Suppress Dendrite Formation Research Articles

Surface Adsorption of Polyethylene Glycol to Suppress Dendrite Formation on Zinc Anodes in Rechargeable Aqueous Batteries

AbstractAqueous metal batteries routinely suffer from the dendritic growth at the anode, leading to significant capacity fading and ultimately, battery failure from short‐circuit. Herein, we utilize polyethylene glycol to regulate dendrite growth and improve the long‐term cycling stability of an aqueous rechargeable lithium/zinc battery. PEG200 in the electrolyte decreases the corrosion and chronoamperometric current densities of the zinc electrode up to four‐fold. Batteries with pre‐grown dendrites also perform significantly better when PEG is present in the electrolyte (41.4 mAh g−1 vs. 7.9 mAh g−1 after 1000 cycles). X‐ray diffraction and electron microscopy studies show that dendrites in the PEG‐containing electrolyte have been inhibited, leading to much smaller/smoother surface features than those of the control. The facile preparation process of the aqueous electrolyte combined with low cost and vast performance improvement in batteries of all sizes indicates high upscaling viability.

Present understanding of the stability of Li-stuffed garnets with moisture, carbon dioxide, and metallic lithium

Fast lithium-ion conducting garnet-type metal oxides are promising membranes for next-generation all-solid-state Li batteries and beyond Li-ion batteries, including Li-air and Li-S batteries, due to their high total Li-ion conductivity and excellent chemical stability against reaction with elemental Li. Several studies have been reported on structure-chemical composition-ionic conductivity property in Li-stuffed garnet-type metal oxides. Here, an overview of the chemical and electrochemical stability of lithium-based garnets against moisture/humidity, aqueous solutions, carbon dioxide, sulfur, and metallic lithium are analyzed. Moisture and aqueous stability studies focus on understanding the crystal structure stability, the proton exchange capacity as a function of Li content in Li-stuffed garnets, and how the protonated species affect the crystal structure and mass transport properties. H+/Li+ exchange was found to be in the range of 2–100%. Stability concerning Li-ion conductivity and morphology under carbon dioxide are discussed. Interfacial chemical stability with lithium metal characterized by electrochemical stability window, Li dendrite formation and area specific resistance (ASR) for the reaction Li⇌Li++e− are presented. Recent attempts to suppress dendrite formation and to reduce ASR via surface modification are also highlighted. Li and Li-stuffed garnet interface ASR values are shown to be as high as >2000 Ω cm2 and as low as 1 Ω cm2 at room temperature for surface modified Li-stuffed samples. Furthermore, recent studies on Li-S battery utilizing chemically stable Li – garnet electrolyte are also discussed.

One-pot solution coating of high quality LiF layer to stabilize Li metal anode

The high reactivity of Li metal anodes towards liquid electrolytes leads to an unstable and accumulated solid electrolyte interphase (SEI) film, which results in dendrite growth and low Coulombic efficiency (CE). Lithium fluoride (LiF) coating is considered as a reliable and dense SEI film to protect the reactive anode, however, the chemistry to form uniform, conformal and high quality LiF protection layer on Lithium metals remains as a major challenge. Here we develop a simple solution method to obtain LiF coating on Li metal anodes. We have discovered a chemical method to fabricate LiF coating via the in-situ reaction between metallic Li and polyvinylidene fluoride (PVDF)-dimethyl formamide (DMF) solution. Owing to the chemically and mechanically stable artificial SEI film, the LiF-coated Li anode delivers a better cycling performance than bare Li anode under various current densities in symmetrical cells. Stable cycling over 300 plating/striping cycles was achieved with LiF-coated Li electrodes under a high current density of 3 mA cm−2. The LiF coating also effectively suppresses dendrite formation and reduces side reactions between the metallic Li and the carbonate-based electrolyte. Therefore, this simple and low-cost method may benefit the future applications of the next generation Li metal batteries.

Suppressing Li Dendrite Formation in Li2S‐P2S5 Solid Electrolyte by LiI Incorporation

AbstractSolid electrolytes have been considered as a promising approach for Li dendrite prevention because of their high mechanical strength and high Li transference number. However, recent reports indicate that Li dendrites also form in Li2S‐P2S5 based sulfide electrolytes at current densities much lower than that in the conventional liquid electrolytes. The methods of suppressing dendrite formation in sulfide electrolytes have rarely been reported because the mechanism for the “unexpected” dendrite formation is unclear, limiting the successful utilization of high‐energy Li anode with these electrolytes. Herein, the authors demonstrate that the Li dendrite formation in Li2S‐P2S5 glass can be effectively suppressed by tuning the composition of the solid electrolyte interphase (SEI) at the Li/electrolyte interface through incorporating LiI into the electrolyte. This approach introduces high ionic conductivity but electronic insulation of LiI in the SEI, and more importantly, improves the mobility of Li atoms, promoting the Li depositon at the interface and thus suppresses dendrite growth. It is shown that the critical current density is improved significantly after incorporating LiI into Li2S‐P2S5 glass, reaching 3.90 mA cm−2 at 100 °C after adding 30 mol% LiI. Stable cycling of the Li‐Li cells for 200 h is also achieved at 1.50 mA cm−2 at 100 °C.

Directly Formed Alucone on Lithium Metal for High-Performance Li Batteries and Li-S Batteries with High Sulfur Mass Loading.

Lithium metal is considered the "holy grail" of next-generation battery anodes. However, severe parasitic reactions at the lithium-electrolyte interface deplete the liquid electrolyte and the uncontrolled formation of high surface area and dendritic lithium during cycling causes rapid capacity fading and battery failure. Engineering a dendrite-free lithium metal anode is therefore critical for the development of long-life batteries using lithium anodes. In this study, we deposit a conformal, organic/inorganic hybrid coating, for the first time, directly on lithium metal using molecular layer deposition (MLD) to alleviate these problems. This hybrid organic/inorganic film with high cross-linking structure can stabilize lithium against dendrite growth and minimize side reactions, as indicated by scanning electron microscopy. We discovered that the alucone coating yielded several times longer cycle life at high current rates compared to the uncoated lithium and achieved a steady Coulombic efficiency of 99.5%, demonstrating that the highly cross-linking structured material with great mechanical properties and good flexibility can effectively suppress dendrite formation. The protected Li was further evaluated in lithium-sulfur (Li-S) batteries with a high sulfur mass loading of ∼5 mg/cm2. After 140 cycles at a high current rate of ∼1 mA/cm2, alucone-coated Li-S batteries delivered a capacity of 657.7 mAh/g, 39.5% better than that of a bare lithium-sulfur battery. These findings suggest that flexible coating with high cross-linking structure by MLD is effective to enable lithium protection and offers a very promising avenue for improved performance in the real applications of Li-S batteries.

An ordered mesoporous silica framework based electrolyte with nanowetted interfaces for solid-state lithium batteries

An ionic liquid incorporated mesoporous silica has been developed as electrolyte to suppress dendrite formation in solid Li metal batteries.

(Invited) Enabling New Domains of Energy Storage through Atomic Layer Deposition

The portfolio of materials accessible by atomic layer deposition (ALD) processes has encompassed all key components of electrochemical energy storage (EES) – cathodes, anodes, solid electrolytes, and interphases. This provides a rich environment in which to advance the science of EES, particularly due to the exceptional thickness and conformality control inherent in underlying ALD mechanisms. Here we highlight three regimes where ALD is most promising to impact battery technology. (1) ALD-based electrode protection layers seem to offer the shortest term technology impact, providing ion permeability while serving as passivation against the varied modes chemical, electrochemical, and mechanical degradation regularly found in batteries, improving cycle life and suppressing dendrite formation. (2) ALD-based solid state batteries offer benefits in structural simplicity and control well beyond that available in commercial devices employing sputtered films. ALD solid electrolytes play a critical role in both protection layers and solid state batteries. (3) 3D solid state batteries exploit high surface areas and thin conformal layers over high aspect ratio topography to achieve higher power-energy performance than planar counterparts. Examples illustrating these opportunities include ALD LiPON protection of metal anodes and conversion electrodes, new pathways to solid electrolyte synthesis, and planar and 3D solid state batteries employing ALD for most or all components. Supported as part of the Energy Frontier Research Center (EFRC) Nanostructures for Electrical Energy Storage (NEES), funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DESC0001160.

Solid State Electrolytes and Composite Cathodes for Li-S Batteries

Advanced lithium battery chemistries beyond lithium-ion have demonstrated high energy density (>300 Wh/kg) but need further work to improve and demonstrate cycle life, shelf life, rate capability, and safety matching or exceeding that of lithium-ion batteries. A lithium sulfur battery can theoretically reach energy densities of 2600 Wh/kg and has high potential to meet energy density needs for portable power including electric vehicles. Nevertheless, the Li-S system has not yet been implemented because of multiple obstacles: poor electrical conductivity of elemental sulfur, lack of a system that reduces the capacity robbing polysulfide shuttle (PS) effect, a suitable electrolyte that can suppress dendrite formation, and thicker cathode layers necessary to realize the energy density of a lithium sulfur couple. Past research to improve sulfur cathode conductivity and eliminate the PS effect has included infusing sulfur within electrically conductive carbon micro- and nano-scale particles. This approach addresses both the PS shuttle and sulfur’s poor electrical conductivity; however it presents a barrier for lithium ions, which slows reaction, reduces power, and limits cathode thickness1. Effective sulfur encapsulation require both electronic and ionic conduction to build thicker cathode structures that retain battery power, capacity, and cycle life. Typically liquid electrolytes facilitate high sulfur loadings and cathode capacity in a lithium sulfur battery however they also encourage the polysulfide shuttle through the porous polymer separator and don’t prevent dendrites. Excessive amounts of liquid electrolyte also reduces the practical energy density of a lithium sulfur cell. Solid-state electrolytes have the potential to play at least three significant roles in a lithium sulfur battery: (1) provide a barrier to stop PS shuttle effect, (2) prevent lithium dendrite formation, and (3) reduction of liquid electrolyte. This presentation will discuss the development of a lithium sulfur battery based on combining a solid state electrolyte, entrapped sulfur cathode, and a lithium metal anode necessary to meet needs for high energy density, rechargeable energy storage. New processing methods that improve performance of sulfur carbon composites for cathodes will be discussed. The feasibility of low cost practical carbon materials for sulfur carbon composite cathodes will also be discussed in relation to the new processing methods. Methods and results of using solid state electrolytes in lithium sulfur cell design will also be discussed related to their impact on liquid electrolyte reduction and cathode capacity improvement. Finally optimization targets for a metallic lithium anode, solid electrolyte, and sulfur cathode materials will be discussed in relation to goals for cell specific energy. 1) Manthiram, Arumugam, et al. "Rechargeable lithium-sulfur batteries." Chem. Rev 114.23 (2014): 11751-11787.

Surface Fluorination of Reactive Battery Anode Materials for Enhanced Stability.

Significant increases in the energy density of batteries must be achieved by exploring new materials and cell configurations. Lithium metal and lithiated silicon are two promising high-capacity anode materials. Unfortunately, both of these anodes require a reliable passivating layer to survive the serious environmental corrosion during handling and cycling. Here we developed a surface fluorination process to form a homogeneous and dense LiF coating on reactive anode materials, with in situ generated fluorine gas, by using a fluoropolymer, CYTOP, as the precursor. The process is effectively a "reaction in the beaker", avoiding direct handling of highly toxic fluorine gas. For lithium metal, this LiF coating serves as a chemically stable and mechanically strong interphase, which minimizes the corrosion reaction with carbonate electrolytes and suppresses dendrite formation, enabling dendrite-free and stable cycling over 300 cycles with current densities up to 5 mA/cm2. Lithiated silicon can serve as either a pre-lithiation additive for existing lithium-ion batteries or a replacement for lithium metal in Li-O2 and Li-S batteries. However, lithiated silicon reacts vigorously with the standard slurry solvent N-methyl-2-pyrrolidinone (NMP), indicating it is not compatible with the real battery fabrication process. With the protection of crystalline and dense LiF coating, LixSi can be processed in anhydrous NMP with a high capacity of 2504 mAh/g. With low solubility of LiF in water, this protection layer also allows LixSi to be stable in humid air (∼40% relative humidity). Therefore, this facile surface fluorination process brings huge benefit to both the existing lithium-ion batteries and next-generation lithium metal batteries.

Stable Li Plating/Stripping Electrochemistry Realized by a Hybrid Li Reservoir in Spherical Carbon Granules with 3D Conducting Skeletons.

Lithium metal is a promising battery anode. However, inhomogeneous mass and charge transfers across the Li/electrolyte interface result in formation of dendritic Li and "dead" Li, and an unstable solid electrolyte interphase, which incur serious problems to impede its service in rechargeable batteries. Here, we show that the above problems can be mitigated by regulating the interfacial mass/charge transfer. The key to our strategy is hybrid Li storage in onion-like, graphitized spherical C granules wired on a three-dimensional conducting skeleton, which enhances the negativity of surface charge of the C host to contribute to a uniform Li plating while also forming stable Li/C intercalation compounds to offset any irreversible Li loss during cycling. As a result, the anode shows a suppressed dendrite formation and a high Li utilization >95%, enabling a practical Li battery to strike a long lifespan of 1000 cycles at a surplus Li of merely 5%.

Suppression of Dendrite Formation and Corrosion on Zinc Anode of Secondary Aqueous Batteries.

Novel zinc anodes are synthesized via electroplating with organic additives in the plating solution. The selected organic additives are cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), polyethylene-glycol (PEG-8000), and thiourea (TU). The synthesized zinc anode materials, namely, Zn-CTAB, Zn-SDS, Zn-PEG, and Zn-TU, are characterized by powder X-ray diffraction and scanning electron microscopy. The results show that each additive produces distinctively different crystallographic orientation and surface texture. The surface electrochemical activity is characterized by linear polarization when the zinc is in contact with the battery's electrolyte. Tafel fitting on the linear polarization data reveals that the synthetic zinc materials using organic additives all exhibit 6-30 times lower corrosion currents. When using Zn-SDS as the anode in the rechargeable hybrid aqueous battery, the float current decreases as much as 2.5 times. The batteries with Zn-SDS, Zn-PEG, and Zn-TU anodes display the capacity retention of 79%, 76%, and 80% after 1000 cycles of charge-discharge at 4C rate, whereas only 67% obtained from the batteries using the anode prepared from commercial zinc foil. Among these electroplated anodes, Zn-SDS is the most suitable for aqueous batteries thanks to its low corrosion rate, low dendrite formation, low float current, and high capacity retention after 1000 cycles.

Rechargeable Sodium All-Solid-State Battery.

A reversible plating/stripping of a dendrite-free metallic-sodium anode with a reduced anode/ceramic interfacial resistance is created by a thin interfacial interlayer formed in situ or by the introduction of a dry polymer film. Wetting of the sodium on the interfacial interlayer suppresses dendrite formation and growth at different discharge/charge C-rates. All-solid-state batteries were obtained with a high cycling stability and Coulombic efficiency at 65 °C.

Investigating the effect of ionic strength on the suppression of dendrite formation during metal electrodeposition.

The effect of ionic strength on the electrodeposition of silver has been investigated in acetonitrile (MeCN) containing TBAPF6 or in the ionic liquid [EMIm][OTf]. The use of an ionic liquid allows a greater ionic strength to be investigated as the solubility limits of supporting electrolytes in organic solvents can be overcome using neat ionic liquid. The SEM and XRD data show that polycrystalline silver is deposited in a fcc structure and that dendrite formation is retarded at high ionic strength. Electrochemical measurements undertaken in electrolytes of low ionic strength indicate that the deposition and growth of a few nuclei is preferred and leads to dendrite formation. However, at higher ionic strength, the deposition and growth of significantly more nuclei is observed and therefore dendrite growth rates and tip currents are lower leading to the deposition of spherical particulates. Crucially, the data shows that if the ionic strength of the electrolyte is controlled there are no differences between ionic liquids and molecular solvents for the electrodeposition of silver.

Suppression of Dendrite Formation by Using a Hydrogel Separator for Zinc Alkaline Battery

Suppression of Dendrite Formation by Using a Hydrogel Separator for Zinc Alkaline Battery

Molecular Dynamics Study of a Dual-Cation Ionomer Electrolyte.

The poly(N1222 )x Li1-x [AMPS] ionomer system (AMPS=2-acrylamido-2-methylpropane sulfonic acid) with dual cations has previously shown decoupled Li ion dynamics from polymer segmental motions, characterized by the glass-transition temperature, which can result in a conductive electrolyte material whilst retaining an appropriate modulus (i.e. stiffness) so that it can suppress dendrite formation, thereby improving safety when used in lithium-metal batteries. To understand this ion dynamics behavior, molecular dynamics techniques have been used in this work to simulate structure and dynamics in these materials. These simulations confirm that the Li ion transport is decoupled from the polymer particularly at intermediate N1222+ concentrations. At 50 mol % N1222+ concentration, the polymer backbone is more rigid than for higher N1222+ concentrations, but with increasing temperature Li ion dynamics are more significant than polymer or quaternary ammonium cation motions. Herein we suggest an ion-hopping mechanism for Li+ , arising from structural rearrangement of ionic clusters that could explain its decoupled behavior. Higher temperatures favor an aggregated ionic structure as well as enhancing these hopping motions. The simulations discussed here provide an atomic-level understanding of ion dynamics that could contribute to designing an improved ionomer with fast ion transport and mechanical robustness.

Polymeric Ionic Liquid Gel Electrolyte for Room Temperature Lithium Battery Applications

Free-standing gel polymer electrolytes (GPE) composed of the polymeric ionic liquid poly[diallyldimethylammonium] bis(trifluoromethane) sulfonimide, the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethane) sulfonimide, and lithium salt are reported for their use in lithium batteries. The GPEs are thermally stable and contain ionic liquid and salt contents of up to 80wt.% which results in highly ionically conductive electrolyte films with σ=3.35mScm−1. The affinity of the polymeric ionic liquid with the ionic liquid and salt components of the GPE allows wide electrochemical stability window −0.1–4.9V and increased lithium ion transference number. In addition, the GPEs suppressed dendrite formation compared to ionic liquid electrolytes and in turn enabled the use of these GPEs in batteries with lithium anodes. Galvanostatic charge/discharge cycling of Li/GPE/LiFePO4 cells shows discharge capacity of 169.3mAhg−1 at C/10, 126.8mAhg−1 at 1C, and impressive capacity retention capability for 40 cycles at up to 5C rate, at 22°C.

Influence of surfactants as additives to electrolyte solutions on zinc electrodeposition and potential oscillation behavior

The effects of surfactants as organic additives to electrolyte solutions on potential oscillation behavior and Zn electrodeposition were observed. Applying a constant current density (−20 mA cm−2), we induced the potential oscillation of electrochemical Zn deposition in aqueous solutions of KOH, ZnO, and surfactants. Potential oscillation behavior for Zn electrodeposition was strongly affected by the presence of surfactants. While an anionic surfactant (sodium dodecyl sulfate) slightly increased the period of potential oscillation, even small amounts of nonionic (Triton X-100) and cationic surfactants [cetyltrimethylammonium bromide(CTAB)] greatly increased the period of potential oscillation. The presence of CTAB in an electrolyte produced small spherical Zn deposits, which clearly implies that CTAB plays a role in suppressing dendrite formation during Zn deposition.

Ultrathin Coating of Nitrogen and Sulfur Co-Doped Graphene Nanosheets on Polymer Separator for Suppressing Dendritic Lithium Growth in Lithium Metal Batteries

The advent of electric vehicles and other high energy density applications has intensified the research efforts on lithium metal-based batteries, as metallic lithium can provide a high specific capacity (~3,862 mAh g-1), enabling it as a promising negative electrode for next-generation battery systems [1,2]. However, the instability of lithium electrodes is one of the greatest challenges hindering the successful development of lithium metal batteries. Lithium metal is unstable against nearly all chemical species and reacts with organic solvents and salts in liquid electrolytes. Moreover, continuous deposition and stripping of lithium may induce uncontrollable dendritic Li growth, which in turn leads to internal short circuits, failure, and eventually explosions. In this work, we demonstrated that an ultrathin nitrogen and sulfur co-doped graphene (NSG) layer deposited on a PE separator could effectively stabilize the lithium electrode surface, suppress dendrite formation, and improve the cycling stability of lithium metal batteries. The NSG coating layer is very thin as compared to other ceramic coatings in micrometer scales, which can provide higher energy density of the cell with NSG separator. The incorporation of heteroatom dopants could induce structural deformations due to local strains induced in the carbon framework, thereby allowing for easy ionic migration while maintaining a uniform ionic flux on the Li metal surface. Moreover, the lone pair electrons in the heteroatom dopants led to the generation of negative charge, resulting in enhanced interfacial interactions between the NSG-coated separator and the lithium electrode. The NSG coating also imparted thermal stability to the PE separator, thus preventing thermal shrinkage of the separator at elevated temperature and enhancing battery safety. The cycling performance of the lithium metal cell employing a NSG coated separator was remarkably improved as compared to the cell with a pristine PE separator.

A Novel Ceramic-Polymer Composite Electrolyte for Lithium Batteries

Lithium metal is being intensively pursued as an anode due to its high specific capacity. However, dendrite formation, Li loss and short circuiting upon cell cycling presently impede its use. Furthermore, the flammability of liquid electrolytes poses a severe safety hazard. Replacement of organic liquids by solid electrolytes could pave the way for using lithium metal, simultaneously improving specific energy and battery safety. Efforts continue on ceramic electrolytes. Challenges include the formation and manufacture at scale of sufficiently thin, highly dense, pinhole-free sheets of ceramic electrolytes, required for high power devices. Such electrolytes must also maintain contact with the solid electrodes while inhibiting Li dendrites and be durable towards volume changes of the electrodes as well as to external shock. Polymer electrolytes have been developed for a number of years. They can exhibit good adhesion and contact to the electrodes, but typically have lower conductivity and limited capability of suppressing dendrite formation.[i]To date, ceramic and polymer electrolytes remain a challenge. Composites of particulate ceramics embedded within polymer electrolytes have been investigated to improve the conductivity and mechanical properties. [ii] Our approach is to create ordered composite electrolytes, which allows modification of the mechanical properties of the composite while retaining good overall ionic conductivity. The conductivity of the polymer-ceramic composite is 1.5E-4 S/cm at 25 °C. The results for different ceramic-polymer compositions indicate that the mechanical properties of the composite can be modified by the presented approach. Mechanical testing and the results of galvanostatic cycling will be reported. [i] G. M. Stone, S. A. Mullin, A. A. Teran, D. T. Hallinan Jr., A. M. Minor, A. Hexemer, N. P. Balsara, J. Electrochem. Soc., 2012, 159, A222–A227. [ii] Y.-C. Jung, S.-M. Lee, J.-H. Choi, S. S. Jang and D.-W. Kim, J. Electrochem. Soc., 2015, 162, A704–A710.

Micro‐Patterned Lithium Metal Anodes with Suppressed Dendrite Formation for Post Lithium‐Ion Batteries

Repressing uncontrolled lithium (Li) dendrite growth is the top priority for enabling the reliable use of Li metal secondary batteries. On the other hand, the technique controlling the metal plating behavior during metal plating indeed has been considered very difficult to achieve. For instance, how can one plate metal ions on the favored selected region during plating? The present study describes how to achieve this goal, i.e., dendrite‐free Li deposition, by mechanical surface modification using a simple stamping technique, where finite‐element method simulation using COMSOL Multiphysics was used to design the micro‐patterns of the stamp. After stamping, the transferred micro‐patterns on Li metal anodes suppress dendrite growth during repeated Li deposition/stripping processes and exhibit improved long‐term cycling stability of Li metal anodes. During the repeated Li plating processes, the pattern holes are filled by the liquid‐like and/or granular forms of Li metal without resulting Li dendrite growth. These holes are then reversibly drained during the Li stripping process, reverting to their original dimension. This study investigated the correlation of this unique Li plating/stripping behavior as a function of the current density.