Solid Electrolyte Interphase Film Research Articles

Synchrotron Near-Field Infrared Nanospectroscopy and Nanoimaging of Lithium Fluoride in Solid Electrolyte Interphases in Li-Ion Battery Anodes.

Lithium fluoride (LiF) is a ubiquitous component in the solid electrolyte interphase (SEI) layer in Li-ion batteries. However, its nanoscale structure, morphology, and topology, important factors for understanding LiF and SEI film functionality, including electrode passivity, are often unknown due to limitations in spatial resolution of common characterization techniques. Ultrabroadband near-field synchrotron infrared nanospectroscopy (SINS) enables such detection and mapping of LiF in SEI layers in the far-infrared region down to ca. 322 cm-1 with a nanoscale spatial resolution of ca. 20 nm. The surface sensitivity of SINS and the large infrared absorption cross section of LiF, which can support local surface phonons under certain circumstances, enabled characterization of model LiF samples of varying structure, thickness, surface roughness, and degree of crystallinity, as confirmed by atomic force microscopy, attenuated total reflectance FTIR, SINS, X-ray photoelectron spectroscopy, high-angle annular dark-field, and scanning transmission electron microscopy. Enabled by this approach, LiF within SEI films formed on Cu, Si, and metallic glass Si40Al50Fe10 electrodes was detected and characterized. The nanoscale morphologies and topologies of LiF in these SEI layers were evaluated to gain insights into LiF nucleation, growth, and the resulting nuances in the electrode surface passivity.

Low-Surface-Area Nitrogen-Doped Carbon Submicrospheres as High-Coulombic-Efficiency and High-Capacity Anodes for Practical Sodium-Ion Batteries.

Nitrogen-doped carbon submicrospheres (NCSMs) are synthesized via an efficient and environmentally friendly one-pot polymerization reaction at room temperature, in which dopamine hydrochloride serves as the source for both carbon and nitrogen. Through leverage of its distinctive structure characterized by minimal surface area, fewer oxygen-containing functional groups, and a heightened presence of active nitrogen-doping sites, the synthesized NCSM showcases a noteworthy initial Coulombic efficiency (ICE) of 84.8%, a remarkable sodium storage capacity of 384 mAh g-1, an impressive rate capability of 215 mAh g-1 at 10 A g-1, and a superior cyclic performance, maintaining 83.0% of its capacity after 2000 cycles. The submicron spherical structure, with its limited surface area and scarce oxygen-containing moieties, effectively curtails the irreversible sodium-ion loss in solid-electrolyte interphase film formation, resulting in heightened ICE. The abundant nitrogen doping can expand carbon-layer spacing as well as improve the electron/ion-transport dynamics, guaranteeing a high sodium storage capacity and a strong rate capability. Crucially, the synthesis method presented here is straightforward, effective, and amenable to scaling, offering a novel avenue for the commercialization of sodium-ion batteries.

Topological Defect-Regulated Porous Carbon Anodes with Fast Interfacial and Bulk Kinetics for High-Rate and High-Energy-Density Potassium-Ion Batteries.

Carbonaceous materials are regarded as one of the most promising anodes for potassium-ion batteries (PIBs), but their rate capabilities are largely limited by the slow solid-state potassium diffusion kinetics inside anode and sluggish interfacial potassium ion transfer process. Herein, high-rate and high-capacity PIBs are demonstrated by facile topological defect-regulation of the microstructure of carbon anodes. The carbon lattice of the as-obtained porous carbon nanosheets (CNSs) with abundant topological defects (TDPCNSs) holds relatively highpotassium adsorption energy yet low potassium migration barrier, thereby enabling efficient storage and diffusion of potassium inside graphitic layers. Moreover, the topological defects can induce preferential decomposition of anions, leading to the formation of high potassium ion conductive solid electrolyte interphase (SEI) film with decreased potassium ion de-solvation and transfer barrier. Additionally, the dominant sp2-hybridized carbon conjugated skeleton of TDPCNSs enables high electrical conductivity (39.4 S cm-1) and relatively low potassium storage potential. As a result, the as-constructed TDPCNSs anode demonstrates high potassium storage capacity (504mA h g-1 at 0.1 A g-1), remarkable rate capability (118mA h g-1 at 40 A g-1), as well as long-term cycling stability.

Identifying ultrathin dielectric nanosheets induced interface polarization for high-performance solid-state lithium metal batteries

Solid-state lithium metal batteries (SSLMBs) with polymer electrolytes are promising due to enhanced safety and high energy density, but the low ionic conductivity of polymer electrolytes and the unstable interface of lithium metal anode hinder the development of SSLMBs. Herein, we propose a unique strategy to address these challenges by coupling ultrathin high-dielectricity Ca2Nb3O10 (CNO) nanosheets with PEO-based electrolyte. The interfacial polarization originating from the distortion of NbO6 octahedra along the vertical direction of CNO nanosheets is maximized and so the interaction between CNO and LiTFSI, which greatly supports the dissociation of LiTFSI and improves the ionic conductivity (2.0 × 10−4 S cm−1) of the composite polymer electrolyte, compared to that without CNO. The optimized interfacial polarization effect is thoroughly demonstrated by theoretical calculation and experimental results. Moreover, due to a homogeneous, robust and LiF-rich solid electrolyte interphase film with promoted Li ion transport being formed at the lithium metal interface, the superior cycling stability (90 % capacity retention after 440 cycles at 0.5 C) and rate capability for LFP||Li full batteries are achieved. This design of composite polymer electrolyte with ultrathin dielectric nanosheet fillers demonstrates a new approach to the development of high-performance polymer electrolytes for SSLMBs.

Lithium fluorosulfonate-induced low-resistance interphase boosting low-temperature performance of commercial graphite/LiFePO4 pouch batteries

The performance of Li-ion batteries (LIBs) at sub-ambient temperatures is limited by the resistive interphases due to electrolyte decomposition, particularly on the anode surface. In this study, lithium fluorosulfonate (LFS) was added to commercial electrolytes to enhance the low-temperature electrochemical performance of LiFePO4 (LFP)/graphite (Gr) pouch cells. The addition of LFS significantly reduced the charge transfer resistance of the anode, substantially extending the cycle life and discharge capacity of commercial LFP/Gr pouch cells at −10 and −30 °C. Compared with the capacity retention rate of the baseline electrolyte at −10 °C (80 % after 25cycles), the capacity retention rate of the LFS electrolyte after 100 cycles under 0.5 C/0.5 C was retained at 94 %. Further mechanistic studies showed that the LFS additive induced the formation of a solid electrolyte interphase (SEI) film comprising inorganic-rich LiF, Li2SO4, and additional organic fluorides and sulfides to maintain good stability at the Gr/electrolyte interface during low-temperature operation. LFS suppressed electrolyte decomposition by forming a robust and low-resistance SEI film on the anode. These results demonstrate that LFS is a promising electrolyte additive for low-temperature LFP/Gr pouch cells.

Conformation inversion of succinonitrile towards long-life solid-state lithium metal batteries

Solid-state lithium metal batteries are considered as the next-generation energy storage devices, but their application is significantly hindered by poor interfacial compatibility between Li anodes and solid-state electrolytes, especially for succinonitrile (SN) based electrolyte. Herein, this issue is addressed by a conformation inversion strategy via introducing a PE separator grafted with poly-(lithium 2-acrylamido-2-methylpropanesulfonic acid) (PAMPSLi) brushes into a SN-based electrolyte. The PAMPSLi brushes inverse the conformation of SN molecules through the multiple interactions between −SO3Li and cyanide groups, alleviating the corrosion reactions of SN on Li anodes. Significantly, the PAMPSLi brushes regulate Li+ transport pathway with the inversed SN molecules at the anode/electrolyte interface to achieve uniform Li deposition. Notably, the PAMPSLi brushes contribute to a solid electrolyte interphase (SEI) film rich in LiF and Li3N. Consequently, the solid-state Li||LiFePO4 batteries with the resulting electrolyte exhibit a specific discharge capacity of 115.0 mAh/g and a considerably long cycle life of 1500 cycles at 3 C. A pouch cell with a high-loading LiFePO4 cathode (18 mg cm−2) also exhibits a high areal capacity and superior safety. This study provides a novel strategy for achieving a stable electrolyte/anode interface in SN-based electrolytes, which facilitates the practical application of solid-state batteries with long life and high energy density.

Design of dual carbon encapsulated porous micron silicon composite with compact surface for enhanced reaction kinetics of lithium-ion battery anodes

Developing high-performance composites with fast charging and superior cycle life is paramount for lithium-ion batteries (LIBs). Herein, we synthesized a double-shell carbon-coated porous structure composite with a compact surface (P-Si@rGO@C) using low-cost commercial micron-sized silicon (Si) instead of nanoscale silicon. Results reveal that the unique P-Si@rGO@C features high adaptability to volume expansion, accelerates electron/ion transmission rate, and forms a stable solid electrolyte interphase (SEI) film. This phenomenon arises from the synergistic effect of abundant internal voids and an external double-layer carbon shell with a dense surface. Specifically, the P-Si@rGO@C anode exhibits a high initial coulombic efficiency (ICE) (88.0 %), impressive rate-capability (612.1 mAh/g at 2C), and exceptional long-term cyclability (972.2 mAh/g over 500 cycles at 0.5C). Further kinetic studies elucidate the diffusion-capacitance hybrid energy storage mechanism and reveal an improved Li+ diffusion coefficient (from 3.47 × 10-11 to 2.85 × 10-9 cm2 s-1). Ex-situ characterization confirms the crystal phase change of micron-sized Si and the formation of a stable LiF-rich SEI. Theoretical calculations support these findings by demonstrating an enhancement in the adsorption ability of Si to Li+ (from -0.89 to -0.97 eV) and a reduction in the energy migration barrier (from 0.35 to 0.18 eV). Additionally, practical LixSi powder is shown to increase the ICE of full cells from 67.4 % to 87.9 %. Furthermore, a pouch cell utilizing the prelithiated P-Si@rGO@C anode paired with LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode delivers a high initial reversible capacity of 7.2 mAh and 76.8 % capacity retention after 100 cycles. This work provides insights into the application of commercial silicon-aluminum alloy powder in the anode of high-energy LIBs.

Synergistic Effects of Confinement Structure and Local‐Expanded Interlayer Spacing in Fe2Mo3O8@C@MoS2 Toward High‐Efficient Sodium Ion Storage

AbstractDeveloping multicomponent composite materials with delicate morphology and tailored structure is of vital importance for designing advanced sodium‐ion batteries (SIBs). Herein, a confinement‐structured Fe2Mo3O8@C@MoS2 with local‐expanded interlayer spacing is designed via high‐temperature phase transition from FeMoO4 to Fe2Mo3O8 and the tactically introducing dopamine molecules into the interlayer of MoS2 nanosheets. By analysis of the in situ generated solid electrolyte interphase film in different electrolytes, the favorable compatibility of Fe2Mo3O8@C@MoS2 in ether‐based electrolytes is well illustrated. Importantly, the sodium storage mechanism and detailed structural evolution of Fe2Mo3O8 are established for the first time by in situ X‐ray diffraction. Furthermore, theoretical calculations indicate the unique structure facilitates internal charge transfer and enhances Na+ adsorption ability. Thanks to the unique confinement structure, local‐expanded interlayers and robust framework, the Fe2Mo3O8@C@MoS2 composite achieves a high reversible specific capacity of 636 mAh g‒1 at 0.1 A g‒1, excellent rate capability (301 mAh g‒1 at 5.0 A g‒1) and ultralong cycling stability (365 mAh g–1 after 6000 cycles at 2.0 A g–1). The study provides an essential understanding of the Na storage mechanism of Fe2Mo3O8 and a promising strategy for constructing high‐performance anodes for SIBs.

Graphene-doped silicon-carbon materials with multi-interface structures for lithium-ion battery anodes

The carbon nanomaterials are usually used to improve the electrical conductivity and stability of silicon (Si) anodes for lithium-ion batteries. However, the Si-based composites containing carbon nanomaterials generally show large specific surface area, leading to severe side reactions that generate large amounts of solid electrolyte interphase films. Herein, we embedded graphene oxide (GO) and silicon nanoparticles (Si NPs) uniformly in pitch matrix by solvent dispersion. The internally doped GO reduces the exposed surface and improves the electrical conductivity of the composite. Meanwhile, the multi-interface structures are constructed inside to limit the domains of Si NPs and improve the structural stability of the material. When evaluated as anodes, the Si/graphene/pitch-based carbon composite anode exhibits the outstanding electrochemical properties, delivering a reversible capacity of 820.8 mAh/g at 50 mA g−1, as well as a capacity retention of 93.6 % after 1000 cycles at 2 A/g. In addition, when assembled with the LiFePO4 cathode, the full cell exhibits an impressive capacity retention of 95 % after 100 cycles at 85 mA g−1. This work provides a valuable design concept for the development of Si/carbon anodes.

Towards industrial applications: Ultra-stable silicon-based pouch cell conducted via a lithiated polymer binder over a wide temperature range from −25 °C to 25 °C

Due to the large volume expansion, the multiple issue of severe pulverized Si particles, irreversible damaged electrode structure, and incompatible solid electrolyte interphase (SEI), have greatly restricted the practical application of Si-based anodes. Herein, a neutral partially lithiated binder (PVA1-g-LiPAA3) is successfully synthesized and applied in high-loaded SiOx||Li, 200 mA h and 4 A h SiOx/graphite||LiCoO2 pouch cells. The rich netural -OH and -COOLi groups show strong interaction with the Si particles during long-term cycling processes. Neutral PVA1-g-LiPAA3 binder can induce the formation of a homogenous and stable “core-shell” SEI film on the SiOx anodes, forbidding the structural evolution and volume expansion. This -CF3-rich SEI film can also improve the ionic conductivity and accelerate the electrochemical kinetics reaction. Moreover, the integrity of fluid collection and polar ears can also be protected. Thus, the manufactured 4 A h SiOx/graphite||LiCoO2 full pouch cell maintains a high 700th discharge capacity of 3.13 A h with capacity retention of 81.3% under 25 °C and 3 C, as well as 300th discharge capacity of 2.73 A h with capacity retention of 98.6% even under 0°C and 1.5 C. This work proves the industrical applications of Si-based anodes over a wide temperature range with high energy density and long cycle life.

Correlating Graphite Surface with Interphase for Fast‐Charging and Low‐Temperature Operation

AbstractThe properties of graphite surface can not only affect the interaction between graphite and electrolyte but also induce the formation of solid electrolyte interphase (SEI) film. Herein, the graphite surface is purposely treated to incorporate oxygen‐containing functional groups, which facilitates a desired Li2CO3‐rich SEI with high ionic conductivity and good mechanical stability. The modified graphite electrodes exhibit significant enhancement in electrochemical performance during rapid charging at the rate of 15 C, where an impressive capacity of 225 mAh g−1 is still maintained, corresponding to a capacity retention of 60.8%. Moreover, the modified electrodes showcase outstanding performance under wide temperature ranging from −50 to +65 °C, with an amazing capacity retention of 97.6% under −20 °C, the conceivable capacity of 105 mAh g−1 at −50 °C as well as excellent stability at both −20 °C and +65 °C. These findings offer valuable insights into the design of a thin and robust Li2CO3‐rich SEI layer via a facile chemical treatment of the graphite surface.

Suppressing the damage of deposited Mn(II) ions to graphite anode in lithium‐ion batteries by electrolyte additive agent and positive material coating

AbstractSEM and EDS techniques are carried out to demonstrate the variation of morphology and chemical compound on the surface of graphite anode, which suggest a well‐accepted concept that the manganese ions have serious influence on the reversible capacity fade of graphite anode in lithium ion batteries. Based the main chemical compounds of the inorganic layer on the graphite surface, the evolution steps of graphite structure damaged by Mn ions are derived. Although the amount of deposited manganese ions is small, these play an important role in the catalytic decomposition of the electrolyte. Moreover, Raman analysis shows that the structure of the graphite anode becomes irregular at initial SEI formation cycles and tends to be stable at subsequent cycles. This structure variation is probably generated from the manganese ion deposition and the solid electrolyte interphase (SEI) film formation. According to the capacity tests, the cycling performance of NCM811/graphite lithium‐ion batteries could be improved 50% by FEC additive and B2O3 surface coating. FEC additive maybe benefit graphite forming a stable SEI film in the early stages of cycling to suppress the damage of Mn2+ ions, then improving the cycling performance.

In Situ Chemical Modulation of Graphitization Degree of Carbon Fibers and Its Potassium Storage Mechanism.

Graphite is considered to be the most auspicious anode candidate for potassium ion batteries. However, the inferior rate performances and cycling stability restrict its practical applications. Few studies have investigated the modulating the graphitization degree of graphitic materials. Herein, a nitrogen-doped carbon-coated carbon fiber composite with tunable graphitization (CNF@NC) through etching growth, in-situ oxidative polymerization, and subsequent carbonization process is reported. The prepared CNF@NC with abundant electrochemical active sites and a rapid K+/electron transfer pathway, can effectively shorten the K+ transfer distance and promote the rapid insertion/removal of K+. Amorphous domains and short-range curved graphite layers can provide ample mitigation spaces for K+ storage, alleviating the volume expansion of the highly graphitized CNF during repeated K+ insertion/de-intercalation. As expected, the CNF@NC-5 electrode presents a high initial coulombic efficiency (ICE) of 69.3%, an unprecedented reversible volumetric capacity of 510.2 mA h cm-3 at 0.1 A g-1 after 100 cycles with the mass-capacity of 294.9 mA h g-1. The K+ storage mechanism and reaction kinetic analysis are studied by combining in-situ analysis and first-principles calculation. It manifests that the K+ storage mechanism in CNF@NC-5 is an adsorption-insertion-insertion mechanism (i.e., the "1+2" model). The solid electrolyte interphase (SEI) film forming is also detected.

Dual‐gradient Engineering of Urchin‐like Silver@Copper Oxide Heterostructures for Highly Stable Lithium Metal Anodes

AbstractLithium‐metal anodes with excellent theoretical specific capacities (3680 mAh g−1) have attracted considerable attention for overcoming the capacity bottleneck of conventional graphite anodes. However, they often suffer from uncontrolled dendrite growth and undesirable side reactions, considerably limiting their practical application in lithium‐metal batteries. In this study, urchin‐like silver@copper oxide (Ag@CuO) heterostructures with gradient electrical conductivity and lithiophilicity are prepared using a facile liquid‐phase reduction method. The unique amphiphilic lithium mechanism of the alloying and conversion reactions effectively reduces the nucleation overpotential of the lithium metal anode and promotes a uniform lithium deposition process. Meanwhile, the in situ‐generated Li2O‐rich solid electrolyte interphase (SEI) film can further induce uniform and reversible lithium plating/stripping. All these characteristics endow the Ag@CuO anode with a high Coulombic efficiency of 98.89%, even after 1200 cycles, and long cycle life of 2800 h at a current density of 0.2 mA cm−2, thus demonstrating that such modified Li metal anodes exhibit superior compatibility with major commercial cathode materials, such as LiCoO2 (LCO) and LiNi0.8Co0.1Mn0.1O2 (NCM‐811). Hence, this study provides an effective strategy for developing practical lithium metal anodes.

Lignin‐derived carbon with pyridine N‐B doping and a nanosandwich structure for high and stable lithium storage

AbstractBiomass‐derived carbon is a promising electrode material in energy storage devices. However, how to improve its low capacity and stability, and slow diffusion kinetics during lithium storage remains a challenge. In this research, we propose a “self‐assembly‐template” method to prepare B, N codoped porous carbon (BN‐C) with a nanosandwich structure and abundant pyridinic N‐B species. The nanosandwich structure can increase powder density and cycle stability by constructing a stable solid electrolyte interphase film, shortening the Li+ diffusion pathway, and accommodating volume expansion during repeated charging/discharging. The abundant pyridinic N‐B species can simultaneously promote the adsorption/desorption of Li+/PF6− and reduce the diffusion barrier. The BN‐C electrode showed a high lithium‐ion storage capacity of above 1140 mAh g−1 at 0.05 A g−1 and superior stability (96.5% retained after 2000 cycles). Moreover, owing to the synergistic effect of the nanosandwich structure and pyridinic N‐B species, the assembled symmetrical BN‐C//BN‐C full cell shows a high energy density of 234.7 W h kg−1, high power density of 39.38 kW kg−1, and excellent cycling stability, superior to most of the other cells reported in the literature. As the density functional theory simulation demonstrated, pyridinic N‐B shows enhanced adsorption activity for Li+ and PF6−, which promotes an increase in the capacity of the anode and cathode, respectively. Meanwhile, the relatively lower diffusion barrier of pyridinic N‐B promotes Li+ migration, resulting in good rate performance. Therefore, this study provides a new approach for the synergistic modulation of a nanostructure and an active site simultaneously to fabricate the carbon electrode material in energy storage devices.

Robust Anode‐Free Sodium Batteries with Durably Sodophilic Interfaces by Suppressing Sodium‐Alloy Transformation

AbstractAnode‐free sodium batteries (AFSBs) are a desirable choice for high‐energy‐density and low‐cost battery systems. However, the rapid capacity decline resulting from irreversible sodium plating and stripping remains a big challenge for AFSBs. Herein, a copper‐dominated Cu2Sb composite coating employing a co‐sputtering strategy is designed to improve the sodophilicity of copper foils. The Cu2Sb coating can construct a durably sodophilic and stable interface by suppressing the alloying transition of the sodophilic phase and alleviating the volumetric deformation of the coating. This stable alloy interface can greatly enhance sodium nucleation and improve ion transport at the interface by forming homogeneous NaF‐rich solid electrolyte interphase (SEI) film. Ultimately, the AFSB assembled using this unique substrate with a highly loaded Na3V2(PO4)3 (NVP) cathode (≈10 mg cm−2) can cycle 600 cycles deliver a discharge capacity of 75.4 mAh g−1 with a capacity retention of 74.2%, which is much higher than those of the untreated one or antimony coating one (<30% after 200 cycles). This co‐sputtering strategy provides new insights into the design of sodophilic coatings with sodium‐alloying ability and can be extended to the optimization of zinc‐metal batteries.

Relocatable Hollow Multishelled Structure‐Based Membrane Enables Dendrite‐Free Lithium Deposition for Ultrastable Lithium Metal Batteries

AbstractLithium metal anode holds great promise due to its highest theoretical capacity and lowest redox potential. However, its practical application is hindered by lithium dendrite growth and exhaustive side reactions, which poses concerns to both cell performance and safety. Herein, a relocatable composite membrane is developed to simultaneously inhibit dendrite growth and stabilize solid electrolyte interphase (SEI) film. The compact packing of hollow multishelled structure (HoMS) provides percolated lithium ion channels and uniform ion flux, while the combined elastic polymer endows membrane structural flexibility to dynamically accommodate volume changes, which results in dendrite‐free lithium deposition inside HoMS and underneath the membrane and stable SEI film restricted to the outer surface of HoMS. Consequently, the membrane‐modified lithium metal half cell achieves an impressive Coulombic efficiency of 99.6% for over 600 cycles. Notably, full cell paired with LiFePO4 cathode stably runs for over 700 cycles, with a decay rate of only 0.045% per cycle, while the one paired with LiNi0.8Co0.1Mn0.1O2 cathode demonstrates a high capacity of 164.1 mAh g−1 at 1 C and a good capacity retention. This HoMS‐based composite membrane opens up new opportunities to realize the practical application of lithium metal batteries.

Binding FSI− to Construct a Self‐Healing SEI Film for Li‐Metal Batteries by In situ Crosslinking Vinyl Ionic Liquid

AbstractThe solid electrolyte interphase (SEI) membrane on the Li metal anode tends to breakdown and undergo reconstruction during operation, causing Li metal batteries to experience accelerated decay. Notably, an SEI membrane with self‐healing characteristics can help considerably in stabilizing the Li‐electrolyte interface; however, uniformly fixing the repairing agent onto the anode remains a challenging task. By leveraging the noteworthy film‐forming attributes of bis(fluorosulfonyl)imide (FSI−) anions and the photopolymerization property of the vinyl group, the ionic liquid 1‐vinyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (VMI‐FSI) was crosslinked with polyethylene oxide (PEO) in this study to form a self‐healing film fixing FSI− groups as the repairing agent. When they encounter lithium metal, the FSI− groups are chemically decomposed into LiF & Li3N, which assist forming SEI membrane on lithium sheet and repairing SEI membrane in the cracks lacerated by lithium dendrite. Furthermore, the FSI− anions exchanged from film are electrochemically decomposed to generate inorganic salts to strengthen the SEI membrane. Benefiting from the self‐healing behavior of the film, Li/LiCoO2 cells with the loading of 16.3 mg cm−2 exhibit the initial discharge capacities of 183.0 mAh ⋅ g−1 and are stably operated for 500 cycles with the retention rates of 81.4 % and the average coulombic efficiency of 99.97 %, operated between 3.0–4.5 V vs. Li+/Li. This study presents a new design approach for self‐healing Li metal anodes and durable lithium metal battery.

Binding FSI- to Construct a Self-Healing SEI Film for Li-Metal Batteries by In situ Crosslinking Vinyl Ionic Liquid.

The solid electrolyte interphase (SEI) membrane on the Li metal anode tends to breakdown and undergo reconstruction during operation, causing Li metal batteries to experience accelerated decay. Notably, an SEI membrane with self-healing characteristics can help considerably in stabilizing the Li-electrolyte interface; however, uniformly fixing the repairing agent onto the anode remains a challenging task. By leveraging the noteworthy film-forming attributes of bis(fluorosulfonyl)imide (FSI-) anions and the photopolymerization property of the vinyl group, the ionic liquid 1-vinyl-3-methylimidazolium bis(fluorosulfonyl)imide (VMI-FSI) was crosslinked with polyethylene oxide (PEO) in this study to form a self-healing film fixing FSI- groups as the repairing agent. When they encounter lithium metal, the FSI- groups are chemically decomposed into LiF & Li3N, which assist forming SEI membrane on lithium sheet and repairing SEI membrane in the cracks lacerated by lithium dendrite. Furthermore, the FSI- anions exchanged from film are electrochemically decomposed to generate inorganic salts to strengthen the SEI membrane. Benefiting from the self-healing behavior of the film, Li/LiCoO2 cells with the loading of 16.3 mg cm-2 exhibit the initial discharge capacities of 183.0 mAh ⋅ g-1 and are stably operated for 500 cycles with the retention rates of 81.4 % and the average coulombic efficiency of 99.97 %, operated between 3.0-4.5 V vs. Li+/Li. This study presents a new design approach for self-healing Li metal anodes and durable lithium metal battery.

Cycling performance of Li metal anode in localized high concentration electrolyte and dynamic mechanism analysis

In this work, we investigated the apparent cycling performance of lithium metal at different chemical compositions and series current densities; examined the microscopic morphology and thickness variation of the deposition layer on the surface of lithium metal anode and the concentration-depth distribution of trace elements in the solid electrolyte interphase (SEI) film; and characterized the kinetic behavior and features of the elementary steps (mass transfer, charge transfer, electro-crystallization) at Li-electrolyte interface using microelectrode technology and various electrochemical test methods. The results show that the lithium metal anode has better cycling performance in high concentration and localized high concentration electrolyte. At the same time, the experimental results confirm that the formation of spherical crystal nucleus is favored only under certain chemical conditions and certain reaction rate; under these conditions, the induction period and the self-smoothing process of critical crystal nucleus can be found. It suggests that there are determined causal among the apparent performance of lithium metal anode, the kinetic parameters of the interfacial charge transfer step and the electro-crystallization step, and these correlations can be used as a reference for screening and evaluating electrolyte systems and battery operating conditions, providing a reliable kinetic basis for future work.