Li Plating Research Articles

The Strategy to Tune Li Stripping/Plating Behavior in Li Alloy Anode

Li metal anode is the most promising anode for high-energy-density batteries due to its high specific capacity (3860 mAh/g) and highest oxidation potential. However, the high reactivity of Li metal with electrolytes and the resultant formation of Li dendrites restrict its practical applications. To tune the reactivity and Li deposition behavior, Li alloys were widely studied and demonstrated to perform better than Li in Li metal batteries.1-4 Here, we studied the electrochemical behavior of one solid-solution phase Li alloy. In this work, the phase transition in the Li stripping process and phase separation after Li plating were observed, which can be attributed to the sluggish Li diffusion in the solid-solution phase of the alloy. To unlock the Li stripping capacity without phase transition, we designed a bi-phase Li composite anode by introducing Li+ conductive materials. Due to the reduced diffusion length, Li can diffuse into the Li solid-solution phase after plating back on the bi-phase Li composite anode, resulting in uniform Li deposition morphology. Accordingly, the bi-phase Li composite anodes showed much better rate performance than the Li alloy or pristine Li. With these findings, it is expected that the new bi-phase Li composite anodes are a promising direction for long-life, high-power, and high-energy Li metal batteries, including Li-S batteries.

Physics-Based State of Health Prediction of Lithium-Ion Battery during Fast Charging

Electrification of the transportation sector and increased use in consumer electronics have driven the increasing demand for lithium-ion batteries (LiBs) (1). Despite their high energy density and long service life, LiBs suffer from capacity degradation due to continuous growth of solid electrolyte interface (SEI) layer and plating of lithium on the anode surface. Graphite, the anode in most LiBs, has a high tendency to catalyze the degradation of the electrolyte consisting of LiPF6 and ethylene carbonate to form an SEI of Li-rich carbonate, phosphate, and fluoride compounds (2, 3). The SEI film grows during service due to the deposition of reaction products and repeated cycles of damage and reformation due to the contraction and expansion associated with volume changes during Li-ion intercalation and deintercalation. Additionally, fast or low-temperature charging of batteries results in lithium plating on the anode surface because the elevated concentration of Li+ on the anode surface results in graphite potential falling below 0V vs. Li+/Li and increased likelihood of Li deposition compared to intercalation (4). Lithium loss due to the side reactions of SEI growth and plating contributes to capacity loss and may increase the likelihood of battery failure. Hence, accurate modeling of the side reactions is required to determine the state of health (SOH) and predict the remaining capacity of LiBs during operation (5).We report an experimentally validated single particle model (SPM) to estimate the influence of SEI growth and Li plating on the capacity changes in Lithium Cobalt Oxide (LCO)/Carbon cells during repeated cycling (6-8). The SPM model idealizes each electrode as a single particle to approximate the cell response. A. Sarkar et al. (5) included the influence of SEI growth, plating, SEI fracture, and temperature in the SPM model to determine the influence of the side reactions on battery performance. The parameters corresponding to side reactions, such as the SEI film growth rate, conductivity of the SEI film, and reversibility of the plating reaction, were determined through comparison of numerical predictions of cell voltage and capacity change with experimental response measured at charging rates of 0.1C and fast charging rate of 2C on PowerStream 35 mAh LCO/C coin cells (Lir2032) as shown in Figure 1. In addition, the coin cells were subjected to charge/discharge experiments at charging rates varying from 0.1C – 5C for 100 cycles. Experimental measurements of the cell capacity changes were compared to model predictions for the different charging rates to validate the modeling assumptions and determine the efficacy of the estimated parameters in describing the cell degradation. The agreement between the model prediction and measured experimental response showed that the single particle model augmented with side reaction mechanisms can describe the cell degradation and is suitable for predicting the remaining capacity and safety of LiBs subjected to a range of charging rates. The model can also predict the accumulation of irreversibly plated lithium on the anode surface during repeated fast charging. The amount of plated lithium determines the severity of dendritic growth, and thus, model predictions of lithium accumulation may be used to estimate the likelihood of battery failure under fast charging conditions. Acknowledgment:This work was supported by the National Science Foundation, Iowa State University, and University of Connecticut.

Characterization of Degradation Mechanisms of Alternative Electrolytes Solutions in Fast Charging Li-Ion Batteries

While the idea that fast charging batteries could be utilized in electric vehicles is enticing, current fast charging batteries face significant challenges that must be mitigated before this application is realized. Fast charging batteries currently suffer from capacity loss and degradation over time which not only affects battery life but poses a safety hazard. The current electrolyte, 1.2 M LiPF6 in 3:7 wt.% EC/EMC (Gen2), contains the salt LiPF6 that when exposed to moisture can form dangerous hydrofluoric acid and contains a carbonate-based solvent that when exposed to oxygen can ignite. In addition, batteries experience degradation over many cycles of fast charging which results in capacity fade and poor battery performance. However, previous studies have shown the potential for other electrolyte systems to mitigate these problems, specifically by using highly concentrated electrolytes1. These studies claim that using these electrolytes results in the formation of a solid electrolyte interphase (SEI) that passivates Li ions better than the Gen2 electrolyte. The SEI is a layer that forms on the anode within the battery and serves as a protective layer that allows for Li intercalation into graphite and can therefore protect against degradation. By using different electrolytes, a different SEI is formed, and different degradation mechanisms are observed. In this way, the SEI can be tuned to improve Li passivation and ionic conductivity by changing the electrolyte’s composition and concentration2. This research focuses on such alternative electrolyte systems and aims to characterize the different degradation mechanisms corresponding to each electrolyte. Favorable performance has been observed using 1.2 M LiFSI in 3:7 wt.% EC/EMC as an electrolyte. We are studying LiFSI in acetonitrile (AN) at higher concentrations than traditional Gen2 to quantify the SEI. We expect AN to form an anion derived SEI, a composition of which results in improved passivation of Li ions1. In this study, we characterize degradation of alternative electrolyte systems through x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Through these methods we can observe and quantify both crystalline, amorphous degradation products due to loss of Li inventory and loss of active material. XPS allows quantification of compositional changes in the SEI layer at the surface of the electrode. The SEM provides qualitative information on degradation such as visualizing lithium plating and dendrite formation. We implement quantitative XRD to measure the crystalline phases of the graphite anode, showing the degree of lithium intercalation and further quantifying degradation such as Li plating. Putting the results of these three characterization techniques together in tandem with electrochemical cycling data paints a picture of the degradation that happens on the anode of a fast-charging lithium-ion battery with respect to electrolyte composition.[1] Yamada, Y., Wang, J., Ko, S., Watanabe, E., & Yamada, A. (2019). Advances and issues in developing salt-concentrated battery electrolytes. Nature Energy. [2] Logan, E. R., & Dahn, J. R. (2020). Electrolyte Design for Fast-Charging Li-ion Batteries. Trends in Chemistry.

(Invited) Lifetime Predictive Model of Capacity Loss, Resistance Increase, and Irreversible Thickness Growth

We present a battery lifetime model that predicts Irreversible battery thickness change under constant pressure operation as the battery ages, along with capacity loss and resistance growth. These metrics are very important for predicting lithium-ion battery state of health (SOH) and remaining useful life due to their interdependence with battery packaging and safety. To design and operate battery storage systems safely, we must be able to predict and detect changes in all three SOH metrics over life accurately and simultaneously. Traditionally, these three SOH metrics have been modeled separately. However, we developed a single model that simultaneously predicts battery capacity, resistance, and expansion over its lifetime.In this work, battery degradation is modeled using the single particle model (SPM) framework, including mechanical damage in the electrodes, which results in loss of active material (LAM), and the side reactions for SEI growth and Li plating, which result in loss of lithium inventory (LLI). We introduce an equivalent stress and concentration dependence of stress to the mechanical damage model. Commonly used fatigue models assume symmetric cycles (zero-mean stress) [1]. To account for cycling conditions with different currents on charge and discharge, an equivalent stress that adjusts for non-zero mean stress is needed. The concentration dependency of strain and the resulting stress allows us to capture different degradation rates for cells cycled at different depths of discharge (DOD). Lithium plating at the separator interface is often described as a spatially non-uniform process using the pseudo-2D (P2D) model. This phenomenon can be captured in the SPM framework using a current-dependent dynamic term to account for spatial-nonuniformity of electrolyte dynamics at higher currents.Experimental data from cells cycling with periodic reference performance tests were used to tune the degradation model. In addition to the standard I, V, and T measurements, continuous measurements of the thickness change of the battery pouch cells were recorded. From this data, we extracted the capacity, electrode state of health (eSOH), resistance, and reversible and irreversible expansion. The test conditions were designed to excite different dominant degradation mechanisms (e.g. mechanical damage) by cycling the cells at different conditions (C-rate, temperature, preload pressure, and DOD). The tuning, which uses accelerated aging simulations [2] (to speed up the tuning process), results in a single set of parameters that predicts capacity loss, resistance growth, and irreversible thickness change as the battery ages, even for conditions that were not used for parameter tuning.The tuning is performed in two sequential steps. First, the parameters related to the electrochemical and mechanical degradation rates, which result in LLI and LAM, are tuned to match the extracted eSOH variables at each Reference Performance Test (RPT). The first tuning gives us the amount of plated Li, SEI growth, and mechanical damage in the particles. We then relate these quantities to irreversible expansion using a linear relationship in the case of SEI and mechanical damage and quadratic in the case of Li plating [3]. The same relationship is used for all cells, and this represents the 2nd tuning step. Our data set and calibration are unique in that the dominant degradation mode is the loss of lithium inventory due to the loss of active anode material. Most prior work on lifetime predictive models relied on SEI growth as the dominant degradation mode. Figure 2 shows the tuned model prediction of the three performance metrics over the cycle life of cells for various cycling conditions. The markers represent the measurement at each reference performance test, and the lines correspond to the model.

Diagnosing NMC Battery Aging Modes Using Digital Twin

Traditional lithium-ion battery (LiB) modeling does not provide sufficient information to accurately verify battery performance under real-time dynamic operating conditions, particularly when considering various aging modes and mechanisms. This paper proposes a lithium-ion battery digital twin that can capture real-time data and integrate the strong coupling between SEI layer growth, anode crack propagation, drying up of Electrolytes, and lithium plating. It can be utilized to predict the degradation behavior, voltage-current profiles in dynamic aging conditions, and analyze the lithium inventory loss (LLI) of Nickel-Manganese-Cobalt-Oxide (NMC) lithium-ion batteries.Commercially available 18650 cylindrical NMC Samsung battery cells were investigated. The cathode and anode materials are LiNi0.5Co0.2Mn0.3O2 and synthetic graphite, respectively. Four dynamic aging test cases using 1C, 1.3C, MC (multistep charging), and 2C, were designed and performed at 25 °C. The reference performance test (RPT) was repeated every 100 full equivalent cycles (FECs) until the cells reached 20 % capacity fade. Figure 1 shows the real-time voltage and current profile captured and predicted by the digital twin.The model takes into account LLI induced by SEI growth and lithium plating, aligning with the LLI calibrated from the differential voltage (DV) endpoint shift (Figure 1h). Based on the model results, SEI growth is found to be the primary contributor to capacity loss before 500 FECs. SEI-induced degradation is minimal under the MC protocol, with the capacity loss varying by less than 5.22% across four test cases (Figure 1e). After 500 FECs, anode cracking becomes a non-linear accelerated aging factor. The crack propagation stabilizes in the initial 200 FECs, followed by unstable accelerated growth leading to capacity loss. Subsequently, a rapid acceleration in capacity loss occurs after 700 FECs (Figure 1f). The growth of anode cracks under the MC aging protocol has a much slower effect on capacity loss compared to the 2C and 1.3C before 500 FECs, as strongly confirmed by the post-mortem analysis. In addition, the lithium plating phenomenon triggers two orders of magnitude less capacity loss than SEI growth and cracking at 25 °C. The MC protocol demonstrates an effective reduction in lithium plating capacity loss compared to the other three traditional charging protocols (Figure 1g). This digital twin can represent a firm physical foundation for future physics-informed machine learning development to predict LiBs degradation behavior.Figure 1. Real-time voltage and current captured and predicted by our designed digital twin under (a) 1C-WLTC, (b)1.3C-WLTC, (c) MC-WLTC, and (d) 2C-WLTC aging profiles. Additionally, (f) illustrates capacity loss density for the four protocols attributed to (e) SEI film growth, (f) anode crack propagation, (g) Li plating, and (h) LLI prediction by the digital twin and DV measurement. Figure 1

(Invited) Developing Periodically-Aligned Fibrous Structures to Suppress Lithium Dendrites for Anode-Free Batteries

We have developed electrospinning-based manufacturing capability for dendrite-free anode-free and anode-less batteries. Electrospinning is a widely used, feasible manufacturing approach to create nano- and micro-porous layers of functional fibers. By tailoring fiber compositions, the electrospun layers can afford a wide variety of functionalities applicable to biomedical templates, separation membranes, and energy storage. Its manufacturing capability is, however, limited to producing randomly oriented fibrous structures. Topology and tortuosity of the electrospun fibrous layers are poorly controlled, making it difficult to systematically investigate structure-property relationships for any given applications, especially electrochemical systems.In this presentation, we will demonstrate how to improve the controllability of fiber construction geometry by electrospinning. Unlike conventional electrospinning, our approach employs a mobile stage that allows precise alignment of fibers. Produced fibrous structures will be used to construct current collectors of the anode-free batteries, one of the proposed beyond-lithium (Li)-ion battery systems for high energy density. While direct, yet reversible, Li plating and stripping on and from the current collector has proven difficult due to uncontrolled dendrite growth, we found that the flat copper foil reinforced by the three-dimensional fibrous structure can enhance Li storage efficiency over an extended number of cycles, outperforming the planar case. We will discuss the effect of fiber compositions and controlled geometrical configurations on stabilizing Li plating and stripping morphologies to suppress Li dendrite growth and provide a fundamental design principle to construct anode-free and anode-less battery cells. Battery manufacturing advanced by this work will offer a systematic strategy to develop next-generation energy storage systems for a sustainable energy future.

High-Frequency Electrochemical Impedance Spectroscopy for Detecting Li Deposition Toward Assessing Thermal Stability in LiBs

Li-deposition is a critical factor in one of the degradation modes of lithium-ion batteries (LiB). The Li-deposition increases the risk of internal short circuits and lowers thermal runaway onset temperature, compromising safety1. Detecting the Li-deposition is possible through disassembly or analysis using large-scale equipment such as muonic X-ray visualization 2. On the other hand, a non-destructive and convenient evaluation technique is required to assess batteries’ safety in commercial use.A novel inspection technique using high-frequency electrochemical impedance spectroscopy (HF-IS) has been developed to detect the presence of Li-deposition3. Electrochemical impedance spectroscopy (EIS), which nondestructively observes ionic diffusion, reaction, and charge transfer in 10 mHz to 10 kHz response, is commonly used for diagnosing the state of battery degradation4. Compared to the conventional EIS, the HF-EIS uses the real part of battery impedance Re(Zbat ) above 100 kHz, allowing observation of only the electronic behavior of the battery in high-frequency regions where ion behavior cannot be tracked. It utilizes the phenomenon of current concentration at interfaces of materials with different conductivities, known as the "skin effect," which is caused by a high-frequency electromagnetic field. Since the Li-deposition occurs at the interface between the negative electrode and the electrolyte, the interface within the high-frequency current path changes from the negative electrode to the Li-metal. This change induces alterations in the electromagnetic field and the high-frequency current path, subsequently resulting in a variation in Re(Zbat ).Figure 1 displays a representative result illustrating the relationship between the thermal runaway onset temperature and the change in Re(Zbat )| freq =1MHz. We conducted a degradation test to deposit Li-metal and a thermal runaway test using two types of 18650 cylindrical cells (NCA-3400 mAh, NCM-2650 mAh). Two batteries subjected to excessive charging C-rates demonstrated the proportional relationship between the decrease in thermal runaway onset temperature and the reduction in Re(Z bat)| freq =1MHz in individual cases. The results indicate that different battery types have different thermal stability of LiB against the Li-deposition.The HF-EIS is not only a safety diagnostic tool but can also contribute to developing battery materials by reducing destructive testing costs. This method of on-the-spot safety quantification diagnosis is expected to contribute to the safer proliferation of the LiBs.Reference1 Li, Y. L. et al. Thermal Runaway Triggered by Plated Lithium on the Anode after Fast Charging. Acs Applied Materials & Interfaces 11, 46839-46850 (2019). https://doi.org/10.1021/acsami.9b165892 Umegaki, I. et al. Nondestructive High-Sensitivity Detections of Metallic Lithium Deposited on a Battery Anode Using Muonic X-rays. Analytical Chemistry 92, 8194-8200 (2020). https://doi.org/10.1021/acs.analchem.0c003703 Ishigaki, M. et al. Operando Li metal plating diagnostics via MHz band electromagnetics. Nature Communications 14, 7275 (2023). https://doi.org/10.1038/s41467-023-43138-w4 Barsoukov, E. Impedance Spectroscopy Theory, Experiment, and Applications Second Edition Preface. Impedance Spectroscopy: Theory, Experiment, and Applications, 2nd Edition, XII-+ (2005). Figure 1

Molecular Understanding of Li Metal Anode

Developing new liquid electrolyte is a promising approach to enable the next-generation high-energy Li metal battery for wide-ranging application such as electric vehicles (EV). However, the high reactivity of Li metal interface renders it crucial to form favorable solid-electrolyte interphase (SEI), via active electrolyte decomposition, for highly reversible operation of Li-metal anode (LMA). Therefore, deeply understanding how the molecular structures of electrolyte species precisely control both the interfacial reactivity and the operational reversibility of LMA, can further guide and inspire new electrolyte systems with progressively improved battery performance.Herein, we systematically investigated the impact of Li salts with different imide anions dissolved in ether-based solvent, on the resulting Coulombic efficiencies (CE) of LMA, whereas beneficial and detrimental molecular motifs were first identified. By leveraging the non-washing XPS protocol newly developed at Stanford, we managed to uncover the distinct molecular reactivity leading to reductive bond cleavage as well as new bond formation at Li-metal potential. Such nanoscale reactivity of SEI-forming reactions was discovered to profoundly govern the macroscopic performance of LMA, which simultaneously emphasized the significance of electric double layer (EDL). Importantly, aided by gas-titration experiments to quantify the by-products in SEI, we revealed the critical molecular origins of irreversible capacity loss of LMA during continuous Li-metal plating and stripping. These new insights allow us to formulate rational strategies of molecular engineering to design LMA interface with high reversibility and minimal side reactivity.

A Multiscale Computational Modeling Framework to Quantify Microstructural Effects on Nucleation of Li Metal on Carbon Scaffold Architectures

Carbon materials with scaffold architecture have been shown to mitigate the non-uniform Li plating/stripping issues during cycling, which is critical for achieving significantly enhanced energy densities and improved safety of Li metal batteries. However, optimal design of the architecture and microstructure of the carbon materials requires fundamental understanding of the Li metal nucleation behavior at different length scales. In this poster, we present a multiscale computational modeling framework to quantify the microstructural effects of carbon materials on the tendency of Li metal nucleation during plating by integrating atomic-scale simulation, mesoscale microstructure-based homogenization, continuum-scale electrochemistry modeling, and classical nucleation theory. We modeled the architecture of the carbon scaffold and the electrochemistry of Li transport across the electrode and electrolyte by finite element simulation to determine boundary conditions for our mesoscale models. We then generated different porous microstructures of various carbon materials by stochastic and physics-based simulations informed from experiments and performed multiphysics-based simulations at mesoscale to identify the electro-chemo-mechanical hotspots which are sensitive to the microstructure morphology. We calculated the energy barriers for Li to form clusters on graphene surfaces as a function of local Li concentrations and electric fields by ab initio molecular dynamics simulations. The synergistic deployment of different models across scales allows us to theoretically estimate the Li metal nucleation tendency based on a modified classical nucleation theory for different microstructures under various electroplating conditions. Comparison of the theoretical predictions and experimental results will be briefly discussed. The insights obtained from this multiscale framework offer new understanding and strategies for the design of carbon scaffold architectures to mitigate the non-uniformity of Li plating and issues in Li metal anode deployment in solid-state batteries.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and 22-ERD-043.

Electrolyte Formulation By Design of Experiments: The Hidden Correlations in the Li-Mediated Nitrogen Reduction Reaction for Ammonia Production

Ammonia, a fundamental building-block for fertilizers and other many commodities, is responsible, through the Haber-Bosh (HB) process, of around 1.4% of the global greenhouse gas emissions. Indeed, HB operates in severe conditions (200 atm), and is fossil fuel dependent, since the few huge, centralized plants are combined with steam reforming for H2 production. To find a renewable-driven and delocalized electrochemical process for NH3 production, complementary to HB, could be a key solution for our society that is facing climate change crisis and that is demographically growing [1].In view of process electrification, the Li-mediated (Li-m) pathway represents the most promising solution in the N2 reduction reaction (NRR) challenging field. Exploiting the unique reducing power of this alkali metal, this strategy achieves the highest Faradic efficiency (FE) and NH3 production rate [2,3,4].Li+ ions from the aprotic electrolyte are electrodeposited on the cathode, where N2 is reduced and protonated into NH3 thanks to a proton donor or a proton shuttle, as EtOH. On the plated Li, a solid electrolyte interphase (SEI) unavoidably forms, and its nature and morphology are straightly dependent on the electrolyte composition. The different diffusion rate of Li+, N2, and H+ trough the SEI layer determines the selectivity towards NH3 formation. The correct reactant ratio at the electrode surface is essential to hinder both the hydrogen evolution reaction and an excessive Li plating, maximizing the FE [5,6].Design of experiment (DoE) together with response surface methodology (RSM) are a powerful tool that can reveal, with a restricted number of experiments (e.g. 9), the optimal composition of the electrolyte towards the highest FE and the hidden intercorrelations among variables. In particular, we aimed at studying two key variables, i.e. EtOH and Li-salt concentration; to this purpose, the Doehlert design with two factors and three replicates of the central point was chosen and RSM was employed to model the response and determine the optimal conditions.The study was repeated with two different fluorinated Li-salt, LiBF4 and LiFOB. LiBF4 has recently shown an improved stability and FE for the Li-m NRR process, correlated to the LiF presence in the SEI layer. The optimal combination of the electrolyte components obtained from the DoE for LiBF4 is in accordance with previous study, validating the statistical methodology applied. The newly proposed salt showed an increase of the 25% in the FE with respect to LiBF4 in the same conditions [7,8]. Experiments was conducted under 20 bar N2 in an autoclaved glass cell with a proper gas purification. As in previous study with this Li-m strategy in this set-up, even in this case the total NH3 amount obtained overcame the amount of possible impurities coming from the N2 gas, moreover controls tests with Ar instead of N2 were performed.

Battery Deactivation for Safe and Efficient Recycling

With the substantial increase in the demand for lithium-ion batteries (LIBs) for the adoption of electrification to reduce CO2 emission, safe and efficient recycling of spent LIBs is essential to utilize LIBs sustainably1. In hydrometallurgy-based or direct LIB recycling systems, which are expected to become mainstream in the future because of their low environmental impacts, deactivation is a crucial pretreatment step to safely handle LIBs during the processes2, 3. However, a common deactivation method, in which an external short circuit is induced using electronic loads or conductive liquid, cannot deactivate LIBs with disconnected electrical circuits or metallic Li plating on the negative electrode surface, despite their high safety risks.We propose the advanced deactivation method, injecting a redox mediator (RM) solution inside the LIBs. The RM delivers electrons from the negative electrode to the positive electrode by cycling the reduction and oxidation on the negative and positive electrodes, respectively (redox shuttle reaction), resulting in discharging LIBs. In other words, the RM causes a short circuit inside the LIB. Therefore, it is possible to discharge a LIB that cannot be discharged externally, for example, a LIB with disconnected electrical circuits due to a safety device operation. Furthermore, the RM can strip Li metal plated on the negative electrode even though it is “dead lithium.” This unique characteristic contributes to the improvement in the safety and the Li collection rate in the recycling processes. Additionally, in this presentation, the deactivation mechanism of LIBs and its relationship with the electrochemical properties of the RMs will be discussed. The present findings will be beneficial and helpful for designing RMs for deactivation of more and more diversified spent LIBs. References J. Neumann, et al.: "Recycling of Lithium‐Ion Batteries—Current State of the Art, Circular Economy, and Next Generation Recycling" Adv. Energy Mater. 12, (2022). A. Kwade, et al.: "Recycling of lithium-ion batteries" The LithoRec Way, Switzerland: Springler International Publishing AG (2018). H. Rouhi, et al.: "Voltage behavior in lithium-ion batteries after electrochemical discharge and its implications on the safety of recycling processes" Journal of Energy Storage 35, (2021).

(Invited) Strategic Cutoff Potential Selection Enables Safe and Long Cycle Life Li4Ti5O12/LiNi0.9Mn0.05Co0.05O2 Batteries for Behind-the-Meter Storage Applications

Behind-the-meter storage (BTMS) encompasses storage and distribution systems that bypass the electric grid. For example, energy stored in BTMS stationary batteries can be used for various purposes including electric vehicle charging or lowering the cooling load demands for large buildings. Many previous studies have focused on Li4Ti5O12/LiMn2O4 (LTO/LMO) batteries for BTMS applications1–3 rather than the more conventional electric vehicles comprised of graphite anodes paired with LiFePO4 or layered oxide materials. LTO/LMO batteries are appropriate for BTMS because they provide a favorable balance of cost, safety, and cycle life, which are the most important criteria for BTMS batteries. LTO’s minimal strain, high operating voltage, and relatively earth abundant materials promote cyclability, safety, and reasonable cost.4 LMO is very attractive to pair with LTO for BTMS applications due to abundancy of Mn, safety, and relatively high operating voltage to enable a higher voltage when paired with LTO.5 While LTO/LMO fulfills many requirements for BTMS applications, the high voltage of LTO and the low capacity of LMO limit energy density and specific energy. Improving energy density has the potential to decrease cost in addition to enabling a smaller battery footprint for space-constrained BTMS applications.With the goal of increasing the cathode capacity at high voltage to improve the BTMS battery energy density relative to LTO/LMO, we investigated LTO paired with LiNi0.90Mn0.05Co0.05O2 (NMC90-5-5). We selected NMC90-5-5 for its low Co content to minimize the impact of the cost volatility and supply chain challenges with Co in accordance with BTMS program goals. We investigated long term cycle life and rate capability of LTO/NMC90-5-5 coin cells with two different N/P ratios and two different charge termination potentials. Without the risk of Li plating at high LTO potentials, the cathode can be safely oversized in LTO systems (N/P < 1) such that the excess cathode capacity provides additional Li inventory to overcome losses during cycling and enables longer cycle life. We compared cells fabricated with N/P < 1 with N/P > 1 and we found that cells with N/P < 1 provided higher cell capacity during 1000 cycle tests. We also varied the full cell termination charge potential (2.6 V versus 2.7 V) for each N/P condition. While the 2.7 V termination potential enabled higher capacity, the 2.6 V termination enabled more stable cycling during 1000 cycle tests. Furthermore, because high Ni content layered oxide systems typically exhibit safety challenges,6,7 we also fabricated 18650 LTO/NMC90-5-5 full cells for accelerating rate calorimetry (ARC) testing. ARC testing revealed a significantly lower heating rate as well as a higher temperature where the max heating rate occurred for cells cycled to 2.6 V versus 2.7 V. These data suggest that the termination potential in NMC90-5-5 is critical for optimizing these cathodes for the long cycle life and safety required for BTMS applications.This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. This work was performed, in part, at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC (NTESS), a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration (DOE/NNSA) under contract DE-NA0003525. Funding was provided by the U.S. Department of Energy's Vehicle Technologies Office under the Behind-the-Meter Storage (BTMS) Consortium directed by Samuel Gillard and managed by Anthony Burrell. The electrodes used in this manuscript are from Argonne's Cell Analysis, Modeling and Prototyping (CAMP) Facility, which is fully supported by the DOE Vehicle Technologies Office (VTO). The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.(1) Y. Ha et al., Journal of The Electrochemical Society 2023, 170 (5), 050520.(2) Y. Ha et al., Journal of The Electrochemical Society 2021, 168 (11), 110536.(3) Y. Ha et al., Energy Storage Materials 2021, 38, 581–589.(4) G. Xu et al., Coordination Chemistry Reviews 2017, 343, 139–184.(5) Z. Radzi et al. Journal of Electroanalytical Chemistry 2022, 116623.(6) L. Gan et al., Applied Physics Letters 2022, 121 (20).(7) J. Lamb et al., Journal of The Electrochemical Society 2021, 168 (6), 060516.

Correlating Homogeneity and Microstructure of in Situ plated Li in “Anode-Free” Solid-State Batteries

Solid-state batteries utilizing Li metal anodes have the potential to offer increased safety and higher energy density compared to state-of-the-art Li-ion batteries. To achieve these energy density gains, the Li metal anode must be thin (<25 µm). Manufacturing of thin Li metal anodes is complicated by the reactivity of Li metal, which forms a thin passivation layer even in controlled environments. The “anode-free” cell manufacturing approach provides an alternative to these challenges. These cells are manufactured with a bare anode current collector (CC) and the Li metal anode is plated in situ at the CC/solid-state electrolyte interface during the first charging step using the Li stored in the cathode active material. While manufacturing cells with in situ formed Li anodes may offer benefits, removing all excess Li in the cell also poses many challenges. The Coulombic efficiency of these cells must be >99.99% to retain 90% capacity over 1,000 cycles [1]. Therefore, when the Li anode is formed in situ during the first charge, the temperature, pressure, and current density must be carefully tuned to optimize the reversibility of the plated Li. To achieve high reversibility of Li metal anodes, the plated Li should be dense, conformal to the current collector and solid-state electrolyte, homogeneous in thickness, and ideally have a small grain size. These objectives can be achieved by tuning the plating parameters during in situ Li deposition, including pressure, temperature, and current density. It has been previously shown that applying 5 MPa of pressure could improve the homogeneity of in situ formed Li anodes in solid-state cells [2].However, applying pressures >1 MPa is undesirable for practical applications [3]. Therefore, it is necessary to alter the in situ plated Li using other parameters, including the temperature and current density used during plating. Here, we show the effect of plating current density and temperature on the homogeneity and microstructure of in situ formed Li anodes in solid-state cells. It is demonstrated that optimized plating current protocols can improve the homogeneity of plated Li without the need for elevated temperatures. Finally, the relationship between the homogeneity of the in situ plated Li and the reversibility upon stripping is studied using unidirectional stripping experiments. These results illustrate the importance of carefully controlling the parameters for Li plating to enable high Coulombic efficiency in situ formed Li anodes in solid-state cells.

Nucleation, growth and dissolution of Li metal dendrites and the formation of dead Li in Li-ion batteries investigated by operando electrochemical liquid cell scanning transmission electron microscopy

Li metal dendrites, which can form on the anode of Li-ion batteries during charging, not only accelerate their aging but may also pose a safety hazard when causing a short-circuit within the battery. Therefore, a fundamental understanding of the mechanisms governing the early stages of Li plating, the progression into dendrites, and the formation of dead Li, is imperative. Here, we employ operando electrochemical liquid cell scanning transmission electron microscopy (ec-LC-STEM) to monitor, in real-time, nanoscale processes occurring at the anode-electrolyte interface of a Li-ion battery during charge/discharge. Our results indicate that Li metal dendrites nucleate as spherical Li nanoparticles beneath the solid electrolyte interphase (SEI) and subsequently grow until dendritic Li metal is formed. During discharge, Li dendrites undergo incomplete dissolution, leading to the formation of dead Li. Interestingly, the SEI layers play a pivotal role in both the growth and the dissolution processes. Our findings reveal that the growth of Li dendrites is a multi-step process: (i) nucleation, (ii) root growth, and (iii) tip growth. We elucidate that the formation of dead Li is associated with the morphology of the initially developed dendrites and the structure of the SEI layer. The thinning of the inhomogeneously thick Li whiskers leads to the contraction of the root before the tip, ultimately resulting in the creation of electrically isolated Li metal. This work sheds light on dendritic Li growth as well as on the formation of dead Li and provides significant insights for future electrode designs.

Fabrication of a Porous Copper/Graphite/Zirconium Oxide Hybrid Anode via Screen Printing for Lithium‐Ion Batteries

AbstractRedesigning anode structures in Li‐ion batteries (LIBs) has been a focus of research aimed at surpassing the energy density of conventional LIBs. Although anode‐free LIBs present a promising architecture, their low Coulombic efficiency is a major drawback. This paper introduces a novel hybrid anode that integrates the current collector (CC) and active materials into a single, cohesive porous structure, which supports both de/intercalation and de/plating reactions. The hybrid anode consists of a porous Cu matrix with embedded ZrO2 powders and graphite; the quantity of graphite is only a third of that present in a traditional graphite anode. The porous structure and additives enhance the electrochemical performance of the hybrid anode by minimizing the Li–electrolyte interactions, forming a stable solid–electrolyte interface and Li4Zr3O8 passivation layer, and reducing the nucleation overpotential. Especially, the unique surface morphology, characterized by a negative curvature between sintered Cu particles, lowers the diffusion potential, which further reduces the nucleation overpotential. Additionally, the periodic mesh‐imprinted top surface, created via screen printing, promotes uniform Li plating. The results demonstrate that the cycling performance and energy density offered by the fabricated hybrid anode are superior to those of conventional graphite anodes.

Evolution of Lithium Metal Anode Along Cycling in Working Lithium–Sulfur Batteries

AbstractThe cycling lifespan of high‐energy‐density lithium–sulfur (Li–S) batteries is dominantly limited by the rapid failure of Li metal anodes. Herein, the evolution of Li metal anode along cycling is systematically investigated in Li–S batteries to clarify the Li plating and stripping behaviors, the generation and accumulation of inactive Li, and the failure mechanism of Li metal anodes. Concretely, plated Li strips preferentially than bulk Li to leave massive stripping Li shells during initial discharge, and the stripping Li shells are refilled by plated Li during the subsequent charge to generate thick Li dendrites. During the following cycles, inactive Li generates and accumulates on top of bulk Li due to solid electrolyte interphase formation and incomplete removal of plated Li. Eventually, the accumulation of inactive Li hinders the diffusion of Li ions through the inactive Li layer to induce cell polarization at the end of the second discharge plateau and rapid decay of discharge capacity. This work elucidates the detailed evolution mechanism of Li metal anode along cycling in working Li–S batteries and highlights the reactivation of inactive Li as an effective strategy to prolong the cycling lifespan of Li–S batteries.

Sustaining Surface Lithiophilicity of Ultrathin Li-Alloy Coating Layers on Current Collector for Zero-Excess Li-Metal Batteries.

Zero-excess Li-metal batteries (ZE-LMBs) have emerged as the ultimate battery platform, offering an exceptionally high energy density. However, the absence of Li-hosting materials results in uncontrolled dendritic Li deposition on the Cu current collector, leading to chronic loss of Li inventory and severe electrolyte decomposition, limiting its full utilization upon cycling. This study presents the application of ultrathin (≈50nm) coatings comprising six metallic layers (Cu, Ag, Au, Pt, W, and Fe) on Cu substrates in order to provide insights into the design of Li-depositing current collectors for stable ZE-LMB operation. In contrast to non-alloy Cu, W, and Fe coatings, Ag, Au, and Pt coatings can enhance surface lithiophilicity, effectively suppressing Li dendrite growth, thereby improving Li reversibility. Considering the distinct Li-alloying behaviors, particularly solid-solution and/or intermetallic phase formation, Pt-coated Cu current collectors maintain surface lithiophilicity over repeated Li plating/stripping cycles by preserving the original coating layer, thereby attaining better cycling performance of ZE-LMBs. This highlights the importance of selecting suitable Li-alloy metals to sustain surface lithiophilicity throughout cycling to regulate dendrite-less Li plating and improve the electrochemical stability of ZE-LMBs.

Comprehensive aging model coupling chemical and mechanical degradation mechanisms for NCM/C6-Si lithium-ion batteries

The aging of lithium-ion batteries (LIBs) is synergistically influenced by multiple chemical/mechanical degradation mechanisms. Therefore, conventional models that incorporate only partial mechanisms exhibit limited predictive accuracy and applicability, failing to fully reflect the effects of chemical/mechanical degradation under complex operating conditions. Here, we propose an aging model for NCM/C6-Si LIBs coupled with comprehensive chemical/mechanical degradation mechanisms. The model includes chemical mechanisms at the C6-Si anode solid electrolyte interface (SEI), Li plating, and NCM cathode electrolyte interface (CEI), as well as mechanical mechanisms of loss of active material (LAM) for C6, Si, and NCM. Based on this model, we comprehensively investigate the effect of capacity loss by (dis)charge rates and ambient temperatures, obtaining the aging characteristics and the contribution of each mechanism to loss under different variables. Furthermore, we quantitatively analyze the sensitivity and response characteristics of the degradation sub-mechanism to (dis)charge rate and temperature. This study introduces an advanced aging analysis model for NCM/C6-Si LIBs, which can effectively decouple the operational characteristics of the degradation mechanism and provide guidance for developing next-generation high-energy LIBs.

Intrinsically Safe Lithium Metal Batteries Enabled by Thermo-Electrochemical Compatible In Situ Polymerized Solid-State Electrolytes.

In situ polymerized solid-state electrolytes have attracted much attention due to high Li-ion conductivity, conformal interface contact, and low interface resistance, but are plagued by lithium dendrite, interface degradation, and inferior thermal stability, which thereby leads to limited lifespan and severe safety hazards for high-energy lithium metal batteries (LMBs). Herein, an in situ polymerized electrolyte is proposed by copolymerization of 1,3-dioxolane with 1,3,5-tri glycidyl isocyanurate (TGIC) as a cross-linking agent, which realizes a synergy of battery thermal safety and interface compatibility with Li anode. Functional TGIC enhances the electrolyte polymeric level. The unique carbon-formation mechanism facilitates flame retardancy and eliminates the battery fire risk. In the meantime, TGIC-derived inorganic-rich interphase inhibits interface side reactions and promotes uniform Li plating. Intrinsically safe LMBs with nonflammability and outstanding electrochemical performances under extreme temperatures (130°C) are achieved. This functional polymer design shows a promising prospect for the development of safe LMBs.

Understanding and Strategies for High Energy Density Lithium‐Ion/Lithium Metal Hybrid Batteries

AbstractA pressing need for high‐capacity anode materials beyond graphite is evident, aiming to enhance the energy density of Li‐ion batteries (LIBs). A Li‐ion/Li metal hybrid anode holds remarkable potential for high energy density through additional Li plating, while benefiting from graphite's stable intercalation chemistry. However, limited comprehension of the hybrid anode has led to improper utilization of both chemistries, causing their degradation. Herein, this study reports an effective hybrid anode design considering material properties, the ratio of intercalation‐to‐plating capacity, and Li‐ion transport phenomena on the surface. Mesocarbon microbeads (MCMB) possesses desirable properties for additional Li plating based on its spherical shape, lithiophilic functional group, and sufficient interparticle space, alongside stable intercalation‐based storage capability. Balancing the ratio of intercalation‐to‐plating capacity is also crucial, as excessive Li plating occurs on the top surface of the anode, eventually deactivating the intercalation chemistry by obstructing upper pores. To address this issue, electrospun polyvinylidene fluoride (PVDF) is introduced to prevent Li metal accumulation on the upper surface, leveraging its non‐conductive, polar nature, and high dielectric constant. By implementing these strategies, a LiNi0.8Co0.15Al0.05O2 (NCA)‐paired pouch cell delivers an outstanding energy density of 1101.0 Wh L−1, highlighting its potential as an advanced post‐LIBs with practical feasibility.