Modeling Additively Manufactured Electrodes to Assess Device-Level Performance in Lithium-Ion Batteries

Last developments in polymers for wearable energy storage devices

Lithium-ion Batteries Fabricated Entirely with Additive Manufacturing Craig Milroy1,2, Tim Phillips1, Abhimanyu Bhat1,3, David Bourell1, Joseph Beaman1 1Department of Mechanical Engineering, University of Texas, Austin; 2Texas Research Institute, Austin; 3Evonik/Structured Polymers, Inc.There is an immediate need for disruptive battery manufacturing technologies that enable novel architectures and improve energy density by reducing packaging, interconnect, and integration requirements. Most conventional batteries are packaged in rigid metal containers with a restricted range of cell geometries and form factors; this poses major challenges for minimizing footprint and integrating batteries into small spaces. Additive manufacturing (AM) methods fabricate parts layer-by-layer by precisely assembling materials according to digitized instructions, and offer a means for simplified, top-down battery production, which provides enormous freedom to create innovative two-dimensional (2D) and 3D electrode architectural designs, customize battery form factor, and enable on-demand manufacturing. As such, AM offers a paradigm shift in electrochemical device design and manufacturing to accommodate novel geometries, improve energy density, and reduce costs. However, AM is still an emerging field, and while there have been numerous reports describing the use of AM techniques to produce components for batteries and supercapacitors, the vast majority of these efforts have focused on single components (typically the electrodes), rather than on complete systems comprising printed electrodes, separators, and cases.In this presentation, we describe methods to fabricate all necessary components of coin and pouch cells for functional prototype lithium-ion (Li-ion) batteries, using a variety of AM techniques. For example, functional graphite anodes, and cathodes based on nickel-manganese-cobalt oxide (NMC) and lithium iron phosphate (LFP), were fabricated with pneumatic extrusion, screen printing, and selective laser sintering (SLS); polymeric separators were fabricated with SLS; cases/enclosures were fabricated with SLS and direct metal laser sintering (DMLS), and metal components (e.g., foils and tabs) were fabricated with DMLS.We also utilized AM as a rapid-prototyping tool to implement novel component design approaches that improve battery performance, for example:(1) we identified improved electrode configurations by fabricating a wide range of free-standing anodes and cathodes (i.e., electrodes that do not contain or require a metal current collector) using a range of SLS fabrication parameters, then quantified the internal electrode structure/porosity with X-ray computed tomography (XCT) analyses, and used the XCT data to investigate the relationship between AM build parameters and electrochemical performance;(2) we fabricated separators with SLS using a variety of materials (i.e., polypropylene, aluminum oxide, polypropylene-polyethylene copolymer, polyether ether ketone (PEEK), polyester, and blends of these materials). SLS is well-suited to producing porous films, since spherical particles can be lightly melted to create a continuous object with ample void space, minimal membrane thickness, and maximum planar uniformity by preconditioning the printing powders (to prevent clumping), and using a machined build-plate to limit powder depth.The cycle performance of NMC-based cathodes fabricated with extrusion/direct-write and screen-printing was essentially identical to tape-cast (control) cathodes; however, the extrusion-printed cathodes exhibited more pronounced capacity-fade, and there was evidence of electrode-maturation processes, indicating the need for further optimization. The electrochemical performance of LFP-based cathodes fabricated with SLS was found to depend strongly on build setpoints and discharge rate, but exhibited robust extended cycle performance for > 300 cycles.The capacity of graphite-based anodes increased steadily over the first ~20 cycles, and strongly depended on post-SLS processing methods and the charge/discharge rate. We attribute this to the properties of the binder used in the SLS process, and to electrode maturation processes.Printed separators were tested with either tape-cast NMC-based cathodes or additively manufactured anodes/cathodes, and were cycled continuously at rates between C/5 and 2C. Specific capacity was stable and consistent at all rates, and remained above 100 mAh g-1 with no observable capacity fade for any of the rates below 2C. Extended cycling at C/1.5 stable (or even increasing) capacity for approximately 85 cycles, at which point slight capacity fade began.We evaluated the cooperative functionality of printed components (i.e., printed electrodes and separators) in both half-cell and full cell configurations (this work is ongoing). Cells containing an SLS-fabricated separator and a screen-printed NMC cathode charged at C/10 and discharged at C/5 delivered reversible capacity ~160 mAh g-1 for 100 cycles.We will also present ongoing work that uses additive manufacturing to produce flexible batteries and batteries with conformal form-factors. Figure 1

The growing demand for electric vehicles and portable electronics has created a significant interest in the scalability, recyclability, and economics of both traditional and emerging battery technologies. Although lithium-ion batteries (LiB) are approaching their theoretical energy density, they will remain a widespread and promising technology as alternative (e.g., Li-metal) chemistries and solid-state architectures are still in relatively early stages of commercial scale-up. Yet, LiB performance can be improved by redesigning the cell geometry to move from planar to 3D designs. 3D designs enable the use of thick electrodes to increase the cell level energy density by minimizing the volume and mass contributions of inactive components, such as current collectors or separators. The rationale for 3D full cell designs lies in the relationship between electrode geometry and the respective energy and power densities. When compared to a planar design, 3D architectures allow for a higher surface area for the same volume and footprint of cell. As a result, a given volume of active material can be distributed with a lower electrode feature thickness. Compared to a planar electrode of a given energy density, the lower thickness contributes to a quadratic improvement in power density which decouples the inherent tradeoff between the energy density and power density that is experienced by planar cells. This suggests that a high aspect ratio 3D cell would give greater power per footprint area while retaining high areal energy density. To meet these criteria, the materials used in fabricating 3D cells must be processable in a manner enabling precise control over geometry, layer conformality and porosity.We are developing thick 3D “honeycomb” full cells by starting with patterned, vertically aligned carbon nanotubes (VA-CNTs) as current collectors. CNTs are widely known to have high thermal and electrical conductivities, and to be mechanically durable; properties which make them an ideal scaffold for 3D cell development. VA-CNTs (“forests”) form by self-organization of CNTs during chemical vapor deposition (CVD) on substrates using common hydrocarbon sources (e.g., C2H2, C2H4). However, well-established CNT growth techniques utilize rigid non-conductive substrates, such as silicon wafers, which necessitates a transfer to a suitable substrate for electrochemical applications. Recently, we translated insights from CNT growth on silicon wafer substrates to grow CNT forests on thin metal foils (Cu) suitable for electrode fabrication. We did this by optimizing the moisture level within the CVD furnace, and using a thin-film stack that forms high-density nanoparticles upon annealing while preventing the poisoning of the Fe catalyst by diffusion of Cu. The resulting CNT forests can reach thicknesses over 350 μm and can be grown from patterned catalyst films having regular hole arrays with feature sizes as small as ~5 μm.Thick composite electrodes are then created by coating CNT forests with Si thin films by CVD. The inherent nanoporosity of the CNT forests (>95%) allows for precursor diffusion into the entirety of the forest cross-section and conformal coating of the individual CNTs. The CVD process is tuned to create dense electrodes with tailored Si loading that can range from ~10 to ~90 at.%. Half-cells using monolithic and honeycomb patterned Si-CNT electrodes (~250 μm tall), Li-metal foil, and a liquid electrolyte/separator combination have been cycled over a range of current densities, demonstrating the electronic connection between the deposited Si and Cu foil via the aligned CNTs. At low current densities and high Si loadings these honeycomb electrodes can exhibit large gravimetric (~1500 mAh/gSi) and areal (~12 mAh/cm2) capacities, with honeycomb Si-CNT composites exhibiting reduced capacity fading when compared to non-patterned electrodes.We continue by investigating these Si-CNT composites as a template for a 3D full cell design. In literature, the difficulty of producing 3D full cells comes from the need to produce high conformality electrolyte films that are pinhole free and which demonstrate sufficient ionic conductivity. To address this issue, we utilize an initiated chemical vapor deposition (iCVD) process to deposit conformal poly(hydroxyethyl methacrylate-co-ethylene glycol diacrylate) thin films on the high aspect ratio CNT forests. These copolymer films are doped with lithium salts to exhibit ionic conductivities on the order of ~10-6 to 10-5 S/cm, which is among the highest conductivities ever exhibited by conformal electrolyte technologies. To complete a full cell design, a slurry-based cathode will be infiltrated into the iCVD coated Si-CNT composite electrodes, from which we aim to assess the cycling behavior and compare the areal energy and power densities of non-patterned and honeycomb architectures.

The Electrochemical Society Interface • Spring 2016 • www.electrochem.org 61 A lthough there has been tremendous growth in the capabilities of additive manufacturing in recent years, its roots go back hundreds of years. In many ways, some of the first electrochemists were also the first practitioners of additive manufacturing when they demonstrated that a low cost base metal could be coated with a premium finish in a conformal manner at room temperature in minutes. The first electrodeposition experiments date back over 200 years when Luigi Valentino Brugnatelli first electrodeposited gold upon silver, at first for academic experiments, and then for commercial application. Since that time, scaled commercial applications of electrodeposition have been critical to many aspects of science and engineering. More recently, the emergence of affordable, commercially-available 3D printers capable of depositing electrically insulating media via extrusion printing and additive photocuring methods have offered a wonderful complement to traditional electrodeposition, enabling both rapid prototyping and precise, high-throughput freeform manufacturing. In this issue of Interface we explore some of the benefits and opportunities that modern additive manufacturing methods offer for the practice of electrochemical analysis, engineering, and energy storage. In the first paper of this issue, Robert B. Channon, Maxim B. Joseph and Julie V. Macpherson, demonstrate the use of low cost additive manufacturing based on stereolithography, to create (micro) fluidic flow cells at scales that are either difficult or impossible to achieve with traditional methods. The ability to create high resolution, customized flow cells allows researchers to study fluid transport and electrochemical phenomena, as well as enabling highly accurate electroanalytical sensing with small analyte volumes and high throughput for a wide range of applications. With the methods described in this section, (micro)fluidic analysis systems can go from a sketch to a practical system within an afternoon, and that same device can be effortlessly replicated with slight variations in device geometry to create an array of parallel experiments. Trevor Braun and Dan Schwartz provide an article exploring the intersection of freeform patterning and electrodeposition with the use of software reconfigurable scanning electrodeposition cells. In traditional electrodeposition, the volume of the electrolyte is far larger than that of the deposited materials. This article shows that when the ratio is inverted, the small electrolyte volume can be used to direct growth and structure in exceptional ways without the limitations of traditional maskor stamp-based patterning techniques. Another exciting development that is discussed in this article is the use of bipolar electrochemistry to perform localized freeform electrodeposition without an electrical contact to the substrate, a development that greatly expands the utility and throughput of electrodeposition-based additive manufacturing. The final paper by Corrie Cobb and Christine Ho demonstrates how additive manufacturing and rapid prototyping methods can improve the performance and the range of applications of electrochemical energy storage. Given the particle/composite structure of most secondary storage devices, the materials selection available is largely the same as those for traditional batteries. A device designer, using the methods described here, can embed a battery optimized not only between power and energy density, but also between conformable, flexible, and stretchable factors. Critical to this new paradigm in product design is a deep level of interaction between the design of the battery, powertrain, and the device itself. With modern rapid prototyping methods, all three components can be iteratively edited and optimized with unprecedented speed. Beyond device integration, these new manufacturing methods for batteries may improve batteries for traditional applications: Rational integration of separator and electrode can allow for thicker electrodes at a given power density, improving cost per unit energy and energy density at a system level. Taken together, these three pieces provide an excellent overview of how recent advances in electrochemical engineering and electroanalytical tools can be merged with modern prototyping tools to create new opportunities for sensing, device production, and electrochemical energy storage. However, we believe that these examples are only the tip of the iceberg, and that the integration of electrochemical engineering and additive manufacturing will only accelerate in the years to come. While these articles are not meant to be comprehensive reviews of additive manufacturing, we hope that they inspire Interface readers to learn more about these powerful new tools and invent novel ways that additive manufacturing can advance electrochemistry, and that electrochemistry can advance additive manufacturing. Electrochemical engineering, the first in additive manufacturing and rapid prototyping, still has much to contribute to this growing field. In the spirit of access knowledge sharing, DS has recently created a website (echem.io) where users can share (via GitHub) 3D cad design files and other open source hardware and software tools that were generated as a part of electrochemistry-focused research and development efforts. We hope you check it out!

Microstrip patch antennas (MPAs) are compact and easy-to-fabricate antennas, widely used in long-distance communications. MPAs are commonly fabricated using subtractive methods such as photolithographic etching of metals previously deposited using sputtering or evaporation. Despite being an established technique, subtractive manufacturing requires various process steps and generates material waste. Additive manufacturing (AM) techniques instead allow optimal use of material, besides enabling rapid prototyping. AM methods are thus especially interesting for the fabrication of electronic components such as MPAs. AM methods include both 2D and 3D techniques, which can also be combined to embed components within 3D-printed enclosures, protecting them from hazards and/or developing haptic interfaces. In this work, we exploit the combination of 2D and 3D printing AM techniques to realize three MPA configurations: flat, curved (at 45∘), and embedded. First, the MPAs were designed and simulated at 2.3 GHz with a −16.25 dB S 11 value. Then, the MPA dielectric substrate was 3D-printed using polylactic acid via fused deposition modeling, while the antenna material (conductive silver ink) was deposited using three different AM methods: screen printing, water transfer, and syringe-based injection. The fabricated MPAs were fully operational between 2.2–2.4 GHz, with the flat MPA having a higher S 11 peak value compared to the curved and embedded MPAs. Development of such AM MPAs in various configurations demonstrated in this work can enable rapid development of long-range antennas for novel applications in e.g. aerospace and Internet of Things sectors.

Shakedown-reliability based fatigue strength prediction of parts fabricated by directed energy deposition considering the microstructural inhomogeneities

Although a significant amount of technical, commercial, and academic resources have been invested in laser and electron beam-based additive manufacturing (AM) of metals and alloys over several decades, challenges and limitations associated with repeated local melting and processing complexity along with the cost of equipment and operation have sparked interest in research on solid-state AM methods as an alternative. This paper reviews the capabilities and challenges of major solid-state metal AM techniques by dividing it into two broad categories (plastic deformation based and sinter based) depending on the metallurgical bonding mechanisms, range of processible alloys, and resulting microstructures. The limited and recent data available in literature show that, while deformation-based AM techniques are primarily limited to relatively ductile alloys, a larger variety of materials are suitable for manufacturing through sinter-based AM. Deformation-based methods generally refine the microstructure by recrystallization, while in most cases sinter-based AM methods lead to grain growth due to high-temperature processing and a more isotropic microstructure. Among the solid-state AM methods summarized here, the binder jetting and additive friction stir AM methods stand out with isotropic microstructures and mechanical properties close to the wrought properties.

Biomaterials are in high demand due to the increasing geriatric population and a high prevalence of cardiovascular and orthopedic disorders. The combination of additive manufacturing (AM) and biomaterials is promising, especially towards patient-specific applications. With AM, unique and complex structures can be manufactured. Furthermore, the direct link to computer-aided design and digital scans allows for a direct replicable product. However, the appropriate selection of biomaterials and corresponding AM methods can be challenging but is a key factor for success. This article provides a concise material selection guide for the AM biomedical field. After providing a general description of biomaterial classes—biotolerant, bioinert, bioactive, and biodegradable—we give an overview of common ceramic, polymeric, and metallic biomaterials that can be produced by AM and review their biomedical and mechanical properties. As the field of load-bearing metallic implants experiences rapid growth, we dedicate a large portion of this review to this field and portray interesting future research directions. This article provides a general overview of the field, but it also provides possibilities for deepening the knowledge in specific aspects as it comprises comprehensive tables including materials, applications, AM techniques, and references.

Additive manufacturing (AM) is a rapidly developing technique which presents both substantial opportunities and challenges for manufacturing industry. However, the internal defects will influence the mechanical behavior of AM structures, and thus characterization of the defects of AM materials becomes an interesting issue. In this study, a non-destructive testing technique for AM structures is proposed based on the reflective coherent gradient sensing (CGS) method. Using this method, the slope of a reflective surface can be measured accurately. In the study, the measured structure is firstly prepared a reflective film using replication technique, and then is exerted an external load. The full filed slope of the structure can be measured using CGS and will show a turbulence which can be used to determine the location of the defects of structure (pores or cracks). Using this technique, the spatial resolution of defect size can reach 200μm. From the experimental results, the method shows the merits of full-field, non-contact and real-time measurement. The successful experimental results show that reflective CGS method is effective for detecting the internal defects of AM structures, and will have a good prospect of further application.

Analytical and experimental investigation on elastic modulus of reinforced additive manufactured structure

The development of advanced electrode materials is crucial for improving lithium-ion batteries (LIBs), which are increasingly in demand for portable electronics, electric vehicles, and grid storage applications. Traditional electrode fabrication methods often rely on the use of harmful solvents (such as the commonly used NMP), which increases energy consumption, can pose environmental challenges, and at times limit the performance of the electrodes. The use of additive manufacturing (AM) techniques such as direct ink writing (DIW), fused filament fabrication (FFF), and inkjet printing (IJP) has gained significant interest recently due to their potential to fabricate complex, customizable structures without the need for solvents. Yet that potential has not been reached and currently these 3D printing approaches still rely on solvents. A solventless approach can lead to greener manufacturing processes, a decrease in production cost, and the enhancement of electrode performance through precise control over material architecture.Previous studies have explored the potential of additive manufacturing in fabricating electrodes for LIBs, demonstrating the capability to produce three-dimensional structures that maximize the surface area and facilitate efficient ion transport. These materials have shown comparable or superior performance to traditionally fabricated electrodes, with enhanced cycling stability and improved rate capability. These improvements are attributed to the optimized microstructure and better material utilization, which are achievable through precise control over the additive manufacturing process. Other studies have proven the feasibility of solventless fabrication of electrodes by yielding similar results while also saving on costs by cutting down on energy consumption. However, little to no work exists combining the complete elimination of solvents and the AM process. In this work, we employ advanced additive manufacturing techniques to fabricate solventless electrodes for lithium-ion batteries, followed by comprehensive electrical and performance testing to evaluate the cells' efficiency, capacity, and long-term stability. By optimizing the composition and structure of the electrode materials, we aim to enhance these electrochemical. Electrochemical and particle characterization has revealed that solventless electrodes fabricated through optimized additive manufacturing exhibit different microstructures than those of the conventional slurry casted electrodes. Parameters such as printing fidelity, layer thickness, and active material composition can be varied to study their effects on the mechanical, thermodynamic, and electrochemical properties of the electrodes. Using these insights, the next generation of rechargeable batteries can be built with the ability to control design not only making them more efficient, but more applicable.This work aims to investigate a possible method of additive manufacturing that can be used in conjunction with the fabrication of a solventless electrode for lithium-ion batteries. The findings will contribute to the development of greener, more efficient energy storage devices with tailored performance characteristics for a wide range of applications.

The development of advanced electrode materials is crucial for improving lithium-ion batteries (LIBs), which are increasingly in demand for portable electronics, electric vehicles, and grid storage applications. Traditional electrode fabrication methods often rely on the use of solvents (such as the commonly used NMP), which increases energy consumption, can pose environmental challenges, and limit the performance of the electrodes. The use of additive manufacturing (AM) techniques such as direct ink writing (DIW), fused filament fabrication (FFF), and inkjet printing (IJP) has gained significant interest due to their potential to fabricate complex, customizable structures without the need for solvents. Yet that potential has not been reached and currently these 3D printing approaches still rely on solvents. A solventless approach can lead to greener manufacturing processes, a decrease in production cost, and the enhancement of electrode performance through precise control over material architecture.Previous studies have explored the potential of additive manufacturing in fabricating electrodes for LIBs, demonstrating the capability to produce three-dimensional structures that maximize the surface area and facilitate efficient ion transport. These materials have shown comparable or superior performance to traditionally fabricated electrodes, with enhanced cycling stability and improved rate capability. These improvements are attributed to the optimized microstructure and better material utilization, which are achievable through precise control over the additive manufacturing process. Other studies have proven the feasibility of solventless fabrication of electrodes by yielding similar results with the additional benefit of saving costs by cutting down on energy consumption. However, little to no work exists combining the complete elimination of solvents and the AM process. In this work, we will employ advanced additive manufacturing techniques to fabricate solventless electrodes for lithium-ion batteries. By optimizing the composition and structure of the electrode materials, we aim to enhance the electrochemical properties such as capacity, cycling stability, and rate capability. Electrochemical and particle characterization has revealed that solventless electrodes fabricated through optimized additive manufacturing exhibit different microstructures than those of the conventional slurry casted electrodes. Parameters such as printing fidelity, layer thickness, and active material composition can be varied to study their effects on the mechanical, thermodynamic, and electrochemical properties of the electrodes. Using these insights, the next generation of rechargeable batteries can be built with the ability to control design not only making them more efficient, but more applicable.This work aims to investigate a possible method of additive manufacturing that can be used in conjunction with the fabrication of a solventless electrode for lithium-ion batteries. The findings will contribute to the development of greener, more efficient energy storage devices with tailored performance characteristics for a wide range of applications.

Additive manufacturing (AM) for printed electronics (PE), though still in its infancy, has seen major growth in the past few years. AM techniques have several benefits over traditional manufacturing, namely the reduction of waste material and the increased efficiency in producing prototypes. However, there are disadvantages associated with AM, the most prevalent being a low throughput of parts. Limited research has been done to increase the throughput to the scale of traditional manufacturing methods. To combine the benefits of both AM and traditional manufacturing techniques, this paper discusses a hybrid printed circuit board (PCB) assembly that employs an additively manufactured interposer to serve as a DC interconnect between the AM structure and the PCB manufactured with traditional methods.

This review paper provides insights the into current developments in additive manufacturing (AM) techniques. The comprehensive presentations about AM methods, material properties (i.e., irradiation damage, as-built defects, residual stresses and fatigue fracture), experiments, numerical simulations and standards are discussed as well as their advantages and shortages for the application in the field of nuclear reactor. Meanwhile, some recommendations that need to be focused on are presented to advance the development and application of AM techniques in nuclear reactors. The knowledge included in this paper can serve as a baseline to tailor the limitations, utilize the superiorities and promote the wide feasibilities of the AM techniques for wide application in the field of nuclear reactors.

Structures that are very difficult to produce with classical manufacturing methods have become easily produced with the development of additive manufacturing (AM) technique. AM technique allows creating special infill patterns with gaps in the internal structures of the products to be produced. These special infill patterns ensure that the product has maximum rigidity and strength while also providing minimum mass. For this reason, it is important to investigate the effects of infill patterns produced by AM technique on the mechanical properties of the product. In this study, the compression characteristics of compression test samples produced in five different infill patterns (octet, grid, cubic, quarter cubic, gyroid) using the AM method were experimentally investigated in three different axes. Test samples were produced from PLA material with a 3-dimensional (3D) printer in accordance with the ASTM C365-16 standard. Compression tests were repeated three times at a compression speed of 0.5 mm/min, with five different infill patterns and three different axes for each parameter. According to the results obtained, the octet infill pattern provided the best compressive strength in all three axes. It has been determined that the infill pattern or load axis change greatly affects the compression performance of the product.