Atomic Layer Deposition Coatings Research Articles

Improved Performance of High‐Entropy Disordered Rocksalt Oxyfluoride Cathode by Atomic Layer Deposition Coating for Li‐Ion Batteries

Lithium‐excess cation‐disordered rocksalt materials are a promising class of transition metal‐based cathodes that exhibit high specific capacity and energy density. The exceptional performance is achieved through participation of anionic redox in addition to cationic redox reactions in the electrochemistry. However, anionic redox reactions accompanied by oxygen evolution, accelerated electrolyte breakdown, and structural evolution lead to voltage hysteresis and low initial Coulombic efficiency. Herein, an Al2O3 layer with varying thickness has been coated onto a high‐entropy disordered rocksalt oxyfluoride cathode through atomic layer deposition to enhance battery performance. The results indicate that the utilization of a uniform Al2O3 coating improves the capacity retention and rate capability of the cathode, with the performance being strongly dependent on the layer thickness. Further investigation into cathode–electrolyte interfacial reactions reveals that the thin protecting Al2O3 coating can reduce the decomposition of electrolyte on the cathode surface but cannot prevent bulk phase degradation during prolonged cycling. These findings highlight the need for optimized coating design on the disordered rocksalt cathode to improve battery performance.

Advanced TiO2/Al2O3 Bilayer ALD Coatings for Improved Lithium-Rich Layered Oxide Electrodes.

Surface modification is a highly effective strategy for addressing issues in lithium-rich layered oxide (LLO) cathodes, including phase transformation, particle cracking, oxygen gas release, and transition-metal ion dissolution. Existing single-/double-layer coating strategies face drawbacks such as poor component contact and complexity. Herein, we present the results of a low-temperature atomic layer deposition (ALD) process for creating a TiO2/Al2O3 bilayer on composite cathodes made of AS200 (Li1.08Ni0.34Co0.08Mn0.5O2). Electrochemical analysis demonstrates that TiO2/Al2O3-coated LLO electrodes exhibit improved discharge capacities and enhanced capacity retention compared with uncoated samples. The TAA-5/AS200 bilayer-coated electrode, in particular, demonstrates exceptional capacity retention (∼90.4%) and a specific discharge capacity of 146 mAh g-1 after 100 cycles at 1C within the voltage range of 2.2 to 4.6 V. The coated electrodes also show reduced voltage decay, lower surface film resistance, and improved interfacial charge transfer resistances, contributing to enhanced stability. The ALD-deposited TiO2/Al2O3 bilayer coatings exhibit promising potential for advancing the electrochemical performance of lithium-rich layered oxide cathodes in lithium-ion batteries.

Anodic Porous Alumina Membranes with Chemical Stability Improved by Atomic Layer Deposition Coating of TiO2

Anodic porous alumina (APA) membranes with a high density of uniformly sized pores are promising materials for microfiltration. However, such membranes obtained by anodizing Al are amorphous, chemically less stable, and cannot be used to filter acidic or basic solutions. The chemical stability of APA membranes can be improved by heat treatment at temperatures above 1000 °C, resulting in membrane filters with excellent chemical stabilities. However, such a high-temperature treatment makes APA membranes brittle owing to alumina crystallization, which reduces their mechanical strength and makes them less durable. In this study, a membrane filter with both chemical resistance and mechanical strength was fabricated by coating an APA membrane with a TiO2 layer by atomic layer deposition (ALD). The resulting membrane filters showed improved chemical stability in acidic and basic solutions because the TiO2 layer coated on the surface of the APA membrane protected the membrane against its dissolution. In addition, the resulting TiO2-coated APA membrane retained its high mechanical strength, as the membrane itself was not exposed to high-temperature conditions during TiO2 coating by ALD, and the crystallization of the alumina layer did not proceed. The obtained TiO2-coated APA membranes are promising as microfiltration membranes applicable to acidic and basic solutions.

Atomic layer deposition niobium oxide and lithium niobium oxide as a protection technique for anode‐free batteries

AbstractAs demand for extended range in electric vehicles and longer battery lifetimes in consumer electronics has grown, so have the requirements for higher energy densities and longer cycle lifetimes of the cells that power them. One solution to this is the implementation of an “anode‐free” battery. By removing the anode and plating lithium directly onto the current collector, it is possible to access the same capacities and voltage windows as traditional lithium metal batteries, with the entirety of the lithium source coming from the cathode. Herein, a copper foil current collector coated with niobium oxide or lithium niobium oxide through atomic layer deposition (ALD) is applied to extend the cycling life of the anode‐free batteries by reducing dendrite formation and improving the stability of the lithium metal surface throughout cycling. The ALD coatings are able to extend the cycle lifetime in full coin cells from 20 cycles to 80% capacity retained in the bare copper controls to 50 and 115 cycles for the NbO and LiNbO coatings, respectively. Over the lifetime of the cells, the ALD‐LiNbO is able to cumulatively offer a staggering improvement of an additional 100 kWh L−1 compared to the bare copper control.

Scaling a Gas Phase Residual Lithium Conversion Process on Ni-Rich NMC Cathode Materials in Commercial Fluidized Bed Reactors

‘Residual lithium’, the LiOH and Li2CO3 surface contamination that is ubiquitous to Ni-rich NMC manufacturing, is a significant obstacle in the large-scale production and handling of high-nickel layered oxides. These hydroxide and carbonate surface phases influence reproducibility and shelf stability of the NMC powder and cause gelation and particle aggregation during electrode casting. There is ample evidence in the literature that atomic layer deposition (ALD) possesses a two-fold solution to this problem.1-3 First, reactive organometallic species such as trimethylaluminum (TMA) can convert insulating residual lithium to a Li-rich LixAlyO conducting layer. Customizable ALD layers can then be added to inhibit the re-formation of the carbonate layer and to deter negative side reactions of the CAM surface with the liquid electrolyte. While highly impactful, these studies have mostly been relegated to small, lab-scale demonstrations of <50 g. As such, there remains a need to enable this ALD-assisted-technology for high-throughput commercial applications.In this talk, we will explore the progression of a residual lithium conversion process from lab (10 – 1000 mL) to industrial-scale (10 L – 100 L) fluidized bed equipment and how scale and material-dependent parameters can impact performance. Using a commercial NMC 811 cathode as a case study, we first applied aluminum phosphate ALD coatings on a lab-scale fluidized bed reactor to examine the interfacial and electrochemical changes of the CAM material under various process conditions. ICP-OES measurements confirmed linear and reproducible deposition versus ALD cycle number between 200- 300°C. XPS analysis showed the ALD coated NMC 811 powder had an 80% reduction in Li2CO3 versus the pristine material and that a reduction persisted even after 10 days of storage in atmospheric conditions. At standard (0.5C/1C) cycling to 4.4V, AlPO4 coatings increased cycle life by 44% versus the uncoated powder. Under optimized conditions, the process was scaled first to 1 kg and finally to 10 kg in a pilot-scale reactor. In-situ mass spectrometry indicated that residual lithium conversion byproducts such as CO2 could be used to monitor reaction progress and optimize chemical usage efficiency. Fluidization aids including vibration and mechanical stirring were used to inhibit and break up powder agglomerates. ICP-OES and electrochemical cycling data confirmed reproducible deposition and cycle life benefits versus the small scale runs and pristine materials, demonstrating a pathway for these ALD-enhanced materials to transition from lab-scale demonstration to viable product. We will discuss strategies for continuing the scaling process to 100 kg batches for commercial applications.[1] M. Young et al., The Journal of Physical Chemistry C 2019 123 (39), 23783-23790[2] P. Darapaneni et al., ACS Applied Energy Materials 2022, 5, 8, 9870–9876[3] J. Li et al., Coatings 2022, 12(1), 84

Platinum Catalysts via Fluidized Bed Atomic Layer Deposition for PEM Fuel Cells

One of the major challenges for viable and durable proton exchange membrane fuel cells (PEMFC) in heavy duty applications is the development of stable and high-performing catalysts. The highest mass activities and stabilities can be achieved with platinum nanoparticles supported on a porous carbon support. However, these systems still suffer from degradation processes during cell operation, such as carbon corrosion and Ostwald ripening. [1] Atomic layer deposition (ALD) is an attractive alternative to the conventional wet chemical deposition of the platinum catalyst onto the carbon, promising to counteract these problems. [2,3]ALD is a surface coating method, which employs self-limiting half-reactions between gaseous precursor molecules and a solid substrate surface. Usually, two half-reactions separated by purging or vacuuming steps represent one ALD cycle. By performing a defined number of cyclic repetitions, thin films or nanoparticles can be grown on the substrate surface with atomic-layer precision. [4]Typically, ALD is used to coat flat surfaces. To achieve homogeneous coatings on powders, so-called fluidized bed ALD reactors fluidize the nanoparticle-powders in a gas flow, which also contains the gaseous precursor materials. This method ensures a high utilization of the precursor molecules while providing a good mixing of the sample. Thin films and nanoparticles can be deposited in a homogeneous manner onto the powder surface and into its pores. [4]Carbon corrosion of PEMFCs can be suppressed by applying conformal ALD coatings onto the support structure. Additionally, a porous overcoating can fixate the nanoparticles against detachment and dissolution while still leaving access to the reactive sites. [5] Applying ALD to deposit fuel cell catalysts with monodisperse and highly dispersed platinum nanoparticles can counteract Ostwald ripening. [2,6]In this study we show platinum particles deposited via ALD, which are highly dispersed and show a monodisperse size distribution. We further show TiO2-overcoatings to protect the carbon.Literature:[1] J. C. Meier, Beilstein J. Nanotechnol., 2014, 5, 55-67. [2] W-J. Lee, Adv. Mater. Interfaces, 2019, 6 1901210. [3] B. J. O’Neill, ACS Catal., 2015, 5, 1804. [4] W. W. McNeary, Appl. Catal. B, 2019, 254, 587-593. [5] Q. Liu, Chem. Soc. Rev., 2022, 51, 188-236. [6] Z. Xu et al., Appl. Catal. B, 2012, 111-112, 264.

New insights into dry-coating-processed surface engineering enabling structurally and thermally stable high-performance Ni-rich cathode materials for lithium ion batteries

Nickel-rich layered oxides with high capacity and acceptable cost have established their critical status as cathode materials in high energy density lithium ion batteries. However, their mass production and application are still challenged by rapid capacity fading and poor thermal stability, which drives the research on surface protective coating techniques in both academic and industrial fields. Intensively investigated techniques like wet method or atomic layer deposition coatings are time-consuming and complicated, which may cause negative effects like surface lithium deficiency and phase reconstruction. Herein, a feasible and economic powder dry coating strategy assisted by high-energy mixer is proposed. Ni-rich LiNi0.8Co0.1Mn0.1O2 cathodes with Al(OH)3 nanoparticles are selected as the model case to reveal the distinct chemical evolution on cathode surface by elucidating the specific mechanism nuances between samples under different coating amounts in this process. Instructively under the good tuning of LiAlO2/Al2O3 role, coated cathode exhibits significant improvement in cycling stability, rate capability, attributed to proper surface protection against side reactions and lithium ion transferring enhancement. Moreover, the ambient storage stability and thermal stability are also improved successfully. This work attempts to remedy the research gap between lab research and industry engineering, and provides universal insights into simplified and controllable strategies for wider range of cathode material and their coatings under practical application scenarios.

Understanding the multilevel phenomena that enables inorganic atomic layer deposition to provide barrier coatings for highly-porous 3-D printed plastic in vacuums

The potential of 3-D printing polymers to achieve low-weight space flight hardware has seen increasing interest. Additionally, robust 3-D printed polymer vacuum equipment would provide highly attractive low-cost alternatives to conventional industrial-scale tools for the scientific community. Inorganic barrier coatings of plastic parts can be used to minimize outgassing and damage to polymers from extreme vacuum environments. Among different coating technologies in this area of research, atomic layer deposition (ALD) has shown the most promise. Nevertheless, the exact formation morphology of ALD coatings on 3-D printed polymers under vacuum are not yet well understood, which hinders use of 3-D printed polymers in vacuum environments. In this study, the film formation mechanisms of ALD alumina on porous 3-D printed polymers are investigated via SEM, EDS, XRD, ATR-FTIR, and XPS. ALD alumina is deposited on 3-D printed pigmented and un-pigmented acrylonitrile butadiene styrene, polycarbonate, commercially available polypropylene, and pure polypropylene. The results reveal that the formation of the ALD barrier layer, its thickness, and diffusion of ALD precursor materials into the polymer substrate is a multi-scale phenomenon, and that substrate porosity and polymer functionality both dominate film formation behavior. Additionally, this study demonstrates that during ALD processes on 3-D printed polymers a vapor phase infiltration (VPI) growth mode also occurs, especially where porosity is present.

Characterization of the Local Atomic Structure of ALD Coated Interfaces

To accelerate technological innovations using atomic layer deposition (ALD) coatings, we need to establish better understanding of structure-property relationships for ALD films. Historically, the ALD community has had difficulty connecting the atomic structure of ALD films with their performance, largely because of the significant challenge in determining the atomic-scale structure of ultrathin ALD films that are often amorphous, polycrystalline, or defective. In this work, we describe a series of recent efforts that collectively aim to improve understanding of the atomic structure of ALD coatings and inform structure-property understanding. These efforts employ experimental measurements including (a) inert-transfer XPS, (b) in-situ synchrotron high energy X-ray diffraction, and (c) cryogenic electron diffraction. Of particular focus in this talk is the use of X-ray and electron diffraction measurements in combination with pair distribution function (PDF) analysis and reverse Monte Carlo (RMC) structural modeling. We describe a newly developed approach employing alternating RMC and molecular statics steps (RMC-MS) that improves the physical accuracy of model structures derived from experimental diffraction data with minimal additional computational cost over conventional RMC modeling. We also describe efforts using localized cryogenic electron diffraction and PDF analysis (cryo-ePDF) with a ≤ 5 nm spot size to measure atomic structure at ALD interfaces. Together, these advances allow us to quantify differences in the atomic structure as a function of position through the depth of ALD films. A simple two-phase model comprised of bulk and interfacial layers with distinct atomic structure features is consistent with our measurements for both aluminum oxide and zinc oxide ALD coatings. The approaches we report yield atomic structure models that can be used to inform computational studies of the properties if ALD films and will aid in the selection and modification of ALD coating chemistries to address technological needs.

Conversion Reactions and Redox Changes on the Surface of Lithium-Ion Battery Cathode Materials during Chemical Vapor Treatment for ALD

Atomic layer deposition (ALD) has emerged as a promising technology for applying ultrathin protective coatings on lithium-ion battery (LIB) cathode surfaces to improve their cycling stability. While there have been numerous reports evaluating the electrochemical performance of these surface-modified cathode materials, the chemical changes induced on the surface of the cathode materials by the ALD coatings and the individual ALD precursors are not fully studied. We performed a systematic investigation to understand the interfacial changes of 12 different cathode materials upon coating with aluminum oxide (Al2O3) using trimethyl aluminum (TMA) and H2O, and aluminum fluoride (AlF3) using TMA and hydrogen fluoride pyridine (HFPy). We also explored the effects of the individual TMA and HFPy precursors on the cathode surfaces. The surface composition and microstructure of these cathode materials, which range from simple transition metal oxides (e.g., NiO and MnO) to complex multi-element cathode materials (e.g., LiNixMn1-x-yCoyO2, NMC), were studied via X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). The XPS measurements reveal that the transition metals in the cathode materials undergo selective oxidation/reduction depending upon the nature of the precursor, the coating, and the cathode material. Furthermore, XPS and STEM measurements show the conversion of surface carbonate species to the corresponding metal fluorides upon HF exposure. This conversion reaction is self-limiting but extends hundreds of nanometers below the surface in the case of Li2CO3. ALD and chemical vapor treatment provide new avenues to systematically control the interface of the cathode materials in LIBs that are not possible by conventional coating methods.

(Invited) Interfacial Engineering of Battery Materials Using Atomic Layer Deposition

In batteries, like all electrochemical systems, interfacial phenomena play a critical role in thermodynamic stability, charge transfer kinetics, and ionic transport phenomena. For example, in Li-ion batteries, the solid-electrolyte interphase (SEI) layer enables stabilization of liquid electrolytes against continual electrolyte decomposition. In solid-state batteries, the dynamic morphological evolution of the interface results in unique electro-chemo-mechanical properties, which dictate performance, degradation, and ultimate failure.As a result of these coupled phenomena, there is a continued need to improve both our fundamental understanding of interfacial dynamics, as well as new strategies to engineer rationally-controlled interfaces. Among the various interfacial engineering methodologies, atomic layer deposition (ALD) has risen in interest in recent years, owing to its unparalleled ability to impart atomically-precise control of surface composition and structure, while maintaining conformal coating of ultra-high aspect ratio structures.In this talk, I will describe recent progress in applying ALD for battery applications. In the field of Li-ion batteries, I will show how deposition of a single-ion conducting solid electrolyte on the surface of graphite anodes can eliminate electrolyte decomposition and SEI formation, resulting in a four-fold decrease in interfacial resistance [1]. This results in lower cell polarization during fast charging, eliminating deleterious Li plating on the anode. In the field of Li metal batteries, I will also show how ALD coatings can influence nucleation and growth, resulting in improved Coulombic efficiency [2]. Finally, I will describe efforts towards incorporation of ALD films into solid-state batteries, where mechanical properties play a critical role [3-4].[1] E. Kazyak, K.-H. Chen, Y. Chen, T. H. Cho, N. P. Dasgupta, Adv. Energy Mater. 12, 2102618 (2022).[2] K.-H. Chen, A. J. Sanchez, E. Kazyak, A. L. Davis, N. P. Dasgupta, Adv. Energy Mater. 9, 1802534 (2019).[3] A. L. Davis, R. Garcia-Mendez, K. N. Wood, E. Kazyak, K.-H. Chen, G. Teeter, J. Sakamoto, N. P. Dasgupta, J. Mater. Chem. A 8, 6291 (2020)[4] E. Kazyak, M. Shin, W. S. LePage, T. H. Cho, N. P. Dasgupta, Chem. Commun. 56, 15537 (2020).

(Invited) ALD Coatings for Li-Ion Battery and All-Solid-State Battery Applications

Lithium-ion batteries (LIBs) are essential for modern life, and their improvement is crucial for the more widespread adoption of electric vehicles.[1] Layered lithium transition metal oxides, such as LiNixCoyMnzO2 (often referred to as NCM or NMC), are among the most widely used cathode active materials (CAMs) for automotive applications, owing to their technological maturity and high energy density. However, they typically require a surface coating for stabilizing interfaces, both in liquid-electrolyte based LIBs and in solid-state battery (SSB) environments. For the preparation of protective CAM coatings, atomic layer deposition (ALD) stands out with its ability to produce conformal films on complex substrates.This presentation encompasses several examples of successful improvements in cycling performance of Ni-rich NCM CAMs in LIBs and SSBs by ALD of binary oxides. The low-temperature deposition of AlxOy onto ready-to-use cathode sheets will be discussed.[2] ALD or ALD-related surface protection enables increased stability by suppressing detrimental surface corrosion and metal leaching (side reactions) in LIBs.[2,3] Moreover, we report about the application of ALD coatings to Ni-rich NCM CAMs in SSBs with lithium thiophosphate solid electrolytes. Specifically, the effect that both HfO2 and ZrO2 have on the cell cyclability will be shown, with emphasis placed on the role of post annealing.[4] [1] Goodenough et al. J. Am. Chem. Soc. 2013, 135, 1167.[2] Neudeck et al. Sci. Rep. 2019, 9, 5328.[3] Neudeck et al. Chem. Commun. 2019, 55, 2174.[4] Kitsche et al. ACS Appl. Energy Mater. 2021, 4, 7338.

Atomic Layer Deposition of ZnO on the 3D Porous Ni(OH)2 Nanostructure for Supercapacitor Applications

Atomic Layer Deposition (ALD) is a unique vapor-phase non-line-of-sight deposition process, it can provide excellent control over the wall thickness of nanostructures at the sub-angstrom scale and can be used to create highly conformal coatings of dense inorganic film even on the nano-sized templates with high aspect ratios. Due to these inherent merits, it has become an inevitable process in current semiconductor industries. Following the success of ALD in the semiconductor industries, ALD is recently focused because it can efficiently enhance the performance of energy conversion and storage devices.As a representative example, electrochemical supercapacitors, as one type of novel power device, have attracted universal research interest because of their great potential to be applied in many fields. In particular, pseudocapacitor is recently focused due to its larger capacitance. The electrochemical energy conversion and storage performance of pseudocapacitors depends strongly on the intrinsic properties of the active electrode materials and their surface area. To maximize these performance, various nano-morphologies and transition metal oxides/hydroxides, such as NiO, Co3O4, MnO2, Ni(OH)2 and etc., having a large theoretical capacitance has been extensively investigated. Those psuedocapacitor materials, however, generally showed a high electrical resistivity and it remain unable to achieve high theoretical capacitance in practical applications.To solve these drawbacks, ultrathin conductive ALD coatings can be considered. As a representative example, we design and fabricate a novel hybrid 3D Ni(OH)2@ZnO nanostructured electrode material with a high surface area and high conductivity using a hydrothermal method and ALD. ALD-ZnO thin films were deposited on the surface of a 3D porous Ni(OH)2 nanostructure. The optimization of ALD-ZnO was performed to achieve a high conductivity and electrochemical performance. And, it was exhibited that this hybrid 3D core-shell structure, which benefits from the synergistic effects of both Ni(OH)2 and ZnO, can result in a much improved supercapacitor performance.

The Role of Al2O3 ALD Coating on Sn‐Based Intermetallic Anodes for Rate Capability and Long‐Term Cycling in Lithium‐Ion Batteries

AbstractThe electrochemical performances of CoSn2 and Ni3Sn4 as potential anode materials in lithium‐ion batteries (LIBs) are investigated using varying thicknesses of an alumina layer deposited by the atomic layer deposition (ALD) technique. Rate capability results showed that at high current densities, Al2O3‐coated CoSn2 and Ni3Sn4 electrodes after 10‐ALD cycles outperformed uncoated materials. The charge capacities of coated CoSn2 and Ni3Sn4 electrodes are 571 and 134 mAh g−1, respectively, at a high current density of 5 A g−1, while the capacities of uncoated electrodes are 363 and 11 mAh g−1. When the current density is reduced to 1 A g−1, however, the cycling performances of Al2O3‐coated CoSn2 and Ni3Sn4 electrodes fade faster after almost 40 cycles than uncoated electrodes. The explanation is found in the composition of the solid‐electrolyte interface (SEI), which strongly depends on the current rate. Thus, X‐ray photoelectron spectroscopy analysis of SEI layers on coated samples cycles at a low current density of 0.1 Ag−1, revealed organic carbonates as major products, which probably have a low ionic conductivity. In contrast, the SEI of coated materials cycled at 5 Ag−1 consists mostly of mixed inorganic/organic fluorine‐rich Al‐F and C‐F species facilitating a higher ionic transport, which improves electrochemical performance.

Measuring Local Atomic Structure Variations through the Depth of Ultrathin (&lt;20 nm) ALD Aluminum Oxide: Implications for Lithium-Ion Batteries

Understanding the atomic structure of ultrathin (<20 nm) atomic layer deposition (ALD) coatings is critical to establish structure–property relationships and accelerate the application of ALD films to stabilize battery interfaces. Previous studies have measured the atomic structure of nanoscale ALD films using cryogenic electron diffraction with a large (∼200 nm) beam diameter. However, for ultrathin ALD coatings, these measurements provide only ensemble average structural information and cannot be used to directly measure differences in atomic structure through the depth of the ALD film. In this study, we localize the electron beam to a small (∼5 nm) spot size using cryogenic scanning transmission electron microscope (STEM), and we collect electron diffraction data at multiple points along the depth of a 12 nm thick ALD AlOx film deposited onto a carbon nanotube (CNT) substrate without a contribution from the substrate. We couple these diffraction measurements with pair distribution function (PDF) analysis and iterative reverse Monte Carlo-molecular statics (RMC-MS) modeling to compare atomic structure metrics at different positions in the film depth. We interpret the modeling results considering the three-dimensional (3D) concentric cylindrical sample geometry of a CNT with uniform AlOx coating. These measurements confirm a two-phase bulk/interface structural model proposed previously for ALD AlOx and indicate that the interfacial layer at the CNT–AlOx interface is 2.5 nm thick─5 times larger than previously reported. This report demonstrates direct measurement of atomic structural variations across nanoscale material interfaces that is of broad interest for electrochemical applications and will help inform the use of ALD coatings to stabilize lithium-ion battery interfaces.

Atomic Layer Deposition Coating on the Surface of Active Pharmaceutical Ingredients to Reduce Surface Charge Build-Up.

Active pharmaceutical ingredients (APIs) typically consist of solid therapeutic particles that may acquire electrostatic charge during milling and grinding operations. This may result in the agglomeration of particles, thereby reducing the flowability and affecting the homogeneity of the drug formulation. Electrostatic charge build-up may also lead to fire explosions. To avoid charge build-up, APIs are often coated with polymers. In this paper, atomic layer deposition (ALD) using metal oxides such as Al2O3 and TiO2 on APIs, namely, palbociclib and pazopanib HCl, has been utilized to demonstrate a uniform coating that results in a significant reduction in the surface charge of the drug particles. Kelvin probe force microscopy (KPFM) shows a 4-fold decrease in the surface contact potential of uncoated pazopanib HCl (2.3 V) to 0.52 and 0.82 V in TiO2-and Al2O3-coated APIs, respectively. Also, the ζ potential indicated a 4-fold decrease in the surface charge on coating pazopanib HCl, i.e., from -32.9 mV to -7.51 and -8.51 mV in Al2O3 and TiO2, respectively. Surface morphology, thermal stability, dissolution studies, and cytotoxicity of the drug particles after coating were also examined. Thermal analysis indicated no change in the melting temperature (Tm) after coating. ALD coating was found to be uniform and conformal as observed in images obtained from scanning electron microscopy (SEM) and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS). The rate of dissolution was found to be delayed by the coating, and thus ALD offers slower drug release. Coating APIs with TiO2 and Al2O3 did not induce statistically significant cytotoxicity compared to the uncoated samples. The results presented in this study demonstrate that ALD coating can be used to reduce surface charge build-up and enhance the bulk properties of the drug particles without affecting their physicochemical properties.

Ultralong Lifespan for High-Voltage LiCoO2 Enabled by In Situ Reconstruction of an Atomic Layer Deposition Coating Layer

Although the rapid development of electrical energy storage devices has slowed down environmental pollution, their large-scale application has posed huge challenges to battery-related mineral resources; thus, extending the lifespan of high-voltage lithium cobalt oxide (LCO) is of great importance. Surface oxide coating is considered as the most common low-cost modification method for addressing unstable cycling performance. However, studies have shown that the oxide layer would further react with an electrolyte, while the investigation on the corresponding component evolution is lacking. Herein, a typical example utilizing the above reaction to realize surface reconstruction is presented. Applying atomic layer deposition (ALD), originally, an ultrathin Al2O3 layer is coated on the LCO surface; however, this coating layer has undergone reconstruction after reacting with electrolyte decomposition products during the cycling. Compared with simple coating, the in situ formed Li3AlF6 layer has a tighter binding to the LCO surface while possessing good Li+ conductivity and electrochemical stability. In addition, the unique properties of the ALD technology allow us to achieve ultrathin (1 nm) and conformal coating, which is beneficial for electronic conductivity and cycling stability. Furthermore, the surface phase transition layer stripping failure mechanism has first been revealed to explain the loss of Co and O, while the reconstructed Li3AlF6 effectively suppresses the surface stripping. Thus, excellent high-voltage performance has been realized (an 89% capacity retention after 1000 cycles at 4.5 V and an 88% capacity retention after 200 cycles at 4.6 V). This work casts a new understanding on the surface reconstruction of the oxide coating layer, which is also significant for other electrode materials' modification.

Antibacterial and Osteogenic Properties of Ag Nanoparticles and Ag/TiO2 Nanostructures Prepared by Atomic Layer Deposition.

The combination of titania nanofilms and silver nanoparticles (NPs) is a very promising material, with antibacterial and osseointegration-induced properties for titanium implant coatings. In this work, we successfully prepared TiO2 nanolayer/Ag NP structures on titanium disks using atomic layer deposition (ALD). The samples were studied by scanning electron microscopy (SEM), X-ray diffraction, X-ray photoelectron spectroscopy (XPS), contact angle measurements, and SEM-EDS. Antibacterial activity was tested against Staphylococcus aureus. The in vitro cytological response of MG-63 osteosarcoma and human fetal mesenchymal stem cells (FetMSCs) was examined using SEM study of their morphology, MTT test of viability and differentiation using alkaline phosphatase and osteopontin with and without medium-induced differentiation in the osteogenic direction. The samples with TiO2 nanolayers, Ag NPs, and a TiO2/Ag combination showed high antibacterial activity, differentiation in the osteogenic direction, and non-cytotoxicity. The medium for differentiation significantly improved osteogenic differentiation, but the ALD coatings also stimulated differentiation in the absence of the medium. The TiO2/Ag samples showed the best antibacterial ability and differentiation in the osteogenic direction, indicating the success of the combining of TiO2 and Ag to produce a multifunctional biocompatible and bactericidal material.

Impact of ultrathin coating layer on lithium-ion intercalation into particles for lithium-ion batteries

Ultrathin film coatings on battery materials via atomic layer deposition (ALD) have been demonstrated as an efficient technology for battery performance enhancement. However, the fundamental understanding on lithium intercalation into active materials through the interface between the coating and active materials is unclear, which makes it difficult to optimize ALD coating strategies. Further, like most active materials, a coating layer can undergo volume change during the intercalation process, which can produce detrimental structural changes and mechanical failure of the layer. In this work, first-principles calculations are conducted to reveal the behavior of a coating layer on an active material particle by focusing on the intercalation energy variation, lithium-ion transport, electron chemical potential change, and structural changes of the coating layer. The analysis comprehensively explains an experimental observation that a CeO2 coating on LiMn2O4 particles exhibits better performance in capacity and cycling than an Al2O3 coating on the same particles. The fundamental knowledge imparted from this work provides an important understanding about the beneficial role of ALD coatings in lithium-ion battery performance and capacity retention.

AlF3-Al2O3 ALD Thin-Film-Coated Li1.2Mn0.54Co0.13Ni0.13O2 Particles for Lithium-Ion Batteries: Long-Term Protection.

Improving the performance of existing cathode materials of lithium-ion batteries (LIBs) through surface modification has been proven to be an effective way to improve the performance of LIBs. However, it is a challenge to use a traditional method to prepare an effective coating film, which meets the requirements of uniformity, continuity, electrochemical stability, and strong mechanical properties. In this study, an ultrathin AlF3-Al2O3 film was coated on the surface of Li1.2Mn0.54Co0.13Ni0.13O2 (LRNMC) particles by atomic layer deposition (ALD) in a fluidized bed reactor. A cathode electrolyte interphase layer mainly composed of inorganic components was formed on the surface of AlF3-Al2O3-coated LRNMC during the charge/discharge cycling process, which led to the enhancement of capacity and cycling stability. In addition, the coating layer significantly increased the shelf life of the cathode particles. For LRNMC particles with one cycle of Al2O3 ALD and one cycle of AlF3 ALD coatings, there was no obvious degradation of electrochemical performance after being stored for more than 1 year, indicating long-term protection of ALD films for LIB cathode particles.