Sustaining Surface Lithiophilicity of Ultrathin Li-Alloy Coating Layers on Current Collector for Zero-Excess Li-Metal Batteries.

Zero-excess Li-metal batteries (ZE-LMBs) have emerged as the ultimate battery platform, offering an exceptionally high energy density. However, the absence of Li-hosting materials results in uncontrolled dendritic Li deposition on the Cu current collector, leading to chronic loss of Li inventory and severe electrolyte decomposition, limiting its full utilization upon cycling. This study presents the application of ultrathin (≈50 nm) coatings comprising six metallic layers (Cu, Ag, Au, Pt, W, and Fe) on Cu substrates in order to provide insights into the design of Li-depositing current collectors for stable ZE-LMB operation. In contrast to non-alloy Cu, W, and Fe coatings, Ag, Au, and Pt coatings can enhance surface lithiophilicity, effectively suppressing Li dendrite growth, thereby improving Li reversibility. Considering the distinct Li-alloying behaviors, particularly solid-solution and/or intermetallic phase formation, Pt-coated Cu current collectors maintain surface lithiophilicity over repeated Li plating/stripping cycles by preserving the original coating layer, thereby attaining better cycling performance of ZE-LMBs. This highlights the importance of selecting suitable Li-alloy metals to sustain surface lithiophilicity throughout cycling to regulate dendrite-less Li plating and improve the electrochemical stability of ZE-LMBs.

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.

Role of inner solvation sheath within salt-solvent complexes in tailoring electrode/electrolyte interphases for lithium metal batteries.

Functional electrolyte is the key to stabilize the highly reductive lithium (Li) metal anode and the high-voltage cathode for long-life, high-energy-density rechargeable Li metal batteries (LMBs). However, fundamental mechanisms on the interactions between reactive electrodes and electrolytes are still not well understood. Recently localized high-concentration electrolytes (LHCEs) are emerging as a promising electrolyte design strategy for LMBs. Here, we use LHCEs as an ideal platform to investigate the fundamental correlation between the reactive characteristics of the inner solvation sheath on electrode surfaces due to their unique solvation structures. The effects of a series of LHCEs with model electrolyte solvents (carbonate, sulfone, phosphate, and ether) on the stability of high-voltage LMBs are systematically studied. The stabilities of electrodes in different LHCEs indicate the intrinsic synergistic effects between the salt and the solvent when they coexist on electrode surfaces. Experimental and theoretical analyses reveal an intriguing general rule that the strong interactions between the salt and the solvent in the inner solvation sheath promote their intermolecular proton/charge transfer reactions, which dictates the properties of the electrode/electrolyte interphases and thus the battery performances.

Light-Designed Shark Skin-Mimetic Surfaces.

Sharks, marine creatures that swim fast and have an antifouling ability, possess dermal denticle structures of micrometer-size. Because the riblet geometries on the denticles reduce the shear stress by inducing the slip of fluid parallel to the stream-wise direction, shark skin has the distinguished features of low drag and antifouling. Although much attention has been given to low-drag surfaces inspired from shark skin, it remains an important challenge to accurately mimic denticle structures in the micrometer scale and to finely control their structural features. This paper presents a novel method to create shark skin-mimetic denticle structures for low drag by exploiting a photoreconfigurable azopolymer. The light-designed denticle structure exhibits superior hydrophobicity and an antifouling effect as sharks do. This work suggests that our novel photoreconfiguration technology, mimicking shark skin and systematically manipulating various structural parameters, can be used in a reliable manner for diverse applications requiring low-drag surfaces.

Sequential Effect of Dual-Layered Hybrid Graphite Anodes on Electrode Utilization During Fast-Charging Li-Ion Batteries.

To recharge lithium-ion batteries quickly and safely while avoiding capacity loss and safety risks, a novel electrode design that minimizes cell polarization at a higher current is highly desired. This work presents a dual-layer electrode (DLE) technology via sequential coating of two different anode materials to minimize the overall electrode resistance upon fast charging. Electrochemical impedance spectroscopy and distribution of relaxation times analysis revealed the dynamic evolution of electrode impedances in synthetic graphite (SG) upon a change in the state of charge (SOC), whereas the natural graphite (NG) maintains its original impedance regardless of SOC variation. This disparity dictates the sequence of the NG and SG coating layers within the DLE, considering the temporal SOC gradient developed upon fast charging. Simulation and experimental results suggest that DLE positioning NG and SG on the top (second-layer) and bottom (first-layer), respectively, can effectively reduce the overall resistance at a 4 C-rate (15-min charging), demonstrating two times higher capacity retention (61.0%) over 200 cycles than its counterpart with reversal sequential coating, and is higher than single-layer electrodes using NG or NG/SG binary mixtures. Hence, this study can guide the combinatorial sequence for multi-layer coating of various active materials for a lower-resistivity, thick-electrode design.

Structural and Chemical Evolutions of Li/Electrolyte Interfaces in Li-Metal Batteries: Tracing Compositional Changes of Electrolytes under Practical Conditions.

Despite the promises in high-energy-density batteries, Li-metal anodes (LMAs) have suffered from extensive electrolyte decomposition and unlimited volume expansion owing to thick, porous layer buildup during cycling. It mainly originates from a ceaseless reiteration of the formation and collapse of solid-electrolyte interphase (SEI). This study reveals the structural and chemical evolutions of the reacted Li layer after different cycles and investigates its detrimental effects on the cycling stability under practical conditions. Instead of the immediately deactivated top surface of the reacted Li layer, the chemical nature underneath the reacted Li layer can be an important indicator of the electrolyte compositional changes. It is found that cycling of LMAs with a lean electrolyte (≈3 g Ah-1 ) causes fast depletion of salt anions, leading to the dynamic evolution of the reacted Li layer structure and composition. Increasing the salt-solvent complex while reducing the non-solvating diluent retards the rate of depletion in a localized high-concentration electrolyte, thereby demonstrating prolonged cycling of Li||NMC622 cells without compromising the Li Coulombic efficiencies and high-voltage stability.

Diagnosis of Current Flow Patterns Inside Fault-Simulated Li-Ion Batteries via Non-Invasive, In Operando Magnetic Field Imaging.

With the growing popularity of Li-ion batteries in large-scale applications, building a safer battery has become a common goal of the battery community. Although the small errors inside the cells trigger catastrophic failures, tracing them and distinguishing cell failure modes without knowledge of cell anatomy can be challenging using conventional methods. In this study, a real-time, non-invasive magnetic field imaging (MFI) analysis that can signal the battery current-induced magnetic field and visualize the current flow within Li-ion cells is developed. A high-speed, spatially resolved MFI scan is used to derive the current distribution pattern from cells with different tab positions at a current load. Current maps are collected to determine possible cell failures using fault-simulated batteries that intentionally possess manufacturing faults such as lead-tab connection failures, electrode misalignment, and stacking faults (electrode folding). A modified MFI analysis exploiting the magnetic field interference with the countercurrent-carrying plate enables the direct identification of defect spots where abnormal current flow occurs within the pouch cells.

Highly Reversible Cycling of Zn-MnO2 Batteries Integrated with Acid-Treated Carbon Supportive Layer.

Zn-MnO2 battery with mild-acid electrolytes has been considered as a promising alternative to Li-ion battery for safe and cost-effective energy storage systems (ESSs), and for full electrification. However, the governing mechanism of MnO2 electrochemistry has not been fully elucidated, hindering further advances in highly reversible MnO2 cathodes. Eventual Mn2+ ion dissolution into the electrolyte adversely triggers the irreversible loss of Mn2+ ions and the excessive precipitation of zinc hydroxyl sulfate (Zn4 SO4 (OH)6 ·xH2 O, ZHS), leading to irreversible capacity loss upon prolonged cycling. To overcome these drawbacks, a rationally renovated cell structure is proposed by integrating an acid-treated carbon supportive layer (aCSL) in the MnO2 cathode, which can play multifunctional roles rendering the additional reaction sites for the reversible formation/decomposition of ZHS and re-utilization of the dissolved Mn2+ ions. Furthermore, the improved affinity of the aCSL toward the electrolyte is beneficial for increasing active surface area and facilitating charge transfer at the cathode side. Benefiting from these features, compared to the conventional cell configuration, the aCSL-integrated Zn-MnO2 cell exhibits superior cycling over 3000 cycles with negligible capacity decay (85.6% retention) at a current of 3 A g-1 .

Identification of LiH and nanocrystalline LiF in the solid-electrolyte interphase of lithium metal anodes.

A comprehensive understanding of the solid-electrolyte interphase (SEI) composition is crucial to developing high-energy batteries based on lithium metal anodes. A particularly contentious issue concerns the presence of LiH in the SEI. Here we report on the use of synchrotron-based X-ray diffraction and pair distribution function analysis to identify and differentiate two elusive components, LiH and LiF, in the SEI of lithium metal anodes. LiH is identified as a component of the SEI in high abundance, and the possibility of its misidentification as LiF in the literature is discussed. LiF in the SEI is found to have different structural features from LiF in the bulk phase, including a larger lattice parameter and a smaller grain size (<3 nm). These characteristics favour Li+ transport and explain why an ionic insulator, like LiF, has been found to be a favoured component for the SEI. Finally, pair distribution function analysis reveals key amorphous components in the SEI.

Lithium Dendrite Suppression with a Silica Nanoparticle-Dispersed Colloidal Electrolyte.

Developing a safe and long-lasting lithium (Li) metal battery is crucial for high-energy applications. However, its poor cycling stability due to Li dendrite formation and excessive Li pulverization is the major hurdle for its practical applications. Here, we present a silica (SiO2) nanoparticle-dispersed colloidal electrolyte (NDCE) and its design principle for suppressing Li dendrite formation. SiO2 nanoclusters in the NDCE play roles in enhancing the Li+ transference number and increasing the Li+ diffusivity in the vicinity of the Li-plating substrate. The NDCE enables less-dendritic Li plating by manipulating the nucleation-growth mode and extending Sand's time. Moreover, SiO2 can interplay with the electrolyte components at the Li-metal surface, enriching fluorinated compounds in the solid electrolyte interface layer. The initial control of the Li plating morphology and SEI structure by the NDCE leads to a more uniform and denser Li deposition upon subsequent cycling, resulting in threefold enhancement of the cycle life. The efficacy of the NDCEs has been further demonstrated by the practical battery design, featuring a commercial-level cathode and thin Li-metal (40 µm) anode.

Enhanced Capacities of Mixed Fatty Acid-Modified Sawdust Aggregators for Remediation of Crude Oil Spill.

Mixed fatty acid-modified aggregators have been developed as potential crude oil sorbents. Cheap pine wood flour was first modified with oleic acid (OA) and further modified with a second fatty acid by a leaving group chemistry, where a surface hydroxyl group is first replaced by p-toluenesulfonyl group and a fatty acid forms a covalent bond on sawdust surface through esterification at the elevated temperature (55 °C). Two OA-modified base materials, pine/OA-106 and pine/OA-124, with different OA-coverages were first prepared and the second fatty acids with C3, C6, C8, C10, C12, C14, or C16 alkyl chains were applied to cover the remaining surface hydroxyl groups. The crude oil sorption capacities of the mixed fatty acid-modified aggregators were studied and compared with those of the base materials. The results showed that mixed fatty acid-modified aggregators increased up to 45.6% more crude oil sorption than those of OA-modified base materials. A correlation between surface property and sorption capacity was studied by moisture sorption, Fourier transform infrared spectroscopy, X-ray diffraction, 13C cross polarization and magic angle spinning nuclear magnetic resonance, thermal gravimetric analysis, and scanning electron microscopy. To our knowledge, no report has been published for mixed fatty acid-modified herders or aggregators in the environmental remediation.

Tuning Two Interfaces with Fluoroethylene Carbonate Electrolytes for High-Performance Li/LCO Batteries.

Various electrolytes have been reported to enhance the reversibility of Li-metal electrodes. However, for these electrolytes, concurrent and balanced control of Li-metal and positive electrode interfaces is a critical step toward fabrication of high-performance Li-metal batteries. Here, we report the tuning of Li-metal and lithium cobalt oxide (LCO) interfaces with fluoroethylene carbonate (FEC)-containing electrolytes to achieve high cycling stability of Li/LCO batteries. Reversibility of the Li-metal electrode is considerably enhanced for electrolytes with high FEC contents, confirming the positive effect of FEC on the stabilization of the Li-metal electrode. However, for FEC contents of 50 wt % and above, the discharge capacity is significantly reduced because of the formation of a passivation layer on the LCO cathodes. Using balanced tuning of the two interfaces, stable cycling over 350 cycles at 1.5 mA cm-2 is achieved for a Li/LCO cell with the 1 M LiPF6 FEC/DEC = 30/70 electrolyte. The enhanced reversibility of the Li-metal electrode is associated with the formation of LiF and polycarbonate in the FEC-derived solid electrolyte interface (SEI) layer. In addition, electrolytes with high FEC contents lead to lateral Li deposition on the sides of Li deposits and larger dimensions of rodlike Li deposits, suggesting the elastic and ion-conductive nature of the FEC-derived SEI layer.

High-Rate Cycling of Lithium-Metal Batteries Enabled by Dual-Salt Electrolyte-Assisted Micropatterned Interfaces.

We present a synergistic strategy to boost the cycling performance of Li-metal batteries. The strategy is based on the combined use of a micropattern (MP) on the surface of the Li-metal electrode and an advanced dual-salt electrolyte (DSE) system to more efficiently control undesired Li-metal deposition at higher current density (∼3 mA cm-2). The MP-Li electrode induces a spatially uniform current distribution to achieve dendrite-free Li-metal deposition beneath the surface layer formed by the DSE. The MP-Li/DSE combination exhibited excellent synergistic rate capability improvements that were neither observed with the MP-Li system nor for the bare Li/DSE system. The combination also resulted in the Li||LiMn2O4 battery attaining over 1 000 cycles, which is twice as long at the same capacity retention (80%) compared with the control cells (MP-Li without DSE). We further demonstrated extremely fast charging at a rate of 15 C (19.5 mA cm-2).

An Ultrahigh Capacity Graphite/Li2S Battery with Holey-Li2S Nanoarchitectures.

The pairing of high-capacity Li2S cathode (1166 mAh g-1) and lithium-free anode (LFA) provides an unparalleled potential in developing safe and energy-dense next-generation secondary batteries. However, the low utilization of the Li2S cathode and the lack of electrolytes compatible to both electrodes are impeding the development. Here, a novel graphite/Li2S battery system, which features a self-assembled, holey-Li2S nanoarchitecture and a stable solid electrolyte interface (SEI) on the graphite electrode, is reported. The holey structure on Li2S is beneficial in decomposing Li2S at the first charging process due to the enhanced Li ion extraction and transfer from the Li2S to the electrolyte. In addition, the concentrated dioxolane (DOL)-rich electrolyte designed lowers the irreversible capacity loss for SEI formation. By using the combined strategies, the graphite/holey-Li2S battery delivers an ultrahigh discharge capacity of 810 mAh g-1 at 0.1 C (based on the mass of Li2S) and of 714 mAh g-1 at 0.2 C. Moreover, it exhibits a reversible capacity of 300 mAh g-1 after a record lifecycle of 600 cycles at 1 C. These results suggest the great potential of the designed LFA/holey-Li2S batteries for practical use.

Electrode Edge Effects and the Failure Mechanism of Lithium-Metal Batteries.

The very high specific capacity of Li metal makes it an ideal anode for high-energy batteries. However, Li dendrite growth and the formation of isolated (or "dead") Li during repeated Li plating/stripping processes leads to a low coulombic efficiency (CE). In this work, we discovered, for the first time, that electrode edge effects play an important role in the failure of Li-metal batteries. The dead Li formed on the edge of Cu substrate was systematically investigated through SEM, energy-dispersive X-ray (EDX) spectroscopy, and 2D X-ray photoelectron spectroscopy (XPS). To minimize the Li loss at the edge of the Cu exposed to pressure-free space, a modified Li∥Cu cell configuration with a Cu electrode smaller than Li metal is preferred. It was clearly demonstrated that using an electrode configuration with a minimal open space or pressure-free space across electrodes can reduce accumulation of dead Li during cycling and increase Li CE. This phenomenon was also verified in Li-metal batteries (Li∥LiNi1/3 Mn1/3 Co1/3 O2 ) and should be considered in the design of practical Li-metal batteries.

Plasticized Polymer Interlayer for Low-Temperature Fabrication of a High-Quality Silver Nanowire-Based Flexible Transparent and Conductive Film.

Silver nanowires (AgNWs) are one of the most promising materials to replace commercially available indium tin oxide in flexible transparent conductive films (TCFs); however, there are still numerous problems originating from poor AgNW junction formation and improper AgNW embedment into transparent substrates. To mitigate these problems, high-temperature processes have been adopted; however, unwanted substrate deformation prevents the use of these processes for the formation of flexible TCFs. In this work, we present a novel poly(methyl methacrylate) interlayer plasticized by dibutyl phthalate for low-temperature fabrication of AgNW-based TCFs, which does not cause any substrate deformation. By exploiting the viscoelastic properties of the plasticized interlayer near the lowered glass-transition temperature, a monolithic junction of AgNWs on the interlayer and embedment of the interconnected AgNWs into the interlayer are achieved in a single-step pressing. The resulting AgNW-TCFs are highly transparent (∼92% at a wavelength of 550 nm), highly conductive (<90 Ω/sq), and environmentally and mechanically robust. Therefore, the plasticized interlayer provides a simple and effective route to fabricate high-quality AgNW-based TCFs.

Enhancing the Cycling Stability of Sodium Metal Electrodes by Building an Inorganic-Organic Composite Protective Layer.

Owing to the natural abundance of sodium resources and their low price, next-generation batteries employing an Na metal anode, such as Na-O2 and Na-S systems, have attracted a great deal of interest. However, the poor reversibility of an Na metal electrode during repeated electrochemical plating and stripping is a major obstacle to realizing rechargeable sodium metal batteries. It mainly originates from Na dendrite formation and exhaustive electrolyte decomposition due to the high reactivity of Na metal. Herein, we report a free-standing composite protective layer (FCPL) for enhancing the reversibility of an Na metal electrode by mechanically suppressing Na dendritic growth and mitigating the electrolyte decomposition. A systematic variation of the liquid electrolyte uptake of FCPL verifies the existence of a critical shear modulus for suppressing Na dendrite growth, being in good agreement with a linear elastic theory, and emphasizes the importance of the ionic conductivity of FCPL for attaining uniform Na plating and stripping. The Na-Na symmetric cell with an optimized FCPL exhibits a cycle life two times longer than that of a bare Na electrode.

Sustainable Redox Mediation for Lithium-Oxygen Batteries by a Composite Protective Layer on the Lithium-Metal Anode.

A synergic combination of a soluble -redox mediator and a protected Li metal -electrode to prevent the self-discharge of the redox mediator is realized by -exploiting a 2,2,6,6-tetramethylpiperidinyl 1-oxyl (TEMPO) redox mediator and an Al2 O3 /PVdF-HFP composite -protective layer (CPL). Stabilization of Li metal by simple CPL coating is effective at -suppressing the chemical reduction of the oxidized TEMPO and opens up the possibility of sustainable redox mediation for robust cycling of Li-O2 batteries.

Structural modulation of lithium metal-electrolyte interface with three-dimensional metallic interlayer for high-performance lithium metal batteries.

The use of lithium (Li) metal anodes has been reconsidered because of the necessity for a higher energy density in secondary batteries. However, Li metal anodes suffer from 'dead' Li formation and surface deactivation which consequently form a porous layer of redundant Li aggregates. In this work, a fibrous metal felt (FMF) as a three-dimensional conductive interlayer was introduced between the separator and the Li metal anode to improve the reversibility of the Li metal anode. The FMF can facilitate charge transfer in the porous layer, rendering it electrochemically more active. In addition, the FMF acted as a robust scaffold to accommodate Li deposits compactly in its interstitial sites. The FMF-integrated Li metal (FMF/Li) electrode operated with a small polarisation even at a current density of 10 mA cm(-2), and it exhibited a seven times longer cycle-life than that of an FMF-free Li electrode in a symmetric cell configuration. A Li metal battery (LMB) using the FMF/Li electrode and a LiFePO4 electrode exhibited a two-fold increase in cycling stability compared with that of a bare Li metal electrode, demonstrating the practical effectiveness of this approach for high performance LMBs.

Ionomer-Liquid Electrolyte Hybrid Ionic Conductor for High Cycling Stability of Lithium Metal Electrodes.

The inhomogeneous Li electrodeposition of lithium metal electrode has been a major impediment to the realization of rechargeable lithium metal batteries. Although single ion conducting ionomers can induce more homogeneous Li electrodeposition by preventing Li(+) depletion at Li surface, currently available materials do not allow room-temperature operation due to their low room temperature conductivities. In the paper, we report that a highly conductive ionomer/liquid electrolyte hybrid layer tightly laminated on Li metal electrode can realize stable Li electrodeposition at high current densities up to 10 mA cm(-2) and permit room-temperature operation of corresponding Li metal batteries with low polarizations. The hybrid layer is fabricated by laminating few micron-thick Nafion layer on Li metal electrode followed by soaking 1 M LiPF6 EC/DEC (1/1) electrolyte. The Li/Li symmetric cell with the hybrid layer stably operates at a high current density of 10 mA cm(-2) for more than 2000 h, which corresponds to more than five-fold enhancement compared with bare Li metal electrode. Also, the prototype Li/LiCoO2 battery with the hybrid layer offers cycling stability more than 350 cycles. These results demonstrate that the hybrid strategy successfully combines the advantages of bi-ionic liquid electrolyte (fast Li(+) transport) and single ionic ionomer (prevention of Li(+) depletion).