Active Material For Lithium-ion Batteries Research Articles

Elucidating the Morphology of Partially Lithiated Microscale Silicon Particles using Transmission Electron Microscopy

Partial lithiation of silicon active materials for lithium-ion batteries recently gained attention as a promising mitigation strategy for the degradation phenomena associated with the severe volume expansion upon the lithiation, particularly in the case of large, microscale silicon particles. It was suggested that this is caused by the formation of a stabilizing core–shell-like particle structure in the first cycles, consisting of a crystalline core and amorphous silicon shell. In this study, we investigated the microstructure of partially lithiated microscale silicon particles using transmission electron microscopy (TEM). When observed via TEM, the contrast difference in amorphous and crystalline silicon is utilized to reveal previously lithiated areas inside the silicon microparticle. We investigated the influence of lower cutoff potentials and amorphization progress in half-cells. We also examined the changes over prolonged cycling in full-cells with an NCA cathode after 12 and 243 cycles. Silicon particle pulverization was not observed for any sample, even though we found that substantial parts of the particles’ insides had been lithiated. We suggest that the diffusion of Li along grain boundaries and stacking faults plays an essential part in the amorphization and cycling of microscale Si particles but does not lead to their cracking or pulverization.

Exploring Electrode-Preparation Methods of Si Anodes with Li+-Containing Organic Ionic Plastic Crystals for High-Energy-Density Solid-State Batteries

Silicon has an extremely high theoretical capacity (3,579 mAh/g for Si ⇄ Li15Si4), which is almost 10-fold greater than that of a commercialized anode active material in lithium-ion batteries (LIBs), i.e., graphite (371.9 mAh/g for C ⇄ Li6C). Therefore, the successful use of silicon is required for “beyond” LIBs to offer drastically higher energy density than current LIBs. In contrast to lithium metal, silicon is not sensitive to moisture, i.e., no risk of vigorous hydrolysis, which enables the manufacturing of silicon anodes in an ambient condition and provides safer rechargeable batteries than lithium−metal batteries.1 However, reported “beyond” LIBs using silicon anodes often show poor cycle performance primarily because of the large volume change of silicon particles during their alloying and dealloying reactions with lithium species. Prolonged cycling of silicon anodes is prone to particle cracking and new surfaces are exposed to the electrolyte solution, where further electrolyte decomposition (i.e., the formation of solid-electrolyte interphase, SEI) occurs, consuming both lithium inventory and electrolyte.1 To extend the cyclability of silicon anodes, the loss of lithium inventory needs to be minimized.On the other hand, solid-state batteries (SSBs) are regarded as a promising battery format for silicon anodes because solid electrolytes are unlikely to flow through the electrode layer and, therefore, they would experience less aggressive SEI formation on silicon than liquid electrolyte solutions. This concept has been proven by an outstanding cycle performance of Si | solid electrolyte (Li6PS5Cl) | LiNi0.8Mn0.1Co0.1O2 cells.2 However, their cycle performance was strongly dependent on the external pressure on the cells and it had to be sufficiently high (i.e., ≥50 MPa) to ensure intimate electrode–electrolyte contacts.2 To realize the operation of silicon-based SSBs under moderate or no external pressure, replacing the solid electrolyte with a soft one will be beneficial, but silicon composite anodes with soft solid electrolytes have not been widely explored.1 Herein, we present solid-state silicon composite electrodes with an emerging class of soft solid electrolytes, i.e., Li+-containing organic ionic plastic crystals (OIPCs).3 We explored four methods of incorporating OIPC electrolytes into a silicon electrode (Si : carbon black : sodium carboxymethyl cellulose = 70 : 15 : 15 wt%) to provide insights into the process–structure–property relationship for silicon–OIPC composite electrodes (Fig. 1). Cross-section structures and elemental distributions of silicon–OIPC composite electrodes containing 15 wt% of the OIPC electrolyte, i.e., the equimolar mixture of N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ([C2mpyr][FSI]) and LiFSI, were resolved by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), respectively. The half-cell performances of silicon–OIPC composite electrodes were evaluated in a coin-cell (CR2032) configuration, where electrospun poly(vinylidene fluoride) (PVDF)–Li0.50[C2mpyr]0.50[FSI] composite membranes were used as solid-electrolyte interlayers.4 Fig. 2 shows the delithiation capacities of silicon–OIPC composite electrodes made by four different methods over the first five cycles. Except for the one made by the drop-cast method, all silicon–OIPC composite electrodes showed high delithiation capacities that were close to or even greater than that of a silicon electrode (without the OIPC electrolyte) in a liquid electrolyte solution. Elemental mapping of the electrode clearly suggested the localization of the OIPC electrolyte for the drop-cast sample, whereas in the other silicon–OIPC composite electrodes, it was homogeneously distributed, highlighting the importance of OIPC-electrolyte addition to a silicon composite slurry before coating. In the presentation, we will also present differences in Nyquist plots (i.e., bulk, interphase, and charge-transfer resistances) between various silicon–OIPC composite electrodes. The results unveiled the effect of electrolyte-preparation methods on electrode structures and consequent electrochemical performances in SSBs, which will lay a robust foundation for high-energy OIPC-based SSBs with practical cycle life. Acknowledgment The authors acknowledge the Australian Research Council (ARC) for the financial support under the Linkage Project scheme [grant number: LP180100674]. H. Ueda would like to thank Deakin University for providing an Alfred Deakin Postdoctoral Research Fellowship. References X. Wang, K. He, S. Li, J. Zhang and Y. Lu, Nano Res., 16, 3741 (2022).D. H. S. Tan, Y.-T. Chen, H. Yang, W. Bao, B. Sreenarayanan, J.-M. Doux, W. Li, B. Lu, S.-Y. Ham, B. Sayahpour, J. Scharf, E. A. Wu, G. Deysher, H. E. Han, H. J. Hah, H. Jeong, J. B. Lee, Z. Chen and Y. S. Meng, Science, 373, 1494 (2021).H. Ueda, F. Mizuno, M. Forsyth and P. C. Howlett, J. Electrochem. Soc., 171, 020556 (2024).Y. Zhou, X. Wang, H. Zhu, M. Yoshizawa-Fujita, Y. Miyachi, M. Armand, M. Forsyth, G. W. Greene, J. M. Pringle and P. C. Howlett, ChemSusChem, 10, 3135 (2017). Figure 1

Understanding Electrochemical Measurements of Lithium Diffusion in Porous LiNiO2 Cathodes

The chemical diffusion coefficient of lithium in cathode active materials is one of the key parameters determining battery performance. Fast diffusion allows fast charging and access to higher capacities before the potential limits of typical cycling routines are reached. Understanding the measurement of this crucial parameter through simple, non-invasive, in-situ electrochemical methods facilitates the investigation and optimization of cathode active materials for lithium-ion batteries. In this presentation, these electrochemical procedures are applied to LiNiO2 cathodes as a model system of the Ni-rich cathode active materials in liquid electrolyte cells.These measurement routines have a history of almost 5 decades and have been adapted and modified since then. Recently they have received renewed interest for the reasons mentioned above. The presented electrochemical methods, including variations of galvanostatic and potentiostatic intermittent titration techniques (GITT and PITT), electrochemical impedance spectroscopy (EIS) and newer adaptations such as the Atlung method for intercalant diffusion (AMID) and Intermittent current interruption (ICI), are compared and reviewed with respect to underlying physical concepts of solid state diffusion and their application in typical porous cathodes for liquid electrolyte lithium ion batteries. Figure 1 gives a schematic view of lithium concentration in a cathode particle during delithiation and its relation to the electrode potential and the diffusion process.The aim of this presentation is to enable more researchers to include diffusion measurements into their experiments and to facilitate the choice of method by comparing different techniques. By revisiting the fundamentals of solid state diffusion, it allows a deeper understanding of the chemical lithium diffusion coefficient and its measurement. Figure 1

Influence of Transition-Metal Order of Lnmo Spinel on Li Ion Diffusion and Thermodynamics of LNMO

A key strategy to enhance the energy density and improve the sustainability of cathode active materials for lithium-ion batteries (LIBs) is to develop more cost-effective, cobalt-free, higher-energy-density alternatives. The LiNi0.5Mn1.5O4 (LNMO) spinel phase is a promising cathode active material for LIBs as it is Co-free chemistry and exhibits a high specific energy density of 650 Wh/kg, which is attributed to its high operating voltage of approximately 4.7 V vs. Li+/Li. LNMO exists in two phases depending on the ordering of transition metals (TM) in the crystal lattice. In the disordered phase, Ni and Mn ions are randomly distributed on the 16d sites of the Fd3̅m cubic unit cell, whereas in the ordered phase, the Ni and Mn atoms occupy the 4b and 12d sites of the P4332 cubic cell, respectively. In this work, a commercially available, disordered LNMO sample was used as the starting point of the investigations. To initiate the ordering of the Ni and Mn ions, the disordered LNMO was subjected to heat-treatment at 650°C in air. The impact of transition metal (TM) ordering on fundamental parameters such as the unit cell size, electrode expansion, and Li-ion diffusion coefficients at different states of charge were explored using in-operando x-ray diffraction (XRD), in-situ dilatometry, galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS) measurements. The electrodes for these studies were prepared using both PVDF and water-based binders in order to gain key insights into the effect of aqueous electrode processing on the Li+-ion transport parameters, interface resistances, and electrode expansion during cycling.Furthermore, a thermodynamic dataset containing the Gibbs free energy description of the LNMO phase was used to calculate the open circuit voltages and lattice parameters of crystalline LNMO as a function of state of charge and Ni and Mn contents in LNMO. The results of the calculations were compared to those from our experimental investigations to assess the predictive quality of the thermodynamic simulations. Our results show a good agreement between the calculated and quasi-equilibrium open circuit voltages measured by GITT and during cycling. In addition, the experimentally determined volume change of the crystal lattice during intercalation and de-intercalation of Li, as measured by in-operando XRD, was well reproduced by the thermodynamic simulation. Therefore, the second aspect of this work, focused on the thermodynamics of LNMO, shows that Gibbs free energy descriptions of cathode active materials can be used to model and assess their electrochemical performance and structural behaviour during cycling.

Amorphization Progress of Microscale-Silicon Studied via Operando and in Situ X-Ray Diffraction during Formation and Cycling

Silicon as an anode active material for lithium-ion batteries has a theoretical gravimetric capacity of 3579 mAh g-1, considering the highest electrochemically lithiated phase of Li3.75Si.1 Hence, silicon has gained increasing interest in the last years to either partially or completely replace graphite in commercial lithium-ion batteries to increase energy density.2 However, the expansion of silicon of up to 300% upon complete lithiation bears challenges such as particle cracking, loss of electrical contact to the active material, and the continuous formation of the solid-electrolyte interphase (SEI). To decrease these detrimental effects, partial lithiation of microscale silicon was introduced, limiting the used capacity of silicon to ~1200 mAh g-1 and thus reducing its overall expansion, rendering ~250 cycles in full-cells possible.3 XRD measurements during the initial lithiation of crystalline silicon revealed that it is irreversibly amorphized in the first cycle when its potential drops below ~170 mV vs. Li+/Li.4 In the case of partial lithiation of microscale silicon, cycling above this potential limit leads to amorphized silicon particles with a remaining crystalline fraction. In this state, the amorphized part forms a lower lithiated phase LixSi (with x~2), which can be reversibly de-/lithiated.5 In this study, the amorphization progress of microscale silicon full-cells using a single-layer pouch cell setupwas investigated operando over the first four formation cycles and in situ after extended cycling. The anodes consisted of 70% silicon (d 50 =4.5 µm, Wacker Chemie AG), 8% LiPAA binder (Sigma Aldrich), 2% conductive carbon (Super C65, Imerys), and 8% graphite (KS6L, Imerys). The cathode consisted of a nickel-rich transition metal oxide cathode active material (LiNi0.83Co0.12Mn0.05O2, BASF SE). As electrolyte, a 1 M LiPF6 in FEC:DEC 2:8 (v:v) was used. As shown in Figure 1, the cycling performance in pouch cells, reaching 80% state-of-health (SOH) after ~250 cycles at 25 °C matches well with the literature.6 Figure 1 highlights the cycles at or after which XRD measurements were performed. To accomplish operando XRD measurements, a custom-made pouch cell holder with glassy carbon windows was used, which allows for an operating compression of 2 bar. In this setup, an XRD pattern could be taken every ~15 min for the first four cycles at 0.1 h-1. Using the XRD analysis method developed previously,5 the XRD data confirm a significant amorphization in the first charge, while no amorphization occurs during the relaxation phase and during discharge of the cell. In the second charge, the amorphization continues only after ~70% of the capacity was transferred. The start of amorphization aligns with the anode onset potential of ~170 mV vs. Li+/Li, in accordance with the literature.4,5 With increasing cycling number, the progress of amorphization per cycle decreases. Although only ~33% of the silicon capacity (i.e., 1200 mAh/g) is reversibly used, the amorphization reaches ~70% after 50 cycles, highlighting the significant particle usage. Continuous cycling up to 500 cycles leads to no significant further amorphization of the silicon.

(Invited) Investigation of Oxygen Release from Cathode Active Materials for Lithium-Ion Batteries Based on Anion Defect Chemistry

Ensuring safety and reliability of the battery is crucially important for further widespread of electric vehicles. For that purpose, understanding lattice oxygen stability of cathode active materials is important fundamental knowledge, because exothermic reaction between flammable organic liquid electrolyte and oxygen come out from cathode active material triggers thermal runaway. Operando/in-situ measurements and simulations revealed oxygen release of de-lithiated cathodes by thermal decomposition and heat generation in a commercial battery [1-3]. Although these works revealed exothermic reaction in a real battery cell, inherent lattice oxygen stability of cathode materials is not understood well. In this work, we investigate oxygen release behavior and lattice oxygen stability of Li(Ni,Co,Mn)O2 (NCM) to demonstrate the effectiveness of defect chemical and thermodynamic evaluations. NCM powders were synthesized by solid-state reaction from Li(OH)·H2O and Ni-Co-Mn hydroxide precursors obtained by co-precipitation. Equilibrium oxygen release behavior was evaluated by coulometric titration and thermogravimetry. The electrochemical cell for coulometric titration was fabricated from Yttria stabilized Zirconia (YSZ) tube with Au current collectors. The specimen was placed in the YSZ tube and sealed. Titration was carried out at 673-873 K. Reduction behavior due to oxygen release was investigated by X-ray absorption spectroscopy. Equilibrium relation between oxygen content as functions of temperature and PO2 was obtained by coulometric titration and thermogravimetry. With increasing Ni, NCMs release lattice oxygen easily. To quantitatively confirm this tendency of stability, partial molar enthalpy of oxygen which represents necessary energy for oxygen release is estimated based on thermodynamic analysis. It was found that high-valent Ni destabilize lattice oxygen drastically. When partial molar enthalpy of oxygen is plotted as a function of the amount of released oxygen, two groups were clearly classified. One is oxygen release by reduction of high-valent Ni which requires about 0.5 eV, and the other is that by reduction of Co which requires more than 2 eV. This tendency strongly suggests that lattice oxygen stability is essentially determined by reduction species and high-valent Ni deteriorate the stability of lattice oxygen drastically. In the presentation, detailed experimental procedures and experimental results are going to be shown and discussed [4, 5]. In addition, recent work on anion defect chemistry of cathode active material will be shown in the presentation.Reference[1] D. Finega, Nat. Commun., 2015, 6, 6924.[2] S. Bak, Chem. Mater., 2013, 25, 337.[3] Q. Wang, J. Power Sources, 2012, 208, 210.[4] X. Hou, Adv. Energy Mater., 2021, 11, 2101005.[5] X. Hou, ACS Energy Lett., 2022, 7, 1687.AcknowledgementThis work is supported by KAKENHI grant No. 24H02205, ASAHI Glass Foundation and JRP-LEAD with DFG.

Low Temperature Synthesis for Mn Series Positive Electrode Active Material

Introduction Conducted a series of synthesis of various manganese-based cathode active materials for lithium-ion batteries via hydroflux process. We obtained poorly crystalline ortho-LiMnO2 and Li2MnO3 mixture using MnO as the starting materials. ortho-LiMnO2 single phase was successfully synthesized using Mn2O3 and calcined under inert atmosphere. The control of oxidation state of Mn is critical to obtain the target material by hydroflux process. Experimental methods The starting materials were LiOH-H2O and NaOH and various Mn oxides ground by a ball mill. The precursors were mixed in a molar ratio of 1.5:0.5:1 for each metal elements and then watered to obtain a slurry or pellet-like precursor. The precursor was calcined in a tube furnace at 300 °C for 12 h to obtain samples. Excess alkali metal hydroxide in the obtained samples was washed and dried using ethanol and water, and then the samples were identified by powder X-ray diffraction measurement and their surface morphology was observed by SEM observation. A positive electrode was prepared by adding acetylene black and PVdF to the obtained positive electrode active material, preparing a slurry, and coating it on an Al foil. Half-cells were prepared using metallic lithium as the counter electrode and 1 molL-1 LiPF6 EC/DEC (1:1 vol) solution as the electrolyte, and charge-discharge measurements were performed at C/10 at 25 °C. Results and Discussion At first, we investigated the conditions for synthesis from divalent starting materials as in the synthesis of LiCoO2. When MnO was used as the starting material, a mixed phase of ortho-LiMnO2 and Li2MnO3 with a zigzag layered structure was obtained. Despite the addition of water, the peaks attributed to both phases were broad, indicating low crystallinity. SEM observations showed that the grain size remained similar to that of the starting material MnO, and no traces of crystal growth during synthesis were observed. Referring to the Pourbaix Diagram of Mn, the oxidation potential of Mn2+ is lower than that of Co2+, suggesting that the rapid oxidation reactions to Mn3+ and Mn4+ inhibited the crystal growth.Therefore, we investigated synthesis in an inert atmosphere to prevent oxidation reactions of the starting materials. In order to obtain a single phase of ortho-LiMnO2, Mn2O3 was used as the starting material and synthesized in an inert atmosphere, and observed patterns attributed to ortho-LiMnO2. The crystallinity was also improved.Charge-discharge measurement of the obtained ortho-LiMnO2 as positive electrode active material showed typical charge-discharge behavior of ortho-LiMnO2, such as phase transition to spinel phase in the first cycle.These results indicate that the control of the oxidation state of Mn is an important parameter in obtaining the desired compound. In the presentation, we will also report the results of our investigation of other synthesis conditions. References Maeda, R. Nakanishi, M. Mizuhata, and M. Matsui, Inorg. Chem., in press Li, Z. Su, and Y. Wang, Journal of Alloys and Compounds, 735, (2018) 2182–2189.

Influence of Oxygen Defects on Electrochemical Performance of Ni-Rich Layered Oxides for Future Lithium-Ion Batteries

Ni-rich layered cathode active materials (CAMs) are promising candidates for application in lithium-ion batteries due to their high reversible capacity. To further improve the performance of lithium-ion batteries, changing the transition metal composition in CAMs is a good approach to gain a higher capacity, better capacity retention as well as higher rate capability and safety. The oxygen lattice has been considered and widely accepted to be electrochemically inactive, even though it plays a key role in the phase transformations that occur at high degrees of delithiation, as oxygen is released during these high delithiation states. In addition, released oxygen can cause thermal runaway, by exothermic reaction with electrolyte 1,2. However, the effect of oxygen defects and vacancies on the electrochemical performance of cathode active materials in lithium-ion batteries has been scarcely investigated. Research has mainly focused on lithium-rich layered materials, where oxygen vacancies have led to improved battery performance in terms of rate capability, higher discharge capacity and reduced oxygen evolution 3. However, many of these publications suffer from an unprecise content of oxygen deficiencies within the cathode active material with large errors. In this work, a solid-state reactor for electrochemical extraction of oxygen is used to obtain an accurate oxygen deficiency with low error for Ni-rich layered NCM 811 4. Using this process, 1 mol%, 2 mol% and 5 mol% oxygen deficient NCM 811 are produced and (electro)chemically characterized. The effect of oxygen defect concentration on discharge capacity, capacity retention, rate capability and structural stability is investigated in liquid cells. In addition, electrochemical impedance spectroscopy (EIS) is used to reveal changes in electrode resistances. To obtain the cathode impedance only, a three-electrode setup is used, which utilizes a μ-reference electrode made of gold wire.References 1 R. Jung, M. Metzger, F. Maglia, C. Stinner and H. A. Gasteiger, J. Electrochem. Soc., 164, A1361 (2017). 2 R. Jung, P. Strobl, F. Maglia, C. Stinner and H. A. Gasteiger, J. Electrochem. Soc., 165, A2869 (2018). 3 B. Qiu, M. Zhang, L. Wu, J. Wang, Y. Xia, D. Qian, H. Liu, S. Hy, Y. Chen, K. An, Y. Zhu, Z. Liu, and Y. S. Meng, Nat. Commun., 7, 12108 (2016). 4 T. Nakamura, H. Gao, K. Ohta, Y. Kimura, Y. Tamenori, K. Nitta, T. Ina, M. Oishi and K. Amezawa, J. Mater. Chem. A, 7, 5009 (2019).

Review on the Polymeric and Chelate Gel Precursor for Li-Ion Battery Cathode Material Synthesis.

The rapid design of advanced materials depends on synthesis parameters and design. A wide range of materials can be synthesized using precursor reactions based on chelated gel and organic polymeric gel pathways. The desire to develop high-performance lithium-ion rechargeable batteries has motivated decades of research on the synthesis of battery active material particles with precise control of composition, phase-purity, and morphology. Among the most common methods reported in the literature to prepare precursors for lithium-ion battery active materials, sol-gel is characterized by simplicity, homogeneous mixing, and tuning of the particle shape. The chelate gel and organic polymeric gel precursor-based sol-gel method is efficient to promote desirable reaction conditions. Both precursor routes are commonly used to synthesize lithium-ion battery cathode active materials from raw materials such as inorganic salts in aqueous solutions or organic solvents. The purpose of this review is to discuss synthesis procedure and summarize the progress that has been made in producing crystalline particles of tunable and complex morphologies by sol-gel synthesis that can be used as active materials for lithium-ion batteries.

Microstructure impact on chemo-mechanical fracture of polycrystalline lithium-ion battery cathode materials

Anisotropic volume change of layered oxide cathode active material such as Ni-rich nickel–manganese–cobalt-oxide (NMC) during cycling significantly contributes to mechanical degradation, emerging as a primary factor leading to instability issues in these high-capacity cathode active materials for lithium-ion batteries. Despite their commendable energy density, these challenges hinder the broader application of NMC, underscoring the need for rational analysis and innovative solutions to address the associated mechanical instability. In this contribution, we utilize a chemo-mechanically coupled cohesive fracture model, complemented by its 3D finite element implementation, to simulate and analyze the performance and cracking behavior of polycrystalline high-Ni nickel–manganese–cobalt cathode active materials. Thereby the two-way coupling between mechanics and diffusion is regarded both in the bulk and at grain boundary. In particular, novel algorithms are introduced to model the electrolyte penetration along the inter-granular cracks, capturing its intricate impact on particle performance. Utilizing simulations on synthetic and reconstructed microstructure samples derived from experimental images, extensive parameter studies were conducted. These investigations unveiled the intricate influence of various microstructure aspects, encompassing grain morphology, grain/particle sizes, and texture. The findings indicate that secondary active material particles exhibiting smaller grains and radially elongated primary particles, coupled with radially oriented high-diffusivity planes, demonstrate enhanced resistance to inter-granular mechanical damage.

Temperature Driven Phase Evolution of FeF3as Active Material in Lithium-Ion Batteries

Temperature Driven Phase Evolution of FeF₃as Active Material in Lithium-Ion Batteries

Analytical computation of stress intensity factor for multi-physics problems

This work presents a methodology for the analytical calculation of the stress intensity factor when the stress distribution on the crack surfaces is non-homogeneous. At first, a polynomial function is used to express the non-homogenous stress distribution. Subsequently, the principle of superposition of effects is applied, and the stress intensity factor is computed by multiplying each polynomial term by its respective geometric factor. Finite element fracture model is used to compute the geometric factor of the single polynomial grade. To explain the method, a spherical body is considered, with central and superficial cracks. Each geometric factor depends on a normalized geometrical parameter (the ratio between the crack length and sphere radius). The proposed methodology is applied to determine the stress intensity factor in the case of a crack driving force caused by diffusive fields, such as the concentration gradient in particles of electrodes active material in lithium-ion batteries. The methodology allows to speed up the fracture computation, then it is used to give electrode design guidelines to limit the fracture likeliness and mechanical degradation in lithium-ion batteries, as well as it is the basis for the development of algorithms assessing the capacity loss and the remaining useful life of lithium-ion batteries in real-time.

Mesoscale mechanical models for active materials in lithium-ion batteries using the multi-particle finite element method

The stability and mechanical integrity of electrode active materials have a significant impact on the safety and performance of lithium-ion batteries (LIBs). The study of mechanical properties of active materials is crucial for the safety design of batteries. Researchers have conducted several models for describing the mechanical behavior of active materials. However, an accurate mechanical model that can reflect the packing structure of active particles and achieve the multiscale mechanical analysis of active materials is still lacking. To bridge this gap, a three-dimensional (3D) mesoscopic model based on the multi-particle finite element method (MPFEM) is proposed in the present study. The numerical simulation results show that the established model is in good agreement with the experimental results for the description of the compression behavior of the active material. Based on the model, the effects of various factors on the mechanical behavior of the active materials are analyzed. The results deepen the understanding of the multiscale mechanical behavior of anode active materials and provide fundamental insights for the future development of safety design for LIBs.

A method for estimating the state of health of lithium-ion batteries based on physics-informed neural network

Data-driven methods have been widely used to estimate the State of health (SOH) of Lithium-Ion batteries (LIBs). However, these methods lack interpretability. In response to this issue, this article proposes a method called Physics-informed neural network (PIFNN) to enhance the interpretability of predictions made by a feedforward neural network (FNN). First, the features are extracted from incremental capacity (IC) curves and differential temperature curves, which can characterize battery aging from different perspectives. Specifically, the peaks of the IC curves (P-IC) reflect the electrochemical reactions that occur during the charge-discharge processes of LIBs. The decline of the P-IC is related to the loss of active materials in LIBs, which is a major cause of the decrease of the SOH. This article converts the monotonous relationship between the P-IC and the SOH into physical constraints to guide the “learning process” of the model. In the prediction process, a physics-constrained secondary “training” is applied to the FNN predictions to further enhance interpretability and improve prediction accuracy. The feasibility of the proposed method is validated using the Oxford and NASA battery datasets. The results indicate that PIFNN effectively improves prediction accuracy and reduces errors to below 1.5 %.

Isostructural dual-ligand-based MOFs with different metal centers in response to diverse capacity lithium-ion battery anode

Metal-organic frameworks (MOFs) have become one of the most promising active materials in lithium-ion batteries (LIBs) due to their designable molecular architecture and tunable functionality. Herein, we report a series of isostructural three-dimensional MOFs of divalent Mn (1), Co (2), and Zn (3), [MII2(H2O)2(4,4′-bipy)(mal)2]n as anode materials for LIBs. The MOFs can be prepared within a few minutes using a facile microwave-heating technique. Investigations on electrochemical properties and performance as active materials for LIBs anodes showed that Co-MOF 2 has higher efficiency than the Mn and Zn congeners, with an excellent specific capacity of 732 mA h g−1 after 200 cycles, which is distinguished electrochemical performance in specific capacity and rate cycle performance over the previous MOF-based materials. First-principles computations revealed the importance of the metal center of MOFs on the Li-ion batteries performance since it is involved in the Li diffusion mechanism.

Degradation Diagnostics of Ni-Rich NMC in Lithium-Ion Batteries Aged in Different Degrading Conditions

Ni-rich Nickel Manganese Cobalt Oxides (NMC) such as LiNi0.6Mn0.2Co0.2O2 (NMC622) and LiNi0.8Mn0.1Co0.1O2 (NMC811) have been widely used as the cathode active materials in lithium-ion batteries (LIB) of electric vehicles due to their high capacity. Thus, we can foresee millions of tons of end-of-life LIB will be accumulated by the next decades. This means that the efficient recycling method of batteries material, especially NMC which has the highest value, should be developed to reduce the cost and increase the efficiency of recycling. Direct recycling which is a novel method to recover cathode active materials in lithium-ion batteries by directly regenerating the chemical and physical structure of cathode materials, skipping the usage of harsh chemical and high energy consumption such as those of other recycling methods i.e. pyrometallurgy and hydrometallurgy. Such an attempt to directly reprocess the spent NMC back into the as good as new cathode requires and understanding what has happened with the materials through the battery life. This implies that the understanding of degradation mechanisms of Ni-rich NMC in different usage conditions is required to up-scale the direct recycling of Ni-rich NMC from degraded lithium-ion batteries.In this work, we investigated failure mode in controlled aged samples of LIB cells to understand the degradation mechanism of NMC622 and NMC811 which are to be connected with the method for direct regeneration. Lithium-ion batteries composed of NMC622 or NMC811 cathode active materials were aged through 1C-rate charge/discharge cycling at 25°C, 45°C or 55°C until 20% or 40% capacity fading. The degraded cells were analyzed via incremental capacity analysis (ICA), volume change measurement, electrochemical impedance spectroscopy (EIS). Ex-situ X-ray powder diffraction (XRD), Scanning electron microscopy analysis (SEM), X-ray photoelectron spectroscopy (XPS) and Inductively Coupled Plasma Optical Emission spectroscopy (ICP-OES) were used to characterize the chemical and physical structure of degraded NMC from each different degrading conditions.Inspection of degraded cells shows that NMC811 cells exhibit larger cell expansion compared to NMC622 cells going through the same degrading condition. EIS results show that the solution resistance (R S) does not vary much between the different cells, while solid-electrolyte interphase resistances (R SEI) were found to increase with temperature at approximately similar level for both NMC622 and NMC811. Fig. 1a and Fig. 1b show the contour plot on the variation of charge transfer resistance (R CT) ratio after and before degradation of NMC622 and NMC811 cells. It can be seen that R CT in NMC811 cells were found to increase for the more highly cycled NMC811 coupled with high temperature. However, temperature does not seem to have much role in the increment of R CT in NMC622. Investigating the change in structure of the cycled NMCs at different temperatures and to level of different degradation, it was found that the results show that at the same level of capacity remaining, NMC622 has a much larger change in c/a ratio after vs. before compared to NMC811.The above impedance analysis coupled with the XRD results imply that the main cause of capacity fade of NMC811 cells is likely due to electrolyte decomposition which generates gas, resulting in high degree of cell expansion, causing loss of electrical contact. The electrolyte decomposition in NMC811 cell is further facilitated by the increment of temperature due to the lower onset potential limit for gas evolution in NMC811, causing more capacity fading in NMC811 cell at high temperature [1]. On the other hand, the capacity fading in NMC622 cells is mainly from the chemical/structural change in the cycled NMC622 cathode.These insight information on the degradation mechanism of LIB cells and structural variation of Ni-rich NMC after ageing in each degrading condition is then further inspected to elucidate the method to effectively directly regenerate both NMC622 and NMC811 cathode in the spent Li-ion batteries.

Exploration of the lithiation/de-lithiation mechanisms of MoSe2@rGO composite anode by operando X-ray absorption spectroscopy

Owing to their inherent advantages of large inter-planar spacing and high-rate capability transition metal di-chalcogenides have attracted much attention as active materials for lithium-ion batteries (LIBs). Herein, MoSe2 and hybrid MoSe2@rGO nanocomposites have been successfully synthesized via hydrothermal processes and have been employed as anodes in LIBs. LIBs with bare MoSe2 and MoSe2@rGO anodes yield initial discharge capacities of 825 mAhg−1 and 979 mAhg−1 respectively at the current density of 100 mAg−1 and 619 mAhg−1 and 850 mAhg−1 respectively at the high current density of 500 mAg−1 in a voltage range of 0.1–3 V respectively. Thus, LIBs with MoSe2@rGO anode showed enhanced electrochemical performance compared to that with bare MoSe2 anode. Further, LIB with MoSe2@rGO anode during the 1st discharge/charge cycle has been investigated by operando X-ray Absorption Spectroscopy (XAS) measurements using synchrotron radiation which provides a detail insight into the intercalation/conversion processes that take place during lithiation/de-lithiation. The operando measurements reveal formation of LixMoSe2 in the initial phase of Li intercalation (discharge process) followed by conversion of LixMoSe2 into Mo, Li2Se and Se. The Li de-intercalation (charging process) shows oxidation of Mo to MoSe2, though the process is found to be not fully reversible and residual unreacted Mo and Se may lead to capacity fading of the LIBs during long cycling. Thus in the present work, the distinctive lithium reaction pathway in LIBs with MoSe2@rGO anodes has been deciphered by synchrotron radiation based operando XAS study.

Modeling Silicon-Dominant Anodes: Parametrization, Discussion, and Validation of a Newman-Type Model

Silicon is a promising anode material and can already be found in commercially available lithium-ion cells. Reliable modeling and simulations of new active materials for lithium-ion batteries are becoming more and more important, especially regarding cost-efficient cell design. Because literature lacks an electrochemical model for silicon-dominant electrodes, this work aims to close the gap. To this end, a Newman p2D model for a lithium-ion cell with a silicon-dominant anode and a nickel-cobalt-aluminum-oxide cathode is parametrized. The micrometer silicon particles are partially lithiated to 1200 mAh gSi−1. The parametrization is based on values from the electrode manufacturing process, measured values using lab cells, and literature data. Charge and discharge tests at six different C-rates up to 2C serve as validation data, showing a root-mean-squared error of about 21 mV and a deviation in discharge capacity of about 1.3%, both during a 1 C constant current discharge. Overall, a validated parametrization for a silicon-dominant anode is presented, which, to the best of our knowledge, is not yet available in literature. For future work, more in-depth studies should investigate the material parameters for silicon to expand the data available in the literature and facilitate further simulation work.

Charge–discharge properties of LiMn 2 O 4 -group positive electrode active materials for lithium-ion batteries using high-throughput experimental screening and machine learning models

Charge–discharge properties of LiMn ₂ O ₄ -group positive electrode active materials for lithium-ion batteries using high-throughput experimental screening and machine learning models

Cross-linked Si@SiC nanowires prepared by vacuum DC arc method embedded in phenolic resin as high electrochemical performance anode active materials for lithium-ion batteries

Cross-linked Si@SiC nanowires prepared by vacuum DC arc method embedded in phenolic resin as high electrochemical performance anode active materials for lithium-ion batteries