Volume Changes Research Articles

Influence of Mechanical Degradation in Polycrystalline NMC Particles on the Electrochemical Performance of Lithium-Ion Batteries

Lithium-ion batteries (LIBs) have gained widespread popularity for energy storage systems owing to their high coulombic efficiency and energy density. Within the cathode electrode materials of LIBs, the structural integrity of secondary particles, composed of randomly oriented single-crystal primary active particles, is crucial for sustained performance. The fracture of these particles can occur due to both mechanical stress and chemical interactions within the solid. Modeling LIBs presents a multiphysics challenge as it involves addressing the electro-chemo-mechanical phenomena and their interactions across various length scales. During electrochemical cycling, volume changes in active particles induce mechanical stresses, while the mechanical state of the battery influences the diffusion of lithium.This study proposes a numerical modeling framework to investigate the degradation of active material particles and its impact on electrochemical performance. The model integrates mechanical and electrochemical processes, solving nonlinear equations related to surface charge transfer, lithium diffusion, and mechanical stresses. By incorporating phase field damage, the model tracks crack evolution and mechanical failure of active particles. The coupled equations are solved within a finite element framework using COMSOL Multiphysics.Notably, the model offers numerical insights into intergranular and transgranular fracture within secondary active material particles. The infiltration of liquid electrolyte into cracks is identified as a positive effect, reducing electrochemical overpotential by increasing electrochemically active surface area from particle cracking. However, prolonged cycling with particle cracking poses a notable threat to battery performance and capacity. This comprehensive numerical modeling approach provides valuable insights into the intricate interplay of mechanical and electrochemical factors governing LIB performance and degradation.

The Effect of Silicon Nanoparticle Size on Cycle and Calendar Life

Lithium-ion batteries are now ubiquitous in modern electronics, electric vehicles, and many other applications. As the battery industry continues to push for better, longer lasting batteries, many have turned to using a different anode material that would provide higher-energy density and require less frequent charges. While graphite is the tried-and-true anode material for lithium-ion batteries, a silicon anode battery could provide up to ten times higher theoretical energy density than graphite. However, there are a lot of challenges standing in the way between silicon anode batteries and commercialization—the large volume expansion of silicon (around 200-300% expansion, compared to graphite at 10%) and the unstable solid-electrolyte-interface (SEI) of silicon results in anodes that mechanically degrade and calendar age faster than their graphite counterparts.Previous research has demonstrated that plasma-enhanced chemical vapor deposition (PECVD) silicon nanoparticles with a hydrophilic coating such as polyethylene oxide (PEO) results in silicon anodes with good cycle life [1, 2, 3, 4]. In this system, smaller particle sizes typically yielded better cyclability than larger particle sizes, which is contrary to conventional wisdom that more surface area is detrimental as it allows for more SEI formation and side reactions. However, since silicon anodes experience large volume changes during cycling, the surface area might not be the dominant contribution to capacity fade. Larger silicon particles result in larger total expansions of the electrode, which causes more mechanical damage like cracks to form, exposing fresh surface area to electrolyte and SEI formation.This research investigates the performances of PEO-coated PECVD Si electrodes with nanoparticles ranging from 3 to 27 nm in diameter. We measure the cycle life at a rate of 0.333C, as well as the calendar lifetimes of each electrode. We characterize each electrode with SEM imaging, tortuosity measurements, and electrochemical impedance spectroscopy to understand the differences in microstructure that contribute to capacity fade and impedance rise.

Physics-Based State of Health Prediction of Lithium-Ion Battery during Fast Charging

Electrification of the transportation sector and increased use in consumer electronics have driven the increasing demand for lithium-ion batteries (LiBs) (1). Despite their high energy density and long service life, LiBs suffer from capacity degradation due to continuous growth of solid electrolyte interface (SEI) layer and plating of lithium on the anode surface. Graphite, the anode in most LiBs, has a high tendency to catalyze the degradation of the electrolyte consisting of LiPF6 and ethylene carbonate to form an SEI of Li-rich carbonate, phosphate, and fluoride compounds (2, 3). The SEI film grows during service due to the deposition of reaction products and repeated cycles of damage and reformation due to the contraction and expansion associated with volume changes during Li-ion intercalation and deintercalation. Additionally, fast or low-temperature charging of batteries results in lithium plating on the anode surface because the elevated concentration of Li+ on the anode surface results in graphite potential falling below 0V vs. Li+/Li and increased likelihood of Li deposition compared to intercalation (4). Lithium loss due to the side reactions of SEI growth and plating contributes to capacity loss and may increase the likelihood of battery failure. Hence, accurate modeling of the side reactions is required to determine the state of health (SOH) and predict the remaining capacity of LiBs during operation (5).We report an experimentally validated single particle model (SPM) to estimate the influence of SEI growth and Li plating on the capacity changes in Lithium Cobalt Oxide (LCO)/Carbon cells during repeated cycling (6-8). The SPM model idealizes each electrode as a single particle to approximate the cell response. A. Sarkar et al. (5) included the influence of SEI growth, plating, SEI fracture, and temperature in the SPM model to determine the influence of the side reactions on battery performance. The parameters corresponding to side reactions, such as the SEI film growth rate, conductivity of the SEI film, and reversibility of the plating reaction, were determined through comparison of numerical predictions of cell voltage and capacity change with experimental response measured at charging rates of 0.1C and fast charging rate of 2C on PowerStream 35 mAh LCO/C coin cells (Lir2032) as shown in Figure 1. In addition, the coin cells were subjected to charge/discharge experiments at charging rates varying from 0.1C – 5C for 100 cycles. Experimental measurements of the cell capacity changes were compared to model predictions for the different charging rates to validate the modeling assumptions and determine the efficacy of the estimated parameters in describing the cell degradation. The agreement between the model prediction and measured experimental response showed that the single particle model augmented with side reaction mechanisms can describe the cell degradation and is suitable for predicting the remaining capacity and safety of LiBs subjected to a range of charging rates. The model can also predict the accumulation of irreversibly plated lithium on the anode surface during repeated fast charging. The amount of plated lithium determines the severity of dendritic growth, and thus, model predictions of lithium accumulation may be used to estimate the likelihood of battery failure under fast charging conditions. Acknowledgment:This work was supported by the National Science Foundation, Iowa State University, and University of Connecticut.

Enabling Rhenium Electrodeposition in Water-in-Salt Electrolytes through Isolated Anodic Reactions

Perfluorosulfonic Acid (PFSA)/Polytetrafluoroethylene (PTFE) copolymer and cation-exchange membranes were used to elongate the use water-in-salt electrolytes for rhenium electrodeposition. Water-in-salt electrolytes are a common technique used to minimize the amount of free water in solution by including high concentrations of salts, thus solvating the water molecules and lowering activity of the solution. This expands the electrochemical window in which deposition is possible and minimizes unnecessary hydrogen evolution reactions (HER) in the electrodeposition system by reducing available protons.Lithium chlorine (LiCl) is a common salt for this purpose due to low costs. However, in the LiCl electrolyte, the necessary oxygen evolution reaction (OER) competes with chlorine evolution, which increases water activity and is visually identifiable with a color change from clear to yellow. When chloride ions are depleted, further deposition is no longer possible, and the electrolyte breaks down.A solution to this issue is using membranes to isolate the anode and cathode, thus preventing the chlorine evolution reaction from occurring. Since rhenium is a system with a small electrochemical window, possible oxide intermediates, and an overpotential for hydrogen evolution, the system requires the use of a stable water-in-salt electrolyte for elongated deposition.In this experiment, three membranes were examined to compare the impact on rhenium depositions in an H-cell. To compare the impact of each membrane, the change of pH of the DI side of the H-cell was monitored across time alongside the volume changes on both sides of the H-cell as a function of time due to LiCl inclusion. The quality and thicknesses of the coatings was examined by SEM as well as the impact on the morphologies of the rhenium of the deposits between each of the membranes.

Scaling and Commercializing Continuous Supercritical Hydrothermal Single Crystal Cathode Active Material Manufacturing

Current polycrystalline cathode active materials (CAMs) in the market face a significant challenge during charge-discharge cycles. The lithiation and de-lithiation processes induce volume changes within the CAMs, leading to strain along grain boundaries. This strain, arising from the expansion of crystals in different orientations, often results in material pulverization, creating void fractions. Such deterioration leads to increased impedance, capacity degradation, and shorter cycle life.Addressing these challenges, there is an emerging demand for single crystal (SC) CAMs, which promise enhanced performance by eliminating internal void fractions and grain boundaries. The continuous supercritical hydrothermal process, invented at Argonne National Laboratory, offers an innovative and cost-effective method to produce SC CAMs. This method effectively reduces energy consumption and production costs, while also lowering carbon emissions.In this presentation, we provide a comprehensive overview of the advancements in scaling up and commercializing continuous supercritical hydrothermal process for SC CAM manufacturing. Our focus is on the efforts undertaken by ACT-ion Battery Technologies, the industry commercialization partner, highlighting the significant strides made towards implementing this promising solution on a practical level.

(Invited) The Role of Carbon in Enabling Stable Solid State Batteries

Carbonaceous materials are widely used as the anode materials in rechargeable lithium-ion batteries. In that context, they serve as the host for lithium ions. Their structural stability and limited volume changes underpin the long-term stability of the batteries. In solid-state batteries, however, their roles have evolved. With the focus on raising cell energy density and the promise of stable operation of lithium metal due to the absence of organic solvent, carbon has not been widely studied as an anode material. Unfortunately, the promise of lithium metal has encountered significant challenges: it chemical reacts with virtually all known solid state electrolytes; lithium also grows dendrites which can eventually lead to shorting; the stripping of lithium is also often inhomogeneous which had led to void formation at the interface. To address these challenges, carbonaceous materials have been reintroduced.In this talk, we overview several applications of carbonaceous materials in solid state batteries. We have shown that graphite can be engineered as a 3D host for lithium deposition. Lithiated graphite becomes lithiophilic with low nucleation barrier for lithium metal deposition. The voids between the graphite particles can accomodate lithium metal. As a result, the critical current density and cycling stability of both full cells and symmetric cells have greatly improved. We note that in this context, the anode is essentially a graphite electrode that experiences intentional overlithiation.In a second application, we show that carbon can serve as an effective interlayer between lithium and the solid electrolyte. This interlayer reduces the side reaction between lithium and the electrolyte, thus greatly improving the cycle life and coulombic efficiency. It is rather surprising that upon lithiation, the interlayer enables lithium transport and preferential lithium deposition at the carbon/lithium interface, rather than the carbon/electrolyte interface. This desirable outcome is observed despite the fact that the interlayer itself is electrically conducting. We studied a wide variety of carbon materials in terms of surface area, crystal structure, and defect density. With the optimized carbon material, critical current densities of over 30 mA/cm2 have been observed. The mechanism of lithium transport will be discussed along with the design criteria for using carbon as an effective mixed electron and ion conductor.

Mechanical Failure of Core-Shell Cathode Particles: The Effects of Concentration-Dependent Material Properties and Phase Field Fracture Modelling

The use of core-shell cathode particles in lithium-ion batteries is an attractive approach to enhancing energy density whilst retaining lifetime, through reducing undesired reactions at the electrode-electrolyte interface and limiting the volume change of the electrode particles. However, mechanical failure through the fracture and debonding of the core-shell interface is a major challenge. In this work, we employ a coupled finite-element model to predict and mitigate the mechanical failure of core-shell cathode structures, taking as example a particle of NMC811 (core) coated with NMC111 (shell). In particular, we focus on two aspects:The first one involves the assumptions of material properties as inputs of the model. The material properties are often considered constant by battery modelling researchers, yet these parameters can vary significantly during charge/discharge. For example, experiments have unveiled a three-orders-of-magnitude drop in the diffusion coefficient of NMC materials during discharge [1]. Here, we incorporate material properties obtained from experimental data, including concentration-dependent diffusion coefficient obtained from GITT measurement and partial molar volume derived from in situ X-ray diffraction data. Our results indicate that when assuming a concentration-dependent partial molar volume, the maximum values of tensile hoop stress in the shell are nearly three times lower than those predicted with constant average properties, diminishing the likelihood of fracture.When accounting for concentration-dependent diffusion coefficient, large concentration gradient is observed near the outer surface of the core due to reduced lithium mobility at high states of lithiation, hindering full electrode capacity utilisation. The significant concentration gradient and capacity underutilisation align with direct observations from experiments [2]. Notably, these phenomena cannot be captured in modelling if assuming constant diffusion coefficient. These findings offer new perspectives on the performance and design of core-shell electrode particles. Safe design maps in terms of core size and shell thickness to mitigate fracture and debonding are obtained.The second focus of this work is the utilisation of phase field fracture model in predicting cracking behaviours within the core-shell particle. Phase field modelling provides a continuous representation of cracks, enabling the tracking of complex cracking patterns [3]. We predict cracking behaviors caused by volume changes during charge/discharge, as well as inaccessible capacity and newly created active surface area caused by cracking. Our multiphyics model can hopefully act as a catalyst, accelerating the development process of the core-shell structured cathode particles and shortening the time to market of advanced batteries with extended lifetime.

Effect of Lithiation and Delithiation on the Mechanical Properties of Electrodeposited LiCoO2 Cathode

Mechanical degradation of cathode active material, such as cracks result from volume changes and phase transitions, is one of the main causes of capacity fading in lithium-ion batteries. Understanding the active material’s deformation behavior during cycling and the impact of electrochemical charging on mechanical properties is crucial for understanding the mechanical degradation mechanism and extending battery lifetime.Herein, we investigate the mechanical properties of an electroplated LiCoO2 (LCO) cathode with crystallographic texture as a function of state of charge/discharge. Nanoindentation mapping is used to detect the differences in mechanical behavior between grain boundary and grain interior region. To determine the charged LCO crystals’ mechanical properties and avoid the effects from grain boundaries and air-exposure, in-situ nanoindentation experiments are conducted in a custom mechanical testing system within a scanning electron microscope. Considering the anisotropy of LCO, electron backscatter diffraction analysis is utilized to clarify the crystallographic orientation of the electrodeposited LCO cathode. Our result shows a decreasing tendency in elastic modulus and hardness with state of charge, which can be attributed to the expansion of LCO layered structure. The recovery of mechanical properties after discharge indicates that the changes in measured mechanical properties mainly come from Li deintercalation and intercalation rather than intergranular fracture during cycling. By releasing the relationship between mechanical properties and degree of delithiation, our study provides an insight into modeling studies of electro-chemo-mechanics for electrode materials. Figure 1

Operando X-Ray CT Analysis of Silicon/Solid Electrolyte Mechanical Interface of All-Solid-State Battery during Charging and Discharging Reaction

Silicon has a theoretical capacity about 10 times that of graphite, so it is expected to be one of the next-generation anode materials to further increase the capacity of batteries. However, silicon has a large volume change during charging and discharging, which result in poor cyclability. Although morphological change of silicon has been shown in a lot of previous studies, most of them are ex-situ observations using electron microscopes such as SEM and are two-dimensional observations1). Moreover, many previous studies target liquid battery. It is necessary to understand the expansion and shrinkage mechanism of silicon to improve all-solid-state battery performance using silicon anode. Synchrotron X-ray computed tomography (X-ray CT) is a technique that can measure the internal structure of a battery in three dimensions with micrometer-order spatial resolution in a short time. In addition, operando X-ray CT measurement is possible under charging and discharging in an all-solid-state battery2). In this study, we analyzed that morphological changes of silicon during charging and discharging by operando X-ray CT measurements.We used LiNi1/3Co1/3Mn1/3O2 (NCM), Li6PS5Cl (LPSCl) and acetylene black (AB), which were mortar-mixed in a mass ratio of 1:1:0.1 as the cathode composite material, and Si, LPSCl and AB in a mass ratio of 1:2.78:0.42 as anode composite material. Si｜LPSCl｜NCM all-solid-state cells were assembled. X-ray CT measurements at SPring-8 BL20XU using 20 keV X-rays while performing constant current charge/discharge measurement at 2.3×10-3 A cm-2. The pixel resolution was 0.5 µm. A silicon particle was extracted from the X-ray CT images obtained from X-ray CT measurements to observe the morphological changes of silicon during charging and discharging reaction. Then, change of the silicon volume and the contact area fraction of silicon particle and LPSCl solid electrolyte were calculated.Volume expansion was observed with lithiation of silicon and volume shrinkage with delithiation of silicon. As the lithiation process, silicon density decreased, and silicon was observed to be darker. As the delithiation process, cracks appeared in the silicon particle as the expanded silicon shrank. In addition, the silicon/solid electrolyte interface changed so that the silicon formed shell voids at the surface of silicon particles. This indicates that the plasticity of the LPSCl solid electrolyte cannot follow the form change of the interface. However, shell voids in the interface were formed for all directions, but some parts remained in contact area between the silicon particle and the solid electrolyte. After the second cycle of lithiation, cracks in the particle and the voids in the interface between the silicon particle and the solid electrolyte that had been formed due to the shrinkage of silicon as the delithiation disappeared by the re-lithiation. However, the re-delithiation caused cracks in the particle in the same area and formed shell voids in the interface again. Moreover, as the second delithiation process, the number of cracks in the particle increased compared with that as the first delithiation. This suggests that the number of cracks in the particle increases as silicon repeated lithiation and delithiation, and so silicon is miniaturized. In addition, a correlation was confirmed between the silicon volume change and the contact area fraction change. After the first cycle, the volume didn’t return to pristine silicon volume and the contact area fraction was reduced compared to pristine silicon. The isolation of the silicon particle from the solid electrolyte interface is suggested to be one of the factors causing the poor cycle performance because of the lithium ion reaction path is limited.1) T. Li, J. Y. Yang, S.G. Lu, H. Wang and H. Y. Ding, Rare Metals, 32, 299-304 (2013).2) Y. Sakka, H. Yamashige, A. Watanabe, A. Takeuchi, M. Uesugi, K. Uesugi and Y. Orikasa, J. Mater. Chem. A, 10, 16602–16609 (2022).

One-Dimensional Van Der Waals V2Se9 As a Conversion-Type Anode Material for Advanced Li Rechargeable Batteries

Volume expansion of active materials during lithium storage is one of the main issues in Li-ion batteries (LIBs) that should be addressed. In particular, large volume changes and particle cracking are problematic for electrode materials based on conversion reaction, which are considered attractive anode materials with high energy densities. In this study, a one-dimensional van der Waals (1D vdW) material, V2Se9, is proposed as a conversion-type anode material for LIBs. The V2Se9 electrode material has a 1D chain molecular structure with vdW interactions between chains to form a bulk crystal structure. The spaces between the 1D chains act as structural buffers and provide short Li+ diffusion paths that can improve the electrochemical performance of the electrode materials. The V2Se9 electrode exhibits a high reversible capacity of 563.3 mAh g-1 at 100 mA g-1 and a high rate capability of 109.1 mAh g-1 at 3200 mA g-1. The capacity retention of V2Se9 electrodes is 83.72 % after 100 cycles. Synchrotron X-ray diffraction and X-ray absorption spectroscopy reveal the formation of Li2Se and V metal, indicating that Li ion storage occurs via the conversion reaction. The structural stability of V2Se9 is demonstrated using SEM measurements of the discharged and charged V2Se9 electrodes during cycling. These results demonstrate the reaction mechanism of V2Se9 and highlight the potential of 1D vdW materials as high-performance anode materials in LIBs.

Aridity record of the Arabian Peninsula for the last 200 kyr: Environmental magnetic evidence from the western equatorial Indian ocean

The evolution of aridity and its forcing mechanisms in the Arabian Peninsula are of significance for better understanding the environmental response of the region to global change and the impact of past climate shifts in human evolution. Paleoclimatic reconstructions for the region are predominantly derived from fragmentary terrestrial records. Here, we present a detailed environmental magnetic record for marine sediments from the western equatorial Indian Ocean, which constitute the terminal sink for eolian material originated from the Arabian Peninsula. The dominant magnetic minerals identified in the studied sediments include magnetite, maghemite, and hematite. The hard isothermal remanent magnetization (HIRM), widely used as a proxy for the abundances of the high coercivity mineral hematite, has been used to track variations in the concentration of Arabian dust over the last 200 kyr. Dust concentrations are lowest during interglacial periods of maximum boreal summer isolation, and coincide with intervals during which lake and fluvial systems developed and speleothems formed across most of southern and central Arabia. Our results point to a sharp decrease in the production of dust due to the expansion of vegetation cover up to 30°N during these periods. West African Monsoon appears to be the major source of increased rainfall across Arabia, while the Indian Summer monsoon likely contributed to enhance rainfall in the south and southeastern parts of the peninsula. Variation in the supply of Arabian dust were also driven by changes in high-latitude ice volume and atmospheric CO2, as indicated by highest dust concentration found during glacial periods. We interpret that the expansion of high-latitude ice sheets increased the global meridional temperature gradient, weakened the monsoon system, and resulted in a more southerly, colder and descending subtropical westerly jet, leading to the retreat of vegetation cover and the enhanced production of dust from the Arabian deserts. Our results highlight a link between the production of Arabian dust and orbital-scale climate variability, including both monsoon and northern hemisphere ice sheets dynamics.

Electrolyte and Cutoff Potential Effects on Cycle Life of Li4Ti5O12/LiNi0.9Mn0.1O2 Batteries for Behind-the-Meter Storage Applications

Behind-the-Meter Storage (BTMS) is a stationary battery energy storage system that is connected to the electrical distribution system on the customer’s side of the utility’s service meter. BTMS systems are used to store electrical energy from the grid as well as inconstant, renewable energy, such as local solar and wind generation. A successful BTMS system will allow the customer to pair their energy generation and storage to optimize electrical consumption from the grid, improving reliability and minimizing cost. For BTMS applications, batteries must be designed and optimized with different set of criteria from other leading segments of the Li-ion battery market, like transportation, due the system being stationary and proximal to the residential or commercial building it’s benefitting. BTMS applications prioritize safety, cost (low/no-critical materials), reliability (20-year calendar life), and durability (10,000 cycle life), while having the ability to (minimally) compromise energy density and rate capability.Lithium titanate (Li4Ti5O12, LTO) is a promising anode candidate for BTMS applications due to its high safety and capacity retention, while maintaining a reasonable 160 mAhg-1 reversable capacity and composition of relatively abundant materials. (1) Specifically, LTO has a high working voltage which helps to prevent Li dendrite formation, improving safety. Furthermore, LTO also has negligible lithiation-based volume change, leading to less mechanical pulverization, or loss of active material, upon cycling. For the cathode, materials with little or no Co are of high interest due to the high cost and low abundance of Co. LiMn2O4 (LMO) has been paired with LTO for BTMS applications in the past due to its safety, low cost (abundancy), and reasonably high operating voltage. (2-4) However, the low capacity of LMO limits energy density and specific energy. While not the highest priority for BTMS applications, increasing energy density will enable deployment in space constrained BTMS applications and decrease total cost. LiNi0.9Mn0.1O2 (LNMO) is a recently developed material with promise due to its high operating voltage and relatively low price. (5) However, Ni-rich layered oxides, including LNMO, tend to struggle with capacity retention during high-voltage cycling due to mechanical pulverization, irreversible phase transitions, and unstable solid-electrolyte interphase.The study presented here focuses on building an understanding of how electrolyte solvent and varied cutoff potentials will impact the cycle life of LTO/LNMO cells. Specifically, a comparison is provided between ethylene carbonate (EC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), and Gen2 electrolyte solvents with 1M Lithium hexafluorophosphate (LiPF6) salt, cycling to two upper termination potentials, 2.6V and 2.7V. Electrochemical testing and diagnostics (e.g., differential capacity analysis, area specific impedance, constant voltage hold, and rate capability) and post-mortem characterization will be used to understand the aging behavior and failure mechanisms of the 8 cell combinations (four electrolytes and two voltage cutoffs). Cells with FEC electrolyte showed a lower initial capacity compared to cells with Gen2, EMC, and EC cycling at both voltages; however, the cells with FEC showed consistent trends in capacity retention with 2.6V and 2.7V termination potentials, while the cells with the other electrolytes showed much higher rates of capacity loss when cycling to the higher voltage. These results indicate that FEC may play a role in improving durability of high-voltage, Ni-rich electrode systems for use in high-cycle applications, such as BTMS.This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding was provided by the U.S. Department of Energy's Vehicle Technologies Office under the Behind-the-Meter Storage (BTMS) Consortium directed by Samuel Gillard and managed by Anthony Burrell. The electrodes used in this manuscript are from Argonne's Cell Analysis, Modeling and Prototyping (CAMP) Facility, which is fully supported by the DOE Vehicle Technologies Office (VTO). The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.

Constructing and Investigating a Ceria-Based Electro-Chemo-Resistivity Switch

Coupling between an electrochemical reaction and a functional material property has been termed electro-chemo-X, or EC-X, where X can refer to mechanical, optical, magnetic, or thermal properties. Recently, our group has demonstrated a two-terminal electro-chemo-mechanical (ECM) membrane actuator operating under ambient conditions and containing a Ce0.8Gd0.2O1.9 (20GDC) solid electrolyte (SE) layer sandwiched between two Ti oxide/Ce0.8Gd0.2O1.9 (Ti-GDC) nanocomposite thin films. Reducing one nanocomposite film while oxidizing the other was observed to produce reversible volume change thereby driving actuator operation. Here, we use the same electrolyte and nanocomposite layers to further explore the EC-X effect: we present, as proof-of-concept, a functioning, three-terminal, thin film based EC-electrical switching device operating at room temperature.The stacked lamellar structure which comprises the device (Figure 1) was fabricated by first depositing, using magnetron sputtering, a ~200nm thick layer of Ti metal on a sapphire substrate. This was followed by patterning with photolithography and etching, using a commercial, buffered oxide etch solution, thereby creating a 1mm wide channel. The resulting bottom electrode pair ("source" and "drain"), which could be temporarily shorted together when necessary, were subsequently covered by the WB/SE/RV stack, where the same co-sputtered, ~200nm thick Ti-GDC nanocomposite (<40nm grain size; 39at% Ti) was used for both the working body (lower: WB) and the reservoir (upper: RV) layers; a ~400nm thick 20GDC layer served as the SE. Upon WB deposition, the 1mm channel between the source and drain electrodes was filled with the nanocomposite material. The upper electrical contact, a ~200nm Ti layer, covered the RV, and using the same photolithography and etching process already described, the top "gate" electrode was defined. To avoid oxidation of the ion reservoir (RV) surface by atmospheric oxygen during device operation, a ~500 nm thick Ta-oxide layer was deposited by reactive magnetron sputtering and patterned by lift-off techniques.We find that following two hours application of -/+ 6V bias between the "gate" and (temporarily shorted) "source" / "drain" electrodes under ambient conditions, the average change in ohmic resistance of the WB in the 1mm channel upon reversal of electrode bias was determined, by cyclic voltammetry between the source and drain electrodes, to be 6.5 ±1.8Gohm with statistical uncertainty based on at least 3 cycles, 5 samples. Negative "gate" bias produced the lower resistance values. The low resistance state decayed during approx. 24 hours, as monitored by cyclic voltammetry. Raising the temperature above ambient (333K) further reduced resistance. We interpret these observations as follows: Negative bias voltage application to the "gate" produces a gradient of the chemical potential of diffusing oxygen ions at the SE-WB interface. This gradient leads to the injection of ions into the WB, thereby promoting an electrochemical oxidation reaction. The nanocomposite in the 1mm channel decays from the more highly conductive state during approximately twenty-four hours. Reversing the bias polarity extracts ions from the WB, with the opposite results. To complement the findings of the E-field promoted oxidation, we performed annealing at 633K for 23 hours in air of a device which lacked the SE/RV/"gate" electrode/Ta-oxide layers, i.e. the WB was uncovered. We observed an increase of two orders of magnitude in the conductivity of the nanocomposite in the 1mm channel, which then relaxes with time. As a control, the same thermal treatment was conducted under vacuum. In this case no change was observed in channel conductivity.A possible explanation for how oxidation increases the Ti-GDC nanocomposite conductivity may be found in a suitable variant of the space charge model [1, 2]. We note that nanocrystallinity introduces such a high density of interfaces/grain boundaries that total conductivity may become interfacially controlled. Grain boundaries in doped ceria lack long range order and are relatively rich in oxygen vacancies (VO) and Ce3+, which, along with a space charge zone which forms for charge neutrality, produce a blocking effect for ion conduction. Oxidation of Ce3+ => Ce4+ leads to a lowering of total real charge, causing the spatial extent of the space charge zone to shrink as well. Finally, this succeeds in lowering the potential barrier for ion diffusion across the grain boundary, which increases the overall conductivity. Reduction of the Ti-GDC nanocomposite produces the opposite effect.[1] S. K. Kim, S. Khodorov, I. Lubomirsky, S. Kim, Phys Chem Chem Phys 2014, 16, 14961, https://doi.org/10.1039/c4cp01254b[2] S. Kim, J. Maier, J. Elecrochem. Soc. 2002, 149, J73, https://doi.org/10.1149/1.1507597 Figure 1

High-Performance Lithium-Sulfur Batteries with Atomic V- and Co-Modified Ketjen Black-Sulfur Composite Cathode

Lithium-sulfur (Li-S) batteries are potential alternatives to lithium-ion batteries, which are known to have certain drawbacks. This has drawn special technological attention. Sulfur’s low electrical conductivity, shuttling of the intermediate polysulfides, the slow conversion reaction kinetics of various lithium polysulfides (LiPS), and the major volume change of sulfur in the lithiation reaction are some of the main issues that still need to be resolved before Li-S batteries can be used in practical applications. Additionally, it is likely because there are not enough prognostic models determining energy densities at the cell and pack level based on materials and cell design, most of the articles do not report system-level metrics, specific energy (Wh kg-1), and energy density (Wh L-1).To overcome these problems, atomic vanadium (V) and cobalt (Co) modified ketjen black-sulfur composite (VCKBS) was prepared and used as a cathode in Li-S batteries. The synthesized composite was characterized by various techniques, e.g., XRD, Raman, SEM, HR-TEM, HAADF-STEM, and XPS spectra. The polysulfide adsorption test showed that V had increased the adsorption ability, and cyclic voltammetry displayed the increased catalytic activity resulting from Co, offering a large number of interfacial active sites and ensuring smooth electron transfer. Cycling performance tests showed an initial specific capacity of 1329 mAh g−1, maintained at 1249 mAh g−1 after 100 cycles. Under a higher sulfur loading (2.4 mg cm−2), at 0.2 C, Li-S cells demonstrated an initial specific capacity of 1201 mAh g−1 and retained 985 mAh g−1 after 300 cycles with a low fading rate of 0.059% per cycle. The rate performance tests showed that the prior capacity is nearly recovered, going from 1C back to 0.1C, demonstrating the superiority of the VCKBS material.In addition to the experimental characterization of the Li-S cell performance, energy densities were also predicted by a proposed system-level performance model. The 1st and 100th discharge capacities were used to forecast the system-level specific energies and energy densities. The system-level specific energies and energy densities based on the 100th discharge capacity of VCKBS cathodes had improvements of 1342 and 568%, respectively. This suggests that an easy route to construct the highly stable cathode material may pave the way for the development of highly efficient Li-S batteries. Acknowledgments Hira Fazal acknowledges support from the Türkiye Scholarship/Research Fellowship Program sponsored by the Prime Ministry of Turkey Presidency for Turks Abroad and Related Communities (21PK070917). Damla Eroglu acknowledges support from the Istanbul Development Agency (Award No: TR10/21/YEP/0001). We also thank the National Natural Science Foundation of China (22171180) and the Science and Technology Commission of Shanghai Municipality (20520710400).

A level set approach to modelling diffusional phase transformations under finite strains with application to the formation of [formula omitted]

This paper presents a sharp interface formulation for modelling diffusional phase transformations. Grain boundary motion is, in accordance with diffusional phase transformation kinetics, determined by the amount of flux towards the interface and is formulated in a level set framework. This approach enables a computational efficiency that can be expected to be higher than what can be achieved with conventional phase field methods. Compatibility of the interfaces is obtained through an interface reconstruction process, in which the locations of triple junction points are also determined. To ensure local equilibrium and a continuous chemical potential across the interfaces, the chemical composition is prescribed at the phase interfaces. The presented model is used to study the growth of the intermetallic compound (IMC) Cu6Sn5 for a system with Sn electroplated on a Cu substrate. A finite strain formulation is incorporated into the model to investigate the effects of the volume change resulting from the IMC formation. In this formulation, the Cu and Sn phases are allowed to deform plastically. The numerical simulations demonstrate IMC growth rates in agreement with experimental measurements. Moreover, the IMC evolves into a scallop-like morphology, consistent with experimental observations.

(Battery Division Postdoctoral Associate Research Award Sponsored by MTI Corporation and the Jiang Family Foundation) Science of Multiphysics Behavior of Si/C Composite Anodes in High-Energy-Density Lithium-Ion Batteries

The rapidly growing demands on energy storage technologies over the last decade have imposed further requirements for the high energy/power density, safety, and durability of lithium-ion batteries (LIBs). Si/C composite materials have attracted enormous research interest as the most promising candidates for the anodes of next-generation lithium-ion batteries, owing to their high energy density and mechanical buffering property. However, the major disadvantage of materials with ultra-high capacities, such as Si-based materials, is the significant volume change during cycling, which further leads to mechanical and electrochemical degradation. However, a sophisticated and quantitative understanding of the highly electrochemical-mechanical coupling behaviors is still lacking.A comprehensive computational model is indispensable in the developing process of the excellent performance of anode material due to the low-realizability, inconvenience, and high-cost of experiments, which also provides powerful tools for fabrication guidance of novel Si/C composites designs. Hence, a multiphysics modeling framework is established with a detailed geometric description to quantitatively reveal the underlying governing mechanisms of Si/C composite anode behaviors. We studied the effects of the Si weight percentage, the Si-related particle distribution, the Si-related particle size, the mechanical constraint, and the binder domain gradient on the battery performance regarding the potential behavior, capacity delivery, mechanical stress/strain, Li plating, and polarization evolution. In our study, we used silicon monoxide (SiO) as the Si element source and graphite (Gr) as the C element source. Results discover that an 8-10 wt% of SiO would be an optimal choice regarding capacity delivery and minimizing Li plating under 1C constant current charging condition. Positioning SiO particles near the separator and reducing the sizes of SiO particles are also demonstrated to be beneficial for electrochemical performance with trivial influence on mechanical mismatch. In addition, the mechanical constraint demonstrates a balanced effect on the overall performance of cells and the local behaviors of particles. Our findings also indicate that reducing the proportion of carbon-binder domain (CBD) in the upper domain (near the anode surface) compared to the lower domain (near the current collector) positively influences electrochemical performance, particularly in terms of capacity and Li plating. However, such an arrangement introduces potential risks of mechanical failures and we recommend to incorporate a higher proportion of CBD alongside the SiO particles. Finally, an anode design with a lower CBD proportion in the upper domain exhibits superior rate performance.This study explores the multiphysics behavior of Si/C anodes material using a comprehensive methodology combining experimental and FEA techniques, systematically revealing the coupling mechanism among various physical fields, as well as providing efficient and powerful tools in the design, development, and evaluation of high energy density lithium-ion batteries.

Microstructure-Aware Mesoscale Modeling of Chemomechanical Stress Evolution during Cycling in Solid Electrolyte-Cathode Composite

The volume change of cathode active materials during charge-discharge cycling is responsible for the capacity fading of all-solid-state Li batteries due to mechanical degradation in the cathode such as delamination and crack formation. Many strategies to alleviate the chemomechanical stress buildup have been proposed in experiments but rationale of the stress release mechanisms at the mesoscale remain elusive. In this presentation, we present a microstructure-aware mesoscale model to quantitatively predict the stress distribution during cycling in a secondary particle agglomerate of the cathode active material embedded within a solid electrolyte matrix, taking the LiCoO2-Li7La3Zr2O12 (LCO-LLZO) as a model system. We find that the mechanical stress hotspots develop at different stages within the grain boundaries of the LCO agglomerate and the LCO-LLZO interfaces. We investigate the influences of microstructural morphology (columnar versus equiaxial), grain orientations (textured versus random), mechanical properties at the grain boundaries and heterogeneous interfaces, and anisotropy of chemical expansion on the stress hotspot evolution and provide optimal mitigation strategies. The theoretical results can help gain mechanistic understanding on cathode degradation and inform guidelines for experimental design of mechanically optimized cathode materials for long-life solid-state batteries.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and 22-ERD-043.

Dynamic Coupling of Internal Strain Field and Lithium Pathway within Individual Battery Particles in Solid State Batteries

In all-solid-state batteries (ASSBs), (electro)chemo-mechanical aspects such as uneven interfaces, cathode-electrolyte interphase formation, delamination, fracture, defects, etc., are the major factors in capacity fade but remain largely unknown.Nonhomogeneous transfer of lithium ions can cause significant variations in strain and stress within battery electrodes, leading to degradation in battery performance. In all-solid-state batteries (ASSBs), the lithium pathway and the associated strain/stress field become more intricate due to the (electro)chemo-mechanical reaction at the electrode-electrolyte interfaces. The dynamic volume change in active particles are heavily influencing by strength of the solid electrolyte and interfacial conformality. This can continually alter the lithium pathway and the internal stress field, leading to recurrent redefinitions of (electro)chemo-mechanical environment.Here, we have developed an operando coherent X-ray imaging platform and associated analysis methodologies. This technology can track the nanoscale transport of lithium and the strain evolution of individual electrode particles in ASSBs. With this platform, we gained a comprehensive electrochemical and mechanical understanding of the cycling properties of single electrode particles in ASSBs.

Chemical Substitution Strategies for Tailoring P2- and O3-Type Layered Oxide Cathodes in Sodium-Ion Batteries

Among cathodes for sodium-ion batteries (SIBs), layered transition metal oxides Na x MO2 (M = transition metal) are very promising due to their easy synthesis and high theoretical capacity.1,2 In this class, Ni/Mn/Fe-based layered oxides are attractive due to the high redox potential of Ni2+/ Ni4+ and Jahn Teller inactive centers (Ni2+, Fe3+,and Mn4+).3 However, complex phase transitions, Na+/vacancy ordering and transition-metal (TM) migration degrade their electrochemical performances.4 To address the issues, a widely studied cathode- P2-type Na0.67[Ni0.33Mn0.67]O2 is chosen and Li+ is substituted in the TM-layer to tailor a series of high Na-content cathodes. Among them, Na0.85[Li0.14Ni0.29Mn0.57]O2 cathode with optimal Li-substitution exhibits a reversible capacity of 168 mAh g-1 at 0.1 C rate and good cycling stability (82% retention after 100 cycles).5 In-situ XRD measurement reveals a complete solid-solution formation and X-ray absorption spectroscopy studies confirm the participation of Ni4+/Ni2+ and Mn4+/Mn3+ redox couples during Na+-extraction/insertion. Lastly, a full Na-ion cell with hard carbon is demonstrated with an energy density of 420 Wh kg-1. In subsequent work, a Li and Ti co-substitution strategy is applied to design a high-entropy O3-type NaLixNiyFezMn0.5Ti0.5-aO2 cathode.6 It retains 77% of its initial capacity after 400 cycles at a 2 C rate with a facile O3-P3-OP2-P3-O3 phase transition. The co-substitution strategy uplifts the average voltage of the system, improves the reversibility of the high-voltage OP2 phase, and enhances the Na-ion diffusion rate. A mere 1.32% unit cell volume change and diminishing electrochemical cell resistance over cycling ensure its superior long-term cycling performance. A full cell is fabricated, which holds 62% of its initial capacity even after 1000 cycles at a 0.5 C rate. Therefore, mono- and di-ion substitution strategies hold enormous potential for designing high-performing P2- and O3-type cathode materials for practical SIBs. References T. Hosaka, K. Kubota, A. S. Hameed, and S. Komaba, Chem. Rev., 120, 6358–6466 (2020).J. Y. Hwang, S. T. Myung, and Y. K. Sun, Chem. Soc. Rev., 46, 3529–3614 (2017).F. Zhang, J. Liao, L. Xu, W. Wu, and X. Wu, ACS Appl. Mater. Interfaces, 13, 40695–40704 (2021).Z. Lu and J. R. Dahn, J. Electrochem. Soc., 148, A1225 (2001).A. Ghosh, B. Senthilkumar, S. Ghosh, P. Amonpattaratkit, and P. Senguttuvan, J. Electrochem. Soc., 170, 030538 (2023).A. Ghosh, R. Hegde, and P. Senguttuvan, J. Mater. Chem. A., submitted(2023).

Determination of Electrochemically Active Surface Area in All-Solid-State Batteries

All-solid-state batteries (ASSBs) are currently receiving much attention as one of the most promising next-generation rechargeable battery systems due to their promise of high energy density and high safety. Despite many efforts to commercialize ASSBs, however, there are still many unresolved technical challenges. Unlike conventional lithium-ion batteries (LIBs), the interface between the cathode and electrolyte in ASSBs exhibits a complex degradation pattern that combines chemical and mechanical degradations. In particular, the high Ni content cathode materials in ASSBs are commonly known to suffer from significant additional degradation mechanism, e.g., volume expansion/contraction due to H2-H3 phase transitions at high voltages, resulting in particle cracking. This degradation of the integrity of the active material leads to a reduction in electrochemically active surface area (active area afterward) due to loss of contact between the active material and solid electrolyte, slow diffusion rate of lithium in the active material, and isolation of the active material. These issues are recognized as major contributors to cell performance degradation. Among these issues, the changes in the active area have a decisive impact on the rate of redox reactions that are key to battery charging and discharging kinetics, so accurate determination of the active area is crucial for the diagnosis and improvement of batteries. In the electrochemical analysis of ASSBs, the poor contact between the solid electrolyte and the active material, or the change of the contact properties during the battery operation, should be a very important consideration. Especially when determining kinetic factors such as charge transfer resistance and chemical diffusion coefficient of cathode material by electrochemical methods, the models we usually use include the electrode surface area value as an important variable, so the accurate estimation of the active area is indispensable for obtaining reliable electrochemical properties. Unlike typical LIBs, in ASSBs the active material/electrolyte interface contact properties change relatively significantly during repeated cycling, so devising a reliable technique to analyze the active area of active materials in ASSBs is very crucial for the research and development of ASSBs. However, to the best of our knowledge, there are still very few studies on this.In this study, we propose promising methods to measure the contact characteristics between the cathode material and the solid electrolyte in ASSBs, namely the electrochemically active surface area, and discuss their reliability based on intercomparison and literature reports. For this purpose, first, the method for determining the active area of active materials based on galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) reported in conventional LIBs was reviewed. Then, its applicability to ASSBs was explored, and a way to improve the reliability of the analysis was proposed. Specifically, a three-electrode cathode half-cell experiment was conducted to analyze the active area of the Ni-rich cathode. The active area was calculated by comparing the diffusion coefficient measured by EIS with that obtained by GITT. When comparing the active area determined at different voltages, it was observed that the active area varies significantly with voltage most likely due to the volume change caused by the H2-H3 phase transition. The second electrochemical method performed for the determination of the active area of the active material is based on the quantification of the lithium intercalation sites on the cathode surface based on the analysis of the frequency factor in Arrhenius expression. For this purpose, battery at different charge states were kept at high temperatures for long periods of time to induce interfacial degradation. The temperature-dependent charge transfer resistance was then determined by EIS analysis, which was used to interpret the redox (or lithium absorption/desorption) reactions kinetically. The experimental results showed that the redox reaction rate followed exactly the Arrhenius relationship for all the charge states used, but the activation energies and frequency factors changed differently depending on the charge state. In this study, we discuss these results in relation to various phenomena that may occur during high-temperature aging, such as the formation of rock salt structures and cracks on the nickel-rich cathode surface, and try to estimate the change in active area. In this study, the electrochemical analysis methods of the contact characteristics between the cathode and the solid electrolyte in ASSBs will be examined in depth and their reliability will be assessed. In addition, further improvements in active area analysis techniques for active materials in ASSBs will be discussed.