Li Surface Research Articles

Tidal Mixed Ionic/Electronic Conductive Interlayer Enables Supersmooth Lithium Deposition for Stable Lithium Metal Batteries

AbstractLithium metal is the ultimate anode material for Li‐based battery chemistries with high energy density. However, inhomogeneous charge distribution derived from the unbalanced ion/electron transport is usually generated at the electrode/electrolyte interface, leading to uncontrollable dendrite growth with poor reversibility. Herein, a mixed ionic/electronic conductive (MIEC) interlayer activated from the in situ conversion and nano‐alloying reactions between the sputtered AlN arrays and metallic Li is efficiently constructed on the Li surface via facile mechanical calendaring. The 3D interconnected polyimide scaffolds with the extensive Li3N/Li9Al4 dual‐decoration promote charge redistribution while enhancing electrochemical kinetics. The significantly reduced nucleation/plateau overpotentials, the overwhelming bottom‐up lithium growth pattern derived from the tidal MIEC interlayer, combined with the inorganics‐dominating solid electrolyte interphase synergistically regulates the uniform Li nucleation/growth. As demonstrated, a prolonged lifespan of the symmetric cell over 7500 h with an ultralow polarization of 12 mV is achieved at 5 mA cm−2@5 mAh cm−2, further improving the rate capability and cycling performance of LiFePO4‐based practical full cells with a capacity retention of 85.4% after 220 cycles. The proposed approach is also applicable to match the roll‐to‐roll production process, presenting an efficient strategy to realize the high‐performance composite anode of industry‐adaptable potential.

Self-Induced Dual-Layered Solid Electrolyte Interphase with High Toughness and High Ionic Conductivity for Ultra-Stable Lithium Metal Batteries.

Lithium (Li) metal is considered as one of the most promising candidates of anode material for high-specific-energy batteries, while irreversible chemical reactions always occur on the Li surface to continuously consume active Li, electrolyte. Solid electrolyte interphase (SEI) layer has been regarded as the key component in protecting Li metal anode. Herein, a controllable dual-layered SEI for Li metal anode in a scalable, low-loss manner is constructed. The SEI is self-induced by the predeposited LiAlO2 (LAO) layer during the initial cycles, in which the outer organic layer is produced due to the electrons tunneling through LAO, resulting in the reduction of electrolyte. The robust inner LAO layer can promote uniform Li deposition owing to its favorable mechanical strength and ionic conductivity, andthe outer organic layer can further improve the stability of SEI. Benefiting from the remarkable effects of this dual-layered SEI, enhanced electrochemical performance of the LAO-Li anode is achieved. Additionally, a large-size LAO-Li sample can be easily obtained, and the preparation of the modified Li metal anode shows huge potential for large-scale production. This work highlights the tremendous potential of this self-induced dual-layered SEI for the commercialization of Li metal anode.

Converting LiNO3 additive to single nitrogenous component Li2N2O2 SEI layer on Li metal anode in carbonate-based electrolyte

With the increasing demand for high energy density energy storage device, Li metal has received intensive attention for its ultrahigh capacity and the lowest redox potential. LiNO3 is widely used as electrolyte additive for ether electrolyte, which can improve the cycle performance of Li metal anode. Compared to ethers, carbonates are more suitable for Li metal batteries with high voltage cathode because they have a wider electrochemical window. However, LiNO3 performs poor solubility in carbonate electrolyte, restricting its application in high voltage Li battery. Herein, we presented a facile method to introduce abundant LiNO3 additive to carbonate electrolyte system by introducing LiNO3-PAN es as the interlayer of the cell. LiNO3-PAN es is in sufficient contact with the electrolyte so that it can continuously releases LiNO3 to assist the formation of Li2N2O2-rich single nitrogenous component SEI layer on Li surface. With the help of LiNO3-PAN es, Li metal anode shows excellent cycle stability even at a high current density of 4 mA/cm2, so that the cycle performance of the full cells was significantly improved, whether in the anode-free Cu||LFP cell or the Li||NCM622 cell.

Role of copper as current collectors in the reductive reactivity of polymers for anode-free lithium metal batteries - Insights from DFT and AIMD studies

Understanding the role of current collectors (CCs) in the reductive reactivity of polymers on Li metal and the resultant solid electrolyte interphase (SEI) formation is essential for improving the performance of anode-free lithium metal batteries (AFLMBs). In this study, we have examined the reactivity of three polymeric hosts: poly(ethylene oxide) (PEO), poly(ε-caprolactone) (PCL), and poly(trimethylene carbonate) (PTMC) at Li metal supported on Cu surfaces (Li/Cu) using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. In particular, the effect of copper (Cu) CCs on polymer stability, electronic structure, and their reduction reactions is investigated and compared to that of pure Li (100) surface. Through time-dependent Bader charge transfer analysis, electron transfer is identified as the triggering factor for polymer reduction. Based on the simulations, we find that the Cu CCs have a significant influence on the charge distribution of the Li metals, which increases electron transfer to the polymers and thereby accelerates polymers reduction. This thereby leads to different reaction mechanisms as compared to on Li-metal. The findings suggest that utilization of Cu CCs avoids the production of CO molecules and improves the quality of the formed SEI layer.

Toward thin and stable anodes for practical lithium metal batteries: A review, strategies, and perspectives

AbstractThe lithium metal battery (LMB) is a promising energy storage platform with a distinctively high energy density in theory, outperforming even those of conventional Li‐ion batteries. In practice, however, the actual achievable energy density of LMBs is significantly limited due to the Li metal anode (LMA) being too thick (50–250 μm), and there are difficulties with expanding the highly reactive Li metal into large‐format cells due to safety concerns. Therefore, the recent focus of LMB research is headed toward the development of a thin and stable LMA. However, as the thickness of Li anode decreases (≤20 μm) and the absolute size of the battery cell increases, interfacial reactions on the Li surface become more active, potentially leading to fatal thermal runaway. In this regard, there is still much demand for the development of novel manufacturing technologies to overcome this issue and produce thin and stable Li metal. Considering these things, in this review, we initially examine the fundamentals regarding the deployment of LMAs using a number of essential metrics. Then, we introduce recent strategies employed for designing thin and stable Li anodes including host matrix architecturing, interface stabilization, and other advanced modifications. Finally, we propose future directions for the realization of practical LMBs and their potential applications in various battery systems, encompassing Na, K, and Zn‐based batteries. We anticipate that ultra‐thin and ultra‐stable metal anodes would find widespread utilization in secondary battery applications with high‐power requirements.image

Liquid-source plasma technology for construction of dual bromine-fluorine-enriched interphases on lithium metal anodes with enhanced performance

The electrochemical performance of Li metal anode is closely bound up with the interphase between Li and lithium-loaded skeleton as well as solid electrolyte interphase (SEI) on Li surface. Herein, for the first time, we propose a novel liquid-source CHBr2F plasma technology to simultaneously construct dual bromine-fluorine-enriched interphases: NiBr2-NiF2 interphase on sponge Ni (SN) skeleton and LiBr-LiF-enriched SEI on Li anode, respectively. Based on density functional theory (DFT) calculations and COMSOL multiphysics simulation results, SN skeleton with NiBr2-NiF2 interphase can effectively decrease the local current density with good lithiophilicity. And the LiBr-LiF-enriched SEI on Li surface can function to block electron tunneling and hinder side electrochemical reduction of electrolyte components, thus suppressing the growth of dendrite and facilitating the homogeneous transportation of lithium ions. Consequently, the Li/SN electrodes with modified interphases show remarkable stability with a low overpotential of 22.6 mV over 1800 h at 1 mA cm–2/1 mAh cm–2 and an exceptional average Coulombic efficiency of 99.6%. When coupled with LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode, the full cells deliver improved cycling stability with a capacity retention of 79.5% even after 350 cycles at 0.5 C. This study provides a facile and new plasma method for the construction of advanced Li anodes for energy storage.

Nanospinbar-Assisted Convective Ionic Transfer Toward Dendrite-Free Li Metal Batteries

Building high-energy-density batteries with Li-metal anodes (LMAs) featuring ultrahigh specific capacity (3860 mAh g−1) and low working voltage (−3.04 V vs. SHE) have been revisited to surpass the energy density limit of current Li-ion batteries. For instance, a successful transition from conventional graphite (372 mAh g–1) to ultrathin LMAs can deliver higher cell energies (over 500 Wh kg–1). Nonetheless, Li electrodeposition is challenging due to the dendrite formation and random growth. Extensive Li dendrite growth can enlarge the active surface area where side reactions occur, thereby severely deteriorating the Li surface and depleting the electrolyte, leading to poor cycling stability. Eventually, the Li dendrite tips can pierce the separator, causing cell short-circuiting, thereby increasing the safety risk. This is a major hurdle that must be overcome prior to commercialization. Therefore, inhibiting uneven dendritic Li plating is essential for safe and stable cycling of rechargeable lithium metal batteries (LMBs).Inhibiting uneven, dendritic Li electroplating is crucial for the safe and stable cycling of LMBs. Homogeneous, fast Li+ transport toward the Li surface is required for uniform, dendrite-free deposition. Electrodeposition strongly depends on the mass transfer of the ionic species. In a diffusion-limited regime, such as higher currents and lack of convection, inherently limited Li+ diffusion causes a strong concentration gradient or even total Li+ depletion. Moreover, traditional ionic transport of static liquid electrolytes involving electromigration and molecular diffusion can trigger a greater disparity in Li concentration over the Li surface, leading to irregular dendrite growth.This study presents a microturbulence-assisted convective Li+ transfer for suppressing dendrite growth using a magnetic nanospinbar (NSB)-dispersed colloidal electrolyte. We synthesized an ultrahigh-aspect-ratio NSB consisting of a paramagnetic Fe3O4 nanoparticle array and a silica outer coating. Manipulating the external electromagnetic force can remotely control the rotation of individual NSBs without dispersion failure, thereby generating a microturbulence flow inside the cell. Regardless of the electrolyte composition, rotating the NSB can reduce the Li+ diffusion layer thickness from the bulk and evenly redistribute Li+ flux over the Li surface, thereby suppressing Li dendrite growth. The NSB-dispersed electrolyte with advanced salt/solvent compositions demonstrated stable cycling of LMBs over 600 cycles at 70% capacity retention, thereby outperforming the NSB-free cell.Figure. 1. Concept of convective Li+ transfer assisted by remote NSB stirring. Apart from stagnant electrolytes, magnetic-field-responsive NSB dispersed in the liquid electrolyte can redistribute Li+ flux near LMA through remote stirring, enabling facile, homogenous Li+ transfer and thereby leading to uniform, dendrite-free Li electroplating Figure 1

Lithium Morphology Evolution through Crosslinked Poly(ethylene oxide) Solid Polymer Electrolyte

Solid-state, lithium metal batteries are promising candidates for developing the safe, energy-dense devices needed to transition to an electrified economy. However, lithium is highly reactive, making it thermodynamically unstable when in contact with many electrolyte materials. Achieving uniform Li plating and stripping during cycling is the key for enabling high energy Li metal batteries. The lithium stripping and plating mechanism is complicated as it can be affected by the cathode, electrolyte and lithium anode, and the resulting solid electrolyte interphase (SEI). In particular, the mechanism is not well understood in solid polymer electrolytes.In this work, we investigate lithium morphology evolution through a solid polymer electrolyte at different stages of battery cycling. Crosslinked poly(ethylene oxide) (xPEO) solid polymer electrolyte is used as a model electrolyte and full cells using single crystal LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode, dry xPEO electrolyte and lithium from two commercial sources are assembled. Our results show that different lithium sources lead to different Coulombic efficiencies and capacity fade rate of the full cells assembled. The lithium morphology evolution at different stages of cycling is examined using scanning electron microscopy and the lithium plating/stripping mechanism are compared between these two commercial lithium anodes. Furthermore, the lithium morphology is compared to a gel polymer composite electrolyte with the same host polymer (xPEO). The dry solid polymer produces a smoother morphology than the gel polymer composite electrolyte without pit formation. A better understanding of the roles of each of these components (pristine Li surface chemistry, microstructure, dry vs gel polymer electrolyte) is essential to control for uniform lithium stripping and plating.

The Impact of Li Surface Heterogeneity and Morphology on Performance in Solid-State Batteries

Solid-state Li metal batteries have the potential to enable both fast charging and more than a 30% increase in energy density. Two of the most pervasive and limiting challenges in these materials are the interface between the Li metal and the solid electrolyte and the formation of Li filaments that penetrate the solid electrolyte leading to cell shorting. Currently, most efforts to solve these problems are focused on solid electrolytes. Here we present our work investigating the Li side of the equation. This work compares four thin Li sources (<40 µm), three rolled Li from commercial suppliers, and a fourth prepared in-house using thermal evaporation. Using X-ray photoelectron spectroscopy (XPS) and attenuated total internal reflection infrared spectroscopy (ATIR), we determined that the surface layers on these different Li films varied significantly in composition and thickness. Subsequent electrochemical testing of these films in liquid, polymer, and ceramic solid electrolytes, showed that variation in the surface thickness and chemistry significantly impacted the interfacial resistance. Furthermore, an analysis of cell failure due to shorting led to the clear conclusion that in addition to the surface contamination, the Li microstructure also had a significant impact in determining when failure will occur. Acknowledgments: Simon Thompson and the DOE EERE Vehicle Technology office Battery Material Research Program for funding supporting this work.

Ultrathin, Smooth Li-Metal Anode Via Electrodeposition for Stable Cycling of Li-Betal Batteries Under Practical Conditions

Lithium (Li) metal anodes (LMAs) with high specific capacity (3860 mAh g–1) and lowest redox voltage (–3.04 V vs SHE) are considered superlative candidates for high energy batteries. Ultra-thin, large-area LMA is crucial for building Li-metal batteries (LMBs) that can deliver high volumetric and gravimetric energy density in practice. As the charging and discharging continue, the growth of Li dendrite is regarded as one of the significant challenges. The surface nature of LMAs is the main aspect of Li dendrite formation and interface reaction. However, most studies overlooked the initial condition of LMA surface. Native passivation layer (NPL) of commercial Li foils is inherently uneven composed of Li2CO3, LiOH, and Li2O, and its chemical nature is mostly determined under manufacturing conditions. Incomplete passivation at an initial stage can trigger sporadic Li dendrite growth and chemical/structural deterioration of LMAs, adversely affecting the cycling stability of LMBs.This work presents the electrochemical pre-passivation to build an electrolyte-derived native layer (electro-native layer, E-NPL) through Li electrodeposition method. Electrodeposited LMA (ed-LMA) was prepared by pre-deposition at the Cu foil using localized high-concentration electrolyte (LHCE) and post calendaring for smooth LMA surface. As-prepared ed-LMA has 4.13 mAh cm-2 of areal capacity with ~22 µm, and reduced roughness, which is much lower than that of manufactured LMA (m-LMA). Particularly, the E-NPL derived by LHCE can tailor the LMA surface by enriching the inorganic SEI compounds such as LiF, and N-SOx. In addition, decreased amount of passivated components such as Li2CO3, LiOH, and hydroxide were found in XPS analysis of the anodes. Compared to manufactured LMA (m-LMA), the ed-LMA exhibited lower overpotential for Li plating/stripping cycles and enhanced capacity retention. Benefiting from better compatibility with newly plated Li, it showed higher plating density without electric isolation from beneath Li surface, mitigating the anode swelling during subsequent cycling. We successfully demonstrated battery cycling stability of Li||NMC622 cells exploiting ed-LMA (195 cycle at 80% retention), superior to m-LMA (110 cycle at 80% retention) under stringent conditions.

Multifunctional Zeolite Coated Separators for Improved Performance and Safety of Lithium Metal Batteries

Lithium (Li) metal batteries are attractive due to their high gravimetric and volumetric energy densities. However, they can fail catastrophically due to dendritic nucleation, growth, and penetration through the polypropylene (PP) or polyethylene (PE) separators. Poor electrolyte wetting and non-uniform Li ion flux are known to affect Li dendrite formation, especially since the PP/PE separators have broad gaussian pore size distribution and typically organic electrolytes do not wet them well. In this work, we demonstrate that a multifunctional zeolite coating on a commercial PP separator (Z-PP) can improve electrolyte wettability and in-plane ionic conductivity, giving rise to more uniform Li flux. Consequently, Z-PP can effectively delay dendrite penetration and enhance cell performance and safety. Firstly, electrochemical impedance spectroscopy (EIS) was used to establish that the thin zeolite coating on PP separator had little effect on through-plane ionic conductivity. For electrochemical cycling behavior, PP and Z-PP separator based symmetric cells and half-cells were studied by monitoring the cell overpotential (symmetric cell) and discharge capacity (half-cell). For the Z-PP separator, lower overpotential and better discharge capacity retention were observed in the respective symmetric and half-cell studies, suggesting improved electrolyte wetting and relatively uniform Li flux. Scanning electron microscopy (SEM) equipped with energy dispersive x-ray spectroscopy (EDS) studies helped in understanding coating microstructure and cycled electrode morphologies. SEM images of cycled Li metal harvested from the Z-PP cells show much smoother Li surface for Z-PP cell as compared to PP cells. This work suggests that overall cell performance and safety can be improved by employing Z-PP separators.

Tellurium Nanowires for Lithium‐Metal Anode Stabilization in High‐Performance Anode‐Free Li–S Batteries

Enhancing the reversibility of Li is crucial for extending the cycle life of Li‐limited anode‐free lithium–sulfur (Li–S) batteries. Incorporating tellurium (Te) in the system has proven to be highly effective by its reaction with polysulfides and forming a passivating interfacial layer on Li surface, which reduces the Li‐ion diffusion barrier. However, due to the poor utilization of Te, a significant amount of Te is required to improve cell cycling performance. To address this, nanowire‐structured Te (TeNW) is synthesized via a hydrothermal method and applied to Li2S‐based anode‐free cells to minimize the Te content in the system while extending the cell cycle life. Coating TeNW onto the separator greatly enhances Te utilization and demonstrates a significant cycle life improvement (38% retention over 300 cycles) with only 4 wt% TeNW content relative to the active material. The versatility of TeNW is further demonstrated by utilizing them with carbon nanotubes as the anode substrate. The exceptional performance of TeNW is attributed to the high‐surface‐area nanostructure and excellent conductive network, facilitating efficient electron transfer during cell cycling. These advantageous properties position TeNW as a promising material to enhance the cycle life of Li‐limited Li–S batteries.

A functional SnS2-engineered separator for durable and practical lithium metal battery

Lithium (Li) metal is one of the most promising anodes for next-generation high-energy-density batteries. However, the practical application of Li metal anodes (LMAs) is hindered by uncontrollable solid electrolyte interphase (SEI) formation and detrimental Li dendrites growth. Herein, a well-designed SnS2 nanoflakes coating is utilized to modify the commercial polypropylene (PP) separator (denoted as SnS2@PP), providing a solution to tackle above issues. Impressively, an artificial SEI consisting of Li2S, Li5Sn2, and Li7Sn2 species with high ionic conductivity and superior Li affinity is generated on the Li surface to regulate homogeneous Li plating/stripping. Consequently, the Li||Li symmetric cells exhibit a stable cycling behavior of over 2700 h at 1 mA cm−2 for 1 mAh cm−2. Remarkably, SnS2@PP enables over 600 cycles at 2 C with a capacity retention of ∼80% in a Li||LiFePO4 coin cell and more than 110 cycles at 0.3 C with a capacity retention of ∼97% in a Li||LiFePO4 pouch cell under high cathode loading (13 mg cm−2), ultrathin Li foil (50 µm), and lean electrolyte (2.8 g Ah−1 after sealed) conditions. This work extends the scalable technology into a platform to control Li deposition and SEI formation toward practical Li metal batteries (LMBs) with ultralong life spans.

Method for Benchmarking Li Metal Anodes: A Mandatory Step toward Reliable Lithium Metal Batteries

All-solid-state batteries are known to be the new energy storage holy grail that will lead to safer batteries with higher energy density than current Li-ion batteries. The use of a solid electrolyte enables the use of lithium metal as the anode material. However, its composition, its thickness, and the quality/nature of its passivation layer can strongly affect the performance of the battery. For this reason, we propose a simple benchmarking method that evaluates and compares the quality and electrochemical performance of various Li anodes. This method can be easily reproduced, especially concerning the electrochemical evaluation that uses a commercial liquid electrolyte and the widely spread coin-cell format. In total, ~285 coin cells were assembled to benchmark our in-house lithium metal foil (Lithium HQ) with two commercial ones and the results showed the superior performance of our Li metal anode. The performance of the cells seems closely related to the quality and uniformity of the Li surface. In addition, we propose including in the benchmarking method the effect of Li aging in a dry room on the electrochemical performance. This effect is important to consider because the fabrication of all-solid-state batteries is conducted in such an environment.

Advantageous surface engineering to boost single-crystal quaternary cathodes for high-energy-density lithium-ion batteries

Single-crystalline Ni-rich cathode active materials (CAMs) are considered as promising candidates for high-energy-density lithium-ion batteries (LIBs) with favorable cycling stability and safety, due to their grain boundaryless characteristics efficiently alleviate the structural degradation of intergranular microcracks in poly-crystalline counterparts. However, their practical application not only suffers from sluggish Li diffusion kinetics, surface reconstruction and parasitic cathode/electrolyte interfacial reactions upon repeated cycling but also encounters chemical instability during storage and slurry processes. Herein, we constructed a uniform LiAlO2/Li3PO4 protective layer with gradient Al doping (LAP modification) on the surface of single-crystalline LiNi0.90Co0.05Mn0.04Al0.01O2 (SCNCMA) CAMs through an in situ modification process to relieve these intrinsic instability issues. This advantageous surface engineering significantly reduces Li+/Ni2+ mixing, inhibits parasitic side reactions and surface phase transformation, and notably improves Li+ diffusion kinetics. Therefore, LAP-modified SCNCMA exhibits superior cycling performance with a capacity retention of 74.4% at a high voltage of 4.5 V after 200 cycles at 1C compared to that of SCNCMA. Moreover, the enhancement of air storage properties after modification was further confirmed by the reduced surface residual lithium, improved rheological properties and well-maintained electrochemical performance. This work provides an effective strategy for the modification of single-crystal Ni-rich cathodes and further accelerates their practical application.

Modulating Ionic Transport and Interface Chemistry via Surface-Modified Silica Carrier in Nano Colloid Electrolyte for Stable Cycling of Li-Metal Batteries.

Tailoring the Li+ microenvironment is crucial for achieving fast ionic transfer and a mechanically reinforced solid-electrolyte interphase (SEI), which administers the stable cycling of Li-metal batteries (LMBs). Apart from traditional salt/solvent compositional tuning, this study presents the simultaneous modulation of Li+ transport and SEI chemistry using a citric acid (CA)-modified silica-based colloidal electrolyte (C-SCE). CA-tethered silica (CA-SiO2 ) can render more active sites for attracting complex anions, leading to further dissociation of Li+ from the anions, resulting in a high Li+ transference number (≈0.75). Intermolecular hydrogen bonds between solvent molecules and CA-SiO2 and their migration also act as nano-carrier for delivering additives and anions toward the Li surface, reinforcing the SEI via the co-implantation of SiO2 and fluorinated components. Notably, C-SCE demonstrated Li dendrite suppression and improved cycling stability of LMBs compared with the CA-free SiO2 colloidal electrolyte, hinting that the surface properties of the nanoparticles have a huge impact on the dendrite-inhibiting role of nano colloidal electrolytes.

Dynamic surface protective layer on a metallic lithium anode with electronic and ionic dual conductivity

A dynamic surface protective layer is formed by the electrochemical polymerization of polycyclic aromatic hydrocarbons. The newly formed Li dendrites can become dissolved in the protective layer, forming a conjugated Li+ and a dislocated e− π system. The protective layer is electronic and ionic dual conductive, which significantly reduces the interfacial impedance. Li dendrite formation can be mitigated since the newly formed Li dendrite becomes dissolved in the protective layer. The dissolved Li can disperse throughout the Li electrode surface and become re-deposited. Due to the elastic nature of the protective layer, it can stay on the Li surface during the Li volume change. The dissolution of Li dendrite and the formation of the elastic protective layer are visually observed in an in-situ electrochemical optical experiment.

LiF-Rich Interfacial Protective Layer Enables Air-Stable Lithium Metal Anodes for Dendrite-Free Lithium Metal Batteries.

Lithium (Li) metal is considered as a promising anode candidate for high-energy-density batteries. However, the high reactivity of Li metal leads to poor air stability, limiting its practical application. Additionally, the interfacial instability, such as dendrite growth and an unstable solid electrolyte interphase layer, further complicates its utilization. Herein, a dense lithium fluoride (LiF)-rich interfacial protective layer is constructed on the Li surface through a simple reaction between Li and fluoroethylene carbonate (denoted as LiF@Li). The LiF-rich interfacial protective layer consists of both organic (ROCO2Li and C-F-containing species, which only exist on the outer layer) and inorganic (LiF and Li2CO3, distribute throughout the layer) components with a thickness of ∼120 nm. Specifically, chemically stable LiF and Li2CO3 play an important role in blocking air and hence improve the air durability of LiF@Li anodes. Notably, LiF with high Li+ diffusivity facilitates uniform Li+ deposition, while organic components with high flexibility relieve volume change upon cycling, thereby enhancing the dendrite inhibition capacity of LiF@Li. Consequently, LiF@Li exhibits remarkable stability and excellent electrochemical performance in both symmetric cells and LiFePO4 full cells. Moreover, LiF@Li maintains its initial color and morphology even after air exposure for 30 min, and the air-exposed LiF@Li anode still retains its superior electrochemical performance, further establishing its outstanding air-defendable capability. This work proposes a facile approach in constructing air-stable and dendrite-free Li metal anodes toward reliable Li metal batteries.

Promoting Air Stability of Li Anode via an Artificial Organic/Inorganic Hybrid Layer for Dendrite‐Free Lithium Batteries

AbstractLithium metal is a promising candidate for the high‐energy‐density batteries. However, the high instability of Li against air and dendrite growth during cycling are the key challenges hindering the commercial application of the Li metal battery (LMB). In this study, an organic/inorganic hybrid artificial solid electrolyte interphase (SEI) is introduced on Li surface via dipping Li into 0.1 m zinc trifluoromethanesulfonate solution for 1 min. The key components that endow stability to Li in air for 4 h are analyzed via theoretical calculations. The results confirm that LiF and Zn absorbed with CF3 organic groups can reduce the absorption energy of O2, H2O, and CO2 on Li, thereby limiting the reaction of Li with ambient air. The Li anode with an organic/inorganic hybrid SEI cycles over 600 h at 0.5 mA cm−2 in symmetric cell and 500 cycles in a Li||LiFePO4 full cell, after exposure to ambient air for 4 h. Moreover, the organic/inorganic SEI can facilitate the Li+ transformation and suppress the growth of Li dendrites. The designed air‐stable and dendrite‐free Li metal anodes are promising for practical applications of LMBs.

Molecular Dipoles as a Surface Flattening and Interface Stabilizing Agent for Lithium-Metal Batteries.

Reaching the border of the capable energy limit in existing battery technology has turned research attention away from the rebirth of unstable Li-metal anode chemistry in order to achieve exceptional performance. Strict regulation of the dendritic Li surface reaction, which results in a short circuit and safety issues, should be achieved to realize Li-metal batteries. Herein, this study reports a surface-flattening and interface product stabilizing agent employing methyl pyrrolidone (MP) molecular dipoles in the electrolyte for cyclable Li-metal batteries. The excellent stability of the Li-metal electrode over 600 cycles at a high current density of 5mAcm-2 has been demonstrated using an optimal concentration of the MP additive. This study has identified the flattening surface reconstruction and crystal rearrangement behavior along the stable (110) plane assisted by the MP molecular dipoles. The stabilization of the Li-metal anodes using molecular dipole agents has helped develop next-generation energy storage devices using Li-metal anodes, such as Li-air, Li-S, and semi-solid-state batteries.