Surface Phase Research Articles

Nickel doped tungsten disulfide grown on carbon cloth for flexible supercapacitors

We present the synthesis of flower-shaped nickel-doped tungsten disulfide on flexible activated carbon cloth (ACC) using a simple hydrothermal technique for flexible symmetric supercapacitors. The nickel-to-tungsten disulfide doping ratio is optimized by adjusting the mass ratio of nickel and tungsten disulfide (Ni:WS2 = 0.5:3, 1:3, and 1.5:3) to enhance charge storage capability, surface area, impedance behavior, specific capacity, and rate capability. The improved supercapacitor performance is attributed to the increased electrochemically active surface area, reduced impedance, and phase engineering from 2 H to 1 T achieved through optimal nickel doping. At a current density of 1 A g−1, the flexible symmetric supercapacitor device (Ni-WS2-ACC device) demonstrates a specific capacitance of 259.2 F g−1, an energy density of 22.4 Wh kg−1, and a power density of 803 W kg−1. Moreover, the Ni-WS2-ACC device maintains consistent supercapacitive performance under various bending conditions. These results present a promising strategy for further enhancing tungsten disulfide-based flexible supercapacitors as energy storage devices.

Promoting subsurface Sn incorporation at Nb(100) oxide surface sites leading to homogeneous Nb3Sn film growth for superconducting radiofrequency applications

For next-generation superconducting radiofrequency (SRF) cavities, the interior walls of existing Nb SRF cavities are coated with a thin Nb3Sn film to improve the superconducting properties for more efficient, powerful accelerators. The superconducting properties of these Nb3Sn coatings are limited due to inhomogeneous growth resulting from poor nucleation during the Sn vapor diffusion procedure. To develop a predictive growth model for Nb3Sn grown via Sn vapor diffusion, we aim to understand the interplay between the underlying Nb oxide morphology, Sn coverage, and Nb substrate heating conditions on Sn wettability, intermediate surface phases, and eventual Nb3Sn nucleation. In this work, Nb-Sn intermetallic species are grown on a single crystal Nb(100) in an ultrahigh vacuum chamber equipped with in situ surface characterization techniques including scanning tunneling microscopy, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. Sn adsorbate behavior on oxidized Nb was examined by depositing Sn with submonolayer precision on a Nb substrate held at varying deposition temperatures (Tdep). Experimental data of annealed intermetallic adlayers provide evidence of how Nb substrate oxidization and Tdep impact Nb-Sn intermetallic coordination. The presented experimental data contextualize how vapor and substrate conditions, such as the Sn flux and Nb surface oxidation, drive homogeneous Nb3Sn film growth during the Sn vapor diffusion procedure on Nb SRF cavity surfaces. This work, as well as concurrent growth studies of Nb3Sn formation that focus on the initial Sn nucleation events on Nb surfaces, will contribute to the future experimental realization of optimal, homogeneous Nb3Sn SRF films.

Response characteristics of platinum coated titanium bipolar plates for proton exchange membrane water electrolysis under fluctuating conditions

Voltage fluctuations in energy input not only impact the overall hydrogen production efficiency and stability of Proton Exchange Membrane Water Electrolysis (PEMWE) systems but also pose significant challenges to the long-term service life of individual components. This study focuses on the key component − bipolar plates and investigates the response behavior of platinum-coated titanium bipolar plates under simulated fluctuating voltage conditions. By integrating surface phase analysis and electrochemical testing results, this research elucidates the response characteristics of the bipolar plates to different voltage waveforms and frequencies. And the findings hold substantial significance for the upstream energy control in hydrogen production through water electrolysis.

Effect of AlCrCuFeNi high entropy alloy reinforcements with and without B4C on powder characteristic, mechanical and wear properties of AA5083 metal-metal composites

This study presents a novel approach to enhancing the properties of the AA5083 alloy by incorporating a high entropy alloy (HEA), specifically AlCrCuFeNi, through mechanical alloying. The Al/HEA composites were thoroughly characterized in terms of powder morphology, microstructure, fracture and wear surface morphology, phase composition, and oxidation behavior using XRD, SEM-EDS, and TGA. The impact of HEA, both with and without B4C reinforcement, on the hardness, density, tensile strength, and wear properties of the AA5083 matrix composites was comprehensively evaluated. The findings revealed that the AA5083 alloy exhibited a baseline hardness of 74.7 HB and a tensile strength of 174.1 MPa. However, with the addition of HEA + B4C, these properties were markedly enhanced, with the hardness increasing to 150.1 HB (a 100 % increase) and tensile strength to 247.1 MPa (a 50 % increase). Furthermore, the wear resistance of the composite experienced a substantial improvement, with a nearly six-fold increase due to the HEA + B4C reinforcement.

Investigating the Relationship between Building Orientation and Surface Properties of Stainless Steel Prepared via Selective Laser Melting

In our investigation of the influence rules and mechanisms of the building orientation on the surface properties of 316L stainless steel created via selective laser melting, we used X-ray diffractometry, scanning electron microscopy, and electron backscatter diffraction to investigate the phases, microstructures, and textures of specimens. In addition, we employed a digital microhardness tester, friction, and wear-testing apparatus, along with an electrochemical workstation, to examine variations in the surface properties. The results indicated that the surface phase compositions of the specimens with different building orientations were similar; however, they displayed anisotropic behavior in grain size, orientation, and texture. Notably, the surface densification of the specimens at 0°, 30°, 45°, and 60° initially decreased before subsequently increasing. In contrast, the surface roughness showed a pattern of first increasing and then declining. Moreover, the microhardness, wear resistance, and corrosion resistance decreased with an increasing inclination angle.

Response of variation of electrical control parameters to coatings prepared in organo-silicon electrolyte by plasma electrolytic oxidation

This study aims to explore the influence of control parameters from the perspective of the amorphous ceramic coating formation process. Three preparation processes were preferred based on the thickness, appearance and corrosion resistance of the coatings by orthogonal experiment. The surface morphology, cross-sectional structure, phase composition and micro-hardness of PEO coatings were examined using scanning electron microscopy (SEM)/Energy dispersive X-ray spectroscopy (EDS), X-ray diffractometry (XRD) and hardness measurement techniques. Findings indicate that voltage exerts the most significant impact on coating thickness and appearance, whereas the influence of other parameters becomes more pronounced as the voltage increases. Three amorphous ceramic coatings prepared in 20 min with thicknesses of 27.4 μm, 83.2 μm and 193.3 μm increased the surface hardness of 6061 aluminium alloy by 6–8 times, and decreased the corrosion current density of 6061 aluminium alloy by 3 orders of magnitude in 1 mol L−1 HCl solution. Moreover, the thickening of the coating primarily occurs within a few minutes after the voltage reaches its peak, and high frequency and low duty ratio are prerequisites for better appearance under higher voltage conditions.

K-Rich Spinel Interface of Air-Stable Layered Oxide Cathodes for Potassium-Ion Batteries.

Potassium-containing transition metal layered oxides (KxTmO2), although possessing high energy density and suitable operating voltage, suffer from severe hygroscopic properties due to their two dimensional (2D)layered structure. Their air sensitivity compromises structural stability during prolonged air exposure, therefore increasing the cost. The common sense for designing air-stable layered cathode materials is to avoid contact with H2Omolecules. In this study, it is surprisingly found that P3-type KxTmO2 forms an ultra-thin, potassium-rich spinel phase wrapping layer after simply water immersion, remarkedly reduces the reaction activity of the material's surface with air. Combined with Density Function Theory (DFT) calculations, this spinel phase is found to be able to effectively withstand air deterioration and preserving the crystal structure. Consequently, the water-treated material, when exposed to air, can largely maintain its good electrochemical performance, with capacity retention up to 99.15% compared to the fresh samples. Such an in situ surface phase transformation mechanism is also corroborated in other KxTmO2, underscoring its effectiveness in enhancing the air stability of P3-type layered oxides for K+ storage.

Assessment of the microstructure, adhesion and elevated temperature erosion resistance of plasma-sprayed NiCrAlY/cr3C2/h-bn composite coating

This study uses an air jet erosion tester to investigate the erosion behavior of NiCrAlY/Cr3C2/h-BN composite coatings that are plasma-sprayed at three different temperatures and 40 m/s on T22 boiler steel alloy. 30 and 90° are the impingement angles. To identify the erosion mechanism, SEM and X-ray diffraction techniques are used to analyze the surface morphology and phase generated on the eroded surface. Findings of erosion test indicate that the erosion resistance was notably enhanced by addition of Cr3C2 and h-BN because of its lubricating characteristics and capacity to reduce frictional forces during erosion. The combined influence of Cr3C2 and h-BN enhanced the coating hardness and erosion wear resistance, thereby improving its overall resistance to erosion. The weight loss method was employed to calculate the erosion rate, and the NiCrAlY/Cr3C2/h-BN coating showed up to 30.55% and 34.48% lower erosion rate as compared to uncoated T22 substrate at 600 °C for 30° and 90° impact angles, respectively. This characteristic is affected by the hard reinforcement Cr3C2's high-temperature stability, the h-BN's self-lubricating ability, the formation of a protective oxide layer that forms at 600 °C, and the eroded coating's ductile behavior of material removal. The study also reveals that the NiCrAlY/Cr3C2/h-BN coating system on T22 boiler steel alloy has excellent erosion resistance, making it suitable for use in high-temperature and erosive environments in boiler systems and similar industries.

Electrowinning for Room-Temperature Ironmaking: Mapping the Electrochemical Aqueous Iron Interface.

A promising route toward room-temperature ironmaking is electrowinning, where iron ore dissolution is coupled with cation electrodeposition to grow pure iron. However, poor faradaic efficiencies against the hydrogen evolution reaction (HER) is a major bottleneck. To develop a mechanistic picture of this technology, we conduct a first-principles thermodynamic analysis of the Fe110 aqueous electrochemical interface. Constructing a surface Pourbaix diagram, we predict that the iron surface will always drive toward adsorbate coverage. We calculate theoretical overpotentials for terrace and step sites and predict that growth at the step sites are likely to dominate. Investigating the hydrogen surface phases, we model several hydrogen absorption mechanisms, all of which are predicted to be endothermic. Additionally, for HER we identify step sites as being more reactive than on the terrace and with competitive limiting potentials to iron plating. The results presented here further motivate electrolyte design toward HER suppression.

A green inorganic binder for material extrusion of ultra-low shrinkage and relatively high strength metakaolin ceramics at low sintering temperature

Ultra-low shrinkage and relatively high strength metakaolin ceramics printed by material extrusion were innovatively fabricated using inorganic aluminum dihydrogen phosphate (Al(H2PO4)3) as a binder and low sintering temperature. The optical microscopy, scanning electron microscopy (SEM), electronic vernier caliper, three-point bending test, Archimedes method and X-ray diffraction (XRD) were used to measure and evaluate the surface morphology, microstructure, dimensional shrinkage, flexural strength, porosity and phase composition of the printed ceramics sintered at different temperatures. The results showed that when the mass ratio of metakaolin, Al(H2PO4)3 and deionized water was 17:6:2, the rheological characteristic of the purely green inorganic ceramic slurry was very suitable for material extrusion additive manufacturing, and the corresponding printed ceramic green bodies possessed high-quality formability. The ceramic samples sintered at 750 °C possessed the best whiteness, the lowest shrinkage (<2%), relatively high flexural strength (9.02 MPa). As the sintering temperature increased, Al(H2PO4)3 transformed to aluminum metaphosphate Al(PO3)3, and then decomposed into aluminum phosphate (AlPO4) and phosphorus pentoxide gas (P2O5), which caused pores and reduced strength, and alumina oxide (Al2O3) and silicon oxide (SiO2) in metakaolin gradually transformed to mullite and cristobalite with more stable structure and higher strength.

Significant effect of salinity on zinc adsorption on tropical coastal and floodplain soils

AbstractRising sea levels due to climate change are causing increased salinisation of low‐lying coastal and floodplain soils, and the impact of this process on the bioavailability of plant nutrients needs to be understood as mitigation strategies are adapted. Zinc (Zn) is an element of particular importance due to its function as a micronutrient for plants including rice and other staple foods. In the current study, our aim was to investigate the effects of salinisation on zinc adsorption onto soils representing at‐risk coastal and floodplain environments, addressing in particular our knowledge gap concerning the roles that solution chemistry and soil composition play. To this end, we conducted batch adsorption experiments in the laboratory and ran geochemical models in saline solutions up to 0.7 mol L−1 ion strength incorporating both (i) a multi surface model (MSM) for surface reactions containing three phases, that is iron hydroxides, organic matter and phyllosilicate clays, and (ii) aqueous‐phase complexation to dissolved organic and inorganic ligands. Surface reactions were modelled using the diffuse double layer model, the NICA–Donnan model and an ion exchange model using the Gaines–Thomas convention. We combined the experimentally determined mass composition of surface phases with generic modelling parameters taken from the literature. We first show that increasing salinity enhances the formation of aqueous Zn‐chloride complexes in the presence of dissolved organic matter and bicarbonate, thereby decreasing the availability of free Zn2+ and supressing the partitioning of zinc to the adsorbed phase. We demonstrate using batch adsorption experiments with a calcareous hydraquent and a tropaquept, that salinity decreases zinc adsorption strongly in the pH range between 3 and 6. Satisfactory agreement between experiments and model calculations was achieved with root‐mean‐square errors ranging for different salinities between 2.88% and 2.92% for the hydraquent and between 4.59% and 2.74% for the tropaquept soil. Model predictions of adsorption were slightly inferior at low salinity for the hydraquent soil and at high salinity for the tropaquept soil, pointing possibly to an incomplete geochemical model or to a need to parametrise surface adsorption models at higher ionic strengths. Present surface models have been largely parametrised at lower ionic strength. We lastly apply the MSM to examine zinc adsorption in five endoaquepts soils, representing soil series from Bangladesh. We show that increasing salinity decreases zinc adsorption to the soil organic matter and the clay fractions. We conclude from our findings that increased soil salinity due to rising sea levels and climate change will have a significant impact on zinc cycling and possibly other micronutrients in areas where coastal soils and floodplain soils overlap, such as deltas and estuaries. In particular, we predict a decrease in zinc adsorption in acidic to neutral soils. The availability of zinc for biouptake through the roots of crop plants including rice will be significantly disturbed following salinisation, most likely affecting crop production. Our study demonstrates the potential that geochemical modelling combined with experimental data has to improve our capability to assess the effects of salinity due to rising seawater levels in vulnerable regions of the world.

A synergistic approach to synthesize nitrogen-doped nanobiochars with high adsorptive performance

Developing versatile and energy-efficient processes to synthesize functional nanomaterials is of significant in response to economic concerns, enviroment, and technological challenges. This study presents a synergistic route for the facile, green, and low-cost synthesis of nitrogen-doped nanobiochars (NNBs) from an agriculture waste without any chemical supplements, promoting environmental sustainability. Specifically, rice husk is treated at 800 °C for 5 min in an enclosed reactor, followed by quenching in water and ultrasonic vibration in a water/ethanol mixed solvent. Surface morphology, specific surface area, crystalline structure, phase component, and chemical composition of the NNBs are characterized by electron microscopy, Brunauer–Emmett–Teller, x-ray diffraction, Raman, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy measurements, respectively. The results indicate that the NNBs possess porous structures with a high specific surface area of 303.4 m2/g and a large pore volume of 1.23 cm3 g−1. Moreover, the porous nature and functional groups, including C=NH (55.0%) and N-H (34.35%), in NNBs are harnessed for removing Ciprofloxacin, a common antibiotic pollutant in water, via hydrogen bonding and other interactions. As expected, NNBs demonstrate a high removal efficiency of 72.73% and and adsorption capacity of 7.27 mg g−1 at a pH of 5 and contact time of 150 min. These findings therefore opens new possibilities for scalable production of value-added materials from agriculture wastes for water treatment, enhancing public health and environmental protection.

Multiphase modeling of pressure-dependent hydrogen diffusivity in fractal porous structures of acrylonitrile butadiene rubber-carbon black composites with different fillers

The hydrogen diffusivities of acrylonitrile butadiene rubber (NBR) composites with different types and contents of carbon black (CB) fillers were investigated in the exposure pressure range of 0.5–10 MPa using a volumetric analysis system. These measured diffusivities exhibited distinct pressure-dependent behavior. The diffusivities of unfilled NBR and NBR composites containing medium-thermal CB filler decreased from 39.7 × 10−11 m2/s to 9.4 × 10−11 m2/s as the pressure increased. On the other hand, the pressure-dependent diffusivities of NBR composites containing high-abrasion furnace, fast-extrusion furnace and semireinforcing furnace CB fillers revealed left-biased unimodal shaped curves, with peak values ranging from 19.7 × 10−11 m2/s to 5.6 × 10−11 m2/s. To model this observed behavior, the diffusion resistance theory with a heterogeneous NBR–CB composite and a fractal porous structure for H2 was introduced. The theoretical parallel diffusion resistance model was found to coexist independently as the surface, Knudsen, and bulk diffusion phases. This theoretical multiphase modeling was applied to the measured diffusivities, determining diffusion resistance parameters for each phase. The obtained individual parametric characteristics for each diffusion were interpreted by considering the CB filler content and volume fraction of the filler. As a result, the diffusivities calculated by multiphase diffusion modeling were in quite agreement with the measured diffusivities for all investigated specimens, where the determined squared correlation coefficient (R2) by fitting process was in the range from 0.69 to 0.97.

Attaining high-rate hydrogen evolution via SILAR deposited bimetallic nickel cobalt boride electrode: Exploring the influence of Ni to Co ratio

For the first time, a bimetallic Nickel Cobalt Boride (NCB) film with varying Ni to Co ratios was synthesized on stainless steel via the SILAR method. The NCB2 film (1:1 ratio) exhibited a mixed phase of metal boride and oxy-hydroxide with a highly porous, flaky-type morphology, while NCB1 (1:3 ratio) and NCB3 (3:1 ratio) showed only oxidized metal phases and agglomerated clusters. EDX confirmed the purity of the samples, and XPS indicated higher oxidation in NCB1 and NCB3 compared to NCB2. For HER, NCB2 showed the lowest overpotential (80 mV) compared to NCB1 (96 mV) and NCB3 (101 mV), and the smallest Tafel slope value (71 mV/dec). HER kinetics followed a Volmer-Heyrovsky mixed reaction path. NCB2 exhibited the highest Cdl value (16.55 mF/cm2) and the largest electrochemical active surface area (413.7 cm2), outperforming NCB1 (333.125 cm2) and NCB3 (205 cm2). At an overpotential of 100 mV, NCB2's TOF value was 8.23 s⁻1, higher than NCB1 (1.4 s⁻1) and NCB3 (1 s⁻1). For OER, NCB2 showed the highest Cdl value (106 mF/cm2) and ECSA value (2650 cm2). The Faradic efficiency of NCB2 was ∼98% after 190 h. Hydrogen evolution rates for NCB1, NCB2, and NCB3 as cathodes were 952 mL/h, 1022 mL/h, and 800.8 mL/h, respectively. In a prototype electrolyzer, NCB2 enhanced the hydrogen evolution rate by 30% in bifunctional mode to 1334.6 mL/h. After 100 h, performance declined by only 2.7% due to surface oxidation and phase changes. This achievement marks a milestone towards low-cost green hydrogen production, achieving the highest rate of hydrogen evolution as ever reported.

Chromoionophoric probe decorated porous polymer monolithic scaffold as solid-state colorimetric sensor and concentrator for target specific capturing of ultra-trace copper and cobalt ions

The present work reports on the development of an affordable aqueous-compatible two-in-one solid-state sensor engineered through the systematic suffusion of a chromoionophoric probe onto the porous poly(BTM-co-EGD) monolithic scaffolds for the selective colorimetric sensing of ultra-trace Cu2+ and Co2+ that are of industrial importance and environmental nuisance. The structurally regulated dual pore poly(BTM-co-EGD) template offers a high surface area for voluminous/homogenous imbuement of the probe molecules in a frozen geometrical alignment. The intriguing properties such as surface morphology, pore dimensions, structural network, phase identification, purity/elemental composition and thermal stability of the polymer monolith and probe-inoculated sensor were studied using XPS, BET/BJH, HR-TEM-SAED, FE-SEM-EDAX, XRD, FT-IR and DTG analysis. The ion recognition efficacy of the sensor material is evaluated through naked-eye color transformations and UV-Vis-DRS-based analysis. The sensor imposes a vibrant color transitional from pale yellow (blank) to intense olive brown and dark reddish brown for Cu2+ and Co2+, respectively, due to stable ligand-to-metal charge transfer complex formation. The sensor imposes high sensitivity with a response linear range of 0–200 and 0–150 ppb, with a detection limit of 0.13 and 0.16 ppb for Cu2+ and Co2+, respectively. The sensor exhibits impressive workability in the pH range of 7.0–8.0, with 0.05 mmol/g probe coating onto the poly(BTM-co-EGD) template, with an enriched response of ≤50 s, using 4 mg of the sensor material. Upon practical testing with natural/synthetic samples, the sensor executes stable characteristics with reliable and reproducible data (RSD ≤1.98 %). The proposed sensing methodology is simple, cost-effective and can be reused over eight sensing trails for the ultra-trace detection of Cu2+ and Co2+. The portable sensor has the potential for commercialization based on its effortlessness in real-time utility.

Mitigating degradation and modulating electronic structure via an epitaxial perovskite protection for Li-rich layered oxides

Li-rich layered oxides are highly promising cathode materials for the next-generation lithium-ion batteries due to their extraordinary specific capacity and hence high energy density. However, their practical application is hindered by the structural and surface instabilities as well as sluggish reaction kinetics. Herein, a low-crystallinity perovskite oxide (NdTiO3) is developed to epitaxially conform the surface of a typical Li-rich layered oxide Li1.2Mn0.54Ni0.13Co0.13O2 to overcome these drawbacks. Experimental and computational results confirm that this surface phase not only mitigates structural deformation and interfacial side reactions, but also can modulate the electronic structure of Li2MnO3 for the higher electron conductivity. As a result, the epitaxially-protected cathode material displays much better cycle stability (222.02 mA h g−1 after 200 cycles at 1C compared to 185.06 mA h g−1 for the uncoated one) and excellent rate capability (155.71 mA h g−1 at 5C). A pouch-type full cell using commercial graphite anode demonstrates an energy density (381.38 Wh kg−1 based on the cathode and anode) and a capacity retention of 91.1% after 100 cycles.

Prewetting couples membrane and protein phase transitions to greatly enhance coexistence in models and cells.

Both membranes and biopolymers can individually separate into coexisting liquid phases. Here we explore biopolymer prewetting at membranes, a phase transition that emerges when these two thermodynamic systems are coupled. In reconstitution, we couple short poly-L-Lysine and poly-L-Glutamic Acid polyelectrolytes to membranes of saturated lipids, unsaturated lipids, and cholesterol, and detect coexisting prewet and dry surface phases well outside of the region of coexistence for each individual system. Notability, polyelectrolyte prewetting is highly sensitive to membrane lipid composition, occurring at 10 fold lower polymer concentration in a membrane close to its phase transition compared to one without a phase transition. In cells, protein prewetting is achieved using an optogenetic tool that enables titration of condensing proteins and tethering to the plasma membrane inner leaflet. Here we show that protein prewetting occurs for conditions well outside those where proteins condense in the cytoplasm, and that the stability of prewet domains is sensitive to perturbations of plasma membrane composition and structure. Our work presents an example of how thermodynamic phase transitions can impact cellular structure outside their individual coexistence regions, suggesting new possible roles for phase-separation-prone systems in cell biology.

Introduced Iron-Based Catalysts for Low-Temperature Upcycling Regeneration of Spent Graphite towards Ultra-Fast Lithium Storage Properties.

Spent graphite, as the main component of retired batteries, have attracted plenty of attentions. Although a series of recycling strategies are proposed, they still suffer from high cost of regeneration and large CO2 emission, mainly ascribed to the full-recovery of surface and internal phase at ultra-high temperature. However, the existing of suitable internal defects is conductive to their energy-storage abilities. Herein, with the introduction of Fe-based catalysts, spent graphite is successfully repaired at low temperature with the tailored surface traits, including conductivities, isotropy and so on. As Li-storage anodes, all of samples can display a capacity of 340mAhg-1 above at 1.0 C after 200 cycles. At high rate 5.0 C, their capacity can be also kept ≈300mAhg-1, and remained ≈233mAhg-1 even after 1000 cycles. Assisted by electrochemical and kinetic behaviors, their cycling traits with dynamic surface transformations are detailed explored, including activated/fading mechanism, Li-depositions forming etc. Moreover, the calculated constant time of as-optimized regenerated sample is ≈3.0×10-4s, further revealing the importance of surface designing. Therefore, the work is expected to shed light on their energy-storage behaviors, and offer low-temperature regenerated strategies of spent graphite with high value.

Cost‐Effective Layered Oxide – Olivine Blend Cathodes for High‐Rate Pulse Power Lithium‐Ion Batteries

AbstractSustainability and supply‐chain concerns require lithium‐ion batteries (LIBs) free from critical minerals, such as nickel and cobalt. While recent advances provide encouraging signs that cobalt can be removed, the question remains how much Ni can be removed from Co‐free layered oxide cathodes before sacrificing critical performance metrics. This study highlights the effect of reducing Ni by benchmarking several Co‐free cathodes with decreasing Ni content. Keeping the energy density the same by increasing the charge voltage, cathodes below 80% Ni content exhibit worsened capacity fade due to increasing oxygen release and electrolyte decomposition. Charge transfer and diffusion kinetics are also hindered with increasing Mn content and exacerbated by resistive surface phases formed at high voltages, rendering lower‐Ni, Co‐free cathodes less competitive than high‐Ni cathodes for high energy and power applications. It is demonstrated blending layered oxide with olivine as an effective alternative to deliver energy density and cycling stability comparable to lower‐Ni cathodes with moderate charging voltages. Blending with 30 wt% olivine LiMn0.5Fe0.5PO4 (LMFP) virtually eliminates the diffusion limitation of layered oxides at low state‐of‐charge, with enhanced pulse power characteristics rivaling the high‐Ni counterparts. Cathode blending can further reduce the overall Ni content and cost without the performance limitations of lower‐Ni, Co‐free cathodes.

Surface phase stability of high-nickel layered oxides by titanium and sulfur co-modifications

High-nickel layered oxides are promising cathodes for lithium-ion batteries due to relatively high capacity and low cost, which however are still faced with safety issues because of poor stability against cycling. Herein, a facile one-pot solid-state method is employed for preparation of trace Ti/S co-doped LiNi0.98Co0.02O2. Ti and S co-doping enhances both rate capability and intrinsic stability greatly in a mutually promoting manner compared with individual Ti and S doping. The co-doped samples show excellent rate capability with 170.9 mAh/g at 5 C and superior intrinsic stability with a capacity retention of 88.6% at 1 C after 200 cycles at room temperature, in sharp contrast with 132.2 mAh/g and 61.6% for the pristine samples. Full cells achieve excellent long-term stability with a retention of 92.7% after 400 cycles at 1 C. The improved performance can be ascribed to the formation of stronger Ti–O bonds and of a thin rock-salt protective layer enabled by sulfur with the stability enhanced by Ti modifications, and the activation of extra redox reactions triggered by sulfur. The mutually promoting enhancement effect by doping different alien elements opens a new and unique design strategy for performance improvement of electrode materials.