Li2CO3-affiliative mechanism for air-accessible interface engineering of garnet electrolyte via facile liquid metal painting

Synergistically Engineering Grains and Grain Boundaries toward Li Dendrite-Free Li7La3Zr2O12

Cation-doped cubic Li7La3Zr2O12 is regarded as a promising solid electrolyte for safe and energy-dense solid-state lithium batteries. However, it suffers from the formation of Li2CO3 and high electronic conductivity, which give rise to an unconformable Li/Li7La3Zr2O12 interface and lithium dendrites. Herein, composite AlF3-Li6.4La3Zr1.4Ta0.6O12 solid electrolytes were created based on thermal AlF3 decomposition and F/O displacement reactions under a high-temperature sintering process. When the AlF3 is thermally decomposed, it leaves Al2O3/AlF3 meliorating the grain boundaries and F- ions partially displacing O2- ions in the grains. Due to the higher electronegativity of F- in the grains and the grain-boundary modification, these AlF3-Li6.4La3Zr1.4Ta0.6O12 deliver optimized electronic conduction and chemical stability against the formation of Li2CO3. The Li/AlF3-Li6.4La3Zr1.4Ta0.6O12/Li cell exhibits a low interfacial resistance of ∼16 Ω cm2 and an ultrastable long-term cycling behavior for 800 h under a current density of 200 μA/cm2, leading to Li//LiCoO2 solid-state batteries with good rate performance and cycling stability.

High ionic conductivity materials Li3YBr6and Li3LaBr6for solid-state batteries: first-principles calculations

High ionic conductivity solid-state electrolytes are essential for powerful solid-state lithium-ion batteries. With density functional theory andab initiomolecular dynamics simulations, we investigated the crystal structures of Li3YBr6and Li3LaBr6. The lowest energy configurations with uniform distribution of lithium ions were identified. Both materials have wide electrochemical stability windows (ESW): 2.64 V and 2.57 V, respectively. The experimental ESW for Li3YBr6is 2.50 V. Through extrapolating various temperature diffusion results, the conductivity of Li3YBr6was obtained at room temperature, approximately 3.9 mS cm-1, which is comparable to the experimental value 3.3 mS cm-1. Li3LaBr6has a higher conductivity, a 100% increase compared with Li3YBr6. The activation energies of Li3YBr6and Li3LaBr6through the Arrhenius plot are 0.26 eV and 0.24 eV, respectively, which is also close to the experimental value of 0.30 eV for Li3YBr6. This research explored high ionic conductivity halide materials and will contribute to developing solid-state lithium-ion batteries.

An electron-blocking interface for garnet-based quasi-solid-state lithium-metal batteries to improve lifespan

Garnet oxide is one of the most promising solid electrolytes for solid-state lithium metal batteries. However, the traditional interface modification layers cannot completely block electron migrating from the current collector to the interior of the solid-state electrolyte, which promotes the penetration of lithium dendrites. In this work, a highly electron-blocking interlayer composed of potassium fluoride (KF) is deposited on garnet oxide Li6.4La3Zr1.4Ta0.6O12 (LLZTO). After reacting with melted lithium metal, KF in-situ transforms to KF/LiF interlayer, which can block the electron leakage and inhibit lithium dendrite growth. The Li symmetric cells using the interlayer show a long cycle life of ~3000 hours at 0.2 mA cm-2 and over 350 hours at 0.5 mA cm-2 respectively. Moreover, an ionic liquid of LiTFSI in C4mim-TFSI is screened to wet the LLZTO|LiNi0.8Co0.1Mn0.1O2 (NCM) positive electrode interfaces. The Li|KF-LLZTO | NCM cells present a specific capacity of 109.3 mAh g-1, long lifespan of 3500 cycles and capacity retention of 72.5% at 25 °C and 2 C (380 mA g-1) with an average coulombic efficiency of 99.99%. This work provides a simple and integrated strategy on high-performance quasi-solid-state lithium metal batteries.

Versatile Patterning of Liquid Metal via Multiphase 3D Printing

This paper presents a scalable and straightforward technique for the immediate patterning of liquid metal/polymer composites via multiphase 3D printing. Capitalizing on the polymer's capacity to confine liquid metal (LM) into diverse patterns. The interplay between distinctive fluidic properties of liquid metal and its self-passivating oxide layer within an oxidative environment ensures a resilient interface with the polymer matrix. This study introduces an inventive approach for achieving versatile patterns in eutectic gallium indium (EGaIn), a gallium alloy. The efficacy of pattern formation hinges on nozzle's design and internal geometry, which govern multiphase interaction. The interplay between EGaIn and polymer within the nozzle channels, regulated by variables such as traverse speed and material flow pressure, leads to periodic patterns. These patterns, when encapsulated within a dielectric polymer polyvinyl alcohol (PVA), exhibit an augmented inherent capacitance in capacitor assemblies. This discovery not only unveils the potential for cost-effective and highly sensitive capacitive pressure sensors but also underscores prospective applications of these novel patterns in precise motion detection, including heart rate monitoring, and comprehensive analysis of gait profiles. The amalgamation of advanced materials and intricate patterning techniques presents a transformative prospect in the domains of wearable sensing and comprehensive human motion analysis.

In-Situ Formed Electron Inhibitor Enabling Dendrite-free Garnet Electrolytes: A Case Study of Fumed Silica

Ta-doped Li7La3Zr2O12 (LLZTO) solid-state electrolytes (SEs) show great promise for solid-state batteries due to its high conductivity and safety. However, one of the challenges it faces is lithium dendrite propagation upon long-term cycling. To address this issue, we propose the incorporation of fumed silica (FS) at the grain boundaries of LLZTO to modify the properties of the garnet pellet, which effectively inhibits the dendrite growth. The introduction of FS has demonstrated several beneficial effects. Firstly, it reduces the migration barrier of lithium ions, which helps prevent dendrite formation and propagation. Additionally, FS reduces the electronic conductivity of the SEs pellet, suppressing the dendrite formation. Moreover, the formed lithium silicates from FS might also be acted as electron inhibitor, thus inhibiting the lithium dendrite growth upon cycling. By investigating the use of FS as a modifier in LLZTO-based electrolytes, our study contributes to advancing dendrite-free solid-state electrolytes and thus the development of high-performance all-solid-state batteries.

Liquid Metal Mediated Heterostructure Fluoride Solid Electrolytes of High Conductivity and Air Stability for Sustainable Na Metal Batteries

Fluoride-based solid electrolytes (SEs) have emerged as a promising component for high-energy-density rechargeable solid-state batteries (SSBs) in view of their wide electrochemical window, high air stability, and interface compatibility, but they still face the challenge of low ion conductivity and the lack of a desired structure for sodium metal SSBs. Here, we report a sodium-rich heterostructure fluoride SE, Na3GaF6-Ga2O3-NaCl (NGFOC-G), synthesized via in situ oxidation of liquid metal gallium and in situ chlorination using low-melting GaCl3. The distinctive features of NGFOC-G include single-crystal Na3GaF6 domains within an open-framework structure, composite interface decoration of Ga2O3 and NaCl with a concentration gradient, exceptional air stability, and high electrochemical oxidation stability. By leveraging the penetration of gallium at NaF grain boundaries and the in situ self-oxidation to form Ga2O3 nanodomains, the solid-phase reaction kinetics of NaF and GaF3 is activated for facilitating the synthesis of main component Na3GaF6. The introduction of a small amount of a chlorine source during synthesis further softens and modifies the boundaries of Na3GaF6 along with Ga2O3. Benefiting from the enhanced interface ion transport, the optimized NGFOC-G exhibits an ionic conductivity up to 10-4 S/cm at 40 °C, which is the highest level reported among fluoride-based sodium-ion SEs. This SE demonstrates a "self-protection" mechanism, where the formation of a high Young's modulus transition layer rich in NaF and Na2O under electrochemical driving prevents the dendrite growth of sodium metal. The corresponding Na/Na symmetric cells show minimal voltage hysteresis and stable cycling performance for at least 1000 h. The Na/NGFOC-G/Na3V2(PO4)3 cell demonstrates stable capacity release around 100 mAh/g at room temperature. The Na/NGFOC-G/FeF3 cell delivers a high capacity of 461 mAh/g with an excellent stability of conversion reaction cycling.

Achieving the High Capacity and High Stability of Li-Rich Oxide Cathode in Garnet-Based Solid-State Battery

Solid-state batteries (SSBs) based on Li-rich Mn-based oxide (LRMO) cathodes attract much attention because of their high energy density as well as high safety. But their development was seriously hindered by the interfacial instability and inferior electrochemical performance. Herein, we design a three-dimensional foam-structured GaN-Li composite anode and successfully construct a high-performance SSB based on Co-free Li1.2 Ni0.2 Mn0.6 O2 cathode and Li6.5 La3 Zr1.5 Ta0.5 O12 (LLZTO) solid electrolyte. The interfacial resistance is considerably reduced to only 1.53 Ω cm2 and the assembled Li symmetric cell is stably cycled more than 10,000 h at 0.1-0.2 mA cm-2 . The full battery shows a high initial capacity of 245 mAh g-1 at 0.1 C and does not show any capacity degradation after 200 cycles at 0.2 C (≈100 %). The voltage decay is well suppressed and it is significantly decreased from 2.96 mV/cycle to only 0.66 mV/cycle. The SSB also shows a very high rate capability (≈170 mAh g-1 at 1 C) comparable to a liquid electrolyte-based battery. Moreover, the oxygen anion redox (OAR) reversibility of LRMO in SSB is much higher than that in liquid electrolyte-based cells. This study offers a distinct strategy for constructing high-performance LRMO-based SSBs and sheds light on the development and application of high-energy density SSBs.

Designing electrolytes and interphases for high-energy lithium batteries

High-energy and stable lithium-ion batteries are desired for next-generation electric devices and vehicles. To achieve their development, the formation of stable interfaces on high-capacity anodes and high-voltage cathodes is crucial. However, such interphases in certain commercialized Li-ion batteries are not stable. Due to internal stresses during operation, cracks are formed in the interphase and electrodes; the presence of such cracks allows for the formation of Li dendrites and new interphases, resulting in a decay of the energy capacity. In this Review, we highlight electrolyte design strategies to form LiF-rich interphases in different battery systems. In aqueous electrolytes, the hydrophobic LiF can extend the electrochemical stability window of aqueous electrolytes. In organic liquid electrolytes, the highly lithiophobic LiF can suppress Li dendrite formation and growth. Electrolyte design aimed at forming LiF-rich interphases has substantially advanced high-energy aqueous and non-aqueous Li-ion batteries. The electrolyte and interphase design principles discussed here are also applicable to solid-state batteries, as a strategy to achieve long cycle life under low stack pressure, as well as to construct other metal batteries.

Fluorinating All Interfaces Enables Super-Stable Solid-State Lithium Batteries by In Situ Conversion of Detrimental Surface Li2 CO3

Li-stuffed battery materials intrinsically have surface impurities, typically Li2 CO3 , which introduce severe kinetic barriers and electrochemical decay for a cycling battery. For energy-dense solid-state lithium batteries (SSLBs), mitigating detrimental Li2 CO3 from both cathode and electrolyte materials is required, while the direct removal approaches hardly avoid Li2 CO3 regeneration. Here, a decarbonization-fluorination strategy to construct ultrastable LiF-rich interphases throughout the SSLBs by in situ reacting Li2 CO3 with LiPF6 at 60 °C is reported. The fluorination of all interfaces effectively suppresses parasitic reactions while substantially reducing the interface resistance, producing a dendrite-free Li anode with an impressive cycling stability of up to 7000 h. Particularly, transition metal dissolution associated with gas evolution in the cathodes is remarkably reduced, leading to notable improvements in battery rate capability and cyclability at a high voltage of 4.5 V. This all-in-one approach propels the development of SSLBs by overcoming the limitations associated with surface impurities and interfacial challenges.

Revealing the role of hydrogen bond coupling structure for enhanced performance of the solid-state electrolyte

Achieving practical applications of PEO-based composite solid electrolyte (CPE) batteries requires the precise design of filler structures at the molecular level to form stable composite interfacial phases, which in turn improve the conductivity of Li+ and inhibit the nucleation growth of lithium dendrites. Some functional fillers suffer from severe agglomeration due to poor compatibility with the polymer base or grain boundary migration, resulting in limited improvement in cell performance. In this paper, ILs@KAP1 is reported as a filler to enhance the performance of PEO-based batteries. Thereinto, the hypercrosslinked phosphorus ligand polymer-containing KAP1, designed at the molecular level, has an abundant porous structure, hydrogen bonding network, and a rigid skeleton structure of benzene rings. These can be used both to improve the flammability with PEO-based and to reduce the crystallinity of the polymer electrolyte. Ionic liquids (ILs) are encapsulated in the nanochannels of KAP1, and thus a 3D Li+ conducting framework could be formed. In this case, it could not only facilitate the wettability of the contact interface with the electrode, significantly promoting its compatibility and providing a fast Li+ transport path, but also facilitate the formation of LiF, Li3N and Li2O rich SEI components, further fostering the uniform deposition/exfoliation of lithium. The LFP||CPE||Li battery assembled with ILs@KAP1-PEO-CPE has a high initial discharge specific capacity about 156 mAh/g at 1C and a remaining capacity about 121.8 mAh/g after 300 cycles (capacity retention of 78.07%).

Low-Temperature In Situ Lithiation Construction of a Lithiophilic Particle-Selective Interlayer for Solid-State Lithium Metal Batteries

Unexpected interface resistance and lithium dendrite puncture hinder the application of garnet-type solid-state electrolytes in high-energy-density systems. Different from the previous high-temperature (>180 °C) molten lithium that promotes the alloying reaction between the coating layer and Li to enhance the interface contact, herein, we introduce liquid-metal-like SbCl3 to construct a three-dimensional Li+ directional-selection interlayer by in situ low-temperature lithiation (80 °C). An interlayer with a more negative interface energy composed of SbLi3 and LiCl exhibits a superior affinity with Li and LGLZO, which reduces the interface resistance and suppresses the growth of Li dendrites by an insulated electron. The introduction of the SbCl3 modification layer into Li/Li symmetric cells enables charge/discharge at a current density of 6.0 mA cm-2 and operation for more than 1000 h under 2.0 mA cm-2 at room temperature. The full cells with the LiFePO4 cathode exhibit a high residual capacity of 144.8 mAh g-1 at 0.5 C after 1000 cycles and excellent cycling stability with a retention ratio of 94.7% at 1 C after 600 cycles. The low-temperature lithiation method based on an energy-saving perspective should be applied to other types of solid-state electrolyte modification strategies.

"Win-Win" Modification of LiCoO2 Enables Stable and Long-Life Cycling of Sulfide-Based All Solid-State Batteries

Interfacial side reactions and space charge layers between the oxide cathode material and the sulfide solid-state electrolytes (SSEs), along with the structural degradation of the active material, significantly compromise the electrochemical performance of all-solid-state batteries (ASSLBs). Surface coating and bulk doping of the cathodes are considered the most effective approaches to mitigate the interface issues between the cathode and SSEs and enhance the structural integrity of composite cathodes. Here, a one-step low-cost means is ingeniously designed to modify LiCoO2 (LCO) with heterogeneous Li2 TiO3 /Li(TiMg)1/2 O2 surface coating and bulk gradient Mg doping. When applied in Li10 GeP2 S12 -based ASSLBs, the Li2 TiO3 and Li(TiMg)1/2 O2 coating layers effectively suppress interfacial side reactions and weaken space charge layer effect. Furthermore, gradient Mg doping stabilizes the bulk structure to mitigate the formation of spinel-like phases during local overcharging caused by solid-solid contact. The modified LCO cathodes exhibit excellent cycle performance with a capacity retention of 80 % after 870 cycles. This dual-functional strategy provides the possibility for large-scale commercial implementation of cathodes modification in sulfide based ASSLBs in the future.

Robust and Intimate Interface Enabled by Silicon Carbide as an Additive to Anodes for Lithium Metal Solid-State Batteries

Garnet-type solid-state electrolytes are among the most reassuring candidates for the development of solid-state lithium metal batteries (SSLMB) because of their wide electrochemical stability window and chemical feasibility with lithium. However, issues such as poor physical contact with Li metal tend to limit their practical applications. These problems were addressed using β-SiC as an additive to the Li anode, resulting in improved wettability over Li6.75 La3 Zr1.75 Ta0.25 O12 (LLZTO) and establishing an improved interfacial contact. At the Li-SiC|LLZTO interface, intimacy was induced by a lithiophilic Li4 SiO4 phase, whereas robustness was attained through the hard SiC phase. The optimized Li-SiC|LLZTO|Li-SiC symmetric cell displayed a low interfacial impedance of 10 Ω cm2 and superior cycling stability at varying current densities up to 5800 h. Moreover, the modified interface could achieve a high critical current density of 4.6 mA cm-2 at room temperature and cycling stability of 1000 h at 3.5 mA cm-2 . The use of mechanically superior materials such as SiC as additives for the preparation of a composite anode may serve as a new strategy for robust garnet-based SSLMB.

A liquid metal-fluoropolymer artificial protective film enables robust lithium metal batteries at sub-zero temperatures

Batteries that are both high-energy-density and durable at sub-zero temperatures are highly desirable for deep space and subsea exploration and military defense applications. Our design incorporates a casting membrane technology to prepare a gallium indium liquid metal (LM)/fluoropolymer hybrid protective film on a lithium metal anode. The LM not only spontaneously forms a passivation alloy layer with lithium but also reduces the nucleation potential barrier and homogenizes the Li+ flux on the surface of the lithium anode. The fluoropolymer's polar functional groups (-C-F-) effectively induce targeted dispersion of gallium indium seeds, and the unique pit structure on the surface provides oriented sites for lithium plating. By implementing these strategies optimally, the protected lithium metal anode remains in operation at a current density of 20 mA cm-2 with an over-potential of about 50.4 mV after 500 h, and the full cells have a high capacity retention rate of up to 98.5% at a current density of 0.5 C after 100 cycles. Furthermore, the battery shows improved low temperature performance at -30 °C, validating the potential of the protective film to enable battery operation at sub-zero temperatures.

Titanium-Oxygen Clusters Brazing Li with Li6.5La3Zr1.5Ta0.5O12 for High-Performance All-Solid-State Li Batteries

Garnet-based solid-state electrolytes are considered crucial candidates for solid-state Li batteries due to their high Li+ conductivity and nonflammability; however, poor interfacial contact with the Li anode and growth of Li dendrites limit their application. Herein, a high-activity titanium-oxygen cluster is used as a brazing filler to braze the Li6.5La3Zr1.5Ta0.5O12 (LLZTO) with an Li anode into the whole unit. The brazing layer leads to a significantly lower interfacial impedance of 8.32 Ω cm2. Furthermore, the brazing layer is an isotropic amorphous ion-electron hybrid conductive layer, which significantly promotes Li+ transport and regulates the distribution of the electric field, therefore inhibiting the growth of Li dendrites. The cell exhibits an ultrahigh critical current density of 2.3 mA cm-2 and stable cycling of over 4000 h at 0.5 mA cm-2 (25 °C).

Design Strategies for Anodes and Interfaces Toward Practical Solid-State Li-Metal Batteries

Solid-state Li-metal batteries (based on solid-state electrolytes) offer excellent safety and exhibit high potential to overcome the energy-density limitations of current Li-ion batteries, making them suitable candidates for the rapidly developing fields of electric vehicles and energy-storage systems. However, establishing close solid-solid contact is challenging, and Li-dendrite formation in solid-state electrolytes at high current densities causes fatal technical problems (due to high interfacial resistance and short-circuit failure). The Li metal/solid electrolyte interfacial properties significantly influence the kinetics of Li-metal batteries and short-circuit formation. This review discusses various strategies for introducing anode interlayers, from the perspective of reducing the interfacial resistance and preventing short-circuit formation. In addition, 3D anode structural-design strategies are discussed to alleviate the stress caused by volume changes during charging and discharging. This review highlights the importance of comprehensive anode/electrolyte interface control and anode design strategies that reduce the interfacial resistance, hinder short-circuit formation, and facilitate stress relief for developing Li-metal batteries with commercial-level performance.

Understanding and Engineering Interfacial Adhesion in Solid-State Batteries with Metallic Anodes

High performance alkali metal anode solid-state batteries require solid/solid interfaces with fast ion transfer that are morphologically and chemically stable upon electrochemical cycling. Void formation at the alkali metal/solid-state electrolyte interface during alkali metal stripping is responsible for constriction resistances and hotspots that can facilitate dendrite propagation and failure. Both externally applied pressures (35-400 MPa) and temperatures above the melting point of the alkali metal have been shown to improve the interfacial contact with the solid electrolyte, preventing the formation of voids. However, the extreme pressure and temperature conditions required can be difficult to meet for commercial solid-state battery applications. In this review, we highlight the importance of interfacial adhesion or 'wetting' at alkali metal/solid electrolyte interfaces for achieving solid-state batteries that can withstand high current densities without cell failure. The intrinsically poor adhesion at metal/ceramic interfaces poses fundamental limitations on many inorganics solid-state electrolyte systems in the absence of applied pressure. Suppression of alkali metal voids can only be achieved for systems with high interfacial adhesion (i. e. 'perfect wetting') where the contact angle between the alkali metal and the solid-state electrolyte surface goes to θ=0°. We identify key strategies to improve interfacial adhesion and suppress void formation including the adoption of interlayers, alloy anodes and 3D scaffolds. Computational modeling techniques have been invaluable for understanding the structure, stability and adhesion of solid-state battery interfaces and we provide an overview of key techniques. Although focused on alkali metal solid-state batteries, the fundamental understanding of interfacial adhesion discussed in this review has broader applications across the field of chemistry and material science from corrosion to biomaterials development.

Phase-Changeable Dynamic Conformal Electrode/electrolyte Interlayer enabling Pressure-Independent Solid-State Lithium Metal Batteries

Lithium-metal-based solid-state batteries (Li-SSBs) are one of the most promising energy storage devices due to their high energy densities. However, under insufficient pressure constraints (<MPa-level), Li-SSBs usually exhibit poor electrochemical performances owing to the continuous interfacial degradation between the solid-state electrolyte (SSE) and electrodes. Herein, a phase-changeable interlayer is developed to construct the self-adhesive and dynamic conformal electrode/SSE contact in Li-SSBs. The strong adhesive and cohesive strengths of the phase-changeable interlayer enable Li-SSBs to resist up to 250 N pulling force (=1.9 MPa), affording Li-SSBs ideal interfacial integrality even without extra stack pressure. Remarkably, this interlayer exhibits a high ionic conductivity of 1.3 × 10^-3 S cm^-1 , attributed to the shortened steric solvation hindrance and optimized Li⁺ coordination structure. Furthermore, the changeable phase property of the interlayer endows Li-SSBs with a healable Li/SSE interface, accommodating the stress-strain evolution of the lithium metal and constructing the dynamic conformal interface. Consequently, the contact impedance of the modified solid symmetric cell exhibits a pressure-independent manner and does not increase over 700 h (0.2 MPa). The LiFePO₄ pouch cell with the phase-changeable interlayer shows 85% capacity retention after 400 cycles at a low pressure of 0.1 MPa.

Building K-C Anode with Ultrahigh Self-Diffusion Coefficient for Solid State Potassium Metal Batteries Operating at -20 to 120 °C

Solid state potassium (K) metal batteries are intriguing in grid-scale energy storage, benefiting from the low cost, safety, and high energy density. However, their practical applications are impeded by poor K/solid electrolyte (SE) interfacial contact and limited capacity caused by the low K self-diffusion coefficient, dendrite growth, and intrinsically low melting point/soft features of metallic K. Herein, a fused-modeling strategy using potassiophilic carbon allotropes molted with K is demonstrated that can enhance the electrochemical performance/stability of the system via promoting K diffusion kinetics (2.37 × 10^-8 cm² s^-1 ), creating a low interfacial resistance (≈1.3 Ω cm² ), suppressing dendrite growth, and maintaining mechanical/thermal stability at 200 °C. A homogeneous/stable K stripping/plating is consequently implemented with a high current density of 2.8 mA cm^-2 (at 25 °C) and a record-high areal capacity of 11.86 mAh cm^-2 (at 0.2 mA cm^-2 ). The enhanced K diffusion kinetics contribute to sustaining intimate interfacial contact, stabilizing the stripping/plating at high current densities. Full cells coupling ultrathin K-C composite anodes (≈50 µm) with Prussian blue cathodes and β/β″-Al₂ O₃ SEs deliver a high energy density of 389 Wh kg^-1 with a retention of 94.4% after 150 cycles and fantastic performances at -20 to 120 °C.

Bonding Lithium Metal with Garnet Electrolyte by Interfacial Lithiophobicity/Lithiophilicity Transition Mechanism over 380 °C

Garnet electrolytes, possessing high ionic conductivity (10^-4 -10^-3 S cm^-1 at room temperature) and excellent chemical/electrochemical compatibility with lithium metal, are expected to be used in solid-state lithium metal batteries. However, the poor solid-solid interfacial contact between lithium and garnet leads to high interfacial resistance, reducing the battery power capability and cyclability. Garnet electrolytes are commonly believed to be intrinsically lithiophilic, and lithiophobic Li₂ CO₃ on the garnet surface accounted for the poor interfacial contact. Here, it is proposed that the interfacial lithiophobicity/lithiophilicity of garnets (LLZO, LLZTO) can be transformed above a temperature of ≈380 °C. This transition mechanism is also suitable for other materials such as Li₂ CO₃ , Li₂ O, stainless steel, and Al₂ O₃ . By using this transition mechanism, uniform and even lithium can be strongly bonded no-surface-treated garnet electrolytes with various shapes. The Li-LLZTO interfacial resistance can be reduced to ≈3.6 Ω cm² and sustainably withstood lithium extraction and insertion for up to 2000 h at 100 µA cm^-2 . This high-temperature lithiophobicity/lithiophilicity transition mechanism can help improve the understanding of lithium-garnet interfaces and build practical lithium-garnet solid-solid interfaces.

Understanding the evolution of lithium dendrites at Li6.25Al0.25La3Zr2O12 grain boundaries via operando microscopy techniques

The growth of lithium dendrites in inorganic solid electrolytes is an essential drawback that hinders the development of reliable all-solid-state lithium metal batteries. Generally, ex situ post mortem measurements of battery components show the presence of lithium dendrites at the grain boundaries of the solid electrolyte. However, the role of grain boundaries in the nucleation and dendritic growth of metallic lithium is not yet fully understood. Here, to shed light on these crucial aspects, we report the use of operando Kelvin probe force microscopy measurements to map locally time-dependent electric potential changes in the Li_6.25Al_0.25La₃Zr₂O₁₂ garnet-type solid electrolyte. We find that the Galvani potential drops at grain boundaries near the lithium metal electrode during plating as a response to the preferential accumulation of electrons. Time-resolved electrostatic force microscopy measurements and quantitative analyses of lithium metal formed at the grain boundaries under electron beam irradiation support this finding. Based on these results, we propose a mechanistic model to explain the preferential growth of lithium dendrites at grain boundaries and their penetration in inorganic solid electrolytes.

H3PO4-Induced Nano-Li3PO4 Pre-reduction Layer to Address Instability between the Nb-Doped Li7La3Zr2O12 Electrolyte and Metallic Li Anode

Solid-state batteries based on a metallic Li anode and nonflammable solid electrolytes (SEs) are anticipated to achieve high energy and power densities with absolute safety. In particular, cubic garnet-type Nb-doped Li₇La₃Zr₂O₁₂ (Nb-LLZO) SEs possess superior ionic conductivity, are feasible to prepare under ambient conditions, have strong thermal stability, and are of low cost. However, the interfacial compatibility with Li metal and Li dendrite hazards still hinder the applications of Nb-LLZO. Herein, a quick and efficient solution was applied to address this issue, generating a nano-Li₃PO₄ pre-reduction layer from the reaction of H₃PO₄ with the ion-exchanged passivation layer (Li₂CO₃/LiOH) on the surface of Nb-LLZO. A lithiophilic, electrically insulating interlayer is in situ created when the Li₃PO₄ modified layer interacts with molten Li, successfully preventing the reduction of Nb⁵⁺. The interlayer, which mostly consists of Li₃P and Li₃PO₄, also has a high shear modulus and relatively high Li⁺ conductivity, which effectively inhibit the growth of Li dendrites. The Li|Li₃PO₄|Nb-LLZO|Li₃PO₄|Li symmetric cells stably cycled for over 5000 h at 0.05 mA cm^-2 and over 1000 h at a high rate of 0.15 mA cm^-2 without any short circuits. The LiFePO₄ and S/C hybrid solid-state batteries using the modified Nb-LLZO electrolyte also demonstrated good electrochemical performances, confirming the practical application of this interfacial engineering in various solid-state battery systems. This work offers an efficient solution to the instability issue between the Nb-LLZO SE and metallic Li anode.

Metal-air batteries: progress and perspective

The metal-air batteries with the largest theoretical energy densities have been paid much more attention. However, metal-air batteries including Li-air/O₂, Li-CO₂, Na-air/O_2, and Zn-air/O₂ batteries, are complex systems that have their respective scientific problems, such as metal dendrite forming/deforming, the kinetics of redox mediators for oxygen reduction/evolution reactions, high overpotentials, desolution of CO₂, H₂O, etc. from the air and related side reactions on both anode and cathode. It should be the main direction to address these shortages to improve performance. Here, we summarized recently research progress in these metal-air/O₂ batteries. Some perspectives are also provided for these research fields.

Dynamic Liquid Metal Catalysts for Boosted Lithium Polysulfides Redox Reaction

Designing efficient electrocatalysts with high electroconductivity, strong chemisorption, and superior catalytical efficiency to realize rapid kinetics of the lithium polysulfides (LiPSs) conversion process is crucial for practical lithium-sulfur (Li-S) battery applications. Unfortunately, most current electrocatalysts cannot maintain long-term stability due to the possible failure of catalytic sites. Herein, a novel dynamic electrocatalytic strategy with the liquid metal (i.e., gallium-tin, EGaSn) to facilitate LiPSs redox reaction is reported. The combined theoretical simulations and microstructure experiment analysis reveal that Sn atoms dynamically distributed in the liquid Ga matrix act as the main active catalytic center. Meanwhile, Ga provides a uniquely dynamic environment to maintain the long-term integrity of the catalytic system. With the participation of EGaSn, a tailor-made 2 Ah Li-S pouch cell with a specific energy density of 307.7 Wh kg^-1 is realized. This work opens up new opportunities for liquid-phase binary alloys as electrocatalysts for high-specific-energy Li-S batteries.

High-Performance Composite Lithium Anodes Enabled by Electronic/Ionic Dual-Conductive Paths for Solid-State Li Metal Batteries

Solid-state lithium metal batteries (SSLMBs) promise high energy density and high safety by employing high-capacity Li metal anode and solid-state electrolytes. However, the construction of the composite Li metal electrode is a neglected but important subject when the extensive research focuses on the interface between the solid electrolyte Li_6.4 La₃ Zr_1.4 Ta_0.6 O₁₂ and Li metal anode. Here, an electronic-ionic conducting composite Li metal anode consisting of Li-Al alloy and LiF is constructed to achieve the stable electronic-ionic transport channel and the intimate interface contact, which can realize the uniform Li deposition and the efficiency utilization of lithium in composite Li metal electrode. Therefore, the symmetric battery with composite Li metal electrode exhibits the high critical current density with 1.2 mA cm^-2 and stable cycle for 1500 h at 0.3 mA cm^-2 , 25 °C. Moreover, the SSLMBs matched with LiFePO₄ and LiNi_0.8 Co_0.1 Mn_0.1 O₂ achieve the outstanding electrochemical performance, verifying the feasibility of composite Li metal electrode in various SSLMBs systems.

Design of a lithiophilic and electron-blocking interlayer for dendrite-free lithium-metal solid-state batteries

All-solid-state batteries are a potential game changer in the energy storage market; however, their practical employment has been hampered by premature short circuits caused by the lithium dendritic growth through the solid electrolyte. Here, we demonstrate that a rational layer-by-layer strategy using a lithiophilic and electron-blocking multilayer can substantially enhance the performance/stability of the system by effectively blocking the electron leakage and maintaining low electronic conductivity even at high temperature (60°C) or under high electric field (3 V) while sustaining low interfacial resistance (13.4 ohm cm²). It subsequently results in a homogeneous lithium plating/stripping, thereby aiding in achieving one of the highest critical current densities (~3.1 mA cm^-2) at 60°C in a symmetric cell. A full cell paired with a commercial-level cathode exhibits exceptionally long durability (>3000 cycles) and coulombic efficiency (99.96%) at a high current density (2 C; ~1.0 mA cm^-2), which records the highest performance among all-solid-state lithium metal batteries reported to date.

Plastic Monolithic Mixed-Conducting Interlayer for Dendrite-Free Solid-State Batteries

Solid-state electrolytes (SSEs) hold a critical role in enabling high-energy-density and safe rechargeable batteries with Li metal anode. Unfortunately, nonuniform lithium deposition and dendrite penetration due to poor interfacial solid-solid contact are hindering their practical applications. Here, solid-state lithium naphthalenide (Li-Naph(s)) is introduced as a plastic monolithic mixed-conducting interlayer (PMMCI) between the garnet electrolyte and the Li anode via a facile cold process. The thin PMMCI shows a well-ordered layered crystalline structure with excellent mixed-conducting capability for both Li⁺ (4.38 × 10^-3  S cm^-1 ) and delocalized electrons (1.01 × 10^-3  S cm^-1 ). In contrast to previous composite interlayers, this monolithic material enables an intrinsically homogenous electric field and Li⁺ transport at the Li/garnet interface, thus significantly reducing the interfacial resistance and achieving uniform and dendrite-free Li anode plating/stripping. As a result, Li symmetric cells with the PMMCI-modified garnet electrolyte show highly stable cycling for 1200 h at 0.2 mA cm^-2 and 500 h at a high current density of 1 mA cm^-2 . The findings provide a new interface design strategy for solid-state batteries using monolithic mixed-conducting interlayers.

Li-stuffed garnet electrolytes: structure, ionic conductivity, chemical stability, interface, and applications

Current lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and peak power demand. However, the organic liquid electrolytes used in the lithium-ion battery are flammable and not stable in contact with elemental lithium and at a higher voltage. To eliminate the safety and instability issues, solid-state (ceramic) electrolytes have attracted enormous interest worldwide, owing to their thermal and high voltage stability. Among all the solid-state electrolytes known today, the Li-stuffed garnet is one of the most promising electrolytes due to its physical and chemical properties such as high total Li-ion conductivity at room temperature, chemical stability with elemental lithium and high voltage lithium cathodes, and high electrochemical stability window (6 V vs. Li+/Li). In this short review, we provide an overview of Li-stuffed garnet electrolytes with a focus on their structure, ionic conductivity, transport mechanism, chemical stability, and battery applications.

Grain Boundary Design of Solid Electrolyte Actualizing Stable All-Solid-State Sodium Batteries

Advanced inorganic solid electrolytes (SEs) are critical for all-solid-state alkaline metal batteries with high safety and high energy densities. A new interphase design to address the urgent interfacial stability issues against all-solid-state sodium metal batteries (ASSMBs) is proposed. The grain boundary phase of a Mg²⁺ -doped Na₃ Zr₂ Si₂ PO₁₂ conductor (denoted as NZSP-xMg) is manipulated to introduce a favorable Na_{3-2 δ} Mg_δ PO₄ -dominant interphase which facilitates its intimate contact with Na metal and works as an electron barrier to suppress Na metal dendrite penetration into the electrolyte bulk. The optimal NZSP-0.2Mg electrolyte endows a low interfacial resistance of 93 Ω cm² at room temperature, over 16 times smaller than that of Na₃ Zr₂ Si₂ PO₁₂ . The Na plating/stripping with small polarization is retained under 0.3 mA cm^-2 for more than 290 days (7000 h), representing a record high cycling stability of SEs for ASSMBs. An all-solid-state NaCrO₂ //Na battery is accordingly assembled manifesting a high capacity of 110 mA h g^-1 at 1 C for 1755 cycles with almost no capacity decay. Excellent rate capability at 5 C is realized with a high Coulombic efficiency of 99.8%, signifying promising application in solid-state electrochemical energy storage systems.

Excellent Performances of Composite Polymer Electrolytes with Porous Vinyl-Functionalized SiO2 Nanoparticles for Lithium Metal Batteries

Composite polymer electrolytes (CPEs) incorporate the advantages of solid polymer electrolytes (SPEs) and inorganic solid electrolytes (ISEs), which have shown huge potential in the application of safe lithium-metal batteries (LMBs). Effectively avoiding the agglomeration of inorganic fillers in the polymer matrix during the organic–inorganic mixing process is very important for the properties of the composite electrolyte. Herein, a partial cross-linked PEO-based CPE was prepared by porous vinyl-functionalized silicon (p-V-SiO₂) nanoparticles as fillers and poly (ethylene glycol diacrylate) (PEGDA) as cross-linkers. By combining the mechanical rigidity of ceramic fillers and the flexibility of PEO, the as-made electrolyte membranes had excellent mechanical properties. The big special surface area and pore volume of nanoparticles inhibited PEO recrystallization and promoted the dissolution of lithium salt. Chemical bonding improved the interfacial compatibility between organic and inorganic materials and facilitated the homogenization of lithium-ion flow. As a result, the symmetric Li|CPE|Li cells could operate stably over 450 h without a short circuit. All solid Li|LiFePO₄ batteries were constructed with this composite electrolyte and showed excellent rate and cycling performances. The first discharge-specific capacity of the assembled battery was 155.1 mA h g⁻¹, and the capacity retention was 91% after operating for 300 cycles at 0.5 C. These results demonstrated that the chemical grafting of porous inorganic materials and cross-linking polymerization can greatly improve the properties of CPEs.

Design Principles and Applications of Next-Generation High-Energy-Density Batteries Based on Liquid Metals

Increasing need for the renewable energy supply accelerated the thriving studies of Li-ion batteries, whereas if the high-energy-density Li as well as alkali metals should be adopted as battery electrodes is still under fierce debate for safety concerns. Recently, a group of low-melting temperature metals and alloys that are in liquid phase at or near room-temperature are being reported for battery applications, by which the battery energy could be improved without significant dendrite issue. Besides the dendrite-free feature, liquid metals can also promise various high-energy-density battery designs on the basis of unique materials properties. In this review, the design principles for liquid metals-based batteries from mechanical, electrochemical, and thermodynamical aspects are provided. With the understanding of the theoretical basis, currently reported relevant designs are summarized and analyzed focusing on the working mechanism, effectiveness evaluation, and novel application. An overview of the state-of-the-art liquid metal battery developments and future prospects is also provided in the end as a reference for further research explorations.

Consecutive Nucleation and Confinement Modulation towards Li Plating in Seeded Capsules for Durable Li-Metal Batteries

A dual modulation strategy of consecutive nucleation and confined growth of Li metal is proposed by using the metal-organic framework (MOF) derivative hollow capsule with inbuilt lithiophilic Au or Co-O nanoparticle (NP) seeds as heterogeneous host. The seeding-induced nucleation enables the negligible overpotential and promotes the inward injection of Li mass into the abundant cavities in host, followed by the conformal plating of Li on the outer surface of host during discharging. This modulation alleviates the dendrite growth and volume expansion of Li plating. The interconnected porous host network enables enhancement of cycling and rate performances of Li metal (a lifespan over 1200 h for Au-seeding symmetric cells, and an endurance of 220 cycles under an ultrahigh current density of 10 mA cm^-2 for corresponding asymmetric cells). The hollow capsules integrated with lithiophilic seeds solve the deformation problem of Li metal for durable and long-life Li-metal batteries.

Applications of Low-Melting-Point Metals in Rechargeable Metal Batteries

Low-melting-point (LMP) metals represent an interesting family of electrode materials owing to their high ionic conductivity, good ductility or fluidity, low hardness and/or superior alloying capability, all of which are crucial characteristics to address battery challenges such as interfacial incompatibility, electrode pulverization, and dendrite growth. This minireview summarizes recent research progress of typical LMP metals including In, Ga, Hg, and their alloys in rechargeable metal batteries. Emphasis is placed on mainstream electrochemical storage devices of Li, Na, and K batteries as well as the representative multi-valent metal batteries. The fundamental correlations between unique physiochemical properties of LMP metals and the battery performance are highlighted. In addition, this article also provides insights into future development and potential directions of LMP metals/alloys for practical applications.