Li-ion Battery Electrodes Research Articles

Powder Compaction Characteristics and Modeling of Calendering Process for Powder-based Solvent-free Manufacturing of Electrodes for Lithium-ion Batteries

Abstract Powder-based solvent-free manufacturing of electrodes for Li-ion batteries represents an emerging and promising technology in electrode fabrication. This method involves a two-roll powder calendering process, where electrode powder materials are compressed onto a current collector to form electrodes with desired properties. The calendering or compaction of dry powders onto a current collector is a crucial step in solvent-free electrode manufacturing, significantly impacting the microstructures, mechanical properties, and electrochemical performance of the produced electrodes. In this paper, we investigate the compaction characteristics of electrode powders to gain insights into their behavior. A powder-on-current collector calendering model is developed based on Johanson's rolling theory of granular solids. This model enables us to infer the underlying calendering parameters essential for the solvent-free manufacturing of Li-ion batteries. To validate the model, we compare it with experimental calendering results, utilizing measured powder properties and roll design parameters as inputs. This approach offers a comprehensive understanding of the effects of roll geometries, particularly roll diameter, and various equipment design parameters on final electrode properties. Such insights have not been thoroughly explored in the emerging field of solvent-free battery electrode manufacturing, thereby contributing to advancements in this area.

Instability analysis of Li-ion battery electrode particles induced by chemomechanical growth using incremental deformation theory

Volumetric swelling due to lithiation into active battery materials is a well-known phenomenon. A chemo-mechanical framework can suitably explain the deformations of the electrode and the generation of diffusion-induced stresses (DIS). Various experimental works have shown that the effects of DIS further cause the active material to lose its structural stability. However, relatively few frameworks exist that can investigate such phenomena in a comprehensive manner. These are mainly based on the Euler–Bernoulli beam theory and the von-Karman plate theory. In the present work we present a generalized three-dimensional instability framework incorporating the theory of incremental deformation. We use this theory on a widely used chemo-mechanical framework. Notably, similar existing instability investigations on negative electrode materials are based only on incompressible material behaviour. As opposed to it, in this work we have considered a compressible material. Also, we account for the spatial and temporal nature of growth, which is a significant departure from the existing instability frameworks. Therefore, this current work brings the investigation of structural instability of electrode material closer to physical reality. In our study, we use the compound matrix method to find the critical lithiation parameter. Then we consider three sets of problems, each with a particular combination of boundary conditions applied on the inner and outer cylindrical surfaces of hollow cylindrical anode particles. These are free-free, fixed-free, and free-fixed, where each combination represents a particular type of interaction between an electrode particle and its surroundings. Most importantly, we find that the free-free and fixed-free conditions show only a pure axial and mixed mode of instability, and do not show the pure circumferential mode. The free-fixed conditions, however, shows all three modes of instability. Additionally, the presence of mode crossover makes the instability pattern of such electrode particles significant.

Synergy of Artificial SEI and Electrolyte Additive for Improved Performance of Silicon Electrodes in Li-Ion Batteries.

Maintaining the electrochemically and mechanically stable solid electrolyte interphase (SEI) is of highest importance for the performance of high-capacity anode materials such as silicon (Si). Applying flexible Li-ion permeable coatings to the electrode surface using molecular layer deposition (MLD) offers a strategy to improve the properties of the SEI and greatly contributes to an increase in the cycle life and capacity retention of Si electrodes. In this study, the long-term cycling of Si electrodes with an MLD alucone coating is investigated in the context of more stable SEI formation. When the joined strategy introducing both MLD coating and anFEC electrolyte additive was realized, high performance of Si anodes was achieved, capable of delivering more than 1500 mAh g-1 even after 400 cycles. The reason for the significantly improved longevity is the ability of the alucone layer to react with HF present in LiPF6-based electrolytes already under OCV-like conditions, fluorinating most of the available -OH groups in the alucone structure. This reaction not only partially scavenges hydrofluoric acid but also does not disturb the confining effect of alucone-like fluorinated artificial SEI. This study shows the significance of searching for synergetic solutions, such as a combination of electrode surface modification and electrolyte composition, for maximizing the capacity retention of Si as an active material or as a capacity-enhancing additive to graphite electrodes, and as well can be applied to other high-energy battery materials with large volume changes during cycling.

Crystal Structure and Li-Fe Order in Synthetic Mg(2-2x)LixFe3+x(SiO4) Olivine Structure.

Olivines are naturally occurring silicates consisting of isolated (SiO4)4- tetrahedra linked through M1O6 and M2O6 octahedra. In this study, we report the structural and crystal-chemical characterization of synthetic olivine crystals containing up to 25% Li-Fe3+ synthesized using the flux growth technique. Based on site scattering, <M1-O> and <M2-O> mean bond lengths, and charge neutrality of the chemical formula, we found a perfect ordering of Li and Fe3+ at the two distinct M1 and M2 sites. Unrestrained linear extrapolation to a hypothetical isostructural LiFe3+(SiO4) composition aligns well with the tabulated ionic radii of Li and Fe3+. Comparison made with the isostructural LiSc(SiO4) reveals that the Li-centered M2O6 octahedron has a significant capacity to distort in order to accommodate structural stresses, due to the relatively weak Li-O bond, while still achieving a bond valence sum that closely matches the formal charge of Li+. This behavior suggests the potential feasibility of an extended Li + Fe3+ for 2 Mg coupled substitution within the olivine structure. The reported structure of the LiFe3+(SiO4) endmember in the literature, despite its apparent matching of cell dimensions and space group with olivine, exhibits extremely unconventional crystal chemical features, raising questions about its validity. Given the importance of the suitability of Li-insertion in LiFeSiO4 as electrodes in rechargeable Li-ion batteries, further studies are needed to investigate its crystal structure and crystal chemistry.

Lift-Out Specimen Preparation and Multiscale Correlative Investigation of Li-Ion Battery Electrodes Using Focused Ion Beam-Secondary Ion Mass Spectrometry Platforms.

Advanced characterization is paramount to understanding battery cycling and degradation in greater detail. Herein, we present a novel methodology of battery electrode analysis, employing focused ion beam (FIB) secondary-ion mass spectrometry platforms coupled with a specific lift-out specimen preparation, allowing us to optimize analysis and prevent air contamination. Correlative microscopy, combining electron microscopy and chemical imaging of a liquid electrolyte Li-ion battery electrode, is performed over the entire electrode thickness down to subparticle domains. We observed a distinctive remnant lithiation among interparticles of the anode at the discharge state. Furthermore, chemical mapping reveals the nanometric architecture of advanced composite active materials with a lateral resolution of 16 nm and the presence of a solid electrolyte interface on the particle boundaries. We highlight the methodological advantages of studying interfaces and the ability to conduct high-performance chemical and morphological correlative analyses of battery materials and comment on their potential use in other fields.

Influence of 3D Structural Design on the Electrochemical Performance of Aluminum Metal as Negative Electrode for Li-Ion Batteries.

Aluminum (Al) is one of the most promising active materials for producing next-generation negative electrodes for lithium (Li)-ion batteries. It features low density, high specific capacity, and low working potential, making it ideal for producing energy-dense cells. However, this material loses its electrochemical activity within 100 cycles, making it practically unusable. Several claims in the literature support the idea that a dual degradation mechanism is at play. First, the slow diffusion of Li in the Al matrix causes the electrochemical reactions to be partly irreversible, making the initial capacity of the cell drop. Second, the stress caused by cycling make the active material pulverize and lose activity. Recent work shows that shortening the diffusion path of Li by 3D structuring is an effective way to mitigate the first capacity loss mechanism, while alloying Al with other elements effectively mitigates the second one. In this work, we demonstrate that the benefits of 3D structuring and alloying are cumulative and that a mesh made of an Al-magnesium alloy performs better than both a pure Al foil and a foil of an Al-Mg alloy.

Machine learning-based design of electrocatalytic materials towards high-energy lithium||sulfur batteries development

The practical development of Li | |S batteries is hindered by the slow kinetics of polysulfides conversion reactions during cycling. To circumvent this limitation, researchers suggested the use of transition metal-based electrocatalytic materials in the sulfur-based positive electrode. However, the atomic-level interactions among multiple electrocatalytic sites are not fully understood. Here, to improve the understanding of electrocatalytic sites, we propose a multi-view machine-learned framework to evaluate electrocatalyst features using limited datasets and intrinsic factors, such as corrected d orbital properties. Via physicochemical characterizations and theoretical calculations, we demonstrate that orbital coupling among sites induces shifts in band centers and alterations in the spin state, thus influencing interactions with polysulfides and resulting in diverse Li-S bond breaking and lithium migration barriers. Using a carbon-coated Fe/Co electrocatalyst (synthesized using recycled Li-ion battery electrodes as raw materials) at the positive electrode of a Li | |S pouch cell with high sulfur loading and lean electrolyte conditions, we report an initial specific energy of 436 Wh kg−1 (whole mass of the cell) at 67 mA and 25 °C.

Scalable Self-Assembly of Composite Nanofibers into High-Energy-Density Li-Ion Battery Electrodes.

The application of nanosized active particles in Li-ion batteries has been the subject of intense investigation, yielding mixed results in terms of overall benefits. While nanoparticles have shown promise in improving rate performance and reducing issues related to cracking, they have also faced criticism due to side reactions, low packing density, and consequent subpar volumetric battery performance. Interesting processes such as self-assembly have been proposed to increase packing density, but these tend to be incompatible with scalable processes such as roll-to-roll coating, which are essential to manufacture electrodes at scale. Addressing these challenges, this research demonstrates the long-range self-assembly of carbon-decorated V2O5 nanofiber cathodes as a model system. These nanorods are closely packed into thick electrode films, exhibiting a high volumetric capacity of 205 mA h cm-3at 0.2 C. This surpasses the volumetric capacity of unaligned V2O5 nanofiber electrodes (82 mA h cm-3) under the same cycling conditions. We also demonstrate that these energy-dense electrodes retain an excellent capacity of up to 190.4 mA h cm-3(<2% loss) over 500 cycles without needing binders. Finally, we demonstrate that the proposed self-assembly process is compatible with roll-to-roll coating. This work contributes to the development of energy-dense coatings for next-generation battery electrodes with high volumetric energy density.

Waste polyethylene terephthalate-derived organic-inorganic hybrid materials as sustainable dual electrodes for Li-ion batteries

The hybrid Fe-Li2TP structure is constructed from waste polyethylene terephthalate (w-PET) derived dilithium terephthalate (Li2TP) and conventional Fe2O3 by hydrothermal reaction. It is being studied for both anode and cathode for LIBs. As an anode, it exhibits a reversible capacity of 505 mAh/g after 100th cycle at 1 C-rate with ∼100 % coulombic efficiency (CE). In addition, as a cathode, it shows highly reversible charge/discharge capacities of 107.50/107.52 mAh/g after the 100th cycle at 0.1 C-rate with 100 % CE. Further, in the cathodic studies via galvanostatic intermittent titration technique (GITT), the average lithium diffusion (DLi+) coefficients are calculated to be 2.96 × 10-10, 3.89 × 10−10 cm2 s−1 and the electrical (µ) mobilities to be 5.86 × 1011 m2 V−1 s−1, 1.12 × 1011 m2 V−1 s−1 for charge and discharge pulses, respectively. The combined nano-rod and nano-spherical morphologies reduce the diffusion length, and adding 10 % SWCNTs during electrode fabrication enhances the electronic conductivity. This organic–inorganic hybrid strategy of Fe-Li2TP strongly mitigates the electrode dissolution, reducing the structural strain and preventing electrolyte decomposition at higher voltage. Computational studies show an optimized Fe-Li2TP structure with a 2.7-fold lower band gap value (1.9040 eV) than the pristine Li2TP.

Investigating mass transport in Li-ion battery electrodes using SECM and SICM

Lithium-ion batteries (LIBs) are indispensable as global energy production transitions to sustainable production. Nevertheless, the use of LIBs in renewable energy storage applications is challenging due to their limited power densities. To comprehend the origin of this limitation, it is crucial to investigate the effect of electrode architecture on the Li+ ion transport within their pores (solution-phase). In this work, the solution phase transport in various porous Li4Ti5O12 (LTO) films was investigated using scanning ion conductance microscopy (SICM) and scanning electrochemical microscopy (SECM). When the porosity of LTO film increases, SECM and SICM approach curves show an increase in current. This is attributed to the ion transport through the film pores. The 2D topographical mapping using both techniques shows their ability to detect the LTO film's heterogeneity. Most importantly, this work gives insight into the complementary nature of the two scanning probe techniques as demonstrated by the comparable MacMullin numbers.

Zinc Dicyanamide: A Potential High-Capacity Negative Electrode for Li-Ion Batteries.

We demonstrate that the β-polymorph of zinc dicyanamide, Zn[N(CN)2]2, can be efficiently used as a negative electrode material for lithium-ion batteries. Zn[N(CN)2]2 exhibits an unconventional increased capacity upon cycling with a maximum capacity of about 650 mAh·g-1 after 250 cycles at 0.5C, an increase of almost 250%, and then maintaining a large reversible capacity of more than 600 mAh·g-1 for 150 cycles. Such an increased capacity is primarily attributed to the increased level of activity in the conversion reaction. A combination of conversion-type and alloy-type mechanisms is revealed in this anode material via advanced characterization studies and theoretical calculations. This mechanism, observed here for the first time in transition-metal dicyanamides, is probably responsible for the outstanding electrochemical performance. We believe that this study guides the development of new high-capacity anode materials.

(Invited) MAX Phase Oxidation As a Novel Approach to Highly Reversible Oxide Nanocomposite Electrodes for Lithium-Ion Batteries

Among the materials utilized for the negative electrodes in Li-ion batteries, there is notable interest in oxides that can undergo reactions with Li+ through processes like intercalation, conversion, or alloying. These oxides exhibit high specific capacities but face challenges related to inadequate mechanical stability. A novel approach to constructing nanocomposites involves the partial oxidation of the tin-containing MAX phase within the Ti3Al(1-x)SnxO2 composition. By employing this strategy, and optimizing the Sn amount and the oxidation process, we have developed composite electrodes comprising Sn/TiOx and MAX phase, demonstrating exceptional durability with over 600 cycles in half cells. These electrodes exhibit charge efficiencies exceeding 99.5% and specific capacities comparable to graphite, surpassing those of lithium titanate (Li4Ti5O12) or MXene-based electrodes. These remarkable electrochemical performances extend to full cell configurations when combined with a low cobalt content layered oxide. The success of these electrodes is elucidated through a thorough chemical, morphological, and structural investigation, revealing the intimate contact between the MAX phase and oxide particles. Throughout the oxidation process, electroactive nanoparticles of TiO2 and Ti(1-y)SnyO2 emerge on the surface of the unreacted MAX phase, which serves both as a conductive agent and a buffer to maintain the mechanical integrity of the oxide during lithiation and de-lithiation cycles.

Energy Changing Paths for Li-Ion Batteries Under Nonequilibrium Process

It has been discovered that the electrodes of Li-ion batteries have abnormal phase transition phenomena during nonequilibrium process. As a two-phase-coexistence material, LiFePO4 (LFP) shows single phase during both high-rate lithiation and delithiation. Furthermore, a far from equilibrium state results in LFP particles with meta-stable amorphous structures and layered oxides exhibiting two-phase-coexistence during high rate delithiation. It is well known that a stable single-phase structure is an important characteristic for the electrodes with better high-rate performance, since the energy barriers of nucleation and growth for new phases are eliminated. Understanding the mechanisms of the abnormal phase transition during nonequilibrium process is therefore essential for designing the electrodes with fast (dis)charging. In this work, we model the free energy of electrodes with a series of order parameters based on nonequilibrium thermodynamics and continuum mechanics. Developed governing equations for the kinetics of the order parameters reveal the mechanism of the abnormal phase transitions for LFP and layered oxides under high rate (de)lithiation. The generation of dislocations is cross-coupled with the chemical reaction of Li-ion on the surface of electrode particles. Such coupling is the origin of materials choosing various energy changing paths under different (dis)charging conditions and resulting in various lattice parameters and structures. The dislocation density is the key parameter for the path selection since it alters dislocation-induced energy. In the simulations for LFP and layered oxides, the changes of order parameters agree with the abnormal phase transition observed in existing experimental studies. Our study indicates a potential strategy of introducing dislocations with surface engineering for optimizing the (dis)charging path of electrode materials to obtain stable single-phase characteristics and promote the kinetic capability.

Synchrotron Infrared Nano-Spectroscopy and Imaging of Lithium Fluoride in the Solid Electrolyte Interphase on Li-Ion Anodes

The solid electrolyte interphase layer that forms on the surface of the negative electrode in Li-ion batteries is crucial for battery cycle/calendar life, rate performance and safety. This 10's of nanometers layer is formed from the decomposition of the liquid electrolyte and its passivation properties are very sensitive to its formation and aging conditions. Despite this critical role, there is still a lack of fundamental understanding of how its structure and composition relate to its stability and passivation performance.Amongst the SEI products that form during the decomposition of liquid electrolyte, lithium fluoride (LiF) is a ubiquitous component and many attribute its presence to be a determining factor of a well passivated interface. Despite the importance, LiF’s nanostructure and distribution within the SEI layer is rarely investigated due to the lack of suitable characterization techniques. X-ray photoelectron spectroscopy (XPS) is the main tool to identify LiF in the SEI layer, but its micron scale lateral resolution precludes any nanometer scale mapping of LiF’s distribution which limits its ability to identify the role LiF plays in the SEI layer.Recently our group has been characterizing the SEI layer of Li-ion negative electrodes with nano-Fourier transform infrared spectroscopy (nano-FTIR).1,2 Nano-FTIR is a scanning probe technique based in a typical atomic force microscope (AFM) in which a broadband laser illuminates a metallic tip/sample interface. The metallic tip acts as an antenna, focusing the infrared light adjacent to the interface and creating a near-field interaction. By operating in constant tapping mode and due to the nonlinearity of the near-field signal on the tip/sample distance, the corresponding backscattered light from the near-field interaction with the sample can be separated from the background with lock-in amplification. The result is IR reflection and absorption spectra with lateral resolution close to the tip radius (ca. 20 nm). This far exceeds the diffraction limited resolution of typical IR microscopy (~10’s µm) creating new opportunities for IR characterization on nanometer length scales.In this talk, we’ll discuss our recent work related to utilizing synchrotron-based nano-FTIR to characterize and image LiF in the SEI layer of Li-ion based negative electrodes. The synchrotron infrared light source allows the detection of photons out to the far-IR (322 cm-1 limit) which enables the detection of the vibrational modes of Li containing inorganic phases such as LiF, Li2O, and LiH. By comparing model thin film LiF nano-FTIR spectra with experimental spectra take from the surfaces of Cu, Si thin film, and a novel metallic glass anode, we can gauge the heterogeneity of the LiF in the SEI layer and then suggest different LiF formation mechanisms. Based on the results, we believe that nano-FTIR with a synchrotron based light source will be a key tool to unravelling the nanoscale structure of the SEI layer due to its nanoscale chemical sensitivity and nondestructive nature.This research was supported by the US Department of Energy (DOE)’s Vehicle Technologies Office under the Silicon Consortium Project directed by Brian Cunningham and managed by Anthony Burrell. This research used resources of the Advanced Light Source from beamline 2.4, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. References (1) Dopilka, A.; Gu, Y.; Larson, J. M.; Zorba, V.; Kostecki, R. Nano-FTIR Spectroscopy of the Solid Electrolyte Interphase Layer on a Thin-Film Silicon Li-Ion Anode. ACS Appl. Mater. Interfaces 2023, 15 (5), 6755–6767.(2) He, X.; Larson, J. M.; Bechtel, H. A.; Kostecki, R. In Situ Infrared Nanospectroscopy of the Local Processes at the Li/Polymer Electrolyte Interface. Nature Communications 2022, 13 (1), 1398.

Glassy Oxides as Positive Electrode Materials for Sustainable and High Energy Density Li-Ion and Na-Ion Batteries: First Attempts to Establish Relationships between Glass Compositions, Physicochemical Characterizations and Electrochemical Properties with Machine Learning and Design of Experiments Approaches

Today, rechargeable lithium-ion batteries (LIBs) represent one of the best alternatives to reduce our dependency on fossil fuels. LIBs are using cathode materials based on polycrystalline oxides or polyanionic compounds [1]. However, their performances can be limited by their crystalline structure when other compounds suffer from metallic dissolution and irreversible phase changes during cycling [2]. To overcome these key shortcomings, implementing glasses or glass-ceramics as cathode materials is an interesting approach [3]. Glasses have a structure composed of more free volume, and, in the literature that is mainly concerning glasses containing Vanadium transition metal, the glasses can so accept a large amount of lithium [4] and easily accommodate structural changes upon lithium ions extraction/insertion [5]. Furthermore, glass production is a scalable process and can be commercially easier to implement than most of synthesis processes of conventional cathode materials.The main objective targeted is to develop high capacity positive electrodes (up to 300mAh/g) for Li-ion batteries based on glassy oxides without critical transition metals such as Cobalt and Vanadium. The ambitious target is to exceed 1000Wh/kg at the active material level and so enable energy densities of 300-350 Wh/kg at the Li-Ion cell level. Additionally, the electrochemical behavior of some alkali-free glass compositions will be evaluated in sodium-ion configuration. The major scientific objective is to correlate the most relevant physicochemical properties of glass with the corresponding electrochemical performances using machine learning approaches or design of experiment methodology. For a better understanding of involved processes, three oxides glass families are studied as promising cathode materials for sustainable and high energy density lithium batteries. These oxides are composed of: i) a glass network-forming element (Si, B, P) leading to the 3 different families, ii) a transition metal (Mn, Fe, ...) and optionally iii) an alkali (Li, Na).The influence of the nature of the transition metal and the polyanionic group corresponding to the network-forming element (PO4, BO3, SiO4) on the electrical properties of the as-prepared glasses measured at different temperatures will be presented mainly for the lithiated compounds. For microstructural characterization, several techniques were coupled such as X-Ray Diffraction (XRD), SEM-EDX, DTA/TGA, Raman, IR and UV-Vis spectroscopies, Electrochemical Impedance Spectroscopy (EIS) and chronoamperometry.Finally, the electrochemical properties in terms of specific capacity, redox potentials, first cycle capacity loss, coulombic and energetic efficiencies of these materials were investigated in coin-cells vs lithium (or sodium) metal electrode. To understand the electrochemical processes involved in these materials at room temperature, SEM-EDX, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Mossbauër Spectroscopy for iron based compounds were coupled and performed on the as-prepared glasses and on ex-situ (after cycling) materials at different electrochemical states of charge.All the generated data and measurements were analyzed by machine learning approach and tools and in some cases compared with a more classical Design of Experiments (DOE) approach. For instance, figure 1 illustrates the contour diagram of first discharge capacities in the mixture diagram of phosphate glasses based on 3 different transition metal oxides. The final goal is to establish more precisely the relationships between the different glassy oxides structures and their electrochemical performances. First results of this important work of elaboration, characterization and data analysis will be presented here. This new study will bring significant elements to optimize both the glass composition and its elaboration conditions to obtain high performance cathode materials without critical materials.[1] Nitta, N. et al., Li-ion battery materials: present and future. Materials Today 18, 252–264 (2015).[2] Tesfamhret, Y. et al., On the Manganese Dissolution Process from LiMn2O4 Cathode Materials. ChemElectroChem 8, 1516–1523 (2021).[3] K. Kercher et al., « Mixed polyanion glass cathodes: Glass-state conversion reactions », J. Electrochem. Soc., vol. 163, no 2, p. A131-A137, 2016, doi: 10.1149/2.0381602jes [4] Afyon, S. et al., New High Capacity Cathode Materials for Rechargeable Li-ion Batteries. Scientific Reports 4, 7113 (2015).[5] Kindle, M. et al., Alternatives to Cobalt. ACS Sustainable Chemistry Engineering 9, 629–638 (2021). Figure 1

Charge-Sharing Based Stabilization of Nano-Porous Organic Electrode for Rechargeable Li-Ion Battery

Organic-based lithium-ion batteries have garnered increasing attention due to their potential for cost-effectiveness, sustainability, and high energy density. Despite the promising theoretical prediction, the actual battery performance of organic-based electrodes has frequently fallen below the expected values. This discrepancy is primarily attributed to a low density of active sites, limited ion diffusivity, and high solubility to the electrolyte. This study introduces 5,10-dihydro-5,10-dimethylphenazine (DMPZ) as an organic active material, demonstrating superior electrochemical performance characterized by high capacity and prolonged cycle performance. To achieve a high capacity, a cryogenic milling is employed to create a porous nanostructure, enhancing the surface-to-volume ratio without altering the molecular structure. Consequently, the initial specific capacity of the porous DMPZ electrode reaches 184 mAh g-1 at 0.6 C, representing a remarkable 180% increase compared to non-milled DMPZ. To improve cycle stability, a charge-sharing reaction among organic active materials is facilitated by forming an organic nanocomposite comprising DMPZ and various n-type organic materials. The organic nanocomposite effectively mitigates the elution of organic active materials, ensuring unprecedented cycling stability with a capacity retention exceeding 90% over 500 cycles with initial specific capacity of 248 mAh g-1. C-rate tests at 1.2, 2, 4, and 8 C demonstrate outstanding rate capability, with an average capacity of 105 mAh g-1 at 8 C. The performance enhancement mechanism of the organic nanocomposite cathode is elucidated through experimental analyses, including ex-situ XPS, PiFM, and FTIR. These analyses collectively contribute to a comprehensive understanding of the mechanisms underlying the observed improvements in battery performance.

Si1-XGex Alloys As Negative Electrodes for Li-Ion Batteries: Impact of Morphology in the Li+ Diffusion, Performance and Mechanism

Si1-xGex alloys present interesting cycling performance as Li-ion anodes, owing to the synergetic effect from silicon’s high capacity and germanium’s electrical conductivity and Li+ diffusion. Various morphologies of Si1-xGex powders were obtained, micron-sized by ball-Milling (BM) and nano-sized by laser pyrolysis (LP) to study the effect of the morphology and composition on the electrochemical behavior. The electrical conductivity was measured and shows an increase with the Ge content, from 4.58E-03 for Si to 0.11 S m-1 for Si0.5Ge0.5. Half-cells were cycled at C/5, LP samples showed a better capacity retention than their BM counterparts (88% vs 72% at the 35th cycle for Si0.5Ge0.5). To rationalize these trends, Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS) were used to determine the apparent Li+ Diffusion in the Si1-xGex series. It was shown that the apparent Li+ Diffusion is dependent to the state of charge. Moreover, it gave insight about phase transformations during cycling. During lithiation, similar values (10-11 cm2 s-1 ) were obtained for BM and LP Si0.5Ge0.5. However, a big variation (10-13 – 10-10 cm2 s-1) was found for the BM sample delithiation, which is attributed to the conversion of c-Li15(Si0.5Ge0.5)4 phase into amorphous Lix(Si0.5Ge0.5) (x<3.75). Asymmetric C-rate tests evidenced lithiation as the limiting mechanism for the Si1-xGex negative electrodes. Figure 1

Voltammetric Study of Phase Separating Anode Materials in Li-Ion Battery Using Phase Field Model

The increasing demand for higher energy capacity in lithium-ion batteries has underscored the significance of modeling lithiation with alternative electrode materials, such as silicon (Si) and tin (Sn). This research addresses the need for comprehensive insights into the (dis)charging process, particularly focusing on the intricate phase transformations in the anode. Phase-field modeling has proven effective in capturing these transformations [2], revealing volumetric deformations of up to 300% during (dis)charging cycles [1]. Unfortunately, these deformations compromise material integrity, leading to reduced battery cycle life and reliability.To address these challenges, our work presents a novel framework for modeling lithiation in materials exhibiting two-phase diffusion using phase field modeling. Unlike previous models limited to single-phase diffusion, our framework provides a more realistic representation of the diffusion process. This realism is achieved by incorporating the time-dependent voltage applied to the anode, a crucial factor in understanding the electrochemical response during lithiation [3].Furthermore, we leverage the currents generated during the lithiation and delithiation processes to conduct a comprehensive voltammetric study. This study goes beyond existing research by considering the impact of phase separation on the currents developed during Li-ion battery operation. Our findings aim to contribute valuable insights into optimizing battery performance and addressing challenges associated with phase transformations, ultimately advancing the development of high-capacity anodes for lithium-ion batteries. REFERENCES [1] McDowell M. T., Lee S. W., Nix W. D., Cui Y. 25th Anniversary Article: Understanding the Lithiation of Silicon and Other Alloying Anodes for Lithium-Ion Batteries. Adv. Mater., Vol. 25 (36), pp. 4966–4985, 2013.[2] Chen L., Fan F., Hong L., Chen J., Ji Y. Z., Zhang S. L., Zhu T., Chen L. Q. A Phase-Field Model Coupled with Large Elasto-Plastic Deformation: Application to Lithiated Silicon Electrodes. J. Electrochem. Soc., Vol. 161 (11), pp. F3164–F3172, 2014.[3] Swaminathan, N., Balakrishnan, S., & George, K. Elasticity and Size Effects on the Electrochemical Response of a Graphite, Li-Ion Battery Electrode Particle. Journal of The Electrochemical Society, 163(3), A488–A498, 2016. Figure 1

Predicting Effective Transport Properties of Randomly Oriented Polycrystalline Li-Ion Battery Electrodes

Widely practiced Li-ion battery models, such as pseudo-two-dimensional (P2D) models [1-3], use representative spherical electrode particles with assumed isotropic transport properties. Electrode particles, such as NMC, are typically composites that are comprised of numerous randomly oriented crystallites. Each of the single-crystal primary particles that compose secondary particle can have strongly anisotropic transport properties that affect the intercalation process. The empirically approximated effective properties (e.g., diffusion coefficients) as reported in literature vary by as much as six orders of magnitude. In many cases, the effective diffusion coefficients are determined as a part of a parameter-fitting procedure to represent battery polarization measurements.The present approach develops both analytical and computational homogenization methods that derive effective properties based upon the intrinsic single-crystal properties of the crystallites. Homogenization techniques are computationally effective methods to predict macroscale behavior based on microscale properties.As illustrated in Fig. 1, the computational approach begins by assembling over 1000 randomly oriented single-crystal primary particles, with each crystallite having anisotropic properties associated with the crystal lattice. The dodecahedron-shaped primary particles are tightly assembled into a secondary particle that is approximately spherical. A three-dimensional finite-element model predicts transient Li-intercalation fractions throughout a secondary particle during charge or discharge processes. In graphite, the transverse and normal diffusion coefficients differ by approximately six orders of magnitude. Based on the cut plane in Fig. 1, and despite extreme anisotropy within the crystallites, the homogenized macroscopic behavior is nearly isotropic.The analytical approach extends a self-consistent method (SCM) for polycrystalline materials first presented by Ponte-Castañeda and Willis [4], which mathematically combines tensors describing diffusion pathways for every primary particle. The present study considers the concentration-dependent and anisotropic diffusion parameters collected by Persson et al. [5] and Zhou et al. [6] for graphite and NMC, respectively. Another homogenization method is the use of an orientation distribution function (ODF) [7], which predicts the effective diffusion parameters based on the statistical average of every possible primary particle orientation. Fig. 2 shows the predicted effective diffusion coefficients bounded by Hashin-Shtrikman bounds for anisotropic composites proposed by Willis [8] and the experimentally determined diffusion coefficients. The predicted effective diffusion coefficients are lower than the experimentally determined values in transverse direction but are significantly larger than the values in the normal direction. Additionally, the in-plane diffusion dominates the curvature of the predicted effective properties.[1] M. Doyle, T. F. Fuller, and J. Newman. Modeling of galvanostatic charge and discharge of the lithium/polymer/insertion cell. J. Electrochem. Soc., 140:1526–1533, 1993.[2] T. F. Fuller, M. Doyle, and J. Newman. Simulation and optimization of the dual lithium ion insertion cell. J. Electrochem. Soc., 141:1–10, 1994.[3] M. Doyle, J. Newman, A. S. Gozdz, C. N. Schmutz, and J.-M. Tarascon. Comparison of modeling predictions with experimental data from plastic lithium ion cells. J. Electrochem. Soc., 143:1890–1903, 1996[4] P.P.- Castañeda and J.R. Willis. The effect of spatial distribution on the effective behavior of composite materials and cracked media. J. Mech. Phys. Solids, 43:1919–1951, 1995[5] K. Persson, V. A. Sethuraman, L. J. Hardwick, Y. Hinuma, Y. S. Meng, A. van der Ven, V. Srinivasan, R. Kostecki, and G. Ceder. Lithium diffusion in graphitic carbon. J. Phys. Chem. Lett., 1:1176–1180, 2010[6] H. Zhou, F. Xin, B. Pei, and M. S. Whittingham. What limits the capacity of layered oxide cathodes in lithium batteries? ACS Energy Lett., 4:1902–1906, 2019[7] S. Nemat-Nasser, M. Hori, and J. D. Achenbach. Micromechanics: Overall properties of heterogeneous materials. In Micromechanics, volume 37. Elsevier Science I& Technology, The Netherlands, 1993[8] J.R. Willis. Bounds and self-consistent estimates for the overall properties of anisotropic composites. J. Mech. Phys. Solids, 25:185–202, 1977 Figure 1

Efficacy of atomic layer deposition of Al2O3 on composite LiNi0.8Mn0.1Co0.1O2 electrode for Li-ion batteries

LiNi0.8Mn0.1Co0.1O2 (NMC811) is a popular cathode material for Li-ion batteries, yet degradation and side reactions at the cathode-electrolyte interface pose significant challenges to their long-term cycling stability. Coating LiNixMnyCo1−x−yO2 (NMC) with refractory materials has been widely used to improve the stability of the cathode-electrolyte interface, but mixed results have been reported for Al2O3 coatings of the Ni-rich NMC811 materials. To elucidate the role and effect of the Al2O3 coating, we have coated commercial-grade NMC811 electrodes with Al2O3 by the atomic layer deposition (ALD) technique. Through a systematic investigation of the long-term cycling stability at different upper cutoff voltages, the stability against ambient storage, the rate capability, and the charger transfer kinetics, our results show no significant differences between the Al2O3-coated and the bare (uncoated) electrodes. This highlights the contentious role of Al2O3 coating on Ni-rich NMC cathodes and calls into question the benefits of coating on commercial-grade electrodes.