Dynamics of Lithium Dendrite Growth and Inhibition: Pulse Charging Experiments and Monte Carlo Calculations

From Lab to Application: Challenges and Opportunities in Achieving Fast Charging with Polyanionic Cathodes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs), recognized for balanced energy density and cost-effectiveness, are positioned as a promising complement to lithium-ion batteries (LIBs) and a substitute for lead-acid batteries, particularly in low-speed electric vehicles and large-scale energy storage. Despite their extensive potential, concerns about range anxiety due to lower energy density underscore the importance of fast-charging technologies, which drives the exploration of high-rate electrode materials. Polyanionic cathode materials are emerging as promising candidates in this regard. However, their intrinsic limitation in electronic conductivity poses challenges for synchronized electron and ion transport, hindering their suitability for fast-charging applications. This review provides a comprehensive analysis of sodium ion migration during charging/discharging, highlighting it as a critical rate-limiting step for fast charging. By delving into intrinsic dynamics, key factors that constrain fast-charging characteristics are identified and summarized. Innovative modification routes are then introduced, with a focus on shortening migration paths and increasing diffusion coefficients, providing detailed insights into feasible strategies. Moreover, the discussion extends beyond half cells to full cells, addressing challenges and opportunities in transitioning polyanionic materials from the laboratory to practical applications. This review aims to offer valuable insights into the development of high-rate polyanionic cathodes, acknowledging their pivotal role in advancing fast-charging SIBs.

Pulse Charge Suppressing Dendrite Growth at Low Temperature by Rapidly Replenishing Lithium Ion on Anode Surface

Dendrite growth of lithium (Li) metal anodes is considered as one of the most tough issues for Li metal batteries with a theoretically high energy density. This is attributed to the rapid exhaustion of Li ions at the electrode/electrolyte interface, which is even worse at low temperatures with poor diffusion kinetics of Li ions. Here, pulse charge with intermittent rest time during battery charging is proposed to handle the dendrite growth issue of Li metal anodes at low temperatures. The depleted Li ions near the interfaces can be rapidly replenished during the rest time, thus effectively suppressing the dendrites growth. Further investigation found that the large dendrites can be suppressed at the Li ion nucleation stage. The equivalent lifespan considering the rest time is proposed. At -10 °C, the lifespan of Li||Li batteries cycled under 3 mA cm-2 and 1 mAh cm-2 is increased from 24 h to equivalent 64 h. Li||LiNi0.5Co0.2Mn0.3O2 batteries with 80% capacity retention can be stably operated from 39 cycles to 56 cycles. This design presents an efficient and convenient strategy to regulate the deposition behaviors of Li metal anodes with a dendrite-free morphology.

A dynamically equivalent atomistic electrochemical paradigm for the larger-scale experiments

Electrochemical systems possess a considerable part of modern technologies, such as the operation of rechargeable batteries and the fabrication of electronic components, which are explored both experimentally and computationally. The largest gap between the experimental observations and atomic-level simulations is their orders-of-magnitude scale difference. While the largest computationally affordable scale of the atomic-level computations is ∼ns and ∼nm, the smallest reachable scale in the typical experiments, using very high-precision devices, is ∼s and ∼μm. In order to close this gap and correlate the studies in the two scales, we establish an equivalent simulation setup for the given general experiment, which excludes the microstructure effects (i.e., solid-electrolyte interface), using the coarse-grained framework. The developed equivalent paradigm constitutes the adjusted values for the equivalent length scale (i.e., lEQ), diffusivity (i.e., DEQ), and voltage (i.e., VEQ). The time scale for the formation and relaxation of the concentration gradients in the vicinity of the electrode matches for both smaller scale (i.e., atomistic) equivalent simulations and the larger scale (i.e., continuum) experiments and could be utilized for exploring the cluster-level inter-ionic events that occur during the extended time periods. The developed model could offer insights for forecasting experiment dynamics and estimating the transition period to the steady-state regime of operation.

Multiscale dynamics of charging and plating in graphite electrodes coupling operando microscopy and phase-field modelling

The phase separation dynamics in graphitic anodes significantly affects lithium plating propensity, which is the major degradation mechanism that impairs the safety and fast charge capabilities of automotive lithium-ion batteries. In this study, we present comprehensive investigation employing operando high-resolution optical microscopy combined with non-equilibrium thermodynamics implemented in a multi-dimensional (1D+1D to 3D) phase-field modeling framework to reveal the rate-dependent spatial dynamics of phase separation and plating in graphite electrodes. Here we visualize and provide mechanistic understanding of the multistage phase separation, plating, inter/intra-particle lithium exchange and plated lithium back-intercalation phenomena. A strong dependence of intra-particle lithiation heterogeneity on the particle size, shape, orientation, surface condition and C-rate at the particle level is observed, which leads to early onset of plating spatially resolved by a 3D image-based phase-field model. Moreover, we highlight the distinct relaxation processes at different state-of-charges (SOCs), wherein thermodynamically unstable graphite particles undergo a drastic intra-particle lithium redistribution and inter-particle lithium exchange at intermediate SOCs, whereas the electrode equilibrates much slower at low and high SOCs. These physics-based insights into the distinct SOC-dependent relaxation efficiency provide new perspective towards developing advanced fast charge protocols to suppress plating and shorten the constant voltage regime.

Dendritic propagation on circular electrodes: The impact of curvature on the packing density

The dendritic growth in rechargeable batteries is one of the hurdles for the utilization of high energy-density elements, such as alkaline metals, as the electrode. Herein we explore the preventive role of the curved electrode surface in the cylindrical electrode design versus the flat geometry on the stochastic evolution of the dendritic crystals. In this regard we establish a coarse-grained Monte Carlo paradigm in the polar coordinates (r,θ), which runs in a larger scale of time and space (∼μs,∼nm ) than those of interionic collisions (∼fs, Å). Subsequently we track the density and the maximum reach of the microstructures in real time, and we elaborate on the underlying mechanisms for their correlation of the relative dendrite measure with the electrode curvature. Such quantification of the positive impact of the curvature on suppressing dendrites could be utilized as an effective longevity design parameter, particularly for the cases prone to dendritic propagation.

Effect of Fast Charging on Lithium-Ion Batteries: A Review

<div>In recent years we have seen a dramatic shift toward the use of lithium-ion batteries (LIB) in a variety of applications, including portable electronics, electric vehicles (EVs), and grid storage. Even though more and more car companies are making electric models, people still worry about how far the batteries will go and how long it will take to charge them. It is common knowledge that the high currents that are necessary to quicken the charging process also lower the energy efficiency of the battery and cause it to lose capacity and power more quickly. We need an understanding of atoms and systems to better comprehend fast charging (FC) and enhance its effectiveness. These difficulties are discussed in detail in this work, which examines the literature on physical phenomena limiting battery charging speeds as well as the degradation mechanisms that typically occur while charging at high currents. Special consideration is given to charging at low temperatures. The consequences for safety are investigated, including the possible impact that rapid charging could have on the characteristics of thermal runaway (TR). In conclusion, knowledge gaps are analyzed, and recommendations are made as regards the path that subsequent studies should take. Furthermore, there is a need to give more attention to creating dependable onboard methods for detecting lithium plating (LP) and mechanical damage. It has been observed that robust charge optimization processes based on models are required to ensure faster charging in any environment. Thermal management strategies to both cool batteries while these are being charged and heat them up when these are cold are important, and a lot of attention is paid to methods that can do both quickly and well.</div>

Mechanistic Underpinnings of Morphology Transition in Electrodeposition under the Application of Pulsatile Potential

We quantitatively investigate the role of voltage fluctuation in terms of different waveforms on the electrodeposition dynamics and morphology for varying electrolyte concentrations. Dependent on the electrolyte concentration, a wide range of morphologies ranging from highly branched dendrites to comparatively closed packed electrodeposits has been captured. We mechanistically map the deposition dynamics by image analysis and demonstrate the highly porous dendritic dynamics to be independent of external perturbation. Additionally, comparatively closed packed morphological features show significant sensitivity toward the frequency and nature of the waveforms. The results provide fundamental insights into the correlation between the time scales of voltage fluctuation and growth dynamics. We comprehensively analyze the effect of the waveform nature on the average deposition height and show sinusoidal fluctuation to be preferred over square and pulse for metal batteries for lower deposition heights.

Nucleation and growth mechanism in the early stages of nickel coating in jet electrodeposition: a coarse-grained molecular simulation and experimental study

In jet electrodeposition, microscopic nucleation and growth in the early stages of nickel coating are curcial and directly related to the consistency and reliability of the coating structure. We set up a three-electrode device with flow-injection function based on the vertical distribution and further studied the early stages of nanocluster formation corresponding to parallel and vertical distribution states. According to the nucleation diffusion and growth analysis, a coarse-grained molecular dynamics model is established for the first time to reveal the influences of different growth environments on the microscopic nucleation growth of the coating structure. Thus, the ion dynamic diffusion and nucleation kinetic mechanism could be further achieved, these vary under different electrodeposition conditions. In addition, the physical structure of the surface coating can be obtained by element analysis and density functional theory (DFT) calculations. These findings provide a theoretical and experimental basis for the efficient preparation of nickel coatings.

A coarse-grained molecular dynamics model and the vertical three-electrode device with flow-injection function are established to reveal the influences of different growth conditions on the microscopic nucleation growth of coating.

Potential Oscillated Electrochemical Metal Recovery System with Improved Conversion Kinetics and High Levelized Quality

Electrodeposition, which is an eco-friendly process with high efficiency, is one of the most promising technologies for metal recovery. However, the kinetics are often limited by the polarization and uncontrollable quality of deposits during the electrodeposition process, which restrict the efficiency and controllability of metal recovery. To ameliorate the limitations of the deposition rate and as-formed deposit quality, transient electrodeposition was introduced to control the microinterfacial reaction by regulating the relationship between charge and mass transfer. The Cu²⁺ removal efficiency and kinetic coefficient during 1 kHz transient electrodeposition were 17.4 and 17.7% higher than those under the conventional steady electric stimulus, respectively. Based on the combined results of X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS), it was found that the chemical composition of the deposits from transient electrodeposition was more homogenous, as indicated by the low content of metal oxides. The in situ Raman spectra explained the homogenous composition based on the weak interaction of the electrode with the anions during the transient electrodeposition, which was mainly due to the enhanced dehydration under the oscillating or alternating electric field. The potential oscillation induced by the transient electric field also facilitated dehydration, charge transport, and mass transfer, which led to rapid and high-quality metal recovery. Transient electrodeposition will have a great guidance value in the field of metal electroplating and heavy metal recovery from wastewater by electrodeposition.

Effect of diffusion constant on the morphology of dendrite growth in lithium metal batteries

Lithium dendrites can lead to a short circuit and battery failure, and developing strategies for their suppression is of considerable importance. In this work, we study the growth of dendrites in a simple model system where the solvent is a continuum and the lithium ions are hard spheres that can deposit by sticking to existing spheres or the electrode surface. Using stochastic dynamics simulations, we investigate the effect of applied voltage and diffusion constant on the growth of dendrites. We find that the diffusion constant is the most significant factor, and the inhomogeneity of the electric field does not play a significant role. The growth is most pronounced when the applied voltage and diffusion constant are both low. We observe a structural change from broccoli to cauliflower shape as the diffusion constant is increased. The simulations suggest that a control of electrolyte parameters that impact lithium diffusion might be an attractive route to controlling dendrite growth.

Real-time control of dendritic propagation in rechargeable batteries using adaptive pulse relaxation

The non-uniform growth of microstructures in dendritic form inside the battery during prolonged charge-discharge cycles causes short-circuit as well as capacity fade. We develop a feedback control framework for the real-time minimization of such microstructures. Due to the accelerating nature of the branched evolution, we focus on the early stages of growth, identify the critical ramified peaks, and compute the effective time for the dissipation of ions from the vicinity of those branching fingers. The control parameter is a function of the maximum interface curvature (i.e., minimum radius) where the rate of runaway is the highest. The minimization of the total charging time is performed for generating the most packed microstructures, which correlate closely with those of considerably higher charging periods, consisting of constant and uniform square waves. The developed framework could be utilized as a smart charging protocol for safe and sustainable operation of rechargeable batteries, where the branching of the microstructures could be correlated with the sudden variation in the current/voltage.

From Dendrites to Hemispheres: Changing Lithium Deposition by Highly Ordered Charge Transfer Channels

Metallic lithium as an anode is an ultimate ideal for rechargeable lithium batteries with high energy density such as lithium-oxygen batteries and lithium-sulfur batteries. However, the excess reactivity and asymmetrical dissolution-deposition of the metallic lithium anode make it impossible to support a stable long charge-discharge cycling. To protect the metallic lithium anode, apparently it needs to adjust the dissolution and deposition of lithium ions, but more essentially, it should reasonably change the distribution and transport of electrons on the surface and interface of the metallic lithium. In this work, anodic aluminum oxide (AAO) membranes are used to build highly ordered channels on the lithium anode surface in which lithium ions can transfer in the channels and electrons can be transported by the lithiation reaction of alumina with an oxygen vacancy-involved process. As a result, the cyclic reaction actually is partially transferred to the AAO surface, and lithium deposition occurs there as a hemispherical appearance but not as dendrites. Meanwhile, the highly ordered characteristics provide a physical effect to make the deposited lithium hemispheres a uniform distribution on the AAO surface. The AAO-regulated lithium anodes could be widely used to improve the cycling performance for metal lithium batteries.

Molecular Simulations of the Microstructure Evolution of Solid Electrolyte Interphase during Cyclic Charging/Discharging

Lithium (Li) metal is regarded as one of the most promising anode materials for use in next-generation high-energy-density rechargeable batteries because of its high volumetric and gravimetric specific capacity, as well as low reduction potential. Unfortunately, uncontrolled dendritic Li growth during cyclic charging/discharging leads to low columbic efficiency and critical safety issues. Hence, comprehensive understanding of the formation mechanism for Li-dendrite growth, particularly at the onset of dendrite formation, is essential for developing Li-metal anode batteries. In this study, reactive molecular dynamics (MD) simulations in combination with the electrochemical dynamics with implicit degrees of freedom (EChemDID) method were performed to investigate the formation and evolution of solid electrolyte interphase (SEI) films for a Li-metal anode under cyclic charging/discharging processes in two distinct dimensions, namely, electrolyte compositions and initial surface morphologies. Our simulations indicated that regardless of the electrolyte compositions and initial anode morphologies, inhomogeneous Li reduction, namely, the formation of Li-reduction "hotspots" during cyclic charging cycles, took place and could serve as the seed for subsequent dendrite growth. The fluorine-containing electrolyte additives could notably mitigate the Li-anode roughening processes by forming dense-SEI-layer products or suppressing electrolyte decomposition. A series of Li-ion-drifting simulations suggest that Li ions navigate through the SEI layer via pathways composed of low-density atoms and become reduced at these reduction hotspots, promoting inhomogeneous deposition and subsequent dendrite growth. The present study reveals atomistic details of the early stage of dendrite growth during cyclic loadings under different electrolyte compositions and anode morphologies, thereby providing insights for designing artificial SEI layers or electrolytes for long-life, high-capacity Li-ion batteries.

Dendrites in Zn-Based Batteries

Aqueous Zn batteries that provide a synergistic integration of absolute safety and high energy density have been considered as highly promising energy-storage systems for powering electronics. Despite the rapid progress made in developing high-performance cathodes and electrolytes, the underestimated but non-negligible dendrites of Zn anode have been observed to shorten battery lifespan. Herein, this dendrite issue in Zn anodes, with regard to fundamentals, protection strategies, characterization techniques, and theoretical simulations, is systematically discussed. An overall comparison between the Zn dendrite and its Li and Al counterparts, to highlight their differences in both origin and topology, is given. Subsequently, in-depth clarifications of the specific influence factors of Zn dendrites, including the accumulation effect and the cathode loading mass (a distinct factor for laboratory studies and practical applications) are presented. Recent advances in Zn dendrite protection are then comprehensively summarized and categorized to generate an overview of respective superiorities and limitations of various strategies. Accordingly, theoretical computations and advanced characterization approaches are introduced as mechanism guidelines and measurement criteria for dendrite suppression, respectively. The concluding section emphasizes future challenges in addressing the Zn dendrite issue and potential approaches to further promoting the lifespan of Zn batteries.

Effects of Pulse Charging by Triboelectric Nanogenerators on the Performance of Solid-State Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) are an emerging technology because they can effectively solve the safety problem facing the lithium-ion batteries with nonaqueous liquid electrolyte. However, the lithium dendrite problem in SSLMBs can still occur at the sites of grain boundaries and defects. It is reported that effective charge procedures enable to suppress the growth of lithium dendrite, especially the pulse charging mode. In this work, SSLMBs were charged by a vertical contact-separation triboelectric nanogenerator (TENG). The effects of the pulse current on the lithium dendrite growth of SSLMBs are studied. It is found that the lithium ions can diffuse uniformly during the intermittent period of the pulse current compared to the constant current charge, so the growth rate of the lithium dendrites is effectively inhibited by the pulse current. At the same time, it is found that the lower the frequency of TENG is, the slower the growth rate of lithium dendrites is. This work provides a guideline for designing an appropriate charging method for durable SSLMBs.

Double-Edged Effect of Temperature on Lithium Dendrites

Lithium metal, although attracting renewed interest for the next revolution in energy storage, continues to be challenged with the detrimental dendrite formation. Recent experimental reports have demonstrated the contrasting impact of thermal attributes on the electrodeposition morphology, showcasing the alleviation and/or aggravation of dendrite formation. Herein, we present a comprehensive discourse to discern the thermally activated physical mechanisms governing lithium electrodeposition morphology. We report that the synergistic effect of enhanced electrolyte transport and surface self-diffusion under a uniform thermal field (∼75 °C) enables adequate dendrite suppression, even at high reaction rates. However, in contrast to this, a localization of the thermal field substantially increases the exchange current density of the confined region, instigating the growth of needle dendrites. Based on our mesoscale analysis, we demarcate safety limits for such an event, beyond which dendrite growth is inevitably triggered. Therefore, though the operational strategy of elevating the cell temperature promises to resolve the challenge of stable electrodeposition, it comes along with the caveat. This fundamental study provides a detailed insight into underlying electrochemical-thermal complexations, critical to the performance and safety of metal-based rechargeable batteries.

Mg Doped Li-LiB Alloy with In Situ Formed Lithiophilic LiB Skeleton for Lithium Metal Batteries

High energy density lithium metal batteries (LMBs) are promising next-generation energy storage devices. However, the uncontrollable dendrite growth and huge volume change limit their practical applications. Here, a new Mg doped Li-LiB alloy with in situ formed lithiophilic 3D LiB skeleton (hereinafter called Li-B-Mg composite) is presented to suppress Li dendrite and mitigate volume change. The LiB skeleton exhibits superior lithiophilic and conductive characteristics, which contributes to the reduction of the local current density and homogenization of incoming Li+ flux. With the introduction of Mg, the composite achieves an ultralong lithium deposition/dissolution lifespan (500 h, at 0.5 mA cm-2) without short circuit in the symmetrical battery. In addition, the electrochemical performance is superior in full batteries assembled with LiCoO2 cathode and the manufactured composite. The currently proposed 3D Li-B-Mg composite anode may significantly propel the advancement of LMB technology from laboratory research to industrial commercialization.

Finite-pulse waves for efficient suppression of evolving mesoscale dendrites in rechargeable batteries

The ramified and stochastic evolution of dendritic microstructures has been a major issue on the safety and longevity of rechargeable batteries, particularly for the utilization of high-energy metallic electrodes. We analytically develop criteria for the pulse characteristics leading to the effective halting of the ramified electrodeposits grown during extensive timescales beyond inter-ionic collisions. Our framework is based on the competitive interplay between diffusion and electromigration and tracks the gradient of ionic concentration throughout the entire cycle of pulse-rest as a critical measure for heterogeneous evolution. In particular, the framework incorporates the Brownian motion of the ions and investigates the role of the geometry of the electrodeposition interface. Our experimental observations verify the analytical developments, where the dimension-free developments allows the application to the electrochemical systems of various scales.

Triboelectric Nanogenerator-Enabled Dendrite-Free Lithium Metal Batteries

Lithium metal batteries (LMBs) are prominent among next-generation energy-storage systems because of their high energy density. Unfortunately, the commercial application of LMBs is hindered by the dendrite growth issue during the charging process. Herein, we report that the triboelectric nanogenerator (TENG)-based pulse output with a novel waveform and frequency has restrained the formation of dendrites in LMBs. The waveform and operation frequency of TENG can be regulated by TENG-designed and smart power management circuits. By regulating the waveform and frequency of the TENG-based pulse output, the pulse duration becomes shorter than the lithium dendrite formation time at any current of pulse waveform, and lithium ions can replenish in the entire electrode surface during rest periods, eliminating concentration polarization. Therefore, the optimized TENG-based charging strategy can improve the Coulombic efficiency of lithium plating/stripping and realize homogeneous lithium plating in LMBs. This TENG-based charging technology provides an innovative strategy to address the Li dendrite growth issues in LMBs, and accelerates the application of TENG-based energy collection systems.

Machine Learning Enabled Computational Screening of Inorganic Solid Electrolytes for Suppression of Dendrite Formation in Lithium Metal Anodes

Next generation batteries based on lithium (Li) metal anodes have been plagued by the dendritic electrodeposition of Li metal on the anode during cycling, resulting in short circuit and capacity loss. Suppression of dendritic growth through the use of solid electrolytes has emerged as one of the most promising strategies for enabling the use of Li metal anodes. We perform a computational screening of over 12 000 inorganic solids based on their ability to suppress dendrite initiation in contact with Li metal anode. Properties for mechanically isotropic and anisotropic interfaces that can be used in stability criteria for determining the propensity of dendrite initiation are usually obtained from computationally expensive first-principles methods. In order to obtain a large data set for screening, we use machine-learning models to predict the mechanical properties of several new solid electrolytes. The machine-learning models are trained on purely structural features of the material, which do not require any first-principles calculations. We train a graph convolutional neural network on the shear and bulk moduli because of the availability of a large training data set with low noise due to low uncertainty in their first-principles-calculated values. We use gradient boosting regressor and kernel ridge regression to train the elastic constants, where the choice of the model depends on the size of the training data and the noise that it can handle. The material stiffness is found to increase with an increase in mass density and ratio of Li and sublattice bond ionicity, and decrease with increase in volume per atom and sublattice electronegativity. Cross-validation/test performance suggests our models generalize well. We predict over 20 mechanically anisotropic interfaces between Li metal and four solid electrolytes which can be used to suppress dendrite growth. Our screened candidates are generally soft and highly anisotropic, and present opportunities for simultaneously obtaining dendrite suppression and high ionic conductivity in solid electrolytes.

Developing High-Performance Lithium Metal Anode in Liquid Electrolytes: Challenges and Progress

Lithium metal anodes are potentially key for next-generation energy-dense batteries because of the extremely high capacity and the ultralow redox potential. However, notorious safety concerns of Li metal in liquid electrolytes have significantly retarded its commercialization: on one hand, lithium metal morphological instabilities (LMI) can cause cell shorting and even explosion; on the other hand, breaking of the grown Li arms induces the so-called "dead Li"; furthermore, the continuous consumption of the liquid electrolyte and cycleable lithium also shortens cell life. The research community has been seeking new strategies to protect Li metal anodes and significant progress has been made in the last decade. Here, an overview of the fundamental understandings of solid electrolyte interphase (SEI) formation, conceptual models, and advanced real-time characterizations of LMI are presented. Instructed by the conceptual models, strategies including increasing the donatable fluorine concentration (DFC) in liquid to enrich LiF component in SEI, increasing salt concentration (ionic strength) and sacrificial electrolyte additives, building artificial SEI to boost self-healing of natural SEI, and 3D electrode frameworks to reduce current density and delay Sand's extinction are summarized. Practical challenges in competing with graphite and silicon anodes are outlined.

Self-heating–induced healing of lithium dendrites

Lithium (Li) metal electrodes are not deployable in rechargeable batteries because electrochemical plating and stripping invariably leads to growth of dendrites that reduce coulombic efficiency and eventually short the battery. It is generally accepted that the dendrite problem is exacerbated at high current densities. Here, we report a regime for dendrite evolution in which the reverse is true. In our experiments, we found that when the plating and stripping current density is raised above ~9 milliamperes per square centimeter, there is substantial self-heating of the dendrites, which triggers extensive surface migration of Li. This surface diffusion heals the dendrites and smoothens the Li metal surface. We show that repeated doses of high-current-density healing treatment enables the safe cycling of Li-sulfur batteries with high coulombic efficiency.

Lithium batteries: Improving solid-electrolyte interphases via underpotential solvent electropolymerization

Understanding the mechanism of formation of solid-electrolyte interphases (SEI) is key to the prospects of lithium metal batteries (LMB). Here, we investigate via cyclic voltammetry, impedance spectroscopy and chronoamperometry the role of kinetics in controlling the properties of the SEI generated from the reduction of propylene carbonate (PC, a typical solvent in LMB). Our observations are consistent with the operation of a radical chain PC electropolymerization into polymer units whose complexity increases at lower initiation rates. As proof-of-concept, we show that slow initiation rates via one-electron PC reduction at underpotentials consistently yields compact, electronically insulating, Li⁺-conducting, PC-impermeable SEI films.

Suppression of dendritic lithium growth in lithium metal-based batteries

We describe the challenges of high-energy lithium-metal batteries and outline the future directions that are expected to drive their progress.

Understanding the molecular mechanism of pulse current charging for stable lithium-metal batteries

High energy and safe electrochemical storage are critical components in multiple emerging fields of technologies. Rechargeable lithium-metal batteries are considered to be promising alternatives for current lithium-ion batteries, leading to as much as a 10-fold improvement in anode storage capacity (from 372 to 3860 mAh g-1). One of the major challenges for commercializing lithium-metal batteries is the reliability and safety issue, which is often associated with uneven lithium electrodeposition (lithium dendrites) during the charging stage of the battery cycling process. We report that stable lithium-metal batteries can be achieved by simply charging cells with square-wave pulse current. We investigated the effects of charging period and frequency as well as the mechanisms that govern this process at the molecular level. Molecular simulations were performed to study the diffusion and the solvation structure of lithium cations (Li+) in bulk electrolyte. The model predicts that loose association between cations and anions can enhance the transport of Li+ and eventually stabilize the lithium electrodeposition. We also performed galvanostatic measurements to evaluate the cycling behavior and cell lifetime under pulsed electric field and found that the cell lifetime can be more than doubled using certain pulse current waveforms. Both experimental and simulation results demonstrate that the effectiveness of pulse current charging on dendrite suppression can be optimized by choosing proper time- and frequency-dependent pulses. This work provides a molecular basis for understanding the mechanisms of pulse current charging to mitigating lithium dendrites and designing pulse current waveforms for stable lithium-metal batteries.

In-situ Multimodal Imaging and Spectroscopy of Mg Electrodeposition at Electrode-Electrolyte Interfaces

We report the study of Mg cathodic electrochemical deposition on Ti and Au electrode using a multimodal approach by examining the sample area in-situ using liquid cell transmission electron microscopy (TEM), scanning transmission X-ray microscopy (STXM) and X-ray absorption spectroscopy (XAS). Magnesium Aluminum Chloride Complex was synthesized and utilized as electrolyte, where non-reversible features during in situ charging-discharging cycles were observed. During charging, a uniform Mg film was deposited on the electrode, which is consistent with the intrinsic non-dendritic nature of Mg deposition in Mg ion batteries. The Mg thin film was not dissolvable during the following discharge process. We found that such Mg thin film is hexacoordinated Mg compounds by in-situ STXM and XAS. This study provides insights on the non-reversibility issue and failure mechanism of Mg ion batteries. Also, our method provides a novel generic method to understand the in situ battery chemistry without any further sample processing, which can preserve the original nature of battery materials or electrodeposited materials. This multimodal in situ imaging and spectroscopy provides many opportunities to attack complex problems that span orders of magnitude in length and time scale, which can be applied to a broad range of the energy storage systems.

First-Principles Investigations of the Working Mechanism of 2D h-BN as an Interfacial Layer for the Anode of Lithium Metal Batteries

An issue with the use of metallic lithium as an anode material for lithium-based batteries is dendrite growth, causing a periodic breaking and repair of the solid electrolyte interphase (SEI) layer. Adding 2D atomic crystals, such as h-BN, as an interfacial layer between the lithium metal anode and liquid electrolyte has been demonstrated to be effective to mitigate dendrite growth, thereby enhancing the Columbic efficiency of lithium metal batteries. But the underlying mechanism leading to the reduced dendrite growth remains unknown. In this work, with the aid of first-principle calculations, we find that the interaction between the h-BN and lithium metal layers is a weak van der Waals force, and two atomic layers of h-BN are thick enough to block the electron tunneling from lithium metal to electrolyte, thus prohibiting the decomposition of electrolyte. The interlayer spacing between the h-BN and lithium metal layers can provide larger adsorption energies toward lithium atoms than that provided by bare lithium or h-BN, making lithium atoms prefer to intercalate under the cover of h-BN during the plating process. The combined high stiffness of h-BN and the low diffusion energy barriers of lithium at the Li/h-BN interfaces induce a uniform distribution of lithium under h-BN, therefore effectively suppressing dendrite growth.

Electrochemical migration of Sn and Sn solder alloys: a review

The schematic diagram of electrochemical migration of Sn solder alloys joints.

Real-time 3D imaging of microstructure growth in battery cells using indirect MRI

Lithium metal is a promising anode material for Li-ion batteries due to its high theoretical specific capacity and low potential. The growth of dendrites is a major barrier to the development of high capacity, rechargeable Li batteries with lithium metal anodes, and hence, significant efforts have been undertaken to develop new electrolytes and separator materials that can prevent this process or promote smooth deposits at the anode. Central to these goals, and to the task of understanding the conditions that initiate and propagate dendrite growth, is the development of analytical and nondestructive techniques that can be applied in situ to functioning batteries. MRI has recently been demonstrated to provide noninvasive imaging methodology that can detect and localize microstructure buildup. However, until now, monitoring dendrite growth by MRI has been limited to observing the relatively insensitive metal nucleus directly, thus restricting the temporal and spatial resolution and requiring special hardware and acquisition modes. Here, we present an alternative approach to detect a broad class of metallic dendrite growth via the dendrites' indirect effects on the surrounding electrolyte, allowing for the application of fast 3D (1)H MRI experiments with high resolution. We use these experiments to reconstruct 3D images of growing Li dendrites from MRI, revealing details about the growth rate and fractal behavior. Radiofrequency and static magnetic field calculations are used alongside the images to quantify the amount of the growing structures.

Stabilizing lithium metal using ionic liquids for long-lived batteries

Suppressing dendrite formation at lithium metal anodes during cycling is critical for the implementation of future lithium metal-based battery technology. Here we report that it can be achieved via the facile process of immersing the electrodes in ionic liquid electrolytes for a period of time before battery assembly. This creates a durable and lithium ion-permeable solid–electrolyte interphase that allows safe charge–discharge cycling of commercially applicable Li|electrolyte|LiFePO₄ batteries for 1,000 cycles with Coulombic efficiencies >99.5%. The tailored solid–electrolyte interphase is prepared using a variety of electrolytes based on the N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide room temperature ionic liquid containing lithium salts. The formation is both time- and lithium salt-dependant, showing dynamic morphology changes, which when optimized prevent dendrite formation and consumption of electrolyte during cycling. This work illustrates that a simple, effective and industrially applicable lithium metal pretreatment process results in a commercially viable cycle life for a lithium metal battery.

Suppressing dendrite formation at lithium anodes during cycling is critical to development of lithium battery technology. Here, the authors show that immersion of lithium electrodes in ionic liquid electrolytes prior to battery assembly produces a durable and lithium ion permeable solid-electrolyte interphase.

Dendrite-Free Lithium Deposition Induced by Uniformly Distributed Lithium Ions for Efficient Lithium Metal Batteries

Li dendrite-free growth is achieved by employing glass fiber with large polar functional groups as the interlayer of Li metal anode and separator to uniformly distribute Li ions. The evenly distributed Li ions render the dendrite-free Li deposits at high rates (10 mA cm(-2)) and high lithiation capacity (2.0 mAh cm(-2)).

A Review of Solid Electrolyte Interphases on Lithium Metal Anode

Lithium metal batteries (LMBs) are among the most promising candidates of high-energy-density devices for advanced energy storage. However, the growth of dendrites greatly hinders the practical applications of LMBs in portable electronics and electric vehicles. Constructing stable and efficient solid electrolyte interphase (SEI) is among the most effective strategies to inhibit the dendrite growth and thus to achieve a superior cycling performance. In this review, the mechanisms of SEI formation and models of SEI structure are briefly summarized. The analysis methods to probe the surface chemistry, surface morphology, electrochemical property, dynamic characteristics of SEI layer are emphasized. The critical factors affecting the SEI formation, such as electrolyte component, temperature, current density, are comprehensively debated. The efficient methods to modify SEI layer with the introduction of new electrolyte system and additives, ex-situ-formed protective layer, as well as electrode design, are summarized. Although these works afford new insights into SEI research, robust and precise routes for SEI modification with well-designed structure, as well as understanding of the connection between structure and electrochemical performance, is still inadequate. A multidisciplinary approach is highly required to enable the formation of robust SEI for highly efficient energy storage systems.

Suppression of lithium dendrite growth by introducing a low reduction potential complex cation in the electrolyte

A low reduction potential complex cation (LRPCC) N-methyl-N-butylpiperidinium was introduced to the LiPF₆/EC/DEC electrolyte to investigate its effect on the interface properties of a lithium anode.