The benefits of producing particles with tailored interfaces using the atomic layer deposition (ALD) technique have been widely demonstrated in the field of energy storage. As mobility and portability requirements grow, so does the need for higher energy density materials, higher power density systems, and enhanced lifecycles of devices, all of which create additional stresses at interfaces within energy storage modules such as lithium-ion batteries, fuel cells, and supercapacitors. It is now widely accepted that the interfaces of lithium-ion battery electrode materials can be highly dynamic in nature, and are the source of detrimental effects such as electrolyte decomposition, particle fracturing, crystal phase transformations and other causes of performance fade. The next generation of energy storage devices will be designed and engineered with tailored interfaces, and the cost of ALD on particles has fallen to a price point that is compelling enough to be adopted into product development cycles for mobile and stationary power applications. Here, we will discuss ALD methodologies and best-suited applications in an effort to clarify the most appropriate steps towards the industrialization of an ALD-enabled energy storage future. There are many metrics with which to evaluate the adoption of ALD-enabled particles into any technology, however all can be distilled down to a cost per relevant unit basis. Typically a significant amount of technological input is required from the value chain to formulate the ALD value proposition in an unbiased manner. In the case of energy storage applications, the final product must have a justifiably lower cost per energy unit per charge/discharge cycle, or $/Wh/cycle. For batteries, in order to arrive at the cost savings attributable to tailored interfaces, consideration must be given to the following three stages of ALD development: Discovery and Demonstration - Determining the optimal ALD method and/or chemistry in coin and/or small pouch cells, and validating performance in cells of appropriate size and format for the market segment. Pack/Module Performance – Comparing ALD-enabled battery performance to its base competitor battery Manufacturing Considerations – Quantifying materials, labor and capital costs required to implement the optimized ALD process into a battery manufacturing line and manufacturing risks associated with how the ALD process is implemented Ultimately the scientific and industrial community alike have still only scratched the surface of the ALD-enabled energy storage story. Conventional ALD coatings such as Al 2 O 3 , TiO 2 and ZnO have shown tremendous promise, while next generation coatings that have atomically-precise tailored compositions or morphologies remain under development. Next generation coatings that can deliver higher conductivities suitable for advanced batteries can remove the perceived tradeoff between barrier coatings and performance. ALD is a means to engineer an energy storage future on an atomic level, with the potential for revolutionizing the battery as we know it, and having the potential to significantly impact other energy storage and generation systems.

The benefits of producing tailored interfaces using the atomic layer deposition (ALD) technique have been widely demonstrated in the field of energy storage. As mobility and portability requirements grow, so does the need for higher energy density materials, higher power density systems, and enhanced lifecycles of devices, all of which create additional stresses at interfaces within energy storage modules such as lithium-ion batteries, fuel cells, and supercapacitors. It is now widely accepted that the interfaces of lithium-ion battery electrode materials can be highly dynamic in nature, and are the source of detrimental effects such as electrolyte decomposition, particle fracturing, crystal phase transformations and other causes of performance fade. The next generation of energy storage devices will be designed and engineered with tailored interfaces, and the cost of ALD has fallen to a price point that is compelling enough to be adopted into product development cycles for mobile and stationary power applications. As it pertains to secondary battery technologies, there exist two distinct approaches for how to apply ALD onto cathodes and anodes, namely particle coating and electrode coating. From an electrode-electrolyte interface perspective, the features and benefits of ALD on particles (ALDP) and ALD on Electrodes (ALDE) may appear to be similar, however the implications on when and how these coatings can be industrialized within the value chain are drastically different, resulting in different cost metrics and scaling requirements and accompany different manufacturing risks. Here, we will discuss ALD methodologies and best-suited applications in an effort to clarify the most appropriate steps towards the industrialization of an ALD-enabled energy storage future. There are many metrics with which to evaluate the adoption of ALD into any technology, however all can be distilled down to a cost per relevant unit basis. Typically a significant amount of technological input is required from the value chain to formulate the ALD value proposition in an unbiased manner. In the case of energy storage applications, the final product must have a justifiably lower cost per energy unit per charge/discharge cycle, or $/Wh/cycle. For batteries, in order to arrive at the cost savings attributable to tailored interfaces, consideration must be given to the following three stages of ALD development: Discovery and Demonstration - Determining the optimal ALD method and/or chemistry in coin and/or small pouch cells, and validating performance in cells of appropriate size and format for the market segment. Pack/Module Performance – Comparing ALD-enabled battery performance to its base competitor battery Manufacturing Considerations – Quantifying materials, labor and capital costs required to implement the optimized ALD process into a battery manufacturing line and manufacturing risks associated with how the ALD process is implemented There has been increasing attention placed on whether ALDP or ALDE is ‘better’ from a performance perspective without fully quantifying all facets of performance, what performance benefits are of value to particular applications, and costs and risks to deliver these benefits to the marketplace. It is hypothesized that a majority of this attention stems from the different goals being sought by academic institutions as compared to industrial entities. For example, ALDE experimentation may be better aligned with the objectives of an academic institution or research-based facility whose focus may be discovery/exploration relying on small quantities of material. In such a research based scenario, ALDE facilitates rapid and comparable data collection as one electrode can be sectioned and used for a panel of chemistry/coating conditions which coincides well with early stage “Discovery and Demonstration” above. Conversely, a company seeking to produce and sell batteries will be more focused on “Pack/Module Performance” and “Manufacturing Considerations” as these will determine if a particular technology has a value proposition that can be brought to market. In this particular scenario ALDP would be the best avenue as it lends more readily to the production of commercial scale quantities of material. Ultimately the scientific and industrial community alike have still only scratched the surface of the ALD-enabled energy storage story. Conventional ALD coatings such as Al2O3, TiO2 and ZnO have shown tremendous promise using both ALDP and ALDE approaches, but next generation coatings that have atomically-precise tailored compositions or morphologies are under development that remove the tradeoff between barrier coatings and performance, providing for higher conductivities suitable for advanced batteries. ALD is a means to engineer an energy storage future on an atomic level, with the potential for revolutionizing the battery as we know it, and having the potential to significantly impact other energy storage and generation systems.

It is now widely accepted that both high-end (Gen 3 materials) and low-end (e.g. Gen 1-2 LiCoO2, NCA, NMC, etc.) electrode powders alike can benefit from surface coatings as a means to provide an optimized interfacial transition between the electrode and the electrolyte, independent of type of battery or system. In spite of the significant public and private investment in new battery materials, efforts on those that are under development today still tend to focus on features and attributes of the bulk materials. Significant cost savings can be realized without sacrificing performance by encapsulating today’s materials with coatings tailored to improve the electrode-electrolyte interface. The two primary surface coating technologies that have been studied are Co-Precipitation (CP) and Atomic Layer Deposition (ALD), with results showing significant favor to ALD as shown in Figure 1. ALD coatings, which can be optimized for each system for composition, thickness, and uniformity, have been proven to reduce capacity fade with cycling, improve thermal stability, allow for safe charging to higher voltages, and reduce degradation under high temperature storage. These coatings can also reduce costs by eliminating the need for overbuilding, and be done without affecting capacity or internal resistivity. ALD has found enormous application in the semiconductor industry owing to its conformal sub-nanometer thickness deposition capability, but until recently has been regarded as non-scalable technology for powder materials due to excessive capital cost of processing. Early research on ALD applications for batteries focused on coatings for electrodes with a drive toward roll-to-roll processing. However, through significant effort it has been determined that roll-to-roll processing of battery electrodes via ALD is prohibitively expensive. Particle ALD has been extensively studied as well and shown improved performance of battery materials comparable to electrode-ALD improvements, and in many cases shown even greater performance enhancement. Similar to electrode-ALD coating however, particle-ALD has remained a small scale laboratory-only research tool due to of the inability to scale-up the primary processing technique, which is a vacuum fluidized bed reactor. Even though ALD as a process has been proven to impart significant benefit to batteries materials, the capital cost of commercial scale production has to-date prevented its widespread adoption. To remove the cost barrier of ALD-enabled batteries, PneumatiCoat Technologies (PCT) has developed a semi-continuous high throughput particle-ALD (HTP-ALD) pilot plant which has demonstrated the capability to meet the needs of commercial demand for battery materials with little increase in at-scale cost per kg of battery materials. PCT has refined and validated a pilot-scale high throughput ALD coating system capable of 200kg/day scale, for Li-ion cathode powders that can meet the automotive industry mandate of low add-on cost (at scale). The price point attainable with PCT’s high throughput gas-phase processing is significantly cheaper than even the most generous projections for manufacturing liquid-phase co-precipitation techniques ($3-5/kg) or batch-based ALD systems ($7-10/kg). Equally as important as meeting cost and performance criteria, PCT has demonstrated the semi-continuous technology to be capable of producing materials with a high degree of repeatability, a factor not often found with fluidized bed treatments and lab scale systems. Figure 2 shows a radar plot for 35 sub-batches of material coated using an early prototype of PCT’s original semi-continuous HTP-ALD system. The HTP-ALD pilot plant is also designed for plug-and-play scale-up capability in which simply making components larger or setting up automatic feeding systems will allow for nearly any desired level of production using existing powder processing techniques. With the PCT pilot plant meeting projected cost targets and capability for producing high quality materials at pilot scale, the barriers to commercial scale ALD-enabled batteries have been greatly reduced. Ultimately this technology will allow battery manufacturers to eliminate the embedded costs of overbuilding, and these higher performance materials can be adopted at lower net cost and thereby reduce the cell and pack level $/kWh. Figure 1

Isothermal Water Splitting Solar concentrators can create extremely high temperatures that can drive chemical reactions, including the thermal splitting of water to provide hydrogen. A metal oxide catalyst is needed that is usually cycled between hotter conditions where it is reduced and cooler conditions where it is reoxidized by water. This cycling can limit catalyst lifetime, which can be costly. Muhich et al. (p. 540 ; see the Perspective by Roeb and Sattler ) developed an approach that allowed the redox cycle to be driven isothermally, using pressure swings.

Graphite particles have been coated with Al2O3 via atomic layer deposition. Alumina content was measured via inductively coupled plasma spectrometry (ICP), LECO combustion analysis, and thermogravimetric analysis (TGA). While alumina was present, adherence was limited, and nonconformal films were deposited on the graphite particles. Coatings produced changes in particle interactions and dispersability. These changes were observed via sedimentation rates of particle suspensions in water, Zeta potential values, and particle size distributions. Alumina‐Graphite composites were sintered using coated and uncoated particles. Differences in bulk thermal properties are ascribed to enhanced dispersability of the coated particles in presintered powder mixtures. EDS mapping of the sintered composites confirms the enhanced dispersion of the coated graphite particles. Particle coating through atomic layer deposition provides a means to improve particle dispersion with low material loadings. It has been shown that changes in particle interaction characteristics can be achieved even without uniform and conformal coatings. These particle interaction changes can result in sintered composites with enhanced thermal properties.

There are three primary reactions in the sodium manganese oxide high temperature water splitting cycle. In the first reaction, Mn2O3 is decomposed to MnO at 1,500°C and 50 psig. This reaction occurs in a high temperature solar reactor and has a heat of reaction of 173,212 J/mol. Hydrogen is produced in the next step of this cycle. This step occurs at 700°C and 1 atm in the presence of sodium hydroxide. Finally, water is added in the hydrolysis step, which removes NaOH and regenerates the original reactant, Mn2O3. The high temperature solar-driven step for decomposing Mn2O3 to MnO can be carried out to high conversion without major complication in an inert environment. The second step to produce H2 in the presence of sodium hydroxide is also straightforward and can be completed. The third step, the low temperature step to recover the sodium hydroxide is the most difficult. The amount of energy required to essentially distill water to recover sodium hydroxide is prohibitive and too costly. Methods must be found for lower cost recovery. This report provides information on the use of ZnO as an additive to improve the recovery of sodium hydroxide.

Alumina thin film structures were produced by coating high surface area polymer particles via atomic layer deposition (ALD), using the polymer as a sacrificial template. Burnout of the polymer material left high surface area, high pore volume structures, with 15 nm wall thickness. Further deposition of up to 27 mol% Co and Fe was performed via ALD to produce high surface area CoFe2O4 particles for thermochemical water splitting. The ALD particles were thermally cycled in electrically heated lab reactors and on-sun using a concentrated solar, reflective cavity reactor. Surface area measurements of cycled ALD particles showed improved surface area retention as compared to bulk Fe2O3 nanopowders. Reaction rates as high as 15.2 and 9.8 mu mol/s/g were observed, on-sun, for H2O and CO2 splitting respectively. Thermochemical cycling in a concentrated solar cavity reactor showed an order of magnitude increase in solar utilization efficiency between ALD particles and bulk Fe2O3 nanopowders. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

It is shown that the dissociation of Mn2O3 to MnO in a short residence time aerosol flow reactor can achieve high conversions approaching 75% when the concentration of oxygen is kept below 0.25%. Significant recombination reaction occurs when the oxygen content exceeds ∼0.25% by volume. A dual reaction mechanism for Mn2O3 dissociation was found: RAvrami−Erofeev=−A1e−Ea,1/RTn(1−X)[−ln(1−X)](n−1)/nROrder_of_reaction=−A2e−Ea,2/RT(1−X)n with the transition from one mechanism to the other occurring at an extent of reaction of approximately 0.6. Rate constants for the two mechanisms were calculated to be 1.8×107±1.3×107 and 5.6×103±4.1×103s−1, respectively, for oxygen concentration<0.25%. High levels of dissociation are achievable when the reaction is carried out in an inert gas environment using a reactor configuration that limits the reverse reaction.

The steam-gasification of biochar with concentrated solar radiation is experimentally investigated using a 3 kW solar reactor prototype consisting of a cylindrical cavity-receiver containing an opaque tubular absorber. Particles of beech charcoal are used as the biomass feedstock in a continuous steam-particle flow through the tubular absorber. A reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is formulated and validated by comparing numerically computed and experimentally measured temperatures and carbon conversions. The simulation model is further applied to examine the thermal performance of 100 kW and 1 MW scaled-up solar reactor containing multiple tubular absorbers, yielding a theoretical maximum solar-to-chemical energy conversion efficiency of 39% and 50%, respectively. Major sources of irreversibility are associated with re-radiation losses through the cavity's aperture.