Effect of interlayer design on friction and wear behaviors of CrAlSiN coating under high load in seawater

In this paper, CrAlSiN coatings with different interlayer designs (without interlayer, Cr interlayer, CrN interlayer and Cr/CrN interlayer) were successfully obtained on 316L stainless steel and single crystal silicon by multi-arc ion plating technique. Coating microstructure, mechanical, anticorrosion and tribological behaviors in artificial seawater were systematically investigated by XRD, SEM, XPS, TEM, nanoindentation, electrochemical workstation and frictional tester system. Results showed that the CrAlSiN layer presented a typical nanocrystalline/amorphous structure, which consisted of CrN, AlN and Si₃N₄ phases. The Cr/CrN interlayer could obviously improve the adhesion, hardness and toughness of CrAlSiN coating. Compared with single CrAlSiN coating, the corrosion current density of Cr/CrN/CrAlSiN coating system was improved by 2 orders of magnitude and its inhibition efficiency was up to 98.82%. Under high applied load (15 N) condition, the CrAlSiN coating with Cr/CrN interlayer revealed the lowest COF (0.107 ± 0.009) and wear rate (7.3 × 10⁻⁸ ± 8.4 × 10⁻⁹ mm³ N⁻¹ m⁻¹) in seawater, which primarily attributed to the synergistic effect of ideal adhesion force, outstanding toughness and effectively barrier ability.

In this paper, CrAlSiN coatings with different interlayers (without interlayer, Cr interlayer, CrN interlayer and Cr/CrN interlayer) were successfully obtained on 316L stainless steel and single crystal silicon by multi-arc ion plating technique.     

Chloride corrosion behavior on heating pipeline made by AISI 304 and 316 in reclaimed water

In order to transport reclaimed water safely through stainless steel (SS) heat-supply pipeline networks during their idle period, one must understand the degree to which chlorine in reclaimed water is corrosive to SS. In this study, electrochemical methods were used to evaluate the corrosion resistances of two types of SS materials, AISI 304 and AISI 316, in simulated reclaimed water at chloride concentrations of 25 to 400 mg L⁻¹, which are similar to those present in practice. The differences in corrosion resistance between the two types of SS material were investigated using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests (Tafel curves). The passivation layers on the two types of SS exhibited obvious similarities under several experimental conditions. However, EIS, polarization resistance, effective capacitance, Tafel curve, and Scanning Electron Microscope (SEM) data showed that AISI 316 has better corrosion resistance than AISI 304. The corrosion behaviours could be described as a series of reactions between Fe, Cr, and H₂O that generate several precipitated products such as Fe₂O₃, Cr₂O₃, FeOOH, and CrOOH.

It would be economical if heating pipes were used to transport reclaimed water during its idle period. The most important thing is to study the causes and processes of the corrosion on it for practical application.     

PbO2 modified with TiO2-NTs composite materials with enhanced OER electrocatalytic activity for Zn electrowinning

The high oxygen evolution overpotential of the Pb–Ag anode is one of the main reasons for the high energy consumption in Zn electrowinning. PbO₂, owing to its high conductivity, good corrosion resistance and low cost, is widely used as an excellent coating material. In present research, a novel composite Ti/TiO₂-NTs/PbO₂ material was synthesized through a facile anodization, annealing, electrochemical reduction and galvanostatic deposition. The surface morphology, internal structure and the mechanisms of TiO₂-NTs enhancing electrochemical performance were discussed. The results show that the self-organized high aspect ratio TiO₂-NTs with diameter of ∼120 nm and length of ∼8 μm were obtained on Ti substrate. The Ti/TiO₂-NTs/PbO₂ composite material exhibits excellent oxygen evolution performance and good stability in Zn electrowinning simulation solution (50 g L⁻¹ Zn²⁺, 150 g L⁻¹ H₂SO₄) at 35 °C. Its oxygen evolution overpotential is only 630 mV under current density 50 mA cm⁻², which is 332 m lower than that of Pb-0.76 wt% Ag (η = 962 mV) and only increases 22 mV after 5000 cycles of CV scanning. Its outstanding electrochemical performance is mainly ascribed to the introduction of TiO₂-NTs in Pb(CH₃COO)₂ media since it refines the crystal grains, increases the electrochemical surface area, greatly reduces the charge transfer resistance (25.4 Ω cm² to 2.337 Ω cm²) and enhances corrosion resistance. Therefore, the Ti/TiO₂-NTs/PbO₂ material prepared in Pb(CH₃COO)₂ medium may be an ideal anode for Zn electrowinning.

The high oxygen evolution overpotential of the Pb–Ag anode is one of the main reasons for the high energy consumption in Zn electrowinning.     

Polybenzimidazole/Nafion hybrid membrane with improved chemical stability for vanadium redox flow battery application

In order to increase the chemical stability of polybenzimidazole (PBI) membrane against the highly oxidizing environment of a vanadium redox flow battery (VRFB), PBI/Nafion hybrid membrane was developed by spray coating a Nafion ionomer onto one surface of the PBI membrane. The acid–base interaction between the sulfonic acid of the Nafion and the benzimidazole of the PBI created a stable interfacial adhesion between the Nafion layer and the PBI layer. The hybrid membrane showed an area resistance of 0.269 Ω cm² and a very low vanadium permeability of 1.95 × 10⁻⁹ cm² min⁻¹. The Nafion layer protected the PBI from chemical degradation under accelerated oxidizing conditions of 1 M VO₂⁺/5 M H₂SO₄, and this was subsequently examined in spectroscopic analysis. In the VRFB single cell performance test, the cell with the hybrid membrane showed better energy efficiency than the Nafion cell with 92.66% at 40 mA cm⁻² and 78.1% at 100 mA cm⁻² with no delamination observed between the Nafion layer and the PBI layer after the test was completed.

Novel polybenzimidazole (PBI)/Nafion hybrid membranes for the VRFB are made by spray coating a Nafion layer to protect PBI from chemical degradation.     

Nanowires of polyaniline festooned silver coated paper electrodes for efficient solid-state symmetrical supercapacitors

This paper demonstrates a facile strategy for the development of nanosilver decorated polyaniline coated (PAg) paper-based electrodes for the fabrication of solid-state symmetrical supercapacitors. PAg based printing paper was developed through a two-step process involving initial silver nucleation and growth on the paper followed by aniline polymerization. The developed electrically conductive paper exhibited a highly porous structure and excellent mechanical stability. Further symmetrical supercapacitors having the configuration PAg/electrolyte/PAg were fabricated and evaluated for electrochemical performance such as specific capacitance (483 F g⁻¹ and 613 F g⁻¹ in aqueous 1 M H₂SO₄ and PVA–H₂SO₄ gel electrolytes respectively), energy density (69.56 and 85.13 W h kg⁻¹), and power density (243.44 and 405.375 W kg⁻¹) and cycling stability (90% of its capacitance retention even after 2000 cycles), exhibiting excellent performance under various bending conditions. All these exciting results suggest that the developed paper-based flexible solid-state energy device can serve as an efficient, sustainable, and low-cost energy storage system for portable microelectronic devices which are expected to revolutionize the perception of energy-storage devices in the electronics industry.

This paper demonstrates a facile strategy for the development of nanosilver decorated polyaniline coated (PAg) paper-based electrodes for the fabrication of solid-state symmetrical supercapacitors.     

High-efficiency solid-phase microextraction performance of polypyrrole enhanced titania nanoparticles for sensitive determination of polar chlorophenols and triclosan in environmental water samples

In this work, a polypyrrole (PPy)/TiO₂ nanocomposite coating was fabricated by the direct electropolymerization of pyrrole on annealed TiO₂ nanoparticles and evaluated as a novel direct immersion solid phase microextraction (DI-SPME) fiber coating for extraction of trace amounts of pollutants in environmental water samples. The functionalized fiber is mechanically and chemically stable, and can be easily prepared in a highly reproducible manner. The effects of the pyrrole monomer concentration, polymerization voltage and polymerization time on the fiber were discussed. Surface morphological and compositional analyses revealed that the composite coating of nano polypyrrole and titanium dioxide nanoparticles (TiO₂NP_s) uniformly doped the Ti substrate. The as-fabricated fiber exhibited good extraction capability for phenolic compounds in combination with high performance liquid chromatography-UV detection (HPLC-UV). At the optimum SPME conditions, the calibration curves were linear (R² ≥ 0.9965). LODs and LOQs of less than 0.026 μg L⁻¹ and 0.09 μg L⁻¹ , respectively, were achieved, and RSDs were in the range 3.5–7.2%. The results obtained in this work suggest that PPy/TiO₂ is a promising coating material for future applications of SPME and related sample preparation techniques.

A PPy/TiO₂ nanocomposite coating was fabricated by direct electropolymerization of pyrrole on annealed TiO₂ nanoparticles and evaluated as a novel direct immersion solid phase microextraction fiber coating for the extraction of trace pollutants in water.     

A uniform few-layered carbon coating derived from self-assembled carboxylate monolayers capable of promoting the rate properties and durability of commercial TiO2

The poor cyclability and rate property of commercial TiO₂ (c-TiO₂) hinder its utilization in lithium-ion batteries (LIBs). Coating carbon is one of the ways to ameliorate the electrochemical performance. However, how to effectively form a uniform thin carbon coating is still a challenge. On the basis of the strong interaction of the TiO₂ surface with carboxyl groups, herein a new tactic to achieve uniform and thin carbon layers on the c-TiO₂ particles was proposed. When mixing c-TiO₂ with citric acid containing carboxyl groups in deionized water, the high-affinity adsorption of TiO₂ for carboxyl groups resulted in self-assembled carboxylate monolayers on the surface of TiO₂ which evolved into a uniform few-layered amorphous carbon coating during carbonizing at 750 °C. The product derived from the mixture of c-TiO₂ and citric acid with a mass ratio of 1 : 0.3 exhibits the optimal performance, revealing a high specific capacity (256.6 mA h g⁻¹ after 50 cycles at 0.1 A g⁻¹) and outstanding cycling stability (retaining a capacity of 160.0 mA h g⁻¹ after 1000 cycles at 0.5 A g⁻¹). The greatly enhanced capacity and cyclability correlate with the uniform few-layered carbon coating which not only ameliorates the electronic conductivity of c-TiO₂ but also avoids the reduction in ionic conductivity caused by thick carbon layers and redundant carbon.

The uniform and thin carbon-coating formed on c-TiO₂ particles by virtue of the high-affinity adsorption of TiO₂ for carboxyl groups results in superior rate and cycling performance.     

Deposition of an ultra-thin polyaniline coating on a TiO2 surface by vapor phase polymerization for electrochemical glucose sensing and photocatalytic degradation

Here, we have synthesized an ultra-thin coating of polyaniline on a TiO₂ nanoparticle surface (PANI–TiO₂) using a simple vapor phase polymerization method. By this method, an ultra-thin layer of PANI is obtained selectively on the TiO₂ surface. This ultra-thin coating exhibits the properties of both the parent materials due to the composite surface causing an effective synergistic effect. SEM, TEM, and EDX studies and elemental mapping confirmed the formation of ultra-thin films on the TiO₂ surface. TGA, UV/Vis and XRD studies were also done for further characterization. The composite has been used as a biosensor for glucose detection by immobilization of the enzyme glucose oxidase (GOx). Cyclic voltammetry, electrochemical impedance spectroscopy and amperometry studies were performed for glucose sensing. The linear range was observed from 20 to 140 μM glucose concentration from the amperometric analysis. The LOD of the biosensor was found to be 5.33 μM. The composite has also been used for photocatalytic degradation of the cationic dye Rhodamine B (RB). The order of degradation efficiency of RB is found to be PANI < TiO₂ < PANI–TiO₂. The synergetic effect of PANI and TiO₂ is the reason for the enhanced degradation efficiency of the composite PANI–TiO₂.

Here, we have synthesized an ultra-thin coating of polyaniline on a TiO₂ nanoparticle surface (PANI–TiO₂) using a simple vapor phase polymerization method.     

Two-dimensional lamellar polyimide/cardanol-based benzoxazine copper polymer composite coatings with excellent anti-corrosion performance

The economic loss and environmental damage caused by metal corrosion is irreversible. Thus, effective methods, such as coating technologies are used to protect metal surfaces from corrosion. In this work, cardanol-based benzoxazine (CB) was synthesized by a solvent-free method using cardanol, paraformaldehyde and n-octylamine. A cardanol-based benzoxazine copper polymer (CBCP) with good mechanical properties was then prepared by CuCl₂ catalysis and can be cured at room temperature. Subsequently, polyimide corrosion inhibitors with a two-dimensional sheet structure (pyromellitic dianhydride polyimide (PDPI) and 1,4,5,8-naphthalene tetracarboxylic dianhydride polyimide (NDPI)) were designed and prepared. Lastly, PDPI or NDPI was mixed with CBCP to obtain two-dimensional lamellar polyimide/cardanol-based benzoxazine copper polymer composite coatings. The Tafel curves and electrochemical impedance spectroscopy (EIS) measurements showed composite coatings with good corrosion resistance in different corrosive media. Compared to CBCP coating, the anticorrosion performance of the composite coatings improved obviously, especially the coating obtained with 0.5 wt% PDPI. It exhibits a high polarization resistance (3.874 × 10⁹ Ω), a high protection efficiency (99.99% and 97.98%) and low corrosion rate (3.376 × 10⁻⁶ mm year⁻¹). This work suggested a facile and eco-friendly strategy for preparing bio-based anticorrosive composite coatings from low cost and abundant cardanol and polyimide corrosion inhibitors, which will significantly promote their application in metal anticorrosion.

Room temperature cured two-dimensional lamellar polyimide/cardanol-based benzoxazine copper polymer composite coatings were successfully prepared, which exhibited excellent mechanical properties and anticorrosion properties.     

Efficient photoelectrochemical water oxidation using a TiO2 nanosphere-decorated BiVO4 heterojunction photoanode

Constructing heterojunctions by coupling dissimilar semiconductors is a promising approach to boost charge separation and charge transfer in photoelectrochemical (PEC) water splitting. In this work, we fabricated a highly efficient TiO₂/BiVO₄ heterojunction photoanode for PEC water oxidation via a simple hydrothermal method. The resulting heterojunction photoanodes show enhanced PEC performance compared to the bare BiVO₄ due to the simultaneous improvements in charge separation and charge transfer. Under simulated sunlight illumination (AM 1.5G, 100 mW cm⁻²), a high photocurrent of 3.3 mA cm⁻² was obtained at 1.23 V (vs. the reversible hydrogen electrode (RHE)) in a neutral solution, which exceeds those attained by the previously reported TiO₂/BiVO₄ heterojunctions. When a molecular Co–cubane catalyst was immobilized onto the electrode, the performance of the TiO₂/BiVO₄ heterojunction photoanode can be further improved, achieving a higher photocurrent density of 4.6 mA cm⁻² at 1.23 V, an almost three-fold enhancement over that of the bare BiVO₄. These results engender a promising route to designing an efficient photoelectrode for PEC water splitting.

Constructing heterojunctions by coupling dissimilar semiconductors is a promising approach to boost charge separation and charge transfer in photoelectrochemical (PEC) water splitting.     

Ion-triggered calcium hydroxide microcapsules for enhanced corrosion resistance of steel bars

Herein, we synthesized Ca(OH)₂ microcapsules with ion-responsive shells composed of cross-linked poly-ionic liquids (CPILs). By exchanging PF₆⁻ with Cl⁻ in water, the hydrophobic poly-ionic liquids (PILs) on the shell are converted to hydrophilic channels. The encapsulated Ca(OH)₂ can permeate through the hydrophilic channels and release OH⁻. Meanwhile, the Cl⁻ content can be reduced. The release rate of Ca(OH)₂ is influenced by the content of monomers and concentration of Cl⁻ ions in water. SO₄²⁻ can also trigger the release of Ca(OH)₂ from the microcapsule. With these microcapsules, Q235 steel exhibited promising corrosion resistance in simulated seawater. These results indicate that encapsulation of corrosion inhibitors is highly desirable for enhanced corrosion resistance of steel bars and the proposed approach can be used to encapsulate various corrosion inhibitors and functional materials for a wide range of applications.

By exchanging PF₆⁻ of the CPILs with Cl⁻, Ca(OH)₂ can penetrate out of the microcapsule through the formed hydrophilic channels.     

An investigation of Li2TiO3–coke composite anode material for Li-ion batteries

Anode material Li₂TiO₃–coke was prepared and tested for lithium-ion batteries. The as-prepared material exhibits excellent cycling stability and outstanding rate performance. Charge/discharge capacities of 266 mA h g⁻¹ at 0.100 A g⁻¹ and 200 mA h g⁻¹ at 1.000 A g⁻¹ are reached for Li₂TiO₃–coke. A cycling life-time test shows that Li₂TiO₃–coke gives a specific capacity of 264 mA h g⁻¹ at 0.300 A g⁻¹ and a capacity retention of 92% after 1000 cycles of charge/discharge.

Anode material Li₂TiO₃–coke was prepared and tested for lithium-ion batteries. The as-prepared material exhibits excellent cycling stability and outstanding rate performance.     

Influence of Cl− ions on anodic polarization behaviour of API X80 steel in high potential/current density conditions in Na2SO4 solution

Pipeline steel has considerable risk of corrosion in the high voltage direct current interference cases. Thus, under high potential/current density conditions, the anodic polarization behaviour of X80 steel in Na₂SO₄ solution and the influence of Cl⁻ ions were investigated using reversed potentiodynamic polarization, the current interrupt method, galvanostatic polarization, scanning electron microscopy, and X-ray photoelectron spectroscopy. In the Na₂SO₄ solution free of Cl⁻ ions, steel was passivated above 0.120 A cm⁻² and the potential increased from −0.32 V to 1.43 V. The passive film was composed of Fe₃O₄, γ-Fe₂O₃, and FeOOH. The addition of Cl⁻ ions observably influenced the passivation by attacking the passivate film. Low concentration of Cl⁻ ions (<5 mg L⁻¹ NaCl) could set higher demands of current density to achieve passivation and increase the requirement of potential to maintain passivation. A high concentration of Cl⁻ ions (>5 mg L⁻¹ NaCl) completely prevented passivation, showing strong corrosiveness. Thus, the X80 steel was corroded even under high-current-density conditions. The corrosion products were mainly composed of Fe₃O₄, α-Fe₂O₃, and FeOOH.

X80 steel gets passivated in high potential/current density conditions in Na₂SO₄ solution. Low concentration of Cl⁻ ions weakens the passivation. High concentration of Cl⁻ ions totally prevents the passivation.     

The fabrication of TiO2-supported clinoptilolite via F− contained hydrothermal etching and a resultant highly energetic {001} facet for the enhancement of its photocatalytic activity

TiO₂-supported clinoptilolite (TiO₂/CP) was synthesized in the presence of F⁻ ions. Various characterizations demonstrated that the particle size of loaded TiO₂ increased linearly with an increase in the temperature and concentration of F⁻ ions. In particular, the additive F⁻ ions were favored to produce the mutually independent co-exposed {001} and {101} facets of loaded TiO₂, while TiO₂/CPs synthesized in the absence of F⁻ ions were dominated by the thermodynamically stable {101} facet. As photocatalysts for the removal of crystal violet or methyl orange dyes under UV-irradiation in aqueous solutions, TiO₂/CPs (ACP6) synthesized in the presence of F⁻ ions significantly improved the degradation efficiency, as compared to ACP3 obtained in the absence of F⁻ ions. These results elucidated that the highly energetic {001} exposed facet, large particle size and fine dispersion of loaded TiO₂ in TiO₂/CP accounts for its best photocatalytic performance. The effected mechanism of operational parameters on the degradation performances is proposed.

TiO₂-supported clinoptilolite (TiO₂/CP) was synthesized in the presence of F⁻ ions.     

Improving the structural stability and electrochemical performance of Na2Li2Ti6O14 nanoparticles via MgF2 coating

To improve their electrochemical performance and structural stability, Na₂Li₂Ti₆O₁₄ (NLTO) nanoparticles were synthesized and then coated with a very thin MgF₂ layer. Microscopy confirmed that the MgF₂-NLTO particles are about 150–250 nm in size, and that the thickness of the MgF₂ layer for the MgF₂-NLTO-5 sample is ∼5 nm. Electrochemical measurements showed that the charge–discharge specific capacities of the five samples under a current density of 50 mA g⁻¹ after 100 cycles are 110.4/110.7, 150.7/151.3, 181.1/182.1, 205.7/206.9 and 238.9/239.2 mA h g⁻¹, showing that the performance of MgF₂-NLTO-5 is the best among all the samples. Thanks to the thin coating layer, the polarization of the anode was reduced significantly, and its reversibility and lithium diffusion dynamics were also improved obviously. The performance improvement can be attributed to the suppression of surface corrosion and the enhancement of structural stability.

Combination of nanocrystallization and surface coating techniques was improved to be helpful for improving the electrochemical performance of NLTO.     

Rigid TiO2−x coated mesoporous hollow Si nanospheres with high structure stability for lithium-ion battery anodes

Rigid oxygen-deficient TiO_2−x coated mesoporous hollow Si nanospheres with a mechanically and electrically robust structure have been constructed through a facile method for high-performance Li-ion battery anodes. The mesoporous hollow structure provides enough inner void space for the expansion of Si. The oxygen-deficient TiO_2−x coating has functions in three aspects: (1) avoiding direct contact between Si and the electrolyte; (2) suppressing the outward expansion of the mesoporous hollow Si nanospheres; (3) improving the conductivity of the composite. The combined effect leads to high interfacial stability and structural integrity of both the material nanoparticles and the whole electrode. By virtue of the rational design, the composite yields a high reversible specific capacity of 1750.4 mA h g⁻¹ at 0.2 A g⁻¹, an excellent cycling stability of 1303.1 mA h g⁻¹ at 2 A g⁻¹ with 84.5% capacity retention after 500 cycles, and a high rate capability of 907.6 mA h g⁻¹ even at 4 A g⁻¹.

A conductive TiO_2−x shell suppresses the outward expansion of Si to maintain high interfacial stability and structural integrity.     

Fabrication of low-density carbon-bonded carbon fiber composites with an Hf-based coating for high temperature applications

A novel Hf-based anti-oxidation coating has been prepared on the surface of low-density carbon-bonded carbon fiber composites (CBCFs). The coating exhibits a gradient transition structure, with mainly HfB₂, Hf₂Si and SiC ceramics. Oxyacetylene torch testing has been utilized to evaluate the ablation resistance under the condition ranging from 1.6 MW m⁻² to 2.2 MW m⁻² for 300 s. The experimental results show that the as-prepared Hf-based coating can effectively protect CBCFs under high-temperature oxidation conditions. The surface maximum temperature can reach 1616–2037 °C, and the mass ablation rates vary from −3.5 × 10⁻⁵ g s⁻¹ cm⁻² to 1.5 × 10⁻⁵ g s⁻¹ cm⁻². The formation of a dense SiO₂ glass layer embedded with HfO₂ grains or particle accumulation in the HfO₂ layer is responsible for the good ablation resistance.

A novel low-density CBCF composite with an Hf-based coating was designed and prepared, which exhibited a good ablation resistance at the maximum temperature range of 1616–2037 °C for 300 s.     

Corrosion behaviour of micro-arc oxidation coatings on Mg–2Sr prepared in poly(ethylene glycol)-incorporated electrolytes

Microarc oxidized calcium phosphate (CaP) ceramic coatings were fabricated on Mg–2Sr alloy from silicate electrolytes with different concentration gradient poly(ethylene glycol) (PEG₁₀₀₀). The microstructure, phase and degradability of the ceramic coatings were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and simulation body fluid (SBF) immersion tests respectively. An electrochemical workstation was used to investigate the electrochemical corrosion properties of the coatings. It is found that microstructure, thickness, adhesive strength and degradation rate are influenced by PEG₁₀₀₀ incorporation through adjusting the electrolyte activity and then altering the coating growth mechanism. Similar thicknesses (39.0–42.2 μm) are observed in PEG₁₀₀₀-containing coatings while their PEG₁₀₀₀-free counterparts possess the maximum value (51.5 μm). The weight gain in the first two days of SBF immersion suggests that a new layer containing CaP apatites is generated. Results show that ceramic coatings prepared in the electrolyte containing 8 g L⁻¹ PEG₁₀₀₀ exhibits the highest corrosion resistance and lowest degradation rate.

The highest corrosion resistance and lowest biodegradation are observed on the ceramic coating prepared in electrolytes containing 8 g L⁻¹ PEG₁₀₀₀.     

Strategy for enhanced performance of silicon nanoparticle anodes for lithium-ion batteries

The modification of silicon nanoparticles for lithium-ion battery anode materials has been a hot exploration subject in light of their excellent volume buffering performance. However, huge volume expansion leads to an unstable solid electrolyte interface (SEI) layer on the surface of the silicon anode material, resulting in short cell cycle life, which is an important factor limiting the application of silicon nanoparticles. Herein, a dual protection strategy to improve the cycling stability of commercial silicon nanoparticles is demonstrated. Specifically, the Si/s-C@TiO₂ composite was produced by the hydrothermal method to achieve the embedding of commercial silicon nanoparticles in spherical carbon and the coating of the amorphous TiO₂ shell on the outer surface. Buffering of silicon nanoparticle volume expansion by spherical carbon and also the stabilization of the TiO₂ shell with high mechanical strength on the surface constructed a stable outer surface SEI layer of the new Si/s-C@TiO₂ electrode during longer cycling. In addition, the spherical carbon and lithiated TiO₂ further enhanced the electronic and ionic conductivity of the composite. Electrochemical measurements showed that the Si/s-C@TiO₂ composite exhibited excellent lithium storage performance (780 mA h g⁻¹ after 100 cycles at a current density of 0.2 A g⁻¹ with a coulombic efficiency of 99%). Our strategy offers new ideas for the production of high stability and high-performance anode materials for lithium-ion batteries.

The rational structural design of the spherical carbon and TiO₂ shell results in a significant improvement in the lithium storage performance of commercial silicon nanoparticles, particularly in terms of cycling stability.     

Controllable TiO2 coating on the nickel-rich layered cathode through TiCl4 hydrolysis via fluidized bed chemical vapor deposition

Surface coating of metal oxides is an effective approach for enhancing the capacity retention of a nickel-rich layered cathode. Current conventional coating techniques including wet chemistry methods and atomic layer deposition are restricted by the difficulty in perfectly balancing the coating quality and scale-up production. Herein, a highly efficient TiO₂ coating route through fluidized bed chemical vapor deposition (FBCVD) was proposed to enable scalable and high yield synthesis of a TiO₂ coated nickel-rich cathode. The technological parameters including coating time and TiCl₄ supply rate were systematically studied, and thus a utility TiO₂ deposition rate model was deduced, promoting the controllable TiO₂ coating. The FBCVD TiO₂ deposition mechanism was fundamentally analyzed based on the TiCl₄ hydrolysis principle. The amorphous and uniform TiO₂ coating layer is compactly attached on the particle surface, forming a classical core–shell structure. Electrochemical evaluations reveal that the TiO₂ coating by FBCVD route indeed improves the capacity retention from 89.08% to 95.89% after 50 cycles.

Surface coating of metal oxides is an effective approach for enhancing the capacity retention of a nickel-rich layered cathode.