High C-rate Research Articles

Technology Suitability Assessment of Battery Energy Storage System for High-Energy Applications on Offshore Oil and Gas Platforms

Selecting a battery energy storage technology for application on offshore platforms or marine vessels can be a challenging task. Offshore oil and gas platforms (OOGPs) require battery energy storage systems (BESSs) with high volumetric density, high gravimetric density, high safety, a long life span, low maintenance, and good operational experience, amongst other BESS properties. No single battery chemistry can satisfy all these factors perfectly, which implies that there is a need for a method that determines the most suitable battery chemistry for a given application. To this end, this paper proposes an improved version of a 7-step procedure proposed in the literature to systematically and logically determine the most suitable BESS for high-energy applications on OOGPs. In order to implement the 7-step procedure, a review of the state-of-the-art of consolidated and emerging battery chemistry is done. As part of the 7-step procedure, the operational experience of the battery chemistry was also reviewed. The 7-step procedure was then applied to a case study (with two test cases) of a real OOGP in the North Sea. The first test case considers BESS for peak shaving, for which six battery chemistries were assessed in detail. A technology suitability assessment (TSA) weighted score is calculated, which is based on five attributes critical for the energy storage choice in the considered application, which are weight, space, safety, life cycle cost, and operational experience. Of the six battery chemistries assessed, lithium iron phosphate (LFP) has the highest technology suitability assessment (TSA) weighted score and is therefore deemed the most suitable battery chemistry for peak shaving. The second test case considers BESS for spinning reserve. Since this is a high C-rate application, only battery chemistry capable of high C-rate was evaluated. From the TSA evaluation, LFP and lithium nickel manganese cobalt have the joint highest TSA weighted score and are therefore deemed the most suitable battery chemistry for spinning reserve.

Use of Hydrothermal Carbonization to Improve the Performance of Biowaste-Derived Hard Carbons in Sodium Ion-Batteries.

Over the last years, hard carbon (HC) has been the most promising anode material for sodium-ion batteries due to its low voltage plateau, low cost and sustainability. In this study, biomass waste (spent coffee grounds, sunflower seed shells and rose stems) was investigated as potential material for hard carbon preparation combining a two-step method consisting of on hydrothermal carbonization (HTC), to remove the inorganic impurities and increase the carbon content, and a subsequent pyrolysis process. The use of HTC as pretreatment prior to pyrolysis improves the specific capacity in all the materials compared to the ones directly pyrolyzed by more than 100 % at high C-rates. The obtained capacity ranging between 210 and 280 mAh g-1 at C/15 is similar to the values reported in literature for biomass-based hard carbons. Overall, HC obtained from sunflower seed shell performs better than that obtained from the other precursors with an initial Coulombic efficiency (ICE) of 76 % and capacities of 120 mAh g-1 during 1000 cycles at C with a high capacity retention of 86-93 %.

Coupled electrochemical-thermal-mechanical stress modelling in composite silicon/graphite lithium-ion battery electrodes

Silicon is often added to graphite battery electrodes to enhance the electrode-specific capacity, but it undergoes significant volume changes during (de)lithiation, which results in mechanical stress, fracture, and performance degradation. To develop long-lasting and energy-dense batteries, it is critical to understand the non-linear stress behaviour in composite silicon-graphite electrodes. In this study, we developed a coupled electrochemical-thermal-mechanical model of a composite silicon/graphite electrode in PyBaMM (an open-source physics-based modelling platform). The model is experimentally validated against a commercially available LGM50T battery, and the effects of C-rates, depth-of-discharge (DoD), and temperature are investigated. The developed model can reproduce the voltage hysteresis from the silicon and provide insights into the stress response and crack growth/propagation in the two different phases. The stress in the silicon is relatively low at low DoD but rapidly increases at a DoD >∼80%, whereas the stress in the graphite increases with decreasing temperature and DoD. At higher C-rates, peak stress in the graphite increases as expected, however, this decreases for silicon due to voltage cut-offs being hit earlier, leading to lower active material utilisation since silicon is mostly active at high DoD. Therefore, this work provides an improved understanding of stress evolution in composite silicon/graphite lithium-ion batteries.

Novel multicomponent composite with TiO2/Y2O3 as cathode material and interlayer for Li-SPAN batteries cycled at high C-rates

Novel multicomponent composite with TiO2/Y2O3 as cathode material and interlayer for Li-SPAN batteries cycled at high C-rates

Zeolite Coated Separators for Improved Performance and Safety of Lithium Metal Batteries

Lithium (Li) metal batteries are attractive due to their high gravimetric and volumetric energy densities. However, they can fail catastrophically due to dendritic nucleation, growth, and penetration through the polypropylene (PP) or polyethylene (PE) separators. Poor electrolyte wetting and non-uniform Li ion flux are known to affect Li dendrite formation, especially since the PP/PE separators have non-uniform pore size distribution and typical organic electrolytes do not wet them well. In this work, we demonstrate that a porous zeolite coating on a commercial PP separator can improve electrolyte wettability and through plane ionic conductivity, giving rise to more uniform Li flux. Consequently, coated separator can delay dendrite penetration and enhance cell performance and safety. We tested Celgard 2400 (uncoated) and zeolite-coated separator (coated) in high energy NMC||Li cells for their rate capability and cycle life performance. Rate capability test for these cells shows that the additional resistance due to the zeolite coating can negatively impact the cell performance at high C-rates. However, cells with the coated separator outperform those with uncoated separator in the cycle life test with improved capacity retention. Symmetric cell studies performed to understand the differences in Li plating morphology indicate initial lower overpotential for the coated separator cells, revealing improved electrolyte wetting and relatively uniform Li flux. Scanning electron microscopy (SEM) reveals zeolite-coating microstructure with evenly distributed zeolite particles and cycled Li metal electrode morphologies. SEM images show much smoother Li plating morphology on Li metal surface in the cells with coated separators. This study highlights the potential of using zeolite-coated separators to enhance lithium metal battery (LMB) performance and safety.

Parameter sensitivity analysis and parameter identifiability analysis of electrochemical model under wide discharge rate

The increasing demand for electric vehicles, grid stability, and high pulse power loads has driven the development of new high-power lithium-ion batteries (LIBs) that are capable of discharging at extremely high C-rates. Accurately identifying physical parameters in electrochemical models is crucial for the rational design and optimization of these new high-power LIBs. Since high-rate discharge can significantly reduce discharge time, it is essential to investigate the impact of double-layer capacitors. In this study, we present a P2D coupled double-layer capacitor model and conduct a comprehensive analysis of the sensitivity of all 32 physical parameters to terminal voltage during constant current discharge over a wide rate range of 1C to 40C. This is the first time such an analysis has been performed. We classified the parameters into three groups based on their normalized parameter sensitivity index: high sensitivity, sensitive, and insensitive, and identified 14 physical parameters that can be recognized under constant current discharge conditions. We used a genetic algorithm to identify these parameters, achieving a root mean square error below 13 mV and an average absolute error below 10 mV between the simulation results of the model and the experimental data. This work provides guidance and inspiration for the parameter identification of high-power LIBs electrochemical models.

(Invited) Theoretical Analysis of Reaction Inhomogeneity and Lithium Plating Onset at Fast Charge Rates for Lithium Ion Batteries

Inhomogeneous reactions in porous anodes may lead to lithium plating at high C-rates. Inhomogeneous lithium intercalation behavior in cathodes and anodes has been studied on particle and macroscale (i.e., cell) length scales. The effects of various physical and electrochemical phenomena (e.g., ionic transport, mass transport, interface reaction kinetics, and electrode thermodynamic behavior) have been studied in the context of reaction inhomogeneity. However, an accurate theoretical understanding of how these accelerate lithium metal plating has not been established in fast charging applications. Here, analytical and numerical modeling is used to develop a more complete understanding of how these coupled, nonlinear electrochemical and physical effects interplay to cause lithium plating. Specifically, it is shown that simple analytical solutions (which are functions of one or several nondimensional numbers) can with surprising accuracy approximate the onset of lithium plating predicted by calibrated numerical models of graphite half-cells. These analytical and numerical results are compared against in situ experimental observations of lithium plating onset during fast charging. This work attempts to use simplified analytical analysis to clarify and unify findings in more complex numerical models, which can ultimately provide strategies for mitigating Li metal plating during fast charging. Application of this theory for design and optimization of electrodes with engineered architectures is discussed.

Electrolyte/Electrode Interface Reaction in Polysulfides Insoluble Lithium-Sulfur Battery Using Li-Glyme Solvate Ionic Liquid

Lithium-Sulfur (Li-S) battery is attracting attention as a new generation secondary battery. However, one of the major problems is dissolution of discharge products of lithium polysulfides (Li2Sn: n = 1, 2, 4, 6 and 8) that cause the self-discharge. Solvate ionic liquids (SIL), which consist of a solvate ion and its counter ion, are a subclass of ionic liquids. Li-Gn SIL is yielded by equimolar mixing lithium bis-(trifluoromethanesulfonyl)amide (LiTFSA) and glyme, an oligoether such as triglyme and tetraglyme (Gn : CH3O-(CH2CH2O) n -CH3, n = 3, 4). Watanabe and Dokko et al. [1] reported that the Li-glyme SIL had low solubility of the polysulfides, and proposed polysulfides insoluble Li-S batteries using these electrolyte solutions. Recently, a sulfolane-based super-concentrated electrolyte solution (SCES) also exhibits low solubility of the polysulfides and has been applied to Li-S battery [2]. Both of Li-Gn SIL and the SCES are polysulfide insoluble electrolytes, however, the Li-S batteries with the SCES has better battery performance than that with Li-Gn SIL, implying that the different discharge reaction paths. In this contribution, in situ electrochemical impedance spectroscopy (EIS), which can acquire charge-discharge curves and impedance spectra simultaneously, is applied to the Li-S battery using the Li-Gn SIL to obtain further insight into the discharge behavior.A positive electrode slurry was obtained by mixing a sulfur S8, a Ketjen black (KB, EC600JD, Lion Corporation) and a carboxymethyl cellulose (CMC2200, Daicel) at a weight ratio of 60 : 30 : 10. The slurry was spread on an Al foil to obtain a KB-S composite electrode. The typical loading of the sulfur was 1.0 mg cm-1. A negative electrode and a separator were used a lithium metal foil (Honjo Metal) and a glass separator (GA-55, Advantec), respectively. The Li-Gn SIL electrolyte solution was prepared by mixing LiTFSA, G4 and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) as the molar ratio of 1 : 1 : 4. The Li-S batteries were assembled using the CR 2032 coin-type cell in an Ar-filled glove box. In situ EIS measurements were conducted at different C-rate under constant-current discharging/charging condition using an electrochemical measurement system (SP-150, BioLogic). The current values were 336 and 84 μA. The DC current was superimposed with a small AC current adjusted so that the response voltage amplitude did not exceed 10 mV. The measurements were carried out in the frequency range from 500 kHz to 10 mHz.The voltage drop is observed at the DOD = 20-35 %, in the discharge profile measured at the high C-rate (336 μA), whereas that measured at the low C-rate (84 μA) has no voltage drop. The compensation for the changes over time [3,4] was performed on the obtained impedance spectra to determine instantaneous impedance spectra at a specific DOD (depth of discharge). Two capacitive semicircles and a straight line are observed for all of the investigated systems. The semicircle in the high frequency range (< 10 Hz) is asymmetrical, as if two semicircles in the high frequency range from 500 kHz to 1 kHz and in the middle frequency range from 1 kHz to 10 Hz are overlapped. For the high C-rate, the diameter of the semicircle in the middle frequency range increases with increasing DOD and remarkably increases at DOD = 20-35 %. By contrast, in the low C-rate, the diameter does not change during discharging. This semicircle is assigned to the charge transfer resistance of the negative electrode. According to the previous studies [5, 6], when the charge transfer reaction of lithium is faster than the diffusion rate of G4, the solvation structure changes due to the lack of G4 coordinating to Li+. This solvation structure change causes suppression of Li+ elution to increase the charge transfer resistance of the negative electrode. References 1) K. Dokko et al., J. Electrochem. Soc., 160, A1304-A1310 (2013).2) A. Nakanishi et al., J. Phys. Chem. C, 123, 14229-14238 (2019).3) Z. B. Stoynov et al., J. Electroanal. Chem., 183, 133-144 (1985).4) M. Itagaki et al., J. Power Sources, 135, 255-261 (2004).5) N. Serizawa et al., J. Electrochem. Soc., 160(9), A1529–A1533, (2013).6) A. Miki et al., J. Mater. Chem. A, 9, 14700–14709, (2021).

Scalable Aqueous Battery Electrode Processing Strategy to Improve High C-Rate Capability of Lithium-Ion Battery Electrodes

N-methyl-2-pyrrolidone (NMP) is a popular solvent in the battery industry, but its environmental impact has caused a shift towards aqueous-based slurry compositions. However, its use is limited in several nations due to its hazardous effects on humans and the environment. Developing environmentally friendly aqueous processing for electrode manufacturing is crucial as a countermeasure. To implement green and sustainable production method, a water-based battery electrode processing is devised to replace NMP, the standard organic solvent. In addition, the manufacturing procedures of lithium-ion battery electrodes must be tuned for the electrodes to provide equivalent performance to those produced by conventional processing. In this study, we developed a simple aqueous battery electrode manufacturing method to form channels to reduce tortuosity and kinetic limitation of thick, high mass loading LIB battery electrodes and, more importantly, to improve rate performance at high C-rate while ensuring scalability and lowering electrode manufacturing cost

The Effect of Particle Size and the Material Loading to the Performance and Stability of the LFP Batteries

LiFePO4 (LFP) is one of the most studied materials for Li-ion battery cathodes. It provides excellent safety and long cycle life; however, it displays limited capacity when compared to other cathode materials. The physical properties of LFP strongly affect the performance and stability of the final battery. Among them, particle size is known to be crucial and, in addition, the maximum acceptable electrode loading certainly depends on it. Herein, the effect of particle size as well as the loading of the coating on the performance and stability of the LFP electrode is studied by using both galvanostatic charge-discharge and electrochemical impedance spectroscopy. Two powders displaying average particle sizes of 0.88 µm (LFP-1) and 0.26 µm (LFP-2) have been selected to prepare two different sets of electrodes via water-based spray with Xanthan Gum binder. Different coating loadings were prepared on circular current collectors (Æ = 1.55 mm): 3 mg (1.59 mg/cm2), 6 mg (3.17 mg/cm2) and 12 mg (6.35 mg/cm2). Half-cells were analysed according to their capacity, electrochemical properties and capacity retention after cycling.First, the effect the loading on the capacity of the cells was determined within both LFP-1 and LFP-2 sample groups (Figure 1). Results show that both groups are indeed affected by increasing the active mass loading, but the LFP-2 series to a lower extent, whatever the cycling rate. In the meantime, the rate capabilities of the electrodes were studied by comparing the electrode capacity as a function of the C-rates. Overall, electrodes with the lowest loading (3 mg) can sustain their capacity on higher C-rates regardless of the sample group. It confirms that lower loadings of the coating are preferable for high C-rate applications. The difference between LFP-1 and LFP-2 sets are much more apparent for 6 mg and 12 mg-loaded electrodes as the relative difference can reach 25%; this result shows that active materials with smaller particle size are more suitable for high C-rate applications.Capacities and capacity retention results were investigated by using EIS in order to understand the electrochemical property difference between the two powders as well as between the different electrode loadings. Firstly, effect of loading amount has been observed and for LFP-1 cells, when the loading increases (from 3 mg to 12 mg), a resistance (Rs) increase (from 15 to 56 Ω) can be observed. Secondly, effect of particle size change has been observed and it has been seen that the charge transfer resistance (Rct) decreases strongly (from 93 to 53 Ω) between LFP-1 and LFP-2 for 3mg loading cells respectively. This is a direct consequence of higher surface area of LFP-2.Second, the stability of the electrodes was examined. To that aim, half-cells were submitted to a sequence of varied C-rate cycling similar to the performance measurement. Then, they were cycled for 100 cycles at C and, finally, the varied C-rate sequence was applied again. The first and second sequences were compared with each other to obtain capacity retention between the the first and second sequences, which enables observing the effect of ageing.Results (Table 1) show electrodes with lower loading get less effected by the degradation, regardless of the LFP used. For both powders, the capacity remains high even at high C-rates. The reverse can be told for the electrodes with the highest loading. Regardless of the LFP chosen, the degradation is quite harsh as it can go as low as 28% capacity retention. This suggests that thin coatings are affected less by the degradation while it is quite dramatic when the loading increases. Comparison between LFP-1 and LFP-2 shows the impact of the powder particle size: electrodes made of smaller particles are less effected by the degradation. The difference can go up to 36% and 69% between LFP-1 and LFP-2 respectively.Electrochemical properties were investigated for 3 mg-loaded electrodes with the EIS before and after cycling. Increase in all observed values (Rs and Rct) has been observed after cycling (Table 2). The increase in values are much more dramatic for LFP-1, which explains the worse stability performance upon long-term cycling.Overall, LFP-2 cells display lower Rs and Rct as a direct result of high surface area resulting from their lower particle size. Those properties give them the advantage of being more tolerant to increasing loadings and increasing C-rate. In addition, cells prepared with smaller LFP particles are affected less by the degradation, possibly because the morphology is less affected by the cycling. Further study of morphology or crystallography modifications will be conducted to determine the origin of degradation. Figure 1

High C-Rate Dynamic Lithium (de)Insertion Pathway Investigated via Synchrotron-Based Operando XRD and Operando Scanning x-Ray Microscopy

Lithium-ion insertion kinetics fundamentally hinges upon phase transformation behavior during (dis)charging and understanding the rate-dependent kinetics is crucial for the development of high-power batteries. At high c-rates, kinetic hysteresis is amplified and phase evolution becomes heterogeneous and unpredictable. Specifically, discharge becomes more sluggish than charging of most battery electrodes including LiNixMnyCozO2 (NMC) and LiFePO4 (LFP). Here, we developed an operando soft x-ray microscopy to simultaneously observe surface charge transfer and bulk lithium diffusion in facet-controlled individual battery particles over a wide range of cycling rates (0.01 – 10C). Our result unambiguously reveals that dynamic asymmetry between fast charging and discharging originates from auto-inhibitory Li-rich and autocatalytic Li-poor surface domains, respectively. In addition, we developed synchrotron-based operando fast XRD to track phase evolution during fast cycling. We directly observed that sluggish Li diffusion at high Li content induces different phase transformations during charging and discharging, with strong phase separation and homogeneous phase transformation during charging and discharging, respectively. Moreover, by electrochemically manipulating the lithium-ion concentration distribution within NCM particles, phase separation pathway could be redirected to solid-solution kinetics even at 7 C-rate. Our work lays the groundwork for developing high-power applications and ultrafast charging protocols Figure 1

Li Metal Anode with a LiZn Alloy Interlayer for Li-Metal Polymer Batteries

All-solid-state batteries (ASSB) require stable and safe Li metal anode, which needs surface preparation to increase lithium diffusion and impede the formation of dendrites. In this work, the formation of a thin LiZn layer on lithium metal using sputter deposition is reported. This method was selected due to the absence of solvents and by-products generated during the modification, for its rapidity and because the formation of the alloy is performed in a clean and controlled atmosphere. Zinc has been chosen for its low cost and high Li+ ion diffusion coefficient of the corresponding LiZn alloy that is 1000 times higher than lithium. Different parameters for the Zn deposition were investigated such as the distance between the Zn target and Li foil, the effect of substrate tilt and the direct current applied to the target. Electrochemical performance of LiFePO4/solid polymer electrolyte/Li ASSB demonstrated the superiority of the LiZn anodes and the clear influence of deposition parameters on the durability and performance at high C-rates. Scanning electron microscopy images of the cross-sectional view of LFP/SPE/Li stackings extracted from pouch cells after cycling showed an evident migration of Zn into the bulk Li metal anode as well as the formation of AlZn nanoparticles. In addition, the formation of Li dendrites was effectively reduced for the cells made with the LiZn-protected Li metal anode. Finally, we reported an interesting observation concerning the influence of sputter conditions on the variation of morphology of Li grains.

Ceramic Fillers for Improved Lithium-Sulfur Batteries

With the decarbonization of transportation, the demand for electric vehicles (EVs) and batteries that can power these EVs has been increasing. Lithium-ion-based batteries are already well-established and are considered the main chemistries to power current EVs. However, limited specific energy (< 300 Wh/kg) prevents these batteries from having high mileage vehicles. Lithium-sulfur batteries are considered the most promising next-generation energy storage system as they high theoretical capacity (~1675 mAhg-1), low cathode materials cost, and cell energy densities that can exceed 700 Wh/kg [1,2]. However, some major drawbacks prevent the Li-S battery system from being applicable in energy devices and hinder its commercialization, that include low power density and rapid capacity degradation during their cycling life. In addition, the lithium metal anode in Li-S batteries bring various issues to the forefront such as continuous solid electrolyte interface growth, dendrite formation, and loss of active lithium and electrolyte. These issues are further exacerbated at high C-rates which increases the possibility of an internal short-circuit and sudden cell failure [3]. In order to promote longer life cycles and prevent sudden cell failure, a thorough understanding of the cell’s electrochemical behavior is crucial for the development of a stable and practical Li-S battery system. The introduction of oxide fillers such TiO2, Al2O3, SiO2, etc. has been previously studied in various lithium-ion systems and has been shown to improve the cell’s lithium-ion transport properties, which in turn improve the performance of Li-S cells [4]. When used as interlayers they can also trap soluble polysulfides diffusing out of the cathode and reduce their crossover to the anode which helps reduce the shuttle effect of said polysulfides.In the present study, the use of a polysulfide immobilizing system to reduce sulfur loss and improve capacity retention has been demonstrated. The galvanostatic charge-discharge cycling study shows that cells retain higher capacity during the course of cycling. The initial capacity for Li-S cells with the filler average 1300+ mAh/g (C/10) while the capacity stabilizes around 1000 mAh/g after 3 cycles (C/5). The capacity retention at C/5 after 75 cycles was approximately 875 mAh/g which represents a rate 0.17% drop per cycle. When compared to control cells, the cells containing no fillers had lower initial capacity that averaged 1050 mAh/g and that rapidly declined to stabilize around 650 mAh/g. However, after this major drop, the cells remained stable no with measurable drop after 75 cycles. The behavior indicates that the cells with fillers delayed the effect of sulfur loss experienced in cells without fillers; however, the slow capacity drop that ensued, indicates that while polysulfide trapping was efficient it was unable to fully prevent it. The effect of fillers on the Coulombic efficiency (CE) also supports the polysulfide “trapping” mechanism and shows the ability of the cell to reduce the shuttle effect that contributes to lower CE values. Further electrochemical studies have been performed to understand the mechanisms of the improvement of the cell.

(Invited) Solvation and Double Layer Structures in Nonaqueous Electrolytes for Facile Electrochemical Kinetics

Nonaqueous electrolytes are indispensable for high-voltage/high-energy electrochemical systems. They are particularly important for batteries that can work normally at very low temperatures and can be recharged at high C-rates. Under these extreme conditions, solvation and double layer structures at the electrolyte-electrode interfaces, which were considered less critical than other processes like solid-phase diffusion, appear to play an important role in enabling fast reaction kinetics. Due to the use of multiple co-solvents, salt mixtures, and various additives in novel nonaqueous electrolytes, the interfacial solvation and double layer structures are no longer as simple as the classical understanding based on aqueous electrolytes. In this presentation, we will introduce our recent efforts in realizing fast ion intercalation (both anions and cations) in graphite electrodes and ideally stable alkali metal plating in nonaqueous electrolytes in wide ranges of current densities and temperatures. By combining classical molecular dynamic (MD) simulations of the interfacial electrolyte structure near a charged electrode, density functional theory (DFT) calculations of the distorted solvation structures, operando microscopy of the electrode reactions, and postmortem chemical analysis of the solid-electrolyte interphase (SEI) layers, we confirmed the importance, necessity, and principle of formulating high-performance electrolytes based on molecular scale understandings of the complex interfacial structures.

Mathematical Toolbox for Joint Structural and Electrochemical Analysis of Lithium-Ion Battery Cells

Increasing interest in the automotive field for electrification has led to an increased demand for lithium-ion batteries (LIB). LIB remain the most popular and widely applied energy storage technology. The microstructure of the positive electrode of LIBs governs its electrochemical performance. For this reason, it is quite imperative to determine an optimal electrode microstructure design to achieve the best possible energy properties. Mechanistic simulation models can be a powerful tool in analyzing the effect of microstructural parameters on the battery cell performance. Not only do they negate costs for necessary materials, but they also allow analysis and optimization while avoiding time-consuming experiments.Doyle-Fuller-Newman (DFN) models, being pseudo-2-dimensional (P2D), are computationally less expensive than their higher dimension counterparts; however, they often apply the Bruggeman relation to compute effective parameters such as the electrode conductivity of the electrode. Despite its simple implementation (i. e. a correction factor to reflect effective parameters), the Bruggeman relation delivers inaccurate results. [1, 2]In this work [1], we coupled a DFN model with the structure surrogate model from [2], excluding the Bruggeman relation. The model predicts the effective transport parameters and thus the battery performance more accurately. With this coupled model, we investigated the effect of the cathode mass loading and density on the achievable volumetric discharge energy density. [1] Furthermore, we developed a numerical optimization tool, which can predict the optimal structural parameters for maximum energy density. Our findings suggested different optimal designs for different current densities; whereas higher mass loading was preferred at lower C-rates, it was less favorable at higher C-rates. The concentration profiles of lithium-ions across the cathode thickness at the end of discharge suggest transport limitations to be the main reason behind this. As a further step, we carried out an uncertainty analysis to determine the robustness of the optimal designs to structural fluctuations with respect to their energy density.Our findings provide a deeper understanding into the influence of structural parameters on the discharge performance of lithium-ion battery cells, using only simulative methods. Additionally, our methodology of numerical optimization and subsequent uncertainty analysis allows for a quick and simple method for determining optimal structural parameters and their robustness against fluctuations. This approach can assist to produce battery cell electrodes with an optimized design in industry as well as help simulative and experimental researchers to further investigate optimal electrode design.[1] Karaki et al., Energy Technology 2022 [2] Laue et al., E. Acta 2019 Figure 1

Demystifying the Asymmetry in Lithiation/Delithiation Behaviors of Silicon Anodes for Lithium-Ion Batteries

One critical factor that impedes the wide adoption of electric vehicles is the charging time, which is considerably longer when compared to the refuel time of internal combustion vehicles. To shorten the charging time to less than 6 minutes, extremely fast charging (XFC) of more than 10C is required. In recent years, silicon was regarded as a promising candidate for fast charging because it has a high energy density and is less prone to lithium dendrite growth. However, existing Silicon technologies have not surpassed the 6-minute charging goal. Here, we discuss the possibility for XFC of a three-dimensionally engineered electrically conductive porous Ni/Si composite anode. This anode structure can effectively alleviate the huge volume change upon cycling and provide a pathway for fast electron and ion conduction. Although it shows excellent delithiation (discharging) rate capabilities when coupled with an optimized electrolyte, the lithiation capacity is severely limited at higher C-rates. To study the asymmetry in lithiation/delithiation and the mechanism of relatively sluggish lithiation, we performed rate performance test, Galvanostatic Intermittent Titration Technique (GITT) and Direct Current Electrochemical Impedance Spectroscopy (DCEIS). Based on our findings, we propose the potential rate limiting step for lithiation, which is believed to improve the charging rates substantially when overcome.

Experimental challenges for electrochemical evaluation of cathodes in lithium-ion battery half-cells

The rising demand for lithium-ion batteries and the constant requirements for better performance have stimulated the development and improvement of materials. Reliable procedures and careful evaluations are needed in order to guarantee quality of the improvements proposed. Thus, in the current work several steps from material characterization to electrochemical analysis were investigated for NMC811 cathode. It is demonstrated that slurry rheology is affected by materials characteristics, preparation, and mixing, parameters that must be controlled to obtain adequate electrode. Calendering and uncaledering electrodes were studied with porosity values of 28, 38, and 61 %. As confirmed by rate capability and impedance measurements, calendering improves performance; however, optimization is required to ensure morphology integrity of the NMC particles, as evidenced by scanning electron microscopy analysis. The effects of separator were also evaluated, where an interesting approach using glass fibers is demonstrated to be appropriated for electrochemical evaluation in half-cells. Two distinct cathode mass loadings (4 and 17 mg·cm−2) were investigated to demonstrate how it can lead to different results, especially at high C-rates and over stability measurements. The influence of all the mentioned factors is reported and discussed in detail. The experimental results show the importance of careful analysis of several aspects of half-cell preparation and measurements.

State-of-health estimation for lithium-ion battery using model-based feature optimization and deep extreme learning machine

Accurate and reliable estimation of state of health (SOH) is essential for the safe and efficient operation of battery energy storages. However, random charging/discharging behaviors and ambient conditions complicate the online SOH estimation. Aiming at an accurate and robust online SOH estimation for lithium-ion batteries, this paper proposes a SOH estimation method using model-based feature optimization and improved machine learning. First, an empirical model-based voltage reconstruction method is proposed to reconstruct the voltage curve for solving disturbance-free different time (DT) curves under measurement noises and high C-rates and extract model-associated health features (HFs). Then, an optimal charging voltage window (CVW) determination method is proposed, which extracts the CVW-associated HFs by determining the optimal CVW from partial charging voltage ranges. Finally, a set of informative and multi-attribute HFs are extracted to train an improved deep extreme learning machine (DELM) mode for online SOH estimation. The proposed method is validated based on three datasets of batteries with different materials. The results demonstrate high accuracy and strong robustness to partial voltage range, noise corruption, and ambient temperature fluctuation.

Syringeless electrospun non-woven separator membrane for high-energy and high-power Li-ion battery application

Developing separators to meet the various requirements of next-generation Li-ion batteries (LIBs) is quite challenging because safety issues (good mechanical and thermal properties) and high power and energy density (small thickness and large porosity) exhibit a negative correlation, resulting in a technical contradiction. In general, an electrospun nonwoven membrane is a potential candidate for use in next-generation LIBs, but sufficiently thin electrospun-based nonwoven webs cannot be used as separators owing to their poor mechanical properties and exceedingly large porosity, which fail to prevent dendrite growth. To overcome these shortcomings, we fabricated a composite nonwoven separator using polyvinylidene fluoride (PVDF) and lithium lanthanum zirconium oxide (Li6.4La3Zr2Al0.2O12, LLZO) particles via a syringeless colloidal electrospinning method. To demonstrate the feasibility of our separator membrane for use in high-power and high-energy LIBs, we evaluated the electrochemical performance of an assembled LiNi0.6Co0.2Mn0.2O2 (NCM622)/graphite cell at a high C-rate. The assembled cell containing our separator membrane delivered an outstanding capacity of 115 mAh∙g-1 with a capacity retention of 97% after 100 cycles, even at 3 C. In addition, a Li-metal cell with our PVDF/LLZO separator achieved capacity retention of 86% after 250 cycles at 0.5 C.

Crosslinked Hyperbranched Polyglycerol-Based Polymer Electrolytes for Lithium Metal Batteries

Tailored partially methylated and methacrylated hyperbranched polyglycerols (hbPG-MAx/OMey) combined with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as conducting salt were investigated after crosslinking with respect to their application as solid polymer electrolytes (SPE) in lithium metal batteries. For sample preparation and coating, a straightforward solvent-free photopolymerization method was applied. With the aim of finding the right balance between mechanical and electrochemical properties, electrolytes with different crosslinking densities were studied. High crosslink density increases mechanical integrity but reduces local chain motion and thus ionic conductivity at the same time. Differential scanning calorimetry (DSC), chronoamperometric and impedance measurements show that the hyperbranched polyether structure interacts strongly with lithium cations. Finally, the SPE with the lowest crosslinking density was selected and investigated in cycling tests due to the parameters of highest absolute values in conductivity (2.1 × 10−6 S cm−1 at 30 °C; 2.0 × 10−5 S cm−1 at 60 °C), lowest Tg (from DSC: −39 °C), electrochemical stability window (4.3 V vs. Li/Li+) and mechanical strength (1.6 ± 0.4 MPa at 25 °C). At low C-rates and elevated temperatures (60 °C), cells were cycled with high Coulombic efficiency. At high C-rates, a distinct decrease in specific capacity was observed due to insufficient ionic conductivity.