In Situ Formed Tribofilms as Efficient Organic/Inorganic Hybrid Interlayers for Stabilizing Lithium Metal Anodes

Stable Lithium Anodes Enabled by the Hardening and High Li+ Flux Interlayer

The commercial use of lithium metal batteries is greatly limited by dendrite formation and slow Li+ transport at the anode-electrolyte interface. Herein, the constructed high-modulus polymer interlayer suppressed the Li dendrite formation, leading to dense deposition and enhanced Li+ transport. Meanwhile, this formed robust organic solid-electrolyte interphase inhibited the side reactions occurring at the anode-electrolyte interface while promoting a high Li+ flux. By constructing the polymer interlayer, the Li@P3DDT||Li@P3DDT symmetric cells demonstrated an impressive stability lifespan of over 3400 h at 1 mA/cm2 and 1 mAh/cm2. The LFP||Li@P3DDT full cells exhibit a remarkable capacity retention of 85.0% over 300 cycles at 4 C. Furthermore, the 50 μm Li@P3DDT||LiCoO2 pouch cell with 380 Wh kg-1 maintained over 99.9% retention of capacity over 60 cycles at 0.5 C. The research paves the way for the advancement of stable lithium anodes.

Three-dimensional nanostructured composite lithium soap fibers for constructing high-performance lithium metal anode interfacial layers

Lithium metal batteries are regarded as promising energy storage devices due to their high theoretical capacity, low density, and low electrode potential. However, the high reactivity of lithium leads to side reactions with the electrolyte and dendritic growth which hinder their commercial application. In this study, a lithium metal anode material with a three-dimensional nanostructured interface was prepared through interfacial modification engineering. The linear flexible molecular chains of the chelating agent, which crosslink with lithium stearate, result in a highly entangled, strong, and flexible three-dimensional porous structure of composite lithium soap fibers. The strong electrostatic interaction between the terminal RCOO- groups and Li+ attracts Li+ ions into the three-dimensional matrix, constructing a lithiophilic protective layer at the micron and nanoscale. This enhances the stability of the SEI layer and the Li+ transport rate. The large specific surface area and abundant pores provide more reaction sites for lithium deposition and stripping. The unique mesh-like molecular structure, with high liquid transport performance, regulates the distribution of the electrolyte and homogenizes the lithium ion flux, effectively suppressing dendritic growth. The Li@DA symmetrical coin cells exhibits a long-term cycling performance of over 6800 hours, and the full battery maintains a high capacity retention of 92.04% after 530 cycles at a 2C rate with a high loading of 12 mg cm-2. This three-dimensional nanostructured interfacial layer holds great potential for advancing the development of high-performance lithium batteries.

Flexible Organic-Polyphosphates Interfacial Layer for Stable Lithium Metal Anode

Lithium (Li) metal is regarded as a desired anode candidate for high-energy-density rechargeable battery systems in the future because of its high specific capacity and low redox potential. However, Li dendritic growth and volume expansion during cycling severely hinder its practical application. Herein, an artificial organophosphorus-inorganic Li hybrid flexbile solid electrolyte interphase (SEI) layer was designed by a prereaction between phytic acid (PA) and lithium hydroxide (LiOH) to generate metal chelates for quick Li+ conductivity. The organic-polyphosphate (PALi) layer not only can provide numerous channels for Li+ to migrate quickly but also can improve its lithiophilicity due to the uniform distribution of phosphorus (P) in the PALi layer; meanwhile, flexibility due to the existence of hydrogen bonds in the PALi layer effectively alleviates the effect of Li volume expansion on the SEI layer. Therefore, the PALi@Cu∥Li cells exhibit a high Coulombic efficiency of 98.85% over 500 cycles at a current density of 0.5 mA cm-2, and the PALi@Cu-Li∥Li symmetrical cells also can maintain good cycling stability with low voltage hysteresis of 20 mV for 2000 h at a current density of 1 mA cm-2. This organic-inorganic hybrid strategy provides a feasible way to fabricate a stable and efficient artificial SEI layer for the practical applications of Li metal batteries.

Half-Covered 'Glitter-Cake' AM@SE Composite: A Novel Electrode Design for High Energy Density All-Solid-State Batteries

All-solid-state batteries (ASSBs) are pursued due to their potential for better safety and high energy density. However, the energy density of the cathode for ASSBs does not seem to be satisfactory due to the low utilization of active materials (AMs) at high loading. With small amount of solid electrolyte (SE) powder in the cathode, poor electrochemical performance is often observed due to contact loss and non-homogeneous distribution of AMs and SEs, leading to high tortuosity and limitation of lithium and electron transport pathways. Here, we propose a novel cathode design that can achieve high volumetric energy density of 1258 Wh L-1 at high AM content of 85 wt% by synergizing the merits of AM@SE core-shell composite particles with conformally coated thin SE shell prepared from mechanofusion process and small SE particles. The core-shell structure with an intimate and thin SE shell guarantees high ionic conduction pathway while unharming the electronic conduction. In addition, small SE particles play the role of a filler that reduces the packing porosity in the cathode composite electrode as well as between the cathode and the SE separator layer. The systematic demonstration of the optimization process may provide understanding and guidance on the design of electrodes for ASSBs with high electrode density, capacity, and ultimately energy density.

Tuning the Unloading and Infiltrating Behaviors of Li-Ion by a Multiphases Gradient Interphase for High-Rate Lithium Metal Anodes

The random distribution of organic-phases (OPs) and inorganic-phases (IOPs) in native solid electrolyte interface (SEI) derived a sluggish Li-ion de-solvation and transmission, impairing the high-rate performance of lithium metal anodes (LMAs). Herein, a multiphases gradient distribution hybrid interface is constructed on metallic Li by surface chemical reconstruction. Theoretical simulations and experiments verify that the Li-ion unloading and infiltrating behaviors are tuned by functional complementary effects, enabling speedy kinetics. The upper OPs with polar functional group (─COO-) convert near-surface solvation structure, pushing Li-ion to unload the solvation cluster. Simultaneously, the bottom IOPs with plenty of crystal boundary accelerates Li-ion infiltration. Moreover, flexible OPs cooperate with rigid IOPs to buffer volume fluctuation and suppress dendritic Li growth. Consequently, the lifespan of the composited electrode is significantly prolonged over 520 h at 5 mA cm-2. The full cells also exhibit an exhilarated rate performance and capacity retention even under a low N/P ratio (≈2.5). This work offers a characteristic insight for the rational design of gradient hybrid interface on the practical LMAs.

Scalable Production of Thin and Durable Practical Li Metal Anode for High-Energy-Density Batteries

Utilization of thin Li metal is the ultimate pathway to achieving practical high-energy-density Li metal batteries (LMBs), but its practical implementation has been significantly impeded by formidable challenges of poor thinning processability, severe interphase instability and notorious dendritic Li growth. Here we report a practical thin (10-40 μm) Li/Mo/Li2Se with concurrently modulated interphase and mechanical properties, achieved via a scalable mechanical rolling process. The in situ generated Li2Se and Mo not only enhance the mechanical strength enabling the scalable fabrication of thin Li metal, but also promote homogeneous Li electrodeposition. Significantly, the Li/Mo/Li2Se demonstrates ultrahigh-rate performance (15 mA cm-2) and ultralong-lifespan cycling sustainability (2700 cycles) with exceptional anti-pulverization capability. The Li|LiFePO4 cells show substantially prolonged cyclability over 1200 cycles with an ultralow decay rate of ~0.01 % per cycle. Moreover, the Li|LiNi0.8Co0.1Mn0.1O2 pouch cells deliver enhanced cycling stability even under the extremely harsh conditions of low negative-to-positive-capacity (N/P) ratio of ~1.2 and lean electrolyte of ~0.95 g Ah-1, showing an exceptional energy density of 329.2 Wh kg-1. This work sheds light on facile pathway for scalable production of durable thin Li metal anode toward reliable practicability.

Bimetallic MOFs-Derived NiFe2O4/Fe2O3 Enabled Dendrite-free Lithium Metal Anodes with Ultra-High Area Capacity Based on An Intermittent Lithium Deposition Model

In practical operating conditions, the lithium deposition behavior is often influenced by multiple coupled factors and there is also a lack of comprehensive and long-term validation for dendrite suppression strategies. Our group previously proposed an intermittent lithiophilic model for high-performance three-dimensional (3D) composite lithium metal anode (LMA), however, the electrodeposition behavior was not discussed. To verify this model, this paper presents a modified 3D carbon cloth (CC) backbone by incorporating NiFe2O4/Fe2O3 (NFFO) nanoparticles derived from bimetallic NiFe-MOFs. Enhanced Li adsorption capacity and lithiophilic modulation were achieved by bimetallic MOFs-derivatives which prompted faster and more homogeneous Li deposition. The intermittent model was further verified in conjunction with the density functional theory (DFT) calculations and electrodeposition behaviors. As a result, the obtained Li-CC@NFFO||Li-CC@NFFO symmetric batteries exhibit prolonged lifespan and low hysteresis voltage even under ultra-high current and capacity conditions (5 mA cm-2, 10 mAh cm-2), what's more, the full battery coupled with a high mass loading (9 mg cm-2) of LiFePO4 cathode can be cycled at a high rate of 5 C, the capacity retention is up to 95.2 % before 700 cycles. This work is of great significance to understand the evolution of lithium dendrites on the 3D intermittent lithiophilic frameworks.

In Situ-Constructed Multifunctional Composite Anode with Ultralong-Life Toward Advanced Lithium-Metal Batteries

Metallic lithium is the most competitive anode material for next-generation high-energy batteries. Nevertheless, the extensive volume expansion and uncontrolled Li dendrite growth of lithium metal not only cause potential safety hazards but also lead to low Coulombic efficiency and inferior cycling lifespan for Li metal batteries. Herein, a multifunctional dendrite-free composite anode (Li/SnS2) is proposed through an in situ melt-infusion strategy. In this configuration, the 3D cross-linked porous Li2S/Li22Sn5 framework facilitates the rapid penetration of electrolytes and accommodates the volume expansion during the repeated Li-plating process. Meanwhile, the lithiophilic Li2S phases with a low Li+ transport barrier ensure preferential Li deposition, effectively avoiding uneven electron distribution. Moreover, the Li22Sn5 electron conductors with appropriate Li+ bonding ability guarantee rapid charge transport and mass transfer. Most importantly, the steady multifunctional skeleton with sufficient inner interfaces (Li2S/Li22Sn5) in the whole electrode, not only realizes the redistribution of the localized free electron, contributing to the decomposition of Li clusters, but also induces a planar deposition model, thus restraining the generation of Li dendrites. Consequently, an unprecedented cyclability of over 6 500 h under an ultrahigh areal capacity of 10 mAh cm-2 and a current rate of 20 mA cm-2 is achieved for the prepared Li2S/Li22Sn5 composite anode. Moreover, the assembled Li/SnS2||LiFePO4 (LFP) pouch full-cells also demonstrate remarkable rate capability and a convincing cycling lifespan of more than 2 000 cycles at 2 C.

Molecule-Level Multiscale Design of Nonflammable Gel Polymer Electrolyte to Build Stable SEI/CEI for Lithium Metal Battery

The risk of flammability is an unavoidable issue for gel polymer electrolytes (GPEs). Usually, flame-retardant solvents are necessary to be used, but most of them would react with anode/cathode easily and cause serious interfacial instability, which is a big challenge for design and application of nonflammable GPEs. Here, a nonflammable GPE (SGPE) is developed by in situ polymerizing trifluoroethyl methacrylate (TFMA) monomers with flame-retardant triethyl phosphate (TEP) solvents and LiTFSI-LiDFOB dual lithium salts. TEP is strongly anchored to PTFMA matrix via polarity interaction between -P = O and -CH2CF3. It reduces free TEP molecules, which obviously mitigates interfacial reactions, and enhances flame-retardant performance of TEP surprisingly. Anchored TEP molecules are also inhibited in solvation of Li+, leading to anion-dominated solvation sheath, which creates inorganic-rich solid electrolyte interface/cathode electrolyte interface layers. Such coordination structure changes Li+ transport from sluggish vehicular to fast structural transport, raising ionic conductivity to 1.03 mS cm-1 and transfer number to 0.41 at 30 °C. The Li|SGPE|Li cell presents highly reversible Li stripping/plating performance for over 1000 h at 0.1 mA cm-2, and 4.2 V LiCoO2|SGPE|Li battery delivers high average specific capacity > 120 mAh g-1 over 200 cycles. This study paves a new way to make nonflammable GPE that is compatible with Li metal anode.

Enhancement of tribological performance of lubricants using polydimethylsiloxane powder additives

This study explored the potential enhancement of lubrication performance by incorporating polydimethylsiloxane (PDMS) powder as a lubricant additive. The PDMS powder was successfully synthesized via mechanical and thermal processes, exhibiting a particle size distribution with an average diameter of 39 μm. XRD and FTIR analyses confirmed the amorphous structure and chemical composition of the PDMS-based silicone rubber powder. XPS analysis provided evidence of increased crosslinking in the crosslinked PDMS powders, with shifts in binding energies and changes in elemental ratios, supporting enhanced Si-O-Si network formation. The addition of the powder to the Poly alpha Olefin (PAO)-based lubricating oil induced notable changes in the physicochemical properties, including viscosity and contact angle. Friction tests revealed that the introduction of silicone rubber powder did not compromise the friction behavior of the lubricating oil owing to the soft and deformable nature of the powder particles, which minimized direct metal-to-metal contact. A significant observation was the decreasing trend in the wear rate with increasing powder concentration, which reached a minimum at 2 wt%. This phenomenon is attributed to a synergistic combination of particle deformation, stress absorption/dispersion effects, and lubricating film formation. Optical microscopy analysis provided visual evidence supporting the low wear rate, with specimens containing 1 wt% and 2 wt% concentrations exhibiting narrow wear widths and reduced wear particle adhesion. Further augmentation of the wear resistance and durability is anticipated through the addition of silicone rubber curing agents, which are expected to bolster the mechanical strength and load-bearing capacity of PDMS powder particles while enhancing the stability of the lubricating film.

Lithium metal based battery systems with ultra-high energy density beyond 500 W h kg-1

As industries and consumption patterns evolve, new electrical appliances are increasingly playing critical roles in national production, defense, and cognitive exploration. However, the slow development of energy storage devices with ultra-high energy density (beyond 500 W h kg-1) has impeded the promotion and widespread application of the next generation of intelligent, multi-scenario electrical equipment. Among the numerous ultra-high specific energy battery systems, lithium metal batteries (LMBs) hold significant potential for applications in advanced and sophisticated fields. This potential is primarily due to lithium metal's high specific capacity (3860 mA h g-1). However, LMBs face numerous challenges, including the growth of lithium dendrites, poor cycle stability, and safety concerns. In recent years, research on the mechanisms of Li metal-based battery systems, innovation in electrode materials, and optimization of device configurations have made significant progress. In this highlight, we provide a comprehensive overview of the storage mechanisms and the latest advancements in high-energy-density LMBs, represented by systems such as Li-Li1-xMO2, Li-S/Se, Li-gas (CO2/air/O2), Li-CFx, and all-solid-state LMBs. By integrating the current research findings, we highlight the opportunities and future research directions for high-energy-density LMBs, offering new guiding perspectives for their development under practical conditions.

Homogeneously Planar-Exposure LiB Fiber Skeleton Toward Long-Lifespan Practical Li Metal Pouch Cells

LiB alloy is promising lithium (Li) metal anode material because the continuous internal LiB fiber skeleton can effectively suppress Li dendrites and structural pulverization. However, the unvalued surface states limit the practical application of LiB alloy anodes. Herein, the study examined the influence of the different exposure manners of the internal LiB fiber skeleton owing to the various surface states of the LiB alloy anode on electrochemical performance and targetedly proposed a scalable friction coating strategy to construct a lithiated fumed silica (LFS) functional layer with abundant electrochemically active sites on the surface of the LiB alloy anode. The LFS significantly suppresses the inhomogeneous interfacial electrochemical behavior of the LiB alloy anode and enables the exposure of the internal LiB fiber skeleton in a homogeneously planar manner (LFS-LiB). Thus, a 0.5 Ah LFS-LiB||LiCoO2 (LCO) pouch cell exhibits a discharge capacity retention rate of 80% after 388 cycles. Moreover, a 6.15 Ah LFS-LiB||S pouch cell with 409.3 Wh kg-1 exhibits a discharge capacity retention rate of 80% after 30 cycles. In conclusion, the study findings provide a new research perspective for Li alloy anodes.

Boosting High-Voltage Practical Lithium Metal Batteries with Tailored Additives

The lithium (Li) metal anode is widely regarded as an ideal anode material for high-energy-density batteries. However, uncontrolled Li dendrite growth often leads to unfavorable interfaces and low Coulombic efficiency (CE), limiting its broader application. Herein, an ether-based electrolyte (termed FGN-182) is formulated, exhibiting ultra-stable Li metal anodes through the incorporation of LiFSI and LiNO3 as dual salts. The synergistic effect of the dual salts facilitates the formation of a highly robust SEI film with fast Li+ transport kinetics. Notably, Li||Cu half cells exhibit an average CE reaching up to 99.56%. In particular, pouch cells equipped with high-loading lithium cobalt oxide (LCO, 3 mAh cm-2) cathodes, ultrathin Li chips (25 μm), and lean electrolytes (5 g Ah-1) demonstrate outstanding cycling performance, retaining 80% capacity after 125 cycles. To address the gas issue in the cathode under high voltage, cathode additives 1,3,6-tricyanohexane is incorporated with FGN-182; the resulting high-voltage LCO||Li (4.4 V) pouch cells can cycle steadily over 93 cycles. This study demonstrates that, even with the use of ether-based electrolytes, it is possible to simultaneously achieve significant improvements in both high Li utilization and electrolyte tolerance to high voltage by exploring appropriate functional additives for both the cathode and anode.

Adjusting Ion Diffusion Kinetics of Li Deposition Enabled by an Elastic Porous Melamine Sponge Host for Stable Lithium Metal Anodes

Lithium (Li) dendritic growth and huge volume expansion seriously hamper Li-metal anode development. Herein, we design a lightweight 3D Li-ion-affinity host enabled by silver (Ag) nanoparticles fully decorating a porous melamine sponge (Ag@PMS) for dendrite-free and high-areal-capacity Li anodes. The compact Ag nanoparticles provide abundant preferred nucleation sites and give the host strong conductivity. Moreover, the high specific surface area and polar groups of the elastic, porous melamine sponge enhance the Li-ion diffusion kinetics, prompting homogeneity of Li deposition and stripping. As expected, the integrated 3D Ag@PMS-Li anode delivered a remarkable electrochemical performance, with a Coulombic efficiency (CE) of 97.14% after 450 cycles at 1 mA cm-2. The symmetric cell showed an ultralong lifespan of 3400 h at 1 mA cm-2 for 1 mAh cm-2. This study provides a facile and cost-effective strategy to design an advanced 3D framework for the preparation of a stable dendrite-free Li metal anode.

Artificial LiF-Rich Interface Enabled by In situ Electrochemical Fluorination for Stable Lithium-Metal Batteries

Lithium (Li)-metal batteries are promising next-generation energy storage systems. One drawback of uncontrollable electrolyte degradation is the ability to form a fragile and nonuniform solid electrolyte interface (SEI). In this study, we propose the use of a fluorinated carbon nanotube (CNT) macrofilm (CMF) on Li metal as a hybrid anode, which can regulate the redox state at the anode/electrolyte interface. Due to the favorable reaction energy between the plated Li and fluorinated CNTs, the metal can be fluorinated directly to a LiF-rich SEI during the charging process, leading to a high Young's modulus (~2.0 GPa) and fast ionic transfer (~2.59×10-7  S cm-1 ). The obtained SEI can guide the homogeneous plating/stripping of Li during electrochemical processes while suppressing dendrite growth. In particular, the hybrid of endowed full cells with substantially enhanced cyclability allows for high capacity retention (~99.3 %) and remarkable rate capacity. This work can extend fluorination technology into a platform to control artificial SEI formation in Li-metal batteries, increasing the stability and long-term performance of the resulting material.