffer against the microstrain. Similar to the tempered glass which has different states of stress in the surface and bulk material to increase the strength,3 the proposed cathode structure suppresses the formation of microcracks by creating a non-uniform spatial distribution of microstrain within the cathode particle. The electrochemical performance of the proposed cathode is correlated with the microstructure, and the mechanism suppressing the formation of microcracks in the Ni-rich NCMA cathode is demonstrated. Reference s : [1] General Motors Co. LYRIQ Show Car Leads Cadillac Into Electric Future, 2020; https://media.gm.com/media/us/en/cadillac/news.detail.html/content/Pages/news/us/en/2020/aug/0806-lyriq.html (accessed December 2020).[2] H.-J. Noh, S. Youn, C. S. Yoon, Y.-K. Sun, J. Power Sources, 2013, 233, 121.[3] A. L. Zijlstra, A. J. Burggraaf, J. Non-Cryst. Solids, 1968, 1, 49.

Calcite in combination with olive pulp biochar reduces Ni mobility in soil and its distribution in chili plant

The presence of Ni above the permissible limit in agriculture soils poses negative effects on soil health, crop quality, and crop productivity. Surprisingly, the usage of various organic and inorganic amendments can reduce Ni mobility in the soil and its distribution in the crops. A pot experiment was conducted to elucidate the effects of olive pulp biochar (BR), calcite (CAL), and wheat straw (WS), as sole amendments and their mixtures of 50:50 ratio, added to Ni polluted soil on Ni mobility in the soil, Ni immobilization index (Ni − IMi), soil enzymatic activities, Ni distribution in parts of chili plant, Ni translocation factor and bioaccumulation factor in fruit, plant growth parameters and oxidative stress encountered by the plants. Outcomes of this pot experiment revealed that amendments raised soil pH, improved soil enzymatic activities, values of Ni − IMi, while significantly reduced bioavailable Ni fraction in the post-harvest soil. However, the highest activities of acid phosphatase, urease, catalase, and dehydrogenase by 50, 70, 239, and 111%, respectively, improvement in Ni − IMi up to 60% while 60% reduction in the bioavailable Ni fraction was observed in BR + CAL treatment, compared to control was noted. Among all amendments, the top most reduction in Ni concentrations in shoots, roots, fruit, Translocation Factor (TF), and Bioaccumulation Factor (BAF) values of fruit by 72%, 36%, 86%, 72%, and 86%, in BR + CAL treatment, compared to control. Moreover, the plants growing on BR + CAL amended Ni contaminated soil showed the topmost improvement in plant phonological parameters while encountered the least oxidative stress. Such findings refer to the prospective usage of BR + CAL at 50:50 ratio than BR, CAL, WS alone, and BR + WS as well as WS + CAL for reducing Ni mobility in the soil, improving Ni − IMi, soil enzymatic activities, plant phonological and oxidative stress while reducing Ni distribution in plant parts. Novelty statement In this experiment, it was hypothesized that amending Ni polluted soil with olive pulp biochar (BR), CAL, and WS as alone soil amendments and their combinations at 50:50 ratios can reduce Ni bioavailability in soil, Ni distribution in chili plant and oxidative stress encountered by the plants. Moreover, these amendments may improve, soil enzymatic activities, Ni immobilization index, plant phenological traits. Therefore, it was aimed to undertake useful scientific planning and research, to restore and rehabilitate the dwellings, biological resources and to minimize the sufferings of the peoples in nutrient-poor Ni contaminated soils, by improving soil health and chili productivity.

Structure and magnetic behavior of sol-gel grown spinel NixMn3-xO4 nanoparticles: Effect of Ni fraction and induction of superparamagnetism at room temperature

Spinel NixMn3-xO4 nanostructures have attracted a huge research interest due to their applications in catalysis, electrocatalysis, high-performance supercapacitors, lithium-ion batteries, among others. However, those applications strongly depend on the Ni:Mn ratio, valence states and spatial distribution of cations in the spinel lattice. Using a low-temperature sol-gel process, we synthesized NixMn3-xO4 nanoparticles of 14–26 nm average sizes with different Ni contents. Effects of Ni incorporation on the morphology, structure and magnetic properties of the nanostructures were studied by SEM, XRD, XPS, Raman spectroscopy and VSM. While a high Ni content in the spinel nanostructures causes lattice shrinkage, lattice expansion at lower Ni content occurs due to higher occupancy of Mn2+ ions in tetrahedral sites. Structural and magnetic behaviors of the nanostructures were explained by considering the crystal field stabilization energies of the cations. We demonstrate that superparamagnetic behavior can be induced in the NixMn3-xO4 nanostructures by incorporating Ni at x>1.0.

Mn5−xGe3Nix refrigerant for active magnetic refrigeration

Mn5−xNixGe3 (x = 0, 0.025, 0.075, 0.1, 0.15, 0.2, 0.25, and 0.4) alloys were synthesized to demonstrate that the magnetocaloric (MCE) properties [Curie temperature, magnetic entropy change (ΔSM), and adiabatic temperature change (ΔTad)] can be fine-tuned by changing the Ni fraction. An active magnetic regenerative (AMR) cycle testbed was built in-house to investigate the suitability of Mn5−xNixGe3 as a solid magnetic refrigerant operating at room temperature and as a composite refrigerant for an AMR cycle. The maximum temperature difference between the hot and cold ends, ΔTspan, measured from the AMR testbed was 7.5 K and 5.6 K for Gd and Mn5Ge3, respectively. The ΔTspan values were reasonable considering the inferior ΔSM and ΔTad for Mn5Ge3 compared to those of Gd. A two-layer composite refrigerant consisting of Mn5Ge3 and Mn4.975Ni0.025Ge3 produced ΔTspan of 6.3 K, which is 13% higher than that of the single Mn5Ge3 refrigerant, indicating the effectiveness of a multi-layer refrigerant selected to closely match the temperature gradient in an AMR cycle. This work highlights the importance of tailoring the MCE properties as required to build a composite refrigerant.

Comparison of Ni-Rich Li[Ni1 −x−YCoxAly]O2(NCA) Cathodes for Lithium-Ion Batteries Depending on Extent of Microcracks

Ni-rich layered cathode materials Li[Ni1 − x − yCoxMy]O2 (M = Al and Mn are denoted as NCA and NCM, respectively) are typical cathodes for the batteries of electric vehicles (EVs). In particular, Tesla, one of the most promising EVs producers, uses the Panasonic NCA cathode in its Model S. For the wide adoption of EVs, driving range need to be raised by the increase in energy density of lithium ion batteries (LIBs). However, developing LIBs which have high energy density with stable cycle life is mainly hampered by the cathode materials.The general strategy for increasing the reversible capacity of NCM and NCA cathodes is to increase the relative Ni fraction in their composition. However, it is well acknowledged that increasing the Ni composition in NCM cathodes leads to the deterioration in both cycling performance and thermal stability.1 The fast capacity fading of Ni-rich NCM cathode is mostly attributed to the H2–H3 phase transition at the charged state, inducing an anisotropic lattice volume change generating internal microcracks in the particles.2 The extent of microcrack, which is a crucial factor dictating a performance of cathode material, increases as Ni fraction increases. Similar to NCM cathodes, Ni-rich NCA cathodes are also supposed to suffer from capacity fading and thermal instability problems owing to microcracks. To apply Ni-rich NCA cathodes in high-energy batteries for EVs, it is important to establish the capacity-cycling stability-thermal stability relationship depending on the extent of microcracks.Based on the results in NCM cathodes, we investigated the comparative study of NCA cathodes whose Ni fraction are 80%, 88%, and 95% to assess their cycling stability and to determine the capacity limit that can be attained by Ni-rich NCA cathodes without substantial sacrifice of the cycling stability. In addition, The extent of microcracks during charging and discharging was focused to identify the capacity-fading mechanism of these Ni-rich NCA cathodes. The results can provide the technical and scientific basis for further material development of these cathodes. Reference s 1. H.-J. Noh, S. Youn, C. S. Yoon and Y.-K. Sun, J. Power Sources, 2013, 233, 121.2. H.-H. Ryu, K.-J. Park, C. S. Yoon and Y.-K. Sun, Chem. Mater. 2018, 30, 1155.

Effect of Copper-Doping on LiNiO2 Positive Electrode for Lithium-Ion Batteries

LiNiO2 (LNO) is one of the most potential alternatives to LiCoO2 in Li ion batteries (LIBs). However, it still suffers from poor cyclability. Meanwhile, the recycling processes of LIBs are widely investigated to enable effective recycling for the growing amounts of LIB waste. Cu is one of the dominating impurities in LIB recycling fractions. In this work, LNO and 0.2 mol% Cu-doped LNO are studied. Cu-doping is demonstrated to stabilize the LNO lattice structure, reduce cation mixing and improve the reversibility of phase transitions during electrochemical processes. Consequently, the rate capability of LNO is improved by Cu-doping, especially at high C-rates. The Cu-doped LNO shows much higher capacity retention of 85% than that of 66% for the undoped LNO at the current density of 100 mA·g−1 after 100 cycles in a voltage window of 2.5–4.5 V. Our results show that a possible Cu contamination in the Ni fraction of the LIB material recovery process can be used to enhance the electrochemical properties of newly synthetized Ni-based positive electrode materials.

Roles of Mn and Ni in Li-rich Mn-Ni-Fe oxide cathodes

Cobalt free, lithium-rich manganese, nickel, and iron composite oxides (nanoscale mixture of monoclinic, Li2MnO3, and rhombohedral, LiMO2, phases) are promising cathodes as they show attractive electrochemical performance in initial cycles and can reduce the cost and toxicity of lithium ion battery. However, capacity and voltage fading on cycling are the downsides. To better understand the electrochemical performance and degradation mechanism, a series of Li1.2Mn0.40+xNi0.30-xFe0.10O2 materials with x = 0, 0.05, 0.10, and 0.15 was synthesized and systematically studied. The results of this study suggest that two phase composition is beneficial for superior electrochemical performance. The series showed first discharge capacity at 0.1C of 267, 204, 226, and 277 mAhg−1 for x = 0, 0.05, 0.10, and 0.15 respectively, with capacity retention after 100 cycles at 0.3C of 57 %, 57 %, 94 % and 67 %. For the first time we report EXAFS data analysis at all three K-edges: Mn, Ni and Fe before and after extended cycling. Ni reduction to Ni2+ after cycling and voltage fading increased with Ni fraction in the series. There is no trend of Mn reduction (Li2MnO3 activation) on cycling with Mn content indicating composition selection is crucially important for improved performance. The information on changes in electronic states and atomic distances, which allows proposing comprehensive electrochemical (role of Li2MnO3 phase) and degradation (Li+/Ni2+ exchange, voltage fading, and capacity fading) mechanisms.

Periodical changes of dissolved organic matter (DOM) properties induced by biochar application and its impact on downward migration of heavy metals under flood conditions

The migration of heavy metals has strong correlation with dissolved organic matters (DOM) in the soil while biochar contains abundant DOM, so this study aimed to find out how soil DOM properties changed triggered by biochar and whether it would promote the migration of heavy metals under flood conditions. In this work, a 90-day soil column incubation experiment was conducted to simulate the migration of heavy metals in actual flood conditions environment. Different depth of porewater was collected every 30 days. The sampled pore water was analyzed by spectroscopic analysis (PARAFAC, UV-VIS) to observe DOM property changes and then NICA-Donnan model was used to illustrate heavy metals complexation with soil DOM. Results showed that DOM release in biochar-added soil was 57.5% higher than that in biochar-free soil after 90 days and the DOM characteristics were different from those in biochar-free soil. It was also found that DOM continuously released in biochar-added soil was easily complexed with metals. According to two first-order reactions (TFOR), DOM fraction of Ni in biochar addition treatment was 33.3% higher compared to the biochar free treatment after 90 days, and therefore resulted in more significant downward migration trend of Ni. This is also supported by the fact that Ni concentration in the subsoil of biochar addition treatment increased nearly 9 fold after 60 days. Moreover, labile Cd and Ni fraction increased in biochar-added soil, from 16.2% to 28.7% and from 22.2% to 57.2%, respectively. These results suggest a possible risk in wetlands soil and for groundwater pollution by biochar under flood conditions.