Surface Of Active Particles Research Articles

Development, characterization and validation of a novel physics-informed equivalent circuit model for silicon–graphite battery cells

The widespread deployment of electric vehicles (EVs), as well as the growing requirements both from manufacturers and consumers, necessitate an increase in energy density with regard to current lithium-ion batteries (LIBs). In this regard, one of the most promising alternatives is the addition of silicon to conventional graphite anodes, thus giving rise to energy-dense LIBs. However, this entails a significant increment in modeling, parameterization and computational complexities due to the interactions between both negative electrode materials. In this article, we present a novel physics-informed equivalent circuit model for cells with blended electrodes, which is able to provide accurate results with respect to a state-of-the-art electrochemical model, not only for the output voltage (≤25 mV RMS), but also internal states, namely active material particle surface concentrations (≤1.2 %) and current distribution (≤2.6 %) at a much lower computational cost. Furthermore, this formulation also allows for a notable simplification of model parameterization. Hence, we describe thorough static and dynamic parameterization processes from half-cell experimental data and impedance measurements. Finally, we validate the proposed model in constant-current as well as dynamic operation, highlighting the influence that the choice of hysteresis model has on the latter. We understand that the presented model is an interesting alternative for the modeling of cells with blended electrodes, and is also suitable for its implementation in Battery Management Systems (BMSs) in EVs.

When and Where Lithium Plating Occurs, Its Correlation with Microstructure Heterogeneity, and the Mechanisms That Initiate and Self-Regulate Electrochemical Heterogeneity

A microstructure scale electrochemical LIB model was used to investigate lithium plating onset, material non-uniform utilization, and in-plane heterogeneities for an NMC-graphite full cell [1]. Model predicts active material particle surface roughness and size distribution (respectively, non-uniform curvature within and between particles) initiate in-plane heterogeneity, and that particle size heterogeneity at the separator interface controls the lithium plating preferential deposition (“Where”). These in-plane heterogeneities are then exacerbated by through-plane heterogeneities induced at fast charge as electrolyte depletion occurs and concentrates intercalation reaction near the anode-separator interface. Also, overall magnitude and occurrence of lithium plating is controlled by effective, or macroscale, microstructure parameters (“When”).As local states of charge start to diverge between nearby active material regions, overpotential differences induced by OCP difference kick in and contribute to reduce these SOC local heterogeneities. However, for staged materials such as graphite, with OCP profile alternating between plateaus and varying regions, this balancing mechanism is, respectively, inactive and active. This leads to a dynamic, non-monotonic, in-plane heterogeneity time evolution for state of charge and Faraday current density, for which their respective in-plane heterogeneity magnitude alternates. Such behavior has been modeled both for the whole electrode at the microstructure scale and at the particle scale. In-plane heterogeneities are usually considered to be detrimental, as they result in material non-uniform utilization (i.e., under and over stressed regions) and earlier degradations. However, this work provides a more granular approach as it discriminates between a harmful in-plane heterogeneity (non-uniform curvature) that triggers SOC in-plane heterogeneity, and a beneficial in-plane heterogeneity (Faraday current density) that contributes to reduce SOC in-plane heterogeneity.This work comprehensively explains the mechanisms that initiate, exacerbate, and regulate heterogeneity at the microstructure scale, while providing some design suggestions to reduce both in-plane and through-plane heterogeneities, as summarized in the graphical abstract.[1] F. L. E. Usseglio-Viretta, A. M. Colclasure, J. Allen, D. P. Finegan, P. Graf, and K. Smith, Microstructure Scale Lithium-ion Battery Modeling, Part I: on lithium plating prediction and heterogeneity, in preparation. Figure 1

Particle Shape Resilient Framework for Long-Lasting Li-Ion Batteries

The lattice structural dynamics of active materials within Li-ion batteries, contingent upon their state of charge (SoC), introduce challenges associated with volume expansion or contraction in a both particle and electrode levels1-2. This phenomenon induces mechanical fractures and alters electrode thickness, particularly problematic for high-Ni cathodes characterized by pronounced c-lattice changes during cycling, leading to substantial mechanochemical degradation and hindrance to long-term cycle retention3-4. This study proposes a resilient framework employing multi-wall carbon nanotubes to decorate the surface of active particles, imparting recoverable characteristics to high-Ni cathode materials. This surface framework, endowed with the capacity to absorb mechanical energy, effectively preserves the original secondary particle shape throughout multiple charge cycles, mitigating the serve propagation of cracking. Additionally, the control of particle shape alterations results in a noteworthy reduction of over 50% in electrode thickness changes. The consequential impact of this elastic framework particle engineering is exemplified by outstanding performance, even in a carbon-additive-free electrode with a density of 20 mg/cm². The battery exhibits superior cycle life, retaining 85% of its initial capacity after 500 cycles in a pouch cell. This advancement establishes a universal paradigm for the systematic design of Li-ion batteries with markedly extended cycle life, presenting a transformative prospect for robust and enduring energy storage W. Li, E. M. Erickson, A. Manthiram, Nat. Energy 5 , 26-34 (2020). J. Langdon, A. Manthiram, Energy Stor. Mater. 37 , 143-160 (2021). W. Li, H. Y. Asl, Q. Xie, A. Manthiram, J. Am. Chem. Soc. 141 , 5097-5101 (2019). X.-H. Meng, T. Lin, H. Mao, J.-L. Shi, H. Sheng, Y.-G. Zou, M. Fan, K. Jiang, R.-J. Xiao, D. Xiao, J. Am. Chem. Soc. 144 , 11338-11347 (2022).

Interplay of phoresis and self-phoresis in active particles: Transport properties, phoretic, and self-phoretic coefficients.

Self-propelled synthetic particles have attracted scientific interest due to their potential applications as nanomotors in drug delivery and their insight into bacterial taxis. Research on their dynamics has focused on understanding phoresis and self-phoresis in catalytic Janus particles at both the nano- and microscale. This study explores the combined effects of self-diffusiophoresis and self-thermophoresis induced by exothermic chemical reactions on the surface of active particles moving in non-electrolyte media. We examine how these phoretic phenomena interact, influenced by the coupling between chemical reactions, heat generation, and the concentration and temperature fields at the particle interface. Using a theoretical framework based on the induction of surface tension gradients at the particle interface, we analyze the phoretic dynamics, quantifying parameters such as effective diffusivities, transport coefficients, and, most importantly, phoretic coefficients. Our findings provide insights into the conditions that dictate coupled or independent phoretic behaviors, with implications for drug delivery and nanomotor applications, enabling customized transport processes at the nanoscale.

Polyacrylonitrile as a binder realizes high-rate activated-carbon-based supercapacitors

Highly polar CN functional groups on polyacrylonitrile (PAN) facilitate strong hydrogen bonding and dipole-dipole interactions with hydroxyl groups on the surfaces of active materials and current collectors. Here we report that the strong interaction between PAN and carbon black (CB) particles facilitates a uniform distribution of CB particles within the electrode and forms a well-connected conductive network on the surface of active material particles. This significantly enhances electron transport within the electrode, offering superior rate performance and cycling stability beyond traditional binders like polyvinylidene fluoride (PVDF). Activated carbon (AC) electrodes containing 7.70 wt.% PAN binder (AC-7.7PAN) deliver areal capacitances over 0.60 F cm⁻2 at a scan rate of 500 mV s⁻1, and exhibits a high gravimetric energy density (Eg) of 26.20 Wh kg⁻1 and high areal energy density (Ea) of 0.33 mWh cm⁻2 at a current density of 1 A g⁻1. An AC-7.7PAN coin-cell supercapacitor maintains up to 62 % of its initial capacitance at a scan rate of 200 mV s⁻1, while a controlled AC-7.7PVDF coin-cell keeps only 37 % under the same conditions. The AC-7.7PAN coin-cell retains 91 % of its capacity even after 50,000 charge/discharge cycles at a constant current of 5 A g⁻1. The ability of PAN to evenly distribute conductive agents might be attractive for other power-type electrochemical electrodes, for which effective electron transport are extremely required.

Direct numerical simulation of supercritical CO2 near the critical point flowing over a single Stefan flow-affected spherical particle

scCO2 (supercritical CO2) is now an efficient, clean, and pollution-free solvent widely used in industrial productions, such as extraction, printing and dyeing, as well as pharmaceutical productions. In general, a radial mass flux will exist on the surface of active component particles or drug particles during the process of particle dissolution or re-forms due to variations in operating condition of scCO2, which is called Stefan flow. Comparing with the conventional fluids (0.744 < Pr(Prandtl number) < 1.5), typical high-Pr characteristic (Pr > 10) of scCO2 near critical point will present a unique heat transfer performance, while the relative variations of density and viscosity near critical point affect the mechanics characteristic of particle and distribution details of flow field near particle surface, especially considering the effect of different intensities and directions of Stefan flow. To this, based on the PR-DNS (Particle Resolve-Direct Numerical Simulation) method, this work investigates the Stefan flow-affected drag of the sphere, the flow and temperature field near sphere surface, as well as the interphase heat transfer on the sphere surface. We pay more attention to the high-Pr characteristic and relative variations of density and viscosity of scCO2 near critical point. Results point out that the correlation of Nu (Nusselt number) vs. Resf (Stefan Reynolds number) is no longer linear compared with the cases of conventional fluids, and variable physical properties lead larger drag coefficient while worse heat transfer performance.

On the Impact of Mechanics on Electrochemistry of Lithium-Ion Battery Anodes

Models exploring electrochemistry-mechanics coupling in liquid electrolyte lithium-ion battery anodes have traditionally incorporated stress impact on thermodynamics, bulk diffusive transport, and fracture, while stress-kinetics coupling is more explored in the context of all solid-state batteries. Here, we showcase the existence of strong link between active particle surface pressure and reaction kinetics affecting performance even in liquid electrolyte systems. Traction-free and immobile particle surface mechanical boundary conditions are used to delineate the varying pressure magnitudes in graphite host during cycling. Both tensile and compressive stresses are generated in traction-free case, while a fixed surface subjects the entire particle to a compression state. Pressure magnitudes are nearly two to three orders of magnitude higher for the latter resulting in significant depression of open circuit potential and improvement of exchange current densities compared to stress-free state. The results demonstrate the need for incorporating stress-kinetics linkage in models and provide a rationale for putting battery electrodes under compression to improve kinetics.

Temperature-Dependent Gassing Analysis By on-Line Electrochemical Mass Spectrometry of Lithium-Ion Battery Cells with Commercial Electrolytes

Li-ion batteries (LiBs) are known to evolve gases during their first few formation cycles due to the formation of a solid electrolyte interphase (SEI) at the anode active material particle surface. Simultaneously, the electrolyte can react by other mechanisms leading to the formation of volatile species. 1,2 At a high state-of-charge, the cathode can also release reactive oxygen which causes the formation of CO and CO2 from the oxidative decomposition of the electrolyte.3,4 Consequently, by the analysis of evolved gas species one can study the effect of electrolyte additives, reveal substantial degradation processes within LiBs, and rationalize optimized formation strategies.4–6 The evolution of gaseous species is typically quantified in-situ by monitoring the cell pressure (e.g., via the so-called Archimedes principle) or by online mass spectrometry.5,7 Concerning the latter, an on-line electrochemical mass spectrometer (OEMS) was developed for the application in LiB research and proved to be particularly powerful, since it allows a quantitative analysis and the identification of the evolved and consumed gas during the operation of a battery.4,7 The quantification of OEMS data, however, is challenging when the vapor pressure of the electrolyte is high, which, e.g., is the case for linear carbonates, particularly at elevated temperatures. Mixtures of linear and cyclic carbonates are widely used in LiB applications due to their low viscosity, high salt solubility, and high conductivity. In contrast to the cyclic ethylene carbonate (EC) with a vapor pressure of 0.25 mbar, the vapor pressure for the typically used linear carbonates dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) can vary from 23 to 80 mbar at room temperature.8 Their vapor pressure further increases by a factor of ~3 when increasing the temperature from room temperature to 45 °C.9 Thus, a significant share of the gas in the head-space of the OEMS cell consists of electrolyte vapor. As they undergo fragmentation in the mass spectrometer, a background signal is superimposed on the relevant mass traces related to hydrogen, ethylene, carbon monoxide, oxygen, and carbon dioxide.1 Furthermore, the cell pressure inherently decreases due to the continuous leak through the capillary (with a leak rate of ~1 µL/min) that connects the OEMS cell (~10 mL volume) with the mass spectrometer. Because of the liquid reservoir of electrolyte in the OEMS cell and its constant vapor pressure, this results in an enrichment of the gas phase with electrolyte vapor. Analyzing the pressure-dependent flow of gaseous species into the mass spectrometer allowed us to introduce corrections for signal normalization, electrolyte background change, and signal quantification.In the present study, we applied these corrections in the investigation of the influence of LP57 (1 M LiPF6 in EC:EMC 3:7wt/wt) and LP47 (1 M LiPF6 in EC:DEC 3:7wt/wt) electrolyte on the gassing characteristics during the formation of full-cells with a graphite anode and a Ni-rich cathode from low (10 °C) to high (45 °C) temperatures. From that, we were able to conclude how the formation temperature influences the gas evolution related to SEI formation as well as the trans-esterification of the electrolyte and the lattice oxygen reactivity towards different electrolytes. A comparison to a model electrolyte (1.5 M LiPF6 in EC) with a low vapor pressure (< 0.25 mbar) allowed us to assess the detection limits of all the signals depending on the electrolyte’s vapor pressure and to evaluate the validity of our proposed signal corrections. Acknowledgment: The authors thank BMW AG for their financial support.

Diffusiophoretic propulsion of an isotropic active colloidal particle near a finite-sized disk embedded in a planar fluid–fluid interface

Breaking spatial symmetry is an essential requirement for phoretic active particles to swim at low Reynolds number. This fundamental prerequisite for swimming at the micro scale is fulfilled either by chemical patterning of the surface of active particles or alternatively by exploiting geometrical asymmetries to induce chemical gradients and achieve self-propulsion. In the present paper, a far-field analytical model is employed to quantify the leading-order contribution to the induced phoretic velocity of a chemically homogeneous isotropic active colloid near a finite-sized disk of circular shape resting on an interface separating two immiscible viscous incompressible Newtonian fluids. To this aim, the solution of the phoretic problem is formulated as a mixed-boundary-value problem that is subsequently transformed into a system of dual integral equations on the inner and outer domains. Depending on the ratio of different involved viscosities and solute solubilities, the sign of phoretic mobility and chemical activity, as well as the ratio of particle–interface distance to the radius of the disk, the isotropic active particle is found to be repelled from the interface, be attracted to it, or reach a stable hovering state and remain immobile near the interface. Our results may prove useful in controlling and guiding the motion of self-propelled phoretic active particles near aqueous interfaces.

Constructing Interfacial Nanolayer Stabilizes 4.3 V High‐Voltage All‐Solid‐State Lithium Batteries with PEO‐Based Solid‐State Electrolyte

AbstractThe complicated interfacial problems of poly(ethylene oxide) (PEO)‐based solid polymer electrolytes (SPEs) at high voltages severely hinder its practical applications for high‐energy‐density all‐solid‐state lithium batteries (ASSLBs). Herein, the failure mechanisms of ASSLBs with LiNi0.6Co0.2Mn0.2O2 (NCM)‐PEO are studied. It is found that the ASSLBs after charge generates a sharp drop of 0.62 V at the cut‐off voltage of 4.30 V, and induce a high interfacial resistance due to forming an uneven thick cathode electrolyte interface on the NCM surface, as well as cause the destruction of NCM surface structure during storage, leading to serious performance degradation. Constructing the interfacial nanolayer with aromatic polyamide (APA) on the surface of NCM active particles (NCM@APA) can mitigate interfacial side reactions between NCM and SPE. Robust interfacial nanolayers not only effectively protect the crystal structure of NCM but also provide a steady interfacial environment for Li+ diffusion kinetics. Accordingly, NCM@APA||SPE||Li ASSLBs exhibit an acceptable voltage drop of 0.27 V after 10 days storage and a substantially improved electrochemical performance with an average coulombic efficiency of 99.1% and capacity retention of 76.7% at 30 mA g−1 after 80 cycles.

Next Generation Low-Cost NMP/PVDF-Free Fast-Charging Ni-Rich NMC Cathode Electrodes for High Power Energy Storage Device Applications

Longer range, faster charging, safer, and more durable and affordable batteries are required in order to promote the shift to an EV society powered by renewable energy. However, the current battery performance is limited by the conventional PVDF-NMP processing based cathode, which has lower electrical and ionic conductivity. The high molecular weight PVDF binders are the main cause of non-uniform porosity distribution, material agglomeration in active layer, and poor electrical conductivity. This problem is more prominent in high mass loading thick cathodes (>5 mg/cm2) that are required in high energy density battery designs. For examples, these cathode electrodes are not compatible with fast charging as they have high impedance and do not allow moderate to high C-rates in both charge and discharge.Nanoramic has re-invented how electrodes are manufactured by completely removing high molecular weight polymers such as PVDF and the toxic NMP solvent from the active layer of electrode. This dramatically improves Li-ion battery and Li-metal battery cell performance while decreasing the cost of manufacturing and the capital expenditures related to mixing, coating and drying, NMP solvent recovery, and calendering. In the Neocarbonix™ electrodes, a 3D nanocarbon matrix works as a mechanical scaffold for the electrode active material and mimics the polymer chain entanglement. The engineered surface chemistry of the nanocarbon materials, active materials (NMC), and the current collector promotes excellent mechanical stability for the resulting electrode architecture. As opposed to PVDF polymer, the 3D nanocarbon matrix is highly electrically conductive, allows for significantly thicker cathode active layer while improving the electrical conductivity of the electrode. By using eco-friendly solvents that are easily evaporated, the electrode throughput is higher, and more importantly, the energy consumption from electrode drying process is reduced by 30% due to reduction of temperature from 150 ⁰C-180 ⁰C required by the NMP to 60-70 ⁰C.In the Neocarbonix cathode electrodes the 3D carbon matrix is formed during a proprietary slurry preparation: high aspect ratio 1D and 2D carbon materials are properly dispersed and chemically functionalized using a 2-step proprietary slurry preparation process. The chemical functionalization is designed to form an organized self-assembled structure with the surface of active material particles (e.g. NMC particles). The so formed slurry is usually based on low-boiling point environmental green solvents for Ni-Rich NMC cathodes and are very easily evaporated and handled.After coating and drying, the electrodes undergo a calendering to control the density and porosity of the active material. In NMC811 cathode electrodes, densities of ≥3.6 g/cc and ≤20% porosity can be achieved. Depending on mass loading and battery cell requirements, the porosity can be optimized. Nanoramic projects a reduction in $/kWh of up to 20% with such cathode design. Figure below displays the preliminary results comparing the Neocarbonix (NX) NMP-PVDF free Ni-Rich NMC cathode electrodes with the conventional PVDF based NMC cathode electrodes in Li-Metal based half pouch cells (Li metal is the counter electrodes). Preliminary data shows that NX electrodes can maintain 62-66% capacity retention under 7C-Rate while the PVDF based electrodes can only maintain ~39% of initial capacity, which proves 27% improvement under high C-Rate discharge power performance. Also the NX NMC622 electrodes shows excellent fast-charging capability with 87.1% charge capacity within 15 mins constant current (CC) region fast-charge. Even for the higher areal loading NMC811 cathode (5.2-5.6 mAh/cm2) under 3.4C-Rate fast-charging, NX NMC811 displays 77.3% capacity retention within 17 mins CC region fast-charge, while the PVDF NMC811 control electrode only shows 35.9% capacity retention under 3.4C-Rate fast-charging, which proves that high capacity loading ~5.6 mAh/cm2 Neocarbonix Ni-rich NMC cathode can improve >2X in high-rate 15mins fast-charging capability compared with conventional PVDF electrodes in the electric vehicle (EV) applications. Figure 1

A Defect Spinel Cathode Material for Long-Life and High-Energy-Density Magnesium Rechargeable Batteries

Magnesium rechargeable batteries (MRBs) have been a promising candidate for next-generation batteries due to the following reasons: (i) Mg can deposit without dendritic formation, enabling us to safely use Mg metal itself as a high-capacity (2205 mAh/g) anode. (ii) The electrode potential of Mg (-2.4 V vs. SHE) is relatively low among metal anodes for multivalent batteries, which is attractive for achieving high cell voltage. (iii) Mg is an abundant and non-toxic element. The development of MRBs, however, has been hindered by the lack of high-performance cathode materials. The difficulty in the development of cathode materials is derived from the high charge density of divalent Mg2+ ion, which is almost twice that of monovalent Li+ ion since their ionic radii are similar. This leads to the high activation energies for Mg2+ diffusion in cathode materials by the strong electrostatic interaction with anions. High-temperature operation is a way to prevent the problem of the sluggish Mg2+ diffusion; thus, we have been developing high-potential spinel oxide cathode materials that can work at 150℃. We have found several promising cathode materials (e.g., MgCo2O4, ZnCo2O4) [1,2], but they show rapid capacity fading during battery cycling. Such stoichiometric spinel oxides coherently transform to the rocksalt structure accompanied by Mg insertion in the two-phase reaction [1]. Therefore, the cycle degradation can be attributed to the formation of the rocksalt phase on the surface of active material particles, which would impede the diffusion of Mg2+ ions and degrade the reversibility of structural change in discharge/charge.Very recently, we have proposed a strategy of utilizing defect spinel oxides, which contain cation deficiencies at the octahedral sites in the spinel structure, to suppress the structure transition into the densely packed rocksalt phase in the early stage of discharge (i.e., Mg insertion) [3]. We have chosen ZnMnO3 as a promising candidate for defect spinel-type cathode material in that Zn stabilizes the spinel structure [2] and Mn allows the valence change from tetravalent to divalent [1]. By the theoretical and experimental approach, we have confirmed that ZnMnO3 with cation deficiencies at the octahedral sites is stable, and Mg2+ ions are preferentially inserted into the cation-deficient sites at the potential of 2–3 V vs. Mg2+/Mg with keeping spinel-based structures. As a consequence, it has been demonstrated that ZnMnO3 cathode exhibits a long-term cyclability exceeding 100 cycles (see Figure 1), which is in strong contrast to the previous stoichiometric spinel oxides. In this presentation, we will show a general guideline for designing spinel cathode materials suitable for MRBs, and discuss the origin of the high performances of defect spinel ZnMnO3 in terms of element selection, structure modification, and phase-change behavior.

Optimization mechanism of Li2ZrO3-modified lithium-rich cathode material Li[Li0.2Ni0.2Mn0.6]O2 for lithium-ion batteries

To achieve lithium-ion batteries with high energy and power density, it is necessary to develop alternative high-capacity cathode materials for traditional LiCoO2 or LiFePO4, such as lithium-rich manganese-based cathode materials. However, there are still some practical problems that Li-rich materials need to be further improved, such as structure transformation issue and poor rate capability. Here, the modification of Li[Li0.2Ni0.2Mn0.6]O2 cathode material by lithium-ion conductor (Li2ZrO3) has been achieved by a sol–gel method, and the optimization mechanism is preliminarily explored. The first charge/discharge specific capacities of the modified material coated with 1 wt.% Li2ZrO3 can reach 272.1 and 196.1 mAh g− 1 at 0.5 C, which are obviously higher than those of the pristine material. The rate capability has also been improved at 2 C and 5 C. As a fast lithium-ion conductor with good chemical stability, Li2ZrO3 material can form a continuous and uniform coating layer on the surface of active particles, which can inhibit the side reaction between the electrolyte and the electrode material, effectively prevent the corrosion of cathode material by HF attack, and reduce electrode polarization at high rates, leading to the improvement of the specific capacity and the structure stability of Li-rich material.

Modeling of Chemo-Mechanical Multi-Particle Interactions in Composite Electrodes for Liquid and Solid-State Li-Ion Batteries

Modeling of the chemo-mechanical interactions between active particles in battery electrodes remains a largely unexplored research avenue. Of particular importance is modeling the local current densities which may vary across the surface of active particles under galvanostatic charging conditions. These depend on the local, stress-coupled electrochemical potential and may also be affected by mechanical degradation. In this work, we formulate and numerically implement a constitutive framework, which captures the complex chemo-mechanical multi-particle interactions in electrode microstructures, including the potential for mechanical degradation. A novel chemo-mechanical surface element is developed to capture the local non-linear reaction kinetics and concurrent potential for mechanical degradation. We specialize the proposed element to model the electrochemical behavior of two electrode designs of engineering relevance. First, we model a traditional liquid Li-ion battery electrode with a focus on chemical interactions. Second, we model a next generation all-solid-state composite cathode where mechanical interactions are particularly important. In modeling these electrodes, we demonstrate the manner in which the proposed simulation capability may be used to determine optimized electro-chemical and mechanical properties as well as the layout of the electrode microstructure, with a focus on minimizing mechanical degradation and improving electrochemical performance.

Multimodal Nanoscale Tomographic Imaging for Battery Electrodes

AbstractAccurate representations of the 3D structure within a lithium‐ion battery are key to understanding performance limitations. However, obtaining exact reconstructions of electrodes, where the active particles, the carbon black and polymeric binder domain, and the pore space are visualized is challenging. Here, it is shown that multimodal imaging can be used to overcome this challenge. High‐resolution ptychographic X‐ray computed tomography are combined with lower resolution but higher contrast transmission X‐ray tomographic microscopy to obtain 3D reconstructions of pristine and cycled graphite‐silicon composite electrodes. This cross‐correlation enables quantitative analysis of the surface of active particles, including the heterogeneity of carbon‐black and binder domain and solid‐electrolyte interphase coverage. Capturing the active particles as well as the carbon black‐binder domain allows using these segmented structures for electrochemical simulations to highlight the influence of the particle embedding on local state of charge heterogeneities.

Effect of Electrode Fabrication Process on the Crystallinity of PVDF Binder and Electrochemical Performance of Electrode

In lithium ion battery in fabrication of electrode with good mechanical performance, active materials and conductive agent have to be mixed with specific polymer as binder to binding the other components together. As an effective binder, the polymer should meet some requirements for battery performance and production, such as excellent adhesion to current collector, suitable cohesion to active material and conductive agent, good electrochemical stability over a wide voltage window, high lithium ion conductivity, and so on. Because the binder may coat on the surface of active material particles, the binder layer should have high ionic conductivity and lithium ion can pass through the binder. Poly (vinylidene fluoride) (PVDF) is the mostly common used binder in lithium ion battery production. The amorphous phase in PVdF is a good matrix for polar molecules, and lithium ions can pass through a thin layer of swollen PVdF[1]. PVDF is a semi-crystalline polymer with a repeating unit of –CH2-CF2-. The spatial arrangement of the CH2 and CF2 groups along the polymer chains can contribute to the unique properties of PVDF from its crystalline phase. But it is seldom researched that the effect of crystalline structure of PVDF on the electrochemical performance in lithium ion battery. In our recent study, we found that the impedance of electrode is dependent on the drying temperature of coated slurry[2]. In this research we investigated the relationship of process conditions with crystalline phases of PVDF binder in the electrode and the dependence of the electrochemical performance of the electrode on the process conditions.[1]. K. Tsunemi , H. Ohno , E. Tsuchida , Electrochimica Acta , 28 (6) , 591 (1983) .[2]. Y. Fu, X. Song, G. Liu, V. Battaglia, 236th ECS Meeting ,353, Oct. 13-17, 2019, Atlanta, GA. Figure 1

Hydrogen production via catalytic propane partial oxidation over Ce1-xMxNiO3-λ (M=Al, Ti and Ca) towards solid oxide fuel cell (SOFC) applications

Indirect hydrogen production routes presented extensive compatibilities for distributed solid oxide fuel cell systems. Catalyst activity directly determines hydrogen production and profoundly affects the power generation. In this work, Ce1-xMxNiO3-λ (M = Al, Ti and Ca) were synthesized for hydrogen production from propane partial oxidation (POx). From the results, it indicated that the choice of catalyst compositions could directly affect the microstructure during the preparation process. Also, different Ce1-xMxNiO3-λ catalysts displayed distinctive carbon tolerance performances due to the different active particle sizes and surface properties of the catalysts. In general, the synthesized Ce1-xMxNiO3-λ catalysts showed higher hydrogen production than a commercial nickel cerium catalyst. From the observation of a SOFC test system powered by injecting the generated H2 from catalytic propane POx reaction, the obtained power density of CNO–Al displayed an increase of 22.6% compared to the commercial nickel cerium catalyst. It was quite impressive that the equivalent hydrogen (160 ml/min) produced over CNO–Al and the obtained power density (482.6 mW/cm2) of SOFCs were competitive while CNO–Ca presented an excellent stability with a better carbon tolerance performance for the long-term tests. The achievements of this work might offer a novel point of view for developing low-cost catalyst towards indirect hydrogen production for SOFC.

How do particle number, surface area, and mass correlate with toxicity of diesel particle emissions as measured in chemical and cellular assays?

Increasingly stringent particulate matter (PM) emission standards have brought forth engine design improvements, cleaner-burning fuels, and aftertreatment technologies. Reductions in tailpipe PM mass have concomitantly reduced accumulation-mode particle emissions. However, some strategies promote the emission of nucleation-mode particles, which are typically quantified on a number (PN) basis. We previously demonstrated that PN emissions from heavy-duty diesel vehicles equipped with various aftertreatment systems were inversely correlated, and gravimetric PM mass was positively correlated, with two in vitro assays. This present work expands on the analysis of PM mass and PN with in vitro assays to also include four additional PM metrics: suspended PM mass, active particle surface area, aggregate particle surface area, and accumulation-mode particle number. This new analysis shows that like gravimetric PM mass, suspended particle mass and accumulation mode particle number are well correlated with dithiothreitol consumption rate (DTT) and macrophage reactive oxygen species consumption rate (ROS) assays (R2 = 0.61–0.96). Data suggest that PM mass emissions dominated by nucleation-mode particles induce equal or slightly greater toxicity compared to PM mass dominated by accumulation-mode particles. Data also show that among all PM metrics, those used for regulating PM in the United States and Europe, namely gravimetric mass and solid PN are overall most correlated with in vitro toxicity. Moreover, continued exploration of alternative, low-cost, and more appropriate PM metrics is warranted to better understand the reproducibility of these findings on other engine applications, fuel types, and aftertreatment platforms.

Surface Characterization of Li-Substituted Compositionally Heterogeneous NaLi0.045Cu0.185Fe0.265Mn0.505O2 Sodium-Ion Cathode Material

The understanding of surface chemical and structural processes can provide some insights into designing stable sodium cathode materials. Herein, Li-substituted and compositionally heterogeneous NaLi0.045Cu0.185Fe0.265Mn0.505O2 is used as a platform to investigate the interplay between Li substitution, surface chemistry, and battery performance. Li substitution improves the initial discharge capacity and energy density. However, there is no noticeable benefit in the long-term cycling stability of this material. The Li substitution in the transition-metal (TM) layer also seems to influence the transition-metal (TM) 3d–oxygen (O) 2p hybridization. Upon desodiation, the surface of active particles undergoes significant transition-metal reduction, especially Mn. Furthermore, the presence of electrolyte drastically accelerates such surface degradation. In general, the Li-substituted material experiences severe surface degradation, which is partially responsible for the performance degradation upon long-term cyc...

Thermodynamically consistent derivation of chemical potential of a battery solid particle from the regular solution theory applied to LiFePO4

The chemical potential of lithium in LixFePO4 active cathode nanoparticles and the surface free energy between LixFePO4 and electrolyte were determined with the novel thermodynamically consistent application of the regular solution theory. Innovative consideration of crystal anisotropy accounts for the consistent determination of the dependency of the chemical potential on the mechanistically derived enthalpy of mixing and the phase boundary gradient penalty. This enabled the analytic, thermodynamically consistent determination of the phase boundary thickness between LiFePO4 and FePO4, which is in good agreement with experimental observations. The obtained explicit functional dependency of the surface free energy on the lithium concentration enables adequate simulation of the initiation of the phase transition from FePO4 to LiFePO4 at the surface of active cathode particles. To validate the plausibility of the newly developed approaches, lithium intercalation into the LixFePO4 nanoparticles from electrolyte was modeled by solving the Cahn-Hilliard equation in a quasi-two-dimensional domain.