Anode Active Material Research Articles

Design of Continuous Kneading System for Active Anode Material Fabrication Using Retrofitted Assembly of Co-Rotating Screw Extruder

As the demand for artificial graphite for lithium-ion battery (LIB) anode materials is on the rise, technologies for optimizing the manufacturing processes and reducing the production costs of artificial graphite are crucial. At the same time, globally, regulations on the generation of harmful volatile substances during the artificial graphite production process are also becoming increasingly stringent. In this study, we focused on a continuous kneading process that minimizes the emission of volatile substances during the manufacturing of artificial graphite. To this end, a carbonized material was first prepared from a mixture of needle coke and binder pitch and processed at 3200 °C using two types of co-rotating twin-screw extruder-based continuous kneading equipment to ultimately obtain artificial graphite. The physical properties of the carbonized as well as graphitized materials were analyzed, which revealed the superior performance of the LIB anode material, namely a discharge capacity of greater than or equal to 350 mAh/g, and an initial efficiency of 91% or higher. Thus, a continuous kneading manufacturing process that emits less harmful volatile substances and provides artificial graphite with sufficient battery performance was demonstrated.

Influence of different anode active materials and blends on the performance and fast-charging capability of lithium-ion battery cells

To further extent the driving range of battery electric vehicles, an increase of the energy density of lithium-ion battery cells is necessary. One way to increase the energy density is the use of high-capacity electrodes. The challenges for this kind of electrodes are transport limitations, like the long lithium-ion diffusion path to the layers near the substrate of the electrode, leading to performance degradation during cycling. To get a better understanding on how the material selection influences the battery cell performance, various active materials (graphite, silicon, and hard carbon) are investigated, both, pure and in blends and the relation between material, structure and performance is studied. On material level pure silicon active material has a very high electric resistance compared to carbon-based materials. Nevertheless, on electrode level, the high gravimetric energy density, and the round-shaped particle morphology of silicon result into a lower tortuosity and layer thickness, hence, ionic resistance of the electrode. With respect to cell performance, the ionic resistance seems to have a greater impact compared to the charge-transfer and electric resistance. Therefore, silicon-based electrodes show the best performance.

Investigation of the Influence of Silicon Oxide Content on Electrolyte Degradation, Gas Evolution, and Thickness Change in Silicon Oxide/Graphite Composite Anodes for Li-Ion Cells Using Operando Techniques

This research paper investigates the influence of varying silicon oxide (SiOx) content on the performance and aging of lithium-ion cells. In-depth investigations encompass charge and discharge curves, thickness changes, electrolyte degradation, gas evolution, and chemical analysis of cells with different silicon oxide proportions in the anode and their associated cathodes. The results show that a higher silicon oxide content in the anode increases the voltage hysteresis between charge and discharge. Moreover, the first-cycle efficiencies decrease with a higher silicon oxide content, attributed to irreversible LixSiy formation and the subsequent loss of active lithium from the cathode during formation. The anodes experience higher thickness changes with increased silicon oxide content, and peaks in differential voltage curves can be correlated with specific anode active materials and their thickness change. A gas analysis reveals conductive salt and electrolyte intermediates as well as silicon-containing gaseous fragments, indicating continuous electrolyte decomposition and silicon oxide aging, respectively. Additionally, a chemical analysis confirms increased silicon-derived products and electrolyte degradation on electrode surfaces. These findings underscore the importance of a holistic aging investigation and help understand the complex chemical changes in electrode materials for designing efficient and durable lithium-ion cells.

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

Environmental and economic assessment of a higher energy density and safer operation lithium-ion cell for stationary applications

Europe has made significant progress in decarbonizing the planet by increasing the share of renewable energy, with solar, wind, and water being the primary sources of renewable electricity. Energy storage systems, especially batteries, are critical in integrating high shares of renewable energy and ensuring grid stability. Lithium-ion batteries are the preferred choice due to their acceptable cycle life, safe operation at high voltages, and high energy density. However, there is still room for improvement increasing energy density, safety during operation and producing sustainable batteries. This study has identified new materials that can be incorporated into a high-voltage Co-free spinel cathode cell to enhance its electrical performance and ensure safe operation. These materials include a silicon-containing carbonaceous composite as a long-life high-capacity anode active material and a custom-made porous separator based on PVDF, which facilitates the development of a gel-type electrolyte, improving the cell's safety and providing higher cyclability performance. The introduction of the new silicon-containing carbonaceous composite and the PVDF- based membrane is studied in this work from an environmental and economic perspective. An environmental study is performed using the LCA tool to evaluate the sustainability of the Lithium-ion cell production process. An economic study is also performed to calculate the cost of the cells, including raw materials, transport, production process, and externalities costs related to the production process. The Almagrid cell, which has a safer porous separator and an anode made of silicon-containing carbonaceous composite, showed enhanced safety and similar environmental performance compared to the reference cell. However, Almagrid technology will have the potential to improve its sustainability and cost when in-house synthesized components are optimized and scaled up becoming commercially available.

Experimental and Computational Study on SEI Composition and Electrochemical Performance of Lithium-Ion Battery with Silicon Oxide-Graphite Composite Electrode

Demand on batteries with high energy density is surging. Conventionally, carbon materials have been used as an anode active material, but recently silicon materials are likely to be incorporated to form a composite anode in lithium-ion batteries (LIBs) for higher energy density. However, LIBs which include silicon materials in anode tend to show a low cycle performance especially the ratio of silicon materials in the anode increases. Commercial LIBs still have difficulty in incorporating large amount of silicon materials especially under the requirements where multiple aspects like safety, charging rate and energy density should be totally met.One potential pathway to improve the cycle performance in LIBs with silicon materials is to tune the nature of solid electrolyte interphase (SEI), a thin film which forms at the interface between anode active material and electrolyte. The nature of SEI is particularly important for LIBs with silicon materials because such silicon active materials show large volume changes during battery operation and SEI is dynamically reconstructed. It has been qualitatively reported so far that LiF is an important component for better battery performance. Our work suggests that the ratio of LiF in initially formed SEI is a crucial factor to realize improved cycle performance in such LIBs.In our work, anode with silicon oxide (SiOx)-graphite composite is considered. We investigated the relationship between electrochemical performance of the cell with such composite electrode and the nature of the film estimated by characterization and molecular simulation. We systematically changed the composition of liquid electrolyte to form various types of SEI on anode surface. For characterization, both fresh and aged cells with different electrolytes were dismantled, and SEI components were extracted by designated solvents, then NMR (nuclear magnetic resonance) was applied to identify the SEI species and quantify the amounts of major SEI components. Comparison between the evolution of SEI amount and an impedance element in electrochemical impedance spectroscopy during aging indicates that degradation of the cells is closely related to the growth of SEI. To further deepen understanding the role of LiF, molecular dynamics simulation was carried out, where the mixture of LiF and typical organic SEI was modelled. Correlation between calculated mechanical property and measured electrochemical performance of the cells were revealed. In our presentation, the requirements that SEI should satisfy will be discussed from the insight of electrochemical measurements, NMR characterization and modeling approaches.

Comparing the Lithiation and Sodiation of Hard-Carbon Using Online Electrochemical Mass Spectrometry

Sodium-ion batteries (SIBs) are a promising alternative to lithium-ion batteries (LIBs), especially for applications in which weight and size play a subordinate role.1 In contrast to LIBs, graphite is not a viable anode active material for SIBs since sodium cannot be inserted into graphite. So-called hard-carbons are promising anode active materials for SIBs because of their easy synthesis, high capacity, and high cycling stability.2 Major challenges are the high irreversible capacity in the first cycle and the stability of the solid electrolyte interphase (SEI).3 - 4 Online electrochemical mass spectrometry (OEMS) is a powerful tool for identifying and quantifying evolved gasses during SEI formation, giving insight into the mechanism of SEI formation. For LIB research, our group had developed a two-compartment OEMS cell design that enables the investigation of evolved gases from one of the electrodes of a battery cell without interference from the gases evolved from the other electrode, which is particularly useful for the mechanistic study of electrolyte additives or impurities without influences of the counter electrode.5–8 In this study, we investigate the gas evolution during the first lithiation/delithiation cycles of a hard-carbon anode active material using our existing two-compartment cell design. This will then be compared to the gas evolution during the first sodiation/desodiation cycles of the same hard-carbon material using a newly developed two-compartment OEMS-cell design for the study of sodium-ion batteries, which is based on a gas impermeable solid electrolyte separator composed of sodium ion conducting β-alumina. We compare the quantities of evolved gasses and look at the onset potentials of gas evolution during the first alkaline metal insertion. On the basis of gassing and impedance data,9,10 the differences in SEI formation and its properties will be discussed.Acknowledgments: We gratefully acknowledge funding by the BMBF (Federal Ministry of Education and Research, Germany) for its financial support under the auspices of the ExZellTUM III project, grant number 03XP0255

Developing Tin Anodes for Aqueous Batteries

Aqueous batteries based on metal anodes present an attractive alternative to lithium-ion for long-duration energy storage due to their low-cost, high-safety, and theoretically high energy density. Still, despite many efforts towards development and commercialization, metal anode systems remain hampered by irreversible hydrogen evolution (HER), detrimental shape change, and passivation during cycling. Recognizing the immediacy required to enable the renewable energy transition, our research is focused on developing alternative anode chemistry based on Tin (Sn) for aqueous batteries.Sn metal has been used in aqueous battery systems as additives or current collectors to mitigate side reactions due to its high overpotential for HER. However, little attention was paid to its potential use as a redox active material in aqueous electrolytes. In this talk, we will discuss our efforts to develop Sn as an aqueous anode with high capacity and cyclability. We will first present our development of pouch cells to enable aqueous cells while minimizing the side reactions from cell components other than the active materials. Preliminary data demonstrate the feasibility of using Sn as anode active materials via a 4-electron process in aqueous systems. To investigate the mechanism and improve the Coulombic efficiency, we perform operando X-ray diffraction (XRD), rotating ring disk electrochemistry (RRDE), electrochemical quartz crystal microbalance (EQCM), and 117Sn nuclear magnetic resonance (Sn-NMR) on the Sn system. Lastly, we will show our improvement based on the mechanistic understanding that enables Sn-based full cells with high Coulombic efficiency, high areal capacity, high utilization rate and long capacity retention.

Solvent-Based Electrode Recovery for Direct Recycling of Li-Ion Batteries

The surging demand for Li-ion batteries (LIBs) in electric vehicles and consumer electronics drives the enormous expansion of cell manufacturing globally, resulting in a significant amount of manufacturing scraps and vast stockpiles of spent LIBs in near future. Recycling those waste LIBs and reintegrating the recovered materials into the battery supply chain are becoming critical to build a sustainable battery ecosystem. Cathode active materials (e.g., LiCoO2, NCA, NMC) and anode active materials (e.g., graphite) are tightly adhered to metal current collectors (Al and Cu) through organic binders (e.g., PVDF). Separation of those electrode materials from metal foils is challenging yet an enabling step for the direct recycling of LIBs. In this talk, a simple yet efficient solvent-based recovery process for delaminating electrode films from metal foils will be presented. Because of the absence of harsh chemicals, the recovered electrode films and metal foils are battery grade and free of damage in terms of physical and chemical properties. Additionally, reintroducing the recovered electrode materials into a new loop of cell manufacturing will be discussed. This environmentally friendly and cost-effective separation technique not only presents a closed-loop recycling approach but also greatly advances battery recycling into a new paradigm.

(Invited) Recent Progress Towards Giga-Scale Sodium-Ion Batteries

Ongoing lithium-ion minerals supply chain volatility has driven price increases and supply shortages, and motivates the development and commercialization of alternative cell chemistries not dependent on those minerals.1-2 Among these alternative chemistries, sodium-ion cells offer promise due to the abundance and low cost of both sodium salts and typical electrode active species such as iron and manganese.2-3 Among sodium-ion electrode systems, Prussian blue analogues offer unique performance advantages including high C-rate charge and discharge, long cycle life, and thermal stability.4-6 Natron Energy has commercialized a unique sodium-ion cell in which each of the anode and cathode active materials are Prussian blue analogues. Products based on these cells are capable of full discharge at up to 60C, full recharge at up to 20C, and operate for tens of thousands of cycles without risk of thermal runaway. However, their energy density is limited by relatively low electrode specific capacities and cell voltage. This presentation will introduce the key materials science concepts that make Prussian blues a commercially viable materials system, as well as those that limit product performance, manufacturability, and the resulting applicable markets. In addition, Natron’s recent progress towards mass manufacturing of cells based on these materials will be summarized. This presentation will conclude with an overview of the key open scientific questions that must be answered for cost effective, giga-factory scale manufacturing of sodium-ion cells to become a reality.

High Areal Capacity Ni-Rich NMC Water-Based Electrodes with Excellent Long-Term Cycling Stability

Research efforts in the last three decades have resulted in a steady increase in the energy density of Li-ion batteries (LIBs), leading to their integration into electric vehicles (EVs). Therefore, car manufacturers have increased the number of EVs in their fleets and successfully introduced them to the mass market, with 200M of EVs expected to be sold by 2025 [1] . In such a fast-growing market, the cost and the environmental impact of LIB production play major roles. A crucial step in battery manufacturing is the processing of anode and cathode active materials to produce electrode coatings. While commercial anode electrodes (i.e. graphite, silicon-graphite) are already water-based, cathode electrodes (i.e. LiNixMnxCoxO2 (NMC), LiNi0.5Mn1.5O4 (LNMO) etc.) are still largely processed using organic solvents, specifically N-methyl-2-pyrrolidone (NMP), with poly(vinylidene difluoride) (PVDF) as a binder. However, the NMP-PVDF combination has many disadvantages [2]. Firstly, the binder is considerably more expensive than water-soluble binders and not easy to dispose of at the end of the battery life. Secondly, NMP is also costly and toxic, and being a volatile organic compound (VOC), needs solvent recovery at commercial scale. On the other hand, water-soluble binders such as Na-carboxymethylcellulose (Na-CMC) and styrene butadiene rubber (SBR) are not only cheaper but also easier-to-recycle [3]. Additionally, the use of water as a solvent would remove the need for solvent recovery. It is then clear that switching to water-based processing for cathode materials would decrease cost and improve the environmental sustainability of LIB production. Nevertheless, aqueous cathode processing has many challenges [2], the major one being the instability of the active material in water. The leaching of Li+ ions gives rise to very high pH (~ 12) values which, in turn, leads to the corrosion of the current collector (aluminium) and gas evolution during coating. Consequently, electrodes usually show cracks and pinhole defects and exhibit poor flexibility. These issues are even more enhanced for thick coatings, which are needed to achieve high energy density cells. Therefore, the electrochemical performance of water-based cathode electrodes is generally poorer than that for NMP-based electrodes.In this work, the effect of additions of phosphoric acid (H3PO4) on slurry rheology, adhesion strength, electrode morphology and the electrochemical performance of Ni-rich NMC cathodes prepared via water-based processing was investigated. To effectively bridge the gap between lab-scale investigations and industrially applicable procedures, pH control of the slurries and roll-to-roll electrode coating were performed at the pilot scale, and only electrodes exhibiting commercially relevant areal capacities (~ 4 mAh cm-2), high active material contents (> 90%) and low binder amounts (3 wt.%) were investigated. Phosphoric acid was added in amounts between 1.5 and 3 wt.%, and a fast-mixing procedure was developed to minimize the contact time between the NMC particles and water. The pH evolution over time showed that at least 2 wt.% of H3PO4 is required to keep the pH below the corrosion threshold of aluminium (pH < 9) for 6-8 hours, which is a usual time scale for industrial electrode processing. All slurries showed shear thinning behaviour with the viscosity of the water-based slurries being slightly lower than that for NMP-based slurries at the shear rate used for coating. Optical micrographs of coated electrodes showed no evidence of defects or agglomerates and good homogeneity. The adhesion to the current collector decreased with increasing amount of acid, e.g., electrodes prepared using 3 wt.% H3PO4 showed cracks at the edges of the coating and delamination.The electrochemical performance of the electrodes was studied in full-cell configuration vs graphite. NMC cathodes prepared with 1.5 wt.% acid showed a specific capacity of around 180 mAh g-1 at C/10 and 165 mAh g-1 at C/3. The specific capacity of the cells decreased with increasing the acid amount. However, electrodes prepared with 1.5 wt.% and 2.25 wt.% acid showed excellent cycling stability, achieving a capacity retention above 90% after 500 cycles, which is comparable to NMP-based electrodes.

An Identifiability Study of Lithium-Ion Battery Capacity Fade Using an Electrode-Specific Cell OCV Model

To achieve more accurate aging diagnosis and more effective management of lithium-ion batteries, it is essential to distinguish among the symptoms caused by different degradation mechanisms and be able to model them. So far, a lot of work has been focused on building mechanistic aging models for certain parameters of a cell model, but thorough examination of the extent to which these parameters can affect the detailed voltage response, and in turn be identified from such measurements, is scarce in literature. Moreover, capacity fade and power fade are often entangled in existing studies using a finite-current discharging/charging setup.As an initial step to unravel such intricate parametric influences and identifiability, we adopt a cell OCV (open circuit voltage) model and ignore polarization due to kinetic effects to focus on degradation manifested in the full-cell OCV curve and total capacity only. This cell OCV model , which is adapted from [1], is parametrized by two electrode OCP (open circuit potential) curves and three independent parameters: the cyclable lithium inventory, and the amount of anode and cathode active materials, all of which are directly related to capacity fade. We visualize and quantify the different impacts of LLI (loss of lithium inventory) and LAM (loss of active materials) on different segments of the cell OCV curve and on total capacity using gradients and Fisher information. Moreover, we use mutual information in a Bayesian setup to identify the amount and kind of measurements required to identify these parameters given a priori knowledge of them. Along the way, we also clarify the differences between electrode SOC (state of charge) and electrode lithium stoichiometry, and their implications for using electrode OCP and determining electrode capacity, which can at times cause confusion.Finally, we demonstrate how some of the degradation patterns outlined in [2], [3] can be cast among the continuum of capacity fade scenarios characterized by this simple cell OCV model. In particular, we show how incorporating electrode coulombic efficiencies into the model unifies and simplifies existing results about accounting for side reaction effects on cyclable lithium inventory [3]–[5].

Dual-Protective Artificial Layer on Lithium Metal Anodes for Improved Electrochemical Performance – an in-Depth Morphological and Electrochemical Characterization

The energy density of traditional lithium ion batteries (LIB) based on graphite intercalation compounds as negative active material is approaching the theoretical limit and are restricting the increasing demand of high energy battery systems for various mobile and stationary applications.[1] Consequently, the implementation of active materials with high specific energies became prerequisite for future battery technologies. Therein, lithium metal is one of the most promising anode active materials to replace state-of-the-art graphite active materials, due to its high theoretical capacity and low electrode potential.[2]However, poor cycling performance, low Coulombic efficiency, and the uncontrollable Li dendrite growth during lithium electrodeposition/dissolution processes remain as predominant challenges.[3] Several approaches were proposed to eliminate dendrite formation by implementing a mechanically and electrochemically stable artificial solid electrolyte interphase or artificial protective coatings (aPC) by in-situ or ex-situ surface modifications.[4] These designed aPCs should feature an increased and uniform Li-ion flux, mechanical robustness and/or protection against electrolyte decomposition, during substantial volume changes upon electrodeposition/dissolution. However, aPCs fail to support long term cycling stability in lithium metal batteries since they cannot cover all requirements.[5] Therefore, it is crucial to design and understand dual- and multilayer system that address multiple aforementioned requisites.[6] In this contribution, a dual-protective artificial layer is constructed on Li metal by physical vapor deposition consisting of an intermetallic LiZn-layer, providing a uniform Li-ion flux, and an inorganic Li3N-layer, which is electron-blocking, thus reveal surface protective properties. In addition to electrochemical characterization, the Li electrodeposition/dissolution behavior was investigated by cryo-FIB/SEM analysis to unravel the mechanism behind the enhanced cycling stability in symmetrical Li||Li cells and cells with a layered oxide-based positive electrode.[1] R. Schmuch, R. Wagner, G. Hörpel, T. Placke, M. Winter, Nature Energy 2018, 3, 267.[2] J. Liu, Z. Bao, Y. Cui, E. J. Dufek, J. B. Goodenough, P. Khalifah, Q. Li, B. Y. Liaw, P. Liu, A. Manthiram, Y. S. Meng, V. R. Subramanian, M. F. Toney, V. V. Viswanathan, M. S. Whittingham, J. Xiao, W. Xu, J. Yang, X.-Q. Yang, J.-G. Zhang, Nature Energy 2019, 4, 180.[3] T. Placke, R. Kloepsch, S. Dühnen, M. Winter, Journal of Solid State Electrochemistry 2017, 21, 1939.[4] N. Delaporte, Y. Wang, K. Zaghib, Frontiers in Materials 2019, 6.[5] D. Lin, Y. Liu, Y. Cui, Nature Nanotechnology 2017, 12, 194.[6] S. Lee, K.-s. Lee, S. Kim, K. Yoon, S. Han, M. H. Lee, Y. Ko, J. H. Noh, W. Kim, K. Kang, Science Advances 2022, 8, 1.

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

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

Li Electrodeposition Modeling for Analyzing the Effect of Li+ Redistribution in Li Metal Secondary Batteries

To meet the high-energy-density requirement of Li secondary batteries for EV applications, Li metal is still being re-examined extensively beyond conventional carbon-based anode active materials. However, unlike intercalation mechanism-based anodes, Li metal anodes (LMAs), suffering from significant surface morphology changes during electroplating and stripping, can accompany several issues such as Li dendrite growth and continuous side reactions, thereby leading to the poor electrochemical performance and cycle stability. Among various reasons of the Li dendrite formation, inhomogeneous and slow Li+ transport to the LMAs are representatively known, accelerating irregular electrodeposition and rapid Li+ depletion on the LMA surface.In this study, we attempted to simulate Li dendrite growth under practical current conditions by developing a 2D Li electrodeposition model. Based on this model, we analyzed the geometric-electrochemical characteristics of Li metal interface depending on Li+ concentration distribution in the electrolyte and SEI. Furthermore, in order to verify a nanomaterial-based micro-convection effect in the electrolyte for improving mass transfer, the Li+ concentration change nearby the interface was calculated while simulating the Li dendritic growth. Also, real 2D morphologies of the Li dendrites were reconstructed and analyzed together in a similar way. As a result, the micro-convection enables relatively uniform Li+ distribution at the LMA interface and enhances the mass transport in the electrolyte, which can suppress the Li dendrite growth even at 5.0 mA cm-2.

3D Microstructure Modeling of Lithium Ion Batteries during Rapid Charging

Battery models can be used to predict conditions ripe for lithium metal plating in the anode during rapid charging. One common procedure is to simulate a rapid charge using a pseudo-two-dimensional (P2D) model and determine if and when the minimum local potential reaches 0.0 V with respect to metallic lithium in the anode. This normally occurs at higher states of charge during a DC fast charging or rapid regenerative charging event. However, we have recently determined that three-dimensional (3D) models, while broadly agreeing with P2D results, demonstrate much variation in the in-plane and through plane direction, which P2D models cannot resolve. Because P2D models employ effective medium approximations, any “local” value in the P2D space along the through-plane coordinate represents an average across a slice of the domain. Therefore, it may be insufficient to use minimum anode potentials from P2D models as indicators of local plating and may only be representative of global lithium plating onset.In this work, the results of rapid-charge 3D microstructure simulations are compared to P2D results. This allows us to verify whether rapid charging induces negative local potentials at the anode active material surface that are left undetected in a P2D model. The expected result implies that the 3D microstructure model is necessary to predict the onset of lithium plating.

Operando X-Ray CT Analysis of Composite Electrode in All-Solid-State Battery Using Silicon Anode

As a next-generation rechargeable battery, all-solid-state battery is expected for used in practical applications, in which electrolyte solution of the current lithium-ion battery is replaced with a solid electrolyte. To further increase the capacity of all-solid-state batteries, silicon is used as the anode active material forming an alloy with lithium. However, in the charge and discharge reaction using silicon anode, poor cycle capability due to the volume change of the silicon alloying reaction has been known. Many reports are limited to the analysis of the volume change of the whole electrode, and there are few reports on the quantitative analysis of the volume change of the silicon active material itself. In this study, X-ray computed tomography (X-ray CT) was used to analyze the expansion and contraction of silicon-active materials in all-solid-state battery. X-ray CT analysis can provide the contacted state information between electrode active materials and solid electrolytes [1]. By operando X-ray CT analysis, the expansion and contraction behavior of silicon particles during charging and discharging on the electrode was studied.Nb-coated LiNi1/3Co1/3Mn1/3O2(NCM), Li10GeP2S12(LGPS), acetylene black (AB) mixed at a weight ratio of 1:1:0.2 were used as the cathode composite. Silicon, LGPS, AB mixed at a weight ratio of 1:1:0.1 were used as the anode composite. All-solid-state battery, Si | LGPS | NCM was assembled in a cylinder with an inner diameter 1 mm. The cell was brought into SPring-8 BL20XU beamline, and the operando X-ray CT measurement was carried out. From the obtained X-ray CT images, the three-dimensional analysis of silicon particles was performed.Mean expansion coefficients of silicon‐particles traced during charging and discharging were calculated. The expansion of silicon particles by charging (lithiation) and the contraction of silicon particles by discharging (delithiation) are confirmed. Furthermore, the volume expansion rate of the silicon particles after the charging is average exceeded 300%. After discharge, silicon shrinkage is observed with delithiation, but the solid electrolyte cannot follow the volume change, and the silicon/solid electrolyte interface is broken. However, the contact is not completely failed, maintaining the partial contact between silicon and the electrolyte.[1] Y. Sakka, H. Yamashige, A. Watanabe, A. Takeuchi, M. Uesugi, K. Uesugi and Y. Orikasa, J. Mater. Chem. A, 10 16602–16609 (2022).Acknowledgement: This work was partially supported by the New Energy and Industrial Technology Development Organization (NEDO), JPNP20004.

Silicon Hysteresis and Voltage Relaxation Phenomena: Implications on Overpotential Analysis

Currently, many strategies are being developed to enable a successful implementation of silicon anode active material into commercial lithium-ion cells with the goal of increasing their specific capacities and energy densities. Compared to the commonly used graphite active material, silicon gives rise to a number of challenges owing to its large voltage hysteresis. Next to a decrease in energy efficiency and a significant corresponding heat evolution during cycling,1 the path-dependency of the potential and the resulting ambiguous voltage vs. SOC correlation complicates the development of battery control systems. While the origin of the voltage hysteresis is not yet fully understood, several studies suggest that it can, to a large part, be explained by compressive and tensile stress on the silicon material induced by its lithiation and delithiation respectively.2, 3 Another hysteresis effect which may also be explained by changes in mechanical stress is the unusual voltage relaxation of silicon at open-circuit voltage (OCV) conditions: the voltage undergoes significant changes at open-circuit and the voltage relaxation is still significant over extended periods of time.4 The implications of this voltage relaxation/hysteresis behavior on the commonly used experimental methods for the analysis of overpotentials (EIS, GITT, DCIR) have, to the best of our knowledge, not been analyzed in the literature.In this study we characterize the hysteresis and voltage relaxation behavior of a silicon-dominant electrode containing 70 wt% micro-scale silicon particles (Wacker Chemie AG) for which the amorphous silicon fraction is reversibly lithiated to the composition Li2Si (reversible capacity: 1200 mAh/gSi).5, 6 We find an offset of ~60 mV between the voltage after a 2 h OCV phase compared to the voltage at a very slow rate of C/20, which is surprisingly large compared to the voltage differences observed between different C-rates (e.g., ~10 mV between C/20 and C/2, see Fig. 1). This suggests that a form of structural relaxation may occur in the silicon material once there is no ongoing (de-)lithiation. As a result of this, the offset between the potential under load and at open-circuit cannot be used to calculate a resistance or a diffusion coefficient, as would typically be done for other active materials.7 By comparing charge/discharge potential curves recorded at different C-rates for thin silicon electrodes (1.0 mAh/cm2), effective cell resistances are estimated. Based on these results, methods used for the characterization of the kinetics of silicon are critically analyzed for their significance. We compare galvanostatic impedance (GEIS) measurements performed under load to potentiostatic impedance (PEIS) measurements performed at OCV. Further, we compare ΔE/ΔI values calculated at different points in time after the current has been turned off or on in order to analyze the impact and time-scale of the current-independent OCV relaxation. All results are compared to the same measurements performed for a graphite electrode. We ultimately show that the analysis of overpotentials of silicon active materials, when done incorrectly, can yield parameters which are physically meaningless and misleading for the characterization of the kinetics of silicon electrodes. Acknowledgements We gratefully acknowledge the German Federal Ministry of Education and Research (BMBF) for its financial support within the AQua HysKaDi project (03XP0321B). We also thank Wacker Chemie AG for kindly providing the silicon material. References V. L. Chevrier, Z. Yan, S. L. Glazier, M. N. Obrovac and L. J. Krause, 168, 030504 (2021).V. A. Sethuraman, V. Srinivasan, A. F. Bower and P. R. Guduru, 157, A1253 (2010).B. Lu, Y. Song, Q. Zhang, J. Pan, Y.-T. Cheng and J. Zhang, Physical chemistry chemical physics : PCCP, 18(6), 4721–4727 (2016).K. Pan, F. Zou , M. Canova and Y. Zhu, 413, 20-28 (2019).D. Jantke, R. Bernhard, E. Hanelt, T. Buhrmester, J. Pfeiffer, and S. Haufe, 166(16), A3881 (2019).M. Graf, C. Berg, R. Bernhard, S. Haufe, J. Pfeiffer and H. A. Gasteiger, 169(2), 020536 (2022).D. W. Dees, S. Kawauchi, D. P. Abraham, and J. Prakash, 189, 263-268 (2009). Figure 1 Silicon electrode potentials measured against a lithium reference electrode in a half-cell (Swagelok® T-cell setup) plotted against the estimated composition of lithium in the amorphous silicon fraction. (De-)lithiation potentials are shown for the C-rates of C/20 and C/2 and are compared to potentials recorded after 2 hours at OCV. The gray inset shows the offset between the two C-rates and the OCV at the estimated composition of ~Li1Si. Loading: 0.8 mgSi/cm2; areal capacity: 1.0 mAh/cm2; electrolyte: 1M LiPF6 in FEC/DEC (2:8 v:v); separator: two glassfiber separators (VWR); cycling: CC capacity limited lithiation, CCCV delithiation to 1.0 V. Figure 1

Comparative analyses of MIL-88B(Fe) and MIL-100(Fe) metal organic frameworks as active anode materials for Li ion batteries

Two Fe based metal organic framework (MOF) nanorod structures, MIL-88B(Fe) and MIL-100(Fe), were synthesized and their performance as working electrodes for Li ion half-cell batteries was evaluated under identical testing conditions. It was found that MIL-88B(Fe) provides a charge / discharge capacity of 468 mAh/g at the current density of 100 mA/g, which is over 3 times higher as compared to that of MIL-100(Fe) under the same conditions. Nevertheless, after an impressive charge / discharge capacity in the first few cycles, a slow capacity degradation was noticed in the case of the MIL-88B(Fe) material. Energy dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy results suggest that capacity degradation may be due to strained metal coordination in the MIL-88B(Fe) network. In contrast, despite moderate charge / discharge capacity such issues are identified to be minimal in the case of MIL-100(Fe). Electrochemical impedance spectroscopy (EIS) analyses suggest that ohmic and polarization resistance are smaller for MIL-88B(Fe) as compared to MIL-100(Fe) (both cycle 1 and 100). This makes MIL-88B(Fe) an attractive anode over MIL-100(Fe) for Li ion batteries, but stability issues remain a concern with MIL-88(B)Fe.

Constructing Pure Si Anodes for Advanced Lithium Batteries.

ConspectusWith the escalating demands of portable electronics, electric vehicles, and grid-scale energy storage systems, the development of next-generation rechargeable batteries, which boasts high energy density, cost effectiveness, and environmental sustainability, becomes imperative. Accelerating these advancements could substantially mitigate detrimental carbon emissions. The pursuit of main objectives has kindled interest in pure silicon as a high-capacity electroactive material, capable of further enhancing the gravimetric and volumetric energy densities compared with traditional graphite counterparts. Despite such promising attributes, pure silicon materials face significant hurdles, primarily due to their drastic volumetric changes during the lithiation/delithiation processes. Volume changes give rise to severe side effects, such as fracturing, pulverization, and delamination, triggering rapid capacity decay. Therefore, mitigating silicon particle fracture remains a primary challenge. Importantly, nanoscale silicon (below 150 nm in size) has shown resilience to stresses induced by repeated volume changes, thereby highlighting its potential as an anode-active material. However, the volume expansion stress not only affects the internal structure of the particle but also disrupts the solid-electrolyte interphase (SEI) layer, formed spontaneously on the outer surface of silicon, causing adverse side reactions. Therefore, despite silicon nanoparticles offering new opportunities, overcoming the associated issues is of paramount importance.Thus, this Account aims to spotlight the significant strides made in the development of pure silicon anodes with particular attention to feature size. From the emergence of nanoscale silicon, the following nanotechnology played a crucial role in growing the particle through nano/microstructuring. Similarly, bulk silicon microparticles gradually surfaced with the post-engineering methods owing to their practical advantages. We briefly discuss the special characteristics of representative examples from bulk silicon engineering and nano/microstructuring, all aimed at overcoming intrinsic challenges, such as limiting large volume changes and stabilizing SEI formation during electrochemical cycling. Subsequently, we outline guidelines for advancing pure silicon anodes to incorporate high mass loading and high energy density. Importantly, these advancements require superior material design and the incorporation of exceptional battery components to ensure compatibility and yield synergistic effects. By broadening the cooperative strategies at the cell and system levels, we anticipate that this Account will provide an insightful analysis of pure silicon anodes and catalyze their practical applications in real battery systems.