Mitigating storage-induced degradation of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode material by surface tuning with phosphate

The Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ layered oxide (NCM811) is attracting considerable attention as a high-capacity cathode material for rechargeable Li-ion batteries. However, due to its inherent structural/chemical/electrochemical instability, NCM811 with high Ni content suffers from significant performance degradation upon storage even in ambient atmospheres as well as during charge–discharge cycling. Herein, we demonstrate a simple but effective surface-tuning approach to mitigate storage-induced degradation of NCM811, which is based on the conversion of undesirable Li residues to a protective Li₃PO₄ nanolayer via phosphate treatment. The accelerated storage stability test shows that phosphate-modified NCM811 exhibits remarkably improved electrochemical performance (capacity, cycle life, and rate capability) over the pristine one after being stored under harsh environmental conditions. A combined analytical study indicates that surface tuning through phosphate treatment enhances the storage stability of NCM811 by eliminating impurity-forming Li residues and producing a Li₃PO₄ nanolayer that inhibits parasitic reactions at the electrode–electrolyte interface. Furthermore, Li₃PO₄ provides an effective barrier to H₂O and CO₂ infiltration into the particle agglomerates, thereby suppressing the loss of particle integrity.     

Recent progress in coatings and methods of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode materials: A short review

LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) is a typical nickel (Ni)-rich ternary cathode material with several advantages, such as high specific capacity, low-cost, and environmentally friendly, making it a good candidate for use in lithium-ion batteries. However, its Ni content is as high as 80%; therefore, several new problems have emerged with gradually increasing applications. In this review, Li–Ni disorder and corresponding modification methods are first briefly reviewed, and then the origin of complex surface defect, which has a crippling effect on diffusion processes of Li⁺ at electrolyte/cathode interface, is discussed in detail. Analyses showed the importance of selecting appropriate surface modification material/technique for enhancing electrochemical properties. Therefore, popular surface coating materials and methods including metal oxides, fluorides, phosphates, fast ion conductors, and other compounds/elements used for the development of NCM811 are subjected to extensive and thorough research. Finally, several new perspectives and insights related to stability and safety at high voltages and temperatures, and the optimization of production process are also proposed.     

Effects of Al2O3 and LiAlO2 Co-coating on electrochemical properties of LiNi0.8Co0.1Mn0.1O2 cathode materials

Lithium-ion batteries are widely used in aerospace, power vehicles, portable electronic devices and other fields because of their environmental friendliness, rechargeable cycle and high energy density. The nickel-cobalt-manganese ternary materials with high nickel has high specific discharge capacity and is regarded as one of the most promising cathode materials. However, with the increase of the number of cycles, the cycle performance becomes worse and the specific capacity decays sharply. In this work, Al₂O₃ and LiAlO₂ were coated on the surface of NCM811 by combining ball milling mixing and solid-phase synthesis to prepare the AL-NCM811 cathode material. The coating thickness formed by Al₂O₃ and LiAlO₂ was 10–70 nm, which effectively improves the cycle stability and rate performance of NCM811 material. When charged and discharged at 0.1C, the first discharge specific capacity and capacity retention rate after 100 cycles of 0.5AL-NCM811 were 196.26 mAh/g and 96.47%, respectively, while those of NCM811 were only 193.78 mAh/g and 72.18%, respectively. When the current density was 5.0C, the discharge specific capacity of 0.5AL-NCM811(139.16 mAh/g) was 55.368 mAh/g higher than that of NCM811(83.80 mAh/g).     

Al-Doped Li[Ni0.78Co0.1Mn0.1Al0.02]O2 for High Performance of Lithium Ion Batteries

Li[NixCoyMnz]O₂ (NCM) layered materials have been successfully adopted in commercial lithium ion batteries (LIBs). The presence of higher Ni content in cathode materials helps to improve the capacity. However, increased cation mixing on the surface of layered material leads to unstable structure. Aluminium (Al) doping is known to enhance the performance of cathode material by rendering thermal and structural stability. In this article, we synthesize Li[Ni_0.8Co_0.1Mn_0.1]O₂ (Bare NCM811) and Li[Ni_0.78Co_0.1Mn_0.1Al_0.02]O₂ (Al-Doped NCM811) using simple co-precipitation process followed by calcination process. The electrochemical, morphological, and structural characteristics of the Al-Doped NCM811 are investigated and compared with the Bare NCM811. The discharge capacity of the Bare NCM811 and the Al-Doped NCM811 maintained 73.59% and 96.15% after the 100th cycle at a room temperature of 20?°C and 87.32% and 94.38% after the 50th cycle at an elevated temperature of 60?°C, respectively. The enhanced electrochemical performance of Al-Doped NCM811 is attributed to the improved thermal and structural properties of the electrode, as confirmed using differential scanning calorimeter (DSC) and particle compression tester (PCT).     

Enhancing high-potential stability of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode with PrF3 coating

It is still a huge challenge to improve the safety and stability of Ni-rich (LiNi_0.8Co_0.1Mn_0.1O₂) cathode materials at elevated potential. Herein, the PrF₃ layer is employed to protect LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) via a simple wet chemical process. It was confirmed by XRD, HR-SEM, TEM, EDS, and XPS tests that PrF₃ is evenly covered throughout the surface of NCM811 without affecting the particle size and surface morphology. In particular, 1 wt% PrF₃ coated NCM811 exhibits excellent stability and rate capability with the capacity retention of 86.3% after 100 cycles at 1 C under a cut-off potential of 4.3 V, while the retention of pristine one is only 73.8%. Moreover, the capacity retention of 1 wt% PrF₃ coated samples enhances from 74.5% to 88.5% after 50 cycles at 1 C under higher cut-off voltage of 4.6 V. The superior performance for coated samples can be attributed to the fact that PrF₃ can effectively isolate the active material and the electrolyte from HF corrosion, and at the same time, reduce the generation of micro-cracks on the surface during prolonged cycles. Furthermore, as a physical barrier, PrF₃ alleviates the dissolution of transition metals in the electrolyte largely. These results suggest that the stability of NCM811 can be greatly upgraded at high voltage by PrF₃ coating.     

LiAlO2-coated LiNi0.8Co0.1Mn0.1O2 and chlorine-rich argyrodite enabling high-performance all-solid-state lithium batteries at suitable stack pressure

All-solid-state lithium batteries (ASSLBs), which are consisted of Li_5.5PS_4.5Cl_1.5 electrolyte, metal lithium anode and LiNi_0.8Mn_0.1Co_0.1O₂ (NCM811) cathode, are speculated as a promising next generation energy storage system. However, the unstable oxide cathode/sulfide-based electrolyte interface and the dendrite formation in sulfide electrolyte using the lithium metal anode hinder severely commercialization of the ASSLBs. In this work, the dendrite formation in sulfide electrolyte is investigated in lithium symmetric cell by varying the stack pressure (3, 6, 12, 24 MPa) during uniaxial pressing, and uniformly nanosized LiAlO₂ buffer layer was carefully coated on NCM811 electrode (LiAlO₂@NCM811) to improve the cathode/electrolyte interface stability. The result shows that lithium symmetrical cell has a steady voltage evolution over 400 h under 6 MPa stacking pressure, and the assembled LiAlO₂@NCM811/Li_5.5PS_4.5Cl_1.5/Li battery under the stack pressure of 6 MPa exhibits large initial discharge specific capacity and excellent cycling stability at 0.05 C and 25 °C. The feasibility of using the lithium metal anode in all-solid-state batteries (ASSBs) under suitable stack pressure combined with uniformly nanosized LiAlO₂ buffer layer coated on NCM811 electrode supply a facile and effective measures for constructing ASSLBs with high energy density and high safety.     

Fabrication and properties of CNT/Ni/Y/ZrB2 nanocomposites reinforced in situ

Carbon nanotubes (CNTs) were synthesized in situ by chemical vapor deposition of methane over nano‐ZrB₂ matrix using Ni/Y catalysts. Well‐grown CNTs with tangled and long bodies and mainly composed of well‐crystallized graphite were obtained when the Ni content reaches 10 wt%. The CNT/ZrB₂ nanocomposites obtained by spark plasma sintering at 1400°C exhibited full density and optimal mechanical properties. The flexural strength and fracture toughness of the nanocomposites were 1184 ± 52 MPa and 10.8 ± 0.3 MPa·m^1/2, respectively. Results indicated that the dispersion of CNTs in situ can improve composite performance, rendering the mechanical properties of the CNT/ZrB₂ nanocomposites synthesized in situ considerably superior to those of monolithic ZrB₂ nanoceramics and CNT/ZrB₂ nanocomposites synthesized using the traditional method. The toughening mechanisms included crack deflection, crack bridging, CNT debonding, pull‐out, and fracture.     

Electrophoretic deposition of carbon nanotube–ceramic nanocomposites

The purpose of this paper is to present an up-to-date comprehensive overview of current research progress in the development of carbon nanotube (CNT)–ceramic nanocomposites by electrophoretic deposition (EPD). Micron-sized and nanoscale ceramic particles have been combined with CNTs, both multiwalled and single-walled, using EPD for a variety of functional, structural and biomedical applications. Systems reviewed include SiO₂/CNT, TiO₂/CNT, MnO₂/CNT, Fe₃O₄/CNT, hydroxyapatite (HA)/CNT and bioactive glass/CNT. EPD has been shown to be a very convenient method to manipulate and arrange CNTs from well dispersed suspensions onto conductive substrates. CNT–ceramic composite layers of thickness in the range <1–50 μm have been produced. Sequential EPD of layered nanocomposites as well as electrophoretic co-deposition from diphasic suspensions have been investigated. A critical step for the success of EPD is the prior functionalization of CNTs, usually by their treatment in acid solutions, in order to create functional groups on CNT surfaces so that they can be dispersed uniformly in solvents, for example water or organic media. The preparation and characterisation of stable CNT and CNT/ceramic particle suspensions as well as relevant EPD mechanisms are discussed. Key processing stages, including functionalization of CNTs, tailoring zeta potential of CNTs and ceramic particles in suspension as well as specific EPD parameters, such as deposition voltage and time, are discussed in terms of their influence on the quality of the developed CNT/ceramic nanocomposites. The analysis of the literature confirms that EPD is the technique of choice for the development of complex CNT–ceramic nanocomposite layers and coatings of high structural homogeneity and reproducible properties. Potential and realised applications of the resulting CNT–ceramic composite coatings are highlighted, including fuel cell and supercapacitor electrodes, field emission devices, bioelectrodes, photocatalytic films, sensors as well as a wide range of functional, structural and bioactive coatings.     

Synthesis,microstructure and electrical conductivity of carbon nanotube–alumina nanocomposites

Carbon nanotube–alumina (CNT–Al₂O₃) nanocomposites have been synthesized by direct growth of carbon nanotubes on alumina by chemical vapor deposition (CVD) and the as-grown nanocomposites were densified by spark plasma sintering (SPS). Surface morphology analysis shows that the CNTs and CNT bundles are very well distributed between the matrix grains creating a web of CNTs as a consequence of their in situ synthesis. Even after the SPS treatment, the CNTs in the composite material are still intact. Experimental result shows that the electrical conductivity of the composites increases with the CNT content and falls in the range of the conductivity of semiconductors. The nanocomposite with highest CNT content has electrical conductivity of 3336 S/m at near room temperature, which is about 13 orders of magnitude increase over that of pure alumina.     

Surface modification of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode materials via a novel mechanofusion alloy route

This study aimed to prepare a composite coating material comprising a solid ionic conductor of lithium aluminum titanium phosphate (Li_1.4Al_0.4Ti_1.6(PO₄)₃, LATP) and porous carbon through a sol-gel method. LiNi_0.8Co_0.1Mn_0.1O₂ (LNCM811) cathode material with dual-functional composite conductors (i.e., LATP@porous carbon), denoted as LATP-PC, was prepared. The dry-coating method, also called the “mechanical-fusion alloy route,” was used to modify Ni-rich LNCM811 cathode materials. X-ray diffraction (XRD), micro-Raman spectroscopy, and X-ray photoelectron spectroscopy confirmed that the LATP ionic conductor generated herein was uniformly deposited on 3D porous carbon and served as a dual-functional composite coating on LNCM811. Furthermore, the capacity retention of LATP-PC@LNCM811 was approximately 85.57% and 80.86% after 100 cycles at −20 °C and 25 °C, respectively. By contrast, pristine LNCM811 had the capacity retention of 78% and 74.96% at −20 °C and 25 °C, respectively. Furthermore, the high-rate capability of the LATP-PC@LNCM811 material was markedly enhanced to 169.81 mAh g⁻¹ at 10C relative to that of pristine LNCM811, which was approximately 137.67 mAh g⁻¹. The electrochemical performance of LNCM811 was enhanced by the uniform dual-conductive composite coating. The results of the study indicate that the LATP-PC@LNCM811 composite material developed herein is a potentially promising material for future high-energy Li-ion batteries.     

Enhanced electrical properties of polycarbonate/carbon nanotube nanocomposites prepared by a supercritical carbon dioxide aided melt blending method

Polycarbonate/carbon nanotube (CNT) nanocomposites were generated using a supercritical carbon dioxide (scCO₂) aided melt blending method, yielding nanocomposites with enhanced electrical properties and improved dispersion while maintaining the aspect ratio of the as-received CNTs. Baytubes^® C 150 P CNTs were benignly deagglomerated with scCO₂ resulting in 5 fold (5X), 10X and 15X decreases in bulk density from the as-received CNTs. This was followed by melt compounding with polycarbonate to generate the CNT nanocomposites. Electrical percolation thresholds were realized at CNT loading levels as low as 0.83 wt% for composites prepared with 15X CNT using the scCO₂ aided melt blending method. By comparison, a concentration of 1.5 wt% was required without scCO₂ processing. Optical microscopy, transmission electron microscopy, and rheology were used to investigate the dispersion and mechanical network of CNTs in the nanocomposites. The dispersion of CNTs generally improved with scCO₂ processing compared to direct melt blending, but was significantly worse than that of twin screw melt compounded nanocomposites reported in the literature. A rheologically percolated network was observed near the electrical percolation of the nanocomposites. The importance of maintaining longer carbon nanotubes during nanocomposite processing rather than focusing on dispersion alone is highlighted in the current efforts.     

Magnesia–Carbon Nanotubes (MgO–CNTs) Nanocomposite: Novel Support of Ru Catalyst for the Generation of COx-Free Hydrogen from Ammonia

Magnesia–carbon nanotubes (abbreviated as MgO–CNTs) nanocomposites were prepared by impregnation of CNTs with Mg(NO₃)₂·6H₂O in ethanol solution, followed by drying at 353 K and calcination at 873 K, respectively. The nanocomposites are thermally more stable than CNTs in a H₂ flow. The use of the nanocomposites as support yielded more efficient Ru catalysts for the generation of CO _x -free hydrogen from NH₃ decomposition.     

Micromechanical properties of hydroxyapatite nanocomposites reinforced with CNTs and ZrO2

This study examined the mechanical properties, wettability, and tribology of hydroxyapatite (HA)–zirconia (ZrO₂)–carbon nanotube (CNTs) ceramic nanocomposites (with various CNT ratios (x): 1, 5, and 10 wt%). HA–ZrO₂–CNT-x powders were hydrothermally synthesized. Hot isostatic pressing (HIP) and cold isostatic pressing were used to manufacture solid and dense tablets; consolidation was performed by sintering the nanocomposites under Ar gas at 1150 °C during HIP. The microstructure and morphology of the nanocomposites were characterized via transmission electron microscopy, energy-dispersive X-ray spectroscopy, powder X-ray diffractometry, Fourier transform infrared (FTIR), and scanning electron microscopy. The effects of ZrO₂ and CNTs on the mechanical characteristics of the nanocomposites were examined via nanoindentation, reciprocating wear, and Vickers hardness tests. The microhardness of HA–ZrO₂–CNT-1% and HA–ZrO₂–CNT-5% increased by 36.8% and 66.67%, respectively, compared with that of pure HA. The nanohardness of the HA–ZrO₂–CNT-1%, HA–ZrO₂–CNT-5%, and HA–ZrO₂–CNT-10% samples was 8.3, 9.65, and 8.02 Gpa, and the corresponding elastic modulus was 83.72, 114.34, and 89.27 GPa, respectively. Both of these parameters were higher than those of pure HA. However, in the nanocomposite reinforced with 10% CNT, as opposed to those with lower CNT ratios, their values were lower. Additionally, HA–ZrO₂–CNT-10% was the most hydrophilic nanocomposite synthesized in this study with a contact angle of 48.8°.     

Synthesis of carbon nanotube/mesoporous TiO2 coaxial nanocables with enhanced lithium ion battery performance

Well-organized hybrid nanocables consisting of carbon nanotube (CNT) core and mesoporous TiO₂ sheath has been synthesized through a combined sol–gel and hydrothermal process. By using hexadecylamine as a structure directing agent, mesoporous TiO₂ with thickness ranging from 40 to 70 nm was uniformly deposited on multi-walled CNTs. The resultant one dimensional CNT core/mesoporous TiO₂ sheath (CNT@mesoporous TiO₂) hybrid nanocables shows well-crystallized quality, porous feature and large surface area, favoring its electrochemical performance. Compared with reference TiO₂ without CNTs, the CNT@mesoporous TiO₂ hybrid nanocables shows largely enhanced rate performance, which could be attributed to its unique structure as well as the improvement of electronic conductivity by adding conductive CNTs.     

Hierarchical carbon nanotube membrane with high packing density and tunable porous structure for high voltage supercapacitors

We reported the fabrication of a hierarchical carbon nanotube (CNT) membrane by using the 90% granulated double- or triple-walled CNTs and 10% 100 μm long multiwalled CNTs as the linker. The membrane with packing density of 420 kg/m³, excellent electrical conductance and good mechanical strength, functioned as both the electrode and current collector and allowed the weight ratio of CNTs increased up to 45–50% based on the weight of CNT, electrolyte and separator. The granulated double or triple walled CNTs, by the aggregation at high temperature etching using CO₂, simultaneously exhibited high surface area and tunable pore structure and high pore volume, and were favorable for the ion transport of organic electrolyte, due to the effect of opening cap or side wall by the CO₂. The CNT membrane electrode, exhibited the capacitance of 57.9 F/g and the energy density of 35 W h/kg, as operated at 4 V.     

Controlling the sizes of in-situ TiC nanoparticles for high-performance TiC/Al–Cu nanocomposites

TiC/Al–Cu nanocomposites were fabricated in Al–Ti–C powder systems using carbon black, a mixture of C and carbon nanotubes (C + CNTs), and CNTs via an in-situ method involving combustion synthesis and hot pressing. As the carbon source changed from pure carbon black to the C + CNT mixture and pure CNTs, the size of the TiC nanoparticles decreased gradually. The nanocomposites synthesized based on the C + CNT mixture exhibited the most uniform dispersion of TiC nanoparticles. The 30 vol% TiC/Al–Cu nanocomposite prepared from the C + CNT mixture had the best comprehensive mechanical properties (yield strength (411 MPa), compressive strength (712 MPa), fracture strain (17.2%), hardness (206.8 HV), and wear resistance under the experimental conditions due to having the most uniformly dispersed TiC nanoparticles. The wear mechanism was a combination of plastic deformation, abrasion, and adhesion. This method may be a low-cost and convenient means to control the sizes of in-situ TiC nanoparticles and prepare high-performance TiC/Al–Cu nanocomposites.     

Improving the electrochemical performance of Ni-rich cathode materials using a fast ion conductor coating of Li2O–B2O3–LiBr

The high-Ni layered metal oxide, LiNi_0.8Co_0.1Mn_0.1O₂ (LNCM811), has received widespread attention in the energy field because of its high specific capacity, but its large-scale applications are hindered due to severe capacity fading. Herein, a uniform and thin Li₂O–B₂O₃–LiBr-glass (LBBrO-glass) coating was deposited on LNCM811 by a liquid-phase coating and thermal treatment method. The experimental results suggested that the LBBrO-glass coating acted as a protective layer that inhibited transition metal dissolution and side reactions, which helped improve the electrochemical properties of LNCM811. Remarkably, after 200 cycles, the 2 wt% coating (LBBrO@LNCM-2) delivered a superior capacity retention of 88.9%, while only 71.8% was obtained for the pristine material (LNCM811). The discharge capacity of LBBrO@LNCM-2 was 163.5 mAh g^?1 at 5C, while it was only 139 mAh g^?1 for the pristine material.     

Microstructural and mechanical behavior of multi-walled carbon nanotubes reinforced Al–Mg–Si alloy composites in aging treatment

Microstructural and mechanical behavior of heat treatable Al–Mg–Si (6XXX series) alloy composites reinforced with multi-wall carbon nanotubes (MWCNTs) fabricated by powder metallurgy process were investigated by SEM-EDS, XRD, tensile test and Vicker’s hardness test. As-extruded P/M 6063 alloy composites with CNT reinforcements indicated a small increment of mechanical strength compared to the monolithic 6063 alloy with no CNT before T6 heat treatment. When T6 heat treatment was applied to the specimens, the 6063 composite with CNTs showed a noticeable decrease of yield stress (YS) improvement, compared to the monolithic Al alloy. It means that Mg₂Si precipitates hardening effect by the artificial aging treatment was insufficient for the composite containing CNTs. This was mainly because Mg alloying elements were diffused around CNTs and consumed to form Al₂MgC₂ compounds, and resulted in the incomplete matrix strengthening behavior by Mg₂Si precipitation after the aging treatment.     

Multi-Directional Growth of Aligned Carbon Nanotubes Over Catalyst Film Prepared by Atomic Layer Deposition

The structure of vertically aligned carbon nanotubes (CNTs) severely depends on the properties of pre-prepared catalyst films. Aiming for the preparation of precisely controlled catalyst film, atomic layer deposition (ALD) was employed to deposit uniform Fe₂O₃ film for the growth of CNT arrays on planar substrate surfaces as well as the curved ones. Iron acetylacetonate and ozone were introduced into the reactor alternately as precursors to realize the formation of catalyst films. By varying the deposition cycles, uniform and smooth Fe₂O₃ catalyst films with different thicknesses were obtained on Si/SiO₂ substrate, which supported the growth of highly oriented few-walled CNT arrays. Utilizing the advantage of ALD process in coating non-planar surfaces, uniform catalyst films can also be successfully deposited onto quartz fibers. Aligned few-walled CNTs can be grafted on the quartz fibers, and they self-organized into a leaf-shaped structure due to the curved surface morphology. The growth of aligned CNTs on non-planar surfaces holds promise in constructing hierarchical CNT architectures in future.     

Field emission properties from aligned carbon nanotube films with tetrahedral amorphous carbon coatings

Tetrahedral amorphous carbon (ta-C) film was coated on aligned carbon nanotube (CNT) films via filtered cathodic vacuum arc (FCVA) technique. Field electron emission properties of the CNT films and the ta-C/CNT films were measured in an ultra high vacuum system. The I–V measurements show that, with a thin ta-C film coating, the threshold electric field (E_thr) of CNTs can be significantly decreased from 5.74 V/μm to 2.94 V/μm, while thick ta-C film coating increased the E_thr of CNTs to around 8.20 V/μm. In addition, the field emission current density of CNT films reached 14.9 mA/cm² at 6 V/μm, while for CNTs film coated with thin ta-C film only 3.1 V/μm of applied electric field is required to reach equal amount of current density. It is suggested that different field emission mechanisms should be responsible for the distinction in field emission features of CNT films with different thickness of ta-C coating.