Vacancies-Induced Delocalized States Cobalt Phosphide for Binder-Free Anode Toward Stable and High-Rate Sodium-Ion Batteries.

Metal phosphides with easy synthesis, controllable morphology, and high capacity are considered as potential anodes for sodium-ion batteries (SIBs). However, the inherent shortcomings of metal phosphating materials, such as conductivity, kinetics, volume strain, etc are not satisfactory, which hinders their large-scale application. Here, a CoP@carbon nanofibers-composite containing rich Co─N─C heterointerface and phosphorus vacancies grown on carbon cloth (CoP1-x@MEC) is synthesized as SIB anode to accomplish extraordinary capacity and ultra-long cycle life. The hybrid composite nanoreactor effectively impregnates defective CoP as active reaction center while offering Co─N─C layer to buffer the volume expansion during charge-discharge process. These vast active interfaces, favored electrolyte infiltration, and a well-structured ion-electron transport network synergistically improve Na+ storage and electrode kinetics. By virtue of these superiorities, CoP1-x@MEC binder-free anode delivers superb SIBs performance including a high areal capacity (2.47 mAh cm-2@0.2 mA cm-2), high rate capability (0.443 mAh cm-2@6 mA cm-2), and long cycling stability (300 cycles without decay), thus holding great promise for inexpensive binder-free anode-based SIBs for practical applications.

Oxygen Vacancies Driven by Co in the Deeply Charged State Inducing Intragranular Cracking of Ni-Rich Cathodes.

Intragranular cracking within the material structure of Ni-rich (LiNixCoyMn1 - x - y, x ≥0.9) cathodes greatly threatens cathode integrity and causes capacity degradation, yet its atomic-scale incubation mechanism is not completely elucidated. Notably, the physicochemical properties of component elements fundamentally determine the material structure of cathodes. Herein, a diffusion-controlled incubation mechanism of intragranular cracking is unraveled, and an underlying correlation model with Co element is established. Multi-dimensional analysis reveals that oxygen vacancies appear due to the charge compensation from highly oxidizing Co ions in the deeply charged state, driving the transition metal migration to Li layer and layered to rock-salt phase transition. The local accumulation of two accompanying tensile strains collaborates to promote the nucleation and growth of intragranular cracks along the fragile rock-salt phase domain on (003) plane. This study focuses on the potential risks posed by Co to the architectural and thermal stability of Ni-rich cathodes and is dedicated to the compositional design and performance optimization of Ni-rich cathodes.

Origin and Regulation of Interface Fusion during Synthesis of Single-Crystal Ni-Rich Cathodes.

Interface fusion plays a key role in constructing Ni-based single-crystal cathodes, and is governed by the atomic migration related to kinetics. However, the interfacial atom migration path and its control factors are lack of clearly understanding. Herein, we systematically probe the solid-state synthesis mechanism of single-crystal LiNi0.92 Co0.04 Mn0.04 O2 , including the effects of precursor size, Li/transition metal (TM) ratio and sintering temperature on the structure. Multi-dimensional analysis unravels that thermodynamics drives interface atoms migration through intermediate state (i.e., cation mixing phase) to induce grain boundary fusion. Moreover, we demonstrate that smaller precursor size (<6 µm), lager Li/TM ratio (>1.0) and higher temperature (≥810 °C) are conducive to promote the growth of the intermediate state due to reaction kinetics enhancement, and ultimately strengthen the atomic migration-induced interface fusion.

Nickel-Rich Layered Cathode Materials for Lithium-Ion Batteries.

Nickel-rich layered transition metal oxides are considered as promising cathode candidates to construct next-generation lithium-ion batteries to satisfy the demands of electrical vehicles, because of the high energy density, low cost, and environment friendliness. However, some problems related to rate capability, structure stability, and safety still hamper their commercial application. In this Review, beginning with the relationships between the physicochemical properties and electrochemical performance, the underlying mechanisms of the capacity/voltage fade and the unstable structure of Ni-rich cathodes are deeply analyzed. Furthermore, the recent research progress of Ni-rich oxide cathode materials through element doping, surface modification, and structure tuning are summarized. Finally, this review concludes by discussing new insights to expand the field of Ni-rich oxides and promote practical applications.

Investigation of the Ecological Roles of Putative Keystone Taxa during Tailing Revegetation.

Metal contamination released from tailings is a global environmental concern. Although phytoremediation is a promising remediation method, its practice is often impeded by the adverse tailing geochemical conditions, which suppress biological activities. The ecosystem services provided by indigenous microorganisms could alter environmental conditions and facilitate revegetation in tailings. During the process, the keystone taxa of the microbial community are assumed an essential role in regulating the community composition and functions. The identity and the environmental functions of the keystone taxa during tailing revegetation, however, remain unelucidated. The current study compared the microbial community composition and interactions of two contrasting stibnite (Sb2S3) tailings, one revegetated and one unvegetated. The microbial interaction networks and keystone taxa were significantly different in the two tailings. Similar keystone taxa were also identified in other revegetated tailings, but not in their corresponding unvegetated tailings. Metagenome-assembled genomes (MAGs) indicated that the keystone taxa in the revegetated tailing may use both organic and inorganic energy sources (e.g., sulfur, arsenic, and antimony). They could also facilitate plant growth since a number of plant-growth-promoting genes, including phosphorus solubilization and siderophore production genes, were encoded. The current study suggests that keystone taxa may play important roles in tailing revegetation by providing nutrients, such as P and Fe, and promoting plant growth.

VV Reduction by Polaromonas spp. in Vanadium Mine Tailings.

Vanadium (V) is an important metal with critical industrial and medical applications. Elevated V contamination, however, can be a threat to the environment and human health. Microorganisms can reduce the more toxic and mobile VV to the less toxic and immobile VIV, which could be a detoxification and energy metabolism strategy adopted by V-reducing bacteria (VRB). The limited understanding of microbial responses to V contamination and the mechanisms for VV reduction, however, hamper our capability to attenuate V contamination. This study focused on determining the microbial responses to elevated V concentration and the mechanisms of VV reduction in V tailings. The bacterial communities were characterized and compared between the V tailings and the less contaminated adjacent mineral soils. Further, VV-reducing enrichments indicated that bacteria associated with Polaromonas, a genus belonging to the family Burkholderiaceae, were potentially responsible for VV reduction. Retrieved metagenome-assembled genomes (MAGs) suggested that the Polaromonas spp. encoded genes (cymA, omcA, and narG) were responsible for VV reduction. Additionally, Polaromonas spp. was metabolically versatile and could use both organic and inorganic electron donors. The metabolic versatility of Polaromonas spp. may be important for its ability to flourish in the V tailings.

Catalytic Conversion of Glycerol to Lactic Acid Over Hydroxyapatite-Supported Metallic Ni0 Nanoparticles.

Catalytic conversion of low-priced biomass glycerol to value-added lactic acid is an alternative route to the conventional fermentation process using sugar as the starting material. Nanosized hydroxyapatite-supported metallic Ni0 nanoparticles (Nix/HAP) prepared by the wetness chemical reduction method effectively catalyzed the conversion of high-concentrated glycerol (1.5-3 mol L-1) to lactic acid in a NaOH aqueous solution. The Nix/HAP catalysts exhibited higher catalytic activity for glycerol conversion to lactic acid than the sole metallic Ni0 nanoparticles. When the reaction was carried out over the Ni0.2/HAP catalyst with the initial glycerol and NaOH concentrations of 2.0 and 2.2 mol L-1 at 200 °C for 2 h, the selectivity of lactic acid reached 94.7% at the glycerol conversion of 92.1%.

Emerging Pollutants - Part I: Occurrence, Fate and Transport.

Part I: Occurrence, Fate, and Transport (this review) is a sequel of Emerging Pollutants. This review compiles research in 2015 for investigating emerging pollutants in wastewater and environmental sources of emerging pollutants. It investigates the occurrence, fate, transport of emerging pollutants in the environment. This review further discusses the monitoring approaches, modeling, and toxicological impacts of these compounds that are relevant to wastewater.

Formulating Local Environment of Oxygen Mitigates Voltage Hysteresis in Li-Rich Materials.

Li-rich cathode materials have emerged as one of the most prospective options for Li-ion batteries owing to their remarkable energy density (>900 Wh kg-1). However, voltage hysteresis during charge and discharge process lowers the energy conversion efficiency, which hinders their application in practical devices. Herein, the fundamental reason for voltage hysteresis through investigating the O redox behavior under different (de)lithiation states is unveiled and it is successfully addressed by formulating the local environment of O2-. In Li-rich Mn-based materials, it is confirmed that there exists reaction activity of oxygen ions at low discharge voltage (<3.6 V) in the presence of TM-TM-Li ordered arrangement, generating massive amount of voltage hysteresis and resulting in a decreased energy efficiency (80.95%). Moreover, in the case where Li 2b sites are numerously occupied by TM ions, the local environment of O2- evolves, the reactivity of oxygen ions at low voltage is significantly inhibited, thus giving rise to the large energy conversion efficiency (89.07%). This study reveals the structure-activity relationship between the local environment around O2- and voltage hysteresis, which provides guidance in designing next-generation high-performance cathode materials.

Microwave-assisted synthesis of Co-free Li[Li0.2Ni0.2Mn0.6]O2 cathodes with a spinel-layered coherent structure for high-power Li-ion batteries.

Li- and Mn-rich layered oxides (LMLOs) are regarded as the most promising cathode materials for Li-ion batteries (LIBs), but they suffer from poor rate capability. Herein, a promising and practical method (i.e. a hydroxide coprecipitation method in combination with a microwave heating process) is developed to controllably synthesize cobalt-free Li[Li0.2Ni0.2Mn0.6]O2 with a layered/spinel heterostructure (LLNMO-LS). The cathode made of the LLNMO-LS delivers an excellent electrochemical performance, demonstrating a discharge capacity of 147 mA h g-1 at 10C.

Kinetically controlled synthesis of low-strain disordered micro-nano high voltage spinel cathodes with exposed {111} facets.

High-voltage LiNi0.5Mn1.5O4 (LNMO) is one of the most promising cathode candidates for rechargeable lithium-ion batteries (LIBs) but suffers from deteriorated cycling stability due to severe interfacial side reactions and manganese dissolution. Herein, a micro-nano porous spherical LNMO cathode was designed for high-performance LIBs. The disordered structure and the preferred exposure of the {111} facets can be controlled by the release of lattice oxygen in the high-temperature calcination process. The unique configuration of this material could enhance the structural stability and play a crucial role in inhibiting manganese dissolution, promoting the rapid transport of Li+, and reducing the volume strain during the charge/discharge process. The designed cathode exhibits a remarkable discharge capacity of 136.7 mA h g-1 at 0.5C, corresponding to an energy density of up to 636.4 W h kg-1, unprecedented cycling stability (capacity retention of 90.6% after 500 cycles) and superior rate capability (78.9% of initial capacity at 10C). The structurally controllable preparation strategy demonstrated in this work provides new insights into the structural design of cathode materials for LIBs.

Developing an abnormal high-Na-content P2-type layered oxide cathode with near-zero-strain for high-performance sodium-ion batteries.

Layered transition metal oxides (NaxTMO2) possess attractive features such as large specific capacity, high ionic conductivity, and a scalable synthesis process, making them a promising cathode candidate for sodium-ion batteries (SIBs). However, NaxTMO2 suffer from multiple phase transitions and Na+/vacancy ordering upon Na+ insertion/extraction, which is detrimental to their electrochemical performance. Herein, we developed a novel cathode material that exhibits an abnormal P2-type structure at a stoichiometric content of Na up to 1. The cathode material delivers a reversible capacity of 108 mA h g-1 at 0.2C and 97 mA h g-1 at 2C, retaining a capacity retention of 76.15% after 200 cycles within 2.0-4.3 V. In situ diffraction studies demonstrated that this material exhibits an absolute solid-solution reaction with a low volume change of 0.8% during cycling. This near-zero-strain characteristic enables a highly stabilized crystal structure for Na+ storage, contributing to a significant improvement in battery performance. Overall, this work presents a simple yet effective approach to realizing high Na content in P2-type layered oxides, offering new opportunities for high-performance SIB cathode materials.

Fabricating Heterostructures for Boosting the Structure Stability of Li-Rich Cathodes.

Li-rich Mn-based oxides are regarded as the most promising new-generation cathode materials, but their practical application is greatly hindered by structure collapse and capacity degradation. Herein, a rock salt phase is epitaxially constructed on the surface of Li-rich Mn-based cathodes through Mo doping to improve their structural stability. The heterogeneous structure composed of a rock salt phase and layered phase is induced by Mo6+ enriched on the particle surface, and the strong Mo-O bonding can enhance the TM-O covalence. Therefore, it can stabilize lattice oxygen and inhibit the side reaction of the interface and structural phase transition. The discharge capacity of 2% Mo-doped samples (Mo 2%) displays 279.67 mA h g-1 at 0.1 C (vs 254.39 mA h g-1 (pristine)), and the discharge capacity retention rate of Mo 2% is 79.4% after 300 cycles at 5 C (vs 47.6% (pristine)).

Enhancing the Integral Structural and Thermal Stability of Ultrahigh-Ni Cathodes via Morphology Refinement and In Situ Interfacial Engineering.

Nickel-rich layered oxides are promising cathodes in commercial materials for lithium-ion batteries. However, the increase of the nickel content leads to the decay of cyclic performance and thermal stability. Herein, in situ surface-fluorinated W-doping LiNi0.90Co0.05Mn0.05O2 cathodes enhance integral lithium-ion migration (transfer in bulk and diffusion in the interface) kinetics by synergistically solving the problems of bulk and interface structural degradation. Owing to the introduction of tungsten, the growth of primary particles is regulated toward the (003) crystal plane and with the acicular structure, which further stabilizes the bulk structure during cycling. Moreover, the LiF coating layer on the cathode/electrolyte interface physically isolates the attack of the electrolyte on the surface cathodes and accelerates the lithium-ion diffusion rate, ultimately ameliorating the interfacial dynamics and structural stability. Dual-modified LiNi0.90Co0.05Mn0.05O2 exhibits superior electrochemical properties, especially more remarkable cyclic retention (88.16% vs 70.44%) after 100 cycles at 1 C and more outstanding high current rate properties (173.31 mAh·g-1 vs 135.97 mAh·g-1) at 5 C than the pristine one. This work emphasizes the probability of an integrated optimization strategy for Ni-rich materials, which provides an innovative idea for ameliorating (bulk and interfacial) structure degradation and promoting the diffusion of lithium ions during cycling.

Addressing voltage hysteresis in Li-rich cathode materials via gas-solid interface modification.

Li-rich layered materials have attracted much attention for their large capacity (>250 mA h g-1) stemming from anion redox at high voltage. However, inherent problems, such as capacity decay and voltage decay/hysteresis during cycling, hinder their commercial progress. In this work, an oxygen vacancy-accompanied spinel interface layer is constructed by gas-solid reaction via NiCO3 treatment at 650 °C, which reduces the asymmetry of anion redox and improves structural stability. Therefore, a 1 mol% NiCO3-modified sample powerfully reduces the voltage hysteresis (∼0.23 V) in the first cycle, simultaneously exhibiting an excellent discharge capacity of 275 mA h g-1 at 0.1 C with a capacity retention of 90% for 200 cycles at 1 C.

Manipulating the crystal plane angle within the primary particle arrangement for the radial ordered structure in a Ni-rich cathode.

Ni-rich cathodes with a radial ordered microstructure have been proved to enhance materials' structural stability. However, the construction process of radial structures has not yet been clearly elaborated. Herein, the formation process of radial structures induced by different doped elements has been systematically investigated. The advanced Electron Back Scatter Diffraction (EBSD) characterization reveals that W-doped materials are more likely to form a low-angle arrangement between crystal planes of the primary particles and exhibit twin growth during sintering than a B-doped cathode. The corresponding High Angle Annular Dark Field-Scanning Transmission Electron Microscopy (HAADF-STEM) analysis further proves that the twin growth induced by W doping can promote the migration of Li+. Simultaneously, the W-doped sample reduces the (003) plane surface energy and promotes the retention of the crystal plane, which can effectively alleviate the structural degradation caused by Li+ (de)intercalation. At a cut-off voltage of 4.6 V, the W-doped cathode displays a capacity retention rate of 94.1% after 200 cycles at 1C. This work unveils the influence of different element doping on the structure from the perspective of crystal plane orientation within primary particles and points out the importance of the exposure and orientation of the crystal plane of the particles.

Effective and Low-Cost In Situ Surface Engineering Strategy to Enhance the Interface Stability of an Ultrahigh Ni-Rich NCMA Cathode.

Ultrahigh Ni-rich quaternary layered oxides LiNi1-x-y-zCoxMnyAlzO2 (1 - x - y - z ≥ 0.9) are regarded as some of the most promising cathode candidates for lithium-ion batteries (LIBs) because of their high energy density and low cost. However, poor rate capacity and cycling performance severely limit their further commercial applications. Herein, an in situ coating strategy is developed to construct a uniform LiAlO2 layer. The NH4HCO3 solution is added to a NaAlO2 solution to form a weak alkaline condition, which can reduce the hydrolysis rate of NaAlO2, thus enabling uniform deposition of Al(OH)3 on the surface of a Ni0.9Co0.07Mn0.01Al0.02(OH)2 (NCMA) precursor. The LiAlO2-coated samples show enhanced cycling stability and rate capacity. The capacity retention of NCMA increases from 70.7% to 88.3% after 100 cycles at 1 C with an optimized LiAlO2 coating amount of 3 wt %. Moreover, the 3 wt % LiAlO2-coated sample also delivers a better rate capacity of 162 mAh g-1 at 5 C, while that of an uncoated sample is only 144 mAh g-1. Such a large improvement of the electrochemical performance should be attributed to the fact that a uniform LiAlO2 coating relieves harmful interfacial parasitic reactions and stabilizes the interface structure. Therefore, this in situ coating approach is a viable idea for the design of higher-energy-density cathode materials.

Citric acid and AMF inoculation combination-assisted phytoextraction of vanadium (V) by Medicago sativa in V mining contaminated soil.

The use of citric acid (CA) chelator to facilitate metal bioavailability is a promising approach for the phytoextraction of heavy metal contaminants. However, the role of the CA chelator associated with arbuscular mycorrhizal fungi (AMF) inoculation on phytoextraction of vanadium (V) has not been studied. Therefore, in this study, a greenhouse pot experiment was conducted to evaluate the combined effect of CA chelator and AMF inoculation on growth performance and V phytoextraction of plants in V-contaminated soil. The experiment was performed via CA (at 0, 5, and 10 mM kg-1 soil levels) application alone or in combination with AMF inoculation by Medicago sativa Linn. (M. sativa). Plant biomass, root mycorrhizal colonization, P and V accumulation, antioxidant enzyme activity in plants, and soil chemical speciation of V were evaluated. Results depicted (1) a marked decline in plant biomass and root mycorrhizal colonization in 5- and 10-mM CA treatments which were accompanied by a significant increased V accumulation in plant tissues. The effects could be attributed to the enhanced acid-soluble V fraction transferring from the reducible fraction. (2) The presence of CA significantly enhanced P acquisition while the P/V concentration ratio in plant shoots and roots decreased, owing to the increased V translocation from soil to plant. (3) In both CA-treated soil, AMF-plant symbiosis significantly improved dry weight (31.4-73.3%) and P content (37.3-122.5%) in shoots and roots of M. sativa. The combined treatments also showed markedly contribution in reduction of malondialdehyde (MDA) content (12.8-16.2%) and higher antioxidants (SOD, POD, and CAT) activities in the leaves. This suggests their combination could promote growth performance and stimulate antioxidant response to alleviate V stress induced by CA chelator. (4) Taken together, 10 mM kg-1 CA application and AMF inoculation combination exhibited a higher amount of extracted V both in plant shoots and roots. Thus, citric acid-AMF-plant symbiosis provides a novel remediation strategy for in situ V phytoextraction by M. sativa in V-contaminated soil.

Isolation and Identification of Uranium Tolerant Phosphate-Solubilizing Bacillus spp. and Their Synergistic Strategies to U(VI) Immobilization.

The remediation of uranium (U) through phosphate-solubilizing bacteria (PSB) is an emerging technique as well as an interesting phenomenon for transforming mobile U into stable minerals in the environment. While studies are well needed for in-depth understanding of the mechanism of U(VI) immobilization by PSB. In this study, two PSB were isolated from a U-tailing repository site. These bacterial strains (ZJ-1 and ZJ-3) were identified as Bacillus spp. by the sequence analysis of 16S ribosomal RNA (rRNA) genes. Incubation of PSB in liquid medium showed that the isolate ZJ-3 could solubilize more than 230 mg L-1 P from glycerol-3-phosphate and simultaneously removed over 70% of 50 mg L-1 U(VI) within 1 h. During this process, the rapid appearance of yellow precipitates was observed. The microscopic and spectroscopic analysis demonstrated that the precipitates were associated with U-phosphate compound in the form of saleeite-like substances. Besides, scanning electron microscopy coupled with energy-dispersive X-ray (SEM-EDS) and Fourier transform infrared spectroscopy (FTIR) analysis of the precipitates confirmed that the extracellular polymeric substances (EPS) might also play a key role in U sequestration. Furthermore, SEM and FTIR analysis revealed that part of U(VI) was adsorbed on the bacterial surface through cellular phosphate, hydroxy, carboxyl, and amide groups. This study provides new insights into the synergistic strategies enhancing U immobilization rates by Bacillus spp. that uses glycerol-3-phosphate as the phosphorus source, the process of which contributes to harmful pollutant biodegradation.

Microstructure-Controlled Li-Rich Mn-Based Cathodes by a Gas-Solid Interface Reaction for Tackling the Continuous Activation of Li2MnO3.

Li-rich Mn-based cathodes have attracted much attention due to their high capacity stemming from anion redox above 4.5 V. However, the continuous activation of Li2MnO3 in Li-rich Mn-based materials, which correlates with O2 release and TM migration, is usually unfavorable to structural stability. Herein, based on a gas-solid interface reaction, we tackle this continuous activation phenomenon by restricting the capacity release of Li2MnO3 via NH4HCO3 treatment in the Li1.2Ni0.36Mn0.44O2 cathode. After modification, oxygen vacancies associated with the spinel phase are introduced on the surface. The 4 mol % NH4HCO3-modified material's capacity starts at 182 mAh g-1 at 1 C instead of increasing from 173 to 186 mAh g-1 for 25 cycles in the pristine material. Meanwhile, it also exhibits an excellent capacity retention of 93.24% after 200 cycles (at 1 C), with a small voltage decay rate of 1.19 mV cycle-1.