Article

Self-Diffusion Barriers: Possible Descriptors for Dendrite Growth in Batteries?

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Abstract

Dendrite formation is one of the most pressing issues in nowadays battery research. Lithium based batteries are prone to forming short-circuit causing dendrites, while magnesium based batteries are not. Recently it was proposed that the tendency towards dendrite growth is related to the height of the self-diffusion barrier with high barriers leading to rough surface growth which might subsequently cause dendrite formation which was supported by density functional theory calculations for Li, Na and Mg [ J. Chem. Phys. 141, 174710 (2014)]. We now extend this computational study to zinc and aluminum which are also used as battery anode materials, and we additionally consider diffusion barriers that are relevant for three-dimensional growth such as barriers for diffusion accross steps. Our results indicate in agreement with experimental observations that Li dendrite growth is an inherent property of the metal, whereas Zn dendrite growth results from the loss of metallic properties in conventional Zn powder electrodes.

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... Replacing monovalent Li + /Na + with multivalent ions is one attractive way to achieve high-energy-density commercial rechargeable batteries. Magnesium (Mg) metal stands out as an ideal substitute for its abundant content (crustal element ranks 8th), low reduction potential (− 2.356 V vs. NHE), twice/three folds the volumetric energy density of Li/Na (3833, 2062/1165 mAh mL − 1 , respectively), and less tendency to dendrite formation due to the diffusion-controlled plating model [1][2][3][4][5]. However, the lack of suitable electrolytes remains the critical challenges in constructing rechargeable magnesium batteries (RMBs) with high energy densities. ...
... The practical utilization of the Zn anodes in ZIBs has been hampered by the dendrite formation during cycling. The nonuniform Zn 2+ plating/stripping between the electrolyte and Zn-anode surface is believed to be the dominating factor for Zn dendrite growth [44], which could eventually pierce through the separator, resulting in internal short circuits. To evaluate the reversibility of the Zn plating/stripping, the galvanostatic cycling test is conducted using the Zn/ZA-based HGPE or wet separator/Zn symmetric cells at a current density of 1 mA cm −2 and an areal capacity of 1.0 mAh cm −2 . ...
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... In addition to the general electronic properties study of oxygen vacancies in LaNiO 3 , we also perform Nudged Elastic Band (NEB) calculation to investigate the energy barrier of a single oxygen vacancy diffusion as there is no such study that has been done prior to our study. Energy barrier studies are used in a variety of fields, for instance, to study the energy barrier of Li ion diffusion in battery materials [26]. By gaining sufficient knowledge on the diffusion of Li, such troubles could be avoided. ...
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Manipulating oxygen vacancies in strongly correlated rare-earth nickelate perovskites (RNiO$_3$) enables the tuning of their elusive metal-insulator transition (MIT), providing a better handle for control over their electronic properties. In this paper, we investigate the effect of various oxygen vacancy configurations on the MIT of LaNiO$_3$ by studying their spectral functions and the corresponding diffusion energy path using dynamical mean field theory (DMFT) and density functional theory plus U (DFT+U). To consider all possible configurations for a fixed vacancy concentration, we use a symmetry-adapted configurational ensemble method. Within this method, we can reduce the configurational space which needs to be considered, thus lowering the computational cost. We demonstrate that controlling the oxygen vacancy position can tune the occurrence of MIT. We also show that the nudged elastic band (NEB) energy barrier heights and energy profile obtained using DMFT are lower and different than those obtained using DFT+U due to dynamical quantum fluctuations among non-degenerate correlated orbitals not properly treated in DFT+U.
... The basic Li kinetic processes at the Li metal/ SSE interfaces include Li-ion transport, interfacial charge transfer, the Li adatom, and vacancy diffusion (9,10). Because of the extremely low intrinsic diffusion coefficient (<10 −11 cm 2 s −1 ) (11)(12)(13), the Li stripping-derived Li vacancies cannot be completely replenished and are accumulated as the Li voids neighboring interfaces (14,15). Therefore, the Li vacancy diffusion is the rate-determining step for dynamic evolution of interfacial morphology (16). ...
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... Likewise, electronic lab notebooks (ELNs) must be standardized to allow seamless integration of data into automatic workflows. Dedicated data-analysis and AI tools will be developed and demonstrated that help to identify the key descriptive physicochemical parameters [12][13][14][15] . This will allow for predictions that go beyond the immediately studied systems and will show trends and enable the identification of materials with statistically exceptional properties 16 . ...
... Specifically, voids form because vacancies condensate (Cuitiño and Ortiz, 1996) or annihilate at available sinks such as dislocations, grain boundaries and free surfaces. Void growth is further enhanced by adatom diffusion, as the transport of atoms along the void surfaces is faster than bulk vacancy diffusion (Jäckle et al., 2018). Voiding can be minimised by the application of mechanical pressure, as shown in Fig. 2c. ...
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We present a mechanistic theory for predicting void evolution in the Li metal electrode during the charge and discharge of all-solid-state battery cells. A phase field formulation is developed to model vacancy annihilation and nucleation, and to enable the tracking of the void-Li metal interface. This is coupled with a viscoplastic description of Li deformation, to capture creep effects, and a mass transfer formulation accounting for substitutional (bulk and surface) Li diffusion and current-driven flux. Moreover, we incorporate the interaction between the electrode and the solid electrolyte, resolving the coupled electro-chemical-mechanical problem in both domains. This enables predicting the electrolyte current distribution and thus the emergence of local current 'hot spots', which act as precursors for dendrite formation and cell death. The theoretical framework is numerically implemented, and single and multiple void case studies are carried out to predict the evolution of voids and current hot spots as a function of the applied pressure, material properties and charge (magnitude and cycle history). For both plating and stripping, insight is gained into the interplay between bulk diffusion, Li dissolution and deposition, creep, and the nucleation and annihilation of vacancies. The model is shown to capture the main experimental observations, including not only key features of electrolyte current and void morphology but also the sensitivity to the applied current, the role of pressure in increasing the electrode-electrolyte contact area, and the dominance of creep over vacancy diffusion.
... Specifically, voids form because vacancies condensate (Cuitiño and Ortiz, 1996) or annihilate at available sinks such as dislocations, grain boundaries and free surfaces. Void growth is further enhanced by adatom diffusion, as the transport of atoms along the void surfaces is faster than bulk vacancy diffusion (Jäckle et al., 2018). Voiding can be minimised by the application of mechanical pressure, as shown in Fig. 2c. ...
Preprint
We present a mechanistic theory for predicting void evolution in the Li metal electrode during the charge and discharge of all-solid-state battery cells. A phase field formulation is developed to model vacancy annihilation and nucleation, and to enable the tracking of the void-Li metal interface. This is coupled with a viscoplastic description of Li deformation, to capture creep effects, and a mass transfer formulation accounting for substitutional (bulk and surface) Li diffusion and current-driven flux. Moreover, we incorporate the interaction between the electrode and the solid electrolyte, resolving the coupled electro-chemical-mechanical problem in both domains. This enables predicting the electrolyte current distribution and thus the emergence of local current 'hot spots', which act as precursors for dendrite formation and cell death. The theoretical framework is numerically implemented, and single and multiple void case studies are carried out to predict the evolution of voids and current hot spots as a function of the applied pressure, material properties and charge (magnitude and cycle history). For both plating and stripping, insight is gained into the interplay between bulk diffusion, Li dissolution and deposition, creep, and the nucleation and annihilation of vacancies. The model is shown to capture the main experimental observations, including not only key features of electrolyte current and void morphology but also the sensitivity to the applied current, the role of pressure in increasing the electrode-electrolyte contact area, and the dominance of creep over vacancy diffusion.
... 1−4 Although Mg dendrites have been observed and could cause short circuits in batteries, 5−7 the tendency to form dendrites is much weaker compared with that of Li, Na, Al, and Zn metals under similar cycling conditions. 8 Combined with the air stability of Mg metal (as a result of the formation of a passivating MgO surface film), Mg−metal batteries are a much safer option than Li−metal batteries. ...
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... Likewise, electronic lab notebooks (ELNs) must be standardized to allow seamless integration of data into automatic workflows. Dedicated data-analysis and AI tools shall be developed and demonstrated that help identifying the key descriptive physicochemical parameters 33,34,35,36 . This will allow for predictions that go beyond the immediately studied systems and will reveal trends and enable identifying materials with statistically exceptional properties 37 . ...
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The prosperity and lifestyle of our society are very much governed by achievements in condensed matter physics, chemistry and materials science, because new products for sectors such as energy, the environment, health, mobility and information technology (IT) rely largely on improved or even new materials. Examples include solid-state lighting, touchscreens, batteries, implants, drug delivery and many more. The enormous amount of research data produced every day in these fields represents a gold mine of the twenty-first century. This gold mine is, however, of little value if these data are not comprehensively characterized and made available. How can we refine this feedstock; that is, turn data into knowledge and value? For this, a FAIR (findable, accessible, interoperable and reusable) data infrastructure is a must. Only then can data be readily shared and explored using data analytics and artificial intelligence (AI) methods. Making data 'findable and AI ready' (a forward-looking interpretation of the acronym) will change the way in which science is carried out today. In this Perspective, we discuss how we can prepare to make this happen for the field of materials science.
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Significant challenges remain in developing rechargeable zinc batteries mainly because of reversibility problems on zinc metal anodes. The dendritic growth and hydrogen evolution on zinc electrodes are major obstacles to overcome in developing practical and safe zinc batteries. Here, a dendrite‐free and hydrogen‐free Zn metal anode with high Coulombic efficiency up to 99.6% over 300 cycles is realized in a newly‐designed nonaqueous electrolyte, which comprises an inexpensive zinc salt, zinc acetate, and a green low‐cost solvent, dimethyl sulfoxide. A surface transformation on Cu substrate plays a critical role in facilitating the dendrite‐free deposition process, which lowers the diffusion energy barrier of Zn atoms, leading to a uniform and compact thin film for zinc plating. Furthermore, the in situ electrochemical atomic force microscopy reveals the plating process via a layer‐by‐layer growth mechanism and the stripping process through an edge‐dissolution mechanism. In addition, Zn||Mo6S8 full cells exhibit excellent electrochemical performance in terms of cycling stability and rate capability. This work presents a new opportunity to develop nonaqueous rechargeable zinc batteries. This article is protected by copyright. All rights reserved
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Garnet-type Li7La3Zr2O12 (LLZO) has been recognized as a candidate solid electrolyte for high-safety Li-anode based solid-state batteries because of its electro-chemical stability against Li-metal and high ionic conductivity. Solvent (e.g., isopropanol (IPA)) has been commonly applied for preparing LLZO powders and ceramics. However, the deterioration of the proton-exchange between LLZO and IPA/absorbed moisture during the mixing and tailoring route has aroused less attention. In this study, a solvent-free dry milling route was developed for preparing the LLZO powders and ceramics. For orthogonal four categories of samples prepared using solvent-free and IPA-assisted routes in the mixing and tailoring processes, the critical evaluation was conducted on the crystallinity, surficial morphology, and contamination of as-calcinated and as-tailored particles, the cross-sectional microstructure of green and sintered pellets, the morphology and electro-chemical properties of grain boundaries in ceramics, as well as the interfacial resistance and performance of Li anode based symmetric batteries. The wet route introduced Li-rich contaminations (e.g., LiOH∙H2O and Li2CO3) onto the surfaces of LLZO particles and Li-Ta-O segregations at the adjacent and triangular grain boundaries. The LLZO solid electrolytes prepared through dry mixing in combination with the dry tailoring route without the use of any solvent were found to the optimal performance. The fundamental material properties in the whole LLZO preparation process were found, which are of guiding significance to the development of LLZO powder and ceramic production craft.
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The development of solid‐state batteries has become one of the most promising directions in rechargeable secondary batteries due to their considerable energy densities and favorable safety. However, solid‐state batteries with higher energy density and more durable and stable cycle life should be developed for large‐scale energy storage and adaption to the rapidly increasing lithium battery production and sales market. Although inorganic solid electrolytes (ISEs) and composite solid electrolytes (CSEs) are relatively advantageous solid‐state electrolytes, they also face severe challenges. This review summarizes the main stability issues related to chemical, mechanical, thermal, and electrochemical aspects faced by ISEs and CSEs. The corresponding state‐of‐the‐art improvement strategies have been proposed, including filling of modified particles, electrolyte pore adjustment, electrolyte internal structure arrangement, and interface modification. This review summarizes the main stability issues related to chemical, mechanical, thermal, and electrochemical aspects faced by inorganic solid electrolytes and composite solid electrolytes. The state‐of‐the‐art strategies have been proposed to address the stability issues in solid‐state batteries.
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Rechargeable magnesium batteries are particularly advantageous for renewable energy storage systems. However, the inhomogeneous Mg electrodeposits greatly shorten their cycle life under practical conditions. Herein, the epitaxial electrocrystallization of Mg on a three-dimensional magnesiophilic host is implemented via the synergy of a magnesiophilic interface, lattice matching, and electrostatic confinement effects. The vertically aligned nickel hydroxide nanosheet arrays grown on carbon cloth (abbreviated as "Ni(OH)2@CC") have been delicately designed, which satisfy the essential prerequisite of a low lattice geometrical misfit with Mg (about 2.8%) to realize epitaxial electrocrystallization. Simultaneously, the ionic crystal nature of Ni(OH)2 displays a periodic and hillock-like electrostatic potential field over its exposed facets, which can precisely capture and confine the reduced Mg0 species onto the local electron-enriched sites at the atomic level. The Ni(OH)2@CC substrate undergoes sequential Mg-ion intercalation, underpotential deposition, and electrocrystallization processes, during which the uniform, lamellar Mg electrodeposits with a locked crystallographic orientation are formed. Under practical conditions (10 mA cm-2 and 10 mAh cm-2), the Ni(OH)2@CC substrate exhibits stable Mg stripping/plating cycle performances over 600 h, 2 orders of magnitude longer than those of the pristine copper foil and carbon cloth substrates.
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Uniform magnesium (Mg) plating/striping under high areal capacity utilization is critical for the practical application of Mg metal anode in rechargeable Mg batteries. However, the Mg metal anode failure has raising concerns when cycling under practical areal capacity (> 4 mA h cm–2) . The mechanism behind these failures remains controversial. In this work, we illustrate that the initial plating Mg can be undoubtedly uniform in wide range of current densities (≤ 5 mA cm–2) and under a practical areal capacity (6 mA h cm–2) . However, an unusual self‐accelerating pit growth is observed in the Mg stripping side under the moderate current densities (0.1‐1 mA cm–2), which severely deteriorates the anode integrity and subsequent Mg plating uniformity, causing Mg metal anode failure or short circuit of battery. The stripping morphology depends on the applied current density, as non‐uniformity versus the current density displays a volcano plot during the stripping process. Through in‐situ spectroscopy, we illustrate that this current dependent behavior is determined by the evolution of chlorine‐containing complex ions near the interface. This research reminds that the plating/stripping process of Mg metal anode must be considered comprehensively for the practical Mg metal batteries. This article is protected by copyright. All rights reserved
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Magnesium/sulfur batteries have emerged as one of the considerable choices for next-generation batteries. However, its low voltage platform caused by the passivation of magnesium anode limits its actual energy density. Herein, a magnesium-lithium alloy is screened out as a passivation-free anode, which hinders the passivation reaction on the anode through the substitution reaction between lithium in the alloy and the magnesium ions in the electrolyte. The alloy anode exhibits an improved interfacial reaction kinetics, and the impedance is reduced by 5 orders of magnitude compared to that of magnesium anode. With passivation-free Mg-Li alloy anode, the magnesium/sulfur battery achieves an enhanced discharge voltage platform of 1.5 V and an energy density of 1829 Wh kg⁻¹. This study provides a novel design of passivation-free magnesium alloy anode for high-energy-density magnesium/sulfur batteries.
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Alkali metals are expected to be used for rechargeable metal anode batteries owing to their low electrode potentials and large capacities. However, they face the well-known fatal problem of “dendritic growth” while charging. Here, we present a detailed investigation on electrolytes where alkaline earth salts are introduced to inhibit dendrite growth in alkali metal electrodeposition. Specifically, focusing on CaTFSA2 as an exemplary additive, we reveal that dendrite-free morphology upon alkali metal electrodeposition can be attained by modifying the solvation structures in dual-cation electrolytes. Addition of Ca²⁺ promotes alkali cation (Li⁺ or Na⁺) to form the contact ion pairs (CIPs) with the counter anions, which replaces the solvent-separated ion pairs that commonly exist in single-cation electrolytes. The strong binding of the CIPs slows the desolvation kinetics of alkali cations and, consequently, realizes a severely constrained alkali metal electrodeposition in a reaction-limited process that is required for the dendrite-free morphology.
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Metal anodes with a plating/stripping electrochemical behavior are promising anode materials for rechargeable batteries due to their low electrochemical potential, superior electronic conductivity, good machinability, and high theoretical specific capacity. These metal anodes include Li, Na, K, Mg, Ca, Al, Fe, Zn, Mn, etc. Nevertheless, several issues affect their development and application, such as high chemical reactivity, uneven electrochemical deposition, unstable solid electrolyte interphase (SEI), and large volume change of electrodes during cycling. Recently, room-temperature liquid metals (RLM) such as metallic Ga, Ga-based alloy (GaIn, GaSn, GaZn, GaInSn, GaInSnZn, etc), metallic Hg, and liquid Na-K alloy have exhibited large potential in addressing the issues of metal anodes and a lot of advances have been reported. Here these advances are summarized and analyzed in detail. Meanwhile, some perspectives and outlooks are put forward. RLM can effectively solve the issues of metal anodes by constructing 3D current collectors, regulating nucleation, designing artificial interface layer, fabricating composite anodes, heat conduction, eliminating already existing dendrites, stress release, etc. This review can promote the development of multifunctional RLM as well as rechargeable metal based batteries.
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The prosperity and lifestyle of our society are very much governed by achievements in condensed matter physics, chemistry and materials science, because new products for sectors such as energy, the environment, health, mobility and information technology (IT) rely largely on improved or even new materials. Examples include solid-state lighting, touchscreens, batteries, implants, drug delivery and many more. The enormous amount of research data produced every day in these fields represents a gold mine of the twenty-first century. This gold mine is, however, of little value if these data are not comprehensively characterized and made available. How can we refine this feedstock; that is, turn data into knowledge and value? For this, a FAIR (findable, accessible, interoperable and reusable) data infrastructure is a must. Only then can data be readily shared and explored using data analytics and artificial intelligence (AI) methods. Making data 'findable and AI ready' (a forward-looking interpretation of the acronym) will change the way in which science is carried out today. In this Perspective, we discuss how we can prepare to make this happen for the field of materials science. A findable, accessible, interoperable and reusable (FAIR) data infrastructure is discussed to turn the large amount of research data generated by the field of materials science into knowledge and value.
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Solid electrolytes are widely considered as the enabler of lithium metal anodes for safe, durable, and high energy density rechargeable lithium-ion batteries. Despite the promise, failure mechanisms associated with solid-state batteries are not well-established, largely due to limited understanding of the chemomechanical factors governing them. We focus on the recent developments in understanding solid-state aspects including the effects of mechanical stresses, constitutive relations, fracture, and void formation, and outline the gaps in the literature. We also provide an overview of the manufacturing and processing of solid-state batteries in relation to chemomechanics. The gaps identified provide concrete directions towards the rational design and development of failure-resistant solid-state batteries.
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Tremendous improvements in the Li⁺ conductivity of inorganic solid electrolytes over the past 15 years have renewed interest in developing solid state batteries, with a particular focus on realizing the lithium metal anode. Despite initial hopes, solid electrolytes pressed against flat lithium metal anodes have so far been unable to mitigate the penetration of the solid electrolyte by lithium dendrites. Our understanding of how lithium dendrites grow through solid electrolytes has also evolved. Based on the current literature, it appears that the root cause of lithium penetration is the low self-diffusion of Li⁰, coupled with lithium plating/stripping hot spots. Many different approaches to mitigate lithium penetration have been attempted. Some approaches, in particular, may warrant deeper insight, such as high-surface-area substrates for lithium deposition, lithium-alloys and artificial SEIs. Separately from the challenges of lithium metal, solid-state cathodes must contend with crack formation due to the expansion and contraction of the active material. Soft electrolytes, such as composite electrolytes, may be able to somewhat alleviate this. Herein we explain the challenges facing solid state cells, the attempts that have been made to mitigate them and our opinion of the most promising routes to success.
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Enabling high Mg ion mobility, spinel‐type materials are promising candidates for cathode or solid electrolyte applications. To elu‐ cidate the factors governing the observed high mobility of multivalent ions, periodic DFT calculations of various charge carriers (A = Li, Na, K, Mg, Ca, Zn and Al) in the ASc2 S4 and ASc2 Se4 spinel compounds were performed, resulting in the identification of a Brønsted‐Evans‐Polanyi‐type scaling relation for the migration barriers of the various charge carriers. Combining this scaling relation with the derivation of a descriptor, solely based on easily accessible observables, constitutes a conceptual framework to investigate ion mobility in d0‐metal‐based spinel chalcogenides with significantly reduced computational effort. This approach was exemplarily verified for various d0‐metal‐based spinel chalcogenide compounds AB2X4 (B = Sc, Y, Ga, In, Er and Tm; X = O, S and Se) and led to the identification of d0 ‐metal‐based CaB2O4 spinels as promising compounds possibly enabling high Ca ion mobility.
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Alkali metal ion batteries, and in particular Li-ion batteries, have become a key technology for current and future energy storage, already nowadays powering many devices in our daily lives. Due to the inherent complexity of batteries and their components, the use of computational approaches on all length and timescales has been largely evolving in recent years. Gaining insight in complex processes or predicting new materials for specific applications are two of the main perspectives computational studies can offer, making them an indispensable tool of modern material science and hence battery research. After a short introduction to battery technology, this review will first focus on the theoretical concepts that underlie the functioning of Li- and post-Li-ion batteries. This will be followed by a discussion of the most prominent computational methods and their applications, currently available for the investigation of battery materials on an atomistic scale.
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Metallic Mg is a promising anode material for rechargeable magnesium-ion batteries (MIBs) due to its low electrochemical potential and high theoretical capacity. However, low Mg²⁺ conductivity on the interface of Mg electrode caused by liquid electrolyte passivation hinders its development. In addition, whether Mg dendrites can be formed in Mg metal anodes is controversial. Herein, we find that Mg dendrites can be formed in Mg metal anodes. The diameter of most Mg dendrites is below 100 nm, which is much smaller than Li and Na dendrites. The nanoscale Mg dendrites can easily pierce through the separators with large pore size and cause the internal short circuit of batteries. A simple strategy is proposed to address the issues of Mg metal anodes by painting a liquid metal Ga layer on Mg foil. Metallic Ga can spontaneously alloy with metallic Mg to form a stable, Mg²⁺-conductive, corrosive-resistant, and magnesiophilic Ga5Mg2 alloy layer. Under the regulation of the Ga5Mg2 alloy layer, a highly reversible, stable, and dendrite-free Mg metal anode is obtained. Enhanced electrochemical performance is achieved both in symmetric cells and Mg-S full cells. This study paves the way for high-energy Mg-metal batteries.
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There is a strong need to improve the efficiency of electrochemical energy storage, but progress is hampered by significant technological and scientific challenges. This review describes the potential contribution of atomic-scale modeling to the development of more efficient batteries, with a particular focus on first-principles electronic structure calculations. Numerical and theoretical obstacles are discussed, along with ways to overcome them, and some recent examples are presented illustrating the insights into electrochemical energy storage that can be gained from quantum chemical studies.
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The Solid-Electrolyte-Interphase (SEI) model for non-aqueous alkali-metal batteries constitutes a paradigm change in the understanding of lithium batteries and has thus enabled the development of safer, durable, higher-power and lower-cost lithium batteries for portable and EV applications. Prior to the publication of the SEI model (1979), researchers used the Butler-Volmer equation, in which a direct electron transfer from the electrode to lithium cations in the solution is assumed. The SEI model proved that this is a mistaken concept and that, in practice, the transfer of electrons from the electrode to the solution in a lithium battery, must be prevented, since it will result in fast self-discharge of the active materials and poor battery performance. This model provides [E. Peled, in “Lithium Batteries,” J.P. Gabano (ed), Academic Press, (1983), E. Peled, J. Electrochem. Soc., 126, 2047 (1979).] new equations for: electrode kinetics (io and b), anode corrosion, SEI resistivity and growth rate and irreversible capacity loss of lithium-ion batteries. This model became a cornerstone in the science and technology of lithium batteries. This paper reviews the past present and the future of SEI batteries.
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Next-generation high-energy batteries will require a rechargeable lithium metal anode, but lithium dendrites tend to form during recharging, causing short-circuit risk and capacity loss, by mechanisms that still remain elusive. Here, we visualize lithium growth in a glass capillary cell and demonstrate a change of mechanism from root-growing mossy lithium to tip-growing dendritic lithium at the onset of electrolyte diffusion limitation. In sandwich cells, we further demonstrate that mossy lithium can be blocked by nanoporous ceramic separators, while dendritic lithium can easily penetrate nanopores and short the cell. Our results imply a fundamental design constraint for metal batteries (“Sand's capacity”), which can be increased by using concentrated electrolytes with stiff, permeable, nanoporous separators for improved safety.
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The surface energy is a fundamental property of the different facets of a crystal that is crucial to the understanding of various phenomena like surface segregation, roughening, catalytic activity, and the crystal’s equilibrium shape. Such surface phenomena are especially important at the nanoscale, where the large surface area to volume ratios lead to properties that are significantly different from the bulk. In this work, we present the largest database of calculated surface energies for elemental crystals to date. This database contains the surface energies of more than 100 polymorphs of about 70 elements, up to a maximum Miller index of two and three for non-cubic and cubic crystals, respectively. Well-known reconstruction schemes are also accounted for. The database is systematically improvable and has been rigorously validated against previous experimental and computational data where available. We will describe the methodology used in constructing the database, and how it can be accessed for further studies and design of materials.
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Since their discovery, ionic liquids (ILs) have attracted a wide interest for their potential use as a medium for many chemical processes, in particular electrochemistry. As electrochemical media they allow the electrodeposition of elements that are impossible to reduce in aqueous media. We have investigated the electrodeposition of aluminium from 1-butyl-3-methyl-imidazolium chloride ((Bmim)Cl)/AlCl3 (40/60 mol %) as concerns the effect of deposition parameters on the quality of the deposits. Thick (20 μm) aluminium coatings were electrodeposited on brass substrates at different temperatures and mixing conditions (mechanical stirring and sonication). These coatings were investigated by means of scanning electron microscope, roughness measurements, and X-ray diffraction to assess the morphology and the phase composition. Finally, electrochemical corrosion tests were carried out with the intent to correlate the deposition parameters to the anti-corrosion properties.
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A critical overview of the latest developments in the aluminum battery technologies is reported. The substitution of lithium with alternative metal anodes characterized by lower cost and higher abundance is nowadays one of the most widely explored paths to reduce the cost of electrochemical storage systems and enable long-term sustainability. Aluminum based secondary batteries could be a viable alternative to the present Li-ion technology because of their high volumetric capacity (8040 mAh cm−3 for Al vs 2046 mAh cm−3 for Li). Additionally, the low cost aluminum makes these batteries appealing for large-scale electrical energy storage. Here, we describe the evolution of the various aluminum systems, starting from those based on aqueous electrolytes to, in more details, those based on non-aqueous electrolytes. Particular attention has been dedicated to the latest development of electrolytic media characterized by low reactivity towards other cell components. The attention is then focused on electrode materials enabling the reversible aluminum intercalation-deintercalation process. Finally, we touch on the topic of high-capacity aluminum-sulfur batteries, attempting to forecast their chances to reach the status of practical energy storage systems.
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Lithium-ion batteries (LIBs) have some serious safety problems, such as lithium dendrite formation during charging/discharging cycles that may cause internal short-circuiting, fires, and even explosions. A new double-scale in situ experimental setup, which can record all phenomena during the electrochemical testing, was developed. Lithium dendrite growth behavior of commercial LIBs during small-current-density charging at room temperature was observed in situ. The formation, growth, and dissolution of lithium dendrites, and dead lithium residue were all observed and recorded using this new experimental test system. A detailed model of lithium electrodeposition and dissolution processes was proposed. The electrode structures were determined by X-ray diffraction (XRD). The surface morphologies were examined by scanning electron microscopy (SEM). The texture and surface morphology of the graphite active layer affected lithium dendrite initiation as well as its growth processes.
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We present a computational study of the interface of a Pt electrode and an aqueous electrolyte employing semi-empirical dispersion corrections and an implicit solvent model within first-principles calculations. The electrode potential is parametrized within the computational hydrogen electrode scheme. Using one explicit layer, we find that the most realistic interface configuration is a water bilayer in the H-up configuration. Furthermore, we focus on the contribution of the dispersion interaction and the presence of water on H, O, and OH adsorption energies. This study demonstrates that the implicit water scheme represents a computationally efficient method to take the presence of an aqueous electrolyte interface with a metal electrode into account.
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To explore the potential of molecular gas treatment of freshly cut lithium foils in non-electrolyte based passivation of high energy-density Li anodes, density functional theory (DFT) has been used to study the decomposition of molecular gases on metallic lithium surfaces. By combining DFT geometry optimization and Molecular Dynamics, the effects of atmospheric (N2, O2, CO2) and hazardous (F2, SO2) gas decomposition on Li(bcc) (100), (110), and (111) surfaces on relative surface energies, work functions, and emerging electronic and elastic properties are investigated. The simulations suggest that exposure to different molecular gases can be used to induce and control reconstructions of the metal Li surface and substantial changes (up to over 1 eV) in the work function of the passivated system. Contrary to the other considered gases, which form metallic adlayers, SO2 treatment emerges as the most effective in creating an insulating passivation layer for dosages <= 1 mono-layer. The substantial Li->adsorbate charge transfer and adlayer relaxation produce marked elastic stiffening of the interface, with the smallest change shown by nitrogen-treated adlayers.
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The low cost, significant reduction potential and relative safety of the zinc electrode is a common hope for a reductant in secondary batteries, but it is limited mainly to primary implementation due to shape change. In this work, we exploit such shape change for the benefit of static electrodes through the electrodeposition of hyper-dendritic nanoporous zinc foam. Electrodeposition of zinc foam resulted in nanoparticles formed on secondary dendrites in a three-dimensional network with a particle size distribution of 54.1-96.0 nm. The nanoporous zinc foam contributed to highly oriented crystals, high surface area and more rapid kinetics in contrast to conventional zinc in alkaline mediums. The anode material presented had a utilization of ~88% at full depth-of-discharge (DOD) at various rates indicating a superb rate capability. The rechargeability of Zn0/Zn2+ showed significant capacity retention over 100 cycles at a 40% DOD to ensure that the dendritic core structure was imperforated. The dendritic architecture was densified upon charge-discharge cycling and presented superior performance compared with bulk zinc electrodes.
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The development of new rechargeable battery systems could fuel various energy applications, from personal electronics to grid storage. Rechargeable aluminium-based batteries offer the possibilities of low cost and low flammability, together with three-electron-redox properties leading to high capacity. However, research efforts over the past 30 years have encountered numerous problems, such as cathode material disintegration, low cell discharge voltage (about 0.55 volts; ref. 5), capacitive behaviour without discharge voltage plateaus (1.1-0.2 volts or 1.8-0.8 volts) and insufficient cycle life (less than 100 cycles) with rapid capacity decay (by 26-85 per cent over 100 cycles). Here we present a rechargeable aluminium battery with high-rate capability that uses an aluminium metal anode and a three-dimensional graphitic-foam cathode. The battery operates through the electrochemical deposition and dissolution of aluminium at the anode, and intercalation/de-intercalation of chloroaluminate anions in the graphite, using a non-flammable ionic liquid electrolyte. The cell exhibits well-defined discharge voltage plateaus near 2 volts, a specific capacity of about 70 mA h g(-1) and a Coulombic efficiency of approximately 98 per cent. The cathode was found to enable fast anion diffusion and intercalation, affording charging times of around one minute with a current density of ~4,000 mA g(-1) (equivalent to ~3,000 W kg(-1)), and to withstand more than 7,500 cycles without capacity decay.
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Lithium (Li) metal is an ideal anode material for rechargeable batteries due to its extremely high theoretical specific capacity (3860 mA h g À1), low density (0.59 g cm À3) and the lowest negative electrochemical potential (À3.040 V vs. the standard hydrogen electrode). Unfortunately, uncontrollable dendritic Li growth and limited Coulombic efficiency during Li deposition/stripping inherent in these batteries have prevented their practical applications over the past 40 years. With the emergence of post-Li-ion batteries, safe and efficient operation of Li metal anodes has become an enabling technology which may determine the fate of several promising candidates for the next generation energy storage systems, including rechargeable Li–air batteries, Li–S batteries, and Li metal batteries which utilize intercalation compounds as cathodes. In this paper, various factors that affect the morphology and Coulombic efficiency of Li metal anodes have been analyzed. Technologies utilized to characterize the morphology of Li deposition and the results obtained by modelling of Li dendrite growth have also been reviewed. Finally, recent development and urgent need in this field are discussed.
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This comparative work studies the self-enforcing heterogeneity of lithium deposition and dissolution as the cause for dendrite formation on the lithium metal anode in various liquid organic solvent based electrolytes. In addition, the ongoing lithium corrosion, its rate and thus the passivating quality of the SEI are investigated in self-discharge measurements. The behavior of the lithium anode is characterized in two carbonate-based standard electrolytes, 1M LiPF6 in EC/DEC (3:7) and 1M LiPF6 in EC/DMC (1:1), and in two alternative electrolytes 1M LiPF6 in TEGDME and 1M LiTFSI in DMSO, which have been proposed by others as promising electrolytes for lithium metal batteries, more specifically for lithium/air batteries. As a result, the electrolyte decomposition, the SEI and dendrite formation at the lithium electrode as well as their mutual influences are understood in the development of the overpotentials, the surface resistances and the lithium electrode surface morphologies in subsequent lithium deposition and dissolution processes. A general model of different stages of these processes could be elaborated.
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Lithium-ion batteries are prone to failure at low temperatures and dendrite growth during charging is one suspect. We attempt to understand lithium dendrite growth by observing their number, initiation time and growth rate at ambient and sub-ambient temperatures: −10◦C, 5◦C, and 20◦C using an in-situ optical microscopy cell (Li0|Li0).We find that while dendrites initiate quickly at −10◦C, the cells at 5◦C short-circuit most rapidly due in part to a favorable morphology at this temperature. The experimental approach has broad applicability to other electrochemical energy storage technologies where mass transport limitations are present at low temperatures, particularly Li-air, Li-S, and Zn-air batteries.
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Lithium and magnesium exhibit rather different properties as battery anode materials with respect to the phenomenon of dendrite formation which can lead to short-circuits in batteries. Diffusion processes are the key to understanding structure forming processes on surfaces. Therefore, we have determined adsorption energies and barriers for the self-diffusion on Li and Mg using periodic density functional theory calculations and contrasted the results to Na which is also regarded as a promising electrode material in batteries. According to our calculations, magnesium exhibits a tendency towards the growth of smooth surfaces as it exhibits lower diffusion barriers than lithium and sodium, and as an hcp metal it favors higher-coordinated configurations in contrast to the bcc metals Li and Na. These characteristic differences are expected to contribute to the unequal tendencies of these metals with respect to dendrite growth.
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Lithium/air batteries, based on their high theoretical specific energy, are an extremely attractive technology for electrical energy storage that could make long-range electric vehicles widely affordable. However, the impact of this technology has so far fallen short of its potential due to several daunting challenges. In nonaqueous Li/air cells, reversible chemistry with a high current efficiency over several cycles has not yet been established, and the deposition of an electrically resistive discharge product appears to limit the capacity. Aqueous cells require water-stable lithium-protection membranes that tend to be thick, heavy, and highly resistive. Both types of cell suffer from poor oxygen redox kinetics at the positive electrode and deleterious volume and morphology changes at the negative electrode. Closed Li/air systems that include oxygen storage are much larger and heavier than open systems, but so far oxygen- and OH--selective membranes are not effective in preventing contamination of cells. In this review we discuss the most critical challenges to developing robust, high-energy Li/air batteries and suggest future research directions to understand and overcome these challenges. We predict that Li/air batteries will primarily remain a research topic for the next several years. However, if the fundamental challenges can be met, the Li/air battery has the potential to significantly surpass the energy storage capability of today's Li-ion batteries.
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A novel, dendrite-free electrorefining of aluminum scrap alloys (A360) was investigated by using a low-temperature AlCl3-1-ethyl-3-methyl-imidazolium chloride (EMIC) ionic liquid electrolyte on copper/aluminum cathodes. The bulk electrodeposition of aluminum was carried out at a fixed voltage of 1.5 V, temperatures 323 K to 383 K (50 °C to 110 °C), stirring rate (0 to 120 rpm), concentration (molar ratio AlCl3:EMIC = 1.25 to 2.0), and electrode surface modification (modified/unmodified). The study investigated the effect of electrode surface modification, cathode materials, temperature, stirring rate, electrolyte concentration, and deposition time on the deposit morphology of aluminum, cathode current density, and their role in production of dendrite-free aluminum deposit, which is essential for decreasing the production cost. The deposits were characterized using scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). It was shown that electrode surface modification, cathode overpotential, and stirring rate play an important role in dendrite-free deposit. Modified electrodes and stirring (60 rpm) eliminate dendritic deposition by reducing cathode overpotential below critical overpotential ( $ \eta_{\text{crt}} \approx - 0.53V $ ) for dendrite formation. Pure aluminum (>99 pct) was deposited for all experiments with a current efficiency of 84 to 99 pct and energy consumption of 4.51 to 5.32 kWh/kg Al.
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The first working Mg rechargeable battery prototypes were ready for presentation about 13 years ago after two breakthroughs. The first was the development of non-Grignard Mg complex electrolyte solutions with reasonably wide electrochemical windows in which Mg electrodes are fully reversible. The second breakthrough was attained by demonstrating high-rate Mg cathodes based on Chevrel phases. These prototypes could compete with lead–acid or Ni–Cd batteries in terms of energy density, very low self-discharge, a wide temperature range of operation, and an impressive prolonged cycle life. However, the energy density and rate capability of these Mg battery prototypes were not attractive enough to commercialize them. Since then we have seen gradual progress in the development of better electrolyte solutions, as well as suggestions of new cathodes. In this article we review the recent accumulated experience, understandings, new strategies and materials, in the continuous R&D process of non-aqueous Mg batteries. This paper provides a road-map of this field during the last decade.
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Formation of lithium dendrite/fibers during charging-discharging cycles not only causes short circuit but is also known as a major safety issue. In this work, an electrochemical cell was constructed inside a transmission electron microscope to observe the real-time nucleation and growth of the lithium fibers inside a nanoscale Li-ion battery. Our results show that during the lithiation process, the lithium ions nucleate at the interface of anode and electrolyte and then grow into fibers. These fibers grew parallel to the direction of the applied electric field. Such observations can assist the nanoscale design of better electrodes and electrolyte materials needed for safe and high power Li-ion batteries.
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The kinetic processes taking place on the surface and influencing the depth distribution of components during deposition of multilayers are considered by proposed kinetic model. The depth distribution of components in growing structure, broadening of interfaces between layers and shape of concentration peaks of multilayers are analyzed with respect of evolution of surface roughness during deposition. Surface roughness depends on adsorption rate and on surface diffusion. In presented model, the process of surface diffusion is subdivided into up-diffusion and down-diffusion. It is shown that atomic fluxes of up-diffusion and down-diffusion do not compensate each other even in the case of equal diffusion coefficients as they depend on coverage of different monolayers. Down-diffusion results in smoother surface, in contrary, up-diffusion makes it rougher. It is quantitatively shown by kinetic modeling that with increase of down-diffusion the amplitude of concentration peaks of components increases, the broadening of interface between layers decreases and concentration peaks become asymmetrical. The asymmetry of concentration peaks is found even in the case of equal diffusion coefficients of different components. At different diffusivity of components, the asymmetry is following: the concentration peaks of heavy-component (less diffusivity) show enhanced trailing tails on the back profile side (for light-component on the contrary). Up-diffusion results in increase of surface roughness and broadening of interface between layers. The quantitative functions of surface roughness on ratio of up- and down- diffusion coefficients are calculated and analyzed.
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One limiting phenomenon for the cycle life of metal-oxygen batteries is the growth of dendrites during metal plating (cell charging). For the relatively new sodium-oxygen cell, this subject has been investigated scarcely until now. Therefore, dendrite formation is systematically investigated in this work with the aim to gain a more detailed understanding of the underlying mechanisms and the relevant control parameters. Electrochemical impedance spectroscopy, cycling experiments and optical characterization techniques are applied in situ and ex situ, sodium dendrite growth is directly visualized for the first time by means of a tubular glass cell. The growth of instable surface morphologies is discussed from a theoretical perspective to comprehend the experimentally observed dendrite growth. Furthermore, counter-measures against issues with dendrites are discussed, aiming to increase the cycle life of sodium-oxygen batteries.
Article
Aluminum metal foil is the optimal choice as an anode material for aluminum-ion battery for its key advantages such as high theoretical capacity, safety and low cost. However, the metallic nature of aluminum foil is very likely to induce severe dendrite growth with further electrode disintegration and cell failure, which is inconsistent with the previous reports. Here, we discover that it is aluminum oxide film that efficiently restricts the growth of crystalline Al dendrite and thus improves the cycling stability of Al anode. The key role of surficial aluminum oxide film in protecting Al metal anode lies in decreasing the nucleation sites, controlling the metalic dendrite growth and preventing the electrode disintegration. The defect sites in aluminum oxide film provide channels for electrolyte infiltration and further stripping/depositing. Attributed to such a protective aluminum oxide film, the Al-graphene full cells can attain up to 45,000 stable cycles.
Article
Zinc can compete with lithium Although lithium-based batteries are ubiquitous, there are still challenges related to their longevity and safety, as well as concerns about material availability. Aqueous rechargeable batteries based on zinc might provide an alternative, but they have been plagued by the formation of dendrites during cycling. Parker et al. show that when zinc is formed into three-dimensional sponges, it can be used with nickel to form primary batteries that allow for deep discharge. Alternatively, the sponges can be used to produce secondary batteries that can be cycled thousands of times and can compete with lithium ion cells. Science , this issue p. 415
Article
The electro-oxidation of methanol on Pt(111) is studied based on periodic density functional theory calculations. The aqueous electrolyte is taken into account using an implicit solvent model, and the dependence of the reaction energetics on the electrode potential is derived using the concept of the computational hydrogen electrode. The total oxidation of methanol becomes thermodynamically preferred at electrode potentials above U = 0.6 V relative to the standard hydrogen electrode. We propose a most favorable reaction path involving surface carboxyl as the last reaction intermediate before CO2 formation, which can either be formed in a indirect mechanism from adsorbed CO or in a direct mechanism from formic acid. The presence of the aqueous electrolyte significantly stabilizes reaction intermediates that contain hydrophilic groups. This also leads to a selectivity for the initial C-H bond breaking process with respect to the initial O-H bond breaking of methanol that is increased by 3 orders of magnitude at room temperature when solvent effects are considered.
Article
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.
Article
To improve the cycling performance of rechargeable zinc-air batteries, the dendritic morphology of electrodeposited zinc should be effectively controlled. It is of crucial importance to understand the formation mechanism of the zinc dendritic structure. Here we show that an electrochemical phase-field model is established to simulate dendrite growth of electrodeposited zinc, and several measures including the pulsating current and the electrolyte flow are taken to suppress dendrite growth in the charging process. The results demonstrate that dendrite propagation is mainly controlled by diffusion dependent on overpotential and surface energy anisotropy, and dendritic morphology can also give rise to non-uniform distribution of the electric field and ion concentration in the electrolyte. The proposed model and solutions will be available for studying dendrite growth of metal-air batteries as well as metal electrodeposition.
Article
Dendritic morphology evolution during zinc electrodeposition is a major roadblock in the development of rechargeable zinc anodes in alkaline zinc batteries. In the present work, we report the use of branched polyethylenimine (PEI, M.W. = 800 g/mol) as an effective electrolyte additive for suppressing dendrite formation during zinc electrodeposition from typical alkaline electrolytes used in secondary zinc batteries. Dendrite suppression is characterized as a function of the PEI concentration via ‘live’ observation of the dendrite propagation using an in-situ optical microscopy setup. Steady-state and transient electrochemical polarization measurements on a rotating disk electrode, combined with electrochemical quartz crystal microgravimetry and ex-situ scanning electron microscopy, reveal the mechanism by which PEI suppresses dendrites, i.e., PEI adsorption on the zinc surface leading to suppression of the zinc electrodeposition kinetics. Our work presents a comprehensive characterization of the role of polymeric additives, such as PEI, in suppressing dendritic growth during alkaline zinc electrodeposition.
Article
Higher energy density batteries are desired, especially for mobile electronic devices. Lithium metal anodes are a possible route to achieving high energy and power density due to their light weight compared to current graphite anodes. However, whisker growth during lithium electrodeposition (i.e. charging) represents a serious safety and efficiency concern for both lithium metal batteries and overcharging of graphite anodes in lithium-ion batteries. The initial morphology of deposited lithium nuclei can have a significant impact on the bulk material deposited. The nucleation of lithium metal from an organic ethylene carbonate: dimethyl carbonate (EC:DMC) and an ionic liquid (trimethylbutylammonium bis(triflouromethanesulfonyl)imide) electrolyte has been studied. Whisker extrusion and tip-based dendrite growth was observed ex-situ, and confirmed by in-situ optical microscopy experiments. The nucleation of a non-dendritic sodium co-deposit is also discussed. A model based on nuclei geometry is provided which gives insight into the deposition rate at constant overpotential.
Article
Lithium electrodeposition and -dissolution in a commercial battery electrolyte (1 M LiPF6 in EC:DMC) has been studied in situ by light microscopy and ex situ by scanning electron microscopy (SBM). We describe the transition between lithium filaments, which are most likely whiskers, and lithium moss and report in detail on the growth of mossy lithium structures. In the case of mossy lithium, the deposition can occur at the tips or the base of the growing structure. However, the growth is not limited to these locations, but can also occur by insertion at further growth points distributed inside the mossy Li deposit. We show that two different growth modes have to be distinguished: the unusual non-tip-growth by lithium metal insertion into the metallic moss backbone, and the condition where the deposition at the top of the mossy structure is not possible anymore because it was electrically isolated from the current collector due to a previous lithium dissolution step. After a dissolution period causing insulation of Li ("dead Li"), whole moss remnants can get pushed outside by metal structures growing underneath.
Article
In this article, we report on the electroplating and stripping of lithium in two ionic liquid (IL) based electrolytes, namely N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (Pyr14FSI) and N-butyl-N-methylbis(trifluoromethanesulfonyl)imide (Pyr14TFSI), and mixtures thereof, both on nickel and lithium electrodes. An improved method to evaluate the Li cycling efficiency confirmed that homogeneous electroplating (and stripping) of Li is possible with TFSI-based ILs. Moreover, the presence of native surface features on lithium, directly observable via SEM imaging, was used to demonstrate the enhanced SEI-forming ability, i.e. fast cathodic reactivity, of this class of electrolytes, as well as the suppressed dendrite growth. Finally, the induced inhomogeneous deposition allowed witnessing the SEI cracking, revealing previously unreported bundled Li fibers below the pre-existing SEI, as well as non-rod-shaped protuberances resulting from Li extrusion.
Article
We measured the average lengths λ of lithium dendrites produced by charging symmetric Li0 batteries at various temperatures, and performed allied Monte Carlo computations dealing both with Li+ transport in the electrolyte and thermal relaxation of Li0 electrodeposits. We show that experimental λ(T) variations cannot be solely accounted by the reported temperature dependence of Li+ mobility in the solvent, but require the involvement of competitive Li-atom transport from metastable dendrite tips to smoother domains over ∆ER‡ ~ 20 kJ mol-1 barriers. A transition state theory analysis of Li-atom diffusion in solids yields a negative entropy of activation for the relaxation process: ∆SR‡ ≈ - 46 J mol-1 K-1, which is consistent with the transformation of amorphous into crystalline Li0 electrodeposits. Significantly, our ∆ER‡ ~ 20 kJ mol-1 value compares favorably with the activation barriers recently derived from DFT calculations for self-diffusion on Li0 (001) and (111) crystal surfaces. Our findings underscore the key role the mobility of interfacial Li-atoms plays in determining the morphology of dendrites at temperatures above the onset of surface reconstruction: T ≈ 0.65 TM,B (TM,B = 453 K is the melting point of bulk Li0).
Article
The effect of mechanical surface modification on the performance of lithium (Li) metal foil electrodes is systematically investigated. The applied micro-needle surface treatment technique for Li metal has various advantages. 1) This economical and efficient technique is able to cover a wide range of surface area with a simple rolling process, which can be easily conducted. 2) This technique achieves improved rate capability and cycling stability, as well as a reduced interfacial resistance. The micro-needle treatment improves the rate capability by 20% (0.750 mAh at a rate of 7C) and increases the cycling stability by 200% (85% of the initial discharge capacity after 150 cycles) compared to untreated bare Li metal (0.626 mAh at a rate of 7C, 85% of the initial discharge capacity after only 70 cycles). 3) This technique efficiently suppresses Li formation of high surface area Li during the Li deposition process, as preferred sites for controlled Li plating are generated.
Article
Zinc-based batteries offer a safe, inexpensive alternative to fire-prone lithium-based batteries, but zinc-based batteries do not exhibit sufficient rechargeability—yet. Breaking through the centuries-old roadblock to zinc-based rechargeable batteries requires rethinking the electrode structure in order to control how zinc converts to zinc oxide during battery discharge and how the oxide is reversed back to metal upon recharging. We address the problems of inefficient zinc utilization and limited rechargeability by redesigning the zinc electrode as a porous, monolithic, three-dimensional (3D) aperiodic architecture. Utilization approaches 90% (728 mA h gZn−1) when the zinc “sponge” is used as the anode in a primary (single-use) zinc-air cell. To probe rechargeability of the 3D Zn sponge, we cycled Zn-vs.-Zn symmetric cells and Ag-Zn full cells under conditions that would otherwise support dendrite growth, and yet the Zn sponges remain dendrite-free after extensive cycling up to 188 mA h gZn−1. By using 3D-wired zinc architectures that innately suppress dendrite formation, all zinc-based chemistries can be reformulated for next-generation rechargeable batteries.
Article
In spite of the strong relevance of electrochemical energy conversion and storage, the atomistic modeling of structures and processes in electrochemical systems from first principles is hampered by severe problems. Among others, these problems are associated with the theoretical description of the electrode potential, the characterization of interfaces, the proper treatment of liquid electrolytes, changes in the bulk structure of battery electrodes, and limitations of the functionals used in first-principles electronic structure calculations. We will illustrate these obstacles, but also indicate strategies to overcome them.
Article
Although lithium dendrites have important implications on the safety and reliability of lithium-based batteries, an understanding of their growth mechanism is still lacking. Electron microscopy and in situ light microscopy were used to investigate the growth of lithium filaments and dendrites. Lithium was deposited by thermal evaporation in vacuum as well as electrochemically using two different electrolytes. Filaments grow in all three cases by an insertion mechanism, suggesting that neither a solid-electrolyte interphase (SEI) nor electrolytes are required to form lithium filaments. The role of the electrolyte becomes apparent in the detailed morphology of the deposits. These findings indicate that instead of ionic transport and electrochemistry, lithium diffusion and crystallization are key processes which need to be modified in order to control the growth of lithium dendrites.
Article
Motivated by recent experiments on electrochemically controlled Pb atomic-scale switches we have studied the self-diffusion of Pb on flat and stepped surfaces since diffusion processes play an important role in the growth of metal substrates. Kinetic modelling based on Monte-Carlo simulations using a model potential suggests that exchange processes play an important role in the contact formation at the nanoscale. Periodic density functional theory indeed find that the barriers for exchange diffusion across the steps are significantly lower than for hopping diffusion. The consequences for the contact formation in electrochemically controlled switches are discussed.
Article
We review work from our laboratory that suggests to us that most Li-ion battery failure can be ascribed to the presence of nano- and microscale inhomogeneities that interact at the mesoscale, as is the case with almost every material, and that these inhomogeneities act by hindering Li transport. (Li does not get to the right place at the right time.) For this purpose, we define inhomogeneities as regions with sharply varying properties—which includes interfaces—whether present by “accident” or design. We have used digital image correlation, X-ray tomography, FIB-SEM serial sectioning, and isotope tracer techniques with TOF-SIMS to observe and quantify these inhomogeneities. We propose new research approaches to make more durable, high energy density lithium-ion batteries.
Article
Batteries with metallic lithium anodes offer improved volumetric and gravimetric energy densities; therefore, future batteries including the promising lithium-sulfur and lithium-air systems would benefit from them. The electrodeposition of lithium metal - which is an unwanted incident in lithium ion systems - often results in fine filaments or moss, called dendritic lithium, which leads to strong capacity fading and the danger of internal short circuiting. To study the mechanisms of dendritic growth and the behavior during lithium dissolution, lithium deposits have been observed in situ in 1 M LiPF6 in EC:DMC by light microscopy. The high resolution optical microscopy provided information on the growth and electrodissolution of single lithium filaments. The growth areas could be identified in detail: The lithium wires can grow either from the substrate-lithium interface, at kinks or in a region at or close to the tip. Based on these observations, we suggest a growth model for lithium filaments predicated on defect-based insertion of lithium at the aforementioned locations. This type of growth is not compatible with previous models of dendritic growth, for example, it is hardly influenced by electric fields at the tip and does not depend on the direction of the electric field.
Article
Increased propensity for dendritic lithium electrodeposition during sub-ambient temperature operation has been widely reported in lithium battery systems, yet is not fully understood. In the present paper, a mathematical model is developed to quantify the dendritic growth rate during lithium electrodeposition at sub-ambient temperature. This model builds on a diffusion-reaction framework presented recently by Akolkar [J. Power Sources 232 (2013) 23-28]. Using a steady-state diffusion model with a concentration-dependent diffusion coefficient, the lithium-ion concentration depletion in the stagnant Nernst diffusion boundary layer near the lithium surface is modeled. A surface electrochemical reaction model is then employed to correlate the lithium concentration depletion to the dendrite growth rate. Temperature effects on the lithium-ion transport and its electrochemical surface reaction are incorporated in the model via an Arrhenius-type temperature-dependence of the diffusion coefficient and the apparent charge transfer coefficient. It is shown that lowering the system temperature has the effect of increasing the lithium-ion diffusion resistance and decreasing the surface film thickness - conditions favorable for the formation of dendrites during lithium electrodeposition.
Article
Major aspects related to lithium deposition in lithium-ion and lithium metal secondary batteries are reviewed. For lithium-ion batteries with carbonaceous anode, lithium deposition may occur under harsh charging conditions such as overcharging or charging at low temperatures. The major technical solutions include: (1) applying electrochemical models to predict the critical conditions for deposition initiation; (2) preventions by improved battery design and material modification; (3) applying adequate charging protocols to inhibit lithium deposition. For lithium metal secondary batteries, the lithium deposition is the inherent reaction during charging. The major technical solutions include: (1) the use of mechanistic models to elucidate and control dendrite initiation and growth; (2) engineering surface morphology of the lithium deposition to avoid dendrite formation via adjusting the composition and concentration of the electrolyte; (3) controlling battery working conditions. From a survey of the literature, the areas that require further study are proposed; e.g., refining the lithium deposition criteria, developing an effective AC self pre-heating method for low-temperature charging of lithium-ion batteries, and clarifying the role the solid electrolyte interphase (SEI) plays in determining the deposition morphology; to facilitate a refined control of the lithium deposition.
Article
Failure caused by dendrite growth in high-energy-density, rechargeable batteries with lithium metal anodes has prevented their widespread use in applications ranging from consumer electronics to electric vehicles. Efforts to solve the lithium dendrite problem have focused on preventing the growth of protrusions from the anode surface. Synchrotron hard X-ray microtomography experiments on symmetric lithium-polymer-lithium cells cycled at 90 °C show that during the early stage of dendrite development, the bulk of the dendritic structure lies within the electrode, underneath the polymer/electrode interface. Furthermore, we observed crystalline impurities, present in the uncycled lithium anodes, at the base of the subsurface dendritic structures. The portion of the dendrite protruding into the electrolyte increases on cycling until it spans the electrolyte thickness, causing a short circuit. Contrary to conventional wisdom, it seems that preventing dendrite formation in polymer electrolytes depends on inhibiting the formation of subsurface structures in the lithium electrode.